Microoil ignition system for pulverized coal boiler

1. Overview

After years of research and ignition tests on fuel and coal burners, engineering and technical personnel from Xuzhou Jieneng Electric Power Equipment Co., Ltd. have summarized theoretical and practical experience in boiler combustion, applied high-efficiency intensified combustion technology to boiler pulverized coal ignition, and developed the "XWY pulverized coal boiler micro oil ignition" technology, achieving normal startup and low load stable combustion of the boiler under low oil consumption.

The micro oil ignition system is applied to coal-fired boilers in industries such as electric power, steel, metallurgy, and petrochemical industries. It can ignite bituminous coal, lignite, lean coal, and blended coal, and can save a large amount of oil for start-up, stable combustion, and new unit commissioning, resulting in significant economic and environmental benefits.

2. Technical Principles

The oil burner is inserted into the center of the pulverized coal burner with a certain distance from the nozzle. The oil flame that undergoes high intensity combustion during ignition will instantly heat the primary air powder passing through the pulverized coal burner to the ignition temperature of the pulverized coal. The primary air powder mixture is impacted by the high temperature oil flame, and the volatile matter rapidly precipitates and starts combustion. The combustion of the volatile matter releases a large amount of heat, supplementing the heat consumed during this time. The primary air powder is continuously heated to a temperature higher than the ignition temperature of the coal type,  Thereby causing the carbon particles in the pulverized coal to start combustion, forming a high-temperature flare. This oil burner is developed from the high-pressure forced air and oil burner of an aircraft engine. It emits a high-temperature flame through graded forced air distribution. The flame surface temperature is measured at 1500 ℃, the center temperature is not lower than 1800 ℃, and the oil burnout rate is above 99%.

The output range of the oil burner is between 50 kg/h and 300 kg/h, and the types of coal that can be ignited include bituminous coal, inferior bituminous coal, lignite, lean coal, and blended coal; The combustion methods include tangential combustion at four corners of a DC burner, wall opposed combustion with a swirl burner, etc; The types of pulverizing systems include direct-fired pulverizing systems using medium speed mills, fan mills, and double inlet and double outlet steel ball mills, as well as intermediate storage pulverizing systems using single inlet and single outlet steel ball mills.

3. Composition of XWY Microoil Ignition System

The tiny-oil ignition system mainly includes: tiny-oil ignition oil burner, tiny-oil ignition pulverized coal burner, auxiliary system, control system, cold furnace startup and hot air preparation system, etc.

(1) The tiny-oil ignition oil burner mainly includes tiny-oil gun, ignition gun, flame detection device, air distribution cylinder, combustion cylinder, etc. The oil gun and ignition gun do not work in high temperature areas, and do not need to be equipped with advance and retreat devices, resulting in fast input speed. The burnout efficiency of the oil burner is as high as 99% or more. During the startup and shutdown stages, electric dust removal can be put into operation, which solves the environmental protection problems of the power station boiler during the startup and shutdown stages.

(2) The micro-oil ignition pulverized coal burner adopts a staged intensified combustion technology. The pulverized coal is first ignited in the central cylinder, and the amount of pulverized coal entering the central cylinder varies from 500 kg/h to 800 kg/h. This part of pulverized coal is stably combusted in the central cylinder, and a stable secondary pulverized coal ignition source is formed at the outlet of the central cylinder, which is gradually amplified to ignite a maximum amount of 12 t/h pulverized coal, forming a pulverized coal flare at the outlet of the burner. The ignited pulverized coal is used to increase the temperature and load of the boiler to achieve the purpose of saving fuel oil.

(3) Auxiliary systems mainly include fuel supply system, purging pipeline system, oil gun combustion air supporting system, pulverized coal burner wall temperature monitoring system, image flame monitoring system, etc.

