Abstract: This paper introduces a distributed control system (DCS) built using the Homeywell system to achieve real-time monitoring of key parameters of the boiler, turbine, power grid, and heating network, and to realize automatic control of key process variables. Based on this, a steady-state parameter optimization model was established for the boiler combustion system, which has a significant impact on energy saving, and the parameters of the steady-state parameter optimization model were obtained. Guided by the results of this optimization model, the energy utilization rate of the power plant was improved by approximately 4%. Keywords: Boiler combustion control, Honeywell, DCS, steady-state optimization control. The energy provided by a power plant mainly comes in the form of electricity and heat. Typically, steam is generated by the boiler, a portion of which is supplied to the turbine for power generation, and the other portion is directly supplied to users as heat. Regardless of the final form of energy provided, the boiler load is always changing. The load includes both electrical and thermal loads. In recent years, various control methods have been adopted both domestically and internationally to solve the problem of optimal control of the boiler combustion process. Although these methods improve thermal efficiency to a certain extent, they cannot completely solve the control problem of boiler combustion because it is difficult to establish an accurate mathematical model of the controlled object [1-2]. Manual adjustment of boiler operation based on load changes is still necessary to keep the boiler combustion process in a relatively balanced state for more time, thereby improving combustion efficiency. To achieve this goal of improving combustion efficiency, a distributed control system using the Honeywell S9000 system is a good solution. This system establishes a monitoring system for the boiler, turbine, power grid, and heating network, enabling comprehensive monitoring of the system's status. The system can store monitoring data in a management database, allowing operators to quickly and accurately understand the system's operating status, and enabling managers to analyze the operating conditions and make production management decisions. By implementing automatic control of some key process variables, the entire system can operate completely and effectively throughout the entire process. Based on this, a steady-state parameter optimization model is established for the boiler combustion system, which has a significant impact on energy saving, and the steady-state optimization model parameters are obtained. Guided by this optimization result, boiler combustion optimization control can be implemented. 1. Monitoring System for Boiler, Turbine, Power Grid, and Heating Network Operating Parameters Based on Honeywell DCS The Honeywell modular automation control system is a small-to-medium-sized control system that falls between large distributed control systems and single-loop controllers/programmable controllers. The S9000 system is an excellent system based on the 9000 series multi-loop controllers. It integrates all major control hardware into a single, user-friendly and efficient unit, realizing loop control, logic control, data acquisition, and operator interface functions. Honeywell's network communication capabilities provide flexibility for an open system. Operators/engineers and process controllers are connected via an Ethernet network based on the TCP/IP protocol, allowing them to exchange information and communicate with the upper-level plant-level computer. This open system communication platform facilitates the establishment of management-level applications, enabling information exchange with upper-level plant computer system resources and providing real-time access to system-wide information. This important feature enhances the user's ability to make rapid and effective decisions. Therefore, the Honeywell S9000 system is used to monitor the operating parameters of the power plant's turbines, boilers, power grid, and heating network, displaying real-time data, historical trend graphs, and fault alarms on four monitoring screens. The main monitoring parameters for steam turbines include: speed, power, main steam temperature, pressure before main steam valve, pressure after main steam valve, steam flow rate, cumulative steam flow rate, extraction steam pressure, cumulative extraction steam flow rate, extraction steam temperature, extraction steam flow rate, exhaust vacuum, subcooling, exhaust steam temperature, and condensate temperature. The main monitoring parameters for boilers include: drum pressure (controlled), main steam pressure (controlled), feedwater pressure, main steam flow rate, feedwater flow rate, flow rate before desuperheating water, flow rate after desuperheating water, drum water level (controlled), furnace negative pressure (controlled), furnace temperature, furnace outlet temperature, and oxygen content. The main monitoring parameters for the boiler combustion system include: left pressure of the low-temperature preheater, right pressure of the low-temperature preheater, left pressure of the high-temperature preheater, right pressure of the high-temperature preheater, primary air pressure (controlled), secondary air pressure, fuel oil flow rate, return oil flow rate, fuel oil pressure, exhaust steam temperature, fuel oil temperature, induced draft fan opening, induced draft fan current, forced draft fan opening, forced draft fan current, coal feeder current, and coal feeder speed. The main monitoring parameters for the power grid include: voltage, current, and active power of each turbine; grid current, voltage, active power, and reactive power. The main monitoring parameters for the heating network include: steam flow rate and steam pressure of major users. 