Passivation:Rendering a substance inactive or inert by chemical action. Aluminum, for example, is passivated when it reacts with the air to form a protective layer of aluminum oxide which prevents further air-aluminum reaction. Similarly, iron is passivated when it reacts with nitric acid to form a layer of iron oxide.

Passivation, in physical chemistry and engineering, refers to a material becoming "passive," that is, being less affected by environmental factors such as air and water. Passivation involves a shielding outer-layer of base material, which can be applied as a microcoating, or which occurs spontaneously in nature. As a technique, passivation is the use of a light coat of a protective material, such as metal oxide, to create a shell against corrosion. Passivation can occur only in certain conditions, and is used in microelectronics to enhance silicon.[1] The technique of passivation is used to strengthen and preserve the appearance of metallic.A Flame Arrestoris a device which allows gas to pass through it but stops a flame in order to prevent a larger fire or explosion. There is an enormous variety of situations in which flame arrestors are applied. Anyone involved in selecting flame arrestors needs to understand how these products work and their performance limitations. For that purpose, this paper provides an introduction to the technology and terminology of flame arrestors and the types of products available

CONGEALING POINT-Temperature at which a liquid changes to plastic or a solid.

cloud point

Also found in: Wikipedia. cloud point[klaud pint] (chemical engineering) The temperature at which paraffin wax or other solid substance begins to separate from a solution of petroleum oil; a cloudy appearance is seen in the oil at this point.

cloud point (plural cloud points)1. (chemistry) The temperature at which one component of a mixture of liquids begins to solidify (or a mixture of liquids starts to become immiscible) on cooling, resulting in visible cloudiness; as for example in diesel fuel in freezing temperatures; the consolute point

Cloud point

Also found in: Encyclopedia. Cloud point The cloud point of a fluid is the temperature at which dissolved solids are no longer completely soluble, precipitating as a second phase giving the fluid a cloudy appearance. This term is relevant to several applications with different consequences

The pour point of a liquid is the temperature at which it becomes semi solid and loses its flow characteristics.Pour point

Pour point of a liquid can be defined as the lowest temperature at which the liquid begins to flow or can be poured. Alternatively, it is the minimum temperature, below which the liquid will seize to flow. This term is usually used for crude oils and is a rough estimation of temperature range when the oil becomes pumpable.

Pour Point The pour point of an oil is the lowest temperature at which the oil will just flow, under standard test conditions. Threshold Limit Values (TLV)

The following excerpts are taken from ACGIH 99: Threshold Limit Values refer to airborne concentrations of substances and represent conditions under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse health effects. Threshold Limit Value Time-Weighted Average (TLV-TWA) the time-weighted average concentration for a conventional 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect Threshold Limit Value Short-Term Exposure Limit (TLV-STEL) a 15-minute TWA exposure which should not be exceeded at any time during a workday even if the 8-hour TWA is within the TLV-TWA

Viscosity Dynamic Viscosity Viscosity is a measure of a fluid's resistance to flow; the lower the viscosity of a fluid, the more easily it flows. Like density, viscosity is affected by temperature. As temperature decreases, viscosity increases. The SI unit of dynamic viscosity is the millipascal-second (mPas). This is equivalent to the former unit of centipoise (cP).

Viscosity index (VI) is an arbitrary measure for the change of viscosity with variations in temperature. The lower the VI, the greater the change of viscosity of the oil with temperature and vice versa. It is used to characterize viscosity changes with relation to temperature in lubricating oil.Definition The viscosity index is an arbitrary number indicating the effect of change of temperature on the kinematic viscosity of an oil. A high viscosityIndex signifies a relatively small change of kinematic viscosity with temperature

Henry's Law Definition: Henry's Law is a chemistry law which states that the mass of a gas which will dissolve into a solution is directly proportional to the partial pressure of that gas above the solution.Henry's LawThe solubility of a gas (unless it is highly soluble) is directly proportional to the pressure applied to the gas.When a gas is dissolved in a liquid, the concentrations will eventually reach equilibrium between the source of the gas and the solution. Henry's Law shows the concentration of a solute gas in a solution is directly proportional to the partial pressure of the gas over the solution.

LE CHATELIER'S PRINCIPLE

This page looks at Le Chatelier's Principle and explains how to apply it to reactions in a state of dynamic equilibrium. It covers changes to the position of equilibrium if you change concentration, pressure or temperature. It also explains very briefly why catalysts have no effect on the position of equilibrium.

Important: If you aren't sure about the words dynamic equilibrium or position of equilibrium you should read the introductory page before you go on

It is important in understanding everything on this page to realise that Le Chatelier's Principle is no more than a useful guide to help you work out what happens when you change the conditions in a reaction in dynamic equilibrium. It doesn't explain anything. I'll keep coming back to that point!

Using Le Chatelier's PrincipleA statement of Le Chatelier's Principle If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.

Using Le Chatelier's Principle with a change of concentrationSuppose you have an equilibrium established between four substances A, B, C and D.

Note: In case you wonder, the reason for choosing this equation rather than having just A + B on the left-hand side is because further down this page I need an equation which has different numbers of molecules on each side. I am going to use that same equation throughout this page.

What would happen if you changed the conditions by increasing the concentration of A?According to Le Chatelier, the position of equilibrium will move in such a way as to counteract the change. That means that the position of equilibrium will move so that the concentration of A decreases again - by reacting it with B and turning it into C + D. The position of equilibrium moves to the right.

This is a useful way of converting the maximum possible amount of B into C and D. You might use it if, for example, B was a relatively expensive material whereas A was cheap and plentiful.What would happen if you changed the conditions by decreasing the concentration of A?According to Le Chatelier, the position of equilibrium will move so that the concentration of A increases again. That means that more C and D will react to replace the A that has been removed. The position of equilibrium moves to the left.

This is esssentially what happens if you remove one of the products of the reaction as soon as it is formed. If, for example, you removed C as soon as it was formed, the position of equilibrium would move to the right to replace it. If you kept on removing it, the equilibrium position would keep on moving rightwards - turning this into a one-way reaction.

ImportantThis isn't in any way an explanation of why the position of equilibrium moves in the ways described. All Le Chatelier's Principle gives you is a quick way of working out what happens.

Note: If you know about equilibrium constants, you will find a more detailed explanation of the effect of a change of concentration by following this link. If you don't know anything about equilibrium constants, you should ignore this link.If you choose to follow it, return to this page via the BACK button on your browser or via the equilibrium menu.

Using Le Chatelier's Principle with a change of pressureThis only applies to reactions involving gases:

What would happen if you changed the conditions by increasing the pressure?According to Le Chatelier, the position of equilibrium will move in such a way as to counteract the change. That means that the position of equilibrium will move so that the pressure is reduced again.Pressure is caused by gas molecules hitting the sides of their container. The more molecules you have in the container, the higher the pressure will be. The system can reduce the pressure by reacting in such a way as to produce fewer molecules.In this case, there are 3 molecules on the left-hand side of the equation, but only 2 on the right. By forming more C and D, the system causes the pressure to reduce.Increasing the pressure on a gas reaction shifts the position of equilibrium towards the side with fewer molecules.

What would happen if you changed the conditions by decreasing the pressure?The equilibrium will move in such a way that the pressure increases again. It can do that by producing more molecules. In this case, the position of equilibrium will move towards the left-hand side of the reaction.

What happens if there are the same number of molecules on both sides of the equilibrium reaction?In this case, increasing the pressure has no effect whatsoever on the position of the equilibrium. Because you have the same numbers of molecules on both sides, the equilibrium can't move in any way that will reduce the pressure again.

ImportantAgain, this isn't an explanation of why the position of equilibrium moves in the ways described. You will find a rather mathematical treatment of the explanation by following the link below.

Note: You will find a detailed explanation by following this link. If you don't know anything about equilibrium constants (particularly Kp), you should ignore this link. The same thing applies if you don't like things to be too mathematical! If you are a UK A' level student, you won't need this explanation.If you choose to follow the link, return to this page via the BACK button on your browser or via the equilibrium menu.

Using Le Chatelier's Principle with a change of temperatureFor this, you need to know whether heat is given out or absorbed during the reaction. Assume that our forward reaction is exothermic (heat is evolved):

This shows that 250 kJ is evolved (hence the negative sign) when 1 mole of A reacts completely with 2 moles of B. For reversible reactions, the value is always given as if the reaction was one-way in the forward direction.The back reaction (the conversion of C and D into A and B) would be endothermic by exactly the same amount.

What would happen if you changed the conditions by increasing the temperature?According to Le Chatelier, the position of equilibrium will move in such a way as to counteract the change. That means that the position of equilibrium will move so that the temperature is reduced again.Suppose the system is in equilibrium at 300C, and you increase the temperature to 500C. How can the reaction counteract the change you have made? How can it cool itself down again?To cool down, it needs to absorb the extra heat that you have just put in. In the case we are looking at, the back reaction absorbs heat. The position of equilibrium therefore moves to the left. The new equilibrium mixture contains more A and B, and less C and D.

