Large-scale Coal-fired Power Plants Research Articles

Natural draft direct dry cooling system performance at various application scales under windless and windy conditions

The natural draft direct dry cooling system (NDDDCS) presents a promising alternative to conventional forced draft air-cooled condensers (ACCs) and indirect natural draft dry cooling systems, overcoming their limitations by efficiently condensing process steam directly and passively. The NDDDCS achieves superior thermal efficiencies while reducing system complexities, operational costs, and auxiliary power consumption. Potential reductions in operational expenses for the system may offset initial capital investments, resulting in lower lifetime costs. While research to date has focused on large-scale NDDDCS performance under varying wind conditions, this work addresses a critical gap by investigating the system’s scalability for various applications, including a large-scale coal-fired power plant (900 MWt, 165 m total height), a medium-scale concentrated solar power plant (CSP) (100 MWt, 65 m total height), and a small-scale water desalination plant (1 MWt, 11.5 m total height) under both windless and windy conditions. To achieve this, a steady-state 3-D computational fluid dynamics (CFD) model is developed, validated and scaled, incorporating innovative features such as an atmospheric pressure gradient and the ability to capture reversed flows through the system’s heat exchangers. Additionally, the model assesses inlet air temperature data at a per-cell resolution, enabling the ability to predict non-uniform temperature distributions in the heat exchangers, including hot-spots caused by airflow recirculation. Analysis of velocity and temperature fields across all scales reveals that recirculation effects negatively impact NDDDCS performance, particularly at the middle circumferential heat exchanger sector. The hyperbolic shape of the tower shell induces internal recirculation zones and reduces the effective flow volume. Under windy conditions, performance losses of 44%, 40%, and 40% are observed at crosswind speeds of 3 m/s, 6 m/s, and 9 m/s for small, medium, and large-scale towers, respectively. Beyond these speeds, the relationship between system performance and draft driving potential becomes non-linear due to crosswind effects dominating. Furthermore, a novel effect is identified at wind speeds of 9 m/s, 15 m/s, and 18 m/s for small, medium, and large-scale systems, respectively, where an inflection point allows for system performance recovery. This study underscores the NDDDCS’s potential as a cooling solution for modern power cycles across various scales, while highlighting the implications of scaling the system for medium- and small-scale thermal applications.

Overlooked CO2 emissions induced by air pollution control devices in coal-fired power plants

China's efforts to mitigate air pollution from its large-scale coal-fired power plants (CFPPs) have involved the widespread use of air pollution control devices (APCDs). However, the operation of these devices relies on substantial electricity generated by CFPPs, resulting in indirect CO2 emissions. The extent of CO2 emissions caused by APCDs in China remains uncertain. Here, using a plant-level dataset, we quantified the CO2 emissions associated with electricity consumption by APCDs in China's CFPPs. Our findings reveal a significant rise in CO2 emissions attributed to APCDs, increasing from 1.48 Mt in 2000 to 51.7 Mt in 2020. Moreover, the contribution of APCDs to total CO2 emissions from coal-fired power generation escalated from 0.12% to 1.19%. Among the APCDs, desulfurization devices accounted for approximately 80% of the CO2 emissions, followed by dust removal and denitration devices. Scenario analysis indicates that the lifespan of CFPPs will profoundly impact future emissions, with Nei Mongol, Shanxi, and Shandong provinces projected to exhibit the highest emissions. Our study emphasizes the urgent need for a comprehensive assessment of environmental policies and provides valuable insights for the integrated management of air pollutants and carbon emissions in CFPPs.

