换热网络的最优设计

基于Ｌｉｎｎｈｏｆｆ的Ｐｉｎｃｈ－Ｐｏｉｎｔ方法，提出外加冷热负荷最小费用模型，该模型在获得最小费用的同时，可确定外加冷热负荷的数目及其流量，并在此基础上提出了换热网络最小建造费用的数学模型，并与换热网络最小单元数模型进行分析比较，结果证明，求解换热网络的最低建造费用更具有实际意义。     

基于状态空间超级结构的多流股换热网络最优设计

多流股换热器以其结构紧凑、高效低耗等特点,成为过程强化研究的热门领域,但对于多流股换热的过程与设备优势所在仍然值得商榷。基于多流股换热匹配改进状态空间超级结构,将多流股换热网络综合转化为超级换热器设计。首先,构造级联多流股换热器匹配过程操作算子,通过相邻换热流股匹配,传递温位效应,实现多流股间传热严格计算;借助热容流率混合分配机制,实现各流股间任意分混操作。然后,考虑散热因素,改进目标函数,引入冷热损失和保温材料费用项,清晰体现多流股换热器因换热面互相覆盖而带来的外表面封包优势。进而,建立相应非线性数学规划模型,实现公用工程、设备投资、冷热损耗同步优化。最终,通过文献示例对所提方法可行性与优越性进行验证。     

环氧丙烷装置换热网络的分析与优化

利用夹点技术对某环氧丙烷装置换热网络进行了分析,并提出优化改造方案。基于MATLAB的操作型夹点分析表明,现行换热网络夹点温差偏大(34℃)。优选夹点温差为20℃,可得最小加热和冷却公用工程量分别为1 981 kW和9 132 kW,而现行换热网络中加热和冷却公用工程量分别为3 049 kW和10 201 kW,存在较大节能潜力。进一步分析表明,现行换热网络存在违背夹点设计原则的现象,导致用能不合理。考虑换热网络变动的复杂程度和经济性,提出了一种简便的优化改造方案,可减少冷热公用工程量各300.5 kW。     

Margin design,online optimization,and control approach of a heat exchanger network with bypasses

During the life cycle operation of a heat exchanger network (HEN), factors such as equipment aging, gradually decrease heat transfer performance and increase energy consumption. Industrial HEN design currently fails to effectively solve these problems. To resolve this problem, we present an online optimization and control approach method for an HEN with bypasses. The approach is based on the principles of sustainable energy conservation during the life cycle. The area margin of the heat exchanger is gradually released via bypass adjustment, thereby resulting in energy conservation. First, bypasses are set on the HEN to enhance HEN control and enable optimal manipulation of the equipment. Then, the total cumulative cost increment of the HEN, including the increment of utility costs and equipment investment costs, is regarded as the objective function. The effects of the heat transfer efficiency of the heat exchanger and the effects of bypass adjustment are also taken into account. We solve the optimal design margin of the HEN, thereby providing an operational space for optimal control. Finally, using the margin optimization design of the HEN with bypasses as basis, we treat the cumulative costs of the HEN in a certain cycle as the objective function to solve the optimal opening dynamically. While, we present an optimal control structure, which is combined with existing conventional control loops. The HEN of a given crude distillation unit in a refinery is chosen as the research object. And, results illustrate the effectiveness and application prospects of the proposed method.     

Bypass control of heat exchanger network under uncertainty

The dynamic control of the heat exchanger network is important for developing energy-efficient and safe industrial processes. In such a system, the control is achieved through the bypass stream around the heat exchanger. This work aims to track the setpoint temperature of the mixed stream by manipulating the bypass fraction of the cold stream around the heat exchanger. The implemented control is in a non-linear model predictive control (NMPC) framework. The first-principles model of a shell and a tube heat exchanger is used. The orthogonal collocation technique is used to discretize the first-principles model into the system of algebraic equations. In this work, uncertainty is also considered in the inlet temperature of the hot stream. The uncertain optimal control problem is dealt with by using a scenario tree-based approximation along with the affine policy-based method. The results show that, under different scenarios of uncertainty, the controlled variable efficiently tracks the setpoint. In comparison, considering the same scenarios of uncertainty used, the deterministic optimization approach shows significant deviation in the controlled variable from the setpoint as time passes.     

