COALESCING PLATE PACKS

Horizontal Cross-Flow (HCF) Plate-Pack

1. Fundamental Concepts of the Horizontal Cross-Flow (HCF) Plate-Pack
The HCF is designed to remove additional amounts of oil from the bulk water phase. Two basic fluid dynamic principles, as well as innovative physical dimensions, govern the HCF operation of separating liquid phases. Laminar, stable flow maintained between the HCF’s corrugated plates (3/8″ to 1″ apart), allows convention settling (i.e. in accordance with Stoke’s Law) to be much more efficient. Decreasing the travel distance to an interface (and subsequent removal) from a few feet (as in conventional settling tanks) to a shorter distance reduces the retention time required to effectively treat a given volume of water.

2. Physical Process
A circular framed 3-dimensional housing containing stacks of corrugated plates acts as the working media. Made of DION® Corr-Press Vinyl Ester reinforced with fiberglass, each pack contains plates inclined at a 45º angle and spaced from 3/8″ to 1″ apart. As they impinge upon the plate above, coalescence of droplets takes place and the larger droplets which are formed migrate to the top of the Plate-Pack and are removed. The materials with specified gravity greater than water separated and fall to the bottom. The HCF Plate-Pack rests upon a perforated plate which acts as a collection point for the solids.

3. Flow Scheme

1. The oil-contaminated water stream feeds directly to the vessel. Immediately those larger particles heavier than water will normally settle to the bottom of the primary separation compartment of the vessel. A pressure drop entering into the degassing section causes most of the gas remaining to break out. As the basic premise of HCF operation depends upon laminar flow and adherence to Stoke’s Law, the flow pattern must be smoothed and a laminar flow regime established. Anything done to bring the flow within this range and to reduce the Reynold’s number improves the efficiency.
2. Prior to entering the HCF Plate-Pack the largest oil droplets have separated out although the major portion of the oil (in contaminated water flows into the
3. Plate-Pack where the basic process begins. Upon developing laminar flow a short distance in the pack. Stoke’s Law becomes applicable. As the various sized oil droplets flow through the pack, they settle to a peak in the plate bounding the upper side of the flow-path. Coalescence takes place and forms larger oil droplets which, due to greater buoyancy, migrate to the top of the Plate-Pack. Here oil flows upwards in the gutters and into a concentrated oil phase where it is skimmed off into the oil box.
4. From a water quality standpoint, the materials remaining in the flow-stream are those finer materials with a higher specific gravity than water and trace quantities (PPM) of oil which exists as oil droplets too small to be removed by the Plate-Pack. The larger materials of higher specific gravity fall through the perforated plate and out the bottom. There these particulates fall downward and settle to the bottom of the vessel. The flow, consisting of water, trace oil and trace fines (both free and oil encapsulated) moves into a chamber which contains the weir controlling the water level. Some of the trace oil which may be separated in the upward flow channel can be removed through a manual secondary oil drain on top of the water section of the vessel.

4. Maintenance
The solids fall out at the bottom of the Plate-Pack due to its incline; therefore, the unit is basically self-cleaning. All our coalescing plate packs are built in segments which can be removed from the vessel supports for inspection, cleaning and replacement.