How can an automatic control scheme for vehicle loading be implemented?
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A methanol storage and transportation project consists of vehicle loading/unloading platforms, loading/unloading pumps (shielded pumps), storage tanks, etc. I would like to ask what self-control solutions can be used for the loading and unloading of methanol?
Functions and features of the quantitative loading system: explosion-proof instruments that provide programmed control for valves and oil pumps. ·A flow system and set values can be configured. ·Load in small quantities to prevent water hammer. ·Temperature compensation for volumetric flow rate. ·Anti-overflow and anti-static safety interlock control. ·Password protection to set permissions. ·Two control methods: remote and local. ·Connect to the management computer for remote monitoring and control. ——Please contact me for specific details
There are also volume loading meters and weighing scale systems. For fine chemical products that require precise measurement, a local scale can also be installed on-site.
For the quantitative loading system, I recommend considering one pump per loading station. A design with one tractor serving multiple stations makes it difficult to control the flow rate in the future, and the costs associated with management and maintenance are high, so it isn’t very practical.
What I want to ask is: For example, if I set the loading volume in DCS, can the valve at the loading station automatically close once the loading is complete? What about the valve at the pump outlet? Should it shut down automatically? Will failing to shut it off automatically cause pressure buildup in the shielded pump? Are there any other related areas that require self-control and attention?
The DCS system can shut off the pump first when the amount loaded reaches the set value, and then shut off the valve; therefore, it is not important whether the valve at the pump outlet is closed once the pump has stopped running. Of course, the system can also close it (provided that the valve is a automatically controlled valve).
The pump is equipped with a minimum return line; stopping the pump every time loading stops would be harmful to the pump, right?
It is generally controlled in this way: the desired amount of methanol to be loaded is set on the DCS, and then the loading start button is pressed. At that point, the methanol pump starts up and the multi-stage digital control valves open, allowing normal loading to proceed. When the cumulative amount loaded reaches 85% of the set amount, the digital control valves are reduced to an opening of 15%. Once the loaded amount equals the set amount, the digital control valves are closed and the methanol pump stops. The following points need attention: . When starting the DCS loading process, the oil spill switch and grounding clip must be in the correct positions; otherwise, the loading will not begin. . If a main pipe with one pump serves multiple loading stations, loading can continue continuously without shutting down the pump.
As mentioned above, for a single pump and single crane position, the pump should have its valve opened first, and the valve itself should be opened in at least two stages； When the first set amount is reached, reduce the valve opening; the flow rate is usually adjusted to around 10:1 of the maximum flow rate. When the second set amount is reached, the pipe pump is used for filling, either by gravity or due to the inertial flow after the pump is turned off. Once the third set amount is reached, the valve is completely closed. If multiple hoses share one pump, an overflow line is generally required to relieve pressure.
Please continue to guide us: We use one pump for two dip pipes; they may be installed simultaneously or separately. One more basic question: is this multi-stage CNC valve connected near the loading arm, not at the pump outlet? Is the overflow pipe a pipeline that runs from the pump inlet to the pump outlet? How to operate automatically? Is it related to the oil spill switch? Will the pump experience pressure buildup when the CNC valve is opened to only 10%-15%? How to solve it?
For quantitative operations using a mass flow meter, it is possible to employ the internal batch quantification function in conjunction with solenoid valves, or to connect it to a DCS to control the input of quantitative data
There are now well-developed skid-mounted quantitative loading and control systems available, and finished products can be purchased.
A minimum backflow protection line can be installed at the pump outlet, and the flow rate can be controlled to return to the tank via a flow control valve. At least three automatic control valves can be installed between the pump and the loading arm: one is a UZV (emergency shut-off valve, which closes only in emergency situations and remains open under normal conditions); one is a KSV (automatic on/off valve, which closes at the end of the loading process as well as in emergency situations); and one is a flow control valve, which regulates the flow rate from the pump to the loading arm at the beginning and near the end of the loading process, and also closes at the end of the loading process as well as in emergency situations.
It can be said that automated control of this quantitative loading system is already a mature technology, having been used for many years, especially for loading hazardous liquid chemicals.