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THE EL TREMEDAL UNDERGROUND COAL GASIFICATION FIELD TEST IN SPAIN
FIRST TRIAL AT GREAT DEPTH AND HIGH PRESSURE
by
Robert Chappella, Associate Consultant
and Marc Mostadeb, Senior Engineer-Chief Engineer
a AEA Technology plc, Harwell, Didcot, Oxfordshire OX11 0RA,United Kingdom
b Institution pour le Développement de la Gazéification Souterraine (IDGS),
rue du Chéra, 200, B-4000 Liège, Belgium
ABSTRACT
The "El Tremedal" Underground Coal Gasification (UCG) trial sponsored by Belgian, Spanish and
United Kingdom government organisations and the European Community has conducted two
gasification phases during the summer-autumn of 1997, of nine and five days duration respectively. A
gas of good quality has been obtained on both occasions.
During the active gasification phases, which lasted in total 12.1 days, an estimated 237.2 tonnes of
coal moisture-ash-free were affected and an average power of 2.64 MW based on the lower calorific
value of the product gas was developed underground. The test utilised oxygen and nitrogen as the
injection reactants (no steam injection). Access to the 2-3 metres sub-bituminous coal seam situated at
an average depth of 560 metres was provided by an in-seam deviated well drilled close to the bottom
of the 29 degrees dipping seam. A vertical well was used for the exhaust of the gasification products
and the production counter-pressure was maintained in near equilibrium with the underground
hydrostatic head (50 - 54 bars). Three Controlled Retraction Ignition Point (CRIP) manoeuvres were
achieved.
Analysis of the raw process data was conducted to calculate mass and energy balances, and to
determine influences of process conditions on gas composition, shift and methanation equilibrium,
water influx and oxygen/coal conversion efficiencies.
paper presented at the Fifteenth Annual International Pittsburgh Coal Conference, September 14-18,
1998, Pittsburgh, USA
1
THE EL TREMEDAL UNDERGROUND COAL GASIFICATION FIELD TEST IN SPAIN
FIRST TRIAL AT GREAT DEPTH AND HIGH PRESSURE
by
Robert Chappella, Associate Consultant
and Marc Mostadeb, Senior Engineer-Chief Engineer
a AEA Technology plc, Harwell, Didcot, Oxfordshire OX11 0RA,United Kingdom
b Institution pour le Développement de la Gazéification Souterraine (IDGS),
rue du Chéra, 200, B-4000 Liège, Belgium
ABSTRACT
The "El Tremedal" Underground Coal Gasification (UCG) trial sponsored by Belgian, Spanish and
United Kingdom government organisations and the European Community has conducted two
gasification phases during the summer-autumn of 1997, of nine and five days duration respectively. A
gas of good quality has been obtained on both occasions.
During the active gasification phases, which lasted in total 12.1 days, an estimated 237.2 tonnes of
coal moisture-ash-free were affected and an average power of 2.64 MW based on the lower calorific
value of the product gas was developed underground. The test utilised oxygen and nitrogen as the
injection reactants (no steam injection). Access to the 2-3 metres sub-bituminous coal seam situated at
an average depth of 560 metres was provided by an in-seam deviated well drilled close to the bottom
of the 29 degrees dipping seam. A vertical well was used for the exhaust of the gasification products
and the production counter-pressure was maintained in near equilibrium with the underground
hydrostatic head (50 - 54 bars). Three Controlled Retraction Ignition Point (CRIP) manoeuvres were
achieved.
Analysis of the raw process data was conducted to calculate mass and energy balances, and to
determine influences of process conditions on gas composition, shift and methanation equilibrium,
water influx and oxygen/coal conversion efficiencies.
INTRODUCTION
The recently completed El Tremedal field test
was the most successful UCG field test
performed to date in the world at great depth.
The project was sponsored by Belgian, Spanish
and United Kingdom government
organisations and the European Community.
A first pre-UCG field test at great depth was
realised in the framework of a Belgo-German
collaboration in Belgium (Thulin experiment,
1986-1987). This test, limited in size, is the
first demonstration of UCG at great depth [1].
