Pielkenrood has been involved in developing oil/water separators right from the beginning. We are one of “the founding fathers” of the separators in use today and a leading specialist in this field. Presently we mainly use CFI and IPI separators in our designs, combining cost effectiveness with the best technical solution for each specific project.
These separation systems are used in for example:
• first and second stage separators for extraction sites
• oil refineries
• down stream plants
• off shore rigs
• ballast water and slop oil treatment facilities
• LNG plants
Our abilities range from preparing the basic design to delivering a complete project on a turn-key basis. Please refer for more detailed information to the next paragraphs.
One of the earliest ways of separating oil from waste water was introduced in the 1950s with the American Petroleum Institute (API) Separator. This type of separator is a rectangular, in most cases concrete tank through which the oil containing waste water flows at a typical rate of approximately 15mm/sec. Surface area in combination with throughput determine the efficiency of separation. Therefore API separators have to be relatively large basins. Due to hydraulic factors such as short circuit currents and turbulence in the separator basin, the API performance is limited to intercepting oil droplets with a minimum size of 150 micron only.
In the basic and smaller API separators, the floating oil is skimmed off at the exit side using a slotted pipe. Settled sludge is removed through a well, located at the exit side or by manual periodic draining and cleaning. Larger and more complex API separators incorporate baffles, chain-scrapers for sludge and/or surface oil.
API separators require frequent maintenance. In addition to this they also have the following disadvantages:
1. In order to achieve efficient separation, either a very low flow rate or a very long tank is needed. Still, it is impossible to avoid short circuit currents and turbulence. Thus very small particles cannot be completely separated.
2. Wind and rain can disrupt the liquid surface, which induces turbulence and interferes with oil skimming. This can be prevented by constructing a roof over the basin, but this is costly.
3. API separators generally emit a unpleasant odour.
4. The separated oil contains water and may require further separation.
Although the API separator served its purpose, in due course environmental regulations became stricter. As new rules could not be met by using APIs, a better separator was needed.
By the end of the 1950s, Royal Dutch Shell began research to improve oil/water by gravity separation. Following experiments and sophisticated hydraulic calculations, in 1962 the Parallel Plate Interceptor (PPI) was put into use.
The two crucial design advances were to pass the waste water between rows of parallel, flat steel plates, mounted in the direction of the flow and enclosed in a narrow deep tank of steel or concrete, and the setting of these plates at an angle, so that the rows sloped upwards at 450 from the bottom centre line of the tank in V-configuration. The separated oil flowed up the invert sides of the plates and so to the top between the plate edges and the basin side. The plates were covered and completely enclosed by a curved steel plate, providing a semi-circular space along the length of the plates, completely filled by separated oil. Sludge and heavy particles fell to the tank base and were slowly carried by the current to a separation well at the discharge end.
Although the PPI separator offered an important improvement in separating oil from water, a major problem remained: the efficient removal of separated oil and sludge. The solution to these problems was found by a Shell engineering, Mr. Jan Cornelissen and by Mr. Jacob Pielkenrood, who jointly invented and developed an entirely new separator: the CPI
Where the PPI used parallel horizontally positioned metal plates installed in a chevron configuration, the CPI used plates that were arranged in a plate pack which was installed at an angle of 45°. Another main difference was the use of corrugated plates. The separated oil droplets would collect in the tops of the corrugations, while solids would deposit in the troughs. Separated solids would slide down and separated oil drops would adhere to the invert side of the plates and gently move upwards due to its lesser density than water.
Mr. Pielkenrood was aware of the fact that steel plates would quickly corrode and he designed plastic plates, made of GRP. The fact that Pielkenrood-Vinitex BV was also a pioneer in the field of plastics in general and plastic welding in particular, did certainly influence this design decision. The use of corrugated plates also contributed to the rigidity of the plates. At the bottom and top the plate packs were fitted with chutes to guide the separated oil and sludge out of the pack.
This new separator was thoroughly tested and proved to be a considerable improvement as compared with the PPI. The design became known as the Corrugated Plate Interceptor, CPI and it was patented by Shell. Appointed licensed manufacturers were Pielkenrood-Vinitex BV of Holland, Japan Gasonline Corporation of Japan and Monarch of the USA.
CPI separators are counter current separators. Oily water enters the pack at the top and flows between the parallel plates in a downward direction. Separated oil droplets adhere to the plate surface, coalesce and move upward, counter to the downward moving main flow. The separated oil droplets leave the CPI plate pack at the top. Moreover CPI plate packs can also be used for the separation of heavier particles. With this application the water enters the plate pack at the bottom side and moves through the pack in an upward direction. Separated particles subsequently slide down along the surface of the plates and leave the plate pack at the bottom. For this application, the angle of the plates is increased to 55° or 60°. The CPI was such an improvement in separating oil from water that it became Shell’s standard oil separator. Even the CPI however, had a disadvantage: clogging of the plate packs, caused by sludge accumulation in the guide chutes. The chutes also formed an obstacle for cleaning the plate packs with water jets. The plate packs had to be lifted out of their basins before they could be cleaned. However due to the accumulated sludge, the weight of a plate pack increased significantly over time. Consequently, many a plate pack collapsed when lifted out of its basin. Figure 4: flow pattern of CPI/TPI plate packs
Mr. Jacob Pielkenrood introduced a modified plate pack: the Tilted Plate Interceptor or TPI. He replaced the guide chutes by strips, solving the problem of clogged plate packs and at the same time increasing efficiency with 30%. The increase in efficiency can be explained because the chutes caused turbulence in the water flowing between the plates. The strips in the TPI facilitate a laminar flow between the plates, thereby enhancing the plate pack’s efficiency. Pielkenrood-Vinitex patented this new design and successfully sold thousands of TPI plate packs worldwide. Many of these are still in use today.
