Patent Application
20100049561
The present disclosure relates generally to the optimization of a fluidized bed combustion process and, more particularly, a tool and a method for analyzing and optimizing a fluidized bed combustion process using design of experiments, neural network modeling and optimization techniques.
Fluidized bed combustion (FBC) is a combustion technology used in power plants primarily to burn solid fuels. FBC power plants are more flexible than conventional power plants in that they can be fired on coal, coal waste or biomass, among other fuels. The term FBC covers a range of fluidized bed processes, including circulating fluidized bed (CFB) boilers, bubbling fluidized bed (BFB) boilers and other variations thereof. Fluidized beds suspend solid fuels on upward-blowing jets of air during the combustion process, resulting in turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides a means for more effective chemical reactions and heat transfer.
Fluidized-bed boilers evolved from efforts to find a combustion process able to control pollutant emissions without external emission controls (such as scrubbers). During the combustion process of fuels which have a sulfur-containing constituent, e.g., coal, sulfur is oxidized to form primarily gaseous SO2. In particular, FBC reduces the amount of sulfur emitted in the form of SO2 by a desulfurization process. A suitable sorbent, such as limestone containing CaCO3, for example, is used to absorb SO2 from flue gas during the combustion process. In order to promote both combustion of the fuel and the capture of sulfur, FBC power plants operate at temperatures lower than conventional combustion power plants. Specifically, FBC power plants typically operate in a range between about 850° C. and about 900° C. Since this allows coal to combust at cooler temperatures, NOx production during combustion is lower than in other coal combustion processes.
Boiler systems of FBC power plants are generally associated with limestone feed systems for sulfur capture. Processed limestone fed to a boiler is typically conditioned by means of size reduction machines to specific size ranges to allow for the desulfurization process to proceed efficiently.
An air system in an FBC power plant is designed to perform many functions. For example, air is used to fluidize the bed solids consisting of fuel, fuel ash and sorbent, and to sufficiently mix the bed solids with air to promote combustion, heat transfer and control (reduction) of emissions (e.g., SO2, CO, NOx and N2O). In order to accomplish these functions, the air system is configured to inject air, generally defined as either primary air (PA) or secondary air (SA), at various locations and at specific velocities and quantities.
A distributed control system (DCS) is generally used to control the processes described above in an FBC power plant, based upon operator input. To this end, an operator adjusts FBC system parameters in an attempt to maintain optimal operating conditions. For example, the operator adjusts the FBC system parameters in order to maximize combustion of the fuel with minimal SO2 emissions. While the operator may have significant experience working with a given FBC power plant, it is difficult to provide the operator with practical tools to assess interplay and/or tradeoffs between numerous operating parameters. Further, the FBC process involves interactions between many variables, as described above, some of which can be manipulated or controlled, and others which cannot be manipulated or controlled. In addition, many of the variables in the FBC process are nonlinear and/or have complex relationships with other variables. As a result, models which effectively simulate these multi-interdependent variable relationships have thus far been inaccurate, inefficient and difficult and/or time consuming to work with.
Therefore, most FBC power plants currently use testing based on a trial and error approach in attempting to determine optimum plant operating conditions. The results of such testing depend significantly on the experience level of personnel performing the tests, among other things. Furthermore, testing time is generally restricted, since changing plant conditions to perform the tests may have undesired affects on plant operations, such as increasing SO2 emissions and/or reducing combustion efficiency of the fuel. As a result of the limited testing time, the trial and error approach normally does not include sufficient variations in plant parameters to obtain statistically significant results. Accordingly, these empirical diagnostic determinations based upon the trial and error approach are generally inaccurate.
Although some offline optimization tools have been developed, these are focused on optimizing conventional combustion power plants. Furthermore, these optimization tools have been focused on solving very specific, localized optimization problems rather than global optimization of plant operations. Thus, a more systematic approach, e.g., an approach utilizing design of experiments (DOE), has been suggested to provide broader results. However, the associated statistical analysis for conventional combustion power plants is based upon an assumption of linear relationships between variables. As a result, the associated statistical analysis for conventional combustion power plants is inaccurate when used to analyze the complex, nonlinear dynamics of an FBC process.
