Coal-fired Power Plants In China Research Articles

Characterizing of water-energy-emission nexus of coal-fired power industry using entropy weighting method

The coupled relationships among water, energy, and emission, i.e., water-energy-emission nexus (WEEN), are found to be spatial-temporally characterized. This research is aimed at evaluating the spatial-temporal characteristics of the WEEN of the selected 227 coal-fired power plants in China from 2012 to 2014 by employing the entropy weighting method. Firstly, the WEEN performances (the sub-indicators, i.e., the emissions, water for cooling, water for pollutant removal, energy for electricity generation, and energy for pollutant removal) of the plants are computed. Then, each sub-indicator of the WEEN performances is compared at plant level. Finally, the entropy weighting factor is introduced to evaluate the overall performances of WEEN (defined as the WEEN indicator). The results show that NOx and SO2 removal sub-indicators were with the highest entropy weights. Overall, the WEEN indicator improves significantly from 0.21 (2012) to 0.37 (2014), which means the increases of pollutant removal were more significant than the changes in water and energy inputs. The power plants located in Northern China and Central China grids show more significant improvement. This is mainly contributed by the improvement of the three emission sub-indicators and the larger amount of removed pollutants. By evaluating the improvement of WEEN indicators, the overall performances of WEEN with the simultaneous consideration of water, energy and emission are quantitatively addressed, which reflect the technology improvement and the strict policies and regulations behind it. This research provides a quantifiable and integrated way to evaluate and compare the various aspects of WEEN at the plant level.

Characteristics of condensable particulate matter before and after wet flue gas desulfurization and wet electrostatic precipitator from ultra-low emission coal-fired power plants in China

Total particulate matters emitted from coal-fired power plants generally include condensable particulate matter (CPM) and filterable particulate matter (FPM). Based on the on-site sampling of CPM, this study investigated four typical coal-fired power plants equipped with ultra-low emission facilities in north China. In order to clarify the characteristics of CPM before and after wet flue gas desulfurization (WFGD) and wet electrostatic precipitator (WESP), the mass concentrations, organic and inorganic compositions of the CPM were analyzed. Among the four test power plants, the emission concentrations of CPM were 2.20–7.33 mg/Nm3, accounting for 57.74–91.79% of PM2.5. The organic component accounted for 59.64% of the total mass concentration of CPM on average. Alkanes, esters and amides were the major organic components. And the water-soluble ions contributed significantly to the inorganic component of CPM. The proportion of SO42− was the highest, followed by Cl− and NO3−. In addition, this study found that the concentration of SO42− increased significantly while SO3 decreased from WESP inlet to outlet. It was indicated that ultrafine particles and soluble SO2 in flue gas could contribute to the formation of SO42− in CPM besides SO3. As an important part of CPM, further studies should be conducted on the factors affecting SO42−.

Non-Negligible Stack Emissions of Noncriteria Air Pollutants from Coal-Fired Power Plants in China: Condensable Particulate Matter and Sulfur Trioxide.

In this study, we investigated the emission characteristics of condensable particulate matter (CPM) and sulfur trioxide (SO3) simultaneously through ammonia-based/limestone-based wet flue gas desulfurization (WFGD) from four typical coal-fired power plants (CFPPs) by conducting field measurements. Stack emissions of filterable particulate matter (FPM) all meet the Chinese ultralow emission (ULE) standards, whereas CPM concentrations are prominent (even exceed 10 mg/Nm3 from two CFPPs). We find that NH4+ and Cl- increase markedly through the ammonia-based WFGD, and SO42- is generally the main ionic component, both in CPM and FPM. Notably, the occurrence of elemental Se in FPM and CPM is significantly affected by WFGD. Furthermore, the established chemical profiles in FPM and CPM show a distinct discrepancy. In CPM, the elemental S mainly exists as a sulfate, and the metallic elements of Na, K, Mg, and Ca mainly exist as ionic species. Our results may indicate that not all SO3 are included in CPM and they co-exist in stack plume. With the substantial reduction of sulfur dioxide (SO2), S distributed in SO3, CPM, and FPM becomes non-negligible. Finally, the emission factors of CPM and SO3 under typical ULE technical routes fall in the ranges of 74.33-167.83 and 48.76-86.30 g/(t of coal) accordingly.

