Thermal Power Units Research Articles

Variety-duty Characteristic Analysis and Optimal Operation of Cold-End System of 600MW Direct Air-cooled Thermal Power Unit

The operating backpressure of the direct air-cooled unit is a significant economic parameter, and the optimal backpressure is corresponding to the best efficiency of the unit, which is mainly affected by ambient temperature, steam turbine exhaust flow, and face velocity in the operation of the cold-end system. A calculation model of the condenser of a 600MW direct air-cooled unit using the ε-NTU method was established to analyze the off-design performance. Compared with the characteristic curve provided by the manufacturer, the maximum error of the calculation results is 1.68%, meeting the engineering accuracy requirements. In order to obtain the optimal backpressure and optimal face velocity under off-design conditions, a cold-end optimization calculation model based on genetic algorithm is established with the maximum net power output as the objective function. The influence of the exhaust steam flow, ambient temperature and face velocity on the pressure of condenser is analyzed. In addition, the changing rules of the net power output with face velocity and backpressure under different conditions are studied. The results indicated that the working pressure of the condenser increases with the increment in ambient temperature and exhaust steam flow, and decreases with the rise of face velocity. The net power output of unit increases first and then decreases with the increment in backpressure and face velocity. Moreover, the higher the ambient temperature, the larger optimal face velocity and optimal backpressure of the unit, as well as the more cooling air volume is required under the optimal air face velocity. Keywords: Direct air-cooled unit, Off-design condition, Characteristic analysis, Optimal backpressure, Genetic algorithm DOI: 10.7176/JETP/13-1-02 Publication date: January 31 st 2023

Acoustic resonance analysis of new water drop labyrinth control valve for thermal power units

Acoustic resonance analysis of new water drop labyrinth control valve for thermal power units

Prediction of reduction products in the preheating process

Under the current requirements of environmental protection, carbon peaking and carbon neutrality goals, the capacity of the new energy interconnection network is increasing day by day. The thermal power unit requires the ability of rapid load adjustment to meet the requirements of real-time power balance. However, when the unit is in a variable load condition, the denitrification system is inefficient or even inoperable. The NOx emission is large, which makes it difficult to meet environmental protection requirements. In this study, a new method for predicting reductive products in the preheating process is proposed, introducing the gasification mechanism into the pulverized coal preheating process. The effects of air coefficient on combustion temperature, velocity, O2, CO2, CO, CH4, and H2, volatile matter and NOx emission are investigated by numerical simulation. It is demonstrated that the gasification mechanism is applicable to predict the reduction products and NOx during preheating. Internal combustion burners can stabilize the precipitation of volatile matter, CH4, CO, and H2. The burner outlet temperature and flow rate decrease with decreasing air coefficient. The local maximum concentration of volatile matter and CH4 are 8.3 vol.% and 2.54 vol.%, respectively. The CO concentration increases with decreasing air coefficient under the effect of CO2 gasification reaction. When the air coefficient is 0.33, the NOx concentration at the burner outlet is 2.8 mg/Nm3 (at 6% O2).

Optimization of Valve Flow Characteristics Based on Improved Particle Swarm Algorithm

After long-term operation, the flow characteristics of the high-pressure regulating valve of a thermal power unit may be shifted to a certain extent, resulting in inconsistent changes in the total valve position and opening degree, which in turn affects the PFR function of the unit. Based on the historical operation data of a thermal power unit, the flow characteristics of the unit's high-pressure regulating valve are optimized using an improved particle swarm algorithm. By experimentally verifying the primary FM in different total valve position intervals, the influence of valve flow characteristics on the primary FM function is discussed. The results of the primary FM example show that, with the optimized valve flow characteristics, the output response index of the unit in 15 and 30 seconds is increased to 85.44% and 94.11%, respectively, which meets the assessment requirements of the grid-connected operation and management of the power plant for the primary FM, and optimizes the primary FM performance of the unit.

