[Weekly Topic] Discuss ways to save fuel when starting boilers (November 7th – November 14th)

1. Oil gun atomization: Select the appropriate atomizing element and adjust the pressure of compressed air or steam to achieve an optimal atomization effect with the oil gun. 2. The thickness of the bedding material has a direct impact on the amount of oil used: with thicker bedding, it takes longer to heat the material and for its temperature to rise, resulting in higher oil consumption ； The bedding is thin, resulting in uneven fluidization ； Based on practical experience, if there is ash returning to the ash return bin at the bottom of the cyclone separator during operation, it is advisable to use less bed material, with the bed thickness maintained between 600 and 800 mm. If no ash returns to that bin during operation, it is recommended to keep the bed thickness between 1000 and 1200 mm. 3. Control of fluidization air volume during ignition: Ensure proper fluidization of the bed material, and prevent poor fluidization or overheating-induced coking ； Ensure an adequate amount of air is available for the combustion of the ignition oil, with the excess air coefficient maintained above 1.2. 4. Adopt pulsating coal feeding: Feed coal at a rate of 10%~15% of the boiler’s full-load coal feeding rate; feed coal for 90 seconds, then stop feeding. After that, observe the changes in bed temperature and oxygen content to decide whether to feed coal again, and repeat this process until the boiler’s bed temperature reaches above 720°C.

1 Fuel savings during boiler startup. The startup of a power unit is a comprehensive process that requires close coordination among the steam turbine, electrical systems, and thermal control systems. Additionally, the condition of the equipment and the control of parameters during startup all have a significant impact on this process. Whether the boiler starts successfully plays a decisive role in determining the amount of fuel used for startup. Conduct the necessary tests and inspections prior to startup. 2. Before igniting the boiler, bottom heating should be activated in a timely manner. In units with a capacity of over 300 MW, a auxiliary steam system is generally installed, and bottom heating devices are provided on the boiler’s water wall. During the cold-start of the boiler, using auxiliary steam for bottom heating can effectively help to reduce startup time and save fuel. 3 Air volume control during boiler startup: The oil guns used in boilers typically generate a force of around 1 ton of oil per gun. When igniting the boiler, 4 oil guns are considered; their output is generally only about 5% of the boiler’s full load. The FSSS protection system in boilers is equipped with a low air volume protection feature – the MFT mechanism is activated when the ventilation volume in the furnace is less than 30%. Therefore, at the initial stage of ignition, the ventilation volume in the furnace is much greater than the amount of air required by the actual oil guns. This leads to two problems: first, when 1–2 oil guns are in use at the beginning of ignition, the flue gas temperature at the furnace outlet rises only slightly, usually around 150°C, resulting in significant heat loss and a slower increase in the boiler’s operating parameters ； Secondly, due to the low temperature in the furnace, the fuel does not burn completely, resulting in black smoke being emitted from the chimney and causing environmental pollution.

The last edit to this post was made by ffgh0123 on 2011-11-7 at 20:26. 1. Activate bottom heating in a timely manner before starting the boiler. When starting a cold boiler, first use steam from the high-pressure auxiliary header to activate bottom heating; control the amount of steam used for heating initially, and follow the specified conditions for increasing temperature and pressure, so as to ensure proper expansion of the boiler drum and tube metal. Once a certain temperature (60°C) is reached, the amount of air supplied can be increased, or steam at high temperature and pressure from an adjacent furnace (steam drawn directly from that furnace’s steam drum) can be introduced to accelerate the heating process. Once the wall temperature of the steam drum exceeds 100°C, it becomes easier to use oil for heating until the conditions for starting up the system are met, thereby **reducing the time required for oil heating**. Investing in bottom heating in a timely manner not only saves fuel but also has the following advantages: it increases the temperature of the furnace chamber ； Reduce startup time ； Eliminate the thermal stress caused by uneven temperatures, thereby preventing the weld seams from being damaged or cracked due to this thermal stress ； Stable combustion`. 2. Oil-to-air ratio during boiler startup Boiler manufacturers generally design the output of the ignition oil gun at 30% of the boiler’s full load. For a single ignition burner, the difference between the actual amount of oil sprayed by the oil gun and the theoretical amount required based on the air supply to the burner at the time of ignition is often around 50% of the actual oil spray volume. Most of the difference constitutes incomplete combustion losses, of which mechanical incomplete combustion losses account for the largest proportion. 3. Use of plasma ignition: By employing plasma ignition technology, not only can significant fuel savings be achieved in power plants, but three other benefits are also obtained: first, the operating costs associated with ignition in the power plant are reduced. Power plants that utilize this technology typically have ignition operation costs that are only 10% to 20% of those incurred with fuel-based ignition. The second is safety. It prevents fires and injuries at power plants caused by excessive storage and use of fuel. Third is environmental protection. It reduces the problem of black smoke emission and the release of harmful substances caused by the inability to use electric dust collectors for fuel ignition. It enables the ignition and stable combustion of power plant boilers while replacing the oil gun to inject fuel for combustion support. 　4. Start the coal grinder as early as possible during boiler startup. During the boiler startup process, once the temperature of the hot air reaches the conditions required to start the coal grinder, start it promptly. After it is started, keep four oil burners either at the upper or lower level of the coal grinder in operation. Increase the amount of auxiliary air adjacent to the coal grinder to ensure thorough mixing of the coal powder and the oil flame; at the beginning of coal feeding, the minimum amount of coal can be used, with this amount gradually increased according to the requirements for temperature and pressure rise. If the boiler is started from a cold state and connected to the grid by using oil guns to raise the temperature and pressure, along with medium-speed warming up, it will take at least six hours. Starting the coal grinder in advance allows for the use of 2–4 fewer oil guns, resulting in a fuel savings of over 10 tons. If further tests are conducted, it will take dozens of hours, and the amount of fuel saved in that case would be considerable. Adding powder in advance overcomes the constraint of adding it only after grid connection, **which reduces fuel consumption; it also enables faster load increase after grid connection. 5. Prevent oil leakage. Often during oil injection, leaks occur due to defects in the oil gun; when the oil gun is removed, it isn’t fully withdrawn and the oil valve isn’t actually closed, resulting in oil being sprayed into the furnace. Therefore, when inserting or removing the oil gun, it is necessary to check from the operation screen and on-site to confirm that the oil gun has been withdrawn fully and that the oil valve is airtight with no leaks.

