Coal Drying and Grinding

Drying

And

Grinding

Of

Coal

Coal Drying and Grinding

02/10/2011 Edited and linked by UTM 1

Table of contents

1. Introduction 2. Different coal types, composition and analyses

2.1. Analyses of solid fuel 2.2. Hard-grove Grindability Index 2.3. Abrasion Index 2.4. Coal Dewatering

3. Necessary Fineness of Coal 4. Drying of Coal 5. Mills for Grinding Coal

5.1. The Tirax Mill 5.2. Vertical Roller Mills 5.3. Ball Mills Compared with Vertical Roller Mills

6. Arrangement of Coal Grinding Plants 6.1. Direct Firing 6.2. Semi-Direct Firing 6.3. Indirect Firing 6.4. Central Coal Grinding Plants 6.5. Inert Coal Grinding Plants

7. Instrumentation and Automation of the Coal Grinding Plant 8. Raw Coal stocking 9. Filters and Coal-dust Hoppers 10. Safety Precautions

10.1. Temperature monitoring 10.2. Gas Analyzing Equipment 10.3. Inertisation System 10.4. Explosion Relief venting



DRYING AND GRINDING OF COAL FOR FIRING IN CEMENT KILNS

1. INTRODUCTION During the last two decades a large number of existing cement plants have been converted from oil to coal firing, and new cement plants have often been arrange for coal firing. The growing interest in coal firing was caused by the increase in oil prices during the seventies.

The coal grinding plants constructed since then have normally been designed with due consideration to the latest regulations regarding construction, lay-out and operation of coal handling facilities. The current safety regulations, as well as the introduction of modern fuel efficient kiln types, have had a great influence on the up to date design of coal grinding plants, which will be dealt with in the following.

2. DIFFERENT COAL TYPES, COMPOSITION AND ANALYSES The volatile content of a coal normally depends on the age of the coal, where the oldest coal type “Anthracite” has a very low volatile content, and the youngest type “Lignite” a high volatile content.

In fig.1 is shown an example of coal types with typical contents of volatile, ash and hygroscopic moisture.

In the later years “Petcoke” is taking over an increasing part of the market due to an attractive price.

In fig.2 can be seen a description of petcoke. The petcoke used in the cement industry is normally of the type called “Green Delayed Petroleum Coke”.



2.1 Analyses of solid fuel When buying coal on the world market, the cement plant normally receives a “Certificate of Analyses” based on which the plant is paying for the coal. An example of such certificate is shown in fig.3.

The cement plant laboratory further makes analyses as shown in fig.4. for determination of the net heat value and the ash composition, and at times also the abrasion index and the grindability index.

The ash amount and composition is used to calculate the necessary correction of the rawmix.

2.2 Hardgrove Grindability Index All cost can be analyzed for grindability in the laboratory according to Hardgrove. The grindability index is often named HG index or Just HGI.

The method is performed after either ISO 5074 or ASTM 409-93A. An increasing HGI indicates an easier grindable coal.

In fig.5 is shown the relation between HGI and mill specific power consumption for grinding to different sieves on 90μ in a ball mill.

In fig.6 is shown the same relation for grinding in vertical mill.

2.3 Abrasion Index To be able to calculate the wear of the different parts in the grinding installation, it is necessary to know the abrasiveness of the coal. The abrasion index is investigated in the laboratory according to BS 1016, part 19 (British Standard) and is measured in mg/kg. In FLS we define normal abrasive coal to have a AI index not higher than 20 mg/kg.

The abrasion can also be expressed as a YGP index (Yancey Geer and Price). The relation between YGP and AI index is as follows:

YGP=4xAI



2.4 Coal Dewatering Before the first start-up with a new type of coal, it is advisable to make a dewatering curve. The determination of the dewatering curve is shown in fig. 7.

In fig. 8 can be seen dewatering curves for different coal types. Based on the dewatering curve can be selected the most appropriate and safe mill outlet temperature for the first start-up.

3. NECESSARY FINENESS OF COAL To ensure a complete combustion of the coal dust, this must be ground to a fineness which is dependent of the content of volatiles and where to be burned.

In fig. 9 is shown the recommended fineness of coal dust for calciner and kiln as a function of the volatiles (daf) content.

