CA1263517A - Method for recovering elemental sulfur from coal-gas - Google Patents

Abstract

Abstract of the Disclosure An improved method for the recovery of elemental sulfur(S) from a coal-gas containing hydrogen sulfide (H2S) wherein hot lime (CaO) is used and then regenerated according to the following chemistry:
CaO + H2S = CaS + H2O
CaS + O2 = CaO + SO2 SO2 + C = S + CO2 These chemical reactions are conducted in-situ while the supply of carbon (C) for the formation of the elemental sulfur(S) is derived from a component of the coal-gas itself to increase the overall efficiency of desulfurization, in-crease the uniformity of the carbon deposit into the hot lime (CaO), and elimi-nate the extra and cumbersome steps of physically moving the spent lime (CaO) for regeneration and returning it after regeneration, and the step of adding coal to react with the sulfur dioxide (SO2) formed as an off-gas during regeneration.

Description

~2~3~l7 S P E C I F I C A T I O N

METHOD FOR RECOV~RING ELEMENTAL SULF~R FROM COAL-GAS

Background of the Invention The instant invention relates to the dry clean-up of gases in hot llme (CaO) wherein the lime (CaO) is regenerated and sulfur(S) ~s recovered ln elemental form.
In particular this invention is an lmprovement over the process descrlbed on pages 94 and 95 of the 1981 Generation Planbook edition, entitled "Gasifler Produces Clean Fuel from Resid and Lignlte for Natural-gas-fired Boller"~ a copy of the artlcle being attached for reference.
This reference describes the in~ection of a hlgh-sulfur fuel such as oil or coal, into a hot bed of calclned limestone (CaO) which is contalned in a flrst reactor, the calcined limestone (CaO) being fluldlzed by a mixture of flue-gas and air to g~slfy the oil or ~oal. When the calclned limest~ne (CaO) becomes spent and takes the form of calcium sulfide (CaS) it i3 physlcally transferred while hot to a ~econd reactor for regeneration ~ith air (~2) to convert the calcium sulflde (CaS) back to calcined limeston2 (CaO~ and thereby yield a sulfur dioxide (SO2) off-gas. The hot regenerated calcined li~estone (CaO) is then physically returned to the first reactor for further sulfur collection from the high-sulfur oil or coal. The sulfur dioxide (SO2) .off-gas produced is directed from the second reactor to a third reactor where coal is charged to supply the carbon needed for forming elemental sulur(S). Ash from the coal leaves as a residue from the third reactor.

~26~5~7 The disadvanta~ees of the reference sre as follows:
l. The fuel such as the oil or coal is gasifled wlth the llme (CaO~; thls causes the creation of excessive fines and the mlxing of the ash wlth th~ de-sulfurizlng agenc (CaO), which decreases thP efflciency of sulfur(S) collection by the lime (CaO) thereby causing the increase of lime (CaO) consumpt10n snd 9 greater disposal problem.

2. The physlcal transfer of the hot spent llme in the form of calcium sulflde (CaS) to a second reactor for regeneratlon and the physical transfer of the hot regenerated lime (CaO) back to the reactor where the gasification takes place are movements which necessitate the moving of hot material which is erosive and abrasive resulting ln the lncrease of maintenance costs and the creating of addLt~onal fines which must be disposed of.

3 The directlng of the sulfur dioxide (S02) to a third reactor where it mixes with coal for the formation of elemental sulfur(S), generates a tail gas whlch must be recycled, ash from the coal that must be disposed of, and the reaction of coal with sulfur dioxide (S02) requlres control air which must be fed to the third reactor.

4. The capital and operating costs are too high.

Summary of the Invention The instant invention eliminates the above disadvantages by gasifying a carbonaceous fuel by any one of the known process~s to make a raw-gas containing by way of example the following components.
CO, C02, H2, CH4, N2- 2~ H2S, H20, and in certain cases, aro~atics are also part of the raw-gas depending upon the gaslfication process used.

Thiq raw-gas, whlle still hot ls passed through a fixed bed of lime (CaO), preferably pebble llme whose temperature i~ malntained above the cracking temperature of hydrocarbons contained in the gaq ln order to crack such hydrocarbons to cause the deposit oE carbon (C) into the pebble lime (CaO) while the hydrogen sulfide (H2S) in the gzs reacts with the lime (CaO~ yield~
ing calcium sulfide (CaS) and water (H20). This simultaneous carbon deposit and sulfur collection by the li~e (CaO) yields a carbon impregnated calcium qulfide (CaS) whlch when e~posed to oxygen efflciently converts back eo lime (CaO) without degradation yieldlng sulfur dioxide (SO2) which 1~
lmmediately exposed to the impregnated carbon to react with lt in-sieu to in turn yield elemental sulfurtS) in vapor form and carbon dioxide (CO2).

