An Extended Pinch Analysis and Design procedure utilizing pressure based exergy for subambient cooling

A new methodology for process synthesis extending traditional Pinch Analysis with exergy calculations is described. The methodology shows great potential for minimizing energy requirements (total shaft work) in subambient processes. This is achieved by optimizing compression and expansion work for the process streams together with the work needed to create necessary cooling utilities. The procedure, referred to as Extended Pinch Analysis and Design (ExPAnD), is illustrated by two examples, first in a simple example on how to utilize pressure based exergy in a cold stream for subambient cooling of a hot stream, then in the main example describing the use of the design methodology to develop a novel process for liquefaction of natural gas to LNG.     

The heat exchanger network design as a paradigm of technology integration

The work presents evidence from experiments that attempt to combine optimisation technologies of different qualities and advantages. The evidence is illustrated in relevance to the design problem of heat exchanger networks (HEN). The HEN problem has been addressed separately by Pinch technology, mathematical programming, and stochastic optimisation. Pinch methods account for conceptual principles driven by an overall understanding of the problem. Mathematical programming applications have spanned across the entire spectrum of formulations and include LP, MILP, NLP, and MINLP problems. Stochastic optimisation is presented mostly in the form of simulated annealing and genetic algorithms. Considered in isolation, the different optimisation methods are both blessed and baffled in that they simultaneously enable and disable particular features. The paper presents scientific experiments as a paradigm for the development of an integrated methodology with a purpose to restrain limitations, compound merits and produce a syncretism of complimentary venues for synthesis and optimisation.     

Total Site Hydrogen Integration with fresh hydrogen of multiple quality and waste hydrogen recovery in refineries

This paper proposes a novel method combining Pinch Methodology and waste hydrogen recovery, aiming to minimise fresh hydrogen consumption and waste hydrogen discharge. The method of multiple-level resource Pinch Analysis is extended to the level of Total Site Hydrogen Integration by considering fresh hydrogen sources with various quality. Waste hydrogen after Total Site Integration is further regenerated. The technical feasibility and economy of the various purification approaches are considered, demonstrated with a case study of a refinery hydrogen network in a petrochemical industrial park. The results showed that fresh hydrogen usage and waste hydrogen discharge could be reduced by 21.3% and 67.6%. The hydrogen recovery ratio is 95.2%. It has significant economic benefits and a short payback period for Total Site Hydrogen Integration with waste hydrogen purification. The proposed method facilitates the reuse of waste hydrogen before the purification process that incurs an additional environmental footprint. In line with the Circular Economy principles, hydrogen resource is retained in the system as long as possible before discharge.     

Pinch locations at heat capacity flow-rate disturbances of streams for minimum utility cost heat exchanger networks

The work deals with heat exchanger network (HEN) targeting under heat capacity flow-rates of streams disturbances. In particular, the aim is to calculate all pinches that can exist in a HEN with utilities of minimum cost when stream heat capacity flow-rates (CPs) are allowed to change within given ranges. It is assumed that the disturbances are stochastic. The knowledge of pinches at certain as well uncertain data is of great importance in designing HENs. For instance, Pinch Technology is based on pinch phenomenon and its influence on HEN operation and design. In case of parameter disturbances, this is even more important since additional application in HEN’s control (see e.g. [1], [2]). It is worthnoting that in case of disturbances, pinches behave in very complex manner as it was shown in [1], [2], [3], [4], [5]. A rigorous approach has been developed for calculating all feasible locations of pinches that can occur in minimum utility cost of HENs operating at varying heat capacity flow-rates of process streams. The method is based on recursive solution of mixed-integer linear programming (MILP) optimisation model that requires quite moderate number of binary variables. Examples of method application and analysis of results are presented in the work.     