The El Tremedal field trial, first significant
UCG trial at great depth, generated valuable
data and results that demonstrate the capability
to transfer the technology from shallow to
great depth.
A description of the drilling, well completion
and engineering activities in preparation of the
gasification operations was given in a previous
paper [2].
This new paper is intended as an analysis and a
first interpretation of the gasification results
with emphasis on preliminary mass balance
definition, and the impact of process variable
changes and uncontrolled process events.
A comparison with the most comparable UCG
field trial at shallow depth in the USA, the
Centralia Partial Seam CRIP test (fall of 1983),
is also presented.
2
REACTOR CHARACTERISTICS
The El Tremedal UCG site is located in the
Teruel coal basin, approximately 100 km east
of Zaragoza, Spain. The coals of the Teruel
basin are Lower Cretaceous coals of low rank
and with high to very high sulphur content.
In the area selected for the project, the coal
bearing strata belong to the Val de la Piedra
formation (Aptian-Albian) lying un-
conformably over the Jurassic and down to the
Utrillas. Two coal seams are present in most
places of the area, separated by limestone. The
targeted coal seam for the El Tremedal UCG
operations was the upper coal seam. The upper
coal seam has a clayey sand roof. More details
of the site selection are given in the previous
paper [2].
The coal seam thickness in the gasification
area varies between 2 and 3 metres, and the
coal seam dipping angle is about 29 degrees.
The average depth of the gasification area is
approximately 560 metres.
The average proximate analysis (as received
basis) values of the upper coal seam are: 22.2
wt % moisture, 14.3 wt % ash, 36.0 wt % fixed
carbon and 27.5 wt % volatile matter. The
average higher heating value of the coal on the
same basis is about 18,000 kJ/kg. The total
sulphur content (as received basis) of the coal
seam is 8.4 wt %, distributed in 52.4 % pyritic,
1.2 % sulphate and 46.4 % organic.
Average elemental content of the upper coal
seam on a moisture and ash free basis is: 71.4
wt % carbon, 3.9 wt % hydrogen, 0.6 wt %
nitrogen, 6.4 wt % sulphur and 17.7 wt %
oxygen. The swelling index of the coal seam is
zero.
GASIFICATION CHRONOLOGY AND
MAJOR EVENT DESCRIPTION
The plan was to create, by the way of the
Controlled Retraction Injection Point (CRIP)
manoeuvres, two gasification reactors: (i) a
first reactor with a length of about 20 metres
and (ii) a second reactor with a length of about
80 metres.
Due to surface and well equipment problems,
the development of the first reactor was
stopped in its middle (first gasification phase
from July 21 to July 29) and renewed
afterwards, and the development of the second
reactor was stopped soon after its starting
(second gasification phase from October 1 to
October 5).
The reasons that necessitated the shutdown of
the first reactor were considered minor and
consequently, the equipment was adapted
easily between the two gasification phases.
The reasons that necessitated the shutdown of
the second reactor were judged more serious,
requiring significant repairs to the injection
well equipment. In view of the high-
anticipated cost of these repairs, it was decided
to terminate the gasification operations and to
concentrate efforts in the post-burn
investigation of the underground cavity
(programme actually in progress).
During the active gasification phases, which
lasted in total 12.1 days and corresponded
mainly with the development of the first
reactor, an estimated 237.2 tonnes of coal
moisture-ash-free were affected and 89.9
tonnes of oxygen were injected.
First gasification phase
The coal was first ignited on July 21 at 12:20.
A pyrophoric liquid was used to ignite a
methane burner downhole, which, in turn,
destroyed the in-seam liner and ignited the coal
seam. For this first successful ignition, the tip
of the burner was located in the deviated in-
seam injection well at a measured depth of 625
meters that corresponds approximately to a
reactor length of 4 meters (distance from
burner tip to the vertical production well).
Progressively, during the first day of
gasification, indications of a continuous
reverse burning of the liner were recorded by
the thermocouples and the fibre optics
positioned along the liner and at the tip of the
downhole burner.
