Application of ozone treatment and pinch technology in cooling water systems design for water and energy conservation

Re‐circulating cooling water systems offer the means to remove heat from a wide variety of industrial processes that generate excess heat. Such systems consist of a cooling tower and a heat‐exchanger network that conventionally has a parallel configuration. However, reuse of water between different cooling duties allows cooling water networks to be designed in a series arrangement. This results in performance improvement and increased cooling tower capacity. In addition, by the integration of ozone treatment into the cooling tower, the cycle of concentration can be increased. The ozone treatment also dramatically reduces the blow‐down that, in turn, is environmentally constructive. In this study, a new environmental‐friendly and cost‐effective design methodology for cooling water systems was introduced. Using this design methodology, Integrated Ozone Treatment Cooling System (IOTCS), achievement of minimum environmental impacts and total cost were afforded through a simultaneous integration of the cooling system components using an ozone treatment cooling tower and optimum heat‐exchanger network configuration. Moreover, in the proposed method, the cooling tower optimum design was achieved through a mathematical model. The IOTCS design method is based upon a complex design approach using a combined pinch analysis and mathematical programming that provides an optimum heat‐exchanger configuration while maximizing water and energy conservation and minimizing total cost. Related coding in MATLAB version 7.3 was used for the illustrative example to obtain optimal values in the IOTCS design method computations. The results of the recently introduced design methodology were compared with the conventional method. Copyright © 2009 John Wiley & Sons, Ltd.     

基于夹点技术的航煤加氢换热网络优化

针对某航煤加氢装置现行换热网络夹点温差不合理导致能耗较大的现状,利用夹点技术对该装置换热网络进行分析、优化。在该装置实际工况下的夹点温差附近选取相应的夹点温差,计算出不同夹点温差对应换热网络的年总费用,得出年总费用最小的夹点温差,即最优夹点温差。在最优夹点温差的基础上生成新的换热网络,结果表明,节能效果显著。     

Design of water and energy networks using temperature-concentration diagrams

The reduction of energy and water demand is a critical issue in various industrial sectors like the pulp and paper industry. This objective may be achieved through properly designed heat and mass transfer networks. This work introduces a new methodology for the synthesis of these systems.The procedure here presented is specifically conceived for networks with two distinct sections: the simultaneous heat and mass transfer sub-network, which main goal is the removal of pollutants from processes and the heat exchange sub-networks (direct and indirect), which main goal is the thermal management of the water flows and the heat recovery. To keep the two sections separate, water reuse in the simultaneous heat and mass transfer network is operated by allowing non-isothermal mixing between the streams. These irreversibilities produce a negative impact on the primary energy savings, which is discussed, but have some advantages in terms of operation, design simplicity and in retrofit applications.     

Improving energy recovery for water minimisation

A graphical approach for the design of heat-integrated water systems has been proposed to improve conceptual understanding for implications of heat recovery in water systems, as well as to provide systematic design guidelines for selecting most appropriate integrated options in practice. The developed design method aims to fully exploit water reuse potentials between water-using operations, and simultaneously to minimise any potential degradation of energy recovery resulted from water reuse. Graphical representations of heat-integrated water systems and their manipulation have been applied to investigate systematically design interactions, impacts associated with stream merging and splitting, and influences of non-isothermal mixing on heat recovery. Water Energy Balance Diagram has been developed to improve energy recovery in water reuse network. Energy-efficient and cost-effective configuration for heat recovery has been identified, using improved Separate System Approach. The proposed approach significantly reduces both water and energy requirements for single-contaminant water systems.     

Biochemical production of ethanol and fatty acid ethyl esters from switchgrass: A comparative analysis of environmental and economic performance

As advances in biotechnology have continued at a rapid pace, interest in the biochemical production of so-called “drop-in” fuels has increased as a way to avoid the well-known shortcomings of ethanol as a fuel molecule and to potentially exploit the processing advantages of a water-immiscible fuel to reduce product recovery costs and energy requirements. In the current study, processes to produce either ethanol or a representative fatty acid ethyl ester (FAEE) via the fermentation of sugars liberated from lignocellulosic materials pretreated in acid or alkaline environments are analyzed in terms of economic and environmental metrics. Simplified process models are introduced and employed to estimate fuel production, greenhouse gas emissions, net energy consumption, minimum fuel selling price, and water consumption for both processes. Monte Carlo analyses were carried out to identify key sources of uncertainty and variability, and an analysis of the impact of potential improvements to the FAEE process was performed. We find that the near-term performance of processes to produce FAEE is significantly worse than that of ethanol production processes for all metrics considered, primarily due to poor fermentation yields and higher electricity demands for aerobic fermentation. Even if these issues are addressed in the longer term, the reduced cost and energy requirements of FAEE separation processes will be at least partially offset by inherent limitations in the relevant metabolic pathways that constrain the maximum yield potential of FAEE from biomass-derived sugars.     