Neural network (NN) modeling has also been used for conventional power plants such as pulverized coal combustion power plants, but implementing NN modeling for an FBC power plant has thus far required a prohibitive amount of time and effort. This is primarily due to a need to collect a statistically significant amount of test data to develop a validated NN model for the more complex process dynamics associated with the FBC power plant.
Accordingly, it is desired to develop an FBC power plant optimization tool which overcomes the problems described above.
According to the aspects illustrated herein, there is provided a device for optimizing a modeled fluidized bed combustion power plant. The device includes a model of a fluidized bed combustion system and an optimizer. The model of the fluidized bed combustion system provides at least one simulated output parameter of the fluidized bed combustion power plant in response to a user selected parameter of the fluidized bed combustion power plant. The optimizer provides at least one optimized simulated output parameter of the fluidized bed combustion power plant in response to at least one user selected optimization setting and the at least one simulated output parameter.
According to the other aspects illustrated herein, a method for optimizing a modeled fluidized bed combustion power plant includes: receiving user selected parameters of the fluidized bed combustion power plant; receiving at least one user selected optimization setting; providing at least one simulated output parameter of the fluidized bed combustion power plant using a model of a fluidized bed combustion system in response to a user selected parameter of the fluidized bed combustion power plant; optimizing at least one optimized simulated output parameter of the fluidized bed combustion power plant in response to the at least one user selected optimization setting and the at least one simulated output parameter; and providing the at least one optimized simulated output parameter of the fluidized bed combustion power plant to a user.
According to still other aspects illustrated herein, an optimization tool for optimizing a fluidized bed combustion process includes a model, a genetic algorithm optimizer, a prediction module, a sensitivity analysis module, an optimization module, a user interface including one or more of symbols, images and icons, an input interface which inputs input data to the model, and an output interface which outputs processed data from at least one of the prediction module, the sensitivity analysis module and the optimization module. The input data includes at least one of fuel flow, limestone flow, primary air flow, secondary air flow, secondary air head pressure, combustor differential pressure, load demand, fuel property, ambient temperature, bed temperature, oxygen level, fly ash reinjection rate, historical test data, design test data, heat rate, loss on ignition, CO2 capture cost, CO2 processing cost, CO2 transportation cost, CO2 storage cost, CO level, NOx level, NOx trade price, NOx trade price (in ozone season), SOx level, SOx trade price, fuel cost, fuel flow, limestone cost, limestone flow, ash disposal cost and ash flow.
The above described and other features are exemplified by the following figures and detailed description.
Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:
Disclosed herein is an optimization tool or device 100 for analysis, simulation and optimization of the combustion process of a modeled fluidized bed combustion (FBC) power plant. The optimization tool provides design and installation personnel (performance and commissioning staff) and external customers (power plant engineers and managers) with a user-friendly methodology and software tool for off-line evaluation and optimization, economic analysis and decision support for production management. The tool is helpful to obtain insights into the process behavior through simulation and sensitivity analysis.
Referring to
In an exemplary embodiment, the FBC furnace 16 is a circulating fluidized bed (CFB) boiler or a bubbling fluidized bed (BFB) boiler. Further, the FBC power plant 10 according to an exemplary embodiment is not limited to the components shown in
An optimization tool 100 for the FBC power plant 10 will now be described in further detail with reference to
As shown in
Furthermore, one skilled in the art would appreciate that the other modeled plant parameters 120 may be used, including parameters associated with an air pollution control (APC) system, a flash dryer absorber (FDA), a spray dryer absorber (SDA), a flue gas desulfurization (FGD) system and/or an electrostatic precipitator (ESP). The sensitivity analysis settings 124 include a range of parameters for one or more selected modeled plant parameters 120, which will be described in greater detail hereinafter.
