Can ULPA be used directly in air containing oil mist or high dust?

The short answer is: It is not recommended to match it directly.

But what’s more worth saying is why. The design position of ULPA is terminal fine filtration, and the filter section in front of it should intercept most of the load. Sending the airflow containing oil mist or high dust directly into the ULPA is equivalent to letting the terminal filter element do work it should not do. The result is usually a rapid increase in resistance, frequent replacement, and in severe cases, damage to the filter material structure.

This is not a problem with ULPA itself, but a problem with the division of labor in the system.

Let’s first see clearly what form the pollutants are in

Oil mist and high dust actually cover several different things, and they are handled in different ways.

Dry dust : granular, with good fluidity, it is more effective to intercept it step by step with suitable pre-filtration sections. Particle size distribution and concentration determine how many stages of filtration are required and how much load each stage bears.

Liquid oil mist : Oil droplets move with the air flow, are highly viscous, and easily adhere to the surface of the filter material to form an oil film. Ordinary filters are effective against dry dust, but have limited effect on oil mist, and a special mist removal device may be required.

Solvent vapor : This part is not a particle, but a gaseous pollutant. ULPA cannot be stopped and requires chemical filtration or other treatment methods.

Mixed form : In actual working conditions, several types are often mixed together. For example, the oil mist generated by mechanical processing contains oil droplets, metal shavings and gaseous volatiles at the same time. In this case, the pretreatment program should be designed according to the main pollutants, taking into account the effects of other components.

Confusing these forms is the most common mistake in pretreatment program design. Oil mist does not equal smell, and particle filtration cannot replace gaseous pollution control. The two treatment paths are completely different.

How to arrange upstream processing

After determining the form of pollutants, the idea of ​​​​pre-stage configuration is roughly as follows:

Where dust loads are high , graded pre-filtration is used. The initial effect blocks large particles, and the medium effect further reduces the load, reducing the dust concentration in the air entering the ULPA to a reasonable range. The replacement cycles of filters at each level should be set separately. If the front-stage maintenance is not in place, the end pressure will increase significantly.

In situations containing oil mist , first evaluate the effectiveness of defogging measures. The location, form and efficiency of the defogger device directly affect how long the subsequent filter can last. It is also necessary to check the impact of residual oil on filter media, colloids and equipment - even if the oil mist concentration is reduced after defogging, long-term trace exposure may change the performance of the filter media.

Where there are gaseous pollutants , a separate chemical filter section must be configured. The sequence, resistance superposition, and replacement cycle of this section and the particle filter section all need to be considered during system design.

The key principle is: let each filter stage handle the load it is good at. If you do more on the front stage, the ULPA at the end will be able to run stably for a longer time.

What changes can be observed during operation?

Whether the preprocessing configuration is reasonable or not, the running data will give you the answer.

Rise speed of differential pressure : If the differential pressure of ULPA rises significantly in a short period of time, first doubt whether the front-stage protection is in place. For specific troubleshooting ideas, please refer to the instructions related to the increase in filter pressure difference, and pay attention to distinguish whether it is a change in working conditions or dust accumulation in the filter element.

Surface condition of the filter material : When replacing the filter element, check whether there is an oil film, viscous deposits or abnormal color on the surface. These traces can reflect the actual situation of upstream processing and are more intuitive than running data.

Front-stage maintenance records : The replacement cycle of the front-stage filter and the degree of dirt during replacement are also a reference for judging the terminal load. If the front stage is replaced frequently and is heavily soiled, it indicates that the upstream pollution source may be stronger than expected.

Fan operating status : The increase in ULPA resistance will change the fan operating point. Supporting In the FFU fan filter unit system, if it is found that the unit needs to continuously increase the gear to maintain the air volume, it is necessary to go back and check the status of the end filter element instead of simply adjusting the speed to cover up the problem.

When to re-evaluate configuration

If the following situation occurs, it is recommended to suspend the terminal replacement and go back to analyze the upstream configuration first:

The replacement cycle of the filter element appears to be too short many times in the same location, and the replaced filter element has obvious oil stains or abnormal dust accumulation.

The frequency of replacement of the front-stage filter has increased significantly, or the front-stage filter itself has lost its filtering effect.

The process has changed - for example, a new dust-generating process has been added, or the type of cutting fluid or cleaning agent has been changed, resulting in a change in the composition of the airflow.

In these cases, simply replacing the terminal ULPA will only push the problem back. What really needs tweaking is the preprocessing section. Device-side applications such as The EFU equipment-end fan filter unit has a compact internal space. Whether and where a pretreatment section can be added needs to be considered together with the equipment structure at the planning stage.

Project judgment example

After a piece of equipment was replaced with ULPA, sticky dust accumulated within a short period of time, and the pressure difference rose rapidly.

The inspection found that the airflow contained oil mist generated during the processing process, and the original system only had one primary filter and had basically no ability to intercept oil mist. ULPA directly bears the oil mist load, and the filter material is quickly contaminated.

The adjustment direction is not to change to a higher grade ULPA, but to add defogging measures and appropriate pre-filtration upstream so that the air components entering the end meet the design conditions of ULPA. involving The selection of different levels of HEPA/ULPA air filters should also be judged together with this set of pretreatment plans.

Selection and Acceptance Checklist

About Aili Industrial’s pretreatment packages

The prerequisite for designing a pretreatment plan is to understand the form and load of pollutants. The more complete this information is, the more targeted the front-end configuration will be.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide different levels of ULPA ultra-high efficiency filter and supporting air supply equipment. For projects that require front-stage filtration or mist removal measures, the specifications, resistance, and replacement methods of filters at all levels can be checked together during the planning stage to avoid the terminal ULPA alone bearing a load beyond the design scope.

Providing contaminant composition, concentration, temperature and run time when enquiring, can help determine what level of pretreatment is required. The specific configuration is subject to the technical documents and operating data confirmed by the project.