Acoustic reconstruction of the vortex field in the nonuniform temperature field of a simulated furnace

The high-temperature thermal vortex flows generated by the tangential combustion of large-scale coal-fired power plant boilers represent a complex medium that causes acoustic ray bending. In this paper, nonlinear acoustic tomography is combined with particle swarm optimization as a means of reconstructing the two-dimensional thermal vortex field. The nonuniform and large-gradient temperature distribution is the main cause of acoustic ray bending. We establish curved paths of acoustic propagation that are closely related to the temperature distribution. Based on these curved paths, a set of radial basis functions combined with Tikhonov regularization is derived to achieve more accurate reconstruction of the temperature field. The nonuniform temperature field affects the reconstruction of the flow field information. Our model considers a variation in the angle between the direction vector of the acoustic curved paths and the horizontal and vertical components of the flow velocity, and incorporates a priori information and a six-parameter hypersurface into the flow field reconstruction scheme. Particle swarm optimization is applied to minimize the objective function and obtain the vortex velocity field. Numerical experiments show that the proposed mathematical model of acoustic ray bending improves the reconstruction accuracy of the temperature distribution and vortex flow field. The acoustic time-of-flight is experimentally measured through the generalized cross-correlation with different window functions. The temperature and vortex fields reconstructed based on the actual time-of-flight are compared with thermocouple and anemometer measurements to demonstrate the validity and robustness of the proposed reconstruction model.

Mass flows and characteristic of mercury emitted from coal-fired power plant equipped with seawater flue gas desulphurization

This study investigated the characteristics of mercury emitted from a large-scale coal-fired power plant in Taiwan via intensive sampling campaigns. The air pollution control devices equipped in this coal-fired power plant include selective catalytic reduction, fabric filter and seawater flue gas desulfurization. During three sampling campaigns, mercury concentrations emitted from this large-scale coal fired power plant ranged from 0.04 to 0.35 μg Nm−3. In addition, solid and liquid samples including coal, bottom ash, fly ash and inlet/outlet seawater were collected and analyzed for mercury content to provide the mass flows of mercury in this plant. The results indicate that mercury emitted from this coal-fired power plant is dominated by Hg0, and the emission factor of mercury ranges from 0.37 to 3.37 mg Hg t−1 coal, which is relatively lower than those reported in other studies. The relative enrichment factor of mercury in fly ash (0.23–1.22) is significantly higher than that of bottom ash (0.10 × 10–3–0.89 × 10–3). Although this coal-fired power plant has a relatively low mercury atmospheric emission which accounts for 6.4% of the total mercury output, it is essential to further control mercury released from fly ash (62.6% of the total mercury output) and discharged seawater (33.7% of the total mercury output) to reduce environmental damage and human health effects.

Real-time prediction of SO2 emission concentration under wide range of variable loads by convolution-LSTM VE-transformer

In this paper, a sulfur dioxide (SO2) emission concentration real-time dynamic prediction model is proposed to achieve the control target of ultra-low SO2 emissions and economical desulfurization system operation at a large-scale coal-fired power plant. First, a vision-expansion self-attention strategy is adopted on the Transformer algorithm structure for better time-series information feature extraction. Second, to adapt to the vision-expansion self-attention strategy, convolution and long short-term memory (LSTM) are combined to process input information position encoding, which can obtain long time-series information absolute position encoding. Then, a Convolution-LSTM VE-Transformer model is constructed by combining the above two proposed parts. The mutual information method and the differential evolution algorithm are combined to calculate correlations between variables and obtain the optimal delay time. Finally, a real-time dynamic prediction model of SO2 is established. In this model, the structure of the input and output variables is determined by the delay time and the influence of coal quality on the SO2 concentration. The quantitative comparison results show the superior accuracy and generalization ability of the proposed prediction model to related popular methods, indicating that the model has strong potential for use in further controller design and applications.

Estimating CO2 Emissions from Large Scale Coal-Fired Power Plants Using OCO-2 Observations and Emission Inventories

