| Ethoxylation is significant in the polyoxyethylene ether nonionic surfactants industry that are base-catalyzed reactions of hydrophobic substrates containing active hydrogen. Nowadays, external loop device is the most widely used equipment of ethoxylate production. The device is operated at semi-batch mode and involves reactor and heat exchanger system and also covers pre-treatment tank for start reaction material treating and post-treatment tank for product handling. The heat exchanger system of external loop ethoxylation plant consists of material heat exchanger, heat transfer medium cooler(HTMC) and heat transfer medium heater(HTMH). Because ethoxylation reaction is operated under high temperature of 410～455K and has strong exothermic characteristics, the process has both heating and cooling demand. Design and controlling of heat exchanger system is the key to affecting production efficiency. This paper focuses on the problem such as poor adjustment effect, low growth ratio and long production cycle in design and operation, based on PEG industrial plant. By building mathematical model and using HYSYS simulation method, the study of heat exchanger system of external loop device was carried out. The results obtained in this paper will be further used to guide simulation analysis, operation, controlling, improvements and energy-using optimization and so on.The basic strategy adopted in this paper consists of the following aspects:(1) The affluence of the key equipments and key parameters on the production device was analyzed. The results demonstrate that the volume of materials heat exchanger is the key factor of growth ratio, but the influence weaken when reactor volume is bigger. For bi-circulating heat system, production cycle is shortening with the heat exchanger area of minor cycle increase. For single-circulation heat system, average production cycle is longer with the growth ratio of intermediate production increase. Flow rate of external loop is related to the refresh time of the material in reactor. Longer refresh time would be bad for producing narrow molecular weight distribution; shorter refresh time would be hindering EO reacts completely in reactor. For this reason, higher flow rate should be used on condition that EO reacts completely in reactor. The flow rate and temperature of Heat transfer medium (HTM) have indirect influence on rate of polymerization (ROP) of EO while the ROP is under bottleneck. ROP of EO approximate has linear increase with the flow rate of HTM growth, but has a parabola change with the inlet temperature of HTM. A specific temperature that make ROP of EO largest is exist in different flow rate of HTM. In addition, the simulation results show that ROP of EO is more sensitive with the flow rate of HTM than the inlet temperature of HTM.(2) Utilizing of reaction heat of external loop ethoxylation plant was studied. The researches show that the release energy Equivalent to about 60 times the need energy in the process, a great energy saving potential can be expects. But the existing process has no feasibility to recycle the reaction heat by direct heat exchange. Therefore, an improved process that can recover the reaction heat of the system was developed. The main characteristics of the process were added a heat recovery circulation system. A case study demonstrates that the heat investment decreased to 16.7% of existing process and the power investment increased 9.1%. The total energy investment reduces to 30.2% of existing process and the payback time is only two months. A remarkable energy saving effect and good feasibility could be expected.(3) Using the HYSYS dynamic simulation method, the thesis studied the dynamic response of the heat exchanger system under different adjustment way. The results show that the time of the outlet temperature of material heat exchanger got stable is 90s if adjust the flow rate of HTM while the got stable time is 155s if change the temperature. The simulation results demonstrate that the heat exchanger system has delayed time while the operation parameters changed and the delayed time of flow rate adjustment mode is shorter than temperature adjustment mode, which indicate that the flow rate adjustment mode could get better adjustment effect. |
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