Thread Content
The selection of plasma ignition and micro-oil ignition stable combustion technologies in coal-fired power plants mhtml:file://D:\Downloads\Combustion and Ignition Technologies\The Selection of Plasma Ignition and Micro-Oil Ignition Stable Combustion Technologies in Coal-Fired Power Plants – Technological Innovation – Modern Corporate Culture Network – Magazine “Modern Corporate Culture” WWW_XDQYWH_COM.mht! With the rapid and healthy development of China’s economy, there is a soaring demand for electricity. By the end of 2005, the installed capacity had exceeded 500 million kW, of which thermal power accounted for 75.6% of the country’s total installed capacity. Starting, stopping the unit, and maintaining stable combustion at low loads require a large amount of petroleum resources, with an annual fuel consumption of 13.22 million tons. By 2020, the installed capacity of coal-fired power generators in our country will reach 1 billion kW. Currently, international crude oil prices are rising steadily, reaching as high as $135 per barrel; therefore, controlling the fuel consumption of boilers has become an unavoidable reality for all coal-fired power plants. The traditional large oil gun ignition method can no longer meet the increasingly strained situation regarding oil resource supply; various oil-free or low-oil ignition technologies aimed at stable combustion and fuel savings, such as plasma ignition and small oil gun ignition techniques, are continually emerging. The plasma ignition and micro-oil ignition steady-combustion fuel-saving technologies not only help save fuel but also allow the electrostatic precipitator to be put into operation during ignition, offering good environmental benefits; they have thus been recognized by a wide range of users. This article will discuss and compare the advantages and disadvantages of the two stable combustion technologies to provide a reference for new unit construction and retrofitting of existing units. I. Plasma Ignition Technology (A) Working Principle of the Plasma Ignition System A direct current generates an arc under certain medium pressures, and under the control of a strong magnetic field, a directed flow of air plasma with stable power is produced. This plasma creates a local high-temperature core with a temperature of T>4000K in the ignition burner. When coal dust particles pass through this plasma \"core,\" their volatiles are rapidly released, further volatiles are generated, and the coal dust particles break apart, thereby enabling rapid combustion and achieving the purpose of ignition as well as accelerating the combustion of the coal dust. Plasmas contain a large number of chemically active particles, such as atoms (C, H, O), ions (O2-, H+, OH-), and electrons. They can accelerate thermochemical conversion and promote complete combustion of fuel. The plasma generator consists of a coil, a cathode, and an anode. The cathode and anode are made of special materials with high electrical conductivity, high thermal conductivity, and oxidation resistance, in order to withstand the impact of high-temperature arcs. The coil has the ability to resist DC high-voltage breakdown under high-temperature conditions. The power supply uses full-wave rectification and features constant current performance. Its ignition principle is as follows: under certain output current conditions, when the cathode moves forward and makes contact with the anode, the system enters a short-circuit state; when the cathode slowly moves away from the anode, an arc is generated, and this arc is pulled out of the nozzle under the influence of the coil’s magnetic field. Under the action of an arc, compressed air is ionized into high-temperature plasma, which then enters the burner to ignite the coal powder. The structure of the plasma burner is shown in the figure below: （II）Composition of the plasma ignition system The plasma combustion system consists of two main parts: the ignition system and the auxiliary systems. The ignition system consists of a plasma burner, a plasma generator, a power control cabinet, an isolation transformer, and a control system ； The auxiliary systems consist of a compressed air system, a cooling water system, an image flame detection system, and a primary air online speed measurement system, among others. (III) Technical Features 1. Antioxidant materials are used for the anode and cathode, allowing the plasma carrier to be air under compression, which is inexpensive and readily available; this reduces operating costs ； 2. The output electrical power can reach over 100 KW, the anode has a long service life (≥1000 hours), and it is suitable for use with various burners ； 3. The burner utilizes technologies such as staged combustion, gas film cooling, and rich-poor separation, which enable it to work with a wide range of coal types, require no special specifications regarding coal powder fineness, offer high output, are resistant to coking, wear-resistant, and have a long service life ； 4. The power supply and control unit employ a bus-based communication method, which facilitates switching. Two unit boilers can share one power supply while using separate operation interfaces, thereby saving significant initial investment and improving the utilization rate of the equipment. (IV) Application of plasma ignition for stable combustion and fuel savings technology in Huilai Power Plant’s 2×600MW units 1. Overview of the 2×600MW boilers at Huilai Power Plant. The boilers for the 2×600MW units in the first phase of Huidian Power Plant were designed and manufactured by Dongfang Boiler Factory. They are supercritical pressure once-through boilers with primary intermediate reheating, counterflow combustion across the front and rear walls, and a positive-pressure direct-fired coal grinding system using medium-speed coal mills. The designed coal type is Shenhua Huasheng coal, while the verified coal type is Shanxi North Shuozhou coal. The Yantai Longyuan plasma ignition and stable combustion technology is adopted. 2. Fuel-saving achievements of Huidian Power Plant’s 2×600MW units. During the pipe flushing process of Unit 1, advanced plasma ignition technology was employed, resulting in no fuel additives being used; this saved nearly 1,800 tons of fuel and led to direct cost savings of 10 million yuan. Actual operation has shown that the success rate of one-time activation of the plasma igniter is 99%. This system is safe and reliable, and zero fuel consumption was achieved throughout the trial operation period, making it both economical and environmentally friendly. At present, the coal source for the power plant is mainly Shenhua Huasheng coal, supplemented by Shanxi mixed bituminous coal. These coal types have good ignition and combustion properties as well as stable quality, which are essential conditions for the successful application of plasma ignition and stable combustion technologies at Hui’an Power Plant. II. Micro-oil ignition and stable combustion technology (A) Working principle of the micro-oil ignition burner The micro-oil burner consists of an oil combustion chamber, a primary pulverized coal combustion chamber, a secondary pulverized coal combustion chamber, and a tertiary pulverized coal combustion chamber. This burner enables safe and stable ignition, and it can also function as a main burner, maintaining the original performance of the main burner. Schematic diagram of the micro-oil coal powder burner structure: Working principle of the micro-oil burner: The micro-oil nozzle vaporizes and ignites the fuel within the micro-oil combustion chamber; the resulting high-intensity flame enters the primary combustion chamber of the burner, where it mixes with the stream of coal powder that has entered this chamber. A vigorous chemical reaction takes place, during which the coal powder breaks down and releases large amounts of volatiles, which are then ignited. The ignited coal powder flame moves along with the air flow to the secondary combustion chamber, where it ignites the stream of coal powder that has entered there. This process continues sequentially to the tertiary combustion chamber, enabling staged combustion and gradual increase in energy. In the end, the vast majority of the coal powder is ignited, resulting in a coal powder flame at approximately 1200°C at the outlet of the burner. (II) Composition of the micro-oil system The micro-oil system consists of three main components: the micro-oil ignition system, the primary air heating system, and the control system. The micro-oil ignition system consists of a micro-oil supply pipeline, a compressed air pipeline, a micro-oil burner, combustion air for the micro-oil, as well as mechanisms for micro-oil ignition, flame detection, and monitoring of the furnace wall temperature ； The direct-blowing coal grinding system should also be equipped with a primary air preheating system ； The control system primarily incorporates the ignition system and the primary air heating system into local and remote DCS control, enabling both local and remote operation. This facilitates safe protection and interlocking for the boiler’s micro-oil ignition and combustion processes, ensuring the safe, stable, and reliable operation of the boiler. (III) Technical characteristics of micro-oil combustion 1. It significantly reduces the oil consumption during boiler