A new type of district heating system based on distributed absorption heat pumps

Large district heating (DH) system accounts for 70% of urban building heating in China. In North China, this proportion is even higher (The North China is the north of the Huai River and Qinling Mountains). Many cities in North China can exploit various kinds of low-grade renewable energy. This paper presents a new heating method to realize renewable energy recovery by absorption heat pumps associated with municipal network. In the DH substations, absorption heat pumps are driven by the exergy-difference originated from the larger temperature difference of heat exchange between primary and secondary heat network. There are two configurations—type I and type II substations based on the temperature of renewable energy. A reasonable parameter setting of system is suggested. The equipment operational performance was optimized based on a practical example. The low-grade renewable energy can be recovered effectively in this method. As a result, both heating capacity and energy efficiency of the DH system can be improved. Furthermore, operating costs may be reduced remarkably, due to the reduction in both the coal consumption of heat production unit and the power consumption of delivery pump. Therefore, the system is superior in energy conservation and has a promising application prospect.     

Heuristic approach for heat exchanger networks

A systematic approach based on few heuristics for the synthesis of optimum heat exchanger networks has been developed. The approach, which is simple and easy to apply, consists of three sequential steps. In the first pre-analysis step, the optimum temperature approach is determined. In this step, a set of heuristic constraints are used to determine minimum utility requirements. In the second step, heat exchanger networks are generated using the H/H heuristic of matching hot and cold streams. In the third step, the initially generated networks evolve through loop breaking and energy relaxation to achieve the target of the minimum number of units. The effectiveness of the approach developed has been tested on a number of literature test problems ranging in size from four to ten streams and on an industrial case involving a recovery heat exchanger network around a topping tower. The approach produced simple network structures and improved energy recovery. The cost results obtained in this work agree favourably with optimal solutions reported in the literature.     

A decomposition approach for retrofit design of energy systems in the sugar industry

Sugar factory retrofit often includes improvements in the factory’s energy system comprising power plant, multiple-effect evaporator and process heating equipment. To reduce the energy consumption, the evaporator subsystem and the process heating subsystem should be retrofitted to make improved heat recovery possible. The retrofit design procedure includes two stages: targeting for various options of the evaporator structure and selecting the most promising one, and designing both subsystems for targets so determined. At the targeting stage, one is confronted with the problem of designing the evaporation process and simultaneously considering the energy consumption. This constitutes an extension of the established targeting approach that assumes process conditions to be fixed. The problem can be transformed by decomposing the energy system, that is, conceptually separating the evaporator (in which vapours and condensates are generated) from the process heating subsystem (in which these heat carriers can be regarded as utilities). The transformed problem is one of targeting under constraints and can be solved iteratively by combining pinch analysis algorithm with evaporator simulator. The second stage of the retrofit design procedure requires defining the details of process heating subsystem that includes a heat exchanger network. This problem is conveniently solved using the network pinch approach.     

污水污泥热解过程的能量平衡与反应热分析

依据能量守恒定律,通过分析污水污泥热解过程的能量利用、耗散和回收情况,提出了污泥热解制取三相产物处理系统的能量平衡模型,分析计算了污泥热解反应热,并利用回收率和耗能比对热解处理系统的耗能状况进行了评价.结果表明:能量利用过程中总存在能源的耗散,减少能耗的主要方式是尽可能提高产物的能值、降低热消耗和废弃的能量;在不同的热解工况下,热量损失的差别明显,热解停留时间长、升温速率慢、热解温度高均会导致输入能量和热损失增大;能耗评价也验证了热解技术能够回收更多的能量,可以获得更大的能耗比.     

Application of an exhaust heat recovery system for domestic hot water

Typically, a great deal of heat is wasted in the drainage systems of large-scale public shower facilities, such as those in schools, barracks, and natatoriums. This paper enhances a heat pump system used in public shower facilities for exhaust heat recovery. The system consists of three sections for exhaust heat recovery: solar energy collection system, drainage collection system, and heat pump system. In the system, the energy from the solar energy collection system is used for the initial heating the shower's tap water. Afterwards, the drainage collection system collects the used shower water. Finally, the electric heat pump recycles the exhaust heat from the collected water to heat the shower's tap water. The operational practice of the system was presented. The drainage temperature and equipment capacity was optimized based on a practical example. The advantages of this heat pump system compared to gas-fired (oil-fired, coal-fired, electric) boilers are lower energy consumption, less pollution, and lower operating costs. Therefore, the system is superior in energy conservation and has a promising application prospect.     

