District Heating and Power Generation Based Flue Gas Waste Heat Recovery

European Mechanical Science 2017, Vol. 1(2): 63-68 Research Paper EUROPEAN MECHANICAL SCIENCE District heating and power generation based flue gas waste heat recovery§ Caglar Karaoglu1, Arif Ozbek2* Cukurova University, Institute of Natural and Applied Sciences, Mechanical Engineering Department, Adana, Turkey 2 Cukurova University, Ceyhan Engineering Faculty, Mechanical Engineering Department, Adana, Turkey 1 Abstract In this study, integration of appropriate renewable methods are going to be applied on conventional coal fired steam power plant which has 660 MW full load capacity and including 4 Turbines (1 HP, 1 IP and 2 LP), one Benson type boiler and having multi pre heater stages for each unit. Steam parameters are 177 Bar and 541 o C super-heater section and 50 bar 539 oC for re-heater section. Primary fuel is coal except for startup and shut down operations. It is aimed by retrofitting some renewable energy methods on existing power plant, thus eliminating conventional type power plants adverse effects on thermodynamically, environmental and economic issues. One of the most important issue of conventional steam power plant operation is waste heat recovery management. A widespread techniques has been developed on this topic. It’s possible to handle low grade heat by considering thermodynamic and environmental facts and also dealing with restrictions and opportunities after fulfilled feasibility study. In this study, it is being proposed waste heat recovery by combining OrganicRankine Cycle (ORC) with steam-Rankine cycle at available section. Brief summary of operation is ORC takes place after regenerative air preheater section and the target is to utilize waste heat of flue gas either via district heating or power generation up to few MW values. Depending upon the calculation and results additional modifications can further be needed as well. Keywords: Waste heat recovery, flue gas, steam power plant 1. INTRODUCTION Energy is the power and vital part of life. In the future, we must have a sustainable, affordable and environment friendly energy supply. Conventional fossil energy sources will be replaced by renewable sources, gradually. Renewable technologies are considered as clean sources of energy and optimal use of these resources minimize environmental impacts, produce minimum secondary wastes and are sustainable based on current and future economic and social needs. [1]. A major challenge for the future electric grid is to integrate renewable power sources such as solar, wind and biomass [2]. Such sources are variable and intermittent, unlike traditional sources that provide a controllable, steady stream of power. Instead of fully replacing renewable by conventional systems, it’s better to implement partial integration of renewable methods on such conventional power plants already in operation. Renewable energy systems are increasingly being used for electricity generation, either at small-scale decentralized systems with capacity in the kW scale or even medium-scale systems (often called utility-scale) with capacity of afew MW. However, the large-scale systems with capacity of some hundreds of MW are still using conventional technologies based on fossil fuels. One of the most important disadvantages of conventional technologies is the environmental impact. The combustion of fossil fuels leads to the inevitable production of carbon dioxide (CO2), while most of the times harmful emissions are produced, such as carbon monoxide (CO), nitrogen oxides (NOX), sulfur oxides (SOX), unburned hydrocarbons (HC), and solid particles. Another critical disadvantage of conventional technologies is that they need continuous fuel supply to operate, which contributes to the operating costs. On the other hand, renewable energy technologies do not require any fossil fuel during normal operation. Their operation is based on the exploitation of natural resources, such as the sun and wind, having relatively lower operating costs, *Corresponding authour Email: (A. Özbek) § This paper was presented in the IMSEC-2016 although they still require some maintenance. The most important disadvantage of renewable energy technologies is the fluctuation of their power output [5]. Figure 1: Additional Installed Capacity by years It is generally expected that coal will continue to play a key role in the future energy mix as it is the most abundant and cheapest fossil fuel source.Such solid fossil fuels are combusted insteam power plants, where the power cycle is based on the steam-Rankine thermodynamic cycle, using a steam turbine. Figure 2: Electricity Generation Distribution Depend on Energy Sources (2016) Figure 2: A path of Air/Flue-gas 64 European Mechanical Science (2017); Volume 1, Issue 2 Additionally, pulverized coal firing system, integrated with its components, in the steam generator (boiler) is to provide through the combustion of certain bituminous coals the necessary thermal energy for the generation of steam which in turn is required for driving the downstream turbine with downstream generator for power generation. Flue gases leaving the boiler combustion chamber pass over the convection banks of the super-heaters, re-heaters and then enter regenerative air heater. There the gases exchange their thermal energy with the primary and secondary air. The temperature of the gas entering the air heater is reduced from about 400 oC to 150 oC. The cooled gases then pass to electrostatic precipitator where most of the dust is removed. Via induced draft fan, the cleaned gases then pass to the FGD plant for desulfurization and then to atmosphere via the stack [4]. It is possible to see several studies that deal with renewable energy integration to conventional systems related to thermodynamic analysis. 1.1 Literature Survey Gang Xu et al. (2014) studied integration of waste heat recovery system on flue gas path. To achieve extra work, installed low temperature economizer after ESP takes place. Exergy analysis and economic analysis have been done and discussed on results [6]. C. Li et al. (2016) investigated on generated waste heat quantities during industrial production. In order to maximize net power output, an optimal combination of cycle configuration, fluid and cycle parameters under different heat source condition, the following researches have been performed. To sum up, results indicate that the regenerative organic trans-critical cycle produces the maximum power output at source temperatures up to about 500 oC, and different optimum working fluids are obtained under different heat source temperature [7]. Chengyu Li et al. (2016) has been studied for waste heat recovery from flue gas in a wide range temperature. The study also dealing with optimum relationship between selected fluid and heat source in order to achieve better thermal efficiency. Evaluation, optimization comparison of many cycles has been evaluated. Xiaoqu Han et al. (2016) studied on flue gas waste heat (...truncated)