Drying moisture control system
Background: At present, most of the drying equipment in many industries does not have online moisture monitoring and control. Basically, the material is dried and then taken to the laboratory for measurement, and then the drying temperature is adjusted according to the moisture content, or the operation is based on the experience of workers. Such control is seriously lagging, often due to insufficient moisture drying, resulting in product quality degradation, or even due to excessive drying, causing the material to catch fire and cause a fire.
Based on our experience in installing moisture meters in such industries, we have proposed a moisture measurement control system that uses a drying method to control moisture.
Application industry: wood chips or wood fiber drying in particleboard and fiberboard industry
Drying of feed, bran, etc.
1. Install a feed belt scale at the entrance of the dryer to measure the flow of raw materials
2. Install a moisture meter 1 above the feed belt to measure the moisture of the raw material
3. Install temperature detection (thermal resistance or thermocouple) inside the dryer to measure the temperature inside the dryer
4. Add a corresponding proportional control valve at the inlet of the heating pipe (steam pipe or thermal oil pipe) of the dryer to adjust the heating amount
5. Install a moisture meter 2 at the position of the conveyor belt at the outlet of the dryer to measure the moisture of the material after drying
Principle: When the material passes through the feeding belt scale, the weight of the material is measured. The system calculates the material flow according to the material weight and belt scale speed. The system automatically adjusts the belt scale speed to control the raw material feed flow and the process setting value. ; The moisture meter 1 above the feed belt measures the moisture content of the raw material. When the moisture content of the raw material is high, the system automatically increases the amplitude of the proportional valve to increase the flow rate of the thermal oil and the dryer heats up; when the moisture content of the raw material is low, the system automatically Reduce the amplitude of the proportional valve, reduce the flow of heat transfer oil, and cool the dryer. This control process uses PLC for PID automatic control. After the material is dried, it passes through the conveyor belt and is measured by the upper moisture meter 2 to the dried moisture. This moisture data is simultaneously transmitted to the system and compared with the target moisture value set by the process. The system automatically adjusts the PID proportional coefficient and integral And differential parameters make the system's automatic control of moisture more stable, and the drying moisture of materials is stable.
1. Through the feeding belt scale, automatically control the flow of materials to avoid affecting the drying effect due to changes in the flow of materials.
2. The moisture meter 1 above the feed belt measures the moisture of the raw material. The system controls the opening of the proportional valve through PID, automatically adjusts the temperature of the dryer, realizes the pre-control of the moisture of the material, and avoids certain lag caused by re-detection after drying .
3. Install a moisture meter on the discharge conveyor belt to monitor the moisture of the material after drying. According to the moisture data after drying, the system can automatically adjust the PID parameters to further ensure that the dryer controls the moisture of the material more uniformly.
4. Only need to set the process index of the flow and moisture of the material, the system controls the drying equipment in a linked manner, the drying equipment can be started with one key, and unmanned operation can be realized.
5. The system can set the upper and lower limits of the dryer temperature. When it exceeds the allowable temperature range, it can realize automatic shutdown or alarm and other functions.
Remarks: Due to the different on-site process requirements, equipment conditions and operating habits of users, the automatic control of moisture content needs to be designed according to the user's process conditions, and the customization of the combined on-site conditions.