Air Blowers Connected in Series

This has 2 possibilities: electrically in series, or mechanically? The last solution, when "in pipe" blowers, take care of air transportation over longer distance. When too close however some types can over rev.

Why use two machines when one will do the job?

With the miniscule amount of information provided, I'd say both prior responses are valid.

Only pro I can think of would be fewer spare parts.

Well we deal in Coal gasifier. We have three gasifier which produce Producer Gas which is fed into the Re rolling furnace. Each gasifier has dedicated Blowers of their own. In case all the three gasifiers are in operation at one time, the blowers which are connected with one common header, have to be in operation to feed the gasifiers. My apprehension is that, whichever blower is tuned to give the air at lower pressure, may be overcome by the blower/s which are at higher pressure, therefore, the gasifiers may starve for want of Oxygen through the air. Now which is better, to connect the blowers individually or in series

Common header on inlet side?

Common header on the outlet of the blowers, i.e. on the side feeding the air to the gasifier

The pro is being able to double the pressure with relatively lower cost fans. I have seen this done with paper scrap fans with high pressure drops and long duct runs.

The con is having twice as many moving parts to maintain.

Given the added info from Mr. Rao, my answer is not applicable to this situation.

I would think that either back-draft dampers and/or pressure controller should be installed on the blowers. You want to avoid the situation of the other blowers reducing or stopping the flow of air from one of the blowers.

This sort of thing is pretty common on municipal waste water works. Numbers of blowers feed a common discharge header routing the air to sewage aeration lanes. Effectively, the blowers are in parallel. The control regime involves modulating the lane supply valves to achieve final dissolved oxygen setpoints. When one lane modulates, the flow from the common header changes, so the blowers are ramped up or down in speed to achieve the overall required flowrate band for the number of lanes in service.

The cons of putting blowers in series, as conceive in the original post, include the loss of redundancy; if one of the blowers is out for maintenance or fault-chasing, all of the blowers stop, and no air is passed. Which is sort-of-why it isn't done.