Underground Coal Gasification UCGUnderground Coal Gasification UCG

Or Or

InIn--situ Coal Gasification ISCGsitu Coal Gasification ISCGA very unconventional gasA very unconventional gas

Barry RyanBarry Ryan

ConsultantConsultant

bryan@islandnet.com

DisclaimerI am not an expert in UCG

Talk uses public sources with added interpretation/opinion by author

Contains more detail than can be covered here May be useful later

A lot of “Average” numbers used in calculations

Results only indicative at best

Use with extreme caution

Listener beware

Be critical

Introduction to UCG

Some generalities

What is

Underground Coal Gasification UCGBurn coal insitu and recover a low btu gas at surface

link air injection hole and gas recovery holeBurn can move towards air injection hole (counter current circulation )

or in same direction as air towards gas recovery hole (co current circulation)

Courtesy ErgoExergy

Coal seam

Putting UCG in perspective

Coal gasification and liquefaction at surface are commercial processes around the world

Over 30% of petroleum used in South Africa is produced from coal by SASOL

UCG involves similar reactions but in an environment that is harder to test and control

Coal

Time Minutes

Surface GasificationHigh Volatile Bituminous Coal (Rm 0.61%)

Coal Valley Luscar

Surface and Underground Coal Gasification

produces a low btu gas

of

varying composition depending on conditions

Gas from UCG

A very Unconventional Gas

UCG Gas is multi gas composition has low btu contains moderate CO2 content

Approximate comparisons natural gas CBM Shale Gas UCG Gas

compositionCH4 98 98 98 4

CO2 2 2 2 15

CO 0 0 0 6H2 0 0 0 12

N2 0 0 0 63Heat value

Mj/m^3 39 39 39 3.87Kcal/m^3 9300 9300 9300 925

Kg CO2/m^31.97 1.97 1.97 0.49

CO2 Kg per 1000 Kcal

methane 0.2coal 0.4UCG gas 0.53

using HHV and SG at 0 CMj/m^3 Kcal/m^3 Kcal/g

C 8.1CH4 39.8 9505 13.3CO 13.6 3255 2.6H 12.8 3045 34.2

Example from Hanna USA

A brief History of UCG

Much of the early research was

Behind the Iron Curtain

Russia (Former Soviet Union = FSU)

Various methods developed in the FSU

History of UCG

Initial Development Began Behind the Iron Curtain

With vast coal reserves and in 1930’s limited natural gas reserves; FSU aggressively investigated opportunities for UCG

A lot of detailed science and experience stayed behind the Iron Curtain till 1970’s

FSU developed a number of techniques and gasified different ranks of coal in different geological environments but generally low rank coal at shallow depth

Important to develop a pathway from air injection hole though burn zone to gas recovery hole. Initially FSU tunneled to connect injection and gas recovery holes later they used directional drilling along seam

FSU used forward and counter current directions for injected air flow ie burn progresses in same direction as injected air or progresses towards injected air

Trials in FSU in steep dipping seams using co current combustion (Juschno-Abinsk) were moderately successful.

Main Locations of Russian (FSU) UCG

Summary of Russian (FSU) Data from main locations

Another version compare later

Basin Donets Basin Kuznets Basin Moscow Basin Tashkent AreaPlant Donbass Kuzbass Podmoskovnyi AngrenCoal deposit Lisichansk Yuzhno-Abinsk Tula AngrenStart date 1933 1955 1940 1962rank bituminous bituminous Lignite ligniteash % 6 to 16 4 to 10 27 to60 11vols % 25-35 20 to 30 17 to 27 25 to 30moist % 15 5 to 8 20 to 30 30S % 1 to 5 1heat Kcals/kg 4500-5000 5000-6000 2000-5000 3650geology steeply dipping steeply dipping horizontal sub horizontalseam thick metres 0.4 to 1.5 2 to 9 2 to 4 4 to 24depth metres 400 40 to 60 110 to 250gasificationheat content Kcal/m^3 800 to 1000 1000 700 to 900 800 to 850

Early FSU Methods for UCG in Dipping SeamsInitial linkage injection hole to gas removal hole was a tunnel

Injection and gas removal holes drilled down dip in coal seam

Burn zone moves up dip with coke and rubble collapsing down dip into cavity

Roles of holes periodically reversed to ensure even burn along linkage

Bulldoze alluvium to seal fractures limit gas leak

Kreinin and Revva (1966)

Cavity development in steep dipping seams is similar to fixed bed surface gasification (Lurgi gasifier) with air injected at the bottom and fresh coal fed by gravity at top.

