[align=left] 0 Introduction When Premier Wen Jiabao delivered the government report at the 10th National People's Congress on March 5, 2005, he emphasized the need to focus on the conservation and rational utilization of energy resources. Premier Wen said, "To alleviate the contradiction between China's energy resources and socio-economic development, we must base ourselves on domestic resources and significantly improve the efficiency of energy resource utilization." Announcement No. 65 of 2005, jointly issued by the National Development and Reform Commission, the Ministry of Science and Technology, and the State Environmental Protection Administration, listed the micro-oil cold furnace ignition technology for pulverized coal boilers as a technology encouraged by the state. The micro-oil cold furnace ignition and ultra-low load stable combustion technology uses a small amount of oil (20-40 kg/h) to ignite a large amount of pulverized coal (2-12 t/h) through a specially designed burner, thereby achieving the purpose of cold furnace micro-oil ignition, low load and ultra-low load stable combustion of boilers. The application of micro-oil cold furnace ignition technology in the No. 6 boiler of Taizhou Power Plant shows that the technology has the following significant characteristics: (1) The oil saving rate of cold furnace heating (coal instead of oil) can reach 97%, and the economic benefits are very significant. (2) Due to the use of multi-stage gas film cooling, the burner wall temperature does not exceed 400℃, and the reliability is high. (3) The micro-oil ignition logic design can ensure the safe operation of the boiler, and will not cause deflagration and secondary combustion, will not aggravate slagging in the furnace, and will not increase the combustibles in fly ash, and the safety is good. (4) The entire process of micro-oil ignition is automatically monitored and programmed, and the workload of operation is not increased. (5) There are no strict requirements for changes in parameters such as wind speed, coal powder concentration, and coal quality, and the adaptability is strong. (6) The system is simple, with basically no maintenance workload, and is convenient for production management. [b]1 Overview of Taizhou Power Plant No.6 Boiler[/b] Taizhou Power Plant No.6 Boiler is a SG-420/13.7-M415 type single steam drum natural circulation boiler produced by Shanghai Boiler Factory. The rated evaporation capacity of the boiler is 420 t/h, the rated steam temperature is 540℃, and a single intermediate reheat system is adopted. The original rated output of the unit was 125MW, and after the turbine flow modification, the rated output increased to 135MW. The pulverized coal burner is a tangentially arranged, direct-flow burner with four corners. The burner arrangement (from bottom to top) is: 2, 1, 1, 2, 1, 2, 2, 3, a total of 3 layers of primary air nozzles, 4 layers of secondary air nozzles, and 1 layer of tertiary air nozzles. The primary air nozzles are oscillating, and the secondary air nozzles have a large bellows structure. Burner design parameters are shown in Table 1. Two large oil guns are arranged at each corner, located in the lower and lower middle rows of secondary air nozzles respectively. The oil gun output is 900 kg/h, using 0# light diesel oil. The fuel oil is mechanically atomized at an atomization pressure of 3.5 MPa. 2. Micro-oil Cold Furnace Ignition Technology: Principle and Scheme Design 2.1 Micro-oil Cold Furnace Ignition Technology: Micro-oil combustion technology consists of a micro-oil gasification gun and a micro-oil cold furnace ignition burner. The working principle of micro-oil gasification combustion is to use mechanical atomization and a high-speed jet of compressed air to squeeze, tear, and break up the fuel oil, producing ultra-fine oil droplets, which are then ignited by a high-energy igniter. Simultaneously, the heat generated by combustion is cleverly used to heat the fuel oil, causing it to evaporate and gasify in a very short time. Because the fuel oil burns in a gasified state, the flame temperature can be greatly increased, and the combustion time can be drastically shortened. The flame after gasification combustion has a center temperature as high as 1800–2000℃. It acts as a high-temperature flame core to rapidly ignite primary pulverized coal in the pulverized coal burner. The cold furnace micro-oil ignition burner is shown in Figure 1. Its working principle is as follows: the high-temperature oil flame generated by the micro-oil gasification gun is introduced