U.S. patent number 3,861,885 [Application Number 05/412,840] was granted by the patent office on 1975-01-21 for carbon black fuel production.
This patent grant is currently assigned to Institute of Gas Technology. Invention is credited to Frank C. Schora.
United States Patent |
3,861,885 |
Schora |
January 21, 1975 |
CARBON BLACK FUEL PRODUCTION
Abstract
The application discloses a method of production of nonpolluting
ash free, sulfur free carbon black solid fuel from a polluting
solid carbonaceous fossil fuel, such as coal or coal char. The coal
is first pretreated to remove a hydrocarbon stream and the
resultant devolatilized coal is gasified to produce carbon monoxide
and hydrogen preferably with substantially no entrained produced
carbon. The carbon monoxide and hydrogen product gases are then
cooled under controlled conditions in a fluidized bed to
precipitate out carbon black in a finely divided state. At least a
portion of the hydrocarbon stream, preferably after sulfur removal
by hydrodesulphurization, is then admixed with the carbon black
product to produce a product useful as a nonpolluting ash free,
sulfur free fuel for coal-fired turbines, as an additive to diesel
fuel, and as a material for pipelining to areas where air pollution
ordinances require a fuel with low sulfur content. The process
disclosed for converting coal or coal char to a solid carbon black
suitable for use as a nonpolluting fuel includes four basic steps:
(a) devolatilization of the coal to produce a hydrocarbon stream;
(b) production of a hot carbon oxide containing gas, rich in carbon
monoxide, by partial combustion of the devolatilized coal with air,
oxygen or an oxygen enriched air, at elevated temperature and
pressure under catalytic conditions; (c) controlled removal of heat
from the gas in a fluidized bed to promote the deposition of
carbon; and (d) admixing at least a portion of the hydrocarbon
stream, preferably after desulphurization, with the carbon
produced. Preferably, the hot gas is enriched by intermediate
clean-up to remove particulate matter and sulfur. All steps are
preferably conducted at high pressures which favor formation of
carbon and carbon dioxide from carbon monoxide. Preferably,
substantially no carbon is formed in the first step, and the carbon
deposition step is not appreciably auto-catalytic with respect to
carbon deposition.
Inventors: |
Schora; Frank C. (Palatine,
IL) |
Assignee: |
Institute of Gas Technology
(Chicago, IL)
|
Family
ID: |
26878437 |
Appl.
No.: |
05/412,840 |
Filed: |
November 5, 1973 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
182805 |
Sep 22, 1971 |
|
|
|
|
795498 |
Jan 31, 1969 |
|
|
|
|
Current U.S.
Class: |
44/574; 44/545;
44/607; 44/627; 48/210; 422/150; 423/453; 423/459 |
Current CPC
Class: |
C10L
9/02 (20130101); C09C 1/56 (20130101); C10L
5/00 (20130101); C10L 1/322 (20130101); F02B
3/06 (20130101); Y02A 50/20 (20180101); C01P
2006/80 (20130101) |
Current International
Class: |
C10L
9/00 (20060101); C09C 1/56 (20060101); C09C
1/44 (20060101); C10L 1/32 (20060101); C10L
9/02 (20060101); C10L 5/00 (20060101); F02B
3/00 (20060101); F02B 3/06 (20060101); C10l
005/00 (); C10l 009/10 (); C09c 001/48 () |
Field of
Search: |
;423/449,459,453,454
;23/259.5 ;48/203,202,197 ;44/1R,1C,1F |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Meros; Edward J.
Attorney, Agent or Firm: Molinare, Allegretti, Newitt &
Witcoff
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of my copending
application Ser. No. 182,805 filed Sept. 22, 1971, now abandoned,
which in turn is a continuation-in-part of my earlier application
Ser. No. 795,498 filed Jan. 31, 1969, and now abandoned.
Claims
What I claim is:
1. A process for the production of a non-polluting substantially
ash free, sulphur free carbon black fuel comprising:
a. devolatilizing a pulverized solid carbon-aceous fossil fuel
containing ash and sulphur to provide a devolatilized fossil fuel
and a hydrocarbon stream;
b. oxidizing the devolatilized pulverized solid carbonaceous fossil
fuel with a gas containing oxygen to form carbon monoxide-rich gas
containing sulphur and ash;
c. removing the sulphur and ash from the carbon monoxide-rich
gas;
d. passing said carbon monoxide-rich gas through a fluidized bed of
solid material in a carbon deposition zone at least partly
catalytic with respect to carbon deposition, said bed being
maintained at a temperature below said carbon monoxide-rich gas
temperature;
e. maintaining said solid bed material at a substantially constant
temperature by contact with heat exchange surfaces to quench said
carbon monoxide-rich gas to said bed temperature and to precipitate
in said bed finely-divided carbon by the conversion of said carbon
monoxide-rich gas while forming an exhaust gas therefrom;
f. maintaining the flow of said carbon monoxide-rich gas and said
exhaust gas to entrain said carbon black therein;
g. desulphurizing the hydrocarbon stream; and
h. admixing at least a portion of the desulphurized hydrocarbon
with said carbon black to produce a nonpolluting substantially ash
free, sulphur free fuel having good ignition and combustion
characteristics.
2. A process as in claim 1 in which said oxygen-containing gas is
air.
3. A process as in claim 1 in which said carbonaceous fossil fuel
is coal 80% reduced in size to minus quarter mesh.
4. A process as in claim 1 in which said oxidation step includes
the steps of:
i. combusting a portion of said carbonaceous fossil fuel with said
oxygen-containing gas to produce a combustion gas rich in CO.sub.2
and H.sub.2 O, and
ii. reacting said CO.sub.2 and H.sub.2 O with the remainder of said
solid fossil fuel to produce said carbon monoxide-rich gas.
5. A process as in claim 4 in which said oxygen-containing gas is
air.
6. A process as in claim 1 which includes maintaining said coal
that is oxidized with said combustion gas in a substantially
fluidized condition.
7. A process as in claim 1 which includes the steps of:
a. reacting residual carbon oxides in said exhaust gases with
hydrogen to form carbon monoxide, and
b. recycling said carbon monoxide to said fluidized bed.
8. A process as in claim 1 wherein said heat exchange surfaces are
disposed in said bed.
9. A process as in claim 1 wherein said solid bed material is a
catalyst capable of promoting carbon formation and promoting a
water gas shift reaction.