Unified efficiency measurement of coal-fired power plants in China considering group heterogeneity and technological gaps

Abstract China's coal-fired power generation has accounted for a large proportion of the power supply for a long time and the resulting environmental pollution and waste of resources have hindered the sustainable development of the power industry. To solve this problem, this study combines the concept of natural and managerial disposability with the non-concave meta-frontier method to determine the unified efficiency measurement of 251 coal-fired power plants in China from 2012 to 2014 and to investigate the sources of inefficiency in different areas. The results show that although the unified efficiency of China's coal-fired power plants improved significantly during 2012–2014, much room for improvement remains in terms of power generation and environmental performance. Due to the advanced technology of coal-fired power plants, the eastern area has the highest unified efficiency in terms of natural and managerial disposability. The western region has the lowest operational performance and the northeast region has the lowest environmental performance. The decomposition of the sources of inefficiency indicates that the inefficiency of coal-fired power plants in eastern China is mainly caused by management factors, whereas the inefficiency in northeastern China is due to a lag in technology. In the central and western areas, technical inefficiency and management inefficiency both account for a considerable proportion in their sources of inefficiency. Therefore, these regions need to improve both the management (e.g., reasonable allocation of utilization hours) and technology (e.g., clean coal technology) aspects to improve the unified performance of coal-fired power plants.

Cost analysis of environmental protection price of coal-fired plants in China.

In the paper, the achievements obtained from carrying out the policy of environmental protection price for promoting air pollution control in coal-fired power plants in China during more than a decade were summarized. Based on the situation of current electricity market reform, the role and effectiveness of environmental protection price for controlling the normal air pollutants, such as sulfur dioxide, nitrogen oxides, and dust in China's coal-fired power generation plants, were investigated, including the price structure of electricity environmental protection for coal-fired power generation enterprises in different regions, generating units, and power demands. The policy suggestions were proposed, namely, the reform of electricity environmental protection price would be carried out gradually, the relationship between electricity environmental protection price policy and other environmental protection policies would be matched under the relative overcapacity condition, and the environmental protection price regulation would be integrated into other environmental policies.

Large eddy simulation of a 660 MW utility boiler under variable load conditions

Large eddy simulation (LES) has become a promising tool for pulverized coal combustion with the development of computational fluid dynamics (CFD) technologies in recent years. LES can better capture the unsteady features and turbulent structures of coal jet flame than Reynolds averaged Navier Stokes (RANS). The coal-fired power plants in China are now required to be operated in a wide load range and quickly respond to the electric grid. The boiler performance of variable loads should be evaluated in terms of flow, heat transfer, and combustion processes. In this paper, LES was applied to simulate a 660 MW ultra-supercritical boiler under BMCR (boiler maximum continue rate), 75%THA-100, and 50%THA-100 conditions. The predicted gas velocities agree well with the thermal calculation and the temperature error is less than 130 K. The simulation results show that the operation load has significant effects on the boiler performance. It is also proved that LES can provide guidance for the design and operation of advanced coal-fired boilers.

Early Warning of Critical Blockage in Coal Mills Based on Stacked Denoising Autoencoders

Coal mills have a significant influence on the reliability, efficiency, and safe operation of a coal-fired power plant. Coal blockage is one of the main reasons for coal mill malfunction. It is highly essential to accurately detect the critical blockage in coal mills to ensure a safe and stable operation of the unit. Taking advantage of unsupervised learning methods and historical process data from distributed control systems (DCS), a stacked denoising autoencoder (SDAE) network–based approach for monitoring critical blockage in a coal mill is proposed in this work. The SDAE model with optimized parameters is applied to reconstruct the operating data during normal operating conditions. The intrinsic relationship between all input variables was captured by training a multilayer network model. The monitoring indicator was obtained from the reconstruction errors, and the threshold for monitoring indicators was obtained using kernel density estimation (KDE) during normal operation. The proposed network is independent of fault data, requires a reduced on-line calculation, and demonstrates a better real-time performance compared to conventional methods. The abnormal variables analysis may provide a theoretical evidence for critical blockage. The effectiveness of the proposed method is validated using operating data collected from an actual coal-fired power plant in China. The results demonstrated that the proposed method can effectively detect critical blockage in a coal mill and issue a timely warning, which allows operators to detect potential faults.

