Production of demercurized synthesis gas, reducing gas, or fuel gas

A process for the production of demercurized synthesis gas, reducing gas or fuel gas. Mercury-containing fossil fuels e.g. coal were reacted by partial oxidation to produce gaseous mixtures comprising H.sub.2, CO, H.sub.2 O, CO.sub.2, H.sub.2 S, COS, entrained slag and/or ash, mercury vapor, and optionally CH.sub.4, NH.sub.3, N.sub.2 and Ar. Unexpectedly, the mercury vapor was produced in the reaction zone; and it was found to be thermodynamically stable even in the presence of H.sub.2 S under the strong reducing conditions that prevailed in the gas generator. No new sulfides of mercury were formed. The mercury vapors were removed from the main body of the process gas stream in a pressurized solvent scrubber at a relatively low temperature. By this means, the mercury vapor was condensed and simultaneously the mercury and sulfur contents of the clean process gas stream were reduced to low levels. In one embodiment, the last vestiges of mercury were removed from the demercurized product gas stream by carbon sorption.

FIELD OF THE INVENTION 
This invention relates to a process for producing demercurized synthesis 
gas, reducing gas, or fuel gas from mercury-containing fossil fuels. 
BACKGROUND OF THE INVENTION 
Synthesis gas, reducing gas, and fuel gas are gaseous mixtures comprising 
H.sub.2, carbon oxides, H.sub.2 O, and CH.sub.4. Synthesis gas and 
reducing gas are rich in H.sub.2, CO and have varying H.sub.2/ CO mole 
ratios. Fuel gas is rich in CH.sub.4 and has a high heat capacity. These 
gases are commonly made by the gasification of fossil fuels e.g. liquid 
hydrocarbonaceous fuels such as crude oil, and solid carbonaceous fuels 
such as coal and petroleum coke. Mercury contamination in the synthesis 
gas, reducing gas, and fuel gas occurs when the feedstock to the gasifier 
contains mercury. For example, reported values of mercury concentrations 
in coal feedstocks range from about 0.012 to 33 ppm (parts per million) 
with an average value of about 0.2 ppm for certain U.S. coals. When large 
amounts of coal e.g. about ten thousand tons per day of a coal containing 
about 0.25 ppm to Hg are burned upwards of 5 pounds per day of mercury 
would be discharged into the atmosphere posing health and environmental 
hazards through mercury entering the food chain. U.S. Pat. No. 4,196,173 
found that it was only practical to remove mercury from air in a bed of 
activated carbon of critical thickness and chlorine content. In U.S. Pat. 
No. 4,044,098, H.sub.2 S was added to natural gas to precipitate the 
sulfides of mercury. The excess H.sub.2 S was absorbed by a solvent. 
Technology for control of mercury emissions from such large sources as 
coal fired furnaces has not been developed although mercury has been 
observed in flue gas sulfur oxide scrubber effluent liquid. In one study, 
about 90% of the mercury in the fuel used for a large coal fired furnace 
was released and appeared as vapor discharged in the stack gas. 
The partial oxidation process is a well known process for converting liquid 
hydrocarbonaceous and solid carbonaceous fuels into synthesis gas, 
reducing gas, and fuel gas. See coassigned U.S. Pat. Nos. 3,988,609; 
4,251,228, and 4,436,530 for example, which are incorporated herein by 
reference. The removal of acid-gas impurities from synthesis gas is 
described in coassigned U.S. Pat. Nos. 4,052,175, and 4,081,253, which are 
incorporated herein by reference. However, the aforesaid references do not 
teach nor suggest the subject process for the production of demercurized 
synthesis gas, reducing gas, or fuel gas. By the subject process, the 
amount of mercury in synthesis gas, reducing gas, and fuel gas may be 
reduced to a safe level to avoid contaminating the atmosphere and 
catalysts, and to prevent possible health problems. 
