Title:
GAS COMBUSTION RETORT PROCESS
United States Patent 3617466


Abstract:
An improved method for obtaining oil from oil shale by the gas combustion retort process. The offgas from the retort containing oil, fuel and other combustion products is treated first to remove the oil and second, to burn the fuel components. The resulting gas is recycled into the retort to pass countercurrently to the shale travel. Temperatures in the combustion zone of the retort are moderated and clinker formation is eliminated. The heat from the fuel burning can be used as a power source.



Inventors:
TODD JOHN C
Application Number:
04/781766
Publication Date:
11/02/1971
Filing Date:
12/06/1968
Assignee:
Atlantic Richfield Company (New York, NY)
Primary Class:
Other Classes:
201/16, 201/29, 201/37, 208/427
International Classes:
C10G1/02; (IPC1-7): C10B53/06
Field of Search:
201/27,28,29,37 208
View Patent Images:
US Patent References:
3487004CATALYTIC OXIDATION IN OIL SHALE RETORTING1969-12-30Berry
3318798Retorting of oil shale1967-05-09Kondis et al.
2752292Shale retorting process1956-06-26Scott



Primary Examiner:
Davis, Curtis R.
Claims:
It is claimed

1. An improved method for recovering oil from shale which comprises:

2. The method of claim 1 wherein the oxidant gas is air.

3. The method of claim 1 wherein part of the resulting flue gas is also mixed with the oxidant gas prior to introduction in the retort.

4. The method of claim 1 wherein the preheat zone is at a temperature of 60°-750° F., the retorting zone is at a temperature of 750°-1,200° F., the combustion zone is at a temperature of 1,200°-1,800° F., and the heat recovery zone is at a temperature of 1,800°-2,000° F.

5. The method of claim 1 wherein the spent shale contains 1 to 5 percent carbon.

6. In the process for retorting oil shale by the gas combustion retort process in which oil shale is introduced into a retort and passed through a preheat zone, a retort zone, a combustion zone wherein at least some carbon content in the spent shale from the retort zone is burned with an oxidant gas and a heat recovery zone and the offgas is withdrawn from the retort and recycled after the oil is removed from it back into the heat recovery zone of the retort to travel countercurrently to the flow of the shale, the improvement which moderates the temperature of the combustion zone and avoids clinker formation which comprises removing fuel from the offgas after the oil is removed and prior to its recycling into the retort and recycling at least part of the gas resulting from removal of the fuel from the offgas into the retort through the combustion zone during combustion of the spent shale in the combustion zone.

7. The improvement of claim 6 wherein the fuel removal is by burning the oil-depleted offgas in a boiler.

8. The improvement of claim 6 wherein the spent shale has a carbon content of 1 to 5 percent.

Description:
It is well known that certain sedimentary rocks, commonly referred to as oil shale, yield upon heating appreciable quantities of relatively crude oil as well as gaseous hydrocarbons and other gases. The oil may be refined into valuable products such as gasoline, diesel oil, jet fuel and fuel oil. Valuable byproducts such as tar acids, and waxes are also recoverable from the crude shale oil. Extensive deposits of oil shale are found in this country, particularly in the so-called Green River shale formation located in the states of Colorado, Utah, and Wyoming. Important oil shale deposits are also found in other parts of the world. With diminishing world reserves of oil and the proposed mining of oil shale using nuclear explosives there has been considerable interest in developing a commercially feasible process suitable for application on a large scale for retorting (i.e., destructive distilling) of oil shale to recover its potential yield of crude oil. However, to date the retorting of oil shales has not been extensively practiced on a commercial scale.

In one of the retorting methods presently considered for the recovery of oil from oil shale, the shale is passed downward countercurrently to gases used to separate the oil from the oil-bearing solid material. The retort column is divided in the direction of shale travel into a shale preheating zone, a shale retorting zone, and a shale combustion zone and a heat recovery zone, all zones being relatively stationary within the retort. Another similar method uses an upwardly traveling shale column with the oil and gaseous effluents being drawn off downwardly countercurrent to the shale travel. These processes are well known to those skilled in the art. The size of each of the relatively stationary zones in the retort is dependent upon such factors as particle size, gas velocity, temperature, mass rate of the shale, etc., but the actual retorting zone generally can be defined by temperature since essentially all of the kerogen is recovered from the shale at temperatures in the range of about 500° to 1,800° F., preferably 750° to 1,200° F. The upper limit is defined as being the temperature at which coking or cracking of the recovered oil vapors is a significant economic problem.

The gas combustion retort in its present stage, however, has poor operability due to clinker formation. The heating of the oil shale in the preheating and retort zones produces not only the effusion of oil but also many fuel gases, such as CO2, H2, H2 S, CH4 and higher hydrocarbons, e.g. ethane and hydrocarbons of more than two carbon atoms. In the usual oil shale retort process, the oil is removed from the offgas and the offgas is recycled back to the retort. The clinker formation is the result of excessive heat produced by the combustion of the fuel of the recycle gas within the retort apparatus and results in congestion to the extent that regular shutdowns of the gas retorting device are necessary to affect a clean out. Even in the best runs, the retort appears to be on the verge of clinkering which requires a more exacting control to prevent shale flow stoppage.

