PLANT DESIGN FOR THE PRODUCTION OF 400,000 METRIC TONNES OF NITRIC ACID PER ANNUM FROM AIR OXIDATION OF AMMONIA GASBYANDREW OFOEDUDEPARTMENT OF CHEMICAL ENGINEERINGFEDERAL UNIVERSITY OF TECHNOLOGY, OWERRI.SEPTEMBER 2013

EXECUTIVE SUMMARYThis report describes the detailed design of a plant to produce 400000 tonnes of nitric acid per year by Ostwald Process. The single pressure process was selected as the most advantageous, having considered several factors one of which is efficient energy management. The process begins with the vaporization of ammonia at 1000 kPa and 35C using process heat. Steam is then used to superheat the ammonia up to about 80C. Filtered air is compressed in an axial compressor to a discharge pressure of about 740kPa and temperature of 155C. Part of the air is diverted for acid stripping. This preheated air and the ammonia vapour are then mixed and passed through the platinum/rhodium catalyst gauze in a converter for oxidation. The reaction gas flows through a series of heat exchangers for recovery of energy as either high-pressure superheated steam, or as shaft horsepower from the expansion of hot tail gas in the turbine. Considering the proximity to market, sea port and source of raw materials, it was decided to site the plant in Eleme, Rivers State. The plants estimated capital investment is 5.41 billion. The rate of return on investment is 26.25% and the payback period is estimated to be 3 years and 7 months. Thus, the project is both technically and economically feasible.

TABLE OF CONTENTTitle pageiExecutive Summary---------------------------------------------------------------------------iiTable of content-------------------------------------------------------------------------------iii

CHAPTER ONE 1.0 Introduction11.3 Design justification-------------------------------------------------------------------31.4 Design Objectives---------------------------------------------------------------------4 CHAPTER TWO 2.0 Literature review------------------------------------------------------------------------52.1 History of Nitric acid production-------------------------------------------------------52.2 Ammonia oxidation chemistry----------------------------------------------------------82.3 Emission and Control-----------------------------------------------------------------------142.4 Structure and bonding---------------------------------------------------------------------152.5 Reactions-------------------------------------------------------------------------------------162.6 Uses---------------------------------------------------------------------------------------------192.7 Safety-------------------------------------------------------------------------------------------212.8 Pinch technology in modern plant------------------------------------------------------222.9 Plant Location 24 2.9.5 Plant layout-----292.9.6 Process routes for the production of nitric acid-----33

CHAPTER THREE 3.0 Material balance 423.1 Conservation of mass 423.2 Methods of material balancing 433.3 Materials balance assumptions443.4 Summary of material balance calculations443.5 Material balance for each unit44

CHAPTER FOUR 4.0 Energy balance 534.1 Conservation of energy544.2 Energy balance assumptions 564.3 Summary for energy balances56

CHAPTER FIVE5.0 Chemical Engineering design--------------------------------------------------------615.1 Process units of Nitric acid Production--------------------------------------------61

CHAPTER SIX6.0 Equipment design and specification 666.1 Problem specification676.2 Analyzing the problem solution686.3 Preliminary design-----------------------------------------------------------------------686.4 Material Selection-----------------------------------------------------------------------696.5 Design optimization---------------------------------------------------------------------696.6 Summary of design and equipment specification calculation---------------70

CHAPTER SEVEN7.0 Process control and instrumentation737.1 Objective-----------------------------------------------------------------------------------737.2 Plant control instrumentation747.3 Alarms and safety trips 777.4 Lining, piping, valves and pumps787.5 Pipe support81CHAPTER EIGHT8.0 Safety and environmental considerations---------------------------------------828.1 Safety------------------------------------------------------------------------------------828.2 Hazard and Operability (HAZOP) study-------------------------------------------898.3 Environmental impact assessment-------------------------------------------------97CHAPTER NINE9.1 Overview1039.2 Economic Consideration1039.3 Cost estimation---------------------------------------------------------------------------106

9.6 Economic analyses calculation108CHAPTER TEN10.0 Start up and shut down procedure11310.1 Emergency shut down and emergency depressurization11410.2 Notification11410.3 Record keeping 11510.4 Startup operation116

CHAPTER ELEVEN11.0 Conclusion/ Recommendation----------------------------------------------------11811.1 Conclusion------------------------------------------------------------------------------11811.2 Recommendation -------------------------------------------------------------------119

