Heat losses of the tunnel kiln mainly come from four aspects: heat dissipation from the kiln body surface, heat leakage through kiln doors and gaps, waste of residual heat in the cooling zone, and heat absorption loss of kiln cars and kiln furniture.
I,Four Core Types of Heat Losses
1,Surface Heat Loss of Kiln Body
This is one of the most important heat loss paths.
The tunnel kiln body is usually tens or even hundreds of meters long with a large outer shell surface area.
Although the kiln body is equipped with insulation layers, high temperatures (typically 800–1400°C) conduct and radiate heat outwards through the kiln wall, raising the surface temperature and dissipating heat directly into the workshop atmosphere.
2,Heat Leakage at Kiln Doors and Gaps
It belongs to "structural heat leakage", which commonly occurs at the joints and operating sections of the kiln body.
The kiln doors at the charging and discharging ends on both sides of the kiln body need to be opened when kiln cars enter and exit. This directly causes overflow of high-temperature flue gas and ingress of cold air, resulting in heat loss.
For gaps at segmented kiln joints, observation holes, temperature measuring holes and other locations, even with sealing, ageing of seals after long-term operation will lead to leakage of high-temperature gas and continuous heat dissipation.
3,Inadequate Recovery of Residual Heat in the Cooling Zone
If the heat in the cooling zone is not utilized, it will be wasted directly.
Cold air is introduced into the cooling zone of the tunnel kiln to cool the fired products down to a temperature suitable for discharge. During this process, the cold air absorbs a large amount of heat and turns into hot air.
If no waste heat recovery system is equipped (e.g. for preheating combustion air or heating the workshop), this hot air will be discharged directly outdoors, resulting in substantial heat loss.
4,Heat Absorption Loss of Kiln Cars and Kiln Furniture
This is a unique "mobile heat loss" issue for tunnel kilns.
Products are placed on kiln furniture (such as shelf plates and saggers) mounted on kiln cars before entering the kiln. The kiln cars and kiln furniture themselves absorb a large quantity of heat.
When the kiln cars exit the cooling zone, the heat they carry will gradually dissipate into the ambient atmosphere during cooling and standing. This portion of heat cannot be recycled, constituting a fixed heat loss.