Clinkering occurs generally in the combustion zone. This zone, along with the retorting zone and the portion of the heat recovery zone adjacent to the combustion zone are located generally in the central portion of the retort. The temperature of the combustion zone is usually about 1,200°-1,800° F. However, the homogeneous reaction of the oxygen in the air with the fuel in the recycle gas produces extremely hot gases which can be in excess of 3,000° F. This generation of intense heat is usually localized. Since the burning of the carbon of the spent shale is a heterogeneous reaction depending on diffusion of oxygen into the particle to contact the carbon, a large excess of carbon is left on the spent shale; also many particles do not even have the surface carbon removed. The oxygen needed to remove it has been burned with the fuel in the recycle gas prior to contact with carbon on the spent shale. These observations of excessive fuel left on the spent shale show the localization of the burning produced by the fuel in the recycle gas.

The present invention is an improvement in the method of obtaining oil from solid organic-mineral complex material, particularly oil shale, wherein better operability is achieved due to the decreased likelihood of clinker formation and smoother flow of shale. In accordance with the invention, the gas combustion retort process is improved by the removal of fuel components of the offgas by burning externally to the retort prior to its recycling in the retort. This improvement is generally available to modify the processes of any of the several known gas heat transfer retorting processes.

This invention has the advantage of better utilization of the fuels produced as they may be used to provide heat for power generation. A greater portion of the carbon content of the spent shale is used for retort heat, thus utilizing this carbon content rather than disposing of it. Also, a more even temperature distribution is produced in the combustion zone and subsequently in the retort zone because concentrated, localized burning of recycle gas does not occur. Less decomposition of the shale matrix causes less dust to be produced in the retort and decreased carbonate decomposition produces less inert gas in the offgas resulting in more efficient utilization of hydrocarbons in the offgas. Another advantage in the removal of fuel from the offgas before recycling to the retort, is better heating efficiency because heat is utilized to decompose kerogen and for heating the shale to the retorting temperature rather than to decomposing or melting rock. Finally a better yield of oil results from better temperature distribution producing a greater residence time and less likelihood of oil appearing in the spent shale.

The FIGURE is a diagrammatic representation of the process of this invention in a retort having downwardly flowing oil shale.

A typical oil shale gas combustion retort is shown in the FIGURE as member 1. The raw shale 2 enters the top of the retort through a valve 3. The raw shale passes downwardly first through a preheat zone, generally indicated at 4, where the temperature range is 60°-750° F., then the retort zone 5 where the temperature range is 750°-1,200° F., then the combustion zone 6 where the temperature range is 1,200°-1,800° F., into the heat recovery zone 7, temperature range of 1,800°-2,000° F. and the spent shale 8 containing 1 to 5 percent carbon is discharged through the valve 9 at the bottom of the retort. The oxidant gas 10, which is usually air, enters the retort through compressor 11 at inlet 12 which is located at about the bottom of the combustion zone 6. The offgas 13 containing oil and fuel passes out of the outlet 14, near the top of the retort, preheating the raw shale on its passage out, and passes first through an oil collection means 15, such as an electrostatic precipitator, to collect the oil 16.

The remaining offgas 17 is then conveyed to a boiler 18 with a catalytic burner where the fuel in the offgas is mixed with air 19 and burned to provide heat for use, such as in the stream turbine power generation apparatus 20. The remaining flue gas 21 composed mainly of CO2, SO2, N2 and H2 O is then recycled in the gas combustion retort 1 through compressor 22 and inlet 23. Excess flue gas is vented at vent 24 or it may be used, if necessary, to dilute the oxidant gas 10.

The removal of the fuel from the offgas 13 prior to recycling into the retort 1 results in all the burning in the combustion zone 6 occurring on the spent shale carbon. Because burning of the spent shale is a heterogeneous reaction depending on diffusion of oxygen into the particle to contact carbon, the reaction mechanism is slow compared to the burning of fuel in the recycle gas. Therefore, the amount of heat generated at localized spots in the combustion zone will be decreased and thus the temperature level will spread over a longer vertical section and over a greater cross-sectional area of the retort. The air is distributed so that most of the shale particles will receive some burning. The invention, by spreading the combustion zone and moderating the peak temperatures produced, eliminates the clinkering.

By removing the fuel from the recycling gas, the localized high temperatures are eliminated, eliminating clinker formation, as well as the mechanism of clinker formation wherein a small clinker is formed by the burning gases which deflect the gases to fuse the shale in juxtaposition to the clinker, resulting in the formation of very large clinkers.