Design of heat exchanger network based on entransy theory

The heat exchanger network (HEN) synthesis problem based on entransy theory is analyzed. According to the characteristics of entransy representation of thermal potential energy, the entransy dissipation represents the irreversibility of the heat transfer process, the temperature difference determines the entransy dissipation, and four HEN design steps based on entransy theory are put forward. The present study shows how it is possible to set energy targets based on entransy and achieve them with a network of heat exchangers by an example of heat exchanger network design for four streams. In order to verify the correctness of the heat exchanger networks design method based on entransy theory, the synthesis of the HEN for the diesel hydrogenation unit is studied. Using the heat exchange networks design method based on entransy theory, the HEN obtained is consistent with energy targets. The entransy transfer efficiency of HEN based on entransy theory is 92.29%, higher than the entransy transfer efficiency of the maximum heat recovery network based on pinch technology.     

基于全周期节能的有旁路换热网络裕量优化设计

换热网络全周期运行期间,由于设备老化等因素,换热性能逐步下降,能耗逐步提高。而当前工业换热网络的裕量设计并没有有效地解决此问题。因此提出了一种基于有旁路换热网络全周期节能优化的裕量优化设计方法,通过旁路调节,逐步释放有效面积裕量,达到全周期节能的目的。该优化方法以换热网络运行全周期内总累积费用为目标函数,同时考虑结垢热阻对换热器换热效果的影响以及旁路对换热网络的调节作用,在满足工艺条件的基础上求解换热网络的最优裕量,最终实现换热网络的持续节能。最后,以某炼油厂的常减压脱盐前换热网络为具体的研究对象,说明所提方法的有效性和使用前景。     

基于实际热负荷分布的换热网络优化改造

采用非等温混合分流分级超结构,建立了基于实际热负荷分布的换热网络改造模型,以由改造费用和运行费用组成的年度化总成本为目标,并采用遗传算法进行求解。改造费用涉及现有换热器增加换热面积、配置新换热器、重新布置管道以及移动现有换热设备所产生的费用,充分考虑了原有换热网络经改造后结构的变化所引起的改造成本。在回用原有换热设备后,根据设备实际面积来计算换热网络的热负荷分布和温度分布,即基于实际热负荷分布对换热网络进行改造。案例研究表明,改造后的换热网络结构具有良好的节能效益,合理地再利用了原网络中的旧换热设备,并以较少的改造成本实现了较高的能量回收,投资回报期仅为0.43年,验证了所提改造方法的有效性和实用性。     

基于热损失的换热网络夹点设计法

现行的换热网络目标方法,在进行换热网络价格估算时,未考虑热物流的热损失。在真实的设计中,换热器壳体保温后仍与环境温度相差较大,则其热损失不可忽略。文章提出了一个新的基于热损失的换热网络夹点设计法,该方法首先以综合费用最小为目标确定出最小温差,然后建立问题表格确定出夹点位置及最小公用工程消耗,最后再进行换热网络设计。文中采用某石油常减压换热网络系统为典型算例对该方法的前两步进行了分析研究,论证了该方法的必要性及可行性。结果表明:该方法与基本Linnhoff夹点技术法估算的投资费用有较大的差距之外,在一定的最小温差下,其与基本Linnhoff夹点技术法确定的夹点位置不同,公用工程消耗也有较大的差距。     

Development of a catalytic combustor with heat exchanger

Catalytic combustion is thought to be a considerable improvement on the traditional one under specific conditions. Due to its special features, catalytic combustion has two strong points compared to flame: no NO_x emission and high reaction efficiency. However, the preheating process of catalytic combustion is an obstacle that deteriorates profitability in operation. So the HTHE (High Temperature Heat Exchanger) is adapted to the system to reinforce the preheating process, and we show that the catalytic combustion is maintained steadily without exceptional heat injection. As a result, the stability on the catalytic surface is the most important operational factor. To achieve it, both mixture gas property and temperature distribution should be controlled.     

