Efficiency Of Coal-fired Power Plants Research Articles

A Hybrid Soft Sensor Model for Measuring the Oxygen Content in Boiler Flue Gas.

As an indispensable component of coal-fired power plants, boilers play a crucial role in converting water into high-pressure steam. The oxygen content in the flue gas is a crucial indicator, which indicates the state of combustion within the boiler. The oxygen content not only affects the thermal efficiency of the boiler and the energy utilization of the generator unit, but also has adverse impacts on the environment. Therefore, accurate measurement of the flue gas's oxygen content is of paramount importance in enhancing the energy utilization efficiency of coal-fired power plants and reducing the emissions of waste gas and pollutants. This study proposes a prediction model for the oxygen content in the flue gas that combines the whale optimization algorithm (WOA) and long short-term memory (LSTM) networks. Among them, the whale optimization algorithm (WOA) was used to optimize the learning rate, the number of hidden layers, and the regularization coefficients of the long short-term memory (LSTM). The data used in this study were obtained from a 350 MW power generation unit in a coal-fired power plant to validate the practicality and effectiveness of the proposed hybrid model. The simulation results demonstrated that the whale optimization algorithm-long short-term memory (WOA-LSTM) model achieved an MAE of 0.16493, an RMSE of 0.12712, an MAPE of 2.2254%, and an R2 value of 0.98664. The whale optimization algorithm-long short-term memory (WOA-LSTM) model demonstrated enhancements in accuracy compared with the least squares support vector machine (LSSVM), long short-term memory (LSTM), particle swarm optimization-least squares support vector machine (PSO-LSSVM), and particle swarm optimization-long short-term memory (PSO-LSTM), with improvements of 4.93%, 4.03%, 1.35%, and 0.49%, respectively. These results indicated that the proposed soft sensor model exhibited more accurate performance, which can meet practical requirements of coal-fired power plants.

Design of a Coal Drying System with Solar-Assisted Heat Pump and Waste Heat Utilisation

The increase in global energy demand has directed researchers towards making low-quality coals into an environmentally friendly energy source by reducing their high moisture content. Drying coal is a high-energy and time-consuming process, so reducing the required energy and drying time is crucial for drying technology. Coal drying increases the thermal value of coal and makes it easier to transport. In this study, a coal drying system was designed using waste heat recovery systems, R-134a refrigerant as working fluid, air source heat pumps, and vacuum tube solar collectors to provide hot air. Firstly, the moisture content of the coal and the desired moisture content after drying were determined, and then the heat required to dry the coal was calculated. Next, the capacity of the solar collector required to provide the necessary heat to the heat pump was determined, and the type and capacity of the heat pump that could produce the required heat were selected. Finally, the coal dryer was designed based on the specific requirements of the power plant and the type of coal used. As a result, the coal drying system designed with solar-assisted heat pumps and waste heat utilization can increase the efficiency of coal-fired power plants by reducing the moisture content of coal before combustion.

Analysis on temperature vacuum swing adsorption integrated with heat pump for efficient carbon capture

Carbon capture and storage (CCS) is gathering the momentum to achieve the ultimate target of carbon neutrality. Temperature vacuum swing adsorption (TVSA) has uncovered its superiority due to large working capacity, CO2 purity and recovery rate. However, high energy demand in the regeneration process of adsorbent leads to the loss of net efficiency of coal-fired power plant (CFPP) after retrofitted. This paper initially proposes and evaluates an integrated system which is composed of an adsorption carbon capture unit (ADCCU) and a single-effect absorption heat transformer (SAHT). Then a general concept of sorption carbon capture integrated with heat pump could be introduced. Results indicates that CO2 purity and recovery rate of the integrated system vary from 91.20 % to 92.75 % and from 95.62 % to 98.11 % when flowrate range from 48 NL·min−1 to 60 NL·min−1. Under the condition of 140 °C regeneration temperature of ADCCU and 80 °C generation temperature of SAHT, exergy efficiency of SAHT achieves the maximum value of 85.28 %. Moreover, a vapor compression heat pump (VCHP) system is coupled to provide moderate temperature heat for SAHT when waste heat of CFPP is inadequate. The effect of waste heat and electricity consumed on performance of CFPP is also taken into consideration. When recovery rate is lower than 27 %, performance of the proposed integrated system is more favorable than that using steam evacuated from the turbine. It is demonstrated that heat pump assisted adsorption capture for CFPP may be a promising solution to reduce energy consumption in the near future.