FSU Method for UCG in Steep Dipping Seams Initial injection holes vertical Later holes drilled below coal seams

Gas recovery holes drilled in seams Vertical water recovery holes drilled into cooled rubble zone

An overview of Soviet effort in underground gasification of coal Gregg et al 1976

FSU Design for UCG in Steep Dipping Seams

Kreinin and Revva (1966)

FSU UCG Steep Dipping Seams

Developed early version of horizontal drilling to connect injection and gas recovery holes

Second stage air injection holes drilled in footwall clear of subsidence

Kreinin and Revva (1966)

FSU also developed UCG in Horizontal Seams

Generally at shallow depth using vertical holes

800’C

Coal seam

Pyrolysis products

Water influx

800-1200’Ç

Overburden

Pyrolysis

productsGas losses

Rubble

Gas recovery hole

150’CInjection air

FSU Vertical Drill Pattern for horizontal seams

Plan views of developing geometry by stage

Air injection holeGas recovery hole

Stage 1

Form linkage along line of vertical holes counter current burn

Stage 2

Complete linkage using counter current flow

Stage 3

start parallel line of holes link to first row of holes using co current flow

Burn progression

Gas flow

FSU Vertical Drill Pattern into Horizontal Seam

Plan view of air injection and gas recovery holes as development progresses

Gregg et al 1976 An Overview of Soviet Effort in Underground gasification of Coal

Recent Development in UCG geometry

End view of injection hole and burn cavity

Width height ratio about 6/1 therefore seam thickness controls amount of resource around each hole

Gas moves in same direction as injected air through previous burn zone to recovery hole

Recent Important Development in UCG Geometry CRIP (Controlled Retractable Injection Points)

Makes use of modern horizontal drilling techniques applied to horizontal seams

Coal S

eam

Injection hole

gas recovery hole

initial ignition in gascounter current gas flow recovery hole

later ignitions retreat along injection holeco current gas flow

ignition point

Must drill along base of seam

Development of the CRIP Method (Controlled Retractable Injection Points)

Centralia Washington (Toni 1) 1983

Hanna Wyoming (Rocky Mountain RM1) 1987Tests showed that CRIP process is capable of producing consistently high quality gas from single injection hole for extended time.

CRIP in horizontal injection hole, has advantage over vertical injection holes. Maintains air low in seam for optimal resource recovery.

Provides a method for re-ignition of coal at different locations when gas quality declines as maturing reactor begins to interact with overburden.

CRIP in sub-bituminous and lower rank coals has reached a level where remaining technical uncertainties and risk to commercial development are reduced.

RM1 CRIP module operated for 93 days and gasified over 10,000 tonnes of coal, Gas average dry product heating value of 253 kJ/mol (287 Btu/scf=2554 Kcal/m^3).

CRIP adapted by British Gas (Knife edge CRIP)

Gas production horozontal holes up to 500 metres along seam drilled parallel to horizontal oxygen+steam injection holes

Injection started with a vertical hole

Injection holes completed with slotted liner + ignition source which is pulled back along hole.

Gas flows thru coal from injection hole to production hole

Prior to ignition it is possible to hydro frac the injection hole ??

Orientation of injection and gas recovery holes drilled to take advantage of cleat geometry ??

Development of UCG

Ergo Exergy, εUCG technologyCompany adapted and patented FSU methodology, but not much published on εUCG process and Ignition and Injection procedures.

May be using vertical holes

Don’t know differences between FSU UCG, εUCG and CRIP

Don’t know methods used in εUCG to establish reliable connections between injection and production wells.

Don’t know how εUCG compares with CRIP in terms of reproducibility, reliability, cost

UCG Activity Around the World

UCG Activity around the World in 2007-2008

UCG Activity around the World

Interest in UCG spread around world following increase in oil and gas prices

A lot of expertise is still in FSU

Friedmann Burton UpadhyeLawrence Livermore National Laboratory 2007

For CO2 storage

“Best Practices in Underground Coal Gasification”, E.Burton, J.Friedman, R. Upadhye,

Lawrence Livermore Nat. Lab., DOE Contract No. W-7405-Eng-48

Evolution of Test Site Experience

Progression Trying deeper seams Trying thinner seams

Minimum thickness

Trying deeper

and thinner

United States More than 30 experiments between 1972 and 1989Introduced Continuous Retraction Injection Point (CRIP) process.

