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Low E paint on gas fired heater. - shawn - 06-20-2013 03:47 PM

I have a gas fired heater for heating oil in a natural gas refinery. The surface of the heater is mainly rust with patches of paint. I am trying to figure out how to calculate the payback time for sandblasting and painting with low emissivity paint. Any ideas on where to start on this?


RE: Low E paint on gas fired heater. - JKEngineer - 06-22-2013 09:22 AM

You need to estimate the heat loss from the shell as is and from the shell after cleaning and painting. The difference will be the heat savings in fuel and the value will be based on the cost of fuel. I don't think that told you anything you did not already know.

The calculations will depend on the area of the heater's surface, how it is insulated, its surface temperature, radiational background, ambient conditions -- including air T and wind, duty cycle of the heater, etc. That may be what you were really asking. I'd be glad to contract to do the calculations for you.
Jack

Jack M. Kleinfeld, P.E.
Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering


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RE: Low E paint on gas fired heater. - shawn - 06-26-2013 03:18 PM

Thank you for your response. We used some software in the Thermography Level 2 school that i think would help with this but i cannot find it and i dont remember the name of it. I am trying to justify painting the heater to management, so i need to take current heat loss and try to calculate the projected difference in heat loss with a known emmissivity paint. The problem i am having is tryiing to figure out the projected cost difference in fuel. Not sure about the math in converting btu of heat loss to MMbtu fuel cost. Any suggestions on how to tackle this?


RE: Low E paint on gas fired heater. - Gary Orlove - 06-26-2013 04:21 PM


  1. Calculate the radiation heat loss rate from the wall surface to the environment (based on average conditions for your locale).
  2. Calculate the convection heat loss rate from the wall surface to the environment (based on average conditions for your locale, estimate the convective coefficient based on still air or wind speed).
  3. Add the two together, answer should be units of energy per unit time (e.g. Btu/hr).
  4. Multiply your answer by hours in a year (8760).
  5. Answer should be Btu's / year.
  6. Multiply this by $$/Btu, then divide by efficiency of the energy conversion.
  7. Your final answer will be in $$ of approximated heat loss per year.

To perform a more accurate analysis, you can download weather data from several web sources and perform the above calculation on a per day basis, then sum up the data for the year.

Sources of weather data:
http://www.degreedays.net/
http://weathersource.com/past-weather/weather-history-reports/free?gclid=CLuHm_TFgrgCFUGk4AodoUQAtw
http://www.wunderground.com/history/


RE: Low E paint on gas fired heater. - shawn - 06-27-2013 09:09 AM

This is exactly what i was looking for, thanks for pointing me in the right direction. I think in addition to this I am going to take my surface temperature measurements at night to eliminate the effect of the sun heating the surface.


RE: Low E paint on gas fired heater. - Gary Orlove - 06-27-2013 09:26 AM

(06-27-2013 09:09 AM)shawn Wrote:  This is exactly what i was looking for, thanks for pointing me in the right direction. I think in addition to this I am going to take my surface temperature measurements at night to eliminate the effect of the sun heating the surface.


Good idea, but also remember that the heat from the sun also effectively reduces heat loss as well.


RE: Low E paint on gas fired heater. - shawn - 06-27-2013 09:54 AM

i agree, just trying to eliminate as many variables as possible.