Rotational Particle Separato r: an efficient method to separate mists from gases in confined spaces.

In a quite a number of processes micron sized droplets, formed by condensation have to be separated from a large volume gas flow. Examples include condensate removal from wet natural gas and CO2/H2S capture by cryogenic techniques. To keep residence times and volume of the separating unit at reasonable sizes, an efficient separator of micron sized droplets is necessary. In case of mechanical separation it is necessary to have a force on the droplets and a wall where they can be collected. In a traditional settling tank the force is the gravitational force that is balanced by the Stokes force. In the case of 1 micrometer droplets this leads to large residence times (>10 s) and correspondingly bulky equipment. Cyclones can be used to replace gravitational force by centrifugal force thus reducing the footprint, but are limited to separating droplets in the order of 10 micrometer for larger scale installations. The performance of a cyclone can be enhanced by adding a rotating filter element consisting of a multitude of axially oriented small channels: the rotational particle separator (RPS). Thus the distance to the wall is reduced at the cost of adding a rotating element inside the cylindrical housing. The RPS is able to separate an order of magnitude smaller particles than the axial cyclone is able to, at equal-residence time, specific energy consumption and volume flow. Equally, for the same separation performance, the RPS is an order of magnitude smaller in size and thus offers significant space advantages as separation device in offshore applications. The diameter of the channels is typically 1-2 mm, its length 0.2-0.5 m. The element is about 0.4-1m in diameter. After entering the channels of the rotating body, liquid mist particles entrained in the gas are centrifugated towards the collecting wall. They then form a film of liquid flowing downwards parallel with the gas. At the exit of the channels, the liquid film breaks up into droplets of 50-100 µm in diameter. These droplets are centrifugated to the casing wall and subsequently leave the device via a liquid drain. The process is demonstrated at laboratory scale for CH4 - CO2 and N2 - CO2 mixtures. Results of experiments confirm theoretical predictions concerning the removal rate and droplet sizes. Using the experimental results, an industrial scale prototype separator is designed to operate at field scale throughput, pressure and temperature conditions. For fast preliminary separator testing purposes, a full size model separator (based on water/air) has been built to study liquid removal and separation efficiency. In the presentation attention is focused on latest experimental results obtained from an industrial version installed at a gas distribution station of Enexis, a gas provider in the Netherlands.. The unit demonstrates the potential of the RPS as a compact device suited for demisting gasses in (offshore) plants where space is limited.