10. A process as in claim 1 wherein said solid bed material is in
the form of granules substantially spherical in shape, and range
from about 100 U.S. mesh to one-quarter inch in diameter.
11. A process as in claim 9 wherein said catalyst is selected from
iron, cobalt, and nickel, alloys thereof, and oxides, hydroxides
and carbonates of sodium, cobalt, nickel and alloys thereof.
12. A process as in claim 11 wherein said catalyst is a mixture of
iron and iron oxides.
13. A process as in claim 12 wherein said catalyst is Wustite.
14. A process as in claim 1 wherein the desulphurized hydrocarbon
is admixed with the carbon by passing the liquid to the carbon
deposition zone.
15. A process as in claim 1 where the desulphurized hydrocarbon is
vaporized prior to admixing with the carbon black.
16. A process as in claim 1 wherein the desulphurized hydrocarbon
is admixed with the carbon in the amount of 1 to about 25 wt. % of
the final product.
17. A process as in claim 1 wherein a portion of the hydrocarbon
stream is passed to the oxidation step for conversion to CO.
18. A process as in claim 1 wherein the hydrocarbon stream is also
subjected to cracking.
Description
FIELD OF THE INVENTION
This invention relates to the production of an ash free, sulfur
free carbon black for use as a nonpolluting fuel from solid
carbonaceous fossil fuels, particularly coal or coal char. The coal
is first devolatilized, the devolatilized coal gasified to produce
gaseous carbon oxides, principally carbon monoxide, and hydrogen at
elevated temperature and pressure, the gases are cooled under
controlled conditions to precipitate out carbon black in a finely
divided state and the volatile liquids and/or gases recovered from
the devolatilization step are admixed with the carbon black to
provide a relatively ash free, sulfur free fuel.
"Carbon black" is a term applied to a number of relatively pure,
fine carbon materials that are produced by thermal cracking or
incomplete combustion of natural gas or petroleum products such as
oil. The carbon black is predominantly used for reinforcing rubber,
and as a pigment in ink and paint manufacture. Carbon black has not
yet found large scale utilization as a fuel source.
PRIOR ART METHODS OF CARBON BLACK PRODUCTION
Three methods of producing carbon black are now in use and include
the channel process, the furnace combustion process, and the
furnace thermal process. The processes, however, are designed to
produce relatively low amounts of carbon black for specialty uses
such as in the manufacture of tires. These processes do not
contemplate nor are they suitable for large scale high volume
production of carbon black as a fuel source.
THE CLASSIC CHANNEL PROCESS
In the classic channel process, carbon black is made by impinging
small natural gas flames on a relatively cool metal surface or
"channel." The distance between the burner pipe and the channel is
varied to control the yield. A carbon black deposit is scraped from
the channel, processed to remove unwanted grit, passed into a
cyclone to separate it from heavy foreign particles, collected,
pelletized, and then stored for shipment. The channels and burner
pipe are contained in a so-called "hot house," a standard
construction which contains ten parallel burner pipes and which can
produce 300 to 400 pounds of rubber-grade carbon black per day.
Common practice is to assemble 30 to 110 hot houses into a unit,
with 2 to 12 units constituting a channel plant. A plant burning 30
to 40 MM SCF of natural gas per day will produce about 75,000 lbs.
of channel black per day. Assuming that this gas is all methane,
the calculated conversion efficiency is only 6.75%. Because of the
development of furnace processes with better control and
efficiency, the channel process has been largely abandoned.
Further, there is generally no need to convert natural gas, a good
fuel, to a solid carbon fuel.
FURNACE COMBUSTION PROCESS
The furnace combustion process produces blacks of a larger particle
size than the channel process and is also used mainly to produce
carbon black for the rubber industry. In the furnace combustion
process, a large volume of gas or preferably a mixture of oil and
air undergoes combustion and cracking in firebricklined furnaces.
The resultant carbon black is suspended in the spent reaction gases
and is collected by a combination of electrostatic precipitators
and centrifugal force. Compared to the channel process, the furnace
combustion process provides more precise control of the opening
variables and improves the maximum yield to about 30%. However, as
in the case of the channel process, this process cannot be
realistically used to produce a carbon fuel due to its low yield
and the suitability of the feed material, without substantial
treatment, as a fuel source.
FURNACE THERMAL PROCESS
In the furnace thermal process, carbon black is produced by thermal
decomposition rather than by partial combustion of hydrocarbons.
There are two variations of this process: one uses natural gas, an
intermittent operation, and the other uses acetylene or petroleum
products. Air and gas in proper proportion for complete combustion
are fired into an insulated furnace filled with checker work. When
the checkers have reached a sufficiently high temperature, the
heating is discontinued and gas alone is charged. Thermal
decomposition occurs in the gas phase, and the free carbon is
removed in the gas stream. After a certain degree of cooling, the
cycle is repeated. Reportedly up to 60% of the carbon in petroleum
oil is recoverable as carbon black by this process. Again, despite
higher yields, this process cannot realistically be used to produce
a carbon fuel due to the ready suitability of the hydrocarbon feed
as a fuel.
In all three of the above types of processes the hydrocarbon gas or
oil goes directly to carbon black whether it occurs by a starved
combustion, thermal cracking process such as a sooty flame produced
by partial combustion of oils or gas, or by an incomplete chemical
combustion process that produces carbon directly. Further, as
indicated, none of these processes is designed to produce a carbon
black product for use as a fuel.
An example of the prior art furnace thermal process in the Krejci
U.S. Pat. No. 2,781,247 in which a cylindrical reactor furnace is
heated by tangential fuel and oxidant streams that swirl throughout
the axial length of the furnace, and a hydrocarbon oil is cracked
at the high temperatures of the furnace. Antonsen, U.S. Pat. No.
2,733,744 illustrates a thermal process in which the cracking
occurs in an atmosphere of hot hydrogen inert to the hydrocarbon.
The hydrogen is heated by a conventional pebble-heater heat
exchanger. The Ayers U.S. Pat. No. Re 22,886 appears to be a hybrid
process best classifiable under the furnace combustion type of
process. In Ayers, crude oil under extremely high pressure is
sprayed in atomized form into a cylindrical furnace chamber.