startup and shutdown as well as during stable operation at low loads; the oil savings rate can exceed 95% ； 2. In the early stage of ignition, the coal powder burnout rate is high, reaching over 80% (for bituminous coal), and it enables effective control of black smoke emission during the initial ignition of a cold furnace. During the startup and shutdown phases of the boiler, electrostatic dust removal can be activated to meet environmental regulations ； 3. It has a wide range of coal adaptability, enabling it to achieve the capability of igniting coal powder through micro-oil combustion with an oil consumption of <250 kg/h per oil gun. For bituminous coal, it is generally sufficient to keep the rate at <80 kg/h (per oil gun) to meet the requirements of 600MW units ； For lean coal and anthracite, an oil gun with a capacity of 200 Kg/h is required ； 4. High-specification materials resistant to heat and wear are used, along with air film cooling technology, ensuring safe operation of the burner ； 5. The operating parameters of the micro-oil burner (coal powder concentration, primary air velocity) have a wide range of adjustable values: the coal powder concentration ranges from 0.2 to 0.8 kg of coal powder per kg of air, while the primary air velocity ranges from 20 to 32 m/s for bituminous coal, and from 18 to 24 m/s for lean coal and anthracite. Within these parameter ranges, the coal powder in the primary air can be ignited effectively ； 6. Significant fuel savings: the fuel savings rate is generally over 95% for bituminous coal, while it ranges from 70% to 80% for subbituminous coal and anthracite ； 7. Low initial investment, simple system, minimal renovation work required, high return on investment, and low operating and maintenance costs ； 8. All thermal signals from the micro-oil system can be sent directly to the DCS, where centralized scheduling and control are carried out; all operations and protections are implemented through the DCS. (IV) Application of micro-oil ignition and stable combustion technology in the renovation of Unit #2 (600MW) at Shanwei Power Plant in Guangdong 1. Overview of Unit #2 at Shanwei Power Plant. The boilers of the 2×600MW units at Shanwei Power Plant were designed and manufactured by Dongfang Boiler Factory; they are supercritical pressure once-through boilers with primary intermediate reheating, counterflow combustion in the front and rear walls, and a positive-pressure direct-fired coal grinding system using medium-speed coal mills. 2. Renovation content. By utilizing the micro-oil ignition and stable combustion technology provided by Hangzhou Yinen Energy Saving Technology Co., Ltd., the six burners corresponding to burner A in the lower layer beneath the rear wall of Boiler #2 were modified into micro-oil ignition pulverized coal burners. This approach enables the boiler to start up using micro-oil for cooling as well as to operate stably at low loads, while ensuring that the momentum and basic performance of the original main burners remain unchanged; moreover, these new burners also fulfill the functions of the main burners. Parameters of the micro-oil ignition gun: operating oil pressure of 0.5–2.5 MPa, with a output of 30–68 kg/h per gun. In direct-fired coal grinding systems, there is a problem where the cold air entering the mill cannot be dried during cold startup due to insufficient temperature of the hot air; this issue is resolved by using steam warmers to heat the cold air entering the mill. 2.4.3 Results of the renovation: (1) Without using large oil injectors, the boiler can employ micro-oil ignition technology to carry out the entire cold-start process, including temperature and pressure increase, turbine startup, and operation under load; this technology is also suitable for maintaining stable combustion at low loads in the boiler. . (2) The micro-oil burner can successfully ignite coal powder, producing a bright flame with stable combustion; during long-term operation, the wall temperature of the burner remains normal and coking does not occur. When the micro-oil gun is withdrawn simultaneously and the vaporized micro-oil burner operates as the main burner, under normal primary air flow rates, the corresponding coal feeding rate can meet the requirements for the boiler to operate at full load, thus satisfying the conditions for use as a main burner. (3) The rated operating parameters of the 6 micro-oil guns (1.5 MPa) result in a fuel consumption of only 300 kg/h, achieving a fuel savings rate of over 90%. III. Advantages and Disadvantages of Plasma Ignition and Micro-oil Ignition (I) Advantages of Plasma Ignition Technology 1. High fuel savings, and it is possible to achieve oil-free startup depending on the type of coal used. 2. It has the conditions to eliminate the oil system and establish a fully oil-free power plant. 