The expenditure of primary energy can be reduced and the economics of process plants in the food industry can be improved by intelligent application of Process Integration (PI). Since a greater part of the products in the food industry is processed in batches, the use of Thermal-Energy Storage (TES) may be required to achieve these improvements. Further improvements may be achieved if there is a need, in the plant, for heating water at low-or-medium-level temperatures for cleaning purposes and there are significant quantities of medium-to-low-temperature heat recoverable. Such conditions are often encountered in the food industry. However, the extent to which PI is utilized is much smaller than the number of potential applications. The present paper will address this topic, give some reasons for the underuse of PI, and indicate some principles, methods, and directions that, when applied, could increase the use and usefulness of PI by incorporating TES, thus fulfilling PI's promises of improved operation, reduced energy consumption, reduced environmental impact, and improved economics. The application of these procedures is illustrated through the description of two cases.

The work reported in the present paper was carried out in connection with a comprehensive process integration study of a fertiliser plant in Lithuania. However, the investigation reported presently only concerns a constructed example with seven process streams. four hot streams and three cold streams.The primary objective of the present work was to gain an understanding of the influence of dramatic economic changes on heat exchanger network (HEN) configurations, their profitability and how an existing HEN could restrict future possibilities of heat recovery.HENs were designed to maximise the net present value (NPV) of investment and savings during a desired depreciation period for the conditions before the economic changes (State 1), after the economic changes (State 2), and for a retrofit of the "State 1" HEN under "State 2" conditions.The study required six different strategies to be considered, and the economic results. expressed as NPV of investment and savings, are presented and discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.

It can be argued that the largest potential for energy savings based on process integration is in the intermediate size industry. But this is also the industrial scale in which it is most difficult to make the introduction of energy saving measures economically interesting.The reasons are that the required engineering effort is too great and therefore too expensive, and that the resulting systems designs often become inordinately complex and therefore not attractive in operation.The present study describes steps that aim at reducing the magnitude of the theoretical work and engineering effort associated with a given process integration study in an intermediate size industry. This is based on the observation that the systems that eventually result from a process integration project and that are economically and operationally most interesting are also quite simple.Four steps that may be used separately or in series ahead of or simultaneously with the conventional process integration procedures (for example, the pinch point method) are described and are applied to an industrial case study.It might be feared that the use of preselections and groupings would limit the "freedom of movement' and therefore lead to non-optimal economic solutions, which may be right. But the objective of the optimisation is not to reach the best economic solution, but to relatively quickly develop the design of a simple and operationally friendly network without losing too much energy saving potential. (C) 2002 Elsevier Science Ltd. All rights reserved.

A method for the automatic synthesis of heat-exchanger networks (HENs) is described here. The method, named COMBINET, is based on combinatorial procedures, no pinch rules are used. The main idea is to find economic HENs. The procedure, however, is well suited for optimizing energy recovery, minimizing heat-exchanger area, minimizing number of matches, etc., The program is capable of storing a specified number of the best HENs from the screening procedure, thereby allowing the user to evaluate which ones best satisfy other requirements. A number of cases from the open classical literature have been studied and the results compared. The studies have shown that in each case a number of different configurations exist that are almost equally good concerning economics, indicating the presence of a flat economic optimum. In six out of a total of nine cases investigated, COMBINET did find several networks which all were better than the hitherto best network reported.

This chapter contains section titled: INTRODUCTION The two-Stage Gasifier Assumptions Description of the Model Comparison of Model and Test Conclusion Acknowledgements Nomenclature References

Interest in heat recovery in batch processes is motivated by the fact that a significant part of industrial products (about 50 percent) are produced in batches. The batch mode-of-operation may be required because of limited supply (dairies), because of process requirements (fermentation), or because of tradition and quality consideration (breweries).

The waste-heat recovery in batch processes has been studied using the pinch-point method. The aim of the work has been to investigate theoretical and practical approaches to the design of heat-exchanger networks, including heat storage, for waste-heat recovery in batch processes. The study is limited to the incorporation of energy-storage systems based on fixed-temperature variable-mass stores. The background for preferring this to the alternatives (variable-temperature fixed-mass and constant-mass constant-temperature (latent-heat) stores) is given. It is shown that the maximum energy-saving targets as calculated by the pinch-point method (time average model, TAM) can be achieved by locating energy stores at either end of each process stream. This theoretically large number of heat-storage tanks (twice the number of process streams) can be reduced to just a few tanks. A simple procedure for determining a number of heat-storage tanks sufficient to achieve the maximum energy-saving targets as calculated by the pinch-point method is described. This procedure relies on combinatorial considerations, and could therefore be labeled the “combinatorial method” for incorporation of heat storage in heat-exchanger networks. Qualitative arguments justifying the procedure are presented. For simple systems, waste-heat recovery systems with only three heat-storage temperatures (a hot storage, a cold storage, and a heat store at the pinch temperature) often can achieve the maximum energy-saving targets. Through case studies, six of which are presented, it is found that a theoretically large number of heat-storage tanks (twice the number of process streams) can be reduced to just a few tanks. The description of these six cases is intended to be sufficiently detailed to serve as benchmark cases for development of alternative methods.

A theoretical investigation of the economics of cogeneration supplemented by warm-water storage and subjected to a three-step price schedule for electricity, has been carried out. Some general guidelines can be derived, but no simple design rules, such as those for cogeneration plants operating with a two-step schedule, seem to govern the design of such plants subjected to the new conditions. Simulation studies have been initiated in order to arrive at sufficiently accurate optimal store dimensions and operational strategy. The results from simulation studies which give the store as a function of cogeneration plant size relative to the total heat demand in the geographical region supplied by the plant are shown

The design and operation of a refrigeration plant in a brewery has been studied. The plant has been evaluated by using mathematical models of the components to simulate responses to real-life load variations. The study shows that the efficiency and economy of the actual refrigeration plant could be improved significantly by a combination of three different approaches: design optimization, improved operation strategy, and load management. The improvements obtainable by each approach and by combinations of approaches are reported. A reduction in primary fuel consumption of 15% is obtainable ideally, while a realistic practical goal is 10%