SUMMARY 
The subject process relates to the production of demercurized synthesis 
gas, reducing gas, or fuel gas comprising: 
(1) reacting a mercury-containing fossil fuel feed by partial oxidation 
with a free-oxygen containing gas with or without a temperature moderator 
in a reaction zone provided with a reducing atmosphere at a temperature in 
the range of about 982.degree. C. to 1649.degree. C. (1800.degree. F. to 
3000.degree. F.) and a pressure in the range of about 10 atmospheres or 
higher to produce a raw effluent gas stream comprising H.sub.2, CO, 
H.sub.2 O, CO.sub.2, H.sub.2 S, COS, entrained slag and/or ash; and 
wherein substantially all of the mercury in the feed is converted into 
elemental mercury vapor which leaves the reaction zone entrained in the 
raw effluent gas stream; 
(2) cooling, cleaning, and demoisturizing the raw effluent gas stream from 
(1); 
(3) introducing the gas stream from (2) into a gas scrubbing zone where at 
a temperature in the range of about -50.degree. C. to 80.degree. C., such 
as about -40.degree. C. to 40.degree. C., say about -10.degree. C. to 
10.degree. C., and a pressure of about 10 atmospheres or higher, said gas 
stream is contacted by a lean stream of gas scrubbing solvent thereby 
condensing about 20 to 100 wt. % of the mercury vapor and absorbing from 
about 90 to 100 wt. % of the sulfur-containing gases; and (4) removing the 
following streams from the gas scrubbing zone: 
(a) a clean and demercurized stream of synthesis gas, reducing gas, or fuel 
gas containing about 0 to 80 wt. % of the mercury entering the gas 
scrubber; 
(b) rich gas scrubbing solvent containing a major portion of the remaining 
mercury entering the gas scrubber entrained in condensed form and 
dissolved sulfur-containing gases; and 
(c) sludge or drainage containing the remainder of the mercury or its 
compounds in condensed form entering the gas scrubber. 
In one embodiment, the clean and demercurized product gas stream was passed 
through a bed of activated carbon to produce a stream of mercury and 
sulfur-free synthesis gas, reducing gas, or fuel gas. 
DESCRIPTION OF THE INVENTION 
The fuel feedstock for the subject process comprises a mercury-containing 
fossil feed, such as a solid carbonaceous fuel containing about 0.01 to 
1,000 parts per million of mercury. The mercury is in the form of 
elemental mercury and mercury compounds such as oxides, sulfides, 
chlorides, sulfates, nitrates, hydroxides, carbonates, acetates, and 
mixtures thereof. The solid carbonaceous fuel also contains 
sulfur-containing compounds e.g. sulfides of Fe, Zn, Cu, and Ca; and, it 
is selected from the group consisting of coal, coke from coal, and 
mixtures thereof. The coal may be anthracite, bituminous, lignite, and 
mixtures thereof. Waste material-containing mercury in the amount of about 
1 to 25 wt. % (basis weight of feed) may be mixed with the solid 
carbonaceous fuel. For example, a mercury-containing inorganic and/or 
organic sludge from an industrial process may be mixed with a fossil fuel, 
such as liquid hydrocarbonaceous fuel, coal or other solid carbonaceous 
fuel. 
By means of a conventional burner, such as shown and described in 
coassigned U.S. Pat. No. 4,443,230, which is incorporated herein by 
reference, mercury-containing fossil fuel feed is introduced into the 
reaction zone of a partial oxidation gas generator along with a stream of 
free-oxygen containing gas and optionally with a temperature moderator. 
The mercury-containing fossil fuel may be introduced into the reaction 
zone as a liquid slurry e.g. aqueous coal slurry, or as a dry feed e.g. 
pulverized coal entrained in a gaseous material, such as air, steam, 
nitrogen, CO.sub.2, and recycle synthesis gas. 
