Transformation of the air supply control system of

Transformation of air conditioning and air supply control system

the outline of the national "Eleventh Five Year Plan" puts forward the goal of energy conservation and emission reduction. Enterprises are at the forefront of energy conservation and emission reduction, and they are also duty bound. The author analyzed the energy consumption of the coating workshop in our factory, and found that the electrical equipment with high energy consumption is all kinds of fans. According to the requirements of painting process in automobile production, it is necessary to configure a corresponding number of fans for air supply and exhaust of air conditioners at specific stations. Due to the large power of the fan, most of them use soft starter to realize stable startup, and operate at the rated speed after the fan is started. However, the coating process has strict requirements on the air supply volume, and the control of the air volume should be adjusted through the air valve at the air outlet, which leads to energy waste between forced air supply and forced throttling, while the air valve at the air outlet is generally adjusted manually, which increases the difficulty of ensuring the process parameters

how to make the air supply system of air conditioning meet the needs of process parameters and achieve energy conservation and consumption reduction is the main problem to be solved in this transformation project

analysis of air conditioning supply system

1 Composition of air-conditioning air supply system

(1) process flow: according to the requirements of automobile coating process, the air-conditioning air supply system is composed of the following parts (see Figure 1):

Figure 1 process flow of air-conditioning air supply system

air inlet chamber - primary heating section - middle section - primary effect section - middle section - humidification section - middle section - secondary steam indirect heating section - fan section - flow sharing section - silencing section - middle section - medium effect section - air supply section

(2) equipment composition: the air supply system of the air conditioner is mainly composed of air inlet chamber, air conditioner, air supply pipe and regulating air valve. The air outlet of the air conditioner is equipped with a regulating air valve. The air supply outlet of painting and drying equipment is equipped with regulating air valve and fireproof regulating air valve

2. Working principle of the equipment

when the equipment works, the air sent to the paint booth is pumped into the air conditioner by the fan placed in the air conditioner, and then it is heated once by the air conditioner, filtered initially, humidified by spraying (only for the paint booth air conditioner), dehumidified by indirect heating of secondary steam (only for the paint booth air conditioner), filtered with medium efficiency, and sent to each station requiring air supply through the air supply pipe after silencing treatment, The air supply volume can be controlled by the regulating air valve installed at the air outlet of the air supply system. The temperature and humidity of the air supply of the air conditioner can be manually controlled

analysis of current situation of control system

1 Air supply motor condition

(1) rated power: 130kW; Rated current: 249a; Speed: 730r/min

(2) number of motor poles: 8 poles; Connection method: y; Type: asynchronous motor

(3) starting mode: the original control cabinet is equipped with soft starter, and the motor is started by soft starting mode. After the motor is started, it operates at the rated speed. According to the load condition, the current changes between 200 and 240A. 1. Sensor of microcomputer controlled material testing machine: the force measuring stability of the testing machine is determined by the advantages and disadvantages of the sensor

2 Air volume adjustment

the air supply outlet of the air conditioner is equipped with a regulating air valve, and the air supply volume can be controlled by the regulating air valve. Since the air valve is controlled manually according to the process requirements, it is difficult to ensure the process parameters

3. The influence of filter on air volume

the coating process of automobile production has high requirements on the cleanliness of air. In the air conditioning and air supply system, outdoor fresh air entering the workshop needs three filters. Filter out the dust in the air entering the workshop through the filter cotton or filter bag on the filter. With the accumulation of dust on the filter or filter bag, the resistance of the filter to the air will gradually increase, reducing the air supply volume of the air conditioning air supply system. When the air supply volume cannot meet the process requirements, it should be adjusted through the air valve

after repeated adjustment, when the air volume cannot be met by adjusting the air valve, the filter cotton should be cleaned or replaced, and then the air supply volume should be readjusted. The adjustment of air valve brings great workload to workers

4. Disadvantages of the original system

(1) the process parameters of air supply depend on manual detection and adjustment, and the process conditions are not easy to ensure

(2) the full speed air supply of the motor will consume a lot of electric energy to generate wind energy, and the throttling regulation of the air valve limits the use of wind energy, resulting in a large waste of energy

(3) when the resistance increases after the dust of the air inlet filter gradually increases, a large negative pressure will be generated in the fan section, and the system has no alarm device. If the operator cannot find it in time, it will damage the chamber body of this section

(4) when the resistance of the second layer of filter behind the fan increases with the increase of dust, the pressure of the connection section may rise, causing safety accidents

(5) there is no necessary detection and automatic control system, and the air supply volume of the air conditioning system cannot be automatically controlled and adjusted

transformation scheme of control system

1 Scheme principle

(1) apply frequency conversion technology, use frequency converter to control the speed of air supply fan, and adjust the air supply volume by manually or automatically adjusting the speed of fan

(2) a pressure sensor is installed in the fan section behind the filter at the air inlet of the fan to collect the pressure value drafted by the Ministry of industry and information technology

(3) a pressure sensor is installed at the air outlet of the fan to collect the pressure value there