Pilots conducted atHanna Wyoming 1972-1973Hoe Creek Wyoming 1976-1979Centralia Washington 1981-1982

UCG Activity around the World

Extracts from from Potential for Underground Coal Gasification in Indiana Phase I Report to CCTREvgeny Shafirovich, Maria Mastalerz, John Rupp and Arvind Varma1Purdue University, September 16, 2008 and other sources

Friedmann Burton UpadhyeLawrence Livermore National Laboratory 2007

US UCG Projects

Hanna

Basin Hanna basinCoal deposit seaam No1Start date 1973rank Sub bituminousash % 23.76vols % 32.64moist % 9.51S % 0.68heat Kcals/kg 4810geology broad synclineseam thick metres 9.1depth metres 91 to 122gasificationheat content Kcal/m^3 1120

Experience from the Hanna UCG Project Wyoming 1973

One of the earliest tests outside FSU

Data from the Hanna Project

Air injection rate drives gas productionAir injection red

Gas production black

900 Kcal/m^3

1800 Kcal/m^3

Synergia Polygen Swan Hills

Laurus Energy

0 300 Km

Location of UCG projects in Western Canada

AustraliaLinc Energy Ltd UCG trial Chinchilla, Queensland using Ergo Exergy’s technologyProject (1999-2003) demonstrated feasibility to control UCG process Gasified coal at 130 metres depth seam thickness 10 metres Gasified 35,000 tons of coal, with no environmental issues. 80 million Nm3 of gas produced at 4.5 - 5.7 MJ/m3 (121-153 BTU/sft)Maximum gasification rate 80,000 Nm3/hr or 675 tons coal/dayGas production over 30 months high quality and consistency of gas 95% recovery of coal resource; 75% of total energy recovery; 9 injection / production vertical wells; 19 monitoring wells; average depth of 140 m; Since 2006 Linc Energy Ltd co-operate with Skochinsky Institute of Mining Moscow; acquired a 60% controlling interest in Yerostigaz, which owns the UCG site in Angren (Uzbekistan)

Cougar Energy Ltd plans pilot burn for a 400MW combined cycle power project

Carbon Energy PL plans 100-day trial to show commercial feasibility of the CRIP UCG process

Chinchilla probably air dried analysis of sub bituminous coal

Linc Linc Energy Limited Presentation 2006Level 7, 10 Eagle StreetBRISBANE, QLD 4000Ph: (07) 3229-0800Email: pab@lincenergy.com

Location

Chinchilla Project

India India has fourth-largest coal reserves in world UCG will be used to tap those India coal reserves that are difficult to extract by conventional technologies. Oil and Natural Gas Corporation Ltd. (ONGC) and Gas Authority of India Ltd. (GAIL) plan pilot projects using recommendations of experts from Skochinsky Institute of Mining in Moscow and Ergo Exergy (Khadse et al., 2007). Scheduled production is 2009 UCG Lignite coal for electric power. It is also reported that AE Coal Technologies India Pvt. Limited, a company belonging to the ABHIJEET GROUP of India, is implementing UCG Projects in India

Western EuropeA number of UCG tests have been carried outA significant difference of these tests is depth of seams (600-1200 m)In 1992-1999, UCG project was conducted by Spain, UK and Belgium at “El Tremedal” (Spain)In 2004, DTI (UK) identified UCG as one of the potential future technologies for development of UK's large coal reserves

New Zealand Solid Energy New Zealand Ltd, company founded on mining coal in difficult conditions plans to use Ergo Exergy’s εUCGTM technology for low cost access to un-minable coal

JapanUniversity of Tokyo and coal companies are conducting technical and economic studies of UCG on a small scale are planning a trial soon

South AfricaEskom, A coal-fired utility, is investigating UCG at its Majuba 4,100 MW power plantErgo Exergy provides technology to build and operate a UCG pilot which was ignited in 2007Project will be expanded in a staged manner, based on success of each preceding phase Project currently generates ~3,000 m^3/hr of flared gas. Volumes will increase to 70,000 m^3/hr early next year and be piped to power station before eventually rising to 250,000 m3/hrSome 3.5 million m^3/hr will be supplied to power station at full production that is anticipated around 2012

Eskom is moving ahead with the next phase UCG project. Declining coal reserves is one of the biggest problems facing Eskom, as it struggles to overcome a power shortages since January. Eskom plans to pipe greater volumes of gas to Majuba power station to help it become more coal efficient.Coal from nearby mines supplies the Majuba Power Station but transportation costs are high because of bad roads. UCG utilizes unmineable coal resources.

 Eskom estimates there are an additional 45 billion tons of coal suitable for UCG in the country, excluding coalfields in KwaZulu-Natal province. Eskom produces about 95% of South Africa's electricity and is spending billions of dollars to expand generating capacity to meet demand from country's growing economy.

Eskom Power Plants

Majuba plant

ChinaChina has largest UCG program Since late 1980s, 16 UCG trials previous or current Chinese UCG trials utilize abandoned coal minesVertical boreholes drilled into abandoned galleries to act as injection and production wells

Commercialization Xin Wencoal mining group has six reactors with syngas used for cooking and heating

A project in Shanxi Province uses UCG gas for production of ammonia and hydrogen

HebeiXin’ao Group is constructing a liquid fuel production facility fed by UCG ($112 million); 100,000 ton/yr of methanol and generate 32.4 million kWh/yr

Researchers investigated the two-stage UCG process proposed by Kreinin (1990) for production of hydrogen, where a system of alternating air and steam injection is used.

