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  Advanced control system for enhanced operation of oscillating combustion in combustorsUSPTO Application #: 20060177785Title: Advanced control system for enhanced operation of oscillating combustion in combustors Abstract: Methods for optimizing emission levels from combustion operations, which include a system and process for optimizing levels of NOx and CO during fuel combustion including supplying flows of fuel (which is predetermined) and main oxidant to a burner. Oscillating combustion is generated by oscillating the fuel flow with an oscillating valve and combusting the oscillating fuel with the main oxidant adjacent the burner to produce combustion products. A post-combustion oxidant is injected into the combustion products where it is combusted with the combustion products. A controller is operatively associated with control units for controlling the main oxidant and post-combustion oxidant flow rates and the oscillating valve. (end of abstract) Agent: Air Liquide - Houston, TX, US Inventors: Rajani K. Varagani, Erwin Penfornis, Omar Germouni USPTO Applicaton #: 20060177785 - Class: 431012000 (USPTO) Related Patent Categories: Combustion, Process Of Combustion Or Burner Operation, Controlling Or Proportioning Feed The Patent Description & Claims data below is from USPTO Patent Application 20060177785. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims benefit under 35 U.S.C. .sctn. 119(e) to provisional application No. 60/635,737, filed Dec. 13, 2004, the entire contents of which are incorporated herein by reference. RELATED ART [0002] The concept of oscillating combustion is a recognized technology for the reduction of NOx in industrial furnaces. The principle and the various methods of implementation are broadly described in U.S. Pat. No. 4,846,665, U.S. Pat. No. 5,302,111, and U.S. Pat. No. 5,522,721. The main idea is to pulse the flow of fuel, or air being supplied to at least one burner of the furnace, to generate successive fuel-rich and fuel-lean zones in a flame; thereby, reducing NOx emissions. [0003] The inventors are only aware of oscillating combustion's commercial implementation in large multi-fired industrial furnaces, such as glass and steel reheating furnaces. In these processes, integration of oscillating combustion to the furnace is relatively easy since the furnace is often operated continuously, at fixed or almost steady load, and in conditions which don't require additional injection of oxidant in the furnace in order to eliminate excessive formation of unburned hydrocarbons, or carbon monoxide (CO). In such furnaces, a stand-alone automated logic control device, as proposed in U.S. Pat. No. 6,398,547, may be used to promote safe and efficient operation of the oscillating combustion system. [0004] Some have proposed to implement the same concept of oscillating combustion in processes presenting more constraints, especially in units with smaller combustion chamber, and operating one burner or a limited number of burners. Typical examples for these units are industrial boilers and process heaters. Some technical solutions have been provided for these processes, some of which include optimized injections of additional oxidant and specific mixing devices located in certain position of the process in order to eliminate excessive formation of unburned hydrocarbons, or carbon monoxide (CO), while maintaining optimum NOx reductions. These so-called post-combustion solutions are described in U.S. Pat. No. 6,398,547, U.S. Pat. No. 6,913,457, and published U.S. Patent Application No. 2003/0134241. In most cases, these proposed processes are running at varying loads without human/operator intervention, and are subject to frequent shut-downs and start-ups. This complicates the operation on top of controlling the additional oxidant flow. In these conditions, some experimental testing of the oscillating combustion has been performed in such processes, yielding attractive performances, such as significant NOx reduction, but only under a tight supervision and command by a team of operators. [0005] Therefore, there is a need for an improved control system and method of the oscillating combustion technology allowing a safe and efficient integration to industrial fired processes such as, but not limited to, industrial boilers and process heaters, in which so-called post-combustion is implemented. [0006] Many problems arise from the implementation of the oscillating combustion technology in these types of processes. The air/fuel stoichiometry at the burner level has to be reduced in order to compensate the injection of additional oxidant downstream of the burner. The oscillating and post-combustion parameters have to be adjusted according to firing rates of the process. The total amount of oxidant injected (both at burner and downstream, in post-combustion step) has to be closely controlled in order to supply enough oxygen for maintaining CO below regulated levels, but not too much in order to keep an optimum boiler efficiency. Additional amounts of oxidant have to be supplied during transient phases in order to maintain the overall excess air above a safe level. The oscillating combustion and post-combustion have to be operated in such a way that the boiler can be started up safely after a shut-down. For this purpose, the valve oscillations have to be interrupted before the boiler starts up again in order to allow a safe establishment of the flame. Finally, the oscillating combustion and post-combustion systems have to allow a safe operation in a non-oscillating mode. This is needed in order to keep the process operating in case of a failure or when maintenance of the oscillating equipment is required. SUMMARY OF THE INVENTION [0007] A process for optimizing levels of NOx and CO during fuel combustion is performed and includes the steps of a flow of a fuel to a burner is supplied, and flow of a main oxidant is supplied to a burner. The flow rate of the main oxidant is controlled by a main oxidant flow rate control unit. Oscillating combustion is generated by oscillating the fuel flow with an oscillating valve and combusting the oscillating fuel with the main oxidant adjacent the burner to produce combustion products. A post-combustion oxidant is injected into the combustion products. The injection rate of the post-combustion oxidant injection being is controlled by a post-combustion oxidant flow rate control unit. The combustion products and the injected post-combustion oxidant are combusted. A rate of the fuel flow is predetermined. A controller is provided