U.S. patent application number 11/249037 was filed with the patent office on 2006-04-13 for process for the recovery of hydrocarbon fractions from hydrocarbonaceous solids.
Invention is credited to Anthon L. Smith.
Application Number | 20060076275 11/249037 |
Document ID | / |
Family ID | 36144192 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060076275 |
Kind Code |
A1 |
Smith; Anthon L. |
April 13, 2006 |
Process for the recovery of hydrocarbon fractions from
hydrocarbonaceous solids
Abstract
Process and apparatus for extraction of oil and hydrocarbons
from crushed hydrocarbonaceous solids (101), such as oil shale,
involving the pyrolyzing of the crushed solids (101) with liquid
hydrocarbon (104) and hot gas such as syn gas (103) rich in
hydrogen, carbon dioxide and carbon monoxide or a solid hydrocarbon
such as gilsonite. Crushed hydrocarbonaceous solids are treated
with a hydrocarbon and hot gas in a rotary kiln (105) where the
crushed solids are cascaded into the hot gas for sufficient time to
strip the volatile liquids and gases found in the solids, removing
the vaporized liquids, enriched hot gas and spent crushed solids
from the kiln, fractionating the vaporized liquids (106) and
enriched syn gas into the desired fractions. Use of hot syn gas is
particularly suited for use in conjunction with combined-cycle
electricity generation (110) and in the preparation of various
by-products. The process efficiently recycles heat and energy to
reduce harmful atmospheric emissions and reliance on external
energy sources.
Inventors: |
Smith; Anthon L.; (Lindon,
UT) |
Correspondence
Address: |
Thorpe North & Western, LLP
P.O. Box 1219
Sandy
UT
84091-1219
US
|
Family ID: |
36144192 |
Appl. No.: |
11/249037 |
Filed: |
October 11, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11035383 |
Jan 12, 2005 |
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11249037 |
Oct 11, 2005 |
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PCT/US03/21926 |
Jul 14, 2003 |
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11035383 |
Jan 12, 2005 |
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10194993 |
Jul 12, 2002 |
6709573 |
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PCT/US03/21926 |
Jul 14, 2003 |
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Current U.S.
Class: |
208/408 ;
208/414 |
Current CPC
Class: |
C10G 1/02 20130101; C10G
1/04 20130101 |
Class at
Publication: |
208/408 ;
208/414 |
International
Class: |
C10G 1/00 20060101
C10G001/00 |
Claims
1. A thermal method for treating crushed hydrocarbonaceous solids
to extract hydrocarbons therefrom, comprising the steps of: (a)
preheating a crushed hydrocarbonaceous solids; (b) treating the
preheated crushed hydrocarbonaceous solids in a substantially
horizontal rotary kiln having an upper end and a slight slope
downward with (i) a hot gas at an elevated temperature, and (ii) an
injected hydrocarbon which vaporizes, wherein pressure inside the
rotary kiln is greater than atmospheric pressure and the crushed
solids are introduced at the upper end of the rotary kiln and are
heated by the hot gas for a sufficient time to vaporize volatile
components from the crushed solids to produce vaporized hydrocarbon
materials and spent solids; and (c) removing the vaporized
hydrocarbon materials and spent solids from the horizontal rotary
kiln.
2. The method of claim 1, wherein the hot gas is injected inside
the rotary kiln and the injected hydrocarbon mixes with the hot
gas.
3. The method of claim 1, wherein the hot gas is directed to an
indirect heating device outside the rotary kiln.
4. The method of claim 3, wherein the indirect heating device is a
concentric shell oriented around at least a portion of the rotary
kiln.
5. The method of claim 1, wherein the hot gas is syn gas, nitrogen
gas, hydrogen gas, carbon dioxide gas, carbon monoxide, or
combinations thereof.
6. The method of claim 5, wherein the hot syn gas containing
hydrogen is introduced into the kiln at a temperature between
700.degree. F. and 2500.degree. F.
7. The method of claim 3, wherein the hot syn gas containing
hydrogen is obtained from coal gasification.
8. The method of claim 1, wherein the pressure inside the rotary
kiln is from about 1 psi to about 100 psi.
9. The method of claim 1, wherein the crushed hydrocarbonaceous
solids are preheated to a temperature between about 100.degree. F.
and 350.degree. F. before being introduced into the kiln.
10. The method of claim 1, wherein the crushed solids have a
residence time in the kiln of from about 5 to 90 minutes.
11. The method of claim 1, wherein the injected hydrocarbon is a
solid gilsonite hydrocarbon.
12. The method of claim 1, wherein the injected hydrocarbon is a
liquid hydrocarbon which is introduced into the kiln at a rate of
between about 5 and 50 gallons of liquid hydrocarbon per ton of
crushed hydrocarbonaceous solids.
13. The method of claim 1, wherein the injected hydrocarbon is
liquid crude oil.
14. The method of claim 13, wherein the crushed hydrocarbonaceous
solids is oil shale.
15. The method of claim 13, wherein the crude oil is introduced
into the kiln at a rate from about 30 and 50 gallons of crude oil
per ton of crushed oil shale.
16. The method of claim 13, wherein the crushed hydrocarbonaceous
solids are tar sands.
17. The method of claim 16, wherein the crude oil is introduced
into the kiln at a rate from about 20 and 25 gallons of crude oil
per ton of tar sands.
18. The method of claim 1, further comprising the step of
fractionating the vaporized hydrocarbon materials into desired
fractions.
19. The method of claim 18, wherein the hot gas is a syn gas which
is injected inside the rotary kiln and forms an enriched gas during
contact with the crushed solids, and wherein the enriched gas from
the step of fractionating is passed through a catalytic converter
to form methanol.
20. The method of claim 18, wherein the hot gas is a syn gas which
is injected inside the rotary kiln and forms an enriched gas during
contact with the crushed solids, and wherein the enriched gas from
the step of fractionating is combined with nitrogen from a coal
gasification process to produce liquid ammonia.
21. The method of claim 1, further comprising the step of producing
electricity in a combined cycle comprising: (a) recovering an
enriched gas from the rotary kiln for use as a fuel gas; (b)
combusting the fuel gas to produce a first heated gas which is
directed to a gas turbine which is operatively connected to a first
generator wherein the first heated gas is reduced in pressure
through the gas turbine to produce a second heated gas; and (c)
using the second heated gas to produce steam which is directed to a
steam turbine which is operatively connected to a second
generator.
22. A system for extracting hydrocarbons from hydrocarbonaceous
solids comprising: (a) a substantially horizontal rotary kiln
having an upper end and a slight slope downward to a lower end and
having a crushed hydrocarbonaceous solids source operatively
connected to the upper end; (b) a hot gas source in thermal
communication with the rotary kiln; (c) a liquid hydrocarbon source
operatively connected to either the upper end or the lower end; and
(d) a separation chamber operatively connected to a lower end of
the horizontal rotary kiln.
23. The system of claim 22, further comprising a fractionation
column operatively connected to the separation chamber.
24. The system of claim 22, wherein the hot gas source is a coal
gasifier configured to produce a hot syn gas.
25. The system of claim 22, further comprising a combined-cycle
electricity generator operatively connected to the separation
chamber.
26. The system of claim 22, further comprising an indirect heating
device oriented around at least a portion of the rotary kiln.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 11/035,383, filed Jan. 12, 2005, which is a
continuation-in-part of PCT Application No. PCT/US2003/021926,
filed Jul. 14, 2003, which designated the United States and claims
priority to U.S. application Ser. No. 10/194,993, filed Jul. 12,
2002, now issued as U.S. Pat. No. 6,709,573, each of which are
incorporated herein by reference in their entireties.
FIELD OF THE INVENTION
[0002] This invention is related to the recovery of hydrocarbons
from solid carbonaceous materials, and more specifically to an
improved process using hot gas and liquid hydrocarbon in a
generally horizontal rotary kiln.
BACKGROUND OF THE INVENTION
[0003] Worldwide demand for hydrocarbons and related petrochemicals
and fertilizers is increasing at a rapid annual rate. Crude
petroleum and natural gas are basic in satisfying these demands
while at the same time many industries have experienced shortages
despite the discovery of new oil and gas sources. Therefore,
alternate solid hydrocarbon sources and feed stocks, such as coal,
tar sands, oil shale and solid crudes present an ever increasingly
attractive source for meeting demand for hydrocarbon products.
