CA1194678A - Manufacture of hydrogen sulfide - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Methods and apparatus adaptable to continuous production of hydrogen sulfide by chemical reaction of sulfur with a gaseous sulfur-reducing reactant selected from methane or other hydrocarbons, hydrogen carbon-containing compounds such as carbon disulfide, gases with high CO contents, e.g., from gasification of coal, or mix-tures of such gases are provided utilizing a separately-fired sulfur heater to vaporize liquid sulfur feedstock. Adding steam with the sulfur reduces the temperature level require-ments of the sulfur vapors and provides H2 and O2 for the hydrolysis reactions. Control of the temperature of the sulfur vapors and steam delivered into the system through the sulfur vaporizer is used to modulate sulfiding reaction temperatures. A major portion of the steam is introduced with the sulfur vapors; a minor portion of the steam can be added with the feedstock reductant gas to assist in heat recovery from the reaction product gases and to facilitate standby conditions. During production, the system is operated at pressures above atmospheric as determined by a back pressure established in removing product gases containing hydrogen sulfide. Controlled movement of reactants and reaction product gases through the system is achieved without requiring mechanical flow control equipment in any of the relatively high temperature zones approaching sul-fiding reaction temperatures or sulfur vaporizing temperature.
Requirements for on-site storage of toxic and explosive hydrogen sulfide are eliminated. The separately-fired sulfur vaporizer provides for circulation of sulfur and/or steam, without feedstock reductant gas in various production stand-by modes, which make production on demand readily available.

Description

This invention relates t~ manufacture of hydrogen sulfide. More particularly~ this invention is concerned with processes and apparatus for contx~l of hydrogen sulfide manufacture in a system adaptable to manufacture of hydrogen sulfide fr~m various reductant gas feedst~cksO
In addition to the long established uses of hydro-gen sulfide in metallurgical Dperations and in the manufac-ture of chemicals f a growing demand for hydrogen sulfide has developed for use in removing sulfur dioxide from industrial waste gas~s such as ~le eEfluent from electrical utility installations which burn sulfur~containing fuels~
For cDmmercial purposes, a locally available source of hydr~gen sulfide is preferred for such waste-gas treatment uses. The present teachings facilitate manufacture of hydro-gen sulflde at a wide range of industrial plant sites by providing a system adaptable to efficient production of hydrogen sulfide from reductant gases of widely differing properties while readily maintaining pDsitiVe process control and eliminating any requirement for on-site stDrage.
Hydrogen sulfide has be~n produced by bubbling hydrogen through liquid sulfur with sensible heat require-ments being added at the reaction zone. Other processes limit reductant gases t~ those with levels of concentrations of carbon monoxide and~or hydrogen such that sufficient heat is generated to heat the reductant gas to reactiDn tempera-tureO Such limitations on selection of reductant gases or the necessity of adding sensible heat for the sulfiding reaction hy ~reheating -the reductant gas are elimina-ted by the present inventionO
According to -the present invention there is provided a method for opera-ting a hydrogen sulfide manufacturing system to eliminate requirements for s-torage of hydrogen sulfide æroduct gases by ~roviding for production of hydrogen sulfide on demand. The manufacturing system includeso a separately fired sulfur vaporizer with means for - controlling heat input to the sulfur vapori~er for controlling heat input to the hydrogen sulfide manufacturing system~
means for controlling delivery of liquid sulfur to such vaporizer for introductlon of sulfur vapors into such system, and means for introducing gaseous sulfur-reducing feedstock to such system including means for interrupting such introduction of sulfur-reducing feedstock~
~ eans is provided for controlling supply of steam to the hydrogen sulfide manufacturing system including means ~0 means for introducing steam through the sulfur vaporizer and means for introducing steam with sulfur-reducing feed-stock. A reaction vessel means is provided for reacting sulfur vapors with such sulfur-reducing feedstock and steam to produce product gaseous including hydrogen sulfide, and discharge means is provided for the product gas including valve means for interrupting discharge of product gases.
~he method allows for interrupting production of hydrogen sulfide and placing the system in standby condition, the method including the steps of interrupting input of such sulfur-reducing feedstock to such system, permitting continued ms/ ~~"`

introduction of sulfur through such sulfur vaporizer at least until reductant feedstock has been removed from the system, and controlling heat input to such sulfur vaporizer to maintain temperatures within such system at a level : related to system temperatures maintained during ~roduction of h~drogen sulfide.
Other f.eatures-, advantages and contributions are considered a more detailed description of the schematic presen-tations of hydrogen sulfide producing systems; in the accompanying drawings:
FIGU~E 1 is a schematic diagram of a hydrogen sulfide producing system embodying the invention utilizing a single reaction zone;
F IGURE 2 is a schematic dia~ram of an embodiment of the invention utilizing multiple reaction zones o~erable at differing temperatures;
FIGURE 3 is a schematic diagram of an embodiment of the invention showing location of valves and other mechanical flow control equipment, with re~resentative tem~eratures encounteredr and FIGURE 4 is an elevational ~ross-sectional view of preconditioner ap~aratus forming vart of the invention for mixing and filtering reactants~
Exam~les of the chemistry involved in typical sul-furization reactions for a number of reductant gases are as follow~:
CH4 + 4S--~ 2H2S + CS2 C3H8 + 10S --~ 4H2S + 3CS2 H2 + S ~, H2S