The concentration of atmospheric carbon dioxide (CO2) has increased rapidly worldwide, aggravating the global greenhouse effect, and coal-fired power plants are one of the biggest contributors of greenhouse gas emissions in China. However, efficient methods that can quantify CO2 emissions from individual coal-fired power plants with high accuracy are needed. In this study, we estimated the CO2 emissions of large-scale coal-fired power plants using Orbiting Carbon Observatory-2 (OCO-2) satellite data based on remote sensing inversions and bottom-up methods. First, we mapped the distribution of coal-fired power plants, displaying the total installed capacity, and identified two appropriate targets, the Waigaoqiao and Qinbei power plants in Shanghai and Henan, respectively. Then, an improved Gaussian plume model method was applied for CO2 emission estimations, with input parameters including the geographic coordinates of point sources, wind vectors from the atmospheric reanalysis of the global climate, and OCO-2 observations. The application of the Gaussian model was improved by using wind data with higher temporal and spatial resolutions, employing the physically based unit conversion method, and interpolating OCO-2 observations into different resolutions. Consequently, CO2 emissions were estimated to be 23.06 ± 2.82 (95% CI) Mt/yr using the Gaussian model and 16.28 Mt/yr using the bottom-up method for the Waigaoqiao Power Plant, and 14.58 ± 3.37 (95% CI) and 14.08 Mt/yr for the Qinbei Power Plant, respectively. These estimates were compared with three standard databases for validation: the Carbon Monitoring for Action database, the China coal-fired Power Plant Emissions Database, and the Carbon Brief database. The comparison found that previous emission inventories spanning different time frames might have overestimated the CO2 emissions of one of two Chinese power plants on the two days that the measurements were made. Our study contributes to quantifying CO2 emissions from point sources and helps in advancing satellite-based monitoring techniques of emission sources in the future; this helps in reducing errors due to human intervention in bottom-up statistical methods.

Emission Characteristics and Formation Pathways of PCDD/Fs from Cocombustion of Municipal Solid Waste in a Large-Scale Coal-Fired Power Plant

This study is based on a 300 MW coal-fired power plant cocombusting 2% of MSW, focusing on the emission characteristics and formation pathway of polychlorinated dibenzo-p-dioxins and dibenzofurans ...

Soil and ambient air mercury as an indicator of coal-fired power plant emissions: a case study in North China.

Coal-fired power plants (CFPPs) are an important anthropogenic mercury (Hg) source in China, and it is crucial to understand the environmental impacts of this detrimental element emitted from this source. In the present study, field experiments were conducted for measuring Hg in ambient atmosphere and upland agricultural soils within a radius of 10 km surrounding a large scale coal-fired power plant (1550 MW) in Tangshan, Hebei province. Short-term (20 min) average of gaseous elemental mercury (GEM or Hg0) in ambient air varying from 1.5 to 9.0 ng/m3 and total Hg (THg) in surface agricultural soil (0-20 cm) varying from 9.2 to 43.5 μg/kg at different sites were observed. THg in two soil cores decreased with depth, with concentrations being 2-2.5 times higher in the surface layer than that in the deep layer (50-60 cm), indicating the possibility of the atmospheric input of Hg. Based on the information of the total atmospheric Hg emission since this CFPP's operation in 1970s and the increased THg in nearby soils, it was estimated that about 3.9% discharged Hg has accumulated in the nearby agricultural soils. The low retention rate of the total emitted Hg by soils is a result of high proportion of Hg0 (79.5%) in stack gas emission and potential loss of Hg from soil surface reemission. The positive shifting (~ 0.5‰) of Hg isotopic signature (δ202Hg) from deep soil to surface soil reflected Hg deposition from nearby CFPP emissions that are featured with much heavier Hg isotopic signatures inherited from feed coal (δ202Hg: -0.50‰) and different combustion products (δ202Hg: -0.95 to 3.71‰) compared with that in deep soil layer (δ202Hg: ca -1.50‰). Overall, this study demonstrated that this CFPP has a slight but distinguishable effect on the elevation of ambient GEM and agricultural soil THg in the local environment.