[0004] Oil shale and tar sands, also known as oil sands and
bituminous sands, are particularly promising sources of these
needed products as large deposits are found in Canada and the
United States. The largest known deposit of oil shale is the Green
River formation in Utah, Colorado and Wyoming with about a third of
such deposits in the state of Utah. The hydrocarbon resource locked
in the Green River formation has been estimated to be in excess of
1.5 trillion barrels. This is a considerable resource considering
known world oil shale reserves amount to just over 2.5 trillion
barrels, by conservative estimates.
[0005] The demand for hydrocarbon resources makes development of
the Green River formation virtually certain. During the 1970s and
1980s several oil shale operations were developed in Colorado and
Utah, however due primarily to economic considerations most of
these operations have since ceased. An average recovery of about 29
to 34 gallons of oil per ton of oil shale was typical of these
previous recovery efforts.
[0006] Green River oil shale is a petroliferous material (heavy
viscous oil material) which is as high as 25% by weight with an
average of 12% by weight hydrocarbon. The recovered oil is about
17.degree.-25.degree. API gravity, frequently averaging about
21.degree., and contains a low amount of sulfur and low
aromaticity. The Green River shale has relatively high moisture
content of between about 0.4% to 6%. Ranges for analysis of several
samples of Green River oil shale are shown in Table 1. The balance
of the components, not shown in the table, are made up primarily of
various minerals and trace metals. TABLE-US-00001 TABLE 1
Components Green River Oil Shale (wt %) Carbon 9.1-19.6 Organic
Carbon 6.7-15.7 Hydrogen 1.1-2.0 Nitrogen 0.2-0.7 Sulfur 0.9-3.4
Fisher Assay Oil 3.4-11.6 Water 0.4-5.9 Residue 83.4-91.0 Gas
liquor 0.8-3.3 Gas and loss 2.1-4.1
[0007] The largest known deposits of tar sands are the Athabasca
sands found in northern Alberta, Canada which underlay more than
13,000 square miles at a depth up to 2,000 ft. Of the 24 states in
the United States that contain tar sands, about 90% of such
deposits are in the state of Utah. The hydrocarbon resource locked
in the Utah tar sands has been estimated to be in excess of 25
billion barrels.
[0008] However, the Utah tar sands, being of non-marine origin,
have somewhat different chemical and physical characteristics than
the Athabascan sands which are of marine origin, and do not respond
as well to the traditional process used to extract oil from tar
sands. Utah tar sands are generally hard consolidated sand stone
closely associated with petroliferous material (heavy viscous oil
material) which is as high as 13% by weight with an average of
10.5% by weight hydrocarbon. The oil is about 13.degree.-18.degree.
API gravity and contains a low amount of sulfur, e.g. less than
about 0.9% by weight, low aromaticity and a very low water content.
The Athabascan sand has an encapsulating water film surrounding
each sand grain, which makes it amenable to a water-wetting
process. The absence of this water film on the Utah sand grain
necessitates using other technology for extracting the oils.
[0009] A comparison of the Athabascan tar sands with a sample of
Utah tar sands obtained from Asphalt Ridge is shown in Table 2.
TABLE-US-00002 TABLE 2 Asphalt Components Athabasca Sands Ridge
Sands Carbon (wt %) 82.6 84.4 Hydrogen (wt %) 10.3 11.0 Nitrogen
(wt %) 0.47 1.0 Sulfur (wt %) 4.86 0.75 Oxygen (wt %) 1.8 3.3
Average Mol. Wt (VPO-benzene) 568 820 Viscosity (poise) 6,380
325,000 77.degree. F. (cone-plate at 0.05 sec) Volatile material
(535.degree. C.) (wt %) 60.4 49.9
[0010] The high viscosity, low sulfur content, low water content
and other significant differences keep the Utah tar sands from
responding well to commonly used extraction processes.
[0011] A number of oil recovery methods related to oil shale and
tar sands have been tested in the laboratory or in small operations
in the field. These processes involve various techniques such as
hot water processes, cold water processes, solvent processes,
thermal processes and the like, but in most cases, they possess
certain limitations which make them unsuitable for use on a
commercial basis. Further, many of these processes leave over 20%
of the organic carbon behind in the spent shale. A process which
would be effective with these particular oil shales and tar sands
would be a significant advance in the art.
[0012] It is desirable, therefore, to provide a new and efficient
process for the extraction of hydrocarbonaceous material from
solids containing such material and particularly from Green River
oil shale. Another desirable goal is to provide unique synergies to
facilitate the economical production of various products from
hydrocarbonaceous solids. It is a further desire to provide such an
extraction process which could utilize equipment now in commercial
use, meet present day EPA standards and could be rapidly put into
commercial production to meet the urgent demand for various
hydrocarbon products.
SUMMARY OF THE INVENTION
[0013] It has now been discovered that these and other desires can
be accomplished by the process of the present invention which
relates to a new and improved process for extracting oil and other
valuable hydrocarbons from crushed hydrocarbonaceous solids, such
as oil shale, by means of a thermal technique using a special
source of heat. The process of the present invention represents an
improvement upon U.S. Pat. No. 4,725,350, hereby incorporated by
reference in its entirety, and which is also the work of the
present inventor.
[0014] Specifically, the present invention provides a new and
efficient process for extracting valuable oils and other
hydrocarbons from crushed hydrocarbonaceous solids which comprises
optional blending of the crushed solids to provide a substantially
uniform feed composition and preheating the crushed
hydrocarbonaceous solids to remove residual water. The crushed
solids are treated in a generally horizontal rotary kiln having a
slight slope downward with hot gas at an elevated temperature and
sprayed liquid hydrocarbon. Preferably, the process within the
rotary kiln occurs in the absence of water, or at least being
substantially free of water. The pressure inside the kiln can be
maintained below 500 psi and the crushed solids can be heated using
the hot gas for sufficient time to strip volatile hydrocarbon
containing liquids and gases found in the crushed solids. The
hydrocarbon rich vaporized materials and spent solids are removed
from the kiln and the gaseous products are fractionated into
desired fractions.
[0015] In a more detailed aspect of the present invention the hot
gas can be introduced into the rotary kiln at a temperature between
700.degree. F. and 2500.degree. F. and the crushed solids are
preheated to a temperature between 100.degree. F. and 350.degree.
F. to reduce the heating load on the kiln.
[0016] In yet a more detailed aspect of the invention the hot gas
is a hot syn gas which is a product of coal gasification. In one
alternative embodiment, the hot syn gas can be injected inside the
rotary kiln such that an enriched syn gas is produced upon contact
with the crushed solids. The enriched syn gas may be used as a
starting material for the manufacture of other products such as
methanol, ammonia, urea and natural gas or combusted and utilized
in a combined-cycle electricity generation step to supplement the
heating and power needs of the process.
[0017] The new process presents distinct advantages over the known
processes for extraction of hydrocarbons from oil shale, and is
particularly adapted for use in the treatment of oil shale and tar
sands obtained from most worldwide deposits. Particular advantage
is found in the fact that Utah oil shale is located near large
deposits of coal and facilitating a unique combination of the two
techniques of coal gasification and the utilization of the syn gas
therefrom directly in the oil shale extraction process. In
addition, the use of the special hydrogen and carbon
dioxide-containing hot gas effects an upgrading of the products as
to yield and quality, e.g. 5 to 25% increase in yield of light
ends, e.g. gasoline and lighter fractions, and thus presents a
desirable economic advantage. As used herein, all percents are by
weight unless specifically identified otherwise. The enriched syn
gas has a variety of potential uses, all of which increase the
economic and practical utility of the process of the present
invention. Among these uses are the production of methanol,
ammonia, urea, natural gas and recoverable heat value. Further, gas
produced in the process may be used for the production of
electricity in a combined-cycle power generation step. This reduces
the need for off-site electrical power and minimizes burning so as
to reduce atmospheric emissions of harmful gases to well below EPA
standards.