If you were aiming to make as much C and D as possible, increasing the temperature on a reversible reaction where the forward reaction is exothermic isn't a good idea!What would happen if you changed the conditions by decreasing the temperature?The equilibrium will move in such a way that the temperature increases again.Suppose the system is in equilibrium at 500C and you reduce the temperature to 400C. The reaction will tend to heat itself up again to return to the original temperature. It can do that by favouring the exothermic reaction.The position of equilibrium will move to the right. More A and B are converted into C and D at the lower temperature.

Summary Increasing the temperature of a system in dynamic equilibrium favours the endothermic reaction. The system counteracts the change you have made by absorbing the extra heat. Decreasing the temperature of a system in dynamic equilibrium favours the exothermic reaction. The system counteracts the change you have made by producing more heat.

ImportantAgain, this isn't in any way an explanation of why the position of equilibrium moves in the ways described. It is only a way of helping you to work out what happens.

Note: I am not going to attempt an explanation of this anywhere on the site. To do it properly is far too difficult for this level. It is possible to come up with an explanation of sorts by looking at how the rate constants for the forward and back reactions change relative to each other by using the Arrhenius equation, but this isn't a standard way of doing it, and is liable to confuse those of you going on to do a Chemistry degree. If you aren't going to do a Chemistry degree, you won't need to know about this anyway!

Le Chatelier's Principle and catalystsCatalysts have sneaked onto this page under false pretences, because adding a catalyst makes absolutely no difference to the position of equilibrium, and Le Chatelier's Principle doesn't apply to them.This is because a catalyst speeds up the forward and back reaction to the same extent. Because adding a catalyst doesn't affect the relative rates of the two reactions, it can't affect the position of equilibrium. So why use a catalyst?For a dynamic equilibrium to be set up, the rates of the forward reaction and the back reaction have to become equal. This doesn't happen instantly. For a very slow reaction, it could take years! A catalyst speeds up the rate at which a reaction reaches dynamic equilibrium.

THEORY OF CATALYST IN FERTILIZER INDUSTRY

THEORY OF CATALYSTS

In the chemical industry, Catalysts are used in order to bring some chosen reaction as close as possible to a selected equilibrium point in the shortest possible time for a reversible type of reaction. Catalyst accelerates the rates of forward and backward reaction so as to attain faster the system towards equilibrium and the Catalyst remains unaltered without taking part in the chemical reaction.

The rate of a Catalysed reaction is changed by varying the temperature, the Catalyst, or the concentrations of reactions and products. Although these variables are not independent, the responses are especially sensitive to the type of Catalyst because each solid of Catalyst introduces unique rate of reaction. For example, in case of Ammonia synthesis reaction appropriate Catalysts must have the highest activity for the Hydrogenation of Nitrogen at as low a temperature as possible. Similarly, in case of reaction of Carbonmonoxide and Hydrogen, an active Catalyst without selectivity should produce CH4 and H2O, which are very stable molecules, whereas a selective Catalyst may produce methanol. It is evident that the selection of suitable Catalysts depends upon the extent of knowledge and the correctness of suppositions concerning the nature of the reaction and of the activity of solids.

THE ACTIVITY OF SOLIDS

The catalyst, as separate particles or agglomerates of particles, is immersed in a fluid medium in motion. Reactants and products diffuse in the gas or liquid phases bathing the boundaries of the solid, and also in the pore spaces of the agglomerates. These diffusions are rate controlling, the reactant, the intermediates and the products combine loosely (Physisorption) or more lightly (Weak and Strong Chemisorption) with the surface of the Catalyst. Solubilities and rates of diffusion in solids are small, so the reaction almost invariably takes place on the solid surface and involves solid substrate interactions, which stretch or dissociate the bonds of the reactants. The overall rate is controlled by diffusion, adsorption, desorption, or by an inter action between surface complexes in a simple reaction, or at some intermediate step in a complex process.

THE PRINCIPAL CHARACTERISTICS

The efficiency of a Catalyst rests upon three factors:

- Activity

- Selectivity

- Life

The activity is the extent to which the catalyst influences the rate of change of the degree of advancement of the (as assessed by the disappearance of reactants) conversion), per unit weight or per unit volume of Catalyst, under specified conditions. The activity per unit volume is of practical importance because process economics can depend critically upon the cost of packed reactor space. The bulk density of the Catalyst must always be as small as possible, consistent with other requirements. The performance of a catalyst is generally assessed in terms of the rate at which it promotes a desired (or sometimes an undesired) reaction. Reaction rate is expressed with well known proportionally termed as 'Catalyst activity'. At equivalent temperatures, pressures, reaction volumes and mole fractions of reactants, reaction rate is proportional to Catalyst activity. Where other reactions are also possible, an assessment is made of Catalyst selectivity. Catalyst selectivity is the ratio between activity for desired and undesired reactions.

With most catalyst used for the production of Synthesis gas and Ammonia this is unimportant because, by careful catalyst selection, high selectivity is achieved under normal operating conditions. The life of the Catalyst is the period during which the Catalyst produces the required product at a space-time yield in excess of or equal to that designated. The activity of most Catalysts decreases sharply at first and then declines much more slowly with time. The selectivity may worsen or improve. The life of a Catalyst terminates because of loss of mechanical strength or because of unacceptable changes in activity and selectivity.

The Catalytic efficacy of a homogeneous solid phase is influenced by the four factors as follows:

a. The exposed area in contact the fluid termed as specific area.

b. The intrinsic chemical characteristics of the surface of the solid. The species forming the surface may be atoms or ions and their chemical properties must depend upon their electronic structure and arrangement.

c. The topography of the surface. Because of the dependence of activity upon geometry and electronic structure, the faces, edges and corners of crystals must possess different activities.

d. The occurrence of lattice defects. The activities to be associated with defects such as grain boundaries; dislocations differ from solid to solid and with the type of reaction Catalysed.

THE SPECIFIC AREA:

The specific area of the solid phases of the Catalyst must be adjusted to suit the requirements of the process. Usually the area is made and maintained large by procedures, which produce either small particles or porous bodies in more or less stable states. The specific area increases with the particle diameter and density of the particles. Higher the specific area, higher is the length of edges and greater number of corners introduces more regions of different activity. Real Catalysts are composed of particles of a range of sizes. One detrimental effect of Catalyst activity is due to phenomena called 'Sintering'. High temperature increases the Sintering of solid particles. Due to sintering, the specific area, length of edges and the number of corners is effected.

Sintering can be restricted to smoothing by dispersing the particles of active phase on the surface of another inert refractory solid of high area called support of the Catalyst or by separating them with refractory spacing blocks called stabilisation surface area can be obscured by debris (dust, rust) or encapsulated by such products of parasitic reactions as liquid polymers and solid coke. If thereby the pore size distribution is changed and the reactions become diffusion limited, then the selectivity as well as the activity may be impaired.

COMPOSITE CATALYSTS

A Catalyst is composite when it contains more than one chemical entity. The addition of a second component may be necessary to support or stabilise the active phase by a second and more refractory solid or because the reaction is complex, involving a series of steps, each requiring selective Catalysts. Almost all industrial Catalysts are composites, if only because the use of a support decreases manufacturing costs and facilitates handling.

The rudiments of Catalyst design rest upon the facts that the efficiency of a solid phase Catalyst is determined by its selectivity, specific activity (activity per unit area) and specific area and by the effects of specific inhibitors or promoters e.g. the Catalyst for Hydrogenation of nitrogen to Ammonia, consists of about 94% Iron oxide with the approximate composition Fe3 O4, the balance being promoters i.e. mainly oxides of Ca, Al and K. The steam reforming of methane over nickel containing Catalysts (such as R-67 and R-67-7H) consists of Nio-16-18 wt%, Magnesium aluminate with free Mg content below 0.5% and SiO2 max. 0.1% in which Ni is the active metal for complex steam reforming reaction and Magnesium aluminate acts as the stabilising agent plus it suppresses the formation of carbon.

OPERATION FOR CATALYTIC REACTOR

Conversion taking place in a reactor filled with selective Catalyst is a function of the following parameters:

1. Gas composition

2. Space Velocity

3. Pressure

4. Catalyst Temperatures

5. Catalyst Activity

The first four parameters do, to some extent, depend on the reactor design, but are, within certain limits, functions of the fifth parameter, the Catalyst activity. Activity of Catalyst, rather specific activity expressed to unit area of the Catalyst cannot be directly measured. However it is a measure of reaction rate which again depends upon the Catalyst size, voidage for packed bed and surface area.

SPACE VELOCITY

Space velocity for catalytic reactor is an indication of the contact time of the following fluid with the surface of Catalyst. It is defined as follows:

Space Velocity = Number of reactor volumes of feed at specified conditions which can be treated in unit time.

= Volumetric feed rate Volumetric feed rate --------------------------- = --------------------- Reactor volume Catalyst volume

During heating of Ammonia converter Catalyst, a high space velocity is maintained to reduce the reduction time by better uniform heating of the catalyst. However, for normal operating reactor the lowering of the space velocity reduces the conversion.

