Method for improving coal gas co-combustion proportion of coal and coal gas co-combustion boiler

Abstract

The invention relates to the technical field of coal-fired boiler multi-gas blending combustion optimization, and discloses a method for improving the coal gas blending combustion proportion of a coal and gas blending combustion boiler, which comprises the following steps: determining the lowest safety coal quantity operation boundary of the boiler under the coal gas blending combustion working condition; establishing a maximum coal gas blending combustion ratio model of the coal-fired boiler, wherein the model is used for determining the maximum coal gas blending combustion ratio under different loads and coal gas resource conditions; a maximum-proportion coal gas blending combustion stable combustion strategy is implemented, so that safe and stable operation of the boiler during high-proportion coal gas blending combustion is maintained; wherein the lowest safe coal quantity operation boundary is determined. The comprehensive coal gas blending combustion heat value of the coal-fired boiler can be obviously increased to 60% from 30% in the prior art. By means of the method, low-calorific-value blast furnace gas (BFG), high-calorific-value coke oven gas (COG) and other by-product gas generated in the steel production process are utilized to the maximum extent, and therefore the gradient utilization efficiency and the overall comprehensive utilization level of regional energy are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of coal-fired boiler co-firing optimization technology, and in particular to a method for increasing the co-firing ratio of coal and gas in coal-fired boilers. Background Technology

[0002] Against the backdrop of increasingly stringent energy structure transformation and environmental protection, the efficient utilization of industrial by-product gas is of strategic significance for achieving green and low-carbon development in the steel industry and ensuring stable economic operation. However, current self-owned power plant coal-fired boilers face significant bottlenecks in co-firing by-product gas, with the co-firing ratio generally low, typically limited to 20% to 30% of the total input calorific value. This constraint mainly stems from the following three technological limitations:

[0003] 1. The challenge of low calorific value of blast furnace gas to stable boiler combustion: The main component of blast furnace gas is carbon monoxide (CO), and it also contains inert gases such as nitrogen (N2). Its calorific value is significantly lower than that of coke oven gas and pulverized coal. When a large proportion of blast furnace gas is blended into the boiler, its inherent characteristics lead to a significant decrease in the furnace combustion temperature. This is not only extremely unfavorable for the stable ignition of pulverized coal, but also causes incomplete combustion of pulverized coal and a decrease in boiler efficiency. In extreme cases, it can even lead to boiler flameout, seriously threatening the safe operation of the boiler. At the same time, a large proportion of blast furnace gas blending will significantly increase the flue gas volume, leading to an imbalance in the air-to-smoke ratio, enhanced convective heat transfer at the boiler tail, and an increase in exhaust gas temperature, affecting the normal operation of the bag filter at the boiler tail.

[0004] 2. Increased Temperature Field Changes in the Furnace When the Boiler Gas Blending Ratio Exceeds the Critical Value: When the blending ratio of boiler gas, especially blast furnace gas, exceeds the critical value of 30%, the temperature field distribution inside the furnace and the heat exchange temperature and pressure of the boiler's heating surfaces will undergo significant changes. This is mainly due to the differences in combustion characteristics between boiler gas and pulverized coal, as well as the stratified combustion design leading to localized low-temperature and high-temperature zones within the furnace, resulting in significant differences in flue gas volume. Localized high-temperature zones may cause severe coking and high-temperature corrosion on the heating surfaces, affecting boiler heat transfer efficiency, shortening component lifespan, and increasing the frequency of shutdowns for maintenance. Localized low-temperature zones, on the other hand, may lead to incomplete combustion and exacerbate chemical corrosion.

