GB2191715A

GB2191715A - Method and apparatus for dedusting and desulfurizing gas

Info

Publication number: GB2191715A
Application number: GB8713004A
Authority: GB
Inventors: Glenn E Hoffman
Original assignee: Midrex International BV Rotterdam Zurich Branch
Current assignee: Midrex International BV Rotterdam Zurich Branch
Priority date: 1986-06-17
Filing date: 1987-06-03
Publication date: 1987-12-23
Anticipated expiration: 2007-06-03
Also published as: DE3719549A1; GB8713004D0; GB2191715B

Description

GB 2 191 715 A 1 SPECIFICATION desired,thefuel gas leaving the second

shaft reactor and fine limestone may be introduced into a hot Method and apparatus for dedusting and cyclone to provide additional desulfurization and desulfurizing gases cleaning.

70 Synthetic fuel gases have also been precooled Backgroundof the invention using various techniques. Typically, the hotfuel gas

The present invention relates to a method and has been mixed with a coolertempering gas to lower apparatus for removing solids and sulfurfrom hot its temperature sufficientlyto permitthe solids and gases. sulfurto be conveniently removed. Generally, these Methods and systems for dedusting and 75 techniques adversely impacted the overall efficiency clesulfurizing fuel gases are well known in the art. It is of the system in that the temperature reducing known, for example, to utilize cyclone cleaners to technique invariably resulted in an irrecoverable remove dustand solidsfrom synthetic gas produced energyloss.

by gasification of coal. Utilizing cyclone cleanersfor Shaft dust removal systems have a longer life dust removal requires that the temperature of the 80 expectancy than hot cyclones, as the gas and fuel gas not exceed 11 WC, which is the upper particulate velocities are substantially lower, which temperature limit of available cyclones. Typically, allows highertemperature gas introduction to the the temperature of fuel gas produced by gasifying shaftwithout concomitant erosion of refractories fossil fuels, such as coal, exceeds the operating and walls of the shaft.

temperature range of typical hotcyclones. 85 Additionally, it iswell known thatfuel gases Summary of the invention containing sulfurand solids can be desulfurized and This invention provides apparatus and a method the solids removed by introducing the fuel gas into a for removing solids and sulfurfrom a hot fuel gas.

shaft reactor in counterf low relationship to a burden Gross solid removal (removal of the larger solids and which can include such materials as limestone and 90 a portion of the smaller solids) is provided by iron oxide. introducing hotfuel gas into a first shaft reactor Gasifiers utilizing coal generate fuel gases usually charged with refractory pellets, large limestone or having a high concentration of solids and dust. dolomitic limestone particles, or a combination Introducing gas streams having a high concentration thereottoform a burden. As the hotfuei gasfiows of dust and solids into shaftfurnace reactors such as 95 through the burden, solids in theform of the Midrex Shaft Reactorfor Producing Metallized particulates, dust, and alkaline substances Iron, may resuR in a variety of undesirable accumulate on the surface of the materials conditions including a high probability of comprising the burden and in the burden interstices.

accumulation of dust, which "plugs" the burden A portion of the burden is periodically discharged including a high probability of accumulation of dust, 100 and replenished, removing the solids and alkaline which "plugs" the burden preventing the normal substanceswhich either adhereto the burden counterflow between the burden and the fuel gas, materials or are trapped in the interstices between and impedes normal burden descentthrough the the solids forming the burden.

furnace. As a result, techniques and apparatus for Hotfuel gas from the first shaft reactor is removing dust interposed between the gasifier and 105 introduced into a second shaft reactorwhich is the shaft reactorare desirable. charged with a material that includes limestone. As Interposing hot cyclones between the gasifierand the hotfuel gas passes upwardlythrough the burden the shaft reactor is one wayof removing such solids in the second shaft reactor, portions of the limestone and dust. Such a technique is illustrated in U.S. are calcined. Sulfur components of thefuel gas Patent Number 4,260,412. The use of hotcyclones 110 reactswith the calcined limestoneto form CaS, may require precooling of the hotfuel gas priorto thereby removing sulfurfrom thefuel gas stream.