[0018] Preferably, substantially no water is present in the
reaction zone as any residual water is removed during the preheat
stage. This has many advantages, such as lower heat requirement
during the reaction in the rotary kiln, as well as improved yield.
Furthermore, there would be no need for building expensive dams and
other water collection projects prior to the operation of the
process. In addition, the process utilizes equipment now in
commercial production and does not require specially produced
equipment which may require long periods of time for
construction.
[0019] Finally the process presents an additional economic
advantage in that the oil vaporized off the oil shale will be in
vapor form and can be sent directly to a fractionating tower for
refining, thereby eliminating the expense of reheating the
hydrocarbons for fractionation.
[0020] Additional features and advantages of the invention will be
apparent from the detailed description which follows, taken in
conjunction with the accompanying drawings, which together
illustrate, by way of example, features of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a flow diagram of the process of the present
invention.
[0022] FIG. 2 is a schematic diagram of one embodiment of the
apparatus and flow path for carrying out a portion of the process
of the present invention.
[0023] FIG. 3 is a schematic diagram showing the potential products
and uses of the enriched syn gas.
[0024] FIG. 4 is a longitudinal cross-sectional view of a rotary
kiln in accordance with the present invention.
[0025] FIG. 5 is an axial cross-section view taken along line 5-5
of FIG. 4, showing a refractory configuration within the kiln.
DETAILED DESCRIPTION OF THE INVENTION
[0026] While the process of the invention is described hereinafter
with particular reference to the processing of oil shale using
specific language to describe the same, it will nevertheless be
understood that no limitation of the scope of the invention is
thereby intended. Alterations and further modifications of the
inventive features illustrated herein, and additional applications
of the principles of the inventions as illustrated herein, which
would occur to one skilled in the relevant art and having
possession of this disclosure, are to be considered within the
scope of the invention. For example, it will be apparent that the
process can also be used to treat a great variety of
hydrocarbon-containing solids, such as tar sands, solid crude oil,
gilsonite, peat, and mixtures of two or more of these materials, or
any other hydrocarbon-containing solids with inert materials.
Process Overview
[0027] The following overview is designed to provide a brief
synopsis of the process of the present invention, while the
particulars of each step will be discussed in greater detail below.
Hydrocarbonaceous solids are treated to recover valuable
hydrocarbon fractions. The process of the present invention
provides several additional advantages which increase the economic
value of the process. Several of these advantages include the
production of an enriched synthetic gas which can be used to
produce a variety of industrial chemicals and may be used in the
production of electricity to supplement various energy requirements
of the process.
[0028] Referring now to FIG. 1, hydrocarbonaceous solids are
crushed at step 101 and then preheated at step 102. The crushed
solids are then treated in a low-pressure rotary kiln at step 105
where substantially all of the volatile hydrocarbons are removed.
The rotary kiln treatment can include the presence of an atmosphere
at an elevated temperature and will be discussed in more detail
below in connection with FIGS. 2, 4 and 5. In one embodiment, this
unique atmosphere is commonly provided using a hot syn gas produced
from a coal gasification step 103, shown in FIG. 1. Further, a
liquid hydrocarbon is provided in step 104 during the rotary kiln
treatment step 105 to improve yields of hydrocarbon products. The
rotary kiln treatment of the crushed solids results in the
production of vaporized hydrocarbons, optionally an enriched (i.e.
modified) syn gas, and a quantity of spent solids. The spent solids
are recovered from the kiln in step 107. The vaporized hydrocarbons
and enriched syn gas are separated in step 106. The vaporized
hydrocarbons are then fractionated in step 108 into desired
hydrocarbon fractions for further refining or sale. The enriched
syn gas is recovered in step 109 and further used in one or more of
several ways. The enriched syn gas contains sufficient heat and BTU
value to drive an appropriately designed combined-cycle power
generation in step 110 to provide electrical energy to other parts
of the process, as depicted by dashed line 115. The enriched syn
gas may also be used in the production of various industrial
chemicals as shown in step 111 for ammonia synthesis, step 112 for
methanol synthesis, step 113 for urea synthesis, and step 114 for
the recovery of natural gas. Each of these steps is discussed in
more detail below in conjunction with the accompanying figures.
Hydrocarbonaceous Solids Preparation
[0029] Referring now to FIG. 1, hydrocarbonaceous solids are
crushed at step 101 to increase the exposed surface area and to
improve the ultimate hydrocarbon recovery. As noted above, the
hydrocarbonaceous solids used in the process of the invention may
be any solid material having hydrocarbons dispersed within or on
the solids. Most often the solids contain at least 8% and
preferably 10% to 70% by-weight of hydrocarbon materials. Such
hydrocarbonaceous material includes, but is not limited to, oil
shale, tar sands, crude oil, gilsonite, peat and mixtures thereof.
Thus, the term "crushed hydrocarbonaceous solids" is intended to
include materials which may not need crushing such as some tar
sands. The hydrocarbonaceous material contained within oil shale
has an average content of: Carbon (wt %) 70-90%, Hydrogen 7 to 15%,
Nitrogen 0.5 to 3%, and Sulfur 0.2 to 4%. The average content of
bitumen in tar sands is: Carbon (wt %) 70-90%, Hydrogen 7 to 15%,
Nitrogen 0.3 to 3%, Sulfur 0.5 to 8%, and Oxygen 1 to 6%. Crushed
tar sands containing over about 15% bitumen tend to agglomerate and
may cause processing difficulties. Crushed oil shale, however,
contains kerogen and does not generally agglomerate during
processing according to the present invention. Kerogen is a high
molecular weight hydrocarbon having an average carbon to hydrogen
weight ratio of between about 7/1 and 8/1. In one aspect, the
crushed hydrocarbonaceous solids can be a Green River oil shale
containing from 5% to 25% by weight of hydrocarbonaceous
material.
[0030] The above-described solid materials are crushed into small
particles before further processing. The target particle size is
less than about 1 inch and ranges from about 0.1 to about 1 inch.
Particle sizes below about 0.1 inches are undesirable as the
particles become entrained in the exit gases. Although, some
entrainment of solid particles is acceptable, down-stream processes
may be adversely affected. Particle sizes between about 0.25 and
0.75 inches give good results under a variety of conditions.
[0031] Due to the nature of many mined materials, the composition
of incoming feed may vary considerably over time. Such variations
often cause undesirable shifts in the required thermal load, rate
of recovery, and fractionation parameters. The composition of the
hydrocarbonaceous material may vary over a wide range and depends
upon the type and geographic origin of the material. Further,
hydrocarbonaceous solid deposits vary in composition from the same
source. In order to reduce this variation, it is often desirable to
blend the hydrocarbonaceous materials either before or after
crushing to provide a substantially uniform feed composition prior
to preheating. This is most often accomplished by stockpiling the
materials horizontally and then taking vertical cuts as feed to the
process.
Preheat
[0032] According to FIG. 1, the crushed solid materials are then
preheated at step 102 before introduction into the rotary kiln.
Preheating serves at least two beneficial purposes. First,
preheating the crushed solids decreases the thermal requirements
later in the process. Second, and more importantly, preheating
drives off excess moisture. The presence of significant amounts of
water later in the process may cause undesirable gas shift
reactions and other difficulties. In the particular embodiment
shown in FIG. 2, the crushed hydrocarbonaceous solids, such as
crushed oil shale, are preheated in vessel 10, and taken to hopper
11 through line 17. Vessel 10 may be any unit capable of heating
the crushed solid materials to the desired temperatures such as a
rotary kiln, furnace or other heat transfer equipment. Preheat
temperatures may vary over a wide range depending upon the material
being treated and the temperature of other materials used in the
reaction kiln. Preheating preferably provides the maximum amount of
heat without vaporizing significant amounts of hydrocarbons.
Temperatures ranging from about 100.degree. F. to about 350.degree.
F. accomplish this purpose while temperatures from about
200.degree. F. to 350.degree. F. provide good results. Preheating
can be accomplished using any number of heating processes such as,
but not limited to, electrical heating, heat exchangers, boilers,
or the like. One option is to use electrical heating where the
electricity used is produced by combustion of enriched syn gas via
a system described in more detail below. Optionally, or in addition
to electrical heating, excess process heat from the enriched syn
gas and/or fractionation products can be used in a heat exchanger
to transfer heat value from these products to the incoming crushed
solids.