Experiments, conducted in Woniushan Mine, Xuzhou, Jiangsu Province, prove feasibility to use UCG for large-scale hydrogen production (Yang et al., 2008).

Rick Wan, Ph.D XinAo Group (www.xinaogroup.com) P. R. China

UCG in China

Long Tunnel、 Large section two Stages

Rick Wan, Ph.D XinAo Group (www.xinaogroup.com) P. R. China

China System

Gasification Reactions

and

Implications for Gas Composition

Gasification Reactions and Implications for Gas Composition

Gas composition depends on reactions initiated by introduction of Air or Oxygen and availability of Hydrogen ( in part from coal mainly from formation water)

As coal burns it provides energy to produce combustible gases CO, H and CH4

As gas is extracted back through burn cavity different reactions take place based on temperature amount of water infiltration oxidizing or reducing conditions

Actual thickness of burn zone is thin ( <0.5 metres) because of low conductivity of coal

Rate of advance controlled by rate of injection of Air or Oxygen to drive process

1 cubic metre of gas requires about 0.4 Kg of coal or 1 tonne coal produces 2500 m^3 gas

Gasification Reactions and Implications for Gas Composition

Changes in composition transverse to burn direction

Equilibrium Calculation for Coal Gasification (From Stephens, 1980).

Provides surface area for gasification reactions

gas recovery holeair injection hole

burn progression

BurnCavity

Ash and char

An Overview of Soviet Effort in Underground

Clasification of Coal Gregg et al (1976)

2/ Combustion ZoneCombustion Zone Oxidation zone exothermic Temperature rising Coal consumed

C+O2 CO2 C+1/2 O2 CO 2CO+O2 2 CO2 CH4+O2 CO2+2H2O

3/ Gasification ZoneGasification Zone Reduction zone Endothermic Temperature falling until reactions stop no more coal consumed

C+CO2 2 CO H2O+C CO+H2

4/ Reduction ZoneReduction Zone Gas transport zone Lower temperature

Shift conversion reaction reduces heat value of gas

CO+H2O CO2+H2

methanation C+2 H2 CH4

General Gasification Zones in Burn Cavity along burn direction

Initiation of cavity using counter current flow1/ De-volatilization zoneDe-volatilization zone

43

21

Adapted from

De-volatilization zone

Methane evolved from coal is consumed

CH4+O2 CO2+2H2O -891 kJ/mol

Reaction provides heat in advance of main burn front

UCG Relationship of Reactions to Location in Burn Zone

Un-affected coal

De-volatilization zone

Combustion zone

Burning at coal face provides heat

Oxidation C+O2 CO2 -406 Kj/mole

Partial Oxidation C+1/2 O2 CO -123 Kj/mole

Main volume of heat generation zone is surprisingly thin

CO2 produced to provide energy to make combustible gases

UCG Relationship of Reactions to Location in Burn Zone

Combustion zone

Gasification zone

As Oxygen is used reduction of CO2 occurs

Boudouard Reaction C+CO2 2 CO +159.9 Kj/mole also reversal 2 CO+O2 2 CO2

Heat is used up to generate a gas rich in CO

The Boudouard Reaction is sensitive to chemistry of ash rubble forming in burn cavity

Gasification zone

UCG Relationship of Reactions to Location in Burn Zone

Reduction zone

Water shift reaction steam enters burn zone

H2O+C CO+H2 +118.5 Kj/mole

Shift conversion reaction CO+H2O H2 + CO2 - 42.3 Kj/mole

Hydrogenating gasification C+2 H2 CH4 –87.5 Kj/mole

methanation CO+3H2 CH4 + H2O -206 Kj/mole

Reactions use heat Temperature falling Reactions use water entering cavity to convert CO to H resulting in a lower heat value gas

Reduction Zone

UCG Relationship of Reactions to Location in Burn Zone

Produced Gas Composition

Implications on Processes

Air injection

Oxygen+Steam (?) injection

Summary of

Gas Composition for

World ProjectsN ?

