US2671723A - Synthesis gas desulfurization - Google Patents

Description

w LI I M. N.. n m m un 1 f m.. 3, m, w 2 N m w M s d A M J G d ON\. s e E I l c m N 'Y Y m z O 1... @n ...f A 4 4|. n QW .5 9 h m M w ZMG L wereld Sor-noms@ Urb/amber@ Patented Mar. 9, 1954' A.

UNITED S'TeTES.

l y 2.71.723. ";g.. r L; 5;.

. DESULFURIZATIGN-,fi charles'. n. Jenni; nea sans, and Edwards i G'ornowsk. Cranford, N. J'., assignors to Standiard Oil Development Company, 'a corporation "i laminating Marchas The present invention,l relates tothe'produc; Y

tion of gases from non-gaseous carbonaceous ma.- terials,4 particularly to the production of gasmixtures containing CQ- and Hz fromv such. nonvolatile carbonaceous materials as' coke, coal. oil shale, heavy oil residues, and the AMore 195o, ssrarNa. 151,482 I' t.. u.v content, but also, for the, production of' feed gases. for hydrogenation processes and particularly for the catalytic syn.-

Y thesis. of hydrocarbons and/or oxygenated' orspecifically,u the present. invention relates to an improved process for producing;l gas. containing CO and H2 from coke or coal by thef'water gas l reaction. and. making the gas. thus 1. \rodi-1ced.`sui-ti-l alble for utilization in the hydrocarbon. synthesis Y reaction, .L In a. cca-pending application, Serial. No. 151,326,

filed March 23. 1950,. by' Sumner Bn Sweetser and Robertl H. Mueller., there is disclosed a two; stagev y cour gasification process on. the production of water gas wherein. high surface area. char from the first stage is used to desu-lionne; the water gas f produced.

It has Iona been. known materials., such as coke.. coal and the; like', may 1 be converted into more valuablegases which can he more easilyhandled and more eiciently used for a greater variety of purposes.. @ne of the most widely practiced gas-generating conversions is the so-called water-gas2 processin which solid that non-volatile fuel fuels;l such as'coal or coke of, any origin. may be reacted` withsteam to produce water or pro p direct-eas mixtures of' CO and Hh in varying proportions, depending mainly on the conversion temperatures., which.l may vary from about 12u69 to? about 2400" E., and the feed ratio ofv steam.

The flexibility of the process may be illustrated by x1 series of. possible chemical reactions about as tollows: v f l C+2H2O- 2Ha+C0z C+HaO-Ha-l-CO COz+C 2CO coal.

garlic compounds from CO and H2 which de.-

pending, onthe. products. desired, requires HzrCO fratios.. varyingA within the wide limitsfoi' 0.54-:2'

voluniesoiv Hz pervolume. of CG. gas process,. particularly for hydrogenation processes. and the production of synthesis. feed gas, has been appreciably impeded by diiculties encountered in heatk supply and continuous operation as Well.. asin the 'substantial removal of sulfur` compounds from the.. gas, the latter being imperative for the. utility of. the. gas in the hydrocarbon synthesis. The. problems of supplying. heat. oi reaction, with continuity of' operation i have been satisfactorily solved heretofore, by the. application of the so-called fluid solids technique wherein the, carbonaceousV charge. is reacted. in, thev form. of a dense` turbulent mass.. of l nely-divided. solids` luidized. by theA gaseous ren aetants and products. However, substantial and economic. desulfurzation of the. water gas. stilll constitutes a.,major problem particularly in practicing the hydrocarbon synthesis based, on

` The catalysts. used in. the synthesis. of; hydro.- carbons from i210y and H2 are sensitive to sulfur poisoning. and consequently, it is necessary to use a...synthesis gas which is low in sulfur, for example, one with a sulfur content of preferably l part perI million or less.. Because of the.. low' vsulfur content. of. some sources. of natural gas, it .y is sometimes unnecessary to desulfurizev the synthesis. gas. prepared from natural gas. .Most coals however, contain appreciable quantities of sulfur and. in the preparation. of synthesis gas from coal. it, is. always necessary to. treat the gas for sulfur removal', prior to contactingI the synthesis gas with the synthesis catalyst. Difliy culties in desulfurzng water. gas. arise from *1 the fact thatthe gas leaving conventional Water,-

cas reaction or alternately in a make and blow fashion` By the application of suitable combos# tion conditions, particularly ofv high temperatures above about l300 Fi, the CO content of the combustion gasesmay be raised to any desired B. t. u. content. The process as such istheresis It WHT be uppreciated from thei'above that the-iff water-gas process permits the production of gas mixtures of widely varying composition and Agas generators contains two diierent types of sulfur compounds, namelyk HZS formed by the reaction of sulfur with H2, and organic, sulfur compounds such as COS. and` CS2 formed. by the f.