The free-oxygen containing gas is a member of the group consisting of air, 
oxygen-enriched air (22 mole % O.sub.2 and higher), and preferably 
substantially pure oxygen (95 mole % O.sub.2 and higher). The use of a 
liquid and gaseous temperature moderator is optional. For example, aqueous 
coal slurries feeds generally require no supplemental temperature 
moderator. Other temperature moderators for use with a dry fuel feed 
include steam, nitrogen, CO.sub.2, and mixtures thereof. 
The reaction zone is located in a vertical cylindrically shaped steel 
pressure vessel, such as shown in coassigned U.S. Pat. Nos. 2,809,104 and 
4,637,823. The reaction zone comprises a down flowing free-flow refractory 
lined chamber with an centrally located inlet at the top and an axially 
aligned outlet in the bottom. Partial oxidation of the mercury-containing 
fossil fuel feed takes place in the reaction zone at an autogenous 
temperature in the range of about 982.degree. C. to 1649.degree. C., such 
as about 1200.degree. C. to 1500.degree. C., and at a pressure in the 
range of about 10 atmospheres or higher, such as at least 20 atmospheres, 
say about 20 to 80 atmospheres. The atomic ratio of free oxygen to carbon 
(O/C ratio) is in the range of about 0.6 to 1.6, such as about 0.8 to 1.4. 
The H.sub.2 O/fuel weight ratio is in the range of about 0.1 to 1.5, such 
as about 0.2 to 0.7. 
The composition of the raw gas stream leaving the gas generator follows in 
mole %: H.sub.2 5 to 60, CO 30 to 60, CO.sub.2 2 to 25, H.sub.2 O 2 to 20, 
CH.sub.4 nil to 25, NH.sub.3 nil to 1, H.sub.2 S nil to 2, COS nil to 0.1, 
N.sub.2 nil to 5.0, and Ar nil to 1.5. Further, entrained in the raw 
effluent gas stream from the reaction zone is molten slag and/or ash, and 
unexpectedly from about less than 1.times.10.sup.-6 to 5.times.10.sup.-4 
mole % or more of mercury vapor. The mercury vapor was found to be 
thermodynamically stable even in the presence of H.sub.2 S under the 
strong reducing conditions that prevailed in the gas generator and 
subsequent cooling. No new sulfides of mercury were formed. The vapor 
pressure of mercury is such that with the limited amounts of mercury 
entering the system, the outgoing raw effluent gas stream can carry the 
mercury in volatile form after when the gas is cooled and water scrubbed. 
While the propensity to form mercuric sulfide may increase as the 
temperature is lowered, elemental mercury is still thermodynamically the 
stable form at ambient temperature in the presence of the pressurized 
synthesis gas. Suitable gas generators provide for passing the hot raw 
effluent gas stream downward through the bottom outlet in the reaction 
zone and then downward through a radiant cooler where it is partially 
cooled and at least a portion of the entrained slag, ash, and particulate 
matter are removed. Alternatively, the hot raw effluent gas stream may be 
discharged downward through a central outlet in the bottom of the reaction 
zone followed by contacting the surface of or passing through a pool of 
quench water located below. These procedures will be described in greater 
detail below. 
The hot raw effluent gas stream leaving the reaction zone containing 
mercury vapor is cooled cleaned, and demoisturized. For example, the hot 
effluent gas stream may be passed down through a radiant cooler located in 
a steel pressure vessel below the gasifier section. Molten slag and/or ash 
drop out of the gas stream and are cooled in a pool of quench water 
located at the bottom of the radiant cooler. By this means the effluent 
gas stream may be cooled to a temperature in the range of about 
500.degree. C. to 800.degree. C. The partially cooled and deashed gas 
stream is then passed through at least one convection cooler, such as a 
conventional shell and tube heat exchanger, and cooled further to a 
temperature in the range of about 150.degree. C. to 700.degree. C. The gas 
stream is then scrubbed with water in a conventional gas scrubber, such as 
shown in coassigned U.S. Pat. No. 3,544,291, which is incorporated herein 
by reference. The gas stream is then dried by being cooled below the dew 
point in a conventional demoisturizer. The aforesaid scheme is further 
described in coassigned U.S. Pat. No. 4,436,530, which is incorporated 
herein by reference. For example, the H.sub.2 O saturated process gas 
stream at a temperature in the range of about 100.degree. C. to 
300.degree. C. may be passed in noncontact heat exchange with a coolant 
and cooled to a temperature in the range of about -50.degree. C. to 
80.degree. C. in a liquid-vapor separator, or demoisturizer. Water 
condensate is separated from the dried process gas stream. 