Integration of CO2 capture unit with membrane distillation technology: CO2 mitigation and freshwater production

The severe consequences of carbon dioxide (CO2) emissions into the atmosphere and a dire need for freshwater are among the biggest global challenges. The desire to meet these challenges has given rise to the motivation of proposing a direct contact membrane distillation (DCMD) technology integrated with the CO2 capture unit to mitigate CO2 and simultaneously produce freshwater. The CO2 capture unit has been modeled with Aspen Plus® V.10 and for the DCMD system, MATLAB software was adopted. MATLAB software was not linked to the Aspen Plus®. Thermal heat contained in both the purged gas and leanout stream was recovered by using a DCMD unit. A blended solution of methyldiethanolamine (MDEA) and piperazine (PZ) was considered as an absorbent to remove CO2 from the flue gas of a large-scale coal-fired power plant (650 MWe). About 85 % of the CO2 in the flue gas has been captured from the top of the stripper column. At MDEA/PZ (concentration ratio of MDEA and PZ in the aqueous solution) concentration of 30/20 wt.%, a reboiler duty of 3.27 MJ/kg CO2 was obtained. Freshwater was produced at a rate of 25.43 m3/day from DCMD unit 1 and 1428.19 m3/day from unit 2.

Flexible operation of large-scale coal-fired power plant integrated with solvent-based post-combustion CO2 capture based on neural network inverse control

Post-combustion carbon capture (PCC) with chemical absorption has strong interactions with coal-fired power plant (CFPP). It is necessary to investigate dynamic characteristics of the integrated CFPP-PCC system to gain knowledge for flexible operation. It has been demonstrated that the integrated system exhibits large time inertial and this will incur additional challenge for controller design. Conventional PID controller cannot effectively control CFPP-PCC process. To overcome these barriers, this paper presents an improved neural network inverse control (NNIC) which can quickly operate the integrated system and handle with large time constant. Neural network (NN) is used to approximate inverse dynamic relationships of integrated CFPP-PCC system. The NN inverse model uses setpoints as model inputs and gets predictions of manipulated variables. The predicted manipulated variables are then introduced as feed-forward signals. In order to eliminate steady-state bias and to operate the integrated CFPP-PCC under different working conditions, improvements have been achieved with the addition of PID compensator. The improved NNIC is evaluated in a large-scale supercritical CFPP-PCC plant which is implemented in gCCS toolkit. Case studies are carried out considering variations in power setpoint and capture level setpoint. Simulation results reveal that proposed NNIC can track setpoints quickly and exhibit satisfactory control performances.

Impact of temporary emission reduction from a large-scale coal-fired power plant on air quality

Abstract This study evaluated the impact of the largest point source of particulate matter ≤2.5 μm (PM2.5) in South Korea (the coal-fired power plant) on the air quality in the southeastern region based on the transient reduction (30% less than the previous month) in coal consumption by the power plant. The impacts of the power plant during the period of coal consumption reduction were assessed based on an in-depth analysis of the forward air mass trajectory, such as the effects of meteorological parameter changes (temperature and relative humidity) on aerosol chemistry and long-range transport, and changes in anthropogenic emissions from May through June 2017. The study determined that the emission reduction from the coal-fired power plant resulted in a significant decrease in the local and regional concentrations of PM2.5, as well as the major inorganic components. The effects of the coal-fired power plant on the air quality downwind were different between local and regional areas, with a higher impact in the regional area due to the significant secondary aerosol formation.

Thermodynamic and economic evaluation of a novel heat supply design using low-pressure feedwater in a cogeneration plant

An innovative heat supply design for cogeneration systems has been proposed. Instead of the conventional heat source (extraction steam of the turbine), the low-pressure feedwater of the heat regeneration system is employed to provide district heat in the new scheme, through warming the supply-water of the primary heating network in a plate heat exchanger. A detailed thermodynamic analysis was conducted to evaluate the proposed design compared with the traditional one, based on a large-scale coal-fired power plant that needed to be retrofitted into cogeneration. The results show that the net power output of the cogeneration system is boosted by 4.68 MW owing to the novel concept. Furthermore, the total system efficiency and effective electric efficiency of the cogeneration system are promoted by 0.43 and 0.46 percentage points. This is because the exergy efficiency of the supply-water heating process is raised by 29.65 percentage points, and the exergy efficiency of the cogeneration system is improved by 0.42 percentage points. Finally, the new design was economically analyzed, and the results indicate that the net present value reaches 16543.2 thousand USD (8381.5 thousand USD more than that of the conventional design). Therefore, the proposed concept is feasible and profitable in engineering.

