Henan Sanli Thermal Coal-fired Boiler Reform Ideas

To improve the environment and reduce pollution, Henan Sanli Thermal Energy is committed to transforming coal-fired boilers into boilers for the combustion of bio-energy (biomass solids molded fuel).

Henan Sanli's heat energy reconstruction project mainly uses the existing or idle chain grate coal-fired boiler body and boiler auxiliary equipment: blower, induced draft fan, slag discharger, economizer, reducer, dust collector, boiler control cabinet and Instrumentation valves, etc., increase 1-3 sets of screw-type biomass particle fuel feeders, 1 set of secondary air supply equipment, and secondary air supply tubes to reduce the investment cost of boilers and auxiliary equipment.

Coal-fired boilers used for production and domestic heating are mostly coal-fired boilers with a capacity of less than 4 tons. Henan Sanli Thermal Power Co., Ltd. reformed coal-fired boiler furnace, furnace arch, furnace wall, waste heat recovery, dust removal device, feeding system, control system, etc., and transformed the coal-fired boiler into a fully-automatic biomass boiler to increase the efficiency to 80. %-85%.

1. Analysis of Combustion Characteristics of Biomass Fuel

Biomass fuel is a renewable carbon source, characterized by huge production, widespread distribution, low*, low nitrogen, rapid growth, and low carbon dioxide emissions.

Biomass fuel combustion is mainly controlled by the following conditions: (1) a certain temperature; (2) a certain amount of air (oxygen); (3) the degree of mixing of fuel and air (oxygen); (4) flammable in fuel The material reacts violently with oxygen in the air.

The ignition temperature of biomass fuel is 250-400°C, which is lower than that of coal (the ignition temperature of coal is 400-500°C). The temperature increase is supplied by the ignition heat. The combustion process of biomass fuel is a process in which the volatilization and flammable components and the oxygen in the air are violently combined and the heat is released. Therefore, the supply of oxygen determines the combustion reaction process. By controlling the oxygen supply, the combustion reaction can be well controlled. If the structure of living and industrial boilers currently operating is directly used biomass fuel without modification, the boiler will experience serious black smoke, low efficiency, and dust pollution. Therefore, biomass-fueled fuel-fired boilers need to be equipped with special secondary air-supplying equipment to enhance the oxygen intake to enable it to fully burn, effectively increasing the furnace temperature, reducing the emission of carbon monoxide and soot, and the loss of heat.

2. Henan Sanli Thermal Energy Co., Ltd. to reform biomass boilers of coal-fired boilers

(1) Use of existing or idle chain grate coal-fired boilers and boiler auxiliary equipment: blowers, induced draft fans, slag dischargers, economizers, retarders, dust collectors, boiler control cabinets, instrumentation valves, etc. Boiler and ancillary equipment investment costs.

(2) The original coal used for coal fuel was changed into a closed biomass hopper, and an anti-tempering device was added.

(3) Install a set of biomass pellet fuel delivery, storage, and feeding devices.

(4) Install a set of screw-type biomass pellet feeder, and open an inspection hole at the uppermost position of the feeding pipe connected with the closed hopper at the top of the screw feeder, and install a limit switch on the spiral type. Feeder motor start, stop automatic control. When the screw feeder is installed, the feeding pipe must have a certain inclination angle with the ground conveying hopper. In order to save the floor space of the boiler room and meet the requirements of the process layout of the boiler room design specifications, the tilt angle of the feed pipe should be ≤60°. Spiral feeder installation shown in Figure 1.

(5) Install one set of secondary air supply equipment and secondary air supply pipe on the side of the boiler. One secondary air supply duct leads to the boiler hearth and one to the closed hopper to ensure sufficient oxygen for fuel combustion to achieve complete combustion. Secondary air supply equipment installation shown in Figure 2.

(6) Issues needing attention in boiler reconstruction

1 The net distance at the front end of the furnace must not be less than 3m. Because the screw feeder is installed, the distance between the ground transportation hopper and the front section of the boiler is 1.9m (take 2t/h coal grate boiler as an example). If it is less than 3m, it is not easy to operate and overhaul.

