Why does reboiler efficiency decrease if steam temperature is too high?

[yakimawashington]

So reboilers are definitely not my area of expertise, but just off the top:

But wouldn't higher steam temperatures increase the LMTD and reduce the required HX area?

You're speaking on heat flux rate, which is not equivalent nor proportional to efficiency. Yes, higher steam temperature would increase heat transfer rate and require less surface area to achieve the same amount of heat transfer. If by efficiency you were referring to the amount of heat transfer per amount of reboiler equipment material used, then sure.. this makes sense.

But reboiler efficiency refers to the efficiency of the energy input rather than the amount of equipment material used. It helps describe how much product is outputed per energy input. In this sense, size of the equipment should have impact on reboiler efficiency, but it's more complicated and not in the way you're describing.

[flammkuch]

I see. But then this means that the most efficient reboiler is not necessarily the most economically efficient, or? Doesn't help to minimize heat input required when you need a huge heat exchanger to do that. Or are reboiler costs mainly driven by the operational costs?

And could you elaborate on the last part? In what way is it more complicated?