Post
by fredrosse » Wed Jun 12, 2019 1:55 am
"Condensate temp should be as low as possible to provide maxiumum vaccum, so adequate cooling water should flow in the condenser and a vac pump to allow this."
ANS: A better way to express this: "Engine exhaust temp/pressure should be as low as possible to provide maximum engine efficiency, so adequate cooling water should flow in the condenser and a vac pump to allow this. Further lowering of the condensate temperature, condensate depression, should be minimized, from a thermodynamics standpoint.
Another issue, the fluid flow transport part of the design, is pumps having trouble with condensate having little to no condensate depression, very hot condensate, near the boiling point. In the utility industry, centrifugal condensate pumps are designed specifically to work with very low "Net Positive Suction Head", and typically the pump impeller is mounted at a low elevation, maybe 15 feet below the condenser hotwell water level. This is not an option for a small steamboat! Having some condensate depression to allow pumping water out of a steamboat keel condenser typically requires some condensate depression, typically only a few degrees is necessary, so the hotwell pump suction does not burst (flash) into steam when the reciprocating pump takes its suction stroke.
"Feed water should be preheated to (temp x) before entring the boiler wether this is done via exhaust heat exchanger or an econimiser or both depends on the systems figures."
ANS: That is correct
"What is the ideal "temp x" aka feed water delivery temp?
As hot as possible? Just before boiling? "
ANS: This is generally correct, from a thermodynamics standpoint. Again, from a fluid flow standpoint, getting feedwater very close to the boiler saturation temperature invites the occasional generation of steam bubbles in the economizer, with potential water hammer problems. Early in the electric power industry (more than 100 years ago) there were several instances of "steaming economizers", but presently the accepted economizer designs for large utility boilers do not heat the economizer outlet so very close to the boiling temperature. The utility industry has other means of squeezing maximum economy out of a boiler system, but that is another story.