CATALYST POISON

The activity of solid catalyst is sometimes appreciably altered by traces of foreign substances. Foreign substances, which tend to inhibit catalytic activity, are known as anti- catalysts or Catalyst poisons. They are more firmly and preferentially adsorbed than the reactants at the surface of a solid catalyst, which is thereby rendered ineffective. The activity of the solid catalyst is reduced or destroyed by adsorption and by alloy or compound formation, when the processor gives rise to a less active or inactive surface. The non-metal species like Oxygen, Sulphur, Arsenic, halogens (Chlorides, Fluorides) and also Carbonmonoxide, Ammonia, Water, Hydrogen Sulphide, Phosphine etc.and their derivatives can be powerful poisons when present as accidental impurities or as reactants, depending upon the facility of the Catalysed reaction. These poisons may be adsorbed or they may react to form compounds in surface layers (Oxides, Sulphides, halides etc).If activity recovers on exclusion of the poison from the reactants, the poisoning is said to be reversible, otherwise the poisoning is permanent.

Temporary poisoning is effected by Oxygen and Oxygen-containing compounds such as H2O, CO and CO2. In case of temporary poisoning, Catalyst activity is restored when feedstock is restored. Permanent poisoning is effected by S, As, C1, F,P, Pb and Carbon deposition from the cracking of Hydrocarbons such as compressor lubrication oil or by the polymerisation of higher Hydrocarbons. The above elements cause permanent damage to the catalyst. Carbon formation on the outer surface of the Catalyst may however be termed as 'Semi- permanent' poisoning since the initial activity can be regained by a regeneration process such as steam blowing of Ni-reforming catalyst.

CRUSHING STRENGTH OF CATALYST

A successful commercial heterogenous Catalyst not only must be capable of Catalysing the desired reactions selectively, it must be also mechanically robust. It must be suitably shaped, so that the fluid or gas can flow through a bed made of it without excessive pressure drop or uneven distribution. And finally it must retain both its reactivity and its mechanical properties over a long life, which includes start ups and shutdowns. Normally, the Catalysts are formed by pelleting (tablets), granulation and extrusion along with various types of binder agent to give adequate strength to the finished Catalyst. A high Catalyst strength is adopted to withstand the following forms of stress:

1. Abrasion (during transit)

2. Impact (when loaded into the Reactor)

3. Internal stresses (resulting from phase changes during reduction or when initially brought online).

4. External stressing (caused by pressure drop, Catalyst weight and possibly, thermal cycling).

ReactorCatalystTypeSizemmVolumeM3Bulk DensityBed ht.mmcompositionLife time (exp)Features

R-201TK-2515X2.58.444802220NiO:2-3%MoO:10%>5

R-202AHTZ-3410.6413002800ZnO:99%

R-202BHTZ-3410.6413002800ZnO:99%Guard

F-201Topsoe R-67-R-7Hprereduced 16X11cylinder with7 holes6.68960NiO:16-18%SiO2:5Cu promoted

R-205LSK

LK-8214.5X4.5

4.3X3.280.31100

10004670CuO,ZnO,Cr2O3CuO,ZnO,Al2O3>5

R-301PK-5526.0>10

R-501KMR (pre-reduced)

KM1.5-3.0

1.526.9

68.42220

2850Prereduced free iron+2wt%O294% Fe3O4 balance:CaO,Al2O3, K2O5-10Catalyst promoters:Ca,Al,KNot pyrophoric at ambient temp.

2.2 DESULPHURISATION CATALYST (NICKEL- MOLYBDENUM CATALYST)

The natural gas feed stock supplied to NFCL contains no H2S, but it is anticipated that future supplies may contain sulphur compounds which have to be removed in order not to poison the reforming catalysts and the LT shift catalyst. Natural Gas from battery limit is heated to 385 deg.C in the Feed stock preheater F-203, and is passed through the Hdrogenator. A bed of Nickel-Molybdenum catalyst is provided to catalyse the hydrogenation of organic sulphur compounds to hydrogen sulphide. There are two types of organic sulphur compounds that may be present in the feed stock. One is called 'Normal Sulphur' containing H2S, COS, CS2 and Mercaptans and the other is called 'Less Reactive Sulphur', containing Thiophenes, Thioethers etc. In case of normal sulphur except Mercaptan Hydrogen recycle gas is not consumed where as for less reactive sulphur, recycle hydrogen is consumed as per the following hydrogenation reactions:

RSH + H2 RH + H2S (Mercaptans)

R1SR + 2H2 RH + R1H + H2S (Thioethers)

R1SSR + 3H2 RH + R1H + 2H2S (Thiophenes) If sulphur is present, natural gas is mixed with recycle gas from synthesis gas compressor first stage discharge with flow of recycle gas around 1306 NM3/hr., in order to avoid Carbon deposition on the catalyst due to catalytic cracking of higher hydrocarbons if any. After preheating to 385 deg.C,the gas mixture passes to Hydrogenator Reactor R-201 and reacts to produce H2S. The above reactions are exothermic but insignificant (which depends on the type of Sulphur that determines the number of moles of hydrogen taken up). H2S produced in R-201 and that already present in Natural Gas is then removed in H2S Absorbers R-202 A/B, thereby the gas will be free of H2S. Each absorber contains one bed of Zno catalyst to absorb the sulphur. The absorbers are operating in series with the second vessel acting as guard. When the Zno in the first vessel is getting exhausted, a break through of H2S from the first vessel may be observed. The operation will then continue with the second vessel in service, while the first vessel is being reloaded with fresh catalyst. The sulphur content at the exit of R-202B shall be less than 0.1 ppm on dry volume basis at all times which is tolerant to reforming catalyst.

The sulphur removal reaction in Zno bed takes place as follows: Zno + H2S ZnS + H2O

Zno + COS ZnS + CO2

Zno reaction with 'S' depend on :

1. Type of sulphur compounds.

2. Temperature: Increase in temperature will generally increase the ability of Zno to remove sulphur.

3. Capacity : As Zno reacts with sulphur it gets saturated with sulphur and looses its activity. Normal life of Zno catalyst depends on the H2S and sulphur concentration in the natural gas.

ReactorCatalystTypeSizemmVolumeM3Bulk DensityBed ht.mmcompositionLife time (exp)

R-201TK-2515X2.58.444802220NiO:2-3%MoO:10%>5

R-202AHTZ-3410.6413002800ZnO:99%

R-202BHTZ-3410.6413002800ZnO:99%Guard

(GENERAL2.3 REFORMING SECTION)

STEAM REFORMING CATALYST

Steam reforming is a vital part of the front end in plants producing Ammonia. Developments in metallurgy have allowed steam reformers to be operated at higher and higher levels of temperatures, pressures and heat flux. The reforming process and the design of the reformer are based on the reaction between methane and higher hydrocarbons present in the natural gas with steam thereby generating CO, CO2 and Hydrogen. The Hydrogen produced by the Methane reforming reaction is used to produce Ammonia by combining with Nitrogen in the ratio of 3 : 1 which is the stoichiometric ratio of hydrogen and nitrogen to produce ammonia.

The most important reactions which are taking place in the reformer are

CH4 + H2O CO + 3H2

CO + H2O CO2 + H2

These reactions are taking place in the presence of a nickel-based catalyst. The operating parameters maintained close to the equilibrium, are 769 deg. C and 30.5 Kg/cm2g and the maximum tube wall skin temperature allowable is 880 deg.C. The methane concentration at the exit of the reformer is 14.03 %. The efficient operation of the reformer at the above conditions will give rise to a methane leakage at the exit of secondary reformer of 0.6%. The higher slippage of methane has been designed taking advantage of P.G.R. unit incorporated. In addition to the recovery of hydrogen from the purge gas, there is energy saving due to the lower heat flux required in the reformer resulting in reduced firing, there by increasing the life of catalyst and reformer tubes.

PRIMARY REFORMING

Raw synthesis gas is produced by reforming natural gas to an intermediate level in the primary reformer F-201 using super heated HS steam in presence of a Nickel based catalyst at 33 Kg/cm2g pressure. The hot desulphurised natural gas and recycle gas mixture from R-202B outlet is combined with HS steam (37 Kg/cm2g 370 deg.C) to give a steam to carbon mole ratio of 3.3 : 1.0. A small quantity of condensate from P-353 A/B containing small percentage of Methanol and Ammonia is also mixed with steam for subsequent recovery of H2 and to avoid pollution. The combined steam-natural gas-recycle gas mixture (Mixed feed) is preheated to 520 deg.C in the process gas convection coil E-201 located in the waste heat recovery section of the primary reformer F-201 utilising the heat from the hot flue gases, leaving the reformer radiant section.

Following preheat, the gases are distributed through hairpin tubes into vertical reformer tubes filled with Nickel catalyst. The tubes are placed inside a Furnace, where sensible heat and endothermic heat of reaction are absorbed in the tubes by radiation from a number of wall burners to the tubes. The primary reforming of natural gas is done in a Topsoe design side fired furnace, in comparison to the top fired furnace, where the maximum heat input is concentrated in the top part of the furnace. In the top fired furnace during start-up conditions with low flow, little or no heat of reaction in the tubes, the maximum temperatures may well be found at the level of flames. In such furnaces, higher than desirable temperatures may be present in the top part of the tubes even when the outlet temperature is not higher than the level recommended.