Alternatively, the hot raw effluent gas stream from the gasifier is cooled 
and cleaned by being passed through a dip tube which discharges the hot 
gas stream onto or into a pool of water contained in a quench tank located 
below the reaction zone. The gas stream is thereby cooled to a temperature 
in the range of about 100.degree. C. to 300.degree. C., and simultaneously 
the entrained molten slag and/or ash is scrubbed from the gas stream with 
water. For example, see coassigned U.S. Pat. No. 4,474,582, which is 
incorporated herein by reference. The saturated gas stream is optionally 
passed through a conventional first gas scrubber where it is scrubbed with 
water, such as previously described. The process gas stream is then cooled 
and demoisturized, as previously described. In one embodiment, the raw 
effluent gas stream from the reaction zone is cleaned by direct contact 
with water to produce a water dispersion comprising H.sub.2 S, NH.sub.3, 
Hg, and ash and particulate solids. Said water dispersion is flashed and 
stripped to produce a flash gas stream comprising H.sub.2 S, NH.sub.3 and 
a trace of Hg vapor which is introduced into an elemental sulfur recovery 
unit along with said other feed-streams. 
The cooled, cleaned and demoisturized gas stream containing mercury vapor 
is introduced into a solvent gas scrubber where it is contacted with a 
lean solvent for the sulfur-containing gases in the process gas stream 
i.e. H.sub.2 S and COS at a temperature in the range of about -50.degree. 
C. to 80.degree. C. and a pressure of about 10 atmospheres or higher. In 
the solvent gas scrubber, about 20 to 100 wt. % of the mercury vapor in 
the entering process gas stream is condensed and about 90 to 100 wt. % of 
the sulfur-containing gases are absorbed by the solvent gas scrubbing 
solvent. In one embodiment for example, the solvent gas scrubbing zone is 
operated at the same pressure as the partial oxidation reaction zone less 
ordinary pressure drop in the lines, and at a maximum temperature of about 
20.degree. C. Suitable gas scrubbing solvents include methanol, 
N-methyl-pyrrolidone, di and triethanolamine, and methyl diethanolamine. A 
demercurized and desulfurized product gas stream leaves from the solvent 
gas scrubber comprising H.sub.2, CO, H.sub.2 O, mercury vapor, and 
optionally CH.sub.4, N.sub.2, and Ar. Depending on the gas composition, 
the product gas stream may be used as synthesis gas, reducing gas, or fuel 
gas. 
The rich solvent and entrained condensed mercury are then introduced into a 
solvent recovery unit to be described further. A small portion of the 
mercury entering the solvent gas scrubber may leave as elemental Hg and/or 
mercuric sulfide in admixture with the sludge from the bottom of the 
solvent gas scrubber. The composition of the sludge will depend on the 
composition of the feedstock and on other upstream operating conditions. 
The sludge would contain FeS (from decomposition of Fe(CO).sub.5 in the 
acid gas scrubber) and trace amounts of fly ash still suspended in the 
process gas stream entering the acid gas scrubber plus possible breakdown 
products of the acid gas scrubber solvent. Anywhere from 0 to 100 wt. % of 
the mercury vapor entering the solvent scrubber leaves entrained in the 
demercurized product gas. The remainder of the mercury vapor entering the 
solvent scrubber leaves adsorbed in the rich solvent and/or as sludge. The 
wt. % range of mercury exiting with the desulfurized process gas stream 
will be highly dependent on (a) the amount of mercury originally in the 
sour process gas stream, and (b) the operating temperature of the acid gas 
scrubber. For example, with an acid gas scrubber operating at 0.degree. C. 
or lower, the Hg content of the exit gas is about 0 to 20 wt. % of the Hg 
in the entering gas stream. However, if the acid gas scrubber is operated 
at a temperature in the range of about 40.degree. C.-60.degree. C., then 
the Hg content of the exit gas would rise to greater than about 50 wt. % 
of that in the entering gas stream. 
