Gas processing unit and method of operating the same

Abstract

A plant ( 1 ) and a gas processing unit (GPU) ( 17 ) of the plant can be configured to operate in accordance with a method that is configured to permit the GPU ( 17 ) to operate such that the optimum operating point for the GPU ( 17 ) at steady state to produce liquid carbon dioxide product from a separation unit ( 117 ) of the GPU ( 17 ) for sending to a storage device ( 19 ) is achieved with a desired purity level while simultaneously maintaining a required minimum carbon capture rate with the minimum consumption of power and/or minimum economic cost associated with operations of the GPU ( 17 ). A controller ( 23 ) can be configured to communicate with elements of the GPU ( 17 ) to receive parameter values to calculate manipulated variables configured to bias set points for parameters used to control operations of different elements of the GPU ( 17 ).

What is claimed is: 
     
         1 . A method of operating a plant having a gas processing unit (GPU), comprising:
 determining parameter values associated with operations of the GPU;   utilizing the parameter values associated with the operations of the GPU to determine biasing values for biasing set points used to control operations of elements of the GPU; and   sending the biasing values for adjusting the set points.   
     
     
         2 . The method of  claim 1 , comprising:
 adjusting the set points based upon the biasing values using proportional-integral-derivative controllers that monitor operations of the GPU.   
     
     
         3 . The method of  claim 1 , comprising:
 determining the biasing values via the formula:
     J=Σ   i=1   N     CV   α(CV i   SP −CV i   PV ) 2 +Σ j=1   N     CT   β(CT j   lim −CT j   PV ) 2 +Σ k=1   N     MV   γΔMV k   2  
 
   where,   CV i   SP : is a reference value of an i-th control variable,   CV i   PV : is a measured value of the i-th control variable,   CT j   lim : is a limit of a j-th constraint variable,   CT j   PV : is a measured value of the j-th constraint variable   ΔMV k : is an actual change of the k-th biasing value,   α: is a weighting coefficient reflecting relative importance of the control variables,   β: is a weighting coefficient reflecting relative importance of the constraint variables, and   γ: is a weighting coefficient penalizing changes of at least a pre-specified value in biasing value.   
     
     
         4 . The method of  claim 3 , wherein the plant is configured to generate electricity or power, and the method comprises:
 capturing, via the GPU, carbon dioxide from flue gas output by a combustion unit of the plant.   
     
     
         5 . The method of  claim 3 , wherein:
 the control variables comprise: (i) carbon dioxide content of a substantially carbon dioxide fluid to be sent from a separation unit of the GPU to a storage device, and (ii) a rate of capture of carbon dioxide from the flue gas; and   the constraint variables comprise: (i) an off gas expander outlet temperature, (ii) an outlet temperature for substantially carbon dioxide liquid output from at least one separation column of a separation unit of the GPU, and (iii) at least one flue gas temperature.   
     
     
         6 . The method of  claim 3 , wherein the biasing values comprise:
 (i) compressor inlet pressure set point values, (ii) off gas expander temperature set point values, and (iii) at least one separation unit temperature set point value.   
     
     
         7 . The method of  claim 3 , comprising:
 determining at least one biasing value utilizing at least one disturbance variable value.   
     
     
         8 . The method of  claim 7 , wherein the disturbance variable value comprises:
 a flow rate of flue gas fed to the GPU.   
     
     
         9 . The method of  claim 3 , wherein values of the constraint variables are selected to prevent formation of dry ice and water ice in the GPU. 
     
     
         10 . An apparatus comprising:
 a gas processing unit (GPU); and   a controller having a processor connected to non-transitory memory, a model predictive control program being stored in the memory;   the GPU being configured to connect to a combustion unit such that flue gas emitted from the combustion unit will be fed to the GPU, the GPU being configured to separate carbon dioxide from the flue gas to capture the carbon dioxide from the flue gas;   the controller being communicatively connected to the GPU to control operations of the GPU with the model predictive control program.   
     
     
         11 . The apparatus of  claim 10 , wherein the model predictive control program is structured to configure the controller to determine parameter values associated with operations of the GPU, utilize the parameter values associated with the operations of the GPU to determine biasing values for biasing set points by which operations of elements of the GPU are controlled, and send the determined biasing values to the GPU for adjusting the set points when the model predictive control program is run by the controller. 
     
     
         12 . The apparatus of  claim 11 , wherein the biasing values are determined by the formula:
     J=Σ   i=1   N     CV   α(CV i   SP −CV i   PV ) 2 +Σ j=1   N     CT   β(CT j   lim −CT j   PV ) 2 +Σ k=1   N     MV   γΔMV k   2  
   where,   CV i   SP : is a reference value of an i-th control variable,   CV i   PV : is a measured value of the i-th control variable,   CT j   lim : is a limit of a j-th constraint variable,   CT j   PV : is a measured value of the j-th constraint variable   ΔMV k : is an actual change of the k-th biasing value,   α: is a weighting coefficient reflecting relative importance of the control variables,   β: is a weighting coefficient reflecting relative importance of the constraint variables, and   γ: is a weighting coefficient penalizing changes of at least a pre-specified value in manipulated variables.   
     
     
         13 . The apparatus of  claim 12 , wherein the GPU comprises:
 a cooling unit, a flue gas compressor system, a purification unit, a dryer unit, a condenser unit, and a separation unit;   the cooling unit being configured to receive flue gas emitted by the combustion unit to cool the flue gas to within a pre-specified temperature;   the flue gas compressor system being connected to the cooling unit to receive the cooled flue gas from the cooling unit, the flue gas compressor system being configured to compress the flue gas to a pre-specified pressure;   the purification unit being connected to the flue gas compressor system to receive the compressed flue gas, the purification unit being configured to remove heavy metals from the flue gas;   the dryer unit being connected to the purification unit to receive the flue gas from the purification unit, the dryer unit being configured to remove water from the flue gas to reduce a dew point of the flue gas;   the condenser unit being connected to the dryer unit to receive the flue gas from the dryer unit, the condenser unit being configured to condense carbon dioxide from the flue gas such that liquid carbon dioxide will be formed from the flue gas; and   the separation unit being connected to the condenser to receive the flue gas and the liquid carbon dioxide from the condenser unit, the separation unit being configured to separate the liquid carbon dioxide from the flue gas.   
     
     
         14 . The apparatus of  claim 13 , comprising:
 a storage device connected to the separation unit to receive a substantially carbon dioxide fluid from the separation unit.   
     
     
         15 . The apparatus of  claim 13  in combination with a plant, the plant comprising:
 a combustion unit connected to the GPU of the apparatus; 
 wherein the flue gas separated from the liquid carbon dioxide will be an off gas; and 
 the separation unit being connected to the dryer unit such that the off gas will be fed from the separation unit to the dryer unit as a drying fluid to pass through the dryer for removing water from the flue gas.