Simultaneously, air under pressure of about 12 lbs. per square inch
is introduced to effect the desired incomplete combustion. The
atomized oil is described to be vaporized and reacted almost
instantaneously to crack and partially burn the hydrocarbons to a
form of elemental carbon. The reactor burners are placed near the
end opposite the high pressure oil jet, and the flame intersects
the spray of oil at right angles. The resulting carbon products
pass through holes in checker works into a collecting chamber. The
cracking temperature of the heavy asphalt base type crude petroleum
is disclosed to be above 2,300.degree.F.
CARBON BLACK PRODUCTION FROM CARBON MONOXIDE
Specialty grade carbon black has been produced by oxidation of
methane of fuel oil to carbon monoxide and then producing carbon
black according to the reaction:
2CO .fwdarw. CO.sub.2 +C
Initially, the process was most commonly practiced in the presence
of a metal catalyst, but the resulting metal particle-contaminated
carbon black was not well suited for many uses, particularly for
rubber reinforcement. Further, the catalysts were not recovered and
recycled thereby adding to the expense of the process. Mayland,
U.S. Pat. No. 2,716,053, describes a process for the production of
carbon black from carbon monoxide in which the catalyst comprises
elemental carbon derived from a tail gas stream. The Mayland
process has been described as "autocatalytic" and takes two forms:
in the first form, methane is oxidized with excess oxygen to
prevent elemental carbon from forming in a combustor at a
temperature between 2,300.degree. and 3,000.degree.F. to produce a
gas containing carbon monoxide. The carbon monoxide stream is then
quenched by a tail gas stream recycled from a later step in the
process. 0.5 to 3 volumes of tail gas are used per volume of carbon
monoxide-containing gas from the combustor. The relatively cold
tail gas stream, containing minor amounts of unseparated carbon
black, quenches the carbon monoxide-containing combustion gas to
between 1,400.degree. and 1,550.degree.F. This is a temperature
below which undesirable side reactions take place, but still in the
range at which carbon monoxide reacts at a high rate to form carbon
black. The quenched gas is then passed to a reaction zone wherein
carbon black is formed from the carbon monoxide. The carbon black
contained in the relatively cold tail gas employed as a quenching
medium acts as a catalyst for the carbon black producing reaction,
hence the term "autocatalytic." The stream containing carbon black
formed in the reaction zone is subsequently further cooled and the
carbon black is recovered. The part of the gas stream remaining
after carbon black recovery and which contains a minor amount of
unseparated carbon black is then used as the catalyst bearing
quench gas for fresh hot gas from the carbon monoxide producing
zone.
In the second alternative process of Mayland, also "autocatalytic,"
the carbon monoxide producing zone is operated with enough oxygen
to prevent too much carbon from forming, but under such conditions
that the hot carbon monoxide containing gas emerging from the
reaction zone will contain a minor amount of elemental carbon which
will act as the catalyst. In the recovery stage, some of the carbon
dioxide recovered may further be reacted with carbon at a
temperature of 1,400.degree. to 2,300.degree.F. to produce a carbon
monoxide which is cycled back to the reaction zone. In this
alternative, 0.05 to 1.0 weight per cent carbon is produced in the
carbon monoxide producing zone to act as a catalyst.
Although the patent broadly indicates that other carbonaceous
materials such as coal, coke, tar, and liquid hydrocarbons, as well
as other normally gaseous hydrocarbons, may be processed utilizing
the inventive concept of quenching the combustion zone effluent
with a relatively cold tail gas containing catalytic amounts of
carbon, the embodiments are restricted to a discussion of methane
and preheated oxygen as the combustion reactants. Mayland discloses
that the pressure in the carbon monoxide producing zone and in the
reaction zone may range from 10 to 40 atmospheres pressure, which
is about 150 to 600 psig. Although air is disclosed as a possible
reactant, it is clear that the use of oxygen or oxygen-enriched air
is important because of the process dependence on recycle gas. This
is because in a recycle process using air, the build-up of nitrogen
would tend to effectively suppress the reactions. Further, Mayland
does not devolatilize coal prior to passage to the oxidation, nor
does Mayland envisage the production of an ash free, sulfur free
solid carbonaceous fuel from coal.
In still another process involving the use of carbon monoxide,
Atkinson U.S. Pat. No. 2,731,328, fuel oil plus oxygen of 90% to
95% purity is reacted at high temperatures in the range of
2,000.degree. to 3,000.degree.F., with a preferred range of
2,000.degree. through 2,500.degree.F., to produce a carbon monoxide
containing gas stream. The effluent gas stream is disclosed to
contain, on a mole basis, about 40% carbon monoxide, 7% carbon
dioxide, 36% hydrogen, and 17% steam. It is disclosed that the
effluent stream containing carbon monoxide is quickly water
quenched to stabilize the gas below 1,200.degree.F., and in any
event below 1,600.degree. to 1,800.degree.F. It is also disclosed
that the water gas shift equilibrium is frozen out, and the
description of the preferred embodiments indicates that the stream
is quenched to between 50.degree. and 200.degree.F. Carbon dioxide
is then removed by monoethanolamine and the resultant gas, at a
temperature of 100.degree. to 150.degree. F. is contacted in a
conversion chamber with gravitationally moving pebbles which have
been cooled with steam to between 300.degree. to 700.degree.F. The
pebbles raise the temperature of the gas sufficiently to permit
formation of carbon black by an exothermic reaction. The effluent
gas and pebbles from that reaction is about 900.degree. through
1,100.degree.F., and in any event below 1,200.degree.F. The gases
are separated from the pebbles and the pebbles are cooled for
recycle to the conversion chamber. It is disclosed that the flow of
reactor effluent gas and pebbles may be either cocurrent or
counter-current, but in both cases the pebbles move by gravitation
in a chamber partly filled with the pebbles. In contrast to
Mayland, the Atkinson process uses the pebbles in the manner of a
catalyst, and the pressure disclosed for the system is from
atmospheric to 15 to 25 psig., although it is stated that 100
through 400 psig may be used. As in Mayland, Atkinson discloses
that low-grade carbonaceous materials, such as pulverized coal,
pitch, petroleum residua, gas oils, fuel oils and the like may be
used, but fails to disclose initial devolatilization of the coal or
the production of an ash free, sulfur free solid carbonaceous
fuel.