CH30H + 3S ~ 2H2S + COS
CO ~ S ~ COS

ms/ ~4~

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~cceptable sulfurization reaction tempera~ures for production of hydrogen sulfide can vary with properties of the reductant gasO A sulfurization temperature above 800F.
to abDut 1350F. can be utilized.
A reactiDn temperature of abDut 1150F. is repre-sentative for most natural gas. Heat to initiate and sus~
tain such a reaction is provided by adding heat of vapori-zation to the sulfur before introducing the sulfur for reaction and, alsoO by superheating the sulfur vapor before the reaction. Controlling heat input to a sulfur vaporizer provides a direct and effective control not otherwise avail-able in prior practice.
Selection of and dependability of sulfur flow are important aspects of the use of sulfur for adding heat to the system as required vr modulating the temperature of the sulfurization reaction. obstacles to achieving a desired mechanical flow control of sulfur are related to the known viscous effect brought about in raising the temperature of liquid sulfur above about 300F. To overcDme these obstacles, the cooled products of reaction are used to mvdify the liquid sulfur viscosity and facilitate pumping.
Without such modification, the pressure differential encountered in heating liquid sulfur inhibits desired flow control of the liquid sulfur input. As previously known, when heating molten sulfur a sharp increase in viscosity is encountered ~ear 315F.; the viscosity rises rapidly to a peak of about 93,000 centi)~ises at about 370F. That the viscosity decreases with fli~ther heating to the boiling temperature d~es not alleviate the prDblem in a continuous process where liquid sulfur fl~w control is utilized as in the invention.
Treating the liquid sulfur while at a relatively low temperature enables the heat input and controls taught to achieve smoo~h continuous operation. This mDdification of the effects of liquid sulfur visc~sity is accomplished by keeping the liquid sul~ur feedstock substantially saturated with dissolved hydrogen sulfide by controlling contact of the liquid sulfur feedstock with ~he cooled product gasesO Part of the hydrogen sulfide dissolved in the liquid sulfur is obtained from condensation of the excess sulfur vapor in the reaction product gases sinc~ such condensate is generally saturated with hydr~gen sulfide. The remaining hydrogen sulfide additions are brought about by direct adsorption Df hydrogen sulfide gas; cooled product gas can be sparged through the liquid sulfur feedstock for these purposes~ With these teachings, a positive displacement pump can be utilized tD facilitate effective selection and adjustment of liquid sulfur feed.
In Figures 1, 2 and 3p similarly functioning struc tures are identified by the same reference numerals. Liquid sulfur feedstock is delivered by sulfur feed pump 10 through c~nduit 12 to sulfur vaporizer 14. A sulfurization reactio~
is carried out in react~r 16 of these figures~
Sulfur feed pump lO can include an adjustable feed stroke ~o control the flow of molten sulfur. The pumping rate can therefore be readily adjusted at selector 17 dependent on the hydrogen sulfide production rate and the amount ~f excess sulfur desired in the reactions~ Facilitat~
ing li~uid sulfur pumping rates is also important to provid~
ing the reaction temperature modulatiDn desired. Sulfur vapor temperature and the amount of sulfur are interrelated for the latter purposeO
Liquid sulfur feed from source 18 is introduced through feed line 20. Filter 21 rem~ves ash and Dther solid impurities which would tend to deposit out in the vaporizer or which could otherwise adversely affect operations~
The liquid sulfur is treated for ViSCDsity contr~l purposes in sulfur feed pretreatment tank 22. Saturating the liquid sulfur with hydrogen sulfide eliminates the rapid rise in viscosity encountered during transition temperatures above 300F. in heating liquid sulfur to vaporizing tempera-ture.
The sulfur vaporizer 14 is a fired process heater for boiling and superheating the sulfur. Direct contr~l of superheat temperature is facilitated by control of combust-ible fuel input.

A large diameter hea-t:ing coil is preferred to help cornpensate for internal build-up Df metal sulfide scale.
Also, the entrance porti~n of the coil can be designed f~r maximum heat transfer rate ~o help shorten heating time dur-ing which the rapid rise in viscosity and the ~bstructingeffects of high viscosity would ordinarily be expected in the vaporizer.
The addition of steam from conduit 24 through the vaporizer 14 increases the adap~ability of the system for production of H2S and enables establishment of standby conditions. Superheating the steam in vaporizer 14 provides additional heat for initiating and sustaining ~he sulfuri-zation reactions and enables placing a reasonable limit ~n the upper temperature requirement of the sulfur within desired quantitative limitations placed on the use of excess sulfur; this in turn increases tube life in the vaporizer by decreasing the c~rrosive reaction of sulfur with the vap~rizer tubesO
Vaporizer 14 provides for preheating of the system and the system can be purged with steam from vaporizer 14 before start-up eliminating the need for a nitrogen purge to remove oxygen from the system. Vaporizer 14 thus enables a hydrogen sulfide installation to be self-contained in the sense of eliminating any requirement for a separate steam producing means for start-up or otherwise since a steam 7~

