Coal-fired Units Research Articles

The importance of flexible hydropower in providing electricity stability during China’s coal phase-out

A rapid coal phase-out is critical if China is to achieve carbon neutrality by 2060. However, this presents a significant challenge in maintaining system flexibility as the number of coal power stations reduce and renewable energy penetration increases. Here we analyze the interactions between flexibly operating hydroelectric facilities in balancing the decommissioning of a typical 600 MW coal-fired power unit across three different provinces with different electricity mixes. Rather than using a constant parameter for the carbon emission intensity for coal, as used in previous studies, we use dynamic intensities across different output levels. Accounting for the higher emission intensities of coal power plants running at below optimal efficiency to provide flexibility increases emissions from 3.4 % to 11.1 % depending on the region. The coal phase-out lowers flexibility indicators, with loss-of-load increasing in the full phase-out scenario in the absence of mitigating technologies such as electricity storage. Flexible hydropower eases peak demand issues significantly and the operating range of hydro-units has no significant effect on system flexibility or emissions. Overall, hydropower shows large potential in supporting decarbonization while maintaining system flexibility, especially for coal-dominated countries with abundant hydropower resources.

Combustion stability and NOX emission characteristics of a 300 MWe tangentially fired boiler under ultra-low loads with deep-air staging

To accomplish the goals of carbon peaking and carbon neutrality in China, coal-fired units are required to implement real-time responses to the requirements of intermittent renewable energy sources. Thus, they typically operate under ultra-low loads, resulting in unstable combustion and high NOX emissions. In this study, the combustion stability and NOX emission characteristics of a 300 MWe tangentially fired boiler operated under ultra-low loads of 90 MWe and 60 MWe and with two pulverized coal (PC)-staging strategies at 90 MWe were investigated by performing experiments and numerical simulations. The results indicate that as the boiler load decreases to 60 MWe, the ignition of the PC flow is delayed and the imaginary circle gradually disappears. At 90 MWe, the shorter ignition distance, lower ignition heat, and higher furnace fullness degree during three-mill operation compared to those during two-mill operation suggest that the combustion is more stable with wider PC staging. As the load decreases from 90 MWe to 60 MWe during two-mill operation, the ignition distance and flame boundary temperature change negligibly and the ignition heat decreases, indicating stable combustion at 60 MWe in the case of easily ignitable coal. The upper burner exhibits greater combustion stability than the lower burner under ultra-low loads. Furthermore, the local mean stoichiometric ratio (LMSR) can be employed to predict corrected NOX concentrations at stable ultra-low loads. The vast majority of NOX is fuel NOX, and the average corrected NOX concentration at 90 MWe and 60 MWe is 795 mg/m3 (O2 = 6%), which indicates that the deep-air-staging effect of the low-NOX combustion system is weakened, particularly when the LMSR is higher than 0.92.

Integrated optimization of coal-fired power plant and CO2 capture system coupled with membrane condenser for recovering flue gas hydrothermal energy

CCS can effectively solve the problem of large-scale carbon emissions from coal-fired units, but at a considerable expense in terms of high energy and water consumption. In this paper, the conventional MEA-based CO2 capture system process is improved and integrated optimization with coal-fired power plant. An MEA-based CO2 capture system coupled with membrane condenser and an improved integrated decarbonization system are proposed based on the recovery potential of waste heat from flue gas and CO2 capture system. Besides, an MEA-based CO2 capture system coupled with membrane condenser is proposed. The membrane condenser is added to exchange heat with the rich solvent flowing from the bottom of the absorber before the flue gas into the absorber for recovering the flue gas hydrothermal energy. The regeneration duty of the CO2 capture system is reduced from 4.341 MJ/kg CO2 to 4.275 MJ/kg CO2. The extraction steam is further utilized by a small steam turbine before being sent to the reboiler. And the heat released by CO2 condensation at the top of stripper and CO2 cooling in the middle of multi-stage compression is used to heat the condensate of coal-fired system. Compared with the simple integration scheme which adopts the same CO2 capture system, the output power of the integrated decarbonization system increases from 510.719 MW to 593.850 MW. Correspondingly, the thermal efficiency increases by 6 %, the exergy efficiency increases by 5.86 % and the cooling water saves 1497.12 kg/s. Moreover, the variation of output power and saving cooling water with the membrane condenser parameters of the improved integrated system is analyzed.

