Safety research in the gasification process of novel multi-thermal-source coal gasifier

Availableonlineatwww.sciencedirectcomMINING°° ScienceDirectSCIENCE ANDTECHNOLOGYELSEVIERMining Science and Technology 19(2009)0210-0215www.elseviercom/locate/jcumtSafety research in the gasification process of novelmulti-thermal-source coal gasifierTIAN Yu-xian, WU Min-huan, WANG Xiao-gang, ZHANG Ya-ping,QIANG Jun-feng, tiaN Xin-wei, WANG Xi-lianCollege of Sciences, Xi' an University of Science Technology, Xi'an, Shaanxi 710054, ChinaAbstract: In order to collect the gas safely produced in the gasification process of the novel multi thermal-source coal gasifier,based on its gasification skill and the characteristics of the products, this paper analyzes the possible dangers in the gasificationprocess, devises the gasifier eruption and explosion experiments, explores the conditions of gasifier eruption and gas explosion,studies their effects on the gasification process and establishes safe operation measures. Gasifier eruption hazard occurs easily inthe gasification process of one-thermal-source coal gasifier when Msio is far higher than that in the normal adjuvant. the gaspermeability in the gasifier is not the same and the power supply is too large. However, similar conditions in the gasification ofmulti-thermal-source coal gasifier do not produce a gasifier eruption accident so easily. When it erupts, the gasifier shouldstopped and then cooled down naturally or inert gas can be sprayed on the gasifier to cool it off, and thus gas explosion can bevoided. There is a possibility of direct gas explosion, but it can be avoided when the gas in the gas collecting space is replacedslowly by supplying a small amount of power or the inert gas fills the space in the previous gasification. The time a fire is lit isstrictly controlled, the gas is drawn in by using the aspirator pump, and the gasifier pressure is kept in the state of micro-positivepressure in the middle and later gasification process. The conclusion is that the gasification process of the novel multi-thermal-source coal gasifier is safe according to normal operation rulesKeywords: coal gasification; novel multi-thermal-source coal gasifier gas explosion; gasifier eruption1 Introduction2 Possible dangersGas is mainly composed of CO, H2 and CH be- 2.1 Gas explosionlonging to a mixed polybasic explosive gas. In rela- Gas explosion refers to a phenomenon where thetive industries and mines, a mixed polybasic gas ex- gas is combusted, expanding intensely in an instant,plosion hazard is characteristic of frequent and rereleasing much energy, and producing a loud sound,peated occurrences which seriously threaten theall at the same time. This phenomenon must conformsafety of people's lives and property. Therefore, it is to three conditions: 1)the combustible gas has a cer-one of many issues to address and it is also worth- tain density and a certain amount of air are mixedwhile to take effective precautions to prevent a mixedgas explosion and minimize its destruction" In re- and air completely fill an airtight container, and 3)thecent years, scholars at home and abroad have done a airtight container is heated up, and none of these con-great amount of research and received much achieve-ditions are indispensible. Seen from the supervisionment regarding solo gas explosions and mixed polyof the gas components produced in the multi-therbasic gas explosions from their use of experimentmal-source coal gasification -, the gas collectingtheories and numerical simulations 24). Nevertheless, space in the gasifier is full of air before gasification.there were almost no reports regarding the safety in a small amount of power is provided and the gasifi-the gasification process of different gasifiers. So in cation begins. The temperature is gradually increased,this paper, experimental studies were carried outthe material is heated and dried, and the free water isabout safety in the gasification of the newly-explored released in the form of H2Oug. Then, as the temperamulti-thermal-source coal gasifier of our research turegroup5, and these studies will guide the normal optilesH中国煤化工 e, and vola-O, CO, CH4, N2,ration of the gasifier and its use in industCNMHGmixed gas in theroject 50174046 supported by the National Natural Science Foundation of ChinaCorresponding author. Tel: +86-29-85583133: E-mail address: tyx@xust.edu.nTIAN Yu-xian et alSafety research in the gasification process of novel multi-thermal-source coal gasifierspace is air, H2O(g) CO, CO2, CH4, N2, H2, O2 and anyone. Therefore, an experiment about gasifierNH3, whose main components are CO, N2 and O2, eruption in a multi-thermal-source coal gasifier wawith H in a smaller amount, and an even smaller devised specifically to explore the conditions of gasiamount of CH4. Then as time progresses during gasi- fier eruption and their effects on the whole gasificafication, a portion of air is removed, a portion of tioncombustible gas is increased, and the gas produced inthe gasification replaces the air a little at a time. Since 3 Gasifier eruption experimentCO. H2, CH4 are combustible and explosive gases,and their explosion limits(percent by volume)in the 3.1 Experimental planair are I2.5%-76%,8.27%~68.8%and6.3%~12.8%,respectively, even a