Of importance is also the relation between the 90μ residue and the 200μ residue. The coarse particles will ignite later and may course CO and temperature increase later in the kiln system.

In fig.10 can be seen the max: recommended value of 200μ residue in relation to the 90μ residue. In general the 200μ residue must be as small as possible.

4. DRYING OF COAL The moisture content of raw coal of various types may well vary within wide limits. It is necessary to dry the coal in order to facilitate procedures during the grinding, transport and possible storing processes.

Beside the free moisture which evaporates at ambient temperature, the coal contains “hygroscopic” or inherent water, which could be defined as water evaporating by heating from 30° to 105°C.



The risk of fire and explosions can be limited considerably, if the coal meal is produced with a certain content of residual water. The recommended residual water content depends on the content of hygroscopic moisture in the raw coal. As a guideline can be recommended to dry 1-2 % away of the hygroscopic water.

The residual moisture for different coal types typically lies in the following range:

Anthracite coal and petcoke: 0.5 – 1.00 %

Bituminous coals: 1.5 – 2.50 %

Lignite coals: 8.0 –12.0 %

Before the initial start of a coal grinding plant and when shifting from one type of raw coal to another, a dewatering curve should be made. This dewatering curve should indicate residual water vs. temperature. A typical dewatering curve appears in fig.11. Based on the curve can be selected mill outlet temperature which gives the correct residual moisture. In this example is found that the set point of the mill outlet temperature shall be 65°C to obtain a residual moisture of 1.5 %.

In practical mill operation is normally seen, that a somewhat higher mill outlet temperature is needed to obtain the wanted residual moisture. The reason for this is, that the retention time for coal dust is much shorter in normal mill operation then in the laboratory oven.

In fig. 12 is shown a practical example for illustration of the selection of set-point and maximum temperature levels based on the actually obtained residual moisture.

It is usually found that the coal mill should be operated with an outlet temperature of 65° - 75°C and in certain cases, up to approximately 80°C. To avoid condensation in ducts and filters, the temperature after a coal mill should be 15° - 25°C higher than the dew point.



Relation between dew point after the mill, quantity and temperature of the drying air, and the moisture content of the raw coal appear from fig. 13. It should be noted that the dew point is solely dependent on the temperature of the drying air and is an increasing function of this temperature. Regarding the dew point, a temperature of the drying air of 300° - 350°C or lower appears to be appropriate. As an example, the following figures can be read from the diagram. If the moisture content in the raw coal is 10% and drying air from a cooler of 300°C is available, 1.2 kg dry air per kg of dry coal will be needed for drying, and the dew point after the mill will be approximately 52°C. The residual moisture in the coal meal has not been included in the calculation.

In case of new mill installation, a dew point calculation is always done as a part of the process design calculations. In existing installations the best way is to go and measure the dew point in the air after the dedusting filter.

5. MILLS FOR GRINDING COAL For coal grinding can be used grinding machinery such as the vertical mill, the ball mill, the Alrilor coal pulverizer, the horizontal impact crusher, the roller press etc.

In this lecture is only described the ball mill and the vertical mill, as these two grinding systems are the most common used.

5.1 The Tirex Mill The Tirex mill shown in fig. 14 is a ball mill design for drying and grinding. The material first passes through a drying compartment with lifters. In coal mill of older designs, the grinding was carried out in two grinding compartments.

However, grinding in larger mills with high capacity and drying by means of inert gas of low temperature implies that the velocity of the air through the mill will usually be high. In order to reduce the



differential pressure over the mill, the mills of today are arranged with only one grinding compartment and classifying lining.

The Tirax mill is a fully air swept mill, so all the mill discharge material is transported to the separator by air. In previously designed mills, the coarse reject material from the separator was transported back to the mill through the outlet trunnion to the fine grinding compartment. At high air velocities, this arrangement is considered to be inconvenient.

Instead, the coarse return material is transported to the inlet end of the mill by a screw conveyor. In the feed chute, the dry material reject is mixed with the wet raw coal thus eliminating the risk that the material ignites at the inlet to the mill.