Modified active disturbance rejection control with pre-compensation for a class of high-order system

With more and more sustainable energy integrated into the bulk power system, the coal-fired unit is obliged to speed up the response to the deep peek and frequency regulation command, and this results in great challenges for the control systems. To improve the control performance of the coal-fired unit, a modified active disturbance rejection control with pre-compensation (PMADRC) is proposed for high-order systems with the type of K/(Ts+1)n. The stability, sensitivity, and robustness of the proposed PMADRC are analyzed. An effective tuning procedure is also provided based on plenty of simulations. Besides, contrastive simulations and experiments based on the water tank level control platform validate the superiority of PMADRC in setpoint tracking and disturbance rejection. The advantages of the PMADRC guarantee high control performance and make it have the potential for applications in coal-fired units.

Analysis and Research on Influencing Factors of Unscheduled Shutdown of Coal-Power Units

This paper makes statistics on the unplanned outage and output reduction of coal-fired power generation units directly transferred to a provincial power grid, analyzes the main influencing factors leading to unplanned outage of coal-fired power generation units, and puts forward targeted improvement measures, which lays a foundation for ensuring that the coal-fired power generation units play a role in ensuring supply under the new power system.

Analysis and research on the impact of carbon market on the clearing price of coal-fired power units

The coal power industry accounts for the largest proportion of carbon dioxide emissions, and is first included in the national carbon market, while the cost of carbon emissions has a certain impact on the coal power clearing price. Based on this, this paper constructs a bidding model of coal-fired power units considering the cost of carbon emissions; Taking Guangdong Province as an example, this paper simulates the change of the clearing price of the spot market of coal power units in the light, medium and heavy carbon market scenarios, and provides relevant suggestions for the construction of the electricity market and carbon market.

Five-year Variations in Air Pollutant Emissions with Ultra-low Emission Retrofits in a 660 MW Coal-fired Power Unit

Five-year Variations in Air Pollutant Emissions with Ultra-low Emission Retrofits in a 660 MW Coal-fired Power Unit

Performance and Operation Strategy Analysis of BEST Cycle 1000MW Double Reheat unit under Different Operating Conditions

Improving steam parameters in a coal-fired power unit boosts cycle efficiency, lowers coal consumption, and reduces emissions. The backpressure extraction steam turbine (BEST) cycle addresses the problem of excessive superheating of extraction steam. This study analyzed a 1000 MW double reheating unit, finding that heat rate in the conventional and BEST cycle systems is heavily influenced by load under THA conditions. At 100% and 75% loads, the BEST cycle’s heat rate decreases but increases at 50% load. For safe operation during flow interruption and high load rates, a pairwise grouping method is recommended for high-pressure heater interruption. When multiple low-pressure heaters are simultaneously cut off, the unit load needs to be limited based on the number of heaters being removed. when multiple low-pressure heaters are simultaneously cut off, the unit load needs to be limited based on the number of heaters being removed. Removing two low-pressure heaters lowers the load to 90%, and three lowers it to 80%. These findings optimize the thermal system’s parameters and enhance overall efficiency.

Numerical simulation of the influence of different oxygen concentration on the combustion characteristics of double tangential boiler at low load

In order to cope with the demand for deep peak regulation of high-parameter coal-fired units, this paper uses numerical simulation methods to systematically explore the influence of different secondary wind oxygen enrichment concentrations on the combustion performance and characteristics of singlefurnace double-cut round boilers during low-load operation, so as to provide theoretical support for the actual operation of power plants. The results are as follows: (1) The use of oxygen enriched secondary air combustion during low-load operation of the boiler can improve the overall temperature of the main combustion zone of the furnace and the local temperature of the burner nozzle section, and enhance the combustion stability of pulverized coal in the furnace. (2) When the secondary air oxygen concentration is 35% and 40%, the overall temperature of the main combustion area of the boiler increases the most obviously, and the combustion is the most stable. (3) Oxygen-enriched combustion effectively reduced the NOx emission concentration in the furnace, and the overall trend of NOx emission decreases first and then increases with the increasing trend of secondary air oxygen concentration.

