CA1099896A - Water feed and effluent treatment for hydrogen sulfide-water system - Google Patents

Abstract

Case D-2 ABSTRACT OF THE DISCLOSURE

A liquid feed and effluent system to recover dissolved process gas (e.g. H2S) from an effluent process liquid (e.g.
water), which liquid may also contain dissolved solid components (e.g. soluble salts); the system heats the feed liquid with heat recovered from the effluent liquid, saturates the so heated feed liquid with process gas, which gas may also contain inert gas components, and separately discharges from the system such inert gas components and effluent liquid from which process gas and heat have been recovered. In the combination the dissolved process gas is preferably recovered from the effluent liquid by flashing at progressively reduced pressures and final vapor stripping thereof at the most reduced pressure.

Description

~98~6 The present invention relates to improvements in feed and effluent treatment particularly but not exclusively adapted to use in dual temperature exchange systems utilizing an external water source as one of the process fluids and a partially water soluble gas as another process fluid.
In my prio~ patents nos. 2,895,803 issued Ju]y 21, 1959 iand No. 3,142,540 issued ~uly 28, 1964 are disclosed a regenerative stripper system for stripping gas (e.g. H2S) from a liquid (e.g.
water) with the aid of steam supplied at temperature considerably higher than the temperature at which -the liquid became saturated with the gas, followed by a partial recovery of the heat by indirect contact heat exchange with a cold process fluid.
The present invention provides an improved feed and effluent treatment system adapted for improving the recovery of a gas (e.g. H2S) from solution in a liquid (e.g. water) which liquid also contains dissolved nonvolatile components (e.g. the nonvolatile solutes of sea water and other con-taminated waters), at low temperatures, and with greater effectiveness than said prior art systems; for conditioning the liquid ~eed supply for such systems in a simple and effective way; and for producing a distilled liquid by-product essentially free of the solubles of the feed.
According to the present invention there is provided a method of operating a gas/liquid contact process in which the gas is at least partially soluble in the liquid, there being a relatively hot contact zone at an elevated pressure, including the steps of extracting at least a portion of the liquid after passage through said hot zone, reducing the pressure of the liquid by flashing through at least one pressure reduction means to remove a portion of the dissolved gas therefrom, and returning the gas thus recovered to the process.

In a particular embodiment of the present invention there is provided a method of operating a yas/liquld contact process in which the gas is at least partiall~ soluble in the liquid, there being a relatively hot contact zone a~ an elevated pressure, includingthe steps of extracting at least a portion of the liquid after passage throuyh said hot zone, reducing the pressure of the liquid by flashing through at least one pressure reduction means to remove a portion of the dissolved gas therefrom, passing the liquid at reduced pressure countercurrent to a flow of the liquid in vapor form to further remove residues of dissolved ~0 gas, and returning the gas thus recovered to the process.
The present invention also provides in an isotope concentration process in which hydrogen sulfide gas is passed in countercurrent contact with water through a hot tower zone, a cold tower zone and humidity control means at an elevated pressure, the method of recovering hydrogen sulfide gas dissolved in the water, including the steps of extracting at least a portion of the water leaving the hot zone, reducing the pressure of the water portion by passage through at least one pressure reduction means to flash off a portion of the gas, and returning the H2S so recovered to the process.
In a particular embodiment thereof the present invention provides an isotope concentration process in which hydrogen sulfide gas is passed in countercurrent contact with water through a hot tower 20ne, a cold tower zone and humidity control means at an elevated pressure, the method of recovering hydrogen sulfide gas dissolved in the water, including the steps of extracting at least a portion of the water leaving the hot zone, reducing the pressure of the water portion by passage -through at least one pressure reduction means to flash off a portion of the gas, and passing the water through a tower at reduced pressure counter-current to a flow of steam to remove a further portion of the gas therefrom, and returning the H2S so recovered to the process.

