考虑本质安全的换热网络多目标优化

由于国内外重大化工事故的频发及化工行业节能降耗的需求日益迫切,研究本质更安全的换热网络多目标优化具有重要意义。采用评价指数的方法,对换热网络的本质安全易爆性、毒性、存量进行量化表征。采用数学规划法分别建立换热网络经济与本质安全易爆性、毒性、存量同步优化数学模型。采用归一化法构建经济和安全的目标函数。通过算例研究发现,考虑易爆性,倾向于不易爆流股间换热,减少易爆流股换热次数;考虑毒性,倾向于减少有毒流股流经换热器的次数;考虑存量倾向于减少换热网络的总存量。最后综合考虑易爆性、毒性、存量作为安全指标与经济同步优化,通过算例研究表明,多目标优化的最优换热网络在很大程度上取决于经济权重的选取。     

综合考虑泵的设备及运行费用的换热网络优化

流体流经换热设备产生的压降是影响换热网络综合的重要因素,且压降会对整个换热网络系统的稳态运行造成影响。因此在进行换热网络综合时,泵的设备购置费、运行泵的能耗费用需同换热设备费用和公用工程费用同时进行考虑。本文基于有分流的非等温混合分级换热网络超结构模型,并且去除流股给热系数为常数的假设,将流股的给热系数作为流股流速的函数,以换热网络最低年总费用作为本文数学模型的目标函数,综合考虑泵的设备购置费用和泵运行时的能耗费用,建立了一个换热网络同步综合的MINLP数学模型。采用改进的拟并行的遗传/模拟退火算法对该数学模型进行求解,可获得最优的压降值及最优流股给热系数下的换热网络结构。最后,通过具体的算例证明了模型的有效性和可靠性,达到了既简化换热网络结构又降低了年总费用的目标。     

考虑非等温混合的能量集成用水网络综合

提出了考虑非等温混合的新的水网络模型,并结合线性规划（LP）转运模型同时优化水网络的水耗及公用工程目标。新的水网络模型引入非等温混合以改善用水网络的能耗特性及减少模型中参与集成换热网络的流股数,从而降低设计换热网络的复杂程度。在确定水网络的水耗及公用工程目标后,采用夹点法设计详细的换热网络结构。两个算例结果表明,新的水网络模型不仅能确定用水网络的最优水耗及公用工程目标,而且还能得到一个更加简单的换热网络。这对节省设备投资及减少操作费用具有重要意义。     

功热交换网络综合的研究进展

功和热是化工工业中使用能源的两种最主要方式,由于流股压力、温度操作需要消耗大量的功热,因此研究功热的协同利用对于提高过程整体能源利用率具有重要的意义。本文首先概述了基于热力学分析的功热交换网络综合的研究情况,以系统?耗最小为目标探讨压缩机、膨胀机优化配置与换热网络用能瓶颈的耦合关系,揭示了功热协同利用的作用机制。然后系统地总结了以年度总费用最小为目标的数学规划模型综合功热交换网络的研究进展,探寻压力操作路径、流股功/热交换匹配、公用工程消耗量及设备投资之间的有效权衡;最后对后续研究进行展望,指出可进一步探究考虑流股冷热性质判定的功热交换网络同步综合、公用工程系统优化与功热交换网络同步设计的耦合等。     

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。     

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。     

考虑生产排序的间歇过程换热网络综合与优化

间歇过程换热网络综合是化工系统工程研究的重要部分,设计时需要考虑时间、设备、生产排序等多方面因素,具有一定的复杂性。本文围绕多批次间歇过程的直接换热问题,考虑生产排序的影响,采用覆盖操作和非覆盖操作,通过调整批间隔增加流股直接换热的可能性,减少设备闲置,得到3种不同的生产方案;针对每一个生产方案,采用启发式方法综合得到初始换热网络,并对该网络进行结构调优,提出渐进调优规则,在公用工程费用和设备费用间作权衡,减少换热器个数和流股分流,得到年度总费用最低且换热设备个数较少的换热网络,使其更符合实际应用;将3种生产方案对比,可以发现生产排序对换热网络的影响。最后将所提方法应用于实际算例,验证所提方法的可行性。     