The NN model 112 processes the modeled plant parameters 120 according to predetermined historical and design data, discussed in greater detail below, and provides the output data to a pre-optimized plant output analyzer 128. The pre-optimized plant output analyzer also receives economic parameters 122 to provide a prediction of the FBC process input and/or output parameters, which will be described in greater detail hereinafter. The output data includes, for example, predicted coal feed rate, NOx output, limestone feed rate, and economic cost, as well as input parameters of the modeled plant. The economic parameters 122 include, for example, fuel and limestone costs, as well as heat rate, loss on ignition, CO2 capture cost, CO2 processing cost, CO2 transportation cost, CO2 storage cost, CO level, NOx level, NOx trade price, NOx trade price (in ozone season), SOx level, SOx trade price, ash disposal cost and ash flow may also be inputted as trial plant parameters 200, but are not limited to the foregoing.
The NN model 112 further processes the sensitivity analysis settings 124, which define a range of selected modeled plant parameters 120. The NN model 112 provides associated predicted plant output parameters over the range of the sensitivity settings 124 to a parameter sensitivity analyzer 130. The economic parameters 122 may also be provided to the parameter sensitivity analyzer 130. In response to the range of predicted plant output parameters and the economic parameters 122, the parameter sensitivity analyzer 130 provides a predicted output indicative of the sensitivity of the plant to changes of the selected plant input parameters over the selected range(s), and also an output of the sensitivity of the economic cost of operating and/or performance of the modeled FBC plant to changes in the selected modeled plant parameters 120, which will be described in greater detail hereinafter.
The NN model 112 further interfaces with the optimizer 114 that provides an output indicative of values for one or more modeled plant parameters 120 to optimally operate the modeled FBC plant in accordance with the optimizations settings 126 inputted into the optimizer 114. Additionally, the economic parameters 122 may be provided to determine the cost of operating the optimized system. The optimization settings 126 include constraints of the modeled plant input and/or output parameters 120 and/or economic parameters 122.
The optimizer 114 uses a global heuristic search algorithm, described in greater detail below, to determine output optimized plant parameters provided by a plant optimization output module 132. The optimized plant parameters may then be used or applied to the FBC power plant 10 to optimize the operation and performance of the power plant. In an exemplary embodiment, the optimization tool 100 is used as a stand alone device to analyze the operation of the modeled plant, simulate the operation and performance of the modeled plant under different plant parameters 120, and/or optimize the operation and performance of the modeled plant. More specifically, the optimization tool 100 is not connected to the FBC power plant 10. As a result, sensitivity and/or economic analysis may be performed without affecting operation of the FBC power plant 10. The optimized plant parameters determined offline may, however, be subsequently manually implemented by an operator of the FBC power plant 10, either manually or by electronic communication between the optimization tool 100 and the FBC plant 10.
As shown in
Based upon the modeled plant parameters 120 which are inputted to the NN model 112, the optimized plant parameters are determined by the NN model 112 and the optimizer 114. The optimized plant parameters provided by the plant optimization output module 132 include oxygen level, fuel flow and/or limestone flow, but are not limited thereto. The optimized plant parameters may be used to operate the FBC power plant 10 such that limestone and fuel are utilized most efficiently, while emissions are minimized, thereby improving operational and/or economic efficiency of the FBC power plant 10.
Referring to the cost functions fcost1, fcost2 and fcost3 shown in
Expanding this concept and referring again to
In general, a neural network includes a group of nodes, or processing elements, interconnected to form a network. A mathematical algorithm is used to determine interactions between the nodes as a signal travels from an input node or nodes, “through” the network and on to an output node or nodes. Further, the algorithm may, over time, alter a preference for interactions between the nodes. As a result, the neural network is effectively an adaptive model. Thus, the neural network adaptively models complex relationships between inputs and outputs.
