With the development of frequency conversion control technology, frequency conversion control of flow pressure difference has been widely used in dyeing and finishing industry. It has become an effective way for dyeing and finishing industry to reduce the energy consumption cost of dyeing yarn and improve the competitiveness of products. Therefore, the application of AC frequency conversion speed regulation device in dyeing vat is of great significance to reduce energy waste.

Main losses in dyeing vat process
Yarn dyeing process is a scheduled periodic action process, that is, the time control of internal flow and outflow to achieve dyeing process. The internal and external flow is mainly realized by commutator, while the yarn flow is mainly realized by the main pump.
The first is hardware loss. The original Y - △ depressurized starting is adopted for the main pump of common dyeing vat, which has large starting torque and current, and accelerates the aging of main pump and accelerated wear of commutator. The maintenance cost and energy waste are increased.
The second is overflow loss. With the different yarn processing procedures, the temperature, flow rate and pressure required by each process are different. For the main pump motor, the load of dyeing cylinder in the dyeing process is in a changing state. The flow of the pump is designed according to the maximum flow required. The original main pump motor provides pressure flow at a constant speed. When the flow required by each pump yarn is less than the maximum flow, the pigment flows through each pound of yarn instead, so that it does not add color in a short time, and this part of energy is lost.
The third is throttling loss. When the water flows through the reversing port of the commutator, there will be a certain amount of flow and pressure, which will increase the torque of the reversing solenoid valve. At the same time, due to the long-term full speed circulation of water and the severe mechanical friction of the reversing device, the sealing ring temperature is too high, the commutator noise is too large, and the mechanical life is shortened.
The fourth is the design margin loss. In general, in the design, the commonality is generally considered, and the design is based on the maximum capacity. Therefore, the design capacity of the main pump motor of the dye vat is much higher than the actual demand. There is a phenomenon of "big horse pulling a small car", resulting in a large waste of electric energy.

Energy saving principle and control system of flow and pressure difference controlled frequency converter
First, speed regulation and energy saving. According to the process requirements of dyeing yarn, The original injection pipe of master cylinder is changed into a flow controller. After being converted into 4-20mA current signal, it is added to the PLC Analog input terminal as the frequency given signal of the frequency converter. PLC samples it in real time and processes it through PID operation, so that the frequency output to the frequency converter changes linearly with the analog signal of the flow controller. After the given pound number is calculated by PLC, pressure and flow are required The motor speed will be automatically adjusted to reduce the output power of the motor. The reversing position switch is installed at the reversing solenoid valve to ensure that the reversing solenoid valve fully acts in place. When the internal and external flow commutation, it will automatically reduce the speed according to the action of the reversing switch, and automatically accelerate to the required frequency after the commutation is completed, so that the energy loss of the motor and the reversing valve in the whole load range reaches a small degree.
Second, it is convenient and cost-effective. The original water level controller and magnet signal of master cylinder are removed and replaced by analog signal controller to control the level of water level. A man-machine interface is installed to check the real-time water level of the master cylinder. The accident caused by no water operation of master cylinder has been avoided. The original analog signal controller is used to control the water level and reduce the maintenance cost and production cost.
Third, improve the power factor and save energy. Reactive power not only increases the line loss and equipment heating, but also reduces the active power of power grid due to the reduction of power factor. It can be seen that the greater the power factor, the greater the active power. The cos φ value of the common main pump is between 0.6 and 0.8, but after using the frequency conversion speed regulating device, due to the compensation function of the filter capacitor in the frequency converter, the cos φ is about 1, thus reducing the reactive power loss and increasing the active power of the power grid.
Fourth, soft start energy saving. As the original motor is directly started or Y / △ started, the starting current is equal to (3-7) times of rated current, which will cause serious impact on mechanical and electrical equipment and power supply network, and will increase the power grid capacity requirements. The large current and vibration generated during starting is extremely unfavorable to the service life of the equipment. After using the frequency conversion energy-saving device, using the soft start function of the frequency converter will make the starting current start from zero, and the maximum value is limited within the acceleration current limit level set by the frequency converter, which generally does not exceed 1.2 times of the rated current, which reduces the impact on the power grid and the requirements for the grid capacity, and extends the service life of the equipment.