Analysis of Main Influencing Factors of the Wastewater Evaporation in Flue Duct

Desulfurization wastewater has the characteristics of small discharge and high pollution, and must be strictly treated. To obtain the main factors affecting the evaporation characteristics of desulfurization wastewater in boiler flue, a 600MW unit of a coal-fired power plant in China was taken as an example. According to the theory of fluid mechanics and heat transfer, the numerical simulation method was used. The results show that the way the nozzle is installed on the upper wall of the flue inlet can enhance the evaporation effect of the desulfurization wastewater. It is also revealed that the influence of the flue gas flow rate on the droplet evaporation effect is relatively small. The smaller droplet diameter and the higher flue gas inlet temperature will obviously enhance the evaporation effect of the droplets in the flue. However these two factors will increase the operating cost and reduce the boiler thermal efficiency. Therefore, the values of the droplet diameter and the flue gas inlet temperature need to be further determined by technical and economic comparison.

Mercury Speciation of Flue Gas Desulphurization By-Products in Coal-Fired Power Plants in China

The aim of this study was to develop and examine the morphology and distribution of mercury (Hg) in flue gas desulfurization (FGD) by-product. Mercury in the coal of coal-fired power plants is concentrated in the by-products of desulfurization process, and it is widely used as an additive in cement, building materials and other industries. Due to the different stability of various forms of mercury in the environment, subsequent use of products containing desulfurization by-product additives will continue to be released into the environment, endangering human health. Therefore, it is very necessary to study the form and distribution of mercury in the by-products of desulfurization in coal-fired power plants to provide a theoretical basis for subsequent harmless treatment. For content and morphology of mercury analysis, 1 sample of dry FGD ash and 6 samples of wet FGD gypsum were analyzed. The total 7 samples were extracted using a modification of sequential chemical extractions (SCE) method, which was employed for the partitioning Hg into four fractions: water soluble, acid soluble, H2O2 soluble, and residual. The Hg analysis was done with United States Environmental Protection Agency (USEPA) method 7471B. Comparing with the wet FGD gypsums of coal-fired boilers, the total Hg content in the dry FGD by-product was as high as 1.22 mg/kg, while the total Hg content in the FGD gypsum is 0.23 - 0.74 mg/kg, which was 2 times over the wet FGD gypsum. The concentration of water soluble Hg in the dry FGD by-product was the highest amount (0.72 mg/kg), accounting for 59.02% of the total mercury. While residual Hg content was 0.16 mg/kg, only about 13.11% of the total mercury. Mercury content in FGD gypsum was expressed in the form of ρ (residual Hg) > ρ (H2O2 soluble Hg) > ρ (water soluble Hg) > ρ (acid soluble Hg). The morphology and distribution of mercury in FGD by-products is supposed to be analyzed before utilization, and the impact of mercury on the environment should be considered.

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.

Variation characteristics of final size-segregated PM emissions from ultralow emission coal-fired power plants in China

