By Ray W. Sheldon and Linda J. Frank
The Advanced Coal Conversion Process (ACCP) being demonstrated in Colstrip, Montana consists of thermal
processing coupled with physical cleaning to upgrade high-moisture, low-rank coals, giving a fuel with improved
heating value and low sulfur content.
The process and product, patented as SynCoal7, has been developed by the Rosebud SynCoal Partnership
(RSCP) as part of Round I of the U.S. Department of Energy's Clean Coal Technology Program. RSCP is a
general partnership formed in December 1990 for the purpose of conducting the demonstration and
commercializing of the ACCP technology. Western SynCoal Company (WSC), a subsidiary of Montana Power
Company's Energy Supply Division, is the managing general partner.
WSC owns the technology and has exclusively licensed it to the partnership. The partnership manages the
demonstration project and all activities related to commercialization. DOE has contributed about $43 million
(41%) to the $105 million demonstration project, with the remainder provided by RSCP.
The plant is located adjacent to the unit train loadout facility within Western Energy Company's Rosebud Mine
near Colstrip, Montana. The production unit, having a capacity of 1,000 tons per day of upgraded coal, is onetenth
the size of a commercial facility and benefits from the existing mine and community infrastructure.
The SynCoal7 process enhances low-rank subbituminous and lignite coals by a combination of thermal
processing and physical cleaning. The process consists of three major steps: thermal treatment in an inert
atmosphere, inert gas cooling of the hot coal, and pneumatic cleaning. The results are a reduction in moisture
content from 25-40% in the feedstock to as low as 1% in the product, concurrently increasing heating value from
5,500 B 9,000 Btu/lb to as high as 12,000 Btu. At the same time, sulfur content is reduced from a range of 0.5 B
1.5% to as low as 0.3%. Each ton of raw Rosebud subbituminous coal produces about 2/3 ton of SynCoal7.
Raw coal from the Rosebud mine unit train stockpile is screened and fed to a vibratory fluidized-bed reactor,
where surface water is removed by heating with hot combustion gas. Coal exits this reactor at a temperature
slightly higher than that required to evaporate water and is further heated to nearly 600EF in a second vibratory
reactor. This temperature is sufficient to remove chemically bound water, carboxyl groups, and volatile sulfur
compounds. In addition, a small amount of tar is released, partially sealing the dried product. Particle shrinkage
causes fracturing, destroys moisture reaction sites, and liberates the ash-creating mineral matter.
The coal then is cooled to less than 150EF by contact with an inert gas (carbon dioxide and nitrogen at less than
100EF) in a vibrating fluidized-bed cooler. Finally, the cooled coal is fed to deep bed stratifiers where air
pressure and vibration separate mineral matter from the coal including the pyrite-rich ash, thereby reducing the
sulfur content of the product. The low specific gravity fractions are sent to a product conveyor while heavier
fractions go to fluidized bed separators for additional ash removal.
The fines handling system consolidates the coal fines that are produced in the conversion, cleaning and material
handling systems. The fines are gathered by screw conveyors and transported by drag conveyors to a bulk
cooling system. The cooled fines are blended with the coarse product or stored in a 250-ton capacity bin until
loaded into pneumatic trucks for off-site sales. When sales lag production, the fines are slurried with water in a
specially designed tank and returned to the mine pit.
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PROJECT HISTORY
The Cooperative Agreement with DOE for the ACCP demonstration facility was signed in September 1990.
Initial operations began in April 1992, with the first 24-hour run occurring in May 1992 and the first significant
shipments in June. Several material handling problems were encountered during initial operations that required
extensive modifications and hampered the efforts to address the product issues of dustiness and spontaneous
heating. Parallel efforts to correct the material handling shortfalls and investigate treatments to mitigate the
product issues were pursued until August 1993, when the demonstration facility reached full production
capability. Efforts have continued since to establish test customers and address the product handling issues for
safe and reliable transportation and handling. Three different feedstocks were trucked to and tested at the facility
in 1993 and early 1994. In 1994, several test burn programs were conducted in both utility and industrial
applications and three regular customers were established. The demonstration facility start focused increasing
amounts of attention on process improvements and operating cost reductions. Since 1995, an additional focus
has been the development of commercial markets.
Through June 1997, 1.6 million tons of raw coal have been processed and over 1 million tons of SynCoal7 has
been produced. Total shipments of SynCoal7 products have exceeded 950,000 tons. The plant has consistently
operated at over 100% of its design capacity and at its target 75% availability. The demonstration facility is
expected to operate through June 1998 under the Cooperative Agreement.