pr~ducing coil can readily be added within the vap~rizer heating chamber t~ pr~vide a sDurce of steam for the system.
Als~, as dis(ussed in greater detail later, teachings of the inventi~n including the use of the separately-fired sulfur vaporizer as a heat source enables the system to be kept in a standby condition with units of the system at or near operating temperature enabling hydrogen sulfide px~duction to be initiated readily upon demand thus eliminating hazards inherent in stcrage of highly t~xic and inflammable hydrogen sulfide.
The reductant gas is added from a source 26 through c~nduit 27. Provision is also made for addition of steam with the reductant gas through line 29. Steam addi-tiDns for hydr~lysis reaction purposes can be made with either the sulfur vapors or the reductant gas. When made with the reductant gas, steam addition can be utilized to m~derate heat-up of the reductant gas feedstock as desired during production and provides steam flow through the reductant gas inlet means during standby conditi~n. Prefer-ably, a minor portiDn of the steam input to the system ismade through the reductant gas feedstock inlet means~
Superheating of the sulfur v~por and steam is con-trolled in vaporizer 14 responsive to operating requirements in reactor 16. Superheating at pressures several times atmospheric is ordinarily used; lower pressures can improve c~nversi~n in lower temperature reactions.

System operatinq pressure is established by pres-sure control in the product g~s removal conduit. The pres-sure of the reductant gas feedstock can influence selecti~n of system operating pressure when the reductant gas at a particular site is available at a suitable operating pres-sure. The system operating pressure determines the pressure of sulfur vapors delivered by vaporizer 14. In general, the system is operated at pressures between about two and about five atmospheres.
In accordance with the invention, the reductant gas, sulfur vapor, and steam are mixed thoroughly in a pre-conditioner vessel 32. This vessel can function to filter entrained particulate, scale, carbon, ana ash, prior to introduction of the mixed reactants through conduik I

34 into the reactor vesselO The premixing of the reactants which can take place at widely differing temperature levels alsD reduces strain in the catalytic reaction zone and facilitates the reaction and its control. The filtering function ~f preconditi~ner vessel 32 helps in maintenance of a desired ~low through ~he system both in producti~n and standby modes.
Reactor 16 includes a reaction zone filled with a catalyst supported to allGw desired contact and passage of reactants and reaction products. The reac~ion products are delivered ~ver conduit 36 and passed in heat exchange _ g _ rela-tiorlship with the reductant gas being introduced t~ the process t'nrough heat rec~very unit 40. Heat recovery aids efficiency. However, hea~ing ~f any reductant gases to a temperature likely to cause c~king is av~ided and is not required since the heat input source f~r any sensible heat requirements for the system is at vaporizer 14. Conduit 42 conveys the reductant gas heated from heat recovery unit 40 intD mixer 32n In practice of the invention, sulfur vapor is introduced into the process in excess of that required stoichiometrically in order to insure maximum p~ssible con-version Df the reductant feedst~ck and to reduce or eliminate hydrogen in the product gasesO Control of sulfur vapor and steam temperature delivered by the sulfur vapori-zer along with quantitative c~ntrol of sulfur feed andsteam are used to modulate reaction temperatures s~ as to maintain such temperature within an optimum range. When reaction temperatures must be moderated~ the extent Gf superheating sulfur and steam in vaporizer 14 is adjusted.
The sulfur vapor can also be used to maintain desired reaction zone temperatures during process turndowns.
The present system is operable should relatively pure hydrogen be available at the site as the reductant gas.
As shown in Figure 1, the product gases from reactor 16 com-prise hydrogen sulfide and excess sulfur in vapor form. In comple~ing the process; the excess sulfur is removed from the product gases and the hydrogen sulfide is delivered for desired usage. Steam is made available when not required for reaction purposes because of its othPr process tempera-ture moderation and system purging advantagesO
Under such circumstances and when the conversionof the reductant gas is sufficient in the main reactor, with-out further reaction being required to produce acceptable product, the prDduct gases can be directed to cooling means and then to the pretreatment tank 22~
In the embodiment of Figure 1, waste heat boiler 46 is used to cool the product. gases which can exit from recovery unit 40 at a temperature around 700F. 900Fo Conduit 44 directs product gases to waste heat bDiler 46 which reduces the temperature of the product gases to approx-imately 300F. Condensed sulfur, which is likely to be saturated with hydrogen sulfide, can be directsd into pre-treatment tank 22 as previously described. For most steady state conditions, a temperature of about 300F. is preferred for the liquid sulfur feedstockO The heat from condensation o sulfur vapor is used to generate steam in the waste heat boiler 46~ Part of the heat recovered in heat recovery unit 40 can also be used to genérate steam.
The reaction gas, cDntaining hydrogen sulfide, passes through an internal mist separator in pretreatment ~ 7 ~
tank 22 and hydrogen sulfide is delivered over conduit 50 for additiDnal coDling (to abou~ 200F~) in pr~duct cooler 52 where sulfur vapor is removed. The hydrogen sulfide gas is delivered through pressure control valve 53 in conduit The adaptability of the present system is directed primarily to the use Df reductant gases other than hydrogen which are more readily and economically available at most installations. Carbon containing reductants (e.g, paraffinic hydrocarbons) can form carbon-sulfur compounds, generally in excess of acceptable levels, in the main reac~or 16~ Hydro-lysis of carbon~sulfur compounds is carried out in accord-ance with the following formulae CS2 -t 2~20 - ~ 2H2S + C2 - 15 00S ~ H2O -~ H2S ~ CO2 Steam additiDns are required fDr such hydrolysis reacti~ns and steam is introduced with the sulfur vapor and/or the reductant gas reactant. As previously mentiGned, adding steam via conduit 24 through vaporizer 14 has additional utility in provid,ing an additional means fDr,establishing and maintaining the desired temperature for the reaction in the reactor 16; a majDr portion~ generally up to abGut 90/
of the steam addition is added in this way. Adding the remaining minor portion of steam additions through conduit 27 has an added benefit in controlling the temperature of the reductant gas feedstock.