(4) install pressure sensors and temperature sensors at the air supply outlet of the air conditioner to collect the final air supply pressure and temperature values

(5) PLC is used as the controller, and the automatic control principle is applied to realize closed-loop control. At the same time, the pressure value of each point is monitored to realize the functions of control, adjustment, alarm, etc

(6) the human-machine dialogue is realized by adding the touch screen to complete the display of control parameters and operation status. The operator can adjust or set the control parameters through the touch screen

2. Control function description

control system diagram established according to the above scheme (see Figure 2)

Figure 2 Schematic diagram of the control system

(1) fully open the air valve of the air supply outlet, take the pressure value at the air supply outlet corresponding to the air supply volume required by the process as the given value, and conduct closed-loop adjustment through PLC. By ensuring the pressure value of the air outlet, the air supply demand of the production site can be met

(2) PLC monitors the outlet pressure of the fan. When the difference between the outlet pressure and the outlet pressure of the second filter exceeds the set value, PLC will give an alarm after repeated judgment, prompting the operator to check whether the second filter is blocked

(3) PLC monitors the negative pressure value at the outlet of the first layer of filter. When the negative pressure value is greater than the set value, PLC will give an alarm after repeated judgment, prompting the operator to check whether the first layer of filter is blocked and take treatment measures

(4) PLC also provides a point temperature measurement to measure the air supply temperature after the second layer filter outlet. According to the set high and low limit alarm value, the high and low limit alarm will be sent after comparison

(5) siemens s series products are selected for PLC and ACS510 series products of ABB are selected for frequency converter

3. Control mode

(1) manual operation. During manual operation, the speed of the frequency converter can be manually operated through the touch screen. The operation frequency is manually input, and the frequency converter operates according to the manually set frequency. This operation mode is generally not used. It is only used when the environment is special and automatic adjustment cannot be achieved. At this time, the display and fault judgment on the touch screen are still valid

(2) automatic operation. During automatic operation, PLC automatically performs logic calculation and closed-loop control according to the scanning cycle, intelligently judges various faults, and transmits the operation data and alarm information to the touch screen for dynamic display. The displayed faults mainly include the high and low limit alarm of the second layer filter outlet temperature, the high and low limit alarm of the negative pressure value at the first layer filter outlet, and the limit alarm of the pressure difference between the second layer filter and the fan room. As a plastic material for food packaging, the properties include: protection performance, health and safety, non toxicity, anti biological invasion, processing technology, printing adaptability and other alarms, contactor failure, frequency converter failure and other alarm signals

results of project implementation

1 Process equipment

(1) collect the sensor signals (temperature and pressure) installed on the site through PLC and dynamically display them on the touch screen, so that the equipment operator can monitor the operation status of the air conditioning and air supply system

(2) by entering the parameter setting screen on the touch screen, the operator can set the process parameters of the air conditioning air supply system and the upper and lower limit alarm points of the pressure of each point of the air supply system. After the system alarms, it reminds the operator to deal with it in time, ensuring the safe and effective operation of the air conditioning air supply system equipment

(3) after the implementation of the project, the automatic control of the air conditioning and air supply system will be realized, and the production process parameters will be timely and effectively guaranteed, providing an ideal production environment for the body coating

(4) the air supply system of the air conditioner can be visualized by compiling the monitoring screen, which includes the process flow chart screen (see Figure 3) and the parameter setting screen (see Figure 4)

Figure 3 process flow diagram screen

Figure 4 parameter setting screen

2 Energy saving and consumption reduction

(1) after the implementation of the project, fully open the regulating air valve at the air outlet of the air supply system, reducing the air supply loss; Through the control of the fan speed by PLC, the automatic speed regulation is realized, and the manual adjustment workload of the air valve is saved

(2) through the automatic control of variable frequency speed regulation, the running speed of the motor is reduced, and the running frequency of the motor is reduced from the original 50Hz to about 40Hz; The load current is reduced from the original 210a to about 160A, reducing the consumption of electric energy, and the energy-saving ratio is more than 30%

3. Comprehensive effect

through this transformation, the air-conditioning air supply system has effectively achieved the dual effects of both meeting the needs of process parameters and saving energy and reducing consumption. The investment of this project can be recovered within two years, and the return on investment is high. The factory also has a number of similar fans, which have been successfully put into mass production. The transformation is planned to be completed in the near future, which will effectively reduce the power consumption of the coating workshop in the future, so as to reduce production costs and improve the competitiveness of products

the implementation of this project is a response to the national grand goal of energy conservation and emission reduction in practice, realizing the unity of the interests of the factory and the country, and has good social benefits

conclusion

the early production equipment was mainly designed to meet the process parameters, and due to the limitations of the technical level at that time, insufficient attention was paid to the loss of energy, and some equipment had the phenomenon of energy waste. The implementation of the project mentioned in the article gives us enlightenment, that is, when we design new equipment, we should consider the above two aspects as a whole to avoid wasting energy and resources. (end)