Post on 31-Mar-2015
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).
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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geothermal gradient ST 10C Grad 30C
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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