Pressure drop considerations for heat exchanger network grassroots design

Pressure drop is an important issue in design of a heat exchanger network (HEN), which has yet to be addressed properly. To overcome pressure losses incurred when streams flow through heat exchangers, pumps/compressors must be installed. The total cost for a system of pumps and compressors consists of the purchase cost of equipment and the electricity cost to run these equipment. This cost could occupy a significant part of the overall cost for a HEN design. Therefore, the pressure drop aspect should be considered together with the costs for heat exchanger area and utility consumption. A new approach is proposed to consider the pressure drop aspect in the overall context of a HEN design. Firstly, the optimal ΔT_min is determined through three-way trade-offs between area, utility and pressure drop at the targeting stage. As a result of targeting, targets for area, utility and pressure drops can be established ahead of the network design. Then a network structure is initialised at the determined ΔT_min and optimised to achieve a final design. In this procedure, the pressure drop is considered at both the targeting stage and the design stage in a systematic manner.     

Integrated FCC riser—regenerator dynamics studied in a fluid catalytic cracking pilot plant

In this paper a dynamic simulator of the fluid catalytic cracking (FCC) pilot plant, operating in the Chemical Process Engineering Research Institute (CPERI, Thessaloniki, Greece), is presented. The operation of the pilot plant permits the execution of case studies for monitoring of the dynamic responses of the unit, by imposing substantial step changes in a number of the manipulated variables. The comparison between the dynamic behavior of the unit and that predicted by the simulator arise useful conclusions on both the similarities of the pilot plant to commercial units, along with the ability of the simulator to depict the main dynamic characteristics of the integrated system. The simulator predicts the feed conversion, coke yield and heat of catalytic reactions in the FCC riser on the basis of semi-empirical models developed in CPERI and simulates the regenerator according to the two-phase theory of fluidization, with a dilute phase model taking account of postcombustion reactions. The riser and regenerator temperature, the stripper and regenerator pressure drop and the composition of the regenerator flue gas are measured on line and are used for verification of the ability of the simulator to predict the dynamic transients between steady states in both open- and closed-loop unit operation. All the available process variables such as the reaction conversion, the coke yield, the carbon on regenerated catalyst and the catalyst circulation rate are used for the validation of the steady-state performance of the simulator. The comparison between the dynamic responses of the model and those of the pilot plant to step changes in the feed rate and preheat temperature reveals the ability of the simulator to accurately depict the complex pilot process dynamics in both open- and closed-loop operation. The dynamic simulator can serve as the basis for the development of a model-based control structure for the pilot plant, alongside its use as a tool for off-line process optimization studies.     

结构可观的换热网络温度测点分析及控制系统设计

复杂换热网络中间温度状态变量众多且变量间耦合严重,若不加以控制与观测,往往不利于物流间的热量传递与安全监测。换热网络的温度测点设置是实施控制的基础,为保证全部状态的可观性,凭经验设置的温度测点往往过多,经济性差,也缺乏理论论证与分析。因此从控制理论的角度,基于结构可观性理论分析换热网络的结构特性。分析旁路设置对换热网络结构可观性的影响,权衡可观性与经济性两方面因素,为实现设置最少的温度测点以满足全部状态的可观性要求,提出了换热网络全部状态可观的温度测点优化设计法。然后,基于相对增益分析,将已有旁路与优化得出的温度测点进行配对,构成换热网络的常规控制系统。最后,以某常减压蒸馏装置脱盐前换热网络为例验证了方法的可行性。     

基于GB150的废液冷却器设备设计

所设计的废液冷却器应用在某核电厂工程2号机组的废液冷却,其管侧和壳侧分别承受0.4MPa和1.0MPa的压力,一旦失效其危害性较大。通过GB150《钢制压力容器》对该设备的材料、设计、制造、检验提出了具体的要求,以确保该设备安全稳定运行。     