基于最优夹点温差的换热网络优化设计

介绍了夹点技术基本原理及其在换热网络优化设计中的原则。利用ASPENPinch软件设计了一个有三股热股流、两股冷股流的换热网络，求得最优夹点温差是23．7℃，设计时取值23℃。夹点温差分别取10、23、30％进行换热网络初步优化设计，在相同换热器情况下，三者的总费用分别是44279、41931、42156美元／a。这证明采用最优夹点温差的换热网络经济性最好。     

Troubleshooting Shell-and-Tube Heat Exchangers

A newly developed methodology for the design of multistream plate-fin heat exchangers in the optimization of heat exchanger networks is described in detail. The designed heat exchanger consists of several block sections with intermediate entry and exit points along its length, and these sections are determined by the composite curves in the Pinch technology. The requirements of heat transfer and pressure drop are fulfilled through proper surface selection. The methodology was applied to an industrial case study, and the detailed design parameters are given. The example confirms the validity of the suggested methodology.     

Pinch design method in the case of a limited number of process streams

The use of Pinch technology is very often strongly limited by the existence of complex chemical process units (combustion, drying, scrubbing, etc.) in the energy system of the plant. Since this methodology, in its standard form, does not account for chemical operation inside those units, only a few process streams can be used for the creation of the heat exchanger network. The final design, in accordance with the overall mass and energy balance of the plant, will generate only slight increase in the energy efficiency.     

西安市供水水库群优化调度函数的神经网络求解方法

水库群联合优化调度函数的传统求解方法难以表示出水库调度决策变量与影响因子间的非线性关系,也不能很好地反映水库之间的相互关系。用改进ＢＰ网络可弥补这方面的缺陷。将该方法用于寻求西安市城市水源供水的三个水库的联合优化调度函数,结果表明,该方法行之有效,且应用简便。     

Synthesis and thermo-economic design optimization of wood-gasifier-SOFC systems for small scale applications

The conceptual design of a biomass integrated gasification fuel cell system for small scale applications (40 kg h⁻¹ woody biomass input with 50% mass fraction water content) is discussed in this work. Two different biomass gasifiers (circulating fluidized bed and downdraft), two different reformers, a solid oxide fuel cell, a gas turbine and a heat recovery steam cycle were investigated. A two-step optimization procedure was used to perform thermo-economic design optimizations of nine system configurations generated by combining different technologies. At the master level an evolutionary algorithm is used to optimize the system intensive parameters following the minimization of the system costs and the maximization of the net power production simultaneously (two-objective). At the inner level, system mass flow rates are optimized by linear programming subject to the thermal balance and to the heat transfer feasibility constraints which were formulated by means of Pinch Analysis techniques. The degree of system internal heat recovery was studied by including the minimum temperature difference between hot and cold streams as a decision variable at the master optimization level. Optimization results are shown by means of an optimal Pareto front for each configuration. The degree of system internal heat recovery of some specific solutions is discussed by means of Pinch Analysis composite curves. The study shows that very high system efficiencies can be obtained but only at the expense of really high system costs mainly because of the high costs of the fuel cell and of the gasifier especially at the small scale level considered here. Minimum specific plant costs of the most cost-effective configuration, based on a hybrid cycle, greater than 7000 $ kW⁻¹ (2010 dollars) are found. The indirect circulating fluidized bed gasifier appears the most promising choice both in terms of cost and of system performance since it allows for better thermal integration at high temperatures and greater hydrogen yields. Auto-thermal reforming is a cheaper solution compared to steam reforming but does not benefit of the system internal heat recovery thus leading to comparably lower system efficiency. Steam reforming is particularly convenient when the system is pressurized and extra power can be recovered by gas expansion since a great amount of steam can be injected prior the reformer and vaporized by recovering the heat from exhaust gases.     

Energy expenditure in the thermal separation of hydrocarbon mixtures using a sequence of heat-integrated distillation columns

The thermal separation of hydrocarbon mixtures is assumed to take place in a sequence of heat-integrated distillation columns (HIDiC) coupled, via a heat exchanger network (HEN), with a refrigeration system. Using the approach based on Pinch Analysis, a procedure is proposed for minimising the compressor shaftwork in the refrigeration system. The theoretical considerations are illustrated by a test example in which a mixture of selected hydrocarbons (methane, ethane, ethene, propene) is separated in a sequence of HIDiC columns coupled with a refrigeration system.     

