I am working on a steam generator efficiency project.
Here is a sample data :
Amount of Feedwater - 12.33 m^3/hour = 12000 kg/hr (assuming density = 1000 kg/m^3)
Amount of Steam generated - 14450 kg/hr
By the following efficiency formula, it is more than 100%
Efficiency = (Steam generated/Amount of feedwater coming in)*100
I have values from the past 3 months and the value consistently stays above 110 %. Can anybody please explain this? I have ruled out error in the measuring instruments.
Honestly, I do not think you have ruled out measurement errors. Simply put, in a steady-state system (or a time-average of the system behavior) the mass must be conserved, hence massflow out must equal massflow into the system. If the outgoing mass flow is less than incoming, leakages may be suspected, if outgoing mass flow is higher than incoming, there is a measurement error (or an incoming flow not accounted for).
I suggest you recheck your calculations, and also make sure that all flow are accounted for.
I don't understand your concept of efficiency. What you're doing is just a mass balance and if you do not get 1 or 100%, it means that there is a steady unbalance. Your evaporator will your case dry out (steam out > water in). Therefore, I agree with Mr. Naess, there must be a mistake in your measurements or evaluation. How do you compute the kg/h of steam? Do you also multiply by a density?
You must apply the mass balance. The mass rate of steam generated equal to mass rate of water inlet when the loses is negligibal . Therefore the efficiency equal to 100%. I think the error in measurement of mass rate was occured. If you measure the volumetric flowrate of steam you must take the value of density for steam from steam table to convert to mass rate
I don't think your measurement or assumptions are correct. Do you add any desuperheater flows in the steam system and you haven't accounted that mass?
efficiency is related to total heat out/ heat in. So check the flows with water and steam enthalpies associated with pressure and temperatures at inlet and outlet.
How do you measure the amount of steam generated ? With which instrument ?
By the way, the efficiency is 14450/12000=120%
in steam generators, except from inlet and outlet flow rates, CBD and IBD as well as snuffling stream, desuperheater .... exist and you should account them. moreover, how you ensure about constant level in mud and steam drums? please clarify the type of your flow meters and pressure and temperature at inlet and outlet of steam generator.
Let me add another perspective to the question of steam measurement. Most likely the problem is with the measurement of the mass of steam generated. The instrument may be" measuring correctly", but either the calibration of the instrument may incorrect or the condition (or quality) of the steam going through the instrument is not truly representative. A measurement of steam quality and overall density at the meter may be different than what is in the process line. we would need to know more about your instrumentation and conditions of measurement in order to truly answer your question. For example, is the meter installed properly where it would not see a non-representative high value for the liquid water content of the steam?
It is not possible. It is the density of steam which is dependant on pressure. If you are measuring the volume at around 6 bar the density will be more than 1000kg.cubic meter,but if you are measuring at around i bar the density will be around 590 or 600kg/ cu.m. inany case you cannot get efficiency higher than 100%.
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