LESSONS LEARNED
MECHANICAL RELIABILITY
Initial operations of the demonstration plant discovered numerous weak links and bottlenecks. The rotary
airlocks between process reactors were under powered and jammed tripping the entire plant. The fines gathering
and conveying system was severely undersized and wore out rapidly. As operations continued, problems with
fan bearings, conveyors and particularly the vibrating reactor vessels were uncovered. Generally all of these
problems have been solved or mitigated by improved design and repair or replacement. These lessons can be
carried forward to the next generation plant design.
PRODUCT ISSUES
The project team has worked continuously to improve the process and product since the initial startup identified
the dustiness and spontaneous combustion issues. Additionally, as with any first-of-a-kind plant, significant
efforts have been directed toward improving process efficiencies and reducing overall costs. A CO2 inerting
system was added to prevent self heating in the storage areas and enhance the product stability in transit to
customers. After verifying the effectiveness of this system, an additional inert gas process was added to reduce
the gas expenses and further test the impact on product stability.
A wide variety of additives and application techniques were tested in an effort to reduce dustiness and
spontaneous combustion. A commercial anionic polymer applied in a dilute concentration with water was found
to provide effective dust control and is environmentally acceptable. A companion product was identified that can
be used as a rail car topping agent to reduce wind losses. The application of the dilute water based suppressant,
which is known as dust and stability enhancement (DSE), also provided a temporary heat sink, helping control
spontaneous combustion for short duration shipments and stockpile storage. This work led to extensive
investigation of stockpile management and blending techniques.
After adapting these lessons, safe and effective techniques for blending SynCoal7 with raw coal, petroleum coke,
and SynCoal7 fines and handling the resultant products have evolved. This work further led to the development
of stabilization process concepts (patents pending) which were successfully piloted at a 1,000 lb/hr scale. A plant
modification was designed, but has not been installed due to the high retrofit costs. The next generation plant is
expected to incorporate the stabilization process technology.
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ENVIRONMENTAL PERFORMANCE
It was originally assumed that SO2 emissions would have to be controlled by injecting chemical sorbents into the
ductwork. However, a mass spectrometer installed to monitor emissions and performance testing, discovered
that the process configuration inherently limits the gaseous sulfur production, eliminating the need for chemical
sorbent injection. The sorbent injection system remains in place should a higher sulfur coal be processed.
Fugitive dust from material handling and coal cleaning operations throughout the plant is controlled by negative
pressure dust collection hoods located at all transfer points and other dust emission sources. High efficiency
baghouses are connected to the dust collection hoods. These baghouses have been effective, as demonstrated
by stack tests on the east and west baghouse outlet ducts and the first-stage drying gas baghouse stack in 1993.
Emission rates are well within the limits specified in the air quality permit, at 0.0013 grains/dry standard cubic
feet (gr/dscf) for the baghouse outlet ducts and 0.0027 gr/dscf for the drying gas baghouse stack. Another stack
survey conducted in May 1994 verified that emissions of particulates, SO2, oxides of nitrogen (NOx), carbon
monoxide (CO), total hydrocarbons, and hydrogen sulfide (H2S) from the process stack are within permitted
levels.
Through June 1997, the demonstration operations have been cited for only five minor violations as a result of
MSHA's regular inspections. It was noted at the celebration of 1 million tons of production that the operating
work force had completed over 300,000 manhours without a lost time accident.
PRODUCT APPLICATIONS
Utility Applications
A SynCoal7 testburn was conducted at the 160 MW J.E. Corette plant in Billings, Montana. A total of 204,000
tons of SynCoal7 was burned between mid-1992 and April 1996. The testing involved both handling and
combustion of DSE treated SynCoal7 in a variety of blends. These blends ranged from approximately 15% to
85% SynCoal7 with raw coal. Overall, the results indicate that a 50% SynCoal7/raw coal blend provides improved
performance, with SO2 emissions reduced by 21% at normal operating loads, and no noticeable impact on NOx
emissions.
In addition, the use of SynCoal7 permitted deslagging the boiler at full load, thereby eliminating costly ash
shedding operations. This also provided reduced gas flow resistance in the boiler and convection passage,
thereby reducing fan horsepower and improving heat transfer in the boiler area, resulting in an increase in net
power generation of about 3 MW.