\k ~ 2 -~6 The ~resent invention will be further illustratecl by way of the accompanying drawings in which, Fig. 1 is a simplified flow diagram of an integrated feed and effluent system for a hydrogen sulfide-water ærocess, accordiny to an embodiment of the invention in which a contaminatecl water (e.g. sea water) is the feed supply and Fig. 2 is a schematic diagram of another embodiment.
The en~odiments shown in the drawings are particularly adapted for supplying treated li~uid feed to, and treating liquid effluent from, a system processing such liquid and a gas partially soluble therein, such as is disclosed in my concurrently filed Canadian patent application Serial No. 137,812, filed March 22, 1972, which exemplifies a gas/li~uid contact system as comprising a relatively hot contact zone, e.g. at 130C, operating at an elevated pressure, e.g. 325 psi, and a relatively cold contact zone, e.g. at 30C, operating at a slightly lower elevated pressure e.g. 305 psi, with a flow of the gas being circulated through the hot and cold zones by pumping said gas from the cold zone at said slightly lbwer elevated pressure to said hot zone at said elevated pressure.
By use of these embodiments, applied in the production of heavy water, advantage may be tak~en of the fact that sea water contains approximately 5~ more deuterium content than do river and lake waters.
Referring to ~ig. 1 of the accompanying drawings:
The feed water (e~g. sea water~ treating system is integrated in operation with the treatment of the impoverished sea water discharged from the hot tower for disposal to waste, and provides the heated, H2S saturated sea water for deuteri.um extraction in the dual temperature exchange s~stem. In the illustrated embodiment, the feedwater has initially been utilized for cooling of process flui.ds in the dual temperature (~
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exchange system and is received slightly heated via 3A for treatment.
The feedwater then passes via 4A through a rubber-lined carbon-steel hydroclone cleaner F-001 where solids are removed in the underflow and discharged as waste. The cleaned feedwater then enters an epoxy~lined carbon-steel feed deaerator T-001 where dissolved oxygen and carhon dioxide gases are removed. Gases are withdrawn by the two stage action of two ejectors J-003 and J-004 and a barometric intercondenser E-001. Water from the bottom of the condenser discharges to a hot well.
Oxygen is removed to prevent corrosion of metal surfaces and to prevent sulfur precipitation when the water comes into -2h-8~?~

contact with H2S used in the process, e.g. by the reaction 2H2S + 2 = 2H2O + 2S. Insoluble sulfur precipitates can cloy the process equipment. Carbon dioxide is removed to prevent the dilution of the H2S process gas, and also to prevent accelerated corrosion of the equipment as a consequence of the carbonic acid formed in aqueous solution thereby. The productivity of the dual temperature system is reduced in proportion to the accumula-tion of inert or non-exchanging contaminants in the process gasO
The cooling water via lgA for the barometric intercondenser E-001 is split from the sea-water flow received via 3A: motive steam for the ejectors is taken off the intermediate pressure steam header.
A pump P-001 withdraws feedwater from the bottom of the deaerlator via 77A and passes it to the tube side of the feed-water h,,eat exchangers ~-107-. A connection is provided in the passage to the exchangers for chemical addition, e.g. sulfuric acid injection. By this means suitable chemical agents or acid may be added to dissolve scale, e.g. precipitated sulfates or carbonates, if such should form on the heat exchanger tubes from the heating of the sea-water.
In the illustrated embodiment the E-lQ7- heat exchangers ale series connected in three parallel trains of four exchangers J
each. Hot sea-water effluent~ from the hot tower of the dual temperature s~stem via 8A, after removal of dissolved hydrogen sulfide gas, is passed via 87A, 88A through the shell side of said exchangers whereby the feedwater in the tube side is heated to approximately 250F. A thexmocompressor J-001 supplies steam, which in part has been recovered via 89A from the sea-water ' effluent by flash evaporakor,D-006, via 94~, to an injector J-00 for further feedwater heating. The steam is injec-ted into the feedwater at a rate controlled so as to maintain a feedwater temperature of 2~6 F.

