If we see the ucg process carefully. It consists of three stages.
High pressure air was injected into the coal seam, anda small stream of air ﬂowed to the production well via naturally occurring cracks andcleats in the coal seam. The coal was ignited at the production well, and burned backtowards the injection well. Once the ﬂame front reached the injection well, a cavitybetween the injection and production wells was established and gasiﬁcation couldproceed.
UCG reactor has unknown and constantly changing dimensions.
UNDER GROUND COAL GASSIFICATION
PRESENTATION TOPICUNDERGROUND COAL GASSIFICATIONPRESENTATION BYKOMAL AROOSHDEPARTMENTCENTER FOR COAL TECHNOLOGYPUNJAB UNIVERSITY LAHORE
** Underground coal gasification (UCG) is the in-situ conversion of coal into combustible gases.In which unmined coal seams are reactedunderground, with insufficient oxygen forcomplete combustion to producesyngas(CO+H2)
*Two wells drilled into thecoal, one for injection ofthe oxidants, another to bringthe product gas tothe surface.
8Two boreholes are drilled into the coal seam and a path between thesetwo borholes is established.UCG – 1st stage
1.Fracture of the coal seam by air pressure orexplosions2.Reverse combustion technique3.Modern directional drilling techniques(magnetic target,magnetic detector)
10Coal is ignited, combustion is maintained by injecting air or oxygen andsteam–
11The resulting gases are brought to surface by the second bore hole–
Operator of an underground coal gasification plant hasfollowing controls over the process.1.Temperature2.Pressure3.Gas flow rate4.Composition of gas at injection and productionwell*
**Flammable gases combust in the ﬁrst ten meters, consuming all ofthe available oxygen and causing a sharp rise in gas temperature.*At the end of the combustion zone, the gases primarily consist ofhot, non-ﬂammable N2,CO2, and H2O. In the following 40 meters,steam and CO2 react with char, so H2 and CO concentrations risewhile steam and CO2 levels fall.*The methanation reaction raises the concentration of methane. Thegas caloriﬁc value increases as the gas ﬂows through the cavity.*The temperature falls due to the endothermic nature of the steamand CO2 gasiﬁcation reactions, as well as the heat required toevaporate water seeping into the cavity. By the time the gasreaches the production well at 50 meters, the temperature is barelysufﬁcient to sustain a signiﬁcant rate of gasiﬁcation.
Temperature 200-550oC Temperature 550-900oC Temperature more than 900oCDrying & Pyrolysis Zone Reduction Zone Oxidation ZoneCoal CH4 + H2OCO + CO2H2 + CHydrocarbonsC + H2O CO + H2CO2 + C 2COCO + H2O CO2 + H2CO + 2H2 CH4C + O2 CO2C +1/2 O2 COCO +1/2O2 CO2Coal + O2 CO2 + CO + H2OSchematic of the processes involved in UCGAir, Oxygen & Steam Product Gases ( CO, CO2, H2, CH4, N2 , Steam & Tar
Coal seam shallower then 150m is rejectedCoal seam Deeper then 600m is rejected.Coal Seams thinner then 10m are also rejectedRecovery fector is 65% and remaining 35% is left for roofsupport.*
1. Most known coal resources in the world are too deeply buriedto be economically mined out. Nearly 85% of known coalreserves are un-mineable with surface mining. So, UCG isproposed for these reserves.2. The costs of drilling air injection and syngas production wellsare a small fraction of the cost of a gasiﬁcation complex, sodeeply buried coal seams may be gasiﬁed at a reasonable cost.3. UCG is producing fuels and hydrocarbon feedstock today fromunrecoverable coal deposits.4. Countries are turning to UCG to fully utilize their coalresources in an economically viable and environmentallyacceptable manner.*
23Facilitates exploitation of deep /unminable coal reservesHigher efficiency coupled with low capitalcosts than conventional coal-fired stationEliminates SO2 emissionRadio active ash remains deep down…UCG - Advantage
24*Environmentally friendly*Significant reduction in CO2, SOx, NOx emissions*No Waste disposal (Ash Trapped Underground)*Reduced emission of Green House Gases byCO2 Sequestration*Short Construction and Commissioning TimeUCG - Advantage
1.Surface subsidence2.Aquifer watercontaminationRemoval of the coal from coal seam cancause the roof fall, when roof collapses thewater from a shallow freshwater aquifermixed with the tar-contaminated coal androck and is contaminated.*
In the last few years there has been significant renewed interest in UCG asthe technology has moved forward considerably.1. China has about 30 projects in different phases of preparation that useunderground coal gasification.2. India plans to use underground gasification to access an estimated 350billion tonnes of coal.3. South African companies Sasol and Eskom both have UCG pilot facilitiesthat have been operating for some time, giving valuable information anddata.4. In Australia, Linc Energy has the Chinchilla site, which first startedoperating in 2000. Carbon Energy has completed a successful 100 daycommercial scale study in Bloodwood Creek in 2008.*