Advanced Exergoeconomic Evaluation of Large-Scale Coal-Fired Power Plant

AbstractConventional exergy-based analysis can only identify the location and magnitude of thermodynamic inefficiencies (exergy destruction), while an advanced analysis can further reveal their sou...

Energy-loss mechanism of boilers system in large-scale coal-fired power plants and the corresponding energy-saving approaches

Energy-loss mechanism of boilers system in large-scale coal-fired power plants and the corresponding energy-saving approaches

Ventilation enhancement for a natural draft dry cooling tower in crosswind via windbox installation

A natural draft dry cooling tower (NDDCT) is demanded to save water for power generation in arid area, but its performance could be degraded greatly by the crosswind. To overcome the degradation, this paper proposes the installation of a windbox, which consists of windbreaks, an enclosure, a back barricade and a wind top to improve the pressure distribution outside the heat exchanger bundle of a NDDCT, so as to increase the ventilation rate under crosswind condition. Full dimensional computational fluid dynamics (CFD) modelling was conducted for the windbox installed around the NDDCT of a large scale coal-fired power plant. Different configurations of the windbox were studied. The flow characteristics along the streamline in the NDDCT were analyzed and quantified by adopting the concept of flow loss factor (FLF). Based on simulation and experiments, the installation of the windbox is shown to be effective. The windbox with a 120 m radius enclosure and a full size louver-type top could improve the ventilation rate of a NDDCT by ∼60% in gale crosswind condition, and keep high performance in breeze crosswind condition. Consequently, an annual reduction of coal consumption of 30,000–45,000 tons could be achieved on a 1000 MW unit, which is ∼3000,000–4500,000 $/a.

Field study on the corrosion and ash deposition of low-temperature heating surface in a large-scale coal-fired power plant

The corrosion and ash deposition of low-temperature heating surface were investigated in a 660MW coal-fired power plant. The temperature-controlled test probes constructed of three materials were tested under different wall temperatures (90°C, 80°C, 70°C, 60°C, 50°C and 40°C). The metal specimens and deposit samples were analyzed by X-ray fluorescence, X-ray diffraction and scanning electron microscope with energy dispersive spectroscopy. The results revealed that when the wall temperature fell to 70°C, viscous deposits began to form on the probes due to the condensation of sulphuric acid, hydrochloric acid and hydrofluoric acid. Meanwhile, the sulphuric acid condensate and hydrochloric acid condensate stimulated the corrosion of the metal surface. The corrosion and deposits increased with the decrease of the wall temperature. The corrosion resistances of the three tested materials were 316L>ND>20#. The corrosion mechanism and ash deposition mechanism of low-temperature heating surface were discussed. The coupling model of acid condensation and fly ash behaviors was proposed, and the main factors affecting the corrosion and ash deposition were summarized. Suggestions were made to alleviate the corrosion and fouling of waste heat recovery devices in coal-fired power plants.

Fouling of the flue gas cooler in a large-scale coal-fired power plant

Abstract The fouling characteristic of the flue gas cooler (FGC) in a large-scale coal-fired power plant was investigated by field sampling. Eleven deposit samples were taken from the FGC in a 660 MW power plant. The elemental compositions, compound compositions and micro-morphologies of the samples were analyzed. The results showed that the fouling characteristic was different at the first stage and the second stage of the FGC. The mechanism of the FGC fouling was discussed. The FGC could help to remove SO 3 /H 2 SO 4 in the flue gas. Recommendations were given on the application and operation of FGCs.

