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Steam temperature is one of the key parameters that must be monitored and adjusted to ensure the safe and efficient operation of boilers and turbines. Due to the numerous factors that affect steam temperature, the processes involved are complex and variable, and the inertia in the adjustment process is high; therefore, it is necessary to conduct frequent analyses and observations regarding steam temperature control, and to adopt a proactive approach to adjustment. When the operating conditions of the unit change, it is necessary to strengthen the monitoring and adjustment of the steam temperature, analyze the factors that influence it and their relationship with changes, and gain some experience in steam temperature control to guide our adjustment operations. The following analyzes some typical operating conditions and proposes some guiding measures. Due to the complexity of steam temperature changes, one must learn to adapt flexibly based on the actual situations encountered during application, rather than following rules mechanically. Steam temperature control during normal operation of the unit: Steam temperature control can be divided into adjustments on the flue gas side and those on the steam side; the adjustment process on the flue gas side has high inertia ； The regulation on the steam side is relatively sensitive. Therefore, during normal operation, the desuperheater should be kept at a certain opening degree, generally greater than 7% ； If the desuperheater is fully closed or its opening is very small, the combustion conditions should be adjusted promptly (by increasing the air flow appropriately or by raising the flame center) in order to raise the steam temperature and allow the desuperheater to open. When the steam temperature drops during soot blowing, soot blowing should be stopped first ； Wait until the steam temperature stabilizes before deciding whether to continue soot blowing. If the opening degrees of all stages of the temperature reducers are relatively high (i.e., greater than 60%), adjustments should also be made on the combustion side, or soot blowing should be carried out in the furnace, in order to reduce the opening degrees of these temperature reducers and ensure that there is sufficient margin for adjustment. In summary, during normal operation of the unit, the temperatures downstream of each stage of the temperature reducers vary under different operating conditions. Monitoring of the temperature behind the temperature reducers at all levels should be strengthened, so as to have a clear understanding of it; this can serve as a reference for adjustments when the steam temperature is abnormal. Avoid large fluctuations in steam temperature. Precautions for controlling steam temperature during the unit’s smooth shutdown: 1. Before initiating the smooth shutdown, it is necessary to perform a thorough soot blowing of the boiler. By reducing the temperature regulator setting, it is possible to better control the steam temperature as it drops, thereby ensuring a smooth shutdown process. 2. During the smooth shutdown process, efforts should be made to reduce the steam temperature by lowering combustion intensity; it is not advisable to use increased cooling water to achieve this. If the rate of temperature decline is slow or the temperature remains high, it is possible to increase the output of the lower grinding unit while reducing that of the upper grinding unit, or even shut down the upper grinding unit in order to reduce the number of operating coal grinding units. On the other hand, the upper secondary air damper can be adjusted to be opened further, while the lower secondary air damper can be closed to some extent, in order to reduce the steam temperature. 3. During the gliding stop, the burners should be kept operating in a concentrated manner as much as possible to maintain stable combustion. Before stopping the mill, the amount of coal fed to it should first be reduced to a minimum, and then the coal mill should be shut down. After stopping one mill, the output of the remaining mills should be increased appropriately to keep the total coal grinding volume changing only slightly, thereby preventing too rapid a drop in steam temperature. 4. During the smooth shutdown process, oil should be removed one cylinder at a time; it is not allowed to remove multiple cylinders at once to prevent the steam temperature from dropping too rapidly. 5. Under normal conditions, when sliding to the main and auxiliary feedwater valves for switching, all the cooling water control valves as well as the main valve should already be fully closed. If, due to improper operation, the various cooling water control valves and the main valve are still open while switching between the primary and secondary feedwater valves in an attempt to reduce the steam temperature, we should consider delaying load reduction; instead, we can adjust things from the combustion side or take advantage of the decrease in furnace heat storage over time to lower the steam temperature, and then close the cooling water valves before making the switch. It is necessary to prevent a sudden increase in the flow rate of the desuperheating water, which could result from a sudden rise in feedwater pressure during switching, and thus cause a sharp drop in steam temperature. (At low loads, the steam flow rate is very low; even a slight increase in the amount of desuperheating water can lead to a significant drop in steam temperature. Therefore, one must be careful when using desuperheating water at lower load levels.) Additionally, it is recommended that the switching between the main and auxiliary valves be carried out at a load of 40–60 MW; before the switch, the coal grinding system should already be completely shut down. If time is limited and the cooling water valves cannot be fully closed, we can first close all the individual cooling water control valves as well as the main valve. Once the main and auxiliary valves have