Two-Timescale Dynamic Energy and Reserve Dispatch With Wind Power and Energy Storage

The integration of volatile renewable resources and energy storage entails making dispatch decisions for conventional coal-fired units and fast-response devices in different timescales. This paper studies intraday dynamic energy-reserve dispatch following a two-timescale setting. The coarse timescale determines the hourly reference output and reserve allocation, which offers a sufficient backup for the fine-timescale operation; the fine timescale determines the adjustment of gas-fired units and energy storage system every 15 minutes in response to the actual wind power. A stochastic dynamic programming method is proposed to make decisions at the coarse timescale while guaranteeing the robust feasibility of the fast process via vertex scenarios of uncertainty set and bounding the state-of-charge intervals for energy storage; the fast-response actions at the fine timescale are updated using a truncated rolling-horizon optimization, which incorporates the cost-to-go functions calculated at the coarse timescale to prevent the fast decisions from being myopic. Case studies on the modified IEEE 5-bus system and 118-bus system validate the proposed framework.

Coordinated control strategy assessment of a virtual power plant based on electric public transportation

With the rapid development of the public transportation industry in recent years, electric public transportation (EPT) with regular operating times and fixed load demands has considerable potential for energy storage. Aiming to solve the problem of insufficient large-scale energy storage and ensure renewable energy development, this study builds the dynamic simulation model of a virtual power plant (VPP) consisting of EPT groups, large-capacity public distributed generations (PDGs) containing a photovoltaic (PV) unit, and a coal-fired unit. Then, the coordinated control strategy, which includes the time-sharing plan part and execution part with multi-section, is proposed to make a trade-off between maximizing the utilization of EPT and ensuring the operational stability of VPP. The control strategy includes two modes (1) gaining benefits through electricity tariff differences and participation in the carbon trading market and (2) peak shaving the consumption of VPP using off-peak grid power. Moreover, the evaluation model related to the control performance and achievement of targets is established. The influence of the EPT number on benefits and peak shaving capability is compared. Results show that the optimal number of EPT for the system is the value at which the energy storage utilization is maximum at the specific period. The optimal daily benefit is 37,300–83,700 yuan, and the optimal daily discharge value is 117.77 MW·h when the maximum peak demand reduction is 38.31 MW. Overall, the proposed strategy makes full use of the energy storage potential of EPT groups, which provide technical support for maintaining grid security and achieving the dual‑carbon target.

FEATURES OF THE USE OF LIQUEFIED PETROLEUM GAS AS A RESERVE AND ALTERNATIVE FUEL AT COAL-BASED CHP PLANTS

The paper analyzes the main properties of liquefied petroleum gas and the peculiarities of its energy use compared to natural gas, including taking into account the specifics of the operation of pulverized coal boiler units of the CHP. The advantages of liquefied petroleum gas compared to heavy fuel oil are shown and a comparative economic assessment of their use is given. It is shown that interchangeability with natural gas is ensured by mixing the vaporized liquefied petroleum gas with air to form a homogeneous mixture — synthetic natural gas, which can be directly used in burners as a direct substitute for natural gas without changes in the composition of the equipment and in the design of the boiler burners. The calculation is presented of the permissible limits of the air fraction for liquefied petroleum gas of different composition according to the criterion of the Wobbe Index correspondence of synthetic natural gas and natural gas. Technical solutions are proposed for the use of liquefied petroleum gas as a reserve and alternative fuel at coal-fired combined heat and power plants in the event of damage of gas supply networks, which provide reliable and economical feeding of a coal-fired boiler unit with synthetic natural gas in such fundamentally different modes as coal jet “lighting” with low consumption and pressure of synthetic natural gas and ignition or emergency operation at a load of 25 % with high consumption and increased synthetic natural gas pressure, with the possibility of switching from natural gas to liquefied petroleum gas and vice versa. Bibl. 17, Fig. 3, Tab. 5.