introduction intothe cyclone. In orderto achieve Additionally, solids carried overfrom the firstshaft high efficiency in a cyclone, pa rticu late velocities are reactortend to adhereto the surface of the calcined extremely high, with the resuitthatthe particulates limestone and other materials comprising the cause high erosion of the cyclone wall, and often 115 burden. Portions of the burden, including the erosion of the cyclone throat. At extremely high limestone, calcined limestone, CaS and other burden temperatures (above 11 WC), high temperature materials are discharged from the second shaft refractories are required,which do not resist high reactorasthe burden is replenished in accordance particulate velocities well. Thus, high erosion of the with a predetermined schedulethus removing the cyclonewali and throat continuesto be a problem. 120 sulfurand the solidsfrom the second shaft reactor Astaught bythis invention, solidstend to adhere and the first gas stream. (Other burden materials to the surface of the burden materials or solids are which include sulfur removing agents such as entrapped in the bed interstices to provide removal dolomite may also be used.) of a portion of the solids. Shaft reactors may be used As the limestone burden in the second shaft for gross solids removal using a burden consisting 125 reactor moves, dust may be liberated and carried primarily of refractory materials which are over into the output of this reactor. As an option, a recirculated while hot. This reduces energy losses. two-stage hot cyclone is provided to remove The partially cleaned fuel gas is introduced into a additional dust and other solids. Additional second shaft reactor and reacts with the burden desulfurization may also be accomplished by therein to remove sulfur and additional solids. If 130 introducing fine limestone or other sulfur reducing 2 GB 2 191 715 A 2 agents into these cyclones. through the bu rden 26, the fuel gas flows through an More specifically, the preferred embodiment of the outlet pipe 28 and is introduced through a bustle and invention comprises apparatus and a method for tuyere system 30 into a second reactorfurnace 32, removing solids and sulfurfrom a hotfuel gas containing burden 34. Solids, as well as interaction stream using a two-stage process in which the hot 70 with the fuel gas, contaminate the materials of fuel gas is introduced into a shaft reactor in burdens 26 and 34 as the fuel gas flows counterflow relationship to a burden including therethrough. This contamination necessitates the refractory pellets, large limestone particles ora periodic replenishment of the materials comprising combination thereof to remove solids and alkalis. the burdens 26 and 34.

After passing through thefirst shaft reactor, the hot 75 More specifically, in the first reactorfurnace 22, fuel gas is introduced into a second shaft reactor in solids, such as dust and alkalis, adhere to the counterflow relationship to a second burden which surfaces of the refractory pellets or large limestone includes calcined limestone. Sulfur containing particlesfor removal asthe burden 26 is replenished.

components of thefuel gas interactwith the calcined Partially cleaned fuel gasfrom thefirst reactor22 limestonetoform solids,thus removing the sulfur 80 flowsthrough pipe 28 as discussed above and into from thefuei gas stream. Additional desulfurization the bustle and tuyere system 30 of the second shaft may be provided by introducing the hotfuel gas reactor 32. A second burden 34 in the shaft reactor32 stream from the second furnace and fine limestone includes calcined limestone, which reacts with the into a hot cyclone. sulfur components ofthe fuel gas to form solid CaS.