little carelessness would cause aThe 20% fine quartz sand was added to the quartzwith the graininess of 0-8 mm and the proportion ofBecause the gas produced in the lab is released di- SiO was 98%o, and then it was blended with the anrectly outside the gasifier and burned up, the gasthracite, whose chemical components could be seenshould be collected in regular intervals to analyze its in Table 1. Its graininess was 0-4 mm according tocomponents. It is especially important that the fire beformula of Mc/Msio 0.61, among which Sionlit at just the right moment and the gasifier's pressure was far higher than that in normal adjuvant;and thenbe supervised, both of which should be watched and put into the gasifiers as shown in Fig. I after ball milldocumented carefullymixing about 2 hours. The size of each gasifier was560mm×740mm×1140mm. The furmace capacity2.2 Gas explosion caused by gasifier eruptionwas 300 kg. The size of each heat carrier wasGasifier eruption is a phenomenon where the gas in mmx40 mmx60 mm. The thickness of the material onthe gasifier is not released evenly from every place in the upper part of each heat carrier was 250 mm,andthe material, but erupted intensively from one or sev-n the bottom was 490 mm. with the heat carriereral places with some graphite, by-product SiC and right above, an empty graphite pipe was insertedmaterial. There are a few reasons gasifier eruptionwhose diameter was 40 mm and heheight was 200 mm.found in one-thermal-source coal gasification: there is A certain ratio volume of pyrolignite of lime wastoo much Sio, in the material: the ventilation of the added into the pipe by the adjuvants mentionedmaterial was not even; there was too much powerthe high surface load of the heat carrier; the graini-Table 1 Chemical components of anthraciteness of the graphite was not even or there was notomponentsenough purity to cause the heat load to not be even;here was too much big coal graininess or smallgraininess in the volume percent of material and itsauxiliary material pyrolignite of lime was not properThere were three experimental plans. First, theor the mixture of both was not even; the crudeness of gasification was carried out after the gas gatheringmaterial in the upper part of the heat carrier and in system of the one-thermal-source coal gasifier thatother parts was not combined properly and seemed to erupted easily, and then the gas on the surface of thebe too thin: the thickness of insulated material in two material would be burned off to increase the power tocharges was not enough, and so on. All these reasonserupt the gasifier(Fig. la). Second, the gasificationwas also carried out in the one-thermal- source coaloften resulted in high temperatures and moreover it gasifier, but the gas was collected, the volume pro-tion more easily when the heat couldn' t be released in portion of the phrolignite of lime in the graphite pipea short amount of timeand the supply power were changed, then the gasifieOn the other hand. in the multi-thermal-source coaleruption phenomenon was be observed through thegasification,the experiment showed that gasifier quartz window(30 mm) which was attached toeruption did not take place easily. However, in practhe gas trap(Fig. 1b). And third, based on the ex-tical gasification, because of such reasons as workers, perimental results of the second plan, a gasifier erucarelessness, the process of material loading, or un-ton experiment was devised using a double-thermal-usual power service, then the gasifier eruption would source coal gasifier (two heat carriers)and in theappear possible. If there was strong gasifier eruption. course of the gasifier eruption a variety of phenomenathe high temperature gas-flow would erupt with the would also be observed through the quartz windowheated material from the gas collecting space, which(Fig. Ic). In all three plans, the gas trap waswould probably pull the gas trap open or even tear itaboV凵中国煤化 Tterial surface, thecausing the quick mixture and combustion between-O mm, and the gasthe gas from the gasifier and the air outside the gasi- PCNMHGwas supervised byfier, or leading to the explosion of the whole gasifier. using a differential U-tube. In principle, the supplyMining Science and TechnologyVol 19 No. 2and within two hours before the reaction a small from the blow-off pipe, and at last, it was burned offamount of power(less than 40 kw) was supplied and two hours later in Fig. Ib and Fig. Ic.ncreased gradually. Gas was guided to the outside×8XXX日(c)The third planFig. 