Total Steam Plant Efficiency
Total Steam Plant Efficiency
(OP)
Hi there,
I'm trying to figure out how can I assess a steam process plant efficiency? not a steam power plant.
I try to scourge through the internet and most of my searches are related to a steam plant which is not my objective.
So consider steam is produced by a 15 ton/hr boiler at saturated 10 bar(a). Feedwater is coming in from the deaerator at 95 degrees C.
The steam is then supplied to a number of autoclaves and no condensate is return back to the system.
Makeup water is coming in at 32 degrees C
The boiler is using Fuel oil.
If I'm going to calculate the boiler efficiency, I would use the below method:
Boiler eff = 15ton/hr X (steam enthalpy @ sat 10 bar - FW enthalpy @ 95 C)/Fuel Oil flow X HHV.
How can I calculate the total steam plant efficiency then?
Does the below equation correct?
Steam Plant Eff = 15ton/hr X (steam enthalpy @ sat 10 bar - Makeup enthalpy @ 32 C)/Fuel oil flow X HHV
How would it change if there is condensate return? Say 50% of steam flow.
Does the total steam plant efficiency is usually lower than boiler efficiency?
The reason is I would like to calculate the increase in efficiency if we do some improvements to the plant.
Thanks. Sorry for the long question
I'm trying to figure out how can I assess a steam process plant efficiency? not a steam power plant.
I try to scourge through the internet and most of my searches are related to a steam plant which is not my objective.
So consider steam is produced by a 15 ton/hr boiler at saturated 10 bar(a). Feedwater is coming in from the deaerator at 95 degrees C.
The steam is then supplied to a number of autoclaves and no condensate is return back to the system.
Makeup water is coming in at 32 degrees C
The boiler is using Fuel oil.
If I'm going to calculate the boiler efficiency, I would use the below method:
Boiler eff = 15ton/hr X (steam enthalpy @ sat 10 bar - FW enthalpy @ 95 C)/Fuel Oil flow X HHV.
How can I calculate the total steam plant efficiency then?
Does the below equation correct?
Steam Plant Eff = 15ton/hr X (steam enthalpy @ sat 10 bar - Makeup enthalpy @ 32 C)/Fuel oil flow X HHV
How would it change if there is condensate return? Say 50% of steam flow.
Does the total steam plant efficiency is usually lower than boiler efficiency?
The reason is I would like to calculate the increase in efficiency if we do some improvements to the plant.
Thanks. Sorry for the long question





RE: Total Steam Plant Efficiency
Other than that, the two are comparable, but I don't see it in your equations.
Net efficiency = "Useful energy supplied" / "Total heat input" (what is burned in the boiler)
RE: Total Steam Plant Efficiency
Lets say Steam is going in the autoclaves at 10 bar and going out as condensate at 120 C.
Would the useful energy supplied be:
15ton/hr X (Steam enthalpy @ 10 bar - condensate enthalpy @ 120 C)?
But the condensate are not returning back to the steam plant.
How can I show by returning condensate the plant efficiency would increase?
RE: Total Steam Plant Efficiency
Now, look at the boiler side.
Now.
15 ton/hour Liquid Water "in" at delivery temperature of what ??? = How much energy_0_in. (40 degrees in winter, 65 deg F in summer maybe).
15 ton/hour steam "out" at your delivery enthalpy = ???? How much energy_0_out
So, condense the water, run it back to the boiler.
Condensate temperature = ???? (Assume something reasonable.)
Your efficiency improvement is the delivery of the hotter water back to the boiler
(T_delivery_water is colder than T_condensate_water) and that energy difference is water that does NOT have to be reheated to boiling.
Plus, you now have pure water back to the boiler, not needing to make up (purchase and filter and purify) 15 tons per hour.
RE: Total Steam Plant Efficiency
Which would then decrease the fuel consumption and increase steam generation efficiency, right?
How about net efficiency:
Net efficiency = "Useful energy supplied" / "Total heat input" (what is burned in the boiler)
Will it increase as well?
Thanks
RE: Total Steam Plant Efficiency
Your "purchased" makeup water temperature will not likely be 30 degrees C (86 deg F). More like 15 deg C (60 F) or lower.
Makeup water (after installing the condensate system) should be less than 2% losses, not 50%.
In the powerplants, there is a tradeoff calculation between generating more power (electricity) by running more steam through the turbine; and by passing the turbine at various points as steam pressure lowers to improve thermal efficiency by pre-heating the condensate and feed water.
Do you pre-heat the current feed water with the boiler exhaust gasses?
RE: Total Steam Plant Efficiency
and since we have touched the point, may I know what is the typical exhaust gas after the economizer if we are running on natural gas.
I have seen the temperature after exhaust reached 90 deg C which I am sceptical because based on the boiler performance data, the lowest is 116 deg C.
RE: Total Steam Plant Efficiency
RE: Total Steam Plant Efficiency
You useful work is the heating of the autoclaves. If they were being electrically heated how much power would it take? Hot condensate or other steam is not producing useful work for you, so it does not count.
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P.E. Metallurgy, Plymouth Tube
RE: Total Steam Plant Efficiency
RE: Total Steam Plant Efficiency
lilliput1 - you mentioned about temperature limitation on the economizer outlet. How low can the exhaust temperature be before it starts to condense?
RE: Total Steam Plant Efficiency
Consider economics (unless Owner wants to get more LEED points). How often is autoclave used. How much steam. Cost of heat exchanger (double sheet to safeguard against contamination) plus pit mounted condensate pump.