85 Additional solids, not removed by or carried over Objects of the invention from thefirst reactor 22, will also tend to adhere to It is an object of this invention to provide an the calcined limestone comprising the burden 34.

economical and energy efficient method for These solids and the CaS are removed as the burden removing solids and suffurfrom a hotfuel gas. 34 is replenished. Hotclean fuel gas exitsfromthe It is anotherobject of this invention to provide a 90 second shaft reactor32 through a suitable pipe 36for method and apparatusfor removing sulfurand use, as desired. In orderto assurethatthe hotfuel solidsfrom afuel gas utilizing shaft reactors. gasflowsthrough the first and second reactors 22 It is also an objectof this invention to provide an and 32 atthe desired rate and quantities, it is efficientand economical method and apparatusfor necessary thatthe system be pressurized.

removing solids and sulfurfrom a hotfuel gas in 95 In charging thefirst reactor22, hot recycled which largersolids are removed by introducing the refractory pellets, and alternatively limestone, are hotfuei gas into afirstshaft reactor charged with preferablyfed to a screening station 50. In orderto refactor materials and the sulfur is removed by flow conveniently through thefirst shaft reactor22, introducing the hotfuel gas into a second shaft the burden materials must be largerthan a reactorwhich is charged with a burden that includes 100 preselected size, because high levels of fine calcined limestone. particulate matter in a mixed size burden tendsto clog shaft reactors and impede burden movement by Brief description of the accompanying drawings promoting "bridging". Properlysized refractory

Figure 1 is a schematic diagram of apparatusfor pellets, and limestone, if desired, from the screening cleaning and desulfurizing a hotfuel gas in which a 105 station 50 arefed into a feed hopper 52through a hotfuel gasto be cleaned and desulfurized flows in a suitable pipe 56.

stream through first and second shaft reactors, the A charging chamber 59 is positioned between first first primarily removing large solids, the second and second charging gates 58 and 60. Feed hopper primarily removing sulfur. 52, charging gate 58, charging chamber 59, and Figure2 is a schematic diagram of a second 110 charging gate 60 are supported by a feed pipe 62 and embodiment of the invention illustrated in Figure 1 attached therebyto the upper end of the first shaft which includes additional sulfur removing reactor 22. A discharge chamber 80 is positioned apparatus. between first and second discharged gates 82 and Figure 3 is a flow diagram illustrating a third 84, with discharge gate 82 in turn being attached to embodiment of the invention using three shaft 115 the discharge pipe 86 of the first particle reactor22.

reactors permitting the burden in thefirst shaft A second charging chamber 90 is positioned reactorto be maintained static during use. between third and fourth charging gates 88 and 92.

Figure 4 is a flow diagram illustrating a fourth Supportforthe feed hopper 86, charging gates 88 embodiment of the invention in which the burdens in and 92, and charging chamber 90 is provided by a all of the reactors are maintained static during use. 120 feed pipe 96 attached to the upperend of the shaft reactor32. A discharge chamber 102 is positioned Detaileddescription of the invention between third and fourth discharge gates 104 and

Referring nowto the embodiment of the invention 106, and attached to the lower end of the shaft illustrated in Figure 1, a hotfuel gas stream is reactor32 by a discharge pipe 108.

introduced through a bustle and tuyere system 20 125 The initial burdens 26 and 34 in the firstand into afirstshaft reactor22from a suitable input pipe second shaft reactors 22 and 32 can be established 24. The hotfuel gas flows upwardlythrough a by closing the first, second, third and fourth packed bed burden 26 within the reactor, which discharge gates 84,86,106 and 108, opening thefirst, includes refractory pellets, limestone, or a mixture of second, third and fourth charging gates 58,60,88, refractory pellets and limestone. After passing 130 and 92, and pouring suitable quantities and types of 3 GB 2 191 715 A 3 charging materials into feed hoppers 52 and 86. 80. Burden materials discharged from the second During operation, the charge and discharge gates shaft reactor32 in replenishing burden 34 are must be operated in a sequence which permits the removed and discharged as solid waste by a suitable burdens 26 and 34to be replenished, while thefirst conveyor105.

