According to a first aspect of the invention, there is provided a process for gasifying coal, which process comprises pneumatically conveying pulverized coal along a coal feed line; feeding the pneumatically conveyed pulverized coal into a gasification chamber through a burner connected to the coal feed line; simultaneously feeding a gasification agent comprising oxygen or an oxygen-containing gas into the gasification chamber through the burner; <BR> <BR> <BR> gasifying the pulverized coal by allowing it to burn<BR> <BR> with a less than stoichiometric amount of oxygen inside the gasification chamber at substantially atmospheric pressure, thereby to form a hot gaseous component comprising carbon monoxide and hydrogen; withdrawing the gaseous component from the gasification chamber as a gaseous product comprising carbon monoxide and hydrogen; and withdrawing slag from the bottom of the gasification chamber.

By'stoichiometric amount of oxygen'is meant the amount of oxygen required to convert all carbon in the pulverized- coal to carbon dioxide.

By'substantially atmospheric pressure'is meant a pressure equivalent to, or not significantly greater than, atmospheric pressure, eg a pressure between 3 kPa (g) and 25 kPa (g), typically about 15 kPa (g).

The gasification chamber may thus be provided by a gasification vessel, with the gasification of the coal thus being effected within the gasification vessel. The gasification vessel and said at least one burner together constitute, or form part of, an atmospheric pressure coal gasifier, which may thus be an atmospheric pressure entrained flow coal gasifier. The gasification vessel may be of elongate form, being square or rectangular in cross-section. A plurality of burners, located in the sides of the gasification vessel towards its lower end, and each having its own coal feed line, may be provided.

The gasification agent may comprise more-or-less pure oxygen, oxygen-enriched air, or even air alone.

Additionally, it may comprise one or more of steam, carbon dioxide, or some of the gaseous product, either before or after treatment thereof as hereinafter described, with the steam, carbon dioxide and/or gaseous product, when present, being fed into the gasification vessel separately and/or together with the oxygen or air.

The gasification vessel will thus comprise a plurality of vessel walls. Each wall may comprise at least one membrane panel comprising a plurality of vertical boiler feed water tubes located alongside one another with metal strips located between adjacent tubes and being attached, eg welded, to the tubes. Insulation and cladding will normally be provided against the tubes, on the outside of the walls. The tubes can, if desired, eg in proximity to the burners, ie in a gasification zone of the gasification chamber, be refractory lined on the inside of the walls, with spaced metal studs protruding from the tubes through

the refractory lining for heat conduction. This lining thus serves to protect the walls against the damaging effects of severe thermal radiation from the gasification flames emanating from the burners, and the corrosive effects of molten slag running down the insides of the walls to a slag outlet located at the bottom of the vessel.

Typically, the walls may be stiffened externally by braces or buckstays, positioned at equally spaced intervals over the height of the gasifier, to withstand the internal pressure in the gasification chamber. The tubes are connected at their upper and lower ends by upper and lower manifolds respectively. In this fashion, fully water cooled gasification vessel walls are provided. The manifolds may thus be connected to a source of boiler feed water so that heating of the boiler feed water is effected, by allowing boiler feed water to pass through the tubes, thereby to be heated by heat generated by the combustion of the pulverized coal in the gasification chamber.

Instead, or, preferably, additionally, the heating of the boiler feed water and/or the steam by the combustion of the pulverized coal in the gasification chamber may be effected by passing boiler feed water through at least one heat exchange device, eg a heating coil, located in the gasification chamber, above the burners, ie in a cooling zone above the gasification zone. A plurality of the heat exchange devices are typically provided.

A steam drum may also be provided, with the upper and lower manifolds of the gasification vessel walls being connected to the steam drum such that boiler feed water passes from the steam drum into the lower manifolds, up the tubes, out of the upper manifolds, and back to the steam drum. In other words, boiler feed water flows by thermosiphon action as the vessel walls absorb waste heat from the coal gasification reaction. The boiler feed water thus circulates by means of natural circulation requiring no

pumps for circulation. The steam drum may thus be integral with the gasifier. The purpose of the steam drum is to hold sufficient water to ensure natural circulation of water through the gasifier walls at all times. The steam drum also contains separating devices which separate steam from the steam-water mixture returning from the gasifier walls, and scrubbing devices which remove any remaining water droplets from the steam so as to ensure that the steam leaving the drum and passing to a superheater as hereinafter described is dry.