Deliveries of SynCoal7 are now being sent to Colstrip Units 1 & 2 in Colstrip, Montana. Testing has begun on the
use of SynCoal7 in these twin 320-MW pulverized coal fired plants. The results of these tests will provide
information on boiler efficiency, power output, and air emissions. A total of 158,000 tons have been consumed
to date. A new SynCoal7 delivery system is being designed which, if installed, would provide selectively
controlled pneumatic delivery of fuel to individual pulverizers in the two units. This system would allow controlled
tests, providing valuable comparative data on emissions, performance and slagging.
Alternative Coal Testing
In May 1993, 190 tons of Center, North Dakota lignite were processed at the ACCP demonstration facility,
producing a 10,740 Btu/lb product, with 47% reduction in sulfur and 7% reduction in ash. In September 1993, a
second test was performed processing 532 tons of lignite, producing a 10,567 Btu/lb product with 48% sulfur
reduction and 27% ash reduction. The Center lignite before beneficiation had 36% moisture, about 6,800 Btu/lb,
and about 3.0 lb of SO2/million Btu.
Approximately 190 tons of these upgraded products were burned in the Milton R. Young Power Station Unit
#1,
located near Center. This initial test showed dramatic improvement in cyclone combustion, improved slag
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tapping, and a 13% reduction in boiler air flow, reducing the auxiliary power loads on the forced draft and induced
draft fans. In addition, the boiler efficiency increased from 82% to over 86% and the total gross heat rate
improved by 123 Btu/kWh.
Similar test programs were also conducted on 290 tons of Knife River lignite from North Dakota and 681 tons of
Amax subbituminous coal from Wyoming producing 10,670 Btu/lb and 11,700 Btu/lb products respectively.
Industry Applications
Several industrial cement and lime plants have been customers of SynCoal7 for an extended period of time. A
total of about 190,000 tons have been delivered to these customers since 1993. They have found that SynCoal7
improves both capacity and product quality in their direct fired kiln applications, because the steady flame
produced by SynCoal7 appears to allow tighter process control and improved process optimization.
A bentonite producer has been using SynCoal7 as an additive in greensand molding product for use in the
foundry industry, having purchased about 37,500 tons. They have found SynCoal7 to be a very consistent
product, allowing their greensand binder customers to reduce the quantity of additives used and improving the
quality of the metal castings produced.
SIGNIFICANCE OF THE TECHNOLOGY
SUPPLEMENTAL FUEL IMPACTS
The utility segment is the largest and most established market for all domestic coal sales. Since the ACCP is by
its nature a value added process and the product has been determined to require special handling, unique
situations must be identified where the addition of SynCoal7 to the firing mix provides sufficient benefit to more
than offset the increased delivered cost compared to raw western coal. These requirements have led RSCP to
focus on marketing the product as a supplemental fuel in utility applications and then only to units that have
specific problems with slagging or flame stability.
Utility plants with design or fuel related limitations such as the J.E. Corette station and Colstrip Units 1 & 2 can
benefit from decreased slagging, reduced SO2 emissions, improved net generation, and reduced heat rate by
burning a controlled amount of SynCoal7 selectively injected into the boiler.
INDUSTRIAL FUEL OPPORTUNITIES
The industrial market segment is much more amenable to special handling since these customers normally
receive much small quantities and are much more sensitive to fuel quality issues. RSCP has developed a
technique of shipments in covered hopper rail cars and/or pneumatic trucks that allows long haul distances and,
when combined with inerted bin storage, provides safe and efficient handling.
SynCoal7 has been found to provide superior performance in direct fired applications particularly as a blend with
petroleum coke. SynCoal7 provides good ignition and stable flame characteristics while the petroleum coke is
low cost and requires a longer burning time, expanding the processing zone. This blend of characteristics has
provided a significant advantage to SynCoal7's cement and quicklime customers. Additionally, recent tests of
SynCoal7/petroleum coke blends have shown improved handling characteristics with regard to dustiness and self
heating.
SynCoal7 produces a gas-like flame when burned alone. In some direct fired applications (such as road paving
asphalt plants), it can be a much lower cost option that propane, providing a small but valuable market.
METALLURGICAL PROCESS OPPORTUNITIES
SynCoal7's consistent characteristics and high volatile matter and carbon contents make it a good reducing agent
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for some metallurgical processing applications. Since low moisture content is a key characteristic for this
segment, the covered hopper rail car and/or pneumatic truck delivery system is readily accepted. SynCoal7 has
been used successfully in ductile iron metal casting applications as a greensand binder additive due to these
characteristics. RSCP has been working with a metallurgical silica producer to determine if SynCoal7 is viable in
their application. RSCP is continuing to pursue alternative markets in various metallurgical reduction
applications and SynCoal7 may even be a viable substitute for natural gas used to reduce metallurgical coke use
in blast furnaces.
