| Method and apparatus for improving steam temperature control -> Monitor Keywords |
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Method and apparatus for improving steam temperature controlRelated Patent Categories: Electric Heating, Heating Devices, With Power Supply And Voltage Or Current Regulation Or Current Control Means, Automatic Regulating Or Control Means, Comprising Voltage And/or Current Measuring And Comparing Or Combining MeansMethod and apparatus for improving steam temperature control description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060191896, Method and apparatus for improving steam temperature control. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] This patent relates generally to computer software, and more particularly to computer software used in electric power generation systems. BACKGROUND [0002] Electric power plants generate electricity using various types of power generators, which may be categorized, depending on the energy used to generate electricity, into thermal, nuclear, wind, hydroelectric, etc., generators. Each of these various types of generators operates under different sets of constraints. For example, an output of a thermal generator is a function of the amount of heat generated in a boiler, wherein the amount of heat is determined by the amount of fuel that can be burned per hour, etc. Additionally, the output of the thermal generator may also be dependent upon the heat transfer efficiency of the boiler used to burn the fuel. Similar types of constraints exist with other types of electric power plants. Moreover, for most power plants using boilers, the desired steam temperature set-points at final superheater and reheater outlets are constant and it is necessary to maintain steam temperature close to the set-points within a narrow range at all load levels. [0003] Fuel burning electric power generators operate by burning fuel to generate steam from water traveling through a number of pipes and tubes in the boiler. The steam is used to generate electricity in one or more turbines. However, burning of certain types of fuel, such as coal, oil, waste material, etc., also generates a substantial amount of soot, slag, ash and other deposits ("soot") on various surfaces in the boilers, including the inner walls of the boiler as well as on the exterior walls of the tubes carrying the water through the boiler. The soot deposited in the boiler has various deleterious effects on the rate of heat transfer from the boiler to the water and thus on the efficiency of power generators using the boilers. Therefore, it is necessary to address the problem of soot in fuel burning power plants that burn coal, oil, and other such fuels that generate soot. It should be noted that while not all fuel burning power plants generate soot, for the remainder of this patent the term "fuel burning power plants" is used to refer to those power plants that generate soot. [0004] Various solutions are used to address the problems caused by generation and presence of soot deposits in boilers of fuel burning power plants. For example, fuel burning power plants use soot removing devices or equipment known as soot blowers as part of operating boilers. Fuel burning power plants use various types of soot blowers to spray cleaning materials through nozzles, which are located on the gas side of the boiler walls and/or on other heat exchange surfaces. Such soot blowers use any of the various media such as saturated steam, superheated steam, compressed air, water, etc., for removing soot from the boilers. [0005] However, soot blowing activity affects many aspects of boiler operations. For example, soot blowing affects heat transfer efficiency, steam temperature control, levels of NO.sub.x inside the boilers, etc. For example, soot blowing in a water wall section of a boiler increases heat absorption rate in the water wall section, which reduces the temperature of the flue gas leaving the furnace section of the boiler. As a result, the flue gases entering the convection section may have a lower temperature, resulting in lower heat absorption in a superheat section and a reheat section of the boiler, and therefore, reducing the steam temperature in these sections as well. On the other hand, soot blowing in the convection section of a boiler increases the heat absorption rate, resulting in increased steam temperature. [0006] Various qualitative effects of soot blowing are well known. However, it is difficult to determine precise quantitative impact of soot blowing on the efficiency and steam temperature of fuel burning power plants. Compensation techniques used by existing control systems include using a feedback PID controller that modulates at least one of spray flow levels, burner tilts, and flue gas bypass dampers, to compensate for the effect of soot blowing. However, often such feedback compensation action is reactionary and it may cause significant steam temperature swings. Therefore, it is necessary to develop a systematic method of