THE PRESENT INVENTION
OBJECTS
It is among the objects of this invention to produce from ash and
sulfur containing solid carbonaceous fossilized fuels such as coal,
char, coke and the like, an ash free, sulfur free carbon black
suitable for use as a solid fuel, preferably by a substantially
non-autocatalytic process employing metal-type catalysts.
It is another object of this invention to provide a simple and
highly efficient process for the production of carbon black for use
as a fuel that operates on air alone as the oxidant, and does not
require the use of enriched combustion gases such as oxygen of high
purity or oxygen-enriched air, although it may be used with such
enriched combustion gases.
It is a further object of this invention to provide a process for
the production of carbon black for use as a fuel from coal in which
a carbon monoxide rich gas and the water gas shift reaction are
both utilized.
It is still a further object of this invention to employ fluidized
beds in both a combustor unit and a depositor unit.
Still other objects will be evident from the description below.
SUMMARY OF THE INVENTION
This invention relates to the production of a relatively ash free,
sulfur free carbon black (i.e., less than about 1 weight % ash and
less than about 0.25 weight % sulfur) from carbonaceous fossile
fuels, such as coal, or coal char, which carbon black is suitable
for use as a fuel source in conventional burners. This process
results in:
1. removal of impurities such as ash, sulphur, and iron, and 2.
conversion of the carbon to a very finely divided form suitable for
use as a solid fuel with good ignition and combustion properties.
For example, the carbon black of the present invention is useful as
a nonpolluting fuel for coal-fired turbines, an additive to diesel
fuel, or as a material for pipelining to areas where air pollution
ordinances require a fuel with extremely low sulfur content. This
is important since the specialty grade carbon blacks such as for
tire production which, despite being substantially pure carbon, are
not readily combustible and are not good fuels.
Broadly, the process involves devolatilizing the coal to produce a
hydrocarbon stream, containing normally gaseous and/or liquid
hydrocarbons including tars or oils gasifying the devolatilized
coal to produce carbon monoxide and hydrogen, cooling these gases
under controlled conditions involving a fluidized bed of solid,
catalytic material to precipitate out carbon in a finely divided
state and admixing at least a portion of the hydrocarbon stream
with the carbon. The entire process is substantially
non-autocatalytic, and is preferably carried out under high
pressures on the order of 50 through 100 atmospheres with a range
of from about 60-75 atmospheres being particularly preferred. In
the initial combustion, pulverized devolatilized coal or coal char
is combusted, with or without addition of steam, under pressure
such as a pressure of about 1,000 psig., at an elevated temperature
such as above about 2,200.degree.F., to produce, in a cyclone
combustion zone, combustion gases, CO.sub.2 and H.sub.2 O. The
combustion gases, while in a partial combustion unit, are then
contacted with a suspended or fluidized bed of coal char where the
reactions
C+CO.sub.2 .fwdarw.2CO
C+H.sub.2 O.fwdarw.CO+H.sub.2
take place thereby producing a gas rich in carbon monoxide, and
which, from material balance determinations, is substantially
carbon free.
The gasification step of the process is followed by the removal of
ash and sulphur from the CO rich gas by conventional separation
techniques. This separation is then followed by precipitation of
the carbon black from the carbon monoxide in a carbon deposition
unit, preferably in the pressure of the hydrocarbons to be sorbed
or admixed with the carbon black, operating at elevated pressures
such as between 50 and 100 atmospheres at elevated temperatures,
such as below about 1,275.degree.F., preferably between about
950.degree. and 1,200.degree.F., for example about 1,000.degree.F.,
but at any event above the temperature at which the water gas shift
reaction is frozen out. The carbon deposition unit is preferably a
fluidized bed of solid, catalytic material, such as iron oxide
"pebbles," which is catalytic in nature with respect to the carbon
deposition. The solids are maintained at a temperature lower than
the CO rich gas. All the steps in the method are conducted at high
pressures in order to favor formation of carbon black and carbon
dioxide from carbon monoxide and to promote the sorption of the
hydrocarbons on the carbon black. Alternatively, the carbon black
recovered from the carbon deposition may be admixed with at least a
portion of the hydrocarbons recovered from the devolatilization
step to produce a relatively ash free, sulfur free nonpolluting
fuel that can be used in conventional burners. When this latter
method is used, the liquid is preferably first converted to a vapor
to avoid any caking or occlusion problems.
In the devolatilization step, the coal or coal char, preferably
after pulverization, is treated at elevated temperatures and
preferably at atmospheric pressure to remove at least a portion, if
not all, of the normally gaseous and liquid hydrocarbons including
volatile tars and oils contained in the coal. The amount of
hydrocarbons recovered is a fraction of the coal treated and can be
as low as about 10%, by weight, for certain anthracite coal and as
high as about 40%, by weight for certain bituminous coals.
Preferably, however, only sufficient hydrocarbons are removed in
the devolatilization step so as to impart good ignition and
combustion characteristics when sorbed on the carbon black or mixed
therewith. Typically, the final carbon black fuel, after
hydrocarbon sorption, should contain about 1-25% volatile matter.
Since the carbon produced usually has a surface area of 50-200
M.sup.2 /g, this amount of volatile hydrocarbon is generally the
maximum amount of hydrocarbons that can be absorbed on the carbon,
particularly when the hydrocarbons are sorbed as a vapor at
elevated temperatures as encountered in the carbon deposition
reaction zone. The equilibrium level of volatile hydrocarbons
sorbed on the carbon black even at the elevated temperatures and
pressure of the carbon deposition zone are sufficiently high to
impart good ignition and combustion characterisitcs to the carbon
black. However, additional volatile hydrocarbons may be added to
the carbon black and the carbon black formed into solid briquettes,
etc. The devolatilization step per se can be effected by means well
known to those trained in the art such as by purging a fluidized
bed, moving bed or fixed bed of pulverized coal particles with gas
such as nitrogen or hydrogen. For a high volatile content coal such
as Illinois Bituminous coal suitable devolatilization conditions at
atmospheric conditions include a temperature of about
800.degree.-850.degree.F. and a holding time of about 10-20
minutes. For a lower volatile content anthracite coal suitable
temperatures are usually higher such as about
850.degree.-900.degree.F. or higher may be used. These conditions
are sufficient to remove sufficient amounts of the volatile
hydrocarbon (i.e., hydrocarbons which can be removed from the coal
and which are gases and/or liquids at standard temperature and
pressure including tars and oils and which typically have an End
Boiling Point of up to about 650.degree.-700.degree.F.) to impart
good ignition and combustion characteristics to the carbon black
when added thereto.