In reaction to this phenomenon, the burner was
progressively retracted to the position of 615
metres MD (July 22 at 14:00), corresponding
to a reactor length of approximately 14 metres
at this time.
3
At this position, no additional reverse burning
of the liner was recorded, probably due to the
protective effect of the limestone (the in-seam
hole was in the limestone floor of the coal
seam at this position).
Day of
experiment
Process
control
Process
events
July 21 at
12:20
O2 = 30 m3/h
P = 52-54 bare
1st CRIP
Rector length
= +/- 4 m
Continuous
retraction of
inject. point
July 22 at
4:00
O2 = 50 m3/h
July 22 at
14:00
Termination
of continuous
retraction
Reactor
length =
+/- 14 m
July 23 at
12:00
O2 = 75 m3/h
July 24 at
7:00
O2 = 150 m3/h
Reactor
pressure drop
increase
July 25 at
12:00
O2 = 170 m3/h
July 27 at
8:00
Progressive
back pressure
increase to
57.5 bare
Water influx
increase
Pressure drop
decrease
July 29 at
10:00
Stop
gasification
Production
lines flooding
Table I. Main events of the first gasification
phase
From July 21 to July 25 12:00, the oxygen
flow rate was increased steadily to the level of
150-170 m3/h (STP). This flow rate was
maintained afterwards.
From July 21 to July 27 at 8:00, the production
well back pressure was held at about 53 bare
(approximately 5 bar above the hydrostatic
pressure at the production well position). This
was done in an attempt to limit the amount of
water entering the underground reactor. From
July 27 at 8:00 to July 29 10:00, a progressive
increase of the back pressure was effected up
to 57.5 bare in order to overcome an increase
of water influx detected during the day of July
27 (see Figure 1). This increase of water
influx could correspond to the first contact of
the reactor with the sand roof of the coal seam.
On July 29, it was decided to make a new
CRIP manoeuvre. During the preparation of
the manoeuvre necessitating a significant
reduction of input flows, a flooding of the
production lines occurred (lost of gas lift
conditions in the production well and
incapacity to vaporise the totality of the liquid
water produced in the surface production
lines). At this point, the decision to stop the
gasification phase was taken in order to adapt
the surface plant to these conditions.
Second gasification phase
After adaptation of the surface plant and
reconsideration of the optimum flow condition
for the production well (gas lift conditions), a
second ignition took place on October 1 at
12:15.
Day of
experiment
Process
control
Process
events
October 1 at
12:15
O2 = 30 m3/h
P = 50-52 bare
2nd CRIP
Rector length
= +/- 16 m
From
beginning to
October 2 at
12:00
Rapid increase
of O2 flow
to 500 m3/h
October 4 at
1:00
O2 = 700 m3/h
October 4 at
13:18
3rd CRIP
Reactor
length = +/-
74 m
From 3rd
ignition
Rapid
injection
pressure
increase to
+/- 75 bare
Lost of
downhole
measurement
at injection
October 5 at
5:00
Termination
of gasification
Lost of
injection well
integrity
Table II. Main events of the second
gasification phase
The tip of the burner was positioned at 613
metres MD (reactor length of approximately
16 m) for this second successful coal ignition.
4
From this moment, the oxygen flow rate was
rapidly increased and set to the level of 500
m3/h (STP) in order to increase significantly
the production flow rate and to put the
production well in optimum gas lift conditions.
Two further increases of the oxygen flow rate
to the levels of 600 and 700 m3/h were made at
the end of October 3 (see Figure 1).
In view of the impossibility of controlling the
water influx by a back pressure increase during
the first gasification phase, the back pressure
was held during the second gasification phase
at a lower level (50 – 52 bare); this decrease
had also a beneficial effect on the gas lift
conditions of the production well.
On October 4, the decision was taken to start
the second reactor and to utilise the CRIP
manoeuvre at 555 metres MD (reactor length
of approximately 74 metres). The third ignition
occurred at 13:18 with control difficulties that
resulted in damaging the downhole
measurement equipment of the injection well.
