Synthesis Of Work Exchange Networks Based On Transshipment Model

With the production of energy crisis and utilizing principle of momentum transport, heat transport, mass transport and reaction engineering in chemical process, energy-conservation and emission-reduction has been being the strategic target in the 21st century. Up to now, study of heat exchange networks(HEN) and water utilization networks(WUN) is quite mature. However, the research on synthesis of work exchange networks(WENs) is still in early stages. Aiming at the problems in the existing WENs synthesis methods, such as the computational complexity, singularity of research methods, restriction of application and lower theory, a novel approach for synthesis of work exchange networks is proposed in this paper based on transshipment model. The main contents and results of this thesis are as follows:(1) An approach for synthesizing the direct work exchange networks based on transshipment model is proposed, which yields the minimum utility consumption with the optimized work exchange networks configuration according to the expanded transshipment model with pressurization utility in all intervals and depressurization utility only in the final interval. First, the work exchange networks are divided into several pressure intervals in a descending order of pressure according to the minimum pressure difference selected by experience and the inlet and outlet pressure of streams. Second, an initial work exchange network is obtained by constructing an intermediate pressure of low-pressure streams. Third, merge the adjacent pressure interval and then construct a new sub-network, which is combined with computing of utility consumption. The work exchange network with the minimum utility consumption is selected to be the finally optimized structure. Two cases have been calculated to illustrate the feasibility and effectiveness of the proposed approach.(2) A synthesized method of indirect work exchange networks considering isothermal process is proposed on the basis of transshipment model. WENs are divided into different pressure intervals according to the maximum compression/expansion ratio in consideration of operating principles of indirect work exchangers and no restriction of pressure constrains for stream match. Then the initial WEN is obtained by solving each sub-network, which is optimized by merging the adjacent pressure intervals. The constructed transshipment model based on the above analysis could be solved as a linear programming method to get the minimum utility consumption and further as a mixed integer linear programming method to determine the minimum number of devices in order to get the optimal work exchange networks configuration. Two cases are calculated to verify the more effective access to the optimal WEN through the proposed method. (3) As for the indirect work exchange networks with adiabatic process, an NLP model is established. Similarly, WENs are divided into different pressure intervals according to the maximum compression/expansion ratio in consideration of operating principles of indirect work exchangers and no restriction of pressure constrains for stream match. Then the initial WEN is obtained by solving each sub-networks, which is optimized by merging the adjacent pressure intervals. However, temperature should be regarded as decision variable with the restriction of inlet and outlet temperature of each sub-network herein. The constructed transshipment model based on the above analysis could be solved as a nonlinear programming method to get the minimum utility consumption and further as a mixed integer nonlinear programming method to determine the minimum number of devices in order to get the optimal work exchange networks configuration, which is proved to be reasonable through exergy analysis. A case is calculated to confirm that the optimal WEN configuration with the minimum utility consumption can be obtained by the proposed method.