The rich liquid solvent absorbent charged with mercury vapor and acid gas 
leaving the first solvent gas scrubber may be regenerated in a first 
solvent recovery zone to produce a sulfur-containing off-gas stream 
comprising H.sub.2 S, COS, CO.sub.2, and mercury vapor. At least one and 
preferably a combination of the following conventional techniques may be 
used to regenerate the solvent: flashing, stripping with steam or an inert 
gas, and boiling. Heating and refluxing at reduced pressure may be used to 
produce a sulfur-containing off-gas stream comprising H.sub.2 S, COS, 
CO.sub.2, and mercury vapor; and a stream of lean gas scrubbing solvent 
which is recycled to the gas scrubbing zone. For example, the stream of 
rich gas scrubbing solvent is regenerated by heating and refluxing at a 
temperature in the range of about 40.degree. C. to 100.degree. C. above 
the absorption temperature range and at a pressure in the range of about 1 
to 2 atmospheres to produce a sulfur-containing off-gas stream comprising 
H.sub.2 S, COS, CO.sub.2 and mercury vapor; and a stream of lean gas 
scrubbing solvent which may be recycled to the gas scrubbing zone. One or 
more absorbent regeneration columns may be used. In one embodiment, liquid 
methanol charged with H.sub.2 S and COS leaving from the bottom of a 
regeneration column may be introduced into another regeneration column 
where, by hot regeneration of methanol, H.sub.2 S and COS are boiled off. 
Thus, the charged methanol is heated to a temperature in the range of 
about 66.degree. C. to 121.degree. C. and a pressure in the range of about 
10 to 100 psig, and the H.sub.2 S and COS are boiled off. The stream of 
lean methanol may be then cooled to a temperature in the range of about 
-45.degree. C. to -62.degree. C. and recycled to said gas absorber. 
Optionally, an additional dehydration still for the lean methanol may be 
included in the system. 
The stream of sulfur-containing gases and mercury leaving from the top of 
the last regeneration column in the first solvent recovery zone is mixed 
with sulfur-containing gas produced in a solvent regenerator for a tail 
gas volatile sulfur recovery unit, such as a Scot unit, and optionally 
with a stream of flash gas from stripping waste waters, to produce a rich 
sulfur-containing feed gas mixture to an elemental sulfur recovery unit, 
such as a Claus unit which comprises in mole %: H.sub.2 S 10-40, COS nil 
to 3, CO.sub.2 60-90, and Hg vapor up to about 200 ppm. This stream of 
gases may be introduced into a conventional Claus unit where about 1/3 of 
the initial H.sub.2 S is oxidized with air to SO.sub.2 at a temperature in 
the range of about 1000.degree. C. to 1300.degree. C. and a pressure in 
the range of about 1 to 10 atmospheres. The stoichiometry of the gas 
stream is such that the basic chemical reactions, for example, between the 
remaining H.sub.2 S and SO.sub.2 , is shown in Equations I and II below. 
