We will focus on the development trend of frequency converter application in the dyeing and finishing industry. For the dyeing and finishing industry, electricity consumption is the main part of its production cost, and the dyeing vat is one of the main energy-consuming equipment for dyeing yarn. With the development of frequency conversion control technology, frequency conversion control of flow pressure difference has been widely used in the dyeing and finishing industry. The energy-saving transformation of the dyeing vat by frequency conversion has also become the most effective way for the dyeing and finishing industry to reduce the energy consumption cost of dyeing yarn and improve product competitiveness. Therefore, the application of AC frequency conversion speed regulation device on the dyeing vat is of great significance for reducing energy waste.
The yarn dyeing process is a predetermined periodic action process, that is, the time control of the internal flow and external flow to achieve the dyeing process. The internal and external flows are mainly realized by the commutator commutation; and the yarn flow is mainly realized by the main pump.
The following are the main losses in the dyeing vat process
(1) Hardware loss. The ordinary dyeing vat main pump adopts the original Y-△ step-down start, and its starting torque and starting current are large, which accelerates the aging of the main pump and the accelerated wear of the commutator. Increase the maintenance cost and energy waste.
(2) Overflow loss. As the yarn processing procedures are different, the temperature, flow rate and pressure required for each process are different. For the main pump motor, the load of the dye vat during the dyeing process is in a changing state. The pump flow rate is designed according to the required maximum flow rate. The original main pump motor provides pressure flow at a constant speed. When the flow rate required for each pump yarn is less than the maximum flow rate, the colorant flows through each pound of yarn, so that it is not colored in the shortest time, and this part of energy is lost.
(3) Throttling loss. When water flows through the reversing port of the commutator, there will be a certain flow rate and pressure, which increases the torque of the reversing solenoid valve. At the same time, due to the long-term full-speed circulation of water and the intense mechanical friction of the reversing device, the sealing ring temperature is too high, the commutator noise is too loud, and the mechanical life is shortened.
(4) Design margin loss. Usually in the design, commonality is generally taken into consideration, and the design is based on the maximum capacity. Therefore, the designed capacity of the dye vat main pump motor is much higher than the actual need, and there is a phenomenon of "big horse pulling a small cart", resulting in a large waste of electricity.
Energy-saving principle and control system of flow pressure difference control
(1) Speed regulation and energy saving. According to the process requirements of yarn dyeing, the original main cylinder injection pipe is changed into a flow controller, which is converted into a 4-20mA current signal and then added to the PLC analog input end as a frequency given signal. The PLC samples it in real time and processes it through PID calculation, so that the output frequency changes linearly with the analog signal of the flow controller; after the given poundage is calculated by the PLC, the required pressure and flow size will automatically adjust the motor speed, thereby reducing the output power of the motor. A reversing position switch is installed at the reversing solenoid valve to ensure that the reversing solenoid valve is fully actuated. When the internal and external flows are reversed, the speed will automatically decrease according to the reversing switch action, and it will automatically accelerate to the required frequency after the reversing is completed, so that the energy loss of the motor and the reversing valve is minimized within the entire load range.
(2) Cost reduction and easy operation. The original water level controller and magnet signal of the main cylinder are removed and replaced with an analog signal controller to control the water level. A human-machine interface is installed to view the real-time water level of the main cylinder. Accidents caused by waterless operation of the main cylinder have been avoided. Remove the tank water level controller and use the original analog signal controller to control the water level, reducing maintenance and production costs.
(3) Improve power factor to save energy. Reactive power not only increases line loss and equipment heating, but more importantly, the reduction in power factor leads to a reduction in active power of the power grid. It can be seen that the greater the power factor, the greater the active power. The COSφ value of an ordinary main pump is between 0.6 and 0.8. After using the variable frequency speed control device, due to the compensation effect of the filter capacitor in the inverter, COSφ≈1, thereby reducing reactive loss and increasing the active power of the power grid.
(4) Soft start energy saving. Since the original motor is directly started or Y/△ started, the starting current is equal to (3-7) times the rated current, which will cause serious impact on the electromechanical equipment and the power supply network, and will also increase the grid capacity requirements. The large current and vibration generated during startup are extremely detrimental to the service life of the equipment. After using the variable frequency energy-saving device, the soft start function will make the starting current start from zero, and the maximum value will be limited to the current limit level set in the acceleration of the inverter, generally not exceeding 1.2 times the rated current, which reduces the impact on the power grid and the requirements for power grid capacity and extends the service life of the equipment.