The grate system serves as the central component of a biomass boiler, whose structural design and operational logic directly determine the combustion efficiency of solid fuels, boiler operating stability, and pollutant emission levels. In the international market, the diversity of biomass boiler grate types often leads purchasers into selection difficulties due to insufficient understanding of the technical characteristics, advantages, and drawbacks of different grates, making it challenging to precisely align with their specific fuel and operational requirements.
The grate plays a critical role in the solid fuel combustion process, functioning both as a support platform for the fuel and as a core component for air distribution and combustion regulation. The movement state of the grate directly influences the residence time of the fuel in the furnace, the uniformity of air-fuel mixing, and the completeness of fuel burnout.
Selecting the appropriate grate type is crucial, as this decision is directly linked to the boiler's thermal efficiency, operational stability, and even long-term maintenance costs and equipment lifespan.
Mechanical grate systems, by virtue of their strong controllability, broad adaptability, and high combustion efficiency, have become the mainstream configuration for industrial-scale biomass boilers. Among these, reciprocating grates and traveling grates dominate biomass combustion applications due to their distinct technical characteristics. Each type emphasizes different aspects in structural design and operational logic, with their advantages and disadvantages forming a complementary profile.
Compared to the shortcomings of fixed grates, such as incomplete combustion, and the weak adjustability of stepped grates, traveling grates excel in continuous operational stability, while reciprocating grates stand out in fuel adaptability and combustion regulation flexibility. Through optimization of their mechanical structures, both types effectively address industry challenges such as slagging tendencies, low burnout rates, and poor adaptability to operational fluctuations in biomass fuel combustion.
The core advantage of the traveling grate lies in its continuous operation capability. It employs a closed-loop, continuously moving structure driven by a transmission mechanism that propels the grate bars at a uniform speed, enabling full automation of the fuel feeding, combustion, and ash discharge processes. The prominent benefits of this design are operational stability, ease of operation, and the ability to sustain high fuel loads over extended periods, making it suitable for continuous production scenarios.
However, its limitations are also notable: the grate bars move as a single unit, preventing localized stirring of the fuel bed. This can lead to the formation of fixed gaps in the fuel layer, necessitating higher uniformity in fuel particle size. Furthermore, the boundaries between the preheating/drying, main combustion, and burnout zones are fixed, resulting in weaker adaptability to fluctuations in fuel moisture content. This can cause issues such as localized incomplete combustion or slagging.
Fuel is evenly distributed onto the grate surface via the feeding system. As the grate moves, the fuel sequentially enters the preheating/drying zone, the main combustion zone, and finally the burnout zone. Air is supplied to each zone according to pre-set ratios. Combustion ash is automatically discharged at the grate's end by an ash removal system, significantly reducing the need for manual intervention. The control logic primarily involves the coordinated adjustment of grate speed and air distribution ratios, offering high regulation precision and maintaining stable combustion conditions.
Its operational characteristics are defined by strong stability, standardized operational procedures, and a control logic focused on the interlinked regulation of grate speed and air distribution, enabling precise management of the combustion process.
The reciprocating grate centers around a segmented structure. Individual grate bars are driven by an eccentric mechanism to perform a back-and-forth reciprocating motion. The relative displacement between adjacent bars facilitates fuel stirring, agitation, and forward propulsion, simultaneously breaking the ash layer on the fuel surface and allowing air to penetrate deep into the fuel bed. This fundamentally addresses issues of localized slagging and incomplete combustion.
Its greatest advantage is exceptional fuel flexibility, enabling it to handle complex biomass fuels with high moisture content and uneven particle size distribution. It also offers strong independent control capabilities for different zones, allowing precise adjustment of temperature and air volume based on the requirements of each combustion stage. However, its mechanical structure is more complex. The reciprocating motion increases wear at connection points and demands higher sealing standards, imposing stricter requirements on manufacturing precision and maintenance proficiency.
During operation, the fuel undergoes thorough agitation, preventing localized slagging while achieving stratified combustion and staged air distribution. This enhances the layering and thoroughness of the combustion process. This design effectively disrupts the ash layer on the fuel surface, facilitating deep air penetration into the fuel.
Each combustion area can independently adjust the operating parameters, precisely controlling the temperature, air volume and propulsion speed according to the requirements of different combustion stages, providing flexible control space for the combustion of complex fuels.
Chain Grate vs. Reciprocating Grate: Which one fits your ROI goals? Let our engineers run a fuel compatibility test for your project.
The diversity and instability of biomass fuels pose the greatest challenge during combustion. Different sources and processing methods of biomass fuels vary significantly in terms of moisture content, particle size, and component proportions, which place extremely high demands on the adaptability of the grate.
The differences in fuel adaptability are the core technical divide between the two types of grates. Chain-type grates rely on the uniformity of the fuel layer thickness, which depends on the accuracy of feed. When dealing with high moisture content (over 45%) or fuels with significant particle differences, they are prone to delayed ignition, uneven combustion speed, and even local flameout, requiring strict fuel pre-treatment procedures.
The reciprocating grate, on the other hand, utilizes mechanical flipping and layer combustion design to adapt to the fuel moisture content and particle size by adjusting the reciprocating frequency. Even if the fuel pre-treatment is insufficient, it can avoid coking and combustion discontinuities, significantly reducing fuel pre-treatment costs, but frequent flipping increases fuel carryover loss. It requires optimizing the grate gap and advancing speed to balance combustion efficiency and loss rate.