REFERENCES120

APPENDIX ITables and Charts--------------------------------------------------------------------------------123APPENDIX IIMaterial Balance Calculation------------------------------------------------------------------126

APPENDIX IIIEnergy Balance Calculation------------------------------------------------------------------132APPENDIX IVEquipment Design Calculation----------------------------------------------------------------137APPENDIX VEquipment Costing Calculation---------------------------------------------------------------141

CHAPTER ONEINTRODUCTION1.1 BACKGROUND INFORMATIONNitric acid is a strong acid and a powerful oxidizing agent with enormous possibilities for applications in the chemical processing industry. It has commercial uses as a nitrating agent, oxidizing agent, solvent, activating agent, catalyst and hydrolyzing agent. In relation to world production, approximately 65% of all nitric acid produced is used for the production of ammonium nitrate (specifically for fertilizer manufacture).Nitric acid is now produced commercially using the stepwise, catalytic oxidation of ammonia with air, to obtain nitrogen monoxide and nitrogen dioxide. These nitrogen oxides are subsequently absorbed in water to yield between 50% and 68% strength nitric acid by weight. For applications requiring higher strengths, several methods of concentrating the acid are used. The traditional methods are:(a) Extractive distillation with dehydrating agents such as sulphuric acid or magnesium nitrate;(b) Reaction with additional nitrogen oxides.The latter technique has the greatest application in industry.The chemistry of ammonia oxidation is remarkably simple with only six main reactions that need to be considered. 1.1.1 PROPERTIES AND USESNitric acid is an oxidizing mineral acid with physical and chemical properties that make it one of the most useful inorganic minerals. It is a colorless liquid at room temperature and atmospheric pressure. It is soluble in water in all proportions and there is a release of heat of solution upon dilution. Its high solubility in water is the basis for the process methods used for commercial nitric acid manufacture. It is a strong acid that almost completely ionizes when in dilute solution. It is also a powerful oxidizing agent with the ability to passivate some metals such as iron and aluminum. A compilation of many of the physical and chemical properties of nitric acid are presented in the Appendix. Arguably the most important physical property of nitric acid is its azeotropic point, this influences the techniques associated with strong acid production. The constant-boiling mixture occurs at 121.9C, for a concentration of 68.4%(wt) acid at atmospheric pressure.Nitric acid has enormously diverse applications in the chemical industry. It has commercial uses as a nitrating agent, oxidizing agent, solvent, activating agent, catalyst and hydrolyzing agent. The most important use is undoubtedly in the production of ammonium nitrate for the fertilizer and explosives industries, which accounts for approximately 65% of the world production of nitric acid.Nitric acid has a number of other industrial applications. It is used for pickling stainless steels, steel refining, and in the manufacture of dyes, plastics and synthetic fibers. Most of the methods used for the recovery of uranium, such as ion exchange and solvent extraction, use nitric acid. An important point is that for most uses concerned with chemical production, the acid must be concentrated above its azeotropic point to greater than 95%(wt). Conversely, the commercial manufacture of ammonium nitrate uses nitric acid below its azeotropic point in the range 50 -65 %(wt.). If the stronger chemical grade is to be produced, additional process equipment appropriate to super-azeotropic distillation is required.There is a potential health hazard when handling, and operating with, nitric acid. Nitric acid is a corrosive liquid that penetrates and destroys the skin and internal tissues. Contact can cause severe burns. The acid is a potential hazard, the various nitrogen oxides present as product intermediates in the process are also toxic. An assessment of the health risk must be fundamental to the design of any process. Further consideration and recommendations for the operating health risk and environmental impact of the plant are presented in the Appendix.

1.2DESIGN JUSTIFICATIONAt present, there is no Nitric acid plant in Nigeria. The little Nitric acid produced mainly by fertilizer plants in the country is used up immediately by them to make their fertilizer. This means that most of the all Nitric acid used in the country is imported.A Nitric acid plant sited in the country producing Nitric acid made available to the Nigerian market will not only reduce importation of the acid but also encourage fertilizer production, create job opportunities as well as develop the area in which it is sited.

1.3 DESIGN OBJECTIVES To design a plant that will deliver 400000 metric tonnes of 60%(wt) Nitric Acid per annum. To determine the technical and economic feasibility of the plant.