Performance analysis of an efficient waste heat utilization system in an ultra-supercritical coal-fired power plant

With the rise of new energy sources in the power industry, improving the efficiency of coal-fired power plants is essential. Currently, the leading main causes of irreversible energy loss are the energy level mismatches of boilers and turbines. An ultra-supercritical coal-fired power plant thermodynamic system was reconstructed based on the first and second laws of thermodynamics to improve the efficiency of power plants, and an efficient condensate water preheating air integrated bypass flue waste heating efficient utilization system is thus herein proposed. Consequently, high and medium steam turbine extraction flow is returned to the steam turbine to do work, and cold source loss is reduced by increasing the extraction steam flow of the low-pressure cylinder. At the same time, the inlet air temperature in the air preheater is significantly increased by preheating the hot air with condensate water, resulting in a reduced heat transfer temperature difference and significantly improved exergy efficiency. Compared with conventional low-temperature economizer and bypass flue waste heat utilization schemes, the results indicate that the heat transfer exergy efficiency increased significantly from 78.49% to 95.88% in the air preheater, and the heat consumption rate of the turbine generator set decreased by 108.06 kJ/(kW⋅h). The generation efficiency increases by 0.74%, while the standard coal consumption rate decreases by 3.92 g/(kW⋅h). In terms of economic investment, the dynamic payback period is 3.31 years and the net present value is $2.20 M/year. This paper provides an effective energy conservation and emission reduction plan for coal-fired power plants to contribute towards achieving national carbon peaking and carbon neutrality goals.

Spatial autocorrelation analysis of the environmental efficiency of coal-fired power plants in China

Spatial autocorrelation analysis of the environmental efficiency of coal-fired power plants in China

ECoalVis: Visual Analysis of Control Strategies in Coal-fired Power Plants.

Improving the efficiency of coal-fired power plants has numerous benefits. The control strategy is one of the major factors affecting such efficiency. However, due to the complex and dynamic environment inside the power plants, it is hard to extract and evaluate control strategies and their cascading impact across massive sensors. Existing manual and data-driven approaches cannot well support the analysis of control strategies because these approaches are time-consuming and do not scale with the complexity of the power plant systems. Three challenges were identified: a) interactive extraction of control strategies from large-scale dynamic sensor data, b) intuitive visual representation of cascading impact among the sensors in a complex power plant system, and c) time-lag-aware analysis of the impact of control strategies on electricity generation efficiency. By collaborating with energy domain experts, we addressed these challenges with ECoalVis, a novel interactive system for experts to visually analyze the control strategies of coal-fired power plants extracted from historical sensor data. The effectiveness of the proposed system is evaluated with two usage scenarios on a real-world historical dataset and received positive feedback from experts.

Heat balance simulation for evaluating a 315 MW low rank coal-fired power plant performance

The domination of coal-fired power plant as power generation due to its feasibility to ensure a stable supply of electricity to customer. Unfortunately, the use of coal as power plant fuel faces an issue of air pollution. Some efforts have been proposed to make the operated coal-fired power plant meeting the environmental regulations. One of the most potential ways to solve the problem is by improving the coal-fired power plant efficiency and then equate to a greenhouse gas reduction. Thus, heat balance simulation of coal-fired power plant which operates in different conditions have to be studied in order to analyse the power plant performance. In this paper, the heat balance of a 315 MW low rank coal-fired power plant is simulated by Cycle-Tempo. The simulations are carried out for several different operation conditions of the power plant. The Heat Rate will increase of 3.66% when all HPH are on off-duty while it increases by 2.63% when all LPH are on off-duty. Furthermore, the increasing of Superheater temperature of 5 °C will decrease the Heat Rate of 0.59% and it will decrease of 0.39% when the temperature of Reheater increases of 5 °C.

Flexible performance and efficiency of coal-fired power plant as a share of renewable energies increases

Flexible performance and efficiency of coal-fired power plant as a share of renewable energies increases

Hollow fiber-based rapid temperature swing adsorption process for carbon capture from coal-fired power plants

