Effects of heat integration on control performance of hydrodealkylation process

Abstract

Hydrodealkylation (HDA) plant with different energy integration schemes is a realistically complex chemical process, since six heat exchanger network alternative can be improved by introducing recycle streams and energy integration into the process. However, the recycle streams and energy integration introduce are the causes of a low level of control performance. Therefore, this work presents three plantwide control structures for three different energy integration schemes (alternative 1, 2, and 5). In order to illustrate the dynamic behaviors of the control structures in HDA plant change in the heat load disturbance of cold stream and change in the recycle toluene flowrates were made. Three control structures have been tested and compared, the first control structure is a modification of Luyben control structure using valve position control concept to control temperature of column. The second control structure was the modification of the first control structure by adding a cooling unit to control the outlet temperature from reactor, instead of using internal process flow. In the third control structure, a ratio control was added to the second control structure for controlling the ratio of hydrogen and toluene within the process. The result shows the third control structure gives a smaller settling time and can reject disturbances better than other control structures. However, the utility consumption of the first control structure is less than thoses of the second and the third control structures. HDA process alternative 5 give the slowest response compare with other alternatives indicated by the IAE values. It can be concluded from this research that the implementation of complex energy integration to the process deteriorates the dynamic performance of the process.