U.S. patent application number 09/954603 was filed with the patent office on 2003-03-27 for clean production of coke.
Invention is credited to Eatough, Craig N., Eatough, Steven R., Heaton, Jon S..
Application Number | 20030057083 09/954603 |
Document ID | / |
Family ID | 25495675 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030057083 |
Kind Code |
A1 |
Eatough, Craig N. ; et
al. |
March 27, 2003 |
Clean production of coke
Abstract
Closed apparatus and processes by which carbon feedstock, is
composed of a mixture of non-coking coal fines and another
carbonaceous material, such as waste coke fines are disclosed. The
coal and coke fines are mixed together and may be formed into solid
pieces. The mixture alone or as solid pieces is fired through
pyrolyzation into solid pieces of coke, with solid and gaseous
by-products of pyrolyzation being recycled for use within the
coke-producing closed system, thereby reducing or eliminating
release of undesirable substances to the environment. A
char-forming binder may or may not be added to the carbon mixture
prior to pyrolyzation.
Inventors: |
Eatough, Craig N.; (Provo,
UT) ; Heaton, Jon S.; (Provo, UT) ; Eatough,
Steven R.; (Provo, UT) |
Correspondence
Address: |
Foster & Foster, LLC
Mr. Lynn G. Foster
602 E. 300 S.
Salt Lake City
UT
84102
US
|
Family ID: |
25495675 |
Appl. No.: |
09/954603 |
Filed: |
September 17, 2001 |
Current U.S.
Class: |
201/21 |
Current CPC
Class: |
C10B 53/08 20130101;
C10L 5/16 20130101; C10L 5/28 20130101; C10B 57/04 20130101 |
Class at
Publication: |
201/21 |
International
Class: |
C10B 057/04; C10B
053/00 |
Claims
What is claimed and desired to be secured by Letters Patent is:
1. A method of producing coke from at least one lower grade
material on a low pollution or no pollution basis, comprising the
acts of: introducing a mixture of low grade coal fines and another
type of carbonaceous fines as an influent into a pyrolyzer;
pyrolyzing the mixture in the pyrolyzer; discharging coke and
pyrolytic by-products as effluents from the pyrolyzer; separating
the pyrolytic by-products into tar and combustible off gas; using
the separated tar as a binder in the mixture, without discharging
the tar to the environment; using the combustible off gas as a
source of fuel in the pyrolyzer without discharging the off gas to
the environment.
2. A method according to claim 1 wherein the introducing act
comprises obtaining a mixture comprising coal fines and coke
fines.
3. A method according to claim 1 further comprising the act of
crushing low grade coal and/or another type of carbonaceous
material, prior to the introducing act, to obtain the fines.
4. A method according to claim 1 further comprising the act of
forming the mixture into solid objects prior to the introducing
act.
5. A method according to claim 4 wherein the discharging act
comprises discharging the coke as solid objects.
6. A method according to claim 1 wherein the using act comprises
combining the separated tar, a synthetic binder and the mixture of
fines prior to the introducing act.
7. A method according to claim 1 wherein the separated tar is fed
back to the mixture prior to the introducing act.
8. A method according to claim 1 wherein the separating act
comprises cooling the by-products and condensing the tar to
separate the tar from the off gas.
9. A method of producing coke from at least one low grade material
on a low pollution or no pollution basis, comprising the acts of:
introducing a mixture of low grade coal fines and another type of
carbonaceous fines as an influent into a pyrolyzer; pyrolyzing the
mixture in the pyrolyzer; discharging coke and pyrolytic
by-products as effluents from the pyrolyzer; separating the
pyrolytic by-products into tar and combustible off gas; using the
separated tar as a binder in the mixture without discharging the
tar to the environment; using the combustible off gas as a source
of fuel in the pyrolyzer without discharging the off gas to the
environment.
10. A method according to claim 9 wherein the introducing act
comprises obtaining a mixture comprising coke fines and coal
fines.
11. A method according to claim 9 further comprising the act of
crushing coke and/or another type of carbonaceous material, prior
to the introducing act, to obtain the fines.
12. A method according to claim 9 further comprising the act of
forming the mixture into solid objects prior to the introducing
act.
13. A method according to claim 12 wherein the discharging act
comprises discharging the coke from the pyrolyzer as solid
objects.
14. A method according to claim 9 wherein the using act comprises
combining the separated tar, a synthetic binder and the mixture of
fines prior to the introducing act.
15. A method according to claim 9 wherein the separated tar is fed
back to the mixture prior to the introducing act.
16. A method according to claim 9 wherein the separating act
comprises cooling the by-products and condensing the tar to
separate the tar from the off gas.
17. A method of producing coke from low grade coal and waste coke
fines on a low pollution or no pollution basis, comprising the acts
of: introducing a mixture of lower grade coal fines and waste coke
fines as an influent into a pyrolyzer; pyrolyzing the mixture in
the pyrolyzer; discharging segregated coke, on the one hand, and
pyrolytic by-products comprising combustible off gas and tar on the
other hand, as effluents from the pyrolyzer; separating the
pyrolytic by-products into segregated tar and combustible off-gas;
using the segregated tar as a binder in the mixture without
discharging the tar to the environment; using the segregated
combustible off gas as a source of fuel in the pyrolyzer without
discharging the off gas to the environment.
18. A method according to claim 17 further comprising the act of
crushing oversized waste coke and/or oversized low grade coal, to
obtain the fines.
19. A method according to claim 17 further comprising the act of
forming the mixture into solid objects prior to the introducing
act.
20. A method according to claim 19 wherein the discharging act
comprises discharging the coke from the pyrolyzer as solid
objects.
