Determination of nitrogen consumption during driving tests
Thread Content
Recently, for the project’s operations, it is necessary to purchase a batch of nitrogen cylinders for purging and displacement (the client does not have an on-site nitrogen generation facility); therefore, procurement is currently underway, with urgency to finalize the design and determine how many cylinders to buy； Previously, when we carried out the calculations, we would first obtain the dimensions of the equipment and pipelines from the pipeline engineering and equipment engineering teams, then calculate the actual volume using process-related formulas, and finally compute the value based on the ideal gas law. However, there was always some error in the results. Do any of you have any good methods or experiences in this regard?
For nitrogen displacement, it is more cost-effective to rent a small cryogenic liquid tank locally, equipped with a vaporizer. The issue with errors in calculating the displacement amount lies in the required precision of the displacement. For small-scale applications, it is best to perform vacuuming followed by replacement, which can save costs.
Air is generally used for purging. The amount of nitrogen required for displacement is calculated as you mentioned: first, determine the volume that needs to be displaced, then use the equation of state to calculate the amount of nitrogen needed based on the number of pressure changes, and finally multiply by a safety factor.
The gas in the cylinder cannot be completely released; I wonder if you have considered this
This is a great choice; I was worried about the problem of storing so many nitrogen cylinders. Thank you, Haiyou
Yes, one issue is that the number of times of pressurization and depressurization is determined based on the actual effectiveness of the gas exchange. Sometimes just one cycle of pressurization and depressurization is sufficient to meet the requirements, but in harsh environments several cycles may be needed, which makes things more complicated. Still, thanks to Haiyou
Well, I have considered it; I’ve taken a 15% margin into account
The replacement effect is predictable. For example, with a straight tube and an adequate flow rate of nitrogen for displacement, very little nitrogen is required – about three times less in volume. If it is not a straight pipe and there are various devices, etc., an approximate 15-fold increase in volume should be considered. If the nitrogen flow rate is low, the pipeline length is long and the diameter is large, you also need to take into account the stratification phenomenon in order to ensure an adequate nitrogen flow rate. Even a simple nitrogen displacement involves its own set of principles!