In the upper part of the top fired reformer, where the methane concentration is high and hydrogen concentration is low, the potential for carbon formation is present. Due to the radial temperature and concentration gradient in the tube, the risk zone extends somewhat down along the hot tube wall. If this zone reaches a temperature level where the rate of the cracking reaction becomes sufficiently high, carbon formation will take place resulting in a "hot band". Top fired furnaces are more prone to this kind of problem. The above disadvantages of using top fired furnace are eliminated by using the side-fired furnaces. In case of side fired furnace, the reformer outlet temperature increases gradually from the top towards bottom. The tube skin temperature along the length of the tube can be better controlled in side fired furnace and more over, the potential for carbon formation with the age of the catalyst, the possibility of higher tube skin temperature at the bottom than from the top, is better controlled using side fired furnace.

The primary reformer furnace consists of 190 tubes, inserted in two parallel chambers called the radiant zone. Each chamber has got 95 tubes in a single row. Each row has been divided into 5 sections. Each section has got 19 tubes. Reformer tube outlets from both chambers are connected to hot collectors through pig tails, which are placed outside the Primary Reformer radiant zone. Hot collectors are again connected with cold collector. The furnace operates with side firing of fuel gas on both sides of each row of tubes to develop a process gas temperature of about 769 deg.C at the catalyst tube outlet.

There are 360 side-fired burners arranged in 6 rows per wall. Each row is having 15 burners. The type of primary reformer burners is of LP Radial Burner, which is of rugged construction. Natural gas pressure reduced to 3 Kg/cm2g at Offsite is used as fuel for the LP Radial Burners. The flame shape should be flat against the heated Muffle Block surrounding the air nozzle. The excess air shall be 10%. The Reformer is loaded with 20.05 M3 of R-67-7H Nickel based unreduced catalyst at bottom and 6.68 M3 of R-67R-7H Nickel based pre- reduced catalyst at top, both cylindrical having seven holes with OD 16 mm and height 11 mm. Inside the catalyst tubes, the natural gas steam reforming reaction takes place.

REFORMING REACTIONS

The following reactions take place simultaneously, producing a mixture of H2, CO, CO2, CH4 and excess H20 when hydrocarbons undergo steam reforming over Nickel catalyst :

Cn Hm + 2n H2O n CO2 + (2n+m/2) H2 - Heat (1)

CH4 + 2 H2O CO2 + 4H2 - Heat (2)

CH4 + H2O CO + 3H2 - Heat (3)

CO2 + H2 CO + H20 - Heat (4)

Reactions start at 500 deg. C for the higher hydrocarbons and 600 deg. C for methane.

ReactorCatalystTypeSizemmVolumeM3Bulk DensityBed ht.mmcompositionLife time (exp)Features

F-201Topsoe R-67-R-7HPrereduced 16X11cylinder with 7 holes6.68960NiO:16-18%SiO2:5Cu promoted

HEAT RECOVERY FROM HT SHIFTED GAS

The final shift reaction is completed in Low temperature shift converter R-205. The gas leaving HTS is cooled to 200 deg.C before entering LT shift converter by recovering waste heat successively in Waste Heat Boiler after Co-converter E-210 and BFW Preheater E-211A/B and Trim Heater E-209. In E-210, KS steam is generated while cooling the gas to 340 deg.C. Part of gas is sent to the Trim Heater E-209 to preheat the methanator feed inlet gas partly. The gas then passes through the shell side of E-211A/B and gets cooled to 200 deg.C. There is a bypass of E-211A/B for controlling LT Shift Converter gas at desired inlet temperature.

LOW TEMPERATURE SHIFT CONVERTER :

The LT Shift Converter R-205 contains 80.3 M3 of the catalyst consisting of oxides of copper, zinc and aluminium. As the catalyst is extremely sensitive to sulphur which may be liberated not only from the preceding HT shift catalyst but also from secondary reforer refractory material, the LT shift converter is bypassed during initial stage until the gas is practically sulphur free. The chlorine may be present in process steam and quench water, due to maloperation of the water treatment system and process air due to atmospheric air pollution in very small amounts. Besides chlorides and sulphur, gaseous Si - compounds are also catalyst poisions. When the catalyst is in a reduced state, temperatures above 250 deg. C must normally be avoided. A short exposure to 300 deg.C. will have no adverse effect on the catalyst. Normal operation should take place at as low a temperature as possible.However, at temperatures near the dewpoint, the activity will decrease because of capillary condensation of water inside the catalyst, thus reducing the free area. During operation, the temperature should, therefore, be kept at least 20 deg. C above the dewpoint of the gas. The reduced catalyst is pyrophoric and has to be oxidized before opening of the converter.The normal operating temperature is between 200 deg.C and 218 deg. C. The actual temperature of the inlet gas to R-205 to be selected is dependent on the activity of the catalyst.

ReactorCatalystTypeSizemmVolumeM3Bulk DensityBed ht.mmcompositionLife time (exp)

R-205LSK

LK-8214.5X4.5

4.3X3.280.31100

10004670CuO,ZnO,Cr2O3CuO,ZnO,Al2O3>5

2.5 CO2 REMOVAL SECTION :

This unit provides process gas free of CO2 (limit 1000 ppm) for the production of ammonia and necessary CO2 for Urea production. In this unit, CO2 in the process gas is absorbed by the GV solution in the Absorber, C-301 thus providing process gas with less than 1000 ppm of CO2. Stripping of the absorbed CO2 is done in the two regenerators and CO2 stripped is supplied to Urea Plant. CO2 removal section know how is by Giammarco-Vetrocoke of Italy. The Vetrocoke solution consists of K2 CO3, Vanadium Pentoxide, Glycine and DEA where V2O5 (Vanadium Pentoxide) is the corrosion inhibitor and glycine/DEA are the activators. The chemistry involved in this unit is chemisorption and is explained as follows :

CO2 + H2O HCO3- + H+ (1)

K2CO3 + HCO3- + H+ 2KH CO3 (2) -------------------------------------------------------------------------------- K2CO3 + CO2 + H2O 2KH CO3 (3)

The reaction rate of (3) depends on the reaction rates of (1) and (2). Reaction rate of (1) is slow and the activator activates this reaction by quickly introducing the gaseous CO2 in the liquid phase. The activator glycine reacts with CO2 and forms glycine carbonate according to the reaction.

NH2 CH2 COO- + CO2 COO-NH CH2 COO- + H+ (4)

COO-NH CH2 COO- + H2O NH2 CH2 COO- + HCO3- (5)

The sum of (4) and (5) gives (1).

In solution regeneration, reaction (3) is reversed by application of heat and pressure reduction and the lean and semilean K2 CO3 solution is recirculated for further absorption of CO2. The process gas from V-208 enters the CO2 removal section at 27.5 Kg/cm2g and 165 deg.C and passes through the reboilers and LP Boiler E-302 and then to E- 306A/B (DM Water Heater) getting cooled down to 113.5 deg. C and condensate is seprated in V-301 before entering the Absorber.

The process gas enters the tube side of E-301A/B giving its heat energy to the GV solution at the shell side of E-301A/B. The solution from the bottom tray of C-302 (Regenerator under pressure) circulates through the reboiler by thermal siphoning. The CO2 and H2O vapour along with solution enters C-302 bottom below the bottom tray and serves as stripping medium. The heat energy released in E-302 shell is used to produce LS steam which is boosted into C-302 through the ejectors L-301A/B. The outlet gas temperature of E-302 is 126.5 deg.C. The gas outlet from E-302 is further cooled in DM water preheaters E-306A/B. The gas is cooled down to 113.5 deg. C. The resulting condensate in the process gas is separated in V-301 before entering the CO2 absorber.

In the CO2 Absorber C-301 process gas flows upwards counter current to the solution flow (the solution is the regenerated GV solution from C-303). Semi-lean solution pumps P-302A/B/C takes suction from the take off tray below the packing of C-303 and pumps the solution to the middle of Absorber as semilean solution at 106 deg.C . Lean solution pumps P-301A/B takes suction from the bottom of C-303 through the cooler E-303 and pumps the solution to the top of the absorber as lean solution. E-303 cools the solution from 109 deg.C to 65 deg.C and in turn heats DM water from 40 deg.C to 104 deg.C. The make up condensate to CO2 removal system is added at the suction of P-301A/B pumps at 59 deg.C to maintain the water balance in the system.

At the bottom of absorbers C-301 where the bulk of CO2 is absorbed, the high temperature improves the reaction rate for reaction No. (3) and for reaction No. (5) according to which the CO2 is absorbed by K2 CO3. In the top part of the absorber, the lower temperature reduces the CO2 vapour pressure in the solution thereby minimising the CO2 content in the process gas. This is made possible by keeping the reaction rate (5) sufficiently high even at this lower temperature by the OH concentrations in the lean solution fed at the top.