[0033] The preheating can be accomplished before being introduced
into the hopper or while being maintained in the hopper.
Conventional heating equipment may be used for this purpose. BTUs
obtained from other portions of the process may also be a suitable
source of heat for the preheating step. Spent solids recovered at
the end of the process, heat from coal gasification, or heat
produced from combustion of various products are several
non-limiting examples of heat sources which could be used to reduce
the requirement of extra-process energy. As shown in FIG. 1, the
preheated crushed solids are then treated in a horizontal rotary
kiln, discussed in more detail below.
Hot Gas Preparation
[0034] An important feature of the present invention is providing a
hot gas at an elevated temperature to the rotary kiln. Non-limiting
examples of suitable hot gases can include syn gas, nitrogen gas,
hydrogen gas, carbon dioxide gas, combustion gases, combinations
thereof, and any other gas having a high heat content which does
not also adversely react with the liquid hydrocarbon, liberated
hydrocarbons, and/or solids. For example, natural gas, waste gas,
or other fuel gases can be combusted to produce heat which can be
in thermal communication with the rotary kiln.
[0035] In one currently preferred aspect, the hot gas can be a hot
gas containing hydrogen and carbon dioxide as shown in step 103 of
FIG. 1. As shown in FIG. 2, hot gas containing hydrogen and carbon
dioxide is delivered to the rotary kiln 14 via line 21. The hot gas
containing hydrogen and carbon dioxide to be used in the process of
the present invention can be obtained from any suitable source. The
gas employed in the process should contain from about 10 vol % to
60 vol % hydrogen, and preferably 30 vol % to 40 vol %, and from
about 5 vol % to about 30 vol %, and preferably from 10 vol % to 20
vol % carbon dioxide. An alternative, and sometimes practical, hot
gas is nitrogen. Nitrogen can be effectively used in the present
invention if a commercially suitable source of hot nitrogen gas can
be provided. Regardless, the hot gas should be at an elevated
temperature above 1000.degree. F., while temperatures from
700.degree. F. to 3000.degree. F. are particularly useful.
[0036] Coming under special consideration is hot gas containing
from 25 vol % to 40 vol % hydrogen and from 10 vol % to 20 vol %
carbon dioxide at a temperature of 1500.degree. F. to 2500.degree.
F. Such hot synthesis gas, i.e. syn gas, may be economically
provided from the gasification of coal. One coal gasification
process which would suffice for purposes of the present invention
is described in Oil and Gas Journal, Jun. 19, 1972, page 26 as the
Koppers-Totzek process. Although a variety of improvements have
been made to the process the basic gasification process remains the
same. According to that process, a mixture of steam and oxygen
entrains the pulverized coal and gasifies it in the gasifier or
combustion chamber 13, shown in FIG. 2, producing a high
temperature gas at about 3500.degree. F. The coal used in the
production of the syn gas can be obtained from any suitable source,
e.g., can contain large or small amounts of sulfur and variable
heat content. A variety of coals can be used such as lignite,
bituminous coal, sub-bituminous coal, anthracite coal, and brown
coal. Lignites and bituminous coals are not only readily available
but also provide good results. Initial pulverization of the coal
dramatically increases the coal surface area and improves both the
rate of reaction and syn gas yields. The coal particle size is
often selected so that about 70% of the solid coal feed can pass
through a 200 mesh sieve.
[0037] In general, the gasification process is carried out by
partially combusting the pulverized coal with a limited volume of
oxygen at a temperature between about 1500.degree. F. and
3600.degree. F. If a temperature of between about 1900.degree. F.
and 3600.degree. F. is employed, the syn gas produced will contain
minimal by-products such as tars, phenols, condensable
hydrocarbons, molten slag particles and salts. The gasification
process is usually carried out in the presence of oxygen and steam,
wherein the purity of the oxygen is at least 90% by volume, with
nitrogen, carbon dioxide and argon being permissible impurities.
Some coals contain significant amounts of water which may require
drying before gasification. The reaction conditions within the
gasifier are maintained by the regulation of the weight ratio of
the oxygen to moisture and ash free coal in the range of 0.6 to
1.0, or the range 0.8 to 0.9. Specific details of the equipment and
procedures employed are known to those skilled in the art and are
described in various sources such as U.S. Pat. No. 4,350,103 and
U.S. Pat. No. 4,963,162. Additionally, in one embodiment, Chevron
gasifiers can be used to provide the hot syn gas. These types of
gasifiers reduce or eliminate the need for cooling the gas prior to
injection into the rotary kiln. The ratio between oxygen and steam
may be selected so that from 0.0 to 1.0 parts by volume of steam is
present per part by volume of oxygen. The oxygen used may also be
heated before contact with the pulverized coal. Although not
necessary the oxygen may be provided at temperatures from about
380.degree. F. to 950.degree. F. The conditions within the gasifier
may also vary widely. The gasifier pressure may vary from about 1
to 500 atm (absolute), with relatively low pressures of up to 40
atm usually being sufficient, and residence times may vary from
about 0.1 to 15 seconds.
[0038] After the pulverized coal, oxygen, and steam have been
reacted, the reaction products, which comprise hydrogen, carbon
monoxide, carbon dioxide, water and various impurities, are removed
from the gasifier. This product stream, which normally has a
temperature between 1500.degree. F. and 3200.degree. F., contains
the impurities mentioned and entrained slag, including various
carbon-containing solids. In order to facilitate removal of these
solids and impurities from the gas, the reaction product stream
should be first quenched and cooled.
[0039] The gas that is produced from coal gasification is
essentially carbon monoxide, hydrogen and carbon dioxide with a
relatively small percentage of nitrogen, hydrogen sulfide, carbonyl
sulfide, and traces of other compounds. This hot syn gas generally
contains from about 10 vol % to about 70 vol %, and preferably from
about 25 vol % to 60 vol % hydrogen, from about 10 vol % to about
70 vol %, and preferably 40 vol % to 60 vol % carbon monoxide, and
from about 5 vol % to about 30 vol %, and preferably 10 vol % to 20
vol % carbon dioxide. In addition, more than 50% of the ash solids
drop down through a quench and is eliminated in gas stream. A coal
gasifier for example, using 3,400 tons of coal a day will produce
over 364 million cu. ft. of 800 BTU/SCF gas daily. This would be
sufficient to produce approximately 50,000 barrels of oil a day
according to the method of the present invention.
[0040] An advantage of using syn gas from coal gasification is the
presence of significant amounts of both hydrogen and carbon
dioxide. As mentioned before, the hydrogen atmosphere aids in
cracking and pyrolysis of the hydrocarbons while the presence of
carbon dioxide further enhances the yield of hydrocarbons. Thus, by
carrying out the process of the present invention in an atmosphere
containing substantial amounts of both hydrogen and carbon dioxide
improved results are obtained.
[0041] Another advantage of using hot syn gas from the gasification
of coal by the Koppers-Totzek process is found in the fact that
this technique produces large amounts of nitrogen in the oxygen
step and this can be further reacted with enriched syn gas from the
present process to produce valuable anhydrous ammonia as a
by-product, described in more detail below. Production of ammonia
in this manner appears more reliable than producing ammonia from
natural gas.
[0042] Referring to FIG. 2, the hot gases leaving the gasifier 13
have a temperature of at least about 2,750.degree. F. The desired
temperature of the hot syn gas to be introduced into the rotary
kiln 14 will vary depending upon the product being treated in the
kiln, preheat temperature of the crushed solids and residence time
in the rotary kiln. In most cases, the desired temperature of the
syn gas upon entry to the kiln will vary from about 1,000.degree.
F. to 2,500.degree. F. This may necessitate cooling of the hot syn
gas before introduction into the rotary kiln. The cooling can be
accomplished by any suitable means, but is preferably accomplished
by use of an optional conventional heat exchanger 20 as shown in
FIG. 2. The hot syn gas from the gasifier 13 is taken through line
22 to a heat exchanger 20 where it is brought to the desired
temperature. The recovered heat value may be optionally transferred
to other parts of the process such as the preheater 10 or used to
produce steam for electricity generation, discussed in more detail
below. Alternative hot gases such as nitrogen can also be used. In
this case, hot nitrogen gas can provide similar recoveries with
slightly longer residence times.
