Coal as an Energy Alternative (Kuliah 11).ppt

8/13/2019 Coal as an Energy Alternative (Kuliah 11).ppt

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Coal as an Energy

Alternative


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Introduction

The essential property thatdistinguishes coal from the other rocktypes is that it is a combustible

material .Coal able to provide alternative formsof energy, such as:

Gas Through chemical treatment to become

liquid fuel By in situ combustion to convert coal to

liquid and gaseous produtcs.


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Gas in Coal

Bituminous coals contain a number ofgases including methane, carbondioxide, carbon monoxide, nitrogen

and ethaneThe amount of gas retained and heldby a coal depends on various factors,

such as: Pressure Temperature

Pyrite content


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Large volumes of gas can be

accommodated on the internal surfacesof coal as result of adsorption.It is released by the removal of

pressure, usually by minning or drilling.The gas may migrate into associatedstrata such as porous sandstones,

which is release the gas into openingssuch as boreholes and mine excavation


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Methane is flammable gas and isexplosive between a lower limit of 5%and upper limit of 15% when mixed

with fresh air, known as firedamp . The methane content of the coal canbe regarded as a significant source of

energy and is the subject of largeamount of research and development.Methane is usually referred to as coal-

bed-methane (CBM)


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Coal-Bed-Methane (CBM)

CBM adalah gas metana (CH4) yangterbentuk secara alamiah dalamproses pembentukan batubara dalam

kondisi terperangkap dan terserapdalam batubara.


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CBM GenerationMajor products of coalification processare CBM (CH 4), CO 2, N 2, waterCBM is generated in two ways:1. During the early stages of coalification

(below 50 0C)This is biogenic methane and is formed bydecomposition of the organic material, and wherebiological activity induces reducing conditionwhich remove oxygen and sulphate. Wheresubsidence and burial are rapid, biogenic CBMmay be trapped in shallow gas reservoirs.


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2. CatagenesisThe process by which organic materaialis altered as a result of the effect ofincreasing temperature.CBM generated at temperature in

excess of 500

C will be due to thisprocess and is reffered to asthermogenic methane .


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Analysis of gas produced from coalbeds shows that 95% is CBM,


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CBM retention

CBM is retention in three ways: As a free gas within pore space or

fractures in the coal As adsorbed molecules on the organic

surface of the coal Dissolved in groundwater within the coal.

Porosity in coals occurs as: fracture porosity and matrix porosity


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Fracture porosity in coal is primarilydue to the formation of fracture calledcleat.

Cleat is a joint or set of jointsperpendicular to the top and bottom ofthe coal seam


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The primary mechanism of CBMretention in coal beds is adsorption onthe coal surface within matrix pore

structure.The maximum amounts of CBM thatcan be adsorbed on to the internal

surfaces of coals according to coalrank and depth .


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CBM production

The production of CBM fromunderground sources is either bydraining old and current mine

workingsor by production from wellssunk into virgin or unmined coal seam


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CBM mine drainage

The increasing depth of coal seamsusually equates with higher CBMcontent; this puts pressure on mine

ventilation systems which have to beincreased require that mines ceaseoperation when methane-in-air levels

exceed a predetermined percentage.


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Drainage methods include verticalwells (vertical premine), gob wells(vertical gob), long hole horizontal

boreholes and horizontal and crossmeasure boreholes


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CBM well production methods

Drilling in deep low permeabilityreservoirs has demonstrated that openfractures can exist at depths 2000-

3000m.The effect of horizontal and verticalstress component on deep lying coal

beds; here test have been shown thatCBM can be produced at economicrates from coal below 1500m underlow to moderate stress conditions.


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There are a number of methods by whichCBM is produced from wells.

The standar means for CBM productionis by reservoir pressure depletion.Reservoir pressure is reduced by

dewatering the coal bed; gas thendesorbs from the matrix and microsporesof the coal by a process of diffusion.

The desorbs gas then flow to the wellbore via the coal cleat and fracturesystem, along with any groundwater stillpresent in the fracture


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CBM di Indonesia (Bulletin BPMigas, No. 18 Januari 2007)

Indonesia memiliki cadanganCBMyang cukup besar.Penelitian awal yang telah dilakukanoleh Pertamina, bekerjasama denganPT Chevron Pacific Indonesia padatahun 2001 mengindikasikan adanya

potensi sumberdaya CBM sekitar 337TCF.Cadangan tersebut merupakan

terbesar ketujuh di dunia dan tersebar


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Selain terdapat di Sumatera Selatan,cadangan CBM yang cukup besar

juga terdapat di Kalimantan yakni dicekungan Barito, Kutai dan TarakanUtara. Masing masing memiliki potensisumberdaya CBM 50-75 TCF padakedalaman 350-2000 m denganketebalan lapisan batubara 20-100m.

Di Sumatera Tengah, CBMdiidentifikasi berada pada kedalamanlebih dari 2000 m pada formasi Kerincidengan kandungan sebesar 50 TCF.


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Bulletin BP Migas No.18 Januari 2007


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Departemen ESDM (Bulletin BP Migas, No.18 Januari2007)


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Underground Gasification


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Underground Coal Gasification(UCG) Technology

The producer gas reactionThe water gas reaction

The methane synthesis


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Steeply dipping bed gasification(SDB)


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Controlled Injection Point (CRIP)


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Coal as a Liquid fuel


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There are various methods of coalliquefaction, the main problem beingthe deficiency of hydrogen in coal

compared to liquid fuel.


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This can be overcome by addinghydrogen to the coal by a number ofprocesses: Direct liquefaction by hydrogenation Indirect liquefaction by the Fischer-

Tropsche synthesis Removal of part of the carbon content

from the coal by pyrolisis.


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Hydrogenation

The H/C ratio is increased by adding ahydrogen donor.Coal is dispersed in a thermally stable

solvent and/or hydrogen donor andpssed into a pressure aututhermalreactor at temperature between 400

and 5000

C


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The Fischer-Tropschesynthesis

Involves the gasification of the coal,carried out in a Lurgi gasifier toproduce synthesis gases carbon

monoxide, hydrogen and methane.The methane is treated in a gasreformer and synthesis in a Kellog

reactor


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Pyrolisis

Involves the heating pulverised coalextremely rapidly in a vacuum, knownas flash pyrolisis.

The feed coal passes through a plasticstage during which the maceralssoften and decompose into gas, char

and tarr liquids.The tars are hydrogenated to produceheavy or lights oil as required.


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Coal Properties forliquefaction

Vitrinite reflectance 0,75%Vitrinite+liptinite >60%Volatile matter (d.a.f) >35%Low concentration of heteroatoms


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Coal as an oil-prone sourcerock


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Coal as an Energy Alternative (Kuliah 11).ppt

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