Solution regeneration is carried out at two pressure levels, one at 1.04 Kg/cm2g and other at 0.1 Kg/cm2g for better utilization of stripping steam compared to the usual technique in which great part of the stripping steam exits the regenerator top as unused excess. The pressure in regenerator C-302 is regulated to obtain a temperature increase between the solution inlet and outlet of the regenerator in order to condense the above mentioned excess steam. The heat stored in the rich GV solution exit the regenerator C-302, is recovered as flash steam which has been experimentally verified to be practically pure steam.

From C-302 top is taken off a rich solution stream at 106.5 deg.C that feeds Regenerator at low pressure C-303. In C-303 the flashed steam regenerates the rich solution stream taken off from C-302 top. The liquid levels at the bottom of C-303 and at the take off tray are maintained by controlling the flow of lean and semilean solution from C-302. The lean solution from the bottom of C-303 at 109 deg.C gets cooled in E-303 and is pumped by lean solution pumps P-301A/B at 65 deg.C to the top of C-301. From the take off tray of C-303 the solution goes to the Semilean pumps P-302A/B/C at 106 deg.C to be pumped to middle of C-301.

The acid gas stream from the top of the Regenerator C-302 is cooled in the DM water preheater E-307 from 102 deg.C to 96 deg.C at 1.04 Kg/cm2g pressure. C-302 pressure is maintained by PIC-015. The vapour condensed is removed in V-304 (OH condensate separator). The acid gas stream outletting the Regenerator C-303 at 94 deg.C and 0.1 Kg/cm2g is cooled in the O/H DM water heater E-308 to 91 deg.C and the vapour condensed is removed in the C-303 1st O/H condensate separator V-305. C-303 pressure is maintained by PIC-001. Again the acid gas is cooled in the condensers E-304A/B to 40 deg.C by cooling water. The vapour condensed is separated in the C-303 2nd OH condensate separator V-302. The CO2 is fed to the Booster compressor K-301 or it can be vented to atmosphere through PIC-026. K-301 boosts the pressure of CO2 from 0.1 Kg/cm2g to 0.96 Kg/cm2g at 96 deg.C. The discharge of Booster compressor joins the stream of CO2 from C-302 at the outlet of V-304 and the mixed stream gets cooled in the final OH condensers E-305A/B from 102 deg.C to 40 deg.C by cooling water. The water vapour condensed is removed in final OH condensate separator V-303 and the CO2 saturated with water flows to Urea Plant. The ammonia Plant battery limit conditions for the CO2 sent to Urea Plant are 0.6 Kg/cm2g and 40 deg.C.

The use of compressor K-301 on a very limited acid gas stream allows to utilise in the most advantageous way, the two pressure levels regeneration technique, since it allows to keep C-303 pressure at a lower level, thereby increasing the flashing steam of the solution coming from C-302 with evident energy saving. At the same time it allows to obtain all CO2 for Urea production at higher pressure.

The condensate separated out at V-304 and V-303 flows to V-305 and V-302 respectively under pressure where as condensate from V-305 and V-302 are pumped out by P-304 and P-305 condensate pumps respectively as make up to CO2 removal section and balance as process condensate to stripping unit. There are two numbers lean solution pumps (P-301A/B) one steam turbine driven and the other motor driven. Out of three semilean solution pumps (P-302A/B/C), two are steam turbine driven and the other motor driven.

Two hydraulic turbines (DPTP-302 A/B) are connected to the turbine driven semilean solution pumps P-302A/B through auto clutch. The letdown turbines sends the rich solution from Absorber bottom which is at a pressure of 27.5 Kg/cm2g to the Regenerator C-302 which is at a pressure of 1.04 Kg/cm2g. The discharge side pressure of hydraulic turbine will be about 9 Kg/cm2g. The differential pressure 18.5 Kg/cm2g is utilised to drive the semilean solution pumps. This pressure energy approximately amounts to a power of 215 KW in each hydraulic turbine thus energy on steam driven turbines DSTP-302A/B is conserved to an extent of 215 KW on each turbine, by clutching Hydraulic turbine to the Semilean solution pumps.

2.6 METHANATION CATALYST

As CO and CO2 are poisons to the Ammonia converter catalyst, the unconverted CO and unabsorbed CO2 in the process gas are reduced to a limit of less than 10 ppm by methanation reaction. In the process, CO and CO2 get converted to CH4 which is an inert in the synthesis of ammonia. In the Methanator R-301, the reverse of reforming reaction takes place in presence of Nickel catalyst.

The reactions are as follows :

CO + 3 H2 CH4 + H2O + Heat CO2 + 4 H2 CH4 + 2 H2O + Heat

The main reason why the reaction is reversed is the lower temperature favouring formation of methane. Other critical variables governing the reactions are pressure and steam content. However, within the allowable temperature range, the equilibrium conditions are so favourable that practically only the catalyst activity determines the efficiency of the methanation. The higher the temperature, the better the efficiency, but at the same time it means a shorter life time for the catalyst.

Further more in case of a possible break through of CO2 and CO to the methanator which would result in a higher temperature rise, a low inlet temperature is preferred as this limits the temperature rise. After the methanator the gas normally contains 10 ppm of CO + CO2. The temperature rise of gas in methanator will normally be about 21 deg.C. Methanator contains 26 M3 of catalyst and has approximately the same characteristics as of reformer, being nickel catalyst on a ceramic base. As the reactions take place at much lower temperature than those prevailing in the reformers, the catalyst must be very active at low temperatu- res. The catalyst is sensitive to Arsenic, Sulphur and Chloride Compounds. The adiabatic temperature rise per mole % of CO is 74 deg. C and per mole% of CO2 is 60 deg. C. The methanation reaction starts at a temperature of about 240 deg. C but in order to ensure a sufficiently low concentration of CO and CO2 in the effluent gas, the operating temperature would be from 280 deg. C to 350 deg.C, depending on the catalyst activity and gas composition. The methanator catalyst should not be exposed to catalyst temperature above 440 deg. C for longer periods of time as it will damage the vessel R-301.

Washed gas from CO2 removal (outlet of V-314) goes to E-311 Gas/Gas exchanger at 26.8 Kg/cm2g and 65 deg. C and gets heated upto the inlet temperature of 310 deg. C by exchange of heat with hot methanator effluent gas. A part of the outlet gas from E-311A/B passes through E-209 and gets heated up with R-204 outlet gas and joins at the inlet of methanator (resultant temperature is 320 deg. C.. The outlet gas from methanator at 341 deg.C gets cooled in the Gas/Gas exchanger E-311A/B to 87.3 deg.C and is further cooled down in E-312A/B (final gas cooler) to 41 deg. C by cooling water and the condensate formed is separated in the final gas separator V-311. The pure synthesis gas enters syn. gas compressor suction at a pressure of 25.1 Kg/cm2g and 41 deg. C. Surplus syn. gas is taken out and sent to Auxiliary boiler to be used as fuel. In case of synthesis gas compressor trip, or prior to the start-up of synthesis gas compressor, gas is vented at PIC-074 and PIC-071 and thus front end pressure is maintained. From the outlet of V-311, the process gas is also taken as recycle H2 to header to feed K-204 (recycle gas compressor). This recycle H2 line is provided with HIC-003, which controls the recycle H2 flow to header. This valve is connected to the Methanation trip signal IS-6 which closes HV-003 on trip signal of IS-6.

ReactorCatalystTypeSizemmVolumeM3Bulk DensityBed ht.mmcompositionLife time (exp)

R-301PK-5526.0>10

NICKEL CARBONYL GAS

Nickel carbonyl gas is a poisonous and toxic gas which may be present in R-301. Under certain conditions, CO in the process gas reacts with the catalyst Ni to form Nickel carbonyl gas.

4 CO + Ni Ni (CO)4

The favourable temperature range of the formation of this gas is between 45 deg.C and 205 deg.C. Hence R-301 catalyst should never be allowed to cool in the presence of CO containing gas. Rather it should be purged out with N2 at the time of shut down.While heating up the catalyst with the process gas containing CO, heating should be done faster in the range of 45 deg. C to 205 deg. C.

2.8 AMMONIA SYNTHESIS CATALYST

The Ammonia Synthesis takes place in the Ammonia converter R- 501 as per the following reaction.

N2 + 3H2 Iron Catalyst 2NH3 + Heat

The reaction is limited by the equilibrium concentration and only part of the Hydrogen and Nitrogen can be converted into Ammonia per pass through the Catalyst bed . The equilibrium concentration of Ammonia is favoured by high pressure and low temperature. However, reaction rate is very much enhanced by high temperature operations. There is a compromise between thermodynamic equilibrium & reaction kinetics. As a result there is an optimum level for the Catalyst temperatures at which the maximum production is obtained. At higher temperatures the equilibrium percentage (which is the theoritically highest obtainable concentration of Ammonia) will be too low while at lower temperature the reaction rate will be too low. The Synthesis loop is designed for a miaximum pressure of 155 Kg/cm2g and the normal operating pressure is in the range of 131-141 Kg/cm2g. The reaction temperature in the catalyst bed is 360 to 520 deg. C which is close to the optimum level. The catalyst is a promoted iron catalyst containing small amounts of non-reducible Oxides. A considerable amount of heat is liberated by the reaction (about 750 Kcal/Kg of Ammonia produced), and this is utilized for production of KS steam and for preheating Boiler feed water. Only about 20% of the Hydrogen and Nitrogen flow contained in the Synthesis gas at converter inlet is converted into Ammonia per pass, and it is therefore necessary to recycle the unconverted synthesis gas to the converter. The Ammonia Converter, R-501 is a Topsoe series 200, Radial Type converter with the gas flowing through the two catalyst beds in RAdial direction. The advantage of the Radial flow converter is that the pressure drop is less. The catalytic activity of small particles is very high and the special advantage of the radial converter is to allow the use of small catalyst particles without a prohibitive pressure drop.