EQU 2 H.sub.2 S+S0.sub.2 - 2 SO.sub.2 +2H.sub.2 O I 
EQU 2 H.sub.2 S+SO.sub.2 - 3S+2H.sub.2 O II 
Above the temperature range of 525.degree. C.-625.degree. C. no catalyst is 
required. Below this temperature range a catalyst e.g. bauxite is required 
to achieve satisfactory conversion rates. Elemental sulfur is produced in 
said Claus unit containing substantially no mercury. A separate tail gas 
stream is produced comprising SO.sub.2, COS, CO.sub.2, CS.sub.2, and 
mercury vapor. In one embodiment, to prevent pollution of the atmosphere, 
the tail gas is incinerated to convert the residual H.sub.2 S into 
SO.sub.2. Any suitable commercially available process may be used to treat 
the incinerated Claus Plant tail-gas. For example, in the Scot process, at 
a temperature in the range of about 280.degree. C. to 310.degree. C., and 
a pressure in the range of about 1 to 10 atmospheres, the incinerated tail 
gas from the Claus unit is reacted with reducing gas e.g. H.sub.2 or a 
mixture of CO and H.sub.2 over a Co-Mo catalyst to reduce the SO.sub.2 to 
H.sub.2 S and to hydrolyze any COS and CS.sub.2. In one embodiment, the 
mixture of H.sub.2 +CO is a portion of the product reducing gas. H.sub.2 
may be produced by passing a portion of the mixture of H.sub.2 +CO product 
gas over a water-gas shift catalyst and then removing CO.sub.2 by means of 
a solvent gas scrubber. After cooling, the reduced gas is absorbed in lean 
aqueous diisopropanolamine (DIPA). In a second solvent recovery zone, the 
rich DIPA solution from a tail gas treating operation such as Scot Unit 
for the recovery of trace amounts of sulfur compounds from the tail gas 
from an elemental sulfur recovery process, such as a Claus Unit, may be 
regenerated with heat and the H.sub.2 S-containing gas may be returned to 
the front of the Claus process. An inert stripping gas e.g. N.sub.2 may 
also be used. The lean DIPA solution is recycled to the Scot unit. The 
solvent scrubbed tail gas from the Scot unit containing trace amounts of 
mercury vapor, CO.sub.2 and H.sub.2 is passed through a bed of activated 
carbon at a temperature in the range of about -20.degree. C. to 40.degree. 
C., and a pressure in the range of about 0.5 to 5 atmospheres. 
Regenerating the bed of activated carbon by removing mercury will 
described below. A mercury and sulfur-free gas stream is produced 
comprising CO.sub.2 and N.sub.2 which may be discharged to the atmosphere. 
Alternatively, the solvent scrubbed Scot tail gas can be (1) cooled to 
condense and separate mercury, (2) compressed and cooled to separate the 
mercury, or (3) passed through a solution of nitric or sulfuric acid with 
potassium permanganate to oxidize the mercury to a non-volatile state. 
The previously described demercurized synthesis gas, reducing gas or fuel 
gas which leaves from the top of the solvent gas scrubber may contain a 
residual amount of mercury vapor. In one embodiment, the demercurized gas 
stream at a temperature in the range of about -50.degree. C. to 80.degree. 
C. and a pressure in the range of about 10 to 80 atmospheres is contacted 
by an activated carbon sorbent and substantially all of the remaining 
mercury vapor and sulfur-containing gases, if any, are removed. The 
activated carbon sorbent by chemical and physical sorption can lower 
mercury pressure by a factor in the range of less than about 100 to 1,000. 
Thus, the ratio ps/pl is &lt;0.01 and preferably &lt;0.001 where ps is the 
equilibrium vapor pressure of Hg in the presence of the sorbent, and pl is 
the equilibrium vapor pressure of the liquid mercury at the same 
temperature. In another embodiment, the activated carbon is impregnated 
with highly dispersed gold to provide a wt. ratio of gold to carbon in the 
range of about 0.005 to 0.20. Hg and S-free synthesis gas, reducing gas or 
fuel gas is thereby produced. In one embodiment the demercurized gas 
stream is passed through a series of sorbent beds moving counter flow to 
the gas streams. By this means, the activated carbon treated process gas 
stream may contain less than 0.004 mg/M.sup.3 of mercury. 
