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Module 1: Gassificazione del carbone

    Study Reminders

    Hi friends, now we will discuss on the topic direct liquefaction of coal.In the previous class, we have discussed on gasification of coal and we have seen thatcoal is gasified to produce syngas and that syngas can be used for different downstreamapplication.One application was FT synthesis that is the Fisher-Tropsch synthesis through which wecan get different types of liquid fuels.So, that liquid film production from the coal was an indirect route and this is important,the production of liquid from the coal because, we can use liquid fuel more easily in differentengines.And if we want to produce it through this indirect route, then obviously, it is involvingnumber of steps, conversion steps.So more the steps, lesser the efficiency, overall efficiency of the process.So, people thought if the coal can be converted directly to liquid and in the introductoryclass, we have seen that coal contains different aromatic rings a chain of aromatic rings wehave seen like this very bigger, it is very complex structure that is why it is solidand less reactive.It is not that high reactive, we have to heat it at higher temperature then only there willbe some combustion at lower temperatures there will be no combustion unlike say plant materials.So, that is why it is solid now, and here also we know that carbon concentration isalso very high with respect to hydrogen.Now, if we can break this some of the rings here and say some double rings are there see,if we can break some double ring and we can add some hydrogen here this thing's then itwill be converted to some organic compound having lower molecular weight and that willbe liquid form that can be liquid form.So, we will be able to get liquid fuel from coal by this process, but what is the; whatis needed here for this conversion one is hydrogen we have to provide sufficient amountof hydrogen and as you know coal is not that reactive.So, hydrogen has to be provided at higher pressure.So, high pressure hydrogen is required and coal particles has to be very particle sizewill be very, very small, the very small particles will be made slurry in some solvent and thensolvent coal slurry.Obviously, more solvent is acquired and then hydrogen at high pressure that will be givingus this conversion, that may give us this conversion and we can use some catalyst therate of the reaction can also be improved.So that way, directly coal can be converted to liquid.And as you have discussed that this technology was developed many years ago in Germany inlab scale or small scale production, but for commercial scale production very recentlythe plant has come in China.So, we will discuss here and our content is direct liquefaction process.And then properties of coal derived liquids, the types of direct coal liquefaction, thata single stage direct liquefaction process or two stage direct liquefaction process andthen we will see the benefits of direct liquefaction process and direct liquefaction challenges.Now, we see in direct liquefaction process different coals are converted to coal liquid.It can be lignite or brown coal, it may be sub bituminous, it may be bituminous coal.Very interesting here, lower the quality of coal more easy to convert it into liquid fueland you see here anthracite is not shown.So, when we are getting the coal liquid, we compare the heating value with respect tothese different types of coals, this is much higher than this.So, energy intensity is increased in the liquid fuel that is one advantage.And you see here we need hydrogenation step, we need hydrogen and catalyst, we need hightemperature and pressure.So, these are the requirement for the direct liquefaction of coal, here any type of coalcan be used, there is no limitation of its quality, but preferably lower quality coalscan be used.And then we will get gas oil, gasoline and kerosene.So, this is the overall process for direct liquefaction of coal.So, it is accomplished under high temperature that is around 400 or more than 400 centigradeand 102 to 204, atmospheric pressure, very high pressure it takes.So, what will be happening just we have discussed, the coal is fragmented, the complex structureis broken down and it is fragmented and then hydrogenation takes place.So, we will be getting some coal liquid, that coal liquid may be requiring for further upgradationthat is obviously for hydrogenation that we are going to discuss.So, now, we are having coal this coal we are getting coal fragments and this is what isthe process the dissolution, hydrocracking and hydrotreating heat pressure and catalyst.So, coal slurry formation then application of heat and pressure maybe catalyst or maynot be catalyst.So, that will be getting coal fragments, then coal fragments will be having some oil partand some also solid part it will be having.So, that solid part it is called preasphaltenes or asphaltenes that is having high molecularweight then what we will do with this another step we can go for hydrocracking, catalytichydrocracking.So, we can get more oils from this asphaltenes also and then further hydrotreating will giveus transportation fuel.So, hydrogen addition may not be in a single step it may be step wise.So, we can increase the hydrogen concentration in the liquid and it will be more usable formin transportation fuels.Now properties of coal derived liquids we see this table shows the properties that isdensity, viscosity, potential aromatic percentage, sulphur, nitrogen, cetane number, Flashpoint,solidification point, cold filter plugging point and oxidation sludge, it is also given.So, naphtha which is generated from the coal liquid and diesel these two properties areshown here and this table we can see that the comparison of some properties would sayand we can get the cetane number here.So, cetane number we can have diesel around 50 here we are getting say 46.7 so, relativelylower than that, but as the coal liquid is coming from the coal which is having verycomplex aromatic structure.So, aromatic compounds in coal liquid will be more.So, octane number will be higher in case of that, but cetane