APPARATUS FOR REDUCING EMISSIONS AND METHOD OF ASSEMBLY
A heat recovery steam generator (HRSG) is coupled to a gas turbine engine that is configured to combust a fuel in air to produce shaft power and a flow of exhaust gases including oxides of nitrogen (NOx). The HRSG includes at least one duct burner for heating the exhaust gases and at least one NOx reduction element coupled downstream from the at least one duct burner and configured to facilitate reducing an amount of NOx in the exhaust gases that are channeled into the at least one NOx reduction element.
The embodiments described herein relate generally to emissions treatment systems and, more particularly, to an apparatus for use in reducing NO2 formation in the exhaust path of a combustion system.
During the combustion of natural gas and liquid fuels, pollutants such as, but not limited to, carbon monoxide (CO), unburned hydrocarbons (UHC), and oxides of nitrogen (NOx) emissions, may be formed and/or emitted into an ambient atmosphere. In general, CO and UHC may be formed during combustion conditions at lower temperatures and/or during combustion conditions when an insufficient amount of time to complete a reaction is available. In contrast, NOx is generally formed during combustion conditions at higher temperatures. At least some known pollutant emission sources include industrial boilers and furnaces, reciprocating engines, gas turbine engines, and/or steam generators.
Modern air quality regulations increasingly mandate reduced emission levels for power generation plants, while also requiring increased fuel efficiency requirements. To comply with stringent emission control standards, it is desirable to control NOx emissions by suppressing the formation of NOx emissions. Oxides of nitrogen include nitric oxide (NO) and nitrogen dioxide (NO2), which is known to produce a visible yellow plume from exhaust stacks and that is alleged to contribute to the creation of “acid rain.” However, known combustion controls may provide only limited emissions control and may prove inadequate in satisfying the increased standards and the often-conflicting goals, such that further improvements of post-combustion exhaust gas treatment systems are desirable.
One known technology for use in controlling NOx in stack emissions is selective catalytic reduction (SCR). In an SCR system, flue gases from power generation plants often have a net oxidizing effect due to a high proportion of oxygen that is provided to ensure adequate combustion of a hydrocarbon fuel. Thus, NOx that is present in the flue gas may be reduced to nitrogen and water with great difficulty. An SCR element may be used to mix anhydrous ammonia with the flue gas, and the gases are channeled over a suitable reduction catalyst at a suitable temperature prior to being released into the atmosphere. However, the reaction rate over the catalyst is dependent on the inlet gas temperature as such the rate of NOx destruction is insufficient until the flue gas is heated to the suitable temperature. Accordingly, during transient phases, such as during startup operations, the SCR element generally does not reduce the NOx to a desired level as the flue gas temperature is to low.
BRIEF DESCRIPTION OF THE INVENTIONIn one aspect, a method is provided for providing a heat recovery steam generator (HRSG) for use with a gas turbine engine. The method includes coupling at least one duct burner within the HRSG and coupling at least one oxides of nitrogen (NOx) reduction element downstream from the at least one duct burner, wherein the at least one duct burner is configured to operate gas turbine engine operations including startup, shutdown, and low-load operations with insufficient exhaust temperatures at the NOx catalyst inlet for desired NOx reduction to increase a temperature of exhaust gases routed through the at least one NOx reduction element to enable the at least one NOx reduction element to facilitate NOx reduction reactions during the gas turbine engine operations.
In another aspect, a heat recovery steam generator (HRSG) is provided, wherein the HRSG is coupled to a gas turbine engine that discharges a flow of exhaust gases including oxides of nitrogen (NOx). The HRSG includes at least one duct burner for heating the exhaust gases and at least one NOx reduction element coupled downstream from the at least one duct burner and configured to facilitate reducing an amount of NOx in the exhaust gases that are channeled into the at least one NOx reduction element.
In another aspect, a combined cycle power plant is provided, including a gas turbine engine and a heat recovery steam generator (HRSG) coupled in flow communication with the gas turbine engine. The gas turbine engine is configured to combust a fuel in air to produce shaft power and a flow of exhaust gases including oxides of nitrogen (NOx). The HRSG includes at least one duct burner for heating the exhaust gases and at least one NOx reduction element coupled downstream from the at least one duct burner and configured to facilitate reducing an amount of NOx in the exhaust gases channeled into the at least one NOx reduction element.