Post-combustion carbon capture is one of the feasible methods to reduce emission of carbon dioxide (CO2) from coal-fired power plants. The biggest challenge in this technology is reduction of energy consumption. This work proposes a hollow fiber based rapid temperature swing adsorption (RTSA) method for capturing CO2 from typical coal-fired power plants. The proposed RTSA approach can shorten the operating time and using low-grade energy for regeneration of adsorption elements. In this study, the tank-in-series model is used to simulate the RTSA process including adsorption and desorption periods. A dual-column operating procedure is then used to treat the flue gas continuously from the coal-fired power plants. Main operating variables including inlet gas volume flow rate (0.1–0.2 m3/s), abandon time (0–10 s), desorption temperature (80–120 °C) on key performance factors such as discharge gas purity, capture ratio of CO2, and energy consumption per unit CO2, etc. are investigated for reducing the energy consumption. This study found that the inlet gas volume flow rate will significantly affect the capture ratio, where smaller gas volume flow rate would be beneficial to increase capture ratio. The abandon time obviously affects the purity of the captured CO2, where the longer abandon time leads to higher purity. Desorption temperature affects both the capture ratio and purity of captured CO2. The higher the desorption temperature, the greater the purity and capture ratio. For one typical basic unit with dual-column hollow fiber-based RTSA, the study found that when the inlet gas volume flow rate is 0.12 m3/s, the desorption waiting time is 7 s, and the desorption temperature is 120 °C, both the CO2 purity and capture ratio can exceed 90%. With considering the possibility of using steam in a low-pressure turbine as a source of heat required for Dual column vacuum RTSA (DC-vRTSA), the impact on the efficiency and stream data of typical coal-fired power plants are calculated. DC-vRTSA at 120 °C, 100 °C and 80 °C will reduce the efficiency of coal-fired power plants by 8.2%, 6%, and 3.4%, respectively.

Flexibility and efficiency enhancement for double-reheat coal-fired power plants by control optimization considering boiler heat storage

Double reheat is a potential technique to increase the efficiency of coal-fired power plants. Large penetration of renewable power requires coal-fired power plants to operate flexibly. The thermal inertia of a double-reheat boiler is extremely high due to its complicated flow, strong coupling and numerous devices, which seriously restrict the operational flexibility of double-reheat coal-fired power plants. In this study, dynamic simulation models and temperature control systems of a double-reheat boiler are developed via GSE software and then validated to understand the heat storage change law. An improved control model considering heat storage changes is proposed. The flexibility of original and improved control strategies is compared. It turns out that steam temperatures in the boiler system with the original control exceed the allowable ranges when the load cycling rate is 1.5% Pe0 min−1. By contrast, steam temperatures in the boiler system with the improved control remain within the allowable ranges when the load cycling rate is 3.0% Pe0 min−1. The response time with the improved control is shorter than that with the original control. This study is expected to provide a detailed reference for improving the flexibility of double-reheat power plants.

Control Strategy for Denitrification Efficiency of Coal-Fired Power Plant Based on Deep Reinforcement Learning

The optimal control of denitrification system in coal-fired power plants in China has recently received widespread attention. The accurate prediction of denitrification efficiency and formulate control strategy of denitrification efficiency can guide the control and operation of the denitrification system better. Meanwhile, it can achieve the effect of energy conservation and Nitrogen oxides (NOx) reduction. In this paper, we take a domestic 1000 MW unit as an example, consider each of the major factors that affect the denitrification efficiency of selective catalytic reduction (SCR). We put forward a deep reinforcement learning (DRL) model by combining the Long short-term memory (LSTM) model and the Asynchronous Advantage Actor - Critic algorithm (A3C). We first use the LSTM to build a prediction model for denitrification efficiency. We then use the DRL model to obtain a control strategy for SCR denitrification efficiency in coal-fired power plants. The experimental results demonstrate that the accuracy of denitrification efficiency prediction model we established is better than other machine learning models, reaching 91.7%. Our control strategy model is industrially feasible and universally applicable.

In situ, portable and robust laser sensor for simultaneous measurement of ammonia, water vapor and temperature in denitrification processes of coal fired power plants

Simultaneous measurement of the ammonia, flue gas temperature and water vapor concentration in denitrification (deNOx) processes is of great importance for improving the deNOx efficiency of coal-fired power plants (CFPPs) and maximizing energy conservation and emission reduction. A portable, robust, low-cost and low-power laser sensor was developed based on wavelength modulation spectroscopy (WMS) with a single near infrared diode laser, which covers the optimized NH3 spectral line at 6612.73 cm−1 and H2O line pair at 6612.02 and 6609.85 cm−1. A calibration-free for WMS with varied modulation amplitude (WMS-VMA) was proposed to improve the performance of the tri-spectral line analysis. A probe, based on Herriott cell structure, coupled with deformation resistance, dust-proof, air-tight and anti-seismic, was design to adapt to the harsh environment of CFPPs. Lab-based sensor evaluation showed that the measurement accuracies for the temperature, H2O and NH3 concentration are 2.9 %, 4.8 % and 5.1 %, respectively. Allan variance analysis shows that the sensor has good stability, and the measurement sensitivity at five-second resolution are 0.1 ppm and 0.03 % for NH3 and H2O concentration, respectively. Furthermore, the feasibility of the sensor system was also verified by field tests at both deNOx inlet and outlet in a practical CFPP, denoting great potential of ammonia injection optimization in deNOx process.

