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					Underground Coal Gasification UCG
                Or
  In-situ Coal Gasification ISCG
            A very unconventional gas

                 Barry Ryan
                    Consultant




                 bryan@islandnet.com
                          Disclaimer
                    I 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 UCG
                        Burn coal insitu and recover a low btu gas at surface
                            link air injection hole and gas recovery hole
               Burn can move towards air injection hole (counter current circulation )
            or in same direction as air towards gas recovery hole (co current circulation)




Coal seam




                                                       Courtesy ErgoExergy
                         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
Surface and Underground Coal Gasification
          produces a low btu gas
                        of
varying composition depending on conditions
                          Surface Gasification
               High Volatile Bituminous Coal (Rm 0.61%)
                           Coal Valley Luscar




               Time Minutes
                                   Gas from UCG
                            A very Unconventional Gas
       UCG Gas is multi gas composition has low btu contains moderate CO 2 content

                                 Approximate comparisons
           natural gas      CBM       Shale Gas   UCG Gas
                         composition                           Example from
CH4                                                            Hanna USA
               98             98         98           4
CO2             2              2          2          15
CO              0              0          0           6
H2              0              0          0          12
N2              0              0          0          63
                         Heat value
Mj/m^3         39             39         39         3.87
Kcal/m^3      9300          9300        9300        925
                         Kg CO2/m^3
               1.97         1.97        1.97        0.49
                         CO2 Kg per 1000 Kcal      using HHV and SG at 0 C
                                                           Mj/m^3 Kcal/m^3       Kcal/g
methane                          0.2                  C                            8.1
                                                     CH4    39.8        9505      13.3
coal                             0.4                 CO     13.6        3255       2.6
UCG gas                         0.53                  H     12.8        3045      34.2
       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
Basin                      Donets Basin     Kuznets Basin     Moscow Basin   Tashkent Area
Plant                         Donbass          Kuzbass        Podmoskovnyi      Angren
Coal deposit                 Lisichansk     Yuzhno-Abinsk         Tula          Angren
Start date                      1933             1955             1940            1962
rank                        bituminous       bituminous          Lignite         lignite
ash            %               6 to 16          4 to 10          27 to60            11
vols           %                25-35          20 to 30          17 to 27       25 to 30
moist          %                  15             5 to 8          20 to 30           30
S              %                1 to 5                                              1
heat           Kcals/kg      4500-5000         5000-6000       2000-5000          3650
geology                   steeply dipping   steeply dipping    horizontal    sub horizontal
seam thick     metres        0.4 to 1.5          2 to 9          2 to 4          4 to 24
depth          metres            400                            40 to 60       110 to 250
gasification
heat content   Kcal/m^3    800 to 1000           1000          700 to 900      800 to 850




Another version
compare later
                 Early FSU Methods for UCG in Dipping Seams
     Initial 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

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.
Bulldoze alluvium to
seal fractures limit
gas leak




Kreinin and Revva (1966)
                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




Injection
air                                                                              150’C



                                               Overburden
                                                                          Gas recovery hole

    Pyrolysis      Water influx
                                           Gas losses
    products

                              800-1200’Ç                    Pyrolysis products
                                                                                           Coal
                                  Rubble                                                   seam
                                                                                         800’C
                  FSU Vertical Drill Pattern for horizontal seams
                               Plan views of developing geometry by stage


                        Gas recovery hole      Burn progression             Air injection hole

Stage 1
Form linkage along line of
vertical holes counter
current burn                                                 Gas flow

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
    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
             Recent Important Development in UCG Geometry
                      CRIP (Controlled Retractable Injection Points)
         Makes use of modern horizontal drilling techniques applied to horizontal seams
                                           initial ignition in gas                 gas recovery
                                           counter current gas flow                hole
                                            recovery hole


                          Injection hole



                              later ignitions retreat along injection hole
                              co current gas flow


                  ignition point



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

                 End view of injection hole and burn cavity



                                                                             Must drill along base of seam
Width height ratio about 6/1 therefore seam thickness controls amount of resource around each hole
                         Development of the CRIP Method
                        (Controlled Retractable Injection Points)
                   Centralia Washington (Toni 1) 1983
               Hanna Wyoming (Rocky Mountain RM1) 1987
Tests 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 technology
Company 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




For CO2 storage




                                                  Friedmann Burton Upadhye
                                                  Lawrence Livermore National Laboratory 2007
       Evolution of Test Site Experience
Progression   Trying deeper seams             Trying thinner seams




                                                             Trying deeper
                                                                   and thinner
                                                                     Minimum thickness



               “Best Practices in Underground Coal Gasification”, E.Burton, J.Friedman, R. Upadhye,
               Lawrence Livermore Nat. Lab., DOE Contract No. W-7405-Eng-48
                             UCG Activity around the World




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

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




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




Hanna




                          Friedmann Burton
                          Upadhye
                          Lawrence Livermore
                          National Laboratory
                          2007
Experience from the Hanna UCG Project Wyoming 1973
                    One of the earliest tests outside FSU