Technical systems of ecological and environmental monitoring associated with large-scale coal-fired power plants: case study in Xilingol, Inner Mongolia

ABSTRACTThe increases in the construction of coal-fired power plants (CFPP) in China have caused ecological damage and environmental pollution. It is essential to monitor ecological and environmental conditions with various technical methods. However, the current monitoring systems have major operational problems, including low levels of automation, high operating costs, and inefficient spatial and temporal coverage. The timely development in the Internet of Things (IoT) provides an opportunity to improve the effectiveness of environmental data collection and analysis. This research takes Xilingol as the study area, which is rich in coal resources and one of the principal regions for CFPP construction in China. We deployed relevant sensors in the study area to obtain the information regarding the quality of atmosphere, surface water, groundwater, and soil. The recorded data were transmitted to a central system platform via wireless communication networks and a general packet radio service. The system platform had the following functions: monitoring environmental quality, assessing environmental impact, supporting environmental management and decision-making, analyzing ecological efficiency, and responding environmental emergency. The government, especially environmental protection department and relevant companies, could easily obtain ecological and environmental information by using this IoT-based technical system.

Characterization of Inorganic Elements within PM2.5 and PM10 Fractions of Fly Ashes from Coal-Fired Power Plants

ABSTRACTIn this study 15 fly ash samples were collected from 15 large-scale coal-fired power plants (CFPPs) in China. The samples were then re-suspended through PM2.5 and PM10 inlets and analyzed for the contents of 39 inorganic elements (IEs) using inductively coupled plasma-mass spectroscopy (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). The results show that the particle size distributions for the 15 FAs samples exhibited bimodal patterns. The Ʃ39IEs (g g–1) for the PM2.5 (0.292–0.564) in all the 15 CFPPs were higher than that of PM10 (0.269–0.403). Except for Cu, all the other 38 IEs were more enriched in the PM2.5 with the PM2.5/PM10 ratios being 1.06–1.73. Considering 13 heavy metals, the same orders occurred between PM2.5 and PM10 with Al >> Cr > Zn > Mn > Cu > V > Pb > Sn > Co > As > Sb > Tl > Cd. More attention should be paid to the high contents of Cr in both PM2.5 (1310 mg g–1) and for PM10 (1240 mg g–1) from all 15 CFPPs. 23 IEs for PM10 and 26 IEs for PM2.5 had the geo-accumulation index (Igeo) values higher than 0, indicating different pollution levels for them. On the other hand, there was moderate to extreme levels of pollution for Cr, Zn, Cu, Pb, Sn, Sb, Tl, Cd and Al based on Igeo values. The element profiles for PM2.5 or PM10 from 15 CFPPs were similar based on low coefficients of divergence for PM2.5 (0.254 ± 0.038) and PM10 (0.244 ± 0.054) according to the comparison between any two CFPPs. Most elements with low relative enrichment factors (REF) as less than 0.70 or 0.70–1.30 indicated no or weak condensation occurred for them during coal combustion, while Cr, Cu, Zn, Sn, W and Pb had REF values higher than 1.30 indicated that significant condensation occurred for these elements.

A comprehensive assessment of ecological sensitivity for a coal-fired power plant in Xilingol, Inner Mongolia

ABSTRACTThe planning and construction of large-scale coal-fired power plants are important components of China’s future energy development strategy in response to global environmental problems, as proposed in China’s Twelfth Five-Year Plan for National Economic and Social Development. With the rapid socio-economic development, research and assessments of ecological risks of large-scale human activities have drawn increasing attention. As large-scale coal-fired power plant are more concentrated in the northern arid and semi-arid areas of China, where the environment is fragile, objective assessments of the ecological risks at large-scale coal power bases are important for ensuring the sustainable development of coal bases and guaranteeing the normal and orderly life of surrounding residents. Ecological sensitivity evaluations reflect the degree of changes in the natural environment due to human disturbance, and explain the possibility of ecological assessments in the region. Based on comprehensive evaluation of ecological sensitivity, combined with geographic information and soil-vegetation data, we analysed soil erosion, desertification sensitivity, and soil salinization. Using the results of single-factor ecological sensitivity evaluation, we then conducted a comprehensive evaluation of the ecological sensitivity of coal-fired power plants. Using Xilingol coal-fired power plant in a case study, we performed single-factor ecological sensitivity evaluation of soil erosion, desertification, and soil salinization. We then assessed the comprehensive ecological sensitivity and the spatial distribution of single-factor and multi-factor ecological sensitivity in this region.