Pinch analysis approach to carbon-constrained energy sector planning

Pinch analysis techniques have been developed for a wide range of applications ranging from process plant thermal or water integration to financial and supply chain management. This paper presents a new application of pinch analysis. A scenario is assumed wherein energy sector planning takes place with carbon emission constraints arising from an effort to reduce climate change effects. A procedure for identifying the minimum amount of zero-carbon energy resource required to achieve the overall emissions target for a country or region, given that the amount of fossil energy resources available are already known. The pinch analysis method can be used for a single overall emissions target, or for cases wherein separate sectors or geographic regions have distinct targets but share a common energy resource. For the latter case the procedure allows the allocation of the energy resources to meet both the overall emissions limit and the individual targets of the different sectors or location. Numerical examples are provided to illustrate the technique, which is intended for use as a preliminary energy sector-planning tool.     

蒸汽温度优化控制在火电厂的应用

由于电力市场竞争的日益激烈,电力企业纷纷采用先进的控制策略和手段来加强市场竞争力。因此,将模糊逻辑、神经网络等智能技术与基于模型的控制技术引入过程控制领域,形成先进过程优化控制的研究得到广泛关注。本文介绍了一种蒸汽温度优化控制系统在火电厂中的应用,设计了两种动态的优化过程,分别基于模糊控制和神经网络,并通过测试验证了该方案的应用,可明显有效地提高电厂运行效率,控制汽温范围,具有较强的现实意义。     

Retrofit of ammonia plant for improving energy efficiency

The aim of this work is to perform a retrofit study of an ammonia plant, in purpose of improving energy efficiency. As a common practice, one can divide an ammonia plant into two parts: the hot-end and the cold-end. In the hot section, two different options are investigated that both lead to a threshold condition and achieve maximum energy saving. The first option covers only process-to-process energy integration, while the second option considers some modification in the convection section of the primary reformer through a new arrangement of the heating coils. Thus, a considerable reduction in cooling water, HP steam and fuel gas consumption is achieved. In the cold section, retrofit study is dominated by reducing the amount of shaft work or power consumption in the refrigeration system. Application of the Combined Pinch & Exergy Analysis revealed that part of the shaft work, which was originally being used, was inefficient and could have been avoided in a well-integrated design. Therefore, by proposing optimum refrigeration levels, reasonable saving (15%) in power consumption was observed without the need for new investment.     

Process integration in bioprocess indystry: waste heat recovery in yeast and ethyl alcohol plant

The process integration of the bioprocess plant for production of yeast and alcohol was studied. Preliminary energy audit of the plant identified the huge amount of thermal losses, caused by waste heat in exhausted process streams, and reviled the great potential for energy efficiency improvement by heat recovery system. Research roadmap, based on process integration approach, is divided on six phases, and the primary tool used for the design of heat recovery network was Pinch Analysis. Performance of preliminary design are obtained by targeting procedure, for three process stream sets, and evaluated by the economic criteria. The results of process integration study are presented in the form of heat exchanger networks which fulfilled the utilization of waste heat and enable considerable savings of energy in short payback period.     

Carbon Emissions Pinch Analysis (CEPA) for emissions reduction in the New Zealand electricity sector

Carbon Emissions Pinch Analysis (CEPA) is a recent extension of traditional thermal and mass pinch analysis to the area of emissions targeting and planning on a macro-scale (i.e. economy wide). This paper presents an extension to the current methodology that accounts for increased demand and a carbon pinch analysis of the New Zealand electricity industry while illustrating some of the issues with realising meaningful emissions reductions. The current large proportion of renewable generation (67% in 2007) complicates extensive reduction of carbon emissions from electricity generation. The largest growth in renewable generation is expected to come from geothermal generation followed by wind and hydro. A four fold increase in geothermal generation capacity is needed in addition to large amounts of new wind generation to reduce emissions to around 1990 levels and also meet projected demand. The expected expansion of geothermal generation in New Zealand raises issues of GHG emissions from the geothermal fields. The emissions factors between fields can vary by almost two orders of magnitude making predictions of total emissions highly site specific.     

