【作者】 吴现力；

【导师】 胡仰栋；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2013， 博士

【摘要】 为了实现节能减排可持续发展的目标，需要对化工过程进行从物质到能量多方面的综合优化。本文以过程系统工程理论为指导，对以水、热、电生产为代表的公用工程系统优化设计问题，以及对包括公用工程在内考虑工艺改进的全过程用能系统的综合优化问题进行了研究。目前，公用工程中的水、热、电供应基本上是分开进行的，或者只是进行热电联产，或水电联产，并没有把三者综合起来考虑。随着水资源的短缺，在沿海缺水地区或者内陆盐水、苦咸水地区进行化工园区建设时，用多级闪蒸或者反渗透海水淡化技术生产淡水，来解决供水问题是一条可行的路径。在此基础上，本文提出了热电厂和多级闪蒸、反渗透海水淡化相结合的水热电联产系统。为了获得优化的联产结构，本文给出了一个通用的优化设计方法。该方法给出了一个包括不同类型热电厂、多级闪蒸和反渗透模块的联产超结构。三者通过能流和物流相互耦合在一起。该超结构包括了水、热、电联产所有可能的生产结构。通过建立完整的过程单元模型和经济模型，以年费用最小为目标函数，满足过程热力学、设备选型、设计要求的约束，把联产系统的设计问题表达为了一个非线性规划问题。通过用GAMS软件求解这个以年费用最小为目标的非线性规划模型，可以得到优化的联产生产结构。根据本文给出的联产系统的设计方法，对考虑原水盐度变化、煤价格变化和满足不同需求的水热电联产系统进行了优化设计，得到如下结论：(1)原水浓度对海水淡化系统影响较大，在低盐度(不大于25kg/m~3)下采用抽汽冷凝式发电和一级反渗透产水的联产方式，可使年费用最低.当海水盐度大于27.5kg/m~3时，采取抽汽冷凝式发电与热膜联合制水的联产结构可获得更好的经济性。随着盐度的增加，多级闪蒸产水量逐渐增加。当海水盐度超过35kg/m~3时，发电模式变为背压发电，背压蒸汽全部用来给MSF加热。在本工作所定的生产规模下，优化联产方案的年费用可降低23%36%.适宜的多级闪蒸产水规模受电厂发电规模限制。(2)煤价格对整个系统的年费用有很大的影响，但不会影响联产系统的结构。煤价格变化时，热电厂，MSF和RO的参数都不会发生变化。(3)不同的水热电需求，其对应的最优的生产结构也不相同。在本文算例中给定的条件下（海水盐度42kg/m~3，成品水浓度低于0.5kg/m~3），用电厂低品位蒸汽作为MSF热源的联产结构具有经济上的优势。当需水量较大，电厂蒸汽不能满足单独MSF产水时，采用MSF/RO混合结构产水，可以获得比较好的经济性。优化的联产结构和分产系统相比，可以减少16.1%~21.7%的年费用。当电、水需求不变，供热量发生变化时，不会影响最优的联产结构，只会对MSF和RO的产水量产生影响。供热量增加时，MSF产水减少，RO产水增加；反之，MSF产水增加，RO产水减少。能量综合是过程系统工程研究的另一重要内容。随着研究的深入，提出了包括火用分析，夹点分析，数学规划法，三环节能量利用模型，以及用能一致性原则等方法。这些方法有些只能对局部用能进行综合优化，有的过程过于复杂，难以进行实际工程应用。本文针对上述情况，提出了基于T-H图的逐步优化的能量利用综合策略。该策略通过分析冷热物流组合曲线，确定系统中能量利用不合理的地方，然后对生产工艺进行微调，或引入热机、热泵，实现能量合理利用,同时增加或减少冷热物流，从而使冷物流组合曲线和热物流曲线相对位置趋于平行，实现能量利用系统热能的最佳匹配。给出了调整的原则：对高温热物流，先产生二次蒸汽，二次蒸汽发电，降级为低品位的蒸汽再换热；升级低温热物流（蒸汽）的品位，使该部分热物流在组合曲线上上移，以去除换热的瓶颈；低温冷物流作为冰机的过冷剂，制冷工质节流膨胀后得到更多高品位的冷剂；调节分离工艺操作条件，使部分分离塔塔顶热物流和塔底冷物流升级或者降级，使冷、热物流具有更好的匹配性。系统中低品位的冷、热物流，除了进行物流之间匹配外，多余的热物流需要用循环水进行冷却，多余的冷物流可以由锅炉蒸汽发电后抽取相应温度的低品位蒸汽来加热。节能并不一定经济，在利用逐步优化的能量综合策略改进的同时，需对改进过程进行了经济性评价，舍弃不经济的改进过程，以实现能耗和经济双目标的优化。基于逐步优化的能量利用综合策略，编制了能量分析软件。该软件能够绘制冷热物流的组合曲线，确定夹点的位置，计算出最小的冷、热公用工程用量，并可以在曲线上对需要改进的或已经加以改进的物流加以标记，可以方便的对系统的用能情况进行分析。利用逐步改进的能量综合优化策略及其软件，对甲醇制烯烃的用能系统系统进行了能量综合优化。通过逐步引入热泵精馏、发电机组和调节塔的分离条件，增加了能量集成的量，对高温热物流先用功，后用能，减少了传热温差和传热不可逆的损失，减少了低温冷剂的用量。构造出了两条近似平行的冷热物流组合曲线，实现了包括公用工程在内的全过程的能量综合优化。经过多次的改进，最终可以节省22%的循环水，90%的11.2℃的丙烯冷剂，29%的-43.7℃的丙烯冷剂。用电量减少了63%。对改进过程同时进行了经济评价。结果表明可以在很短的时间内收回改进的费用，在经济上也是可行的，实现了能量和经济的双目标优化。因此，本工作提出的能量综合优化策略是有效且方便可行的。更多还原