The carbon sorbent may be regenerated by removing the mercury through 
heating to a temperature in the range of about 150.degree. C. to 
500.degree. C. while stripping the sorbent with an inert gas e.g. 
nitrogen. In another embodiment the activated carbon sorbent bed is 
regenerated by the steps of (1) passing steam through the sorbent bed to 
produce a gaseous mixture of stream and mercury vapor, (2) cooling said 
gaseous mixture to condense the steam and mercury, (3) separating the 
mercury from the water, and (4) drying the activated carbon sorbent before 
reuse. For a more detailed discussion of conventional processes for the 
recovery of acid gases e.g. CO.sub.2, H.sub.2 S, and COS, the Claus 
process, and the Scot process, reference is made to Kirk-Othmer, 
Encyclopedia of Chemical Technology, Third Edition 1983, John Wiley and 
Sons, Volume 22, pages 267-272 and 276 to 280, which is incorporated 
herein by reference.

Demercurized synthesis gas, reducing gas or fuel gas in line 1 is produced 
by the following process. The feed to partial oxidation reaction zone 2 
comprises free-oxygen containing gas e.g. oxygen in line 3 and coal-water 
slurry in line 4. Reaction zone 2 is in a free-flow non-catalytic 
down-flowing steel pressure vessel or gasifier 5 lined with thermal 
refractory 6. Burner 7 is mounted in top central inlet 8 of gasifier 5 and 
comprises central passage 9, inner concentric coaxial annular passage 10, 
and outer concentric coaxial annular passage 11. The free-oxygen 
containing gas passes through lines 3, 15 and 16. It then passes through 
burner 7 into reaction zone 2 by way of central passage 9 and outer 
annular passage 11. Simultaneously, the coal-water slurry passes through 
inner annular passage 10 of burner 7 and mixes with the free-oxygen 
containing gas at the tip of the burner in the reaction zone. 
The hot raw effluent gas stream produced in the reaction zone by the 
partial oxidation reaction is discharged through bottom axially aligned 
central outlet 17 and into radiant cooling zone 18 where a portion of the 
heat is removed by noncontact heat exchange with boiler feed water and 
steam. Radiant cooling zone 18 comprises a vertical cylindrically shaped 
steel pressure vessel 19 containing vertical annular shaped tube wall 20 
provided with top and bottom headers 21 and 22 respectively, axially 
aligned centrally located bottom outlet 23 with discharge line 24, side 
outlet 25, and quench water bath 26. A portion of the slag, ash, and 
entrained particulate matter in the raw effluent gas stream drops out of 
the raw effluent gas stream and is quench cooled in the quench water bath 
26 contained in the bottom of vessel 19. Periodically, slurries of quench 
water are removed by way of line 24 and are introduced into a conventional 
lock hopper and waste water reclaiming system (not shown). 
The partially cooled and cleaned process gas stream is passed through side 
outlet 25 of vessel 19, gas transfer line 27, and then though side inlet 
28 into ash separation chamber 29 in the bottom of convection gas cooler 
30. Gas cooler 30 is a conventional shell and tube heat exchanger. The 
deashed partially cooled process gas stream is further cooled by being 
passed up through a plurality of spaced parallel vertical tubes 35 located 
in the upper section 36 of cooler 30. Ash and other solid matter that 
separates out from the gas stream in chamber 29 may be removed through 
bottom central axially aligned outlet 37 and line 38. The cooled gas 
stream passes out through central axially aligned outlet 39 and line 40. 
Cooling water enters upper section 36 through line 41, flows upwardly on 
the outside of tubes 35 and leaves through line 42. Final cleaning of the 
cooled gas stream with water takes place in a first gas scrubber 43. Water 
enters scrubber 43 by way of line 44. A dilute slurry leaves through line 
45 and is directed to a water reclaiming facility (not shown). 
The cooled and scrubbed gas stream leaves first gas scrubber 43 by way of 
line 50 and enters demoisturizer 51 where substantially all of the water 
in the gas stream is removed by conventional means. For example, the gas 
stream may be cooled below the dew point by heat exchange with a coolant 
which enters by way of line 52 and leaves by way of line 53. Condensed 
water is removed from demoisturizer 51 by way of line 54. 