Basic components of the micro-oil ignition system: 1) Micro-oil combustion unit. The micro-oil combustion unit is the core component of this system, and it consists of a high-energy micro-oil vaporization gun, an auxiliary oil gun, and a micro-oil burner. The high-energy gasification nozzle is mounted on the side of the burner, making it easy to remove and maintain. It has a simple structure without any moving parts; it includes a built-in flame detection system and a high-energy ignition device that enables accurate detection of the combustion status of micro-oil flames. When the type of coal changes, auxiliary oil nozzles can be used flexibly to adjust the flame intensity and ensure complete ignition of the coal powder. 2) The fuel system consists of a Φ22 stainless steel pipe that extends from the main fuel pipe in front of the boiler; this pipe passes behind the isolation door, circulates around the boiler, goes through two levels of filtering devices, and then reaches each micro-fuel injector via the fuel quick-shut valve. 3) Pressure cold air system: The pressure cold air is a system essential for providing the oxygen required for combustion in the micro-oil gun, as well as for regular purging and cooling. Depending on the specific conditions of the boiler, pressurized cold air can be supplied from the boiler’s primary air supply, or an additional fan can be installed to provide it. Pressure cold air parameters: pressure of 4–10 Kpa, air flow rate of around 3000 m3/h. 4) Control system: The micro-oil ignition control system consists of ignition control, flame detection, automatic protection, etc. This system supports local and remote control, with flexible switching capabilities. The ignition logic design complies with the boiler safety operation specifications, ensuring safety and reliability. The monitoring and control of the micro-oil system can be carried out using the existing DCS system, or it can be controlled independently with a PLC. Add control screens on the DCS to enable start/stop operations and monitoring of process parameters. 5) Online wall temperature monitoring system. To prevent the burners from being damaged due to overheating, each burner is equipped with wall temperature sensors, which transmit the temperature data to the control room for real-time monitoring via temperature-sensing elements. 6) When starting the boiler with a cold furnace in the coal grinding auxiliary system, to use coal instead of oil, it is necessary to resolve the issue of the source of coal powder. For the stored-grinding system, powder delivery from an adjacent furnace can be adopted. For the direct-fired grinding system, we adopt methods such as supplying hot air from an adjacent furnace, installing warm air heaters, heating the air ducts, or directly using a large oil gun to warm the furnace to start grinding, depending on the specific circumstances. The small oil gun plasma ignition heater is a specialized device used for heating air in the cold-start ignition system of boilers. It features high heating efficiency, rapid temperature rise, compact size, and low wind-side assistance, and can be installed on main pipelines as well as bypass pipelines. The specifications include various models such as those with 200,000, 600,000, 300,000, and 1 million units.

We have completely switched to using methanol for ignition; the heating up and startup of one circulating fluidized bed furnace, as well as the routine standby operation of three coal powder furnaces, all rely on methanol (impure alcohols can also be used). According to the manufacturer that supplied us with the furnace (a circulating fluidized bed) – Zhengzhou Furnace Lining – we are the first to use methanol for furnace drying. We rely on what we produce; we manufacture methanol. How to save fuel? The key is to maintain an appropriate oil-to-gas ratio and use energy-efficient nozzles.

This post was last edited by wjx@chth on 2013-9-10 15:02. Do you use methanol for starting up your coal powder furnaces and for assisting combustion at low load levels? Which company makes the burner? Thank you

Yes, Nanjing Wanhe Boiler Parts Co., Ltd

What is the capacity of your boilers? We are 220t/h high-pressure boilers. Does burning methanol have any negative effects on the furnace? Thank you

We are 240T circulating fluidized bed boilers; methanol is used for starting up and heating the boiler, and we believe there are no negative effects. If the furnace temperature during the initial heating is lower than that in the case of diesel heating.

What is the capacity of your coal powder furnace, and is methanol also used to start it up?