The converter contains two catalyst beds with interbed cooling after 1st bed. There is also a provision of cold shot injection for better control of bed temperatures. A total of 96 M3 Catalyst of type Topsoe KMI/KMIR is used. The first bed has a volume of 28 M3 of KMIR Catalyst and the 2nd bed contains 68 M3 of KMI Catalyst. The KMIR Catalyst is the pre-reduced and stabilized catalyst of KMI type. Stabilisation involves skin Oxidation of the Catalyst where it takes-up an amount of 2% (Wt) of Oxygen. This prereduced catalyst is stable in air below 100 deg.C. Above 100 deg. C it will react with air and spontaneously heats up. The catalyst is activated by reducing Iron-oxide to free Iron. This reduction is carried out with circulating Synthesis gas. The Catalyst activity will decrease slowly during normal operation and the lifetime of Catalyst is 8 to 10 years. This is again influenced by the actual process conditions. notably the temperature in the Catalyst bed and the concentrations of Catalyst poisons in the Synthesis gas at converter inlet. Sulphur compounds and compounds containing Oxygen such as water (H2O), Carbon Monoxide (CO) and Carbon dioxide (CO2) are all poisons to the Catalyst and small amounts of the catalyst poisons will cause a considerable decrease in Catalyst activity. Part of the poisoning effect is only temporary and catalyst activity will recover somewhat when the gas is clean again. A certain permanent decrease in the Catalyst activity will however remain and high concentrations of Oxygen compounds at converter inlet even for short duration should therefore be avoided.

PROCESS CONDITIONS

Ammonia Synthesis reaction is affected by the following parameters :

- Ammonia content in the feed gas

- Inert gas content in the feed gas

- H2 to N2 ratio in the feed gas

- Reaction temperature

- Circulation Rate

- Operating pressure

- Catalyst activity

ReactorCatalystTypeSizemmVolumeM3Bulk DensityBed ht.mmcompositionLife time (exp)Features

R-501KMR (pre-reduced)

KM1.5-3.0

1.526.9

68.42220

2850Prereduced free iron+2wt%O294% Fe3O4 balance:CaO,Al2O3, K2O5-10Catalyst promoters:Ca,Al,KNot pyrophoric at ambient temp.

AMMONIA CONTENT IN THE FEED GAS

A low Ammonia concentration at converter inlet gives a high reaction rate and thus a high production capacity.The Ammonia concentration at converter inlet is dependent on the cooling level in the refrigeration chillers and the operating pressure.4.1% NH3 at converter inlet corresponds to -5 deg.C at a pressure of 132 Kg/cm2g in the Ammonia Separator, V-501.

INERT GASES

The Makeup gas contains 1.33% (Vol.) of argon and methane. These gases are inerts in the sense that they pass through the Synthesis converter without undergoing any Chemical changes. But a high concentration of inerts reduces the partial pressures of Hydrogen and Nitrogen thereby reducing the conversion. Therefore a constant purge of gas from the loop is maintained to keep the inerts level in the converter inlet at about 8%. The catalyst activity decreases with the catalyst age. This can be compensated by either increasing the loop pressure and the circulation rate or by decreasing the inert level.

HYDROGEN/NITROGEN RATIO

By the Synthesis reaction, 3 volumes of Hydrogen react with 1 volume of Nitrogen to form 2 volumes of Ammonia. Therefore the H2/N2 ratio in the loop and makeup gas must be close to 3:1. A small change in H2/N2 ratio of the make up gas will result in a much bigger change in the H2/N2 ratio of the circulating Synthesis gas. The H2/N2 ratio of the makeup gas should normally be about 2.78 so that after addition of recovered hydrogen from PGR Unit the ratio will be about 3.0. The Synthesis loop is designed for operating at the H2/N2 ratio of 3.0, but special conditions may make it favourable to operate the loop at a slightly different ratio in the range of 2.5 to 3.5. When the ratio is decreased to 2.5, the reaction rate will increase slightly (but fall again for ratios below 2.5), while on the other hand, the circulating Synthesis gas will be heavier. Therefore the pressure drop through the loop will increase and the Ammonia separator efficiency may decrease, leading to increased Ammonia concentration at the converter inlet.The H2/N2 ratio in the loop should be kept as constant as possible. The ratio is controlled by the H2/N2 ratio in the makeup gas which will have to be adjusted to get desired ratio in the circulating gas. After making any change in the H2/N2 ratio of the makeup gas sufficient time should be allowed for the system to find its new equilibrium before making further changes.

REACTION TEMPERATURE

The temperatures in the Catalyst bed are usually in the order of 360 deg.C to 520 deg.C. At the inlet to ech Catalyst bed, a certain minimum temperature of 360 to 380 deg.C is required to ensure a sufficient reaction rate. If the temperature at catalyst inlet is below 360 deg. C, the reaction rate may become so low that the heat liberated by the reaction becomes too small to maintain the temperature in the converter, and the reaction will quickly extinguish itself if proper process adjustments (lowering the gas circulation and / or closing the cold shot) are not made immediately. On the other hand it is desirable to keep the catalyst temperatures as low as possible to prolong the catalyst life.It is therefore recommended that the catalyst inlet temperature be kept as close as practically possible to the minimum temperature without extinguishing the reactor. The Synthesis gas entering the converter at 252 deg. C is heated in the interbed heat exchanger by the hot gas coming out of the 1st bed. Before entering the 1st bed, the temperature of this gas is controlled to about 370-380 deg.C by mixing with cold shot. As the gas passes through the catalyst bed, the temperature increases to a maximum temperature at the outlet from the 1st catalyst bed, which is normally the highest temperature in the converter, called the "hot spot". The temperature of the hot spot may be upto 520 deg.C, but should not exceed 530 deg. C. The gas from the 1st bed is cooled in the interbed heat exchanger by the main part of the cold inlet gas to the 1st bed in order to obtain a temperature of approx. 380 deg.C before entering the 2nd bed. In the 2nd bed the gas outlet temperature is about 439 deg. C.

CIRCULATION RATE

The capacity of the synthesis loop with regard to Ammonia production rises with increasing circulation rate. However, the Ammonia production per cubic metre of circulation gas which is proportional to the temperature difference between converter exit and converter inlet, will decrease.

OPERATING PRESSURE

The Synthesis loop is designed for a maximum pressure of 155 Kg/cm2g and it is foreseen that the Synthesis loop can operate at a pressure of 142 Kg/cm2g when operating at design production rate, design inert level and design gas composition. The actual operating pressure is not directly controlled and is dependent on the other process conditions, notably production rate, inert level, ammonia concentration at converter inlet, H2/N2 ratio and Catalyst Activity. The production rate increases with rising pressure and for a given set of process conditions, the pressure will adjust itself so that the production rate corresponds to the amount of Makeup gas fed into the loop. The loop pressure will be increased by increasing the Makeup gas flow to the loop, by decreasing the circulation rate, increasing the inert level or the concentration of Ammonia at converter inlet and by changing the H2/N2 ratio away from the optimum. The decreases in Catalyst activity will also increase the operating pressure.

A TYPICAL REACTOR WITH CATALYST LOADED

LT CATALYST REDUCTION

When the fresh catalyst is loaded it has to be reduced in order to attain full activity before it is actually lined up for the shift conversion reaction i.e. water gas shift reaction.The loaded catalyst vessel is heated to 180oc with nitrogen Circulation continuously in the loop and then hydrogen gas is introduced into the circulationLoop such that the H2 concentration in the loop is around 1.5% slowly the catalystReduction takes place and water is thus formed is continuously removed in theSeparator the H2 concentration is maintained in the loop and the inlet and outletTemperatures and H2 concentrations are monitored every half an hour so as to Keep close control over the reduction. It generally took 36-45 hrs for the reductionTo complete when the inlet and out let H2 gas concentration equals.

During the reduction the temperature of the gas and the catalyst bed risesOwing to the exothermic reaction i.e. oxidation of H2 is taking place as a resultWater is formed in the loop and it has to be removed in order to protect the Catalyst from loss of activity.

When the reduction is completed then the nitrogen circulation is stoppedAnd the process gas is introduced into the catalyst bed and is run for one weekAt about 80% of the rated load. After one week the catalyst gets full activityAnd the reactor is ready for full load. For the next one month the reactor outletCO concentration is monitered on daily basis.The bed temperature is given utmostCare for the first month and it should never cross 240oc crossing which mayResult in sintering of the catalyst.

