Timber Dryer Heating Components

Motorised Valves

Motorised valve motor runs for very short opening and closing cycles. The motor will stop when the valve reaches the fully open or fully close position and will not overheat. They are very lasting and are more robust than solenoid valves.

The linear motorised globe valves can handle high pressure and temperature. Their body is usually made of cast steel. The valve can have ON & OFF or MODULATED flow options. Modulated flow means that the valve can be closed or open partially to a specific position to allow just the right amount of flow reach the target temperature. A modulation signal of 4-20mA or 0 to10 VDC is provided by a controller to close or open the valve proportionately according to the heat demand. ON & OFF flow valves are more common as they are much cheaper and the timber drying process can tolerate slight temperature differentials. Most globe valves when fully closed will still have a small minute ampount of leakage. It is important to check that the valve is seated properly or closed properly when there is unusual temperature rise in the dryer.

Motorised valves can have 2 port or 3 ports, also known as 2 way or 3 way. For steam operation, 2-way valves are used. But for hot water or thermal oil heating medium, motorised 3-way valves must be used. This is because, the

medium has to be directed back to the heater for reheating. Using 2-way valves can be dangerous if the valves are closed which may result in a no-flow situation. If the hot water or thermal oil will stop flowing in the biomass fired heater, overheating will occur. For a hot water heater , overpressure may cause an explosion. For a thermal oil heater, overheating will cause the oil to harden and cause a fire or an explosion. The 3-way valve allows the heated liquid medium to circulate in the main pipeline or flow into the dryer as and when required. The liquid medium will constantly circulate through the heater and the main supply pipe circuit. When heating is required, the 3-way valve will divert the flow into the dryer and flow back to the return pipe circuit back to the heater.

Steam Traps - When a dryer does not heat up even when steam is available, the likely cause will be due to a faulty steam trap. When steam enters the heat exchanger to heat up the timber, it will lose heat energy and eventually condensed into water as condensate. The condensate will flow to the lowest point in the pipeline and flood the heating line. It must be discharged for new steam to enter to continue the heating. The steam trap allows only the condensate to be discharged while trapping the steam in the heating pipeline.

Tritherm recommends the use of Inverted Bucket Steam traps because they are reliable and efficient. The trap releases only water and not live steam. These mechanical traps are easy to service and are not terribly expensive

To learn more about steam traps please click on this link:

1970's NUS training Series Steam Traps

Finned tubes welded in between 2 pipe headers to make into a heat exchanger. The purpose of the fins is to increase the surface area of the heat exchange area. The fins are made of aluminum which is a good heat transfer material.The use of seamless SS304 stainless steel for the base tube is recommended. Corrosion outside the tube can be quite a problem due the hot, humid and corrosive vapour. Corrosion can also take place inside the tube when water is not treated to remove the dissolved oxygen for steam and hot water heating. For thermal oil medium, oxidation of the oil can cause some acidity. Carbon steel base tubes may start to have small leaks in about 3 years due to corrosion. Timbers that are chemically treated with boric borax will produce acidic vapour that can quickly corrode the base tubes from the oiutside.