[0005] 3. Minimum Safe Coal Quantity Boundary for Coal-fired Boilers: Blast furnace gas, as a low-calorific-value fuel, inherently exhibits poor combustion stability, a high ignition point, and difficulty in maintaining stable combustion under low-load conditions. This differs fundamentally from pulverized coal in ignition, combustion speed, and flame morphology, posing a severe challenge to the overall stability of the flame within the furnace. Therefore, sufficient coal input must be ensured to guarantee combustion safety during boiler operation with blast furnace gas co-firing. To achieve maximum gas co-firing, a minimum coal input boundary must be determined, referred to as the minimum safe coal quantity boundary value. This boundary serves as the foundation for ensuring safe and stable boiler combustion, addressing the risk of furnace flameout during periods of large or drastic fluctuations in gas supply. If the minimum safe coal quantity boundary value is high, the boiler needs to burn a larger amount of pulverized coal to meet safety requirements. Even with a large amount of by-product gas available for consumption, it cannot be utilized, directly compressing the space for gas co-firing and thus limiting the proportion of gas co-firing. This becomes a major bottleneck for increasing the total amount of by-product gas consumed and achieving higher energy utilization efficiency.

[0006] Currently, steel companies are generally facing a severe dilemma in the utilization of by-product coal gas. With the continuous release of steel production capacity, the total amount of by-product coal gas has far exceeded the upper limit of the conventional co-firing capacity of self-owned power plants, resulting in a large amount of by-product coal gas being forced to be directly discharged into the atmosphere through venting towers. This not only causes a huge waste of valuable energy and brings significant economic losses, but also exacerbates environmental pollution and carbon emission pressure due to the emission of residual harmful substances in the coal gas and the conversion of greenhouse gases (such as CO).

[0007] Given the limitations of traditional coal-fired boilers in co-firing, there is an urgent need to develop a method that can effectively achieve a large-scale and stable co-firing of coal gas in coal-fired boilers. This will be of great significance for the utilization of by-product coal gas in the steel industry, improving the economic efficiency of boiler operation (such as reducing coal consumption and saving fuel costs), and improving the environment (such as reducing greenhouse gas and pollutant emissions, and contributing to the achievement of carbon peaking and carbon neutrality goals). Summary of the Invention

[0008] This invention provides a method for increasing the blending ratio of coal and gas in coal-fired boilers to solve existing technical problems. It addresses the limitation on the blending ratio of industrial by-product gas in existing coal-fired boilers due to limitations in combustion stability and furnace temperature control.

[0009] To solve the above-mentioned technical problems, according to one aspect of the present invention, more specifically, a method for increasing the proportion of coal gas co-firing in a coal and coal gas co-firing boiler, comprising the following steps:

[0010] S1. Determine the minimum safe coal quantity operating boundary of the boiler under the condition of co-firing coal gas.

[0011] S2. Establish a model for the maximum gas blending ratio of a coal-fired boiler to determine the maximum gas blending ratio under different loads and gas resource conditions;

[0012] S3. Implement a strategy of co-firing coal gas at the maximum ratio to ensure stable combustion, so as to maintain the safe and stable operation of the boiler when co-firing coal gas at a high ratio.

[0013] Furthermore, in step S1, determining the minimum safe coal input boundary aims to precisely establish the minimum coal input required to maintain stable combustion in the boiler under co-firing conditions. Determining this boundary is the safety technical basis for high-proportion, high-efficiency co-firing of coal gas. Specifically:

[0014] S101. Minimum Coal Mill Operation Combination Mode Calibration: Under co-firing conditions in different boiler load ranges, comprehensive and in-depth output testing and precise calibration of the coal mill system are conducted to reduce the number of operating coal mills. This confirms the minimum number of coal mills required for boiler operation while ensuring stable combustion when a large proportion of coal gas is co-fired. This process fundamentally reduces unnecessary redundant coal mill output, directly lowers the coal mill system's own power consumption, and creates stable operating conditions for subsequent precise exploration of the minimum coal feed boundary.