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The reactions can be regulated within the main reactor 16 with sulfurization an~ hydrolysis xeactions occurring tc produce satisfactory product for many uses in a single reaction zone (as in Figure 1). However, for process adaptability and increased hydrogen sulfide conver-si~n efficiency, a trim reactor 56, as shown in Figure 2, is provided in the c~nduit between the heat xecovery unit 40 and the waste heat b~iler 46; conduit 58 connects trim reactor 56 to waste heat boiler 460 Hydrolysis reactions can Gccur at temperatures as low as 500F. In trim reactor 56 hydrolysis is carried out so that sulfur remains in the vapor state. The temperature is selected to accomplish the hydrolyzing reaction suffici-ently above the dew point of the sulfur vapors.
~5 The product gases from trim reactor 56 after hydro~
lyzing reactions inc~ude primarily hydrogen sulfide, excess sulfur vapor, excess water vapor, and CO2. These are directed over conduit 55 to waste heat boiler 46. Cooling the product gases to 300F. condenses sulfur vapors. Pro-duct gases and condensed sulfur are directed, as previously described, to pretreatment tank 22. After additional cool-ing in product gas cooler 52, the pr~duct gases can be treated further to produce substantially pure hydrogen sulfide.

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The gas resulting frorn coal gasificatiDn comprises largely carb~n monoxide and hydrogen, when this gas is used the sulfur vapors are only slightly superheate~ and are added in excess of requirements, typically at percentages ~f 10~/o ab~ve stoichiometry, or higher.
A control objective is to hold temperatures in the sulfurization reaction zDne near the desired optimumO A
reaction temperature is selected and the process regulated with the quantity of sulfur feed and the temperature of the vaporized sulfur and steam to hold reaction temperature within the desired temperature range. The reaction tempera-ture is monitored and the heat input to vaporizer 14 can be controlled responsively to maintain sulfur vapors within an optimum temperature rangeO
In a control procedure utilizing simplified con-trol implementati~n, the sulfur feed rate is set at a pre~
selected level and the temperature of the vaporized sulfur and steam is controlled by operatisn of fuel burners for vaporizer heat source 57. When smooth operations have been established, with the reaction zone ~n the optimum range, the sulfur vapor temperature is m~nitored and used to control cDmbustible fuel input to the fuel burner. Monituring sulfur ~apor temperature for this purpose has the advantage ~f fast response. Reacti~n z~ne temperature, which has a slower time response because of the mass of materials involved~ is ~ 7~
indica-ted and recordedO Process control appara~us for more sophisticated automated control is readily available in the art and adaptable based on operational data.
The properties of sulEur enable it to exercise greater temperature control than steam so that a set rate of sulfur additions for full production may be held when opera-ting at less than full production capacity. But there are practical limits on the amount of excess sulfur that should be added, as discussed above. Also, in order to avDid raising the vaporizer tube temperature to levels which are unduly detrimental to service life, steam can be added for temperature ~odulation purposes in addition to its function in hydrolysis reactions, Typically, the reaction bed in the main reactor (16) is a catalyst material consisting of zirconium aggregate or activated alumina. A qualificatiDn on the type of activated alumina used in such primary reactor is that it have high crushing strength which will not degrade at the high tempera-tures which can be required. Activated alumina catalyst wo~ld typically be used in the trim reactor bed. The reac-tors are refractory lined to minimize heat loss through vessel shells.
Reaction zone temperatures are measured by tempera-ture sensors such as 58 in reactor 16. Because of the response time lag mentioned~ it is preferred to rnonitor the sulfur vapor temperatures at ternperature sensor 59 in the premix and c~nditioning vessel 32.
As shown in Figure 3, valving and other mechanical flow control implementation are located in relatively low temperature zones~ Positive pressure flow is exercised in the high temperature areas without mechanical flDw control implementation in such areasO
F1DW control means can t~pically include pumps and valves. For example, in Figure 3 valve 60 is located in sulfur ~eed line 20; valve 62 is located in the liquid sulfur feed line 12 between sulfur feed pump 10 and vapDrizer 14;
valve 64 is located in steam line 24 and valve 66 is located in steam line 29. Reductant gas is pr~vided at available temperatures and pressures or, pump compressor 68 can provide desired pressure of 50-75 psig. Pressure control valve 70 located in reductant gas feed line 27 introduces reductant gas to the process at or above the system pressure esta-blished through pressure control valve 53 in product gas delivery conduit 54; a representative system pressure is 35 psig.
Reactants are fed intD the system and reaction products fed through the system at pressures above atmos-pheric pressure as described above and tempeatures shown in Figure 3 while limiting mechanical implementation to rela-tively low temperature regions. The pressure at any given point is established by pressure loss through the system and the back pressure maintained by pressure control valve 53.
Flow control between high temperature elements, e.g. from the mixer 32 to the reactor 16, is achieved without mechani-cal flow control implementation in such high temperatureregions.
In a representative Dperation, liquid sulfur is delivered by controlling the feed stroke of sulfur feed pump 10. Sulfur vapor and steam temperature is monitored and controlled through heat input source 57 for sulfur vaporizer 14. Liquid sulfur and steam are delivered as required and sulfur vapor and steam temperature controlled tD maintain the reaction zone temperature in reactor 16 within a desired range. The temperature sensor probe 59 in preconditioner 32 provides an input to controller 78 for burner control Df heat input source 57. While liquid sulfur feed can be set manually by adjusting the feed strDke of pump 10, sulfur feed rate and sulfur vapor temperature can be mtegrated and automated. Such mechanical flow control implementation, sensors, and elPctronic processors are available commerci~
ally and their use in the light of the above teachings is within the skill of the art SD that nD further description of these devices is required for an understanding of the invention~