The separator is often of the static type. Control of the separation is performed by vertical displacement of an internal central tube for the smaller sizes and by vane settings for the larger sizes. Changing the air velocity through the separator will also have some influence on the separation.

In fig. 15 can be seen the recommended ball charge for Tirax coal mill.

5.2 Vertical Roller Mills Vertical mills for grinding coal are produced by a number of manufacturers. Some could be mentioned: Raymond, Loesche, Pfeiffer, Polysius, B & W and FLS.

Fig. 16 illustrates an FLS ATOX mill.

Coal grinding takes place between a rotating table and three grinding rollers. The raw coal is fed to the center of the table and from there it passes between the rollers and the table. After being ground, it flows over the edge of the table and enter the racing current of the hot air coming through the air nozzle ring encircling the grinding table.



The ground coal is carried by the air to the built in static or dynamic separator. The course particles are, via reject cone, return to the mill for further grinding while the fine particles exit the mill with the air through the mill outlet.

For the latest precalciner kiln systems, both ball mills and roller mills equipped with dynamic separators to improve the combustion process in the precalciners.

5.3 Ball Mills Compared With Vertical Roller Mills For grinding an average coal (HGI 55 and 10% > 90μ), the vertical mill consumes about 9 kWh/t for the mill motor and 8 kWh/t for the fan, i.e. in total 17 kWh/t. Under the same conditions the Tirex mill will consume about 19kWh/t for the mill motor and 4kWh/t for the fan, in total 23kWh/t. Thus, the vertical mill consumes approx: 25 % less energy than the ball mill. This corresponds to about 0.7kWh/t of clinker.

The Atox mill requires larger amounts of air for material transport than the Tirax mill. Consequently, when the coal is ground in a vertical mill, larger quantities of air needed to be dedusted than when grinding takes place in a ball mill.

On the other hand, since the vertical mill requires and allows a higher air flow than the ball mill, the vertical mill has a higher drying capacity. For comparison of Tirax mills and vertical mills, the advantages of the latter could be summarized as follows:

Advantages: 1. Lower energy consumption 2. Higher drying capacity 3. Output capacity can easily be varied within a wide range

corresponding to the fuel consumption of the kilns 4. Fast feed-output response 5. Accept larger feed sizes; up to 80mm



6. Lower noise level 7. Requires less building volume

Disadvantages: 1. Larger quantity of air to be dedusted 2. Lass suitable for abrasive coal. Wear parts are expensive and

replacement causes downtime 3. Sensitive to variations in feed rate and feed quality 4. Higher maintenance costs

The vertical mill is to day dominating for new mill installations.

6. ARRANGEMENT OF COAL GRINDING PLANTS Various factors have to be taken into consideration when arranging a coal grinding plant:

• Quality of coal

• Supply of hot air for drying

• Type and number of kilns

• Investment cost

• Maintenance cost

• Reliability

Based on an evaluation of these matters, decision can be made regarding the following:

• Direct, semi-direct or indirect firing

• Inert or non-inert operation

• Ball mill or vertical roller mill

• Bag filter or ESP for possible dedusting

6.1Direct firing Direct firing implies a simple and cheap installation (fig. 17). Adjustment of fuel to the kiln are adjusting the coal feed rate to the mill. This arrangement includes neither a filter nor coal meal bin and



has therefore been considered safer than other arrangements, as far as fires and explosions are concerned.

Today however, very few coal grinding plants in the cement industry are arranged for direct firing since this simple system has serious drawbacks compared to other arrangements:

• Any mill stop will cause a kiln stop.

• Varying and inaccurate dosing of fuel to the kiln causes higher fuel consumption than for arrangements with a more accurate coal feeding system.

• All the mill vent air goes to the kiln as primary air. This will also cause an increase in fuel consumption. The amount of mill vent air is larger than the amount of primary air necessary for combustion of the coal in a modern fuel efficient cement kiln system. By operating with an excess amount of primary air, less hot air from the clinker cooler is used as secondary air.

An example of the calculation for the primary air and the gas amounts from vertical and ball mills is shown on fig. 18 for direct firing. A relation between the amount of primary air and the increase in heat consumption of the kiln is indicated in fig. 19.