21. A method according to claim 17 wherein the using act comprises
combining the separated tar, a synthetic binder and the mixture of
fines in a mixer.
22. A method according to claim 17 wherein the separated tar is fed
back to the mixture of fines.
23. A method according to claim 17 wherein low grade coal comprises
20-40% by weight of the mixture.
24. A method according to claim 17 wherein petroleum coke comprises
40-70% by weight of the mixture.
25. A method according to claim 17 wherein coke breeze comprises
5-10% by weight of the mixture.
26. A method according to claim 17 wherein the pyrolyzing act
comprises heating the introduced mixture to a temperature within
the range of 800-1100.degree. C. at a rate within the range of
1500-2000.degree. C./hour to lower coke volatility below 2%.
27. A method according to claim 17 wherein the separating act
comprises cooling the by-products to about 300.degree. C. and
condensing the tar to separate the tar from the off gas.
28. A method of producing coke on a low pollution or no pollution
basis comprising the acts of: introducing at least one source of
carbon comprising low grade coal fines as an influent into a
pyrolyzer; pyrolyzing the fines in the pyrolyzer; discharging coke,
and pyrolytic by-product comprising combustible off gas, and tar as
effluents from the pyrolyzer; condensing the tar; using the tar as
a binder for coal fines without discharging the tar to the
environment; using the combustible off gas as a source of fuel in
the pyrolyzer without discharging the off gas to the
environment.
29. A method of producing coke on a low pollution or no pollution
basis comprising the acts of: introducing at least one source of
carbon comprising waste coke fines and/or coal fines as an influent
into a pyrolyzer; pyrolyzing the fines in the pyrolyzer;
discharging coke, and pyrolytic by-products comprising combustible
off gas, and tar as effluents from the pyrolyzer; condensing the
tar to separate the tar and off gas; using the tar as a binder for
the fines without discharging the tar to the environment; using the
combustible off gas as a source of fuel in the pyrolyzer without
discharging the off gas to the environment.
30. A method according to claim 29 wherein all condensed tar is
utilized as binder and all combustible off gas is used to fuel the
pyrolyzer.
31. A method according to claim 29 wherein the condensed tar is the
sole binder source and the combustible off-gas is the sole source
of fuel for the pyrolyzer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to clean production
of coke and more particularly to the use of two types of carbon,
one of which comprises low quality coal fines, such as waste coal
fines, and/or waste coke or char fines which, after mixing, may be
fired without formation into objects or formed into objects and
fired to produce solid pyrolyzed objects or pieces, with
by-products from pyrolyzation being recycled for use within the
coke-producing closed system.
BACKGROUND
[0002] Coke heretofore has conventionally been produced from high
quality sources of carbon, such as high quality coking coals. Prior
processes and apparatus for conventionally producing coke typically
are open or partly open systems, which generate by-products
released to pollute the atmosphere.
BRIEF SUMMARY AND OBJECTS OF THE PRESENT INVENTION
[0003] In brief summary, the present invention overcomes or
substantially alleviates problems associated with prior ways of
conventionally producing coke. The present invention may be
summarized as comprising closed system apparatus and processes by
which carbon feedstock, comprised of a mixture of non-coking coal
and/or another carbonaceous material, such as waste coke fines, are
mixed together and pyrolyzed into coke either as solid pieces or
not. When solid pieces or objects of the mixture are formed, they
are fired through pyrolyzation into solid pieces of coke, with
solid and/or liquid and gaseous by-products of pyrolyzation being
recycled for use within the closed coke-producing system, thereby
eliminating release of undesirable substances to the atmosphere.
Feedback tars, with or without a char-forming binder, is added to
the carbon mixture prior to pyrolyzation.
[0004] With the foregoing in mind, it is a primary object of the
present invention to overcome or substantially alleviate problems
of the past associated with production of coke.
[0005] Another paramount object of the present invention is to
produce a novel form of coke and to do so using novel apparatus and
unique processes.
[0006] A further dominant object is to produce coke from a mixture
comprising low quality or non-coking coal fines, which mixture is
pyrolyzed into high quality coke.
[0007] Another important object is to produce coke from a mixture
comprising waste coke fines, which mixture is pyrolyzed into high
quality coke.
[0008] An additional object of importance is to produce coke so as
to avoid contaminating the environment by recycling or
recirculating solid and/or liquid and gaseous by-products within
the closed coke-producing system.
[0009] These and other objects and features of the present
invention will be apparent from the detailed description taken with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a flow diagram of one process by which low quality
coal and another carbonaceous material, such as waste coke fines,
are transformed into metallurgical and other grades of coke;
and
[0011] FIG. 2 is a flow diagram of another similar process by which
low quality coal and other carbonaceous material is transformed
into metallurgical and other grades of coke.
DETAILED DESCRIPTION
[0012] Waste carbonaceous fines have not heretofore been used in
the commercial production of coke. Coke is a fuel universally used
in the iron and steel industry. Currently, nearly all metallurgical
and foundry coke is produced in conventional coke oven facilities
requiring the use of good quality coking coals. These coals are
becoming scarce, difficult to mine, and, therefore, expensive.
Because of the high costs, decreasing supply of these feedstock
materials, and environmental contamination problems associated with
current coke-making practices, there is a need for alternative
coke-making and coke supplementing technologies. Prior attempts to
use various form coke processes have primarily resulted in
commercial failure and, furthermore, excess by-products of
pyrolysis are generated in such processes, which must be refined
into salable liquid fuels. Elimination of the need to process and
market excess aromatic tars from form coke processes has been a
problem. The present invention addresses these problems and
provides processes by which waste coke fines (including coke breeze
generated from conventional coking processes or petroleum coke)
with coal fines are blended to produce a high quality coke
product.