Recovery and utilisation of heat from domestic waste water

The usage of energy in domestic and other dwellings for the production of hot water is compared with the total energy consumption of the establishment, and it is shown that the relative amount is strongly dependent upon the social class and life-style of the occupants.In the middle classes about one-third of the total energy input is used to provide hot water, and a large proportion of this heat is potentially recoverable when the water is discharged to waste.Experimental studies have been carried out on a heat recovery system installed in a house which have shown that a 10 per cent saving in the total energy consumption can be effected for a capital expenditure that is recouped in three years.     

Is there a water–energy nexus in electricity generation? Long-term scenarios for the western United States

Water is required for energy supply, and energy is required for water supply, creating problems as demand for both resources grows. We analyze this “water–energy nexus” as it affects long-run electricity planning in the western United States. We develop four scenarios assuming: no new constraints; limits on carbon emissions; limits on water use; and combined carbon and water limits.We evaluate these scenarios through 2100 under a range of carbon and water prices. The carbon-reducing scenarios become cost-effective at carbon prices of about $50–$70 per ton of CO₂, moderately high but plausible within the century. In contrast, the water-conserving scenarios are not cost-effective until water prices reach thousands of dollars per acre-foot, well beyond foreseeable levels. This is due in part to the modest available water savings: our most and least water-intensive scenarios differ by less than 1% of the region's water consumption.Under our assumptions, Western electricity generation could be reshaped by the cost of carbon emissions, but not by the cost of water, over the course of this century. Both climate change and water scarcity are of critical importance, but only in the former is electricity generation central to the problem and its solutions.     

炼油工业节能仍有许多细致扎实的工作要做

介绍了中国石化炼厂近几年节能取得的成效,炼油综合能耗从2001年的78．86kg标油/t降低到2007年的65．91kg标油／t,炼油单因耗能从2001年的13．1kg标油,（t·因素）降低到2007年的10．11kg标油,（t·因素）。通过炼油能耗评价和节能潜力分析,对中国石化炼油企业节能现状作出了基本评价,指出了今后节能任务艰巨,节能空间较大。分析了中国炼油业面临的新问题和新挑战,对新建和改扩建炼厂能耗进行了剖析。最后对炼油企业挖掘节能潜力提出了建议,包括合理选择原油、生产优化、提高全厂加热炉热效率、深化装置间的热联合、蒸汽系统的优化、低温热能的合理利用、采用高效节能设备、节电、回收凝结水、加强节能管理。     

通过清洁生产审核实现啤酒企业的节能降耗

啤酒生产中能源的消耗约占生产成本的10％。在开展啤酒企业清洁生产审核中，系统分析啤酒企业能源消耗状况，对比国内外先进工艺和技术，提出可以通过加强用能管理，采用麦汁一段冷却工艺、糖化热能回收、糖化热水回收、热电联供回收系统、沼气回收系统，以及在北方利用冬季室外风冷却系统的技术工艺，可以减少能源的消耗，达到节能、降耗、减污、增效的清洁生产目的。     

Heat integration retrofit analysis of a heat exchanger network of a fluid catalytic cracking plant

The impact of a process system on environmental pollution has both a local and global effect. The performance of the heat exchanger network (HEN) in a plant is an important aspect of energy conservation. Pinch technology and its recent extensions offer an effective and practical method for designing the HEN for new and retrofit projects.The fluid catalytic cracking (FCC) is a dominant process in oil refineries and there has been a sustained effort to improve the efficiency and yield of the unit over the years. Nevertheless, benefits and scope for improvement can still be found. The HEN of the FCC process considered here consists of a main column and a gas concentration section. Appropriate data were extracted from the existing network, using flowsheeting simulation. The stream data consists of 23 hot and 11 cold streams and cost and economic data required for the analysis were specified. The incremental area efficiency methodology was used for the targeting stage of the design and the design was carried out using the network pinch method consisting of both a diagnosis and optimisation stage. In the diagnosis stage promising designs were generated using UMIST developed sprint software. The generated design was then optimised to trade-off capital cost and energy savings. The design options were compared and evaluated and the retrofit design suggested.The existing hot utility consumption of the process was 46.055 MW with a ΔT_min of 24°C. The area efficiency of existing design was 0.805. The targeting stage using incremental area efficiency sets the minimum approach temperature at 11.5°C, thereby establishing the scope for potential energy savings. To achieve a practical project, the number of modifications is limited. The selected retrofit design has 8.955 MW saving – 74% of the whole scope. This corresponds to 27% utility cost savings with a payback period of 1.5 years. The modifications include addition of four heat exchanger units and repiping of one existing exchanger.     