The ultralow emission (ULE) retrofits for Chinese coal-fired power plants (CFPPs) are nearing completion. Large-scale and rapid retrofits have resulted in significant changes in the emission level and characteristics of particulate matter (PM). To investigate the variation characteristics of final three size fractions PM (PM2.5, PM10−2.5, PM>10) emissions, we conducted field tests at the outlets of wet flue gas desulfurization (WFGD) and wet electrostatic precipitator (WESP) by a pair of two-stage virtual impactors in eight representative ULE CFPPs. Our results indicate that, after WESP installations, the mass concentrations of final PM are significantly reduced and those of the final total ions and elements decrease as most individual chemical compositions are reduced. WESP presents an excellent removal performance for large particle sizes and high PM concentrations. SO42− is the major ionic component at both the outlets of WFGD and WESP, and its proportion in total ions is reduced to some extent through WESP. Furthermore, the average mass contents of SO42− and most elements in PM2.5 are significantly lower than those in PM10−2.5 and PM>10 whether at the WFGD-outlets or WESP-outlets. By comparison, chemical profiles of PM have substantially changed after ULE retrofits, and those after WFGD (e.g., sulfate, Zn, Pb, and Cu) have also changed relative to existing data. The end-tail emission factors (EFs) of PM2.5, PM10, and PMtotal under the typical ULE technical routes of WESP are calculated in time, and the corresponding EFs are in the range of 2.82–8.97, 15.7–27.6, and 38.6–61.7 g t−1, respectively. We believe the latest detailed PM EFs and the associated chemical profiles provided in this study are more representative of the current emission situations of Chinese CFPPs.

Operation strategy optimization of desulfurization system based on data mining

Desulfurization systems in coal-fired power stations often suffer the problem of high operating costs caused by a rule-of-thumb control strategy, which implies great potential for optimization of the operation. Due to the complex desulfurization mechanism, frequently fluctuating unit load, and severe disturbance, it is challenging to determine the optimal operating parameters based on the traditional mechanistic models, and the operating parameters are closely related to the operational efficiency of the flue gas desulfurization system. In this paper, an operation strategy optimization method for the desulfurization process is proposed based on a data mining framework, which is able to determine online the optimal operating parameter settings from a large amount of historical data. First, Principal Component Analysis (PCA) is used to reduce data redundancy by mapping the data into a new vector space. Based on the new vector space, an enhanced fuzzy C-means clustering (Enhanced-FCM) is developed to cluster the historical data into groups sharing similar characteristics. Taking sulfur dioxide emission concentration as a constraint condition, the system is optimized with economic benefits and desulfurization efficiency as the objective function. When performing optimization, the group that current operating conditions belong to is determined first, then the operating parameters of the best performance are searched within the group and provided as the optimization results. The method is validated and tested based on the data from a wet flue gas desulfurization (WFGD) system of a 1000 MWe supercritical coal-fired power plant in China. The results indicate that the proposed operation strategy can appropriately obtain operating parameter settings at different conditions, and effectively reduce the desulfurization cost under the constraint of meeting emission requirements.

Low temperature economiser in enhancing coal-fired power plant performance

With the increasingly stringent restrictions on the air emission of coal-fired power plant in China and Hong Kong, the measures to reduce air emission deserve an intensive study to conform respective emission limits. Low temperature economiser (LTE), in consequence, becomes one of the solutions in enhancing coal-fired power plant performance to reduce pollution brought to the planet. The evaluation of effectiveness as well as challenges and solutions for the installation of LTE are also explored.

Field test of SO3 removal in ultra-low emission coal-fired power plants.

Under the extensive implementation of ultra-low emission (ULE) facilities in coal-fired power plants of China, sulfur trioxide (SO3) has received increasing attention due to its impact on human health and operation safety of power plants. However, systematic research and evaluation for controlling SO3 emission in various ULE facilities are still lacking. Here, a systematic study was conducted based on 378 in situ performance evaluation tests carried out in 148 coal-fired power plants. The results illustrate that the SO2/SO3 conversion rate of the selective catalytic reduction devices can be controlled within 1% before and after ULE retrofit. Also, the synergistic removal efficiency of SO3 in the low-low-temperature electrostatic precipitator and the wet electrostatic precipitator can be higher than 70%. The removal efficiency of SO3 in the wet limestone-gypsum flue gas desulfurization scrubber is 33-64% before ULE and 31-81% after, and the average efficiency of the double scrubbers is 8.7% higher than that of the single scrubber. Due to the different SO3 removing abilities of various technologies, the overall efficiency of SO3 removal is in the range between 27 and 95% adopting different ULE technical routes. Average concentration of SO3 emission can be decreased by 51.8% after ULE application.

