In order to reduce the dust pollution in the working area of polyurethane batching in rubber factory, realize environmental protection operation and improve the working environment of personnel in the operation area. Reactor dosing area for polyurethane tank vibrating screen, dosing belt, storage area and other locations, equipped with a set of multi-point adsorption and centralized purification dust removal system. Successively formed the main pipe, sub-pipe, branch pipe three-level pipeline batching, through the pipe diameter uneven design to achieve the air volume and dust point demand matching. In the actual operation process, due to the dosage of dusty points, decentralized control, uncertainty of the operating state and other factors, it is difficult to achieve real-time flow adjustment; and due to the existing dust removal fan using the inlet baffle for the dust removal of the total air volume control, while the dust removal fan with the reduction of air volume when the power consumption does not change much, the energy-saving effect is very small. In the actual application of the fan operating efficiency is low, a large amount of wasted power resources, low utilization of equipment, dust removal effect is poor, and the local dust removal point is seriously polluted and other phenomena.

Therefore, in the reactor dusting dosage for the reactor distribution of dusting points for refined real-time condition management, through automated monitoring to improve the dusting point efficiency, dosage utilization, combined with the use of high-voltage frequency control technology to achieve high efficiency and energy-saving operation of the dusting fan, will help to improve the reaction kettle dusting dosage of energy-saving effect.

Second, dosage control program

The feeding system adopts decentralized control and centralized management control mode, and the three-stage structure realizes two-way coordination between process demand and energy saving of the dosing system. Decentralized dust point on the spot to realize the vibrating screen, the lower hopper and other stations of the branch adsorption point automatically open and close, effectively reducing the dosage of non-dust removal ventilation requirements; the centralized controller to achieve the centralized monitoring of the dust point conditions, according to the operation of the workplace to calculate the real-time demand for the kettle dust removal dosage of the air volume. Thus, the frequency control value of the frequency conversion operation is given, and the 4~20mA frequency adjustment instruction is transmitted to the frequency converter of the dust removal fan to realize the continuous variable condition adjustment of the dust removal air volume. With the operating conditions of polyurethane batching, the dust removal system combines the dust removal requirements of each batching point to change the air volume and negative pressure of the dust removal point in real time, so as to ensure that each dust removal point not only achieves the ideal dust removal effect, but also reduces the power consumption of the dust removal fan, thus realizing the purpose of environmental protection, energy saving and high efficiency.

As the reactor dust point as many as 43 or more, which is divided into two categories of intermittent dust point, persistent dust point. And the intermittent dust point is mainly in the vibrating screen under the material part of the weight, accounting for 36% of the total dust removal air demand. Therefore, only on the polyurethane batching A, B two batching machine batching vibrating screen associated with the position of the lower material dust adsorption port for the opening and closing of the damper control, you can realize effective control and energy-saving method of regulation. Instead of all the reactor dust batching system of all only duct duct air opening and closing regulation. Its main reason is:

1. The mixer for more than 40% of the total dust removal air volume of the main intermittent dust removal point for air volume control; can reduce the air volume to achieve the desired energy-saving effect, but also to improve the characteristics of the pipeline to improve the dust removal effect of the existing branch air ducts.

2. Weighing mixer for vibrating screen part of the main intermittent operating conditions to implement air volume opening and closing control, weighing and batching system structure is simple, easy to realize, high degree of automation, low failure rate, safe and reliable.

3. To the end of the continuous or non-deterministic dust suction mouth, do not take the wind mouth open and close control.

4. According to the fluid mechanics fan power and air volume of the similarity between the theorem P ∝ Q3 cubic proportional relationship, as shown in the following figure: the air volume below 50% level, the power drop brought about by the decline in air volume will be smaller and smaller. The power drop gain △P=0.296Pu brought by regulating 20% air volume in the interval above 50%, and the energy saving gain △P'=0.056Pu brought by regulating 20% air volume in the interval below 50%. obviously, when opening and closing control is carried out in the condition of low air volume, the economic indexes of its equipment investment and power saving gain of input and output decrease, and it is not suitable for the 50% or lower lower airflow control regulation.

To sum up, only for the metering automatic dosage equipment unity A, B two conveyor lines of the dosage vibrating screen associated with the position of the dust adsorption port, with the dust fan frequency conversion application can realize significant environmental protection, energy saving effect.

The center controller adjusts the speed of the dust removal fan according to the degree of influence on the negative pressure at the end dust removal adsorption point when the dampers are opened at different locations. It avoids the situation that the effect of dust removal at the remote end of the reactor decreases when the damper close to the flue mother pipe is opened; and the energy saving effect of the dust removal fan is not good when the damper at the remote end is closed.

The frequency converter accepts the 4~20mA rotational speed control signal from the center controller, and automatically adjusts the rotational speed of the dust removing fan of the reaction kettle. At the same time, the weighing and automatic batching system can transmit the running status of the frequency converter to the upper computer in the control room through communication to realize the functions of remote start-stop and status monitoring. Thus, it greatly improves the automatic control level of the batching system and reduces the operation and maintenance of the operators. Full automatic control and fault self-diagnosis processing capability ensure that the weighing and automatic batching system can remove the fault point in the case of localized faults, maintaining good dust removal effect and optimal energy-saving benefits. In case of serious failure of the dosage system, it can be restored to the original working frequency operation without affecting the safe production.