Further, the water vapor coming from the mill and entering the kiln, together with the primary air, has to be heated up to the kiln exhaust gas temperature. This contribution to the heat consumption of the kiln appears in fig. 20.

6.2Semi-Direct Firing Semi-direct firing system only differs from the direct firing installation by a silo for ground coal install between the precipitating cyclone and kiln (fig. 21). This silo for coal meal implies that the kiln will be less dependent on the operation of the mill. The coal meal is extracted from the silo by one or more feeding apparatuses. The mill vent air



goes to the kiln burner, as was the case for the arrangement for direct firing.

6.3Indirect Firing Indirect firing arrangements are today the most common in new cement plants (fig. 22). A coal silo and a filter for dedusting the mill vent air are included in the arrangement.

Consequently, by using this arrangement, the primary air for the kiln burner can be reduced to an amount which is necessary for proper burning of the coal. The kiln can also be operated with minimum fuel consumption.

6.4Central Coal Grinding Plants Indirect firing can be arranged as a central coal grinding plant. It can have its own separate supply of hot air from an auxiliary heat generator, and it will have a number of coal meal silos, each one with equipment for feeding coal meal to a kiln. Central coal grinding plants are often applied for cement kilns with precalciners and are obviously suitable to supply coal to a number of kilns. Examples of central coal grinding plants are shown in fig.23 and 24.

The coal mill systems described so far have been supplied with hot air for drying from a clinker cooler, a kiln hood or an auxiliary heat generator.

For temperature control, the hot air is usually mixed with a certain amount of cold ambient air. The mix of air to mill will, in all cases, have oxygen content close to 21% as for atmospheric air and the operating conditions are called non-inert.

6.5Inert Coal grinding Plants It is well known that explosions occur in the coal grinding plants. The following conditions are required before an explosion can take place:

1. Dry coal meal of suitable fineness.



2. Coal dust concentration in the air between 100 and 2000g/m³. 3. Ignition source. 4. Oxygen content higher than 12-14%.

A condition for a coal dust explosion to take place is that the O ₂ content of the air should exceed the following limits:

14% O₂ for ordinary bituminous coal

12% O₂ for lignite coal

If a coal grinding plant can be operated with an O₂ content in the process air below these limits, coal dust explosion will not take place. When these conditions are fulfilled, the coal grinding plant is, per definition, operated under inert conditions.

Kiln exhaust gas with an oxygen content of typically 3-5% is obviously suited as drying gas for an inert coal grinding plant (fig.25).

The inert conditions of the plant are monitored by a reliable oxygen analyzer at the coal mill filter outlet. If the oxygen content exceeds 10%, the analyzer will first cause an acoustic alarm allowing time for the operator to remedy possible irregularities. However, at 12% O ₂ the plant will stop operation automatically.

Before the mill start, it is necessary to lower the oxygen content after the filter to less than 10%, which is a start condition for the mill. This is achieved by drawing a modest flow of inert kiln gas through the coal grinding system. During this pre-start process, the mill exit temperature must be kept below the maximum temperature alarm limit.

7. INSTRUMENTATION AND AUTOMATION OF THE COAL GRINDING PLANT Fig. 26 show an example of instrumentation, including automatic controllers recommended for a coal grinding plant.



It is very important to maintain a constant temperature after the mill. In this case, it is achieved by automatic control of a cold air valve letting cold air into the hot air from the clinker cooler.

At the entrance of the mill there must be a small negative pressure to avoid dust leaking out. This pressure must be regulated since an overly high negative pressure may cause an excessive amount of false air to leak in to the system. The pressure is maintained by controlling the damper before the hot air booster fan.

The feed rate to the mill is controlled by constant monitoring of the noise level from the mill. The operator will decide when to start the grinding plant and often also when to stop it again.

Start and stop of the individual machinery takes place in certain sequences controlled by the electrical interlocking system. The electrical interlocking system may, however for safety reasons, also cause an automatic stop of the operation. This may, for instance, be the case if a coal meal silo is filled to capacity or if mill exit temperature exceeds the upper of the two maximum alarm limits.

8. RAW COAL STOCKING Today, coal of varying quality is used, and blending is therefore necessary. Fig. 27 shows an example of short term storage for coal with a high blending effect.