In the exemplary embodiment, power plant 100 also includes a heat recovery steam generator (HRSG) 116 that is coupled in flow communication to gas turbine engine 106. Specifically, HRSG 116 is coupled to gas turbine engine 106 via exhaust duct 114 such that HRSG 116 receives the exhaust gases discharged from gas turbine engine 106. In the exemplary embodiment, HRSG 116 includes one or more heat exchangers 118 and emissions treatment equipment 120. Heat exchangers 118 extract heat from the exhaust gases, and the heat is used to generate steam. Emissions treatment equipment 120 processes the exhaust gases, and the processed exhaust gases are subsequently released to the atmosphere via an exhaust stack 122.
A steam turbine 124 is coupled to HRSG 116 such that steam generated by heat exchangers 118 is channeled into steam turbine 124 for use in driving rotation of a second shaft 126. Second shaft 126 is also coupled to a second generator 128, and causes second generator 128 to generate electricity. The spent steam is then channeled into a condenser 130 that includes a plurality of tube bundles 132. Cooling water channeled through tube bundles 132 cools the steam such that the steam condenses into water. The water is then channeled back to heat exchangers 118.
In the exemplary embodiment, a second duct burner 306 is coupled in flow communication downstream from high pressure heat exchanger 304 to selectively increase the temperature of the exhaust gases to facilitate reducing the concentration of, for example NOx, in emissions channeled to stack 122. More specifically, in one embodiment, second duct burner 306 heats the exhaust gases to a temperature of between approximately 500° F. and approximately 800° F. In the exemplary embodiment, a carbon monoxide (CO) catalyst 308 is coupled in flow communication downstream from second duct burner 306 to facilitate oxidizing the nitric oxide (NO) to equilibrium concentrations of NO2 at local exhaust temperatures at the location of CO catalyst 308 in the exhaust gas stream. Specifically, CO catalyst 308 oxidizes NO such that the exhaust gases include approximately 90 ppm NOx, which includes less than approximately 50% NO2, but is SCR catalyst dependent.
In the exemplary embodiment, an injection apparatus 310 is coupled in flow communication downstream from CO catalyst 308. Injection apparatus 310 injects a reducing agent into the flow of exhaust gases to facilitate reducing the concentration of NOx within the exhaust gases. Moreover, in the exemplary embodiment, a NOx reduction element 312 is coupled in flow communication downstream from injection apparatus 310. NOx reduction element 312 channels the exhaust gases, including the reducing agent, over a suitable reduction catalyst to facilitate reducing the concentration of NOx. For example, the reduction catalyst provides an environment suitable for the reduction of NOx, by 120 ppm of NH3, to predominantly NO2, such as approximately 80% NO2. For example, in the exemplary embodiment, NOx reduction element 312 channels the exhaust gases over the reduction catalyst at a temperature between approximately 500° F. and 800° F., wherein NOx reduction element 312 reduces the NOx to a concentration of approximately 9 ppm, which includes approximately 80% of NOx as NO2 and 5 ppm NH3.
In one embodiment, injection apparatus 310 is an ammonia (NH3) injection grid that is coupled in flow communication downstream from CO catalyst 308. NH3 injection grid 310 injects ammonia into the flow of exhaust gases to facilitate reducing the concentration of NOx within the exhaust gases. Specifically, NH3 injection grid 310 injects a gaseous ammonia mixture into the flow of exhaust gases such that a concentration of ammonia is reduced to approximately 120 ppm. In an alternative embodiment, injection apparatus 310 injects a reducing agent such as hydrogen, or an organic reducing agent, such as a hydrocarbon material, into the flow of exhaust gases.
Moreover, in the exemplary embodiment, a NOx reduction element 312, such as a selective catalytic reduction (SCR) element, is coupled in flow communication downstream from NH3 injection grid 310. NOx reduction element 312 channels the exhaust gases over a suitable reduction catalyst at a temperature between approximately 500° F. and 800° F. to facilitate reducing the concentration of NOx. In one embodiment, NOx reduction element 312 uses an organic reducing agent, such as a hydrocarbon material, to reduce the concentration of NOx. For example, in one embodiment, NOx reduction element 312 includes one or more catalysts provided in one or more catalyst zones. The exhaust gases, including the organic reducing agent, are routed through each catalyst zone to interact with the corresponding catalyst. Exemplary catalysts include, but are not limited to only including, a zeolite material, a catalytic metal such as platinum group metals, gallium, and/or a promoting metal such as silver, gold, vanadium, zinc, titanium, tin, bismuth, cobalt, molybdenum, tungsten, indium, and mixtures thereof. In an alternative embodiment, NOx reduction element 312 uses a hydrogen-based reducing agent, such as H2. Typically, the precious metal catalysts used in NOx reduction element 312 having H2 or hydrocarbon as a reducing agent require lower temperatures for the same NOx removal efficiency as NOx reduction element 312 having ammonia as the reducing agent. However, use of H2 or a hydrocarbon reducing agent enables a lower maximum temperature before degrading or oxidizing ammonia to NOx or both. Accordingly, in some embodiments, the precious metal catalysts are located closer to the exhaust of HRSG 116 in a lower temperature operating environment.
