In the context of the global demand for efficient energy conversion and environmental protection is increasing, the innovation of boiler technology has become the focus of attention in the energy field. Among them, the reciprocating grate boiler with its unique combustion technology, biomass fuel utilization, waste disposal and other areas play an important role, and gradually become an important choice for industrial and civil heating.
Reciprocating grate technology can be traced back to the early 20th century. At that time, with the accelerated process of industrialization, the traditional energy conversion methods have been difficult to meet the needs of efficient production. Reciprocating grate technology was developed to address the limitations of traditional chain-grate boilers in handling a wide variety of fuels, especially those with high humidity and irregular shapes. The emergence of this technology has brought new ideas for industrial heating and energy utilization.
With the continuous progress of material science and mechanical engineering, reciprocating grate boiler technology has been continuously developed and improved. The application of new materials to improve the high temperature resistance and service life of the grate, more sophisticated mechanical design to make the movement of the grate more stable and efficient. Nowadays, reciprocating grate boilers have been widely used around the world, especially in the field of biomass energy development and waste treatment, becoming indispensable equipment.
Chain-row boilers use continuously running chain rows to transfer and burn fuel, and are suitable for burning even-sized, drier fuels. The advantage of a reciprocating grate boiler over a chain grate boiler is its flexibility in fuel handling. The reciprocating grate consists of multiple interlocking movable and fixed grate plates, and through the reciprocating movement of the grate plates, it is able to handle fuels with higher humidity and more irregular shapes, such as wood chips, crop waste, and so on.
Comparison With Circulating Fluidized Bed Boiler
Circulating Fluidized Bed (CFB) boilers have strict requirements on fuel particle size, which is usually less than 10mm, and low tolerance of fuel moisture, which is usually not more than 15%. Reciprocating grate boilers can handle fuel with a particle size of less than 50mm, and have a tolerance of up to 60% for fuel humidity. In addition, reciprocating grate boilers offer greater flexibility in the load regulation range of 40 - 110% compared to 30 - 100% for CFB boilers.
Reciprocating Grate Grate Blades are similar to a ladder, with the movable grate blades alternating with the fixed grate blades. In operation, the movable grate sheet in the hydraulic cylinder under the action of push and pull reciprocating movement, this unique structure produces the thrust, so that the fuel from the upper layer of the grate gradually downward movement, until it leaves the surface of the grate.
Grate Layout Types 
Reciprocating grates are usually available in three layout types: tilting layout, horizontal layout and combination layout. Inclined layout (also known as tilting grate) is suitable for uneven shape and size of the fuel, such as garbage, to ensure that the fuel from the inlet to move smoothly to the end of the grate; Horizontal layout is more suitable for high ash content, poor combustion performance of the fuel, can limit the fuel's rapid movement to ensure that the full combustion; when there is a conflict in the characteristics of the fuel, such as high ash and complex dimensions, often used in a combination of layout.
Effective cooling measures are required to prevent damage to the grate blade due to high temperatures. Common cooling methods include air cooling and water cooling. Air-cooled is designed in the bottom of the grate sheet ribs, heat sinks and other structures, the use of air from the air chamber in the combustion before participating in the contact with the grate sheet heat; water-cooled is installed in the fixed grate sheet cooling water pipes, and activities of the grate sheet due to frequent movement, more suitable for air-cooled way.
When the fuel enters the grate, the combustion process does not start immediately, but goes through several stages. Generally speaking, the combustion of fuel on the grate can be divided into 6 stages, including preheating, drying, volatile analysis, combustion, burnout and ash cooling. In this process, rational air distribution is crucial. Primary air is mainly used for preheating and volatilization of the fuel, secondary air provides sufficient oxygen during the combustion phase, and tertiary air is used for the burnout phase and to reduce NOx emissions.
For highly flammable fuels, water-cooled walls are often installed around the feed hopper to prevent them from igniting in the hopper. The water-cooling system ensures safe operation of the hopper by either manual filling or automatic replenishment through float valves.
