Contract for Terraced Filters in China
A major Chinese and Royal Dutch petrochemical company joint venture has selected and awarded Royal Dahlman for the supply of Royal Dahlman Terraced Filters for a new polymer polyol plant in the People’s Republic of China. Royal Dahlman has extensive experience and a proven track record in filtration systems specifically for removing polymer/polyol coarse particles out of highly viscous liquids.
The Dahlman Terraced Filter has found its roots in the filtration of gel particles in the production process of Vinyl Chloride Resin (PVC), Polyols and Resins. Almost three decades ago Dahlman developed the K-type filter, the predecessor of the T-type filter. This filter consists of an element with a conical shape. The filtration direction is from the inside to the outside. As filter septum axial pleated needle material was used in various materials and micron ratings. As a consequence of its conical shape there is a laminar flow distribution over the total filter surface and equal solids build up. The K-filter element holds a filter surface of 2,5 m2. Dahlman‘ s K-type filter has proven during various tests and years of operations that the set design criteria by the operators, namely a high dirt holding capacity (DHC), an excellent removal efficiency on gel particles and easy change-out, has been met.
Further testing and the desire to improve performance has led to a close co-operation between a major operator and Royal Dahlman to achieve this. Also the request from the plants to increase the life time of the element, by increasing the filtration area in the same dimensions, was one of the added criteria for a next generation filter element.
New generation, the patented Dahlman Terraced Filter (T-Filter)
The criteria for the next generation has led to an element which has a sewn construction instead of resin bonded and holds a filter surface area of 5,4 m2 (more than two times the filter area of the K-Type filter element). The name Terraced Filter, abbreviated T-Filter, derives its name of the design lay-out of the filter media. By applying a radial pleated construction instead of the conical axial construction (K-type) an increase of filter surfaced is achieved. One filter element exists of multiple layers, so called terraces. The filtration direction is unchanged and is also from inside to outside. Between each terrace drainage material is foreseen to provide space between each layer. This ensures a proper flow distribution and a very high DHC. The latest development is doubling the length of the element. It still has the same diameter as the standard filter, but by increasing the length it has now a filter surface area of 9,5 m2. Typically this double length element is used for excessive dirt loadings. The Terraced Filters are installed in a pressure vessel holding one or more filter elements. Standard configuration are available with 1, 3, 5, and 7 elements installed with single or double length elements, depending on the flow rate, dirt load and requested pressure drop.