Injected Hydrocarbon
[0043] A hydrocarbon material can be injected along with the
crushed hydrocarbonaceous solids to achieve improved recovery and
results. For example, a liquid hydrocarbon can be injected or
sprayed into the rotary kiln. Alternatively, a solid hydrocarbon
such as gilsonite, peat, residuums, or the like can be provided as
fines and then injected into the rotary kiln, injected along with
the hot gas, or provided in a organic slurry. Preferably the solid
hydrocarbons can be injected in a dry, non-slurry form. These solid
hydrocarbons can preferably be provided as fines having an average
diameter of less than about 0.75 inches, and preferably less than
about 0.5 inches. A finer solid particle will vaporize and
participate in hydrocarbon recovery in a shorter time than larger
particles. In one currently preferred aspect, the solid hydrocarbon
can be gilsonite. This type of additive can be beneficial as it can
be a very cheap feed stock and can improve recovery rates and
efficiencies with minimal additional cost and load on the
process.
[0044] In many circumstances, liquid hydrocarbons can be preferred
over solid hydrocarbons as a material which is injected into the
rotary kiln. A liquid hydrocarbon, such as crude oil or hydrocarbon
product condensates, is also delivered to the rotary kiln 14. The
liquid hydrocarbon may be delivered from a container 12 via line 19
at any point in the kiln 14 or added to the crushed solids prior to
entry into the kiln. For example, in FIG. 4, the liquid hydrocarbon
could be sprayed onto the crushed solids along the screw conveyor
30 or through line 19 and sprayed into the kiln at any point. Thus,
although both FIG. 2 and FIG. 4 show line 19 connecting at the
entry end of the rotary kiln other configurations are within the
scope of the present invention. The sprayed hydrocarbon need not be
heated, but the entry temperature will have an affect on the heat
load of the kiln. The rate of delivery of liquid hydrocarbon
depends largely on the properties of the crushed solids and the
desired product. Thus, the delivery rate of liquid hydrocarbons may
range from about 5 to 60 gallons per ton of crushed solids, while
about 10 to 20 gallons per ton should work well for most feedstock.
For example, crude oil can be introduced into the kiln at a rate
from about 30 to about 50 gallons per ton of oil shale. Similarly,
from about 20 to about 25 gallons of crude oil per ton of tar sands
can be used. Rates outside these ranges can also be effectively
used, depending on the quality and composition of the feedstock and
the desired recovery rates. The addition of the liquid hydrocarbon
increases the rate of recovery and vaporization of the volatiles
contained on the crushed solids. Further, addition of a liquid
hydrocarbon, such as crude oil, has the benefit of increasing the
yields of various hydrocarbon fractions and offers an inexpensive
method for separating various hydrocarbon fractions from the crude
oil.
[0045] In yet an additional aspect, the injected hydrocarbon can be
introduced in a co-current flow configuration such as that shown in
FIG. 2. Alternatively, the injected hydrocarbon can be introduced
in a counter-current manner which can help to improve efficiencies
by increasing yields from nearly spent solids. In this case, the
injected hydrocarbon can be introduced at the lower end of the
rotary kiln. Similarly, the crushed hydrocarbonaceous solids can be
treated with the hot gas in either a co-current or a countercurrent
configuration. Although optimal parameters for a full scale system
have yet to be determined, a lab scale system indicates that
exceptional results can be achieved in a counter-current
configuration.
Horizontal Rotary Kiln
[0046] Referring now to FIG. 4, the crushed solids are brought to
rotary kiln 14 through line 18. Line 18 may contain a screw
conveyor 30, weir or other similar device for facilitating delivery
of the crushed solids to the kiln. Hot syn gas is delivered to the
rotary kiln through line 21, most often as a product of coal
gasification. The point of entry of line 21 being such that the
crushed solids from line 18 entering the kiln cascade over the hot
syn gas and preferably at a point such that the particles cascade
down over the hot syn gas being introduced at a lower point in the
kiln. The liquid hydrocarbon is most often introduced via line 19
in close proximity to the point of entry of the crushed solids.
Spraying of the liquid hydrocarbon results in improved contact and
increased surface area for heating and interacting with the crushed
solids and the hydrocarbon materials contained thereon. The crushed
solids, hot syn gas and liquid hydrocarbon flow co-currently
through the length of the kiln. As these materials pass through the
kiln the temperature of the crushed solids increases resulting in
vaporization of a substantial portion of the volatile
hydrocarbonaceous material originally contained in and on the
crushed solids.
[0047] Although direct heating of the crushed solids can be
preferable in some circumstances, indirect heating using the hot
gas can also provide sufficient recovery of hydrocarbons from the
crushed solids. In one alternative embodiment, the hot gas can be
directed to an indirect heating device outside the rotary kiln. In
this way the crushed solids are treated by the hot gas via heating.
The indirect heating device can be any suitable device for
directing heat from the hot gas toward the interior of the rotary
kiln and the crushed solids contained therein. In one specific
embodiment, the indirect heating device can be a concentric shell
oriented around at least a portion of the rotary kiln. The
concentric shell can have an inlet and an outlet operatively
connected thereto such that hot gas can enter and leave the
interior shell space. The concentric shell can form an enclosed
jacket around at least a portion of the rotary kiln in a manner
similar to a heat exchanger. The hot gas can be syn gas, natural
gas, nitrogen, combustion gases, or any other gas having a
sufficient heat value to vaporize volatile components from the
crushed solids.
[0048] The rate of rotation of the kiln can be adjusted as needed
to bring about the desired separation and volatilization of the
hydrocarbonaceous material. The use of the rotary kiln as described
above permits the use of particles having a moderately fine
particle size such as those that might be present in the solid
materials of the type found in oil shale deposits, although
extremely fine particles may become entrained in the gas and
necessitate additional scrubbing to remove before fractionation.
One also employs a very low pressure in the rotary kiln which will
vary over a narrow range, e.g. 5 psi to 30 psi. Pressures from 5
psi to about 15 psi and from about 5 psi to about 10 psi have
generally provided satisfactory results. However, it has also been
found that increased pressures within the kiln can increase
cracking to produce lighter hydrocarbon fractions, increase
hydrocracking and separation rates to allow for increased
throughput, and improve recovery efficiencies. It is thought that
the increased pressure increases the rate at which gases penetrate
the solids, thus allowing for improved reaction kinetics and
transport kinetics. Further, an increased pressure can prevent
oxygen from being drawn into the rotary kiln which may cause
dangerous explosive conditions. Unfortunately, higher pressures
also create additional practical problems such as leaks and
physical limitations of available equipment. As a general matter,
pressures inside the rotary kiln can be from about 1 psi to about
500 psi. Current equipment makes pressures above about 100 psi
difficult, expensive, and impractical to maintain; however, it is
expected that the principles of the present invention can be
readily applied to higher pressures should appropriate equipment
become available. As a practical matter, pressures from about 1 psi
to about 100 psi may be achieved, and preferably from about 10 psi
to about 50 psi. It should be noted that these pressures are
obviously gauge pressures (psig), i.e. a baseline of 0 psi is
atmospheric. Thus, it can be often desirable to operate the rotary
kiln at the highest practical pressure that can be achieved for a
particular system, depending on the available equipment.
[0049] Although catalysts need not be employed in the process of
the present invention to obtain the desired results, in some cases
it may be desirable to accelerate the production of certain
products or improve pyrolysis to employ catalytic materials in the
rotary kiln. Such catalysts are commercially available and some
common examples include nickel, vanadium, and various heterogeneous
catalysts.
[0050] As the temperature employed in the kiln is important, it is
necessary to maintain proper preheat temperature, syn gas
temperature and liquid hydrocarbon temperature to produce the
needed temperature in the kiln. Shown below in Table 3, is an
illustration of the relationship of preheat temperature and syn gas
temperature to bring about the desired kiln temperature.
