The essence of effective process designing is to use methods which are efficient to engineers in practice and not only to scientists. The proposed design procedure is composed of two steps: conceptual one and optimization one. At the conceptual step, pinch design analysis is used. In the optimization step pinch analysis and mixed-integer nonlinear programming method are applied. In the case Study analysed, a speciality product is to be produced in continuous chemical process with a capacity which causes smaller heat flow rates and needs smaller heat exchanger areas than usual. Therefore, an equation for cost estimation of heat exchangers with areas smaller than 7 m(2) was developed and used in the optimization procedure. Using thermodynamic pinch analysis and mathematical programming method, the heat integrated structures were synthesized and compared with the base process flowsheet. Finally, the optimal structure was determined. (c) 2005 Elsevier Ltd. All rights reserved.

Energy integration between several processes has been applied giving more economical and profitable operation. The method for waste heat integration of several processes was analysed to reduce energy usage in three possible steps:1. retrofit of the individual processes,2. analysis of efficient transfer of waste heat between:existing non-retrofitted processesexisting non-retrofitted and efficiently retrofitted processesefficient retrofits and3. simultaneous integration between some non-retrofitted and some retrofitted existing processes using mixed integer non-linear programming (MINLP).The integration between the processes can be carried out by all the steps, or by the first and the third steps or only by the last step depending on the complexity of the problems. All the steps can be carried out simultaneously and the MINLP algorithm applied with or without the first and the second step. The approach has been illustrated by four complex processes using pinch analysis and MINLP.The optimal solution of pinch analysis and MINLP yields the same additional savings of 526000 USD/a and selects the same structure and parameters as the MINLP one. (C) 2002 Elsevier Science Ltd. All rights reserved.

Influence of utility prices on the optimum process structure was studied. Different prices of utilities and increasing investment costs (inflation) over three different decades have been considered. In one decade the fuel price was very low while in another one it was very high. Process structures in these decades were derived using pinch and nonlinear programming methods on a hydrodealkylation of toluene process with diphenyl recycled. The results showed that structures differed in the three decades because of different prices and for that reason a common process configuration, usable both for eventual future high or low fuel prices, could be developed.

Correct choice of the contributions (Delta(cont)T) to the minimum approach temperature (Delta(min)T) are most important in processes with small differences between the lowest and the highest temperatures of the process. Temperature contributions in such processes have to be very low. It has been found that fixed Delta(coat)Ts sometimes gave higher energy targets than those derived from the simulated base process, In such cases also, the location of available utilities and process units against pinch temperature could be wrong. More realistic results were obtained using an approach based on appropriate areic heat flow rates, i.e. based on heat transfer areas. The best results came from individually calculated contributions for simulated heat exchange units.

This paper discusses the heat integration of mechanical heat pumps which use process fluid as the working fluid. A compressor is integrated in the same way as an exothermal reactor: the heat pump is presented in the temperature-enthalpy flow rate (T/I) diagram as a subsystem consisting of a compressor, heater and cooler. The heater is integrated below pinch temperature and below grand composite curve whereas the cooler is placed above them. Only in this case can the location of a correct pinch temperature be found. A systematic thermodynamic approach has been tested by studying different process configurations of a heat pump fractionator.