A TYPICAL 45 Hr LT CATALYST

REDUCTION H2 INLET AND OUTLET H2 CONCENTRATION

DURATION (Hrs) H2 Conc.,(%)

Inlet Outlet

I

0.58 0.04

5

0.78 0.02

10

0.90

0.01

15

0.94 0.06

20

1.38 0.16

25

1.44 0.19

30

1.55 0.38

35

2.24 1.27

40

4.53 3.97

45 8.53 8.37

CATALYST DISPOSAL

The catalyst which lose its activity has to be disposed in a proper way As the catalysts contain metals their oxides and sometimes salts Which on surface dumping could lead to leaching of metals in to The ground water or surface water causing contamination of the land And water bodies. As most of the catalysts are composed of copper Nickel, iron, platinum. Zinc, molybdinum, vanadium,and chromium. Also some of the organic compounds which acts as promoters Or activators such as D.E.A, Glycine etc.,which are potential pollutents Helamin

Helamin is a water treatment chemical. The name is a registered trademark of Filtro, SA, Geneva, Switzerland[1]. Helamine is one of the commercial fouling, corrosion and incrustation inhibitors. It uses the characteristics of aliphatic polyamine. In contrast to the conventional method of the water treatment, its action is based on a preventive protection of the surfaces.Helamin forms a firmly adhering protective film, which prevents corrosion and fouling on the water-side walls in steam boilers and piping systems. It happens because Helamine has an affinity to metal and oxide surfaces. Crystals which do form in the presence of Helamine are isolated, so that they cannot group themselves any longer. Thus deposit consolidation is inhibited. Already existing oxide surface deposits are gradually Boiler develops a fine, liquid mud, which does not tend to accumulate in the boiler. Helamin does not significantly decompose even at high temperature and pressure employed in the modern sub-critical -water power-plant boilers. Helamin treatment can be successfully employed in steam generators, warm and hot water piping systems, superheaters, as well as cooling circuitsto mitigate some of the difficult problems of the corrosion and fouling. HelaminFrom Wikipedia, the free encyclopediaHelamin is a group of water treatment chemicals.The name is a registered trademark of Filtro, SA, Geneva, Switzerland.[2] Chemically,most of the Helamin types are stated by the manufacturer to be a "mixture of polyaminesand polycarboxylates in aqueous solution", but some also utilize volatile amines, ammonia,polyelectrolytes, organic polymers, and scavengers of dissolved oxygen.[1]Helamin is one of the commercial fouling and corrosion inhibitors. It uses the characteristics of aliphatic polyamine. In contrast to the conventional method of the water treatment, its action is based on a preventive protection of the surfaces.Helamin forms a film (i.e., is one of numerous available "filming amines"), which prevents corrosion and fouling on the water-side walls in steam and piping systems. It happens because Helamin has an affinity to metal and oxide Crystals which do form in the presence of Helamine are isolated, so that they do not tend to group themselves. Thus deposit consolidation is inhibited.Already existing oxide surface deposits are gradually removed. Boiler develops a fine, liquid mud, which is easier to remove from the boiler.Helamin does not significantly decompose even at high temperature and pressureemployed in the modern sub-critical -water power-plant boilers[citation needed]. Helamin treatment can be successfully employed in steam generators, warm and hot water piping systems, superheaters, as well as cooling circuits to mitigate some of the difficult problems of the corrosion and fouling. cation conductivity of water tends to increase with the use of Helamin.[2]HOW IT WORKS ? Helamin products are proprietary formulations of a perfect blend of components that include protective (filming) polyamines, polycarboxylates (dispersants), and volatile (alkalinizing) amines, working in a synergistic way to provide an optimum protection and passivation of all ferrous and non ferrous metal surfacesin the entire water & steam circuit (Turbines included).Helamin is forming a monomolecular, continuous, and hydrophobic protective film on metal surfaces, acting as a barrier between water and metal to prevent corrosion.The use of Helamin "All-in-one" product to treat water and steam carrying such as water/steam and heating circuits, has many advantages over conventionalconditioning which often requires several substances to be added at various locations and needs regular monitoring.In the boiler water of steam generators the polyelectrolytes have a synergetic effect. The polycarboxylates (as sodium salt) cause at every temperature an because of hydrolysis. As a polyelectrolyte it has greater affinity to bivalent cations (e.g. Fe2+ or Ca2+), like a weak acidic ion exchanger. Hence, quite stable calcium or iron salts are formed which can be removed by blow down. At the stoechiometric limits any residual hardness is kept in solution. Any additional quantities are sequestered, suspended and dispersed (i.e. prevented from crystallising and forming scale, or any other deposits).The polyamines have a greater propensity to be adsorbed at the interfaces.In addition to the corrosion-protecting effect of the membrane, they also prevent calcium carbonate crystals from growing on the material surface,especially in the area of the heat transfer. Corrosion products which are transported into the boiler are also prevented from accumulating and any existing deposits can begently removed. If used in steam generators, warm and hot water networks, superheaters,turbines and cooling systems, Helamin is an efficient, economical and ecological solution to the difficult problem of corrosion and scaling.The Helamin range of conditioners provides additional safety thanks to preventivesurface protection, the key to successful and economic operation of your systems

