I would like to ask: I need a gas flow rate of 3.5 m3/min, and therefore I need to purchase two air compressors

Pressure screw compressors with a pressure of 0.85 generally don’t present any problems. As for having one unit in operation and another as a backup, that depends on the capabilities of your company. If money isn’t a concern, then using two screw compressors is a good option; if cost-saving is a priority, one screw compressor along with one piston-type compressor will suffice. Generally, screw compressors don’t break down, provided they are properly maintained according to the instructions on the control panel. The only downside is that the maintenance costs for screw compressors are higher than those of piston-type compressors, but they operate more smoothly than piston compressors and are less likely to fail. Regarding the volume of air output, it depends on your actual needs. The range of possible outputs is quite wide, and it can basically meet the requirements of production processes. The size of the storage tank also depends on your air consumption; it’s usually better to choose a tank that is slightly larger than what’s calculated, so as to prepare for future upgrades or expansions. You should inform the air compressor manufacturer of your requirements, and they will design an appropriate tank for you. As for using cold dryers and desiccants, it depends on the quality of air you need. Desiccants provide a better drying effect than cold dryers, and this choice depends on your specific process requirements

There are many such air compressors available on the market that meet your requirements, and many manufacturers can produce them.