Influence of Foreign Body Blockage in Water Cooling Wall on Flow and Heat Transfer

The ultra (super) critical units, as mainstream thermal power units, often need to participate in deep peak shaving. The variable load and high frequency peak regulation will lead to the partial increase of the temperature of the water-cooled wall and the phenomenon of local over-temperature. Aiming at this situation, the numerical investigation on the water-cooled wall of the #5 boiler in She-yang-gang was performed. The results show that the welding nodules and the foreign bodies in the water-cooled tube have a significant effect on the wall temperature. Moreover, with the increase of the blocking ratio (β), the mass flow in the tube decreases significantly, and the mass flow in the adjacent tubes rising. Further the increase of the mass flow is noteworthy in the nearest tubes. When the β of the target tube is higher than 0.4 the possibility of exceeding the maximum temperature limit of water-cooled wall tube material increases. The deposition of foreign body on the inner wall of the tube weakens the convective heat transfer between the inner wall and the fluid, which makes the wall temperature rise faster than other places. The more serious the deposition, the more obvious this phenomenon is.

Study on Calculation of Inlet Steam and Inlet Water Flow of Drain Pump of Low Pressure Heater

In the traditional drainage system of low pressure heater of thermal power unit, the measuring point of drain pump is usually added to directly measure the water and steam flow of low pressure heater of drain pump with instruments. This method is time-consuming and labor-intensive, and the measurement results are affected by many environmental factors. In order to solve this problem, this paper proposes an automatic calculation method based on the principle of heat balance.

Performance Test of a 660MW Thermal Power Unit Steam Turbine Based on the Background of “Double Carbon”

Under the background of "carbon peaking and carbon neutralization", China proposes a new power system with new energy as the main body. Due to the strong randomness, volatility and anti peak shaving characteristics of new energy power generation, in order to promote the consumption of new energy and ensure the power supply, coal power generation units will assume the dual tasks of deep peak shaving and power supply guarantee in the future, gradually changing from electric power supply to regulated power supply. In order to accurately grasp the thermal performance of the steam turbine after the flow passage transformation of the unit, the thermal performance assessment test of the steam turbine of the unit was carried out. Through thermal test, determine the heat rate and efficiency of high, medium and low pressure cylinders of the unit, and provide reference for future economic operation of the unit.

Analysis of Heating Transformation of Nuclear Power Units

Under the current national conditions and policy support, nuclear heating has flourished. Domestic nuclear power units mainly generate electricity, and nuclear heating as a clean energy source is one of the main ways to solve winter heating in the north. This paper first compares and analyzes the two different ways of nuclear heating, then takes the nuclear heating of Haiyang Nuclear Power Station as an example, based on the mature experience of steam extraction heating transformation of thermal power units, makes an economic analysis on the steam extraction transformation of PWR nuclear power units from the characteristics of the thermal system combined with the Spot market, and finally makes an economic evaluation on the Cogeneration nuclear power units.

Application modelling of intelligent diagnosis for thermal cycle system

In order to solve the problem of intelligent fault diagnosis of thermal system of thermal power unit, the application modelling of intelligent diagnosis of thermal cycle system is proposed. This paper first filters the influence of the change of valve opening of steam turbine on the performance index under the condition of constant power, and qualitatively analyzes the actual change of the performance index compared with the reference working condition when the component fails, so as to eliminate the mutual influence between the components. Then, the selection principle of thermodynamic parameters is determined, the irreversible loss in the structural theory of thermal economics is introduced as the performance index, and the model is used to quantitatively calculate the change of performance index of each component under fault conditions to diagnose the failed component. Finally, APROS simulation software is used to simulate various fault conditions of 330 MW units in a power plant. The experimental results show that the recognition accuracy of the monitoring system designed in this paper can reach 98.33%. In conclusion, the method in this paper proves the feasibility of intelligent fault diag?nosis of thermodynamic system network.

Application Research on Zero Output of Double Low Pressure Cylinder of 600MW Unit

Under the dual carbon target, the rapid development of new energy promotes the increasing peak shaving capacity of thermal power units as basic power sources. Taking 600MW unit as an example, this paper studies the feasibility of zero output of low pressure cylinder for heat supply transformation of 600MW unit, and analyzes the peak shaving capacity of the unit by cutting off double low pressure cylinder and single low pressure cylinder.

