Issues related to gas supply for process instruments in winter

For instrument air in winter, the main concern is freezing and resulting failures, but since measures are in place to maintain a dew point of -60 degrees, freezing will not occur. The capacity of a air compressor is characterized by the volume of air it can draw in; the air delivery volume in winter is the same as in other seasons. However, the density of the air is highest in winter, while the mass flow rate actually increases.

You mean that the volumetric flow rate remains constant while the mass flow rate increases. Is there no change in pressure? ?

I understand what is meant by the second floor: in winter, the density of the air increases, but the volume of compressed air delivered by the compressor remains unchanged; therefore, only the mass of air per unit time increases. Pressure is primarily related to volume and temperature (PV=NRT), and the effect of temperature is minimal, so pressure changes can be disregarded. Please feel free to correct me if I’m wrong!

The most important concern regarding instrument pipes in winter is freezing protection, as compressed gas contains a small amount of water vapor which condenses during transportation, potentially leading to pipe blockages.

The impact of instrument air in winter should not be significant, as the instrument air is already dehumidified. It won’t freeze. It is mainly the instruments that are affected; inaccuracies in these instruments occur frequently due to material crystallization or freezing.

In our company, there was a case where moisture in the instrument air caused freezing; in cold weather, steam was used to thaw it out, and temporary insulation and heating were then applied.

People upstairs said that the gauge gas freezes; we’ve encountered that problem as well. It’s quite confusing. I think I heard that some organizations have managed to solve this issue, but we’re not sure how they did it

Here, we have installed a desiccant at the outlet of the air compressor to remove the condensed water from the air. It was put into use last autumn, and its effects were very noticeable last winter.

I disagree with the opinion of the expert above. Instrument air is air that has been dried using molecular sieves; where could water come from? How can freezing occur if there is no water?

To prevent freezing in winter, it is very important to choose the right type of instruments. It is essential to take proper measures to protect compressed air flow meters, nitrogen flow meters, gas flow meters, and gas flow sensors from freezing; the selection of appropriate products is key to this. When installing these instruments initially, users should consider the operating conditions in which they will be used and opt for instruments that come equipped with insulation features. Based on the category and purpose of the instrument, as well as the location where it is intended to be installed, the insulation and anti-freezing requirements for that instrument are determined, and these requirements are then submitted to the manufacturer for handling. Here are some suggestions for selection provided by users online: 1) For remote signal transmitters and display instruments, the requirements regarding tolerance to environmental temperatures must be taken into account; for those with isolation fluids, the tolerance of such fluids to environmental temperatures also needs to be considered. 2) Mass flow meters, metal rotor flow meters, electric target flow meters, positive displacement flow meters, etc. generally do not require separate heating. 3) First of all, when selecting an instrument, practicality and cost-effectiveness are generally taken into consideration. Practicality refers to ease of maintenance and accurate measurement, while cost-effectiveness simply means low price. The two should be combined; it is not appropriate to choose mass flow meters, metal rotors, electric targets, etc., solely for the sake of convenience and reduced maintenance. Therefore, I believe the proper selection of components is merely one measure to prevent freezing and condensation. When installing instruments, due consideration must be given to preventing freezing and condensation; for example, the pressure transfer pipes should be as short as possible, regular inspections and cleaning should be carried out, and heating systems should be made available – otherwise, no matter how well the instruments are selected, it will be of no use. 4) In some areas in the north, the temperature difference between day and night is extremely large; temperatures can drop below -20 degrees at night. Addressing this issue through product selection would result in a low cost-effectiveness, making it uneconomical. Instead, using insulation and heating systems, along with maintenance methods such as regular inspections and waste removal, are the best solutions to prevent freezing.