Likewise, the NN model 112 of the optimization tool 100 is a multivariate, nonlinear model. More specifically, the NN model 112 uses process data, e.g., the modeled plant parameters 120, to develop an input-output model capable of analyzing a multiple-variable process wherein relationships between variables are complex and nonlinear. Further, the input-output model developed by the NN model 112 is adaptive, as described above, and is therefore based upon learning as opposed to first principles such as explicit equations. As a result, the NN model 112 has a reduced complexity in comparison to conventional analytical models. Consequently, the complex, nonlinear process dynamics of the FBC power plant 10 can be sufficiently analyzed and modeled more effectively, with a reduced demand for testing resources to obtain empirical FBC process data. In addition, the NN model 112 can be easily adapted for other FBC power plants by re-training the NN model 112 for the other FBC power plants.
Historical plant data is used to develop the NN model 112. The NN model is further developed with designed test data obtained using design of experiments (DOE) methodology. In DOE, various effects of factors in a process, as well as interactions of the factors themselves, are efficiently analyzed. This is accomplished by selecting varying input combinations and measuring the output effects of the selected input combinations. Using DOE ensures that sufficient variations in test data are obtained to achieve accurate optimization by the optimizer 114 of data modeled by the NN model 112. At the same time, requirements for physical testing, e.g., trial and error type testing, are substantially reduced or effectively minimized. Therefore, empirical data sufficient to accurately develop the NN model 112 is obtained more efficiently and with minimal variation in operation or down time of the FBC power plant 10.
Still referring to
In alternative exemplary embodiments, the optimizer 114 maybe a global optimization algorithm optimizer which utilizes any global optimization algorithm or method using stochastic and/or deterministic and/or heuristic search mechanisms, but is not limited thereto.
As discussed hereinbefore, the optimization tool 100 is implemented in a spreadsheet software 110 such as EXCEL®, as illustrated in
Referring to
For example, the user may manipulate various modeled plant parameters 120 (e.g., input and output plant parameters and economic parameters) to determine and analyze the effect of the changes to the resulting predicted output parameters of the modeled plant. The tool 100 enables a user to vary or tune the plant parameters 120 to provide the desired output parameters.
The sensitivity module 144 allows the operator to analyze an affect of changing one or more modeled plant parameters 120 on the pre-optimized plant output parameters of the pre-optimized plant output analyzer 128 and/or the optimized plant parameters. More specifically, the operator varies one or more of the modeled plant parameters 120 to determine a relative affect that the variation has on the pre-optimized plant parameters of the prediction module 142 and or the optimized plant parameters of the optimization module 146. The affect of the variation is displayed as a sensitivity analysis output (not shown). Therefore, the operator is able to obtain insight into relationships between specific variables associated with the modeled FBC power plant.
The operator controls operation and settings of the sensitivity module 144 by adjusting the sensitivity analysis settings 124. More specifically, in an exemplary embodiment the operator adjusts the sensitivity analysis settings 124 such that a sensitivity of at least one pre-optimized modeled plant parameter 120 and/or at least one optimized plant parameter of the plant optimization output is determined based upon a variation of one of the modeled plant parameters 120, while all other modeled plant parameters 120 are held constant. In this case, a sensitivity report (not shown) is generated. The sensitivity report includes a sensitivity output worksheet having the sensitivity analysis output, as well as a sensitivity curve worksheet having plots and/or curves of the sensitivity analysis output.
In an alternative exemplary embodiment, the operator adjusts the sensitivity analysis settings 124 to determine relative sensitivities of one pre-optimized modeled plant parameter 120 or one optimized plant parameter and a single modeled plant parameter 120 while the other modeled plant parameters 120 are held constant. In this case, the sensitivity report (not shown) includes a sensitivity focus worksheet and a sensitivity rank worksheet. The focus worksheet and the sensitivity rank worksheet illustrate outputs such as average absolute sensitivity, average sensitivity and peak sensitivity of the one pre-optimized plant parameter or one optimized plant parameter and the single modeled plant parameter 120, for example, but are not limited thereto.
The optimization module 146 optimizes the modeled plant parameters 120 inputted to the NN model 112 to output the optimized plant parameters in accordance with operator-adjusted optimization settings 126. Subsequently, the operator may apply the optimized plant output to a FBC power plant 10, resulting in optimization of the plant. Alternatively, the optimized plant output may be provided directly, e.g., automatically, to the FBC power plant 10 from the optimization module 146. As a result, the plant output characteristics are optimized without requiring the operator to manually apply the optimized plant parameters to the FBC power plant 10.
