In perfecting the new catalyst automatic feeding system before the transformation of the dosing process is: first from the conveying pipeline to the mixing tank into a certain amount of kaolin, and then into a certain amount of dispersant, after 2.2 hours of reaction, and then add the other 7 materials in turn, so that there are the following problems: (1) due to the reaction time is longer, which seriously affects the production efficiency of the product. (2) Due to the backwardness of measuring equipment, human influence factors are heavy, input dispersion dose can not be well controlled, too much input, production costs greatly increased, resulting in waste, too little input, affecting product quality, product failure rate increased, resulting in a large number of waste products. (3) Due to the special chemical nature of the material, corrosive and dust pollution is more serious, seriously affecting the health of workers.

In recent years, the degree of automation of industrial processes and people's awareness of environmental protection, frequency regulation technology with its excellent performance, widely used at home and abroad, especially with China's accession to the WTO, the petrochemical industry, the competition is more intense, and the quality of the product put forward higher requirements. In view of the problems existing in the process of the original automatic feeding system, the relevant leaders discussed the decision to renovate the catalyst automatic feeding system, retaining the other 7 storage tanks unchanged, mainly for kaolin, alumina and dispersant pulping, the renovation program is: (1) kaolin pulping and reserve 2 sets; (2) alumina pulping and reserve 1 set; (3) dispersant pulping and reserve 1 set. The paper focuses on the application of double closed-loop control and green design of frequency conversion speed regulation.

2, the composition and working principle of speed control unit

2.1 Composition of speed control unit

Frequency conversion speed control unit is mainly composed of DCS, PLC, dosing belt scale, star feeder, frequency converter, AI-808 regulator, flowmeter, electrical conversion valve and so on.

2.2 Working principle of speed control unit

Automatic batching system frequency conversion speed control loop constitutes double closed loop electronic belt scale, computer totalizer, frequency converter, AI-808 regulator, star feeder, belt conveyor and other components. The frequency converter is Delta VFD015A43B, which is mainly used for controlling the feeding of the star feeder. The dosing belt scale detects the material flowing through the conveyor and transmits the signal to the computer accumulator, which sends a 4-20mA analog signal to the regulator, which sends two 4-20mA analog signals, one of which is transmitted to the DCS system, which is multiplied by the coefficient K as the target value of the second closed-loop; the other one is sent to the DCS system as the target value of the second closed-loop; and the other one is sent to the DCS system as the target value of the second closed-loop. The other way is transmitted to the frequency converter, and the V/F value of the frequency converter is adjusted through the regulator to regulate the rotational speed of the star feeder, so as to ensure that the kaolin flowing through the belt conveyor is more uniform, and the purpose is to produce a more stable and accurate flow rate; the second closed-loop control is to regulate the dispersant amount according to the amount transmitted by the first way, so as to make the amount of dispersant follow the amount of kaolin to change, and to ensure that the regulating valve works properly on one hand, and on the other hand, it is to ensure that the dispersant is not used in the production process. On the one hand, it ensures that the regulating valve works normally, and on the other hand, it ensures that kaolin and dispersant are mixed according to a certain proportion to ensure the accuracy of the proportion, so as to guarantee the quality of the mixture and improve the reliability of the system.

2、3AI-808 regulator

Characteristics of AI-808 regulator: domestic advanced instrument, internal high-performance ASIC chip and modular hardware design, in the input and output signals are used in the digital correction technology to eliminate the stability of the adjustable resistor brought about by the error; through the application of automatic zeroing technology can be used for a long time and does not produce zero drift, the measurement of digital precision and stability; with a variety of input and output specifications and alarm mode settings. The measurement figures are accurate and stable; with a variety of inputs, outputs, specifications and alarm settings. Not only with manual/automatic non-disturbance switching operation, but also with manual self-tuning and display of output values, etc., as well as used as a servo amplifier to directly control the position of the valve proportional output, the power supply can be fluctuated within a wide range of 85-264VAC (50-60HZ), the strong interference in the environment can also ensure that the accuracy of the measurement and the stability of the work.

At present, there are more domestic and foreign producers of regulators, we choose Xiamen Yuden AI-808 regulator through comparison, mainly based on the following reasons: (1) high cost-effective products; (2) high reliability and stability of the product; (3) after-sales service in a timely manner; (4) 800 toll-free number. Practice has also proved that our initial choice was correct.

