Process for the production of synthesis gas from coal

The overall conversion of coal to synthesis gas by pressurized counter-current gasification is improved by steam reforming the methane values in the gas and heating the steam reformer by means of a fluidized bed combustor fuelled by the coal fines which are too small to be employed in the gasification step. Coal can be crushed to increase the proportion of fines and/or conditions for gasifications and/or steam reforming varied so as to consume lump coal and fines in the desired ratio. The product gas may be used for methanol synthesis.

The present invention relates to a process for the production of synthesis 
gas from coal, for example for the subsequent production of methanol. In 
particular the process is concerned with counter-current gasification of 
coal and involves a subsequent steam reforming step for which heat is 
supplied by means of a fluidised bed. 
The term coal as used herein means not only anthracitic, bituminous and 
brown coal but also lignite. 
Counter-current coal gasifiers such as the gasifier developed by Lurgi 
Kohle and Mineraloltechnik GmbH have been in existence for some decades 
and have been used to convert coal to hydrogen and oxides of carbon which 
may be purified and which in turn are used as synthesis gas for reactions 
such as synthesis via the Fischer Tropsch process to produce liquid 
hydrocarbons, synthesis to produce methanol, or via the OXO synthesis 
route to produce higher alcohols. The gases may also be converted to a 
hydrogen containing gas suitable for hydrogenation reactions, or 
alternatively used as such or suitably purified and possibly converted to 
hydrogen for the reduction of metallic ores. 
The process using such gasifiers, and in particular the process used by 
Lurgi Kohle and Mineraloltechnik GmbH, is well established and it is now 
available in a form which has been developed by the British Gas Council in 
which the ash residue is removed from the gasifier as a slag. 
A desirable feature of the process is that it is capable of being operated 
under elevated pressure. This is of considerable benefit where subsequent 
processing steps and allied processes using the produced gases are also 
operated under pressure since the production of the raw synthesis gas 
under pressure can result in higher efficiencies due to reduction of 
compression requirements and lower capital cost due to the use of compact 
equipment. 
A further desirable feature of the counter-current process is that the 
gases leave the gasifier at a relatively low temperature and thus the heat 
in the high temperature reactants in the base of the gasifier is 
transferred back to the descending fuel bed and reactions such as 
methanation occur above the high temperature zone. The methanation 
reaction and the rising hot gases pre-heat and partially carbonise the 
coal entering the top of the gasifier thus producing together with the 
gases resulting from the reaction at the base of the column additional 
gases and liquid from further gas reactions and the drying and 
carbonisation of the feed coal. This counter-current flow results in a 
high thermal efficiency for the gasifier. 
There are, however, two major deficiencies in the pressurised fixed bed 
counter-current gasifier, namely, the production of increasing quantities 
of methane as the gasifier pressure is increased and the inability of such 
gasifiers readily to accept the coal fines which are produced as a normal 
consequence of mining operations. In addition, there is the problem that 
the process produces an aqueous effluent which contains impurities such as 
phenol, suspended tar and dissolved ammonia and the further problem that 
in some instances the co-produced tars and in particular the heavier 
fractions may be difficult to dispose of. 
The prensence of methane in synthesis gas is not desirable where the gas is 
to be used in reactions, such as the production of methanol, ammonia or 
hydrocarbons via the Fischer Tropsch process or for ore reduction, where 
conversion is incomplete and unreacted gas is therefore recycled to the 
reactor to form a so-called synthesis loop. This is because the methane is 
non-reactive and if not eliminated from the synthesis gas prior to the 
reaction, synthesis or ore reduction, accumulates in the circulating gases 
and must be purged from the synthesis loop together with some of synthesis 
gas. 
Current operating pressures for the Lurgi non-slagging and British 
Gas/Lurgi slagging gasifiers are about 20 to 30 bar but it would be 
desirable to operate these gasifiers at higher pressures, up to about 100 
bar and possibly above. As the pressure is increased there is an 
improvement in coal gasified per unit of fed oxygen as well as an increase 
in the output and efficiency of a given size reactor. In addition, as 
gasification pressure is increased, the need for downstream gas 
compression is reduced. However, as the pressure is increased there is 
also an increase in the amount of methane formed which, as stated above, 
is undesirable for the production of synthesis gas and synthesis gas 
derived products. As a result of this, despite the advantages in operating 
at the higher pressure range, where the gasifiers are used for producing 
synthesis gas, the pressure of operation is kept to the 20-30 bar pressure 
range and pressures of up to 100 bar are planned only for applications 
such as the production of synthetic natural gas where the presence of 
methane is desirable. 