The applicant believes that he has invented a new and useful method for the recovery of elemental sulfur from a raw-gas such as a coal-pas whose main ob~ect is to provide a superior as well as economical method of clean-up of sald gas which clean-up has heretofore been cumbersome and very costly.
Another object of the present invention is the provision of a method wherein the clean-up of the raw-~as and the formation of the elemental s~lfur(S) are performed ln-situ in order to avoid the transfer of the desulfurizing agent and to prevent its disintegration.
Still another ob~ect o the instant invention is the provislon of a ~ethod wherein the raw-gas is passed while hot throuph hot lime (CaO) to greatly ln-crease the reactivity of the sulfur bearing component of the gas with sa~d lime (CaO~ to form calcium sulfide (CaS) and water (H20).
Yet another ob~ect of the present invention is the provi~ion of a method wherein the hot raw-ga~ containing hydrocarbons such as tar, i~ passed through hot lime (CaO) whose temperature is maintained above the cracking temperature ~3~
f ~ald hydrocarbons ln ~rder to cause the depo~it of carbon (C) lnto saLd lime (CaO) simultaneously ~lth the collectlon oE the sulfur(S) component con-talned in said raw-gas to form a carbon ~C) impregnated calciu~ sulfide (CalS) and clean gas vlrtually free of sulfur and hydrocarbons.
Therefore another obJect of the lnstant invention is the provision of a method whereln said llme (CaO) is regenerated from said carbon (C) impregnated calcium sulfide (CaS) ln-situ by oxidi~ing the sulfur(S) in sald calcium sulflde ~CaS) to yield calcium oxide (CaO) and sulfur dioxide (S02).
Further another object of the present invention ls the provision of a method whereln sulfur dioxide (S02) reacts with said deposited carbon (C) ln-sltu eo orm elemental sulfur(S) in vapor form and carbon dioxide ~C02).
Further still another ob~ect of the instant inventlon i9 the provl810n of a method wherein the collectlon ofsaid elemental sulfur(S) in vapor form and sald carbon dioxide are collected and cooled for separating the elemental sulfur(S) from the carbon dioxide (C02).

It is further still another ob~ect of the present inventlon to provlde a method whereln the lime (CaO) used for desulfurlzation becomes physically stronger by vlrtue of the uniform deposit of carbon (C) into said llme (CaO) durlng the raw-gas passage through sald lime (CaO).
Therefore still another ob~ect of the instant ~nventlon i3 the provision of a method wherein two alternating systems are provided in order to Requence the systems back and forth in such a way as to ha~e one ~y~tem on the simul-taneous deposition of carbon (C) and collection of sulfur(S) by said lime (CaO) to form an impregnated calcium sulfide (CaS), and the other system on the simultaneous regeneration of said lime (CaO) from said calclum sulfide ~CaS~
and the formation of elemental sulfur(S).
Other ob~ects of this invention will appear from the following detailed description and appended claims. Before explainlng ln detail the present invention, it is to be understood that this lnventlon i3 not limited to the ~3X~7 details of the following description, since the inventlon ~s capable oE havlng other enbodlments without departlng Erom the spirit of the inventlon. Al~o it is to be understood that the phraseolo~y or termlnology herein set forth is for the purpose of description and not llmltation.