CHAPTER TWO LITERATURE REVIEW2.1 HISTORY OF NITRIC ACID PRODUCTIONUntil the beginning of the 20th century, Nitric acid (HNO3), also known as aqua fortis and spirit of niter was prepared commercially by reacting sulphuric acid with either potassium nitrate (saltpetre) or with sodium nitrate (Chile saltpetre or nitre). Up to four tonnes of the two ingredients were placed into large retorts and heated over a furnace (Kirk 1996). The volatile product vapourized and was collected for distillation. An acid of 93-95 %( wt) was produced (Gregory 1999).In 1903 the electric-arc furnace superseded this primitive original technique. In the arc process, nitric acid was produced directly from nitrogen and oxygen by passing air through an electric-arc furnace (Ray 1990).Gregory (1999, p.40) argues that Although the process benefitted from an inexhaustible supply of free feed material (air), the power consumption for the arc furnace was cost prohibitiveAccording to Ray (1989, p.8) Researchers returned to the oxidation of ammonia in air, (recorded as early as 1798) in an effort to improve production economics. In 1901 Wilhelm Ostwald had first achieved the catalytic oxidation of ammonia over a platinum catalyst. The gaseous nitrogen oxides produced could be easily cooled and dissolved in water to produce a solution of nitric acid. This achievement began the search for an economic process route.By 1908 the first commercial facility for production of nitric acid, using this new catalytic oxidation process, was commissioned near Bochum in Germany (Ray et al 1989). The Haber-Bosch ammonia synthesis process came into operation in 1913, leading to the continued development and assured future of the ammonia oxidation process for the production of nitric acid. (Ray et al 1989)During World War 1, the intense demand for explosives and synthetic dyestuffs created an expansion of the nitric acid industry.Many new plants were constructed, all of which employed the ammonia oxidation process. This increased demand served as the impetus for several breakthroughs in process technology.These included:(a) The development of chrome-steel alloys for tower construction, replacing the heavy stoneware and acid-proof bricks. This enabled process pressures above atmospheric levels to be used.(b) The improved design of feed preheaters enabled higher process temperatures to be attained. Higher temperatures improved the yields and capacities, and also reduced equipment requirements (Ohrue et al 1999).(c) Early developments in automatic process control improved process performance and reduced labor requirements.All of these factors helped to improve the process efficiency. The increasing availability of ammonia reduced processing costs still further.In the late 1920s the development of stainless steels enabled manufacturers to use higher operating pressures. The increase in yield and lower capital requirements easily justified the use of high pressure operation despite increased ammonia consumption.The introduction of higher pressure processes resulted in a divergence of operating technique within the industry. The United States producers opted for a high-pressure system, using a constant high pressure throughout the process. The European manufacturers opted for a split-pressure system. This latter system entails operating the ammonia oxidation section at atmospheric pressure, while the absorption unit is operated at higher pressures, thus capitalizing on improved absorption rates. (Harvin et al 1979)Recent developments in the ammonia oxidation process have included efforts to reduce catalyst losses in the process. Platinum recovery filters have been installed at various stages in the process. (Ohrue et al 1999)Gold/palladium gauze filter pads have been added on the exit side of the catalyst bed, inside the reactor/converter units. These filters have reportedly ensured a platinum recovery of 80% (Anon 1979). Another trend has been for the use of additional filters in the downstream units. These filters are of alumino-silicate construction.Perhaps the greatest progress in nitric acid production technology has been in the manufacture of strong nitric acid (>90% by weight). Advances