It is known, e.g. in the production of methanol from synthesis gas, that 
any methane values in the gas purged from the methanol synthesis loop may 
be converted to produce more synthesis gas by steam reforming but a 
significant part of the purge gas, about 40%, is required to fuel the 
steam reformer, thereby limiting the potential yield of additional 
synthesis gas by this route. 
Fixed bed counter-current gasifiers require coal above a certain size for 
satisfactory operation and for this reason it is necessary to separate 
from the coal supply fines smaller than about 5 mm in size. Such fines 
generally constitute about 20-40% of the coal output from a mine and 
further fines are produced during handling and screening the coal and in 
crushing oversize pieces. Accordingly, maximisation of the production of 
synthesis gas from run-of-mine coal in a plant employing a pressurised 
counter-current gasifier generally requires not only a steam reformer to 
convert the methane values in the gas produced by this gasifier but also 
the provision of an alternative form of gasifier, such as the kind 
developed by Texaco, which is capable of utilizing the fines. 
The present invention provides a process which avoids the above-mentioned 
problems associated with the use of counter-current gasifiers and improves 
the overall utilisation of coal in the production of synthesis gas by a 
counter-current coal gasification process without the capital expense of 
having to employ an additional gasifier. In the process of the invention, 
the fines are used as fuel for a fluidised bed combustor employed to 
provide the heat for steam reforming the methane values in the gas 
produced by the counter-current gasification. 
Thus, according to the present invention there is provided a process 
comprising the steps of dividing lump coal suitable for counter-current 
gasification from a coal supply comprising such lump coal and fines, 
performing counter-current gasification of lump coal divided from the coal 
supply at superatmospheric pressure to form a gas comprising hydrogen 
oxides of carbon and also containing methane values and subsequently steam 
reforming at least a portion of said methane values in a reactor at least 
partially immersed in a fluidised bed of finely divided solid, and wherein 
at least some of the heat for the steam reforming step is provided by 
heating the fluidised bed by combustion of fines divided from the lump 
coal as a result of the first step. The use of high pressure, above 30 
bar, is advantageous because, as stated above, the need for compression 
prior to subsequent processing is avoided. The extra methane produced does 
not lower the efficiency of the process because it is converted in the 
steam reforming step to oxides of carbon and hydrogen which can be 
recycled for further processing. By appropriate choice of conditions, all 
or substantially all of the coal may be used in the process as the lump 
coal is fed to the gasifier while the fines are used to fuel the fluidised 
bed. 
The ratio of lump coal to fines in the coal supply may be controlled so as 
to be substantially equal to the ratio of consumption of lump coal in the 
gasification step to the rate of combustion of fines in providing heat for 
the steam reforming step. For example, coal may be crushed to increase the 
proportion of fines. 
By-products from the gasification step such as hydrogen sulphide, dissolved 
tar and phenols which are normally waste products requiring disposal, may 
also be used as supplementary fuel for heating the fluidised bed. 
The fluid bed combustor for the steam reforming may employ an atmospheric 
pressure fluid bed combustor of simple `plug flow` design or it may employ 
the separate fluidising and combustion gas zones of the `fast bed` 
combustor as developed by Batelle Institute and Lurgi. A preferred 
arrangement for the combustor is the pressurised fluid bed combustor as 
generally described in U.K. patent publication No. 2055891. 
The gasification step of the process need not be carried out using the 
Lurgi or British Gas type of gasifiers and alternatively other kinds of 
counter-current gasifiers could be used. For example the gasification 
could be performed using two or more single stage fluid beds arranged in 
counter-current flow. Such alternatives have in the past had the problem 
that, particularly at high pressures, an undesirable amount of methane is 
produced. 
