Coal-fired Power Units Research Articles

Progress and prospects of innovative coal-fired power plants within the energy internet

The development of electrical engineering and electronic, communications, smart power grid, and ultra-high voltage transmission technologies have driven the energy system revolution to the next generation: the energy internet. Progressive penetration of intermittent renewable energy sources into the energy system has led to unprecedented challenges to the currently wide use of coal-fired power generation technologies. Here, the applications and prospects of advanced coal-fired power generation technologies are analyzed. These technologies can be summarized into three categories: (1) large-scale and higher parameters coal-fired power generation technologies, including 620/650/700 °C ultra-supercritical thermal power and double reheat ultra-supercritical coal-fired power generation technologies; (2) system innovation and specific, high- efficiency thermal cycles, which consist of renewable energy-aided coal-fired power generation technologies, a supercritical CO2 Brayton cycle for coal-fired power plants, large-scale air-cooling coal-fired power plant technologies, and innovative layouts for waste heat utilization and enhanced energy cascade utilization; (3) coal-fired power generation combined with poly-generation technologies, which are represented by integrated gasification combined cycle (IGCC) and integrated gasification fuel cell (IGFC) technologies. Concerning the existing coal-fired power units, which are responsible for peak shaving, possible strategies for enhancing flexibility and operational stability are discussed. Furthermore, future trends for coal-fired power plants coupled with cyber-physical system (CPS) technologies are introduced. The development of advanced, coal-fired power generation technologies demonstrates the progress of science and is suitable for the sustainable development of human society.

Оптимизационные исследования угольного энергоблока на повышенные параметры пара мощностью 660 мвт

This paper carries out optimization studies of the 660 MW coal-fired power unit for elevated steam parameters by the criterion of maximum net efficiency and minimum specific investment. The dependence between the power unit efficiency and the lowest specific investment is built. Taking into account the need for accounting a large number of coal-fired power unit parameters the optimization studies were carried out using gradient methods of nonlinear mathematical programming. Due to the large number of calculations the computerized programming system (CPS) computational environment is used. The maximum efficiency obtained as a result of optimization calculation is 47.74%. The corresponding specific investment equals 3545.7 $/kW and the initial steam parameters are 35.4 MPa, 657/613 о С. The minimum specific investment is 1884.6 $/kW. The corresponding efficiency equals 42.08%. The initial steam parameters are 15.5 MPa, 613/540 о С. The 660 MW coal-fired power unit was optimized for elevated steam parameters by the criterion of maximum net efficiency and minimum specific investment. The dependence of the minimum specific investment on power unit net efficiency was obtained. It is shown that the minimum specific investment was obtained at low pressure and relatively high temperature of the main steam.

Experimental research on performance test after SCR denitration system ultra-low emission retrofit in a 600 MW coal-fired unit

A systematic performance test was carried out for the ultra-low emission modification project of the Selective Catalytic Reduction (SCR) denitration system of a 600 MW coal-fired unit in a thermal power plant. Terms of the performance tests include denitration efficiency, ammonia escape rate, and SO2/SO3 conversion rate. The distribution of gas velocity and NOx concentration in flue gas of SCR inlet and outlet were summarized. The effect of unit load and gas velocity to denitration efficiency, ammonia escape rate and SO2/SO3 conversion rate were discussed after the test. The result favours design and retrofit of the ultra-low emissions coal-fired power unit in China. Through technical trials, a set of practical test methods suitable for the actual situation was concluded.

Selecting optimal conditions for the turbine warm and hot start-up

The changing role of coal-fired power units which are now used more and more often as sources balancing the demand for electricity in the power system calls for a change in the character of their operation. They have to be able to respond appropriately to rapid and substantial variations in loads and they must have the capacity for shortening the start-up time, especially after a few or several hours of downtime. The paper presents an analysis of changes in thermal states in the turbine main elements after short downtime periods and shows the possibilities and consequences of the turbine fast start-up from such states. Optimal warm and hot start-up characteristics are developed. Detailed deliberations are devoted to elements of200 MW turbines, most of which are and will be used as flexible sources of electricity generation in the power system.