The fuel oil supply system adopts a header pipe, which is led from the quick closing valve of the original boiler oil system header pipe. The fuel oil header pipe is equipped with a manual stop valve, filter, pressure gauge, and self operated pressure stabilizing valve. The operating pressure of the oil gun is 0.8 to 1.2 MPa, and the output is 50 to 100 kg/h for bituminous coal, 50 to 150 kg/h for lignite, and 150 to 300 kg/h for lean coal. The fuel main pipe is divided into various fuel branch pipes, which are equipped with manual stop valves, quick closing valves, filters, pressure gauges, metal hoses, etc. The purging medium for the fuel pipeline is compressed air, and the purging pipeline is equipped with manual stop valves, quick closing valves, pressure gauges, etc.

The oil gun combustion air system is designed to provide the necessary air for the full combustion of fuel. The oil and air distribution system adopts a header pipe, which is led from the outlet of the primary air fan, and the air pressure is greater than 4000pa. Electric regulating butterfly valves, backrest pipes, micro differential pressure transmitters, etc. are configured on the oil distribution air main pipe, and manual butterfly valves, bellows compensators, etc. are configured on the oil distribution air branch pipe.

In order to online monitor the wall temperature of the burner during operation and protect the burner from burning loss, two sets of armored thermocouples are installed at the high temperature position of each burner.

(4) The control system mainly includes local manual control and remote protection systems.

Design principles:

(a) Ensure the safety of the boiler during ignition; (b) Does not affect the normal operation of FSSS functions;

(c) Ensure the safety of ignition equipment during the ignition process; (d) The man-machine interface is clear and easy to operate.

Control system functions:

(a) Start and stop program control of micro oil burner; (b) Micro oil ignition fault record;

(c) Burner wall temperature monitoring, overtemperature alarm; (d) Interlock protection function, interface with FSSS.

Operation control mode:

(a) Adopt DCS operation mode;

(b) The micro oil ignition operation control is incorporated into the DCS system and becomes a part of the DCS control system. The control of micro oil ignition can be achieved on the DCS screen, which can facilitate the operation and management of operators;

(c) The tiny-oil ignition system is equipped with a local control cabinet, which is hardwired to the DCS.

(5) Cold furnace startup hot air preparation system: Any type of fuel saving ignition technology uses coal instead of oil to save fuel. The first issue to be addressed in the application of fuel saving ignition technology is to prepare pulverized coal that meets the requirements under cold furnace conditions. For intermediate storage pulverizing systems with adjacent furnace borrowing conditions, the method of borrowing pulverized coal from adjacent furnaces can be used to obtain pulverized coal. For direct blow pulverizing systems and intermediate storage pulverizing systems without adjacent furnace borrowing conditions, the following two schemes can be used to obtain the hot air required for starting the mill.

(a) Using an air duct burner to heat the primary air: The air duct burner is arranged in the elbow of the hot primary air header at the outlet of the air preheater, with a distance of more than 15 meters from the inlet of the coal mill. The output of the air duct burner is 200 to 300 kg/h. Using the air duct burner to heat the primary air, the temperature of the primary air reaches the temperature required for starting the mill, and the mill is started for pulverizing.

(b) Using a steam heater to heat the primary air: The steam heater mainly uses the heat released by converting saturated steam into saturated water to heat the primary air. The temperature that the primary air can reach mainly depends on the parameters of the steam (for example, 0.8MPa steam can only heat the primary air to 160 ℃).

4. Technical advantages

(1) Good adaptability of coal quality: it can ignite the flow of bituminous coal, lignite, lean coal, and mixed coal pulverized coal, meeting the ignition requirements of boilers of various capacity grades and furnace types.

(2) The oil saving rate of new unit commissioning and cold furnace startup can reach 75~90% or more depending on the coal type. Low equipment investment and short return period.

(3) The micro oil ignition pulverized coal burner is used as an ignition burner during ignition and as a main burner during normal operation, without affecting the aerodynamic field and organizational combustion during normal operation of the boiler.

(4) The applicable range for pulverized coal concentration is very wide (0.15~1.0), and the pulverized coal concentration can be adjusted according to the output of the coal mill and the needs of boiler temperature rise and pressure rise.

(5) The system itself has low energy consumption, simple structure, small on-site maintenance workload, and low operating costs.