U.S. patent application number 13/868473 was filed with the patent office on 2013-09-12 for process for improving recovery of condensable hydrocarbons from coal.
This patent application is currently assigned to C20 Technologies, LLC. The applicant listed for this patent is C20 TECHNOLOGIES, LLC. Invention is credited to Franklin G. Rinker.
Application Number | 20130233692 13/868473 |
Document ID | / |
Family ID | 43450153 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130233692 |
Kind Code |
A1 |
Rinker; Franklin G. |
September 12, 2013 |
Process For Improving Recovery of Condensable Hydrocarbons From
Coal
Abstract
A process for treating coal includes introducing coal into a
chamber and passing an oxygen deficient sweep gas into contact with
the coal, the sweep gas being at a higher temperature than the
temperature of the coal so that heat is supplied to the coal. The
process further includes providing additional heat to the coal
indirectly by heating the chamber, wherein the heating of the coal
by the sweep gas and by the indirect heating from the chamber
causes condensable volatile components to be released into the
sweep gas. The proportion of heat supplied to the coal by the sweep
gas is less than 40% of the total heat supplied to the coal. The
sweep gas is then removed from the chamber and treated to remove
condensable components of the coal.
Inventors: |
Rinker; Franklin G.; (Marco
Island, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
C20 TECHNOLOGIES, LLC |
Marco Island |
FL |
US |
|
|
Assignee: |
C20 Technologies, LLC
Marco Island
FL
|
Family ID: |
43450153 |
Appl. No.: |
13/868473 |
Filed: |
April 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12556935 |
Sep 10, 2009 |
8470134 |
|
|
13868473 |
|
|
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|
61225406 |
Jul 14, 2009 |
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Current U.S.
Class: |
201/4 ; 201/30;
201/37 |
Current CPC
Class: |
C10B 53/04 20130101;
C10B 51/00 20130101; C10L 9/08 20130101 |
Class at
Publication: |
201/4 ; 201/37;
201/30 |
International
Class: |
C10B 51/00 20060101
C10B051/00 |
Claims
1-16. (canceled)
17. A process for improving the recovery of condensable hydrocarbon
components from coal, the process comprising: heating coal in a
chamber by (a) direct heat provided by an oxygen-deficient sweep
gas flowed through the chamber and brought into contact with the
coal, and (b) by indirect heat applied externally to the chamber,
said heating of the coal being sufficient to cause volatile
components of coal to be released into the sweep gas, the volatile
components including condensable hydrocarbons, selecting a ratio of
direct heat and indirect heat applied to the coal to increase the
proportion of condensable hydrocarbons in the sweep gas to 15% or
more; and condensing the condensable hydrocarbons from the sweep
gas to recover them from the coal.
18. The process of claim 17 wherein the proportion of direct heat
supplied to the coal by the sweep gas is less than 40% of the total
heat supplied to the coal.
19. The process of claim 17 wherein the proportion of direct heat
supplied to the coal by the sweep gas is about one-third of the
total heat supplied to the coal.
20. The process of claim 17, wherein coal is continuously supplied
into one supply end of a chamber and removed from another discharge
end of the chamber, and the sweep gas is continuously supplied into
one end of the chamber and removed from another end of the
chamber.
21. The process of claim 20, wherein the coal and the sweep gas are
supplied to the same supply end of the chamber to produce a
co-current flow of sweep gas against coal.
22. The process of claim 21 wherein the temperature differential
between the sweep gas and the coal at the supply end of the chamber
is from about 650 F to about 750 F.
23. The process of claim 21 wherein the temperature differential
between the sweep gas and the coal at the discharge end of the
chamber is from about 100 F to about 200 F.
24. The process of claim 21 wherein the log mean temperature
differential between the sweep gas and the coal from the supply end
to the discharge end is from about 300 F to about 400 F.
25. The process of claim 20, wherein the sweep gas is supplied to
the coal discharge end of the chamber to produce a counter-current
flow of sweep gas against coal.
26. The process of claim 17, wherein the chamber is a rotary retort
and wherein the average gaseous residence time within the retort is
within a range of from about 0.2 second to about one second.
27. The process of claim 17, wherein the chamber is a rotary retort
and wherein the average gaseous residence time within the retort is
up to about 1 second.
28. The process of claim 27, wherein the average gaseous residence
time within the retort is up to about 0.3 seconds.
29. The process of claim 17, wherein the condensable hydrocarbons
comprise about 25% to about 75% of the volatile components of
coal.
30. The process of claim 29, wherein condensing the condensable
hydrocarbons further comprises cooling and separating the
hydrocarbons into desirable fractions by boiling point in a
multi-stage downstream absorption system.
31. The process of claim 18, wherein the less than 40% proportion
of direct heat supplied by the sweep gas enables reduced sweep gas
volume, the process further comprising condensing the condensable
hydrocarbons in a downstream absorption system of reduced size
commensurate with the reduced sweep gas volumes.
32. The process of claim 17, wherein, upon introduction to the
chamber, the sweep gas has a temperature from about 1200 F to about
1800 F.
33. The process of claim 17, wherein the sweep gas has a specific
heat of about 0.39 BTU/lb-F.