During the following hours, the oxygen flow
rate was set progressively to the level of 300-
500 m3/h (STP). The injection pressure
increased sharply at the beginning to stabilise
progressively at the level of about 75 bare.
At 5:00 on October 5, a sudden and highly
significant decrease of the injection well
pressure occurred, in consequence of a loss of
integrity of the injection well. It was decided at
this moment to terminate the second
gasification phase.
The main events of the two gasification phases
are summarised in Tables I and II.
GASIFICATION DATA EVALUATION
As the process experiment proceeded,
gasification data were recorded minute by
minute by the data acquisition and control
system to assist the operations staff in
monitoring the progress of the burn and to
provide a basis for initial control of the
experimental conditions.
From these raw data and after additional
refinement, comprehensive analytical work
was undertaken on hourly mean values of the
gasification data in order to provide some
insight into the operational characteristics of
the UCG cavity as it developed.
Figures 1 to 5 summarise the main gasification
data on a hourly mean basis; the reactor
pressures, oxygen flow rate, dry gas
composition, water content, reactor
temperatures, reactor power and dry gas lower
heating value.
In order to have a better insight into the reactor
behaviour, calculations were also made based
on the reactor products to determine the
temperature and the water content at
equilibrium conditions (gas homogeneous
conditions at the reaction zone outlet). The
specific reactions utilised for this equilibrium
calculation are:
CO+ H2O ó CO2 + H2 and
2 CO+2 H2 ó CH4 + CO2
These data are compared in Figures 3 and 4 to
the temperature and the water content at the
reactor outlet (production well bottom).
Initial analysis of the gasification results shows
that H2S and H2 are the most stable elements of
the product gasses and are little influenced by
the process conditions. CO and CO2 are
inversely correlated probably reflecting the
temperature conditions of the underground
reactor. Peaks of CO are registered at each
increase of the oxygen flow rate and a general
tendency of CO decline is also observed as the
reactor develops.
The origin of CH4 is always a subject of
discussion in interpreting UCG results: is CH4
coming from pyrolysis or from methanation?
The fluctuation of the CH4 content at the
production may in fact reflect the relative
importance of the pyrolysis zone in front of the
active gasification zone, and be the
consequence of a non-continuous and non-
smooth evolution of the underground cavity.
The influence of the pressure on the CH4
content should be also emphasised: the El
Tremedal UCG trial at great depth and high
pressure has produced a significally higher
proportion of CH4 than all UCG trials operated
at shallow depth and low pressure.
5
The comparison between the water content
measured at reactor outlet and the water
content calculated at equilibrium (see Figure
3) shows an excellent superposition until July
27 at mid-day. After this moment and until the
end of the second gasification phase, an excess
of water compared to the equilibrium water
was recorded. This increase of water influx
had no major influence on the gas quality.
The first appearance of an excess of water may
correspond to the moment the reactor reached
the sand roof. A more detailed analysis of the
water sources is discussed below in the context
of the mass balance data.
GAS LOSSES
The determination of the reactor recovery rate
is particularly important. This parameter is
necessary to estimate the lost-gas flow rate and
the overall reactor mass balance. Inaccuracy in
its determination will create an algebraically
unstable system of equations for the mass
balance calculation, this instability being more
important in case of low recovery rate
Figure 9. Simplified control volume used for
mass balance calculation
Gas recovery rates during the experiment were
estimated using either argon or nitrogen.
Figure 6 presents both balances all along the
two phases of gasification.
During the first gasification phase, both
recovery rate curves superimpose very closely,
indicating excellent accuracy of both
measurements. During the second gasification
phase that followed a long period of nitrogen
injection, it is expected that an important part
of the nitrogen recovered afterwards came
from the previous nitrogen injection period.
Consequently, the argon recovery rate was
used as reference for all further calculation
presented in this paper.
The first and most fundamental characteristic
deduced from the recovery rate is the reactor
lost-gas flow rate and its possible correlation
with cavity size and/or a pressure driving force
term such as P2
i-P2
p, where Pi is some average
system pressure and Pp is an average gas-sink
pressure.