[0013] These coke processes do not require high quality coking
coals nor are a surplus of pyrolytic products produced. Non-coking
coal fines and coke fines may be blended together in such
proportions that production of pyrolysis by-products is limited to
the amount required for binding and for process heat. Feedback tar
may be combined with additional synthetic or natural binder to
produce prime quality solid coke pieces or objects, such as
briquettes or blocks. The process 1) uses feedstock material more
efficiently than other form coke processes by eliminating discharge
of secondary, low value by-products, and 2) uses undesirable
materials and industrial wastes not heretofore used to produce coke
(i.e., low quality coal and/or coke or char fines) as a feedstock
which represent a current serious environmental problem.
[0014] Energy savings for a steel plant can be exemplified by
assuming a typical coke fines waste rate of 10% of the total coke
production. Energy savings are noted in the increased utilization
of raw materials, including extraction, transportation, and
differences in processing requirements. Based on a steel mill
capacity of about 6,000 tons of hot metal (THM)/day this represents
an energy savings of about 4.5.times.10.sup.11 kJ/year over current
technology.
[0015] Capital costs for the briquetting or solid objects portion
of the process have been estimated based on other similar
briquetting operations at between $20-30 million for a one-half
million ton/year plant. Raw material costs are estimated to be in
the range of $10/ton for waste coal fines and $20/ton for coke
fines. The processing costs for briquetting or formation of solid
objects, which include the price of the additional natural or
synthetic binder, if used, are estimated to be around $18/ton,
depending on the type of binder. Total costs for coke production
from the process are expected to be in the range of $50-60/ton.
Current metallurgical coke prices are in the range of $100-120/ton
and foundry coke is $140-160/ton. For a steel plant producing 6,000
THM/day, at an approximate rate of 500 lbs coke/THM, by
incorporating the proposed process, a net savings of $3.3 to $2.8
million/year is expected.
[0016] The ability to utilize this new coke product, as a partial
coke replacement in the blast furnace, will ultimately be proven by
such an application. The properties of coke produced using the
present invention compare well with other cokes previously or
currently used as blast furnace fuels.
[0017] One concern regarding the use of form coke, made from a
previous process, in a blast furnace is that its reactivity tended
to be higher than standard metallurgical coke produced in slot
ovens. The new coke produced according to the present invention is
expected to be able to replace oven-coke and have reactivities and
strengths as good as or better than standard metallurgical
coke.
[0018] As stated above, coke is a universal fuel used in the iron
and steel industry. Metallurgical coke is commonly required for
operation of iron ore reduction facilities, such as blast furnaces.
Foundry coke is required for scrap melting in cupolas and in
casting operations. Coke is also an important fuel for other
applications, such as the phosphate industry.
[0019] The American steel industry underwent a major restructuring
during the 1980's, resulting in the closing of many steel and
coke-making plants. From 1980 to 1990, approximately 40% of the
United States coke-making capacity was shut down. During this same
time, very few new coke-making facilities were built. Today,
approximately 26 million tons of metallurgical coke and 2 million
tons of foundry coke are produced annually in the United States.
Many of the remaining coking facilities are approaching the end of,
or have been extended beyond, their life expectancies. Nearly 50%
of the current capacity is over 20 years old and 40% is over 30
years old. These older facilities are not only expensive to
maintain and operate but they are difficult to keep in compliance
with environmental regulations.
[0020] Nearly all metallurgical and foundry coke is produced in
conventional coke oven facilities requiring the use of high quality
coking coals. Prime coking coals tend to have a volatile content
between 19-33%. These coals are becoming scarce, difficult to mine,
and, therefore, expensive. In 1995, the average delivered price for
metallurgical coking coals in the U.S. was over $47/ton while steam
coals were about $27/ton.
[0021] Coke ovens have for some time been of serious environmental
concern due to the release of particulate and sulfur gases, as well
as emissions of carcinogenic and mutagenic polycyclic aromatic
hydrocarbons (PAHs) and benzene-toluene-xylenes (BTX).
Consequently, the coke-manufacturing industry is being subjected to
increasingly stringent environmental regulations. Advances in coke
oven design, such as non-recovery ovens and jumbo coking reactors,
show some environmental advantages but still require expensive
coking coals to operate and represent a very large capital
investment. As environmental regulations become more stringent,
existing coking facilities will continue to be closed and capacity
reduced. Furthermore, the high capital cost of building new
cokemaking plants based on current technology and dwindling
supplies of domestic prime coking coals has caused U.S. companies
to look outside the country for coke supplies. The United States
already imports a sizable quantity of coke, some produced from its
own exported metallurgical coals. Because of the high costs,
decreasing supply of feedstock materials, and environmental
problems associated with current coke-making and coke supplementing
technologies.
[0022] An alternative to producing coke from metallurgical coals in
conventional slot ovens, is to use various form coke processes.
Form coke is a term which generally describes carbonized,
briquetted or otherwise formed fuel, made from pyrolyzed coal
chars. In a process known as the FMC process, the coal is crushed
and then charred at temperatures between 600 and 800.degree. C.,
then mixed with a binder, briquetted, and finally carbonized at
900-1000.degree. C. The initial partial devoatilization is designed
to prevent swelling or sticking of the briquettes during the high
temperature treatment. The binders needed for this briquetting are
usually obtained from the combined by-products and tars generated
during the low and high temperature charring and carbonizing steps.
Most form coke processes can utilize non-coking coals for a portion
of the feedstock, combined with expensive coking coals.
[0023] Numerous form coke processes have been unsatisfactorily
experimentally tested. Only a few have reached commercial
production. Exceptions are the above-mentioned FMC Process, which
converts sub-bituminous coal into pillow-shaped coke briquettes for
phosphate production and, also, a process known as the CTC Process,
which was commercially discontinued recently.