34. The process of claim 17, wherein the sweep gas removed from the
chamber includes a concentration of coal fines reduced to about 4.5
wt % or less.
35. The process of claim 31, further comprising passing the sweep
gas stream through a mechanical gas/fines filter to further reduce
the coal fines by up to 95%.
36. The process of claim 17, wherein the sweep gas supplied into
the chamber has an emissivity within a range of from about 0.5 to
0.7.
37. The process of claim 17, wherein the chamber is a rotary retort
and the average velocity of the sweep gas is less than about 900
feet per minute.
38. The process of claim 17, wherein the sweep gas composition
includes carbon dioxide and water, together comprising at least 80%
by weight of the composition, and includes not more than 2% oxygen
by volume.
39. The process of claim 17, wherein the mass ratio of the sweep
gas to the coal supplied to the chamber is less than about
0.50.
40. The process of claim 39, wherein the mass ratio of the sweep
gas to the coal supplied to the chamber is about 0.25 or less.
Description
STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH AND RELATED
APPLICATIONS
[0001] The present invention claims the benefit of U.S. Provisional
Patent Application No. 61/225,406, filed Jul. 14, 2009, the
disclosure of which is incorporated herein by reference in its
entirety. This invention is related to co-pending applications
entitled "Process For Treating Agglomerating Coal By Removing
Volatile Components," and "Process For Treating Bituminous Coal By
Removing Volatile Components," filed concurrently herewith. This
invention was made with no Government support and the Government
has no rights in this invention.
TECHNICAL FIELD
[0002] The present invention relates to the field of coal
processing, and more specifically to a process for treating various
types of coal for the production of coal derived liquids (CDLs) and
other higher value coal derived products for use in various
industries.
BACKGROUND OF THE INVENTION
[0003] Coal in its virgin state is sometimes treated to improve its
usefulness and thermal energy content. The treatment can include
drying the coal and subjecting the coal to a pyrolysis process to
drive off low boiling point organic compounds and heavier organic
compounds. Thermal treatment of coal, including high and medium
volatile bituminous, sub-bituminous and lignite, causes the release
of certain volatile hydrocarbon compounds having value for further
refinement into transportation liquid fuels and other coal derived
chemicals. Subsequently, the volatile components can be removed
from the sweep gases exiting the pyrolysis process.
[0004] Low concentrations of desirable condensable hydrocarbon
compounds evolved in the pyrolysis process is problematic. In
addition, the liquid versus gas separation (absorption) to remove
the low concentration of volatiles is less energy efficient than
that which could be achieved with a higher ratio of condensable
hydrocarbon compounds to sweep gas. It would be advantageous if
coal could be treated in such a manner that would enable the
desirable condensable hydrocarbon liquids to be removed from the
coal at much higher concentrations. A process for the treatment of
coal having a much higher ratio of condensable hydrocarbon
compounds to sweep gas is desirable.
SUMMARY OF THE INVENTION
[0005] In one aspect, there is provided herein a process for
treating coal, comprising:
[0006] introducing coal into a chamber;
[0007] passing an oxygen deficient sweep gas into contact with the
coal, the sweep gas being at a higher temperature than the
temperature of the coal so that heat is supplied to the coal;
[0008] providing additional heat to the coal indirectly by heating
the chamber, wherein the heating of the coal by the sweep gas and
by the indirect heating from the chamber causes condensable
volatile components to be released into the sweep gas, and wherein
the proportion of heat supplied to the coal by the sweep gas is
less than 40% of the total heat supplied to the coal;
[0009] removing the sweep gas from the chamber; and
[0010] treating the sweep gas to remove condensable components of
the coal.
[0011] In certain embodiments, the sweep gas supplied into the
chamber has an emissivity within a range of from about 0.5 to
0.7.
[0012] In certain embodiments, at least 80% of the sweep gas is
comprised of CO.sub.2 and H.sub.2O.
[0013] In certain embodiments, the coal is continuously supplied
into one end of the chamber and removed from another end of the
chamber, the sweep gas is continuously supplied into one end of the
chamber and removed from another end of the chamber, and the mass
ratio of the sweep gas to the coal supplied to the chamber is less
than about 0.50.
[0014] In certain embodiments, the chamber is a rotary retort, and
the sweep gas is continuously supplied into one end of the retort
and removed from another end of the retort, and the average
velocity of the sweep gas is less than about 900 feet per
minute.
[0015] In certain embodiments, the chamber is a rotary retort, and
the sweep gas is continuously supplied into one end of the retort
and removed from another end of the retort, and wherein the average
gaseous residence time within the retort is less than about one
second.
[0016] In certain embodiments, the average gaseous residence time
within the retort is within a range of from about 0.2 second to
about one second.
[0017] In certain embodiments, the coal is continuously supplied
into one end of the chamber and removed from another end of the
chamber, the sweep gas is continuously supplied into one end of the
chamber and removed from another end of the chamber, and the sweep
gas exiting the chamber has a condensable hydrocarbon content of at
least about 15% by weight.