[0015] S102. Determining the Minimum Coal Feed Rate Boundary for Coal-fired Boilers: Based on the calibrated "minimum coal mill combination" operating mode, the coal feed rate of the conveying coal mills is gradually reduced using a progressive method. During this process, a series of key safety indicators must be closely monitored, including the intensity of the flame detection signal, the stability of the main and reheat steam temperatures and pressures, and close attention to the coal mill's own outlet temperature, pressure differential, and other operating parameters to prevent mill blockage or coal shortage due to excessively low coal feed rates. Through multiple rounds of repeated tests and data verification across loads, the critical minimum coal feed rate curve for maintaining safe and stable combustion of the coal-fired boiler under different loads is finally accurately plotted. This critical value constitutes the "minimum safe coal feed rate boundary for coal-fired boilers," which minimizes the boiler's basic requirement for stable combustion of pulverized coal.

[0016] Furthermore, in step S2, the blast furnace gas and coke oven gas produced by the steel plant will change, thus dynamically altering the blending ratio of blast furnace gas and coke oven gas in the coal-fired boiler. Due to the different combustion characteristics of these two gases, a scientific and refined blending ratio model needs to be established to achieve the maximum blending ratio under different loads and gas resource conditions, serving as a practical tool to guide actual production operations. Specifically:

[0017] S201. Maximizing Blast Furnace Gas (BFG) Blending Ratio Model: This model primarily addresses typical operating conditions in steel plants where blast furnace gas is abundant. For each boiler load range, the model is established with the core optimization objectives of "maximizing BFG blending, minimizing COG usage, and maintaining coal quantity within safe limits." While maintaining stable boiler combustion, the BFG feed rate is gradually increased, while simultaneously and precisely adjusted to the pre-defined "minimum safe coal quantity boundary." Simultaneously, the COG feed rate, used for stable combustion and calorific value supplementation, is dynamically reduced to a safe and stable combustion level. Real-time monitoring of boiler furnace flame stability, temperatures of various heating surfaces, and emission concentrations of major pollutants (such as NOx and SOx) is conducted to establish an application model that uses boiler load as input variable and outputs the maximum allowable BFG blending rate, the minimum necessary COG auxiliary amount, and the corresponding minimum coal quantity. This model will guide operators to maximize the utilization of low-cost BFG while ensuring safety.

[0018] S202. Maximizing Coke Oven Gas (COG) Blending Model: This model is primarily applicable to operating conditions with surplus COG, aiming to fully utilize the high calorific value of COG. Similar experimental methods to those in Section 2.1 are employed, but the optimization objective shifts to "maximizing COG blending, maintaining coal quantity within safe limits, and supplementing with BFG." Given that COG is rich in H2 and CH4, its rapid combustion rate and high flame temperature significantly impact furnace combustion kinetics and the thermal NOx formation mechanism compared to BFG. Therefore, independent experiments and data calibration are necessary, with particular attention to controlling the highest furnace temperature to prevent coking and excessive NOx formation. Under the premise of ensuring stable combustion, furnace temperature within limits, and pollutant emissions meeting standards, the maximum COG blending amount corresponding to each load range is determined. The resulting optimized operating model will provide precise operational guidance for the efficient and safe utilization of COG by the boiler under different operating conditions, achieving flexibility in fuel use.

[0019] S203. Establish a dynamic monitoring coefficient for blast furnace gas blending ratio: To provide operators with a real-time, intuitive, and standardized quantitative indicator of gas utilization, an online monitoring coefficient based on total heat input is established. This coefficient uses a model maximizing both blast furnace gas and coke oven gas blending ratios as boundaries to guide operators in making reasonable gas operations. The formula for calculating this coefficient is defined as follows:

[0020]

[0021] Furthermore, in step S3, a maximum proportion of coal gas co-firing and stable combustion strategy is implemented to maintain the safe and stable operation of the boiler when a high proportion of coal gas is co-firing. Specifically:

[0022] S301. Coke Oven Gas (COG) Bottom-Level Stable Combustion Control Strategy: When co-firing a large proportion of blast furnace gas (BFG), the low calorific value of blast furnace gas is detrimental to stable boiler combustion. Utilizing the inherent high calorific value, high hydrogen and methane content, and rapid combustion speed of coke oven gas (COG), it is used as the core stable combustion fuel. Specifically, coke oven gas is introduced into the bottom zone of the boiler furnace combustion area through a dedicated burner. Taking advantage of COG's rapid ignition and high heat release characteristics, a stable high-temperature flame core area is formed below or inside the main combustion zone. This high-temperature core effectively compensates for the decrease in overall furnace heat load and weakened flame stability caused by reduced pulverized coal input (to achieve a high proportion of coke oven gas co-firing). By providing a continuous and strong auxiliary heat source, this strategy ensures stable ignition and continuous combustion of the pulverized coal flame, preventing flame detachment or extinguishment, thus providing a solid guarantee for the safe and stable operation of the boiler under high-proportion coke oven gas co-firing conditions.

[0023] S302. Precise Oxygen Control Strategy: Precise control of oxygen levels in the furnace is crucial for achieving efficient and clean combustion in boilers operating with a high proportion of blended coal gas. Unlike standard blending or all-coal operation, blast furnace gas (BFG) and coke oven gas (COG) are gaseous fuels that burn relatively quickly. With a high proportion of blended coal gas, the amount of coal is less. Therefore, this invention employs an oxygen control strategy. By real-time monitoring of the oxygen content in the flue gas at the furnace outlet or economizer inlet and the CO concentration at the boiler outlet, these are used as the main control variables. The strategy optimizes the boiler combustion oxygen curve and reduces the amount of air entering the furnace when the CO concentration at the boiler outlet is 0. The goal of this strategy is to ensure complete combustion of the fuel (pulverized coal and blended coal gas) to avoid efficiency losses due to incomplete combustion, while also avoiding the introduction of excessive air. Excessive air not only removes additional heat from the boiler, leading to increased flue gas temperature and reduced boiler thermal efficiency, but also increases the power consumption of the induced draft fan. Furthermore, excessively high oxygen levels may exacerbate the formation of thermal nitrogen oxides (NOx). Therefore, by precisely adjusting the total air supply, the oxygen content in the furnace can be controlled within the optimal economic operating range, thereby achieving complete fuel combustion, minimizing heat loss, and synergistically controlling NOx emissions, thus improving the overall economic efficiency and environmental friendliness of the boiler.

[0024] S303, Standby Mill Hot Standby and Rapid Start Control Strategy: This strategy provides the ultimate safety guarantee against abnormal fluctuations in fuel supply. When the boiler is operating at the minimum coal feed threshold, the system has minimal margin to withstand fuel disturbances. Therefore, a non-operating coal mill (usually adjacent to the operating mill) is placed in a "hot standby" state, maintaining the preheating temperature of the mill body and keeping its auxiliary systems, such as lubrication and hydraulic oil, running. The control system (DCS) incorporates rapid start logic, which is automatically triggered upon detecting emergency conditions such as a sharp drop or interruption in gas supply, a coal mill malfunction tripping, or a sudden change in boiler load command. The system will automatically complete a series of complex operations, including purging the standby coal mill, starting the coal feeder, laying bottom coal, and adjusting the hot air damper, putting it into operation in a very short time (e.g., 2-3 minutes). This rapidly replenishes the heat from the pulverized coal, stabilizes the boiler load, effectively prevents serious accidents caused by fuel interruption, and greatly improves the reliability and safety of boiler operation.

[0025] Furthermore, the method for increasing the proportion of coal gas co-fired in coal and gas co-fired boilers is applicable to subcritical or supercritical coal-fired boilers in self-owned power plants of large steel bases, wherein the coal gas includes at least one of blast furnace gas, coke oven gas, and syngas.

[0026] This invention provides a method for increasing the blending ratio of coal and gas in a coal-gas co-firing boiler. Compared with existing technologies, this method achieves the following advantages:

[0027] 1. This invention significantly increases the overall calorific value ratio of co-fired gas in coal-fired boilers from 30% in existing technologies to 60%. This means that by-product gases such as low-calorific-value blast furnace gas (BFG) and high-calorific-value coke oven gas (COG) generated during steel production can be utilized to the maximum extent, thereby greatly improving the cascade utilization efficiency and overall comprehensive utilization level of regional energy. This high proportion of co-firing not only effectively alleviates the excessive dependence of traditional coal-fired power generation on primary energy sources and reduces the demand for external fossil fuel procurement, but also builds an efficient energy recycling chain within integrated steel enterprises, promotes industrial symbiosis, and significantly reduces the overall carbon footprint, providing a solid energy guarantee for the sustainable development of enterprises.