[0024] The FMC process requires multiple, staged, fluid-bed heaters
to char and carbonize the coal. The tars are captured and used as a
binder to form the char into briquettes which are calcined in a
shaft furnace. The process incurs high capital costs.
[0025] The now discontinued CTC process used gasification to char
the feed coal. The char was then crushed, hot-briquetted and
finally calcined. By-products had to be refined into salable liquid
fuels in order for the CTC process to be economically feasible. The
CTC process utilized high grade coking coals for a portion of its
feedstock.
[0026] By contrast, the present processes pertain to making
briquettes from waste coke fines rather than coal char. A
supplemental binder system, if used, may include combining a
natural or synthetic binder with a carbonaceous binder such as tar,
including but not limited to feedback tar from within the system.
Extensive development and testing of the waste coke fines
briquettes has been performed. Indications are that waste coke
fines briquettes formed using the present invention, compare
favorably with other successful form cokes, such as those obtained
from the FMC and CTC processes. See TABLE 1, below:
1TABLE 1 Comparison of briquettes from proposed process with other
successful form cokes. Apparent Abrasion Form Coke Type Specific
gravity Resistance CSR CRI FMC.sup.1 0.8 69 47 75 CTC.sup.2 1.2 54
30 15 New Process.sup.3 1.4 80 50-70 15-30 .sup.1Measured from
samples obtained from FMC. .sup.2Data taken from Young and Musich,
1995. .sup.3Typical values measured from briquettes made using the
present invention.
[0027] The economics of the present coke fines process is improved
by: (1) use of feedback tar, resulting in the elimination of the
need to import the tar portion of the binder and/or (2) elimination
of the requirement to process and sell excess low-value tars. In
order to do this, the present invention contemplates blending coke
fines (e.g. coke breeze generated from conventional coking
processes or petroleum coke) with waste non-coking coal fines. The
coke breeze and/or petroleum coke fines and low grade coal fines
are blended with a binder. The blend may be fed directly into the
pyrolyzer or pressed into briquettes or other solid forms and
subsequently cured. The relative mixture of coke fines with coal
fines can be varied depending on the devolatilization products of
the coal to obtain a process with closed material-loops where all
of the products of devolatilization are used within the
process.
[0028] During the pyrolysis operation, the temperature of the
formed feedstock is elevated at a rate approximately within the
range of 1500-2000.degree. C./hr to a maximum temperature within
the range of 800-1100.degree. C. The devolatilization behavior of
the feedstock varies during heat-up, depending on the feedstock
mixture, but gases and tar evolve, leaving a carbon matrix
behind.
[0029] Devolatilization behavior depends on many factors such as
peak temperature, heating rate, particle size and coal type.
General trends are that occluded carbon dioxide and methane are
driven off at about 200.degree. C. Above this temperature, internal
condensation occurs among the macromolecular structures with the
evolution of carbon dioxide and water.
[0030] In the range of 200-500.degree. C., methane begins to evolve
with its higher homologues and olefin. Most of the oxygen in coal
structures is eliminated as water and oxides of carbon. The
decomposition of both nitrogen structures and organic sulfur
species begins in this temperature range.
[0031] The evolution of hydrogen begins at 400-500.degree. C. with
a critical point at about 700.degree. C. characterized by a rapid
evolution of hydrogen and carbon monoxide.
[0032] In the temperature range of 500-700.degree. C., the volume
of gases such as hydrogen, carbon monoxide, methane, and nitrogen
increase with increasing temperature, while most hydrocarbons
decrease.
[0033] Tar formation begins at around 300-400.degree. C., with a
maximum yield occurring at approximately 500-550.degree. C.,
depending on heating rate and particle size. The character and
composition of the tars will vary with temperature. Low-temperature
tar usually consists mainly of olefin, paraffin hydrocarbons, and
cyclic hydroaromatic structures. The aromatic nature of tar
increases with increasing temperature until high-temperature tars
are composed mostly of aromatic hydrocarbons.
[0034] The tars which evolve from the coal fines are captured and
returned to be used as a binder. Fuel rich gases are used to
operate the pyrolysis furnace. The idea of recycling tar to be used
as the binder is not unique, standing alone. Many form coke
processes utilize this step, among many others. However, since
prior form coke processes typically use only raw coal in their
feedstock they lose a significant portion of their initial weight
(30-50%) as tars and gases. While a portion of these products can
be utilized as a binder and for process heat, the quantity produced
using prior processes is generally larger than can be consumed
within the facility and, therefore, must be appropriately disposed
of or sold to enhance the economic attractiveness of the process.
Due to the high cost of processing these by-products and their
aromatic nature, they must often be sold as low quality feedstock
materials to refiners at low prices.
[0035] The present processes take advantage of the fact that coke
is very low in volatile matter (1-2%) and therefore produces nearly
no pyrolytic products. This process comprises blending coke fines
with coal fines in the proper amount to create just enough
pyrolytic products required to perpetuate the process.
[0036] The mixture of coal/coke fines are cleaned and blended with
tar or other fixed-carbon producing binders. The mix may then be
formed into appropriate solid shapes. These shapes are then fed to
a pyrolyzer, where the temperature is raised to 800-1100.degree. C.
to devolatilize the solid objects driving off tars and gases and
leaving a strong, high carbon-content coke. The gases and tars are
cooled to approximately 300.degree. C., condensing the tars,
allowing them to be separated from the fuel-rich gas and collected.