number is not that higherwith respect to the petrol-diesel?So, direct coal liquid naphtha can be used to make very high octane gasoline component.So, that is one advantage of this or the positive point of this on terms of the quality of thecoal liquid we will derive to gasoline and DCL distillate is a poor diesel because thevalue that cetane number is lower than that of the petrol diesel and raw DCL liquid stillcontains sulphur, nitrogen, oxygen possibly metals also.And so, we need to upgrade this for the removal of these components from the coal derivedliquid for its effective application.Now, we will see; what are the different steps through which the liquid fuel can be producedfrom the coal.So, we have one single stage direct coal liquefaction or double stage direct coal liquefaction.So, the single stage that means gives distillates via one primary reactor and double stage givesdistillate products via 2 reactor stages in series.So, coal dissolution in first stage operated either without a catalyst or with only a lowactivity disposable catalyst.So, in case of single stage reactors, there are some technologies like SRC II and thenExxon donor solvent EDS and H coal.And in double stage we are having integrated 2 stage liquefaction it ITSL and catalyticmultistage liquefaction CMSL.Now, we will see SRC II that is solvent refined coal liquefaction.So, we will be using solvent only no catalyst will be used in this case.So, we are using coal here crushed and grinded very small particles then, we have to makeslurry.So, I need some solvent, so, how will we get the solvent?It will be coming from the process which is generated in the process, this is heavy distillateit is recycle back and it is creating this slurry.So, in this slurry is coming, I need hydrogen.So, hydrogen we may get from the gasification process using again some amount of coal hereand this hydrogen is coming here or we can get the hydrogen here also which is producedin this process.So, then hydrogen addition is made slurry is formed.So, we have to pressurise it, so after slurry preheater it is coming to dissolver wherehigh pressure of hydrogen is created.So, 12 mega Pascal or 440 degrees centigrade, this 15 to 45 minutes time period is requiredhere without any catalyst.So, this will give us the conversion.So, what we will get we will be having the mixture now we will be having vapour liquidseparation where the vapour the hydrogen which you have added that can be recovered and wherealso after gas separation, we will get the fuel gas and solid part will come here thenit is coming slurry light liquid separation at 1 mega Pascal and 290 degree centigrade.So, we are getting light distillate naphtha and then again filter then residue.So this residue is your solid part.So, this is again used in the gasifier for the hydrogen production and this liquid partfrom this filter it will be having the heavy liquid, so, that heavy liquid will be distilledor heating and vacuum distillation then it will give us heavy distillate fuel oil andwash solvent will be coming as a vapour and that can be recycled and this it will giveus SRC coal that is solvent refined coal the rest part which is remaining.Now, we are coming to Exxon donor solvent process.So, that is also one step process.So, here coal slurry making where the solvent is coming from the process which is generatedduring this process.And then recycled solvent slurry making hydrogen is coming from this process and it is preheatingthen it is going to tubular reactor.So, a condition is 425 to 450 degrees centigrade and 175, atmospheric pressure no catalystis used,In this case pressure is higher than the previous one temperature is also slightly higher orin the same range, but the pressure is higher.So, then it is coming for separation so gas separation hydrogen will goes here, we willgo here and then we will go for liquid separation so we will get naphtha and we will get distillatefuel then from the solid we can get Flexi Coker and coke formation here and that liquidwill also go here.So, then and from this part we will get some liquid that can be going through hydro-treating,to improve its quality and that can be used as a recycle solvent.So, this is the flow sheet of EDS process that is Exxon donor solvent process.The yield can be up to 47% for lignites, 50% for sub bituminous and 60% for bituminoustype of coal.The H Coal process is another process which is also single step process and this reactoroperates at temperature 425 to 455 degrees centigrade.And here conventional supported hydro-treating catalyst either nickel molybdenum or cobaltmolybdenum in alumina is used.So, unlike two other processes in this process, catalyst is used and H2 is added and mixedin a pre heated and fed to an Ebullated bed hydrocracker, the hydro cracker reactor bedis also not fixed unlike the other process.So, here the yields are dependent on coal and greater than 95% overall conversion, canbe obtained because you are using the Ebullated bed reactor and yields liquid yields up to50% on dry basis.So, as we are using the Ebullated bed reactor, it has some advantage that is well mixed andtemperature monitoring.So, that is giving some better efficiency than the previous one.And then H-Coal process, H-Coal process this is derived; it is developed by HRI Hydrocarbonresearch incorporation and currently hydrocarbon technologies HTI USA and in this case ebullatedbed reactor is used.So, pulverised coal, recycle liquid, hydrogen and catalyst are brought together in the reactorto convert coal into hydrocarbon liquids and gaseous products just we have discuss thesethings.And the similar way this also takes place and particle size is minus 60 Mesh and temperature345 to 370 and this is 445 to 455 degrees centigrade and up to 200 bar pressure andcatalyst is cobalt molybdenum on alumina.So, this is one technology which is used for the direct coal liquefaction.So, now 2 stage liquefaction if you see the one is our ITSL two stage liquefaction.So, here we are using coal here.So, that coal we have to make slurry, so some solvent is needed.So, those solvent will also come from the process.So, here is after Rose SR solvent recovery and another is your