Energy-Saving Methods

1. Minimizing Heat Loss During the Drying Process

Generally, heat loss in wood chip dryers does not exceed 11%. For properly insulated large- and medium-scale production equipment, heat loss can be reduced to approximately 6%. Therefore, effective insulation of the dryer system is essential. However, excessively thick insulation is not optimal; an optimal insulation thickness should be determined. To prevent leakage in the drying system, forced draft fans and induced draft fans are typically used in series. Proper adjustments ensure the system operates under zero-pressure conditions, preventing a decline in thermal efficiency of the veneer dryer caused by leakage of drying media or infiltration of ambient air in convective dryers.

2. Reducing Evaporation Load of the Dryer

Pre-dehydration treatments such as filtration, centrifugal separation, or evaporation in an evaporator before the material enters the dryer can increase the solid content of the material and reduce the evaporation load on the dryer, making it an effective energy-saving method for drying equipment. For liquid materials (e.g., solutions, suspensions, emulsions), pre-treatment before drying also conserves energy because convective dryers heat materials using sensible air heat, whereas preheating utilizes latent heat from steam or waste heat. In spray drying, preheating the feed liquid also facilitates atomization.

3. Increasing Inlet Air Temperature and Reducing Outlet Exhaust Temperature of the Wood Chip Dryer

As indicated by the dryer's thermal efficiency definition, raising the inlet air temperature (t₁) improves thermal efficiency. However, the inlet air temperature is constrained by the allowable product temperature. In co-current flow granular suspension dryers, the particle surface temperature remains relatively low, allowing the inlet air temperature to exceed the product's allowable temperature significantly. Generally, energy consumption in convective dryers primarily consists of two components: water evaporation and exhaust heat loss, with the latter accounting for approximately 15%–40% (up to 60% in some cases). Reducing the outlet exhaust temperature is constrained by two factors:

• Ensuring the product moisture content meets requirements (excessively low outlet exhaust temperatures increase product moisture).
• Maintaining the exhaust temperature 20–60°C above the dew point when entering cyclones or bag filters.

4. Partial Exhaust Gas Recirculation

As illustrated in the diagram, a drying system employing partial exhaust gas recirculation improves thermal efficiency by utilizing residual heat from the recirculated gas. However, increasing the recirculation rate raises the humidity of the hot air, reducing the drying rate and extending the drying time for wet materials, which increases equipment costs. Therefore, an optimal recirculation rate exists, typically ranging from 20% to 30%.