By means of this invention coal fines and fine low grade coal (which term 
includes lignite) may be used to provide the bulk of the fuel for 
providing the heat for the reformer. The process thereby eliminates or 
substantially eliminates the need to use part of the methane containing 
gas to fuel the reformer and thereby increases the amount of synthesis gas 
produced for a given counter-current gasifier and a given quantity of lump 
coal fed to the gasifier, when compared to the conventional processes. 
By using the process of the invention the pressure of the counter-current 
gasifier may be increased to pressures above 30 bar and to or above 100 
bar at which pressures such gasifiers would not normally be suited to the 
manufacture of synthesis gas. By operation of the gasifier at higher 
pressures the output of the gasifier can be increased, the utilisation of 
oxygen per unit of lump coal gasified increased and the thermal efficiency 
of the conversion of lump coal to crude synthesis gas increased. The 
increased amount of methane produced by operating at such higher pressures 
is no longer a problem since it is reformed using coal fines. The overall 
ratio of fines to lump coal consumption and the production of synthesis 
gas from a given amount of lump coal are thus both increased. As a result 
of this feature, the operating conditions, especially pressure of 
gasification and steam reforming may be selected to ensure that the rates 
of feed of lump and fine coal to the gasifier and reformer respectively, 
are consistent with the available ratio of lump and fines from the related 
mining operation and any subsequent crushing of the lump coal. 
The process of the invention may incorporate a methanol synthesis step 
where gas containing hydrogen and oxides of carbon and produced by the 
gasification step, is supplied to a methanol synthesis zone. 
Advantageously, the methanol synthesis step is performed on gas from the 
gasification step in a synthesis zone with recycle of unreacted gases and 
the steam reforming step is performed on a purge stream containing methane 
values and taken from the methanol synthesis recycle stream and reformed 
gas is returned to the methanol synthesis zone. Alternatively, however, 
gas from the gasification step may first be subjected to steam reforming 
to convert methane values therein to additional hydrogen and/or oxides of 
carbon and the reformed gas is thereafter subjected to said methanol 
synthesis step. 
An important feature of the invention is that it can be employed to improve 
the hydrogen to oxides of carbon ratio towards the optimum required for 
methanol synthesis. The hydrogen to oxides of carbon ratio in the 
synthesis gas produced from gasifiers is usually below that required for 
methanol synthesis and has to be adjusted e.g. by shift reaction of carbon 
monoxide and/or the removal of carbon dioxide by scrubbing. The hydrogen 
to oxides of carbon ratio in the gas produced by the steam reforming of 
methane, on the other hand, is generally above that required for methanol 
synthesis. Accordingly, by means of the invention, it is possible to 
produce a gas in which the ratio approaches the ideal for methanol 
synthesis by utilising the combination of gas from the gasification and 
gas from the reformer as the methanol synthesis feed and adjusting the 
pressure of the gasification which in turn controls the concentration of 
methane available for steam reforming in the gas so produced. 
Hydrogen sulphide present in the synthesis gas leaving the gasifier may be 
removed therefrom and effectively incinerated to sulphur oxides by 
injection into the fluidised bed combustor zone, thus eliminating the need 
for a separate incinerator system or sulphur recovery plant. The fluidised 
bed may include an absorbent for the sulphur oxides. 
Inert gases such as nitrogen and argon which enter the process as 
impurities, e.g. in the oxygen used for the gasification process and/or as 
nitrogen contained in the coal, and which build up in a synthesis loop 
such as in the production of methanol, may be effectively separated by 
taking part of the reformed gas leaving the reformer and separating the 
gases by known means such as a shift reaction followed by carbon dioxide 
removal by scrubbing followed by low temperature separation of the 
remaining hydrogen, nitrogen, argon and methane with the possible return 
to the process of part or all of the hydrogen, methane and carbon dioxide 
streams. 
By means of this invention all or a significant portion of any aqueous 
phenolic effluent and in particular tar/water emulsions, produced as 
by-products of the counter-current gasification may be fed to the 
combustion zone of the fluid bed combustor. In particular, such effluent 
may be used as a slurrying agent for the fines and/or other solid fuel 
employed to heat the fluidised bed. 
Any distillation forming part of the treatment of the product from the coal 
gasification produces a residue containing tar with coal-derived solid 
impurities. Although the residue has a fuel value it cannot readily be 
combusted by conventional means, causing a disposal problem. By means of 
the invention, tar-containing liquid can suitably be withdrawn as a 
by-product from the coal gasification step and used as fuel to heat the 
fluidised bed.