Incoming boiler feed water may thus be passed through a first of the heat exchange devices, thereby to heat the boiler feed water and vaporizing it, with steam thus passing into the steam drum. Steam may then be withdrawn from the steam drum and passed through a second of the heat exchange devices, ie a superheater, to produce superheated steam. Thus, in this fashion, superheated steam, typically at a temperature between about 400°C and 540°C and a pressure between 3 MPa (g) and 8 MPa (g), eg about 6 MPa (g), can be produced.

The tubes of the rear wall of the gasifier may be bifurcated part way up the wall so as to create an internal division wall also comprising a plurality of the tubes, such that the upper cooling zone of the gasification chamber is divided into a front pass and a back pass, with combustion gases flowing up the front pass, passing through openings between the tubes of the internal division wall at the upper end of the wall, down along the back pass, and exiting the gasifier through openings between the tubes in the rear wall.

The geometry and construction of the atmospheric gasifier, as described above, are thus similar to those of atmospheric boilers or furnaces used in the boiler' industry, but which by their nature use an oxidizing

environment rather than a gasifying environment, which uses reducing conditions, as hereinbefore described.

The burners may be of the so-called diffusion type in which the coal and gasification agent pass through separate passages in the burner, with mixing of the coal and gasification agent being effected on discharge thereof from the burners. Instead, the burners may be of the so-called premix type in which the coal is mixed with the gasification agent within the body of the burner.

The pneumatic conveyance of the pulverized coal along the coal feed lines and into the burners is thus effected by using a carrier gas. The carrier gas may be gaseous product, preferably after cooling and cleaning thereof as hereinafter described. Instead, however, the carrier gas may be air, nitrogen, carbon dioxide, or a hydrocarbon gas, eg that recycled from a downstream processing stage.

The process may include pulverizing particulate coal in a pulverizing stage; and feeding hot air or hot flue gas into the pulverizing stage. The hot air or hot flue gas serves to dry the coal. Typically, coal received from the mines has a moisture level of 7%-14% (by mass), with the coal then being dried in the pulverizing stage by means of the hot air or hot flue gas to a moisture level of less than 2% (by mass), typically about 1% (by mass). The hot air or hot flue gas also serves to transport the dried and pulverized coal from the pulverizing stage. The process may thus include transporting the dried and pulverized coal by means of the hot air or hot flue gas, to a separation stage in which the pulverized coal is separated from the hot air or hot flue gas. Typically, the separation stage may comprise a bag filter, which may be located above a pulverized coal storage or service bin, with the coal feed lines leading from the storage bin. The bag filter thus disengages the pulverized coal from the hot air or hot flue

gas stream, which can thus be discharged to atmosphere without a dust load.

In the pulverizing stage, the coal may be pulverized to have a particle size distribution such that 90% of the pulverized coal is typically less than 90 microns, or even less than 70 microns in the case of unreactive coals.

The pneumatic conveyance of the pulverized coal along the coal feed lines may be effected by feeding the pulverized coal from the service bin into the suction side of a dust pump located in each coal feed line, discharging the coal from the pump into the coal feed line downstream of the pump, and simultaneously introducing sufficient of the carrier gas into the coal feed line in proximity to the pump discharge so that the pulverized coal and carrier gas is conveyed along the coal feed line as a dense phase mixture having a density in the range 80-200kg/m3.

The process may include subjecting the hot gaseous product or hot raw gas from the gasifier to fly ash removal.