1 Experimental equipment of gasifier eruptionO Heat carrier;② Graphite pipe;③ Material④ Fumace wal:⑥ Differential U-tube;⑥ Blow-off pipe;⑦ Protective cover;⑥ Gas trap;,@ Quartz windowcould not be seen in the gas trap, indicating there wasan extremely small gasifier eruption. If the way theIn the one-thermal-source gasification, when the material was loaded and the power supply wasgas was not collected (Fig. la), the gasifier eruption changed, and the plan was still adopted that Msioz waswould take place after increasing the power supply to far higher than that in normal adjuvant, but the 50%103 kw for about 10-15 min, and repeat if the above pyrolignite of lime was supplemented into the graphconditions were satisfied. When erupting, the flame ite pipe, and a little power was supplied in the prevon the material surface became big and unsteady. The ous two hours, then the power was increased to 119exterior color of the flame was yellow and the interior kw and after about 60 min, there would be a brilliantwas white and brilliant. A great deal of black smoke light in the gas trap observed through the quartzwas released from the surface material and some window. That is to say, there would be a great gasifiermelted liquid erupted from the nozzle. After stopping eruption. If a larger amount of power was continuedthe power supply, the nozzle became smaller until it to 131 kw in the gasification, then after 30 min or so,closed slowly, and the flame gradually became short there would be a second gasifier eruption. The testuntil it disappeared. There were one or two hard cavi- would also be repeated if the above conditions wereties of melted liquid created which wrapped up some satisfied. The flame in the exhaust outlet was quickmaterial in the nozzle of the surface material after and steady, the outer surface of the gas trap was boilcooling for a long time. Judging from the color, it was ing hot, and there was a lot of smoke releasing from itfused' quartz sand. If the gasifier eruption took too If the power was shut off at once until the gasifiermuch time, the material would subside. On the other cooled down, no explosion would happen. After thehand, when erupting, if the power was unchanged, gasifier stopped working, two hard earth towers wereWhen one-thermal-source gasification was carried graphite and similar to the ones befor way from thethere would be no explosionalso found, which were 150 mm away from theout and the gas was collected, there would be noHowever, under the same conditions, if gas wasgasifier eruption no matter whether the material collected in the double-thermal-source coal gasificaloading plan was changed and the controlled power tion(Fig. Ic), and the power supply was increasedsupply was less than 50 kw.when the plan was and controlled at about 119 kw for a long time, theadopted where the Msioz was far higher than that in gasification would be carried out smoothly. No clearnormal adjuvant, the 20% pyrolignite of lime was signs of the gasifier eruption would beseen and twosupplemented into the graphite pipe to improve the small towers similar to the above would also be foundventilation there. A little power was given in the pre- which were above the graphite pipe and 130 mm onvious two hours, and then the power was increased the left of it after the gas trap was removed. The towut controlled between 80 kW and 100 kW for a long ers included some fused quartz sand, showing thattime. After stopping the power supply, a small tough thereearth tower would be found in some place about中国煤化工CNMHG400 mmx350 mmx 100 mm and included some fusederuption coula De basically achieved in asilica. Through the quartz window, the brilliant light man-devised experiment. From the comparisons ofTIAN Yu-xian et alafety research in the gasification process of novel multi-thermal-source coal gasifithe experimental results in all plans, such findings combustible mixed gas, no explosion happened becould be seen in Fig. 2: when the one-thermal-source cause there was no fire in the experiment, The gasicoal gasification was carried out without a gas trap, fier eruption appeared after the gasification reachedand when the supply power was increased to that about two hours. At this time, the air was replaced bywhich was three times as equal as the approximate the gas completely, although there was fire and highnormal value, and the gasification lasted 10-15 min temperature produced in the gasifier eruption, whichor so, there would be a great gasifier eruption. when was not within the gas explosion limits. Also, no ex-the one-thermal-source coal gasification was carried plosion took place in the gas collecting space. Afterout but the gas was collected, and when the supply the gasifier eruption, the power was shut off at once.power was increased to that which was four times as The gasifier was cooled down, and disassembled. Itequal to the normal value and the gasification lasted was impossible to result in a gas explosion now.about 60 min, there would be the first great gasifier Usually the gasifier eruption didn't bring about aeruption. Under the same conditions, there wasgas explosion and there was no big danger, but whenclear gasifier eruption in the double-thermal-source a gasifier eruption took place, the heat released wouldoal gasifier. Namely, the time of the gasifier eruption suddenly make the temperature of the gas trap riseas delayed by collecting the gas, and the higher Therefore, in the gasifier eruption, the gas collectingpower supply was called for in the multi-thermal- material, adhesive, and coating had to satisfy highersource coal gasification when the gasifier eruption fire- resistant requirements. The fire-resistant gas col-appeared. Compared with the one-thermal-source lecting material chosen in the experiment could with-coal gasifier, the gasifier eruption conditions in the stand such a high temperature, however, the adhesivemulti-thermal-source coal gasifier were harsher. This and coating could not meet the demands. Thewas because when the power supply was