Referring to FIG. 1, the diagram illustrates a process in which coal is 
used to produce synthesis gas for methanol manufacture. A coal screening 
device 2, which receives some coal from an oversize coal crusher 4 
supplies coal to a counter-current pressurised gasifier 6. Gas containing 
hydrogen, oxides of carbon and also some methane values is subsequently 
passed to a gas purification system 8 and thence to a compressor or group 
of compressors 10. The compressed gas then travels to a methanol synthesis 
zone 14 from which unreacted gases are passed through a steam reformer 12 
which is heated by means of a fluidised bed as described below. After 
steam reforming, gases are supplied to separator 16. 
Coal is fed via a conveying device 102 to the coal screening device 2 which 
separates coal into lump coal above 5 mm (or such minimum size as to be 
suitable for the counter-current gasifier 6) which is removed by conveying 
device 104, and into fines smaller than the minimum size. Part of the lump 
coal in 104 may be diverted by conveying device 106 to crusher 4 and the 
crushed material passed back via conveying device 107 to the conveying 
device 102. By regulating the amount of lump coal passed to the crusher 4 
a controlled ratio of fines to lump coal can be maintained. 
The undiverted lump coal in conveying device 104 is passed via conveying 
device 108 to the pressurised counter-current gasifier 6. 
The counter-current gasifier 6 incorporates such devices as feed load 
hoppers, ash lock hoppers, distribution devices and annulus boilers etc. 
and could for example be a Lurgi type gasifier with solid ash discharge or 
a British Gas/Lurgi type slagging gasifier, both types of unit being 
extensively described in readily available technical literature. 
Gasification is carried out at superatmospheric pressure with the 
operating pressure being generally above 5 bar and with the preferred 
range being between 20 and 100 bar. Oxygen is fed to the gasifier via 
pipeline 112, steam is fed via pipeline 114 and water is fed via pipeline 
113. Ash is removed via conveying device 116 and raw gas produced by the 
gasification, comprising hydrogen and oxides of carbon with some methane 
values is removed via pipeline 118. 
The raw gas passes to the gas purification system 8 which may be designed 
in accordance with established practice. The gas is cooled to remove tars 
which leave by pipeline 120 and aqueous liquid which leaves by pipeline 
122. Some carbon dioxide and hydrogen sulphide are removed with purified 
gas in pipeline 128 but the greater part of the hydrogen sulphide and some 
of the carbon dioxide leave via pipeline 130 after which the hydrogen 
sulphide could be disposed of by conversion to elemental sulphur or 
incinerated by known means. In the process illustrated, at least some of 
the hydrogen sulphide containing gas is passed from pipeline 130 to 
pipeline 180 and injected into the combustion zone of the fluid bed 
combustor employed in 12 to heat the steam reformer, where the hydrogen 
sulphide is combusted to assist in heating the fluidised bed and converted 
to oxides of sulphur which leave with flue gases in pipeline 170. If 
desired, the fluid bed may contain dolomite or other sorbent to absorb at 
least some of the sulphur oxides. Spent sorbent leaves with ash in 
conveying device 192. The remaining carbon dioxide leaves by pipeline 132 
after which it may be vented or produced as a by-product. Purified gas 
leaves the gas purification system 8 via pipeline 128. The ratio of 
hydrogen to oxides of carbon produced during the gasification step is 
controlled by selection of the operating conditions, particularly the 
pressure in the gasifier 6. The ratio is preferably the optimum for 
methanol production, allowing for gas supplied to the compressor 10 via 
lines 134 and 138 from the steam reforming step as described below. The 
compressor or compressors may be multi-staged units, for example one or 
more individual units in series, and the compressing section may consist 
of more than one train in parallel. The compressor(s) may be driven by 
steam and/or electricity which may be produced e.g. by combustion of any 
surplus coal fines and/or the compressors may be driven at least in part 
by the hot gas expander associated with the fluid bed combustor of 12 if 
the combustor is pressurised. 
