The core influencing factors of thermal efficiency of biomass pellet mold temperature machine

The biomass pellet mold temperature machine uses biomass pellets as fuel and thermal oil as heat transfer medium. Its thermal efficiency is essentially the proportion of thermal energy generated by fuel combustion that is transferred to thermal oil and effectively utilized. It is mainly influenced by three core factors: fuel quality, equipment structure, and operation regulation. These factors interact with each other to jointly determine the energy utilization efficiency of the equipment.

（1） Fuel quality: the fundamental prerequisite for thermal efficiency

Fuel is the source of thermal energy generation, and its quality directly determines the combustion adequacy, which in turn affects thermal efficiency. For biomass pellet molding machines, the impact of fuel quality is mainly reflected in the following aspects:

1. Particle moisture content: This is a key indicator that affects combustion efficiency. The moisture content of high-quality biomass particles should be controlled between 8% and 12%, at which point the particles will burn fully and the heat release will be complete; If the moisture content is too high (exceeding 15%), a large amount of heat energy is required to evaporate the water before fuel combustion, which not only reduces effective heat production, but also may lead to insufficient combustion and furnace coking, resulting in a significant decrease in thermal efficiency. Usually, for every 1% increase in moisture content, the thermal efficiency may decrease by 0.5% to 1%.

2. Particle density and formability: high-density (≥ 1.1t/m ³), tightly formed biomass particles that are not easily broken or slagging during combustion, have a longer combustion time, and release more stable heat; Low density and loose particles are easily carried away by the airflow during combustion, causing unburned losses, and may also block the gaps in the grate, affecting ventilation and further reducing thermal efficiency.

3. Ash and impurity content: The ash content of biomass particles should be less than 5%. If the ash content is too high, it will form ash accumulation on the heating surface, hinder heat transfer, and increase heat loss; If impurities such as stones and metals are mixed in the particles, it will not only affect the uniformity of combustion, but may also wear down the furnace and heat exchange components, indirectly reducing the thermal efficiency of the equipment.

4. Fuel calorific value: The calorific value of different types of biomass particles varies, for example, the calorific value of sawdust particles is about 4200-4500 kcal/kg, and the calorific value of rice husk particles is about 3800-4000 kcal/kg. Under the same combustion conditions, high calorific value fuels can generate more effective heat energy, and fuel consumption is lower under the same heat load demand, indirectly improving thermal efficiency performance.

（2） Equipment structure: key guarantee for thermal efficiency

The structural design of the biomass pellet mold temperature machine directly determines the efficiency of heat generation, transfer, and recovery. The core influencing components include the combustion system, heat exchange system, insulation system, and waste heat recovery device

1. Combustion system design: Whether the furnace structure is reasonable (such as furnace volume, flame stroke) directly affects the combustion adequacy. The use of a large volume furnace and multiple return combustion channels in the mold temperature machine can prolong the combustion time of biomass particles, ensure full combustion of fuel, and reduce chemical and mechanical incomplete combustion losses; At the same time, the ventilation and air permeability of the grate are also crucial. Reasonable grate gaps and ventilation layout can ensure uniform oxygen supply and avoid insufficient local combustion.

2. Efficiency of heat exchange system: The heat exchange system is the core of thermal energy transfer, consisting of furnace heating surface, heat transfer oil pan tube, etc. The material, area, and arrangement of the heating surface (such as stainless steel and carbon steel) directly affect the heat transfer efficiency. Increasing the heating surface area and using efficient heat transfer structures such as spiral coils can improve the transfer efficiency of heat energy from flue gas to hot oil; In addition, the smoothness of the circulation of the heat transfer oil is also crucial. If the design of the circulation pipeline is unreasonable and there is excessive resistance, it will lead to insufficient heat transfer of the heat transfer oil, which will affect the thermal efficiency.

3. Insulation system performance: The insulation effect of the furnace body and pipelines directly affects the heat dissipation loss. High quality mold temperature machine adopts high-density rock wool, aluminum silicate and other insulation materials, with an insulation layer thickness of not less than 50mm, which can effectively reduce the heat loss of the furnace and pipeline; If the insulation material ages, is damaged, or the insulation layer thickness is insufficient, a large amount of heat energy will be directly dissipated into the environment, resulting in a decrease in thermal efficiency. Generally, equipment with poor insulation performance can experience heat dissipation losses of 5% to 10% of the total heat.

4. Waste heat recovery device: Whether to equip waste heat recovery devices (such as air preheaters, flue gas waste heat exchangers) is an important means to improve thermal efficiency. The temperature of the flue gas generated by the combustion of biomass particles can reach 200-300 ℃, and if directly discharged, it will cause a large amount of thermal energy loss; By using the waste heat of flue gas to heat the air required for combustion through an air preheater, the combustion temperature can be increased, the combustion efficiency can be enhanced, and the flue gas emission temperature can be reduced, which can improve the thermal efficiency of the mold temperature machine by 3% to 5%.

（3） Operational regulation: dynamic optimization factors of thermal efficiency

Even if the fuel quality is excellent and the equipment structure is reasonable, improper operation can still lead to a decrease in thermal efficiency. Scientific operation and control can achieve dynamic optimization of thermal efficiency:

1. Oxygen supply regulation: Insufficient oxygen supply during combustion can lead to incomplete combustion of fuel, while excessive oxygen supply can take away a large amount of furnace heat, both of which can reduce thermal efficiency. The mold temperature machine using variable frequency induced draft fan and blower can accurately adjust the oxygen supply according to the fuel combustion situation, so as to achieve the optimal ratio of air to fuel (usually the excess air coefficient is controlled at 1.2-1.4), ensuring sufficient combustion and minimal heat loss.

2. Load matching during operation: The thermal efficiency of the mold temperature machine reaches its optimum at rated load. If the operating load is too low (less than 60% of the rated load), the furnace temperature will decrease, fuel combustion will be insufficient, and the proportion of heat dissipation loss will increase; If the load is too high (exceeding 110% of the rated load), it will cause heat accumulation in the furnace, high flue gas temperature, and the heat exchange system cannot transfer heat in a timely manner. A large amount of heat energy will be discharged with the flue gas, and the thermal efficiency will also decrease. Therefore, maintaining the operating load at 70% to 100% of the rated load is the key to ensuring high thermal efficiency.

3. Regular maintenance: After long-term operation of the equipment, the heating surface of the furnace and the heat transfer oil coil will accumulate dust and coke, which will hinder heat transfer; Thermal oil will age and deteriorate after a period of use, and its thermal conductivity will decrease; The grate may experience uneven ventilation due to wear and tear. Regular cleaning of accumulated ash and coking, replacement of aging heat transfer oil, and maintenance of furnace grate and fan can ensure that the equipment is always in optimal operating condition and avoid a decrease in thermal efficiency due to equipment aging.