Thus, according to a second aspect of the invention, there is provided a process for gasifying coal, which process comprises feeding pulverized coal into a gasification chamber through at least one burner; simultaneously feeding a gasification agent comprising oxygen or an oxygen-containing gas into the gasification chamber through the same burner; gasifying the pulverized coal by allowing it to burn with a less than stoichiometric amount of oxygen inside the gasification chamber at substantially atmospheric pressure, thereby to form a hot gaseous component comprising carbon monoxide and hydrogen;

withdrawing the gaseous component from the gasification chamber as a gaseous product comprising carbon monoxide and hydrogen; withdrawing slag from the bottom of the gasification chamber; and subjecting the gaseous product to fly ash removal, optionally after effecting some cooling thereof.

The gasification chamber may also be provided by an atmospheric pressure entrained flow coal gasifier, as hereinbefore described.

The fly ash removal may comprise subjecting the hot gaseous product to one or more of the following: scrubbing, eg impingement plate or venturi scrubbing; electrofiltration, eg wet electrofiltration; cyclone separation; and filtration, eg bag filtration.

In particular, the fly ash removal may comprise passing the hot gaseous product from the gasifier through a scrubbing zone where it is scrubbed by countercurrent washing thereof using hot and/or cold water, and subjecting the resultant cooled and scrubbed gaseous product or raw gas from the scrubbing zone to electrofiltration. For example, the hot gaseous product may enter the scrubbing zone at a low level, and pass upwardly along the scrubbing zone, with hot or cold water scrubbing or washing, using hot or cold wash water at a temperature between 10°C and 60°C, eg hot water at about 45°C, taking place at a low level, cold water scrubbing or washing, using cold wash water at a temperature between 10°C and 30°C, eg at about 25°C, taking place at a higher level with the scrubbing zone, cooled and scrubbed gaseous product being withdrawn from the top of the scrubbing zone, and spent wash water carrying fly ash scrubbed from the gas being withdrawn from the bottom of the scrubbing zone. A plurality of impingement plates, for

enhancing scrubbing of the gaseous product, may be provided in the scrubbing zone.

The pressure in the gasification chamber is thus such that further gas compression downstream of the gasification zone, is normally not required.

According to a third aspect of the invention, there is provided a coal gasification installation, which comprises an atmospheric pressure coal gasifier comprising a gasification vessel providing a gasification chamber, and at least one burner through which pulverized coal can be fed into the gasification chamber; and pneumatic pulverized coal feed means for pneumatically feeding pulverized coal into the burner.

By'atmospheric pressure coal gasifier'is meant a gasifier operating at atmospheric pressure or at a pressure not substantially greater than atmospheric pressure, eg operating at a pressure between 3 kPa (g) and 25 kPa (g), eg typically at about 15 kPa (g).

The coal gasifier may, in particular, be an atmospheric pressure entrained flow coal gasifier as hereinbefore described.

The pneumatic pulverized coal feed means may comprise a bulk pulverized coal drum or hopper containing a bulk supply of the pulverized coal, a pulverized coal feed conduit leading from the hopper to each of the burners, a solids or dust pump in each of the pulverized coal feed conduits, and a gaseous medium conduit leading into each of the pulverized coal conduits downstream of the solids pump.

The installation may include pulverizing means for pulverizing particulate coal. The pulverizing means may include a coal pulverizer. The installation may then

include a particulate coal bunker ; a coal transfer line leading from the bunker to the coal pulverizer; hot air feed means for feeding hot air into the pulverizer, with the hot air serving to convey pulverized coal from the pulverizer to a filtering means, eg a bag filter; and transfer means for transferring pulverized coal from the filtering means to the bulk pulverized coal drum or hopper, which forms part of the pneumatic pulverized coal feed means. The filter can, of course, discharge directly into the drum or hopper, if desired.

The installation may also include fly ash removal means connected to a gaseous product outlet of the coal gasifier.

Thus, according to a fourth aspect of the invention, there is provided a coal gasification installation, which comprises an atmospheric pressure coal gasifier comprising a gasification vessel providing a gasification chamber, and at least one burner through which pulverized coal can be fed into the gasification chamber; and fly ash removal means connected to a gaseous product outlet of the coal gasifier.

The fly ash removal means may include one or more of a separator, such as a cyclone separator; a scrubber, such as an impingement plate or a venturi scrubber ; an electrofilter, such as a wet electrofilter; and a filter, such as a bag filter, with a conduit leading from a gaseous product or raw gas outlet of the gasification vessel to the fly ash removal means.