The tars are then recycled to be used within the process as a
binder while the gases are oxidized to provide heat to the
pyrolyzer. Calculations indicate that, with, for example only, a
mix of 55% coke fines, 30% bituminous coal fines and 15% binder,
the amounts of tars and gases generated are appropriate to operate
the process in a closed-loop fashion. Of course these proportions
will vary under control of one skilled in the art, depending on
feedstock properties. At a briquette pyrolysis temperature of
900.degree. C., typical product yields for the various constituents
are shown in TABLE 2, below:
2TABLE 2 Approximate product yields at 900.degree. C. of
constituents in mix (ash free basis) Constituent Fixed Carbon Tars
Gases Coke 100 0 0 Bituminous Coal 52 30 18 Tar Binder 40 40 20
[0037] If these components are blended in the mixture fractions
given above, then the resulting products are 77% fixed carbon (coke
product), 15% tars (used as a binder on a recycle basis), and 8%
gas (used to fuel the pyrolyzer). This gas consists of about 25%
water and carbon dioxide, leaving about 6% of the total feed as a
combustible gas. The heating value of this gas is typical of coke
oven gas (about 21,600 kJ/kg). About 1300 kJ of energy in the form
of fuel rich gas is produced per kilogram of uncoked briquettes.
The amount of energy required to raise the temperature of the
briquettes from ambient to 900.degree. C. is 1100 kJ/kg, assuming a
specific heat of coal of 1.26 kJ/kg.degree. K. Therefore, to
produce the proper amount of tars required within the process, the
attending amount of evolved combustible gas is sufficient to
operate a pyrolysis unit at 84% thermal efficiency. The feedstock
mix can be adjusted according to pyrolysis product requirements.
During the pyrolysis step, the original briquettes typically will
lose only about 20-25% of their weight as opposed to 35-50% in
prior form coke processes. Thus, briquettes or other solid objects
obtained from the present invention have a higher product
yield.
[0038] In summary, among other advantages, the proposed process: 1)
utilizes low-value carbon fines to produce a high-value coke
product; and 2) operates with closed material loops so that the
sale of low-value, secondary products is not required to enhance
its economic viability, a characteristic of prior form coke
processes.
[0039] Nearly all metallurgical and foundry coke is produced in
conventional, by-product recovery, horizontal slot ovens, requiring
high quality coking coals as a raw material. The evolutionary
development of conventional coke ovens is approaching its
technological and economic limits. Because of this, several
alternative coking processes have been attempted. Some of these are
variations of the slot-oven type of systems including the
Jewell-Thompson non-recovery coke oven and the Jumbo coking
reactor. The goal of these types of slot oven technologies is to
improve the efficiency and environmental friendliness in the
production of coke. However, the economics of producing coke using
these new technologies is not an improvement over conventional coke
ovens. Another disadvantage of the new slot oven technologies is
that they still require prime coking coals as a feedstock, which
coking coals are becoming scarce, difficult to mine, and,
therefore, expensive.
[0040] One type of emerging coking technology, different from the
slot oven approach are form coke processes, discussed briefly
above. A wide range of coals have been tested and some of the
processes have produced form coke, the strength and reactivity of
which are in an acceptable range for blast furnace use. However,
strength tends to be at the low end and reactivity at the high end
of that which is generally acceptable. These processes are
performed in closed systems, making them very environmentally
attractive. Their commercialization has been impeded due to
economic considerations and product quality.
[0041] A typical form coking practice requires that the process be
divided into three steps; 1) coal pyrolysis to form a dense char,
2) briquetting of the char with a binder, and 3) curing the
resulting briquettes. Simply binding coal fines together and curing
the resulting briquettes is not acceptable. The resulting
briquettes exhibit considerable mass loss (35-50%), are small,
laden with stress cracks, structurally weak, and likely too
reactive. Excess by-products, such as coal tars, must be collected
and sold to make the process economically feasible. Due to the high
cost of processing these by-products and their aromatic nature they
must often be sold as low quality feedstock materials to refiners
at a low price.
[0042] The processes of the present invention allow the coal
pyrolysis and briquette curing processes to be combined. It does
not require coking coals nor does it necessarily produce a surplus
of pyrolytic products. Coal fines and coke fines are blended
together in such proportions that just the amount of pyrolysis
products are produced needed for perpetuating the binding and
heating phases. The tar portion of the binder may be supplemented
with a synthetic or natural binder, as appropriately determined by
those skilled in the art, which produces a prime quality coke
briquette or block. Since dense, low reactivity discarded or waste
coke fines from conventional coke ovens or petroleum refining
operations are used as a portion of the feedstock, product mass
loss is significantly reduced, resulting in a strong product, where
reactivity is lowered.
[0043] While the present processes more efficiently use feedstock
material than is true of the prior form coke processes, there is
another very significant feature of the present processes. The
feedstock used within this process (i.e. coke fines and coal fines)
are normally discarded and classified as either wastes or
undesirable materials, representing a current environmental
problem. Coke breeze produced at existing coking plants cannot per
se be utilized within the blast furnace and must either be disposed
of, or sold at a relatively low cost. Delayed petroleum coke fines
and fluid-coke are often landfilled. Coal fines are currently
either disposed of in slurry ponds or are landfilled. The
transformation of these waste materials into a high value coke is a
surprising and valuable step forward.
[0044] Tremendous energy resources are normally associated with
coal and coke-intensive industries such as mining, iron and steel
production, metal castings, and other manufacturing processes.
During normal materials handling, significant amounts of fines are
generated which, in the best case, can be sold as a low quality
product, but typically are landfilled. This loss of raw material is
about 5-15% of the total coal or coke production and represents a
significant energy loss. The present processes allow the steel and
mining industries to minimize disposal by utilizing heretofore
unused, potentially valuable wastes, thus reducing material costs,
land-fill charges and other expenses. Energy savings occur as the
consumption of raw materials and the generation of land-filled
waste is reduced. This innovative technology significantly reduces
wastes generated from coking and mining operations and represents a
high end use for petroleum coke fines. Like all effective
process-specific recycles, the amount of raw materials input for a
given output is reduced.