in the areas of super-azeotropic distillation and in high pressure absorption are most significant. (Ohkubo et al 1999)Research work is continually being performed in an effort to reduce nitrogen oxide emissions from nitric acid plants. The Humphreys and Glasgow/Bolme nitric acid process is just one example of a new philosophy being applied to the absorption systems of weak nitric acid plants (50-68% by weight). Nitrogen oxide emissions have been reduced from 2000-5000 ppm to less than 1000 ppm (Ray et al 1989).For the production of stronger nitric acid, tail gases are now being treated by selective or non-selective catalytic combustion systems. These innovative units have reduced the nitrogen oxide emissions to below 400 ppm (Ray et al 1989).2.2 AMMONIA OXIDATION CHEMISTRYNotably, all commercial nitric acid production methods used today are centered on the oxidation of ammonia. It is therefore appropriate to investigate the chemistry of this process, in the knowledge that it is directly applicable to any of the production processes available. (Chilton 1960)The chemistry of the oxidation of ammonia is surprisingly simple. It begins with a single pure compound, plus air and water, and ends with another pure compound in aqueous solution, with essentially no by-products. The process may be described by just six major reactions as shown as follows:1. 3. 4. 5. 6. Reaction 1 is the overall reaction for the process. This net result is achieved from three separate, and distinct, chemical steps. The first is the oxidation of ammonia to nitrogen monoxide (Reaction 2). The second is the further oxidation of nitrogen monoxide to nitrogen dioxide (Reaction 3), then nitrogen dioxide to nitrogen tetroxide (Reaction 4). The third and final stage involves the absorption of these nitrogen-based oxides into water to form the nitric acid product (Reactions 5 and 6). In most commercial processes, each of these three stages is conducted in separate process units. (Chilton 1960)The first step in the process is the heterogeneous, highly exothermic, gas-phase catalytic reaction of ammonia with oxygen (Reaction 2). The primary oxidation of ammonia to nitric acid (over a catalyst gauze of 9:l platinum/rhodium alloy) proceeds rapidly at process temperatures between 900-970C. (Kent 1983)The second step in the process involves two reactions (Reactions 3 and 4). These are the oxidations of nitrogen monoxide to the dioxide and tetroxide forms. The equilibrium mixture is loosely referred to as nitrogen peroxide. Both reactions are homogenous, moderately exothermic, gas-phase catalytic reactions. All reactions shown are highly exothermic. (Chilton 1960)The third step in the process involves cooling the reaction gases below their dew point, so that a liquid phase of weak nitric acid is formed. This step effectively promotes the state of oxidation and dimerization (Reactions 3 and 4), and removes water from the gas phase. This in turn increases the partial pressure of the nitrogen peroxide component. (Chilton 1960)Finally, nitric acid is formed by the reaction of dissolved nitrogen peroxide with water (Reactions 5 and 6). Nitric acid is produced by 2 methods. The first method utilizes oxidation, condensation, and absorption to produce a weak nitric acid. Weak nitric acid can have concentrations ranging from 30 to 70 percent nitric acid. The second method combines dehydrating, bleaching, condensing, and absorption to produce a high-strength nitric acid from a weak nitric acid. High-strength nitric acid generally contains more than 90 percent nitric acid. The following text provides more specific details for each of these processes. (Chilton 1960)2.2.1 WEAK NITRIC ACID PRODUCTIONAccording to Ray(1989, Nearly all the nitric acid produced in the U. S. is manufactured by the high-temperature catalytic oxidation of ammonia. This process typically consists of 3 steps: (1) ammonia oxidation, (2) nitric oxide oxidation, and (3) absorption. Each step corresponds to a distinct chemical reaction.1. AMMONIA OXIDATIONFirst, a 1:9 ammonia/air mixture is oxidized at a temperature of 1380 to 14700F as it passes through a catalytic convertor, according to the following reaction:

