MANAGEMENT PROGRAM FOR SPENT MODIFIED IN SITU RETORTS J. E. Boysen and J. R. Coveil Western Research Institute University of Wyoming Research Corp. P. O. Box 3395, University Station Laramie, WY 82071 By R. G. Vawter Occidental Oil Shale Inc. P. O. Box 880408 Steamboat Springs, CO 80488 K. G. Kofford and J. E. Marshall EMRx Corporation P. O. Box 1550 Palisade, CO 81526 ABSTRACT Following the completion of retorting, modified in situ (MIS) retorts are cooled and treated to produce an environmentally benign structure, which can ultimately be reclaimed in compliance with state and federal environmental regulations. Post-retorting experiments have been conducted for a number of years at the Occidental Oil Shale Inc. Logan Wash site near De Beque, Colorado to collect environmental data from in situ retorts completed nearly a decade ago. The data collected, along with studies conducted by the Western Research Institute, EMRX Corporation, and others have shaped a program for circulating water through spent MIS retorts in a manner that reduces materials which could impact groundwater to acceptable levels and uses process and indigenous waters efficiently. INTRODUCTION Occidental Oil Shale Inc. (OOSI) successfully demonstrated its modified in situ (MIS) oil shale retorting technology by conducting large-scale field tests at its Logan Wash facility near De Beque, Colorado. OOSI operated the Logan Wash MIS retorting facility from 1972 until 1982 (Stevens and Zahradnik 1983). The MIS technology developed by OOSI was proven technically feasible and commercial projections suggest that the technology can be profitable in the future. One of the environmental concerns associated with in situ processing is the impact of the process on local groundwater. Chemical compounds potentially soluble in groundwater are created during MIS retorting. The hot spent retorts must be cooled and then cleaned of these water-soluble chemical compounds to mitigate the process's impact on local groundwater. Spent retorts were cooled and cleaned at Logan Wash by circulating water through the retorts to remove soluble materials. Water produced from the MIS retorts (process water) was used in the cooling and initial stages of the cleaning. Baseline quality groundwater collected in the mine sumps (mine water) was used in the later stages of the cleaning. The groundwater quality from most spent retorts at Logan Wash is restored to near baseline. These experiments, conducted by OOSI and its contractor EMR^, demonstrated that impact on groundwater quality from MIS retorting can be mitigated. However, a commercial-scale operation requires careful water management to ensure that sufficient water is available to clean all spent retorts created. OOSI is developing plans for demonstrating commercial-scale oil production from a federal prototype oil shale lease (Tract C-b) in northwestern Colorado. OOSI contracted with the Western Research Institute (WRI) to conduct laboratory research and analytical studies for optimum commercial-scale water management. OOSI also contracted with EMR^ to continue field tests of potential water management schemes at Logan Wash. The goal of the two efforts is a cost-effective procedure for cleaning commercial spent retorts that optimizes use of the supply of water. This paper discusses the MIS oil shale retorting technology development by OOSI, the post-retorting conditions of spent MIS retorts, the previous research conducted by OOSI and EMRv to mitigate potential groundwater impact, the current research by EMRx anc* WRI to develop cost-effective procedures for cleaning commercial spent retorts, and OOSI's future plans for commercializing MIS oil shale retorting. Development of the MIS Oil Shale Retorting Technology The OOSI MIS process requires that a retort be constructed underground using explosives to fracture the oil shale and create the permeability necessary for retorting. In order to effectively fracture the oil shale and create permeability, a portion of the oil 133
Transcript
MANAGEMENT PROGRAM FOR SPENT MODIFIED IN SITU RETORTS
J. E. Boysen and J. R. Coveil
Western Research Institute
University ofWyoming Research Corp.
P. O. Box 3395, University Station
Laramie, WY 82071
By
R. G. Vawter
Occidental Oil Shale Inc.