Design of Energy Storage for Assisting Extraction Condensing Unit to Peak Regulation and Frequency Modulation

Abstract Coupling energy storage system is one of the potential ways to improve the peak regulation and frequency modulation performance for the existing combined heat power plant. Based on the characteristics of energy storage types, achieving the accurate parameter design for multiple energy storage has been a necessary step to coordinate regulation. In this work, heat storage tank for peak regulation and flywheel energy storage for frequency modulation have been carried out, including the parameters design and performance evaluation for their charging (or discharging) rate and capacity, and the collaborative optimization of dual energy storage systems has been realized. First, the effects of increasing peak depth, load change rate (frequency modulation) range, and energy storage parameters are further analyzed. It is worth noting that the power curves of regional thermal and electrical loads would be adjusted according to the set requirements. Results showed that, the set rate of charge and discharge as well as the capacity of energy storage is conducive to improving the peak regulation depth of the system, and the peak regulation depth would reach its limit at 96.35 MW and 40.83 MWh in the calculation cases, respectively. On this basis, the cooperative regulation of dual energy storage can further increase the capability of peak regulation and frequency modulation. The extreme point is that when the charge and discharge rates are both 3 MW, and meanwhile the peak clipping coefficient, a self-defined parameter, reaches 22.34 MW. Furthermore, an example calculation is carried out to verify the reliability of the design method of energy storage parameter. The specific parameters set include the charging and discharging rate of energy storage tank equipment is 61.67 MW, and its capacity is 10.64 MWh, and the charging and discharging rate of flywheel energy storage equipment is 3 MW. The example results confirmed that there was only a very small error between the set results and the calculation results. Finally, the thermal-electric load region has been drawn to contrast the key roles of dual energy storage systems, which indicates that the heat storage tank can be used for peak regulation and flywheel energy storage for frequency modulation. Overall, the parameter design method for dual energy storage can meet the engineering requirements and provide a new direction for the subsequent parameter design of thermal power unit coupled energy storage system.

RDE cycle simulation by 0D/1D models to investigate IC engine performance and cylinder-out emissions

In this work, the development and application of advanced predictive 0D/1D methodologies to simulate Real Driving Emission (RDE) cycles are described. Firstly, the 1D simulation model is validated on a map of steady state operating points, which allows to use successively the very same model, with its calibration, during an RDE cycle simulation, considering the sequence of varying loads, and rotational speeds. In particular, the validated 1D model is used to simulate a typical RDE transient cycle of approximately 1 h and 45 min. The test case investigated is a modern plug-in hybrid passenger car engine, in which the thermal power unit consists of a 1 L three-cylinder, turbocharged gasoline engine. The experimental and simulated RDE cycle is characterized by a sensibly varying Internal Combustion Engine (ICE) operation, allowing to evaluate engine performance and cylinder out emissions. To speed up the calculation and significantly lower the Central Processing Unit (CPU)/real time ratio a dedicated numerical solver for fast simulation has been implemented and tested, while keeping the fidelity of the results. A predictive 0D, multi-zone model for Spark Ignition (SI) combustion has been applied, together with emission sub-models for the calculation of the main pollutants. Both instantaneous and cumulative emissions have been evaluated. The results of the simulations have been compared to the experimental data of RDE cycles, showing a good predictiveness of the models and the high potential of 0D/1D simulation codes as design tools, in the new scenario of demanding testing procedures. This approach can be applied for any engine configuration operating under any transient condition.

Assessing flexibility options in electricity market clearing

This work presents a model to co-optimize the energy and reserves markets, taking into account the penetration and participation of various flexibility providers in both markets. In particular, a detailed unit commitment model has been developed based on mixed-integer programming techniques incorporating energy storage systems with both charging and discharging options, electric vehicles with both grid-to-vehicle and vehicle-to-grid modes, and demand response programs for cost-optimal energy and ancillary services scheduling. The balancing services considered include Frequency Containment Reserves (FCR), automatic Frequency Restoration Reserves (aFRR), and manual Frequency Restoration Reserves (mFRR), in both upward and downward directions. The impact of all these flexibility providers on operational and economic aspects has been assessed through an illustrative case study of a power system with high penetration of renewable energy sources, including thermal and hydroelectric power units. The results highlight the superiority of results when considering the participation of all flexibility providers, especially in the ancillary services market, in terms of economic competitiveness, renewable energy curtailment, associated CO2 emissions, and utilization of costly energy resources. The growing share of flexibility providers in both energy management and reserve provision mix highlights the importance of these sources for power mixes with low carbon content. The methodological framework developed can be employed by system operators, market participants, and policymakers to provide price signals and optimize their resources and portfolios.