Clean Power Dispatching of Coal-Fired Power Generation in China Based on the Production Cleanliness Evaluation Method

China’s achievements in climate change and clean energy have been recognized by the international community. Although China has achieved successes in the field of clean energy, especially clean power dispatch, power dispatch is still one-sided and incomplete when considering environmental aspects. This paper presents a comprehensive production cleanliness evaluation model to assign a comprehensive environmental value as a reference for clean power dispatch. The model considers all the pollutants currently regulated in China’s coal-fired power plants, carbon emissions, and sustainability as three basic environmental constraints. Then, emergy analysis is used to unify the input/output materials with different units of measurement, and the emergy-based environmental value added (EEVA) value is constructed. As an integrated environmental value, the EEVA can provide an environmental reference for clean power dispatch. Finally, we selected a representative coal-fired power plant in China as a case study. By applying the above model, the dispatching sequence for four generating units was arranged from the perspective of cleanliness.

Mercury accumulation in soil from atmospheric deposition in temperate steppe of Inner Mongolia, China

Mercury (Hg) is a toxic and persistent pollutant and has long-term impacts on ecological systems and human health. Coal-fired power plants (CFPPs) are the main source of anthropogenic Hg emission, and the emitted atmospheric Hg is deposited to the surrounding environments which causes soil pollution. To assess the effects of atmospheric Hg from CFPPs in China on the temperate steppe, Hg contents in the topsoil and subsoil were analyzed for samples collected from 80 sites in central Inner Mongolia during 2012–2015. The average content of Hg in topsoil and subsoil were 14.9 ± 10.4 μg kg−1 and 8.9 ± 5.8 μg kg−1, respectively. The principal components analysis (PCA) indicated that the soil organic matter content and atmospheric deposition were the main factors determining soil Hg content in Inner Mongolia. We used the power plant impact factor (PPIF) to evaluate the impacts of the surrounding CFPPs. The PPIF results showed the most positive correlation with Hg content in topsoil at more than 400 km distances, indicating that the contribution of the long-range transport of Hg emitted from CFPPs is regional in scale. Considering the potential of Hg accumulation in soil, long-term and regional measurements of soil Hg and stricter emission-limit standards for power plants should be implemented to control soil Hg pollution in China.

Migration and Emission Characteristics of Ammonia/Ammonium through Flue Gas Cleaning Devices in Coal-Fired Power Plants of China.

To investigate the up-to-date migration and emission characteristics of NH3/NH4+ in coal-fired power plants (CFPPs) after implementing ultralow emission retrofitting, typical air pollution control devices (APCDs) in CFPPs, including flue gas denitrification, dust collectors, combined wet flue gas desulfurization (WFGD), and wet precipitators are involved in field measurements. The results show that most of the excessive injected and/or unreacted ammonia from the flue gas denitrification system, whether selective catalytic reduction (SCR) or selective noncatalytic reduction(SNCR), is converted into particle-bound NH4+ (>91%), and the rest (less than 9%) is carried by flue gas in the form of gaseous NH3, with a concentration value of 0.15-0.54 mg/(N m3) at the denitrification outlet. When passing through dust collectors, particle-bound NH4+ concentration decreases substantially along with the removal of particle matter. In WFGD, the dissolution and volatilization effects affect the gaseous ammonia concentration, which decreases when using limestone slurry and a 20% solution of ammonia as a desulfurization agent, while liquid ammonia solution with a high concentration (99.8%) may cause the flue gas NH3 concentration to increase considerably by 13 times. Particle-bound NH4+ concentration is mainly influenced by the relative strength of desulfurization slurry scouring and flue gas carrying effects and increases 2.84-116 times through ammonia-based WFGD. Furthermore, emission factors of NH3 for combinations of APCDs are discussed.