and second shaft reactors remain pressurized. 70 As previously described, the first vertical reactor For example, in replenishing the burden 26 in the 22 is charged using refractory material recycled from first reactor 22, charge gate 60 is closed, sealing the the screening station 110 through screening station upper end of the vertical reactor 22 to maintain 50 and feed hopper 52. Similarly, the second vertical pressure therein. Hot refractory pellets and other reactor32 is charged with either limestone or a suitable burden materials from the screening station 75 mixture of iron oxide and limestone by supplying are fed into the feed hopper 52 by pipe 56. The these burden materials to the feed hopper 86 and uppercharging gate 58 is opened, permitting the utilizing thefeed gates 88 and 92 and feed chamber burden materials to flow by gravity into charging 90 to maintain the second vertical reactor 32 in a chamber 59. Afterthe charging chamber 59 isfilled pressurized state while the burden 34 is being to a suitable level, the upper charging gate 58 is 80 replenished.

closed andthe lower charging gate is opened, As described above, the first vertical reactor 22 permitting burden materials to flowfrom the may be charged with refractory pellets, large charging chamber 59 into thefirst reactor 22 to limestone particles or a mixturethereof, and the replenish the burden 26. second vertical reactor32 charged with burden Portions of the burden 26 are discharged through 85 materials which include limestone to remove solids the discharge pipe 86, upper discharge gate 82, and sulfurfrom the hotfuei gas. As an alternative, discharge chamber 80 and lower discharge gate 84, the second vertical reactor 32 may be charged with in a similarfashion. That is, to discharge a portion of limestone, dolomitic limestone or a mixturethereof.

the burden 26, the lower discharge gate 84 is closed or a mixture of iron oxide and limestone and/or and the upper discharge gate 82 is opened, 90 dolomite. If a charge consisting of a mixture of iron permitting burden materials to flow through the oxideand limestone isused in the second vertical discharge pipe 86 and fill the discharge chamber 80. reactor 32, the fuel gas introduced intothesecond After discharge chamber 80 isfilled, upperdischarge vertical reactor32 bywayof the bustle andtuyere gate82isclosed andthe lowerdischarge gate84is system30will react with the iron oxideto produce opened, permitting portions of the burden 26to be 95 metallized iron. Underthese conditions, the burden discharged from the discharge chamber80 intothe material discharged from the second vertical reactor recycling screening station 110. wherein hot 32 will consist of a mixture of calcium sulfide, refractory pellets are separated from the other metallized iron and other solid materials. These burden materials. The hot refractory pellets are materials can be readily separated from each other recycled to the first screening station 50 to be used as 100 by utilizing magnetic techniques to recoverthe burden materials to replenish the burden 26. The metallized iron.

remainder of the discharged burden materials are The sulfur-removing agent in the second reactor removed from shaftfurnace 22 as solid waste. has an average particle diameter of at leastO.5 Dueto the requirement for continuously centimeters. If the particle size istoo small,the bed maintaining the shaft reactors 22 and 32, pressurized 105 will fluidize. The preferred average particle diameter burden 26 cannot continuously flow downward is lessthan 3.0 centimeters. A limestone (or through thefirst shaft reactor 22. This is becausethe dolomitic limestone) average particle diameter of at upper discharge gate 82 must at least be closed least 0.5 centimeters is desirable to effect high during the period when the discharge chamber 80 is utilization of the lime to form calcium sulfide, aswell being emptied. Closing this discharge gate prohibits 110 as requiring short residence times of the burden in discharge of the burden materials through the the shaft reactor, which is amenable to high levels of discharge pipe 86. However, the periods during dust removal from the gas stream. An average which this gate is closed may be selected to be particle diameter greaterthan 3 centimeters renders sufficiently shortthatthe burden 26 essentially the process uneconomical, as short burden moves continuously downward through the first 115 residence times required for good dust removal reactor 22. Alternatively, the burden 26 can remain result in low levels of lime utilization.