In an exemplary embodiment, the prediction model 142, the sensitivity analysis module 144 and/or the optimization module 146 includes an economic cost model (not shown). The economic cost model may be a separate component or integral to the prediction model 142, the sensitivity analysis module 144 and/or the optimization module 146. Further, the economic cost model optimizes the predicted pre-optimized plant parameters of the prediction module 142 to determine economically-optimal optimized plant parameters for a given operating condition such as an ozone season operating mode or a non-ozone season operating mode, for example, of the FBC power plant 10.
For example, the user may select for a desired optimization simulation scenario certain input variables that may be manipulated and other input variables may be fixed or otherwise clamped to their original values. Such manipulated variables may include primary air flow rate (PA_Flow), oxygen level (O2_Level), lower bed temperature (Low Bed Temp), secondary air head pressure (SA Head Pressure), furnace differential or steady pressure (Combustor DP), limestone feed percentage (Perc_of_LS Feed A), and coal feed percentage (Perc_of_Coal Feed B). Such fixed variables may include mass weight demand (MW_DMD), process steam flow (PS_Flow), ambient temperature (Ambient Temp), bar pressure (Bar Pressure), crusher number (Crusher_Num), and fly ash reinjection state (Fly_Ash_Reinj_ON). The output parameters may include the coal feed rate, limestone feed rate and amount of NOx. The tool enabling the user to select the input variables to be used in the simulation, and which of the input variables are fixed or manipulated.
In addition to the components described in further detail above, the optimization tool 100 according to an exemplary embodiment further includes or is utilized with computer hardware and/or software components or systems, including a processor, storage medium, video display, keyboard, mouse, and memory, for example, but alternative exemplary embodiments are not limited thereto.
In summary, the optimization tool 100 according to an exemplary embodiment utilizes DOE and nonlinear NN concepts to optimize operating parameters of a modeled FBC power plant. More specifically, by utilizing a systematic approach to test design, data processing, problem diagnosis and combustion performance optimization, the optimization tool 100 integrates the advantages of NN modeling and DOE techniques to determine global optimization of complex, multivariate nonlinear parameters with a minimized demand for testing resources. Thus, sufficient variations in plant parameters are measured and/or tested to provide an accurate model of FBC power plant processes while minimizing testing costs.
Further, the optimization tool 100 allows users to select different values of process model input variables to generate performance predictions for pre-defined modeled plant parameters 120. The predictions can be used to compute economic cost savings based on unit-specific prices (e.g., fuel price, limestone price, extra processing costs, NOx trade price, SO2 trade price, etc.). The optimization tool 100 also generates process input/output sensitivity curves or data to help the user obtain insights into the relations between the input variables and the output performance variables. The tool also allows users to perform batch prediction “what-if” simulations by defining a “test matrix” with multiple changes to those inputs of the user's particular interests to generate a series of performance prediction values and economic numbers and curves. With such information, a user will be able to more easily select an optimal operating condition and perform better production management of a FBC power plant.
Using the optimization tool 100, engineers, operators and managers can easily perform advanced optimization tasks which normally require specialized knowledge, tools and training by using a simple spreadsheet software application.
Further, the NN model 112 of the optimization tool 100 uses a genetic algorithm which does not require explicit equations, thus providing the advantages of simplicity and flexibility of implementing the model for additional FBC power plants without extensive re-testing as would be required for other models which require explicit equations.
One will appreciate that the optimization tool 100 can predict and optimize input and/or output parameters of the modeled plant parameters 120.
It will be further appreciated that, while exemplary embodiments described herein have made reference to neural network models, alternative exemplary embodiments are not limited thereto. For example, alternative exemplary embodiments may include, but are not limited to, an empirical model (to include a multivariate nonlinear neural network model), a physical model (to include a first principle model), and/or a combination of an empirical model and a physical model.
While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