doubled and fire-resistant adhesive lost its gumminess so that theredoubled, the surface load of the heat carriers was gas trap broke under high temperature and the coatingtoo high and the temperature in the one-thermal- crumpled and even dropped, which affected the gassource coal gasifier was unevenly distributed which collecting and the service life of the gas gatheringeasily caused the temperature to be too high and ex- system. So, in order to realize safe gasification, it wascessively centered. And, because it is difficult to re- suggested that the multi-thermal-source coal gasifierlease the heat in a short time, the gasifier eruption be adopted, among which the material proportion, thehazard takes place easily. At the same time, Msio in process of loading material and service of voltagethe material was far higher than that in normalshould be paid attention to avoid the gasifier eruptionvant and 20% fine quartz sand was included. If too If there was a serious gasifier eruption, the powermuch pyrolignite of lime was added into the graphite supply must be cut off, and the gas gathering systempipe, under a high temperature, some of it would be couldn,t be dissembled until the gasifier cooled downburned, causing the ventilation in the gasifier to be naturally or the inert gas was sprayed directly to dieverely uneven. Si(g) and the gas generated in the lute the gas in the nozzle so that it could be cooledgasification were gathered and high pressure resulted. quickly.Once the pressure reached a certain degree, the gaswould erupt intensely and centrally with the graphite,by-product SiC, and some material, thus forming agasifier eruption. However, in the multi-thermalsource coal gasifier, several graphite heat carriersgave out heat at the same time, and the temperaturefield in the gasifier was balanced by the addition ofheat energy multi-thermal sources, which effectivelyscattered the heat and reduced the temperature gradient. Therefore, under the same conditions, the gasifiereruption hazard was cut down greatlyFig. 2 Gasifier eruption curve of one- thermal-source gasifierIn the four devised gasifier eruption experiments, A. The first gasifier eruption of the first plan: B. The first gasifier eruptionthe gasifier eruption did not bring about the gas ex-plosion. But, what did bring about the gas explosion?The reasons were as follows: in the earlier stage of 4 Gas explosion experimentthe reaction there existed some air in the gas collecting space, but because only a small amount of power 4.1 Experimental planwas supplied to gasify the material at this time, the中国煤化工 vised artificiallytemperature in the gasifier was low and the gas pro- accorduced in the gasification replaced the air gradually. TheCNMHGexplosion(Fig 3)s0-8 mm and theWhat's more, in the replacement stage, although the proportion of the SiOz was 98%)was blended withexplosion limits were reached between the air and the anthracite(the chernponents could be seen inTab 1 and its graininess was 0-4 mm)according to leased in the gasification and if the gas pressure herethe formula of Mo/Msioz=0.67. After ball mill mixing was a little higher than that outside of the gasifier,nofor about 30 min, they were loaded into the gasifier matter whether the fire was lit or whether the powershown in Fig 3. In the earlier stage a small amount of supply power was increased or decreased to produceo.wer(25 kW)was supplied, while in the middle and electric arc, there was no explosion. Nevertheless, ifter stages, an increased amount of power(30-35 in the earlier, middle of, and later gasification, thekw)was supplied. The height of the gas trap, the original air was released to the outside, and there wasblow-off pipe, and the gas pressure supervision for almost combustible gas left in the gasifier, and thethe gas collecting space were similar to those in the temperature was high, The gas in the gas collectinggasifier eruption experiment.space was drawn in by using the aspirator pump.There were four experimental plans. The first plan When the drawing of air was stopped suddenly andwas to remove the aspirator pump( shown in Fig 3) 15 min later the fire was lit, there would be someto make natural exhaust and to light the fire about 40 negative pressure in the gasifier, leading to the factto 60 min after gasification for the best moment of that the exterior air was absorbed into the gasifierlighting. The second plan was to remove the aspirator from the outlet of the blow-off pipe and the crack ofpump(shown in Fig 3)to make natural exhaust and the gasifier, and combined with the gas and reachingto light the fire about 120 min after gasification, then the explosion limits of the combustible mixed gas,to increase and decrease the voltage frequently to would cause the same explosion as mentioned aboveproduce an electric arc and to observe whether there When the gasifier was stopped and the gas trap waswould be a gas explosion. The third plan was to draw removed at once, the air outside was combined withthe gas compulsorily by using the aspirator pump the gas in the gas collecting space and quickly burned,shown in Fig 3, then stop the aspiration suddenly and then no explosion occurred. Once in an experiment,light the fire 15 min after gasification to see whether the aged high temperature