System Status and Reasons for Energy Saving The four 360MW unit generators at Huaneng Luohuang Power Plant are subcritical, intermediate reheat, forced circulation, double-arch furnace, solid ash discharge, W-flame, smokeless coal-fired drum boilers manufactured by STEIN (France); the turbines are subcritical, intermediate reheat, single-shaft, three-cylinder double-exhaust, four low-pressure heaters, two high-pressure heaters, and one deaerator-driven condensing turbines manufactured by STG (France); the generators are 360MW water-hydrogen-hydrogen generators manufactured by STG (France). Under the same load demand, energy saving will greatly reduce the power plant's electricity supply costs, while reducing equipment wear and tear, extending equipment lifespan, and creating economic benefits. Simultaneously, with the gradual implementation of "separation of power plant and grid, competitive bidding for grid connection," energy saving and consumption reduction provide the power plant with a significant competitive advantage in electricity prices. The power plant planners analyzed the energy-saving factors of the 360MW units at Huaneng Luohuang Power Plant, mainly focusing on the following aspects: 1. The problem of air leakage rate in the boiler air preheater. The air leakage rate of the shell-type three-compartment air preheater at Luohuang Power Plant has consistently been high, around 15%. Reducing the air preheater leakage rate is crucial for improving boiler thermal efficiency and reducing energy consumption. Secondly, reducing plant power consumption is also an important aspect of energy conservation. Through systematic statistics and analysis, power plant planners discovered a flaw in the control system's strategy. Under low load conditions, the system required the operation of two electric feedwater pumps, increasing plant power consumption. Simultaneously, two circulating water pumps also needed to operate simultaneously to ensure stable water supply, unnecessarily increasing the plant's power consumption. After fully understanding the performance of the unit's auxiliary equipment and comprehensively considering the equipment's safety, economy, and rationality, power plant personnel proposed feasible energy-saving solutions and technical measures. These included using a single electric feedwater pump in the boiler feedwater system under low load conditions, along with interlocking the operation of the circulating water pumps. This ensured stable low-load operation of the unit, saved equipment consumption, and reduced plant power consumption. 1. System Analysis and Scheme Implementation 1.1. Leakage Problem of Three-Compartment Air Preheater From the perspective of the relationship between the leakage coefficient of air preheater and boiler efficiency in China, for every 0.01 percentage point change in the leakage coefficient of the hot end of the air preheater, the boiler efficiency changes by 0.024 percentage points; for every 0.01 percentage point change in the leakage coefficient of the cold end of the air preheater, the boiler efficiency changes by 0.0065 percentage points. Therefore, the leakage of the boiler air preheater directly affects the change in boiler efficiency. The degree of influence of air preheater leakage on boiler efficiency is as follows: the hot end of the air preheater has the greatest impact, followed by the cold end of the air preheater [1]. Huaneng Luohuang Power Plant boiler adopts Junkers three-compartment air preheater. When the air preheater sealing control system of the two 360MW units in the first phase of the project was introduced, the mechanical probe sealing control method was adopted. The actual sealing effect is not ideal. When the air preheater sealing control system is not put into operation, the air preheater leakage rate reaches about 18% at full load, which greatly increases the power generation cost. In 2002 and 2004, Huaneng Luohuang Power Plant implemented new air preheater sealing control systems on Units #1 and #2, respectively. These systems employed high-temperature corrosion resistant magnetic induction coils to measure the gap between the sealing baffle and the rotor. The system used a closed-loop dynamic tracking method to adjust the distance between the sealing baffle and the rotor, ensuring the sealing gap between them did not exceed 3mm. This was supplemented by motor overcurrent regulation, significantly reducing air preheater leakage. In leakage tests after the sealing baffle modification, the leakage rate of the air preheater was reduced from an average of approximately 15% to approximately 9.5%, directly reducing energy consumption, lowering coal consumption for power generation, and improving the unit's economic efficiency. 