The most commonly used catalyst is made of 90 percent platinum and 10 percent rhodium gauze constructed from squares of fine wire. Under these conditions, the oxidation of ammonia to nitric oxide (NO) proceeds in an exothermic reaction with a range of 93 to 98 percent yield. Oxidation temperatures can vary from 1380OF to 16500F. (Chilton 1960) Higher catalyst temperatures increase reaction selectivity toward NO production. Lower catalyst temperatures tend to be more selective toward less useful products: nitrogen (N2) and nitrous oxide (N2O).Nitric oxide is considered to be a criteria pollutant and nitrous oxide is known to be a global warming gas. The nitrogen dioxide/dimmer mixture then passes through a waste heat boiler and a platinum filter. (Chilton 1960)2. NITRIC OXIDE OXIDATIONThe nitric oxide formed during the ammonia oxidation must be oxidized. The process stream is passed through a cooler/condenser and cooled to 1000F or less at pressures up to 116 pounds per square inch absolute (psia). The nitric oxide reacts non-catalytically with residual oxygen to form nitrogen dioxide (NO2) and its liquid dimmer, nitrogen tetra-oxide:

This slow, homogeneous reaction is highly temperature and pressure dependent. Operating at low temperatures and high pressures promotes maximum production of NO2 within a minimum reaction time (Kent 1983).3.ABSORPTION The final step introduces the nitrogen dioxide/dimmer mixture into an absorption process after being cooled. The mixture is pumped into the bottom of the absorption tower, while liquid dinitrogen tetra-oxide is added at a higher point. De-ionized process water enters the top of the column. Both liquids flow countercurrent to the nitrogen dioxide/dimmer gas mixture. Oxidation takes place in the free space between the trays, while absorption occurs on the trays. The absorption trays are usually sieve or bubble cap trays. The exothermic reaction occurs as follows:

A secondary air stream is introduced into the column to re-oxidize the NO that is formed in Reaction 3. This secondary air also removes NO2 from the product acid. An aqueous solution of 55 to 65 percent (typically) nitric acid is withdrawn from the bottom of the tower. The acid concentration can vary from 30 to 70 percent nitric acid. The acid concentration depends upon the temperature, pressure, number of absorption stages, and concentration of nitrogen oxides entering the absorber.There are 2 basic types of systems used to produce weak nitric acid: single-stage pressure process and dual-stage pressure process (Harvin et al 1979). In the past, nitric acid plants have been operated at a single pressure, ranging from atmospheric pressure to 14.7 to 203 psia. However, since Reaction 1 is favored by low pressures and Reactions 2 and 3 are favored by higher pressures, newer plants tend to operate a dual stage pressure system, incorporating a compressor between the ammonia oxidizer and the condenser. The oxidation reaction is carried out at pressures from slightly negative to about 58 psia, and the absorption reactions are carried out at 116 to 203 psia. (Harvn et al 1979)In the dual-stage pressure system, the nitric acid formed in the absorber (bottoms) is usually sent to an external bleacher where air is used to remove (bleach) any dissolved oxides of nitrogen. The bleacher gases are then compressed and passed through the absorber. The absorber tail gas (distillate) is sent to an entrainment separator for acid mist removal. Next, the tail gas is reheated in the ammonia oxidation heat exchanger to approximately 3920F. The final step expands the gas in the power-recovery turbine. The thermal energy produced in this turbine can be used to drive the compressor.2.2.2 HIGH STRENGTH NITRIC ACID PRODUCTIONA high-strength nitric acid (98 to 99 percent concentration) can be obtained by concentrating the weak nitric acid (30 to 70 percent concentration) using extractive distillation. (Imai et al 1999) The weak nitric acid cannot be concentrated by simple fractional distillation. The distillation must be carried out in the presence of a dehydrating agent. Concentrated sulfuric acid (typically 60 percent sulfuric acid) is most commonly used for this purpose. The nitric acid concentration process consists of feeding strong sulfuric acid and 55 to 65 percent nitric acid to the top of a packed dehydrating column at approximately atmospheric pressure. The acid mixture flow downward, countercurrent to ascending vapors. Concentrated nitric acid leaves the top of the column as 99 percent vapor, containing a small amount of NO2 and oxygen (O2) resulting from dissociation of nitric acid. The concentrated acid vapor leaves the column and goes to a bleacher and a countercurrent condenser system to effect the condensation of strong nitric acid and the separation of oxygen and oxides of nitrogen (NO2) byproducts. (Ohkubo et al 1999) These byproducts then flow to an absorption column where the nitric oxide mixes with auxiliary air to form NO2, which is recovered as weak nitric acid. Inert and un-reacted gases are vented to the atmosphere from the top of the absorption column. Emissions from this process are relatively minor. A small absorber can be used to recover NO2. (Kirk et al 1981)