[0028] 2. This invention significantly optimizes the fuel structure by prioritizing and maximizing the blending of by-product gas produced by steel enterprises, while precisely controlling the consumption of high-priced pulverized coal to the minimum required for the safe and stable operation of the boiler. This optimized fuel ratio directly leads to a significant reduction in the total fuel cost of boiler operation, given that by-product gas typically requires no additional procurement costs, and its transportation, storage, and processing costs are far lower than those of coal. Furthermore, the reduction in coal consumption also means lower operating power consumption and maintenance costs for related auxiliary equipment (such as coal conveying and pulverizing systems), thereby bringing considerable economic benefits and stronger market competitiveness to enterprises. Simultaneously, it effectively mitigates the risks of external fossil fuel market fluctuations, enhancing the economic resilience of enterprise operations.

[0029] 3. This invention constructs a refined optimization model for the maximum coal gas blending ratio in coal-fired boilers and introduces a dynamic monitoring coefficient for the calorific value ratio of the coal gas fed into the boiler. These models and coefficients provide operators with real-time, scientific, and intuitive guidance on fuel proportioning, enabling them to flexibly and quickly adjust the fuel structure based on changes in boiler load, fluctuations in coal gas supply, and the calorific value characteristics of different coal gases to achieve optimal energy utilization. Furthermore, this optimization model can be deeply integrated into the boiler's distributed control system (DCS), thereby significantly improving the automation level of boiler operation and the response speed to load changes, effectively reducing human error, and ultimately improving overall operating efficiency and economy. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the main burner in this invention;

[0031] Figure 2 This is a schematic diagram of the precise oxygen control strategy in this invention;

[0032] Figure 3 This is a flowchart of the rapid start-up process for the standby coal mill in this invention;

[0033] Figure 4 This is a schematic diagram illustrating the actual coal gas blending ratio in this invention. Detailed Implementation

[0034] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figures 1-3 As shown, this case study focuses on a subcritical 350MW co-fired gas boiler at a self-owned power plant in a steel base. Due to a planned shutdown for maintenance, the plant's No. 2 boiler unit experienced a significant surplus of blast furnace gas (BFG) and coke oven gas (COG), posing a substantial risk of venting and energy waste. To address this issue, it was decided to apply the method described in this invention to No. 1 boiler to maximize the utilization of the surplus gas.

[0036] The implementation process is as follows:

[0037] Step 1: Determine the minimum safe coal consumption boundary for boiler operation.

[0038] Before applying this method, under normal operating conditions (coal gas blending with a calorific value ratio of approximately 30%), Boiler No. 1 typically required the operation of 3 to 4 coal mills, maintaining a total coal feed rate of 60-100 t / h to ensure stable combustion. To expand the scope of coal gas blending, a calibration test was first conducted on the minimum safe coal feed rate boundary of Boiler No. 1. While ensuring stable boiler combustion, the operation team gradually reduced the number of operating coal mills through refined combustion adjustments (such as optimizing the primary and secondary air ratios and adjusting the burner angle). The test confirmed that Boiler No. 1 could achieve stable combustion in all major load ranges using a combination of two coal mills.

[0039] Based on this "minimum coal mill combination," further coal reduction tests were conducted. Taking a 350MW full-load operating condition as an example, operators slowly reduced the coal feed rate of the two operating coal mills in very small increments. Simultaneously, the distributed control system (DCS) and flame monitoring system (FSSS) closely monitored a series of key safety indicators, including furnace pressure, steam temperature and pressure, furnace outlet oxygen content, and flame detection signal strength and frequency. After multiple rounds of repeated testing and verification, the minimum stable coal consumption boundary for Boiler No. 1 under different loads was finally determined. As shown in Appendix Table 1, at a 350MW load, its minimum safe total coal consumption is 52t / h.