Furthermore, in the exemplary embodiment, HRSG 116 includes a low pressure heat exchanger 314 coupled in flow communication downstream from NOx reduction element 312. Moreover, in the exemplary embodiment, low pressure heat exchanger 314 cools the exhaust gases to a temperature of approximately 150° F. including approximately 9 ppm NOx and 5 ppm NH3.
In the exemplary embodiment, a controller 316 is coupled to, for example, HRSG 116. Controller 316 controls activation and/or performance of second duct burner 306. For example, during a startup of combined cycle power plant 100 (shown in
In some embodiments, the term “controller” refers generally to any programmable system including computers, systems, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), programmable logic circuits (PLC), and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and thus are not intended to limit in any way the definition and/or meaning of the term controller.
Although the present invention is described in connection with an exemplary power generation system environment, embodiments of the invention are operational with numerous other general purpose or special purpose power generation system environments or configurations. The power generation system environment is not intended to suggest any limitation as to the scope of use or functionality of any aspect of the invention. Moreover, the power generation system environment should not be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment.
Table 1, below, provides exemplary, typical, non-limiting temperature and emissions concentration of the flow of exhaust gases from gas turbine engine 106 at locations within the exhaust stream upstream 318 from first duct burner 302, downstream 320 from high pressure heat exchanger 304, downstream 322 from high pressure evaporator 208, downstream 324 from CO catalyst 308, downstream 326 from injection apparatus 310, downstream 328 from NOx reduction element 312, and downstream 330 from low pressure heat exchanger 314.
Exemplary embodiments of methods and apparatus for use in reducing emissions, such as NOx emissions, are described herein. The embodiments described herein facilitate increasing a temperature of exhaust gases from a gas turbine engine by using a duct burner to enhance an ability of a selective catalytic reduction (SCR) element to reduce the concentration of NOx of the exhaust gases emitted into the atmosphere via an exhaust stack.
Exemplary embodiments of systems, apparatus, and methods of assembly are described above in detail. The systems, apparatus, and methods of assembly are not limited to the specific embodiments described herein but, rather, operations of the methods and/or components of the system and/or apparatus may be utilized independently and separately from other operations and/or components described herein. Further, the described operations and/or components may also be defined in, or used in combination with, other systems, methods, and/or apparatus, and are not limited to practice with only the systems, methods, and storage media as described herein.
A controller, such as those described herein, includes at least one processor or processing unit and a system memory. The controller typically has at least some form of computer readable media. By way of example and not limitation, computer readable media include computer storage media and communication media. Computer storage media include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules, or other data. Communication media typically embody computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and include any information delivery media. Those skilled in the art are familiar with the modulated data signal, which has one or more of its characteristics set or changed in such a manner as to encode information in the signal. Combinations of any of the above are also included within the scope of computer readable media.
The order of execution or performance of the operations in the embodiments of the invention illustrated and described herein is not essential, unless otherwise specified. That is, the operations may be performed in any order, unless otherwise specified, and embodiments of the invention may include additional or fewer operations than those disclosed herein. For example, it is contemplated that executing or performing a particular operation before, contemporaneously with, or after another operation is within the scope of aspects of the invention.
When introducing elements of aspects of the invention or embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
Claims
1. A method of providing a heat recovery steam generator (HRSG) for use with a gas turbine engine, said method comprising:
- coupling at least one duct burner within the HRSG; and
- coupling at least one oxides of nitrogen (NOx) reduction element downstream from the at least one duct burner, wherein the at least one duct burner is configured to operate during gas turbine engine operations including startup, shutdown, and low-load operations with insufficient exhaust temperatures at the NO catalyst inlet for desired NOx reduction to increase a temperature of exhaust gases routed through the at least one NOx reduction element to enable the at least one NOx reduction element to facilitate NOx reduction reactions during the gas turbine engine operations.