[0018] In certain embodiments, the chamber is a rotary retort,
including an inner shell mounted for rotation within a cylindrical
outer shell, the outer shell including a heat source for supplying
indirect heat to the inner shell, and wherein the coal is
continuously supplied into one end of the retort and removed from
another end of the retort, and the sweep gas is continuously
supplied into one end of the retort and removed from another end of
the retort.
[0019] In certain embodiments, the sweep gas removed from the
chamber includes a reduced concentration of coal fines, which is
further reduced by about 95% after passing through a mechanical
gas/fines filter.
[0020] In certain embodiments, the reduced concentration of coal
fines is about 4.5 wt % or less.
[0021] In certain embodiments, resultant coal char has a mercury
content reduced by about 80%.
[0022] In certain embodiments, resultant coal char has an organic
sulfur content of about 45% less than an organic sulfur content in
feed coal.
[0023] In certain embodiments, the temperature of the coal within
the chamber is raised to a temperature within a range of from about
1200.degree. F. to about 1500.degree. F. for removal of organic
sulfur.
[0024] In another broad aspect, there is provided herein a process
for treating coal, comprising:
[0025] introducing coal into a chamber;
[0026] passing an oxygen deficient sweep gas into contact with the
coal, wherein the sweep gas has an emissivity within a range of
from about 0.5 to 0.7, the sweep gas being at a higher temperature
than the temperature of the coal so that heat is supplied to the
coal;
[0027] providing additional heat to the coal indirectly by heating
the chamber, wherein the heating of the coal by the sweep gas and
by the indirect heating from the chamber causes condensable
volatile components to be released into the sweep gas;
[0028] removing the sweep gas from the chamber; and
[0029] treating the sweep gas to remove condensable components of
the coal.
[0030] In still another broad aspect, there is provided herein a
process for treating coal, comprising:
[0031] introducing coal into a chamber, wherein coal is
continuously supplied into one end of the chamber and removed from
another end of the chamber;
[0032] passing an oxygen deficient sweep gas into contact with the
coal, wherein the sweep gas is continuously supplied into one end
of the chamber and removed from another end of the chamber, the
mass ratio of the sweep gas to the coal supplied to the chamber
being less than about 0.50;
[0033] heating the coal directly with the sweep gas;
[0034] providing additional heat to the coal indirectly by heating
the chamber, wherein the heating of the coal by the sweep gas and
by the indirect heating from the chamber causes condensable
volatile components to be released into the sweep gas;
[0035] removing the sweep gas from the chamber; and
[0036] treating the sweep gas to remove condensable components of
the coal.
[0037] Various advantages of this invention will become apparent to
those skilled in the art from the following detailed description of
the preferred embodiment, when read in light of the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a schematic illustration of a process for treating
coal using indirect gas heating according to the present
invention.
[0039] FIG. 2 is an enlarged, schematic cross-sectional view of a
gas-heated retort used in the process of FIG. 1.
[0040] FIG. 3 is an enlarged, schematic side view in cross-section
of the gas-heated retort of FIG. 2.
[0041] FIG. 4 is schematic illustration of a process for treating
coal using indirect electrical heating.
[0042] FIG. 5 is an enlarged, schematic cross-sectional view of an
electrically heated retort used in the process of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0043] The process of the present invention pertains to treating
coal using an increased partial pressure for the production of coal
derived liquids (CDLs) and other higher value coal derived
products, such as a high calorific value, low volatile residue
(char). Desirable condensable hydrocarbon liquids are removed from
the coal at much higher concentrations than capable with
conventional coal treating processes. In particular, the process
combines the advantages of pyrolytic heating with an attemperated,
high sensible heat oxygen deficient gas stream (sweep gas) coupled
with indirect heating by passing a portion of the required heat
through a rotating metal shell of a rotary pyrolyzer retort as
described below.
[0044] It is to be understood that the process in accordance with
the present invention is particularly suited for various types of
coal, including high and medium volatile bituminous, sub-bituminous
and lignite.
[0045] In consideration of the figures, it is to be understood that
for purposes of clarity certain details of construction are not
provided in view of such details being conventional and well within
the skill of the art once the present invention is disclosed and
described herein.
[0046] Referring now to FIG. 1, a schematic illustration of a
process 10 for treating coal 12 using indirect gas fired heating is
shown. A stream of coal 12 is introduced into a chamber or
pyrolytic rotary retort 14. The chamber can be any vessel suitable
for heating coal by convection gases as well as heating indirectly
by radiation and conduction. The coal 12 may be pre-sized to a
range between 6 mm and 50 mm prior to being charged into the
pyrolytic retort 14, but other sizes can be used. A rotary valve 13
controls the flow of the incoming dried coal stream 12, which is
directed continuously into the rotary retort chamber 14.
[0047] The rotary retort 14 used for the combined direct/indirect
pyrolytic heating process may be selected from a type of heat
transfer device for the indirect thermal processing of bulk solid
materials commonly referred to as a rotary calciner. The rotary
calciner consists principally of an alloy rotary shell 16, enclosed
in and indirectly heated on its exterior in a stationary furnace.
