U.S. patent number 3,619,405 [Application Number 04/743,702] was granted by the patent office on 1971-11-09 for gas combustion oil shale retorting with external indirect gas heat exchange.
This patent grant is currently assigned to Continental Oil Company. Invention is credited to John H. Smith.
United States Patent |
3,619,405 |
Smith |
November 9, 1971 |
GAS COMBUSTION OIL SHALE RETORTING WITH EXTERNAL INDIRECT GAS HEAT
EXCHANGE
Abstract
A gas retorting system for recovering oil from shale including a
vertical retort having a raw shale preheating zone at the top; an
external circuit for cooling and separating product vapor and gas
and an external circuit for heating cold recycle gas (from the top
of the shale preheating zone) and reintroducing it into the bottom
of the raw shale preheating zone.
Inventors: |
Smith; John H. (Ponca City,
OK) |
Assignee: |
Continental Oil Company (Ponca
City, OK)
|
Family
ID: |
24989834 |
Appl.
No.: |
04/743,702 |
Filed: |
July 10, 1968 |
Current U.S.
Class: |
208/409; 201/27;
201/29; 201/34; 201/36; 202/215; 202/221; 208/427 |
Current CPC
Class: |
C10G
1/02 (20130101) |
Current International
Class: |
C10G
1/02 (20060101); C10G 1/00 (20060101); C10g
001/00 () |
Field of
Search: |
;208/11 ;201/34,29,27,36
;202/215,109,221 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wyman; Daniel E.
Assistant Examiner: Konopka; P. E.
Claims
What is considered new and inventive in the present invention is
defined in the hereunto appended claims, it being understood, of
course, that equivalents known to those skilled in the art are to
be construed as within the scope and purview of the claims.
1. In a gas combustion process for recovering oil from oil shale
comprising the steps of passing said shale as a downwardly moving
bed through a preheating zone, a retorting zone, a combustion zone,
and a spent shale cooling zone, passing hot gases including
combustion gases upwardly from said combustion zone through said
retorting zone, and recovering the oil and vapor products of the
retorting of said shale, the improvement which comprises:
a. removing the product vapors from the upper portion of said
retorting zone;
b. cooling said product vapors of step (a) by passing said product
vapors in indirect heat exchange with the combined gases of step
(e) hereinafter described;
c. separately recovering shale oil and noncondensable gases from
said cooled product vapors;
d. recycling a portion of said noncondensable gases to the bottom
of said spent shale cooling zone;
e. combining the remaining portion of said noncondensable gases
with the gases recovered from the top of said preheating zone;
f. heating said combined gases of step (e) in two stages with said
first stage being an indirect heat exchange with the product vapors
of step (b) and the second stage being an indirect heat exchange in
a gas fired heater utilizing a part of said combined gases as fuel
for said heater, and introducing said heated gases into the bottom
of said preheating zone; and
g. maintaining a higher pressure at the bottom of this shale
preheating zone than at the top of the retorting zone to aid in
preventing the product vapors at the top of the retorting zone from
mixing with the combined gases of step (f).
2. The process of claim 1 wherein the product vapors of step (a)
are removed at a temperature approximating their dew point.
3. The process of claim 2 wherein the combined gases of step (f)
are heated to about 600.degree.-800.degree. F. before introducing
them into the bottom of said preheating zone.
4. The process of claim 1 wherein the pressure differential
described in step (g) is about 3 inches of water.
Description
BACKGROUND
The simple Bureau of Mines gas combustion retort (e.g., U.S. Pat.
Nos. 2,813,823 and 2,901,402) does not perform well enough on a
large scale to be commercial, because shale oil condenses on the
cold feed rock and refluxes back down into the retorting zone where
the heavier ends are concentrated by redistillation of the lighter
fractions. Then, the heavy tars and coke bind the shale together to
form large agglomerates which hang up on the internals and distort
the flows of air, recycle gas, and shale so badly as to seriously
impair the efficiency of the retort and even force its
shutdown.
It might appear possible to operate the process covered by U.S.
Pat. No. 3,297,562 in such a manner as to accomplish essentially
the results obtained from my process. This could be done by
withdrawing all the product vapors from the retorting section
through valve 67, simultaneously bypassing the retorting section
with sufficient hot gas from the combustion zone through line 96 to
preheat the raw shale to the dew point temperature of the retort
vapors, about 650.degree. F. This would require that the flow of
gases through the combustion zone be roughly twice the amount
passing through either the retorting or preheating zone,
necessitating an oversized combustion zone and considerably higher
cost. Furthermore, the thermal efficiency of the process of that
patent would be much below that of my process, requiring the use of
considerably more air in situ which would cause excessive dilution
of the retort product gas and lead to higher loss of shale oil
product therein as uncondensed vapors.
SUMMARY OF THE INVENTION
This invention involves a gas combustion retort modified to
withdraw the shale oil product while still predominantly vapor at
elevated temperature and condense it externally with a net loss of
only about 37 percent of its contained heat. Roughly one-fourth of
the residue gas is burned to preheat the shale to offset this
loss.