2. A method in accordance with claim 1, further comprising coupling an injection apparatus downstream from the at least one duct burner and upstream from the at least one NOx reduction element, wherein the injection apparatus is configured to inject a reducing agent into the exhaust gases.
3. A method in accordance with claim 1, further comprising coupling the at least one duct burner to a controller that is configured to selectively activate the at least one duct burner based on a temperature of the exhaust gases upstream from the at least one duct burner
4. A method in accordance with claim 3, wherein coupling the at least one duct burner to a controller further comprises configuring the controller to activate the at least one duct burner to heat the exhaust gases during the gas turbine startup.
5. A method in accordance with claim 1, wherein the at least one duct burner includes a plurality of fuel circuits, said method further comprising coupling the plurality of fuel circuits to at least one fuel source.
6. A heat recovery steam generator (HRSG) coupled to a gas turbine engine that discharges a flow of exhaust gases including oxides of nitrogen (NOx), said HRSG comprising:
- at least one duct burner for heating the exhaust gases; and
- at least one NOx reduction element coupled downstream from said at least one duct burner and configured to facilitate reducing an amount of NOx in the exhaust gases that are channeled into said at least one NOx reduction element.
7. An HRSG in accordance with claim 6, wherein said at least one duct burner is configured to be selectively activated based on a temperature of the exhaust gases upstream from said at least one duct burner.
8. An HRSG in accordance with claim 6, wherein said at least one duct burner is configured to heat the exhaust gases to a temperature above approximately 500 degrees Fahrenheit.
9. An HRSG in accordance with claim 6, wherein said at least one duct burner is configured to heat the exhaust gases during any of a startup phase, a shut down phase, and a load condition with insufficient exhaust temperatures at the NOx catalyst inlet for desired NOx reduction.
10. An HRSG in accordance with claim 6, wherein said duct burner comprises a plurality of fuel circuits.
11. An HRSG in accordance with claim 6, further comprising an injection apparatus coupled downstream from said at least one duct burner and upstream from said at least one NOx reduction element, wherein said injection apparatus is configured to inject a reducing agent into the exhaust gases to facilitate NOx reduction reactions.
12. An HRSG in accordance with claim 6, wherein the flow of exhaust gases also includes carbon monoxide (CO), said HRSG further comprising a CO oxidation catalyst element coupled downstream from said at least one duct burner and upstream from said injection apparatus.
13. An HRSG in accordance with claim 6, further comprising:
- a first heat exchanger coupled upstream from said at least one duct burner; and
- at least a second duct burner coupled upstream from said first heat exchanger.
14. An HRSG in accordance with claim 13, further comprising a second heat exchanger coupled downstream from said at least one NOx reduction element.
15. A combined cycle power plant comprising:
- a gas turbine engine configured to combust a fuel in air to produce shaft power and a flow of exhaust gases including oxides of nitrogen (NOx); and
- a heat recovery steam generator (HRSG) coupled in flow communication with said gas turbine engine, said HRSG comprising: at least one duct burner for heating the exhaust gases; and at least one NOx reduction element coupled downstream from said at least one duct burner and configured to facilitate reducing an amount of NOx in the exhaust gases channeled into said at least one NOx reduction.
16. A combined cycle power plant in accordance with claim 15, wherein said at least one duct burner is configured to be selectively activated based on a temperature of the exhaust gases upstream from said at least one duct burner.
17. A combined cycle power plant in accordance with claim 15, wherein said at least one duct burner is configured to heat the exhaust gases to a temperature above approximately 500 degrees Fahrenheit or above a catalyst light off temperature.
18. A combined cycle power plant in accordance with claim 15, wherein said at least one duct burner is configured to heat the exhaust gases during a transient operation phase of said combined cycle power plant.
19. A combined cycle power plant in accordance with claim 15, wherein said at least one duct burner comprises a plurality of fuel circuits.
20. A combined cycle power plant in accordance with claim 15, wherein said HRSG further comprises an injection apparatus coupled downstream from said at least one duct burner and upstream from said at least one NOx reduction element, wherein said injection apparatus is configured to inject a reducing agent into the exhaust gases to facilitate NOx reduction reactions.
Type: Application
Filed: Oct 29, 2010
Publication Date: May 3, 2012
Inventors: Gilbert Otto Kraemer (Greer, SC), Paul Thomas Marks (Taylors, SC), Robert Frank Hoskin (Duluth, GA)
Application Number: 12/915,653
International Classification: F01K 13/00 (20060101); F01K 27/00 (20060101);