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The temperatures shown in Figure 3 fDr sulfur vapors, main reactor input and output, red~ctant gas temperature, and krim reactor temperatures are representa-tive for a natural gas reduc~ant and can vary when the system is adapted for ~ther reductants. The relatively low temperatures shown at regions for mechanical flow c~ntrol equipment are typical with ~ther types of reductant gases.
Prec~nditioner mixer vessel 32 is shown in greater detail in Figure 4. Vessel 32 comprises shell wall 82 with flanges 83, 84 at opposite longitudinal ends f~r attachment and removal of flanged access doors 85, 86. Refractories 88 line the shell and help define chamber 90 which, during usage, is filled with ceramic shapes ~not shown~.
Sulfur vapors ~r sulfur vap~rs and steam are ;

introduced at entry port 92 and reductant gases at entry port 94. The temperature probe for monitoring sulfur vap~r temperature can be mounted thr~ugh port 960 The ceramic shapes in chamber 90 help absorb the thermal sh~ck of mixing vapors from vaporizer 14 and reduc~
ing gas, which reactants can be introduced at widely differing temperatures. The ceramic shapes als~ insure complete mixing of the reactants during upward passage and help remove particulates such as metal sulfid~s and thereby increase the service life ~f the catalytic reaction z~ne and catalyst bed. The ceramic shapes can be readily removed and replaced through the access doors 85, 86.

Mixed reactants are delivered through exit port 98.
A temperature probe can be mounted in port 100 to monitor the temperature of the mixed reactants.
The main reactor 16, in which a sulfurization reaction takes place~ is preferab]y designed with a large diameter catalyst bed to reduce pressure drDp. Catalyst is supported in the reaction zone by ceramic shapes~ Refrac-tory thickness for both reactors and preconditioner vessel is selected to hold shell temperature to approximately 300Y. to minimize m~isture condensation and maintain shell strength.
The heat recovery unit 40 which removes heat from the gases discharging from the main reactor by preheating reductant gas, or reductant gas and steam, can be designed as a single pass shell and tube arrangement with h~t reactor gases on the tube side. Piping and connections are refrac-tory lined. Sufficient heat transfer surface is provided to cool the gases discharging Erom the main reactor to tempera-tures desired in the trim reactor. Any sulfur vapor conden-sate can be removed in a sulfur dropout leg to minimizeclogging problems in the remainder ~f the system~
The trim reactor vessel, which can be used to increase conversion to hydrogen sulfide by hydrolysis reactions, is refractory lined and typically contains an activated alumina catalyst. The trim reactor is generally ~ 19 ~

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operated at about 700F. ~ 900F. with refractory linings controlling heat losses.
In a l~w capacity embodiment, e~g. ~ne hundred lbs/hr H2S, natural gas and steam were reacted with vap~rized elemental sulfur in a catalyst bed containing 3 cubic feet of 4 t~ 10 mesh zirconium aggregate. The reactiDn temperature was maintained at about 1050F. by using 110 tD 300 percent of stoichiometric sulfur requirement. To minimize formation of carbonyl sulfide, 25 percent excess steam was provided. Sulfur vap~x and reductant gas were provided for operatl~ns at about thirty (30) psig ~utlet pressure~ The comp~siti~n ~f the natural gas was approximately 92 percent methane and 6 percent heavier hydrocarbDns. The natural gas flow rate was 3.96 SCFM and the combined reactants pr~vided a space-velocity ~f 470 h~ur~l with a residence time ~f 2,3 sec~nds. The excess sulfur in the reactor product gas was removed by condensatiDn and the analysis on a dry mole basis was 78 percent H2S, 18 percent C02, 1.5 percent COS and 0.6 percent CH4~ The balance in the gas analysis was primarily N2 (from the natural gas) with trace amcunts of CS2 and C0~
Process cDnditions in khe reactor permitted the sulfurizakion and hydr~lysis reacti~ns to DCCUr in the same catalyst bed.
The react~r product yas from the firsk example was cDoled and condensed sulfur rem~ved. The gas was then passed int~ a trim reactor c~ntaining 2.5 cubic feet cf activated alumina in the form of 1/4 inch spheres. This provided a space velocity ~f 500 hour~l and a residence time ~f 3.95 seconds. ~he trim reac~or product gas had a composition on dry mole basis of 79 percent E~2S, 19 percent CO2, 0.4 percent COS, and 0.6 percent CH4. The use of a trim reactor demon-strates that the COS content can be reduced by further hydrolysis to hydrogen sulfide at temperatures lower than the initial sulfurization reactions.
Using the same reactor described in the first example, the use of propane, methanol, and carbon monoxide reductant gases was demonstrated. Steam was added to the reductant gas prior to entering the reactor so that hydro-lysis also occurred in a single catalyst bedu Sulfur was provided at about 300 percent excess in the reactions for propane and for methanol, and at about 700 perc nt excess fox the reaction with carbon monoxide. The steam rate was at 50 percent exces.s fDr carbon monoxide. The following table summarized operation and ~esults:

Main Reactor Reductant Temp. F. Dry Product Analysis, %
Gas In Out H2S CO2 COSCS2 Propane 1,08Q 1,030 76.1 20.2 177104 Methanol 1,100 1,100 74.2 21.6 2.6 0 Carbon 1,000 1,050 50.1 46.8 2.2 0 2S Monoxide Figure 3 sets forth typical operating temperatures - and constituents at several poin~s within the system. In a 7~
typical embodiment using methane as the reductant gast molten sulfur at about 20% in excess of stoichiometric requirements is mechanically pumped by sulfur feed pump 10 from the sulfur feed pretreatment vessel 22 to the sulfur vaporizer 14. Concurrently, steam from source 110 (which can be generated by the system as described earlier) is provided with about 80~/~ of the steam being co-injected with the molten sulfur to ~he sulfur vaporizer 14 and blended with the molten sulfur and the balance being blended with the reductant gas~
Steam is intrDduced with the molten sulfur to the sulfur vaporizer 14 for reduction of sulfidation corrosion of the sulfur vaporizer heat transfer surface, plus lowering of the partial pressures of the steam/sulfur mixturer there-by allowing the subsequent process reactions to take placeat a lower threshold temperature. The mixture Df sulfur and steam is superheated to approximately 1250F. and discharged to the preconditioner vessel 32 to which the reductant gas methane from source 26 and additional steam are added. The mixture of superheated sulfur, steam, and reductant vapor is directed into the main reactor 16 which contains a zirconium catalyst for catalytic conversion to H2S~ The product gases from reactor 16, containing ~I2S, unreacted sulfur and sulfur compounds, are discharged to heat exchanger 40. ~he methane and steam added with the methane provide for heat energy recovery i~ unit 40 and the temperature of product gas from ~ain reactor 16 is reduced to about 700F~ to facilitate the further conversion of sulfur/carbon compounds to H2S in the presence of an alumina catalyst in the trim reactor 56~
Product H2S gas at about 700F. is discharged to the waste heat boiler 46 for energy recovery. cooled H2S
product gas at about 300F. is then discharged into the sulfur feed pretreatment vessel 22 for pretreating (viscosity modification) of the molten sulfur feed. EI2S product is then discharged through a final product cooler fcr condensation of elemental sulfur carryover from the H2S product gas.
Specific values are set forth in Tables I and II below for a higher capacity embodiment, e.g. 3100 lbs/hr of H25O

I

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T~BLE I
Methane Feedstock and Steam Eeed Rates in #/hrO Flow Rates ln #/hr.
.

Fresh Sulfur Steam Natural Main Trim Cooled Sulfur Feed Feed Gas Reactor Reactor Reactor 2925.4 3510.4 1287.9 426.2 5224.~ 5224.6 463g.5 Temperature Fu Pressure (psiq) TABLE II
Com~onent values*under Operatinq Conditions of Table I
Main Trim Cooled Component Reactor Reactor Product S84.53 90.38 90~38 ~2 18.66 22.71 22.71 COS2.83 0.58 0.5~3 CS,,1.90 0.10 0.10 CO 0.09 0,09 0.09 N2 0.30 0.30 0.30 H2 0.24 0.24 0.24 CHAO.74 0.74 0.74 CH3SH 0.06 0.06 0.06 H2032.69 26.84 26.84 *Expressed in pound moles per hour.

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The above described ~rocess and a~aratus for producing hydroaen sulfide is also disclosed and is claimed in copending Canadian Patent A~plication Serial ~lo. 373,~11, filed March 19, 1981.
Controlled production of hydrogen sulfide on demand is a distinct advantage in the adaptability of the present hydrogen sulfide producing svstem to various ~lant site needs.
~ith the control of sensible heat in~ut features of Lhe present invention, the system with e~uipment such as reaction vessels, heat exchangers, pre-mixer vessel, and conduits, can be readily kept at or near a desired operating temperature in standby condition ~ithout producing hydrogen sulfide. By maintaining the system at or near operating temperature/
hydrogen sulfide product gas can be readily nroduced on demand, and re~uiremenLs for storage of hazardous hYdrogen sulfide are eliminated.
Various standby modes with controlled tem~erature are available.
When shifting to standby condition, the reductant gas supply is interrupted by closing valve 70 (Figure 3)O
A portion of the total steam requirements for the standby condition is directed through conduits 29 and 27 for intro-duction to preconditioning vessel 32 through the reductant gas feedstock path.
In any of the various standby modes avilable, sulfur should continue to be added to the system for completion of reaction of any of the feedstock reductant gas in the system;
and, sulfur can continue for short periods thereafter for certain purposes, e.g. for short shutdowns and ~ 25 -ms/~