In any event, the hydrocarbons removed from the devolatilization
step usually contain about the same weight % sulfur as the initial
raw coal and should be desulphurized, preferably by
hydrodesulfurization, to provide a desulfurized product containing
less than 0.5% by weight sulfur, preferably less than 0.1% by
weight sulfur to insure that the final carbon black fuel, after
addition of the volatile matter removed from the coal is relatively
sulfur free.
The hydrodesulfurization of the hydrocarbon, recovered with or
without prior removal of the normally gaseous hydrocarbons which
may be present is effected by means well known to those trained in
the art by contacting the hydrocarbon and hydrogen at
hydrodesulfurization conditions with a non acidic catalyst support
such as alumina containing metallic components having hydrogenation
activity such as a metal selected from Group VIB and/or VIII of the
Periodic Table of Elements. It is also within the scope of the
present invention to crack, preferably by hydrocracking, the
normally liquid hydrocarbons to lighter hydrocarbons either
simultaneously with the desulfurization reaction or in a separate
subsequent reaction. The use of cracking is preferred when the
hydrocarbons recovered from the devolatilization step contains
relatively small amounts of light hydrocarbons (C.sub.6 .sup.-).
The presence of light hydrocarbons in the final fuel is preferred
since it enhances the ignition characteristics of the fuel. The
hydrocracking reaction is also known to the art and usually
includes higher reaction temperature than used for desulfurization
alone and the use of an acidic support instead of a non acidic
support. As indicated, the specific conditions used to desulfurize
or crack the liquid recovered from the coal devolatilization step
are all well known and need not be described in great detail. For
example, reference is made to the patents classified in U.S. Pat.
Office Class 208, subclasses 57, 58 and 59, such as U.S. Pat. Nos.
3,718,575, 3,544,448, 3,364,131 and 3,254,018, the teachings of
which are incorporated by reference herein.
In the combustion step the devolatilized coal or coal char, with or
without the addition of steam, is burned in a partial combustion
unit with an amount of air just slightly deficient for converting
all the carbon and hydrogen of the coal to carbon dioxide and
water. The hot combustion gases are then brought into contact with
a suspended or fluidized bed of pulverized coal, or preferably coal
char, where the carbon dioxide and water react with the carbon of
the coal or coal char to form a gas containing carbon monoxide and
hydrogen, but which is substantially free of produced carbon.
Although the temperature of the combustion gases is preferably
between 2,300.degree. and 3,000.degree.F., the reactions with
pulverized coal or coal char to form carbon monoxide are
endothermic, and absorb heat from the combustion gases so that the
temperature of the gases exiting from the partial combustion unit
is about 2,240.degree.F. After suitable purification, for ash and
sulfur removal, the gases enter the carbon deposition section of
the process. Because of the high temperature in the partial
combustion unit, ash produced in the initial steps can be removed
as molten slag. It is also advisable to remove any dust, fly ash
and char carried over with the exit gases from the partial
combustion unit to insure that the final carbon black product is
ash free. If rapid enough reaction rates are maintained, it is
possible to run the partial combustion unit in one stage, but the
two stage process involving carbon dioxide and water as an
intermediate before the production of the carbon monoxide is the
preferred process. Preferably, the CO-rich gas from the partial
combustion unit is substantially carbon free and may typically have
less than from 0.1 to 0.5 mole % carbon, excluding blown-over
dust.
The sulfur present in the initial devolatilized coal or char is
converted to H.sub.2 S during the partial combustion or oxidation
and must be removed from the gas stream before the carbon
deposition step to prevent imparting of undesirable properties to
the fuel. Further, hydrogen sulfide can be absorbed on the carbon
black, and its presence in the gases can reduce the rate of
deposition of the carbon in the fluidized bed of the carbon
deposition unit. At the high temperatures used in our process,
calcium oxide effectively removes the hydrogen sulfide from the
gases before they pass through the carbon deposition unit. However,
other methods known to the art can be used for H.sub.2 S removal.
Where the carbon deposition rate is satisfactory and the presence
of minor amounts of hydrogen sulfide on the carbon black is not an
undesirable property, sulfur removal may take place after pressure
reduction and carbon black removal, if desired.
In the carbon deposition step of the process, the gases are
carefully cooled to deposit the carbon. The carbon deposition unit
is basically a gas cooler, but not of conventional design since it
involves the use of a fluidized bed. A fluidized bed is necessary
to insured adequate heat control when large amounts of carbon black
are being produced for fuel purposes. In a preferred embodiment,
the carbon deposition unit contains heat exchange tubes within the
bed, but may also use an external recirculating pebble-cooler. The
solids in the fluidized bed are at least in partly catalytic in
nature and are maintained at a relatively constant
(.+-.20.degree.F.), lower temperature than the gases. The solids
provide sites for carbon deposition. The comminuting and scouring
action of the fluidized bed frees the carbon adhering to the bed
material, walls, and heat exchange surfaces. The effluent from the
bed is then cooled further and the carbon black removed from the
gas stream either before or after pressure letdown. As an
alternative to the use of heat exchange tubes in the bed, an
external solid-cooling system may be employed. Residual carbon
oxides in the bed effluent can be reacted with hydrogen to form
additional CO and recycled to the fluidized carbon deposition bed.
Preferably the desulfurized hydrocarbons recovered from the
desulfurization step and which are to be sorbed on or admixed with
the carbon black, are added directly to the carbon deposition unit.
This enables the liquid hydrocarbons which may be present to
volatilize at the high temperature present in the deposition unit
and to be effectively sorbed on the carbon in situ. This avoids the
need for separate processing steps to sorb the hydrocarbons on the
carbon black fuel.
The chemical reactions involved in the process are:
a. The partial combustion reactions
coal + air .fwdarw. CO.sub.2 +H.sub.2 O+CO+H.sub.2 +N.sub.2
CO.sub.2 +C .fwdarw. 2CO
H.sub.2 O+C .fwdarw. CO+H.sub.2
b. The carbon deposition reactions
2 CO .fwdarw. C+CO.sub.2
CO.sub.2 +H.sub.2 .fwdarw. CO+H.sub.2 O
The latter reaction is the so-called water-gas shift reaction
which, since not frozen out of the reactions, assists in achieving
maximum carbon deposition. Known catalysts capable of promoting
this watergas shift reaction are preferred as a bed material for
the fluidized bed in the carbon deposition reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic process flow sheet of the conversion of
carbon black from coal by the process of the present invention.
