The present invention relates generally to the field of reburn systems and, more particularly, to a reburn system with feedlot biomass for increased NOx reduction in power plants.
Acronyms
NOx is produced when fuel is burned with air. The N in NOx can come either from the N-containing fuel compounds (e.g., Coal) and the N from air. The NOx generated from fuel N is called fuel NOx and that generated from N in air is called thermal NOx. Typically, 75% of NOx is from fuel N. The NOx and volatile organic compounds (VOC's; e.g. gasoline vapors from gas station) released from automobiles, utilities, etc. react in the presence of sun light and produce Ozone or Smog (smoke+fog, 0.08 ppm) which can damage cells in the lung's airways, causing inflammation. Thus the NOx, an ingredient for smog, is proposed to be reduced under title IV of CAAA. Table 1 shows the past regulation of NOx and the proposed new regulations.
The current technologies developed for reducing NOx include: Combustion Controls (e.g., staged combustion, low NOx burners, or reburn technology) and Post Combustion Controls (e.g., Selective Non-Catalytic Reduction, SNCR, etc. using urea). In reburn systems, typically coal or natural gas is injected as an additional fuel downstream of the main burners for reducing the NOx. In SNCR system, Ammonia or urea is injected above the combustion for reducing the NOx. Most current technology uses either coal or natural gas as a reburn fuel coupled with SNCR.
In Frazzitta et al. (Ref. 3), a cofiring experiment using a blend of coal (80%) and cattle manure (feedlot biomass) (20%) is described. Although feedlot biomass contains more N than coal, an increase in NOx was not observed in the experiment. Therefore, the need exists for further exploration and technological development using feedlot biomass as a fuel.
The invention includes a method of reducing the amount NOx resulting from combustion of a main or first fuel. In the method a first fuel is combusted then the products resulting from such fuel combustion is provided to a second combustion under slightly rich conditions. The second combustion is a reburn combustion and the reburn fuel includes up to 100% feedlot biomass by weight. The remaining portion of the reburn fuel may be any other fuel. In one embodiment, it is coal. In an alternate embodiment the reburn fuel is feedlot biomass without any additions of other fuels. The feedlot biomass is generally less than approximately 45% ash and for improved performance is preferably less than approximately 20% ash. In some feedlot biomass, the volatile matter levels are as high as 80%.
The first fuel used in the initial step of the combustion method may be any fuel, but will commonly be coal. The feedlot biomass contains nitrogen in the form of urea/ammonia and in proteins. The combustion may take place in a boiler burner or a multiple-burner boiler unit. If a multiple-burner boiler unit is used, at least one first burner may be used to combust the first fuel and at least one second burner may be used to combust the reburn fuel. In one embodiment, several burners may be used to combust the first fuel before the furnace gases are passed by the reburn burner(s). In another embodiment, burners for the first fuel and reburn burners may be alternated.
The invention also includes a boiler burner for combustion of fuel. The boiler includes a blower which directs air flow. The air is initially directed through a propane burner to which a propane source and an ammonia source are operably connected. This simulates NOx from a coal-fired burner. Other burners, including burners employing coal or other fuels for a commercial purpose may be used in place of a propane burner. The boiler also includes a reburn fuel injection point past which the air flow is directed after leaving the propane burner and before exiting the exhaust. The reburn fuel used in the boiler burner includes up to 100% feedlot biomass by weight. It may also possess other characteristics described above for feedlot biomass used in the method of the present invention.
The invention additionally includes a multiple-burner boiler unit for combustion. The boiler unit includes a furnace though which furnace gasses flow. The furnace includes at least one first burner which combusts a first fuel and at least one second burner which combusts a reburn fuel. The furnace gases flow from the first burner to the second burner. The reburn fuel includes up to 100% feedlot biomass by weight. It and the first fuel may also possess other characteristics described above for feedlot biomass used in the method of the present invention.
The feedlot biomass reburn system of the present invention combines the advantages of SNCR along with reburn systems since the feedlot biomass naturally contains urea/ammonia along with a large amount of volatile materials. Other technical advantages will be readily apparent to one skilled in the art.
For a more complete understanding of the present invention, and for further features and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:
a is a diagram illustrating a comparison of =data obtained with feedlot biomass and coal as reburn fuels in an embodiment of the present invention;
b is a diagram illustrating a comparison of data obtained with feedlot biomass, coal and mixtures thereof as reburn fuels in an embodiment of the present invention; and
Preferred embodiments of the present invention and their advantages are best understood by reference to
Referring to
In an exemplary embodiment, the boiler of
Referring to
Referring to
One skilled in the art will appreciate that any number of earlier coal burners may be used in multi-boiler unit 38, so long as penultimate burners 48 are supplied with feedlot biomass 54 with a richer stoichiometry and the final burners 50 are used to complete combustion. In an alternative embodiment of a multi-burner boiler, feedlot biomass may be mixed with coal and used in alternating burners but with reduced secondary air in those burners. A final reburn burner may also be included in this assembly.
For a more detailed understanding of the invention, reference may be had to the following examples, which are provided for illustrative purposes and do not encompass or represent the entire scope of the invention. Variations of the examples and other embodiments of the present invention will be apparent to one skilled in the art.
Recent test results relating to the present invention were obtained in the 30 kW (100,000 BTU/hr) Boiler Burner Laboratory, located in the Department of Mechanical Engineering. While power plants currently use coal or expensive and non-renewable natural gas to reduce NOx by 50–60%, the test results using cheaper, renewable feedlot biomass indicate a 70–80% reduction in NOx. This is likely due to the unusual combination of urea/ammonia and the higher volatile material levels in feedlot biomass.
In order to validate the beneficial combination of feedlot biomass, a boiler burner facility (heat thruput: 100,000 BTU/hr) along with reburn system has been built as shown in
The feedlot biomass used to obtain the results depicted in
Additional characteristics of the fuels used to obtain the results shown in
Feedlot biomass is used herein to designate and includes a variety of animal-based wastes. It may include but is not limited to primarily manure biomass from beef, swine, horses, or poultry (such as chickens or turkeys), preferably from an area where animals are confined and are fed. The feedlot biomass may be raw (fresh) manure, partially composted manure, finished composted manure, or stockpiled manure.
Feedlot biomass may be supplied to the burner (whether in a multiple-burner unit or not) in any form suitable for use in the selected equipment. In some embodiments of the present invention, the feedlot biomass is provided in the form of a fine powder. Variation in water content and particle size may be necessary to achieve optimal results. Such variations will be apparent or readily determined without undue experimentation based upon current knowledge regarding the use of coal and other fuels as reburn fuels and in boiler burner systems. Burner operating parameters may also be adjusted to accommodate variations in the fuel.
Additional experiments with various feedlot biomass sources and mixtures are summarized in Tables 4–26.
Although only exemplary embodiments of the invention are specifically described above, it will be appreciated that modifications and variations of the invention are possible without departing from the spirit and intended scope of the invention.
The following references are incorporated by reference herein.
The present application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 60/278,277, filed Mar. 22, 2001 and incorporated by reference herein.
The present invention has been partially funded by the United States Government through a grant from the U.S. Department of Energy, DOE Grant No. DE-FG26-00NT40810, Contract No. 61980, which may retain certain rights hereto.
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Number | Date | Country | |
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60278277 | Mar 2001 | US |