been switched over and the feedwater pressure has stabilized, we can then decide whether to open the main cooling water valve based on the steam temperature. If the steam temperature drops rapidly at this time, the turbine throttle should be reduced promptly or the load should be lowered to zero. However, attention should be paid to water level changes. Steam temperature control and precautions during sliding parameter startup: 1. For boilers that have been pressurized with water, there is a considerable amount of water remaining in the superheaters and reheaters. As a result, during startup, the pressure in the steam drum rises rapidly while the steam temperature rises more slowly. To ensure that the steam temperature matches the steam pressure, it is recommended to fully open the superheaters and reheaters, as well as all the drain valves in the main and reheater steam pipelines, prior to ignition, in order to allow proper drainage of water ； After ignition, open the high and low bypass valves promptly to drain the water accumulated in the superheater and reheater. When using oil injectors, the CD layer or EF layer injectors can be used first to raise the height of the flame center, thereby accelerating the evaporation of water accumulated in the superheater and reheater. Ensure the matching relationship between superheated steam temperature and pressure. 2. For units in a very hot state, once the turbine trips and the boiler shuts down, all feedwater control valves and main valves should be closed immediately. The exhaust steam electric valve or bypass valve should be opened (provided the turbine permits it), as well as the drain valves of the superheater and reheater. Reduce the drop in superheated and reheat steam temperatures to prepare for a rapid recovery. Before ignition, the bypass valves should be opened as wide as possible to reduce pressure. Upon completion of purging, oil guns must be activated immediately to minimize heat loss in the furnace. When igniting, it is advisable to start with the CD or EF layer oil guns first, maintaining a relatively high flame center height and a high oxygen content; this helps the steam temperature reach the parameters required for turbine startup as quickly as possible. 3. At low loads during the initial startup of the unit, when cooling water is introduced, it is necessary to ensure that the temperature after the primary economizer, as well as the temperature after emergency water injection, is higher than the saturation temperature corresponding to the pressures of the superheated and reheated steam, in order to prevent water accumulation and vibration in the superheater and reheater. 4. During the sliding parameter startup process, once the auxiliary valve is switched to the main valve, a decrease in the speed of the feed water pump leads to a drop in the pressure of the cooling water, thereby accelerating the rise in steam temperature. If the first grinder is started shortly after the main/auxiliary valve is switched, the steam temperature will rise more rapidly. Therefore, it is recommended to avoid using cooling water during the startup process, before the main/auxiliary valve has been switched. If the steam temperature rises too quickly, it is best to adjust the combustion rate in order to control the steam temperature. When starting up the first grinder, in order to minimize the impact on steam temperature, this can be compensated for by switching oil nozzles or adjusting the air volume. Regulation of steam temperature under variable operating conditions: During such conditions, steam temperature fluctuates significantly, and there are many factors at play. Operators must identify the key factors during operation, take appropriate actions, and take preventive measures in a timely manner. If necessary, corrective actions should be taken without delay to avoid steam temperature-related accidents. The changes in steam temperature under variable operating conditions are mainly caused by a mismatch between the combustion load of the boiler and the mechanical load of the turbine. Under normal circumstances, when the thermal load of the boiler is greater than the mechanical load of the turbine, the steam temperature tends to rise; the larger the difference between the two, the faster the steam temperature increases. Therefore, under variable operating conditions, efforts should be made to maintain a match between the thermal load of the boiler and the mechanical load of the turbine. The following is an analysis of several common scenarios: 1. Steam temperature regulation during normal load addition and reduction. During normal load addition, when the opening degree of the control valve remains unchanged, as combustion intensifies, the evaporation rate on the steam side lags behind the increase in thermal load on the combustion side. For superheaters, due to the gradual increase in evaporation rate, there is still a certain capacity to compensate for changes in steam temperature. However, the reheater does not have such a compensation capability. Therefore, during the load increase process, the rise rate of the reheat steam temperature is faster than that of the superheated steam temperature. At this time, we can adjust the steam temperature by opening the throttle valves of the turbine or by appropriately increasing the amount of cooling water used. The load reduction process is the opposite of this. 2. Steam temperature control during rapid load reduction: Rapid load reduction refers to the situation where, for some reason, the throttle valves of the turbine are quickly closed on the turbine side. Based on the previous analysis, it can be seen that the rise rate of the superheated steam temperature is relatively fast. Therefore, while increasing the desuperheating water flow, we should shut down 1–2 coal mills in accordance with the degree of load reduction (the normal procedure should be to shut down the coal mills first when deciding on a rapid load reduction). When the bypass is in operation, the bypass can be activated first (at this time, attention must be paid to the desuperheating water flow in the bypass to prevent any impact on the reheat steam temperature), or the steam temperature can be controlled by opening the exhaust to atmosphere. When releasing steam, attention should be paid to water level changes. 