Abstract: Through the research and analysis of the current operation status of the cement 2 # roller press system, measures are taken to transform the hydraulic station to address the shortcomings of the original hydraulic station during operation. Upgrade and renovate the original hydraulic station, keeping the PLC control in the DCS system unchanged, and achieve stable operation of the roller press through the overall upgrade of the hydraulic station. The design of this oil station is based on self completion. Since the resumption of production, the station has been put into use, ensuring the stable operation of the roller press system and achieving the goal of energy conservation and consumption reduction.
According to the development concept of "innovation driven, energy-saving and consumption reducing", in order to achieve sustainable development of the enterprise, our company has rapidly promoted the implementation of renovation projects in the cement process. The implementation of the hydraulic system upgrade and renovation project for the 2 # roller press is based on the principle of saving renovation costs and later operating costs. With the independent research and design of mechanical technical management personnel, the renovated hydraulic station was officially put into use in mid March 2020 after being verified by a professional manufacturer. At present, the roller press operates efficiently and smoothly, achieving the goal of energy conservation and consumption reduction.
1. Current operating status
The principle of our company's roller press hydraulic station before the renovation is shown in Figure 1. The operation status of the hydraulic station is mainly manifested in the following aspects:
Figure 1 Hydraulic principle picture of hydraulic station before renovation
(1) The oil tank capacity is too small, only 300L, and there is little oil storage. Before production and operation, the normal position of the hydraulic station oil gauge of the roller press is at a height of 200L. When the loading pressure reaches 7.5MPa, the high-pressure oil pump stops and the hydraulic oil returns to the oil tank from the rodless chamber of the oil cylinder. The oil tank will overflow, causing waste of oil. The design defects of the oil station manufacturer greatly increase the labor intensity of the personnel cleaning the oil station. In addition, when the roller press machine experiences material jamming, manual roll retraction operation is required. When the oil is filled to the upper limit, the oil level indicator still shows low after the loading pressure is turned on, and the oil inlet pipe cannot touch the oil level, resulting in the oil pump being unable to supply oil normally and damaging the oil pump and hydraulic components.
(2) Due to the lack of automatic roll retraction function in the roller press, the equipment is forcibly started with load every time it stops, causing certain damage to the torque support structure, reducer, cross universal joint, and main motor of the roller press, laying hidden dangers.
(3) The hydraulic circuit design is unreasonable, and the five overflow valves of the hydraulic station are connected in series in the hydraulic system, resulting in a long troubleshooting time and causing the cement system to shut down for a long time, affecting the normal production of cement. In addition, a one-way valve is not designed in the pressure maintaining state, and the system pressure cannot be locked under working conditions. Only the electromagnetic directional valve is used to cut off it. This design is prone to system pressure leakage and cannot meet the long-term pressure maintaining requirements of the system, resulting in frequent pumping and pressure replenishment of the hydraulic station, greatly reducing the service life of the oil pump and electromagnetic directional valve; At the same time, the impact of the oil also resulted in a shorter service life of the accumulator nitrogen bladder, which needs to be replaced every 3 months.
(4) The layout and component selection of hydraulic pipelines are unreasonable, and the pipeline sealing is prone to leakage. The manual pressure relief valve adopts an integrated valve seat type, and the surface sealing method used can easily cause oil leakage from the valve seat. The unloading valve of the system adopts a pilot operated relief valve, which cannot unload accurately and has a high failure rate; The hydraulic system is not designed with a precision filtration device installed. When metal impurities enter the system, it can cause blockage or damage to hydraulic components, resulting in the inability of the oil station to operate normally.
(5) The selection of high-pressure oil pump flow rate is too small, resulting in a long pressure replenishment time (about 20 minutes) when the equipment is turned on, causing the system to run empty and increasing production electricity costs.
2. Renovation measures
Our company's mechanical technicians conducted a careful comparison and analysis before the renovation, and based on the principle of safety, took advantage of the off-season maintenance opportunity in 2020 to carry out the renovation work after sufficient demonstration by professional manufacturers. Based on the existing problems mentioned above, the specific renovation measures are as follows:
(1) Increase the original 300L fuel tank to 1000L, and equip the new tank with an air filter, liquid level gauge, electronic liquid level controller, drain valve, and maintenance manhole door.
