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本文采用经济学模型来描述跨装置热集成问题,该模型以集成的换热网络和长距离换热匹配费用最小为目标。通过适当提高中间物流进料温度,不仅可避免该物流“在上游装置冷却,下游装置重复加热”的能量利用现状,还可节省一组换热设备投资。若允许物流跨装置热匹配,长距离换热匹配的管线投资会增加,但可获得全局最大能量优化。本模型通过逐步逼近的方法来求解最优出料温度。首先,设定一个较大的步长δT,改变进料温度,计算换热网络的总投资,根据计算结果可绘制进料温度曲线;随后,从曲线中缩小优化区间,设定一个小的δT,在这个小区域内重新计算总投资、迭代数次,可得到优化出料温度。应用案例来验证模型和计算策略的实用性,中间物流温度从50℃提高到97℃,整个系统中的能量利用效率显著提高。由于进料温度提高,下游装置高温能量空余出来,这些能量可输送至上游装置替代热公用工程加热物流,热集成后的系统总投资比装置单独操作降低了20.15%。
In this paper, the economic model is used to describe the thermal integration across devices. This model aims at minimizing the cost of an integrated heat exchange network and matching long-distance heat exchange. By properly increasing the intermediate feedstock feed-in temperature, not only the energy utilization status of the “upstream cooling, downstream heating” can be avoided, but also a set of investment in heat exchange equipment can be saved. Long-distance heat exchange matching pipelines investments will increase if thermal cross-device matching is allowed, but maximum global energy optimization is available. The model solves the optimal discharge temperature by the method of stepwise approximation. First, set a larger step δT, change the feed temperature, calculate the total investment of the heat exchange network, and draw the feed temperature curve according to the calculation result. Then, narrow the optimization interval from the curve and set a small δT , Recalculate the total investment in this small area, and iterate several times to get the optimal discharge temperature. The application case is used to verify the practicability of the model and calculation strategy. The intermediate logistics temperature is increased from 50 ℃ to 97 ℃, and the energy utilization efficiency of the whole system is significantly improved. Due to the increase of feed temperature, the high temperature energy of the downstream unit is left vacant. These energy can be transferred to the upstream unit instead of the thermal utility heating stream. The total system investment after thermal integration is reduced by 20.15% compared with that of the unit alone.