0 2 4 6 8 10 12 14

Gasification at

Gasification at

Gas Composition using

Air or Oxygen Injection

Increasing CO2 production

Increasing CO2 production

Implications of Counter Current and Co Current Burn Geometries

Co Current (forward) Geometries

Co Current more oxygen in channel

Best for continuing gas production

In the CRIP method channel A to B is a slotted liner in a hole

Coal

B

Coal

B

cocurrent

countercurrent

high gas flow thru channel little burn widening not suceptable to plugging

Burn progresses into channel widens and makes better use or resource

An Overview of Soviet Effort in Underground Clasification of Coal Gregg et al (11976)

Coal

B

cocurrent

countercurrent

high gas flow thru channel little burn widening not suceptable to plugging

Burn progresses into channel widens and makes better use or resource

Implications of Counter Current and Co Current Burn Geometries

Counter Current (reverse )

Counter Current Develops small channel with constant diameter

Is less susceptible to plugging caused by coal swelling or plugging by liquids.

Ideal for forming high permeable channels in coal during initial burn but results in poor use or resource for continued burn

Implications for gas composition (??)

In Co Current method product gas stays hotter moves over char rubble zone maybe more reverse shift reaction CO+H2O H2 + CO2

In Counter Current method gas cooler may pick up CH4 form coal may be more CO rich

Gas Composition some Basic Controls using Mass Balancing Some analyses of product gas illustrate basic mass balances of gasification process

Note results are illustrative a number of hidden assumptions

CO2 H2 N2 CO CH4 MJ/m^3

USA 1 1948 6 0.9 79.5 0.5 0.4 1.882 1952 11.7 7.6 70.9 7.1 2.1 2.68

3 1948 44 25.1 16.1 1.9 10.1 8.424 1979 15 12.4 49 8 2.9 4.31

UK 5 1950 15.5 7.9 70.7 4.9 1.0 2.05Italy 6 1979 19.7 15.6 57.8 4.5 2.2 3.43

Belgium 7 1979 36.1 36.1 0 18.5 5.4 8.558 1979 13.4 31.2 2 36.2 3.0 9.67

9 1979 19.3 17.6 0 53.3 0.7 9.27

France 10 1955 19.5 15 57 4 4.5 4.08FSU 11 1952 12.1 14.8 54.1 15.9 1.8 4.18

12 1956 19.5 14.1 55.9 7.1 1.5 3.513 1964 5.6 18.4 44.9 28.7 2.1 6.49

China 14 1958 15.8 15.9 58.1 7.3 1.2 3.8115 1958 8.3 10.7 62.6 15 0.7 3.516 1958 10.3 16 49.2 21.3 2.8 5.5317 1994 12.6 63.6 1.7 11.9 10.2 13.6818 1996 10.5 53.1 4.4 24.8 7.2 12.74

Gas composition some Basic ControlsCarbon

Amount of carbon in produced gas indicates amount of coal consumed per cubic metre of gas recovered = Amount A

Based on heat value of coal (HVB coal with 45% FC; 22 Mj/Kg; 6% H arb) and heat value of gas (6 Mj/Kg) it is possible to calculate minimum amount of coal required = amount B

It is then possible to calculate a thermal efficiency for coal to gas conversion = B/A

0.0

0.5

1.0

1.5

2.0

2.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

m^3 air for 1 m^3 gas

thermal efficiency ratio

Kg coal consumed for 1 m^3 gas

Average gas analyses from various sources compared to a fixed coal composition

Gas composition some Basic ControlsOxygen

Pressure of injected air less than hydrostatic pressure to limit gas loss control water inflow

Therefore seam depth influences injection pressure P1

Amount of oxygen in product gas indicates amount of air being injected per m^3 product gas (assuming air not oxygen)

Rate of air injection controlled by P1 (=seam depth) Permeability Distance between injection and recovery holes and P2 (Pressure maintained in recovery hole)

Gas recovery rate controlled by P2 Low P2 provides high rate but risk high water inflow

Rate of air injected controls rate of burn but must match burn cavity volume

0.0

0.5

1.0

1.5

2.0

2.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

m^3 air for 1 m^3 gas

thermal efficiency ratio

Kg coal consumed for 1 m^3 gas

Average gas analyses from various sources compared to a fixed coal composition

Gas Composition some Basic ControlsHydrogen

Amount of H in product gas indicates how much water other than that in coal is required to make gas ( ie inflow or injected)

Hydrogen in coal is present as H in ultimate analysis (dry basis) (decreases with increasing rank 6% - 1%)H in water in Equilibrium Moisture (decreases with increasing rank 4% - 0.1%)H in water Surface Moisture (variable 0% - 2%)

All these Coal sources of hydrogen tend to decrease as rank increases but total amount of H is never sufficient to provide all H in product gas Excess is expressed as m^3/tonne coal gasified)

0.0

0.5

1.0

1.5

2.0

2.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Cubic metres make-up water per tonne coal gasified