In particular, the fly ash removal means may include a scrubber connected to the conduit leading from the gaseous product outlet of the gasification vessel, and an electrofilter, with a washed gaseous product conduit leading from the scrubber to the electrofilter.

The scrubber may comprise an upright vessel having first washing means for washing gaseous product entering the scrubber with hot and/or cold water as well as second washing means for washing gaseous product with cold water.

The first and second washing means may be spaced vertically apart so that the second washing means is located above the first washing means. A plurality of impingement plates may be provided between the first and second washing means.

The invention will now be described by way of example with reference to the accompanying diagrammatic drawings.

In the drawings, FIGURE 1 shows a simplified flow diagram of a coal gasification installation according to a first embodiment of the invention; FIGURE 2 shows a portion of a coal gasification installation according to a second embodiment of the invention; and FIGURE 3 shows another portion of the coal gasification installation according to the second embodiment of the invention.

In Figure 1, reference numeral 10 generally indicates a coal gasification installation according to a first embodiment of the invention.

The installation 10 includes an atmospheric pressure entrained flow coal gasifier, generally indicated by reference numeral 12. The gasifier 12 comprises an upright elongate square section gasification vessel 14 having a front wall 16, a rear wall 18, and side walls 20. Each wall is in the form of a membrane panel as hereinbefore described, ie comprising a plurality of vertically extending tubes (not shown) located adjacent to each other with adjacent tubes being connected by vertical strips (not shown) to which the tubes are welded. The lower ends of

the tubes are connected to a lower manifold (not shown), while the upper ends of the tubes are connected to an upper manifold (not shown). The walls are provided, on their outsides, with cladding (not shown). The vessel 14 defines a gasification chamber 22 which has a lower gasification zone 24, and an upper cooling zone 26. In the gasification zone 24, the inner surfaces of the walls are provided with refractory linings (not shown) through which extend metal studs (not shown) protruding from the tubes, for heat conduction. The tubes of the rear wall 18 are bifurcated part way up the wall, thereby forming an internal divisional wall 28 in the cooling zone 26. Thus, the cooling zone 26 is divided, by the wall 28, into a front pass 30 and a back pass 32. Thus, in use, gases pass upwardly along the front pass 30, through openings between the tubes at the upper portion of the wall 28, downwardly along the back pass 32, and exit the gasifier through openings between the tubes in the rear wall 18, in the vicinity of the bifurcation thereof.

A molten slag outlet 34 is provided in the vessel 14 at the lower end of the gasification chamber 22, while a gaseous product outlet (not shown) is thus provided in the rear wall 18, with a gaseous product withdrawal conduit 36 leading from the gaseous product outlet.

Two burners 38 are mounted in each of the walls of the vessel 14, within the gasification zone 24 of the gasification chamber 22.

A heating coil 40, constituting an economizer, is provided in the back pass 32 in the cooling zone 26 of the gasification chamber 22. Similarly, another coil 42, constituting a first part of a primary steam superheater is also provided in the back pass 32. Another heating coil 44, constituting a second part of the primary superheater, is located in the front pass 30 and is connected to the

coil 42. Further connected heating coils 46,48 which together constitute a secondary steam superheater, are also located in the front pass 30. All of the coils of the superheaters are arranged in such a way that they are drainable so as to prevent damage which could be sustained during startup of the gasifier. The primary superheater is arranged in counterflow to the gas flow so as to minimize the surface area required for the heat transfer duty. The secondary superheater is. arranged partly in parallel flow with the gas so as to minimize metal temperatures and the tendency for corrosion to occur.

The installation 10 includes a 6 MPa (g) steam drum 50.

Conduits 52 lead from the drum 50 to the lower manifolds of the membrane panels of the walls 16,18,20, with conduits 54 leading from the upper manifolds thereof, and of the wall 28, back into the drum 50.

An inlet of the economizer 40 is connected to a boiler feed water supply conduit 56, with an outlet thereof being connected to a conduit 58 leading to the steam drum 50.