The process material (i.e., coal) 12 moves through the interior of
the rotary shell 16, where it is heated through a combined
radiative and convective/conductive mode of heat transfer through
the rotary shell wall 18. Operating temperatures of up to
2200.degree. F. can be achieved. Rotary calciners can be small
pilot-scale units, or full-scale productions units as large as 10
feet in diameter with a heated length of up to 100 feet. Units can
be heated by a variety of fuels, such as gas (FIGS. 1-3), or by
electric-resistive heating elements (see FIG. 5). Waste heat and/or
external heat sources can also be accommodated for rotary
calciners.
[0048] Materials of construction of the rotary shell 16 are
selected for high-temperature service, corrosion resistance, and
compatibility with process materials. The rotary shell 16 may be
fabricated from a wrought heat and corrosion-resistant alloy steel.
For example, Type 309 alloy is the nominal material for indirectly
heated rotary calciners operating in the 1300.degree. F. metal
temperature range. A variety of features and auxiliary equipment is
available to accommodate many process requirements.
[0049] Rotary calciners are ideal for specialized processing due to
the indirect heating mechanism. As the heat source is physically
separated from the process environment, specific process
atmospheres can be maintained. Processes requiring inert, reducing,
oxidizing, or dehumidified atmospheres, or those with a solids/gas
phase reaction can be accommodated. Depending on the process
requirements, rotary calciners can operate under positive or
negative pressure, and a variety of seal arrangements are
available. Internal appurtenances affixed to the rotary shell
interior 16 can be employed to promote uniform heat transfer and
exposure of the material to a process gas (i.e., sweep gas) 20. The
indirect heating also allows for temperature profiling of the
process, which provides the capability of maintaining the material
temperature at a constant level for specific time periods. Multiple
temperature plateaus can be achieved in a single calciner unit in
this manner. Specifically, indirect heating facilitates
time-temperature profiling along the length of the processing
retort. The material being heated can be exposed to variable
time-temperature conditions so as to alter the thermal process to
achieve optimum results and to attune the time-temperature profile
to deal with variable material conditions such as moisture or
volatile content.
[0050] Indirectly heated rotary calciners are well known to those
knowledgeable with thermal heating of bulk free flowing solids. A
typical rotary retort suitable for heating coal to 1050.degree. F.
is manufactured by The A. J. Sackett & Sons Co. (Baltimore,
Md.) and it is rated for transfer of 6,240,000 BTU/hour having a
surface area of 602.88 ft.sup.2 of indirect rotary calciner surface
and a heat flux in the range of about 10,350 BTU/hr/ft.sup.2.
[0051] For a heating retort having a combination of indirect and
direct heating, when indirect heating is in the range of about two
thirds of the total, the one third balance of heat must be supplied
by a flow of gases (sweep gases 20) passing into contact with the
coal 12. One method of providing sweep gases 20 is to pass a stream
of oxygen deficient gases containing both inert and combustible
components through an indirect heat exchanger (not shown) in which
the temperature of the gas stream may to be heated and/or cooled so
as to provide the optimum temperature and composition. Another
method of providing sweep gases 20 is to admit the oxygen deficient
gas stream containing both inert and combustible components into a
combustion chamber with oxygen or combustion air to release
sensible heat. The gas stream serves a second purpose, other than
partial heat input, serving as a sweep gas to cause the outflow of
gases released in the pyrolytic treatment of the continuously
flowing dried and preheated coal entering the system.
[0052] An advantage of the combined direct/indirect pyrolytic
heating process shown is the co-current flow configuration. The
temperatures of the heated coal residue (char) 32 and the sweep
gases containing the gaseous volatiles having been pyrolytically
released from the solid coal 12 can be brought essentially to
equilibrium at the discharge end 26 of the rotating retort 14. The
heated coal residue (char) 32 can be controllably released at the
discharge end 26 of the retort 14 via a product char outlet rotary
valve 31. In the illustrated embodiment, the temperature
differential between the coal 12 and the sweep gases 20 at the
point of desired pyrolysis process completion is in the range of
from about 100.degree. F. to about 200.degree. F. In one
embodiment, the temperature differential is about 150.degree.
F.
[0053] Although in the embodiment shown in the drawings the flow of
coal 12 and sweep gases 20 is co-current, it is to be understood
that the flow could be counter-current.
[0054] Another advantage of the combined direct/indirect pyrolytic
heating process is the relatively substantial permissible thermal
temperature differential at the charge end 24 of the retort 14.
Differential temperatures between the coal 12 and the sweep gases
20 at the charge end may be in the range of about 650-750.degree.
F., or higher, resulting with an overall retort log mean
differential temperature of about 300-400.degree. F.
[0055] A further advantage of the combined direct/indirect
pyrolytic heating process is found in the fact that the
concentration of condensable volatiles is increased when compared
to a direct heating process employing attemperated high sensible
heat oxygen deficient gas for 100% of the heating. For a
conventional 100% direct gas heated system, processing a
non-caking, non-coking coal, the condensable hydrocarbon
concentration is typically about 6.2% of the gaseous stream 30
exiting from the pyrolyzer 14. On the other hand, with 100%
indirect heating, the condensable component is about 44.2% of the
total gas, including water of pyrolysis released when pyrolytically
processed at 950.degree. F. For a combined indirect/direct heated
system with 50% direct gas and 50% indirect heating, the
condensable hydrocarbon component is expected to be in the range of
about 18% of the gas stream 30 leaving the retort 14.