【Abstract】 In order to achieve energy conservation, sustainable development, the synthesisoptimization, from materials to energy, is needed. Based on the process systemengineering theory, the heat, power and water production system is optimal designed.And considering process improvement, the whole process energy use system,including utility system, is synthesis optimized.This thesis reviewed the research progress on PSE, process energy synthesis,desalination technologies and water, heat, power cogeneration technologies. Theutility system is one of the most energy consumption subsystems. The optimization ofutility has a great significance to save energy and achieve sustainable development.The main task of the utility is water, heat, electricity supply. In the past, water, heat,electricity supply is basically carried out separately. With the shortage of waterresources, desalination technology is a viable path to solve this problem whenchemical industry parks are constructed in water shortage coastal areas or inlandsaltwater, brackish water areas. From the system point, the cogeneration consideredpower generation, heating and desalination together. The material and energy iscascade used. Compared to single production process, cogeneration system canachieve efficient use of energy, raw materials and clean production, and theinvestment cost is lower.In order to obtain the optimized cogeneration structure, a generic optimizationdesign method is given. The cogeneration system consists of a coal-based thermalpower plant (TPP), a multi-stage flash desalination (MSF) module and reverseosmosis desalination (RO) module. After a reasonable simplified, the process modelof each unit has been built. The economical model, including the unit investment andoperation&maintenance cost, is presented. The system design problem has beenpresented as a non-linear programming (NLP). The objective is to minimize theannual cost and is solved by GAMS program. According to different demands ofdesalination water, heat and power production, solving this model, an optimal cogeneration system can be obtained.Using the design method presented in this paper, the optimal cogenerationstructures respectively considering the feed water salinity changes, the coal pricechanges and meeting different demands of desalination water, heat and powerproduction system are studied. The salinity of the feed water has a great impact tothe desalination system. In the low salinity(TDS≤25000mg/l), the optimalcogeneration structure is extraction condensing power generation and one stage ROdesalination; when the TDS＞25000mg/l, extraction condensing power generationand RO/MSF hybrid system is the optimal cogeneration system. With the increase insalinity, the MSF production water is gradually increased. When the salinity exceeds35000mg/l, the power generation mode is changed to backpressure style. Thebackpressure steam is entirely used as the heat sources of MSF. Under the productionscale given in this section, the annual cost of optimal cogeneration system can bereduced by23%~36%. Suitable MSF scale is limited by the scale of powergeneration.Coal price has a great impact on the annual cost of the entire system, but it willnot affect the structure of the cogeneration system. When the coal price is changed,the parameters of thermal power plant, MSF and RO system are not changed.According to different demands of water, heat and power production, solving thismodel, an optimal cogeneration system can be obtained. The result shows that, underthe premise of heat and power supply, the MSF can be used as a priority waterproduction style. The production capacity of MSF is subjected to the amount of steamextracted from the thermal power plant. When the demand of water supply is largerthan the MSF production capacity, the MSF and RO cogeneration system will be abetter choice. Compared to the other cogeneration system, the optimal system canreduce17.7~25.1%of the total annual cost. It indicated this design method waseffective.When only the heat supply changed, the optimal cogeneration structure will notchange, but the MSF and RO scale will change. For the heat increased, MSF waterproduction will reduce and RO will increase; conversely, the MSF scale will increase. Energy synthesis is another important content of PSE research. With thedeepening of the research, exergy analysis, pinch analysis, mathematicalprogramming method, three-link model and consistency principle of process energyutilization model are proposed. Some of these models are only local optimization ofenergy use, and some models are too complex, which are difficult for practicalengineering application.Based on the T-H diagram, the gradual optimization integration strategy forlarge-scale complex process is proposed. Through improving process, introducing theturbine and heat pump to the system, the energy utilization procedure and conversionprocedure are comprehensive considered. The composite curves of the origin processare drawn. And the bottlenecks and unreasonable heat transfer processes are analyzed.Then the parameters of production process and utility system are adjusted. The newstreams information is obtained by process simulation software and the newcomposite curves are drawn, which will guide the further adjustment of the system.Through several improvements, two approximate parallel hot and cold stream curvesare constructed. The heat is reasonable used, the hot streams and cold streams arefully matched, and the amount of utility and power consumption is significantlyreduced.While process is improved, economic evaluation of the improvement processalso has been made. Uneconomic improvement process is abandoned in order toachieve the dual goals of energy consumption and economic optimization.The energy analysis software has been programmed based on the gradualoptimization integration strategy. The software is able to draw the T-H diagram of thehot and cold stream, determine the location of the pinch point, calculate the minimumof hot and cold utilities, and mark on the need to improve or improved streams on thecomposite curves.Applying this strategy, the energy integration of the methanol to olefins plant hasbeen optimized. By gradually introducing heat pump distillation, power generationmodular and adjusting the towers separation conditions, the amount of integrationenergy is increased, the high temperature streams’ heat transfer temperature difference and irreversible loss is reduced, and the amount of low-temperature refrigerant is alsoreduced. Two approximate parallel hot and cold stream curves are constructed. Thewhole process energy use systems, including utility system, are optimized. Afterseveral times improvement, the circulating water,11.2℃and-43.7℃propylenerefrigerant can save22%,90%and29%, and power consumption is reduced63%.The economic evaluation has been done between the improvement processes. Theresults show that the improved cost can be recovered within a very short time, whichdemonstrates the improvement is also economically feasible. The results show thatthis strategy is effective and user-friendly.更多还原