[0045] Energy savings are noted in the increased utilization of raw
materials, including extraction, transportation, and differences in
processing requirements. Energy savings for a steel plant producing
6,000 THM per day can be exemplified by reasonably assuming a
typical coke fines generation rate of 10% of the total coke
production. Use of the briquettes represents a more than 1 to 1
savings in raw materials, since the briquette replaces both the raw
material of appropriate size and the feedstocks that would have
been discarded since they were too fine. To produce the additional
coke required to compensate for the generation of fines that are
too small to use, for the plant size described, requires
approximately 1.1.times.10.sup.12 kJ/year. To convert those fines
into a useable coke product using the proposed process requires
only about 6.5.times.10.sup.11 kJ/year. The resulting energy
savings is about 4.5.times.10.sup.11 kJ/year. Other similar values
could be obtained for the chemical processing, castings, and other
coke consuming industries.
[0046] The capital cost of installing a coke works at an iron
production facility represents a significant portion (about 40%) of
the overall required capital cost. In 1987 the annual investment
costs per ton of coke production was $46-$65. The 1987 maintenance
and repair costs were estimated at about $2.50-$3.25/ton. The
growing emphasis on safeguarding the environment, both the working
environment for the operators and the general environment outside
the works boundary, is escalating the cost of coke ovens. The cost
of the new 2 million ton/year Kaiserstuhl III coke works was about
$800 million, including the cost for coke quenching and the
by-products plant. The rebuilding of a 900,000 ton/year plant at
the Great Lakes Division of National Steel cost in excess of $450
million. It has been argued that the Kaiserstuhl III works
represents the highest development potential of slot-type coke
ovens and that a radical departure from the classical design is
needed to achieve any major reduction in the cost of coke
production.
[0047] The cost associated with form coke plants can vary according
to the process requirements. Capital costs for the 1 million
ton/year FMC plant was estimated at $350 million in 1992. Operating
costs were very sensitive to raw material costs and were most
favorable for western coals priced at $10/ton, where 60% of the
coal weight is lost in the process, as by-products. Total costs
associated with coke production were stated to be about $63/ton
using western coals, $90/ton with Midwestern coals, and $107/ton
with eastern coking coals. The costs for western and Midwestern
coals assume a credit for sale of by-products.
[0048] Detailed capital and operating costs associated with the
present processes remains to be precisely determined. However, some
comparisons with other processes can be made. Capital costs for the
present briquetting operations have been estimated, based on other
similar briquetting operations, at between $20-30 million for a
one-half million ton/year plant. Estimates of operating costs for a
briquetting plant of this size include raw materials costs and
processing costs. Raw materials costs are estimated to be in the
range of $10/ton for waste coal fines and $20/ton for coke fines.
The processing costs for briquetting, which include the price of an
additional natural or synthetic binder, are estimated to be around
$18/ton, depending on the type of binder.
[0049] An FMC formed coke plan, as stated above, uses multiple
fluidized beds for char production and a curing oven and calciner
for coke production. The processing and capital costs associated
with commercial use of the present technology are expected to be
much lower than for prior form coke processes, since the char
production step is eliminated. Total costs for coke production from
the present process are likely to be in the range of $50-60/ton,
without requiring the sale of by-products. Current metallurgical
coke prices are in the range of $100-120/ton and foundry coke is
$140-160/ton.
[0050] For a steel plant producing 6,000 THM/day, at an approximate
rate of 500 lbs coke/THM and at an approximate cost of $100/ton for
coke, the replacement value of the coke normally lost would be
about $5.5 million a year. Reduction in the amount purchased, since
all the coke is initially used or reclaimed and used, represents
another 1% or $0.55 million. With briquette costs expected to be
around $50-60/ton, a net savings of $3.3 to $2.8 million/year is
expected.
[0051] The characteristics of supplemental coke products and cokes
made from alternative coking technologies must fall within the
strict standards necessary for its intended use. The most stringent
requirements for coke are associated with blast furnace use.
Metallurgical coke used in blast furnaces must be (1) a fuel to
provide heat to meet the endothermic requirements of chemical
reactions and melting of the slag and metal, (2) a producer and
regenerator of reducing gases for the reduction of iron oxides, and
(3) an agent to provide permeability for gas flow and support for
furnace burden. Because of the many requirements placed on
metallurgical coke, it must meet stringent standards of strength,
size and composition. As a fuel and producer of reducing gases, the
carbon content should be maximized. As a regenerator of reducing
gas, it should have an adequate reactivity to carbon dioxide and
water vapor. To provide permeability and burden support, it should
be charged in a narrow size range and experience minimal breakdown
as it progresses through the blast furnace.
[0052] Different iron ore reduction reactions occur within the
blast furnace, depending on furnace operation and temperature
region. Indirect reduction occurs at relatively low temperatures
(850-900.degree. C.) in the stack. This exothermic reaction can
occur with carbon monoxide as follows:
3Fe.sub.2O.sub.3(s)+CO.fwdarw.2Fe.sub.3O.sub.4+CO.sub.2 (1)
Fe.sub.3O.sub.4(s)+CO.fwdarw.3(FeO)+CO.sub.2 (2)
[0053] and
FeO(s)+CO.fwdarw.Fe+CO.sub.2 (3)
[0054] The `solution loss` reaction produces carbon monoxide from
carbon dioxide reacting with coke above 900.degree. C. It is highly
endothermic or energy consuming.
