The grate is the core combustion transmission and distribution component of the biomass boiler, which directly affects the boiler's thermal efficiency, operational stability and environmental emission effects. Compared with traditional chain grates, reciprocating grates can dynamically stir fire, break fuel hardening, and adapt to various types of biomass impurities. They are the mainstream supporting equipment for industrial heating and biomass boilers. Due to unreasonable model selection and improper adaptation to working conditions, many companies frequently suffer from problems such as insufficient combustion, coking and ash blocking, rapid grate wear, and excessive smoke exhaust. This article combines practical experience to simplify and sort out the key points of reciprocating grate selection and working condition adaptation skills to help the equipment operate efficiently, low-carbon and stably.
1. Core operating advantages of biomass reciprocating grate
The reciprocating grate is composed of fixed and movable grate pieces. It is driven by mechanical or hydraulic reciprocating motion to automatically complete processes such as fuel transportation, turning and loosening, and burning ash and slagging. It is highly adapted to the combustion characteristics of biomass fuel with high volatile content, large calorific value fluctuations, and easy hardening.
Its core advantages are significant: first, it has wide fuel compatibility and is compatible with wood chips, straw, biomass pellets, agricultural and forestry waste materials, etc., and can withstand high-humidity fuels with a moisture content of 20%-30%, breaking through the limitations of ordinary grates that are only suitable for homogeneous fuels; second, combustion efficiency The efficiency is higher. The reciprocating kneading structure can break the fuel hardening, optimize ventilation conditions, fuel combustion is more complete, and the thermal efficiency is 3%-5% higher than that of the chain grate. Third, the operation and maintenance cost is lower. Automatic fire and slag removal reduces manual operation and maintenance. The wear-resistant structure can adapt to long-term continuous production conditions.
2. Core points of accurate selection of biomass-specific reciprocating grates
Accurate selection is the basis for the stable and efficient operation of the grate. It needs to be matched with the four core dimensions of boiler tonnage, fuel characteristics, driving mode, and material performance to avoid incompatibility issues with working conditions.
1. Match the boiler tonnage and grate parameter specifications
The grate inclination, stroke, effective area, and operating frequency need to adapt to the boiler tonnage. Small boilers of 1-6t/h are suitable for 6° left and right inclination, 130mm short-stroke grate, the operating frequency is controlled at 8-12 times/min, and are suitable for light and finely crushed fuel; large and medium-sized boilers above 10t/h need to use a combined grate with a large effective area and adjustable stroke to ensure that the fuel is fully burned and to eliminate the problem of excessive carbon content in the slag. At the same time, a special grate with a large width and uniform ventilation slot needs to be selected to meet the combustion needs of the biomass boiler with low pressure and large air volume.
2. Select the drive mode as needed
The mainstream drives on the market are divided into two categories: mechanical crank drive and servo motor direct drive. The mechanical crank drive has a simple structure, low failure rate, transmission efficiency of over 92%, high cost performance, and is suitable for working conditions with homogeneous fuel and stable load. The disadvantage is that the parameters cannot be dynamically adjusted. The direct drive of the servo motor has high precision and fast response. It can be adjusted in real time and is suitable for complex working conditions with mixed fuel and large load fluctuations. It also has energy saving effects and is suitable for highly automated production scenarios.
3. Focus on grate material and wear resistance and high temperature resistance
Biomass combustion involves high-temperature oxidation, dust abrasion and slight corrosion. The grate material determines the service life of the equipment. The special reciprocating grate is preferably made of high chromium alloy and heat-resistant and wear-resistant cast iron, which can withstand high temperatures of 1100°C, is resistant to coking, deformation, and wear, and can operate stably for a long time. Ordinary low-quality cast iron grates are prone to high temperature deformation, material leakage and air leakage, which will cause combustion disorders and increase operation and maintenance costs, and must be resolutely avoided.
4. Customized structure to adapt to fuel characteristics
The grate structure needs to be customized according to the fuel form: high-humidity large wood chips and straw fuel, use deep grooves and large ventilation grates to strengthen turning and accelerate dehydration. Avoid accumulation and smoldering; for fine sawdust and powdered fuel, choose a dense-toothed grate to reduce material leakage loss and slow down the overheating speed; for inferior fuel containing sand, soil and impurities, choose a thickened, wear-resistant, anti-blocking structure grate to prevent equipment jamming and damage.
3. Reciprocating grate adaptation and optimization skills under different working conditions
After reasonable selection, dynamic parameter adjustment for different operating conditions can further improve combustion efficiency, reduce energy consumption, and adapt to various production scenarios.
1. High-humidity fuel conditions (moisture content 20%-30%)
High-humidity fuel with a moisture content of 20%-30% is prone to delayed ignition, accumulation and slagging. Adaptation skills: Reduce the operating speed of the grate, extend the fuel preheating and drying time; increase the primary air volume, strengthen bottom ventilation, and use secondary air turbulence to increase the temperature of the front section of the furnace, accelerate the ignition of wet fuel, and avoid incomplete combustion and tail slagging.
2. Finely crushed powder fuel conditions (wood chips, straw powder)
Wood chips and straw finely crushed powder are easy to harden, and the fly ash contains high carbon content. Adaptation skills: Adjust the grate frequency to 1-3 times/min to slow down the fuel delivery speed; use the reciprocating action of the grate to loosen the material layer and prevent heat accumulation and hardening; reduce the primary air speed, strengthen the secondary air turbulence, and extend the residence time of the fuel furnace to more than 3 seconds to fully burn the embers and reduce losses.
3. Load fluctuation conditions (frequent starts and stops, load fluctuations)
Frequent starts and stops, and load fluctuations can easily lead to unstable combustion and reduced thermal efficiency. Adaptation skills: reduce the grate stroke, reduce frequency and material at low loads, and fine-tune the air distribution to maintain a constant temperature in the furnace to prevent flameout at low temperatures; at high loads, simultaneously increase the grate operating speed and air supply volume to match fuel combustion needs; the servo-driven grate can automatically adapt to load fluctuations for better stability.
4. Long-term continuous full-load operation conditions
24h full-load continuous operation conditions require equipment to be stable and wear-resistant. Adaptation skills: Check the grate and transmission mechanism before starting the machine to prevent loosening; regularly fine-tune the operating parameters to avoid local coking caused by fixed working conditions; optimize the waste heat system and control the exhaust gas temperature to ≤180°C; check the grate wear on a regular basis, and replace accessories in a timely manner to avoid air leakage and material leakage.