static as will be subsequently described. The alternative embodiment of Figure 2 is identical Burden 34 in the second reactor 32 is replenished to the embodiment described in Figure 1, with the by utilizing a charging sequence similarto that exception that additional apparatus for removal of described with reference to the first reactor 22. That 120 solids and desulfurization is provided. This is.the uppercharging gate 88, charging chamber90, additional apparatus, enclosed within dotted line and lower charging gate 92 are operating in a 120, includes first and second cyclones 122 and 124.

sequence similarto the charging process previously Hotfuel gas flows from the top of the second vertical described forthe first reactor 22. Similarly, portions reactor 32 to the first cyclone 122 through discharge of the burden 34 are removed from the second 125 pipe 36. Solids removed by either pyclone 122 or 124 reactor 32 utilizing the discharge chamber 102 and are ultimately discharged by a waste discharge pipe upper and lower discharge gates 104 and 106 in a 126 and discarded as solid waste.

fashion very similarto that previously described with The gaseous output of the first cyclone 122 flows reference to the firstvertical reactor 22 and discharge through a pipe 128 to the input of the second cyclone gates 82,84 in conjunction with discharge chamber 130124. Clean and desulfurized fuel gas from the second 4 GB 2 191715 A 4 cyclone 124flowsthrough an exit pipeforfurther previously discussed.

use, as desired.

Fine particulate solids, including limestone, from Summary of the achievement of the objects of the the screening stage 50 are coupled by a suitable pipe invention 130to the input of the second cyclone 124. Portions 70 From the foregoing, it is readily apparentthat 1 of this limestone combine with the remaining sulfur have provided an economical and energy efficient contained in the fuel gasto form solid CaS. The CaS, method for removing solids and sulfurfrorn a hot excess limestone, and other solids are discharged fuel gas, which utilizes shaft reactors.

through discharge pipe 132 and combined with Since those skilled in the art can readily determine gaseous output of the second vertical reactor 32to 75 other possible alternative embodiments, this form the input materials to the first cyclone 22. These invention is to be limited only bythe scope of the solids are ultimately removed from thefuel gas following claims.

stream by the first cyclone 122, as previously

Claims

described. CLAIMS

An embodiment of the invention which permits 80 the burden materials in the first shaft reactorto 1. A method for cleaning a fuel gas in which the remain static during the time that the fuel gas is fuel gas passes through a first burden in a first shaft flowing therethrough is illustrated by Figure 3. This reactor to provide gross solid removal, through a embodiment utilizes three shaft reactors, 110, 112, second burden in a second shaft reactorto provide and 114. Rawfuel gas is introduced through a pipe 85 sulfur removal and fine solid removal, comprising and alternatively directed to either shaft reactor 110 the steps of:

or 112 through valves 118 or 120. Fuel gas leaving the (a) introducing fuel gas into a f irst shaft furnace shaft reactors 110 and 112 is coupled through third having a packed bed burden therein, said burden orfourth valves 122 or 124to the input of thethird including pellets of refractory material; shaftfurnace 114. 90 (b) passing said fuel gasthrough said burden to In operation, the third shaftfurnace 114 is operated cause solids in said fuel gasto adhereto the surface in a manner identical tothe second shaft reactor32, of said pellets of refractory material; previously described with referenceto Figure 1. The (c) introducing said fuel gas into a second shaft first and second shaft reactors of Figure 3, reactors reactor having a second burden therein, including a 110 and 112, are charged with materials identical to 95 sulfur removing agent; shaftfurnace 22, with the fuel gas being directed (d) passing said fuel gas through said sulfur through these shaft reactors through the valves 118 removing agentto cause sulfur components of said and 120 in such mannerthat no fuel gasfiows gas to react with said sulfur removing agent to through the shaft reactorwhile its burden is being remove sulfurfrom said fuel gas; and replenished. This reduces dust carryover during 100 (e) removing said dedusted, desulfurized fuel gas periods when the burdens are being replenished. from said second reactor.