[0040] Table 1 Minimum Safe Coal Quantity Boundaries

[0041]

[0042] Table 1 takes a subcritical 350MW co-fired coal gas boiler as an example. Its pulverizing system adopts a medium-speed mill positive pressure direct-fired hot primary air pulverizing system, and the boiler is equipped with 5 medium-speed coal mills.

[0043] Under normal operating conditions, when the coal gas blending ratio is 30% (calculated by calorific value), the coal feed rate needs to be maintained at 60-100 t / h to ensure stable combustion, which typically requires 3 to 4 coal mills to operate simultaneously. This method, while ensuring stable boiler combustion, gradually reduces the number of operating coal mills, ultimately exploring and determining an operating combination that achieves stable combustion with a minimum of 2 coal mills. Based on this, a comprehensive combustion performance test is then conducted to further reduce the coal feed rate.

[0044] During the experiment, key indicators such as furnace pressure, oxygen content, and flame detection signals were closely monitored. At the same time, it was ensured that the boiler could burn stably and safely under any operating conditions, and that the flue gas temperature did not exceed 160℃. Finally, the minimum stable coal consumption boundary of the boiler under this optimized operating mode was accurately determined.

[0045] Step 2: Optimize fuel ratio using the maximum gas blending ratio model.

[0046] Since the current operating conditions involve a large surplus of blast furnace gas (BFG), the "maximum blast furnace gas (BFG) blending ratio model" established according to this invention (as shown in Appendix Tables 2 and 3) serves as an operational guide.

[0047] Table 2 Model for Maximum Blast Furnace Gas (BFG) Blending

[0048]

[0049] Table 2, specifically for blast furnace gas surplus operation, establishes an application model with the core optimization objectives of "maximizing BFG blending, minimizing COG usage, and maintaining coal quantity within the safety boundary." This model uses the proportions of various boiler fuels as input variables and outputs the maximum allowable BFG blending, the minimum necessary COG stable combustion amount, and the corresponding minimum coal quantity. This model will guide operators to maximize the utilization of low-cost BFG while ensuring safety.

[0050] Table 3 Model for Maximum Blending of Blast Furnace Gas (COG)

[0051]

[0052] Table 3 focuses on the surplus coke oven gas operation, with the optimization objectives of "maximizing COG blending, minimizing BFG usage, and maintaining coal quantity within the safety boundary". Independent experiments and data calibration were conducted, with particular attention paid to the control of the highest furnace temperature to prevent coking and excessive NOx generation, and a corresponding optimized operation model was established.

[0053] Taking boiler No. 1 operating stably at a load of 350MW as an example, the operating steps are as follows:

[0054] Adjust coal quantity: Based on the calibrated minimum safe coal quantity boundary, the total coal feed of the two operating coal mills is precisely reduced and stabilized at 52t / h.

[0055] Adjust the gas flow rate: Referring to the parameters corresponding to the load in Appendix 2, gradually increase the blast furnace gas (BFG) feed flow rate to 320 kNm³ / h, and at the same time adjust the coke oven gas (COG) flow rate, which is used as stable combustion fuel, to 50 kNm³ / h.

[0056] Dynamic monitoring: During the adjustment process, operators used the "Dynamic Furnace Gas Blending Ratio Monitoring Coefficient (Kgas)" established by this invention for real-time online calculation and monitoring. Based on real-time gas calorific value and flow rate data, the gas blending calorific value ratio was confirmed to be stable at 62.6%, successfully exceeding the 60% target.

[0057] Step 3: Implement and maintain a stable combustion and safety strategy with the maximum proportion of coal gas blending.