Detailed Description of Invention This ~nventlon was developed in con~unctlon with the clean-up of coal gases produced during the devolatlllzatlon of hlgh sulfur coal in the absence of oxygen in an 18" diameter cylinder, 4 feet high having a l~" thlck wall. The bottom of the cyl~nder had a l" plate welded to it in order to prevent gases escaping from the bottom. The cylinder was circumferentially insulated with Kaowooi and i~bedded in sand. The top of the cylinder had a flange to which a gasketted cover was tightly bolted. Four inches below the flange an exhaust port was provlded.
A second cylinder of the same dimen~ions and configuration as the first cylinder was located at a distance of 9 feet from the first cylinder. The second cylinder had an lnternal dlaphragm along its Yertical length to provide two chambers withln it. The diaphragm wa~ 44 lnches ln len~th and mounted ln 3uch a way as to have a gap of 4 inche~ between the bottom of the cyllnder and the bottom of the diaphragm. Thls gap was provided for the 8~ses ~o ~low fro~
one chamber to the other as the gas flowed downwardly in the first chamber and upwardly in the second chamber. Four indY~ below the flange of this second cyllnder ewo ports, an entry port and an exhaust port, were provided in such 9 way as to have the entry port in the first chamber and the exhaust port ln the second chamber.
A ~-foot plpe ful~y insulsted interconnected the exhaust port of the first cylinder to the entry port of the second cyllnder, the reason for such in~ulatlon being the preventlon of hydrocarbon condensation. A two-foot long pipe equlpped wlth a control valve was mounted on the exhsu~t port of the second cyllnder, two ~ ~aC~ f k 35~7 ,as sampl~g ports were provided on~ upstream of the second cyllnder ln the 9-foot pipe and the other downstream of the second cyllnder ln the 2-foot p~pe ahead oE the control valve. Pebble llme (CaO~ slzed mlnus 3" to plu9 ~1l was cha~ged in both chambers oE the second cyllnder to two lnche~ below the entry and ex-hnust port~. The pebble lime (CaO) was the same pebble lime as that ~hich 1~
used ln baslc oxygen ~teel~aklng furnaces. A steel cover made of one-inch thick plAte with a gasket was then tl~htly bolted to the flange of the second cyllnder 80 that no gas could escape between the cover and the cyllnder.
A hl~h su~fur Ohlo coal contalnlng 3.2Z ~ulfur(S) ~as charged into the first cyllnder to two-lnche3 below lts exhaust port. A steel cover made of one-inch thick plate wlth a gasket was also tightly bolted to the flange of the first cyllnder.

Operatlon The pebble llme (CaO) in the ~econd cylinder was gradually heated in the absence of oxygen until the temperature of the pebble lime ~CaO) reached 1650F
which took 4 hours:25 mlnute3. After reachlng thiq temperature ln the second cylinder and maintalning same, heat wa~ spplied to the first ln the absence of oxygen, and volatile matter started leavlng the coal at 0 hours:42 mlnutes after start of heat appllcation on the flrst cyllnder.
Observation Rl. Gas leavlng exhaust port of second cyllnder, vlsually clean.
Observatlon 02. Gas sampled up~tream of second cyllnder for hydrogen sulfide (H2S) - - 2.6%.
Observation ~3. Ga~ sampled downstream of ~econd cylinder for hydrogen ~ulfide (H2S) - - 0.05Z.
Ob~ervation ~4. Checked for volatile matter leavlng up~tream of cylinder - - abundant evolution of yello~ish fo~l g~8.

~i3~

Observation 05. Gas le~ving e~haust port of ~econd cylinder, checked for condensables (tar0, oll NH3, etc.) - ~ non-detectable.
Observatlon 06. Gas sampled up stream of second cyllnder for hydro~en sulfide (H2S) agaln - - 1.5X.
Observatlon ~7. Ga~ sampllng of down~trea~ of second cyllnder for hydrogen sulfide (H2S) a~aln - - non-detectable.
Qbservation ~8. ~-foot pipe disconnected, and cover of ~econd cylinder removed - - Calcium oxide (CaO) converted to calcium ~ulEide (CaS) and im-pregnated with carbon (C) all the way through each pebble.
Observation ~9. Carbon (C) impregnated calclum sulfide (CaS) stronger than unused pebble lime (CaO).
Observatlon OlO. Cover replaced on second cylinder and re-sealed. Air was blown in opposite direction of coal-gas flow; namely, from exhaust port through the calcium sulfide (CaS) and out of entry port, elemental sulfur(S) in va-por form and carbon dioxide ~:CO2) released from bed. Bed temperature rose to 2745F~
Observatlon #11. Cover of second cylinder removed - - Calcium sulfide (CaS) converted back to calcium oxide (CaO), thusly regenerated in-sltu.

Conclusion The~efore as long as the temperature of the llme (CaO) is malntained above the cracking temperature of the hydrocarbons contained ln the raw-gas~
the hydrocarbons will crack and will deposit carbon (C) unifor~ly onto, lnto and throughoue the llme (CaO) whlch is very porous. Such porosity is an in-herent result of calclnatlon of limestone (CaC03~ into lime (CaO). Hot calcium oxide (CaO) is very reactive wlth hot hydrogen sulfide (H2S~. Since the raw-gas ls hot when lt lesves the gaslflcatlon chamber and 'llters through hot cal-cium oxide (CaO), calcium sulfide is immediately formed. This simultaneous de-posit of carbon (C) by cracking and the collection of the sulfur by reaction, provides an efficient and dry clean-up system no~ only of the tar, oil and other hydrocarbons but also o the sulfur from the raw-gas.