C(s)+CO.sub.2.fwdarw.2CO (4)
[0055] At high temperatures in the lower part of the furnace, iron
and carbon monoxide are produced by carbon reacting endothermically
with iron oxide by the direct reduction reaction.
FeO(s)+C(s).fwdarw.Fe+CO (5)
[0056] Decreasing direct reduction in favor of indirect reduction
is advantageous because the latter is exothermic and lowers the
overall heat requirements for the blast furnace. Increasing the CO
or H.sub.2 content of the blast furnace gas increases the rate of
indirect reduction.
[0057] Standard testing procedures for cokes to qualify them for
use in blast furnaces have been developed over the years, as the
science and art of blast furnace operation and the requirements of
coke have become better understood. Prior to 1993, standard coke
tests included proximate analysis to determine chemical make-up,
drop shatter and tumbler tests to determine strength, and specific
gravity and porosity tests to measure structural characteristics.
None of these tests were performed under conditions that the coke
might encounter in the blast furnace, such as a harsh chemical
environment, high pressure, and high temperature. In recent years,
the Japanese steel industry developed a procedure that tests coke
strength and breakdown to CO.sub.2 attack under blast furnace
conditions. In 1993, this test was adopted as an ASTM standard test
for coke as ASTM D 5341-93 entitled Standard Test Method for
Measuring Coke Reactivity Index (CRI) and Coke Strength After
Reaction (CSR).
[0058] The joint CSR/CRI test heats a bed of coke in a nitrogen
atmosphere to 1100.degree. C. in 30 minutes, reacts the coke sample
in a flow of CO.sub.2 for 120 minutes with the bed temperature
constant at 1100.degree. C., cools the sample to 100.degree. C.,
transfers the sample to a tumbler, and tumbles the sample for 600
revolutions in 30 minutes. The sample is then sieved in a 3/8 inch
sieve. The CSR is calculated as the remaining portion in the sieve
compared to the amount removed from the furnace.
[0059] The purpose of the CRI test is to give insight into the
ability of CO.sub.2 to react with the carbon in the coke, a
necessary reaction in the blast furnace but which must be
controlled to prevent carbon from being consumed prematurely. The
CSR test provides information about two different issues; 1) the
strength of the briquettes after reacting with CO.sub.2, and 2) the
amount of dust produced by CO.sub.2 attack and bed agitation. Fine
dust can be detrimental in the blast furnace since it can decrease
the permeability of the bed requiring increased blast pressure to
force the air up through the bed.
[0060] Both the FMC and CTC Processes described above have
demonstrated that they are able to produce form coke capable of
blast furnace use. The FMC process utilizes subbituminous coals and
lignites, and yields small (11/4.times.11/8.times.3/4 in, or
7/8.times.3/4.times.1/2 in) coke briquettes, that have performed
well in experimental blast furnace trials. A comparison of FMC
formed coke and a standard metallurgical coke is shown in TABLE 3
(Berkowitz, 1979) and some data from tests of FMC coke in a US
Steel Corporation experimental blast furnace are summarized in
TABLE 4(Berkowitz, 1979).
3TABLE 3 FMC Formed Coke Properties "Standard" FMC Coke
Metallurgical Coke Relative crushing strength, lb/in.sup.2 3000
400-2000 (ASTM) Apparent density, gm/cm.sup.3 0.8-1.2 0.85-1.3 Bulk
density, lb/ft.sup.3 30-45 20-30 Hardness, moh scale 6+ 6+ Surface
area, m.sup.2/gm 50-200 1-25 Chemical reactivity, %/hr 15-50 1-5
Volatile matter, % <3 1-2
[0061]
4TABLE 4 Experimental Blast-furnace Test Data "Standard" 2 .times.
3/4-in FMC Coke Metallurgical Coke Sinter/coke, lb/lb 2.96 2.82
Coke rate, lb/ton hot metal 1062 1096 Production rate, lb/hr 3601
3384 Slag volume, lb/ton hot metal 604 600 Stack dust, lb/hr 20.2
12.7
[0062] The ability to utilize the present new coke product can be
determined by comparing its properties with cokes that have been
proven to be effective blast furnace fuels. TABLE 5 compares some
of the advantages of coke fines briquettes produced according to
the present invention with other cokes previously or currently used
as blast furnace fuels and also lists what is accepted as a
standard metallurgical coke (Berkowitz, 1979). While the coke
fines/coal fines briquettes may vary somewhat from those produced
with coke fines only, the properties will be similar. Testing of
briquettes made with coal/coke blends show crush strength values of
around 1400 psi.
5TABLE 5 Coke Properties "Standard" Coke fines Metallurgical FMC
Coke Briquettes Coke Relative crushing strength, 600 1400-4000
400-2000 lb/in.sup.2 Apparent density, gm/cm.sup.3 0.8-1.2 1.2-1.5
0.85-1.3 Bulk density, lb/ft.sup.3 30-45 na 20-30 Surface area,
m.sup.2/gm 50-200 na 1-25 Relative CO.sub.2 reactivity (CRI) 60-75
15-30 20-30 Coke Strength (CSR) 40-50 50-75 50-65
[0063] Coals charged to standard coke ovens comprise a blend of
coals with differing properties. Typically 3-5 coals are blended
together in such proportions that the properties of the blend will
produce a high quality coke product. If a weakly coking coal of low
fusibility is used in the blend then the strongly coking coal
component must be more fusible and higher in volatile matter to
compensate. Therefore, even though mildly and weakly coking coals
may be used in a particular blend, the blend would be formulated
such that its properties would reflect the parameters outlined
below in TABLE 6. TABLE 6 lists referenced characteristics for high
quality coking coals or blends (Van Krevelen, 1993.) Coal blends
not meeting these characteristics would produce inferior coke.