[0056] A still further advantage of the combined direct/indirect
pyrolytic heating process is the minimization of coal char fines
carryover of the off gas stream 30 from the retort 14. Based on
actual pilot scale tests, the off gas stream 30 from the retort 14
carried 1.4 lbs/hr of material otherwise unaccounted for, i.e.,
coal char fines 36. The input dry coal 12 feed rate is 32.2 lbs/hr
entering the pilot scale rotary retort pyrolyzer 14. The coal char
fines 36 concentration in the exhaust gas stream 30 is about 4.3 wt
%. The concentration of coal char fines 36 will be further reduced
in a mechanical gas/fines filter 34, typically by 95%, resulting
with a concentration of 0.22 wt % in the cleansed gas stream
38.
[0057] Optional internal lifting flights 22 (FIGS. 2 and 5)
attached to the inner wall 18 of the pyrolytic retort 14 may be
used to improve the mixing of coal particles 12 in transition from
the initial temperature to the final desired temperature, and to
improve the efficiency of gas-solid contact. As the retort 14
rotates, the internal lifting flights 22 serve to lift the coal
particles 12 from the moving bed and subsequently allow them to
fall as a cascade back to the surface of the axial flowing coal
bed. In some rotary calciner applications, the lifting flights are
arranged so as to promote continuous lifting and falling of the
particles being thermally treated. Although gas-solid contact is
improved, the repeated lifting and falling of the particles
undesirably may result in the production of large amounts of fines
and dust. The dust and fines may become entrained in the sweep gas
stream and be exhausted with the desirable vapors and gases
released in the pyrolytic process. Optionally, the internal flights
22 may be staged so as to provide the desired gas-solid contact
with a minimum formation of coal char fines 36 and dust prior to
the coal char fines being filtered via a mechanical gas/fines
filter 34. With staged internal flights 22, the bed of coal
particles 12 being treated in the retort 14 will experience one or
more cascades according to the number of stages required to achieve
the desired mixing of coal particles 12 without causing undue
particle dimunitization.
[0058] In some embodiments of the rotary pyrolytic retort 14, the
coal bed 12 moves in a rolling mode according to Hencin's
classification. In this mode, the bed of coal particles 12 can be
considered as those rolling on the surface as opposed as to those
that are embedded. Those on the surface roll due to the effect of
gravity. This surface layer is commonly referred to as the "active
layer". These particles 12 receive heat from the sweep gases 20 by
convection. The oxygen deficient sweep gas 20, containing no
greater than about 1% by volume oxygen, is at a higher temperature
than the temperature of the coal 12 so that heat is supplied to the
coal. In other embodiments, it is contemplated that the oxygen
deficient sweep gas 20 contains no greater than about 2% by volume
oxygen. The active layer is enhanced by virtue of staged lifters 22
so as to promote additional internal convective heat transfer from
the sweep gas 20 to the coal particles. Beneath the active layer is
the mass of the coal bed 12, which is in contact with the metal
wall, receiving indirect heat by conduction, as shown in FIGS. 2
and 5.
[0059] As schematically illustrated in FIGS. 2 and 5, the heat
transfer between the sweep gas 20 and the solid coal particles 12
involves radiation, convection, and conduction. Internal heat
enters the process by cooling of a sweep gas stream consisting of
an oxygen deficient high sensible heat gas 20, entering
co-currently at a temperature in the range of about 1200.degree. F.
to about 1800.degree. F. and leaving the retort 14 at a temperature
in the range of about 900.degree. F. to about 1100.degree. F. In
one embodiment, the sweep gas 20 is introduced at a temperature of
about 1500.degree. F. and the sweep gas is discharged at a
temperature of about 1000.degree. F. For a sweep gas stream of
65,000 lbs/hour (0.6% SO.sub.2, 67.3% H.sub.2O, 2.9% N.sub.2 and
29.2% CO.sub.2) having a combined specific heat of 0.39
BTU/lb-.degree. F., the process thermal component received from the
sweep gas will be in the order of about 12,675,000 BTU/hour. It is
preferable to limit the entering temperature to counter the water
gas reaction and coal overheating. For the co-current flow pattern,
with the coal 12 entering at a preheated temperature in the range
of about 550-650.degree. F., the sweep gas 20 is cooled by
radiation and convection rapidly, perhaps in a matter of one to two
seconds, to a mean temperature in the range of about
1200-1300.degree. F. The coal bed 12 provides a significant heat
sink in the order of 30,000,000 BTU/hour when at a temperature in
the range of from about 600.degree. F. to about 1,050.degree. F.
Further, the sweep gas 20 receives heat from the externally heated
rotating metal retort shell 19, as the sweep gas 20 and vapors are
transferred from the entry end 24 of the retort 14 to the discharge
end 26. The heat released by the sweep gas, 12,675,000 BTU/hour,
represents 42.25% of the nominal 30,000,000 BTU/hour required for
pyrolysis of 141,633 lbs/hour of dried and preheated coal.
