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Heat is released, into the natural atmosphere from all thermal power generating plants through cooling towers, flue gas, or by other means during generation of electric power. Therefore, energy efficiency about the power generation units become very low within 50% to 60% and environment is polluted due to emission of byproduct (NOX, SOX, SO2&CO2) during heating.
In order to use waste heat for improving the overall efficiency of power generation unit and reduction of emitted pollutants during heating CHPED has become an important area of research. In CHPED system, the heat recovery steam generator recovers the waste heat for heating or steam generation and cooling through the use of absorption Chillers. CHPED is a cogeneration system which produces power and process heat simultaneously.
For simplicity the cost function of power unit, heat unit and co-generation unit are represented by quadratic function and is solved by mathematical programming techniques. In practice the higher order nonlinearities and discontinuities due to valve point loading effects are introduced in mathematical formulations. Moreover, due to physical limitations on components of power generating units of CHPED problem, these units may have prohibited operating zones. In view of that, a unit with prohibited operating zones, its whole operating region will be broken into some isolated feasible sub-regions, which makes the CHPED problem discontinuous. So, the operation constraints and non-linearity make the CHPED problem a non-smooth optimization problem having complex and non-convex features with equality and inequality constraints.
To find quality solution, different optimization methods have been applied to get optimal point for power production such that the total demand matches the generation with minimum fuel cost, while satisfying required power demand and other constraints.
Many researchers performed a lot of researches on CHPED during last two decades. To solve CHPED, various optimizations techniques are adopted by various researchers. These methods are categorized into classical mathematical optimization algorithms and intelligent optimization algorithms. The classical algorithms include Lagrangian relaxation (Majd, et al.,2018), classical technique (CT) (Damodaran & Sunil kumar, 2014) etc. which have been successfully applied by the various researchers. Thomson et al. (Thomson, et al., 2000) proposed a statistical process control method to solve CHPED problem. Generally, these methods produce best optimal solutions if the fuel cost characteristics of generating units are linear. However, these traditional approaches cannot be applied directly to a practical CHPED problem because CHPED problem has complex and non-convex characteristics due to the presence of valve point effects, multiple fuel option, prohibited operating zone.