Analysis of common failure cases of DCS control system02/17/2021
At present, cement enterprises mainly rely on the loading machine and manual stacking operation, although the domestic cement industry has also appeared automatic loading and stacking device, but due to a series of problems such as low production efficiency, still cannot meet the delivery demand. When loading cement bags, they will collide, emit dust and pollute the environment, and also affect the health of loading workers. In order to improve the working environment of loading workers and control the dust of cement in loading road, it is urgent to reform the dust collection technology in loading road. But because the loader needs to move back and forth in a certain range, the dust will also change, leading to the general dust collection system cannot well achieve the expected dust collection effect. By comparing the use effect of dust removal devices in several subsidiaries of the group company, the author finally chooses a set of technical improvement plan with better effect. This paper summarizes the technical reform for reference.
01 status quo
The mobile cement bagged loading machine is located above the bagged cement loading road. The loading machine consists of a trolley conveyor belt, a downward inclined belt conveyor, a sliding bag slide plate, a ring chain electrical hoist and an electric control system. The mobile cement bag loader relies on the trolley to move forward or backward to complete the horizontal movement, and the chain electrical hoist drives the lower inclined belt conveyor to complete the lifting and changing amplitude of the lower inclined belt conveyor, so as to facilitate the loading workers to pack the car. When loading cement bags, it is necessary to start all the loading system equipment first, and then start the packaging machine system equipment. After the packing machine packed cement bags, through the baling machine, the baling machine, cleaning aircraft, conveyor belt to the loading machine, and finally by the loading workers manually stack the packaging car. The whole process mainly has two parts of the dust point, one part is in the packaging machine and the charter machine, this part of the design has a more mature dust collection facilities, so this part even if the dust is no dust; The other part of the ash emission point in the carriage when loading, mainly due to the loader dragging stacking yard bags, because of the height difference (about 1.5m) factor, the cement bag under the action of dragging falling inertia collision, dust emission, environmental pollution, but also to the loader’s health has adverse effects.
02 Technical improvement of dust removal
2.1 Selection of dust cover
At the beginning of loading, the dust is mainly concentrated in the interior of the car. When the cement bags are stacked to the level of the railings of the car, the dust will disperse horizontally. At this time, the dust pollution can be visible to two meters away. The previous dust collection technology is installed at the top of the stack position of a dust cover, the use of dust fan to make the dust cover form local negative pressure to collect dust. At the beginning of loading, although this method can collect part of the dust generated during loading, when the cement bags are stacked to the level of the railings of the car, the dust collection effect cannot meet the requirements. After summarizing the previous experience and repeated deliberations, we finally chose the all-inclusive dust collector (see Figure 1). The front and rear dust curtain is a transparent multi-piece hanging curtain, and the dust collector is equipped with a supplementing light inside.
Fig. 1 All-inclusive dust collector
The main characteristics of the all-inclusive dust collector cover are as follows :(1) the two sides of the plate as the dust collector branch pipe, in the lower part of the side plate, according to the size of the vehicle set up the dust suction port, the dust suction port is equipped with an adjustment plate, can according to the actual loading needs to adjust the position and size of the dust suction port. (2) The suction port is mainly selected at the lower part of the side plate. Due to the effect of negative pressure of dust collection, the dust generated by workers when loading and stacking will run downward, and will not reach the facial position of workers, which will affect the health of workers. (3) The dust curtain device is selected before and after the dust cover, which can meet the adjustment of the lower Angle of the loading machine and the entry and exit of transport vehicles. In the loading process, the air flow momentum of the dust collector is relatively large due to the effect of negative pressure. According to the inner loading workers of the dust cover, the inner loading comfort of the dust cover is more appropriate, and there are no problems such as stifling and insufficient light.
2.2 Pipeline selection
(1) Pipeline form. Due to the characteristics of the horizontal back and forth movement of the loading machine and the small cement dust, we choose the telescopic steel pipe to design the pipe (fishing-rod type). The design takes advantage of the smooth inner wall of the pipe, which can effectively avoid the accumulation of cement dust in the duct, and is conducive to the movement of internal dust under the action of the fan.