Ignition burners are mainly used to maintain combustion temperature during boiler startup and shutdown to meet environmental requirements. In large boilers with a high degree of automation, the ignition burner also assumes the function of ignition, which is not available in traditional fixed grate or chain row boilers.
Air Distribution System
Due to the complex structure of the combustion chamber of reciprocating grate boilers, there are more wind shadow zones, which affect the full contact between fuel and oxygen. Therefore, for fuels with high combustible composition, special attention needs to be paid to the design of the secondary air distribution system, while rationally adjusting the primary air distribution to ensure that the various combustion zones (preheating zone, combustion zone, combustion and ash cooling zone) to obtain the appropriate amount of air.
The biomass fuel enters the boiler through a vibrating feeder, which ensures that the fuel is uniformly distributed on the grate, which is especially important for fuels with large differences in particle size (e.g., palm kernel shells and rice hulls) to ensure stable combustion of the fuel on the grate.
Reciprocating grates utilize a patented “Push - Pull” movement pattern with a forward travel displacement of 50 - 100 mm and a return travel time of 10 - 15 seconds. This reciprocating motion constantly stirs the fuel, promotes oxygen penetration, prevents slagging and improves combustion efficiency.
In the segmented combustion process, the air parameters are set differently for the different stages. The primary air temperature is 150-250°C, with 5-8% oxygen content; the secondary air temperature is 300-400°C, with 12-15% oxygen content; and the tertiary air is ambient temperature, with 18-21% oxygen content. By precisely controlling the air volume and temperature of each section, full combustion of fuel is realized.
The ash at the bottom of the grate is discharged through scraper conveyor at a temperature lower than 100°C; the fly ash is collected through bag filters with a filtration efficiency as high as 99.9%, which effectively reduces the dust emission and protects the environment.
Reciprocating grate boilers can burn almost any solid fuel, especially excellent in handling poor-quality fuels, such as fuels with low calorific value, high humidity, and easy slagging of ash. This feature makes them popular for waste incineration and biomass projects.
Uniform air distribution and fuel mixing result in high combustion efficiency in reciprocating grate boilers. By optimizing the combustion process, fuel consumption can be reduced and energy efficiency increased.
The robust structural design and the use of high quality materials make the reciprocating grate boiler low maintenance. Under normal maintenance, the service life of the boiler can reach 20 - 25 years, and the service life of key components, such as the grate sheet, is 8 - 10 years, which ensures the stable operation of the equipment.
By adopting high-pressure secondary air or exhaust air injection technology, the reciprocating grate boiler is able to effectively reduce the emission of nitrogen oxides (NOx), which meets the strict environmental protection standards and reduces the pollution of the air environment.
Reciprocating Grate Boilers have relatively high production costs, especially for the grate part, where the complex structure and the use of special materials lead to increased manufacturing costs.
The air resistance of the grate system is higher, which requires a more powerful fan, thus increasing equipment investment and operating costs.
1.Can reciprocating grate boilers handle municipal solid waste?
Yes, but the grate cooling system needs to be modified and reinforced alloy plates used. Also, the waste needs to be pre-crushed to less than 80mm.
2.What is the service life of a reciprocating grate boiler?
Under normal maintenance conditions, the service life of the boiler as a whole is 20 - 25 years, and the service life of key components such as the grate plate is 8 - 10 years.
3.How to solve the problem of uneven combustion?
Uneven combustion can be improved by adjusting the secondary air baffle (±15°) and ensuring that the fuel layer thickness is within the optimum range of 150 - 300mm.
Reciprocating grate boiler with its unique structural design and operating principle, in terms of fuel adaptability, combustion efficiency and environmental performance and other aspects of the show significant advantages, despite the existence of production costs and air resistance and other aspects of the shortcomings, but in the current energy and environmental protection situation, but still has a broad application prospects. With the continuous progress of technology, I believe that the reciprocating grate boiler will play a more important role in the future energy sector.