[0058] Under high-proportion co-firing conditions, the following coordinated control strategies were strictly implemented to ensure the long-term safe, stable, and economical operation of the boiler:

[0059] Coke oven gas (COG) bottom layer stable combustion control: In accordance with strategy requirements, to cope with the impact of a large amount of low-calorific-value BFG on combustion stability, operators ensured the stable operation of the bottom layer A COG burner (as shown in the attached diagram). Figure 1 The system ensures stable operation of the blast furnace gas (as shown in the figure) and maintains its feed flow rate at 50 kNm³ / h (minimum operating flow rate is 20 kNm³ / h). The high-calorific-value COG forms a strong and stable high-temperature flame core between the blast furnace gas and pulverized coal combustion zone, effectively ensuring stable ignition and complete combustion of the BFG and pulverized coal, and preventing the risk of flameout.

[0060] Precise oxygen control: After blending with a large proportion of coal gas, the fuel characteristics undergo a fundamental change. Strict adherence to the optimized "precise oxygen control strategy" of this invention (as shown in the appendix) is crucial. Figure 2 (As shown). This measure not only ensures complete fuel combustion and avoids heat loss from exhaust gases due to excess air, but also effectively suppresses NOx formation, achieving a win-win situation for both economic and environmental benefits.

[0061] Standby coal mill hot standby and rapid start-up: Considering the extremely limited margin for fuel fluctuations when the boiler is operating at the minimum coal quantity boundary, one non-operating coal mill is set to "hot standby" status. Its main body temperature, lubrication station, and other auxiliary systems are all in operation or standby mode. Simultaneously, a "standby coal mill rapid start-up" interlock logic is preset in the DCS (as shown in the attached diagram). Figure 3 (As shown). Once a sharp drop in the main gas pipe pressure is detected or an emergency such as the coal mill trips, this logic will be automatically triggered. Within 3 minutes, a series of operations such as purging, starting and stopping, and coal feeding of the standby mill can be completed to quickly replenish the heat of the pulverized coal, thereby effectively preventing serious accidents such as boiler fireout due to fuel interruption and greatly improving the reliability of boiler operation.

[0062] Implementation results:

[0063] like Figure 4 As shown, by systematically implementing the above three steps, Boiler No. 1 successfully achieved a major operational breakthrough by maintaining a stable gas co-firing calorific value ratio exceeding 60% across multiple load ranges. See Appendix for details.Figure 3 Under high-proportion co-firing conditions, the boiler exhibits stable combustion, consistent parameters, and flexible adjustments, fully meeting the grid load dispatch requirements. During the entire overhaul of Unit 2, Boiler 1 became the primary source of surplus by-product gas from the steel plant, effectively preventing the waste of millions of cubic meters of gas that would otherwise have been directly released. This transformed low-value by-products into high-value electricity, resulting in substantial direct economic benefits for the company in terms of fuel costs alone. Furthermore, because the amount of pulverized coal was precisely controlled within the minimum safe limit, the operating load of the coal conveying and pulverizing systems was significantly reduced. This not only reduced the power consumption and mechanical wear of related equipment but also correspondingly lowered maintenance costs and spare parts consumption, resulting in significant overall economic benefits.

[0064] In conclusion, the success of this implementation case fully verifies the advanced nature, feasibility, and significant practical value of the method proposed in this invention. It demonstrates that this method is not merely theoretical but can be implemented in complex industrial settings, reliably and stably addressing industry pain points and providing steel companies with a complete and replicable systematic solution for the efficient and environmentally friendly utilization of by-product energy.