Carbon dioxide which is obtained from the gas leaving pipeline 132 or from 
an alternative source and which is sufficiently pure and is supplied at a 
suitable pressure may also be added to the compressor system 10 via 
pipeline 134 for compression with the purified gas, should the average 
carbon oxides to hydrogen ratio in pipelines 128 and 138 be insufficient 
for optimum methanol synthesis. Additional gas for synthesis is also 
recirculated to the compressor system via pipeline 178 as described below. 
The gases in pipeline 138 and 178 may be supplied to the inlet of the 
compressor or to a suitable intermediate compression stage depending upon 
the respective pressure of operation of the gasifier 6, the steam reformer 
12 and the synthesis reactor system 14. 
Combined, compressed, gas for synthesis leaves the compressor system 10 via 
pipeline 136 and passes to the synthesis reactor system 14. The reactor 
system 14 consists of a catalyst filled reactor or reactors, suitably 
tubes, and also heat exchangers, water heaters or boilers, coolers, heat 
exchangers and separators in accordance with the known methods of 
constructing such systems. Crude methanol is produced in the synthesis 
reactor system 14 and is extracted via pipeline 140 after which it may be 
distilled or suitably treated to remove impurities. Unreacted synthesis 
gas i.e. hydrogen and oxides of carbon together with inerts such as 
methane, nitrogen and argon are recovered from the system via pipeline 142 
and passed via pipeline 174, valve 176 and pipeline 178 back to the 
compressor system 10 and thence back to the synthesis reactor system 14. 
The rate of recirculation may be controlled in a suitable manner by valve 
176. Due to this recirculation, the concentrations of inert gas components 
and in particular the methane content in the reactor system will tend to 
increase. Accordingly, in order to maintain these concentrations constant, 
a purge gas stream, rich in methane, generally in the range of 20 to 60% 
by volume, is withdrawn from the recycle stream and this is passed via 
pipeline 144, valve 146 and pipeline 154 to the steam reformer 12. The 
pipeline passes through the heated fluid bed and the methane content in 
the gas therein is substantially reformed to hydrogen and oxides of 
carbon. The resultant reformed gas is then passed via pipeline 138 to the 
compressor section 10. 
The fluid bed combustoremployed in 12 may be a substantially ambient 
pressure combustor but in this example the combustor is pressurised and 
constructed generally in accordance with the design described in 
aforementioned British patent publication No. 2055891. The combustor 
includes suitable coal feed systems which may include coal slurrying and 
pumping apparatus, provision for ash removal, combustion gas clean-up 
systems including cyclones or alternative separation equipment, combustion 
gas cooling, combustion air compression and combustion gas expansion 
devices, reformer feed gas preheating equipment, reformed gas cooling 
apparatus, and waste heat boilers and water heaters as necessary, 
generally in accordance with the arrangement decribed in the patent 
publication referred to above. 
Coal fines from the screening section 2 pass via the conveying device 158 
and fines as necessary for steam raising for process steam and process 
power may be removed via conveying system 160. The remaining fines pass 
via the conveying system 162 and to this may be added via conveying system 
164 lower grades of coal such as washery middlings and possibly washery 
tailings, which would be suitably sized for conveying. The combined fuels 
are fed by conveying device 166 to the fluid bed combustor of 12 and air 
for the combustor is drawn in via duct 168. Sorbent, if used, is provided 
e.g. in the form of limestone or dolomite. The sorbent or a suitable inert 
material maintains the necessary bed height in the combustor and is fed to 
the combustor by conveying device 156. Aqueous phenolic effluent from the 
gas purifier 8 is passed to the combustor of 12 via pipeline 126 and may 
be injected by pumping into the combustor or mixed with the coal fines 
feed and pumped as a fuel slurry component for the combustor. Water for 
steam production is supplied via pipeline 180. Ash and any spent sorbent 
is removed from the combustor by conveying device 192 and flue gas leaves 
via pipeline 170. 
Power may be produced by the expansion of the flue gas exiting from the 
pressurised fluid bed through a turbine and may be provided in the form of 
shaft power which could be coupled direct to compressor drives in the 
compression section 10 and possibly the air for the oxygen plant, and/or 
may be converted to electric power as shown in cable 172 for subsequent 
use by using electric drives for the compressors and possibly other pumps 
and electrical devices allied to the process as a whole as desired by a 
person skilled in the art. 