Optimization and comparison on supercritical CO2 power cycles integrated within coal-fired power plants considering the hot and cold end characteristics

The integration of supercritical CO2 (SCO2) cycle instead of steam Rankine cycle may be a revolutionary technique to increase the efficiency of coal-fired power plants. To effectively extract exergy from the fluegas and convert exergy to power, the characteristics of hot end (heat reservoir) and cold end (heat sink) should be fully considered, and the system multi-parameters should be optimized. In this study, based on a benchmark coal-fired power plant integrated with a recompression SCO2 power cycle, quantitative efficiency enhancements of system improvements of the hot end and cold end for SCO2 power cycle are calculated and compared. The optimized efficiency of benchmark coal-fired plant integrated with recompression SCO2 power cycle is 45.43%. When the fluegas at the economizer outlet is effectively used, the power plant efficiency can be increased by 1.32%. With single and double reheats to decrease the heat transfer irreversibility of the hot end, the power plant efficiency can be increased by 1.77% and 2.24%, respectively. Cold end optimization with single intercooling and cold air preheating can increase the power plant efficiency by 0.32% and 0.33%, respectively. Finally, a simple structure system and a complex structure system are proposed. With optimal system parameters, the power plant efficiencies of the complex and simple systems are 49.32% and 48.52%, respectively.

Performance evaluation of a novel double-reheat boiler with triple-rear passes

Double-reheat technology effectively increases the efficiency of coal-fired power plants. The bases for a double-reheat boiler design are reliability, efficiency, and controllability. A novel double-reheat boiler with triple-rear passes was proposed in this study to address several issues, such as low reliability and control precision of double-reheat steam temperatures of conventional double-reheat boilers. Dynamic models with a control system were developed with GSE software to examine the performance of the proposed boiler. Simulation results under steady-state working conditions showed that double-reheat steam temperatures can achieve design values in a wide load range. Then, the dynamic characteristics of the boiler were studied. Results further showed that a coordinated regulation of dampers in the triple-rear passes can effectively control double-reheat steam temperatures. Moreover, double-reheat steam temperatures can be controlled within an acceptable range during load cycling processes.

Development of a Heating Process of a Slag-Tapping Hole by Syngas Burning in a 150 t/d Entrained-Bed Coal Gasifier

Integrated coal gasification combined cycle systems are expected to raise the power generation efficiency of coal-fired power plants. In Japan, coal gasifiers are required to treat various kinds of coal imported from many countries because almost all of the coal is imported from abroad. In an entrained-bed coal gasifier, the slag-tapping hole must be heated adequately to discharge the molten slag. Thus, a heating technique has been developed to heat the hole from below, without using any auxiliary fuels. The technique is to burn the syngas, which descends through the hole at high temperature, by supplying oxygen from a pair of nozzles facing each other installed just below the hole. In this study, a design procedure to heat the hole by those nozzles was developed through thermal and flow simulations and actual gasification tests in a 150 t/d entrained-bed coal gasifier of pilot scale.

Laser Multi-Pass Narrow-Gap Welding – A Promising Technology for Joining Thick-Walled Components of Future Power Plants

Today, the average worldwide efficiency of coal-fired power plants stands at about 33 percent. The consistent use of state of the art technologies would enable an increase of the average efficiency of up to 47 percent and thus a sharp reduction of greenhouse gas emissions. The importance of improvements in this field becomes apparent when reviewing e.g. plans in Europe in 2017 for new power plants to be built across the continent. About 44 percent of the envisaged 153 gigawatts are still to be generated by fossil-fuel power plants [1]. One technical solution is to increase the steam turbine inlet temperature to 700°C. This, however, requires the use of nickel-based superalloys. Only these alloys satisfy all the requirements with regard to high-temperature, corrosion and oxidation resistance and creep behavior [2], [3]. Due to their relatively poor machinability, forgeability and high material costs compared to the steel-based alloys they are to replace, a more effective welding technology is needed to overcome the disadvantages of conventional welding technologies, i.e. large quantities of filler metal required and high energy input per unit length resulting in distortion and the potential reduction of high-temperature properties.