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minimizing temperature changesO However, when reactions which produce hydrogen sulfide from the feedstock reductant gas in the system are completed, the product gas exhaust valve 53 can be closed dependent ~n the downstream 5 process receiving the product gas. Sulfur and steam flow can continue for relatively shor~ standby periods with sulfur circulation after interrupting feedstock reductant gas intro duction being controlled in order ~o avoid con~ensation of sulfur~ e.g. in trim reac~or 569 should standby conditions at less than full operating temperature be desired. Use Df both sulfur and steam i5 preferred since smoother transition from production to standby and vice-versa are more readily attained~
When standby operations are expected for one or two days, sulfur circulation through the system is preferably terminated by stopping pump 10 and increasing steam additions.
Steam additions through vaporizer 14 without sulfur circula-tion are generally at least double the steam provided under operating conditions when it is desired to maintain the system in standby at approximately operating temperature~ For example, when about 1500 pounds per hour of steam were being introduced during operating conditions~ steam additions are increased tG about 3000 to 4000 pounds per hour with most of such steam being introduced through the vaporizer during standby conditions~ Sulfur and steam or steam alone are con-trolled both as to temperature and quantity so as tD maintainthe desired h~at balance in the system; lower trim reactor (56)-temperatures can be obtained by increasing the percentage Df steam intrDduced thr~ugh reductant feedstDck line 270 The high temperature steam follows the paths thrDugh the system foll~wed by reactant and product gases under operating conditi~ns. This steam can continue to the downstream process receiving the ~2S prDduct gas if that prDcess can accept the water volume; or, the steam is directed t~ a flare exhaust either at a point between the waste heat boiler 46 and vessel 22 or in the line to valve 530 When initiating standby, it is preferred t~ flare after vessel 22 until sulfur has been removed from the reactors and product portion ~f the system when circulation ~f sulfur is termin-ated. Generally, standby conditiDns are established at Dr near atmospheric pressure so that back pressure at valve 53 is not required.

When extended periods of standby cDnditions are expected, e.g. a month or more, the system temperature can be maintained below n~rmal operating temperature t~ save fuel while avoiding complete c~ol-down Df refractDries and purging requirements uf ~tart-upO Sulfur can be used with the steam when reheating fDr resumption of productionO F~r relatively short peri~ds ~f standby cDndition, the system is kept at appr~ximately operating temperature flD~ing sulfur and steam, and prDduction is readily resumed by adding feedstDck reductant gas F~r intermediate periods Df several days, the system can be kept near ~perating temperature with steam - 27 ~

only and pr~ducti~n resumed by recirculating sulfur and adding feedstock reductant gas~
Data are presented for four standby modes as f~llows:
A - circulate sulfur and steam, trim reactor minimum temperature 730F.
B - Circulate sulfur and steam, trim reactor minimum temperature 620F~
C - Steam only, maintain process temperature for restart D - Steam only, lower temperature, reheat b~fore able to restart, trim reactor minimum temperature 300F~
Referring to Figure 3 for designated locations, the flow data presented in Table III bel~w for modes A, B, C~
and D are in pounds per hour~
TABLE III
Flare Between Steam W~IB 26 and F~are Sulfur Steam Line Sulfur Before Mode Line 12 Li.ne 24 29,27 ~ank 22 _ Valve 53 C(valve 62 3150 350 3500 closed) D(valve 62 1350 150 1500 closed)

- 2~ -~q~
In addition to the elimination of safety hazards by being able to produce H2S on demand, there are important advantages fr~m an opera~ional engineering point of view in the standby condition concept taught and the standby modes provided. One of these advantages is related to the sub~
stantial elimination of sulfur solidification in the lines and equipment. Problems associated with sulfur freeze~ due to its insulating properties, are well known so that liquid sulfur tanks and lines are conventionally steam jacketedO
Avoiding the possibility of sulfur freeze-up in other portions of the sys-tem is part of the standby modes taught.
In addition, thermal shock and moisture condensa-tion which can be detrimental to refractories and shell jackets are substantially eliminatedO This extends the useful life of sulfur vaporizer, reactors and other equip ment. Further, the system can be held in standby condition for extended periods and returned to production in a matter Gf hours rather than days.
The separately-fired sulfur vaporizer for control Df sulfur vapor and/or steam temperature contributes to the adaptability of the system t~ various plant site conditions and requirements. ShDuld hydrogen become available as a reductant feedstock so that steam is not required f~r a hydrolysis reaction, the sulfur vapor and steam heater finds utility in start-up, in moderation of the sulfurization reaction temperature, and in standby condition. Further, the o~tions on steam facilitate proper heat balance in the system; e.g. the trim reactor can be operated at a desired temperature level by removing heat frDm the product gases, and hazards associated with overheating certain reductant feedstocks are reduced by introclucing steam with the reductant feedstock. When a reductant feedstock with a high percentage of CO is provided at a plant site, the avail-ability of steam provides hydrogen for the hydrolysis reaction and oxygen for c~nverting carbon monoxide to carbon di~xide.
Various process control parameters and values have been set forth to provide an understanding of the invention and control equipment described in disclosing the invention.
However, in the light of the above teachings, other process control para~eters and va~ues and other flow control apparatus can be utilized by those skilled in the art to effect desired process control utilizing the novel concepts of the present invention. Therefore, for purposes of deter-mining the scope of the present invention, reference shouldbe made to the appendecl claims n

Claims (18)