3. The impact of starting and stopping the coal grinder on steam temperature and its adjustment: When the coal grinder is started, it is equivalent to a sudden increase in the load on the combustion side; therefore, the superheated steam temperature generally shows an upward trend, and over-temperature may occur. Therefore, before starting the coal grinder, the steam temperature can be appropriately reduced; after it starts operating, the output of the other grinders should be lowered accordingly to keep the total amount of coal used within a narrow range. Attention should also be paid to adjusting the air volume – the air volume should be increased appropriately before starting the grinder, as it is not possible to increase the air volume in proportion to the increased amount of coal used, in order to avoid operation under insufficient air supply and to maintain the oxygen level within the range of 4–6%. When starting Mill F, special attention should be paid to changes in the reheat steam temperature. The Technical Department stipulates that Mill F should be started twice a month, usually during the day shift from the 10th to the 15th of each month and again during the day shift from the 25th to the 30th. When starting Mill F, it is advisable to do so while Mill E is still in operation, in order to avoid using oil as an ignition source. Additionally, before starting Mill F, the reheat steam temperature should be reduced to 520–525°C and stabilized before initiation. After starting the mill, the upper swing angle can be adjusted downward appropriately depending on the steam temperature. The situation is the opposite when the coal grinder is shut down. 4. Impact of superheater switching on steam temperature: After the superheater is taken out of service, the feedwater temperature decreases; to maintain the evaporation rate, it is necessary to increase the fuel supply, as a result of which the superheated steam temperature shows an upward trend. However, after the deactivation of the superheater, the steam extracted from stages I, II, and III must enter the turbine to do work, which causes a sudden increase in the unit’s load. Especially at 300 MW, this can lead to overpressure in the boiler and the activation of the safety valves; therefore, it is not appropriate to increase the amount of coal fed into the boiler at this time. On the contrary, the fuel supply should be reduced slightly, and only after the load and pressure have decreased should the fuel supply be increased again. At the same time, adjustments to the superheated steam temperature should be strengthened to prevent overheating; high-temperature heaters should be introduced gradually to avoid causing significant disturbances. The effect of tripping on the reheat steam temperature differs from that on the superheated steam temperature. Due to the reduction in extraction steam volume, the reheat steam pressure increases and its flow rate rises; before any changes occur in the combustion process, the reheat steam temperature temporarily drops (by about 5–10°C). However, as the unit’s operating conditions stabilize, the reheat steam temperature rises rapidly again. Operators must be prepared for this and make timely adjustments. 5. Characteristics and precautions for regulating the reheat steam temperature: Since the specific heat of reheat steam is lower than that of superheated steam, and its compensatory capacity is poor, large fluctuations in the reheat steam temperature can occur easily when the load or flow rate changes, making it difficult to control. Therefore, when starting and stopping the coal grinder as well as during load changes, closer monitoring and adjustment of the reheat steam temperature should be carried out, and appropriate proactive adjustments can be made for anticipated changes. The adjustment of the reheat steam temperature is mainly achieved by changing the angle of the burners (currently, it is planned that the angle of #1K can be adjusted within K15L, while the angle of #2K can be adjusted within ±5°; however, adjusting the angle of the burners results in a greater delay compared to adjusting the desuperheating water). Therefore, during adjustment, more observation is needed, experience should be continuously accumulated, and monitoring of the flame detector should be strengthened. At the same time, it should be kept in mind that when oil is injected, the swing angle of the burner in that layer must be at a horizontal position to prevent the oil gun from getting stuck. ), with minor temperature reduction regulation as a supplement, and an emergency temperature reduction function is also provided. Therefore, the regulation of the reheat steam temperature cannot rely solely on desuperheating water. Additionally, we can also adjust the reheat steam temperature by changing the ratio of bituminous coal to wind coal on the combustion side. For example, we can change the height of the flame center by adjusting the output of each coal grinder (while keeping the total amount of coal constant) and the proportion of each type of secondary air, in order to regulate the temperature of the reheat steam. At present, the automatic control performance of the reheat steam temperature is poor; therefore, enhanced monitoring of the reheat steam temperature is necessary when switching it to automatic control. If the automatic adjustment characteristic shows a divergent trend, it should be immediately switched to manual adjustment, and the thermal control team should be contacted promptly for handling. When operating conditions change significantly, the automatic reheat steam temperature control should be disabled and manual adjustment should be carried out.