Figure 7 gives a comparison of the argon
recovery rate with the reactor injection and
production pressures. The examination of the
curves reveals two tendencies (i) a dynamic
accumulation/relaxation effect of the
underground cavity in phase with the
production pressure fluctuation and (ii) an
increase of the lost-gas flow rate with time and
the pressure difference between the reactor and
the surrounding strata.
Figure 8 indicates the possible correlation
existing between the lost-gas flow rate and the
pressure driving force mentioned previously
during the first gasification phase. During the
second gasification phase, the lost-gas flow
rate seems more influenced by the cavity size
and the determination of a simple correlation
was not possible.
MASS BALANCES
Mass balance closures are extraordinarily
difficult in the analysis of UCG systems since
the streams of coal, char and overburden, and
water influx cannot be directly measured.
Furthermore, an unknown fraction of the coal
can be incompletely processed by being dried
and pyrolysed, but not gasified. The
composition of this char accumulation is also
imperfectly known. This phenomenon is
probably more important during the starting
periods of gasification when the drying and
pyrolysis processes are predominant.
Because of these difficulties/uncertainties, the
estimate of the cavity size can vary
considerably with the assumptions taken for
the mass balance.
Oxygen
injected
Coal MAF
affected
Moisture
of coal
Water
influx
Sulphur in
mineral matter
Gas
losses
(N2 free)
Gas
produced
(N2 free)
Char
deposit
Sulphur
deposit
CONTROL
VOLUME
6
Source
(tonne)
End of 1st
phase
Before 3rd
CRIP
End of 2nd
phase
First reactor
2nd reactor
Oxygen
injected
34.090
81.577
89.899
Coal
affected
87. 130
202.119
237.188
Sulphur in
ash
6.038
14.007
16.437
Coal
moisture
30.457
70.651
82.910
Water
influx
53.092
110.787
145.169
Water
reacted
(32.788)
(52.925)
(71.709)
Char
deposit
29.195
72.890
87.593
Sulphur
deposit
0.535
4.599
6.071
Gas
produced
(N2 free)
136.854
333.658
383.740
Gas losses
(N2 free)
44.223
67.994
94.199
Table III. Mass balance results
Figure 9 represents the simplified control
volume used for the mass balance calculation.
The calculation is made from the reconciliation
of the three C, H and O elemental balances
assuming that the char is a pure carbon
component (no H, O and S remaining in the in-
situ char) and the lost gas has the same
composition as the produced gas.
Figures 10 and 11 give respectively the
evolution of the char/coal ratio and the
gasification rates of the different underground
compounds (coal affected, char deposition,
sulphur, coal moisture and water influx) during
the two gasification phases.
The affected coal figures taken from the mass
balance calculation with the above-mentioned
assumption (pure carbon char) gives the lowest
value for the estimation of the affected zone.
Any elemental hydrogen and oxygen
remaining in the char would increase the
volume of the affected zone (more pyrolysis).
This assumption has also a direct impact on the
water influx estimate as discussed below.
A comparison of the char/coal ratio calculated
from the S and C elemental balances is also
given in Figure 10. With the exception of the
starting periods and the final period after the
third CRIP manoeuvre where the assumption
of pure carbon char is certainly not valid, the
excellent superposition of the two curves
during these intermediate periods demonstrates
the good compatibility of the experimental
results. Table III summarises the mass balance
results based on the pure carbon char
assumption.
WATER INFLUX
Analysis of the water influx is important in
determining the origin of the water and the
factors influencing the rate of ingress; is the
rate of ingress proportional to the initial cavity
volume, or are the extent of the active roof
collapse and the nature of the overburden
dominating factors?
The analysis was made by comparing the water
content at the reactor outlet and at reactor
equilibrium (see Figure 3) with the
underground water sources calculated from the
mass balance (see Figure 11).
Underground water sources are defined as the
water input to the system, from all origins. Our
interpretation defined two different categories
of water: (i) the coal moisture directly
proportional to the coal affected zone and (ii)
the other water sources defined as the water
influx. This water influx includes water from
the drying of surrounding rocks (a possible
additional coal-drying zone outside the
pyrolysis zone is considered here) and the
flows of free water in the underground system.