The main problem with coal stock pile is “spontaneous combustion.” Coals vary a great deal in the tendency to take up oxygen. In general, the tendency is relatively low for high rank (low volatile) coals. It is higher for coals of high bed moisture content, high oxygen content, and high volatile content, all of which characterize a low rank coal.

An important factor in the heating process is the total surface area of the coal exposed to the air: the larger the surface, the greater the risk for the coal to absorb and react with oxygen.



For long-term storage in open stockpiles, the following rules and guidelines are important:

• The storage site should be dry, even and clean and with good drainage.

• Straw, wood, oily rags and other combustible material must be avoided in the storage area.

• The coal delivered to storage should be spread over the entire to a thickness of 0.5m and then compacted before new layer are put on the pile. A practical and effective approach to sealing a coal pile is a continuous layer of fine coal followed by a covering of lump coal to prevent loss of the seal through the action of wind and rain.

• If possible, sized coal should be stored with the fines removed. In such piles, the relatively small coal surface area develops only a small amount of heat which can readily dissipate.

• The temperature of the coal pile should be tested periodically.

• If possible, the storage should be covered, for instance with plastic and/or a thin layer of raw meal.

Raw coal silos It is important that the raw coal silo is design for “mass flow” (opposite of core or funnel flow), to ensure that the silo contains no passive zones where the coal can accumulate.

This is obtained in following way:

• A steep bottom cone inclination ≥ 70°

• Inside lining of the cone with ceramic or stainless steel

• The bottom opening as big as possible

9. FILTERS AND COAL DUST HOPPERS There are particularly two places in the coal grinding plant where a fire could develop:



• The filter

• The coal dust hopper

The filter could be a bag filter or an electrostatic precipitator. The advantage of bag filter is its low price. Disadvantages are the higher pressure drop and higher maintenance costs. When using a bag filter, the air and coal meal from mill separator can be taken directly to the filter. This is not the case for an electrostatic precipitator.

Air from the mill separator, with coal meal in suspension, must be in a cyclone before going to an electrostatic precipitator, in order to reduce the dust concentration to a safe level before the air and residual dust enters the electrostatic field of the filter.

If fire occur in a bag filter, normally all bags must be replaced. To ensure a safe operation, both types of filters should be equipped with the following:

1. Knocking devices at the bottom hopper 2. CO analyzer 3. Thermometers 4. Equipment for inertisation with CO₂ or N₂ 5. Explosion venting devices 6. Heating of bottom hopper with low temperature heat tracing

Coal meal silos should be equally well equipped with safety devices shown in fig. 28.

10. SAFETY PRECAUTIONS A modern coal grinding plant is equipped with several arrangements, first for avoiding fires and explosions, secondly for fire fighting and last for reduction of damage in case of explosion.

• Electrical safety interlocking of machine and process

• CO monitoring

• Inertisation system



• Explosion relief venting.

In fig. 29 is shown a flow sheet with dedusting in a bag filter and a coal dust hopper with extraction to kiln burner and calciner. It can be noticed that the filter is equipped with sealing off valves, and that the coal dust from the filter can be transported out of the system instead of to the coal dust hopper. This possibility can be used in combination with fire fighting in the filter.

10.1Temperature monitoring As well mill filter as coal dust hoppers are equipped with processes temperature monitoring, which is a part of the electrical safety interlocking. It is very important that this equipment and the electrical interlocking always is functional.

10.2 Gas analyzing equipment A gas analyzer measure continuously the CO level in filters and coal dust hopper. In case of inert grinding, also the O₂ level is measured after the main filter outlet. The measured value goes into the electrical safety interlocking.

It is not possible beforehand to inform of the alarm limits for the CO level, as this is different from one coal to another. The best way is to observe where the CO level during mill standstill is stabilizing and then set the alarm limit 100ppm higher than this.

If a fire is developing, it is normal to observe a very sharp increase of the CO level. If the mill receives heat from kiln preheater, the CO level during mill operation shall not go into the electrical interlocking, as it most certain comes from the kiln. In this situation the CO level is used as a startup interlocking.

10.3Inertisation system In case of fire in filter or coal dust hopper is used CO₂ or N₂ injection for fire fighting.