UNCERTAIN FUTURE
TECHNOLOGY DEVELOPMENT NEEDS
Additional development is required to improve two major product characteristics: spontaneous combustion and
dusting. In addition, further market development and customer education are needed to position SynCoal in the
proper market niches and overcome natural resistance to a new product.
The upgraded coal produced to date has exhibited spontaneous heating and combustion. When a coal pile
(more than 1 to 2 tons) is exposed to any significant airflow for periods ranging from 18 to 72 hours, the coal
reaches temperatures at which spontaneous combustion or autoignition occurs. Spontaneous heating of run-ofmine,
low-rank coals has been a common problem but usually occurs after open air exposure periods of days or
weeks, not hours. However, dried, low-rank coals have universally displayed spontaneous heating tendencies to
a greater degree than raw, low-rank coals.
The product is basically dust free when it exits the processing facility due to numerous steps where the coal is
fluidized in process gas or air, which removes the dust-size particles. However, typical of all coal handling
systems, each transfer of the product coal after it leaves the process degrades the coal size and produces some
dust. Because the SynCoal7 product is dry, it does not have any inherent ability to trap small particles on the
coal surfaces. This allows any dust-size particles that are generated by handling to be released and become
fugitive.
In January 1995, a cooperative research project was initiated to determine the effects of different processing
environments and treatments on low-rank coal composition and structure. Specific objectives are (1) to study the
explosivity and flammability limits of dust from the process and (2) to identify the causes of spontaneous heating
of upgraded coals. Other participants in this study are the Amax Coal Company and EnCoal, who have also
experienced similar effects with their upgraded products.
COMPETITIVE IMPACTS
Due to the handling issues, RSCP has taken a three-pronged approach to satisfying customer needs for a safe,
effective way to handle SynCoal7. The first method is to employ DSE treatment, which allows conventional bulk
handling for a short period (about one week) but does degrade the product heat content. The product eventually
becomes dusty and susceptible to spontaneous heating again.
The second technique uses contained storage and transportation systems with pneumatic or minimal exposure
material handling system. This technique provides maximum product quality and actually enhances the material
handling performance for many industrial customers; however, transportation requires enclosed equipment and is
impractical for the bulk coal handling systems of large utility customers.
The third approach is to develop a stabilization process step. SynCoal's previous work has been of great benefit
in the collaborative research with EnCoal. SynCoal hopes to incorporate its stabilization process in the next
generation facility or develop a smaller pilot operation in direct response to a specific customer requirement.
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These approaches should allow SynCoal7 to be tested in some more novel applications such as blast furnace
injection systems and electric arc furnace reducing agents.
CONCLUSION
Rosebud SynCoal has developed an advanced coal conversion process which has the potential to enhance the
utility and industrial use of low-rank western subbituminous and lignite coals. Many of the power plants located
throughout the upper Midwest have cyclone boilers, which burn low ash fusion temperature coals. Presently,
most of these plants burn Illinois Basin high-sulfur coal. SynCoal7 is an ideal supplemental fuel for these and
other plants because it allows a wider range of low-sulfur raw coals to be used to meet more restrictive worldwide
emissions guidelines without derating of the units or the addition of costly flue gas desulfurization systems.
The ACCP has potential to convert inexpensive low-sulfur, low-rank coals into valuable carbon-based reducing
agents for many metallurgical applications, further helping reduce worldwide emissions and decrease the U.S.
dependence on foreign energy sources.
The ACCP produces a fuel which has a consistently low moisture content, low sulfur content, high heating value,
and high volatile content. Because of these characteristics SynCoal7 could have significant impact on SO2
reduction and provide a clean, economical alternative fuel to many regional industrial facilities and small utility
plants allowing them to remain competitively in operation.
Grüsse
Dazu noch gefunden
www.osti.gov/bridge/product.biblio.jsp?osti_id=5018608fossil.energy.gov/programs/powersystems/...l/86-93program.htmlAber dass schonfast 20 Jahre an diesen Techniken geforscht wird zeigt ihre Wichtigkeit für die Zukunft
Bisher scheint mir silverados Technik die sauberste und beste zu sein (siehe 4298)
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