These two. types of sulfur compounds, due` tof their different chemical character. are,dimeultl` 'to remove byany single desuliurzatiorr treat-4 g ment. Therefore, it has been the practice here-` l However; the technical utilization oi the'vraterL tofore ilrst to remove H2S, for example, by a treatment with alkali, hydrated iron oxides, sodium thioarsenate (Thylox process), sodium phenolate (Koppers process), etc., and then to remove the organic sulfur compounds, for example, either by a conversion into HzS in the presence of steam and noble metal catalysts followed by a second H25 removal, or by a single high-temperature catalytic treatment with lead or tin catalysts, etc. The desulfurization procedure requiring two or more separate stages of diile'rent design and operating conditions constitutes a heavy load on the economy of any gas utilization depending on sulfur-free fuel gases of which hydrocarbon synthesis is an outstanding example. I

A further problem associated with the desul- Iurlzing of water gas to be Subsequently employed in the catalytic synthesis of hydrocarbons is that of heat economy. In the prior art practice, as when the sulfur is removed by scrubbing with solutions of amino alcohols, etc., it has been found necessary, in order to have an operative process that the water gas product stream be cooled, say below a temperature of about 110 F. before sulfur is removed, as at higher temperatures absorbent requirements increase because of low absorbing capacity and high vapor losses. This cooling represents a considerable detriment, inasmuch as hydrocarbon synthesis is usually carried out at a temperature of about 450 to 650 F. and the cooled desulfurized gases may require reheating in order to bring them up to the desired pare a gas suitable for employment in the hydrocarbon synthesis reaction. 5 In accordance with the present invention, coal is ground to iiuidizable particle size and subjected to a iiuidized eoking process. The char is withdrawn from the coking vessel and passed to a fluidized solids gasification Vessel wherein it is contacted with steam at temperatures from about 1700 to l900 F. to produce a mixture of carbon monoxide and hydrogen. Heat may be provided either by addition of oxygen or air or by recycling of heated solids from a subsequent combustion vessel. From the water gas generator, spent solids and product gases iiow to a luidized solids sulfur removal system.v This system consists of a vessel containing a fluidized bed of pent char at about 300 to 600 F., a small amount of air equivalent to at least 2% mois air per mol of equivalent HzS in ue gas is fed to the sulfur vremoval vessel and as a result of the contacting of the sulfur-containing water gas with the spent char, sulfur is removed mostly in the form of the element deposited on the char and the spent char now fouled with sulfur is passed to a disposal dump while the puried gases flow to al Qiydrocarbon synthesis plant.

synthesis temperatures. In any event, the required cooling entails additional plant investment and means that more potentially valuable heat content is rejected to cooling water. A further problem encountered in desulfurizing water gas preparatory to its being employed as feed to the hydrocarbon synthesis process is that char iines from the water gas generator are entrained in significant proportions and are carried into the desulfurizing system, the prevention of Which requires expensive dust removal systems, further l Y adding to the initial and operating costs of the process. l

The present invention overcomes the aforementioned diiiculties and affords various additional advantages. These advantages, the nature of the invention and the manner in which it is carried out will be fully understood from the following description thereof read with reference to the drawing which shows a semi-diagrammatic view of apparatus particularly adapted to carry out the invention.

It is, therefore, the principal object of the present invention to provide an improved process for the production of highly valuable combustible gases from solid carbonaceous materials.

Another object is to provide economic means for the substantial desulfurization of combustible Kisses obtained from solid carbonaceous mater als.

Ieo

A still further object of the invention is to r:

provide an improved water-gas process for the Production of gas mixtures substantially free of Sulfur, suitable for the catalytic synthesis of hydrocarbons and/or oxygenated Organic com' hounds from CO and H2.