, ~6 A pump P-0o2 passes the heated sea-water feedwater stream to the -top of the feedwater saturator T~002. The satura-f~ a~
tor is an Incone~-clad steel tower, designed to saturate approxi-mately 2,000,000 pounds of heated feedwa-ter per hour with H2S at 325 psia. An additional stream of heated sea-water that has been used in the upper cooling sections of the waste stripper T-004 and waste flasher T-00~5 for gas cooling, hereinafter described, is also discharged into the top of the saturator T-002.
These streams merge and flow downward against a counter-current flow of H2S gas, becoming saturated, and constitute the sea-water feed supply to the feed section of the ho-t tower of the dual temperature system.
The H2S saturated feedwater is discharged from the bottom of the saturator via 6A and is pumped by the pumps P-003-,~ "
to Inconel hydroclone cleaners F-003- for removal of heavy metal sulfides and other solids formed by reaction of dissolved minerals in the sea-water under the conditions existing in the saturator.
The underflow from these hydroclone cleaners passes via lOlA to a sludge tank D-010 for treatment before being removed, e.g.
discharged into the effluent stream via lO9A. Such treatment may include chemical addition, for example of an acid which reacts with the solids to solublize them and to form H2S gas for return to the dual temperature process gas system via 108A-7A. The saturated sea-water feedwater passes via 55A from the hydroclones to the top of the feed section of the stage 1 hot towers.
The H2S delivered via 5A to the saturator T-002 is bled as a purge stream from the humidification section of the dual temperature stage 1 hot towers. Within the saturator, the H2S reacts with and decomposes dissolved bicarbonate salts, ~0 releasing carbondioxide gas (CO2) and forming the hydrosulfide (HS- ion) and to a small degree the sulfide (S ion) salts in substitution. The CO2 together with other undissolved gases, .

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e.g. nitrogen and hydrogen, are passed through the purge tower section at the top o~ the saturator. A small stream of relative-ly pure water/ e.g. condensate, is introduced via 60A into the top of the purge tower section to absorb H2S contained therein and this water flows downward through the purge section and then merges with the feedwater stream in the saturator. The remaining gas stream, which comprises substantially all of the CO~ and inert gas content of the fluids delivered to the saturator T-002, is removed via 96A from the system, e.g. to a flare for discharge to the atmosphere.
Cooling water for the gas cooling sections on top of the waste stripper T-OOA and on top of the waste flasher T-005 is taken off via lA from the sea-water supply line serving the dual temperature system stage 1 dehumidifier process liquid coolers. This water is passed through a hydroclone cleaner F-002 for removal of solids and the underflow is discharged to waste.
The cleaned water passes to a deaerator T-009.
Chemical addition, e.g. of sulfuric acid, may be added to this sea~water through a connection upstream of the deaerator.
Acid is added to decompose dissolved bicarbonate salts and evolve C2 before this water enters the waste flasher T-005 and waste stripper T-004, where it comes in contact with H2S. The acid-generated C02 and other dissolved gases are removed from the water in the deaerator T-OO9 by the 3-stage action of -three ejectors J-005, J-006 and J-007 and two barometric condensers E-002 and E-003, and the deaerated water is then withdrawn by pump P-Ol9 via 98A and is passed via 61A to the waste stripper T-004 and via 62A to the waste flasher T-005.
The effluent stream leaving via lOOA is comprised principally of deuterium depleted sea-water from the dual temperature stage 1 hot towers together with the treated under-flow from hydroclone cleaners as above described.

A principle purpose of the effluent treating system is to recover the H2S which is present at a concentration of about two percent in the sea-water effluent from the dual temperature system. Another is to recover heat from the effluent which is at 266F when it leaves the stage 1 hot towers. The H2S is-recovered in the waste flashers T-008 to T~005 and the waste stripper T-00~ and returned via 7A to -the dual temperature system. Heat is recovered in the flash evaporator D~006 where the sea-water effluent after removal of H2S is partially flashed to steam for use in part via 90A in the waste stripper and in part via 94A to heat the incoming sea-water feed supply, and also in a series of heat exchangers E-~07- where the remaining heat of the sea-water effluent before its discharge to waste is used to heat the incoming sea-water feed to the dual temperature syste~l.
H2S is recovered by passing the hot sea-water effluent discharged from the feed section of the stage 1 hot tower through a series of four waste flashers T-008, T-007, T-006 and T-005 in that order. These are horizontal pressure vessels made of ~ j Inconel-cladsteel plate and consist of a flashing section and a gas cooling tower section wherein the released hot H2S is cooled by countercurrent direct contact with a flow of cool water. ~s illustrated, three of the waste ~lashers T-008, T-007, and T-006 have integrally mounted contactor cooling towers. One, T-005, operatas in conjunction with a separately mounted contactor tower as is shown by the seal tray at 76A which only allows gas to pass therethrough. The waste flashers operate at successively ~ lower pressures, e.g. 305, 250, 175 and 75 psi, respectively.
- At each stage of pressure reduction, H2S is evolved from the ; effluent. The flashed off H2S flows upward to the gas cooler sections where water vapor is condensed and the H2S is cooled.
The flashed H2S gas is then repressurized, e.g. by compression with gas compressors C-002, C-003 and C-004 to 305 psi, and - . , ~ .