P. O. Box 880408
Steamboat Springs, CO 80488
K. G. Kofford and J. E. Marshall
EMRx CorporationP. O. Box 1550
Palisade, CO 81526
ABSTRACT
Following the completion of retorting, modified in situ (MIS)
retorts are cooled and treated to produce an environmentally
benign structure, which can ultimately be reclaimed in compliance
with state and federal environmental regulations. Post-retorting
experiments have been conducted for a number of years at the
Occidental Oil Shale Inc. Logan Wash site near De Beque,
Colorado to collect environmental data from in situ retorts
completed nearly a decade ago. The data collected, along with
studies conducted by theWestern Research Institute, EMRX
Corporation, and others have shaped a program for circulating
water through spent MIS retorts in a manner that reduces
materials which could impact groundwater to acceptable levels and
uses process and indigenous waters efficiently.
INTRODUCTION
Occidental Oil Shale Inc. (OOSI) successfully demonstrated its
modified in situ (MIS) oil shale retorting technology by conducting
large-scale field tests at its Logan Wash facility near De Beque,
Colorado. OOSI operated the Logan Wash MIS retorting facility
from 1972 until 1982 (Stevens and Zahradnik 1983). The MIS
technology developed by OOSI was proven technically feasible and
commercial projections suggest that the technology can be
profitable in the future.
One of the environmental concerns associated with in situ
processing is the impact of the process on local groundwater.
Chemical compounds potentially soluble in groundwater are
created during MIS retorting. The hot spent retorts must be
cooled and then cleaned of these water-soluble chemical
compounds to mitigate the process's impact on local groundwater.
Spent retorts were cooled and cleaned at Logan Wash by
circulating water through the retorts to remove soluble materials.
Water produced from the MIS retorts (process water) was used in
the cooling and initial stages of the cleaning. Baseline quality
groundwater collected in the mine sumps (mine water) was used in
the later stages of the cleaning. The groundwater quality from
most spent retorts at Logan Wash is restored to near baseline.
These experiments, conducted by OOSI and its contractor EMR^,
demonstrated that impact on groundwater quality from MIS
retorting can be mitigated. However, a commercial-scale
operation requires careful water management to ensure that
sufficient water is available to clean all spent retorts created.
OOSI is developing plans for demonstrating commercial-scale
oil production from a federal prototype oil shale lease (Tract C-b)
in northwestern Colorado. OOSI contracted with the Western
Research Institute (WRI) to conduct laboratory research and
analytical studies for optimum commercial-scale water
management. OOSI also contracted with EMR^ to continue field
tests of potential water management schemes at Logan Wash.
The goal of the two efforts is a cost-effective procedure for
cleaning commercial spent retorts that optimizes use of the supply
of water.
This paper discusses the MIS oil shale retorting technology
development by OOSI, the post-retorting conditions of spent MIS
retorts, the previous research conducted by OOSI and EMRv to
mitigate potential groundwater impact, the current research by
EMRx anc* WRI to develop cost-effective procedures for cleaning
commercial spent retorts, and OOSI's future plans for
commercializing MIS oil shale retorting.
Development of the MIS Oil Shale Retorting Technology
The OOSI MIS process requires that a retort be constructed
underground using explosives to fracture the oil shale and create
the permeability necessary for retorting. In order to effectively
fracture the oil shale and create permeability, a portion of the oil
133
shale in the retort is mined to provide the void volume needed for
the remaining oil shale to expand into when it is fractured with
explosives. To create a rubble bed, explosives are set and ignited
in boreholes drilled from the mined areas into unfractured oil
shale.
The top of the oil shale rubble bed is heated to Ignition
temperature using hot inert gas. When the oil shale is hot enough
for ignition, air is injected into the rubble bed to begin combustion
and retorting of the oil shale. The hot gases, produced by
combusting the residual carbon that remains after retorting, flow
downward through the rubble bed and pyrolyze the kerogen in the
oil shale ahead of the advancing combustion front. Oil from
kerogen pyrolysis and gases from both kerogen pyrolysis and oH
shale combustion are produced at the bottom of the rubble bed
(McCarthy et al. 1976; McCarthy and Cha 1976).