The steam drum 50 is also provided with a level control arrangement, generally indicated by reference numeral 60.

A steam conduit 62 leads from the top of the steam drum 50 to an inlet of the coil 42 of the primary superheater, with a conduit 64 leading from an outlet of the coil 44 of the primary superheater to the inlet of the coil 48 of the secondary superheater. The conduit 64 is provided with a steam attemporator 66 with a boiler feed water conduit 67 leading from the boiler feed water conduit 56 to the steam attemporator 66. A superheated steam conduit 68 leads from the outlet of the coil 46 of the secondary superheater to the plant boundary. 6 MPa (g) superheated steam can thus be withdrawn along the conduit 68. Temperature control means,- generally indicated by reference numeral 70 are provided

between the steam conduit 68 and the boiler feed water conduit 67 supplied to the steam attemporator 66.

A slag withdrawal conduit 72 leads from the ash outlet 34 of the gasifier 12 to a slag extractor 74, with the slag extractor 74 being provided with a submerged chain conveyer 76. The slag extractor 74 is designed such that it can discharge frozen or solidified slag into suitable vehicles 78.

The installation 10 also includes pulverized coal feed means, generally indicated by reference numeral 80.

The coal feed means 80 comprises a service bin 82 with a pulverized coal feed line 84 leading into the bin 82. A separate pulverized coal withdrawal line 86 for each burner 38, leads from the bottom of the bin 82 to a solids or dust pump 88. A pulverized coal feed line 90 leads from the pump 88 to the burner 38.

The coal feed means 80 also includes a carbon dioxide line 92 leading from a source of carbon dioxide to the discharge of each pump 88. Each line 92 is fitted with a flow control arrangement 94. Thus, the carbon dioxide constitutes the pneumatic conveying medium for conveying the pulverized coal pneumatically from the pump 88 to the burners 38.

An oxygen supply line 96 also leads to each of the burners 38.

The installation 10 includes an air supply line 98, fitted with a blower 100, leading into the lines 96, for purging the system with air on startup.

An LPG line 102 also leads to each of the burners 38. A nitrogen purge line 103 leads into the carbon dioxide line 92.

The gaseous product withdrawal conduit 36 leads to a scrubber, generally indicated by reference numeral 104.

The scrubber 104 comprises an upright vessel 106 fitted with a plurality of impingement plates 108. A cold water conduit 110 leads into the scrubber 104 near its upper end, immediately below a meshed entrainment separator 112. A distributor (not shown) for distributing cold water (about 25°C) over the uppermost plate or tray, is operatively connected to the conduit 110. The plates are arranged such that cold water passes over one plate, down a downcomer, across the plate below it, and so forth.

A plurality of downwardly directed spray nozzles 114, located below the impingement plates 108, are connected to a hot wash water (about 45°C) conduit 116.

A spent water conduit 118 which, in use, will convey water containing fly ash scrubbed from the gas in the scrubber 104, leads from the bottom of the scrubber 104. A cold water conduit 120 leads from the conduit 110 to the slag extractor 74, with a spent wash water conduit 122 leading from the slag extractor 74. The conduit 118 leads into the conduit 122, as does a conduit 124 leading from a blowdown drum 126. A condensate line 128 leads from the steam drum 50 to the blowdown drum 126. A vent line 130 leads from the blowdown drum 126.

A washed or scrubbed product line 132 leads from the top of the scrubber 104. A line 134 also leads from the top of the scrubber 104 to a flare seal pot 136, with a flare line 138 leading from the flare seal pot 136 to a flare, generally indicated by reference numeral 140. The flore

140 is fitted with a pilot igniter 142. The flare is used for startup and emergencies only.

The installation 10 includes a control arrangement, generally indicated by reference numeral 150. The control arrangement 150 includes an analyzer 152 in the line 132, for measuring the H2, CO and CO2 content of the gas emerging from the scrubber. It also includes a flow rate measurement device 154 in the flow line 36 for measuring the flow rate of the gas from the gasifier 12. It further includes a flow measurement/control arrangement 156 in the oxygen lines 96 to the burners 38, as well as a flow measurement/control arrangement 158 in the coal feed lines 86. The components 152,154,156 and 158 are connected to a controller 160.

