• Introduction• Why UCG?• Process Description• Benefits• Demerits• World Scenario• Conclusion
Underground coal gasification (UCG) is an industrial process,which enables coal to be converted into product gas.UCG is an in-situ gasification process carried out in non-mined coal seams using injection of oxidants, andbringing the product gas to surface through productionwells drilled from the surface.It is a complex process involving Chemical reactions Heat and mass transfer Complex flow dynamics Growing cavity dimensions
Coal is a readily combustible black or brownish-black sedimentary rock normally occurring in rockstrata in layers or veins called coal beds Composition Primary carbon Secondary sulfur, hydrogen, oxygen, nitrogen
Energy market scenarioHigh and ever-increasing fuel prices.A rising energy consumption in the Developing World.Growing shortages of supply of oil and natural gas.Depletion of several major natural gas fields across theworldEnergy market dynamics are unfolding on mountingconcerns about global warming.
Characteristics of the coal seam i.e. permeability, fault structure of local strata , geology and hydrogeology of area which surrounds target coal seam should be known.Drilling of pilot bore holes to coal seam depth for coring andseam characterization.Seismic survey / 3D survey of whole areaModeling of hydrogeology to meet ground water requirements.
Underground coal gasification projects have specificrequirements regarding the coal seam:The seam lies underground at a depth of between 30 and 800metersThe seam thickness is more than 5 meters;The ash content of the coal is less than 60%;The seam has minimal discontinuities; &There are no aquifers nearby (to avoid polluting suppliesof drinking water).
Responsible UGC projectsrequire careful site selectionand evaluation to identifydeep coal seams that are atleast 650 feet below thesurface. UCG coal beds arebelow fresh water aquifer,isolated from fresh waterand contained by strong,impermeable overlying rocklayers
The process begins by drilling two wells ina coal seam
At one well, operators inject an oxidantsuch as air to start a carefully controlledcombustion reaction
Heat and pressure convert the coal togas:coal+water+oxygen+heat=Hydrogen, CO
Operators control or halt the process bymanaging oxygen supply. Natural waterInflux quenches the reaction, eliminatingthe possibility of unwanted coal seam fires.Ash and other byproducts remainunderground
The second well produces syngas tosurface for processing.
Processing and clean up at the surfacePrepare syngas for near-site use ortransport. Syngas is an energy rich gasproduct that can be handled and used likenatural gas; piped, stored or used to fuel aturbine to generate electricity andupgraded or converted to make syntheticnatural gas or liquid fuel.
UCG with carbon capture and sequestration leaves a carbon footprint that is far smaller than conventional coal and similar to natural gas.CO2 is easily separated from syngas using existing technologies for underground sequestration. Commercial scale carbon capture has successfullyremoved CO2at surface coal gasifier plants
Many experiments have been carried out to developmathematical models for UCG which can be used forcarrying out process calculations.The best suitable match is a MFR followed by a PFR. MFR PFR
UCG offers significant benefits, financial, social andenvironmental, over traditional coal mining or coal gasificationmethods. Environmental benefits Financial benefits Social benefits
Lower capital and operating costs .Reduced cost of plant installation - No Surface Gasifier.Syngas can be piped directly to end-user, reducing need ofrail / road infrastructure.Lowers cost of environmental clean up due to solid wastebeing confined undergroundGT power plants can be switched from natural gas tocheaper UCG product gas.
UCG may not require an external water source to operate, a majorenvironmental advantage over water-intensive coal miningoperations and pulverized-coal-fired energy production methodsLower emissions, because gasification in UCG is undergroundthereby reducing environmental management costsParticulates are generated at half the rate of their surfaceequivalents and stay undergroundLower dust, noise, visual impact on the surfaceLow risk of surface water pollutionReduced methane emissions - coal seam gas is recovered in theprocess, rather than lost in the atmosphere as in most conventionalminingNo dirt handling and disposal at mine sites
No coal washing and fines disposal at mine sites. UCG process creates an immense underground gas and heat storage capacity, which makes the gas supply very stable and robust.USE UCG AND SAVE THE ENVIRONMENT
Risk of injury or death to humans is significantly reducedsince workers need not to enter a mine.Local communities no longer face air pollutionAs mining isnt involved and land degradation reduceskeeping surrounding land fertile .
UCG Gas gives 25% increase in the gas turbine power outputcompared to natural gas.Fewer air emissions: greenhouse gas emissions as low as 30%than natural gas.Cost of power generation is much less than with naturalgas.UCG gas can be produced in abundance for years to comeand used to fuel GT plants .
UCG uses un mined coal and performed in undergroundcoal seams compared to conventional gasificationIt eliminates cost of coal mining & transportIt does not require capital cost of the surface gasification reactor.UCG does not incur cost of ash and slag removal,storage and disposal all inert solids remain underground.UCG is usually produced at lower temperature, easier toprocess and clean up.Unlike UCG, conventional gasification requires coal miningwith environmental and safety issues.Conventional gasification uses large volumes of waterwhereas UCG uses groundwater present in coal seam.
Visual and acoustic Environmental impacts.Air emissions (tough low) and groundwater impact.Geological and hydro geological risks. The voids from whichgas is removed become weak .But with an optimistic approach and technological advancewe can overcome these.
In the last few years there has been significant renewed interest in UCG as the technology hasmoved forward considerably.China has about 30 projects in different phases of preparation that use underground coalgasification.India plans to use underground gasification to access an estimated 350 billion tonnes of coal.In 2007 India compiled a 93-page status report on underground coal gasification thathighlighted interest from many of the countrys biggest companies. Jindal power coming upwith its plant in orissa.South African companies Sasol and Eskom both have UCG pilot facilities that have beenoperating for some time, giving valuable information and data.In Australia, Linc Energy has the Chinchilla site, which first started operating in 2000. CarbonEnergy has completed a successful 100 day commercial scale study in Bloodwood Creek in2008.Demonstration projects and studies are also currently under way in a number of countries,including the USA, Western and Eastern Europe, Japan, Indonesia, Vietnam, India, Australiaand China, with work being carried out by both industry and research establishments.A number of issues remain to be resolved before wider deployment can be achieved
Today high prices of oil and gas and uncertainties aboutpolitical stability is most of oil producing countries, haverenewed interest in all kinds of fuels. A renewable interestin coal gasification is therefore not surprising. Further-more, hydrogen is now a welcome by product because ofcurrent interest in alternatively fuelled vehicles. Ultimately,it could be a substitute for deep mining coal for powergeneration use.