3. Plasma arcs do not require air supply, and their diameter can be made relatively small. 4. There is a track record of over 400 boilers having been successfully installed. 5. The electrostatic precipitator can be put into operation during ignition, offering good environmental benefits. (II) Disadvantages of plasma ignition technology 1. Due to limitations in the generator’s power, the range of coal types that can be used is relatively narrow; it is more suitable for coals with high volatiles that ignite easily, such as bituminous coal. 2. The system is relatively complex, with too many interrelated factors (wind, water, electricity), and its stability and reliability still need further improvement. 3. The cost is high; each furnace costs over 4 million yuan. 4. High operating and maintenance costs; the cathode rod is guaranteed to last 50 hours, with a cost of around 1,200 yuan per rod ； The anode rod has a lifespan guarantee of 1,000 hours, and the cost per rod is approximately 10,000 yuan. 5. The coal combustion chamber uses gas film cooling, which imposes high requirements on this cooling method and can easily lead to slag formation in the combustion chamber. (III) Advantages of low-oil ignition technology 1. The system is simple and reliable; the small oil gun is similar to the conventional large oil gun system, making it easy for power plant maintenance staff to maintain and for operators to use. 2. The output of the oil gun is easy to adjust, allowing it to be used with various types of coal – bituminous coal, lean coal, and anthracite. It is also suitable for use in storage or direct-fired powder production systems. 3. Fuel savings of over 95% can be achieved. 4. The cost of system equipment is relatively low; the renovation cost for boilers that already have an oil system is not high, staying under 2 million yuan. 5. The coal combustion chamber uses gas film cooling, preventing slag formation in the chamber. 6. The electrostatic precipitator can be put into operation during ignition, offering good environmental benefits. (IV) Disadvantages of the low-oil ignition technology 1. Since the flow rate of the small oil gun is very low and the diameter of its nozzle is extremely small – usually only 1 mm – it is prone to clogging; this issue can be resolved by installing a fuel filter before the oil supply system. 2. Due to structural limitations, it is difficult to arrange small oil nozzles axially; therefore, ordinary air-atomized oil nozzles are generally used for axial arrangement at present. 3. The combustion of the small oil gun requires air supply, and its atomization needs a certain angle; therefore, the combustion chamber of the small oil gun must have a certain diameter, which increases the resistance of the coal powder burner to a certain extent. IV. Conclusion As society’s demand for crude oil continues to rise, this resource is becoming increasingly scarce. Whether from the perspective of energy conservation or environmental protection, coal-fired power plants must adopt oil-reduced or oil-free ignition technologies such as plasma ignition or micro-oil ignition to ensure stable combustion. We can decide to use plasma or micro-oil ignition and stable combustion technology based on practical factors such as the type of coal used, the site conditions, and costs. Given the instability of the coal types supplied to the plant, for units that already have a light oil system, adopting micro-oil ignition for stable combustion is a more reliable and economical option. Where there is a reliable coal supply with stable coal quality, and where the coal is of a type such as bituminous coal that has a high volatil content and is easy to burn, we can boldly eliminate the fuel system and adopt plasma ignition for stable combustion right from the start. 【References】 [1] Ma Guangping. A brief analysis of the plasma ignition and stable combustion system for 2×1950 t/h supercritical counterflow combustion boilers. Guangdong Electric Power, 2007, 20(11). [2] Jiang Zhoujin, Chen Huaan. Application and experimentation of gasified small oil gun ignition and stable combustion technology in 1025 t/h boilers. Power Equipment, 2006, 7(5). [3] Shen Mingde, Yan Zhuming, Xiong Kai, Zhou Qiaoming. Application of micro-oil ignition and stable combustion technology in 600MW supercritical units. Guangdong Electric Power, 2008, 21(1). 【Author’s Profile】 Wu Yaoquan (born 1971), male, engineer at Guangdong Yuehua Power Generation Co., Ltd.; research interests: boiler operation and equipment management.