In use, and for each burner 38, pulverized coal is fed, at a controlled rate, from the service bin 82 to the pump 88, and then pneumatically, as a dense phase using carbon dioxide as conveying medium, along the flow line 90, to the burner 38. The dense phase comprises a mixture of pulverized coal or coal dust, and conveying medium or gas, with the mixture having a density in the range 80-200kg/m3.

The control arrangement 94 controls the carbon dioxide flow rate at a fixed value. Each conduit 86 thus delivers pulverized coal via the flow rate measuring device or arrangement 158, to the solids pump 88. The solids pump delivers the pulverized coal into a stream of the carrier gas (carbon dioxide) which in turn carries the coal to the burner. Simultaneously, oxygen is fed, along the flow lines 96, through the burners. The burners are of a so-called diffusion type, with combustion of the oxygen and pulverized coal taking place inside the gasification chamber 22, or of a premix type, as hereinbefore described. Slag, typically at a temperature of about 1400°C, is quenched and extracted by means of the ash extractor 74.

The pulverized coal and oxygen react, on burning within the chamber 22, to produce a gaseous component comprising carbon monoxide and hydrogen, as well as ash. More particularly, a sub-stoichiometric proportion of oxygen is used. The coal first burns in oxygen, thereby to generate carbon dioxide and water, at very high temperature. These gases then react with the remaining coal to yield carbon monoxide and hydrogen. The gaseous component is withdrawn as a gaseous product (temperature typically about 200°C) along the flow line 36 and is scrubbed in the scrubber 104 before being removed as a product gas along the flow line 132.

The heat of combustion generated in the gasification chamber 22 is used to heat directly, ie without any quenching thereof with water, boiler feed water passing along the boiler feed water tubes of the gasifier vessel walls, to heat incoming boiler feed water in the economizer 40 to generate 60 bar steam, and to superheat the steam in the coils 42,44,46 and 48 of the superheaters.

The control arrangement 150 sets the oxygen flow rate to meet a required flow rate of useful gas as measured by the components 152 and 154, and defined as the carbon monoxide and hydrogen in the gas produced. The control arrangement 150 also adjusts the coal to oxygen ratio to maintain a required concentration of carbon dioxide in the gas produced.

The Applicant believes that by using pneumatic conveying of pulverized coal to the gasifier 12, accurate measurement of the coal feed rate can be achieved by monitoring the solids flow rate to the solids feed pump.

In the gasifier 12, all waste heat is recovered as high pressure superheated steam, and an internal water quench i-s not required.

Scrubbing of the gaseous product in the scrubber 104 is efficient, and requires less energy than other washing arrangements.

The pressure drop through the installation 10 is such that gas in the flow line 132 is delivered at a required pressure without the need for a booster blower.

The installation 10 can. be used in the manufacture of any chemicals requiring either carbon monoxide or hydrogen or both as raw materials. Such chemicals include ammonia and its derivatives, methanol and its derivatives, acetic acid and its derivatives, etc. The installation 10 can also form at least part of an integrated electricity generation plant.

It is believed that, in the installation 10, more than 85% of the theoretical waste heat generated in the gasification chamber 22 may be recovered as high pressure superheated steam suitable for driving a steam turbine, where the theoretical waste heat is defined as the heating value of the coal inputted into the gasifier less the heating value of the gas, fly ash and slag exiting the gasifier.

It is also believed that a higher proportion of coal will be converted in the installation 10 than is converted in known gasifiers, thereby reducing the quantities of fly ash produced.

Additionally, in the installation 10, consumption of electricity will be substantially reduced, the consumption of water to quench the raw gas will be eliminated and the safety of the process will be improved, as compared to known processes using quenching of the product gases in the gasifier.

Furthermore, gas produced in the gasifier 12, and which contains highly corrosive components, is kept within a fully water cooled enclosure until the temperature of the gas is below that at which corrosion rates become significant. The temperature of the enclosure itself is maintained at the boiling point of the water within the walls of the gasifier by selecting an appropriate operating pressure. By this means it is possible to select materials for the construction of the gasifier walls which are in common use in the construction of modern industrial boilers.