that is operatively associated with the main oxidant flow rate control unit, the oscillating valve, and the post-combustion oxidant flow rate control unit. A value or values associated with one or more combustion parameters (including a rate of flow of the main oxidant, a rate of flow of the post-combustion oxidant, a frequency of the oscillating fuel flow, an amplitude of the oscillating fuel flow, a duty cycle of the oscillating fuel flow) is determined. The combustion parameter associated with the determined value or values is adjusted. The determined value or values is based upon the predetermined fuel flow rate. The determining step is performed by the controller. [0008] A system for improved operation of a combustion process utilizing oscillating combustion includes: [0009] a supply of fuel; [0010] a supply of a main oxidant; [0011] a supply of a post-combustion oxidant; [0012] a burner for receiving the fuel and main oxidant and initiating combustion thereof to produce combustion products; [0013] an oscillating valve operatively associated with the supply of fuel for achieving an oscillating flow of said fuel at the burner; [0014] walls defining a combustion chamber operatively associated with the burner and enclosing an oscillating combustion space and a post-combustion space; [0015] a main oxidant flow rate control unit operatively associated with the supply of main oxidant and the burner adapted and configured to control a flow rate of the main oxidant; [0016] a post-combustion oxidant flow rate control unit operatively associated with the supply of post-combustion oxidant and the post-combustion space; [0017] a post-combustion injection element operatively associated with the post-combustion oxidant flow rate control unit; and [0018] a controller operatively associated with the main oxidant flow rate control unit, post-combustion oxidant flow rate control unit, and oscillating valve. [0019] The oscillating combustion space is upstream of the post-combustion space. The main oxidant flow rate control unit is adapted and configured to control a flow rate of the oxidant. The post-combustion oxidant flow rate control unit is adapted and configured to control a flow rate of the post-combustion oxidant. The post-combustion injection element is adapted and configured to inject the post-combustion oxidant into the post-combustion space to achieve combustion of the combustion products and the post-combustion oxidant. BRIEF DESCRIPTION OF THE DRAWINGS [0020] For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein: [0021] FIG. 1 is a schematic of one embodiment of the system according to the invention; [0022] FIG. 2 is a flowchart showing the startup sequence of one embodiment of the invention; and [0023] FIG. 3 is a flowchart showing the shutdown sequence for one embodiment of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS [0024] In order to solve the above mentioned problems, the present invention proposes an innovative system and method for operating and controlling the oscillating combustion technology in combustors subject to demanding operating constraints, such as industrial boilers and process heaters. An improvement of the present invention is directed to performing safe startups and shutdowns with a controller. One purpose is to integrate an innovative oscillating combustion control scheme to the existing process in order to allow a safe operation of this process at any time and/or to adjust the various control parameters in order to maintain optimal or satisfactory NOx (and optionally CO) reduction and process efficiency. [0025] The proposed invention can be applied to any industrial application involving the use of at least one burner utilizing oscillating combustion, but is more especially suited for industrial boilers and process heaters utilizing oscillating combustion. Suitable oscillating combustion industrial boiler processes to which this invention may be applied include those described in published U.S. Patent application 2003/0134241 and U.S. Pat. No. 6,913,457. Suitable types of industrial boilers include both firetube, and watertube. Such firetube and watertube boilers are well known to those skilled in the art and need not be described herein. [0026] As best illustrated in FIG. 1, an embodiment of the invention is a system 50 for performing oscillating combustion. Fuel flows from fuel supply 23 flows first to fuel flow rate control unit 27, then to oscillating valve 33 where the flow is pulsed to achieve an oscillating flow, and then to burner 1. The main oxidant flows from main oxidant supply 25 to main oxidant flow rate control unit 29 for controlling the flow rate of the main oxidant, then to burner 1, where combustion of the fuel and main oxidant is initiated. Oscillating combustion of the fuel and main oxidant continues at flame 3 within oscillating combustion space 2 enclosed by inner wall 5. [0027] Fuel flow rate control unit 27 is typically a valve that is operable manually and/or automatically. Fuel flow rate control unit 27 may also be one of any number of well-known to one of ordinary skill in the art for controlling a fuel flow rate in a combustion process, especially for boilers. [0028] The main oxidant flow rate is controlled by a main oxidant flow rate control unit 29. The main oxidant flow rate control unit 29 may be any one of a number of devices well known to one of ordinary skill in the art for combustion processes, especially for boilers. Two typical devices include dampers and variable speed fans. [0029] Post-combustion oxidant from post-combustion oxidant supply 37 is injected through post-combustion oxidant flow rate control unit 39 into post-combustion space 4 enclosed by inner wall 5. In post-combustion space 4, combustion products from the combustion of the fuel and main oxidant at flame 3 within oscillating combustion space 2 are themselves combusted with the post-combustion oxidant to produce flue gas 11. Preferably, staggered baffles or a swirler are disposed within inner walls to enhance mixing of the post-combustion oxidant and the combustion products from the combustion of the fuel and main oxidant. Details regarding these baffles and swirler may be found in U.S. Pat. No. 6,913,457. Continue reading... Full patent description for Advanced control system for enhanced operation of oscillating combustion in combustors Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Advanced control system for enhanced operation of oscillating combustion in combustors patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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