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

1. Method for operating a hydrogen sulfide manu-facturing system to eliminate requirements for storage of hydrogen sulfide product gases by providing for production of hydrogen sulfide on demand, such hydrogen sulfide manufacturing system including a separately fired sulfur vaporizer with means for controlling heat input to the sulfur vaporizer for controll-ing heat input to the hydrogen sulfide manufacturing system, means for controlling delivery of liquid sulfur to such vaporizer for introduction of sulfur vapors into such system, means for introducing gaseous sulfur-reducing feedstock to such system including means for interrupting such introduction of sulfur-reducing feedstock, means for controlling supply of steam to the hydrogen sulfide manufacturing system including means for introducing steam through the sulfur vaporizer and means for introducing steam with such sulfur-reducing feedstock, reaction vessel means for reacting sulfur vapors with such sulfur-reducing feedstock and steam to produce product gases including hydrogen sulfide, and discharge means for the product gases including valve means for interrupting discharge of product gases, such method comprising the following steps for interrupting production of hydrogen sulfide and placing the system in standby condition interrupting input of such sulfur-reducing feedstock to such system, permitting continued introduction of sulfur through such sulfur vaporizer at least until reductant feedstock has been removed from the system, and controlling heat input to such sulfur vaporizer to maintain temperatures within such system at a level related to system temperatures maintained during production of hydrogen sulfide.

2. The method of claim 1 further including the step of adding steam to such system with a major portion of the steam being added through such sulfur vaporizer.

3. The method of claim 2 further including the step of interrupting discharge of product gases.

4. The method of claim 1 further including the step of interrupting introduction of sulfur.

5. The method of claim 4 further including the step after interrupting introduction of sulfur of quantitatively controlling input of steam to the system to maintain system temperatures at such selected level.

6. The method of claim 1 in which the sulfur input to the system after interrupting input of feedstock sulfur-reducing gas is controlled to avoid condensation of sulfur vapor in such reaction vessel means.

7. The method of claim 1 in which heat input to the system is controlled to avoid condensation of sulfur vapor in such system.

8. The method of claim 2 including the step of adding a minor portion of such steam input through the means for introducing feedstock sulfur-reducing gas, such minor portion of steam input being sufficient to maintain a positive flow of steam to prevent back-flow of other gases being delivered by such vaporizer.

9. The method of claim 5 in which the amount of steam input to the hydrogen sulfide manufacturing system made through the sulfur vaporizer is at a level to maintain system heat balance.

10. The method of claim 9 in which steam input through the sulfur vaporizer can be supplemented with sulfur during changeover from standby to operative condition.

11. Method for operating hydrogen sulfide manufacturing apparatus to eliminate requirements for storage of hydrogen sulfide product gases by providing for production of hydrogen sulfide on demand, such hydrogen sulfide manufacturing apparatus including an interconnected system for combining sulfur, sulfur reductant feedstock and steam for reaction to produce hydrogen sulfide, a source of gaseous sulfur reductant feedstock having a predetermined temperature, means for introducing gaseous sulfur-reducing feedstock to such system including means for interrupting such introduction of sulfur-reducing feedstock, vaporizer and superheater means including separately controllable heat source means for vaporizing liquid sulfur and superheating such sulfur vapors, means for supplying liquid sulfur at a predeter-mined temperature, means for delivering such liquid sulfur into the vaporizer and superheater means, means for quantitatively controlling delivery of liquid sulfur to the vaporizer and superheater means, means for supplying steam at a predetermined temperature, means for controlling supply of steam to the hydrogen sulfide manufacturing system including means for introducing steam into the vaporizer and superheater means to be superheated and means for introducing steam through such means for introducing gaseous sulfur-reducing feedstock, reaction vessel means for reacting sulfur vapors with such sulfur-reducing feedstock and steam to produce product gases including hydrogen sulfide, and discharge means for the product gases including valve means for interrupting discharge of product gases, such method comprising the following steps for interrupting the production of hydrogen sulfide resulting from introduction of liquid sulfur, sulfur-reducing feed-stock, and steam into such system and for placing the system in standby condition, interrupting input of such sulfur-reducing feedstock to such system, controllably continuing introduction of sulfur through such vaporizer and superheater at least until reductant feedstock has been removed from the system, controlling the separately controllable heat source means for the vaporizer and superheater means to maintain temperatures within such system at a level related to system temperatures maintained during production of hydrogen sulfide, and controllably continuing introduction of steam to such system with a major portion of the steam being intro-duced through such vaporizer and superheater means and a minor portion being introduced through such means for introducing sulfur-reducing feedstock to maintain a positive flow of steam to prevent back-flow of other gases being delivered by such vaporizer.

12. The method of claim 11 further including the step of interrupting discharge of product gases.

13. The method of claims 11 further including the step of interrupting introduction of liquid sulfur.

14. The method of claim 13 further including the step after interrupting introduction of liquid sulfur of quantitatively increasing input of steam to the system through such vaporizer and superheater means to maintain system temperatures at such selected level related to system temperatures maintained during produc-tion of hydrogen sulfide.

15. The method of claim 11 in which the liquid sulfur input to the system after interrupting input of feedstock sulfur-reducing gas is controlled to avoid condensation of sulfur vapor in such reaction vessel means.

16. The method of claim 11 in which heat input to the system through the separately controlled heat source means for the vaporizer and superheater means is controlled to avoid condensation of sulfur vapor in such system. 36

17. The method of claim 14 in which quantitative input of steam to such system made through the vaporizer and superheater means is at a level to maintain system heat balance.

18. The method of claim 17 in which steam input through the vaporizer and superheater means is supplemented with liquid sulfur during changeover from such standby condition to a hydrogen sulfide producing condition.