Thermodynamic Optimization of Advanced Steam Power Plants Retrofitted for Oxy-Coal Combustion

Abstract

Thermodynamic optimization of power plants based on supercritical (SupC) and ultrasupercritical (USC) steam parameters is reported in this article. The objective is to compute the maximum attainable power plant efficiency in Indian climatic conditions using high ash (HA) indigenous coal. A unit size of 800 MWe presently under development in India is considered for energy and exergy analysis of power plants. Commercially established steam turbine parameters are used for the optimization of SupC power plant, whereas advanced steam turbine parameters currently under research and development are used for the optimization of USC power plant. The plant energy efficiency of the optimized SupC and USC power plant based on air-coal combustion (ACC) show considerable increases of 2.8 and 5.2% points, respectively compared with the current SupC ACC power plant (reference plant) being commissioned in India. The increases in plant exergy efficiency for the same power plants are 2.6 and 4.8% points and the corresponding CO2 reductions are about 6 and 11%, respectively. The maximum possible plant energy efficiency in Indian climatic conditions using HA Indian coal is about 42.7% (USC power plant). The effect of low ash coal on plant energy and exergy efficiencies compared with HA coal is also presented. Further, the effect of oxy-coal combustion (OCC) on the plant energy and exergy efficiencies compared with the ACC is studied for the double reheat SupC and USC power plants to account for the impact of CO2 capture. A significant reduction of 8.8 and 6.6% points in plant energy efficiency is observed for SupC and USC OCC power plants, respectively compared with the reference SupC ACC power plant.

Dynamic Optimization of a Subcritical Steam Power Plant Under Time-Varying Power Load

“…The carbon footprint of the plant also decreased from 0.8 kg/kWh to 0.77 kg/kWh. This efficiency optimization was accomplished by increasing T Air from 200 • C to 248 • C, and increasing T SH from 538 • C to 560 • C. This is consistent with earlier reports [13,14,27,38,[41][42][43], showing that increasing T SH and T Air translates to efficiency improvements. The higher T SH enabled the HP turbine to produce the same mechanical torque at a lower rate of coal consumption, while increasing T Air recovered more waste heat from the boiler exhaust gas.…”

“…Table 2 summarizes the optimization variables, range of variability and efficiency improvements achieved in relevant previous work. In the majority of previous analyses [13][14][15][36][37][38][39][40][41][42][43][44], plant efficiency optimization was performed by manipulating the temperature of superheated steam (T SH ). For example, Xiong et al [41] showed that the higher superheated steam temperature increases the power generated by the HP turbine, improving cycle efficiency.…”

“…In Case Study II, plant optimization was performed by manipulating the set points ofṁ ST , i.e., the set points of the mass flow rates of steam streams extracted from the first IP turbine (IP1), the second IP turbine (IP2), the first LP turbine (LP1), and the second LP turbine (LP2) (ṁ IP1 ,ṁ IP2 ,ṁ LP1 , andṁ LP2 , respectively). The ranges of the admissible inputs, shown in Table 3, were based on common practice and previous work [13][14][15]27,36,38,[41][42][43]45]. The optimization horizon, τ, was set to 24 h in Case Study I and 4 h in Case Study II, and the control action interval, τ n , was set to 1 h. Large control actions were not penalized in the solved optimization problems, as the plant load profiles matched during the real-time plant optimization were relatively smooth.…”

Exergy-based analysis of conventional coal-fired power plant retrofitted with oxy-fuel and post-combustion CO2 capture systems

“…Lee et al 14 presented an approach for performance evaluation of a commercial-scale coal-fired power plant which was considered for retrofitting with oxy-fuel combustion. Suresh et al 15 analyzed and optimized the air–coal combustion supercritical and ultra supercritical steam power plants using high ash coal. They also studied the effect of oxy-coal combustion on thermodynamic performance of the optimized air–coal combustion power plant.…”

Exergoeconomic effect of adding a new feedwater heater to a steam power plant

“…Therefore a moderate pressure is more suitable for the plant. Suresh et al [8] studied a supercritical (SupC) and an ultrasupercritical (USC) steam power plant and optimized the plant's performance. Exergy efficiency of the optimized SupC and USC power plants showed 2.6% and 4.8% increase, respectively.…”