Our separators are of a very high quality, which is underlined by the fact that we recently replaced one of eighteen installed plate packs in a Shell oil/water separator after 30 years of service!
The rapidly developing off shore activities of oil and gas companies generated demand for smaller separators. On rigs and platforms space is very limited and weight must be saved to the maximum possible extent. The traditional CPI and TPI separators have a relatively small plate surface per m3 of separator basin volume and per m2 of separator basin area. It was necessary to maximise the plate surface compared to the separator basin’s dimensions. This was achieved by developing the Cross Flow Separator or CFI.
Operating principle As with the other types of plate packs, the CFI consists of inclined, parallel corrugated plates spaced closely together. Contrary to counter current separators with the entry at the top or bottom, the CFI has an entry at the side. The water flows in a laminar stream between the plates in a horizontal direction. The main advantage of the CFI is that heavy as well as light particles can be separated from the effluent simultaneously. For instance, oil is separated by floating upwards along the tops of the corrugated plates to the surface of the separator tank. Heavier particles at the same time settle along the bottom of the corrugated plates and slide down the plates to be collected in a sludge cone and discharged through a blow-off valve.
CFI advantages The CFI design offers some important advantages:
1. The CFI is considerably lighter and smaller than a comparable CPI or TPI.
2. The CFI can be designed and built in any dimension and shape, as required by the desired basin configuration as long as the total effective separator plate area meets the separation criteria.
3. CFI separators don’t need a deep basin, as the inlet and outlet are not located at the top or bottom, but at the side.
4. CFI separators separate oil as well as heavier particles simultaneously from the effluent.
Plate designs Today we don’t exclusively use corrugated plates. Depending on the purpose of the CFI separator we determine the ideal plate design, which can be flat, corrugated or have a special profile. It is important to know when to use which plate design. A plate profile suitable for the separation of oil from a low viscosity liquid, such as water, is not necessarily suitable for separating oil from a high viscosity liquid.
Furthermore, in the corrugated plate CFIs, the oscillating flow of the effluent between the plates causes turbulence when the flow velocity exceeds the design limits. In fact the critical flow velocity at which turbulence occurs is lower in a CFI, with corrugated plates, than in a CPI/TPI in which a linear flow exists.
Pielkenrood designs plate profiles for each specific process aiming at optimising the CFI performance.
CFI applications CFI separators are the best solution for the following applications:
1. To simultaneously separate light and heavy particles from liquids.
2. To enhance the efficiency of existing separator tanks. For instance three phase separators, free water knock out vessels and drain water separators (especially when used on off shore facilities).
3. When space is limited and dimensions of the separator are dictated by the available space.
4. In pressurised separators.
The CFI concept is also suitable to modify existing CPI/TPI separators. By replacing the CPI/TPI plate packs by CFI type ones, the effective plate surface is increased without altering the outer dimensions of the CPI/TPI basin. Replacing CPI/TPI plate packs by CFI ones, instantly increases the plant capacity and/or separation efficiency. In figure 10 one can see Cross Flow plate packs applied in an existing CPI basin. The original effective CPI pack surface was 130 m2, while the effective Cross Flow pack surface is 500 m2! The only disadvantage of the CFI is that the flow velocity between the plates is limited.
When converting an existing CPI/TPI separator with CFI plate packs, we use mobile IPI separators in order not to disrupt our clients’ plant operation. The only disadvantage of the CFI is that the flow velocity between the plates is limited.
Development didn’t stop with the perfection of the CPI/TPI and introduction of the CFI. We always strive to look further, to develop and to try new ideas. Often this results in a new product or application. In the 1980s Simon Pielkenrood, the son of Jacob Pielkenrood, developed such a new application: the Inclined Plate Interceptor or IPI separator.
The IPI separator combines the advantages of the counter current CPI/TPI and the compact CFI into one system. Although being a counter current separator, the IPI doesn’t make use of traditional plate packs and therefore the design of the separator basin is free. With the introduction of the IPI the disadvantage of the CFI, namely the limitations to flow velocity, were overcome. The IPI separator is an attractive alternative for the CPI/TPI design, in case counter current, linear flow separators are required.
Pressure Cross Flow Interceptor
Especially for oil and gas extraction industry, we supply pressure cross flow interceptors. These can be used to de-hydrate the oil or gas condensate after the first stage separation and for de-oiling the produced water in the second stage.The CFI plate packs are designed specially to fit into any (existing) pressure vessel and offer highly efficient operation.
We design and build new pressure cross flow interceptors, but we also refurbish existing ones in order to increase performance.
We re-fitted the separator with our own plate packs, after which it worked fine. This example shows that know-how and experience are of the utmost importance.
Our current program Pielkenrood has been involved in developing oil/water separators right from the beginning. We are one of “the founding fathers” of the separators in use today and a leading specialist in this field. Presently we mainly use CFI and IPI separators in our designs, combining cost effectiveness with the best technical solution for each specific project. These separation systems are used in for example:
• oil refineries
• down stream plants
• off shore rigs
• ballast water and slop oil treatment facilities
• LNG plants
Our abilities range from preparing the basic design to delivering a complete project on a turn-key basis.