[0064] As used in this specification, low quality coking coals are
any coals, individually and collectively, that fall appreciably
outside one or more of the parameters listed in TABLE 6. Although
such coals may be included in a blend for standard coke oven use,
they do not meet the requirements by themselves. Such coal or coals
could be used as the sole source of coal within the new
process.
6TABLE 6 Main parameters to Characterize coals for carbonization
(coking) Parameter group Parameters Indicative values Rank
parameters C-content, daf (%) 86-90 H-content, daf (%) 5.0 to 5.5
R.sub.m (V-reflectance) 1.0 to 1.35 VM-content, daf (%) 24-28 CV
(MJ/kg), mmmf 34-36 Rheological parameters FSI 6.5-8 (on heating)
Dilation behavior eu-plastic (ortho-pl. type) dil. 100 to 125%
Maximum fluidity 900-1100 Parameters for Ash Less than 7
Contaminants S Less than 0.6
[0065] With reference to the drawings, in light of the foregoing
presentation, numerals are used throughout to identify common
parts. FIGS. 1 and 2 are flow diagrams of processes by which fine
or particulate carbonaceous material, normally considered waste, is
transformed into metallurgical and other grades of coke. FIGS. 1
and 2 are identical flow diagrams, except that char-forming binder
is not added to the mix in the mixer 16. Accordingly, with this
exception, the following description of FIG. 1 applies also to FIG.
2.
[0066] Two sources of feedstock are provided, i.e. low grade coal
10 and discarded or waste coke 12. Any suitable carbonaceous
material, such as petroleum coke fines, coke breeze char, or carbon
black, may comprise material 12, while, coal, or waste coal fines
may comprise material 10. If unsatisfactorily large in size, the
materials 10 and 12 can be crushed to a fine particle size.
Material 10 and material 12, if not sufficiently particulate, are,
therefore, crushed by a commercially available crusher 14, to
obtain suitably sized fine particles. Any suitable crusher may be
used provided, however, in most applications, the crusher must be
able to reduce oversized material to about 1/4" or 1/8" and below.
The percentages of the various materials being fed to the crusher
14 depend largely on the type of materials being fed. Typically,
coal, petroleum coke, and in some cases, metallurgical coke breeze
may be fed to the crusher. Coal may account for 20-40% of the mix,
petroleum coke may be 40-70%, and metallurgical coke breeze 5-10%
of the total mix.
[0067] The mixer 16 must be able to adequately combine the carbon
fines and the fedback tars and pitches as well as integrate liquid
synthetic and/or natural binders, if used. The fines comprising
materials 10 and 12, crushed or not crushed as the case may be, are
blended in mixer 16 with feedback tars including pitches, obtained
during the process (FIG. 2) or feedback tars obtained during the
process are mixed with a suitable natural and/or synthetic binder
(FIG. 1). Suitable char-forming binders comprises tars, pitches,
CAT bottoms and thermosetting resins.
[0068] Mixing continues until a desired homogeneous blend of the
influent materials is obtained.
[0069] The effluent from the mixer 16 may be displaced into a solid
object former 18, which may be a briquette machine when solid coke
objects or pieces are desired. The former 18 compresses the mixture
into a desired shape e.g. briquettes, blocks, etc. Formation of
solid objects or pieces, such as briquettes, is optional, since
coke is usable in a variety of forms. The mixture can be discharged
from the mixer 16 straight into the pyrolyzer 20, without formation
into solid objects. Any suitable type of former may be used
depending on the size and shape desired for the final product, as
specified by the end user.
[0070] The solid objects, such as briquettes, from the former 18
are or material from the mixer 16 is introduced into a pyrolyzer
20, where the same is coked and prepared for final use. The
pyrolyzer furnace 20 must be able to heat the feedstock to around
800-1100.degree. C. at a rate of 1500-2000.degree. C./hr and be
able to capture the resulting off-gases and tars. The Pyrolyzer 20
normally lowers the coke volatility below 2%. This typically
requires temperatures of greater than 800.degree. C., usually
within the range of 800-1100.degree. C. Heat-up rate is important
to prevent cracking of final product and should be no greater than
about 1500.degree. C. per hour. Coke, as solid objects or
otherwise, is discharged from the pyrolyzer 20 at site 22.
[0071] During the pyrolyzing process, gases and tars evolve as
by-products in the pyrolyzer 20. As they evolve they exit the
pyrolyzer at site 24 and become the influent to a separator 28 at
site 26. The separator 28 separates the by-product tars from the
gases. The tars are discharged at site 30 and fed back as a binder
into the mixer 16 at site 34, either with or without the addition
of an additional char-forming synthetic and/or natural binder. The
gases are discharged at site 32 and fed back as fuel for the
pyrolyzer 20. The separator 28 must be able to collect the
off-gases and cool, condense and collect the condensed tars.
[0072] The exact make-up of feedstock 10 and 12 and parameters can
be varied to control the quality of the coke product. Experimental
testing has proven that the most stringent coke requirement (i.e.
for blast furnace use) can be met.
[0073] The present technology's primary objective is to produce
fuel for the steel industry's iron production blast furnaces. The
finished product can also be used in cupolas in the foundry
industry as smokeless fuel, or a general carbon fuel source. The
technology provides a less expensive, high-performance product with
few if any by-product contamination or environmental problems.
[0074] The invention may be embodied in other specific forms
without departing from the spirit of the central characteristics
thereof. The present embodiments therefore to be considered in all
respects as illustrative and not restrictive, the core of the
invention being indicated by the appended claims rather than by the
foregoing description, and all changes which come within the
meaning and range of equivalency of the claims are therefore
intended to be embraced therein.
* * * * *