Coalescence filter for oil mist

Oil mist seperation through coalescence filter

Gas-borne oil droplets must be separated if they damage the environment, pose a health hazard or disrupt the operation of a system/machine. For this purpose, coalescing filters have proven useful for a variety of applications, including crankcase and oil tank ventilation. This type of separator has a core of fine fibers on which small drops of oil hit and stick. The drops grow through coalescence (flowing together) with other drops. As soon as the drop exceeds a critical size, the gas flow transports it through the filter as an oil film. On the back of the filter, the separated oil moves in the direction of gravity to the filter bottom and from there can be fed back into the process.

Crankase ventilation basics

When the engine is running, oil mist is created in the crankcase and must be separated before it can enter the environment or the engine's intake tract. Crankcase ventilation systems are a fundamental part of internal combustion engines, designed to separate this oil mist and return it to the oil pan. In doing so, they make a decisive contribution to reducing oil consumption and particle emissions and thus contribute to compliance with EU, EPA (e.g. Tier 4) and IMO limits for PM emissions. Such systems also regulate the pressure in the crankcase to prevent leaks and reduce wear on seals. This is particularly essential for toxic fuels such as ammonia or methanol.

CRANKCASE VENTILATION: CLOSED (CCV) VS. OPEN (OCV)

Closed crankcase ventilation (CCV), in which the crankcase gases are returned to the intake tract, are being used more and more frequently compared to open systems (OCV). This is particularly true for engines that run on gaseous fuels, as they not only further reduce pollutant emissions, but also increase energy efficiency by returning unburned fuel to the combustion chamber. Such systems require very high separation efficiencies > 99.5% (based on mass) in order to avoid contamination in the intake tract and to ensure reliable operation of the turbocharger.

CRANKCASE VENTILATION FOR H2 ENGINES

Engines that run on hydrogen can create an atmosphere in the crankcase that exceeds the lower explosion limit of 4% H2 by volume. For this reason, adjustments to the crankcase ventilation system are necessary. An active ventilation system with a fan is required to purge the crankcase with filtered air. In addition, ATEX-compliant components further reduce the risk of explosion. An additional challenge arises from the combustion of hydrogen, which forms large amounts of water that must be kept in the gas phase through temperature management. Otherwise the oil quality would deteriorate and emulsions could form that block the filter.

DIGITAL CRANKCASE VENTILATION

The functionality of crankcase ventilation systems can be expanded through digital solutions, such as an additional blower or an electronic pressure regulator (EPR). These enable the precise regulation of the crankcase pressure and the implementation of a purge air system. Additionally, pressure sensors and a UT99 blow-by flow meter (FlowSpin) can be installed. These options generate valuable data that enables smart functions such as monitoring, diagnostics and predictive maintenance. Not only is information about the condition of the crankcase ventilation system, but also about engine wear, which can be determined by analyzing the blow-by flow rate.

LUBRICANT OIL TANK VENTILATION

Oil-lubricated plain bearings in turbines produce oil mist that must be vented at the bearing points (labyrinth seal). This is usually done centrally via the oil tank to which, depending on the system structure, the ventilation lines to the bearing points are connected. Active coalescence filters are ideal for ventilation and oil mist separation because they use a fan to ensure a negative pressure that prevents the uncontrolled escape of oil mist from leaks in the bearings and oil tank. Due to the efficient separation with low pressure loss, minimal oil mist emissions are ensured with low energy requirements. The TA-Luft limit values ​​of 10 or 20 mg/m³ can clearly be met.

Did you already know:

• If designed incorrectly, coalescing filters can themselves become a source of oil droplets, e.g. due to droplet entrainment or bubble bursting.
• Coalescing filters use both inertia and diffusion as separation mechanisms. This means they are able to separate particles larger than 1000 nm and smaller than 100 nm particularly effectively.
• It can take days or even weeks for oil mist filters to begin draining. Only then do they reach an operating state that is constant for a longer period of time.
• A total separation efficiency of 99.9% can reduce the oil mist concentration to below 1 mg/m3. Such emissions are invisible to the human eye.
• The blow-by volume flow allows conclusions to be drawn about engine wear.