Eight MIS retorts were constructed and operated by OOSI at
Logan Wash (Figure 1). The first six were designed to determine
the effects of the geometry of the mined void area, explosive
fracturing tecliniques, and ignition and operating procedures on
retorting efficiency. Retorts 7 and 8, the last two MIS retorts
operated by OOSI, were commercial-scale and operated
simultaneously to simulate commercial operation (Figure 2). These
retorts were designed to demonstrate the technical feasibility of
MIS technology at a commercial scale.
Results obtained from processing Retorts 7 and 8 prove that
commercial-scale oil shale retorting using the OOSI MIS process is
technically feasible. The processing of oil shale using these retorts
confirmed that a high oil yield can be achieved in retorts with low
void volumes. Further, the results confirmed that the
straightforward retort construction and operation used in Retorts 7
and 8 can potentially achieve economic oil recovery(Stevens and
Zahradnik 1983).
Conditions that Cause MIS Groundwater Impact
A better understanding of the MIS groundwater impact
process is needed to minimize the amount of water required to
clean commercial spent retorts. The conditions existing in a MIS
retort after retorting is nearly completed areillustrated in Figure 3.
The rubble bed in the retort consists of three distinct zones: raw
unretorted oil shale, retorted oil shale, and combusted oil shale.
The residual carbon remaining after retorting wascombusted in
the top part of the bed. Unretorted oil shale underwent limited or
no thermal alteration in the bottom of the bed, and it is possible
that heavy fractions of the oil produced from retorted shale
condensed there. Between these zones, retorted oil shale
underwent thermal pyrolysis, which produced oil and gas from the
shale.
After retorting, temperature in the retort remains high. The
temperature in many parts of the combusted shale zone exceed
1500F (816C). The temperatures in the retorted and
unretorted zones are progressively cooler but can be as hot as
1000 and 500F (538 and 260C), respectively. The sides and
bottom of the rubble bed are surrounded by oil shale that was not
explosively fractured (pillars). Also, an air space or void exists at
the top of the retort (Figure 3).
Two sources for potential groundwater impact exist because
of the retort conditions when processing ceases. One source of
impact is water-soluble material remaining in the spent retort.
Another less obvious potential source is water-soluble material
OCCIDENTAL OIL SHALE
RETORT S
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LOWER INTERMEDIATE LEVEL
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Figure 1 . Summary of the MIS Retorts at the Logan Wash Site
134
Figure 2. Isometric View of Retorts 7 and 8
generated by the continuing kerogen pyrolysis in the pillars and
unretorted shale. This post operation pyrolysis occurs as a result
of energy or residual heat stored in the hot spent shale. A spent
MIS retort, similar to Retorts 7 or 8, contains more than 100
billion Btu of residual heat. This energy needs to be removed from
the MIS retort to minimize post retorting pyrolysis and also to
prevent heat conduction into the surrounding pillars, thereby
preventing a reduction of their mechanical strength. In addition,
the amount of energy in the form of residual heat from a
commercial operation is considerable and, if used, can significantly
improve the overall MIS thermal efficiency (Hester and Jacobson
1983).
Effective procedures to clean spent retorts must cool the
retort to preserve mine integrity, use residual heat in the spent
retort to react much of the soluble material into insoluble forms,
and provide a means by which to remove remaining water-soluble
contaminants from the retort. Experiments were conducted at
Logan Wash by OOSI and EMR^ to develop procedures to clean
spent retorts. The following section discusses the results of these
experiments.
Environmental Research Conducted using Retorts 7 and 8
The water management procedures needed for MIS
operation liave been investigated by OOSI and EMR^ since 1982
using Retorts 7 and 8. In November of 1982, a short time after
the completion of processing Retorts 7 and 8, OOSI initiated
water-quenching studies on these full size retorts. Water
quenching was initiated to accelerate the cool down of these spent
retorts. In addition, recovery of residual heat from spent retorts in
135
Raw Oil Shale/Condensed Oil
Product Level Bulkhead
Figure 3. MIS Post-Retorting Conditions
the form of combustible gases generated through steam-carbon
reactions was investigated. The water quenching research also
removed many of the potentially soluble materials from the retorts.
