Combustion boiler control method, combustion boiler, and boiler computation system

Abstract

A combustion boiler control method includes steps of (a) monitoring the current load of a combustion boiler, (b) finding a numerical value for a current computational maximum boiler momentary load for which at least one flue gas factor computed using currently monitored process data with a numerical model of the boiler fulfills an acceptance condition, and selecting the numerical value as the current computational maximum boiler momentary load, (c) indicating the current computational maximum boiler momentary load to an operator and/or, if the current load is (c1) less than the current computational maximum boiler momentary load, (c1i) indicating to the operator that the boiler load may be increased, and/or (c1ii) automatically increasing the boiler load, and/or (c2) greater than the current computational maximum boiler momentary load, (c2i) indicating to the operator that the boiler load exceeds the current computational maximum boiler momentary load, and/or (c2ii) automatically reducing the boiler load.

1 .- 27 . (canceled) 
     
     
         28 . A combustion boiler control method comprising the steps of:
 (a) monitoring a current load (Q h ) of a combustion boiler;   (b) finding such a numerical value (Q h, candidate ) for a current computational maximum boiler momentary load (Q h, max ) for which at least one flue gas factor (df i ) computed using currently monitored process data with a numerical model of the boiler fulfills an acceptance condition, and selecting the numerical value (Q h, candidate ) as the current computational maximum boiler momentary load (Q h,max );   (c) indicating the current computational maximum boiler momentary load (Q h,max ) to a boiler operator and/or, if the current load (Q h ) is
 (c1) less than the current computational maximum boiler momentary load (Q h,max ):
 (c1i) indicating to the boiler operator that the boiler load (Q h ) may be increased; and/or 
 (c1ii) automatically increasing the boiler load (Q h ); and/or 
 
 (c2) greater than the current computational maximum boiler momentary load (Q h,max ):
 (c2i) indicating to the boiler operator that the boiler load (Q h ) exceeds the current computational maximum boiler momentary load; and/or 
 (c2ii) automatically reducing the boiler load (Q h ). 
 
   
     
     
         29 . The method according to  claim 28 , wherein:
 (i) the currently monitored process data of the boiler includes:
 (ia) current flue gas exit temperature (T flue gas,exit,current ) in a flue gas flow channel; and 
 (ib) heat duty (Q fluid,i ) for each heat transfer surface in the flue gas flow channel, 
   and further wherein:   (ii) monitored process data from both (ia) and (ib) is used in computation of the flue gas factor and when finding the numerical value (Q h, candidate ) for the current computational maximum boiler momentary load (Q h,max ).   
     
     
         30 . The method according to  claim 28 , wherein the finding is performed such that, if the at least one flue gas factor (df i ) computed using currently monitored process data with a numerical model of the boiler that fulfills an acceptance condition for the numerical value (Q h, candidate ) for the current computational maximum boiler momentary load (Q h,max ) fails to fulfill an acceptance condition, a next numerical value (Q h, candidate ) is automatically selected. 
     
     
         31 . The method according to  claim 30 , wherein the next numerical value (Q h, candidate ) is selected iteratively. 
     
     
         32 . The method according to  claim 28 , wherein the finding is carried out by performing the computational steps of:
 (I) computing an estimate for boiler flue gas exit temperature (T boiler, exit ) that results in a computational boiler model when the thermal load of the boiler corresponds to the numerical value (Q h, candidate );   (II) computing flue gas mass flow (q m,fluegas );   (III) computing a heat duty (Q fluid, i, candidate ) for each heat transfer surface in the flue gas flow channel with its current heat duty (Q fluid, i, current ) that is corrected by using a numerical boiler model (Q fluid, i, candidate =Q fluid,i,current +S a j,I (Q steam,max ) j −S a j,i (Q steam,current ) j );   (IV) using the computed heat duties (Q fluid, i, candidate ) for each heat transfer surface in the flue gas flow channel to compute flue gas temperatures at each heat transfer surface (T fluegas,in,i , T fluegas,out,i ; i=1, . . . , k) in the flue gas flow channel in the upstream direction of flue gas flow, starting from the heat transfer surface  21   k  that is closest to the flue gas exit using the estimate for the boiler flue gas exit temperature (T fluegas,out,k =T FG, exit ); and   (V) computing a flue gas factor (df i , i=1, . . . , k) for each heat transfer surface in the flue gas flow channel.   
     
     
         33 . The method according to  claim 32 , wherein the flue gas factor includes or is: 
       
         
           
             
               
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         where k i  is a non-zero parameter that may be chosen combustion-boiler specifically, 
         q m,fluegas  is flue gas mass flow, and 
         n is a model parameter that may be chosen combustion-boiler specifically, ρ fluegas,i  is flue gas density at an i th  heat transfer surface and A is a cross section of flue gas channel at the i th  heat transfer surface. 
       