Need infiltration or steam injection of about

1 m^3 water per tonne coal gasified

Gas Composition some Basic ControlsHydrogen The uneasy balance

Gasification requires more H (water) than is available in coal Amount increases with rank High injection pressure may increase subsidence into burn cavity causing increase gas loss (possibly higher heat value) Therefore inject at below hydrostatic pressureIncrease water inflow will degrade heat value of gas especially if seam < 2 metres thickUsing water from surrounding rock draws down hydraulic head Inflow brine brings alkalies into chemical reactions

Mj/m^3

Seam thickness metres

Excess water

Decrease heat value

Thinner seam greater heat loss

Gas Composition some Basic ControlsHydrogen

The uneasy balance excess water increases CO2 content of gas and decreases H2, CO and CH4 contents

Decrease in seam thickness causes decrease in H2, CO and CH4 contents at constant water inflow

0

4

8

12

16

20

0.5 1 1.5 2 2.5 3 3.5 4

specific water inflow m^3/tonne coal gasified

Gas

com

posi

tion

mol

e %

solid lines = 2 m thickdashed lines = 8.5 m thick

CO2

CH4

CO

H2

An Overview of Soviet Effort in Underground Classification of Coal Gregg et al (1976)

900800700600

Temperature Kelvin

Vapour

Water Inflow Implications

As excess water enters cavity it is heated from insitu to burn cavity temperature (40C to 800C ?) Water is converted to high density vapour. There is some expansion which produces extra pressure in burn cavity This may increase permeability connection to surrounding rocks and increase gas loss

Martin Chaplin October, 2008 http://www.lsbu.ac.uk/water/phase.html

Martin Chaplin October, 2008 http://www.lsbu.ac.uk/water/phase.html

Water Contamination

Concentrations of benzene, total phenols, total PAH, at Chinchilla, Hoe Creek and Carbon City.

Condensate water and oil, second and third sets, show high levels of these compounds are produced, but groundwater levels below background (red line) (Blinderman and Jones, 2002).

Based on experience in FSU and Australia Important to keep injection pressure just below hydrostatic pressure This ensures some water inflow which keeps burn chamber hot and oil compounds in vapour phase also forms a steam jacket around burn cavity acts as a dynamic seal

Chinchilla

Coal and Ash

Influence on UCG

Rank Influences on Gasification ReactionsDuring pyrolysis volatiles and moisture are lost from coal causing shrinkage of over 40% for low rank coals 35% to 40% for bituminous coals and 5% to 10% for anthracites, High volatile+moisture content = less residue char volume to gasify and increased burn cavity volume.

UCG works best on low rank, non-caking coals (lignite sub-bituminous) (Burton et al., 2006) These coals tend to shrink upon heating, enhancing permeability and connectivity between injection and production wells.

low rank coals have high reactivity and high moisture and volatile contents.

UCG works on some bituminous coals however they tend to swell (plasticize) (Stephens, et al.,

1985) which may affect permeability required for injected gases.

Tests on bituminous coals at Lisichansk, Russia, and Princetown, USA.

In FSU, one test using semi-anthracite (Thulin), which was not a success.

Gasification of higher rank coals will require more water injection higher combustion

temperatures.

Sources File 19156.pdf Berr.gov.uk Best Practices in Underground Coal Gasification Burton Friedmann Upadhye Lawrence Livermore National Laboratory

Considerations Based on Rank and Coal Quality

Water content Low rank coals require less extra water or steam injection

Plasticity Bituminous coals swell and get sticky during heating can block gas movement ( anthracites do not swell but will not shrink much)

Amount of tars Can condense in pipes decrease permeability in coal enter ground water

Cleating Controls natural permeability of seam aids/inhibits gas water movement

Reactivity Decreases as with rank increases

Shrinkage Less volatiles+moisture as rank increases less shrinkage

Rank

liquids tars

plasticitywater content

Cleat spacing

Incr

easi

ng

Reactivity Steam requirements

shrinkage

Influence of Ash Amount and Composition on Gasification

Ash content from 0% to 40% does not appear to impact heat value of gas

Acts as a heat sink stabilizes gasification reactions

Ash composition effects temperature at which ash softens and melts effects cavity wall

Need a slagging ash lower temperature melting less dry ash in recovered gas seal cavity walls

Need a fouling ash high melting temperature Ash collects in burn cavity with char and helps support burn cavity

In detail ash chemistry probably effects gasification reactions

Effect of Rock Chemistry on Burn Cavity Wall Conditions

Ash chemistry controls temperature at which ash softens and eventually melts

Ash that softens at lower temperature (high propensity to slag) will release less ash into gas and fuse/seal cavity walls better

Controls on slagging melting temp decreases

If Base/Acid ratio higher

If Iron/Calcium ratio higher

If Silica/Alumina ratio higher

If Na+Ka content higher

If Total S content higher

Vaninetti and Busch 1982

1000

1100

1200

1300

1400

1500

0 10 20 30 40 50percent iron

degr

ees

C s

ofte

ning

.

