Constrained thermohydraulic optimization of the flow rate distribution in crude preheat trains

Crude preheat trains are heat exchanger networks which heat the crude oil stream in the petroleum distillation using hot product streams and pumparounds. The final heating step is executed in a furnace. The thermal efficiency of this process is strongly dependent on the crude preheat train performance, and, during the refinery operation, the heat load of the exchangers may decrease due to fouling. Associated to the reduction of the thermal effectiveness of the heat exchangers, fouling also causes an increase of the flow resistances along the thermal equipment. A potential approach to mitigate this problem is based on the optimization of the distribution of the flow rates in the crude preheat train for maximizing the final crude temperature. In this context, this paper presents a constrained nonlinear programming formulation for this task. The equality constraints encompass mass, energy and mechanical energy balances and heat exchanger equations for describing the thermal and hydraulic behavior of the system. The performance of the proposed approach is explored using two examples, a simple network and a crude preheat train based on a real Brazilian refinery.     

Operational optimization of crude oil distillation systems using artificial neural networks

A new methodology for optimizing heat-integrated crude oil distillation systems is proposed in this work. The new procedure considers an artificial neural networks (ANN) model for representing the distillation column. Models of the distillation column and the associated existing heat exchanger network are incorporated in an optimization framework to systematically determine the operating conditions that improve the overall process economics. Of particular interest is the problem of optimizing the net value of the products obtained from the column by increasing the yield of higher-value products at the expense of less valuable products, while taking into account feasibility of the distillation specifications, heat recovery, energy and equipment constraints. A two-stage procedure is applied to first optimize the column operating conditions based on minimum utility requirements. In the second stage the heat exchanger network is designed.     

5.0Mt/a中东原油常减压换热网络优化

利用窄点技术优化5.0 Mt/a中东原油常减压蒸馏装置的换热网络,采用VC++编程技术,确定最小传热温差Δtmin;优化原油分流股数,降低冷公用工程量;热端分段设计以满足初馏塔深拔。优化结果:Δtmin为15℃;热端温度240℃,冷端温度225℃;最小冷、热公用工程量分别为17 139.74 kW和43 378.74 kW。在常渣外甩0.54 Mt/a情况下,原油换后终温为283℃,换热面积为16 935 m2,比同等条件下原装置的换后终温提高31℃,换热面积减少3 967 m2。     

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。     

蒸汽发生器在常减压装置中的应用

炼油装置对蒸汽的消耗是除了加热炉燃料油外的最大用能方式之一,炼油装置的低温余热利用是石化装置节能减排的主要工作思路,在常减压装置适当的工艺部位选择合适的热流作为热源,增加蒸汽发生器,再利用适当的低温余热提高换热终温,可替代原来的燃油蒸汽锅炉,节能减排效果显著,经济效益十分可观。     

与换热网络热集成的精馏塔压优化

调整精馏塔的操作条件是节省塔能耗的有效途径之一，然而在对已有装置进行用能优化时，需同时考虑精馏塔操作条件对塔能耗和换热网络能耗的影响。基于装置所有流股的冷热复合曲线，针对跨夹点的精馏塔，同时考虑了精馏塔的再沸、冷凝以及过程流股，分析了塔压变化对装置公用工程消耗的影响，并对某连续重整装置汽提塔进行了案例分析。结果显示，塔压降低可使冷凝器能耗增加，再沸器能耗减小，而对于塔顶塔底出装置流股，塔压降低可节省冷却公用工程但增加加热公用工程。装置总体的节能效果为塔顶冷凝器、塔底再沸器和塔顶塔底出装置流股节能效果的综合作用。对某连续重整装置汽提塔分析表明，塔压降低200.0 kPa时，其加热公用工程用量将减少577.5 kW。     

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。     

加工俄罗斯原油常压装置设计中应注意的问题

哈尔滨石化分公司为适应原油品种的变化 ,在常压装置技术改造中 ,采用防腐措施 ,调整换热流程 ,换热终温比技术改造前提高 40℃ ;采用热管换热器回收热能 ,能耗较技术改造前平均低 12 5kJ/t原油 ;改造后的常压装置能炼制含硫 <0 5% ,含酸 0 5mgKOH/L原油     

500万t/a常压装置标定能耗分析及预测

中国石油某石化公司500万t/a常压蒸馏装置标定数据显示该装置能耗远低于同类装置能耗水平。从影响装置能耗的各个方面,对比分析了该装置标定能耗与设计能耗之间的差别。通过对比发现,装置区建立联合装置,可以有效提高换热终温;大型机泵电机采用变频可以降低装置电耗。通过分析五套不同地区常压装置的运行能耗及原料性质参数Cp值,发现两者之间存在近似线性关系,对预测常压装置能耗有积极意义。     

SePTA—A new numerical tool for simultaneous targeting and design of heat exchanger networks

Pinch Analysis is an established insight-based methodology for design of energy-efficient processes. The Composite Curves (CCs) is a popular Pinch Analysis tool to target the minimum energy requirements. An alternative to the CCs is a numerical technique known as the Problem Table Algorithm (PTA). The PTA however, does not show individual hot and cold streams heat cascades and cannot be used for design of heat exchanger networks (HEN). This paper introduces the Segregated Problem Table Algorithm (SePTA) as a new numerical tool for simultaneous targeting and design of a HEN. SePTA shows profiles of heat cascade across temperature intervals for individual hot and cold streams, and can be used to simultaneously locate pinch points, calculate utility targets and perform SePTA Heat Allocation (SHA). The SHA can be represented on a new SePTA Network Diagram (SND) that graphically shows a heat exchanger network together with the amount of heat exchange on a temperature interval scale. This paper also shows that SePTA and SND can be a vital combination of numerical and graphical visualisation tools for targeting and design of complex HENs involving stream splitting, threshold problems and multiple pinches.     

