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Application of Fieldbus Batching System in Chemical Industry

source：Central feeding system
Author：Central feeding system
time：2020-08-22 17:11:07

Application of Fieldbus Batching System in Chemical Industry

[Abstract] In the petrochemical industry, the batching section of the finished product production workshop requires a distributed batching scale. After many exchanges with users, it is determined
Realize the bus-type batching and weighing control system scheme, which has been stable and reliable in three years, simple and easy to maintain, and simple to operate; now it is realized
Make a review of the process, and please point out any irregularities.
batching scale; bus; weighing instrument
I. Introduction
Sinopec Shanghai Petrochemical Corporation-the batching section of the finished product production workshop of the catalyst plant, the original batching is an ordinary digital display and an electronic
Platform scale, manually weigh the ingredients according to the material formula, and then pour them into the kneader for mixing of multiple materials, and the mixing reaches a certain time
Enter the next process after time; the batching process is labor-intensive, low efficiency, serious environmental pollution, high work intensity, and low batching accuracy.
The measurement quality has no traceability and has become the bottleneck of the entire section. For this reason, the unit has tendered this section. Jinan Jinzhong Electronic Scale
Co., Ltd. won the bid and provided users with a fieldbus batching system; since the system was put into operation in January 2010,
The performance is stable, and the measurement quality and weighing information of the whole process have been improved by leaps and bounds.
Among them, the weighing and ingredients part completes the quantitative measurement of bulk materials such as powder and small particles. The control part has weighing setting, automatic
Automatic/manual operation, interlocking control of each action, dynamic digital display of weighing weight, automatic feeding, weighing, mobile trolley receiving, fixed point release
Various functions and features such as material and bus control.
2. On-site configuration, working principle and batching process
The on-site configuration of the batching system is mainly composed of 7 hopper scales, electrical control units, frequency conversion control units, trolley receiving control units,
It is composed of host monitoring, PROFIBUS-DP bus communication unit, etc. (see attached picture for system block diagram).
1.7 Hopper scales: They are placed in 7 stations in the process flow site. Each hopper scale mainly consists of the following parts:
(1) The screw feeder is controlled by the frequency conversion speed regulation, which provides nearly balanced coarse and fine two-stage feeding during the weighing process (also available as required
To set up three-level feeding method), the size of the coarse and fine feeding can be adjusted separately to ensure that the system meets the accuracy of weighing and measurement
Requirements and speed requirements.
(2) Weighing hopper, weighing module, discharge gate, hopper cover, flexible connection, etc.: complete the weighing of materials and realize the signal of material weight
Real-time collection.
(3) Unloading door mechanism: complete the unloading of materials in accordance with the process flow and control signals issued by the system.
working principle:
1# to 7# Each sub-batch unit is relatively independent, and is an inseparable part of the automatic weighing and batching control system of the entire production line.
Part, in the manual state, each subsystem can be individually quantified feeding, unloading, valve switching, and feeding motor start and stop.
In the automatic state, the control system adopts the method of controlling each sub-dosing unit to work at the same time, so as to ensure that the system is high
Complete the batching process with high quality and high efficiency to meet the technological requirements. It can also individually control a certain sub-unit system for batching to meet the characteristics of the process
Special requirements.
Batching process
The initial working state of the system: each storage bin has enough materials, each cut-off gate is in the closed state, and each feeding device is in the closed state.
In feeding state rather than emptying state, the weighing unit discharge valve is closed.
According to the process requirements, set the batching parameters of each corresponding material on the weighing instrument or the upper computer; in the automatic state, the system receives
After the batching signal is allowed, click the mouse on the host computer to proceed, and the automatic batching process of the system starts:
a) After receiving the start signal, each weighing instrument will automatically reset to zero;
b) Then open the cutting device at the feeding port of each feeding device, and start the feeder for feeding operation;
c) First, the frequency converter controls the feeder for coarse feeding. When the coarse feeding setting value is reached, the frequency converter controls the screw feeder to perform coarse feeding.
Fine feeding operation;
d) Feeding is automatically stopped when the set target value is reached; the meter also has a drop compensation function, which can further improve the accuracy of the batching;
e) The shutting off device is controlled by solenoid valve;
f) After the batching is finished and the scale body is stable, the meter and computer collect the actual batching value and store it.
Wait for the upper unloading instruction.
Three, system parameters
Some parameters of the batching scale are shown in Table 1.
Some parameters of the trolley are as follows:
a) Trolley volume: 0.5m3
；
b) The moving speed of the trolley: 6～18m/min;
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c) Maximum load: 1500Kg;
d) Temperature: normal temperature;
e) Sound pressure level: ≤150dB (1 meter around the motor);
f) Alignment accuracy: ±10mm.
Fourth, PROFIBUS-DP advantage
PROFIBUS is the fieldbus standard of German standard (DIN19245) and European standard (EN50170). By PROFIBUS-DP,
It is composed of PROFIBUS-FMS and PROFIBUS-PA series. DP is used for high-speed data transmission between dispersed peripherals, suitable for processing automation
field. PROFIBUS supports several transmission methods such as master-slave system, pure master station system, and multi-master and multi-slave hybrid system. The transmission medium is
Twisted pair or optical cable can connect up to 127 sites.
As we all know, the use of fieldbus technology is due to the higher the degree of automation of the system or equipment, the more I/O points, and the parallel connection
The more work he has. This means that significant costs will be invested in project planning, installation, commissioning and maintenance.
— 3 —
In contrast, it is much more convenient and cheaper to use a fieldbus system to serially network components in the field. Single root for fieldbus
The bus cable replaces the parallel cable bundle and connects the various levels from the field level to the control level.
Advantages of the fieldbus system PROFIBUS-DP:
1. The layout is simple and reasonable: only one can be completed;
2. easy to use;
3. More complete functions;
4. It is easier to maintain and has better scalability;
5. Better performance;
6. More reliable and safer.
5. Introduction to weighing instrument
Weighing instrument selects AD-4402
AD-4402 is a multi-function weighing indicator with ingredient weighing and filling. This display has weight sequence control input and output
Features and options.
AD-4402 can provide mixing ingredients of a variety of materials through the formula function, providing nozzle control and mixing sequence functions. Direct drive
Motorized 250V relay, serial interface, parallel interface, analog output, etc. CC-Link, DeviceNet and Profibus-DP are available
selected.
Example: Multi-material mixing hopper scale
AD4402 is a batching weighing instrument that can control 10 silos and 3 gates (namely, large, medium and small) through the I/O port.
Gate) for automatic batching. Automatic mixing and unloading can also be carried out after the ingredients are completed. It can set up to 100 recipes.
— 5 —
Spare random
Memory
The system inputs the start signal, and the meter will do the first material batching according to the formula we set (according to the material setting parameter
Open or close the large, medium and small gates), and automatically start the second material ingredient after completion, and output the formula according to the formula in turn.
The completed signal can also be used for automatic unloading or controlled unloading. When unloading is completed, there is also a signal output of unloading completion.
Six, concluding remarks
Since the system has been put into operation in the petrochemical industry for three years, the user response system is stable and reliable, maintenance is transparent and simple, and the production process is improved
The level and production efficiency also provide a good model for the control system of similar processes in the future.