Oxidizing

Reducingcoal range

1000

1100

1200

1300

1400

1500

0 1 2 3 4silica/alumina ratio

degr

ees

C f

luid

.

coal range

1000

1100

1200

1300

1400

1500

1600

1700

020406080100 basic content %

degr

ees

C f

luid

.coal range

Effect of Rock Chemistry on Gasification Reactions

The Boudouard reaction C+CO2 2 CO +159.9 Kj/mole

Is strongly influenced by presence of alkali elements in coal ash or in roof or floor rocks

There are many studies on coke making for steel industry that document relationship between coke reactivity and alkali elements in coke

Cok

e re

acti

vity

ind

ex

Percent K in coke

Price and Gransden 1987

It has also been suggested that the impurities in lower rank coals improve the kinetics of gasification by acting as catalysts for the burn process. Best Practices in Underground Coal Gasification Burton Friedmann Upadhye Lawrence Livermore National Laboratory

Coke strength after reaction (CSR) and Coke reactivity Index (CRI) TestsCoke is reacted in an atmosphere of CO2 at 1100Ç

If K% changes 0 to 0.1% there is a 15.8% increase in CO% and decrease in CO2 % in off gas

This helps convert excess CO2 and increase heat value of gas

Heat flow per second =conductivity* (temp difference)/( distance)

Temperature increase = heat/specific heat/mass

Rock Properties

Importance of Conductivity and Specific Heat of coal and adjacent rocks

During gasification it is important that heat not escape

Low conductivity of coal helps insulate burn cavity

Collapse of roof may aid gas loss and convective heat loss

If cavity contacts roof rock then there is increase heat loss and change in gas composition

Conductive heat loss is sufficient to significantly increase temperature of adjacent seams and initiate temperature driven methane desorption

conductivity specific heat

Rock Type watt/m/k watt/m/k kj/kg/k kj/kg/k

Coal 0.22 0.55 1.26 1.38

granite 1.73 3.98 0.79

limestone 1.26 1.33 0.84

sandstone 1.83 2.9 0.92

Production

and

Resource Considerations

Production ConsiderationsMust establish high permeability linkage from injection to recovery hole

Production parameters; such as Air Injection Pressure and Rate, Gas Recovery Pressure, Gas Flow Rate, Water Content in gas, Gas Composition, Heat Value; are all inter connected

Coal consumption calculated from gas volume/day and carbon content of gas

Air injection (m^3/hr) controls Gas production (m^3/hr) and coal consumption

Inject air or oxygen at below hydrostatic pressure Some water inflow Minimum gas loss

Air injection rate must match surface area available for burning and oxygen Consumption needs cavity with reactive char

Ash content Moderate ash may be beneficial provides mechanical and thermal stability to burn chamber Promote reactions

At greater depth counter current burn may be difficult depending on linkage method

Deeper seams probably need oxygen injection not air (no 80% N to compress)

Huff and Puff method alternating steam and air or O. produces higher heat value for gas

Steep Dipping seams may cave into burn zone making for better resource utilization

Keep temperature in channel and recovery hole above 150Ç to stop condensation and plugging

Resource Considerations

UCG recovers about 55% of energy in coal CBM recovers 1% to 3%

CRIP type gasification method Must drill injection hole along footwall

Burn chamber width/height ratio about 6 to 1 with 70% utilization of coal within rectangle If thermal efficiencies 55% This gives resource utilization of about 40%

If horizontal hole =1000 metres in 4 metre thick seam about 0.1 million tonnes coal gasified

At 4 mmcf/d (113 m^3/d) this gives ten year life for drill hole infrastructure

Injection hole

sequential gas recovery holes

Need to expand cavity transverse to burn direction

Paired horizontal hole method by British Gas increases resource per hole

Resource Considerations

Inclined seam method can recover more gas per drill hole based on length of linkage

Potential to gasify larger tonnage of coal geometry similar to long wall mining

Second stage air injection holes drilled in footwall clear of subsidence

Kreinin and Revva (1966)

UCG Synergies

and

Problems

UCG Synergies with CBM

CBM production prior to UCG can dewater seam while recovering CH4 May limit problems from water inflow during UCG

CBM horizontal holes adapted for CRIP after CBM extraction

Heating of surrounding seams may stimulate CH4 desorption without pressure decrease

Could be UCG of a seam and CBM recovery of adjacent seams.