The cleaned dewatered process gas stream in line 55, with or without 
preheating depending on the solvent and the pressure, is introduced into 
solvent gas scrubber 56 where it is directly contacted with a suitable 
lean solvent. Mercury vapor in the process gas stream may be condensed. A 
mercury and sulfur-containing sludge is formed comprising droplets of 
mercury and iron and nickel sulfides. The Hg and S-containing sludge is 
removed through lines 57 at the bottom of solvent gas scrubber 56. A clean 
demercurized stream of synthesis gas, reducing gas, or fuel gas containing 
about 0 to 80 wt. % of the mercury entering solvent gas scrubber 56 is 
removed through line 1 at the top of solvent gas scrubber 56. In one 
embodiment, any remaining mercury is removed by passing the gas stream in 
line 1 through line 58, activated carbon bed 59, and lines 60 and 61. Hg 
in line 62 may be obtained by regenerating the activated carbon. For 
example, by the steps of passing steam through the activated carbon, 
condensing the steam and mercury vapor, and separating the Hg from the 
water, the carbon sorbent may be regenerated and reused. If there is no Hg 
and S in the demercurized product gas in line 1, activated carbon bed 59 
may be by-passed by way of line 63. 
The rich solvent leaving through line 68 at the bottom of solvent gas 
scrubber 56 is reactivated by conventional means. For example, steam 
heated reboiler 70 may by used to drive out from the rich solvent a tail 
gas comprising acid gases and mercury vapor in line 71. The lean solvent 
is then recycled to solvent gas scrubber 56 by way of line 72. A 
mercury-containing sludge is removed through line 73 at the bottom of 
solvent recovery zone 69. Alternatively, the rich solvent may be 
reactivated by means of a stripping gas e.g. N.sub.2, with or without 
heat. 
The stream of tail gas in line 71 is passed through line 74 and into 
conventional Claus unit 75 along with H.sub.2 S-containing recycle gas in 
line 76 from solvent recovery zone 77, and a stream of flash gas from line 
78. The flash gas comprises H.sub.2 S, NH.sub.3 and a trace of Hg vapor 
from stripping quench water dispersions comprising H.sub.2 S, NH.sub.3, 
ash and particulate matter. Incineration of the feed streams with air from 
line 79 takes place in Claus unit 75. Substantially all of the H.sub.2 S 
is converted in Claus unit 75 into Hg-free sulfur which leaves through 
line 80. A tail gas stream which leaves by way of line 81 is also produced 
comprising the sulfur-containing gases SO.sub.2, COS, CS.sub.2, and also 
N.sub.2, and trace amounts of Hg. This gas stream is introduced into a 
conventional Scot unit 85 where it is incinerated with air from line 86. 
The incinerated tail gas in contact with a cobalt-molybdenum catalyst 
supported on alumina reacts with a reducing gas from line 87. The reducing 
gas may be a portion of the reducing gas from line 61. After cooling, the 
reduced gas is adsorbed in a lean stream of solvent comprising aqueous 
diisopropanolamine (DIPA) from line 88. The rich solvent in line 89 is 
introduced into solvent recovery zone 77 where it is regenerated by heat 
supplied by steam heated reboiler 90. In one embodiment, a stripping gas 
e.g. N.sub.2 in lines 91, is introduced into solvent recovery zone 77. 
The solvent scrubbed tail gas leaving Scot unit 85 through line 95 and 
comprising CO.sub.2, N.sub.2, and a trace of Hg vapor is passed through a 
bed of activated carbon 96. A stream of Hg-free CO.sub.2 and N.sub.2 is 
removed from carbon bed 96 by way of line 97. Activated carbon bed 96 is 
regenerated by passing steam (not shown) through it to vaporize the 
mercury. Upon cooling condensed Hg separates from the water and leaves by 
way of line 98. 
Various modifications of the invention as herein before set forth may be 
made without departing from the spirit and scope thereof, and therefore, 
only such limitations should be made as are indicated in the appended 
claims.