Optimal Fuel Oil Temp

[rawfordpower]

I am burning a blend of used oil and #6 fuel oil and am trying to figure out the optimal temperature for good atomization. I can figure out how to get the manufacturers recommended viscosity; however, my question is: Is there a disadvantage to heating the oil higher and getting lower viscosity? Wouldn't this improve atomization even more? Thanks

 

[rmw]

You need the check the vapor point of the oil so that you don't heat it up so much that it begins to produce vapor on you.

Since you have a blend of used oil, this point could be below the specified vapor point of std. #6 oil. (If such a thing exists in this day and time.)

rmw

 

[jmw]

Droplet size is a vital factor in burner efficiency.

Large droplets (high viscosity) burn less efficiecntly and travel further resulting in fuel dorplets impinging on the heat exchanger surface and continuing to burn there, contributng to tube failure and excess soot formation.

Small drops (low viscosity) create a fine non-dispersive spray which also burns inefficiently as it does not mix well with the air flow and it burns closer to the nozzle i.e. not in the ideal burn zone.

This link may be useful:

http://navier.stanford.edu/hanson/research/diode/fuelsensors_sprays.htm

Vriable fuel oil quality, a factor with your no 6 oil in any event and especially with used oil blended in, means the viscosity will almost certainly be vary variable and thus too the optimum fuel oil temperature at injection.

If you are using temperature to to control fuel oil heating you may need a number of stratgeis (combined) to optimise flame control:
[ul]
[li]excess oxygen[/li]
[li]visual flame inspection [/li]
[li]frequent laboratory sampling to determine the optimum control temperature [/li][/ul]
(see

http://www.steamesteem.com

for a calculator or visit

http://www.ViscoNanalyser

for a spreadsheet on viscosity Vs temperature)

In the past viscometers proved too susceptible to fouling to be useful for fuel oil to burners (despite a 40 year success with engines, but engines use fuel treatement prior to injection such as settling tanks, centrifuges and filters) but modern viscometers e.g. the Emerson 7829 ViscoMaster(TM) digital viscometer are perfectly suitable for fuel oil heater control even of the dirtiest fuels and provide far better fuel efficiecny by maintaining the optimum fuel heater control with better fuel efficiency and emissions.

A google search for burner fuel droplet size will produce a variety of useful web sites including some on "pre-atomised fuels i.e. fuel water emulsions.

JMW

http://www.ViscoAnalyser.com

 

[0707]

The higher the temperature of the fuel the better the combustion!
Also if the temperature of the oil is the hottest possible it will also help in vaporizing faster. The hottest temperature possible is governed by a few considerations: physical limits of the equipment (tank design temperature, pump seals) also the flash temperature of the oil, it is not wise to be at the flash temperature in the day tank! If the fuel contains asphaltenes it would be good to cut the residual oil with a small amount (5 to 10%)of olefin material such as: CCU clarified oil or CCLGO. Olefins have an ability to prevent asphaltenes from agglomerating into larger particles. Asphaltenes can be seen as shooting stars leaving the flame envelope, observe the boundary of the flame envelope and see if you see stars leaving the flame to disappear into the firebox. Burner tip and adequate atomization is also important. Lots of burner manufacturers and many designs available. What I have seen as the best is the "Y" jet design where steam enters from the bottom and the oil enters at an angle from the side so that the steam hits the oil from behind but in the same axis of flow. Very strong shearing of the oil stream forming small droplets. Another truth of science is that a small hole produces small droplets and a large hole produces large droplets!!! Sounds obvious but it works. So the burner tip should have small oil holes and adjust the quantity of holes to the duty required. Atomizing steam should be superheated and follow the vendor’s requirements for pressure control. Some recommend adjusting the steam pressure to that of the oil pressure and maintaining the delta throughout the range of the burner. The "Y" jet requires that the steam pressure be kept constant

Regards

Luis Marques

 

[bonzoboy]

Hotter is better, but you have to be careful to avoid coking. At the fuel tip, flame radiation will have some tendency to cause coking. With an older steam boiler, I used to use steam atomization to improve the fuel atomization. Not sure if you have steam available. Also, note that the lighter the cut you blend, the higher volumetric flow rate into the burner, so a lighter cut would also give you some better atomization.