How to Size a Fuel Filtration System
As experts in critical fuel systems, a common question we’re asked by consulting engineers is how to determine the size of a filtration system, sometimes called a fuel oil polisher. There are a number of factors you should consider that go well beyond the flow rate and micron rating of the filter elements.
Here’s our complete list of what to consider when choosing a fuel filtration system.
1. Main Tank Size
Knowing your main tank size and answering these questions will help determine what size filtration system you need:
- How big are the main tanks that are going to be cleaned?
- How many main tanks are going to be cleaned at this facility?
- How is the fuel being used – for a boiler, generator, or both?
2. Filter Elements
As the filtration increases in size (larger flow rate), the filtration elements, along with the piping size, will also need to be larger to handle the increase in flow rate. The filter skid will also increase in size as the filter elements and pipe size change. The break point between the typical size and the much larger size is around 1250 gph.
3. Flow Rate
Remember, fuel filtration is not a race. For example, the application may have a 40,000-gallon tank, and the facility wants to keep the size of the filtration system small. In this case, we will use a lower flow rate but run the filtration system longer.
Some facilities will want to filter no longer than eight hours to cover a “work shift.” In this example, a 1220 gph flow rate will turn over the tank in 33 hours (40,000 divided by 1220 and rounded up to the next hour). This can be accomplished in one cycle with a larger system, or they may choose to cycle the filtration unit more often to break down the 33 hours into maybe five cycles, seven hours each.
Or, some facilities will elect to “turn over the tank” twice at a time. In this case, 33 hours turns into 66 hours.
4. Tank Capacity
Please remember that tanks are typically not filled past 90%, so the 40,000 gallons in the above example can be lowered to 36,000 gallons.
5. Number of Filtration Systems
When the facility has several large main tanks, there is a choice between one filtration system that handles all the main tanks or a filtration system for each main tank. The difference is a cost consideration. The design with one filtration system will require tank selection valves at the supply and return of each tank along with additional piping, while a filtration system at each tank involves multiple filtration systems.
6. Number of Pumps
When filtration is not critical, and therefore the use of duplex pumps is not required, a single pump is typically used.
Typically filtration is not considered “mission critical,” i.e. if the system stops to change a filter, the generator will not stop and fuel does not go bad instantly. Therefore they typically only use a single pump and motor. Even if the pump or motor goes bad, they usually can be replaced before the fuel goes bad.
We have seen in some applications where the client takes filtration very seriously in that they will not only have a duplex set of pumps but will include redundant sets of filter runs.
7. Suction Drop Tube Length
The suction drop tube – used to pull the dirty oil out of the tank that is to be cleaned – needs to go to the bottom with no foot valve. The cleaned oil is returned to the opposite end of the tank.
8. Filtration System Location
The filtration system should be mounted close to the main tank, as the pumps will need to establish prime with each run. Place the filtration system next to the main tank if above ground. If it is a buried tank, then the filtration unit should go on a concrete pad directly above the tank. The pump should be located as close to the suction port as possible.
9. Stored Fuel Testing
The fuel oil stored in the tank needs to be tested. This is especially true of a filtration system added to an older tank.
Find an independent testing lab (not the fuel oil supplier) to test the oil. The test can range from as simple as the amount of water in the fuel, to a complete DNA of the fuel. The test results may suggest that the fuel needs to be filtered more often, or it may suggest the addition of chemicals. Chemicals can be added by just dumping the chemicals in the tank, but a far better method is to use a chemical additive system where the chemicals are metered into the returning fuel a few CC’s at a time.
As a note, the fuel test will use a special collection element that will collect oil at the top of the oil, the middle of the tank, and at the bottom.
10. Filtration Frequency
A question we often hear is how often to run the system. Our filtration systems are set up to run on selected months, such as four different months for a quarterly run, or every month.
We suggest that if the fuel is clean (new installation), then start with once every six months. If the yearly fuel test comes back not so good, then move to three times a year, and so on.
Remember to consider the local climate, as an important function of the filtration system is to remove any water. In high humidity areas, the filtration system may need to be run more often.
11. Filter Micron Rating
The filter micron rating determines how large the particles can be and still get through the filter element. It is typically set by the engine manufacturer.
If the system is used to supply oil to the burners on a boiler, the particle size can be relatively large, as the fuel only needs to pass through the orifices of the oil gun in the combustion chamber. But emergency generators are very different in that they use very small orifices on the fuel injectors.
If the application is working with old oil that have may have a large amount of water and particles, the user may elect to start filtration with a high micron rating (15-25 microns) and work down to the required micron rating (1-5 microns), so that they do not have to replace filters quickly. It is possible to clog up low micron level filters in a few minutes with especially bad oil.
Sizing a Fuel Filtration System with Critical Fuel Systems
Fuel filtration systems by Critical Fuel Systems are designed to offer the highest performance in mission-critical situations. Our products are offered in a range of sizes, including industrial, made with easily accessible hard piping instead of hoses, and use particulate filters and coalescing elements to fully remove particles from the oil, not just hide them.
Contact us to speak with one of our exports on how to size a fuel filtration system to best suit your needs.