换热网络控制分析与设计研究进展

回顾了近年来对换热网络可控性方面的研究,即分析了当前换热网络的两种控制策略:控制性能指数法和旁路优化控制方法。阐述了这些方法的优点和尚待改进的问题,并指出换热网络的设计应同时考虑工艺与控制两方面。提出了工艺与控制集成的设计方法的具体研究思路,并指出换热网络工艺与控制集成设计的方法将成为今后换热网络设计与控制方面研究的发展方向。     

考虑工况变迁和兼顾运行的换热网络优化设计

基于固定工况设计的换热网络无法保证变工况下的运行性能,以换热网络的运行优化和动态设计为出发点,提出了换热器旁路调节的方法,结合Grossmann的换热网络分级超结构模型,建立了换热网络旁路调节的数学模型和求解策略。利用蒙特卡罗随机技术和最速下降法混合优化策略获得了最佳旁路开度,保证了工况迁移时换热网络的运行性能。实例应用表明:旁路调节大大增加了换热网络的柔性,降低了运行费用。合理调整旁路开度可使得换热网络的运行始终处在较优状态,获得显著的经济效益。     

基于非逆流传热的热交换网络系统的3E优化

考虑非逆流传热对换热设备传热温差、壳数和面积的影响，对包含非逆流换热设备的热交换网络系统进行优化设计。基于非等温混合分流分级超结构，采用能源、经济和环境（3E）综合评价指标，引入温差修正系数，建立了热交换网络多目标混合整数非线性规划（MO-MINLP）模型，并基于非支配排序遗传算法（NSGA-Ⅱ）提出了系统性的求解策略和求解方法。应用案例研究表明，涉及非逆流传热的热交换网络，其优化设计结果与基于纯逆流换热假设的设计结果有很大区别，且仅对基于纯逆流换热假设的设计结果进行修正并不能得到最优解，必须在建模中考虑温差修正效应的影响，从而保证设计结果的优化性、可靠性和实用性；3E评价反映了热交换网络系统在经济、能耗和环境影响之间的权衡和约束关系，使系统的设计更加实际，同时多目标的优化方法不但可以获得与单目标经济优化相当的最经济的结果，而且提供了多样性的优化解集供选择，提高了设计的灵活性，可以满足不同的设计需求。     

基于热容流率的换热网络夹点设计法

以Linnhoff换热网络夹点技术理论为基础,提出了在进行换热网络设计时,考虑热容流率随温度发生变化时确定夹点位置的方法,并结合实例进行分析计算。该法对夹点位置、最小温差、公用工程用量的确定更加准确,对投资费用的估算也更接近于实际。     

基于智能预测和机理模型的换热网络清洗决策

原油石化装置的换热器常受到结垢影响,导致换热器性能衰退严重,换热网络性能也会随之衰退,同时换热器之间的耦合关系,导致不同换热器的性能衰退对换热网络整体性能变化的影响不同。以往的清洗决策主要是根据单台换热器性能衰退到一定程度来制定的,这会导致换热网络整体可能处在较差的运行状态。因此,本文提出一种基于智能预测和机理模型的换热网络清洗决策方法,基于换热器的运行数据建立智能预测模型,获得换热器性能变化趋势,结合换热网络的性能模拟模型,进一步获得换热网络的性能变化趋势,从而从换热网络整体性能变化的角度来制定清洗方案。研究表明,对收集到的原油换热器运行数据,建立神经网络预测模型,具有较好的预测精度。通过对原油精馏装置换热网络的案例分析,当HE1、HE2和HE5三台换热器同时发生性能衰退时,换热网络年度公用工程能耗费用将增加12.1%。与传统基于单台换热器性能衰退情况制定的清洗方案相比,从换热网络整体性能衰退角度制定的清洗方案,年度额外公用工程费用减少13.1%,损失费用减少14.1%,年度总费用减少13.8%,而清洗次数仅增加3台次。