What is Inlet Air Temperature?
In biogas plant projects, the terms “Inlet Air Temperature” and “Biogas Inlet Temperature” are often confused because of their similar names. In fact, they refer to completely different media and systems.
This article clearly defines both parameters based on international biogas standards and engineering practices, helping to avoid misunderstandings in technical communication.
1.Inlet Air Temperature
In a double membrane cover, Inlet Air Temperature means the ambient air temperature at the blower inlet – the air that the blower draws in to maintain the air cushion.
In simple words: it is air temperature, not biogas temperature. It is an external environmental parameter for the gas holder, not a biogas process parameter.
A double membrane cover consists of two layers: the inner membrane stores biogas, and the outer membrane is kept inflated by an air cushion blown in by a blower. The blower takes in air from the surroundings – the temperature of that air is the Inlet Air Temperature.
This article introduces Inlet Air Temperature mainly to distinguish it from Biogas Inlet Temperature – the two sound similar but involve different media and systems. Inlet Air Temperature is not a biogas process control parameter and does not need to be linked to gas holder pressure stability or membrane life.
2. Biogas Inlet Temperature
Biogas Inlet Temperature refers to the temperature of the biogas as it leaves the anaerobic digester (e.g. glass fused to steel tank) and enters the piping, desulfurization equipment, gas holder, or power generation units.
In simple words: it is biogas temperature, not air temperature, and it is a core biogas process parameter.
When biogas leaves the digester, it carries heat and moisture. If it enters downstream equipment at too high a temperature, problems start to appear.
Water vapor condenses inside pipes, causing corrosion and blockages. Desulfurization efficiency declines. Engines lose performance or may even get damaged. That’s why international standards specify a clear limit.
According to ISO 20675:2018, the temperature of biogas entering downstream equipment must be kept within a reasonable range. The International Electrotechnical Commission (IEC 62297-1) states that gas entering a gas engine should generally not exceed 50°C.
Germany’s VDI 4630 notes that mesophilic digestion runs at 35–42°C, while thermophilic digestion operates at 50–57°C. Chinese national standards also require biogas inlet temperature to be ≤50°C for generator sets. In practice, Biogas Inlet Temperature is generally controlled at ≤50°C.
Why is this number so important? Because this parameter directly affects fermentation activity, condensate formation, desulfurization performance, and engine operation – all critical for the uses of biogas (power generation, heating, etc.) and overall plant safety.
3. Summary
| Parameter | Medium System | Process control | Process control parameter |
| Inlet Air Temperature | Ambient air | double membrane cover (air cushion) | No |
| Biogas Inlet Temperature | Biogas | Digestion & Purification System | Yes (≤50°C) |
Please feel free to send us your questions. In case you need to store biogas, carbon dioxide, or other industrial gases, we can recommend the most suitable biogas domes solutions for your project. We look forward to getting in contact with you.
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