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returned via 7~ to the ~lual ~em2eratllre .st~ge 1 gas system. T~e ~as from waste flasher T-008 is dischar~ed therefrom at the 305 psi pressure of the top of the stage 1 cold tower and therefore does not require further pressure.
After passing through the waste flashers, the sea water effluent is passe~ via 81A, ~7A, 88A ancl lOOA towaste , preferea~l~
through waste stripper T-004 where the remaining ~lissolved IT2S is removed in part by a flash to 35 psi and in part hy action of a countercurrent flow of strippin~ steam. This waste stripper is an "Inconel" tower appro~imately 85 feet high. It consists of an upper cooling section separated as in T-~n5 and a lower 1ashing and stripping section. The H2S is evolved from the effluent in the flashing section an~ rises through the co~ling section, and the effluent liquid proceeds downward to the stripping section where it flows against a countercurrent flow of stripping steam.
H2S concentration in the sea-water Pffluent leavin~ the descri~ed 85 foot waste stripper is less than one ppm and the H2S strippecl therefrom passes to the waste flasher compressor C-`001 for compression a~d return to stage 1 as aforesaia.
2Q The sea-water effluent from the waste stripper T-On4 passes to a flash evaporator D~006 where a part of the water is flashed and evaporated to steam. The 1ash evaporator is a copper-nickel-alloy vess21 approximately 6 feet in diameter and approxi-mately 13 feet long. ~t operates in con~unction with a~'thermo compressox J-001 to recover some of the ~nergy present in the effluent. The thermo c~mpressor creates a reducecl pressure in the evaporator ves~el, converting a portion of the effluent to ~team, which is exhausted via 91A for use as stripping steam via 90A to the waste stripper and for injection via 94A to the main sea-water feed stream to the dual temperaturessystem. The hot effluent from the flash evaporator via 88A is pumpecl hy pump P-017 through khe shell side of the heat exchanqer train ~-107- to heat the main sea-water feedwater stream on the -tube side the,rein.
This cooled effluent is then discharged via lOOA as waste.
The underflow from the sea-water feed hydroclones ~-003-is discharged via lOlA to a sludge tank D-010 where sulfuric acid is added. The sludge tank is an Inconel pressure vessel.
H2S is evolved in the tank from the reaction of acid with sulfides removed in the hydroclone cleaners.
As shown, the evolved H2S vapor is passed to the yas cooler tower on the top of the waste flasher T-007 to join the flow of recovered gas to be returned to the dual temperature stage 1, and the discharge from the sludge tank via 109~ is mixed with the effluent passing from waste flasher T-008 via 84A. Any excess acid which may be present in the sludge tank discharge continues to react with dissolved sulfides in the sea-water effluent to further evolve H2S gas which is chemically or other-wise bound and would not otherwise be released in the flashing and stripping operations.
The evolved H2S gas passes from the waste flashers and the waste stripper to the waste flasher compressors. In -the illustrated embodiment, the compressors C-001, C-002, C-003 and C-004 may be driven by a single stream turbine through a common shaft, which together comprises a multi-stage compressor unit for compression of the released H2S for re-turn to the dual temper-ature system.
Referring now to Fig. 2 of the accompanying drawings:
In this embodiment the cold sea water feed ~e.g. at 20C) is passed through an indirect contact heat exchanger 10 in countercurrent to the treated effluent passing to waste, becoming heated (e.g. to 120C) while the effluent is cooled (e.g. from 135C to ~5C). The heated sea water via 11 passes to a two stage H2S saturator and inert gas and dissolved CO2 remover 12, 13wherein a countercurrent contact with a stream of H2S the water o~9~