     Basin                    Hanna basin
     Coal deposit             seaam No1
     Start date               1973
     rank                     Sub bituminous
     ash             %              23.76
     vols            %              32.64
     moist           %               9.51
     S               %               0.68
     heat            Kcals/kg       4810
     geology                    broad syncline
     seam thick      metres           9.1
     depth           metres       91 to 122
     gasification
     heat content    Kcal/m^3       1120
                                 Data from the Hanna Project
          Air injection   red    Air injection rate drives gas production

          Gas production black




1800 Kcal/m^3




900 Kcal/m^3
Location of UCG projects in Western Canada




                                Synergia Polygen Swan Hills

                                Laurus Energy



 0      300 Km
                                         Australia
Linc Energy Ltd UCG trial Chinchilla, Queensland using Ergo Exergy’s technology
Project (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/day
Gas 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)


                      Chinchilla probably air dried
                      analysis of sub bituminous coal




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
      Location
Chinchilla Project




 Linc Linc Energy Limited
 Presentation 2006
 Level 7, 10 Eagle Street
 BRISBANE, QLD 4000
 Ph: (07) 3229-0800
 Email: pab@lincenergy.com
                                      Western Europe
A number of UCG tests have been carried out
A 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

                                            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
                                        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

                                            Japan
University of Tokyo and coal companies are conducting technical and economic studies of UCG
on a small scale are planning a trial soon
                                         South Africa
Eskom, A coal-fired utility, is investigating UCG at its Majuba 4,100 MW power plant
Ergo Exergy provides technology to build and operate a UCG pilot which was ignited in 2007
Project 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/hr
Some 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
                                            China
China has largest UCG program Since late 1980s, 16 UCG trials previous or current Chinese
UCG trials utilize abandoned coal mines
Vertical 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).
UCG in China




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



    Long Tunnel、Large section two Stages




                                           Rick Wan, Ph.D XinAo Group
                                           (www.xinaogroup.com) P. R. China
     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 CH 4
    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


                                            burn progression
             air injection hole                                         gas recovery hole


                             Burn
             Cavity
                                     Ash and char

                                  Provides surface area for gasification reactions




                                                               An Overview of Soviet Effort in Underground
                      Equilibrium Calculation for Coal
                      Gasification (From Stephens, 1980).      Clasification of Coal Gregg et al (1976)
                                 General Gasification Zones in Burn Cavity
                                           along burn direction
     1/ De-volatilization zone       Initiation of cavity using counter current flow
               2/ Combustion 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 Zone Reduction zone Endothermic Temperature falling
                                          until reactions stop no more coal consumed
                                             C+CO2  2 CO H2O+C  CO+H2


                                        4/ Reduction Zone Gas transport zone Lower temperature
                                            Shift conversion reaction reduces heat value of gas
                                                            CO+H2O CO2+H2
                                                       methanation C+2 H2  CH4




                                                        4
                    1                         3
                                    2
Adapted from
   UCG Relationship of Reactions to Location in Burn Zone


    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




Un-affected coal

        De-volatilization zone
UCG Relationship of Reactions to Location in Burn 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




              Combustion zone
UCG Relationship of Reactions to Location in Burn 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
Produced Gas Composition
Implications on Processes
                                                Summary of
                                            Gas Composition
                                                  for
                         N?
                                              World Projects
                                        Air
                                        injection




                                        Oxygen+Steam
                                        (?) injection




0   2   4   6   8   10        12   14
                                   Gas Composition using
Gasification at

Gasification at                    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




                                                               cocurrent
                             Coal
                                                    B




            Burn progresses into channel widens and makes better use or resource


                                                                 countercurrent
         An Overview of Soviet Effort in Underground Clasification of Coal Gregg et al (11976)
 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.
                                                cocurrent
     Ideal for forming high permeable channels in coal during initial burn but results in poor
                         Coal
    use or resource for continued burn
                                         B
                          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
            Burn progresses into channel widens and makes better use or resource


                                                countercurrent
                        Coal
                                         B




           high gas flow thru channel little burn widening not suceptable to plugging
 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     1.88
            2    1952     11.7      7.6    70.9      7.1      2.1     2.68
            3    1948      44      25.1    16.1      1.9     10.1     8.42
            4    1979      15      12.4     49        8       2.9     4.31
    UK      5    1950     15.5      7.9    70.7      4.9      1.0     2.05
   Italy    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     8.55
            8    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     4.08
    FSU     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      3.5
            13   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     3.81
            15   1958      8.3     10.7    62.6      15       0.7      3.5
            16   1958     10.3      16     49.2     21.3      2.8     5.53
            17   1994     12.6     63.6     1.7     11.9     10.2    13.68
            18   1996     10.5     53.1     4.4     24.8      7.2    12.74
                          Gas composition some Basic Controls
                                        Carbon
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

          Average gas analyses from various sources compared to a fixed coal composition
2.5


2.0                                                                 m^3 air for 1 m^3 gas

1.5
                                                                            thermal efficiency
                                                                            ratio
1.0