It is also believed that the use of the bin 82 and the dust pumps 88, will result in an installation which, as regards its height, is less than that of known dense phase pneumatic conveying installations, leading to lower capital and operating costs, as well as lower maintenance costs.

Referring to Figures 2 and 3, reference numeral 2GO generally indicates a coal gasification installation according to a second embodiment of the invention, and which incorporates the coal gasification installation of Figure 1.

Parts of the coal gasification installation 10 have been excluded from Figures 2 and 3, for simplicity.

Furthermore,. parts of the installation 200 which are the same or similar to those of the installation 10, are indicated with the same reference numerals.

The process 200 includes a raw particulate coal bunker 202, with a coal line 204 leading into the bunker. A coal transfer line 206 leads from the bunker to a pulverizer 208. The pulverizer typically pulverizes raw coal so that it has a particle size distribution such that 90% thereof is less than 90 microns.

A hot air flow line 210 leads into the coal pulverizer. The hot air serves to dry the coal from a typical moisture content of 7%-14% (by mass) to around 1% (by mass). The hot air also serves to transport the dried and pulverized coal, as a dilute phase, along a flow line 212 to a bag filter 214 in which all the pulverized coal is disengaged from the hot air stream. The dilute phase thus comprises a mixture of pulverized coal or coal dust and air, ie conveying gas, and has a density substantially less than 80kg/m3. A discharge line 216, for discharging dust-free hot air into the atmosphere, leads from the bag filter 214, while the pulverized coal feed line 84 leads from the filter to the coal service bin 82, which is typically located below the filter 214 so that the coal is discharged under gravity into the bin 82.

The bunker 202, pulverizer 208 and bag filter 214 thus enable pulverized coal to be produced as part of the process 200. In this fashion, the capital and operating costs of a system for distributing pulverized coal from a mill or mills to a number of feed bins 82 are avoided.

Such systems are normally oversized as regards gasifier coal requirements, leading to additional costs. Such systems can also be prone to blocking, and therefore can be difficult to operate. The pulverizer can thus be sized so that its pulverized coal production matches the coal requirement of the gasifier, thereby reducing costs as compared to known systems. In other words, there is full integration of the pulverizer, the gasifier, and the other components such as the bin 82 and the dust pumps 88.

Additionally, the capital and operating costs associated with distribution systems which are normally required to distribute the coal from the plurality of bins to the gasifier, are at least reduced.

The process 200 also includes a wet electrofilter 218, with the scrubbed product or raw gas line 132 leading from the

scrubber 104 to the wet electrofilter. A wash water line 220 leads from the wash water line 110 into the electrofilter 218. A clean raw gas withdrawal line 222 leads from the electrofilter 218, while fly ash slurry withdrawal lines 224 lead from the electrofilter 218 into the spent water or slurry conduit 118.

The electrofilter 218 permits the product gas from the gasifier 12 to be purified further, ie more fly ash removed therefrom, before it is subjected to further processing, eg ammonia and/or methanol production therefrom.

Instead of using wet dedusting equipment such as the scrubber 104 and the wet electrofilter 218, dry dedusting equipment such as a cyclone separator and/or a bag filter can be used. This will then yield a dry dust, instead of a slurry which can be difficult to dispose of. The dry dust can be refired in the gasifier or fired in an auxiliary boiler, or can be disposed of as a product.

It will be appreciated that the gas leaving the gasifier, ie the hot gaseous component or hot raw gas, comprises a number of components. The principal components, in order of importance, are carbon monoxide (typically 62% by volume), hydrogen (typically 22%), carbon dioxide (typically 7%) and water vapour (typically 7%). The balance of the gas is made up of minor components including, but not limited to, hydrogen sulphide, carbonyl sulphide, ammonia, hydrogen cyanide, methane, nitrogen, argon, nitrous oxides, and hydrogen chloride. The precise composition of the raw gas may vary depending on the analysis of the coal being gasified, the particular operating conditions chosen, and whether or not steam is added to the oxidant stream.