| 초록 |
The present study concentrates on the dynamic modeling of MED process. Some authors have endeavored to simulate the actual situation. Recently, Hackenberg [2] summarized the state of art of dynamic modeling and control of MED with thermo-vapor compressor (TVC) using a case-study approach. The author studied the dynamics of the plant with nonlinear simulation tools and finally analyzed the linear controllability. Narmine and Marwan [3] presented a dynamic model to study the transient behavior of a four-effect evaporation process with TVC. They introduced three lumps of an evaporator; brine, vapor, and tube bundle lumps. Their model simulated the load changes and disturbances in which the plant performance varied significantly. In present study, the effect is modeled to comprise six phases: tube-side vapor, distillate, shell-side vapor, brine, seawater film on tube surface, and tube wall. The feed seawater and the heating steam are introduced respectively into the seawater film on tube surface and tube-si phases. Heat transfer through tube-wall phase causes the heating steam to condense and part of feed seawater to evaporate. The evaporating steam moves into the shell-side phase, and then into the tube-side phase of the next effect. The condensate of tube-side phase called distillate and the rest seawater of shell-side phase called brine accumulate on the pot of each side, and cascade to pot of the next stage. The mathematical model of MED is analyzed in terms of time scales, and more simple and robust simulation method is proposed assuming quasi-steady-state approximation. |