into the primary combustion zone of the pulverized coal burner. When the dense-phase pulverized coal passes through the high-temperature flame core of the gasification combustion, the temperature of the pulverized coal rises sharply, breaks and crushes, releases a large amount of volatiles, and quickly ignites and burns. The ignited dense-phase pulverized coal mixes with the dilute-phase pulverized coal in the secondary chamber and ignites the dilute-phase pulverized coal, realizing the staged combustion of pulverized coal. The combustion energy is amplified step by step to achieve the purpose of ignition and accelerating the combustion of pulverized coal, and significantly reducing the ignition energy required for the combustion of pulverized coal. In order to prevent the burner from burning out and slagging from occurring in the burner, multi-stage gas film cooling air is used to protect the nozzle safety. [font=SimSun] [img=499,188]http://eptchina.cn/files/article/14-2.gif[/img] [/font] 2.2 Micro-oil cold furnace ignition technology scheme design The modification scheme of No. 6 furnace is to modify the primary air nozzles of the bottom layer #1 and #3 corners into micro-oil ignition burners. The micro-oil ignition burner is used as both a cold furnace ignition burner and a main burner. This modification method can fully utilize the original powder feeding system of corners #1 and #3, including the powder feeder, primary air powder feeding pipeline and primary air online detection system, with a small amount of modification work. The micro-oil cold furnace ignition technology consists of a micro-oil cold furnace ignition burner, a micro-oil gasification gun and an auxiliary system. The auxiliary system mainly includes: oil system; compressed air system; air film cooling air system and automatic control system. (1) The main function of the oil system is to provide clean fuel for the micro-oil gun. Since the output of the micro-oil gun is very small, the size of the spray nozzle is very small. Therefore, the fuel needs to be cleaned and filtered to prevent fuel impurities from clogging the spray nozzle. (The design pressure of the micro-oil gasification gun is lower than that of the original fuel system. It needs to be depressurized on the basis of utilizing the original fuel pipeline.) In addition, an electric oil valve needs to be added to the micro-oil fuel system to realize program control operation. (2) The function of the compressed air system is to provide atomization power for the micro-oil gasification gun. (3) The function of the film cooling air is to prevent the burner from burning out at high temperature. The film cooling air is pressurized cold air, which is drawn out from the outlet of the blower. (4) The function of the control system is to realize the programmed operation of the micro-oil combustion technology, the safety protection and interlock of the furnace, and the acquisition and monitoring of process parameters (pressure, temperature, wind speed, etc.). 3 Test results of micro-oil cold furnace ignition technology 3.1 Calibration of micro-oil gasification oil gun output Since the amount of oil used by the micro-oil gun is very small after the adoption of micro-oil technology, the original fuel flow meter is inaccurate. Therefore, it is necessary to perform cold calibration of the output of the micro-oil gasification oil gun. The calibration method adopts the weighing method, that is, to measure the amount of oil injected by the micro-oil gun within a certain time, and then calculate the output of the micro-oil gun per hour. The calibration results are shown in Table 3. [font=SimSun] [img=489,167]http://eptchina.cn/files/article/14-3.gif[/img] [/font] 3.2 Boiler Start-up Process After Overhaul The No. 6 boiler at Taizhou Power Plant started up at 6:00 AM on December 11, 2005, after its overhaul. At 6:48 AM, the main oil guns of the No. 1 and No. 3 corner micro-oil ignition systems were put into operation (micro-oil pressure was 0.8 MPa, and the output of the two oil guns was 42 kg/h), and the micro-oil guns ignited successfully on the first attempt; at 7:10 AM, the No. 1 and No. 3 corner pulverizers were put into operation at a speed of 350 r/min. After the pulverized coal feeder was put into operation, the pulverized coal ignited instantly, and the flame temperature at the nozzle outlet of the micro-oil burner was 665–845℃. Considering the low air and furnace temperatures at the initial startup stage, which were not conducive to complete pulverized coal combustion, two auxiliary