Research on the Frequency Regulation Strategy of Large-Scale Battery Energy Storage in the Power Grid System

Driven by the carbon peaking and carbon neutrality target, the large-scale grid-connected of renewable energy such as wind and solar has increased, and the volatility and randomness have posed new challenges to the stability of the power grid frequency. In this case, battery energy storage is a grid auxiliary resource with fast response and adjustable parameters, which can provide frequency support for the grid system in a short period. This paper studies the frequency regulation strategy of large-scale battery energy storage in the power grid system from the perspectives of battery energy storage, battery energy storage station, and battery energy storage system, respectively. First of all, the droop control based on logistic function and the virtual inertia control based on piecewise function are proposed for battery energy storage frequency regulation, which improves the performance of battery energy storage power output effectively. Second, the weighting factor is set according to the current battery charge to achieve the most optimal distribution of frequency regulation power for each battery pack in the battery energy storage station. In the end, a control framework for large-scale battery energy storage systems jointly with thermal power units to participate in system frequency regulation is constructed, and the proposed frequency regulation strategy is studied and analyzed in the EPRI-36 node model. The results of the study show that the proposed battery frequency regulation control strategies can quickly respond to system frequency changes at the beginning of grid system frequency fluctuations, which improves the stability of the new power system frequency including battery energy storage. In addition, this paper also provides a certain reference for the construction of the new power system dispatching that integrates “Generation-Grid-Load-Storage” in the future.

Design and Optimization of Coal to Hydrogen System Coupled with Non-Nominal Operation of Thermal Power Unit

In an actual thermal power plant, deep peak shaving will cause thermal power units to run under non-nominal conditions for an extended period, resulting in serious problems such as increased equipment wearing, low equipment utilization efficiency and decreased benefits. To this end, in this work, both the design and optimization method for a coal to hydrogen system which is coupled with the expected non-nominal operation of thermal power units are proposed. Aiming towards maximum profit in the context of thermal power plants, a mathematical optimization model for a coal to hydrogen system based on the multi-period operating conditions of thermal power plants is established. The corresponding optimal design scheme of the coal to hydrogen system is determined using variable operating conditions. The superiority of the integrated system compared with an independent system is explored and the feasibility of the proposed method is verified by using the case study of an actual thermal power plant. The results show that compared with the independent system, the economic benefits of the integrated system can increase by 13.56%, where the sale of hydrogen in the coal to hydrogen system accounts for 60.3% of the total benefit. The main expenditure associated with the system is the purchase cost of feedstock coal, accounting for 91.8%. Since the required power and medium-pressure steam in the coal to hydrogen process are provided by thermal power units, the minimum operating load of the thermal power plant in the integrated system increases from 40% to 60.1%, which significantly improves the utilization efficiency and service life of the generator units. In addition, the proposed integration scheme of the system is simple and controllable, which can contribute to the maintenance of the safe and stable operation of power generation and hydrogen production processes. These results are expected to provide the necessary methodological guidance for the integration and optimization of coal-fired power plants and coal to hydrogen systems.

Optimization of Steam Distribution Mode for Turbine Units Based on Governing Valve Characteristic Modeling

With the extensive application of renewable energy generation, thermal power units are required to participate in peak-regulating operations. The mode of steam distribution significantly influences the economy when the steam turbine operates at a low load. The turbine unit’s governing valve characteristics and steam distribution modes are studied in this paper, and the optimal sliding pressure operation curve is derived. Firstly, the theoretical model of the governing stage and the governing valve is derived, and the reliability is verified with field data. Secondly, the overall simulation model of the turbine unit is established, and the turbine off-design performance is analyzed with variable main steam pressure. Finally, the advantages and disadvantages of the three steam distribution modes are discussed thoroughly. The steam distribution modes and optimal main steam pressures are analyzed. The results show that a precise composite sliding pressure operation scheme is recommended, and a sliding pressure operation mode is adopted under 470 MW and constant pressure operation for others.