2.3 EMISSIONS AND CONTROLEmissions from nitric acid manufacture consist primarily of NO, NO2 (which account for visible emissions), trace amounts of HNO3 mist, and ammonia (NH3). By far, the major source of nitrogen oxides (NO2) is the tail-gas from the acid absorption tower. In general, the quantity of NO2 emissions is directly related to the kinetics of the nitric acid formation reaction and absorption tower design. NO2 emissions can increase when there is (1) insufficient air supply to the oxidizer and absorber, (2) low pressure, especially in the absorber, (3) high temperatures in the cooler-condenser and absorber, (4) production of an excessively high-strength product acid, (5) operation at high throughput rates, and (6) faulty equipment such as compressors or pumps that lead to lower pressures and leaks, and decrease plant efficiency. (Leray et al 1979)Roudier (1979) states that the two most common techniques used to control absorption tower tail gas emissions are extended absorption and catalytic reduction. Extended absorption reduces NO2 emissions by increasing the efficiency of the existing process absorption tower or incorporating an additional absorption tower. An efficiency increase is achieved by increasing the number of absorber trays, operating the absorber at higher pressures, or cooling the weak acid liquid in the absorber. The existing tower can also be replaced with a single tower of a larger diameter and/or additional trays.In the catalytic reduction process (often termed catalytic oxidation or incineration), tail gases from the absorption tower are heated to ignition temperature, mixed with fuel (natural gas, hydrogen, propane, butane, naphtha, carbon monoxide, or ammonia) and passed over a catalyst bed. In the presence of the catalyst, the fuels are oxidized and the NO2 are reduced to N2. The extent of reduction of NO2 and NO to N2 is a function of plant design, fuel type, operating temperature and pressure. Space-velocity through the comparatively small amounts of nitrogen oxides is also lost from acid concentrating plants. These losses (mostly NO2) are from the condenser system, but the emissions are small enough to be controlled easily by inexpensive absorbers. Acid mist emissions do not occur from the tail-gas of a properly operated plant. The small amounts that may be present in the absorber exit gas streams are removed by a separator or collector prior to entering the catalytic reduction unit or expander. (Kent 1983)The acid production system and storage tanks are the only significant sources of visible emissions at most nitric acid plants. Emissions from acid storage tanks may occur during tank filling.2.4 STRUCTURE AND BONDING

Fig 2: Two major resonance representations of HNO3.The molecule is planar. Two of the N-O bonds are equivalent and relatively short (this can be explained by theories of resonance. The canonical forms show double bond character in these two bonds, causing them to be shorter than typical N-O bonds.), and the third N-O bond is elongated because the O is also attached to a proton.

2.5 REACTIONS2.5.1 ACID-BASE PROPERTIESNitric acid is normally considered to be a strong acid at ambient temperatures. The pKa value is usually reported as less than 1. This means that the nitric acid in solution is fully dissociated except in extremely acidic solutions. The pKa value rises to 1 at a temperature of 250C. Nitric acid can act as a base with respect to an acid such as sulfuric acid.HNO3 + 2H2SO4 NO2+ + H3O+ + 2HSO4The nitronium ion, NO2+, is the active reagent in aromatic nitration reactions. Since nitric acid has both acidic and basic properties it can undergo an autoprotolysis reaction, similar to the self-ionization of water2HNO3 NO2+ + NO3 + H2O2.5.2 REACTIONS WITH METALSNitric acid reacts with most metals but the details depend on the concentration of the acid and the nature of the metal. Dilute nitric acid behaves as a typical acid in its reaction with most metals. Magnesium, manganese and zinc liberate H2. Others give the nitrogen oxides. (Ababio 2007)Nitric acid can oxidize non-active metals such as copper and silver. With these non-active or less electropositive metals the products depend on temperature and the acid concentration. For example, copper reacts with dilute nitric acid at ambient temperatures with a 3:8 stoichiometry to produce nitric oxide which may react with atmospheric oxygen to give nitrogen dioxide.3 Cu + 8 HNO3 3 Cu2+ + 2 NO + 4 H2O + 6 NO3-With more concentrated nitric acid, nitrogen dioxide is produced directly in a reaction with 1:4 stoichiometries.Cu + 4 H+ + 2 NO3 Cu2+ + 2 NO2 + 2 H2OUpon reaction with nitric acid, most metals give the corresponding nitrates. Some metalloids and metals give the oxides, for instance, Sn, As, Sb, Ti are oxidized into SnO2, As2O5, Sb2O5 and TiO2 respectively. Some precious metals, such as pure gold and platinum group metals do not react with nitric acid, though pure gold does react with aqua regia, a mixture of concentrated nitric acid and hydrochloric acid. However, some less noble metals (Ag, Cu, ...) present in some gold alloys relatively poor in gold such as colored gold can be easily oxidized and dissolved by nitric acid, leading to color changes of the gold-alloy surface. Nitric acid is used as a cheap means in jewelry shops to quickly spot low-gold alloys (