It has now been found that water gas may be substantially desulfurized by employing as the It has in the past been suggested that activated carbon be employed to remove sulfur from gases containing sulfur and its compounds. This removal of sulfur has been accomplished by adsorption of the sulfur on the carbon, usually at low temperatures followed by desorption of the sulfur with steam at elevated temperatures, regeneration of the activated carbon and re-use of the thus regenerated carbon in the process. These carbons are usually prepared from special woods such as beech, coconut, char, etc. and are activated by various physical or chemical means, i..e., by steam, zinc chloride, potassium sulde, etc. 'The relative high cost of these activated carbons and the difficulty of regenerating the adsorbent without consuming the latter, has in general, prevented the commercial application of this type of desulfurizing agent for the hydrocarbon synthesis Process. In addition, the adsorption process is characterized by several problems. It has been found, for instance, that because of the high surface area, polymerizing of the Inaterials and the gases occurs in activating the carbon so that it can not be regenerated. Activated carbon is an expensive material and losses must be minimized in order to maintain a commercially operable process. Furthermore, the maintenance of an activated carbon plant wherein thousands of tons of carbon must be alternately passed to the adsorption zone or the regeneration zone, is a cumbersome and expensive process. Also, provision must generally be made to remove the sulfur compounds released during regeneration, since it is usually undesirable to vent these to the atmosphere.

In accordance with the present invention, however, which employs spent carbon, the regeneration problem and the sulfur disposal problem are readily solved. The spent char is normally reacm-ree rejecting oi the sulfur without regeneration oi' the contacting material whereby the passing of the sulfur gases to the atmosphere is avoided. Since sulfur in the coal feed amounts to about 100 to 200 tons per day, this is an important consideration for plant locations in highly populated areas. Also, when using spent solids to remove sulfur, removal of dust in the gases leaving the gasification vessel is unnecessary.

Use oi spent solids for sulfur removal is only practical under proper conditions. Thus, the process is feasible only at moderate temperatures, e. g. 300-1000 F. At lower temperatures. excessive reaction volumes are required, while at higher temperatures, the degree of sulfur removal is inadequate, and undesirable side reactions may become excessive.

Having set forth its general nature and objects, the invention will best be understood from the `subsequent more detailed description wherein reference will be made to the accompanying drawing which illustrates a system suitable for carrying out a preferred embodiment of the invention.

V Referring now to the drawing, fresh coke or coal ground to a finely divided form preferably capable of passing through a 60 mesh screen and even through a 100 mesh screen is fed from supply hopper i into standpipe 2 which is provided with a plurality of taps t through which slow currents of air or other aeration gas may be injected in order to aerate and suspend the coke or con] therein. The suspension is introduced into generator wherein it is formed into a dense bed iiuidized by a mixture of oxygen and superheated steam admitted through lines 3 and 4, which bed is supported by grid E. Due to the superficial velocity of said steam which is maintained within the limits of about .2 to 3 i'eet per second, the coi-:e or coal is formed into a dense turbulent mass resembling a boiling liquid and having a well defined upper level l. Additional oxidizing gases such as air or oxygen maybe admitted through line 8 if desired. The steam und carbonaceous material react to form water gas, a gasiiorm product containing carbon monoxide and hydrogen. The temperature in this zone is oi the order of from about 1600 to 2000 F. and the gas pressure may be from atmospheric to about 60 p. s. i. g., although pressures up to 500 p. s. i. g. may. under certain conditions, be employed. The heat required for the reaction is furnished substantially by the combustion of part of the carbonaceous solids in reactor 5 by the oxygen admitted through line 8 and/or line 3.

The total supply of oxygen is carefully controlled to generate suihcient heat by combustion to satisiyA the heat requirements of the process. It is understood that under the reaction conditions. when fresh coal is employed as the fresh feed, it becomes coked in the iiuidized bed in generator 5 so that the solid product subsequently withdrawn, is referred to as char rather than coal.

The gaseous products are withdrawn from generator 5 through a dust separator such as cyclone 29 with dip line I0 extending below the upper level 'l of the fluidized bed for the return of separated dust particles. The water gas is then Ded thlOUgh line i l for sulfur removal in a manner described below.

'Ihe h ot earbonaceous solids are allowed to remain within reactor 5 for a sucient period of time to convert a major portion of the carbon to water gas.

As a result of the water gas producing reaction, the carbon content of the coke is usually reduced from about 75 to about 20%.