FIG. 2 is a diagrammatic flow sheet showing the conversion of one
type of coal to carbon based on 100 lbs. of coal feed per
hours.
FIG. 3 diagrammatically shows the integrated cyclone combustor and
the fluidized-bed reformer of the partial combustion unit of the
present invention.
FIG. 4 is a diagrammatic representation of the carbon deposition
reactor of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the Figures, FIG. 1 shows by way of illustrative
example a specific embodiment of the preferred process. Coal, such
as Ireland mine coal containing 4.2 wt. % sulphur and 27 wt. %
volatile matter, is fed by way of conveyor 1 to feed hopper 2
associated with rod mill 2A where the coal is ground to 80% minus
quarter mesh in a single rod mill. The rod mill product is fed to
coal devolatilization zone 3, wherein 60 wt. % of the volatile
matter is removed from the coal by treatment with a continuous
flowing hydrogen stream 3A for 15 minutes at 850.degree.F. The
resultant hydrocarbon stream contains 1.6% by weight sulphur and is
hydrodesulphurized in the presence of additional hydrogen, if
required, entering via line 70 in desulphurization zone 71, to
provide a liquid stream 74, as recovered from separation zone 72,
which is to be added to the final carbon black in carbon deposition
unit 13 to provide a suitable fuel. Off gases are removed via line
73 from separation zone 72.
The devolatilized coal in turn is passed to hopper 4. Both hoppers
2 and 4 are atmospheric type coal hoppers. The atmospheric coal
hopper 4 feeds a first pressure fed hopper 5. The devolatilized
pulverized coal is pressurized in the feed hopper 5 to an
intermediate pressure and fed into high pressure feed hopper 6.
Alternatively, the pressure feed hoppers 5 and 6 may be separated
by a lock hopper and valving system (not shown). The devolatilized,
pulverized coal is then fed by a feeder associated with pressure
feed hopper 6 to partial combustion unit 8 via line 6a. As
discussed in more detail below with respect to FIGS. 3 and 4, the
partial combustion unit 8 comprises a cyclone-type combustor in
combination with a fluidized bed char reformer. Air compressor 26
supplies ambient air at a pressure of about 1,000 psig. to the
partial combustion unit in which the pulverized coal and excess
desulphurized liquid removed from line 74 via line 75 is converted
by oxidation to carbon monoxide via the intermediate state of
carbon dioxide and water. Excess hydrogen, hydrogen sulphide and
light gases are removed overhead from recovery zone 72 via line 73
for subsequent processing. If desired, excess hydrocarbon liquid
can be passed to partial combustion unit 8 via line 75 for
conversion to carbon black in admixture with the devolatilized
coal. Preferably, however, the excess liquid is used as a liquid
fuel or petrochemical feed source and is removed via line 76. The
resulting combustion gases exit by line 9 at a pressure of about
1,000 psig. at 2,249.degree.F., and enter ash cyclone 10 where the
fly ash is drawn off at 11. The hot combustion gases exit from the
ash cyclone by way of line 12 and are directed to the carbon
deposition unit 13 after H.sub.2 S removal via line 21 in suitable
separation zone 80. The temperature of the gases is carefully
lowered by application of water to line 14 in heat-exchange
relationship with the gases and the catalytic pebbles or granules
in the fluidized bed contained within the carbon deposition unit
13. Steam exits from the heat-exchange coils through line 15 at
1,000 psig., and is directed to the drive 27, entering at line 28
and exiting by way of pipeline 29. The drive operates air
compressor 26 which takes in air at 0 psig., 60.degree.F. at line
30 and puts out high pressure air at 1,000 psig., 60.degree.F.,
through line 31 for supply to the partial combustion unit 8 as
previously described.
The carbon deposition unit contains a fluidized bed of material
which is at least partially catalytic in nature and preferably
catalytic with respect to the water gas shift reaction such as 100
U.S. mesh to one-fourth inch diameter, substantially spherical
pebbles or granules of iron, cobalt, nickel, or mixtures or alloys
thereof, or their oxides, hydroxides or carbonates. The fluidized
bed has a linear velocity of 1 foot per second based on the volume
of the inlet gases at operating conditions, and is maintained at a
relatively constant temperature (.+-.20.degree.F.), which
temperature is lower than the inlet CO-rich gas. The unit is a
refractory-lined pressure vessel. The pressure within the vessel
may be from 50 to 100 atmospheres as in the partial combustion
unit, and is preferably in the range of from about 60 to 75
atmospheres, e.g., about 1,000 psig., and operates within the range
of 950.degree. through 1,200.degree.F., preferably about
1,000.degree.F. to take advantage of the water gas shift reaction.
The carbon monoxide within the carbon deposition unit, at the
controlled prevailing temperatures and pressures therein, is
converted to carbon black entrained in the gases. While I do not
wish to be bound by theory, at these conditions the process in
accordance with this invention does not appear to be autocatalytic
in nature.
The constant upward flow of the input gases through line 12 keeps
the bed in the fluidized condition, and that condition promotes a
constant scrubbing of the walls and heat exchange surfaces within
the carbon deposition unit so that all the carbon black is
entrained in the exhaust gases. The exhaust gases pass out by line
16 at approximately 1,000 psig., and 1,000.degree.F., to the carbon
cyclone 17. The carbon black product is taken off through line 18.
The ash and carbon cyclones are both refractory-lined pressure
vessels having a maximum outside wall temperature of about
650.degree.F. and operate at about a linear inlet velocity of 50
feet per second. The by-product gases exiting from the carbon
cyclone 17 pass by line 19 through the expansion turbine 20 and
electrical generator 21 for pressure letdown. The expansion turbine
reduces the pressure of the exhaust gas to approximately 1 psig.
and the associated electrical generator is used to recover the work
done by this expansion. The excess electrical energy may be used to
power the coal conveyor 1, hopper 2, rod mill 2A, or the hoppers 4
through 6. The low pressure exhaust gas has a temperature of about
500.degree.F. and 1 psig., and passes through line 22 to the bag
house 23. Any remaining entrained carbon black is taken off through
line 23a, and the exhaust gas at about 500.degree.F., 0 psig. and
having a heating value of 16.4 BTU/SCF passes by line 24 to flare
25. Alternatively, the residual CO.sub.2 content of the exhaust gas
can be reacted with hydrogen to form carbon monoxide which can be
recycled back to fluidized bed unit 13.
