Multi-variable predictive controller

Abstract

A multi-variable predictive controller is used to separate a multi-phase fluid on an offshore platform, thereby reducing condensable material in the gas product stream. A separation vessel containing a multi-phase fluid is provided, and pressure and temperature associated with the separation vessel are monitored. A Reid Vapor Pressure is calculated for the separation vessel based on the pressure and the temperature associated with the separation vessel. The multi-variable predictive controller actively controls the pressure and the temperature associated with the separation vessel such that the calculated Reid Vapor Pressure for the separation vessel is maintained within a predetermined amount of a reference Reid Vapor Pressure.

What is claimed is: 
     
         1 . A method for separating a multi-phase fluid on an offshore platform, the method comprising:
 (a) providing a separation vessel containing a multi-phase fluid;   (b) measuring a pressure and a temperature associated with the separation vessel;   (c) calculating a Reid Vapor Pressure for the separation vessel based on the pressure and the temperature associated with the separation vessel; and   (d) actively controlling the pressure and the temperature associated with the separation vessel such that the calculated Reid Vapor Pressure for the separation vessel is maintained within a predetermined amount of a reference Reid Vapor Pressure.   
     
     
         2 . The method of  claim 1 , wherein the pressure and the temperature associated with the separation vessel are adjusted simultaneously based on the calculated Reid Vapor Pressure. 
     
     
         3 . The method of  claim 1 , wherein the calculated Reid Vapor Pressure for the separation vessel is maintained within ten percent of the reference Reid Vapor Pressure. 
     
     
         4 . The method of  claim 1 , wherein the calculated Reid Vapor Pressure for the separation vessel is maintained within five percent of the reference Reid Vapor Pressure. 
     
     
         5 . The method of  claim 1 , wherein the temperature associated with the separation vessel is actively controlled by a heat exchanger upstream of the separation vessel. 
     
     
         6 . The method of  claim 1 , wherein the Reid Vapor Pressure is calculated according to the following equations:
     RVP =10 [A−B/(100+C)] +Bias       A =Log  P   1   +B /(T 1   +C)          B =(Log  P   1 −Log  P   ref )/[1/( T   ref   +C )−1/( T   1   +C )].
   
     
     
         7 . The method of  claim 1 , wherein the Reid Vapor Pressure is calculated according to the thermodynamics of butane. 
     
     
         8 . The method of  claim 1 , further comprising generating an empirical dynamic process model of the offshore platform and utilizing the empirical dynamic process model to determine adjustments made to the pressure and the temperature associated with the separation vessel. 
     
     
         9 . A system for separating a multi-phase fluid on an offshore platform, the system comprising:
 (a) a separation vessel that receives a multi-phase fluid;   (b) a pressure sensor that monitors pressure associated with the separation vessel;   (c) a temperature sensor that monitors temperature associated with the separation vessel; and   (d) a multi-variable predictive controller that actively controls the pressure and the temperature associated with the separation vessel such that a calculated Reid Vapor Pressure for the separation vessel is maintained within a predetermined amount of a reference Reid Vapor Pressure.   
     
     
         10 . The system of  claim 9 , further comprising an indicator to calculate the Reid Vapor Pressure for the separation vessel based on the pressure monitored by the pressure sensor and the temperature monitored by the temperature sensor. 
     
     
         11 . The system of  claim 9 , wherein the multi-variable predictive controller maintains the calculated Reid Vapor Pressure for the separation vessel within ten percent of the reference Reid Vapor Pressure. 
     
     
         12 . The system of  claim 9 , wherein the multi-variable predictive controller maintains the calculated Reid Vapor Pressure for the separation vessel within five percent of the reference Reid Vapor Pressure. 
     
     
         13 . The system of  claim 9 , wherein the multi-variable predictive controller further calculates the Reid Vapor Pressure for the separation vessel based on the pressure monitored by the pressure sensor and the temperature monitored by the temperature sensor. 
     
     
         14 . The system of  claim 9 , wherein the Reid Vapor Pressure is calculated according to the following equations:
     RVP =10 [A−B/(100+C)] +Bias       A =Log  P   1   +B /(T 1   +C)          B =(Log  P   1 −Log  P   ref )/[1/( T   ref   +C )−1/( T   1   +C )]
   
     
     
         15 . The system of  claim 9 , wherein the Reid Vapor Pressure is calculated according to the thermodynamics of butane. 
     
     
         16 . The system of  claim 9 , wherein the pressure and the temperature associated with the separation vessel are adjusted simultaneously based on the calculated Reid Vapor Pressure. 
     
     
         17 . The system of  claim 9 , further comprising a heat exchanger upstream of the separation vessel that is used to adjust the temperature associated with the separation vessel. 
     
     
         18 . The system of  claim 9 , wherein the pressure and the temperature associated with a separation vessel are adjusted simultaneously based on the calculated Reid Vapor Pressure. 
     
     
         19 . The system of  claim 9 , wherein the multi-variable predictive controller is further used to generate an empirical dynamic process model of the offshore platform to determine adjustments made to the pressure and the temperature associated with the separation vessel.