Example Application of LGGH High-efficiency Coal-fired Flue Gas Treatment Technology in Yudian Dabu Power Plant

This paper describes the severe air pollution and ultra-low emission process route in China today, based on which it studies and analyzes the LGGH high-efficiency coal-fired flue gas treatment technology applicable to the upgrading of the ultra-low emission with respect to its origin, composition, characteristics and advantages. Then this paper gives a case study on the application of this technology in Yudian Dabu Power Plant where ultra-low emission is required, in particular the project profile of Yudian Dabu Power Plant, and specific proposal, process layout, main design parameters, technical features and operating result of the technology in the power plant. According to the testing, after this technology is put into use in the plant, the dust and SO₃ emissions of Unit 2# chimney drop to 2.3mg/m³ and 2.4 mg/m³ respectively, much lower than the national ultra-low emission limits. All these can demonstrate that the large-scale coal-fired power units can achieve a significant result by adopting the optimized LGGH high-efficiency coal-fired flue gas treatment technology, this technology provides higher precipitation efficiency, energy conservation and emission reduction, and high-efficiency SO₃ removal, solves the problem of "Gypsum rain" and visual pollution, and realizes dry chimney discharge, indicating that this technology deserves promotion and has great potential to become a popular post-combustion flue gas treatment technology.

Improved combustion air preheating design using multiple heat sources incorporating bypass flue in large-scale coal-fired power unit

In this study, a new concept of the combustion air preheating system integrated with a bypass flue (BPF) configuration was put forward and its feasibility was evaluated. In the proposed system, the primary air and secondary air are heated separately with cascade heat exchange and the hot and cold bypassing primary air mixing is avoided, which contributes to enhancing the air preheating and waste heat utilization. Thermodynamic analysis was performed based on a typical 600 MW coal-fired power unit incorporating the new concept. The results indicated that owing to the proposed design, the power generation efficiency promotion reaches 0.78% (absolute value) with a standard coal consumption rate reduction of 5.52 g/kWh as compared to the reference unit, which are 0.14% (absolute value) higher and 0.94 g/kWh larger than those caused by the regular BPF retrofitting, respectively. The energy utilization is more rational in the new design according to the energy and exergy analysis, and the exergy efficiency of the primary air heating process is improved from 75.75% (original design) or 79.62% (regular BPF design) to 84.46% due to the proposed concept. The volume and heat exchange area of the APH decline significantly as well in the modified system.

Energy-saving mechanism and parametric analysis of the high back-pressure heating process in a 300 MW coal-fired combined heat and power unit

Comprehensive and parametric analyses were conducted to investigate the thermal characteristic of the high back-pressure (HBP) heating process based on a 300 MW coal-fired combined heat and power (CHP) unit. The results indicated that the HBP design promoted the thermal efficiency of the unit by 5.97% (absolute value) and cut down the standard coal consumption rate by 23.52 g/(kW·h), attributing to the exhaust steam recovery efficiency of 57% and the unit generation power increase of 24.58 MW. On the grounds of the first and second laws of thermodynamics, the detailed energy-saving mechanism of the HBP heating concept was synthetically explored by the analyses of energy and exergy flows and graphical exergy, and the results showed that the HBP heating configuration improved the unit performance by reducing the exhaust steam energy loss and the extraction steam flow rate and raising the exergy efficiency of the heat exchange process. The impacts of the primary parameters (unit generation load, unit heating load, supply & return-water temperatures and turbine back-pressure) on the performance of the HBP-CHP unit were also examined and optimization suggestions were put forward. Besides, the heat and power coupling characteristic of the HBP-CHP unit was discussed.

Field tests and optimal operation research of WFGD for a 600MW power plant

In this paper, wet desulfurization system for a certain 600 MW coal-fired power unit was studied. The field tests were conducted on the limestone wet flue gas desulfurization system of a coal-fired unit. The influence of absorber entrance concentration of SO2 at different loads, as well as the absorber slurry pH value under variable numbers of slurry circulating pumps on desulfurization efficiency were tested. The experiment results also drawn that the start and stop effects of circulating pump on the efficiency of desulfurization rate under different load and the relationship of the slurry density and gypsum quality. On the basis of operation cost analysis, overall power consumption of desulfurization system and the emission fee would be reduced. The optimal operation mode of the slurry circulating pump is given, and the pH value and slurry density are determined.

Environmental implications of China’s wind-coal combined power generation system

China’s power supply structure is dominated by coal-fired power. As China’s renewable power expands, coal-fired power units are required to improve flexibility to balance power system. However, more flexible operation of coal power units increases energy consumption and pollutant emissions. This paper examines the energy efficiency, CO2 and pollutant emissions characteristics of China's generic wind-coal combined power generation system, and discusses pollution-minimizing dispatch strategies by modeling three hypothetical scenarios of wind-coal combined power generation systems. For day-scale analyses, we find expected displacement rates of coal consumption and CO2 emission decrease by wind fraction rate, indicating reduced energy savings from wind power per unit of increase in wind capacity. For NOx emission, we find that expected displacement rate reaches maximum value of 112% when wind fraction rate is equal to 0.27.For week-scale analysis, we simulate the coal consumption rate and emission factors with and without an operation of shutdown and startup of coal power units in the system. We suggest future study on dispatch decisions of startup/shutdown of coal power units to optimize power generation economically and environmentally.

