Large passage liquid – solids cyclones offer a cost effective solution for the removal of large amounts of course solids from high volume liquid streams found in the process industry. Due to the large passages inside the cyclone (the solids drain connection is the smallest of the cyclone process connections) plugging is virtually impossible.
Unlike basket strainers and filters, cyclones are unaffected by sudden releases of large amounts of solids. The differential pressure depends on the actual flow rate going through the cyclone. Therefore the differential pressure will remain unchanged if the cyclone is confronted with a ‘slug’ of solids. The solids will be removed and the cyclone will continue to operate without maintenance requirements.Due to the nature of the cyclones the efficiency of the solids removal is depending on the flow rate through the cyclone: the closer the actual flow rate is to the maximum design flow rate of the cyclone the better the efficiency will be. The differential pressure from cyclones is, like the efficiency, depending on the actual flow rate.
For reliable operation it is required that the solids removed by the cyclones are continuously removed from the solids storage area. If the drain flow is interrupted for longer periods the solids will build up in the solids storage area causing the drain connection to plug. Therefore the cyclone units are usually equipped with a solids settler drum or a solids filter drum. The solids which are separated in the cyclone will move with a small bleed flow of 0,5 to 1% of the main flow to the solids settler drum or the solids filter drum. There the solids are removed from the bleed. The liquid is returned to the process. The solids can be removed from the solids settler drum by hand, suction truck or transport screw. The solids filter drum provides improved means to wash the solids before removal and allows for efficient steam-out.
Construction of a cyclone
A liquid – solids cyclone consists of a reduced inlet connection located in tangential position in the upper part of a vertical cylindrical pressure vessel, a cylindrical separation area, a solids storage compartment at the bottom of the vessel and an outlet connection at the top of the vessel.
Principle of operation
Due to the reduction of the inlet size the liquid is accelerated before entering the vessel. The accelerated liquid is forced to follow the vessel wall and consequently the liquid will start to rotate at high speed in the vessel. Due to the high angle-speed created by the shape of the vessel the heavier solids particles are forced to the vessel wall. There the solids will start a spiral shaped travelling path towards the solids drain of the cyclone. To assist the removal of the solids and to prevent solids to re-enter the liquid flow the lower part of the cylindrical vessel is provided with a cone. The cone will guide the solids towards the solids drain and due to the reducing diameter the angle-speed remains high although the actual speed reduces. To overcome short interruptions of the drain flow the bottom part of the cyclone vessel allows for storage of limited amounts of solids.
The liquid, after being freed from the solid particles by the centrifugal forces moves into the vortex and is carried upwards through the outlet pipe and into the downstream piping.
The inside of the vessel is especially designed for reducing the wear of the high speed solid particles. The cyclones are provided with a leak detection connection for the upper part where the wear will show first.
Due to the use of centrifugal forces the cyclone does not contain any moving part. The maintenance of the unit is restricted to the occasional inspection of the wear on the unit and the monitoring of the leak detection connection and the solids removal.
The solid particles which are separated in the cyclone are carried through the solids outlet by means of a small amount (usually 0,5 – 1% of the main stream capacity).
In application where the amount of solids is small the solids outlet can be opened periodically to drain of the solids with even smaller amounts of main stream product.
For applications in which the amount of solids is larger (or if the nature of the solids and the liquid does not allow the solids to be drained periodically) the solids can be drained continuously to a settler drum or filter strainer.
Depending on the application the settler drum can be equipped with internal piping for washing and steam-out of the solids before the settler is opened. The Solids filter strainers are always equipped with a washing/steam-out connection. In cases where the main stream liquid or the removed solids are hazardous to the maintenance personnel or the environment washing and steaming is usually required to a high extend. If the time required for this procedure is long it is recommended to install two settler drums or filter strainers. If one settler is in use the other can be cleaned. The continuous removal of solids from the cyclone is secured and the emptying of the settler can take place at a convenient time. If more than one cyclone is installed the solids drains from the cyclones can be combined in the same settler(s) in order to limit the number of settler filters or drums. After the solids have been settled in the solids settler the main stream liquid can be returned to the suction side of the process pump(s), or the unit can be provided with a booster pump to raise the settler outlet pressure to the process pressure. It is recommended to include a flow control valve in the return line to the process. This will allow governing of the flow through the solids drain of the cyclone and the settlers.
Solids Settler Drum series SSD
Solids Settler Drums series SSD are horizontally oriented settler drums. The vessels are equipped with two full opening covers to allow easy access and maintenance. To prevent the settled solids to be washed out of the vessel in case of pressure surges the outlet is provided with a course basket strainer (integrated in the vessel outlet dome). Depending on the application the vessel can additionally be equipped with piping and screens for washing and steam-out. The dimensions of the settlers are depending on the anticipated amounts of solids and the capacity of the main process. Emptying of the solids settler drum can be accomplished by hand, vacuum truck or transport screw.
Solid Filter Strainers series SFSSolids Filter Strainers series SFS are vertically oriented strainer drums. The vessels are equipped with one full opening cover to allow for easy maintenance. The upper half of the vessel is provided with course strainer elements with two open ends. The liquid containing the solids enters from the top of the vessel. The liquid flows through the strainer elements from inside to out. The solid particle which are retained by the strainer can fall through the open bottom end of the strainer elements and settled on the bottom of the vertical vessel. Due to the limited flow velocity the strainers will not block. Since the settling space in the bottom of the vessel is a dead-end the solids will not be effected by pressure surges in the system. Based on operation time or a rise in differential pressure the solids should be removed. After the vessel is disconnected from the process the washing and steam-out can be accomplished with high efficiency. The bottom of the SFS is provided with a removable cover with build in washing/steam-out screen. This allows the washing liquid and the steam to penetrate the solids layer effectively. Additionally the vessel is provided with a back-washing connection to clean the strainer elements without opening the vessel. After the solids are washed and steamed the bottom cover can be removed. The solids which will fall out of the vessel and can be collected in a movable container or waste disposal drum. The dimensions of the strainers are depending on the anticipated amounts of solids and the capacity of the main process.