TABLE-US-00003 TABLE 3 RUN BARRELS/ SYN GAS TEMPERATURE No. DAY OIL
PREHEAT .degree. F. TEMP .degree. F. IN KILN 1 10,000 250 1,800 700
2 10 000 350 2,500 572 3 3,670 350 2,500 900 4 1,380 60 1,800
900
[0051] The parameters are adjusted so that the temperature in the
kiln is between 600.degree. F. and 1,000.degree. F. with
temperatures between 700.degree. F. and 900.degree. F. giving
particularly good results.
[0052] As shown in FIGS. 2 and 4, the kiln is in a substantially
horizontal position with a slight slope and is rotated at a rate
sufficient to maintain the desired residence time. The horizontal
rotary kiln can slope downward at an angle which is sufficient to
provide a desired residence time and mixing characteristics.
Although a slope of up to about 8.degree. can work in the present
invention, typically about 3.degree.-5.degree. slope provides
adequate residence time within the rotary kiln. The required
residence time in the kiln will also vary depending upon the type
of solid being treated, particle size, rate of addition, syn gas
temperature, liquid hydrocarbon temperature, and rate of rotation
of the kiln. Typically, a kiln load of less than 35% and preferably
less than about 15% offers adequate mixing and heating conditions.
These parameters should be adjusted so that the particles remain in
the kiln until they are substantially stripped of the
hydrocarbonaceous material contained therein. Obviously, the
crushed solids, hot syn gas and average kiln temperature will
exhibit a temperature gradient throughout the length of the rotary
kiln. For example, entry temperatures of 2400.degree. F. for the
syn gas, 350.degree. F. for the crushed solids, 100.degree. F. for
the liquid hydrocarbon, and 1600.degree. F. for the refractory the
temperature of each will converge toward an average temperature of
about 1100.degree. F. toward the outlet end of the rotary kiln.
Thus, the various hydrocarbons contained on the crushed solids are
gradually heated to their respective boiling points and/or
pyrolysis temperature.
[0053] According to the method of the present invention, between
about 88% and 99% of the hydrocarbonaceous material in the original
crushed solids is recovered. In most cases, the solids leaving the
kiln should have no more than 1 or 2% of hydrocarbonaceous material
remaining on the solid particles. At a syn gas temperature of about
1000.degree. F. to 2500.degree. F., a crude oil temperature of
about 50.degree. F. to 150.degree. F., a crushed solids entry
temperature of 350.degree. F., and particle size of about 0.75 inch
of oil shale, a residence time of about 10 to 20 minutes should be
sufficient to effect the necessary separation. At 10% load and a
residence time of about 12 minutes, the rate of rotation of the
rotary kiln is between 2 and 5 rpm. Fifteen minute retention times
are current typical operating conditions. However, residence times
from about 5 to 90 minutes can be used to achieve a desired yield
and separation, and most often from about 10 to about 60
minutes.
[0054] These parameters are also controlled so as to minimize the
secondary decomposition of the valuable hydrocarbon material to
form coke and other undesirable by-products. This can be
accomplished in most cases by the use of lower temperatures and
shorter reaction periods. It should be noted here that the hydrogen
atmosphere has several advantages. As the hydrocarbon material is
vaporized and continues to heat, a portion of the material will
pyrolyze and crack to form smaller hydrocarbon chains. As long as
temperatures are controlled to avoid excessive coke formation this
improves the quality and value of the hydrocarbon fractions
ultimately recovered. Hydrogen will react with vapors deficient in
hydrogen to form more light ends for removal at the fractionation
step. The presence of the hydrogen atmosphere brings about a 5% to
25% increase in yield of light end products as compared to the
conventional thermal process using hot gas free of hydrogen.
Further, the hydrogen atmosphere prevents excessive undesirable
secondary decomposition and production of aromatics, toxic
off-gases and coke. Under hydrogen-deficient conditions pyrolysis
is inefficient and a greater amount of char or coke is produced
decreasing the yield of useful hydrocarbons. The hydrogen not only
facilitates removal of the hydrocarbons imbedded in the particles,
but much of the sulfur present in the crushed solids will be picked
up by the hydrogen and may be carried to a sulfur removal unit.
Additionally, the presence of a substantial amount of carbon
dioxide has proven to positively affect the yields of hydrocarbons
from Green River oil shale and Utah tar sands. Typically, a carbon
dioxide content of between about 10% and 20% of the incoming hot
syn gas provides the cited results.
[0055] Any substantially horizontal rotary kiln should suffice for
the present invention. Various internal configurations are also
possible. Referring to FIG. 4, the refractory 31 may be smooth
walled or may contain longitudinal baffles to aid in mixing of the
crushed solids. Although these embodiments are considered within
the scope of the present invention it has been discovered that
mixing is improved by using the following described refractory
configuration. FIG. 5 illustrates an axial cross-sectional view
taken along line 5-5 of FIG. 4, which shows a generally horizontal
rotary kiln in accordance with one embodiment of the present
invention. The rotary kiln 14 may be constructed of a steel shell
76 and lined with a refractory made up of firebrick 74 and 75. As
shown in FIG. 5, the bricks are arranged so as to have certain
bricks 75 set on end rather than flat 74 in a slightly offset
pattern so as to present a series of spiraling baffles such as the
lands in a rifle barrel. The baffles extend only about 3/4 of the
length of the kiln leaving the last quarter containing just the
firebrick liner having bricks laid flat. As shown in FIG. 5, in a
rotary kiln of about 6 feet in diameter, the baffles are arranged
so as to be about 2 to 4 feet apart. Thus, as the kiln rotates, the
baffles cause the crushed particles to be agitated thereby
improving exposure of each particle to the hot syn gas and other
vapors resulting in increased rate of removal of hydrocarbons.
Notice that the spiraling of the baffles permits a gradual shifting
of the solid particles down through the kiln and affords maximum
exposure of the hot syn gas and vapors to the particles. This
spiraled configuration offers increased contact of the crushed
solids with the hot syn gas and other vaporized materials over the
configuration having no baffles or straight baffles which would
lift up a portion of the crushed solids at intervals rather than
continuously down the length of the baffling. Although other rotary
kilns may be used, the removal of hydrocarbons is greatly
facilitated by the construction of the rotary kiln as shown in
FIGS. 4 and 5.
Product Removal
[0056] After the crushed solids travel the length of the rotary
kiln, the resulting enriched syn gas, hydrocarbon containing vapors
and spent solids are removed from the kiln. The enriched syn gas
contains a portion of the original syn gas components, methane,
particulates and other light components. As shown in FIG. 2, at the
end of the residence period in the kiln, the hydrocarbon vapors,
enriched syn gas and residual solids are discharged to a separation
chamber or hopper 16 where the vapors and gas are separated from
the spent solids. In the embodiment shown in FIG. 2 the enriched
syn gas, vaporized hydrocarbons and spent solids are delivered to a
separation hopper 16 where the vapors are discharged through line
24 to fractionation column 15 and the spent solids enter line 23.
The solids are removed by means of a screw conveyor or other
suitable means and taken to a disposal unit, or a unit where the
BTUs can be removed via heat exchange and utilized in the
preheating of the raw crushed solids to be introduced into the
rotary kiln. In one embodiment shown in FIG. 4, line 23 contains a
screw conveyor 32 and interconnects line 33 through which the
solids are discharged. Only a small amount of coke is formed in the
process of the invention. Such a small amount can be processed out
and burned to generate steam or recycled to the coal gasification
step.
[0057] The products taken from the kiln generally comprise 10-30%
enriched syn gases, 5-25% volatilized condensates, 1-10% coke, and
60-85% spent solids. Product yield, excluding the spent solids,
from various types of tar sands is illustrated in Table 4.
TABLE-US-00004 TABLE 4 PRODUCT ATH TST AR PRS WIL Enriched Gases
7.52 5.31 4.80 7.41 6.03 Condensates 76.52 72.82 82.85 76.05 77.04
Coke 15.90 21.87 12.35 16.54 16.93 Key: ATH--Athabasca Sands,
TST--Tar Sand Triangle, AR--Asphalt Ridge, PRS--P.R. Spring,
WIL--Wilmington.
