Regarding CNG refueling issues

This post was last edited by arpcd on 2015-6-3 16:46. Does the original poster want to set up a CNG refueling station? The process at CNG filling stations is well-established. . 1. Why are gas cylinders and pipelines designed with different pressures ； A: Installing gas cylinders and pipelines with different pressure levels is intended to improve the utilization rate of the gas cylinders and reduce the time it takes for the compressor to start up. For example, when supplying gas to buses, low-pressure cylinders are used first; once the pressure in these cylinders equals that in the vehicle’s gas cylinders, the system switches to medium-pressure cylinders, and finally to high-pressure cylinders. When the high-pressure cylinders run out of gas, the compressor is started up. This process is known as sequential gas usage. Using bottle sets with different pressures not only helps to extend the lifespan of the compressor, but also contributes to stable CNG pressure and flow rates. 2. If a CNG vehicle comes to refuel with an empty tank, the back pressure of the tank is very low while the CNG pressure is high; how can refueling take place in such a situation? A: Gas storage cylinders are now modular components, equipped with various modules such as those for measurement and pressure reduction. Gas filling stations can draw gas in sequence at low, medium, and high pressures according to certain ratios, thereby ensuring a stable gas supply. 3. Can pressure reduction be achieved just by adding an air compressor? So what to do if the temperature drops? A: The main functions of a gas filling unit are to measure precisely and to deliver gas in a steady, proportional manner; it also controls the target pressure at which gas is filled. High precision is required for this purpose, and it needs to be equipped with devices such as mass flow meters and emergency ball valves. The unit must constantly monitor the target pressure of the gas tank in the vehicle. Its function is not to reduce pressure, but rather to ensure stability. As for temperature changes, I’m not sure what you mean by that. More gas is filled in winter and less in summer due to differences in temperature; more gas fills result in higher charges, while less gas fills result in lower charges. Gas filling units are equipped with mass flow meters, and pricing is based on volume. It’s necessary to enter the density of natural gas, which is usually set by local regulatory authorities – as a fixed value or based on actual measurements (this is specific to different regions in China, as you know). . . If you’re worried that a drop in temperature could cause CNG to freeze, there’s no need for concern; CNG stations, regardless of their type, are equipped with CNG drying devices.

The answer above is already very detailed; I’ll wait and learn a bit more

Typically, the low-pressure gas cylinder operates at 5-6 MPag. If the on-board tank reaches atmospheric pressure and then refueling takes place at a station, the pressure is reduced from 5-6 MPag to atmospheric pressure; assuming an initial temperature of 5°C (in the north), the temperature drops to around -30°C after the pressure is reduced. Assumed gas components: C1 0.96639 ； N2 0.03361. My concern is that after the pressure is reduced, the temperature drops and ice forms on the outside of the pipes and the on-vehicle air tanks. The gas stations in the north that I’ve seen don’t seem to have any insulation layers, do they? Thank you very much for your reply; thanks. . .

I mean, if it’s really going to freeze over, the filler worker can’t possibly go about his job carrying an ice pop with him! Also, once it’s inside the car, the gas canister turns into an ice block. Or is it one with a heater built into it?