solvent recovery in thishydro generated solvent recovery.So, these two solvent sources it is coming and making the slurry.Then this slurry the first step will be catalytic first stage.So, here hydrogen is added then it will go to catalytic second stage again hydrogen willbe added then it is going for hydrogenated solvent recovery.So, hydrogenated distillate we are getting and then the solid, the heavier part thatis resid plus ash, then we will go for solvent recovery and that is residuum oil supercriticalextraction that is ROSE, residuum oil supercritical extraction this method if we use we will gethere ash contents and heavier solvent will go to this.So, this is the flowsheet of these two stage liquefaction process here we can get 170 atmosphericpressure and here 343 to 412 degree centigrade for the first stage and the second stage 432to 440 degree centigrade.Now, CTSL process that is also a two stage process so, it is ebullated bed reactor inboth the stages, in the first stage 400 to 400 degree centigrade, second stage 435 to440 degrees centigrade, the lower first stage temperature provides better overall managementof hydrogen and also it is 200 bar.So, what is the difference between these and previous one?The nickel molybdenum catalyst NiMo on alumina and CTSL process produces liquid product yieldwith low heteroatom concentration and high H by C ratio, Hydrogen by carbon ratio, theproduct is closer to petroleum.Another is HTI coal process.So, HTI coal process again two stage process.So, the difference is that this uses the proprietary catalyst a dispersed nano-scale iron basedcatalyst.So, in the CTSL process we had nickel molybdenum on alumina catalyst.Now, HTI coal process we are having GelCatTM catalyst that is nano-scale iron based catalystthat is the most important difference.And coal slurry prepared by mixing pulverised coal and catalyst with process derived recyclesolvent is fed in the reactor 435 to 460 degrees centigrade.In the first stage obviously, the breaking of the coal structure, in the second stageis for liquefaction and then this process is used at China ShenHua project in 2008 thatis having the capacity of 3.5 million metric tonnes of coal producing with one MMT of oil.This is the ShenHua DCL project flowsheet, so you see coal is here, slurry preparationtakes place, catalyst is added, solvent is coming from the process derived solvent.So, it is coming and then this is going for liquefaction reaction, then separation, thenhydrogen recovery hydrogen will come and hydrogen recovery we will get here.So, then the liquid part go for hydro-treating it will give us liquid and then by distillationdifferent fractions of liquid we will get and from this part bottom of this the residualpart we can go for gasification and hydrogen we can make.So, that hydrogen can be used here.So, this process is used commercially.And this is the first plant in the world on DCL direct coal to liquid that is first DCLcommercial plant in China production capacities 24,000 barrel per day and this four year ofconstruction 2004 to 2008.These are the some photographs of different fuels derived from the coal directly in thisShenHua DCL plant.Then catalytic multistage liquefaction, so, in this case more than two step is allowableare used.In 1993 the two stage liquefaction system evolved into catalytic multistage liquefactionsystem.In 1993, Department of Energy awarded HRI a contract to conduct demonstrations of directcoal liquefaction in 3 ton per day capacity, therefore a demonstration plant.So, different types of catalyst has been used, you see the same company HRI they are developingthe technology.So, here supported catalyst, Co-molybdenum, Co-nickel and dispersed catalyst Fe, Mo andHTI proprietary GelCat iron based catalyst.So, now, we will see the, what is the scope of the DCL process in India?So, we do not have any additional plant in India.But, this is Oil India Limited Duliajan, they are putting their effort to develop the technologyand they are targeting to use the low ash content Assam coal for this purpose and onestudy was going on I am not aware about the latest status update and IIP Dehradun wascontributing on the upgradations of the coal liquid.And the benefits of Liquefaction, the direct liquefaction technology has higher efficiencyyou see 70 to 75% just we have discussed that when we are involving more steps, obviouslythe efficiency will be less.So, in this case we can get higher efficiency with respect to other technology say IGCClike this indirect way 60 to 65% maximum we can achieve.And then direct liquefaction provides high octane, low sulphur gasoline and distillatethat will require upgrading to make acceptable diesel blending stock.So, these are advantage and development of direct liquefaction technology could leadto hybrid processes producing high quality gasoline and diesel.And direct liquefaction may have better carbon footprints then indirect liquefaction process.But what are challenges?Uncertainty in oil prices as you know, this method is not very cheap method, it will becostlier and will be feasible only when the crude price will be very high, it is feasiblewhen the crude price is more than 70 to 80 $ per barrel.And high capital cost as you see that high pressure systems are required.So, we high capital cost is also needed.And then investment risk is also there that the market what will be the value of crudeoil it fluctuates.So, what will be the stability of the market of these that is also uncertain and so, itis there is a risk for the investment on this and technical challenges.This is you know this process was discovered many years ago, but commercialization takeonly in 2008 because there are many technical challenges although there is one plant commercialplant in China, but still more research is required on this field and to make it to developconfidence on the technology.LCA can be done.So, hybrid technology needs development including integrated demonstration and environmentalchallenges.It has some challenges also carbon dioxide and criteria pollutants as well as water use.So these are also related.These are not well addressed on this plant.Thank you very much for your patience.