becomes saturated therewith first at a lower pressure and then at a higher pressure, and the dissolved carbonates ~herein are converted to hydrosulfides and sulfides, freeing CO2 gas, which is vented together with any inert gas content of the H2S and/or water streams. In the first stage 12 the gas is heated at a low pressure (d.g. 25 psig) approaching the temperature of the H2S
gas stream (about 130C) depending on the quantity of hot gas delivered. In the second stage 13 to which the treated water from the first stage is pumped via 15 the pressure is higher (e.g. 300 psig) and the saturation with the gas at this pressure is accomplished therein. For mineral removal or recovexy, etc.
the liquid (e.g. sea water? may be treated with additives supplied as via 16 for precipitating dissolved materials which can then be removed as by a filterl decanter or other sepa~ator 17, from which the trea-ted liquid saturated with gas at the temperature and pressure of the process feed section 18 (shown as a feed section comprising the lower quarter of the trays section of the hot tower of a dual temperature exchange unit 19 is delivered to said feed water section, as shown.
In thi~ feed section 18 the saturated liquid passes in countercurrent exchange with a circulating stream of gas (~I2S) which has been passed through the heater and humidifier 20 where it is heated and humidified and brought to the temperature of the feed section 18. The gas heating in the form shown is accomplished in part by direct contact with a branched circulation of water entering via 20a and exiting at different temperature levels (e.g. 85 and 45C) via 20b and 20c, augmented by injection of steam via 20d (e.g. at 218C) sufficient to raise it to khe temperature of the feed section 18 and tower 19, (e.g. 130C).
The feed fluid stream leaving the feed section 18 above the seal tray 18a (which allows gas to pass upwardly therethrough but prevents downward flow of feed liquid therethrough) is pumped via -- g ~

22 to the waste stripper 25 operating at a slightly higher pressure to allow stripped gas (H2S) and s~eam to return via 20d to the top of the humidifier section 20. Steam is supplied via ~5a to the bottom of the stripper 25 passing countercurrent to the H2S saturated liquid from 22, whereby the water leaving 25 via 25b is substantially free of gas (e~g. ~2S). Additional steam as needed is supplied to 20d by 20e ~rom a suitable source such as the boiler 30~
In the form shown a portion of the water stripped of H2S is passed from 25b via 25c as feed to the boiler 30 wherein it is partially evaporated by an external heat supply. The unevaporated portion via 30a, and liquid via ~5d may be merged, and be used in part to heat at least a portion of the cyclic flows via 20c and/or 20b in a heat exchanger 35, and may in part be sent to a flasher 40 operating at reduced pressure where steam is evolved which may be used in stripper 41 to strip H2S from a separate flow of H2S saturated condensate formed by the cooling and dehumidification of the hot process gas from 19 (e.g. as shown in applicant's aforesaid Canadian patent application Serial No.
137,812) which is about equal to the quantity of steam introduced at 20d. Said condensate entering 41 uia 41a at about 130C and exiting via 41b at about 132C then passes in countercurrent heat exchange in 50 to heat another portion of said cyclic flows 20b and/or 20c. The remaining liquid from 40 and the cooled liquid from 35 via lOa is passed through the heat exchanger 10, as above described.
While there have been described herein what are at present considered preferred embodiments of the invention, it will be obvious to those skilled in the art that modifications, including changes and omissions and substitutions, may be made without depar-ting from the essence and principle of the invention.
It is therefore to be understood that the exemplar~v embodiments are illustrative and not restrictive of the invention, the scope of which is defined in the appended claims, and that all modifica-..
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modifications that come wi-thin the meaning and range of eqllival-ency of the claims are inte~ded to he descrihed and includecl therein.

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Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of operating a gas/liquid contact process in which the gas is at least partially soluble in the liquid, there being a liquid feed thereto and a relatively hot contact zone at an elevated pressure, including the steps of extracting at least a portion of the liquid after passage through said hot zone, reducing the pressure of extracted liquid by flashing through at least one pressure reduction means to remove and re-cover a portion of the dissolved gas therefrom returning the gas thus recovered to the process, said gas recovered at at least one said pressure reduction means being returned by absorption in liquid feed at pressure not greater than that of the gas which has been flashed at said at least one said pressure reduction means, and pumping said liquid feed containing absorbed gas to said elevated pressure contact zone of the process.