State-wise Efficiency Assessment of Coal-Fired Thermal Power Plants Using Malmquist Index Approach

In India, a majority of darkness disperses due to coal-fired power plants. Knowing the importance of energy, every single State of India tries to improve the efficiency of coal-fired power plants situated in their region through their internal policies, apart from laid rules and regulation by Central authorities. Thus it becomes foremost important to assess the efficiency of these power plants as a group, i.e. State-wise, to know who has better governance. This study identifies the States, whose productivity changes have been progressive and regressive; such identification can guide suitable managerial intervention to improve productivity. Out of 8 non-performing States, the State of Karnataka and Tamil Nadu needs urgent attention from the energy planner. So that natural resources can be saved and increase the accessibility of power to society at a cheaper rate. Hence this research work shows that there is an immense scope of improvement in these two States.

An Improved Flexible Solar Thermal Energy Integration Process for Enhancing the Coal-Based Energy Efficiency and NOx Removal Effectiveness in Coal-Fired Power Plants under Different Load Conditions

An improved flexible solar-aided power generation system (SAPG) for enhancing both selective catalytic reduction (SCR) de-NOx efficiency and coal-based energy efficiency of coal-fired power plants is proposed. In the proposed concept, the solar energy injection point is changed for different power plant loads, bringing about different benefits for coal-fired power generation. For partial/low load, solar energy is beneficially used to increase the flue gas temperature to guarantee the SCR de-NOx effectiveness as well as increase the boiler energy input by reheating the combustion air. For high power load, solar energy is used for saving steam bleeds from turbines by heating the feed water. A case study for a typical 1000 MW coal-fired power plant using the proposed concept has been performed and the results showed that, the SCR de-NOx efficiency of proposed SAPG could increase by 3.1% and 7.9% under medium load and low load conditions, respectively, as compared with the reference plant. The standard coal consumption rate of the proposed SAPG could decrease by 2.68 g/kWh, 4.05 g/kWh and 6.31 g/kWh for high, medium and low loads, respectively, with 0.040 USD/kWh of solar generated electricity cost. The proposed concept opens up a novel solar energy integration pattern in coal-fired power plants to improve the pollutant removal effectiveness and decrease the coal consumption of the power plant.

A meta-study on the feasibility of the implementation of new clean coal technologies to existing coal-fired power plants in an effort to decrease carbon emissions

The renewable energy sector has experienced an incredible growth in the last 15 years. The dependency on fossil fuel based power plants is still likely to continue well into the next half century. The global thermal efficiency of coal-fired power plants (CFPPs) since the 1980s has largely remained stagnant at 30-39% (high heat value basis)(2). Recent advances in materials and thermodynamics technologies has allowed for the efficiency of new pilot plants to be increased to 45%, even beyond 50% in some cases(3). The manufacture of these new highly efficient ultra-supercritical (USC) steam cycle CFPPs is an economically and politically difficult prospect. Therefore, it is necessary to investigates methods to apply the thermodynamic improvements available in modern USC CFPPs to the currently operating majority of subcritical (SubC) power plants without a large overhaul in infrastructure i.e. through retrofitting. This meta study will provide an analysis in the trends of the overall and intra-system efficiency of CFPPs, the development new clean coal technologies, then discuss and conclude the feasibility of applying these processes to current power plant infrastructure. A thermodynamic analysis of the most promising clean coal technologies, i.e. advanced pulverized coal combustion systems, oxy-fuel, pre and post-combustion carbon capture systems, steam reheat cycles, co-firing systems, will allow the investigation into whether retrofitting current power plants will generate a significant increase in efficiency. Thereby allowing for the discussion of the viability of retrofitting for the reduction in CFPP carbon emissions and the recommendation of specific options.

Optimization of a solar aided coal-fired combined heat and power plant based on changeable integrate mode under different solar irradiance

Integrating solar thermal energy into conventional coal-fired power plant has been proved to be an efficient way to use solar energy and improve the generation efficiency of coal-fired power plant. Because of the variability of solar irradiance, an optimization strategy based on switching solar integrate mode according to the solar irradiance is proposed in this paper. A parabolic trough solar aided coal-fired combined heat and power (SACF-CHP) system model is built to analyze the system performance. In order to obtain the minimum Levelized Electricity Costs (LEC), a generic superstructure of solar integrate mode is established, and a mixed integer nonlinear programming approach is applied to optimize the oil-water heat exchanger area and solar integrate mode. The optimized results of a 150MW SACF-CHP system indicate that switching integrate mode according to the solar irradiance would have a lower LEC than fixing the integrate mode invariably, and the optimal LEC of those two integrate modes are 0.0771$/kWh and 0.0794$/kWh respectively. Besides, the LEC decreases at first and then increases with the increase of the oil-water heat exchanger area. And the optimal heat exchanger area for changeable integrate mode are 725m2.