(2) Calculation of pipe diameter. According to the nature of cement dust and the direction of the pipeline layout and other factors, the internal wind speed of the pipeline is controlled in 18 ~ 25m/s. According to Equation (1), the cross-sectional area of the pipeline can be calculated, and finally the diameter of the pipeline can be calculated.
S ₁ ₁ ₁ = Q / 3600 v
S₁ — area of pipe, m²
Q₁ — handles air volume, m³/h
V₁ — internal pipe wind speed, m/s
When V₁=24m/s, calculate the diameter of the duct about 600mm.
2.3 Selection of dust collector and fan
(1) Calculation of filter wind speed and system resistance of filter bag. Because the driveway dust collection system works at room temperature, the dust collected is cement dust, so the filter bag material can choose ordinary polyester needled felt, and the filter bag filter wind speed should be controlled at 1.0 ~ 1.5m/min. Can be calculated according to formula (2) : S₂=Q₂/60V₂
S₂ – dust collector filtering area, M ²
Q₂ – Deal with air volume, m³/h
V₂ – dust collector filter bag filter wind speed, m/min
The bag dust collector is generally installed on the spot. The dust collecting resistance is generally 1.47 ~ 1.77kPa, the dust collecting pipe resistance is generally 1.0kPa, and the negative pressure of the dust collecting cover mouth is considered to be the lowest 0.5kPa. Based on this, the total resistance of the dust collecting system in the whole loading lane can be calculated to be 3.3kPa.
(2) Selection of dust collector and fan. In order to ensure the use effect of dust collector, according to the provisions of GB4915-2013(Cement Industry Air Pollution Discharge Standard), the emission limit of particulate matter in packaging workshop is 20mg/m³, and the key area is 10mg/m³. With reference to the relevant “Dust Collection Engineering Design Manual” and the use of other cement plants’ lane dust collection technology, we choose the wind speed of dust collector is 0.8m/s. According to the design formula (3) : Q₃=2700V’ (10X²+F)
Q₃ — handles air volume, m³/h
V’ — control the wind speed, m/s
X — distance from dust collector to dust point, m
F — area of dust cover suction outlet, m²
Prediction: Q ₃ material after 25000 m/h
Since the dust collector and the fan work at room temperature, the main dust collected is cement dust, and the dust filter bag can meet the demand by selecting ordinary polyester needled felt. When the net filter dust wind speed selection of 1.2m/min, dust cover required air volume selection of 26000m³/h, after calculation can get the dust collector filter area S₂=26000/60×1.2≈347m². After referring to the relevant data and parameters of the dust collector, the pulsed bag dust collector of the type PPC64-6 and the dust collector of the type 4-68-NO.10D are determined to be selected. The power of the dust collector is 55kW, the speed is 1450r/min, the flow is 35420 ~ 61179m³/h, and the full pressure is 3442 ~ 2422Pa.
In order to reduce the impact of the weather on the loading road, both ends of the loading road are sealed with transparent hangings, and the color steel tile ceiling is also installed without power ventilator, so as to reduce the dust of the loading road and improve the site environment.
2.4 Removal design of dust cover
(1) Because the dust collector is an all-inclusive dust collector, there is no need to move up and down. The dust collector is designed with a small gate, which can be used for loading workers to choose the appropriate dust collector according to the height of the car.
(2) The horizontal movement of the dust cover is accomplished by means of the power of the mobile bagged cement loader. In order to ensure the synchronous movement of the dust cover and the mobile bagged cement loader, we will hard connect the dust cover and the loader. Considering that after the hard connection, the load of the walking mechanism of the loader increases, we have improved the power system of the walking mechanism of the mobile cement bagged loader, and changed the power of the driving motor from 1.5KW to 2.2KW.
Although the dust collection scheme of the loading lane invested 520,000 yuan/set (one towing two, equipped with a packaging machine and two loading lanes), it completely improved the high dust working environment of the loading workers and effectively inhibited the dust in the loading lane. When the dust collection system is in normal use, the loading workers can basically fold the bags without masks. Although the investment in dust-collecting technology of loading road cannot directly bring economic benefits to the company, it is of great significance to the health of workers.