(2) Two 160/125-100 roll return hydraulic cylinders and a set of electromagnetic directional valves and oil circuit modules have been added to the system. The roll return system is installed in parallel in the loading circuit (including seamless steel pipes, 90 ° elbows, etc.) and connected to the DCS system for remote control operation.
(3) An electromagnetic directional valve is installed at the pump outlet, and pressure measuring points are designed and installed at the high-pressure oil pump outlet and each pressurization port to provide data support for rapid troubleshooting. Reprocess the valve seat and replace the imported Rexroth valve components to ensure their reliability. Install a one-way valve in the oil circuit design of the loading system to improve the drawbacks of frequent pressure replenishment. The unloading valve of the system adopts a leak free or slightly leaking electromagnetic ball valve, which achieves precise unloading of small flow under good pressure holding conditions. Add a fine filter to the fuel supply to effectively protect the valve components. At the same time, add a magnetic filter to the pipeline of the pressure relief valve returning to the fuel tank to ensure the cleanliness of the oil.
(4) Replace 4 Fenghua Outlet accumulators with a capacity of 40L and match them with the on-site valve seats.
(5) Redesign the on-site pipelines to completely solve the current situation of oil leakage and difficulty in maintenance of the original pipelines. Replace 2 manual pressure relief valves, change the flat sealing structure to a threaded connection at both ends, and weld and seal the original pressure relief valve position with seamless steel pipes, changing the form to a straight through type. The hydraulic cylinder joints are reprocessed to a uniform specification, with each cylinder containing 4 joints and 3 plugs, and 4 metal braided oil pipes are also processed.
(6) Replace the model with CBF-F425-ALP high flow gear pump, with a nominal flow rate of 40mL/r and a flow rate four times that of the original oil pump, as a quick pressure replenishment oil pump when the roller press system is turned on.
(7) During the system debugging process, the loading pressure increased to 11MPa, and the pressure capacity of the entire system can meet the requirements of working conditions.
(8) Successfully tested with materials.
The hydraulic schematic diagram of the modified roller press hydraulic station is shown in Figure 2.
3. Transformation effect
After the hydraulic station was renovated and put into use, it completely solved the design defects and operational drawbacks at the factory, and the transformation effect was good.
Figure 2 Hydraulic principle of the modified roller press hydraulic station
(1) During operation, the hydraulic station is clean and tidy, greatly reducing the workload of cleaning and sanitation for personnel on duty.
(2) It can achieve remote roll retraction through central control, avoiding equipment startup under load and increasing equipment protection factor.
(3) The use of a high flow oil pump can establish hydraulic system pressure in 15 seconds, greatly reducing start-up time.
(4) Under working conditions, the left and right chamber pressures are 10.4MPa and 10.5MPa, respectively. The vibration values of the fixed roller and moving roller reducers are 2.18mm/s and 5.77mm/s, respectively. The loading pressure and roller grinding state are stable, which facilitates the operator to adjust the operating parameters of the roller press according to the material. The hydraulic station and central control screen of the roller press machine that was put into operation after the renovation are shown in Figure 3.
Figure 3: Hydraulic Station and Central Control Screen of the Modified Roller Press Machine
The comparison of data before and after the renovation is shown in Table 1.
Table 1 Comparison of data before and after renovation
Item | Before Modification | After Modification |
Loading Pressure | 7.5 MPa | 11 MPa |
Oil Tank Volume | 300 L | 1000 L |
Oil Pump Model | PV2P1-10-FP vane pump, nominal flow: 10 mL/r | CBF-F425-ALP gear pump, nominal flow: 40 mL/r |
Re-pressurization Time | 20 min | 15 s |
4. Conclusion
Through the optimization and transformation of the hydraulic system of the roller press, the transformed equipment operates well, improves production efficiency, and lays a solid foundation for the enterprise to achieve production increase, consumption reduction, and sustainable development.
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