Heating, boiler and heating elements


Heating and boiler.
    Now we choose a method of heating and solid fuel boiler parameters for a wood drying kiln.
If you are going to dry only softwoods (pine, etc.), the boiler with air agent is a suitable.
If you are going to dry and hardwoods (oak, etc.), the best water system or a combined system.
In the combined heating system, air agent carries the main load, and the small water heating supports the required temperature without large fluctuations that exist in the system with air agent.
Define the capacity of the boiler for the wood drying kiln in the figure.
Calculate the volume of drying lumber for this kiln.
The total volume of stacking - 2.0m × 2.5m × 6.0m = 30m³
Volume drying lumber - 30m³ / 2 = 15m³
My region is the northern Ukraine. To calculate the required capacity of the boiler, we multiply the volume of drying lumber by 3 and get 45 kW.
Such power is needed only in the winter for a quick exit to drying mode when frozen timber loaded. Much less power is needed for drying mode.
    Remember that one m³ drying green wood you have to spend about 270 kW of energy. It does not matter what way you pass energy to the lumber - boiler, electric heating elements, microwaves, infrared radiation, or something else. In any case it is necessary to transform the moisture from one aggregate state to another.
Wood readily gives away the moisture to 30% moisture when water molecules are in the intercellular space. Therefore, to reduce the cost and time of the drying process in a wood drying kiln is better to pre-dry the lumber in a natural way, and then to dry in the kiln.

Heating elements for drying kiln.
Let's look two ways of location of heating elements. In the first method, the heating elements are positioned across the air flow in the second method they stand along the air flow.

kiln-heater-01 kiln-heater-02     In the first case, the air flow blows the heating elements are much better than in the second case. Elements have a smaller area and weight, thus cost is less. But such location of heating elements greatly increases the aerodynamic resistance of system. Therefore, more powerful engines for the fans will be needed. In the second case, the cost of the heating elements is greater but electricity costs is less.
In my opinion, the second method is better.