Modeling Method for Prediction of Primary Frequency Modulation Compensation Capability

The primary frequency modulation function of thermal power units plays an important role in the frequency stability of the power grid. In order to accurately predict the compensation capacity of primary frequency modulation, this paper introduces a modeling method to predict the compensation ability of primary frequency modulation. In this paper, the network source information platform data is used to collect the historical information of the remote test of primary frequency modulation, and the historical data are selected for fitting according to the principle of the closest working condition of the unit, so as to predict the 1-minute compensation ability of the primary frequency modulation of a single generator set. The function has been put into operation on the network source information platform, and the prediction results are verified by the remote test results during the provincial adjustment period. It shows that the error between the prediction results and the actual results is small, and the load changes within 1 min can be expressed more accurately.

Analysis of the compound differential evolution game of new energy manufacturers’ two-stage market behavior under the weight of consumption responsibility

To promote renewable energy consumption and achieve China's low-carbon energy transition, in 2019, China proposed the weight of consumption responsibility (WCR) for renewable energy in each province. This study aims to explore the micro-market behavior of new energy manufacturers in the context of WCR policy. A two-market bidding model for new energy manufacturers is first proposed, and a two-stage compound differential evolutionary game algorithm is proposed for solving the multi-party game problem. By selecting typical electricity demand scenarios, the evolution of new energy manufacturers' strategies in the electricity market and green certificate market as well as under different WCR and different thermal power unit parameters are analyzed. The research results show that when the non-hydropower WCR is relatively low, new energy manufacturers tend to adopt a low-price strategy for generation quotation and a low volume high price strategy for green certificate sales. Other conditions being unchanged, with the increase in non-hydropower WCR, all new energy manufacturers will still adopt a low-price strategy in the electricity market. New energy manufacturers with high installed capacity will increase progressively their certificate quotation. The higher output lower limit for thermal units is not conducive to electricity market bidding by new energy manufacturers.

PID Control of a Superheated Steam Temperature System Based on Integral Gain Scheduling

The high-quality operation of a superheated steam temperature (SST) system is a core fact of the safety, economy, and stability of thermal power units. How to improve the control performance of an SST system under large-varying operating conditions is becoming a research hotspot. To solve this challenge, this paper proposes a proportional integral derivative (PID) control strategy based on integral gain scheduling. Based on the introduction of the SST system and classical model under typical operating conditions, the control difficulties of the SST system are analyzed theoretically. Then, a PID control strategy, based on integral gain scheduling, is introduced for the cascade control structure, and the stability of the proposed control strategy is analyzed by calculating the PID stability region. Finally, the effectiveness of the proposed method is verified under nominal and uncertain conditions, where the proposed method could obtain satisfactory tracking and disturbance rejection control performance. Simulation results show the valuable application prospects of the proposed method.

A new assessment mechanism of primary frequency regulation capability for a supercritical thermal power plant in deep peaking

AbstractWith the rapid development of renewable energy, the primary frequency control (PFC) is becoming more critical and significant to ensure the stability of the electrical power system. As the main role of PFC, the thermal power unit tends to in a wide operation interval, and the changes in PFC characteristics along with working conditions are inevitable. By decomposing and quantifying the dynamic energy conversion process, this paper proposes a novel mechanism to evaluate the PFC capability for the supercritical thermal power plants that covered 30%–100% of the rated load. In the mechanism, a refined steam turbine model is established to reflect the short‐term dynamic response of PFC by combining it with the coupling characteristics of the main steam valve and main steam pressure in the later phase. Meanwhile, as a new prior assessment index, the equivalent electricity has been put forward to quantify the PFC capability for the power plant. In a case study of a 600 MW supercritical power plant, the capacities of PFC under 30%–50% of the rated load are quantified for the first time. Comparison results between theoretical calculation and real PFC test show that the proposed PFC capability assessment mechanism has acceptable accuracy of 96.1%, which could be effective to assess the frequency response reserve and stability margin in the grid.