2 Biomass fuel should not be stored in the open air. It should be protected against rain, wind and corrosion. In addition, during the storage of biomass fuel, the temperature of the fuel must be checked frequently to prevent spontaneous combustion due to excessive temperatures.

3 advantages and disadvantages of biomass fuel boilers

3.1 advantages

(1) Biomass-fired boilers have stable combustion, rapid fire, high flame, fast air up, good running conditions, and high boiler thermal efficiency.

(2) Changing the conventional combustion method, the emission of NO x , fumes and nitrogen oxides is small, the burning rate of fuel is higher than that of coal, and the slag discharge is small.

(3) Biomass fuel is a renewable energy product, which is conducive to the implementation of national energy structure adjustment and energy conservation and environmental protection policies.

3.2 disadvantages

(1) Since the ignition temperature of biomass fuel is much lower than that of coal, the boiler cannot be pressured when it is temporarily stopped for a long time.

(2) When it is necessary to temporarily stop the boiler when receiving notifications of reducing steam consumption or suspending steam, the fuel on the grate must be burned out, and the slag must be discharged cleanly. Otherwise, the slag can easily be caused to ignite the fuel in the fuel tank.

4. Notes on the operation of biomass fuel boilers

From the perspective of the operation of biomass fuel boilers over the past three years, the following points should be noted when operating biomass boilers:

(1) Adjust the fuel supply of the screw feeder according to the actual fuel consumption during boiler operation.

(2) The fuel in the furnace is not burned out, and the drum and draft fan must not be stopped.

(3) When a sudden power outage occurs during operation, the fuel in the furnace must be removed in time.

(4) No biomass fuel may be added before the furnace is shut down.

(5) When the furnace is shut down, there is no need to seal the fire. After the fuel on the grate is exhausted, the drum and the induced draft fan may stop running.

(6) Due to the high content of alkali metals such as silicon, chlorine, potassium and sodium in the biomass fuel ash, the ash has a low melting point and is liable to slag, coke or deposit on the heating surface in the furnace, seriously affecting the combustion of the biomass boiler. The heat transfer can even cause corrosion and affect the operation of the boiler. Therefore, it is necessary to regularly clean the ash and ash in the hearth, folding room and smoke pipe.

5, cost analysis

The transformation of biomass fuel boiler is to use the original or idle chain grate coal-fired boiler body to transform, reduce the investment cost of the boiler body, and its auxiliary equipment such as blower, induced draft fan, slag discharger, economizer, reducer, Dust catchers, boiler control cabinets, instrumentation valves, etc. are the same as the chain grate coal-fired boilers.

Because the biomass pellet fuel is compressed and formed, it has large moisture content, high density, and low volatile matter overflow rate. It is not easy to ignite and burns black smoke. Therefore, to ensure that the biomass fuel is completely burned, the temperature of the furnace must be increased and fully supplied. oxygen. Therefore, some equipment needs to be added to increase the temperature of the furnace, so as to facilitate the rapid overflow of volatile components of the biomass fuel, ensure sufficient combustion of the biomass fuel, and maximize the thermal efficiency of the boiler.

The experience of reforming Henan Sanli thermal energy biomass boiler shows that biomass fuel boilers in Henan have to increase their operating costs by 30%-50% compared to coal boilers, which should be judged based on the age of use of boilers. The longer the boiler is used, the lower the energy efficiency and the larger the cost.

By transforming existing or idle coal-fired boilers into biomass-fired boilers, on the one hand, the amount of CO2 emissions can be reduced and the atmosphere environment can be effectively protected; on the other hand, investment costs for boiler coal and boiler equipment can be reduced. Although the operating cost of biomass-fired boilers is slightly higher than that of coal-fired boilers, it is still relatively low compared with the operating costs of gas-fired boilers, oil-fired boilers and electric boilers.

As a fuel for boilers, biomass fuel is an ideal fuel for natural gas, liquefied petroleum gas, electricity, coal, etc. It has a broad prospect of use, and has good social, economic and environmental benefits.