A first observation is that reactor backpressure
seems to be ineffectual in controlling water
influx. At the end of the first gasification
phase, the reactor backpressure was
continuously increased in an attempt to reduce
the water influx. The water influx seems to be
more dependent on the cavity development and
the reactor geometry.
7
CENTRALIA
(6.81 days of
gasification)
EL
TREMEDAL
(12.1 days of
gasification)
Pressure
(bar)
- injection
- production
4.3
3.7
56.9
54.1
Injection
(tonne)
– steam
– oxygen
- nitrogen
295
147
-
-
90
81
Underground
(tonne)
– coal affected
– coal
moisture
– water influx
- water reacted
– char deposit
370
103
615
(247)
121
237
83
145
(72)
88
Production
(tonne)
– produced gas
– gas losses
1165
249
449
110
Dry gas
(mole %)
- CO2
- CO
- H2
- CH4
- H2S
34.9
20.8
38.1
4.7
1.5
42.1
10.8
24.9
13.8
8.4
Water
content
(mole %)
60.5
46.0
LHV
dry basis
(kJ/m3 STP)
8,734
10,911
Table IV. Comparison of the Centralia and El
Tremedal main average results
Observation of all trends after July 27 indicates
a clear presence of excess water in the vicinity
of the operating gasifier and/or the production
well.
The explanation of this excess of water is
probably twofold: (i) the reactor geometry
(coal seam dipping at about 29 degrees) may
explain a re-injection/re-circulation of water
produced in the reactor drying zones to the
production well level and (ii) the cavity
development may explain the increase of water
influx coming from the sand roof.
As mentioned previously, the assumption of a
pure carbon char accumulation leads to an
over-estimation of the water influx in front of
the coal-derived moisture (i.e. the water source
proportional to the coal affected/pyrolysed
zone). The water influx term in the mass
balance is in fact the result of a global balance
closure that embodies all water sources with
the exception of the coal moisture. All drying
zones (coal and rocks) proportional to the
cavity development are included in the water
influx term.
COMPARISON WITH CENTRALIA
FIELD TRIAL
An interesting comparison was made with one
of the most famous UCG field trial in the
USA, the Centralia Partial Seam CRIP trial.
The characteristics of the first gasification
phase of this trial are in fact, with the
exception of the depth, very similar to those of
the El Tremedal trial.
In both cases, the gasifying agents were
injected via an in-seam well and recovered by
a vertical well situated down-dip. The coal
seam was dipping at 14 degree in the case of
Centralia and 29 degree in the case of El
Tremedal.
The coal gasified in Centralia was of the same
rank, with an average proximate analysis of:
17.3 % moisture, 20.8 % ash, 34.4 % volatile
matter, and 27.5 % fixed carbon. The sulphur
content was lower in the case of Centralia with
a value of 1.2 %.
Table IV presents the comparison of the main
average results in both cases.
The analysis of the dry gas composition in
both cases indicates the influence of the
pressure. The quality of the gas is significantly
higher in the case of the El Tremedal UCG
trial.
In addition, the Centralia UCG trial was
operated with a larger excess of water in the
underground reactor. No steam or water were
injected in the El Tremedal UCG trial.
8
The mass ratio of coal affected to the oxygen
injected (between 2.5 and 2.6) and the ratio of
char accumulation to the coal affected
(between 0.33 and 0.37) are comparable for
both experiments.
CONCLUSIONS
After the demonstration of drilling a long in-
seam hole and of constructing a competent gas
circuit between injection and production wells
at great depth (see previous paper [2]), the El
Tremedal UCG trial has demonstrate the
technical feasibility of UCG at great depth and
high pressure in low rank coals.
The characteristics recorded in the El
Tremedal UCG trial are similar to the
characteristics of the Centralia Partial Seam
CRIP trial. The El Tremedal has also
demonstrated the possibility to gasify a low
rank coal (high in-situ moisture content)
without steam injection.
