Oil Fired Water Heaters

[brb2]

I was looking to see if someone could help me out? I have 3 oil fired water heaters that are coupled together with two 750 Gal hot water storage tanks. The recovery rate is 441 GPH with a combined hot water capacity approximately 5% lower. The fuel consumption is 3.25 GPH. The vent size is 8” in diameter. My problem is that two of the three water heaters already have a cracked shell in less than 3 years. I wanted to make sure the water heaters are actually rated for the demand. The water heaters supply 4 dormitories with each their own lavatory, water closet and sink in each room. In addition they also supply an industrial sized kitchen and cafeteria. I don’t know much about oil fired water heaters and wanted to either replace the entire system with something more cost effective, and durable, or replace the existing water heater with a different oil fired water heater. I am learning as I go along on this project and know bits and pieces of where to start with figuring out the Peak demand, and calculating the GPH to get the correct water heater. I feel like there are a lot of missing pieces and I didn’t have much information on this project. Does any one have good advice in where to start?

 

[goutam_freelance]

Calculate the heat loads and flow rates for each consumer and then construct a heat and mass balance diagram. This, along with specifications of heater suppliers, can assist you in selecting suitable ratings of fired water heaters.

 

[Dhurjati Sen]

What is the material of the water heaters?
It seems you are continuing with the cracked shells as of now.
You may carry out a weld repair and and check its longevity before going for complete replacement.

 

[georgeverghese]

Is combustion flue gas on the shellside ? If so, there may be contaminants in the fuel oil that are not compatible with the shellside material. It may be due to H2S, resulting from incomplete combustion of traces of sulphur in cheaper grades of fuel oil. Condensation of the flue gas on the shell wall may have resulted in wet H2S corrosion. Also check if you have sufficent insulation on the shell exterior that may prevent condensation on the shell inside wall. Talk to a materials selection engineer if there is residual sulphur in this FO to select a suitable grade of plate for shell wall construction. Else switch out to a low sulphur grade fuel oil.

 

[LittleInch]

There is a lot of missing information here. How does your system control temperature? On / off or modulating?

Are you getting lots of short bursts of firing?
Are you getting a hot spot in the shell
What exactly is the fuel? "Oil" is rather vague. Could be kerosene or something else.
Duty is important to know but won't cause your cracking.
What other fuel do you have available?