Injection with CO₂ CO₂ is the most common used media for fire fighting.

The CO₂ can be supplied from either a central CO₂ tank or a battery of CO₂ bottles.

The CO₂ amount for inertisation of a given volume is 2kg of CO₂ per m³ free volume.

Injection with N₂ N₂ can be used in the same way as CO₂ for fire fighting.

N₂ is normally supplied in a battery of bottles due to the high pressure (200 bar).

The N₂ amount for inertisation of a given volume is 1kg of N₂ per m³ free volume.

10.4Explosion relief venting If, in spite of all precautions, an explosion should occur, it is necessary to relieve the explosion pressure to the outside (of building) to avoid damage on personal and machinery.

In fig. 30 is shown the two most common types of explosion relieves, the busting disk and the self closing relief valve.

The self closing valve is the more expensive solution, but also the best, as it do not need to be replaced after the explosion, and because it very fast again closes to the surroundings.

The necessary opening area for explosion venting, and thereby the amount and size of the relief valves, depend on the type of coal to be ground in the installation.

In fig. 31 is shown a table of coal classification based on which the necessary explosion venting area can be calculated.



General Comments: Aside from the already mentioned safety precautions, the following tips should be added to the list regarding safety of coal grinding plants:

• The arrangement for feeding raw coal should be designed to ensure a steady feed of raw coal to the mill. Feed failure and subsequent increase of temperature in the mill have caused explosion in the plant.

• Horizontal surfaces, where coal dust may settle, should be avoided to the greatest possible extent. This applies inside as well as outside the machinery. Duct should have proper inclinations (minimum 60° upward and 45° downward).

• Gas velocity in ducts: minimum 20m/s.

• Mill separator, duct between separator and filter, filter and coal meal silos should be fitted with pressure relief valves, which must open to the outside air, not inside buildings.

• The installation should be well maintained. This includes mechanical maintenance, electrical maintenance, and in particular, safety equipment.

• Building and machinery should be kept clean.

• Finally, but not less important: Common sense must prevail when operating a coal grinding plant. Common sense, combined with a properly designed plant and machinery which is in accordance with current industrial standards, reduces the risk of operation of a coal grinding plant to a minimum.



Fig.1

Coal type Volitiles Ash Hygroscopicmoisture

% % %Anthracite < 8 3--5 < 2Semi-anthracite 5--15 3--5 2--6Quarter rich coal 15--20 5--8 2--6Bituminous coal 20--30 8--15 2--6Rich coal 30--40 10--20 2--6Lignite 40--50 15--30 10--15

Petcoke < 15 < 2 < 1

Typical values of volatiles,ash and hygroscopic moisture for

different coal types



Fig.2

Petroleum coke Petroleum coke is black solid, obtained mainly by cracking and carbonizing residue feed stocks and from the distillation of heavier petroleum oils. The main commercial applications of petroleum cokes depend on their properties and they are typically used as energy sources for solid fuel application such as lime and cement kilns and sometimes as fuel for boilers and power generation. Some calcined cokes are used in the manufacturing of electrodes for aluminium and steel electro-melting.

Petroleum coke exists in the following basic forms:

1. Green coke is the immediate product of a semi-continuous batch coking process known as delayed coking, which contains significant residual hydrocarbon content.

2. Calcined coke, a product derived from green coke, in which the hydrocarbons have been removed by heating under reducing conditions in kiln to temperatures in excess of 1200°C.

3. Fluid coke, the product of a continuous fluidized-bed coking process. 4. Flexi coke, a product from the continuous fluidized-bed coking process, in

which the major part of the coke is gasified to a low calorific value gas for refinery use.

Green coke (delayed coke) has a distinctive hydrocarbon smell. It can contain up to 15% volatile material, mostly hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs). Calcined coke purity is largely feedstock dependent. Needle coke and regular coke are calcined cokes of different purities, the needle coke being the purer from which is used for electrodes production.

Calcined coke, as a consequence of the calcining process, has a virtually zero volatile content. It is inherently a much dustier material than green coke and depending on its use it is usual to add a small amount (0.3% wt or less) of high viscosity oil or a very small amount of surfactant usually in a water solution to act as a dust suppressant.