A quench-water flow rate of 50 gal/min into each of the two
retorts was desired but sufficient quantities of water were not
available at the Logan Wash site to maintain this flow rate in both
retorts. Consequently, quenching research concentrated on Retort
8 where the desired quench-water flowrate was maintained for
several months. Thus, Retort 8 is more thoroughly evaluated
because it has undergone more thorough quenching than Retort 7
which was quenched with less water or Retort 6 which was not
quenched.
Details regarding the results of the initial quenching of these
spent retorts in 1982 and 1983 are reported by Hester and
Jacobson (1983). These initial experiments, using process water,
confirmed that water quenching is a viable procedure by which to
cool spent retorts. Reactions of the quench water with hot
material in the spent retort produced combustible gases and clean
condensate. From 1983 through 1988, periodic water injection
into the retorts continued to examine cooling of the retortsand
material removal from the retorts.
In December 1988, OOSI and EMRX tested another
potential retort cleaning procedure called staged deluge. The
staged deluge removes soluble compounds from spent retorts by
circulating water through the rubble bed. A grid of 26 water
injection points was constructed at the top of the rubble bed by
drilling from the upper mine level (instrument air level). Roughly
170,000 gal of water were injected sequentially into each of the
injection points at a high rate of approximately 1,000 gal/min.
The water collected in the lower portion of the retort was
reinjected into the retorts. During the staged deluge, roughly
500,000 gal of water (approximately three injections) was injected
into each of the 26 injection points.
The concentrations of retort-induced constituents in the
process waters from Retort 8 decrease with time. Figure 4 shows
the concentrations of dissolved organic carbon (DOC) in the
process water as a function of time (retort completion given as July
1982). Vertical dashed lines in the figure represent periods of
quenching or staged deluge. From this figure alone, the impact of
quenching on DOC concentrations is not obvious.
DOC concentrations may also have been reduced as a result
of the staged deluge. Figure 5 shows the DOC concentrations in
process water from Retort 8 for the period January 1, 1985,
through September 21, 1989. Again, vertical dashed lines in the
figure represent the periods of quenching or staged deluge. The
dashed line on day 2334 is the start of the staged deluge. There
are periodic fluctuations in the DOC concentrations. The reasons
for these fluctuations are again not obvious, and the fluctuations
make evaluation of these data difficult. It is also difficult to
determine from this figure if the staged deluge caused the
reduction in DOC concentrations or if the reduction was a
continuation of the short-term natural cleansing trend.
However, comparisons of DOC concentrations in process
water from Retort 8 with process water from other retorts that
were not quenched (Retort 6) or were partially quenched (Retort 7)
show that both quenching and staged deluge do reduce DOC
concentrations to a certain extent. After approximately 87
months (2,610 days), the DOC concentration in process water
from Retort 6 was 175 mg/L (Figure 6). This value compares to
80 mg/L measured in process water from Retort 8 at the
corresponding time after retort completion. Likewise for process
water from Retort 7, the DOC concentration on February 27,1989 was 210 mg/L compared to 95 mg/L for Retort 8 on the
same day. Retort 7 was quenched with roughly 20% of the
amount of process water used in Retort 8.
136
Total dissolved solids (TDS) concentrations in the process
water from Retort 8 show a steady increase since the monitoring
of these concentrations began (Figure 7). During periods of
quenching, TDS concentrations temporarily increased. There is a
linear increase in TDS concentration with time. The major TDS
constituent in the process water is sulfate.
The environmental remediation research conducted by OOSI
using spent Retorts 7 and 8 lead to the following observations.