constructing a feed-forward signal to compensate for the impacts of soot blowing. [0007] In today's competitive electrical utility industry where utilities use various sophisticated control systems to manage operating costs and increase efficiency of power generators, it is important to understand the effects of operating soot blowers so that operators and control systems may make informed decisions about how to compensate for the disturbances caused by soot blowing. Thus, there is a need to provide better quantitative information about the impact of soot blowing so that any adverse or negative impact of soot blowing can be compensated for more effectively. BRIEF DESCRIPTION OF THE DRAWINGS [0008] The present patent is illustrated by way of examples and not limitations in the accompanying figures, in which like references indicate similar elements, and in which: [0009] FIG. 1 illustrates a block diagram of a power distribution system; [0010] FIG. 2 illustrates a block diagram of a boiler used in a fuel burning power plant; [0011] FIG. 3 illustrates a flowchart of a soot blowing analysis program used by the boiler of FIG. 2; [0012] FIG. 4 illustrates a block diagram of a reheat (or superheat) section of the boiler of FIG. 2; [0013] FIG. 5 illustrates a graph showing an operation of the soot blowers of FIG. 4; [0014] FIG. 6 illustrates a time diagram of a feed-forward signal to be applied to spray controls used by the boiler of FIG. 4; and [0015] FIG. 7 illustrates a flow chart of an evaluation program for determining whether a soot blowing sequence is a steam temperature influencing sequence or not. DETAILED DESCRIPTION OF THE EXAMPLES [0016] A system for analyzing the impact of operating soot blowers in a heat transfer section of a power plant determines a steam temperature influencing sequence and calculates a feed-forward signal to be applied to a steam temperature control system of the heat transfer section. The system operates a group of soot blowers a number of times and collects quantitative data related to the steam temperature during and after each soot blowing operation. A computer program used by the system analyzes the quantitative data, generates a number of statistical parameters for evaluating the impact of operating the soot blowers according to a given sequence on the steam temperature, and determines whether the given sequence is a steam temperature influencing sequence. Consequently, the system determines a feed-forward signal based on the steam temperature influencing sequence and applies the feed-forward signal to a steam temperature control system used by the heat transfer section to compensate for any adverse impact of soot blowing. Following figures describe an implementation of this system in a coal or oil burning power plant. [0017] FIG. 1 illustrates a power distribution system 10, including a power grid 12 that may be connected to a load grid 14 and one or more utility grids 16, 18. The utility grid 16 is connected to a second power grid 20, and the utility grid 18 is illustrated as being formed of one or more power plants 22-26, which may include any of the various types of power plants such as nuclear power plants, hydroelectric power plants, thermal power plants, etc. Additionally, each of the power plants 22-26 may include any number of individual power generators. [0018] Operation of the utility grid 18 and the power plants 22-26 can be highly complex. As a result, to maintain the utility grid 18 running smoothly, it is necessary that each of the power plants 22-26 is managed with very high precision and in a highly predictable manner. To ensure that each of the power plants 22-26 can efficiently meet the power load required from them most efficiently, the power plants 22-26 use various control systems to ensure efficient operation throughout various sections of each of the power plants 22-26. [0019] For example, fuel burning power plants that use coal, oil, gas or other fuels to produce electricity use control systems to ensure the quality and quantity of the fuel injected into the furnaces, to ensure that the steam flow through various boilers is at optimum levels, etc. Typically, fuel burning power plants have one or more boilers where superheated steam is created by passing water through a series of tubes located inside the boiler. The superheated steam then enters a steam turbine where it powers the turbine and a generator connected to the turbine to produce electricity. [0020] As noted above, soot, ash and other deposits that settle on the walls of the water carrying tubes result in reduction of heat transferred from the burning of fuel to the water and steam traveling through the tubes. To ensure that maximum heat is transferred to the water and steam passing through the boiler tubes, boiler walls and tubes are provided with soot blowers that routinely blow soot deposited on the tubes. Continue reading about Method and apparatus for improving steam temperature control... 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