Refined assessment of size-fractioned particulate matter (PM2.5/PM10/PMtotal) emissions from coal-fired power plants in China

Chinese coal-fired power plants (CFPPs) are experiencing large-scale and rapid retrofitting of ultralow emission (ULE), causing significant changes in emission level of particulate matter (PM) from CFPPs. In this study, based on coal ash mass balance over the whole process, an integrated emission factors (EFs) database of three size-fractioned particulate matters (PM2.5, PM10, and PMtotal) for CFPPs is constructed, which covers almost all typical ULE technical routes installed in CFPPs. To verify the reliability of PM EFs established in this study, we compare those with related results based on field tests. Overall, the gaps in the EFs of PM2.5, PM10, and PMtotal obtained by the two methods are not outrageous within a reasonable range. By combined with the refined size-fractioned PM EFs and unit-based activity level database, a detailed high-resolution emission inventory of PM2.5, PM10, and PMtotal from Chinese CFPPs in 2017 is established, with the corresponding total emissions of 143, 207, and 267 kt, respectively. Our estimation of PMtotal emission is comparable to the official statistics announced by China Electricity Council (CEC), which further demonstrates the reliability of PM EFs constructed in this study. Moreover, potential reductions of PM from CFPPs at two stages before and after 2017 are assessed under three application scenarios of major ULE technical routes. We forecast the final annual emissions of PM2.5, PM10, and PMtotal until 2020 will be reduced further, which fall within the range of 86–111 kt, 120–157 kt, and 142–184 kt, respectively, if all CFPPs achieve ULE requirements under the three scenarios. We believe our integrated database of PM EFs of CFPPs has good universality, and the forecast results will be helpful for policy guidance of ULE technologies, emissions inventory compilation, and regional air quality simulation and management.

Sulfur trioxide emissions from coal-fired power plants in China and implications on future control

SO3 is a significant gaseous precursor of secondary particulate matter and is also a key for the overall improvement of ambient air quality. In this study, SO3 emission characteristics for coal-fired power plants (CFPPs) from field experiments and existing studies are collected to study the SO3 transformation and removal characteristics and to determine the temporal and spatial distribution of SO3 emissions from CFPPs. The formation ratio of SO3 in boilers and selective catalyst reduction system is 0.9 ± 0.5% and 40.52 ± 19.23%, respectively. The formed SO3 is then removed by dust collectors and desulfurization systems in sequence, approximately 26.52–82.96% and 56.48–96.32%, respectively. Due to the development of air pollution control devices, SO3 emission in 2015 (71.0 kt) is almost equal to the emission in 2000 (70.9 kt) although coal consumption kept increasing. Some areas of the North China Plain have the highest distribution density of CFPPs, which implies more stringent SO3 emission limit may need to be considered in these regions for future control. Also, the monitoring method and control technologies should be developed simultaneously for better application of the emission limit.

Light Extinction Method for Measuring a Low Particle Concentration with White Cell Optics: Relationship between Light Transmittance and Particle Properties

Because particulate matter (PM) emission standards of coal-fired power plants in China are becoming increasingly stricter, a higher sensitivity of traditional PM emission monitoring systems is required to adapt to the proposed ultralow emission (ULE) levels. In this study, a commercial optical structure, white cell optics, was introduced into the traditional extinction system to enhance particulate extinction and lower the detection limit by increasing the light path length. By connecting an aerosol generator and an electrical low-pressure impactor system, the white cell light extinction (WC-LE) system was tested to predict the low particle concentration of spherical silica aerosol and fly ash aerosol. According to the results of real-time testing with spherical silica aerosol, a good response between extinction signal and particle concentration was generally observed over the concentration range of 0–10 mg/m³. An excellent linear correlation between the extinction and particle concentration was obtained from data from short periods without violent feeding fluctuation. Based on the linear correlation, the particle concentration was calculated from the real-time extinction signal. For silica aerosols with different size distributions, the calculated concentration generally showed good correlation with the experimental value; the variation in extinction coefficients derived from the linear correlations was smaller than the theoretical values calculated with the measured size distribution, which seemed to be related to the in-cell mass loss. By testing the system with fly ash aerosols, the real-time response, linear correlation between signals, and concentration measurement also showed satisfactory results. The results of this study show that the WC-LE system is sensitive to small fluctuations in the particle concentration and provides a reliable correlation between the extinction signal and particle concentration, which allows the system to be considered a promising solution for particle emission monitoring at ULE levels.