First, the quenching of spent retorts with water is effective in
reducing the temperatures in the spent retorts and, thereby,
reducing kerogen pyrolysis that occurs after retorting. The current
temperatures monitored in Retort 6, which was not quenched, are
greater than those monitored in Retorts 7 and 8 which were
shutdown much later and were quenched. In addition, the water
quenching removed much of the residual carbon from these retorts
and transported it to the surface in the form of combustible gas.
The gas can be used to supply energy that is required for the plant
operations (Hester and Jacobson 1983). Second, the
concentrations of potential organic contaminants in process water
flowing from the retorts decreases naturally with time but this
decrease can be accelerated by quenching with water. The current
DOC concentration in the process water flowing from Retort 8 is
lower than the current DOC concentrations in the process water
flowing from either Retort 7 or Retort 6 (EMRX 1989).
In August 1989, EMRX modified the staged deluge process
by using clean water for the deluge instead of recycling water from
spent retorts. More soluble constituents were removed from the
spent retort using clean deluge water than were removed using
recycled deluge water. This behavior is typical of mass transfer-
controlled processes.
In a mass transfer-controlled restoration process, the
concentration gradient between the injected waters and the area
being cleaned regulates the rate of constituent removal. In the
initial stages of restoration, the concentrations of soluble materials
in a spent retort are high, and these constituents dissolve readily in
clean water. However, as the retort is cleaned, the concentration
gradient decreases, and the rate of chemical constituent
solubilization into injected waters declines. When this occurs,
removal of the soluble materials from the retort can be increased
by injecting cleaner water to increase the concentration gradient.
The procedure of injecting clean water to decrease the amount of
time required for the final stages of groundwater restoration is
used successfully to restore groundwater from uranium solution
mining wellfields.
Examination of the data presented in Figure 4 shows that the
decline in the concentration of DOC in the process water from
Retort 8 slowed in 1989. This indicated that it was time to inject
cleaner water into the retort to accelerate the further removal of
soluble constituents. Deluges conducted in August 1989
confirmed that using clean water accelerated DOC removal.
However, the major problem with continuing to deluge Retort 8
with clean water is the limited availability of water at Logan Wash.
In January 1990, EMRX continued the staged deluge of
Retort 8 using the relatively clean water flowing into the mine
drifts at Logan Wash. The results of the first two deluges in Retort
8 using mine water were similar to the August 1989 clean water
deluges. Process water produced from these deluges was disposed
of in an evaporation pond near the Logan Wash site rather than
reinjecting it into the retorts. The results thus far show increased
removal of soluble compounds from Retort 8 using mine water in
place of process water for deluging. By using the indigenous
water at the site, the need to acquire clean water for the retort
cleaning was reduced.
In summary, the water quenching and staged deluge of Retort
8 successfully reduced the amount of time required for cleaning
spent MIS retorts. However, the time required for cleaning spent
retorts still needs to be minimized.
Current Research Activities
Currently, OOSI plans to continue pursuing
commercialization of the MIS oil shale retorting technology. The
procedure and schedules required for cleaning spent MIS retorts
need to be developed more quantitatively for commercialization.
EMRX and theWestern Research Institute (WRI) are presently
contracted to quantify the water management procedures for
cleaning the spent retorts. EMRX will continue to investigate the
cleaning of Retorts 7 and 8 at Logan Wash using the staged
deluge procedure, and WRI will conduct laboratory research to
investigate the potential benefits of other procedures that can be
applied with the quenching and deluge procedures to reduce the
time and resources required for cleaning spent retorts.
EMRX continues to deluge Retort 8 using mine water and
then discharges the produced water to the evaporation pond. At
Logan Wash however, the amount of mine water is limited, so
methods to increase the frequency and effectiveness of deluges
without using additional water will be investigated. One method to
achieve more deluges per month without requiring additional clean
137
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1 1 Quenching
Quenching
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i 1 1 i i i i 1
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Figure 4. DOC Concentrations in Retort 8 Waters from 1983 to 1989