Study on Performance Optimization of SCR Denitrification of an Ultra-low Emission Coal-fired Power Unit

The distribution of NOx concentration, flue gas flow field and temperature at the inlet and NOx concentration at the outlet of SCR denitrification were measured in a 330MW ultra-low emission coal-fired power unit, and ammonia injection optimization was carried out to improve the performance of SCR denitrification. The test results show that the distribution of NOx concentration and flue gas temperature at the inlet of SCR reactor is relatively uniform, and the distribution of flue gas flow field at the inlet of SCR reactor is nonuniform. The distribution uniformity of NOx concentration at the outlet of SCR reactor is poor before optimization. The NOx concentration distribution at the outlet of SCR reactor is improved by ammonia injection adjustment, and the relative standard deviation of NOx concentration distribution at the outlet of SCR reactor A and B decrease from 48.7% and 33.8% to 12.1% and 14.7%, respectively.

Cost estimate of the multi-pollutant abatement in coal-fired power sector in China

Seriously stringent emission regulations are applied in the coal-fired power sector in China. GB13223-2011 standards and ultra-low emission limits are promulgated to improve the application of pollutant abatement systems and reduce emissions, respectively. However, the accompanying problem of additional economic burden may affect the operation of power units and sectors. This study proposed a cost estimate model of multi-pollutant control and designed several scenarios to evaluate the total cost of different emission standards in China's coal-fired power sector. The operating costs of NOx, SO2, and PM control of a typical 300 MW unit were 6.9, 11.7, and 4.3 CNY/MWh, respectively, when meeting the GB13223-2011 emission standard and 8.2, 13.8, and 7.9 CNY/MWh, respectively, when meeting the ultra-low emission limits. Investment, energy consumption, and catalyst greatly influenced the operating cost. The scenarios analysis suggested that the total costs of multi-pollutant control under the GB13223-2011 standards and ultra-low emission limits were approximately 141.79–170.28 and 186.35–221.67 billion CNY per year, respectively. Feasible cost reduction strategies were analyzed on the basis of operation management and sector planning. The economic influence of the application of pollutant abatement systems on coal-fired power units should be evaluated comprehensively.

Integrated assessment of the environmental and economic effects of an ultra-clean flue gas treatment process in coal-fired power plant

China’s coal production and consumption levels rank first in the world. Coal-fired power plants currently account for 65.5% of the total electricity output of China’s power grid. Coal-fired thermal power is the main industry consuming coal in China and the main source of atmospheric pollutants. To alleviate environmental pollution, the Chinese government recently released stringent flue gas emission standards for coal-fired power units. These standards require that the emission of dust, sulfur dioxide, and nitrogen oxides does not exceed 10 mg/m³, 35 mg/m³, and 50 mg/m³, respectively, to achieve ultra-clean emissions. Life-cycle assessment and life cycle costing methods are combined to analyze and compare the environmental and economic effects before and after ultra-clean emission retrofit in a 315 MW unit. The environmental impact of flue gas processing for 1000 kWh power plants decreased from 0.1529 to 0.1295 after ultra-clean emission retrofit. Desulfurization and discharged flue gas after treatment are the key processes examined in this case study, while power consumption during desulfurization and residual mercury in flue gas are key substances. Therefore, looking ahead, decreasing power consumption in desulfurization and using mercury removal technology are important aspects for decreasing the environmental impact of flue gas treatment systems in coal power units.

Energy consumption and energy-saving potential analysis of pollutant abatement systems in a 1000-MW coal-fired power plant

ABSTRACTPollutant abatement systems are widely applied in the coal-fired power sector, and the energy consumption is considered an important part of the auxiliary power. An energy consumption analysis and assessment model of pollutant abatement systems in a power unit was developed based on the dynamic parameters and technology. The energy consumption of pollutant abatement systems in a 1000-MW coal-fired power unit that meets the ultra-low emission limits and the factors of operating parameters, including unit load and inlet concentration of pollutants, on the operating power were analyzed. The results show that the total power consumption of the pollutant abatement systems accounted for 1.27% of the gross power generation during the monitoring period. The wet flue gas desulfurization (WFGD) system consumed 67% of the rate, whereas the selective catalytic reduction (SCR) and electrostatic precipitator (ESP) systems consumed 8.9% and 24.1%, respectively. The power consumption rate of pollutant abatement systems decreased with the increase of unit load and increased with the increase of the inlet concentration of pollutants. The operation adjustment was also an effective method to increase the energy efficiency. For example, the operation adjustment of slurry circulation pumps could promote the energy-saving operation of the WFGD system.Implications: The application of pollutant abatement technologies increases the internal energy consumption of the power plant, which will lead to an increase of power generation costs. The real-time energy consumption of the different pollutant abatement systems in a typical power unit is analyzed based on the dynamic operating data. Further, the influence of different operating parameters on the operating power of the system and the possible energy-saving potential are analyzed.