The process is carried out in a gas retorting system including a
vertical retort having a raw shale preheating zone at the top of
the retort; an external circuit for cooling and separation of
product vapor and gas; and an external circuit for heating cold
recycle gas (from the top of the shale preheating zone combined
with noncondensable product gasses) and reintroducing it into the
bottom of the shale preheating zone.
In the preferred system, the cold recycle gas is indirectly heated
first in the product vapor heat exchanger, then indirectly in a
fired heater. Cold gas from the final product separator is recycled
to the bottom of the retort where it is preheated by the spent
shale and then commingled with combustion air to control the flame
temperature.
The purpose of preheating the raw shale is to prevent shale oil
from condensing on the raw shale and refluxing down into the
retorting zone, causing formation of heavy tars and coke which bind
the shale into large agglomerates which impair efficiency.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified flow diagram of the preferred embodiment of
the invention.
FIG. 2 shows the percent distillation as a function of temperature,
for a typical shale oil.
FIG. 3 is a chart showing the percent of a typical shale oil
condensed, within the retort, as it relates to temperature. It also
shows the heat content of the shale oil within the retort as it
relates to temperature.
DETAILED DESCRIPTION
Referring to FIG. 1, the equipment includes a countercurrent gas
combustion retort 1 similar to that developed by the Bureau of
Mines at Anvil Points, Colorado. At the top of the retort is a raw
shale preheating zone 2 separated from said retort by two
approximately spaced tube sheets 3 through which pass conduits for
the gravitational flow of shale from the preheating zone into the
retorting zone 7. These shale conduits extend some distance into
the retorting zone to form a void space 4 below the lower tube
sheet for the purpose of disengaging the product vapors from the
shale and permit their easy withdrawal from the retort. Shielded
conduits 5 extend upward from the top tube sheet for conveyance of
preheating gas from the plenum chamber 6 between the two tube
sheets upward into the raw shale preheating zone 2.
The raw shale feed pipes 8 extend downward from the shale feed
chamber 9 into the raw shale preheating zone a sufficient distance
to form a suitable void space 10 for disengaging the cooled
preheating gases for easy withdrawal and recycle.
The external circuit for the retorting zone 7 consists of an
indirect vapor heat exchanger 12, a vapor cooler 14, a liquid
product separator 16, a liquid product pump 18, a recycle
compressor 20, plus appropriate pipes and control instruments.
The external circuit for the shale preheating zone 2 consists of a
recycle compressor 22 indirect, vapor heat exchanger 12, a fired
gas heater 24 for indirectly heating combined noncondensable
product gases with gases recovered from the top of the preheating
zone, plus appropriate pipes and control instruments.
In operation, raw shale is fed continuously via feed hopper 9 into
the top of shale preheating zone 2. It gravitates through the
preheating zone then through the retorting zone 7. After passing
through the cooling zone at the bottom of the retort, the spent
shale is discharged at a controlled rate from the bottom of the
retort, indirectly controlling the raw shale feed rate.
Air is fed into the middle of the retort proper through a gang of
distributors 30 embedded in the shale. Combustion of gases and
residual coke on the shale in the vicinity of the air distributors
supplies the heat required for retorting. Cold recycle gas is
injected into the bottom of the retort proper through line 21 and
flows upward countercurrent to descending spent shale recovering
heat therefrom.
The preheated recycle gas commingles with the combustion air at the
lower edge of the combustion zone to moderate the intensity of
combustion and limit the flame temperature to substantially below
the spent shale fusion or clinkering temperature (about
2,100.degree. F.). The commingled recycle and combustion gases
(about 1,100-1,400.degree. F.) continue to flow upward
countercurrent to the descending shale, surrendering heat thereto
to effect preheating and retorting of the shale. In the retorting
zone (1 to 3 feet above the combustion zone) the kerogen is
decomposed and forms shale oil vapors. The noncondensable gases and
shale oil vapors mix thoroughly and flow upward countercurrent to
the descending raw shale surrendering heat thereto to bring the
shale up to retorting temperature (about 900.degree. F. max.), the
gases and vapors themselves being cooled in the process to
approximately their dew point, which will vary from about
550.degree.-750.degree. F. depending upon the source of shale and
the operating conditions used. By dew point, I mean the temperature
at which shale oil liquid begins to condense from the vapors.
The thus cooled gases and product vapors are withdrawn from the top
of the retorting zone through line 11 at approximately their dew
point and are further cooled externally in indirect vapor heat
exchanger 12 and vapor cooler 14 to effect condensation of the
shale oil vapors. The major part of this cooling is done by
exchanging heat (in vapor heat exchanger 12) with a second recycle
gas stream (line 13) which is used for preheating the raw shale to
approximately the dew point of the gas-vapor mixture leaving the
retorting zone, before the shale enters the retorting zone. The
cooled mixture of shale oil liquid and noncondensable gases flows
from the final cooler through line 15a into shale oil separator 16
from which the shale oil is pumped into storage on level control.
