Study On Energy Saving Technology Of Aromatics Disproportionation System Based On Energy Level Analysis Method And Fields Synergy Principle

Energy-saving and the improvement of energy efficiency has become a focus of the world's energy strategy nowadays. The energy consumption analysis of individual equipment and heat exchanger networks, application of high-efficiency heat exchangers and advanced surplus heat recovery technology and optimization of heat exchanger networks are effective and dependable ways for energy-saving of chemical process system. Diagnosis and evaluation of energy utilization of the process unit and individual equipment were conducted and study of design method of heat transfer equipment was carried out targeted at one aromatics disproportionation unit. The chief content and innovative achievement are as follows.(1) A new improved method, called composite energy level analysis method, was proposed for analyzing the energy level of complicated heat exchanger networks of multi-streams in this paper. Based on the method, some energy consumption bottlenecks could be found in the reaction and separation systems of the Tatoray Unit. The energy loss of four equipment accounts for 72% proportion of the heat transfer subsystem's, in which EC-502, reaction feed and effluent heat exchanger, had the highest irreversible loss and became the weakest part of energy utilization in system, that further resulted in excessive heat duty to the air cooler EC-503 and the furnace BA-501.(2) Heat transfer enhancing mechanism inside the plate heat exchanger was analyzed with temperature, velocity, vorticity and field synergy angle. It is the longitudinal turbulent flow that can enhance the heat transfer effect in the corrugated channel, attenuate the boundary layer and improve the synergy of flow field. A dimensionless comprehensive performance factorφis put forward to evaluating the heat-exchange enhancing effect of heat transfer surface according to fields synergy principle.(3) Three dimensional numerical simulations were conducted on corrugate channels with different structural parameters (β&h) in order to get laws of performance of heat transfer and flow resistance influenced by them. The influence of corrugation angleβand depth h on heat transfer characteristics and pressure drop of two different corrugated channels was analyzed quantitatively. Comprehensive performance factors of eighteen types of plates with different values of corrugation depth and angle were compared. Taking experimental results into account, the optimal structure parameters,3.5-4.0 mm depth and 30～32.5°angle, were determined.(4) Thermophysical properties and dew points of mixed aromatics with high proportion of non-condensable gases were computed by Aspen Plus using an appropriate property method.The heat-exchange process is divided into three sections for thermal calculation according to different heat transfer forms. Heat balance calculations were made to get the inlet and outlet temperatures and the overall heat-exchange values.The homogeneous model was applied to calculate the total heat transfer area and plate length corresponding with different numbers and widths of plate.(5) Flow rules of the two-phase feed combination distributor were studied by both theoretical and experimental methods. It could be concluded that entrainment fraction was affected obviously by the opening ratio of the gas distributor at the same superficial observation speed within the range of experimental height of the entrainment zone. Based on experimental results, the structural parameters of the liquid distributor and the gas distributor of EA-502 were designed and proved by practical application.(6) Above-mentioned research results were applied to aromatics disproportionation unit from the view of process retrofit and high-efficient heat exchangers. After replaced EA-502 from shell-and-tube heat exchanger with welded plate-shell heat exchanger, the heat transfer coefficient increased by 90% and the heat duty of BA-501 and EC-503 were reduced effectively, which may recover the heat appropriate 1.53MW. The reboil ratio and top reflux were increased by 4.5% and 29.3% by utilizing bottom reboiler of toluene column made of sintered porous surface tubes. About 3.7MW heat loss could be reduced when using heat high-pressure products separator to retrofit systematic process. It could save high pressure steam (3.1Mpa) 36000t/a by using the bottom effluent of stripping column as the heat source of reboiler of toluene column.