[0060] In one embodiment, the proportion of heat supplied to the
coal 12 by the sweep gas 20 is less than 40% of the total heat
supplied to the coal 12. In further embodiments, at least 80% of
the sweep gas 20 includes CO.sub.2 and H.sub.2O, and the mass ratio
of sweep gas 20 to the coal 12 supplied into the chamber 14 is less
than about 0.50. In still further embodiments, at least 80% of the
sweep gas 20 includes CO.sub.2 and H.sub.2O, and the mass ratio of
sweep gas 20 to the coal 12 supplied into the chamber 14 is less
than about 0.25.
[0061] A further advantage of the high specific heat sweep gas 20
is the relatively high emissivity in accordance with the process.
Nitrogen (N.sub.2) is a symmetrical molecular gas, which does not
contribute to the radiative component of the gas stream. Nitrogen
(N.sub.2), Oxygen (O.sub.2), Hydrogen (H.sub.2) and dry air have
symmetrical molecules and are practically transparent to thermal
radiation--they neither emit nor absorb appreciable amounts of
radiant energy at temperatures of practical interest, i.e.,
1,000-1,500.degree. F. On the other hand, radiation of heteropolar
gases and vapors such as CO.sub.2, H.sub.2O, SO.sub.2 and
hydrocarbons are of importance in heat transfer applications. In
one embodiment, the intended sweep gas, 65,000 lb/hour of gas
having a constituency of about 0.6% SO.sub.2, 67.3% H.sub.2O, 2.9%
N.sub.2 and 29.2% CO.sub.2, supplied into the chamber has an
emissivity within a range of from about 0.5 to about 0.7, optimally
with an emissivity of about 0.65. When both CO.sub.2 and H.sub.2O
are present in high concentrations, the emissivity can be estimated
by adding the emissivities of the two components. The primary
components of the composite emissivity with a beam length of 9.0
feet are about 0.45 from water vapor and about 0.20 from the carbon
dioxide, with an internal retort pressure within a range of from
about 0.85 to 1.3 atmospheres or, alternatively, a range of from
about 1.05 to 1.20 atmospheres, and optimally at about 1.15
atmosphere. The optimal internal retort pressure enhances the
downstream oil recovery process as the downstream oil collection
apparatus (absorption apparatus 40) can be smaller in
cross-section, i.e., absorption apparatus can be a lesser diameter,
which contributes to a more effective absorption and a lower cost.
The low N.sub.2 component results from using oxygen for
combustion/preparation of the sweep gas.
[0062] The heating of the coal 12 by the sweep gas 20 and by the
indirect heating from the chamber 14 causes condensable volatile
components to be released from the coal into the sweep gas. In one
embodiment, the temperature of the coal 12 within the chamber 14 is
raised to a temperature within a range of from about 1200.degree.
F. to about 1500.degree. F. in order to improve removal (e.g.,
volatilization) of organic sulfur.
[0063] Seals 28 can be provided to restrain gas and dust flow at
the charge 24 and discharge end 26 of the pyrolytic retort 14. The
seals 28 are typically mechanical in nature with a riding/wear
component, typically graphite or the like. The seal components 28
are restrained with springs so as to maintain the seal between the
static end housings and the rotating cylindrical metal shell 16.
Other types of seals can be used.
[0064] For a typical pyrolytic coal heating process, the heat
required to cause a continuously entering stream of 140,000
lbs/hour of coal previously dried and preheated in the range of
about 550-650.degree. F. to be pyrolyzed has been determined by
heat balance and computation to be about 30,000,000 BTU/hour. The
specific heat requirement is approximately 215 BTU/lb-dried coal
entering at 600.degree. F. For the typical pyrolytic coal heating
process, having an indirect heating effective surface area of
2119.5 ft.sup.2, with a heat flux rate of 10,350 BTU/hr/ft.sup.2,
the heat supplied is therefore about 21,936,825 BTU/hr. The
indirect heating component would be in the order of 21,936,825
BTU/hr divided by the total requirement of 30,000,000 BTU/hr or 73%
of the total. Other rotary calciners examined show heat flux
ratings of from about 4000 BTU/hr/ft.sup.2 to 12,000
BTU/hr/ft.sup.2 with 10,000 BTU/hr/ft.sup.2 being typical for the
present embodiment.
[0065] It should be understood that a very short gaseous residence
time in the retort is desirable to avoid thermal cracking of the
high molecular weight hydrocarbon vapors at temperatures of about
950.degree. F. and higher. For temperatures in the 950.degree. F.
to 1,300.degree. F. range, gaseous residence times of five seconds
or less are desirable to avoid measurable cracking of the desirable
hydrocarbons. Conversely, with gaseous residence times of one to
two seconds, hydrocarbon cracking requires temperatures in the
1,650 to 1,850.degree. F. range. For a 9-foot diameter retort
having a length of 100 feet, the gaseous interior volume is
calculated to be 4,500 cubic feet (30% filled with coal/char). With
a sweep gas flow of 82,000 actual cubic feet per minute, the
residence time is in the range of about 0.3 seconds. In one
embodiment, the average gaseous residence time within the retort 14
is within a range of from about 0.2 second to about one second. In
an alternative embodiment, the average gaseous residence time
within the retort 14 is less than about one second.
