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Upstream boilers for removal of high % content of NCGs (i.e.~ 20%)

Upstream boilers for removal of high % content of NCGs (i.e.~ 20%)

Upstream boilers for removal of high % content of NCGs (i.e.~ 20%)

We have a small (5MW) "portable" single-flash, 4 stage axial impulse turbine (MHI) (Inlet T,P, M_dot = 158°C, 589kPa, 72,500kg/hr). Original design was for 0.6% NCG. In its new, more permanent location however, the NCG is much higher, on the order of 20% (comparable with Kizildere, Turkey).

In reading about options for NCG removal for high NCG content, one oft-mentioned idea (for low-temp cases such as ours) is that of an upstream condensor/reboiler. I can understand the concept of the condensor, and how that works to ditch the vast majority of the NCGs, but I'm confused where the energy comes from for the reboiler, or flash tank. I read that it involves dropping the pressure of the condensed fluid, and maintaining a very low Delta-T with the heat exchanger to drive the system, but I'm unclear if there is additional heat being added in or not.

Is it possible to use a heat exchanger system so that you use heat from the pre-condensed (dirty) steam to re-flash the condensed, "clean" fluid prior to passing it along to the turbine? Is it all just a game of very narrow margins, or is there additional heat being added in somewhere? I keep reading that this option makes great sense (long term) for cases identical to ours, but I'm missing an important point here.

Can anybody shed some light on this?

RE: Upstream boilers for removal of high % content of NCGs (i.e.~ 20%)

Instead on investing in a reboiler, why not invest in a larger gas extraction plant on the condenser?


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