江水源热泵机组年运行能耗预测方法研究

在建筑工程的可行性研究阶段,空调系统冷热源的年运行能耗预测是静态投资回收期分析、全寿命周期成本分析中的核心组成部分,是冷热源选型的重要依据之一.然而,在实际项目中通常选用IPLV/NPLV、设计工况COP进行年运行能耗估算,计算结果与实际能耗有较大的误差.在已知建筑设计冷、热负荷的前提下,引入平衡温度概念,采用BIN方法预测不同温度下的建筑负荷,通过参数修正的方式预测江水源热泵机组在部分负荷率情况下功率,将热泵机组功率修正系数的变化函数拟合为水源侧进水温度和负荷侧回水温度的多项式.对长江上游地区江水温度及气象参数进行监测,并建立了江水温度与空气于球温度的数学关系.提出江水源热泵机组年运行能耗预测方法.该方法反映了系统运行的实际特征,且计算过程较为简单,可以在实际工程中应用.     

Entropy and the cost of complexity in industrial production

The building of an industrial society can be viewed as a process of self-organisation with a decrease in entropy in society and a corresponding increase of entropy through dissipation of energy into the environment. The process is driven by the “degradation” of high quality energy to low-quality heat as energy flows down potential gradients at the same time creating a favourable potential gradient driving the reaction. The post-industrial society is characterised by an increase in complexity, which can be monitored by the exergy consumption. Here a first attempt is made to relate the complexity of a number of products, as represented by the number of their functional parts, to their actual economic value.     

On Minimization of the Number of Heat Exchangers in Water Networks

This article addresses the problem of minimizing the number of heat exchangers for heat recovery as well as the number of mixing and splitting junctions within water networks while maintaining the energy targets determined by the classical pinch analysis. A new systematic approach is proposed to eliminate the kink points and linearize the composite curves. This is based on a systematic strategy that indicates how to mix and split the water streams in order to modify the shape of the initial composite curves. A new graphical thermodynamic rule that avoids the deterioration of energy targets while minimizing the number of heat transfer units as well as the mixing and splitting network complexity has been formalized. This rule permits the control of the procedure of mixing and splitting on the T-H diagram in order to guarantee the pre-established targets. The proposed approach can be used for either the manual design of heat recovery within water networks or the building of a superstructure with a limited number of feasible design options.     

热泵热水器技术及应用

热泵热水器借助外部能量能把不能直接利用的低位热源转换为可以利用的高位热能,从而达到节约部分高位能的目的。阐述了热泵热水器的发展历史与应用现状,分析了空气源热泵的工作原理和节能原理,并将空气源热泵热水机组与电热水器、燃油热水锅炉、燃气热水锅炉等热水供应系统的性能进行了比较。在此基础上,结合企业工程应用实例,指出了推广热泵技术对于节能减排的意义。     

Synthesis of heat exchanger networks featuring a minimum number of constrained-size shells of 1–2 type

In chemical plants requiring a high number of heat exchangers, standard sizes are established so that most of the services can be satisfied through arrays of a limited number of different standard-type units. If such an industrial practice is not taken into account during the heat recovery network synthesis task, the optimality of the proposed design could be doubtful. This paper addresses the HENS problem allocating multiple constrained-size shells rather than a single one to accomplish a heat match. Two cases are considered: (a) pure countercurrent exchangers and (b) shell-and-tube exchangers of 1–2 type. The neighbor-based HENS framework of Galli and Cerdá (1998) has been generalized in order to adopt a more realistic fixed-cost target, i.e. the overall number of constrained-size shells. Therefore, new 0–1 variables have been defined to stand for the additional shells needed to get both, a shell size below the specified upper bound, and simultaneously, an F_T correction factor above the threshold value everywhere. The resulting MILP problem formulation is now able to find network structures reaching the heat recovery target, under some structural constraints on the network design specified by the user, at near-minimum capital cost. The proposed algorithmic approach has been successfully applied to the solution of a couple of example problems and produced significant capital cost savings compared with prior HENS techniques.