综合考虑经济性与效率的换热网络多目标约束优化方法

换热网络优化中不仅要考虑能量回收的“量”,还要考虑能量回收过程中“质”的耗散问题。在换热网络最大能量回收的前提下,基于不可逆传热过程中的耗散理论,以代表能量回收品质的效率最高为目标,建立综合能量回收数量、品质并同时考虑换热网络经济性的多目标混合整数非线性规划（MOMINLP）模型。根据模型目标有主次之分的特点,基于ε约束法对模型进行分步优化并结合BARON软件进行精确求解,依次求解换热网络的最大能量回收量(MER)与最低年均总成本(TAC),再将所得结果乘以松弛系数ε_i作为缩小搜索区域的约束条件,获得能量与成本约束下效率的Pareto前沿。通过对经典10SP1案例进行计算求解,最终得到最大能量回收量下,费用松弛系数为1.05时费效比最小的优化方案,而且本文的多目标约束优化方法能够更快求得综合的最优解。最后通过T-Q图中的换热网络组合曲线对比不同优化方案的效率,将换热网络划分为内部换热部分与剩余流股部分,多目标约束优化方法能够降低内部换热不可逆损失,提高剩余流股的温度。     

基于自适应竞争群优化算法的无分流换热网络综合

换热网络模型具有非凸和非线性的特性,对于大规模超结构优化问题,采用经典的智能算法优化效率低,容易陷入局部最优值。以年综合费用为目标函数,基于自适应竞争群优化算法对无分流分级超结构换热网络模型进行优化。该方法采用对粒子平均位置的递减学习,通过自适应调节速度权重提高换热网络结构的全局优化能力和局部优化能力。通过两个典型算例分析表明,该方法相比量子粒子群算法大幅减少了模型调用次数,缩短了运行时间,并且找到了更好的优化结果。     

基于自适应竞争群优化算法的无分流换热网络综合

换热网络模型具有非凸和非线性的特性,对于大规模超结构优化问题,采用经典的智能算法优化效率低,容易陷入局部最优值。以年综合费用为目标函数,基于自适应竞争群优化算法对无分流分级超结构换热网络模型进行优化。该方法采用对粒子平均位置的递减学习,通过自适应调节速度权重提高换热网络结构的全局优化能力和局部优化能力。通过两个典型算例分析表明,该方法相比量子粒子群算法大幅减少了模型调用次数,缩短了运行时间,并且找到了更好的优化结果。     

带有热储罐的间歇过程换热网络综合

间歇过程流股对时间的依赖性增加了其换热网络综合的难度。提出了一种采用间接换热进行换热网络综合的方法,且考虑了直接换热,同时提出了合并热储罐的方法,并利用热储罐的特点合并间接换热中的换热器,用以减少设备费用,以热储罐中介质的温度为变量以年度总费用最小为目标函数建立非线性规划数学模型,确定热储罐内介质温度,最后将该方法应用于实例中证明此方法的有效性。     

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.     

考虑压降的换热网络研究

在换热网络综合设计中,压降是一重要影响因素。安装泵、压缩机等设备可克服流体流动过程中的阻力损失,这些动力设备的投资费用和能耗费用(简称动力费用)是换热网络总投资的重要部分,所以年总费用目标函数中应包括公用工程费用、换热器投资费用和动力费用,这三者应作权衡处理来决定最优夹点温差ΔTmin,以得到年总费用最小、结构更优化的换热网络。     

A grid-based facilities allocation approach with safety and optimal heat exchanger networks synthesis

A new approach is presented to determine optimal layout of facilities where toxic releases may occur in an existing or new facility. The land area is divided in equally sized rectangular grids, where each grid contains up to one facility surrounded by streets. Some facilities may produce hot and/or cold streams and the associated heat exchangers network (HEN) is simultaneously optimized with the layout problem. The three dimensions of geographical allocation points for each generated stream are included in the model. No additional cost for geographical allocation of heating and cooling services is considered since every facility is expected to contain these services regardless of their use in the HEN. The toxic effect is estimated via probit functions and its associated risk reduction results in providing safety to the combined HEN-facility layout problem. The grid-based allocation eliminates numerical difficulties appearing with conventional non-overlapping and Euclidian distance equations.     