Spent het carbcnaeeous solids are continuously withdrawn from water gas generator -5 through aerated bottom drawo pipe 32, which extends above grid 6. The period ol residence of the coke or coal within reactor 5, in order to eiec't maximum utilization of its carbon content consistent with economic operation, depends upon a plurality of operating factors such as type of coal fed, temperature oi gas generation, ratio of steam to coke fed in the reactor, solids hold-up time,

etc. In general, the residence time and variables exchangers, one of which is shown in the drawing .as heat exchanger i3, and the resultant suspension of char in water gas is cooled to about 400 to 1000 F. The suspension of char and water gas is admixed with a small amount of air, preferably about 2.5 to 5 volumes of air per volumeA of 'equivalent H2S in the gas to be treated, which air is passed into line I4 through compressor i6 and line i5. The suspension of char, sulfur contaminated water gas and air is passed into desulfurizing vessel Il', wherein a iiuid 'bed ofv the spent char is lmaintained by the passage of the gas'mixture therethrough. in general, it is desirable to maintain the temperature within desulfurizer i1 at about 400 to 1000" hence the preceding coolers and heat exchangers. Furthermore, it is also desirable to maintain cooling means such as cooling coil i8 to maintain the desired desulfurizing temperatures. For most .effective desulfurization, the weight ratio of char to sulfur in the gas is of the order of 6 to 50.1 -As a result of the .addition of air, the Sulfur compounds in the gas. i. e, hydrogen sulfide, are

oxidized by air to form free sulfur which is deposited on the carbon, the exothermic heat Aof reaction being dissipated by means of `coil I8. Pressures within desuliurizing tower IT are of the same order of magnitude as in the gas generator and depend upon the pressure employed in the process for which the water gas is the feed.

Puriiied water gas from which substantially all of the sulfur compounds have been removed. is withdrawn upwardly from tower l1 through line I9. To remove traces of entrained fines, the puried gas may be passed to an oil scrubber 2D from which overhead through line 2i may be withdrawn substantially solids-free and sulfurfree water gas. This scrubber also serves to removeany tarry materials present in the gas. If desired, last traces of sulfur may be removed by any conventional process (such as lux masse) and the desulfurized gas is ready for use as a fuel gas, for the synthesis of hydrocarbons and oxygenated organic compounds, etc.

' The char containing sulfur deposited thereon is withdrawn through bottoms drawoi line 23 and may be employed in anyway desired. Thus, where it may be desirable to add heat to the gasiiication stage as the sensible heat -of r'ecycled solids, it may be desirable to Subjectthe spent sulfur contaminated char to a, combustion l'fiie desulfurization bed is sized euch that' about 100 to 1000 CF per hour of gas (measured ut 60' F. and atmospheric pressure) are temper cubic toot ot char.

resaca-:rp wn, amvsemfiaieweiwmwrmwwi operation at a temperature above that obtaining in the water gas generator and recycling a portion of the hot ash thus formed to the water gas generator.

The embodiment of the invention illustrated by the drawing permits of numerous modifications. Thus, it may be desirable to Contact the spent solids countercurrently with the sulfur contaminated water gas rather than concurrently. In such case, the spent char may be admitted into sulfur removal tower l1 through line 25 and as a result of suitable packing or baiiles within the sulfur removal tower, countercurrent flow may be obtained.

The sulfur in the coal feed is of two forms, one as iron sulfide or p-yrites in the ash constituents, and the other as organic sulfur compounds. Much of the sulfur is driven out during the coking reaction, so that the sulfur released into the water gas is correspondingly less. Also, the ferrous constituents in the ash are decomposed during coking and gasiiication, sothat it becomes possible to effect sulfur removal of the final product gas by using the sulfur accepting properties of the ash constituents. Removal of sulfur by this mechanism is an important part of the present invention in many applications.

In cases where a sepaarte heater vessel blown with air is used to supply heat to the generator, the spent ash used for sulfur removal can be regenerated (i. e. sulfur eliminated) by recycling to the heater Vessel, whereby the sulfur is driven oi and leaves as SO2 with the flue gas. Alternatively, a separate regeneration section may be used in order to facilitate collection and recovery of the sulfur. y

'Ihe invention may be further illustrated by the following specific examples.

The char produced along with the gas above was of the order of 2700 T/D, which if used in the sulfur adsorber would pick up only about 2.1% of its weight in sulfur, while purifying the gas. Data indicate that the char could satisfactorily adsorb sulfur up to of its weight, so that the char production rate is more than ample to give adequate sulfur clean-up.

Besides the investment advantages mentioned above, the process herein disclosed would leave a considerable operating cost advantage over conventional processes. The principal reason for this advantage is that the spent char withdrawn from the water gas generator has little value, whereas the normal process loss of amino alcohols or especially activated chars results in substantial operating costs.