大规模复杂过程系统能量综合方法

针对过程系统工程的一个难点－－全过程系统能量综合,提出了“过程用能一致性原则”,从用能的角度上提高系统的集成性,将全过程系统的能量综合问题为相应的虚拟换热网络综合问题;并对大规模虚拟换热网络的求解进行了研究,提出了适用的分解策略;应用自行开发的过程用能夹点分析软件进行用能分析及换热网络匹配,实例分析节能效果显著。     

多流股换热器网络综合方法在原油预热系统中的应用

以原油常减压蒸馏装置原油预热网络为研究对象,进行了多流股换热器网络的实例综合. 基于超结构物理模型建立了改进的多流股换热器网络综合数学模型,提出将该网络综合问题由混合整数非线性规划问题转化为简单的非线性规划问题的求解策略,并利用改进的遗传/模拟退火新算法进行了原油预热网络的综合. 与Hextran软件的综合结果以及现场换热网络的对比表明,本模型和求解策略可以应用于工业规模的多流股换热器网络综合,有可能取得较好的经济效益.     

原油蒸馏过程换热器支出出口温度平衡控制

设计了某原油蒸馏过程换热器支路出口温度平衡控制系统 ,经实际运行检验 ,控制效果很好。     

Studies on simultaneous energy and water minimisation—Part II: Systems with maximum re-use of water

A new systematic design methodology has been developed for the simultaneous management of energy and water systems that also feature maximum re-use of water. A two-dimensional grid diagram is proposed to exploit different options within water systems and also enable reduced complexity of the energy and water network. Isothermal and non-isothermal stream mixing between water streams are introduced to create separate systems between hot and cold water streams in the energy composite curves and provide a design basis for a better structure with fewer units for the heat exchanger network. In addition to allowing re-use of water, issues about heat losses inside unit operations have also been incorporated in the simultaneous management of water and energy.     

200kt/a甲醇精馏系统的优化设计

以粗甲醇为原料,采用四塔精馏工艺,基于Aspen Plus工艺模拟软件,对甲醇精馏系统进行模拟优化设计及塔器水力学计算;运用EDR换热器设计软件,对本装置的换热器进行选型计算。模拟计算结果表明,精甲醇产品纯度为99.99%(wt)、甲醇收率为99.67%、蒸汽单耗为1.09t、循环冷却水单耗为83.24t,产品质量符合GB 338-2011国标优等品及美国联邦AA级标准质量要求,装置能耗水平达到国内先进水平。     

Design of flexible heat exchanger network for multi-period operation

Heat exchanger networks (HENs) increase heat recovery from industrial processes by matching hot and cold streams to exchange heat and reducing utility consumption. The design of HENs is a very complex task which generally involves mixed-integer non-linear programming (MINLP).This work evaluates and critically compares existing HEN design methods. It then presents a systematic methodology in the design of HENs under multiple periods of operation. The model presented in this work is a superstructure-based MINLP model which minimises the total annualised cost containing heat exchanger area cost and utility costs. The model is based on the superstructure by Yee and Grossmann [1990. Simultaneous optimisation models for heat integration—II, heat exchanger network synthesis. Computer & Chemical Engineering 14(10), 1165-1184], which was later formulated for multiple periods by Aaltola [2002. Simultaneous synthesis of flexible heat exchanger network. Applied Thermal Engineering 22, 907-918]. It includes a multi-period simultaneous MINLP model to design the HEN structure, and an NLP model to improve the solution and allow for non-isothermal mixing. Modifications to Aaltola's model include the use of maximum area per period in the area cost calculation of the MINLP objective function, and the removal of slack variables and weighed parameters from the existing NLP improvement model.The new model has been applied to one industrial case study, demonstrating that the new combined MINLP-NLP model can obtain better solutions by not relying on the average area assumption in the MINLP stage.     

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.     

Investigating the trade-off between operating revenue and CO2 emissions from crude oil distillation using a blend of two crudes

Blending of different crude types is frequently used in petroleum refineries to improve their profitability and products yields. However, energy consumption and consequential CO₂ emissions strongly depend on the types of crude being processed. The trade-off between CO₂ emissions and economic objectives, such as net revenue, is investigated for cases of different crude blends using the multi-objective optimization approach. The first objective is the minimization of CO₂ emissions whilst the second objective is maximizing the net revenue from the crude distillation unit (CDU). A rigorous model is used to estimate CO₂ emissions from different sources within the CDU. This emissions model incorporates pinch analysis for heat integration, to optimize the distribution of utilities related to emissions. Blends of two crudes, 36 API and 27.7 API, are used as feedstock to a rigorous CDU model of the atmospheric crude tower, vacuum tower and heat exchanger network. Lighter crude blends recorded higher CO₂ emissions and net revenue compared with the heavier blend due to the greater distilled fraction. However, CO₂ emissions did not vary linearly with the fraction of each crude, as the heat exchanger network also influenced the degree of heat recovery and consequently the level of CO₂ emissions. The multi-objective solutions show the influence of all 13 of the process variables on the objectives.     

常减压蒸馏换热网络节能优化

利用夹点技术对常减压蒸馏换热网络进行分析,优化该常减压蒸馏装置换热网络结构,最大限度的回收热量,节能效果显著。     

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.