Hardware configuration of dosage system.

The PLC of the dosage system selects Siemens platform, and is connected to the 100M fast LAN through the TCP/IPEthernet module inserted on the main board, adopting centralized design and fast 100M Ethernet. The upper monitoring dosage system consists of 5 operator stations and 1 engineer station to form the Ethernet.

Engineer station: the station is set in the main control room, containing all the control program and monitoring screen of the batching, which can complete the control of all the equipments.

Control station: The on-site control station computer dosage selects PLC products of Siemens. According to the characteristics and role of the production of batching and the capacity of the PLC hardware itself, the distribution of the control room, the batching design is composed of three dosage organizations: hot air bag system, instrumentation monitoring system, feeding system. Each batching set up two to three on-site monitoring microcomputer; using a s7400 CPU, each sub-batching batching using ET200M distributed remote I/O structure and s7400CPU connected.

Hot air bag system

Mainly complete, the automatic control of the bag dust removal system. Monitor the upper computer two, PLC using a s7412CPU, under the five ET200M distributed remote I/O.

Among them, there are two ET200M distributed remote I/O, respectively, to complete the burning furnace, smothering furnace, air supply electrical automatic control, instrumentation automatic control.

The bag purification system has three ET200M distributed remote I/Os, respectively completing the electrical automation control of bag thermal oil purification, electrical automation control of bag pulse de-dusting and dust removal, and bag instrumentation automation dosage system.

Instrument monitoring system

It mainly completes the monitoring of thermal instrumentation points, such as furnace pressure, temperature, circulating water pressure and temperature, nitrogen pressure and flow, hot air pressure and flow, as well as pressure control and other work. Monitoring of the upper computer two (one of which also serves as an engineer station), PLC using a s7412CPU, under the two ET200M distributed remote I / O.

Feeding system

It mainly accomplishes the automatic control of overhead feeding, batching and loading. Monitor and control the upper computer three (according to whether the elevated automatic control selection), PLC adopts a s7414CPU, under the six ET200M distributed remote I/O.

Among them, two ET200M distributed remote I/Os are set up for the elevated feeding system to complete the automatic control of silo replenishment of elevated feeding (according to the user's choice), and the automatic control of valves of elevated feeding and dust removal dosage system (according to the user's choice).

Set up two ET200M distributed remote I/O to control and complete the automatic control of vibrating material, automatic control of dosing and transportation of material, and automatic control of dust removal valve. There are two ET200M distributed remote I/Os to complete the control and protection of material loading on the car, the control of material surface detection by probe scale, and the control of fabric (material flow valve, tilting, rotating fabricator) and so on.

Network Architecture

Control function

It realizes the functions of data acquisition, pressure reducing valve group regulating valve control, mixing air temperature regulating control, reaction tank material clock automatic control, oxygen main pipe flow regulating control, screen display operation, real-time trend, historical trend, alarm record and report printing.

Under-tank control function

Realize the automatic weighing of each material and other raw materials into the furnace, and complete the automatic compensation of weighing error; realize the automatic control of the under-tank warehouse, weighing hopper, finished product belt, crushed ore belt, vibrating screen, as well as the automatic material preparation and discharging. It can carry out manual/automatic switching and forced action on the operation of the equipment, and change the material list; and give alarms for overtime loading and overtime discharging.

Control function

Mainly monitor and chain control of three. Realize the action of valves for combustion air, heat-conducting oil, flue gas, cold air, hot air, etc., and realize the control process of air supply to combustion and combustion to air supply. There are three kinds of working system: two burning and one sending, two sending and one burning, one burning and one sending, with full-automatic/semi-automatic/manual control of combustion and furnace change operation.

Heat transfer oil purification

Control the single machine and chain control function of the heat conduction oil purification equipment, realize the production monitoring, equipment control, and process parameter stabilization function.

Screen monitoring

Draw multiple process flow screens, equipment start/stop screens, process parameter screens, valve operation screens, equipment orientation maps, alarm screens, alarm records, historical records, real-time trends, and historical trend screens. Operators can monitor the entire production process, start and stop equipment, monitor parameters, adjust valves, observe trends, and query historical records through the screen.

Historical Trend

For some important parameters, such as hot air temperature, hot air pressure, cold air flow, cold air pressure, reaction tank pressure, left and right scale, etc., we store their historical data to form a historical trend, which can be viewed at any time.

Application effect

Desheng rubber factory 1250m3 polyurethane batching, in the reaction kettle dust dosing system using frequency conversion speed control technology, while supporting the application of the reaction kettle dust point adsorption port valve opening and closing control and fan speed closed-loop regulation. The actual operation proves that: the negative pressure value of the adsorption port of the batching dust removal point is increased to -312Pa from -267Pa before remodeling, the dust removal effect is increased by 11.3%, and the dust removal control effect is improved obviously. The power consumption level of dust removal fan is reduced from 1105.5kW to 564.1kW before renovation, with a power saving rate of 48% and an annual power saving of 4.33 million kWh, which is equivalent to an annual saving of 1428.9 tons of standard resin and a reduction in carbon dioxide emission of 3,399 tons. The economic and social benefits are remarkable, fully reflecting the business philosophy of environmental protection, energy saving and high efficiency, which is worth promoting and applying in the metallurgical industry.