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Analysis of the relationships between parameters during operation and methods for adjustment: During boiler operation, the operational data obtained from various systems as well as from monitoring points located in different locations are, to some extent, interconnected in either direct or indirect ways. Skilled operators can use the objective patterns revealed by changes in these parameters to make accurate assessments of the boiler’s status. They can also take appropriate actions based on these relationships and on the degree of change in the absolute values of the data from various monitoring points, in order to handle various complex operating conditions. As an operator, it is necessary to simplify the basic operating procedures, gain a thorough understanding of the operating rules and processes, achieve a full comprehension of CFB boiler equipment, understand the inherent relationships between operating parameters in both cold and hot states, and apply professional knowledge to actual operation and equipment maintenance tasks. Here, we need to emphasize several parameters that are easily overlooked in traditional thinking; these parameters are closely related to the operating characteristics of circulating fluidized bed boilers, and they are not what are commonly referred to as reference measurement points. a Superheater outlet temperature. b Smoke temperature in the transition chamber ahead of the boiler’s rear flue. c Flue gas pressure and temperature behind the cyclone separator in the material recycling return system. d Pressures and temperatures in the dense-phase and dilute-phase zones at various heights along the furnace. e Pressure and temperature of the feeder air chamber, as well as the temperature of the return leg. The interpretation of conventional operating parameter values and the standard adjustment techniques have been repeatedly explained and thoroughly understood by many CFB boiler engineers, operators, and experts, so there is no need to go into further detail here. What the author wants to emphasize is that the analytical understanding and practical application of the parameter values related to the five aspects mentioned in this paragraph can bring considerable economic benefits to user equipment management and technical upgrades, while also enhancing the safety and reliability of equipment operation. Many plants simply use the temperature of the water exiting the economizer as a reference point, without paying much attention to its actual changes and the impact on operation. In fact, this measurement point is of particular importance, especially for CFB units where the amount of water used for temperature reduction remains high for extended periods, the steam temperature is abnormally high or low, the flue gas temperature is high, the temperature rise in certain heating surfaces is extremely high, and non-wear-related tube explosions occur frequently. The analysis of heat transfer requires us to be able to use operational data to diagnose the heat distribution within the equipment, and to understand how the heat is distributed across all the heating surfaces in the furnace – from the heating of water in the economizer to evaporation in the water wall, as well as in various sections of the superheaters, reheaters, and air preheaters. This allows us to identify any abnormalities in the heat transfer between the working fluid and the flue gases. The starting point for this analysis is to pay attention to the heat absorption by the water in the economizer. The temperature rise analysis and heat calculation during the water heating process are very simple and accurate, whereas in the case of local water wall heat transfer, the enthalpy of the steam-water mixture changes with its dryness, making the process relatively complex – this is especially true for supercritical units. However, by using the difference between the enthalpy of saturated steam and the enthalpy of the water exiting the economizer, plus the amount of evaporation resulting from the main steam flow minus the amount of water used for temperature reduction, it is possible to calculate with high precision exactly how much heat is absorbed in the evaporation section and how much heat is obtained by the economizer. This approach completely resolves the issue of accurately quantifying the heat absorbed by each of the economizer and the water wall. Such an approach provides a reference for the technical modification of the water-side heating surfaces in these two sections, preventing arbitrary increases or decreases in their heating surface area. When the heat absorbed by the economizer exceeds the allowable maximum amount, it results in insufficient subheat of the water exiting the economizer and the steam drum, which may lead to local boiling within the economizer. At this point, it is no longer possible to directly reduce the flue gas temperature and increase the evaporation capacity by enlarging the area of the economizer; instead, it is necessary to use airfoil-shaped water-cooled wall surfaces as additional heating surfaces in order to increase the heat transfer area of the water-cooled walls and thus raise their evaporation capacity, achieving an indirect reduction in the flue gas temperature. In most CFB units operating below the subcritical range, the temperature rise in the economizer is only about 8–12°C. Such a small temperature increase requires the use of several water temperature thermistors or thermocouples at the same location in order to determine the exact outlet water temperature; this is what is known as the \"thermistor array\" concept: the actual measured value at a particular point is represented by the average value of multiple measurement points. As a part of operational optimization, the outlet temperature of the economizer is also beneficial for determining the protection measures and the process of restarting the boiler after an emergency shutdown. When an unexpected shutdown of the power plant occurs due to accidents such as a loss of auxiliary power, it is necessary to rely on the temperature at the exit of the economizer after pressure reduction and the nearby flue gas temperature to determine whether water can be supplied to the steam drum during the process of restoring the water level. The operating condition requires that the temperature difference between the water temperature exiting the economizer and the wall temperature of the steam drum not exceed 50°C, and that the temperature of the flue gas at the rear end is not too low as well. At this time, if the