1.2. Feedwater Pump Single-Pump Operation and Related Combustion System Optimization: Huaneng Luohuang Power Plant's steam drum water level regulation system includes three electric feedwater pumps, the steam drum, a main feedwater control valve, and a bypass feedwater control valve, among other main equipment. The closed-loop regulation and control of the boiler drum feedwater at Huaneng Luohuang Power Plant employs segmented control during unit start-up, shutdown, and operation. During unit start-up, feedwater is supplied via a bypass, while during operation, the main feedwater circuit provides the water. During start-up, the drum feedwater uses single-impulse control via the bypass feedwater regulating valve. After the steam flow reaches the first set value, it switches to three-impulse control. After the steam flow reaches the second set value, if the unit's operating parameters meet the set parameters, the bypass feedwater switches to main feedwater supply and uses three-impulse regulation. During low-load operation, if the unit's feedwater pump operates with only one pump, issues arise such as frequent switching between the main and slave feedwater circuits, problems with feedwater pump cavitation protection, and limited drum feedwater supply. Simultaneously, load return commands may occur in the boiler load return system, leading to unstable boiler combustion and requiring oil-assisted combustion, among other issues. 1.2.1. Control Analysis of Steam Drum Water Level Regulation System When implementing energy-saving measures for steam drum water level regulation using a single electric feedwater pump, the following factors affect feedwater regulation: 1. Performance Parameters of a Single Electric Feedwater Pump First, the technical parameters of the electric feedwater pump must meet the feedwater requirements of the unit load. The electric feedwater pumps at Huaneng Luohuang Power Plant have a large design capacity, meeting the boiler drum water supply needs for units with loads below 220MW. This provides the possibility for implementing energy-saving schemes. The technical parameters of the electric feedwater pumps at Luohuang Power Plant are as follows: 2. Cavitation Protection of Electric Feedwater Pumps and Switching Between Main and Slave Feedwater Regulation During load changes at Huaneng Luohuang Power Plant, feedwater regulation will switch between the main and slave feedwater circuits. Switching conditions include: steam flow rate greater than 25% of full-load steam flow rate, the difference between feedwater header pressure and steam drum pressure greater than 20MPa, and the main electric feedwater valve being open. When operating with a single feedwater pump, the unit's feedwater regulating system is designed with a cavitation protection function for the electric feedwater pump. This means that the feedwater flow rate and pressure of a single pump maintain a specific proportional relationship to ensure the pump is not affected by cavitation. However, when the steam flow rate is between 400 T/H and 660 T/H, the feedwater flow rate is relatively high. Under cavitation protection, the feedwater regulating valve will maintain a certain opening and will not open further with increasing boiler load. In this situation, to ensure feedwater to the steam drum, the feedwater header pressure will fluctuate, resulting in significant pressure differences across the feedwater regulating valve. Since this pressure difference is a condition for the main electric feedwater valve to open and close, this leads to frequent automatic opening and closing of the main electric feedwater valve, causing frequent switching between the feedwater bypass and main circuit, which affects unit safety. [align=center]Figure 1: Schematic diagram of anti-cavitation protection principle[/align] Under the design-permissible conditions, we adjusted the proportional curve of some functions, that is, in the simplified diagram of feedwater pump cavitation protection, by calculation, we adjusted the corresponding F(X) function tuning curve. When the flow rate of a single feedwater pump is large, the feedwater pressure setting is reduced to ensure that the opening of the feedwater regulating valve can change with the boiler load, thereby reducing the change of feedwater regulating valve pressure difference, reducing the fluctuation of the feedwater regulating valve, and preventing abnormal switching of the feedwater master-slave circuit. After the energy-saving measures were put into operation, the feedwater system regulation performance was good under the operation of a single feedwater pump, the master-slave feedwater regulating valves worked normally, the cavitation phenomenon of the electric feedwater pump did not exist, and the equipment operated normally. 1.2.2. Load return control system and combustion system control system analysis and optimization The combustion system of one unit of Huaneng Luohuang Power Plant has 18 pulverizers in 9 groups, arranged on both sides of the boiler furnace, with W-shaped flames. When only one feedwater pump is running, the control system is designed with a 60% load return protection, and the total fuel setpoint is also set to a relatively low value. The pulverizers in combustion systems A and I must also be shut down. Therefore, under single-pump operation, due to the limitation of the total fuel setpoint, the boiler's maximum output is limited to a steam flow rate of approximately 500 T/H, and the unit load is limited to 180 MW. Only after both feedwater pumps are put into operation can the combustion system allow the unit to operate normally at high load. Because the electric feedwater pumps at Huaneng Luohuang Power Plant have a large design capacity (706.48 m³/h), they can handle higher loads for feedwater regulation when operating with a single pump, thus providing considerable adjustment flexibility. Based on a comprehensive analysis of the unit's performance and actual test results, a boiler steam flow rate of 660 T/H is considered a crucial criterion for determining boiler load reversal. Segmented control of load reversal