Blower 20 compresses the gases from the shale oil separator
delivering a portion thereof as unheated recycle gas to the bottom
of the retort on flow rate control through line 21. The net product
gas (from combustion and retorting) plus seal gas amounting to
about 500 cubic feet per ton of shale feed is delivered to the
shale preheating gas loop via line 21a which is on flow rate
control 19a reset by a differential pressure control 19 which
maintains a very slightly higher pressure (less than 3 inches water
column) at the bottom of the shale preheating section than at the
top of the retorting zone. This causes a slight flow of seal gas
from the preheating section into the retort proper to prevent the
flow of shale oil vapors into the shale preheating section.
The gases from the top of the preheating zone are recovered at a
temperature approximating their dew point with respect to water,
i.e., at a temperature of about 110.degree.-160.degree. F. A second
blower 22 compresses these cold gases from the top of the shale
preheating zone delivering a major portion thereof via a flow rate
control 35 to combine with the remaining portion of noncondensable
gases delivered through loop 21a to pass through vapor heat
exchanger 12 then via line 13b through heater 24 into the bottom of
the raw shale preheating zone 2 at about 600.degree.-800.degree.
F., preferably 700.degree.-750.degree. F. A portion of this gas is
used as fuel for the fired heater via line 13a. The net make gas is
delivered offsite via line 40 on pressure control 39 which
maintains essentially atmospheric pressure at the top of the raw
shale preheating section.
Table I lists the compositions and other properties of various gas
streams in the retorting zone. The make gas from the retorting zone
(line 21a) includes the water contained in the feed air and that
formed by combustion, in addition to that formed by decomposition
of the kerogen. The sum total water in the off gas from the
preheating zone and the furnace fuel (lines 13a and 40) also
includes that water released in drying and dehydrating the raw
shale. The net water leaving the retort is equal to that amount
which would saturate the off gas from a single stage retort at
135.degree. F. and 12.5 p.s.i.a. This is based on observations that
the make gas from a typical gas combustion retort is thus
saturated.
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TABLE I
Gas Stream Properties
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Modified Gas Combustion Retort
Make Gas Off Gas Furnace Retoring Preheating Fuel Component, SCF/T
Zone Zone Gas
__________________________________________________________________________
H.sub.2 306 231 75 CO 216 163 53 C.sub.1 -C.sub.4 172 130 42
C.sub.5 + 72 54 18 N.sub.2 3,722 2,810 912 CO.sub.2 1,594 1,203 391
H.sub.2 O 476 1,257 309
__________________________________________________________________________
Total 6,558 5,848 1,800 Pounds 527 440 138 Pounds/mol 30.5 28.5
29.1 LHV/B.t.u./SCF 102.0 86.3 91.0 Heat Content B.t.u./MSCF
135.degree. F. 0 0 300.degree. F. 3,560 3,530 500.degree. F. 8,140
8,070 700.degree. F. 13,160 13,010
__________________________________________________________________________
Table II lists the fractional composition and ideal "K" values
(vapor-liquid equilibrium constants) for a typical shale oil with
gravity and distillation shown in FIG. 1. Table II also lists "K"
values for fractions of the retort off gas. These "K" values were
used for calculating the shale oil condensation curve shown in FIG.
3. ##SPC1##
The following example shows typical specifications, operating
conditions, and results.
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EXAMPLE
(basis: 1 Ton 28 Fischer Assay Shale)
Pounds Flow Rate Temp. Per Ton Per Ton .degree.F.
__________________________________________________________________________
Raw shale to hopper 9 2,000 60 Spent Shale 1,587 400 Shale oil
product (line 17) 195 25 gal. 135 Air rate to 30 360 4,700 s.c.f.
120 Line 40 440 5,848 s.c.f. 150 Line 13 1,695 22,058 s.c.f. 150
Line 13a 138 1,800 s.c.f. 500 Line 13c 1,557 20,258 s.c.f. 717 Line
21 964 12,000 s.c.f. 150 Line 31 1,404 20,848 s.c.f. 135 Line 31a
1,128 15,000 s.c.f. 150 Line 21a 567 7,058 s.c.f. 150 Line 15 1,726
322 Line 15a 1,726 135 Line 11 1,726 19,298 s.c.f. 650 Seal gas:
500 s.c.f.
__________________________________________________________________________
The only drawback of the system of FIG. 1 is the extra cost over
the simple Bureau of Mines version. To help offset the higher cost,
this modified design will give a higher yield from elimination of
refluxing and permitting a higher recycle gas rate. Also, this
modified version is capable of retorting rich shale, assaying up to
40 gallons per ton or more and particles smaller than one-fourth
inch which cannot be processed in the Bureau of Mines retort.
The improved control of the temperature pattern in the retorting
zone will permit a reduction in air rate which enhances yield. The
combination of less mineral carbonate decomposition plus the
recycling of a drier cooling gas results in less hydration of spent
shale. This, together with higher recycle gas rate, lowers spent
shale temperature to lessen disposal problems.
* * * * *