Furnaces – Process – Treating fuel constituent or combustion product
Reexamination Certificate
2000-10-20
2001-12-04
Bennett, Henry (Department: 3749)
Furnaces
Process
Treating fuel constituent or combustion product
C110S263000, C110S232000, C110S224000, C044S608000, C044S620000
Reexamination Certificate
active
06325001
ABSTRACT:
FIELD OF THE INVENTION
The herein disclosed invention is directed to improving combustion using coal for power steam boiler systems which use coal as the primary fuel.
The present invention is directed to the efficient combustion of coal and to reducing the detrimental effects of slag deposits and SOx and NOx emissions in the operation of coal fired boiler systems.
PRIOR ART PATENTS
Rickard, U.S. Pat. No. 4,263,856 provides pre-pulverized coal to the burner feed pipe for the purpose of supplementing the fuel feed quantity when the solid fuel pulverization mill is incapable of providing enough fuel to satisfy the demand requested. The present invention improves the quality of combustion and increases overall efficiency and not just simply increasing the available fuel supply to the boiler.
Westby, U.S. Pat. No. 5,364,421 blends coals with lignitic type ash and bituminous type ash compositions to modify the combined ash melting temperature for the purpose of reducing slag deposition on the heat transfer surfaces. The present invention blends TBLRC, typically containing altered lignitic type ash with other higher moisture coals containing either lignitic or bituminous type ash to improve the quality of combustion and reduce temperature imbalance issues as well as modifying the ash melting temperature. SynCoal specifically reduces the iron sulfide content providing a further beneficial effect.
Archer, U.S. Pat. No. 4,969,408 describes a control technique using an on-line analyzer to forecast coal combustion characteristics and adjusts the air flow to optimize combustion and minimize heat losses. This invention focuses upon the improving the stochiometric ratio through a feedback control system. It does not control the fuel characteristics and alter them in response to combustion monitoring. The subject invention is designed to alter the fuel combustion characteristics through the blending of TBI,RC with the standard solid fuel.
Shimoda, U.S. Pat. No. 4,465,000 describes a periodic injection of powdered limestone to add a high fusion temperature layer on the slag deposits making the slag deposits more friable and easier to remove using conventional soot blowing. Mahoney, U.S. Pat. No. 4,372,227 describes the addition of flue gas conditioner (such as alumina, silicon carbide, aluminum nitride) to nucleate molten particles and cause quicker solidification (crystallization) preventing deposition or making more friable deposits. Merrill, U.S. Pat. No. 4,577,227 describes the addition of amorphous silica particles >30 micron (~95 microns) to reduce the ash's tendency to stick or agglomerate due to increased fusion temperatures. Abrams, U.S. Pat. No. 4,616,574 describes intermittent injection of pressure hydrated dolomitic lime to reduce/modify slagging fouling deposits to lower the sintering strength and increase sintering temperature. Shimoda, Mahoney, Merrill and Abrams are all similar in that they add some non-combustible mineral to alter the coal ash characteristics to make it less likely to form slag or easier to remove with conventional slag removal techniques.
Brown, U.S. Pat. No. 4,319,885 is a method to capture SO
2
by mixing fibrous green crop material containing alkaline materials with coal. This acts like a combustion zone scrubber and will not improve the combustion characteristics. The subject invention improves the combustion characteristics and allows the boiler to function more efficiently as it was designed.
Forster, U.S. Pat. No. 4,396,434 is a method for breaking carbon rich slag deposits by injecting a chemical that embrittles the deposit and then applying acoustic air waves to break the deposit. Cavanagh, U.S. Pat. No. 2,151,264 is a method for breaking slag in open hearth furnaces using compressed CO
2
to fragment the slag and allow faster removal. Both Forster and Cavanagh are techniques to break the slag after it is formed and remove it from the boiler. The subject invention alters the fuel characteristics and improves the combustion characteristics to increase the operating performance of the boiler.
Definitions of Abbreviations as Ued Herein
CPD—Colstrip Project Division, acronym used for the operations group at the Colstrip power plants
ACCP—Advanced Coal Conversion Process, the name of the SynCoal process and the demonstration plant
“Wye”—The rotary locks used to feed the SynCoal to the pneumatic transport line into Unit
2
have a “wye” venting arrangement to prevent the air leaking past the air lock from “bubbling” in the silo above and disrupting SynCoal flow to the rotary lock.
PLC—programmable logic controller, the computerized control brain box
I/O—input/output, refers to the communication between the sensors/PLC/controlled devices
FM—Factory Mutual, the insurance agency's engineering group for review and recommendations
NFPA—National Fire Protection Association, group that provides design guidance for fire protection systems
SCFH—standard cubic feet per hour; it is a measurement of volumetric flow rate.
SCFM—standard cubic feet per minute
MW—mega watts
LRC—low rank coal. The term “low rank coal” broadly encompasses a series of relatively low rank or low grade carbonaceous materials or coals including peat, the lignite coals (which encompass lignite and brown coal), the sub-bituminous coals (conventionally classified as rank A, B and C in the order of their heating values), and the bituminous coals.
HRC—high rank coal
MMI—man-machine interface
BACKGROUND OF THE INVENTION
Overview
The town of Colstrip, in southeastern Montana, is the site of four thermal generating plants, divided into Colstrip Units
1
&
2
and Colstrip Units
3
&
4
. Colstrip Units
1
&
2
are twin 333 gross MW plants that have been in operation since the mid-1970's. Colstrip Units
3
&
4
are twin 805 gross MW plants that have been in operation since the mid-1980's. The entire generating plant complex is referred to as the “Colstrip project”. In operation, a thermally beneficiated low rank coal (TBLRC) trade named SynCoal® is delivered by truck from the ACCP demonstration facility to the Colstrip project for use in Unit
2
on a daily basis. The SynCoal® is stored in a silo, and delivered pneumatically to three (3) of the Unit
2
coal mills at a continuous rate up to about 40 tph.
In conjunction with the U.S. Department of Energy under its Clean Coal Technology program, Western SynCoal LLC, a non-regulated indirect subsidiary of the Montana Power Company, is conducting a full-scale commercial demonstration of a patented technology which enhances Powder River Basin coal. The technology reduces moisture and sulfur and substantially increases BTU content (e.g., from 8,600 BTU/lb to 11,700 BTU/lb). These alterations to the raw coal result in a thermo beneficiated low rank coal trade marked as SynCoal®, a product which is drier, and cleaner-burning. The facility for producing SynCoal® is called the Advanced Coal Conversion Process plant (ACCP), and is located in Colstrip at the Western Energy Company (WECO) mine, and operated by WECo personnel.
SynCoal® is delivered by truck from the ACCP demonstration facility to the Colstrip project for use in Unit
2
on a daily basis. The SynCoal® product is stored in Units
1
and
2
, and delivered pneumatically to three (3) of the Unit
2
coal mills at a continuous rate of up to about 40 tph.
Invention Demonstration Description
Using a single truck with tandem trailers hauling approximately 50 tons of SynCoal® per load, the delivered load from the ACCP is discharged onto the new unloading hopper which incorporates two (2) new 24″ diameter screw conveyors and a new bucket elevator. The material is first fed from the trailer to the unloading screw conveyor positioned parallel to the truck, which in turn feeds the transfer screw conveyor perpendicular to the truck. The transfer screw conveyor in turn feeds a totally enclosed bucket elevator at a rate of 200 TPH. SynCoal® is transferred from the 135′ high bucket elevator to the southern-most lime silo. The modified lime silo, fitted with a bin vent dust collector
Bennett Henry
Bloom Leonard
Rinehart K. B.
Western Syncoal, LLC
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