[0066] FIG. 2 illustrates an enlarged, schematic cross-sectional
view of a gas-heated retort 14 used in accordance with the
illustrated process. In this embodiment, the rotary shell wall 18
can be fitted with an external heat exchange enhancing device 66
and an internal heat exchange enhancing device 68, which can be
referred to as extended heat exchange surfaces, akin to fins on a
heat exchanger surface. The rotary retort inner shell 16 is mounted
for rotation within a cylindrical outer shell 19. The outer shell
19 includes a heat source (e.g., gas combustion products) for
supplying indirect heat to the inner shell 16. At least one
indirect heating gas inlet 70 is configured within the outer shell
19 for entry of the gas 72. At least one indirect heating gas
outlet 74 is configured within the outer shell 19 for removal of
the gas 72. The partially heat depleted oxygen deficient high
sensible heat gases 17 are vented from the outer shell 19 of the
retort chamber 14 to an upstream coal drying and preheating
apparatus (not shown).
[0067] FIG. 3 illustrates an enlarged, schematic side view of the
gas-heated retort 14 of FIG. 2 described above. In this embodiment,
the sweep gas 20 is continuously supplied into one end of the
chamber 14 at the charge end 24 and removed from another end of the
chamber at the discharge end 26, and the average velocity of the
sweep gas is less than 900 feet per minute. In a further
embodiment, when the proportion of the heat supplied to the coal by
the sweep gas is less than 40% of the total heat supplied to the
coal, the sweep gas exiting the chamber 14 has a condensable
hydrocarbon content of at least 12% by weight.
[0068] Following the removal of the sweep gas 20 from the chamber
14, the sweep gas is appropriately treated to remove condensable
components of the coal 12, including hydrocarbons, water vapor, and
other volatile compounds, in accordance with the process 10
schematically illustrated in FIGS. 1 and 4. The sweep gas 20 is
passed into a mechanical filter 34 to separate solid coal char
fines 36 from the desirable gaseous hydrocarbon compounds. The coal
char fines 36 can be controllably released from the filter 34 via a
fines outlet rotary valve 35. The gas stream 38 is next passed into
a single- or multi-stage quench tower absorber system 40 complete
with single or multiple heat removal stages to separate the
desirable condensable hydrocarbon compounds 42 and other compounds
singularly or in a multiplicity of fractions as may be required to
recover the desirable coal derived liquids. A non-condensed process
derived gaseous fuel 44 then exits from the absorption system 40
and flows into a downstream process derived gaseous fuel compressor
46.
[0069] Optionally, the gaseous fuel 44 can be passed through a
final stage quench tower (not shown) to remove a portion of the
contained water vapor. Some of the non-condensed gaseous coal
derived fuel 50 is optionally ducted to a combustor 52 for
combination with an auxiliary fuel, if necessary, and air and/or
oxygen, to form oxygen deficient products of combustion 58 supplied
to the retort as described below. It is to be understood that the
oxygen deficient products of combustion 58 for indirect heating in
the retort 14 need not be entirely oxygen deficient, but can
contain up to no greater than 2% by volume oxygen.
[0070] Optionally, the oxygen deficient products of sweep gas
stream 20 utilized for pyrolysis of the coal 12 is produced by a
gas combustor 60, which is ignited by process derived gaseous fuel
50 after having passed through the gaseous fuel compressor 46. An
oxygen injection manifold 62 is connected to the gas combustor 60
and directs a fuel and air mixture thereto. An optional water
injection manifold 64 can be used to supply water to the sweep
gases. Prior to combustion, a portion of the process derived
gaseous fuel 50 can optionally be vented through vent 48 and
utilized in an upstream coal drying process. When the indirect
heating source is gas, a portion of the process derived gaseous
fuel 50 not combusted for production of the sweep gases 20 can be
passed through an indirect heating gas combustor 52, and compressed
high sensible heat products of combustion 58 for indirect heating
can be removed therefrom and directed into the retort chamber 14.
An auxiliary fuel, such as natural gas, and an oxidant, such as
air, may be added to the combustor 52 along with water and coal
derived gaseous fuel to form oxygen deficient products of
combustion 58 (up to no greater than 2% by volume oxygen) having an
exit temperature in the range of about 1100.degree. F. to
2100.degree. F. to maintain appropriate high sensible heat process
temperatures. Combustion air 56 can be added to the combustor 52
via a combustion air blower 54.
[0071] It is further contemplated that increased energy efficient
volatilization and desorption cooling process stages can be
realized by using less sweep gas, replacing the convective heat
transfer of the sweep gas wholly or partially with additional
indirect heating of the coal being treated in the pyrolytic retort
14. In one embodiment, the condensable hydrocarbon (C5+) components
represent about 50% (25-75 wt %) of the volatiles evolved in the
pyrolysis process. At this concentration, the condensation
temperatures are more representative of the respective boiling
points and the volatile hydrocarbons can be efficiently cooled,
condensed and separated in a multi-stage downstream absorption
system (shown as a single-stage absorption system 40 in FIGS. 1 and
4) into groupings of specific desirable boiling point fractions
(condensed hydrocarbons shown as element 42 in FIGS. 1 and 4).
