Detailed explanation of thermal efficiency of biomass pellet mold temperature machine and small boiler

Thermal efficiency is the core indicator for measuring the energy utilization efficiency of thermal energy equipment, which refers to the percentage of the heat effectively utilized by the equipment and the total heat released by complete combustion of the fuel. The thermal efficiency of biomass pellet molds and small boilers is affected by factors such as fuel type, equipment structure, and operating conditions, and there are clear range differences, as follows:

1、 Thermal efficiency of biomass pellet mold temperature machine

The overall thermal efficiency of biomass pellet mold temperature machine is at a high level, with the thermal efficiency range of conventional commercial models being 83%~87%. Some models that use advanced energy-saving technologies can break through this range, and the core is influenced by equipment structure design, fuel adaptability, and operation control methods.

1. Conventional thermal efficiency range and basis

According to the technical parameters of mainstream models in the market, the design thermal efficiency of ordinary biomass pellet molding machines is generally around 83%. Models that adopt multi return waste heat recovery technology and variable frequency regulation induced draft systems can extend the residence time of high-temperature flue gas in the heat exchange tube bundle, improve fuel combustion efficiency, and reduce heat loss, resulting in a thermal efficiency of over 87%.

2. Relevant standard requirements

It should be noted that biomass pellet molds with a power of ≥ 100kW belong to the category of organic heat carrier boilers and must comply with the energy efficiency standards of organic heat carrier boilers. For example, according to the "DB33/T 974-2015 (2017) Technical Requirements for Energy Efficiency Limits and Monitoring of Organic Heat Carrier Furnaces", the energy efficiency admission value (minimum requirement for new project selection) and the operating energy efficiency quota value (minimum requirement for normal use) for chamber combustion organic heat carrier furnaces using biomass formed fuel as energy and rated thermal power of 700-1400 kW are 80% and 76%, respectively. In actual operation, the thermal efficiency of qualified models can far exceed the rated value, reaching a design level of over 83%.

3. Key factors affecting thermal efficiency

One is fuel quality: selecting biomass particles that are dry, high-density, low ash content, and have uniform particles can ensure sufficient combustion and reduce incomplete combustion heat loss; If the particles are moist and have high ash content, it will reduce combustion efficiency and lead to a decrease in thermal efficiency. The second is the equipment structure: whether it is equipped with a waste heat recovery device (such as an air preheater), the return design of the heat exchange tube bundle, the insulation performance of the furnace body, etc., directly affect the heat recovery and heat dissipation loss. The third is operation regulation: the precise ratio of variable frequency induced draft fans and blowers can optimize oxygen supply, avoid excessive air carrying away heat, and further improve thermal efficiency.

2、 Thermal efficiency of small boilers

The thermal efficiency range of small boilers (using biomass pellet fuel as the core adapted fuel) is 71% to 83%, which is lower than the overall level of biomass pellet mold temperature machines. Its thermal efficiency index is strictly limited by the fuel type, boiler structure, and relevant national standards.

1. Conventional thermal efficiency range and standard basis

According to NB/T 34035-2020 Technical Conditions for Small Biomass Boilers, the thermal efficiency of small biomass boilers (using biomass pellet fuel and water as the medium) is divided into "target value" and "limit value": when using forestry biomass, the target value is ≥ 80% and the limit value is ≥ 74%; When using agricultural biomass or mixed biomass, the target value should be ≥ 77% and the limit value should be ≥ 71%. This means that qualified small-scale biomass boilers need to meet a minimum thermal efficiency requirement of 71% (agricultural biomass) or 74% (forestry biomass) under rated conditions, and the actual thermal efficiency of mainstream standard models is mostly concentrated between 77% and 80%.

In addition, the national standard GB/T 44906-2024 Technical Specification for Biomass Boilers, which will be implemented on May 1, 2025, stipulates that the thermal efficiency limit for layer fired and chamber fired biomass boilers with a rated evaporation capacity of ≤ 10t/h under rated conditions is 83%. This standard is applicable to hot water boilers or organic heat carrier boilers with a rated thermal power greater than 1.4MW, and some large and small boilers (close to the upper limit specification of small boilers) need to meet this requirement.

2. Key factors affecting thermal efficiency

One is the type of fuel: forestry biomass (such as wood chips) has high calorific value, low ash content, high combustion efficiency, and corresponding higher boiler thermal efficiency; Agricultural biomass (such as rice husk particles) has low calorific value and high ash content, which can easily lead to ash accumulation on the heating surface, reducing heat transfer efficiency and resulting in relatively low thermal efficiency. The second is the combustion method: different combustion structures such as chain grate and reciprocating grate have different adaptability to biomass particles. Chain grate has stronger adaptability, more complete combustion, and slightly higher thermal efficiency than other grate types. The third is the operating load: When small boilers burn solid fuels and the operating load is lower than 80% of the rated load, it is easy to encounter problems such as insufficient combustion and an increase in the proportion of heat loss, resulting in a decrease in thermal efficiency.

3、 Summary of Thermal Efficiency Comparison between the Two

1. Overall range difference: The thermal efficiency of biomass pellet molding machines (83%~87%) is significantly higher than that of small biomass boilers (71%~83%). The core reason is that the molding machines use thermal oil liquid phase circulation heat transfer, which reduces heat loss, and are generally equipped with energy-saving technologies such as waste heat recovery and variable frequency control, resulting in higher fuel energy utilization efficiency; Small boilers use water as the medium, resulting in additional energy consumption such as steam emissions and water body heat dissipation, and the upper limit of thermal efficiency is lower than that of the mold temperature machine.

2. Differences in standard requirements: Both have clear industry/national standard limitations on thermal efficiency. Small boilers are set with limit values based on fuel type and boiler capacity classification, while models of organic heat carrier boilers in the mold temperature machine are set with energy efficiency admission and quota values based on rated power. Moreover, the actual operating thermal efficiency of the mold temperature machine is more likely to reach or exceed the standard target value.

3. Commonality of actual impact: The thermal efficiency of both is closely related to fuel quality (humidity, calorific value, particle uniformity) and operation (load stability, oxygen supply ratio). Standardized fuel selection and operation management can stabilize the thermal efficiency within the optimal range.