[0058] Enriched syn gas analyzed by gas chromatography and mass
spectrometry gave the results shown in Table 5 as to the Tar Sand
Triangle run. TABLE-US-00005 TABLE 5 Moles (%) COMPOUND Helium free
basis Hydrogen 14.3 Methane 47.3 Ethylene 1.6 Ethane 10.9 Propylene
3.1 Propane 5.5 1,3-butadiene 0.1 Butenes 2.6 Iso-butane 0.0
n-Butane 2.2 Cyclopentane 0.1 Pentenes 0.7 Isopentenes 0.3
N-Pentane 1.3 Ammonia 0.7 Hydrogen sulfide 5.0 Carbon monoxide 3.9
Carbon dioxide 0.4 Total 100.0
[0059] Typical analysis of the vaporized hydrocarbon is shown in
Table 6 giving the carbon and ring analysis of condensates obtained
from the Tar Sand Triangle run. TABLE-US-00006 TABLE 6 ATOMIC %
TYPE CARBON Paraffinic carbon 55-60 Aromatic carbon 18-20
Naphthenic carbon (saturated) 9-16 Olefin carbon 10-12 Aromatic
rings/molecule 0.07 Naphthenic-olefin ring molecules 1.2
Separation of Gaseous Fractions
[0060] The gaseous products removed from the rotary kiln are
separated in step 106 of FIG. 1 to produce both final products and
precursors for further processing. Referring to FIG. 2, the
vaporized hydrocarbons and enriched syn gas taken along line 24 may
be taken to a cyclone (not shown) where any small fines are
removed. The vaporized hydrocarbons and enriched syn gas are then
delivered to a fractionation column 15 where they can be easily
separated into the desired fractions. The enriched syn gas is
removed via line 25 and taken to tank 34 while the various
hydrocarbon fractions are taken off as desired via lines 26, 27, 28
and 29. The fractionation of the vaporized hydrocarbons, e.g.
above-described condensates, can be accomplished by any suitable
means. The present process presents a special advantage in that the
hydrocarbon condensates to be separated are already at an elevated
temperature, e.g. about 500.degree. F. to 1200.degree. F., and the
fractionation process can be accomplished without having to raise
the temperature of the condensates before introduction into the
fractionation column. Suitable products from such fractionation
include light distillates, such as gasoline, middle distillates,
such as jet fuels, diesel fuel and heating oil, and the residual
products, such as asphalts. A partial range of products that can be
obtained from the condensates derived from the pyrolysis of oil
shale and tar sands is shown in Table 7. Some of the more common
hydrocarbon fractions recovered from the present process can
include gasoline, kerosene, gas oil, heavy gas oil, and vacuum oil.
Table 7 is merely one example of recovered hydrocarbon fractions,
therefore the actual results in may vary considerably depending on
the feedstock solids and the process conditions chosen.
TABLE-US-00007 TABLE 7 Temperature (.degree. F.) Hydrocarbon
Fraction Wt % C+.sup.5-392 Gasoline 9.8 392-527 Kerosene 11.3
527-617 Gas oil 9.7 617-752 Heavy gas oil 17.7 752-995 Vacuum gas
oil 32.6
[0061] The quantity of these components, and particularly those in
the lighter oil range, are significantly improved by the presence
of hydrogen and carbon dioxide in the treating gas as shown in the
example below. Typical recovery of oil from oil shale is between
about 30 and 36 gallons per ton of crushed oil shale, while average
recovery of oil from tar sands is slightly lower at about 20 to 30
gallons per ton of crushed tar sands.
Additional Products
[0062] In the embodiment shown in FIG. 2, the enriched syn gas
removed from the top of fractionation column 15 through line 25 is
taken to tank 34. This enriched syn gas contains various components
which can be used in further reactions to form valuable by-products
such as ammonia, methanol, urea, and natural gas, as shown in FIG.
1 in steps 111 through 114. Although, each individual process is
known the unique integration of production according to the present
invention provides increased energy efficiency and economic value.
FIG. 3 shows a schematic view of the additional products and uses
of the enriched syn gas and is an extension of FIG. 2 starting with
the enriched syn gas tank 34.
[0063] Referring now to FIG. 3, one potential use of the enriched
syn gas is to take a portion of the gas, which is rich in hydrogen,
and combined it with nitrogen to form ammonia. Depending on the
quality of the hydrogen stream, i.e. the enriched syn gas
containing hydrogen and carbon monoxide, various purification steps
such as catalytic water gas shift reactions may be necessary. In
such a process, a portion of the enriched syn gas is taken along
line 39 to gas-shift reactor 40. The hydrogen containing carbon
monoxide is reacted in the gas-shift reactor with steam delivered
via line 57. The steam is produced using any number of heat sources
throughout the process, such as from the combined-cycle step
discussed below. The carbon monoxide reacts with water to produce
hydrogen and carbon dioxide. Thus, the carbon monoxide can be
viewed as "potential" hydrogen, since the stoichiometric ratio in
this reaction is 1:1 according to the following:
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2
[0064] The excess water and carbon dioxide, along with any other
impurities are then removed from gas-shift reactor 40 via line 42
to tank 43 and purified hydrogen is produced which is drawn from
reactor 40 via line 41 and passed to reactor 44. At this point
nitrogen is provided to reactor 44 via line 46 from source 45 (i.e.
from the coal gasification step or an air separation process) to
form liquid ammonia. The reactants are combined and react according
to the equation: 3H.sub.2+N.sub.2.fwdarw.2NH.sub.3
[0065] This process is endothermic and may require some additional
heating to drive the reaction toward the ammonia product which is
taken to tank 49 via line 47 for further use or sale. Actual
parameter determinations are easily made by those skilled in
process design and reaction kinetics depending on the specific
ammonia synthesis process chosen.
[0066] Another step in the process shown in FIG. 1 is the synthesis
of methanol 112. Referring back to FIG. 3, a portion of the
enriched syn gas is taken from tank 34 to a catalytic reactor 36
via line 35 for conversion to methanol which may be subjected to
further conversion in steps, not shown, to products such as
synthetic paraffins, gasoline additives, propane, 1000 BTU gas
line, water, formaldehyde, chloromethanes, acetic acid, methyl
acetate, methyl formate and the production various other
intermediates or products. The predominant commercial source of
methanol is currently from the reaction of syn gas containing
hydrogen and carbon monoxide in the presence of a heterogeneous
copper catalyst. Depending on the catalyst used, the methanol
synthesis process may be a high or low-pressure process. Common
catalysts for methanol synthesis using syn gas include, but are not
limited to; copper, zinc oxide, aluminum oxide, zinc, chromium
oxide and mixtures thereof. The basic reaction is described by the
following equation: 2H.sub.2+CO.fwdarw.CH.sub.3OH Moderate
temperatures and pressures are generally required. For example,
Cu/ZnO and Cu/ZnO/Al.sub.2O.sub.3, catalysts are used at
temperatures between 200.degree. and 300.degree. C. and 50 to 350
atm. Further, the stoichiometric ratio of hydrogen to carbon
monoxide in common syn gas is well suited for this reaction with
carbon monoxide acting as the limiting reagent. The resulting
methanol is then taken from catalytic reactor 36 to tank 38 via
line 37 from which it may be sold or used as a precursor for other
commercial chemicals. Although yields and selectivity for methanol
production vary widely, several processes have improved yields and
selectivity to over 50%, and even over 90%.
[0067] A portion of the enriched syn gas may also be used to
produce urea at step 113, as shown in FIG. 1. Ammonia produced
according to the above-mentioned process or by other methods may be
combined with carbon dioxide to produce urea. Referring to FIG. 3,
ammonia is delivered via line 48 to a reactor 50 and combined with
carbon dioxide delivered from source 51 via line 52. The carbon
dioxide may be recovered from other parts of the process such as
the gas-shift reactor 40 or another suitable source. The reaction
produces urea, an amine, via an ammonium carbamate salt according
to the following overall equation:
2NH.sub.3+CO.sub.2.fwdarw.H.sub.2NCONH.sub.2+H.sub.2O
[0068] The reaction is carried out at moderate temperatures of
about 250.degree. F. and 400.degree. F. and a pressure of between
about 100 and 350 atm. The final urea product is removed from
reactor 50 via line 53 to tank 54. The urea product is then used or
sold and is most commonly used as a fertilizer.