The fuel adaptability of the grate directly affects the daily operational efficiency of the boiler. Insufficient adaptability can lead to frequent shutdowns for cleaning, sudden drops in combustion efficiency, and other issues, increasing the operational burden.
The differences in the air-fuel mixing mechanism directly determine the combustion efficiency and pollutant emission levels of the two types of grates. Chain-type grates rely on uniform air distribution and the layer combustion effect formed by the movement of the grate, with a wide mixing range but weak local targeting. The advantage is stable combustion conditions and small fluctuations in unburned carbon content, but they are sensitive to fuel layer thickness, prone to oxygen deficiency combustion if too thick, and have high heat loss if too thin.
The reciprocating grate enhances local mixing through mechanical flipping, can precisely compensate for the mixing defects caused by uneven fuel layers, has a higher combustion efficiency, lower unburned carbon content, but frequent flipping leads to large fluctuations in furnace pressure, requiring higher response speed of the induced draft system. Improper control can easily result in instantaneous black smoke emissions.
The mixing effect directly affects combustion integrity and thus the unburned carbon content. Efficient mixing reduces waste of unburned fuel, improves boiler thermal efficiency, and reduces pollutant emissions.
When faced with fluctuations in fuel quality, the reciprocating grate, with its flexible zone control capability, has an advantage in combustion stability; while the chain-type grate can maintain a more efficient continuous combustion state when fuel quality is stable.
Operational characteristics and mechanical reliability are core considerations for the long-term operation of both types of grates, and their advantages and disadvantages show significant differences. Chain grates have a regular structure and fewer transmission components; wear is concentrated on the surface of the grate plates and is uniform, resulting in longer replacement cycles and lower maintenance costs. They require lower skill levels from operators, making them suitable for scenarios where the maintenance team has limited technical expertise.
However, their drawbacks include high overall replacement costs for the grate plates, and if local damage occurs, the entire system needs to be shut down for repair, affecting continuous production. Additionally, the air chamber beneath the grate is prone to dust accumulation, requiring regular cleaning; otherwise, it will affect the uniformity of air distribution.
Reciprocating grates, due to their segmented movement and complex connecting structure, experience wear concentrated at the ends of the grate plates, eccentric shafts, and seals. The wear is uneven and occurs in multiple locations, requiring more frequent inspections and localized replacements. This results in higher maintenance frequency and technical requirements, demanding rigorous parameter adjustment and troubleshooting skills from operators.
However, their advantage is that localized repairs and replacements are possible without a complete shutdown, minimizing the impact on continuous production. Furthermore, optimizing the lubrication system and sealing structure can effectively extend the lifespan of critical components, balancing maintenance costs and operational stability.
From the operator's perspective, chain grates offer better long-term reliability and easier troubleshooting; reciprocating grates require enhanced daily inspections to promptly address wear and connection issues.
Choosing an unsuitable grate essentially sacrifices technical suitability for short-term cost advantages, ultimately leading to hidden operational losses. Using a chain grate to process complex fuels will result in efficiency losses and increased maintenance costs due to low combustion efficiency and frequent shutdowns for cleaning. Using a reciprocating grate for homogeneous fuels will incur excessively high equipment investment and maintenance costs, resulting in a waste of technical resources.
When fuel quality is stable, pre-treatment is adequate, and continuous operation with low maintenance costs is desired, the chain grate is the optimal solution. Its advantages of continuous operational stability and low maintenance requirements maximize the reduction of unit energy consumption and labor costs, while its mature technical system ensures long-term operational reliability. When fuel quality fluctuates significantly, has high moisture content, or uneven particle size, and cannot be optimized through pretreatment, a reciprocating grate becomes not just an upgrade option, but a necessary configuration to ensure combustion efficiency and stable operation. Its fuel adaptability and flexible control capabilities effectively mitigate the combustion risks associated with complex fuels, ensuring the boiler's long-term efficient operation.
When selecting a grate, it is necessary to consider both the total life cycle value and initial investment, prioritizing long-term operating efficiency and stability rather than simply pursuing the lowest initial cost.
Before selecting the type, the purchaser needs to clarify three core issues regarding technical compatibility: the moisture content, particle size, and fluctuation range of the fuel; the core requirements of the project for continuous operation time and combustion efficiency; the technical level and maintenance capacity of the operation team. These three dimensions directly determine the boundary of the compatibility of the two types of grates.
The grate type must be precisely matched with the fuel characteristics and operation goals to avoid blindly following popular types and neglecting one's own actual needs.
Professional engineering technical support and combustion design experience are crucial, as they can help the purchaser accurately assess the requirements, optimize the grate selection plan, and avoid operational risks.
Both reciprocating and chain-type grate burners do not have absolute superiority or inferiority. The core difference lies in the balance between fuel adaptability, combustion control flexibility, and operational requirements. The chain-type grate has the core advantages of stability and low consumption, and is suitable for homogeneous fuels and standard operating conditions; the reciprocating grate has the core competitiveness of flexibility and durability, and is suitable for complex fuels and variable operating conditions.
In biomass boiler projects, the selection of grate type is not a simple equipment procurement decision, but a strategic layout that concerns the long-term benefits and stability of the project.