for a single feedwater pump is implemented. Specifically, when the boiler steam flow rate is below 660 T/H, a single feedwater pump can meet the boiler's feedwater regulation needs and ensure safe boiler operation, eliminating the need for load reversal protection. Simultaneously, the A and I pulverizers of the combustion system can be put into operation to ensure stable boiler combustion. Conversely, when the boiler steam flow rate exceeds 660 T/H, a single feedwater pump cannot meet the boiler's feedwater regulation needs and ensure safe boiler operation, necessitating load reversal protection. Furthermore, analysis of the corresponding total fuel quantity setpoint curve determined the appropriate total fuel quantity setpoint for load reversal. This increases the maximum load of a single feedwater pump from the maximum limit of 180 MW to 220 MW, thus ensuring the safety of the entire unit start-up and shutdown control process and the feasibility of energy-saving measures for plant power consumption. [align=center]Figure 2: Manipulative principle of run back[/align] 1.2.3. Analysis of the Circulating Water System Control System In the control strategy of the unit's auxiliary equipment, it is designed that when the load is above 180MW, two circulating water pumps will operate simultaneously to ensure the water supply to the condenser. Therefore, the two circulating water pumps are not designed with interlocking function. When the unit is running at low load, the condenser feedwater demand is relatively small, and the water supply output of a single circulating water pump can meet the needs of the unit. However, if the circulating water pumps do not have interlocking function, the standby circulating water pump will not start automatically when the operating circulating water pump fails, reducing the automatic interlocking performance of the unit equipment. If the operator does not start the standby pump in time, it will affect the safety of the unit. Therefore, we designed to add interlocking protection function to the circulating water pumps to ensure the safety of the unit's circulating water pumps operating individually. The actual application effect is good. 2. Economic Benefit Analysis Huaneng Luohuang Power Plant implemented air preheater sealing control systems for Units #1 and #2 in 2002 and 2004 respectively. The leakage rate of the boiler air preheaters decreased significantly, averaging from 15% before implementation to approximately 9.5%. This greatly saved energy and significantly improved boiler efficiency. Before the energy-saving renovation of plant power consumption in 2000, the average plant power consumption rate of Luohuang Power Plant units was around 9.5%. Starting in July 2000, the plant implemented renovation projects for its two 360MW units, including single-pump operation under low load and the implementation of interlocking functions for circulating water pumps. These energy-saving projects resulted in an average plant power consumption rate of 8.5% in 2001, a decrease of nearly 1% compared to before the renovations (see the graph showing plant power consumption rate before and after the implementation of the energy-saving project at Luohuang Power Plant). In 2002, after all energy-saving projects were fully implemented, the plant power consumption rate decreased by another 0.8%, reaching an average reduction of 7.5%. Based on Luohuang Power Plant's total power generation of 4.896 billion kWh in 2001, this translates to savings of nearly 52 million kWh in plant power consumption, equivalent to nearly 5 million RMB. Furthermore, under low load conditions, the feedwater pumps switched from dual-pump operation to single-pump operation, reducing equipment wear and tear and improving the equipment's equivalent availability factor. Simultaneously, under low load conditions, the stability of coal-fired boiler combustion was optimized, reducing fuel oil consumption, lowering power supply costs, and enhancing the power plant's market competitiveness. It is particularly worth mentioning that the economic benefits generated above were achieved without any equipment or capital investment. It can be said that significant economic benefits were created at zero cost. [align=center]Figure 3: Statistics for efficiency of house load in HIPDCCQ[/align] 3. Conclusions of Energy Saving Practices With the further implementation of "separation of power plant and grid, competitive bidding for grid connection," power plant units are required to have high operational levels and production indicators to be competitive in the market economy. In the energy saving practice of Huaneng Luohuang Power Plant, combined with the actual situation of the unit equipment, the air preheater leakage rate was reduced and boiler efficiency was improved through equipment renovation and modification. Furthermore, the operating mode of the main auxiliary equipment under specific conditions was changed, namely, single-pump operation of feedwater pumps and interlocked operation of circulating water pumps under low load. This tapped the potential of the equipment. Through optimization of the system control strategy, the goal of reducing the power plant's electricity consumption was achieved, equipment losses were reduced, and good economic benefits were generated. At the same time, the power supply cost was greatly reduced, making the power plant more competitive in the market economy.