The methane content of the purge gas from the methanol synthesis reactor 
system is thus constantly removed and subjected to steam reformation in a 
pipeline 154 passing through the fluid bed combustor of 12, heated mainly 
by the combustion of coal fines. However, with recirculation, inerts such 
as nitrogen and argon accumulate in the reaction gases and have to be 
purged from the system via pipeline 148, valve 150 and pipeline 152. The 
purge gas may be treated to recover all or part of the hydrogen, carbon 
oxides and methane values for re-use as reactants or may be used as 
reformer or general purpose fuel. It is also possible for part of the 
reformed gases derived from the methane containing gas entering the fluid 
bed combustor of 12 to be withdrawn via pipeline 182 and pass to the gas 
separation system 16 which could include any of a wide variety of known 
processing devices but which in this example consists of a shift reactor 
to convert carbon monoxide to carbon dioxide, a scrubbing system to remove 
carbon dioxide and a low temperature gas separation plant to separate 
nitrogen and argon, both of which leave the unit via pipleine 188. Methane 
leaves the unit via pipeline 190 and hydrogen leaves the unit via pipeline 
184. Hydrogen returns to the compressor and synthesis systems 10 and 14 
via pipelines 184 and 138 and recovered methane and possibly carbon 
dioxide may also be returned to the methanol synthesis loop. The gas 
separation system 16 would contain the necessary compressors to enable the 
recycle of the recovered gases. 
It will be apparent to those skilled in the art that the fluid bed-heated 
steam reformer may also be used in a similar manner in conjunction with a 
counter-current coal gasifier to produce synthesis gas for hydrogen 
production where the hydrogen may be produced as the final product or 
alternatively where the hydrogen may be used for hydrogenation purposes 
and where the hydrogenation reactor system would effectively replace the 
methanol synthesis reactor 14 in FIG. 1. Alternatively, the synthesis gas 
may be used in the manufacture of ammonia, hydrocarbons or alcohols, or 
for the reduction of metallic ores. 
The arrangement of FIG. 1 could be modified so as to perform the steam 
reforming step in 12 before the methanol synthesis step in 14. Gas from 
the gasifier 6 after purification and compression in compression system 10 
could be passed directly to the steam reformer. The steam reformation 
effected therein would increase the proportion of hydrogen and carbon 
oxides to the detriment of the proportion of methane so that after 
separation in separator 16 gas with only a trace of methane and consisting 
mainly of hydrogen and carbon oxides is supplied to the methanol synthesis 
zone 14. In this modified version it would be necessary to divide a purge 
stream from pipeline 142 containing unreacted gases which would mainly be 
nitrogen and argon with traces of methane. 
The process of FIG. 1 is controlled so that the ratio of the rate of supply 
of lump coal to the gasifier 6 is approximately equal to the rate of 
combustion of fines in fuelling the fluid bed 12. This is achieved by 
crushing an appropriate amount of lump coal in the crusher 4 to increase 
the proportion of fines as necessary and by selecting the operating 
conditions of the gasifier and fluid bed so as to consume the correct 
amount of lump coal and fines, respectively. Also, as described above, the 
relative proportions of hydrogen and oxides of carbon in gas supplied via 
pipeline 136 to the methanol synthesis zone 14 can be adjusted by varying 
the operating conditions of the gasifier and are increased by steam 
reforming. The ratios of the gases may thus be controlled so as to be the 
optimum for efficient methanol production. 
For a typical prior art design of methanol plant using a feed obtained from 
coal fed Lurgi gasifiers operating at 30 bar and incorporating a Lurgi 
autothermal reformer to reform the methane values in the gas obtained from 
the gasifiers, 6,300 Gj/hr of coal feed containing no more than 10-15% 
fines would produce 162 tonnes per hour of methanol with an overall 
thermal efficiency of 50.8%. 
If the autothermal reformer were eliminated the plant would produce 82.2 
tonnes per hour of methanol, 1894 Gj/hr of of SNG (synthetic natural gas) 
and 468 Gj/hr of tar liquids with an overall thermal efficiency of 63.3%. 