adhesive made two gasit would cause an artificial explosion. The fourth plan traps break in the joints, and a great amount of gaswas to remove the gas collecting trap right after stop- with white powder was released from the crack. Theping the work of the gasifier and to observe whether gas trap was removed after 40 min and the gas in thethere would be a gas explosiongas collecting space burned intensely because of thesudden pouring in of air and high temperature, butthere was still no explosionIn view of the truth that three conditions must bemet at the same time in the gas explosion, the following measures should be taken: I)a small amountof power is supplied in the earlier stage of the gasification so that the air replacement in the gasifier canoccur slowly or before the gasification the gasifier isfilled with the inert gas CO2 to replace the air; 2)thegas in the gas collecting space is drawn by using theFig 3 Experimental equipment of gas explosionaspirator pump to reduce the gas pressure here, and isof4.2 Results and discussionthe gasification in order to ensure that it is in the stateAs shown in the artificially-devised explosive ex- or micro-positive pressure from the beginning to theeriment, when the fire was lit within 40 min, be- end, which can prevent the air from flowing back in;cause at the earlier stage of the gasification, the air in 3)a manual reset safety valve should be installed inthe gas collecting space had not been replaced com- the exhaust outlet so that it can be shut off when therepletely by the gas and the gas density was within theis no sudden power supply: 4) people working inexplosion limits of the combustible gas(mixture of relevant field should be taught safety precautions inCO, H2 and CH)and the air. Because it met the fire regular operation, and the gasifier should be checkedon the outside of the blow-off pipe, a sudden gas ex- periodically to ensure that the gasifier seal, the gasstrip would explode and fly away and the gas trapwould burst causing it to crack, which led to outside should be used to separate the gasifier from the sur-air pouring quickly into the gasifier from the crack, rounding area, in case the fragments left in the explo-causing the gas in the gas collecting space to burn at sioXthe personnel or the equipmentonce. Then the gasifier stopped working and the gas中国煤化工 n gas explosion oftrap was removed after it had gradually cooled. This relatsafetCNMHG izEd to createdidn' t bring about gas explosion. When the fire waslit after 60 min, the original air in the gas collecting processspace had been replaced completely by the gas re-TIAN Yu-xian ct alSafety research in the gasification process of novel multi-thermal-source coal gasifier5 ConclusionsScience Foundation of China(Project No. 50174046)We shothanks he1)There are possibilities of direct gas explosionnd gas explosion caused by the gasifier eruption inReferencesthe process of the multi-thermal-source coal gasification. In the one thermal-source coal gasification, the [] Smirnov NN, Tyurnikov M V. Experimental investiga-gasifier eruption would appear only when Msio istion of deflagration to detonation transition in hydrocarmuch higher than that in the normal adjuvant; thebon-air gaseous mixtures. Comb Flam, 1995, 100(4):661668ventilation in the gasifier is severely uneven and[2] Hu Y Y, Zhou B Z, Yang Y F. Study on the explosivepower supply is excessively big. Gasifier eruptionlimit and its container factor of polybuswould not appear easily in the multi-thermal-sourcecoal gasification, even if there is a gasifier eruption.China(series B), 2002, 32(1): 35-39. (In Chinese)and if the power can be shut off right away and the [3] Naam A P, Baraldi D, Jertager B H. Solution adaptivegasifier can be naturally cooled down or the gasifiercould be cooled quickly after the inert gas is sprayedvanous solid obstructions. Journal of loss Prevention inthe Process industries, 2002(15): 189-197.on the nozzle, then there is no gas explosion. And, the [4]Zhou FB, Wang D Mhang Y Jgas explosion can be prevented when a small amountfire and suppressing explosion for a super-large andof power is supplied to slowly replace the air in thehighly gassy mine. Journal of China Universiry of Mingas collecting space or the gas collecting space isg& Technology,2007,17(4):46046filled with inert gas in the earlier stages, the time of [5] Qiang JE. Wang X G Tian X W, Tian Y XCoal newlighting a fire is controlled, and the gas is drawn in bystyle gasification technology and co-production theoryloumal of China Coal Society, 2005(30): 93-96.(Inusing the aspirator pump to reduce the pressure butChinese)ensure the gas pressure in the gasifier is in the state of [6] Tian Y X, Wang X G The study on gas rich in co premicro-positive pressure throughout the middle andred by electro-thermal deoxidized method. Journal oflater stages.China University of Mining Technology, 2007, 36(5)2)According to normal operation rules, the gasifi13-18. (In Chinese)ation process of the novel multi-thermal-source coa[7 Tian Y X, Wang X G Tian X w, Qiang J F Axial tem-perature distribution and its influence factors in multicore gasifier. Xi' an University of Science Technology,2007,27(2):3540.( n Chinese)AcknowledgementsThe paper was supported by the National Natural中国煤化工CNMHG