micro-oil guns were added at 7:30 AM (the total output of the main and auxiliary guns was 87.1 kg/h), and the pulverized coal feeder speed was increased to 400 r/min, achieving a nozzle flame temperature of 1000℃. By adjusting the pulverized coal feeder speed, the boiler's temperature and pressure increases could be smoothly controlled. Boiler #6 started up at 6:00 AM on the 11th. After completing all post-overhaul tests and troubleshooting, the boiler was put into normal production operation at 11 PM on the 18th under load. The startup after the overhaul primarily used the micro-oil burner, with a total of 10 micro-oil burners used, and ignition was generally successful on the first attempt. The micro-oil system was used for a total of 88 hours. Coal quality data during the cold start-up process are shown in Table 2. Pulverized coal fineness R90 = 20%–22%, R200 = 3.8–4%. 3.3 Micro-oil Combustion Adjustment Test 3.3.1 Influence of Primary Air Velocity on Micro-oil Combustion The primary air velocity has a significant impact on the ignition and combustion of pulverized coal in the micro-oil burner. Excessive primary air velocity will delay pulverized coal ignition; while insufficient primary air velocity can easily cause pulverized coal accumulation or even blockage in the primary air duct. Appropriate selection of the ignition primary air velocity is crucial for the stable combustion of the micro-oil burner. Maintaining the feeder speed at 350 r/min and the film air opening at 10%, the primary air velocity was varied, and the outlet flame temperature of the micro-oil burner was measured using a radiation pyrometer. The test data are shown in Table 4. [img=499,94]http://eptchina.cn/files/article/14-4.gif[/img] From the test data and flame observation results, the system operated normally during the process of increasing the primary air velocity from 20 m/s to 27 m/s. Although the flame temperature and combustion chamber temperature decreased slightly, the flame remained bright, and the pulverized coal combustion was stable. 3.3.2 Effect of Coal Feeder Speed ​​(Pulverized Coal Concentration) on Micro-Oil Combustion Experiments were conducted by varying the coal feeder speed at a primary air velocity of 24 m/s and a film cooling air opening of 10%. The test results are shown in Table 5. As the coal feeder speed increased, the outlet temperature of the micro-oil burner increased slightly. [font=SimSun] [img=520,102]http://eptchina.cn/files/article/14-5.gif[/img] [/font] 3.3.3 Effect of Film Cooling Air Opening on Micro-Oil Combustion The role of film cooling air is to protect the burner from burnout and slagging. We conducted tests on film cooling air and burner wall temperature under a higher boiler load (40MW). The test data are shown in Table 6. [img=397,132]http://eptchina.cn/files/article/14-6.gif[/img] Due to the reasonable design of the micro-oil ignition burner, the burner wall temperature is not high, which ensures that the burner does not burn out. 3.3.4 Temperature and Pressure Rise Rates During Startup The temperature and pressure rise rate control of the micro-oil cold furnace ignition burner has a greater advantage than that of the large oil gun. When using the large oil gun, due to the inflexible control of the oil quantity, each operation of the large oil gun leads to significant changes in the unit's fuel quantity, resulting in corresponding large changes in steam temperature and pressure. Micro-oil ignition startup, however, allows for a smooth increase in fuel quantity by adjusting the pulverizer speed, resulting in more gradual changes in steam temperature and pressure. Furthermore, no overheating occurred in the superheater or reheater wall temperatures during micro-oil ignition startup. The temperature and pressure rise curves for micro-oil startup are shown in Figure 2. The startup process is stable, easy to control, and fully meets the boiler startup requirements. 