It should be appreciated that in the present process, since the
exhaust gas is merely a waste gas, there is no build-up of nitrogen
by recycling the exhaust gas as a tail gas to other portions of the
process. If it is so desired, the carbon dioxide content of the
gas, about 13%, may be removed and recycled to the fluidized bed
reformer portion of the partial combustion unit 8. In that event,
some provision for removal of the nitrogen build-up must be made,
since such build-up will suppress the process both in the partial
combustion unit and the carbon deposition unit. It has not proven
worthwhile, from the point of view of increasing the efficiency of
the process appreciably, to retain the small percentage of carbon
dioxide in the exhaust gas due to the associated problems of
nitrogen build-up. The nitrogen build-up is due entirely to the use
of air as a source of coal oxidant. If the benefits of using the
cheap oxidant source, air, is not desired, oxygen or
oxygen-enriched air may be used as the oxidant source. In that
event, the build-up of nitrogen may be avoided and carbon dioxide,
after removal by absorption by contact with an aqueous
alkanolamine, as for example, monoethanolamine, may be utilized by
recycle to the fluidized bed char reformer portion of the partial
combustion unit.
As indicated, a standard H.sub.2 S removal unit 80 such as a unit
containing calcium oxide is interposed in line 12 to remove the
sulphur originally present in the coal and substantially now
converted to H.sub.2 S.
With reference to FIG. 2, devolatilized Ireland mine coal having a
heating value of about 13249 BTU/lb. is fed at the rate of 100 lbs.
per hour at 60.degree.F. to partial combustion unit 8. This coal
has been previously devolatilized to remove 16 wt. % of the coal as
hydrocarbon fraction boiling up to about 700.degree.F. and the
hydrocarbons subsequently hydrodesulphurized to provide a product
containing about 0.1% by weight sulphur. Air from the compressor is
fed in at 60.degree.F. through line 31 at the rate of 4922 SCF/hr.
Ash, partly in the form of slag, and partly in the form of free ash
from the ash cyclone, is shown schematically to be removed from
line 11a at the rate of 13.6 lbs./hr. at a temperature of about
2,240.degree.F. The chemical analysis of the input Ireland mine
coal prior to devolatilization is 68.9% carbon, 4.9% hydrogen, 1.3%
nitrogen, 7.1% oxygen, 4.2% sulfur and 13.6% as ash. Air is assumed
to contain about 78% nitrogen. The output combustion gases exit via
line 9 to the carbon deposition unit 13, and contain about 30.6
mole % carbon monoxide, 0.38% carbon dioxide, 12.3% hydrogen, 0.40%
water, 0.71% hydrogen sulfide, and 55.85% nitrogen. There is no
measurable carbon, other than dust blow-over, in the partial
combustion unit product gas under these conditions.
The carbon black product, recovered from the carbon cyclone and bag
house, is schematically shown as removed by way of line 18a at the
rate of 45.1 lb./hr. The carbon black is a relatively pure carbon
black in a very finely divided form which, when admixed with the
hydrodesulphurized hydrocarbon yields a non-polluting carbon black
fuel containing about 15 wt. % volatile material with good ignition
and combustion characteristics and is substantially ash and sulphur
free. The excess hydrocarbons not deposited on the hydrocarbons can
be used as a liquid fuel source or a petrochemical source. This
form of carbon fuel produced by the process disclosed is useful as
a nonpolluting fuel for coal-fired turbines, as an additive to
diesel fuel, and as a material for coal pipelining to areas where
air pollution ordinances require a fuel with low sulphur content.
The carbon black product is particulate and 95% less than 5.mu. in
size. Based on the recovery rate, the calculated conversion
efficiency of the present process is about 65%. This compares
favorably with the 7% maximum recovery of carbon black from the
channel process and 30% maximum yield in the furnace combustion
process. About 433,500 BTU/hr. is recovered at 1,000.degree.F. in
the form of steam by way of line 15, and may be used to drive the
air compressor as above disclosed. The exhaust gas exits at the
rate of about 5580 SCF/hr. from the carbon deposition unit through
line 19 and contains the following mole percentage of components:
0.53% carbon monoxide, 12.92% carbon dioxide, 2.08% hydrogen,
13.52% water, 0.89% hydrogen sulfide, and 70.06% nitrogen. Since
that exhaust gas has a heating value of only about 16.4 BTU/SCF, it
may be directed to a flare and burned off. Because of the small
size and the low density of the carbon black, the resultant fuel
can be admixed with pipeline gas or other gaseous carrier for
transmission. For example, natural gas flow rates of as little as
0.1 ft./sec. are sufficient to entrain and transport without
settling the carbon black fuel. Alternatively, this carbon black
can be compressed into briquettes.
Referring now to FIG. 3, the coal feed system is shown as in FIG. 1
by feed hopper 4 and pressure feed hoppers 5 and 6. The output
devolatilized pulverized coal is fed from pressure feed hopper 6 to
both a reformer coal feeder 36 and to the combustor coal feeder 46.
Filtered air is fed by air compressor 26 through lines 6a and 31.
Line 31 takes direct feed air to the cyclone combustor 38a, and
line 6a feeds air to entrain the devolatilized coal fed from the
combustor coal feeder 46 through line 47. Coal is entrained and
passed into the cyclone combustor 38a by way of line 32. As above
directed, the cyclone combustor operates under a pressure of
between 50 and 100 atmospheres at a temperature between about
2,300.degree. and 3,000.degree.F. with an amount of air just
slightly deficient for converting all the carbon and hydrogen of
the coal to carbon dioxide and water, with less than 1. to 0.5%
carbon. At those temperatures and pressures, some of the ash may be
removed by slag removal system 40 through 42. The ash passes first
through slag quench tank 40 and then to a slag lock hopper 41 and
out the line 42 as waste ash. The hot combustion gases flow
upwardly from the cyclone combustor 38a to fluidize the coal or
coke 39 in the fluidized-bed reformer 38b. There, the carbon
dioxide and water produced in the cyclone combustor reacts with the
carbon of the coal or coke 39 to form carbon monoxide-rich gases
which pass out line 9. Heavier ash and char fines may be caught in
cyclone 48 and recycled through line 49 to the cyclone combustor.
