Drying process of wood heat pump dryer
Drying process of wood heat pump dryer:
1. Install the wood according to the decoration standards, close the drying room, and turn on the control system.
2. Preheating: Turn on the heat pump and fan, set the upper temperature limit to 45 ℃. In order to save preheating and heating time, turn on the electric auxiliary system, and control the ambient temperature from 20 ℃ to 45 ℃ for heating and insulation time within 14 hours; At this stage, the energy efficiency ratio of the heat pump is around 3.5, operating at full load and the fan at full load.
3. Heating up: Due to the previous drying reference temperature of 62 ℃, during the heating process, due to the high initial moisture content of the wood, the moisture evaporated from the wood can ensure synchronous temperature and humidity; Simultaneously turning on electric assistance to maintain insufficient heat caused by humidification and heating.
4. One stage drying: Set the temperature to around 62 ℃; After cooking, the water flow rate of the wood is relatively fast, and it is also the early stage of wood free water discharge. The benchmark technology adjusts the temperature of the wood to be high inside and low outside. This stage can quickly discharge more than 40% of free water. Assuming that the moisture content of the wood when entering the kiln is 452000 kg, the wood needs to discharge 900 kg of water; According to a 12P machine with a drainage capacity of 30 kilograms, it takes 30 hours.
5. Two stage drying: set the temperature at 66 ℃; At this point, the moisture content of wood is still above the fiber saturation point, and the water outlet speed is also faster. The increase in drying temperature and the decrease in relative humidity can ensure the rapid discharge of moisture content, from 40% to 30%.
6. Three stage drying: set the temperature at 72 ℃, and set the temperature to 60 ℃ when the wood moisture content is above 25%; At this point, the moisture content of the wood is close to the fiber saturation point, and rapid drying may cause drying defects in the wood. Reduce the speed from 30% to 25%.
7. Humidification drying: When the moisture content of the wood reaches 25%, the wood has reached the fiber saturation point. In order to ensure the drying quality of the wood, an intermediate treatment is required to accelerate the drying speed in the later stage.
8. Four stage drying: After humidity adjustment treatment, adjust the temperature back to 72 ℃. The drying speed is significantly accelerated, and the probability of drying defects occurring in wood after humidity adjustment treatment is greatly reduced.
9. Five stage drying: When the moisture content of wood decreases to below 20%, the drying speed will slow down. At this time, the temperature can only be increased to form a relatively dry drying relative humidity, forcing the internal moisture of the wood to be quickly discharged.
10. Six stage drying: When the moisture content of the wood drops below 15%, the moisture content in the wood is already very low, and the drying speed is slower than any previous stage. At this time, the temperature is raised to 80 ℃.
11. Balance treatment: When the moisture content of the wood reaches 12%, it has already reached or is close to the kiln moisture content requirement, and the drying stress in the wood has not been eliminated. The distribution of moisture content in the wood is not very uniform, and final balance treatment is needed.
12. Cooling out of the kiln: After balanced treatment, the moisture content of the wood is basically balanced, and the drying stress is basically eliminated. Only when the temperature drops to 35 ℃ can it be discharged from the drying room (10-15 ℃ higher than the ambient temperature).
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