[0072] The size of the absorption apparatus 40, including the
necessary heat exchangers, is a function of the volume of sweep gas
30 (gas, water vapor and condensable hydrocarbons) exiting from the
pyrolytic retort 14. The size of the apparatus 40 can be much
smaller for gas systems having condensable hydrocarbon
concentrations of about 20% or greater than the sized required for
gases with lower concentrations. In one embodiment, the size of the
apparatus 40 can be reduced by a factor of 725,000 lbs/hr vs.
220,000 lbs/hr (3.3 times) for a pyrolytic process employing 50%
indirect heating and 50% co-current flow high sensible heat oxygen
deficient gas direct heating.
[0073] FIG. 4 is a schematic illustration of an alternative
embodiment of the process 10 of the present invention in which
electric resistance heating is the indirect heating source of the
outer shell 19 of the rotary retort 14. Typically, electric power
is a more costly form of energy, when compared with common
industrial fuels. On the other hand, use of electric resistance
heating is nearly 100% efficient, as compared to gas fired systems,
which are in the range of about 55 to 60% efficient when exhausted
at 1300-1500.degree. F. Electric resistance heating equipment is
generally less costly than a gas fired heating system of the same
effective heat input. A further advantage of electric resistance
heating is the ease of setting up multiple heat control zones along
the length of the retort and profiling of the heating elements so
as to effectively match input and demand for a rotary retort
embodiment adapted for pyrolysis of various types of dried and
preheated coal. As shown in FIG. 4, the rotary retort 14 can be
subdivided into different indirect electric resistant heat zones
76, 78, 80, 82, 84, such as the five shown in the present
embodiment.
[0074] FIG. 5 is an enlarged, schematic cross-sectional view of an
electrically heated retort 14 used in the process of FIG. 4. In
this embodiment, the rotary shell wall 18 can be fitted with an
external metal extended surface 66 and an internal metal extended
surface 68. The rotary retort inner shell 16 is mounted for
rotation within a cylindrical outer shell 19. A plurality of
electric resistance heating elements 86 are selectively positioned
around an inner wall 21 within the outer shell 19 of the rotary
retort 14.
[0075] The present invention is further defined in the following
Example, in which all parts and percentages are by weight and
degrees are Fahrenheit, unless otherwise stated. It should be
understood that this Example is given by way of illustration only.
From the discussion herein and this Example, one skilled in the art
can ascertain the essential characteristics of this invention, and
without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
EXAMPLE
[0076] In a series of actual pilot scale tests, a low rank coal
(i.e., Powder River Basin coal) is upgraded into the equivalent of
a Pocahontas low volatile coal. The volatile content of the coal
was reduced from 45.39% (feed coal) to 9.71% (pyrolyzed coal). The
volatile content of the feed coal (dry basis) was reduced by 87.2%.
Process conditions necessary to accomplish this were a dried coal
feed rate of 32 lbs/hr, a kiln residence time of 22 minutes, and
kiln retort temperatures averaging about 1150.degree. F.
[0077] The solids mass balance includes 32.2 lbs/hr dried coal fed,
18.6 lbs/hr pyrolyzed coal collected, 10.6 lbs/hr (estimated) of
volatiles exhausted, and 1.6 lbs/hour of water vaporized and
exhausted. This leaves 1.4 lbs/hr of material unaccounted for; as
for drying, this is attributed to dust entrained in the exhaust.
This number is greater than for drying due to the higher lofting
tendency of the dried coal as well as the particle size reduction
induced by a second pass of the coal (drying and pyrolyzing)
through the feed auger. The 32.2 lbs/hr of dried coal fed and 18.6
lbs/hr of coal char recovered results in a yield of 0.58 lbs of
char per pound of dried coal fed. Similar yields could be expected
from other Powder River Basin coals.
[0078] Mercury content (dry basis) of the coal was reduced from
0.081 ppm (feed coal) to 0.012 ppm (pyrolyzed coal). This
represents a mercury reduction of 85%. Further, the Powder River
Basin feed coal contained 9.2% ash (dry basis) versus 4.8% ash (dry
basis) in pyrolyzed coal.
[0079] The total sulfur content of the feed coal (dry basis) was
determined by assay to be 0.41% with the organic sulfur component
being 0.40%. The thermal pyrolytic treatment was adequate for
removal of 47.1% of the organic sulfur in the feed coal.
[0080] While the invention has been described with reference to
various and preferred embodiments, it should be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted for elements thereof without departing from the
essential scope of the invention. In addition, many modifications
may be made to adapt a particular situation or material to the
teachings of the invention without departing from the essential
scope thereof.
[0081] Therefore, it is intended that the invention not be limited
to the particular embodiment disclosed herein contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the claims.
* * * * *