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。     

换热器结垢与换热网络裕量设计方法研究进展

从结垢现象影响换热系统正常运行的角度出发,介绍了近几年换热网络裕量设计以及针对结垢问题不同学者研究出的换热网络优化设计。总结了在换热网络设计中对换热器清洗时序、清洗周期优化或者增加换热网络的裕量设计的不同换热网络设计最优方法,但这些方法都是在换热网络设计之初,考虑换热器结垢最严重的情况即换热网络在“最差”工况下进行的优化,因此优化得到的换热网络难以保证换热网络全运行周期的持续节能优化。本文结合现有换热网络设计方法的利弊,针对结垢过程的慢时变、持续特点,提出一种基于长周期持续节能的换热网络设计优化方法,在换热网络设计之初,定量分析结垢对网络结构的影响,以换热网络全周期累积总费用为目标函数,实现换热网络的最优综合。     

Simultaneous MINLP synthesis of heat exchanger networks comprising different exchanger types

This paper describes the simultaneous MINLP synthesis of heat integrated heat exchanger networks comprising different heat exchanger types. The stage-wise superstructure of heat exchanger networks (HEN) by Yee and Grossmann (Comput. Chem. Eng. 14 (1990) p. 1165) is extended to alternative exchanger types. The selection of the types is modeled by disjunctions based on operating limitations and the required heat transfer area. Since different types of heat exchangers involve different design geometries, which influences the inlet and outlet temperatures of heat exchangers, additional constraints are specified to provide a feasible temperature distribution in HEN. The consideration of different exchanger types drastically increases the combinatorics, size and computation effort needed to solve the problem. The integer-infeasible path MINLP approach has been applied to perform an efficient initialization scheme and to halve CPU times for solving MILP master problem of the modified OA/ER algorithm. A special multilevel MINLP procedure in reduced integer space has been proposed to solve medium size HEN problems (20 streams) comprising 10³ and more binary variables.     

换热网络旁路优化设计

提出了一种可以降低已有换热网络运行费用的旁路优化设计方法,使得网络控制自由度增大,运行费用明显降低。该优化设计方法将网络运行总费用作为目标函数,同时考虑结垢热阻对换热器换热效果的影响,经过多次优化计算确定旁路位置和开度,并根据现场具体情况选择合适的旁路开度下限,确定旁路数目,最终实现网络旁路优化设计。通过示例说明了本文所提方法的有效性和实用前景。     

Minimizing investment cost for multi-period heat exchanger network retrofit by matching heat transfer areas with different strategies

Multi-period heat exchanger network (HEN) retrofit is usually performed by targeting and matching heat trans-fer areas. In this paper, based on the reverse order matching method we proposed previously, three strategies of matching heat transfer areas are proposed to minimize the investment cost for the retrofit of HEN in multi-period, in which replacement of heat exchangers, addition of heat exchangers and addition of heat transfer areas are performed. We demonstrate the procedures through three scenarios, including maximum number of substituted heat exchangers after retrofit, minimum additional heat transfer areas in the retrofitted HEN, and minimum investment cost for retrofit. The strategies are extended to a single period HEN retrofit problem. The results of multi-period and single period HEN retrofit problems indicate the effectiveness of the strategies. More-over, these results are better than those reported in literature. The strategies are simple and easy to implement, which are of great benefit to large-scale HEN retrofit in practice.     

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.