2. In an isotope concentration process having a liquid water feed thereto, in which hydrogen sulfide gas is passed in countercurrent contact with water through a hot tower zone, a cold tower zone and humidity control means at elevated pressures, the method of recovering hydrogen sulfide (H2S) gas dissolved in the water, including the steps of extracting at least a portion of the water leaving the hot zone, reducing the pressure of the water portion by passage through at least one pressure reduction means to flash off and recover a portion of the gas, returning the H2S so recovered to the process, said gas recovered at at least one said pressure reduction means being returned by absorption in liquid feed at pressure not greater than that of the gas which has been flashed at said at least one said pressure reduc-tion means, and pumping said liquid feed containing absorbed gas to said elevated pressure contact zone of the process.

3. The method as claimed in claim 1 or 2 wherein said at least one said pressure reduction step is carried out by passage of said portion through a first and a second lower pres-sure reduction device, the gas evolved at the first said device being passed for absorption into feed entering the process.

4. The method as claimed in claim 1, 2 or 3, wherein said portion is depressurized by passage through at least two progressively lower pressure reduction devices, including the step of raising the pressure of gas evolved at the lower pressure of said devices for contact with feed liquid entering the process.

5. The method as claimed in claim 1, 2 or 3, wherein stripped effluent is passed in heat exchange relation with water which is then used to heat and humidify gas circulating through the process.

6. The method of operating a gas/liquid counterflow process in which pressurized gas, being partially soluble in the liquid, is passed upwardly through the pressurized liquid in counterflow relations therewith through a hot exchange zone and a cold exchange zone pressurized to a first pressure above atmos-pheric, including the steps of increasing the pressure of feed liquid entering the process from substantially atmospheric pressure to a second pressure value intermediate atmospheric and said first pressure, passing the pressurized feed liquid to an absor-ber section, extracting from adjacent the bottom of said hot zone at least a portion of hot liquid having said gas absorbed there-in, flashing said liquid from said first pressure to a third pressure value intermediate said first and second values, separ-ating gas evolved by said flashing step from the extracted liquid, passing the separated gas to said absorber section for re-absorption of gas into said feed liquid, and pressurizing said feed liquid having said gas absorbed therein to said first pressure by pumped transference from said absorber section to a said exchange zone.

7. The method as claimed in claim 6, including the further step of passing said extracted hot liquid to a stripping column suitably heated to produce water vapor and remove addit-ional said gas therefrom, and passing the additional gas to said absorber section.

8. The method as claimed in claim 6 or claim 7 includ-ing the preliminary step of flashing said liquid to a fourth pressure greater than said third pressure for re-absorption into said feed liquid.

9. The method as claimed in claim 6, including the step of cooling said evolved gas after flashing to condense water vapor therefrom.

10. The method as claimed in claim 9, wherein said cooling is effected by direct contact with said feed liquid and the condensing water vapor is added thereto.

11. The method of gas recovery and recirculation in a gas/liquid counterflow process for isotopic separation in which hydrogen sulphide is at least partially soluble in the liquid, namely water, there being a pressurized hot isotope exchange zone and a pressurized cold isotope exchange zone for effecting isotope exchange between water and the gas at a predetermined process pressure, including the steps of: extracting at least a portion of liquid effluent having said gas in solution therein;
producing a substantial drop in pressure in said liquid portion to strip hydrogen sulphide gas therefrom at a pressure substan-tially less than that of a said exchange zone; re-compressing said gas to a pressure less than that of said exchange zone;
absorbing the stripped gas into feed water entering the process as a source of deuterium, and pressurizing by pumping the feed water with gas absorbed therein to a said isotope exchange zone to return said stripped gas to said zone.

12. The method as claimed in claim 11 including the step of raising the temperature of said entering feed water by heat exchange relation with said stripped gas.

13. The method as claimed in claim 12 wherein said heat exchange is at least partly effected during said recompressing of said stripped gas, prior to said step of absorbing the strip-ped gas into the incoming feed water.

14. The method as claimed in claim 11 wherein said liquid portion is extracted after passage downwardly through said hot zone, including the step of raising the temperature of the liquid after said drop in pressure, to evolve additional hydrogen sulphide gas, whereby the gas content of liquid passing to waste is further reduced.