2. Optimization of Steady-State Parameters of the Boiler Combustion System The state of the boiler combustion system directly determines the energy utilization rate, and whether the boiler's steady-state operation is optimized plays a crucial role in the combustion system. To ensure efficient system operation, two measures can be taken: first, adopting an automatic control system to ensure long-term stable operation; second, ensuring the optimal steady-state state of the system by optimizing the steady-state operating parameters of the boiler combustion system. 2.1 Optimization Model and Solution Research and practical experience in fuel combustion and thermal control show that maintaining a reasonable coal-to-air ratio can improve boiler thermal efficiency; controlling the induced draft volume to match the forced draft volume, ensuring a suitable furnace negative pressure, can prevent thermal efficiency reduction caused by flameout or air leakage. The greatest energy-saving effect and the least environmental pollution are achieved when combustion efficiency is highest and heat loss is lowest. Therefore, ensuring the combustion process operates in the optimal combustion zone to achieve maximum thermal efficiency is the fundamental task and challenge of combustion control. The operating characteristics of coal-fired chain grate boilers indicate that the quality of the combustion process mainly depends on the coal bed thickness, chain speed, and the reasonable control of forced and induced draft volumes. Therefore, an optimization model is constructed. The main inputs are forced draft volume, induced draft volume, and coal feed rate, while the outputs are oxygen content, furnace negative pressure, and main steam pressure. The objective function is to minimize energy consumption, and the decision variables are forced draft volume (forced draft damper opening), induced draft volume (induced draft damper opening), and coal feed rate. During the optimization process, the basic constraints of boiler operation must be met, namely, each decision variable must vary within a certain range, and the main steam pressure must be controlled within a given range. The optimization model is: min z=c1x1+c2x2+c3x3 (1) where yf_min 3. Real-time control system and its steady-state optimization The real-time control part is composed of the Honeywell system. In order to ensure the long-term stable operation of the system, the combustion control adopts the fuzzy control law. The system block diagram is shown in Figure 1. The main steam pressure control adopts the pressure control method; the air supply volume control ensures that the air supply pressure is within a certain range after the air preheating. Under the condition that the air supply pressure is allowed, the air supply volume is adjusted according to the air-coal ratio deviation to maintain the flue gas oxygen content within a certain range. The air-coal ratio changes according to the load change to achieve economical combustion; the induced draft volume control keeps the furnace negative pressure constant. Among them, the optimal air-coal ratio that changes with the load is obtained by calculating the boiler steady-state optimization program and adding actual experience. In terms of the selection of control algorithm, in order to ensure the stable operation of the control system, the fuzzy control algorithm is used. There are three forms of actual control action: (1) manual operation, in which case the reference control quantity follows the valve position signal change; (2) setting the deviation dead zone and the rate of change dead zone, when the deviation of the controlled parameter and its rate of change are within the dead zone range, it is put into automatic control according to the feedforward variable after being put into operation; (3) after the deviation or the rate of change of the deviation exceeds the dead zone, fuzzy control is performed. All control methods use weighted output when calculating the actual output, that is, calculated according to the following formula: Xc=Xco+KeXce+KcXcc+KfXt (3) Where, Xc is the control variable; Ke is the deviation weight; Kc is the rate of change weight; Kf is the feedforward weight; Xce, Xcc, and Xt are the control variables obtained by looking up the control table according to the deviation, rate of change, and feedforward variables, respectively. By setting the deviation dead zone and its rate of change dead zone, the system allows the controlled variable parameter to change within a certain range, thereby avoiding unnecessary frequent actions of the actuator; by using weighted output, the system can further set the weight table to handle different situations and improve the control quality. 4. Results of Steady-State Parameter Optimization of Boiler Combustion System The steady-state parameter optimization program for the boiler combustion system has the following functions: * Establishing a relationship model between the furnace negative pressure air supply volume, induced draft volume, coal feed volume, and main steam flow rate; * Establishing a relationship model between the flue gas oxygen content and the air supply volume, induced draft volume, coal feed volume, and main steam flow rate; * Establishing a relationship model between the main steam pressure air supply volume, induced draft volume, coal feed volume, and main steam flow rate; * Optimizing boiler steady-state parameters. Since its commissioning in April 2000, the boiler combustion steady-state optimization control system has operated stably and achieved significant energy savings. Experts have determined that the energy savings are as high as 4%. It has essentially eliminated black smoke emissions, reducing environmental pollution. This offline optimization program provides strong support for further understanding the boiler combustion status and improving operational efficiency; it is an easy-to-operate and easy-to-use program.