Shell and tube exchangers in biogas treatment for cogeneration

Cogeneration plants are becoming very much employed, aimed to the combined generation of heat and power using biogas. The biogas is a particular source or renewable energy, generated by the breakdown of organic matter or farm animal waste. Due to its characteristics, biogas is very rich in humidity, which makes it impossible to directly use it into engines, because the content of humidity would seriously damage them.

Biogas is a natural fuel, but in order to be employed in cogeneration plants it requires a special dehumidification treatment. This is achieved using systems composed by a chiller and shell and tube exchangers, especially engineered for this kind of application, which cool and dehumidify the biogas using a very cold mix of water and glicol.

 

In fact, biogas coming from digesters enters the system at temperatures of 35-40° C, and must be cooled at temperatures of approx. 4-5° C, eliminating the maximum possible amount of humidity contained. At this purpose, chillers at very low temperatures are employed, near the freezing point, at +1° C or +2° C.

On the outlet of the exchangers the biogas will then have a relative humidity of 100%, but with an extremely low absolute content of humidity. Installed on the outlet of the exchangers there are also condense separators, big tanks aimed to collect the condenses. Furthermore, on the output of the systems there are also additional filters, providing a further filtration of the biogas, which then is finally ready to enter the engines.

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