基于夹点技术考虑含有复杂相变及碳排放的换热网络综合

Heat Exchanger Network Synthesis with Complex Phase Changes under Consideration of Carbon Emission Based on Pinch Point Technology

以乙烯裂解工艺中6股使用公用工程换热的物流为研究对象,发现存在含有混合物的复杂相变的物流,根据其热负荷和物料特性把相变段折算成一股或多股恒定热容流率的物流,确定温度区间,再用问题表确定夹点。传统夹点法确定最小传热温差△T_(min)为11℃,加入碳排放目标函数后确定△T_(min)为9℃,平均夹点温度为83.8℃,此时该换热网络所需的最小热公用工程量为12727.27 kW,最小冷公用工程量为38719.59 kW。根据夹点技术的设计原则和物流匹配准则,可得到能量最优的换热网络结构。

Heat exchanger network(HEN)is one of the most important parts in the chemical production process.HEN optimization becomes an effective tool to save energy and keep sustainable development.There are many methods to optimize HEN.In principle,mathematical programming seems a comprehensive solution,while the pinch point method is still a handy tool,due to its simplicity and clear physical meaning.Special arrangement is required when phase change is considered in the system.The aim of this paper is to investigate six streams distributed in adjacent sections in an ethylene cracking process from the systematic perspective,as no heat recovery is involved,and only utility is matched to meet their temperature requirement in process.Problem table is used to determine the pinch point for the design of HEN.Due to the complex phase change of the mixture in the heat exchange system,the phase change section is converted into one or more streams with constant heat capacity flow rate according to its thermal load and material characteristics,so as to determine the temperature interval.In the traditional pinch point method,△T_(min) is found as 11℃,and it is determined to be 9℃ with the consideration of carbon emission.The average pinch point is determined by problem table at 83.8℃.Under this condition,the minimum thermal utility required by the heat exchanger network is 12727.27 kW,and the required minimum cold utility is 38719.59 kW.The total annual cost is reduced by 2620585.49$/a,and the carbon emission is reduced by 61453.50 t/a.According to the design principles of pinch technology and stream matching criteria,the energy-efficient heat exchanger network structure is obtained.