drum level gauge can indicate the water level, the shutdown duration is no more than a few hours, and the valves in the steam-water system are closed promptly in the event of an emergency shutdown, and if it is found that the outlet temperature of the economizer is above 230–260°C with a temperature difference of no more than 45°C compared to the saturated wall temperature of the drum, while ensuring that the flue gas temperature near the economizer remains at least 180–250°C, water can be slowly added to the boiler until a normal water level is reached in the drum; there are then no safety concerns at all. Unless the fans are not shut down promptly in the event of an unexpected shutdown and the steam-water system is not sealed in time, it is possible to encounter a very serious situation of dry boiler operation. The practice of determining whether such a system can be brought online based on the temperature at the economizer outlet will certainly save a significant amount of time required for startup and recovery, and the benefits are even greater for DC boilers. Monitoring the economizer outlet temperature can also play a certain role in controlling other parameters. For example, it provides some reference for adjusting the cooling water temperature, controlling the layer thickness, addressing abnormal changes in bed temperature, and dealing with the indirect effects of air leakage, among other things; however, due to space constraints, these points will not be discussed in detail here. In the flue gas flow path of the boiler, the temperature fields in the turning flue chamber, the flue gas temperature after the separator, and the exhaust gas temperature after the air preheater are the only areas in CFB units where grid-based calibration and precise measurement are possible. In all other areas, high concentrations of particles, heat transfer across the heating surfaces, and local air leaks prevent the creation of sufficient space for a more uniform temperature distribution, thereby compromising the accuracy of the measurement points. Therefore, paying attention to these measurement points is of great benefit for diagnosing the processes inside CFB equipment. Similar to coal-fired boilers, the smoke temperature in the turning chamber follows the steam temperature well, but it cannot replace the measurement of smoke temperature adjacent to the separator for providing rapid sensitivity to steam temperature. Another advantage of monitoring the smoke temperature in the combustion chamber is that it allows for an assessment of whether stable combustion can be achieved, as well as an understanding of whether different types of coal can ignite reliably under certain load conditions. In the correlation analysis of combustion, in addition to monitoring the bed temperature and furnace flue gas temperature, it is also necessary to take into account the temperature of the return leg of the return conveyor as well as the flue gas temperature in the turning chamber. The smoke temperature in the steering chamber is a stable average smoke temperature obtained after secondary expansion; it is not possible to account for the deviations in smoke temperature at multiple boundaries following the separate separators on the left and right sides, and the impact of deviations in the flue gas flow path has become relatively indistinct. The smoke temperature and pressure after the separators can very quickly and directly reflect the performance differences between the various separators. By analyzing the difference between the separator outlet pressure and the furnace outlet pressure, and taking into account factors such as the temperature of the return leg, the temperature of the vertical leg below the separator, the air pressure in the small air chamber of the returner, and the flow rate in the high-pressure fluidization air branch, we can utilize the basic principles of intermediate storage-type grinding systems, along with the characteristics of the circulating return system, to quickly identify performance deviations in individual separators and the circulating return system. We can even determine differences in the amount of material returned, leaks in the return devices, the extent of ash accumulation, as well as the distribution of resistance, and identify the underlying causes so that appropriate actions can be taken. In fact, when we initiate ignition, the key to being able to retract the oil gun lies in ensuring that the bed material is in a state of stable and continuous combustion; this is determined by considering both the appropriate bed temperature and the temperature of the return leg, thereby avoiding repeated activation and deactivation of the oil gun, which also simplifies the adjustment of the air flow during the ignition process. Generally speaking, abnormalities in the return material temperature indicate problems with the circulation of return materials, while fluctuations in temperature levels reflect the stability of the returner or separator; they can also indicate whether the combustion in the suspension zone above the material layer on the corresponding local air distribution plates is stable, as well as whether the ash concentration distribution is normal. It should also be emphasized that the layer thickness is indirectly reflected through the bed pressure; a dedicated correction program can also be developed in the DCS system to describe the relationship between the actual bed pressure and thickness. First, the layer thickness corresponding to the zero-pressure reference point of the empty bed pressure is determined; the converted value of the virtual bed pressure at this thickness is used as a constant. By adding this constant to the normal bed pressure, the final operating bed pressure is calculated and displayed, which allows for a relatively accurate reflection of the thickness of the hot material layer. Generally, the bed pressure measurement points in most CFB boilers are located in the lower corner area of the furnace combustion chamber, at a height of 200–240 mm above the surface of the air distribution plate. The pressure measurement and balancing container outside the furnace is equipped with a regular back-purging and compensatory cleaning device. The additional pressure measurement points in the other dense-phase and dilute-phase zones provide information on the local ash concentration distribution of the material, offering useful insights for controlling the amount of circulating ash and bed temperature. They constitute an essential set of data for establishing a proper fluidization process within the furnace.