Pollutants Emission Characteristics of an Ultra-low Coal-fired Power Unit

The concentration of particulate matter (PM), SO2, NOx, SO3, HCl, HF, and PM2.5 were measured in a 330MW ultra low emission coal-fired power unit. The pollutants emission characteristics and the effect of the conventional pollution control devices on non-conventional pollutants were investigated. The test results show that the concentration of NOx, SO2 and PM are 26.9 mg/m3, 18.1 mg/m3, 2.9 mg/m3 respectively. The coal-fired power plant, equipped with WFGD and WESP could well control SO3, HCl, HF, and PM2.5 emission from the flue gas. SO3 removal efficiency of WFGD and WESP are 42.2% and 82.8% respectively. HCl and HF removal efficiency by WFGD are 90.8% and 91.5% respectively. PM2.5 removal efficiency of WESP is 86.9%.

An Integrated Multi-Criteria Decision Making Model and AHP Weighting Uncertainty Analysis for Sustainability Assessment of Coal-Fired Power Units

The transformation of the power generation industry from coal-based to more sustainable energy sources is an irreversible trend. In China, the coal-fired power plant, as the main electric power supply facility at present, needs to know its own sustainability level to face the future competition. A hybrid multi-criteria decision making (MCDM) model is proposed in this paper to assess the sustainability levels of the existing Chinese coal-fired power units. The areal grey relational analysis (AGRA) method is involved in the hybrid model, and a combined weighting method is used to determine the priorities of the criteria. The combining weight fuses the fuzzy rough set (FRS) and entropy objective weighting method together with the analytic hierarchy process (AHP) subjective weighting method by game theory. Moreover, an AHP weighting uncertainty analysis using Monte Carlo (MC) simulation is introduced to measure the uncertainty of the results, and a 95 percent confidence interval (CI) is defined as the uncertainty measurement of the alternatives. A case study about eight coal-fired power units is carried out with a criteria system, which contains five aspects in an operational perspective, such as the flexibility, economic, environmental, reliability and technical criterion. The sustainability assessment is performed at the unit level, and the results give a priority rank of the eight alternatives; additionally, the uncertainty analysis supplies the extra information from a statistical perspective. This work expands a novel hybrid MCDM method to the sustainability assessment of the power generation systems, and it may be a benefit to the energy enterprises in assessing the sustainability at the unit level and enhance its ability in future sustainable development.

Comprehensive Evaluation of Coal-Fired Power Units Using Grey Relational Analysis and a Hybrid Entropy-Based Weighting Method.

In recent years, coal-fired power plants contribute the biggest part of power generation in China. Challenges of energy conservation and emission reduction of the coal-fired power plant encountering with a rapid growth due to the rising proportion of renewable energy generation in total power generation. Energy saving power generation dispatch (ESPGD) based on power units sorting technology is a promising approach to meet the challenge. Therefore, it is crucial to establish a reasonable and feasible multi-index comprehensive evaluation (MICE) framework for assessing the performance of coal-fired power units accessed by the power grid. In this paper, a hierarchical multiple criteria evaluation system was established. Except for the typical economic and environmental indices, the evaluation system considering operational flexibility and power quality indices either. A hybrid comprehensive evaluation model was proposed to assess the unit operational performance. The model is an integration of grey relational analysis (GRA) with analytic hierarchy process (AHP) and a novel entropy-based method (abbreviate as BECC) which integrates bootstrap method and correlation coefficient (CC) into entropy principle to get the objective weight of indices. Then a case study on seven typical 600 megawatts coal-fired power units was carried out to illustrate the proposed evaluation model, and a weight sensitivity analysis was developed in addition. The results of the case study shows that unit 4 has the power generating priority over the rest ones, and unit 2 ranks last, with the lowest grey relational degree. The weight sensitivity analysis shows that the environmental factor has the biggest sensitivity coefficient. And the validation analysis of the developed BECC weight method shows that it is feasible for the MICE model, and it is stable with an ignorable uncertainty caused by the stochastic factor in the bootstrapping process. The elaborate analysis of the result reveals that it is feasible to rank power units with the proposed evaluation model. Furthermore, it is beneficial to synthesize the updated multiple criteria in optimizing the power generating priority of coal-fired power units.