Using the spent char from the fluidized bed reactor or reformer
38b, as feed for the cyclone combustor, minimizes the amount of fly
ash in the gas stream 9a. The fluidized bed reformer or reactor
portion 38b of the partial combustion unit is a fluidized bed
having a linear velocity of about 1 foot per second based on the
volume of the inlet gases from the cyclone combustor 38a at
operating conditions. The unit is a refractory-lined pressure
vessel having an outside maximum wall temperature of about
650.degree.F. As discussed above with reference to FIG. 1, the
carbon monoxide-rich gases pass from line 9a through the ash
cyclone 10 and then to the carbon deposition unit with intermediate
H.sub.2 S removal via line 8 from H.sub.2 S removal zone 80. It
should also be appreciated that the partial combustion unit may be
built as a single unit, in which the combustor is the lower portion
of a single unit, and the ash cyclone may be an internal cyclone
contained in the upper end of the reformer portion of the partial
combustion unit. High pressure steam may be let in at line 45 to
prevent slag-char accumulation at the throat between the combustor
and reformer. The film of steam or water in this critical area, by
transpiration cooling, prevents the slag-char accumulation at the
throat. Further, a slag quench system 40 through 42 is included to
provide for the slag forming that results from some weeping of char
through the gas-entry orifice at the base of the fluidized bed.
FIG. 4 shows a schematic view of the carbon deposition reactor, in
which the carbon monoxide-rich hot combustion gases are fed through
line 12 into the bottom of the fluidized bed of the carbon
deposition unit 13. The linear velocity of 1 foot per second based
on the inlet gas at operating conditions is typical. Line 14 admits
water for cooling into the fluidized bed and an excess of about
33,000 lb./hr. of steam at 1,000 psig. exit line 15 for use, inter
alia, as power for the air compressor drive 27 (FIG. 1). The
fluidized bed is composed of a flowable solid, generally small
granules, which denotes any solid refractory material of flowable
form and size that can be utilized as a surface on which the carbon
black may be deposited, and which, at least in part is catalytic
with respect to the carbon deposition reaction. The granules are
substantially spherical and about 100 U.S. mesh to one-fourth inch
in diameter, and must withstand the temperature at least as high as
the temperature in the carbon deposition unit, on the order of
950.degree. through 1,200.degree.F. One particularly useful bed is
a mixture of "inert" refractory material, with from 25-100% of a
catalytic metal, or metal oxide hydroxide, or carbonate such as
iron oxide, cobalt oxide, nickel oxide, siderite, Wustite or
mixtures or alloys thereof. For the inert refractory materials,
sand metal alloys, ceramics, alumina, periclase, thoria, beryllia,
and mullite may be used in the form of granules. Of course, the
catalytic material may be used alone. Desulphurized hydrocarbons to
be sorbed on the carbon formed enters via line 101 and is sorbed on
the carbon black as it is being formed.
The gases exiting line 16 from the carbon deposition unit 13 carry
the entrained carbon black that has been scrubbed from the surfaces
of the granules by the fluidized bed's action to the cyclone where
the carbon black product is separated at line 18. The exhaust
gases, after pressure drop in the expansion turbine 20, is then fed
through line 22 to a pressure bag filter 23 and additional carbon
black is taken off at line 23a. The remaining exhaust gas passes
through back pressure regulator 50 through line 24 to the burn-off
flare 25.
To investigate the nature of the reaction 2CO .fwdarw. C+CO.sub.2
in the fluidized bed of the process of this invention, a series of
four test runs were made on a pilot plant scale reactor using a 2
inch diameter tube to retain the carbon deposition bed. In the
first two runs, a sand bed having from 1.3 to 2.7% finely divided
carbon intimately mixed therein was run at the conditions listed in
Table 1, to see if under the conditions of this process, the
deposition was promoted by carbon itself, i.e., was
"autocatalytic." In Runs 3 and 4, a catalytically active bed of
iron compount, as described above was used. Specifically, a native
iron carbonate FeCO.sub.3 (Algoma siderite) also known under the
names clay iron stone, Chalybite, or spathic iron ore, was used. At
the run conditions the siderite decomposes to Wustite, a mixed
iron-iron oxide composition of Fe, Fe.sub.3 O.sub.4 and FeO.
The four runs employed a typical range of temperatures, reactor
pressures, and inlet gas flow rates to insure that the results were
not specifically one-condition dependent. The results are shown
below in Table 1.
TABLE I ______________________________________ TEST RUN: 1 2 3 4
______________________________________ Composition of Fluidized Bed
Sand, wt. % 97.3 98.7 -- -- Carbon, wt. % 2.7 1.3 -- -- Iron
Catalyst, wt. % -- -- 100 100 Bed Temperature, .degree.F. 1320 1190
1330 1060 Reactor Pressure, Psig. 994 1024 1005 1000 Gas Flow Rate,
SCFH 250 965 45 755 Feed Gas Composition, Mole % N.sub.2 73.4 58.5
58.3 58.1 CO 26.1 34.8 30.0 30.6 CO.sub.2 0.5 0.92 0.1 0.1 H.sub.2
-- 4.6 11.3 10.9 A -- 0.12 0.3 0.3 CH.sub.4 -- 1.1 -- -- Product
Gas Composition, Mole % N.sub.2 73.0 65.7 66.6 66.3 CO 26.2 34.2
17.1 16.7 CO.sub.2 0.6 0.11 6.9 8.8 H.sub.2 -- -- 8.6 5.8 A 0.02
0.03 0.3 0.3 CH.sub.4 -- -- 0.5 2.0 C.sub.2 H.sub.6 -- -- -- 0.1
Carbon Deposited, % of CO in Feed (Calculated as carbon
disappearance). Nil Nil 28.6 21.2
______________________________________
The lack of production of carbon deposited from the feed CO in Runs
1 and 2 (having finely divided carbon in the bed), as compared to
substantial carbon production in Runs 3 and 4 shows both the
non-carbon-autocatalytic nature of the process of this invention,
and a substantial improvement over the carbon production by prior
art processes.
As will be evident to those skilled in the art, various
modifications can be made or followed, in the light of the
foregoing disclosure and discussion, without departing from the
spirit or scope of the disclosure or from the scope of the
claims.
* * * * *