2.4 Calculation and Setting of Optimal Control and Control Coefficients

The production process is a complex dynamic process, the production process of a certain moment in a certain part of the process seems to be uncontrollable, thus resulting in the production of passive or increased labor intensity. Optimal control should not only realize the optimal production process when it is relatively static, but also require that it should be automatically optimal when it changes from one working condition to another, that is, to achieve dynamic optimal control. The so-called dynamic optimal control is to find out the role of control parameters of a parameter or a group of parameters, so that the function of the target parameters to be controlled to meet the constraints of the optimal.

2.5 Control trend curve

To achieve the purpose of process transformation of the dosing system, it must be required that the dispersant can follow the change of kaolin well, and at the same time, it is required that the feeding amount of kaolin can be stabilized within a certain range. Although there are many influencing factors on the site, through the close cooperation of the majority of personnel, the system was finally commissioned successfully, and the system control trend curve is shown in Figure 3:

3, green design and manufacturing

Green design and manufacturing is the road to sustainable development of mankind, it will be the ecological environment and economic and social linkage into a coordinated development of the organic whole, the requirements of economic development must take into account the long-term carrying capacity of the natural ecological environment, to meet the needs of mankind's long-term generation.

In the process transformation of the batching plant, from the program design of the system to the generation of products, including the production process of turnover, recycling and waste, etc., are fully utilized in the new ideas of green design. For example, when the system program design selection, the new ideas of green design in the first place, in order to meet the automatic dosage system, to ensure product quality under the premise, as much as possible, the use of green design; when in order to meet the automatic dosage system, to ensure product quality and the use of green design conflict, to take the funds tilted policy, in order to meet the actual needs. In the design stage of the dosage system, the environmental factors affecting the environment and measures to prevent pollution are incorporated into the product design, and the environmental performance is taken as the target and starting point of the product design, so as to minimize the pollution of the production to the environment, fundamentally prevent and control the pollution, and save the energy and resources. In the design, HONEYWELL's DCS centralized control system and frequency conversion speed control technology are adopted to truly reflect the humanized design and fully realize the automation of the production process, which greatly reduces the labor intensity, improves the production efficiency, reduces the noise pollution, saves the electric energy and reduces the impact on the power grid. In the logistics process, the material is fully sealed, thus eliminating the pollution of powdery and granular materials (such as alumina, kaolin, etc.) to the surrounding environment and protecting the health of workers. Improve the enterprise market competitiveness and sustainable development ability.

4, process transformation problems and solutions

4, 1 DCS collected data problems and solutions

As the DCS mainly collects 4 ~ 20mA analog current signals, analog current has its own defects, especially the collected 4 ~ 20m flow signal through the regulator for the transmission of the error caused by the greater, and at the same time, due to the use of 2-way 4 ~ 20mA module within the regulator, the interference between each other is more serious, the signals transmitted to the DCS found to be significantly missing. Later on the design considerations, through the test found that there are two ways to solve: one: replace the PID internal 4 ~ 20mA module, the use of optoelectronic isolation module, and the grounding of the system to be dealt with. The second direct collection of analog signals from the computer accumulator, but the accumulator interface is only one, and then the analog output of the accumulator to transform, so that it will be accurate all the way to 4 ~ 20mA analog interface at the same time sent to the regulator and the DCS, not only to ensure that the regulator is normal regulation, but also to meet the DCS accurately collect the flow of materials through the conveyor.

4.2 Regulating valve change frequency too fast

Regulator adjustment process, the system appears serious overshooting phenomenon, the system oscillation is more serious, star feeder stops and turns, the regulator valve frequency changes too fast, can not work properly, easy to damage. The reason is mainly: the bin can not be uniform material, the scene vibration phenomenon is more serious, the accumulator and regulator internal parameters are not set properly. According to the site situation one by one to exclude, so as to ensure that the regulator valve work properly.

4.3 The realization of inverter control program

Weighing and batching system by two bins on the conveyor (equipped with electronic belt scales) for feeding, thus requiring two star feeder for feeding, after various demonstrations and automatic batching system needs, using two sets of frequency converter control, but only provide a 4 ~ 20 analog signals, while the use of frequency converter switch, according to the needs of the production of one of the choice or all the work of the two sets.