Study on Precipitation Kinetics of Calcium Pyro-Vanadate and Thermodynamics of Vanadium Water System

Selective catalytic reduction (SCR) is a technology widely used in large coal-fired units to remove nitrogen oxides from flue gas, but it also generates a large number of waste catalysts every year. At present, the recovery of V from discarded SCR catalysts has good application prospects and environmental significance. In this paper, the kinetics and thermodynamics of vanadium precipitation process are described with the vanadium-containing liquid of waste denitration catalyst recovered by alkali leaching as raw material and CaCl2 as precipitant in order to further explore the mechanism of vanadium precipitation. The kinetics study showed that the crystallization process of calcium pyrovanadate can be well-described by Avrami kinetic model when the precipitation time is 95–130 min, and the vanadium precipitation temperature is 60–80 °C. After that, the Arrhenius equation was used to analyze the fitted kinetic data, and the apparent activation energy Ea of vanadium precipitation reaction was calculated to be 98.196 kJ/mol, and the pre exponential factor A = 8.59 × 1039 min−1. Thermodynamic study showed that when the pH of the vanadium water system is low, the +5 valence vanadium in the solution mainly exists in the form of VO2+ cation. When the pH is between 0–1, the solubility of vanadium reaches the minimum and then increases the solution pH again, and various polymerized anions are formed in the vanadium water system. When the temperature is 25 °C, the activity of vanadium in vanadium-containing solution is 10−1, the pH of solution is 8–12, and the existence form of +5 valence vanadium in solution is mainly HV2O73−. By analyzing the existing forms of V with different activities in a vanadium water system at 25 °C, it can be seen that with the decrease of V activity in liquid, the dominant region of polymerized vanadium-containing species in the potential pH diagram will disappear, indicating that vanadium mainly exists in the form of mononuclear ions in low-concentration vanadium-containing solutions, which is not conducive to precipitation. Therefore, in the process of precipitation of vanadium in solution, the concentration of V should be increased as much as possible.

Quantitative measurement of the stability of a pulverized coal fired flame through digital image processing and statistical analysis

The stability of pulverized coal flames is a well-known problem in the power industry. Unstable flames often lead to lower combustion efficiency, higher pollutant emissions, and other operational problems. Many methods are available for flame monitoring and characterization, but very few are suitable for flame stability monitoring. This paper presents a method for assessing flame stability continuously and quantitatively by introducing a term named numerical indicator of flame stability based on digital image processing. This numerical indicator combines the statistical characteristics of four flame parameters which are derived from the flame images. To evaluate the effectiveness of the proposed method, the numerical indicator of a pulverized coal flame during a routine unit “turning off” process was determined on a 600 MWth coal-fired supercritical unit. Experimental results suggest that the flame stability at different stages of the turning off process is correctly quantified with the numerical indicator.

Analysis of Unit Commitment of Coal-fired Units in a Power Base of Cross-area DC Transmission Lines Under Dual Carbon Targets

China has announced achieving a carbon peak before 2030 and neutralization by 2060. Cross-area UHVDC transmission provides a feasible way for the new energy base to transmit power to the load center on a large scale. Usually, the dispatching of coal power units of DC transmission line power base is divided according to the equal proportion of unit capacity, this paper takes all the units as a group and proposes a unit commitment solution to realize lower carbon emission. As the capacity of new energy in the power base increases, this paper also considers the generation margin for new energy to do the optimization simulation. The results show that by operating coal-fired units as a group, it operates in a more economic and environmentally friendly way.

The role of output-based emission trading system in the decarbonization of China's power sector

The emission trading system (ETS) is a key policy for China to achieve carbon neutrality. China's national ETS started operation and covered the power sector first, which will promote its transformation. This study explores how China's national ETS can support the future decarbonization of the power system. With benchmark tightening, China's ETS can cost-effectively peak CO2 emissions of the power sector before 2030 and reduce 13% of the total emissions by 2035, compared to a No-Carbon-Pricing Scenario. Under the ETS, the allowance price would rise gradually to 350 yuan/tCO2 by 2035. The main driving factor for emissions reduction would be improving the efficiency of coal-fired power generation between 2020 and 2025 and deploying carbon capture and storage (CCS) from 2030, respectively. Fuel-switching away from coal is limited under the ETS with technology-specific benchmarks and free allocation. Regional distributional effects could arise under the ETS. Regions with a higher share of ultra-supercritical units could have allowance surpluses at the beginning, while only regions with CCS-equipped coal-fired units have the potential to gain high allowance surpluses by 2035.