Fluid coke has spherical grains and contains less volatile material than green coke. The normal grain size of fluid coke is less than 6 mm. Flexi coke is similar to fluid coke but contains even less volatile material and has much finer grains and thus is more dusty.

Green coke Bulk Density 0.70-0.90 kg/dm³ Real Density 1.35-1.45 kg/dm³



Fig.3

! June 1, 1995

CASTILO DE ALMANSAGreen Delayed Petroleum cokeHouston, TexasMay 26-30, 1995

Dry-

0.5910.4189.00-

ADDITIONAL ANALYSIS

4.3115,411

42

NOTESRepresentative sample of Green Delayed Petroleum Coke were obtain inaccordance with ASTM standards during actual loading of M/V CASTILLODE ALMANSA on May 26-30,1995.

Composit samples prepared and analysis conducted in accordance withapplicable ASTM standards.

Cargo loaded reported to be 53,699,590 metric Tons

CERTIFICATE OF ANALYSIS

As Received6.350.45

VESSEL NAME:CARGO DESCRIPTION:LOAD PORT:DATE OF LOADING:

PROXIMATE ANALYSIS% Moisture% Ash% Volitile Matter% Fixed Carbon

9.4983.71

% SulphaGross BTU/lb

Hard grove Grindability Index

4.0414,432









Fig.7

Determination of Dewatering for Coal The determination is made as follows:

1. To begin with, crush a representative raw coal sample to 5mm. Weigh out 500grams of the sample and spread it in an open tray to a thickness of approx: 1cm.

2. Dry the sample for 24hrs at 30°C. Coal weight after drying: is

W₃₀g. 3. Now dry the sample for 5hrs at 50°C. Weight after drying: is

W₅₀g. 4. Dry the sample further for 5hrs at 65°C. Weight after drying: is

W₆₅g. 5. Dry the sample further for 5hrs at 85°C. Weight after drying: is

W₈₅g. 6. Finally, dry the sample for 2.5 hrs at 105°C. This will expel all

water. Weight of dry coal: W₁₀₅g.

On this basis, the water content of the coal after drying at t° C can be calculated for each of the five operations, since the water content is calculated in percent of the weight after drying at the temperature concerned:

(Wt-W₁₀₅) x Wt / 100 %

The dewatering curve is drawn by plotting in a co-ordinate system: the water content, thus found as a function of the rising temperature.

















Fig.15

Raw coal feed, precrushed to - 15mm

Older 2 compartment mills.

ф in mm 1st.Comp: Wear Comp: 2nd. Comp: Wear Comp:50 25% 50% * *40 40% 50% * *30 35% * * *25 * * 40% 100%20 * * 40% *15 * * 20% *

(All amounts by weight)

Single compartment mill with classifying lining.

ф in mm 1st.Comp: Wear Comp:50 11% 25%40 18% 25%30 16% 50%25 22% *20 22% *15 11% *

(All amounts by weight)

Recommented Ball chargefor

Tirax Coal Mills







Fig.18

L min: Antracite coal = 0.00139 kg air/kcalFuel = 0.00141 kg air/kcalLignite = 0.00143 kg air/kcal

% Primary air kg air/kg coal10% 0.83415% 1.2520% 1.6730% 2.5

Total = 2 kg air

Direct Firing

Kiln System

Total =1.6 kg air

Kiln fired with antracite coal: Bn = 6000 kcal/kg

L min = 0.00139 x6000 = 8.34 kg air/kg coal

Vertical Mill Ball Mill

Min kg air/kg coal Min kg air/kg coal

Nozzle ring = 1.7-1.8False air = 0.2 Water vapour = 0.2

Mill air = 1.2False air = 0.3-0.4Water vapour = 0.2



























Fig. 31

Coal type

High volitilebituminousLow volitile

Classification of coal

Volatiles%

26--36

11 26

>36

Pmax - valuebar

9.3

8 6

Kst -valuebar x m/s

120

90

9.3150Lignite

Low volitilebituminous

Kst reflacts the speed and strength of the pressurewave from the explosion.

<80.61Anthracite

Pet coke 60 6.9 8--11

11--268.690

Pmax gives the max: pressure to be reachedin a closed container.



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Coal Drying and Grinding

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