A process producing about 350 million standard cubic feet/day of CO-l-Hz generates a raw gas of the following composition:

u Mol percent CO 29.2 Hz 46.9 CO3 8.5 CHI. 5.2 Na 3.0 H2O 6.9 S (expressed as His) 0.3

, The sulfur content of gas is equivalent to about an investment of about $4,000,000. Use of regular activated chars which would require regeneration would necessitate an investment on the order oi $2,000,000.

While the description and exemplary operation have served to illustrate specic applications and results of the invention, other modications obvious to those skilled in the art are within its scope. Thus, the process can be used for removing sulfur from extraneous gases, such as product gas from coking, natural gas, etc. In this case, the

gas generator 5 may be a relatively small vessel,

the primary purpose of which is to supply the char required for sulfur removal.

What is claimed is:

1. In the process for gasiiication of solid carbonaceous materials with steam and oxygen in a water gas generation zone at elevated temperatures, wherein a. sulfur contaminated gaseous product containing hydrogen sulfide as a contaminant and a spent char of only moderate adsorptive capacity having a carbon content of less than 40% by weight are withdrawn from said zone, the improvement which comprises feeding fresh speilithar and the gaseous product from said gas' ation zone together with about 2.5-5 volumes of air per volume of equivalent hydrogen sulde to a desulfurizing zone maintained at a temperature of from about 4001000 F., maintaining intimate contact therein between said spent char and said gasiiication product and air, and desulfurizing said gaseous product with said spent char and air.

2. rthe process of claim 1 in which said solid carbonaceous material is subjected to said gasication reaction in the form of a'dense turbulent iluidized bed of finely divided solids.

3. The process according to claim 1 in which hot spent char contaminated with sulfur in said desulfurizing zone is withdrawn therefrom and hurried to recover useful heat.

4. The process according to claim 1 in which the hot char introduced into said desulfurizing zone contains not more than about 20 Weight per cent carbon, and spent char contaminated with sulfur by said desulfurization is withdrawn therefrom and discarded.

5. An improved process for producing mixtures of CO and H2 substantially free of sulfur which comprises passing a stream of nely divided carbonaceous solid material into a gasification zone, forming a fiuidized mass of solids therein, subjecting said mass to a gasication reaction with steam at temperatures of from about 1600 to 2000 F. to produce a water gas containing sulfur compounds, withdrawing said gas from said zone, withdrawing from said gasication zone a stream of spent carbonaceous solids from which the major portion of the original carbon content has been removed to produce a finely divided ironcontaining coke ash having a carbon content of from about 10% to 40% by weight and a corresponding'ly low free surface area, passing at least a portion of said solids to a sas desulfurization zone, maintaining said gas in intimate contact with freshly introduced spent solids in said lastnamcd zone, withdrawing and discarding from said sone spent solids containing adsorbed and reacted sulfur compounds, and withdrawing a gas from said zone substantially free of sulfur.

6. The process oi claim 5 wherein the temperature in said desulfurizing zone is maintained within the range of about 400 to 1000 F.

CHARLES E. JAHNIG. EDWARD J. GORNOWSKI.

(References on following page) i l aonpaa 10 Country .4. 2 m m5. Dm u J S Y m m u A Pym .a rfv Ntn N.. mm3 E t Row o F m a. m7. mw u2 N

Claims (1)

1. IN THE PROCESS FOR GASIFICATION OF SOLID CARBONACEOUS MATERIALS WITH STEAM AND OXYGEN IN A WATER GAS GENERATION ZONE AT ELEVATED TEMPERATURES, WHEREIN A SULFUR CONTAMINATED GASEOUS PRODUCT CONTAINING HYDROGEN SULFIDE AS A CONTAMINANT AND A SPENT CHAR OF ONLY MODERATE ADSORPTIVE CAPACITY HAVING A CARBON CONTENT OF LESS THAN 40% BY WEIGHT ARE WITHDRAWN FROM SAID ZONE, THE IMPROVEMENT WHICH COMPRISES FEEDING FRESH SPENT CHAR AND THE GASEOUS PRODUCT FROM SAID GASIFICATION ZONE TOGETHER WITH ABOUT 2.5-5 VOLUMES OF AIR PER VOLUME OF EQUIVALENT HYDROGEN SULFIDE TO A DESULFURIZING ZONE MAINTAINED AT A TEMPERATURE OF FROM ABOUT 400*-100* F., MAINTAINING INTIMATE CONTACT THEREIN BETWEEN SAID SPENT CHAR AND SAID GASIFICATION PRODUCT AND AIR, AND DESULFURIZING SAID GASEOUS PRODUCT WITH SAID SPENT CHAR AND AIR.

Images