The fact that, in these conditions (no steam
injection), the gasification at great depth and
high pressure will necessitate only the
compression of the oxygen injected should be
noted. For one kilo of oxygen compressed at
the underground reactor pressure, it is possible
to recover more or less five kilos of product
gasses at the same pressure (the pressure
energy is also recoverable).
The production equipment has demonstrated
reliability in the face of the severe conditions
of UCG at great depth (corrosion, temperature,
gas lift conditions). The optimisation of gas lift
conditions has been demonstrated to be crucial
in the operation of UCG at great depth (liquid
water presence in the production lines).
Two CRIP manoeuvres were operated
successfully by the way of a downhole burner
fixed at the end of a coiled tubing system. The
difficulties encountered during the third CRIP
manoeuvres suggest improvements in the
injection/ignition equipment in the light of the
experience gained during the operations.
ACKNOWLEDGEMENT
The authors are grateful to the organisations,
which provided the finance for this R&D
project. These include:
• European Commission (Directorate
General XVII – THERMIE programme).
• A group of Spanish state organisations led
by the Instituto Tecnológico Geominero de
España (ITGE)
• The Walloon Government and the
Institution pour le Développement de la
Gazéification Souterraine (IDGS),
Belgium
• The Department of Trade and Industry
Clean Coal Technology Programme,
United Kingdom
REFERENCES
1. “The Future Development of UCG in
Europe”, A Comprehensive Report to
CEC, Brussels, April 1989.
2. “Drilling, Well Completion and
Engineering Activities in preparation of
the first UCG Trial in the framework of a
European Community Collaboration,
Alcorisa, Spain” by P. Fiévez, J. M.
González Lago, A. Goode, M. Green, M.
Mostade and A. Obis, 14th Annual
International Pittsburgh Coal Conference,
Sept. 23-27, 1997, Taiyuan, China.
3. “Results of the Centralia UCG Field Test”
by R. Hill, C. Thorness, R. Cena and D.
Stephens, 10th Annual UCG Symposium,
Aug. 12-15, 1984, Williamsburg, USA.
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Flow rate (m3/h STP)
Pressure (bare)
Days
Figure 1 . Reactor pressures and oxygen flow rate
Injection
pressure
Production
pressure
Oxygen injected
10
0
10
20
30
40
50
60
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Mole %
Days
Figure 2 . Dry gas composition (nitrogen free)
CO2
CO
CH4
H2
H2S
11
0
10
20
30
40
50
60
70
80
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Mole %
Days
Figure 3 . Reactor water content (nitrogen free)
Reactor
Outlet
At equil.
12
0
200
400
600
800
1000
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°C
Days
Figure 4 . Reactor temperatures
Reactor Outlet
at equil.
13
0
3000
6000
9000
12000
15000
0
2
4
6
8
10
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Low heating value (kJ/m3)
Power (MW)
Days
Figure 5 . Reactor power and dry gas low heating value
Power
LHV
14
0
20
40
60
80
100
120
140
160
180
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Mole %
Days
Figure 6. Recovery rates (based on nitrogen and argon balances)
N2
Ar
15
0
20
40
60
80
100
120
140
45
50
55
60
65
70
75
80
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Rate (mole %)
Pressure (bare)
Days
Figure 7 . Comparison pressure - recovery rate
Injection pressure
Production
pressure
Argon rate
16
0
5
10
15
20
25
0.0
0.2
0.4
0.6
0.8
1.0
Lost-gas flow rate (kmole/h)
*/* (PI2-PP2)
Figure 8.!Correlation between (PI2-PP2) and lost-gas flow rate
during the first gasification phase
17
0
10
20
30
40
50
60
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Weight %
Days
Figure 10 . Char/coal ratio
C-H-O balance
S-C balance
18
0
50000
100000
150000
200000
250000
300000
350000
400000
450000
500000
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Cumulated weight (kg)
Days
Figure 11 . Underground gasification rates
Water influx
Moisture of coal
Coal MAF
gasified
Sulphur gasified
Sulphur deposit
Char deposit