[0065] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for increasing the proportion of coal gas blending in a coal-gas co-firing boiler, characterized in that, Includes the following steps: S1. Determine the minimum safe coal quantity operating boundary of the boiler under the condition of co-firing coal gas. S2. Establish a model for the maximum gas blending ratio of a coal-fired boiler to determine the maximum gas blending ratio under different loads and gas resource conditions; S3. Implement the maximum proportion of coal gas co-firing and stable combustion strategy to maintain the safe and stable operation of the boiler when the proportion of coal gas co-firing is high. The determination of the minimum safe coal quantity operating boundary includes: calibrating the minimum number of coal mills required to ensure stable combustion of the boiler when co-firing coal gas in different load ranges; and, based on the minimum coal mill operating combination, determining the critical minimum coal quantity curve for maintaining safe and stable combustion of the boiler by gradually reducing the coal feed rate and monitoring safe operating parameters. The maximum coal gas blending ratio model for coal-fired boilers includes: a model for maximizing blast furnace gas blending ratio and a model for maximizing coke oven gas blending ratio; The maximum proportion of coke oven gas blending and stable combustion strategy includes: a stable combustion control strategy for bottom-level coke oven gas, a precise oxygen control strategy, and a backup and rapid start-up control strategy for standby mill heat.

2. The method for increasing the proportion of coal gas co-firing in a coal and coal gas co-firing boiler according to claim 1, characterized in that: In step S1, calibrating the minimum number of coal mills in operation includes: conducting coal mill system output tests and calibrations under co-firing conditions in different load ranges of the boiler, in order to reduce the number of coal mills in operation and confirm the minimum number of coal mills in operation required to ensure stable combustion.

3. The method for increasing the blending ratio of coal and gas in a co-fired boiler according to claim 1, characterized in that: In step S1, the safe operating parameters include at least one of the following: flame detection signal intensity, temperature and pressure of main steam and reheat steam, and coal mill outlet temperature and pressure difference.

4. The method for increasing the blending ratio of coal and gas in a co-fired boiler according to claim 1, characterized in that: The optimization objective of the maximizing blast furnace gas blending ratio model is to maximize the amount of blast furnace gas blended, minimize the amount of coke oven gas used, and maintain the coal quantity at the minimum safe coal quantity boundary while maintaining stable combustion in the boiler.

5. The method for increasing the blending ratio of coal and gas in a co-fired boiler according to claim 1, characterized in that: The optimization objective of the model for maximizing the coke oven gas blending ratio is to maximize the coke oven gas blending amount and maintain the coal quantity at the minimum safe coal quantity boundary, while maintaining stable boiler combustion, controlling the highest furnace temperature, and ensuring that pollutant emissions meet standards.

6. The method for increasing the blending ratio of coal and gas in a co-fired boiler according to claim 1, characterized in that: The method for increasing the blending ratio of coal and gas in a co-fired boiler also includes establishing a dynamic monitoring coefficient Kgas for the blending ratio of the incoming gas, the calculation formula of which is:

7. The method for increasing the blending ratio of coal and gas in a co-fired boiler according to claim 1, characterized in that: The coke oven gas bottom-level stable combustion control strategy includes: introducing coke oven gas into the combustion zone of the furnace through a dedicated bottom-level burner to form a stable high-temperature flame core zone.

8. The method for increasing the blending ratio of coal and gas in a co-fired boiler according to claim 1, characterized in that: The precise oxygen control strategy includes: real-time monitoring of flue gas oxygen content at the furnace outlet or economizer inlet and carbon monoxide concentration at the boiler outlet, thereby optimizing the boiler combustion oxygen curve and controlling the furnace oxygen content within an economical range that ensures complete fuel combustion while minimizing flue gas heat loss and nitrogen oxide generation.

9. The method for increasing the blending ratio of coal and gas in a co-fired boiler according to claim 1, characterized in that: The standby coal mill hot standby and fast start control strategy includes: placing a non-operating coal mill in hot standby state and pre-setting fast start logic in the control system; When a gas supply interruption, a coal mill malfunction, or a sudden change in load command is detected, the logic is automatically triggered to start the standby coal mill within a set time.

10. The method for increasing the blending ratio of coal and gas in a coal-gas co-firing boiler according to any one of claims 1-9, characterized in that: The method for increasing the proportion of coal gas co-fired in coal and gas co-fired boilers is applicable to subcritical or supercritical coal-fired boilers in self-owned power plants of large steel bases, wherein the coal gas includes at least one of blast furnace gas, coke oven gas and syngas.

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