Impacts of carbon markets and subsidies on carbon capture and storage retrofitting of existing coal-fired units in China

Carbon capture and storage (CCS) is a feasible technology option to reduce carbon emission in the power industry. However, the high cost of CCS deployment in power plants precludes its large-scale application. Carbon markets may act as an incentive for CCS, but the impact of auction and quota allocation mechanisms in carbon markets on CCS is unclear. In order to investigate the roles of the auction and quota allocation mechanism on the CCS retrofitting in coal-fired units, the life-cycle cost method was used to evaluate the CCS retrofitting cost of China's coal-fired units in the carbon market after supplementing the existing database. The impact of subsidies on stimulating CCS retrofitting was jointly considered. The results show that most units have a CCS retrofit Levelized additional cost of electricity (Lacoe) of $25.24/MWh to $64.57/MWh, making the CCS retrofitting burdensome, even for ultra-supercritical unit that has a low cost. The combination of grandfathering quota allocation mechanism and subsidy will effectively promote CCS retrofitting of coal-fired units, especially when the auction ratio is 30%–40%, about 400–540 GW units will be retrofitted under the carbon market using grandfathering and 12.05$/MWh-22.77$/MWh subsidies. Additionally, there are significant differences among provinces in terms of the lifetime costs of the CCS retrofitting of coal-fired units. Xinjiang, Guangdong, and Jiangsu, with retrofitting potentials of respectively 20.68 GW, 10.58 GW–43.00 GW and 15.00 GW–52.27 GW are best suited for the CCS retrofitting of coal-fired units.

Coal Plants, Air Pollution and Anaemia: Evidence from India

We examine the impact of pollution from coal–fired power units on the anaemic status of children and women in India. The number of coal units in the district at the time of birth significantly increases the incidence of anaemia in young children as does in utero exposure. The number of coal units in the district also adversely affects the anaemic status of women, although the magnitude of impact is smaller than that for young children. The impacts are driven by the increase in PM2.5 pollution generated by coal-fired units. Our evidence points to anaemia as a significant health cost of coal-fired power generation in rapidly growing economies that use coal as a major source of fuel to meet increasing energy demands.

A study on a novel solar contribution evaluation method for the solar-aided coal-fired power generation system

Solar-aided coal-fired power generation (SACPG) technology is an effective method of solar energy utilization. It could balance the demand of carbon dioxide emission reduction and renewable energy efficient power generation and promote carbon peaking and carbon neutralization. Accurate analysis of the share of solar energy in the unit output power could benefit the selection of the best integration scheme and exploitation of solar energy for further research. A novel solar contribution evaluation method of an SACPG system is put forward. The exergy is taken as the evaluation benchmark, and the method can be applied in an SACPG system with multiple integration positions with solar energy. The solar energy input from different positions in the system is analyzed separately. The solar energy input positions and the impact of solar exergy destruction on the solar energy contribution are considered. The proposed method also analyzes the flow direction and destruction of each solar exergy in different parts of the SACPG system and expresses the solar contribution in the electricity generated by each stage steam turbine in the form of a theoretical formula. Ultimately, the solar exergy contribution in the whole SACPG system is calculated by accumulating each result. Furthermore, the new method is applied to a tower solar-aided coal-fired power generation (TSACPG) system with thermal energy storage (TES) for comparative analysis. Compared with other solar contribution evaluation methods, the comprehensiveness and accuracy of the novel method are analyzed. Meanwhile, the exergy destruction distributions of the TSACPG system are revealed. The method can also be further used to excavate the application potential of solar energy in coal-fired units and provide theoretical support for highly efficient utilization of solar energy.

Thermal system for comprehensive utilization of boiler and steam turbine energy of coal-fired power units based on the S-CO2 cycle

In this study, an additional S-CO2 cycle system configuration for coal-fired power units has been proposed. This system achieves cascade utilization of steam turbine extraction and boiler flue gas energy, to improve the coal-fired power unit generation efficiency. Thermodynamic analyses were carried out for the new thermal system based on energy and exergy analyses. The results show that under the turbine heat acceptance (THA) condition, the proposed thermal system could reduce the standard coal consumption rate by 0.91% in coal-fired power units. Furthermore, the factors affecting the system performance are analyzed, and the effect laws of various elements on the total investment and payback period are derived. The suggested thermodynamic system provides a method for using energy on both sides of the boiler and steam turbine.