NET TG1: Residual stress analysis on a single bead weld on a steel plate using neutron diffraction at the new engineering instrument ‘STRESS-SPEC’

Non-destructive analysis of phase specific residual stresses and textures is only possible by diffraction methods. The new neutron diffractometer STRESS-SPEC was installed at FRM-II in Munich, Germany, for this purpose. It is designed to be equally applied to texture and residual stress analyses by virtue of its flexible configuration. The results of measurements on a single bead on plate weld within the framework of the European Network on Neutron Techniques Standardisation for Structural Integrity (NET) are presented here, in order to demonstrate the reliability and accuracy of the instrument by comparing previous results from other neutron diffraction facilities by using a Bayesian statistical approach.     

An open reversed Brayton cycle with regeneration using moist air for deep freeze cooled by circulating water

This paper presents an open reversed Brayton cycle with regeneration using moist air for deep freeze cooled by circulating water, and proves its feasibility through performance simulation. Pinch technology is used to analyze the cooling of the wet air after compressor and the water used for cooling wet air after compressor. Its refrigeration depends mainly on the sensible heat of air and the latent heat of water vapor, its performance is more efficient than a conventional air-cycle, and the utilization of turbo-machinery makes it possible. The adoption of this cycle will make deep freeze easily and reduce initial cost because very low temperature, about ?55 °C, air is obtained. The sensitivity analysis of coefficient of performance to the efficiency of compressor and the efficiency of compressor, and the results of the cycle are also given. The simulation results show that the COP of this system depends on the temperature before turbine, the efficiency of compressor and the efficiency of compressor, and varies with the wet bulb temperature of the outdoor air. Humid air is a perfect working fluid for deep freeze with no cost to the user.     

Scheduling and control co-design for Networked Wind Energy Conversion Systems

Fieldbus, industrial Ethernet that is simple, reliable, economical, and practical, is widely used in Wind Energy Conversion Systems (WECSs). These techniques belong to the field of networked control systems. Network embedding to Wind Energy Conversion Systems brings many new challenges. Implementing a control system over a communication network causes inevitable time delays that may degrade performance and can even cause instability. This work addresses challenges related to the reliable control of wind energy conversion systems, based on the theoretical framework of networked control systems. A type of WECS with network-induced delay and packet dropout is modeled and adjustable deadbands are explored as a solution to reduce network traffic in WECSs. A method to study the reliable control of WECSs is presented, which takes into account system response as well as the network environment. After detailed theoretical analysis, simulation results are provided, which further demonstrate the feasibility of the proposed scheme.     

Implications of sustainability assessment for electricity system design: The case of the Ontario Power Authority’s integrated power system plan

This paper explores the results and implications of an illustrative application of a sustainability assessment framework in the design and evaluation of a major integrated power system plan. The paper examines the integrated power system plan developed by the Ontario Power Authority in 2007. The basic framework rests on a generic set of evaluation criteria reflecting basic requirements for progress towards sustainability that was adopted, reinterpreted and applied by the Authority in support of its proposed plan. In response to evident deficiencies in the Authority’s work, the authors and colleagues undertook a re-examination using a more fully elaborated sustainability assessment framework, specified for application to power system planning. The results point to a plan and plan components substantially different from those proposed by the Authority. More generally, the results highlight three advantages of applying such a sustainability assessment framework: comprehensive coverage of key requirements for progress towards sustainability while ensuring careful attention to the context and concerns of the sector; emphasis on identifying plan options that avoid major trade-offs among the sustainability criteria and recognition of interactions among the social, ecological, economic and technological realms favouring options that offer multiple, mutually reinforcing and lasting benefits.     

Towards synthesis optimization of a fuel-cell based plant

In a previous work by the authors, the performance of a plant based on solid oxide fuel cells (SOFC) which produces its own fuel by solar energy had been studied. The system consists not only of the fuel/electrolytic cell unit and the gas turbine but also of compressors, pumps, heat exchangers, etc. In the aforementioned work, a “workable” synthesis (structure) of the system had been considered, which is not necessarily the best one. In the meantime, an attempt has been made to improve on the structure and, if possible, to determine the one with the best performance under certain conditions. For this purpose, the Pinch method together with exergy analysis has been applied, while the performance of the system for any configuration has been determined by a simulation model. The results of this work are presented in this article.