The embodiment of the invention illustrated in
2. A method for cleaning a fuel gas in accordance Figure 4 utilizes four shaft reactors 140,142,144, and with claim 1 further comprising repeatedly removing 146. Raw fuel gas is introduced into shaft reactors portions of said hot refractory pellets comprising 140 and 144through first and second valves 148 and 105 said burden, removing solids adhering to the surface 150. Fuel gas leaves the shaft reactor 142 and 146 thereof and recycling said portions of said hot through valves 152 and 154 and pipe 156. In refractory pellets to replenish the burden of said first operation, shaft reactors 144 and 146 are operated in reactorto reduce the loss of energy associated with a manner identical tofurnaces 22 and 32 to clean and replenishing said first burden.

desulfurize fuel gas,while shaft reactors 140 and 142 110
3. A method for cleaning a fuel gas in accordance are being recharged to replenish their burdens. with claim 1 or 2, further comprising the additional Similarly, shaft reactors 140 and 142 are operated to step of introducing said gas into a cyclone cleanerto clean and desulfurize fuel gas while shaft reactors provide an additional stage of solid removal.

144 and 146 are being recharged to replenish their
4. A method for cleaning a fuel gas in accordance burdens. 115 with claim 1, 2 or 3, further comprising mixing This arrangement provides an additional limestone and iron oxide in predetermined ratios to reduction of the dust and solids carryoverfrom the form at least part of said second burden.

shaft reactors to the fuel gas since no shaft reactor is
5. A method for cleaning a fuel gas in accordance operated to clean or desulfurize fuel gas in those with claims 3 and 4, further comprising introducing intervals during which their burdens are being 120 limestone into said cyclone to remove additional replenished. sulfurf rom said fuel gas.

In any of the above discussed embodiments,the
6. A method of cleaning a fuel gas in accordance refractory materials comprising burden 26 may be with claim 5, further comprision discharging and alumina spheres having a diameter greaterthan one separating portions of said second burden to recover half inch. Materials of this size prevent plugging of 125 metallized iron and waste.

the burden 26 and can be easily separated from dust
7. A method according to any preceding claim, and other contaminants adhering thereto by a wherein said sulfur removing agent has an average conventional screening process in station 110 while particle diameter of at least 0.5 centimeters.

the refractory materials are hot. Recycling the
8. A method according to any preceding claim, refractory pellets while hot conserves energy, as 130 wherein said sulfur removing agent has an average GB 2 191715 A 5 particle diameter of less than 3.0 centi meters.
9. A method for cleaning a fuel gas in accordance with any preceding claim, wherein said first burden includes limestone, dolomite, or a mixture thereof.
10. Apparatus for cleaning and desulfurizing a fuel gas stream, comprising in combination:

(a) apparatus for removing solids from said fuel gas stream comprising a first shaft reactor into which said fuel gas stream is introduced in counterflow relation to a burden comprising materials selected to promote adhesion between solids contained in said fuel gas stream and said burden materials; (b) meansfor recycling a portion of the materials comprising said burden wherebysolids adhering to the recycled burden materials are removed and energy losses resulting from cooling of the recycled burden materials are reduced; (c) meansfor directing said fuel gas stream through a second shaft reactorto reactsulfur contained in said fuel gas stream with burden materials to produce solids containing sulfur, thereby removing sulfurfrorn said fuel gas stream.
11. Apparatus for cleaning and desulfurizing a fuel gas stream in accordance with claim 10, wherein said burden includes refractory pellets of a predetermined size.
12. Apparatus for cleaning and desulfurizing a fuel gas stream in accordance with claim 11, wherein said refractory pellets are alumina spheres.
13. Apparatus for cleaning and desulfurizi ng a fuel gas stream in accordance with claim 11 or 12, wherein said refractory pellets have a diameter of at least one centi meter.
14. The methods for cleaning a fuel gas substantially as hereinbefore described.
15. Apparatus for cleaning a fuel gas, substantially as hereinbefore described with reference to the accompanying drawings.

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Published byThe Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies maybe obtained.