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For insuring the safe operation of LNG heat exchanger in the Emergency Stop Operation Process (ESOP), a numerical method is proposed to investigate the stress of Plate-Fin Structures (PFS) in that. The relationship between stress of PFS and ESOP is analyzed in LNG heat exchanger. The results will be obtained that the maximum equivalent stress of PFS is greater at the initial stage of ESOP than that at the last stage when the HMR pressure is more than 5 MPa. The maximum equivalent stress increases with the equilibrium temperature when is greater than 180 K and reaches peak value at the last stage of ESOP. The maximum equivalent stress is larger at the last stage of ESOP than the other stage and increases with the equilibrium pressure. When the temperature difference is more than 5 K in the ESOP, the influence of that is obvious for the stress of PFS. In the ESOP, the equilibrium temperature and temperature difference should be controlled within 240 K and 5 K, respectively.

Purpose: The purpose of this paper is to recover the waste heat of flue gas heat exchanger (FGHE) as efficiently as possible and avoid the acid dew corrosion of that. Design/methodology/approach: A novel flue gas waste heat recovery system was proposed in the paper. The dynamic mathematical models of key equipment in that were established based on theory and experiment method. The proportion integration differentiation-differentiation (PID-P) cascade control method based on particle swarm optimization algorithm was used to control the outlet temperature of FGHE. The dynamic characteristics of the flue gas heat exchange system were simulated by the particle swarm optimization algorithm with different fitness functions. Findings: The PID-P temperature controller parameters can be quickly and effectively obtained by the particle swarm optimization algorithm based on the fitness function of integral time absolute error (ITAE). The overshoot, rise time and adjusting time of the novel system are 2, 83 and 105s, respectively. Compared with the traditional two-step tuning (T-ST) method, the novel system is better in dynamic and steady-state performance. The overshoot and the adjustment time of the system are reduced by 44% and 328s, respectively. ITAE is a performance evaluation index for control system with good engineering practicability and selectivity. Originality/value: The dynamic mathematical model of key equipment in the new flue gas waste heat recovery system is established and the system's control strategies and methods are explored. [ABSTRACT FROM AUTHOR]