2 replies to this topic

[sambucka]

Hello everyone!,

I need some help or ideas in a project that i have just been assigned.
I am currently working with saturated steam (quality equal to 1) exiting a boiler at 120psia and 341.27F with a mass flow of around 5000lb/hr, and was wondering that with this pressure, if I would be able to use a steam turbine to generate an appreciable amount of electricity? For instance to drive a 75hp pump.. Or would it be better to think of other ideas such as heating other fluids for another type of process. Or even use the steam for maybe a cleaning application?

[kkala]

I need some help or ideas in a project that i have just been assigned.
I am currently working with saturated steam (quality equal to 1) exiting a boiler at 120psia and 341.27F with a mass flow of around 5000lb/hr, and was wondering that with this pressure, if I would be able to use a steam turbine to generate an appreciable amount of electricity? For instance to drive a 75hp pump.. Or would it be better to think of other ideas such as heating other fluids for another type of process. Or even use the steam for maybe a cleaning application?

A steam turbine would be a condensing type in this case. From Perry's (7th edition) Table 29-8 (theoretical steam rates for steam turbines at some common conditions) we see that theoretical steam rate would be (say) 13 lb/kWh (vacuum of 4 in Hg). Theoretical energy production 5000/13=385 kW (single stage), actual probably 5 times less, that is about 77 kWh. The result is not rejected, suppliers should be advised whether this size of turbine is commercially available and give more precise figures. Probably available steam pressure and flow rate do not justify electricity production, but a condensing turbine directly connected to the mentioned pump. Evaluation of the relevant capital cost should be made.
I have the impression that electrical generators are bigger (I have seen some using steam of 40 Barg, ~ 400 oC), but there is recent development of small turbogenerators for distant dwellings.

[djack77494]

Commercially, power generation would only occur at a much larger scale than you have proposed. Even using a steam turbine as a driver would probably not be justified at this scale. Better to use the steam for heating or, as you suggested, for cleaning. Your steam is at quite a low pressure as well, and so the overall process would not be very efficient. Better efficiencies come about by generating (much) higher pressure steam. As kkala points out, you might try to compensate for the low pressure steam by condensing it at very low pressure (high vacuum). But you're into complex and expensive systems that I'm sure would not be economically justifiable.