By using the arrangement of FIG. 1, the same gasifiers operating for 
example at 30 bar together with a pressurised fluid bed combustor-heated 
steam reformer with the combustor operating at 20 bar feed air pressure 
and the reformer operating at 30 bar pressure, could consume 7,815 Gj/hr 
of coal having 30 to 35% fines to produce 178 tonnes per hour of methanol 
and 468 Gj /hr of tar liquids with an overall thermal efficiency of 52.7% 
and an increase in the effective thermal conversion of the lump fraction 
of the coal of about 5%. 
FIG. 2 shows a typical arrangement for a conventional prior art 
counter-current gasifier of the type designed by Lurgi incorporating a 
coal crushing and screening unit 202, utilities section 204 producing 
power, steam and oxygen and a gasifier 206 operating at 30 bar and 
incorporating all the necessary coal feed devices and gas cooling and 
purification systems. A methanol synthesis unit 208 operates at 70 bar 
incorporating gas compression and recycling systems, gas cooling, methanol 
removal and distillation systems and a methanation plant 210 produces 
synthetic natural gas. 
Coal which may have been pre-treated by washing is fed via conveyor system 
252 to the crushing and screening unit 202. Coal with a size range between 
5 and 50 mm in passed via conveyor system 256 to the gasifier 206 and coal 
fines smaller than 5 mm are removed by conveyor system 280 and thence 
either via conveyor 282 to the utilities section 204 as fuel or via 
conveyor 284 as a surplus coal fines product. 
Oxygen and steam are added to the gasifier 206, recovered tar is removed 
via pipeline 260 and synthesis gas is transferred via pipeline 258 to the 
methanol synthesis plant 208. Not shown are aqueous effluent and acid gas 
removal systems. 
The methanol synthesis unit 208 produces methanol in pipeline 286 and purge 
gas in pipeline 288 which is passed to the methanation system 210. 
Produced synthetic natural gas leaves the methanation system 210 in 
pipeline 290. The purge gas in pipeline 288 contains untreated methane 
produced initially in the gasifier 206 together with hydrogen and oxides 
of carbon and some nitrogen and argon. 
For a typical bituminous coal the principal energy flows on an hourly basis 
for the process of FIG. 2 are as follows: 
______________________________________ 
Conveyor/Pipeline 
Energy flow/hour (G.j.) 
______________________________________ 
Conveyor 252 8280 G.j. 
Conveyor 256 5400 G.j. 
Conveyor 282 1000 G.j. 
Conveyor 284 1880 G.j. 
Pipeline 260 468 G.j. 
Pipeline 286 1625 G.j. 
Pipeline 290 1894 G.j. 
______________________________________ 
FIG. 3 shows the plant in FIG. 1 modified with a revised utilities section 
302, an enlarged methanol synthesis unit 304 and unit 306 which is a steam 
reformer operating at 30 bar pressure and heated by a fluidised bed 
combustor which is designed to operate with a combustion pressure of 20 
bar. The reformer/combustor is similar in design to the unit described in 
British patent publication 2055891 and incorporates apparatus for fuel 
slurry preparation, ash removal, air compression, flue gas expansion and 
heat recovery and process gas heat exchange and cooling systems. Provision 
is also made for inclusion of circulating gas treatment to remove nitrogen 
and argon inert gases. 
Conveyor 282 in the prior art process is replaced by conveyor 352 and 
conveyor 284 is replaced by conveyor 354 conveying coal fines to the fluid 
bed combustor 306. Purge gas line 288 is replaced by pipeline 356 passing 
purged gas for steam reforming in unit 306 and reformed gas from 306 is 
returned to the synthesis unit 304 via pipeline 358. The other pipelines 
and units having the same numbers as FIG. 2 have the same function and 
flows as those of FIG. 2. The revised energy flows in the modified plant 
are as follows: 
______________________________________ 
Conveyor/Pipeline 
Energy flow/hour (G.j.) 
______________________________________ 
Conveyor 352 800 G.j. 
Conveyor 354 2080 G.j. 
Pipeline 360 3633 G.j. 
______________________________________ 
In addition, up to 80,000 liters per hour of effluent water may be added to 
the 2080 G.j. per hour of coal being fed to the reformer 306. It will be 
seen that operation of the process of the invention exemplified in FIG. 3 
results in greatly increased energy flow per hour from the methanol 
synthesis unit 304 in pipeline 360 as compared with the prior art flow 
rate in line 286 from synthesis unit 208 in FIG. 2.