Electrical Power & Energy Syskvns, Vol. 17, No. 4, pp. 227-233, 1995 Elsevier Science Ltd Printed in Great Britain 0142-0615/95 $lO.OO+O.OO Integrated energy optimization model for a cogeneration based energy supply system in the process industry A Arivalagan and zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA IB G Raghavendra Department of Management Studies, Indian Institute of Science, Bangalore- 2, India A R K Rao Mysore Paper Mills, Badravathi, Karnataka. India zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC Most of the continuous process industries generate electricity by cogeneration using the heat energy required for the process. Electricity is also purchasedfrom external sources such as the grid and generated by internal sources such as diesel gensets. This leads to the decision problem of determining the economically optimum energy-mix during short and long term periods. Also it is important to evaluate the various technologies that can improve the energy supply system. This paper presents a mixed integer (&I) linear programming model to tackle the above decision problem and presents a case study on the application of the model. It is shown that the modelprovides the methods for determining the optimal strategies that minimize the overall cost of energyfor the process industry. Keywords: modelling of energy systems; local, optimal power jaws; mathematical programming I. Introduction Continuous process industries such as refineries and industries producing fetrtilizer, rayon, chemicals (dyes, acid, organic compounds, etc.), textile, paper, sugar, food, etc., consume a considerable amount of heat and electric energy. Heat energy is mostly consumed in the form of process steam at medium and/or low pressure levels. Quite often steam is generated in fossil-fuel boilers, at a much higher pressure than that required for various end uses. This high pressure steam is allowed to flow Received 5 October 1992; revised 13 January 1994; accepted 10 March 1994 through extraction cum condensing turbogenerators and is reduced to process steam pressures, thus generating power by extraction and condensation. Since the quantity of steam that can flow through a turbine is limited by its design capacity, increasing condensation will increase the condensation power but will decrease cogenerated power and vice versa. In addition to the electric energy from steam, power is also purchased from external sources such as State Electricity Boards. Owing to the widening gap between supply and demand of electricity at the state and national levels, some electricity boards impose ‘power-cuts’ of varying intensities for various time periods. During this period some of the manufacturing units use diesel gensets to augment other sources. The cost and efficiency of these sources vary considerably. These lead to the decision problems of determining the economically optimum energy-mix for a process industry under various circumstances. This paper presents a mixed integer (O-l) linear programming model to tackle the above decision problems in a typical process industry. The concept could easily be adopted with appropriate modification in other process industries. II. Typical process configuration and energy related decision problems The configuration of the energy supply system adopted by a typical process industry is shown in Figure 1. The system consists of both steam and power networks which interconnect energy sources, intermediate processing units and end use devices. The strategies for improving energy efficiency in such an energy system involve the maximization of the use of low cost energy sources and 227