[0069] In another aspect of the present invention the enriched syn
gas may be further separated to produce natural gas in step 114, as
shown in FIG. 1, for use as a fuel or otherwise sold. Referring to
FIG. 3, a portion of the recovered enriched syn gas from tank 34 is
taken via line 55 to unit 56. Notice that the enriched syn gas has
a substantial quantity of methane and light hydrocarbons, as noted
in Table 5. These light hydrocarbon fractions may be isolated using
any number of separation technologies known in the art. The
remaining components, predominantly hydrogen, carbon monoxide and a
small amount of carbon dioxide, may be released or sent back to
tank 34 and are ideally suited for the production of methanol,
ammonia and/or urea according to the processes described above.
[0070] In another more detailed aspect of the present invention a
portion of the enriched syn gas is removed for use as a fuel
mixture which is burned and used to generate electricity in a
combined cycle electricity generation step 110 of FIG. 1 for use in
the process. The "enriched" syn gas is intended to emphasize that
the original syn gas composition has not only changed slightly as a
result of hydrogen and carbon dioxide reaction and depletion
through the rotary kiln treatment step 105 but also because of the
addition of light hydrocarbon fractions vaporized from the crushed
solids which are lighter than gasoline, such as light alkanes and
alkenes (see Table 5). This enriched syn gas has a heat value of
about 400 to 500 BTU/SCF, which is sufficient to drive a combined
cycle electricity generation process.
[0071] A simplified view of such a combined-cycle process is shown
in FIG. 3. The enriched syn gas is delivered from tank 34 via line
61 to a gas turbine compressor 62 and compressed to about 100 to
500 psig and then burned to produce hot combustion gas between
about 1500.degree. and 3000.degree. F. The hot combustion gas is
directed via line 63 to a gas turbine 64 which drives a first
generator 72. The electricity produced, shown as a dashed line in
both FIGS. 1 and 3, can be used to drive the compressor 62 and/or
used in other parts of the process, shown generally at point 73.
The combustion gases exiting the gas turbine 64, usually at about
800.degree. to 1500.degree. F., are then directed to a heat
exchanger 66. Heat exchanger 66 is supplied with water or steam via
line 58 wherein a portion of the heat contained in the combustion
gases from line 65 is transferred to produce a high-pressure steam
between about 50 and 3000 psig and a temperature of about
250.degree. to 1400.degree. F. This high-pressure steam exits the
heat exchanger via line 67 and the cooled combustion gases exit via
line 68. The cooled combustion gases may then be stored in tank 69
or released, as the enriched syn gas is extraordinarily clean
burning. The steam in line 67 is directed and expanded through a
steam turbine 70 which drives a second generator 71 to produce
additional electricity for distribution throughout the process. The
expanded steam exits the steam turbine via line 59 and may be used
for a variety of purposes. The steam may be recycled back to the
heat exchanger along line 58 or to the gas-shift reactor 40 via
line 57 discussed above or the remaining heat value can be
recovered and used in other parts of the process, such as the
preheat step 102 or preheating in the coal gasification step 103.
The combined-cycle electricity generation is sufficient to provide
the electrical needs of the entire process and any excess may be
sold or stored.
[0072] Further, the spent solids recovered in step 107 of FIG. 1 at
the end of the process will generally contain latent heat, coke and
generally not more than 1 to 2% unrecovered hydrocarbon. The BTU
units are preferably recycled to use in the preheating of the raw
crushed solids at step 102 and the remaining spent solids are sold
for use as cement feed or otherwise disposed of. Alternatively, or
in addition to use in preheating, the recovered heat value from the
spend solids can be used in various other portions of the process
such as fractionation, chemical synthesis, or the like. Any known
heat recovery unit or process can be used for this purpose, e.g.,
heat exchangers, forced air, etc.
[0073] The description herein is designed to enable those skilled
in the art to practice the method of the present invention and as
such details well within the capacity of those skilled in the art
will require some design and experimentation to determine exact
operating parameters. Further, not all possible interconnections
have been explained and diagrammed. For example, the water source
60 may be supplemented by water condensed from the gas-shift
reactor off-gas tank 43 shown in FIG. 3, the drying/preheat step
102 shown in FIG. 1, the drying of pulverized coal, or from
available make-up water sources.
EXAMPLE
[0074] The operation of the process of the invention is illustrated
by the following example showing the use of hot syn gas obtained
from the gasification of eastern coal and crude oil for the
pyrolysis of Green River oil shale.
[0075] For the hot syn gas production step, 5,000 lbs. of eastern
coal was dried to between 2% and 8% moisture and crushed to
particle size of about 0.75 inch. The crushed coal was conveyed
into a feed bin where it was continuously discharged into a mixed
nozzle where it was entrained in oxygen and low-pressure steam.
Moderate temperature and high burner velocity prevented the
reaction of coal and oxygen before entry into the gasification
zone. The oxygen, steam and coal reacted in the gasifier at a
temperature of 3330.degree. F. The carbon and volatile matter of
the coal was gasified to produce a hot syn gas, and the coal ash
converted into a molten slag. About 50-70% of this slag was dropped
into a water quench tank and was carried from the tank to the
disposal system as a granular solid, and the remainder is entrained
in the gas exiting the gasifier. Gas leaving the gasifier was
quenched to remove any entrained slag droplets and then passed
through a heat exchanger to reduce the temperature to about
2100.degree. F.
[0076] Green River Oil Shale was crushed to particle size of less
than about 0.75 inch at 70.degree. F. and passed into a preheater
where it was preheated to a temperature of 350.degree. F. and then
taken by screw conveyor to a rotary kiln. The particles were
cascaded over the hot syn gas at 2100.degree. F. obtained from the
coal gasification process described above. Further, crude oil at
80.degree. F. was sprayed into the kiln at the entry point of the
hot syn gas. The crushed solids outlet temperature was about
1000.degree. F. and the outlet gas and vaporized materials
temperature was about 1100.degree. F. The kiln at a 5.degree. slope
was rotated at 5 rpm and a residence time of about 20 minutes. The
vaporized hydrocarbons, enriched syn gas and spent solids were then
passed to a separator hopper. The spent solids were removed at the
bottom by screw conveyor and the vapors and gas taken to a cyclone
where fine particles were removed and thence to the fractionation
column. The data from this run is shown in Tables 8 and 9 below.
The yields are calculated excluding the spent solids.
TABLE-US-00008 TABLE 8 Properties Value Bitumen content of feed wt
% 12.2 Oil Shale feed rate, lbs/hr 5.0 Kiln Average Temperature
800.degree. F. Hydrocarbon yield, wt % 69.2 Enriched Gas yield, wt
% 20.6 Coke yield, wt % 10.2 API Gravity of oil, 20.degree. C.
21.1.degree.
[0077] The vaporized hydrocarbon was then subjected to
fractionation resulting in the hydrocarbon fraction yields as shown
in Table 9. TABLE-US-00009 TABLE 9 Fraction Wt % Gasoline 15
Kerosene 17 Gas oil 11 Heavy gas oil 18 Vacuum gas oil 24 Residue
15
[0078] The above process was repeated without the use of a gas
containing hydrogen and carbon dioxide and resulted in much lower
yield of light end products. As noted above, the presence of the
hydrogen and carbon dioxide gives from 5% to 25% increase in the
yield of the light end products.
CONCLUSION
[0079] The process of the invention can be operated on a batch,
semi-continuous or continuous manner and is ideally suited for
large-scale continuous operation. A plant designed to handle 75,000
tons of shale a day would yield 50,000 barrels a day of oil, 1,440
tons of liquid ammonia by-products or the equivalent of 26,300
barrels of methanol, 63,000 tons of cement feed, and minimal
off-gases.
[0080] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics of
the invention. The present embodiment is, therefore, to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims
rather than by the foregoing description, and all changes that come
within the meaning and range of equivalency of the claims are
therefore to be embraced therein.
* * * * *