1. 1. Prepared by: Saba Power Company Cell # +92 321 4598293 2. 2. What is Steam Turbine? A Steam Turbine is a device that extracts Thermal Energy from pressurized Steam and uses it to do Mechanical Energy on a rotating output shaft. Steam Turbine is device where Kinetic Energy (Heat) converted into Mechanical Energy (in shape of rotation). Turbine is an Engine that converts Energy of Fluid into Mechanical energy & The steam turbine is steam driven rotary engine. This Presentation is base on basic of Steam Turbine & 134 MW Toshiba Steam Turbine. 3. 3. Rating & Design Data Turbine Type: SCSF-36, single cylinder, single flow Reheat condensing turbine. Rated output: 134 MW Speed: 3000 RPM Direction of Revolution: Counter-clock-wise (seeing from turbine front End) Steam Condition: Main Steam Press. (before MSV): 16548 kpa (g) Main Steam Temp. (before MSV): 538oC Reheat steam Temp. (before CRV): 538oC Exhaust pressure: 6.77 kpa (g) 4. 4. Rating & Design Data Number of Extraction: 6 Number of Stage: 21 HP Turbine: 9 stages IP Turbine: 7 stages LP Turbine: 5 stages Number of Wheel: 21 5. 5. 6. 6. 7. 7. 8. 8. In order to better understand turbine operation, Four Basic Classifications are discussed. Type of Steam Flow & Division of Steam Flow, describes the flow of steam in relation to the axis of the rotor. indicates whether the steam flows in just one direction or if it flows in more than one direction. Way of Energy Conversion & Type of Blading, Reaction, Impulse and Impulse & Reaction Combine. identifies the blading as either impulse blading or reaction blading. Type of Compounding & Cylinder arrangement refers to the use of blading which causes a series of pressure drops, a series of velocity drops, or a combination of the two. (number of cylinders; whether single, tandem or cross-compound in design) Exhausting Condition & Number of Stages is determined by whether the turbine exhausts into its own condenser or whether it exhausts into another piping system. 9. 9. 1. Type of Steam Flow Turbines may be classified according to the direction of steam flow in relation to the turbine wheel or drum - Axial. - Radial. - Mixed - Tangential Or Helical. - Reentry 10. 10. Radial Flow: A turbine may also be constructed so that the steam flow is in a radial direction, either toward or away from the axis. In figure illustrates an impulse, radial flow, auxiliary turbine such as may be used as a pump drive. The radial turbine is not nor mally the preferred choice for electricity generation and is usually only employed for small output applications 11. 11. Axial Flow: The great majority of turbines, especially those of high power, are axial flow. In such turbines the steam flows in a direction or directions parallel to the axis of the wheel or rotor. The axial flow type of turbi ne is the most preferred for electricity generation as several cylinders can be easily coupled together to achieve a turbine with a greater output. . 12. 12. Reverse Flow In some modern turbine designs the steam flows through part of the high pressure (HP) cylinder and then is reversed to flow in the opposite direction through the remainder of the HP cylinder. The benefits of this arrangement are: outer casing joint flanges and bolts experience much lower steam conditions than with the one direction design reduction or elimination of axial (parallel to shaft) thrust created within the cylinder lower steam pressure that the outer casing shaft glands have to accommodate A simplified diagram of a reverse flow high pressure cylinder is shown in Figure 13. 13. 2. Way of Energy Conversion & Types of Blading - Impulse turbines - Reaction turbines - Impulse & Reaction Combine 14. 14. By Types of Blading: The heat energy contained within the steam that passes through a turbine must be converted into mechanical energy. How this is achieved depends on the shape of the turbine blades. The two basic blade designs are: 1. Impulse 2. Reaction 15. 15. Impulse: Impulse blades work on the principle of high pressure steam striking or hitting against the moving blades. The principle of a simple impulse turbine is shown in Figure. Impulse blades are usually symmetrical and have an entrance and exit angle of approximately 200. They are generally installed in the higher pressure sections of the turbine where the specific volume of steam is low and requires much smaller flow areas than that at lower pressures. The impulse blades are short and have a constant cross section. 16. 16. Reaction: The principle of a pure reaction turbine is that all the energy contained within the steam is converted to mechanical energy by reaction of the jet of steam as it expands through the blades of the rotor. A simple reaction turbine is shown in Figure. The rotor is forced to rotate as the expanding steam exhausts the rotor arm nozzles. In a reaction turbine the steam expands when passing across the fixed blades and incurs a pressure drop and an increase in velocity. When passing across the moving blades the steam incurs both a pressure drop and a decrease in velocity A section of reaction type blading is shown in Figure 17. 17. Impulse stage Whole pressure drop in nozzle (whole enthalpy drop is changed into kinetic energy in the nozzle) Reaction stage Pressure drop both in stationary blades and in rotary blades (enthalpy drop changed into kinetic energy both in stationary blades and in the moving blades in rotor) 18. 18. An impulse stage consists of stationary blades forming nozzles through which the steam expands, increasing velocity as a result of decreasing pressure. The steam then strikes the rotating blades and performs work on them, which in turn decreases the velocity (kinetic energy) of the steam. The stream then passes through another set of stationary blades which turn it back to the original direction and increases the velocity again though nozzle action. 19. 19. In Reaction Turbine both the moving blades and the non- moving blades designed to act like nozzles. As steam passes through the non-moving blades, no work is extracted. Pressure will decrease and velocity will increase as steam passes through these non- moving blades. In the moving blades work is extracted. Even though the moving blades are designed to act like nozzles, velocity and pressure will decrease due to work being extracted from the steam. 20. 20. This utilizes the principle of impulse and reaction. It is shown diagrammatically : There are a number of rows of moving blades attached to the rotor and an equal number of fixed blades attached to the casing. The fixed blades are set in a reversed manner compared to the moving blades, and act as nozzles. Due to the row of fixed blades at the entrance, instead of nozzles, steam is admitted for the whole circumference and hence there is an all-round or complete admission. 21. 21. Compounding of Impulse Turbine This is done to reduce the rotational speed of the impulse turbine to practical limits. (A rotor speed of 30,000 rpm is possible, which is pretty high for practical uses.) Compounding is achieved by using more than one set of nozzles, blades, rotors, in a series, keyed to a common shaft; so that either the steam pressure or the jet velocity is absorbed by the turbine in stages. Three main types of compounded impulse turbines are: a) Pressure compounded, b) velocity compounded and c) pressure and velocity compounded impulse turbines. 22. 22. With pressure compounding the total steam pressure to exhaust pressure is broken into several pressure drops through a series of sets of nozzles and blades. Each set of one row of nozzles and one row of moving blades is referred to as a stage This involves splitting up of the whole pressure drop from the steam chest pressure to the condenser pressure into a series of smaller pressure drops across several stages of impulse turbine. The nozzles are fitted into a diaphragm locked in the casing. This diaphragm separates one wheel chamber from another. All rotors are mounted on the same shaft and the blades are attached on the rotor. Pressure staging is also known as RATEAU staging. 23. 23. When the velocity energy produced by one set of fixed nozzles is unable to be efficiently converted into rotational motion by one set of moving blades then it is common to install a series of blades as shown in Figure. This arrangement is known as velocity compounding. Velocity drop is arranged in many small drops through many moving rows of blades instead of a single row of moving blades. It consists of a nozzle or a set of nozzles and rows of moving blades attached to the rotor or the wheel and rows of fixed blades attached to the casing. 24. 24. This is a combination of pressure-velocity compounding. Most modern turbines have a combination of pressure and velocity compounding. This type of arrangement provides a smaller, shorter and cheaper turbine; but has a slight efficiency trade off. Turbines using this arrangement are often referred to as CURTIS turbines after the inventor. Individual pressure stages (each with two or more velocity stages) are sometimes called CURTIS stages. 25. 25. This setup of a nozzle followed by a set of moving blades, non-moving blades, and moving blades makes up a single Curtis stage. After steam exits the nozzle there are no further pressure drops. However, across both sets of moving blades there is a velocity drop. This causes the Curtis stage to be classified as velocity compounded blading. 26. 26. Turbines can be arranged either single cylinder or multi-stage in design. The multi-stage can be either velocity, pressure or velocity-pressure compounded (discussed as earlier. Single cylinder construction or Single Flow Turbine Single cylinder turbines have only one cylinder casing(although may be is multiple sections). Steam enters at the high pressure section of the turbine and passes through the turbine to the low pressure end of the turbine then exhausts to the condenser. Figure shows a single cylinder turbine with a high, intermediate and low pressure section contained within the one cylinder casing. 27. 27. Tandem construction or Compound Flow Turbine Dictated by practical design and manufacturers considerations modern turbines are manufactured in multiple sections also called cylinders. Greater output and efficiency can be achieved by coupling a number of individual cylinders together in what is referred to as tandem (on one axis). Tandem compound Large electric power generating turbines commonly have a high pressure casing, which receives superheated steam directly from the boiler or steam generator. The high pressure turbine may then exhaust to an intermediate pressure turbine, or may pass back to a reheat section in the boiler before passing to a reheat intermediate pressure turbine. The reheat turbine may then exhaust to one or more low pressure casings, which are usually two exhaust flow turbines, with the low pressure steam entering the middle of the turbine and flowing in opposite directions toward two exhaust end before passing into the condenser. When the turbine casings are arranged on a single shaft, the turbine is said to be tandem compounded. 28. 28. Tandem construction or Compound Flow Turbine A tandem two cylinder turbine with a single flow high pressure (HP) cylinder and a double flow low pressure (LP)cylinder is shown in Figure. 29. 29. Tandem Three Cylinder Turbine It has a double flow LP cylinder with an IP cylinder arranged so that the steam flow through it is in the opposite direction to the HP cylinder. This design also greatly reduces the axial thrust on the rotor. Tandem three cylinder turbine is shown in Figure as under: 30. 30. Tandem Four Cylinder Turbine Large modern turbines are required to deliver high output and are generally constructed of four cylinders with the exhaust steam from the HP cylinder passing through are heater before entering the IP cylinder. Tandem Four cylinder turbine is shown in Figure as under: 31. 31. Tandem Cross-Compounding Turbine In cross compound turbines, the high- pressure, exhaust passes over to intermediate or low pressure casings which are mounted on separate shafts. The two shafts may drive separate loads, or may be geared together to a single load. In some larger overseas installations that operate at 60 hertz (frequency) the use of cross-compounding is some times employed. Cross-compounding is where the HP and IP cylinders are mounted on one shaft driving one alternator while the LP cylinders are mounted on a separate shaft driving another alternator. This is done so as the LP cylinder with its large diameter blading can be operated at a greatly reduced speed thus reducing the centrifugal force. Tandem cross-compounding turbine is shown in Figure: 32. 32. Tandem four cylinder turbine with reverse flow The final turbine arrangement that is becoming increasingly popular is the Tandem four cylinder turbine with reverse flow HP cylinder, double flow IP and twin double flow LP cylinders. This arrangement is shown in Figure: 33. 33. 04. Number of Stages - Single stage - Multi-stage 34. 34. In an impulse turbine, the stage is a set of moving blades behind the nozzle. In a reaction turbine, each row of blades is called a "stage." A single Curtis stage may consist of two or more rows of moving blades. 35. 35. 5. Exhaust Conditions - Condensing - Extraction - Back-pressure 36. 36. By steam supply and exhaust conditions: Condensing Extraction, (Automatic or controlled ) Non-condensing (back pressure), Mixed pressure (where there are two or more steam sources at different pressures), Reheat (where steam is extracted at an intermediate stage, reheated in the boiler, and re- admitted at a lower turbine stage). 37. 37. Condensing The condensing turbine processes result in maximum power and electrical generation efficiency from the steam supply and boiler fuel. The power output of condensing turbines is sensitive to ambient conditions. The cooling water condenses the steam turbine exhaust steam in the condenser creating the condenser vacuum. As a small amount of air leaks into the system when it is below atmospheric pressure, a relatively small compressor (Vacuum pump) or Air Ejector System removes non-condensable gases from the condenser. 38. 38. Extraction In an extraction turbine, steam is withdrawn from one or more stages, at one or more pressures, for heating, plant process, or feed water heater needs. They are often called "bleeder turbines. The steam extraction pressure may or may not be automatically regulated. Regulated extraction permits more steam to flow through the turbine to generate additional electricity during periods of low thermal demand by the CHP system. In utility type steam turbines, there may be several extraction points, each at a different pressure corresponding to a different temperature. The facilitys specific needs for steam and power over time determine the extent to which steam in an extraction turbine is extracted for use in the process. 39. 39. Back-pressure Figure shows the non- condensing turbine (also referred to as a back- pressure turbine) exhausts its entire flow of steam to the industrial process or facility steam mains at conditions close to the process heat requirements. 40. 40. 4. Rotational Speed - Regular - Low-speed - High-speed 5. Inlet steam pressure - High pressure (p>6,5MPa) - Intermediate pressure(2,5MP a