On the control of closed hood ventilation system

In order to effectively regulate and control the air flow and pressure in the hood, control the exhaust temperature and humidity, and better meet the needs of the ventilation system in different seasons and different working conditions and save energy, the paper machine ventilation system is equipped with an automatic regulation control system, which is controlled by the paper machine DCS system, so as to facilitate management.

1. Exhaust dew point (exhaust air volume) control system

The manufacturer of closed hood is equipped with temperature and humidity detection and transmitter on the exhaust air pipe. By detecting the temperature and humidity of exhaust air and sending signals to the DCS system, the frequency converter on the exhaust fan is controlled by the DCS system to adjust the exhaust air volume, so as to achieve the purpose of stabilizing the temperature and humidity of exhaust air.

2. Control system of hood zero position (supply air volume)

A zero position detection device is set in the hood. Through detecting the position of the actual zero pressure point of the hood, the air supply is controlled by the DCS system. If the zero pressure point is higher than the set position value, the air supply is increased by the frequency converter on the blower controlled by the DCS system. If it is lower than the set position value, the air supply is reduced.

3. Air supply temperature control system of hood

The air supply pipe of the closed hood is equipped with temperature detection and transmitter. The temperature of the air supply is detected and transmitted to the DCS system. The temperature control program of the DCS system adjusts the pneumatic control valve on the steam pipe by signal to adjust the air supply temperature or ensure the constant air supply temperature.

4. Heat recovery spray timing control system

The gas gas heat recovery device adopts the automatic spray cleaning system, which is controlled by the DCS system timing program and cleaned every 8 hours for 1 minute.

5 liftdoor control system

The lifting door of the hood is interlocked with the paper breaking signal. In case of paper breaking, the DCS system will control the automatic lifting of the electric lifting door. The lifting door of the hood can also be opened and closed through the manual button on the paper machine operation platform.

6. Fire control system in the hood

A temperature detection device is set in the closed hood. Through detecting the actual temperature of the hood, the DCS system controls the steam fire switch. When the temperature in the hood reaches the fire temperature, the transmitter will give an alarm according to the detected signal, the DCS system will close the exhaust and air supply systems, open the steam fire-fighting electric valve, and spray steam into the hood to achieve the purpose of fire-fighting.