The impact of the control method of cyclic operation on the power unit efficiency and life

The increasing share of renewable energy sources in the overall energy mix forces a change in the character of operation of coal-fired power units. Their task is now to balance the system under variable loads and they have to change from base-to cyclic-load operation. However, cyclic-load conditions involve a decrease in the power unit efficiency and shorten the life of components due to a rise in low cycle fatigue.The paper investigates the possibilities of reducing own-needs electricity consumption by replacing the power unit constant pressure control with sliding pressure control. The problems arising from such a change in the control method are identified. The minimum value of steam pressure upstream the turbine for the conditions of operation under sliding pressure control is determined that does not produce any negative effects in the turbine performance and that makes it possible to obtain a reduction both in unit heat rate and in the amount of power needed to drive the feed water pumps. The calculation results are verified against measurements of a turbine operating with sliding pressure control.The analysis also covers changes in the thermal and stress states of the turbine components during the turbine power drop realized by means of constant and sliding pressure control. The life-related effects of the power unit different control methods are assessed.

Economic Analysis of Waste Heat Utilization for Coal-fired Power Units

Strict energy conservation policies require power plants to minimize energy consumption as much as possible. Low pressure economizer is an effective method to recycle waste heat from boiler exhaust gas. In this paper, the economic analysis model of coal-fired power plant is established by means of equivalent enthalpy drop method, and the waste heat utilization effect on thermal systems is investigated, including boiler efficiency, steam turbine power output, condensate pump, induced draft fan, electro static precipitator and desulfurization system. Then the economic effect on a 1000 MW ultra super critical unit in Shandong Province is calculated. The results show that waste heat utilization could comprehensively reduce standard coal consumption rate by 1.89 g/(kW·h), and the unit could save about 10.8 thousand tons standard coal and 1.29 billion dollars every year. Besides, the energy saving effect is more significant for lower load condition.

Co-benefit of hazardous trace elements capture in dust removal devices of ultra-low emission coal-fired power plants

The co-benefit of hazardous trace elements such as mercury (Hg), arsenic (As), and selenium (Se) capture in dust removal devices of ultra-low emission coal-fired power plants was investigated. Feed fuel and ash samples collected from 15 different coal-fired power units equipped with ultra-low emission systems were characterized to determine the concentrations and distribution characteristics of trace elements. It was found that the low-low temperature electrostatic precipitator (LLT-ESP) and the electrostatic fabric filter (EFF) had greater abatement capacity for Hg than normal cold-side ESP (CS-ESP). Only 0.8%–36.1% of Hg escaped from LLT-ESP and EFF, whereas 42.1%–90.6% of Hg escaped from CS-ESP. With the employment of EFF and ESP (inlet temperature<125 °C), 72.3%–99.1% of As and 70.7%–100% of Se could be captured before the wet flue gas desulfurization (WFGD) system. The significance level of the effects on the abatement capacity for Hg, As, and Se in ESP were analyzed by the Pearson correlation analysis and grey relational analysis. The results indicated that the low inlet temperature of LLT-ESP had significant promotional effect on the simultaneous removal of Hg, As, and Se. The smaller particle size of fly ash can be conducive to the adsorption of hazardous trace elements. The inhibitory effect of sulfur content in coal was significant for the enrichment of Hg and Se in fly ash.

Analysis of a cooling system of the ultra-supercritical coal-fired power unit integrated with CO2 capture

The subject of this paper is analysis of the cooling system of a conceptual advanced ultra-supercritical coal-fired power unit integrated with a CO2 capture and compression unit (CCU). The capture unit, based on wet chemical absorption using MEA (monoethanolamine), was modelled in Aspen PLUS. The obtained results were used in the power unit model developed in Ebsilon Professional. The aim of the calculations was to determine the cooling demand of the CCU and to define the impact of the integration on the power unit operation under nominal and variable ambient conditions. Performed analyses show that, in nominal conditions, CO2 separation and compression involve an increase in the cooling demand by about 21%. In higher ambient temperatures it is not possible to keep the assumed cooling parameters in the CCU. One of the solutions, is an increase in the area of the heat exchangers. Obtained results showed, that the total surface of all heat exchangers in the CCU has to be increased by 77% (48–89% for individual coolers). The need to collect a considerable amount of extra heat results in a rise in the cooling water temperature and in higher pressure in the steam turbine condenser by 0.3 kPa.