3.3.4 Pulverized Coal Combustion Efficiency During Micro-oil Cold Furnace Ignition Using micro-oil cold furnace ignition technology, pulverized coal is added immediately after the micro oil gun is put into operation. Since the furnace temperature and primary and secondary air temperatures are very low during cold furnace ignition, it is not conducive to the complete combustion of pulverized coal. Table 7 shows the measurement results of fly ash combustibles during startup. As can be seen, due to the reasonable burner design, the pulverized coal combustion efficiency reached 79% one hour after cold start-up; with the increase of operating time and the increase of furnace temperature and primary and secondary air temperature, the pulverized coal combustion efficiency gradually increased to 84.33% and 87.54%, respectively. Because the pulverized coal combustion is relatively ideal, even if a large amount of unburned pulverized coal accumulates on the tail heating surface during micro-oil ignition, secondary combustion on the heating surface will not occur. Of course, it is still necessary to blow soot from the tail heating surface in a timely manner during micro-oil start-up. [b]4 Economic Benefit Analysis of Micro-Oil Cold Stove Ignition Technology[/b] The entire start-up process of boiler #6 used micro-oil ignition technology, accumulating 88 hours of use. A comparative analysis of the economic benefits with the traditional large oil gun start-up process is shown in Table 8. The calculation results show that using micro-oil ignition technology for boiler #6 saves 1.15 million yuan in fuel costs compared to large oil gun start-up, demonstrating very considerable economic benefits. [font=SimSun] [b]5 Conclusions[/b] (1) The results of this commissioning show that the micro-oil ignition technology can easily, quickly and stably ignite pulverized coal in a cold furnace state, achieving coal-for-oil substitution and saving 97% of fuel. The ignition and start-up process after the overhaul of No. 6 boiler saved 308.6 tons of fuel oil and 1.15 million yuan in fuel costs. Practice shows that the micro-oil ignition system has a series of advantages such as low investment, simple system, and safe and reliable use, and the economic benefits are very considerable. It is a technology worthy of vigorous promotion and use. (2) When the feeder speed is maintained at 300-650 r/min and the primary air velocity is 20-30 m/s, the pulverized coal can be stably ignited in a cold furnace state, and the burner outlet flame temperature can reach 800-1000℃. The micro-oil ignition technology has a wide adaptability to primary air velocity and pulverized coal concentration. (3) In the initial stage of boiler startup, the film air can be closed or opened at a small degree. At this time, the burner wall temperature is generally below 300℃, and long-term operation will not burn the burner or cause coking. As the load increases, the opening degree of the film air can be adjusted appropriately to control the burner wall temperature. (4) The amount of fuel fed into the furnace can be flexibly adjusted by adjusting the speed of the pulverizer. Compared with the traditional large oil gun startup, it is more conducive to the control of the boiler's heating and pressure rise process. The superheater and reheater wall temperatures did not exceed the limit during the startup process. (1) During the micro-oil startup process, the pulverized coal combustion is relatively ideal. One hour after cold furnace ignition, the pulverized coal combustion rate reaches 79%, and three hours after startup, the pulverized coal combustion rate reaches more than 84.33%. The micro-oil ignition technology will not cause secondary combustion of the tail heating surface when the furnace is cold. References: (1) Report of Zhejiang Provincial Electric Power Research Institute, Report on the Micro-oil Cold Furnace Ignition and Ultra-low Load Stable Combustion Technology Transformation of Taizhou Power Plant No. 6 Boiler, 2005. (2) Hangzhou Zhejiang University Tianyuan Technology Co., Ltd., Taizhou Power Plant #6 Boiler Micro-oil Cooling Furnace Ignition and Ultra-low Load Stable Combustion Technology Retrofit Scheme, 2005. Chi Zuohe: Professor and Doctoral Supervisor at Zhejiang University, has long been engaged in research and engineering practice on low-pollution combustion, slagging, and low-load stable combustion of power plant boilers. He is the recipient of the first National Excellent Doctoral Dissertation Award, and has won one second prize of the National Science and Technology Progress Award, one third prize of the National Science and Technology Progress Award, one second prize of the Science and Technology Award of the Ministry of Education of China, one Science and Technology Award of Chinese Universities, one first prize of the Science and Technology Progress Award of the State Education Commission, one first prize of the Guangdong Provincial Electric Power Science and Technology Award, and many other awards. The pulverized coal rich-lean combustion technology he developed has been used in more than 100 boilers, and he has undertaken the National "863" and "973" projects.