Advances in hydraulic fracturing in horizontal CBM and shale gas holes may have application in preparing injection holes for UCG and improving linkage in CRIP British Gas method of UCG

The CO2 Problem

UCG produces more CO2 per unit of heat than coal

Needs to be paired with carbon capture sequestration (CCS)

Sequestration Options are

Adsorbed on coal

Free gas in burn cavity

Super critical fluid in burn cavity

Other or combination

Using average coal 55% C and 0.35 Kg coal (ash free) required to make 1m^3 gas

1 m^3 of burn cavity responsible for over 2000 m^3 of gas production at stpEquivalent volume of CO2 at surface is about 750 m^3 stp

The CO2 Problem

Adsorb CO2 on Coal Adjacent to Burn Cavity

Coking of coal decreases adsorption ability As documented by decrease adsorption ability of inert coal macerals compared to vitrinite macerals

Coal available for CO2 adsorption per m^3 of cavity limited Adsorption ability low

Very unlikely to be able to adsorb 750 m^3 CO2 per 1 m^3 burn cavity

Free Gas in Burn Cavity above 800 metres

The 750 m^3 CO2 will occupy about 10 m^3 at 800 metres

Sequestering free gas not possible

The CO2 Problem

Super Critical Fluid in burn cavity

Plot shows changes in SG of CO2 above critical point Red line is tract for geothermal gradient

1 m^3 cavity responsible for 750 m^3 CO2 gas with mass of 1470 kg (CO2)

Density of CO2 fluid at 1500 metres is 710 kg/m^3

Volume required to sequester 1.8 Kg CO2 over 2 m^3 but only 1m^3 space available

700700

10001250150017502100

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1750 m 2100 m

The CO2 Problem

Other or Combination

There may be potential for mineral sequestration of CO2 by forming carbonates with oxides in ash left after burning coal

Hydrated oxides of Ca Mg and Fe may form carbonates when CO2 is introduced into burn cavity. However some of the CO2 sequestered was originally present in the ash as carbonates ( no net benefit)

It may be possible to pre treat cooled burn cavity to improve seal prior to CO2 injection

UCG Applications in BC

Where ever UCG is suggested there must be considerable preparatory studies to convince agencies that environmental impacts in terms of Ground Water Contamination - GHG Emissions

- Ground Subsidence Are acceptable

Low rank coals large scale UCG for electrical generation

- Hat Creek has options for UCG in steeply dipping beds similar to early FSU projects

High-volatile bituminous coals deep CRIP UCG

- Gething seams in northern part of Peace River Coalfield are deep and flat dipping similar to present projects in Alberta

Low rank coals local small scale UCG for electrical generation

- Tuya River, Coal Creek shallow flat dipping similar to Chinchilla

High-volatile bituminous coals shallow CRIP UCG

- Telkwa flat dipping shallow

Summary

Summary Facts

UCG can make use of coal resources that might otherwise not be used

UCG can recover over 50% of heat value in coal and up to 70% of coal targeted by drilling

It is possible to sustain and control UCG

Apply to seams thicker than 2 metres

Apply to low rank coals (high-volatile bituminous Rmax 0.5% to 0.8%) non swelling

Use co current flow for continued production

Inject Air or Oxygen at or below hydrostatic pressure control gas loss and water inflow

For deeper UCG use oxygen rather than air to minimize compression costs also gas low N content can be transported (remove CO2) use as syn gas

It may be necessary to extract water from burn cavity during and after burn for treatment

In flow water ensures contaminants removed as steam during cavity cleaning

Summary

Opinion Up Beat

☻ Gas that comes to surface is generally lower in particulates, Hg, SO2 , and tars than Syngas generated by coal gasification at surface

☻ New UCG production methods (CRIP CRIP knife edge) combined with horizontal holes drilled along seam footwall provide better control and access to coal resource

☻ Inject Oxygen to decrease Nitrogen content in produced gas and compression costs

☻ Make use of heat of recovered gas (pre heat injected air?)

☻ Consider ash chemistry to influence Boudouard Reaction to minimize production of CO2

☻ Deep UCG less risk of aquifer contamination problems

☻ Burn cavity may be available for sequestration of super critical CO2 fluid

☻ Gas may contain valuable bi products

Summary

Opinion Down Beat

UCG gas is low heat value must be used close to source

UCG gas high CO2 content Produces more CO2 per unit of heat than burning coal

In future UCG must be paired with CCS ?

A number of pilots had problems controlling water influx and water contamination by organic compounds (Benzene)

Roof subsidence into burn cavity can initiate gas loss and excess water inflow

Recovered gas may contain H2S

Condensates in recovered gas can plug pipes

Temperature in gas production pipes can damage cement bond and pipe steel

Observation

Unconventional Gas

Really is

Gas with increased

Problems Costs Risks

When and Where

To Go

to

CBMShale Gas

UCG gas

Your ChallengeYour Challenge

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Tight Gas

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bryan@islandnet.com