     
     
         34 . The method according to  claim 33 , wherein n is selected to include at least one of the following:
 (i) in the range of 0.9 to 1.1, for using computed flue gas velocity;   (ii) in the range of 2.9 to 3.5, for using computed flue gas caused erosion; or   (iii) in the range of 1.8 to 2.2, for using pressure loss.   
     
     
         35 . The method according to  claim 34 , wherein the value for n is changed over time. 
     
     
         36 . The method according to  claim 34 , wherein the value for n is determined from a group of boilers comprising at least two separate boilers using operational data monitored for each of the boilers. 
     
     
         37 . The method according to  claim 32 , wherein, in the computation in step (I), the flue gas exit temperature is substantially estimated by an equation: 
       
         
           
             
               
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         or its first, second, third, or higher degree approximation, and wherein the respective coefficients (a 0 , a 1 , a 2 , . . . ) have been obtained beforehand by fitting, after measuring flue gas exit temperature (T FG, exit ) values for a number of discrete boiler load (Q steam ) values. 
       
     
     
         38 . The method according to  claim 32 , wherein, in step (II), computation of flue gas mass flow utilizes mass flow (q m,fluegas,m ) of flue gas components, wherein the components include CO 2 , H 2 O, N 2 , SO 2 , and O 2 . 
     
     
         39 . The method according to  claim 32 , wherein, in step (II), the computation of flue gas mass flow includes fuel parameters. 
     
     
         40 . The method according to  claim 28 , wherein the step (b) is performed remotely from the combustion boiler. 
     
     
         41 . The method according to  claim 28 , wherein the step (b) is performed locally at the combustion boiler. 
     
     
         42 . The method according to  claim 28 , wherein any of the currently monitored process data and/or current load is obtained from real-time measurements, treated by filtering, treated by averaging, computing trends, or any combination of these. 
     
     
         43 . The method according to  claim 28 , wherein the acceptance condition includes a hysteresis condition, requiring a predefined minimum change before changing the current computational maximum boiler momentary load (Q h,max ). 
     
     
         44 . The method according to  claim 28 , wherein the acceptance condition includes comparing the computed at least one flue gas factor (df i ) against a respective design value, and wherein, in the method, the numerical value (Q h, candidate ) is rejected if the design value is exceeded. 
     
     
         45 . The method according to  claim 28 , wherein the combustion boiler is a circulating fluidized bed (CFB) or a bubbling fluidized bed (BFB) boiler, and the step (b) is carried out for the combustion boiler heat transfer surfaces, between the furnace and the stack, optionally, including the furnace. 
     
     
         46 . A combustion boiler comprising:
 a furnace and associated passes defining a flue gas flow path and having a number of heat transfer surfaces that are located in the flue flow path;   measurement instrumentation to monitor current load (Q h ) of the combustion boiler;   further, measurement instrumentation, such as sensors, to currently monitor process data; and   a control system configured to carry out the combustion boiler control method according to  claim 28 .   
     
     
         47 . The combustion boiler according to  claim 46 , wherein the control system comprises an edge server that is configured to process real-time measurement results for currently monitored process data and/or current load, namely, by filtering, averaging, and/or computing trends. 
     
     
         48 . The combustion boiler according to  claim 46 , wherein the control system is configured to carry out the method step (b) to determine the current computational maximum boiler momentary load (Q h,max ) locally. 
     
     
         49 . The combustion boiler according to  claim 46 , wherein the control system is configured to send data to a remote computing system that is configured to carry out the method step (b) and to return the current computational maximum boiler momentary load (Q h,max ) to the control system. 
     
     
         50 . The combustion boiler according to  claim 49 , further comprising an edge server that is configured to reduce an amount of measurement data that is passed to the remote computing system. 
     
     
         51 . A combustion boiler computation system comprising:
 a group of combustion boilers comprising at least two separate combustion boilers according to  claim 46 , each boiler comprising a boiler control system comprising an edge server system that is configured to process the real-time measurement results for currently monitored process data and/or current load, namely, by filtering, averaging, and/or computing trends, and to send the processed real-time measurement results to a remote computing system;   a remote computing system configured to receive data processed from real-time measurement results and to compute data using a numerical boiler model for each of the combustion boilers, and to return computation results for each of the combustion boilers,   wherein the control system is configured to adapt its function based on the computation results, and the computing system is configured to find such a numerical value (Q h, candidate ) for a current computational maximum boiler momentary load (Q h,max ) for which at least one flue gas factor (df i ) computed using currently monitored process data with a numerical model of the boiler that fulfills an acceptance condition, and selecting the numerical value (Q h, candidate ) as the current computational maximum boiler momentary load (Q h,max ).   
     
     
         52 . The combustion boiler computation system according to  claim 51 , wherein the combustion boiler computation system is configured to adapt or to calibrate a numerical model for a combustion boiler using processed measurement data for the combustion boiler. 
     
     
         53 . The boiler computation system according to  claim 51 , wherein the boiler computation system is configured to adapt or to calibrate a numerical model for a combustion boiler using processed measurement data also collected from other combustion boilers.