~3~

In the re~eneration step, the spent llme (CaS) is left in-situ and the oxygen in the form of oxygen alone or ln the form of air reacts wlth the calcium sulfide (CaS) to form calcium oxide (CaO) and sulfur dioxide (SO2) but the sulfur dioxide at a temperature above the ignition polnt of carbon (C) reacts wi~h the lmpregnated carbon (C) to result in the simultaneous regener-atlon of the lime (CaO) and the formation of elemental sulfur in vapor for~
in one cingle step. In addition to the formation of elemental sulfur(S), carbon dloxide (CO2) is also evolved. The elemental sulfur(S) and carbon dioxide (CO2) are collected, cooled and separated.

For the commercial application of the present invention, it is proposed to use two beds of pebble lime (CaO) simultaneously but sequenced in such a way as to have the first bed for carbon (C) deposit and sulfur(S) collection by the hot lime (CaO) and the second bed for regeneration of the lime (CaO) and the formation of the elemental sulfur(S), the raw-gas being ~irected through the first bed, and oxygen or air blown through the second bed in the opposite direction of the raw-gas. Once the calcium oxide (CaO) in the first bed is spent, namely converted to calcium sulfide (CaS)~ the raw-gas is directed through the second bed and the oxygen or air blown through the first bed in the opposite direction of the raw-gas; such alternate use of the beds continuing between sulfur(S-) collection and regeneration as a mode of operation.

The instant invention is not limited to only the clean-up of a gas contain-ing hydrogen sulfide (H2S); it can be used for the clean-up of other gases con-taining components of sulfur(S).

All in all it is submitted that the present invention provides a superior and economical method of efficiently cleaning raw-gas for example coal gas, syngas, etc., which regenerates the desulfurizer (CaO) while forming elemental sulfur(S) in-situ.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of processing a gas containing a compound of sulfur and hydrocarbon material, comprising a first step of directing the gas through a fixed bed of hot lime material whose temperature is maintained above the cracking temperature of the hydrocarbon material to simultaneously (i) react the compound of sulfur with the hot lime to produce calcium sulfide in the fixed bed and (ii) crack the hydrocarbon material while impregnating the calcium sulfide with carbon in the same fixed bed, and a second step of reacting the carbon impregnated calcium sulfide with a gas containing oxygen in order to (i) convert said calcium sulfide back to hot lime through regeneration and (ii) produce elemental sulfur.

2. The method as set forth in claim 1 wherein said gas containing oxygen is further characterized as being air.

3. The method as set forth in claim 1 wherein said gas containing oxygen is further characterized as being oxygen which is substantially pure.

4. The method as set forth in claim 1 wherein said second step of reacting the carbon impregnated calcium sulfide with a gas containing oxygen in order to (i) convert said calcium sulfide back to hot lime through regeneration and (ii) produce elemental sulfur is further characterized by the step of extracting said elemental sulfur in vapor form and subsequently condensing it.

5. The method as set forth in claim 4 wherein the step of extracting said elemental sulfur in vapor form and subsequently condensing it is further characterized by the step of separating said elemental sulfur from non-condensibles and collecting said non-condensibles.

6. The invention as set forth in claim 1 wherein said second step of reacting the carbon impregnated calcium sulfide with a gas containing oxygen is further characterized by the step of passing the gas containing oxygen in the opposite direction of the direction of the passage of said gas containing a compound of sulfur and hydrocarbon material.

7. The invention as set forth in claim 6 including the steps of providing at least two fixed beds of pebble lime, directing the gas containing a compound of sulfur and a hydrocarbon material through said one of the beds of hot lime to desulfurize and crack hydrocarbons in said one bed, and then directing the gas containing a compound of sulfur and a hydrocarbon material through another bed of lime and reacting said one bed with oxygen to generate elemental sulfur and to regenerate said one bed, thus allowing the reactions for desulfurization and cracking of the hydrocarbons and the reactions for regeneration and production of elemental sulfur to be alternated between said pair of beds.

8. The method as set forth in claim 1 wherein said gas containing a compound of sulfur and a hydrocarbon comprises a coal gas.

9. The method as set forth in claim 1 wherein said bed of lime comprises a bed of pebble lime.

10. The method as set forth in claim 1 wherein said hydrocarbon material comprises a tar.