0.5

                         Kg coal consumed for 1 m^3 gas
0.0
      1   2     3    4       5    6     7    8     9      10   11   12    13    14   15     16   17   18
                           Gas composition some Basic Controls
                                         Oxygen
Pressure of injected air less than hydrostatic pressure to limit gas loss control water inflow
Therefore seam depth influences injection pressure P 1
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
                     Average gas analyses from various sources compared to a fixed coal composition
           2.5


           2.0                                                                 m^3 air for 1 m^3 gas

           1.5
                                                                                       thermal efficiency
                                                                                       ratio
           1.0


           0.5

                                    Kg coal consumed for 1 m^3 gas
           0.0
                 1   2     3    4       5    6     7    8     9      10   11   12    13    14   15     16   17   18
                           Gas Composition some Basic Controls
                                       Hydrogen
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)

 2.5

 2.0                   Cubic metres make-up water per
                       tonne coal gasified

 1.5

 1.0

 0.5

 0.0
       1   2   3   4   5   6   7   8   9                  15 infiltration
                                           10 11 12 13 14Need 16 17 18      or steam injection of about
                                                          1 m^3 water per tonne coal gasified
                     Gas Composition some Basic Controls
                           Hydrogen 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 pressure
Increase water inflow will degrade heat value of gas especially if seam < 2 metres thick
Using water from surrounding rock draws down hydraulic head
Inflow brine brings alkalies into chemical reactions



         Mj/m^3
                                          Excess water
                                      Decrease heat value




                                  Thinner seam
                                  greater heat loss


                        Seam thickness metres
                                            Gas Composition some Basic Controls
                                                        Hydrogen
                                     The uneasy balance
excess water increases CO2 content of gas and decreases H 2, CO and CH4 contents
Decrease in seam thickness causes decrease in H2, CO and CH4 contents at constant water
inflow


    20                                           solid lines = 2 m thick
                                                 dashed lines = 8.5 m thick


    16                                                                                         CO2


    12
                                                                                             H2
               Gas composition mole %




     8                                                                                         CO


     4
                                                                                            CH4
                                            specific water inflow m^3/tonne coal gasified
     0                                                                                               An Overview of Soviet Effort in
         0.5                            1       1.5          2         2.5          3         3.5    Underground Classification of Coal
                                                                                                             4
                                                                                                     Gregg et al (1976)
                                          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


                                                                      600     700    800          900




                                                                            Vapour




                              Temperature Kelvin
                                                                                       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 Reactions
During 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



                                            Reactivity                          Steam
                                                                                requirements



                                                                   plasticity
                            water content
                              shrinkage                  liquids tars
             Increasing




                                                                                    Cleat spacing


                                                     Rank
       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
                                                                        1500
Controls on slagging melting temp decreases




                                                                                   degrees C softening .
                                                                        1400
If Base/Acid ratio higher                                                                                                                   Oxidizing
                                                                        1300
If Iron/Calcium ratio higher
                                                                        1200
If Silica/Alumina ratio higher                                                                                                           Reducing
                                                                        1100                           coal range
If Na+Ka content higher
                                                                        1000
If Total S content higher                                                      0                                               10   percent iron 30
                                                                                                                                      20                       40   50
                                                                               1700
 1500
                                                                               1600
 1400                                                                          1500




                                                                                                           degrees C fluid .
            degrees C fluid .




                                                                               1400
 1300
                                                                               1300
 1200
                                                                               1200
                                                                                                                                                 coal range
 1100                                     coal range                           1100
                                                                            1000
 1000
                                                                         100                                              80        60 basic content %
                                                                                                                                               40             20    0
        0                            1   silica/alumina ratio
                                                   2            3   4
                                                                                                                                    Vaninetti and Busch 1982
                   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

                                     Coke reactivity index   Price and Gransden 1987




                                                                                            Percent K in coke




               Coke strength after reaction (CSR) and Coke reactivity Index (CRI) Tests
                           Coke 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 CO 2 % in off gas
                          This helps convert excess CO2 and increase heat value of gas

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
                                      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

             Heat flow per second =conductivity* (temp difference)/( distance)
                       Temperature increase = heat/specific heat/mass

                                 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 Considerations
Must 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

                                                           sequential gas recovery   holes

               Need to expand cavity           Injection hole
               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 CH 4 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 stp
           Equivalent 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


                      boundary liquid-gas                                                                               280    K
          1000
                                                                                                                        300   K
           900
                                            geothermal gradient ST 10C Grad 30C                              310    K
           800
                                                                                                   1750 m           2100 m
           700
                                                        1000 m
                      density Kg/m^3




                                        700 m                           1250 m      1500 m
                                                                                                            330     K
           600

           500

           400
                                                      critiical point                                               K
                                                                                                              400
           300

           200

           100
                                                                                 pressure Bars
             0
                 30                    50        70          90         110      130         150      170         190         210
                                     The CO2 Problem
                                     Other or Combination


There may be potential for mineral sequestration of CO 2 by forming carbonates with oxides in
ash left after burning coal



Hydrated oxides of Ca Mg and Fe may form carbonates when CO 2 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 CO 2 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,    SO 2 , 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

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                                      To Go
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