Water Wall

A versatile and cost-effective liquid–liquid separator for oil dispersions in water.

Above: Applications of this equipment include produced water cleanup; marine water/bilge water cleanup; metalworking fluid recycling; and industrial wastewater cleanup.

Water Wall separation system yields an extremely efficient separation of oil dispersions in water. The system is based on a peculiar process, which is patented in Italy and is going to be internationally patented, which exploits the physical properties of oil, water and a specifics liquid –liquid interface support to create the “water wall 2surface barrier against the passage of oil droplets: separation efficiencies can reach extremely high levels, even in presence of quasi-stable emulsion with droplets of sub-micrometric size.

The present report describes the main features of the water wall system, and shows some results concerning the separation efficiency in the treatment of production and run-off waters in the oil industry.

Technofluids’ integrated treatment for production water, which involves other patented technologies developed by Technofluids’ R&D. manager to treat oil , aromatic solvents and solid dispersions in water, is also briefly outlined.

Process description

The process underlying the water wall system is based on the observation that an additional interfacial tension between oil droplets and water arises from the mutual interaction between oil, water and a proper liquid –liquid interface support. This additional interfacial tension leads to the rejection of oil droplets on the top of the liquid-liquid interface support, eventually ending into a surface coalescence of oil droplets. Rejection take place only when the relative velocity between oil droplets and the two phase filtering layer remains below a certain threshold which is directly dependent on the flow rate, on the droplet size and on the physical properties of oil and water. An additional deep bed filtration effect on sub-micrometric droplets which are able to pass through the interfacial tension barrier has been also observed.

A threshold flow rate is therefore determined and verified at design level for the required separation efficiency, given the size distribution and the physical characteristics of the oil dispersion to be treated. In any case as the pressure drop introduced by the liquid-liquid interface support is minimal (around 0,01bar)separation can be usually performed at high flow rates: in some applications, flow rates up to 60 sq.m./hr per sq.m. of the two phase filtering layer can be adopted. Enclosed Figure 1 shows a typical water wall system where the two successive stages are intended to exploit both the deep bed coalescing effect on the first coarser two phase filtering layer and the rejecting barrier of additional interfacial tension generated at different levels both on the first and on the second finer two phase filtering layer. Rejected oil is recovered from the top of both separation chambers. Level controls operate in order to maintain the pressure level on the two phase filtering layer within the desired range: this range allows the system to deal with sudden reduction in the incoming flow rate, as well as with a sudden increase in oil concentration with no effect on the separation efficiency of the system.

Owing to the physics of the separation system, the correct determination of the water velocities on the top of the two-phase filtering layer plays a key role at design level. Technofluids adopts numerical techniques to simulate water flow inside standard and custom-made water wall configurations.

Separation results

Water wall separation system has been tested on several cases of treatment of oily waters, in industrial and environmental streams. Concerning applications to oil industry cases 8enclosed table 1 shows separation results for a field case of run-off water at AGIP Oil Centre in Cavone(Italy) oil is removed almost completely (separation efficiency overtakes 99,9%) while the two-phase filtering layer proves to be also an effective barrier against suspended solids.

The production water was instead generated at ELF EP facilities and consisted in a dispersion of Sahara light oil (45,9°API) with a mean drop diameter of 5,1 micron, in salt water with a salinity of 40 g/l . Figure 2 shows that, during a test run lasting 930 minutes with an average inflow oil concentration of 574 p.p.m. oil concentration at the outlet was never more than 9 p.p.m, with an average value of 5,3 p.p.m, meaning a mean separation efficiency of 99,1% . Similar separation results have been obtained also in the trials with Escravos Nigerian oil (37 °API)and Vic Bilh heavy oil (22 °API)

Integrated treatment for production water

As shown in table 1 water wall system proved to be effective also in separation of solid particles from oily water dispersions. However, this case needs a special care in the design of the back washing system and in the following treatment of the discharged back washing water

Techno floc system is a purification process of polar liquids containing colloidal dispersion of solvated particles, internationally patented by Technofluids’ R&D. manager and based on the addition of a natural, food grade, non soluble molecule. Techno floc improves the efficiency of the removal of suspended solids to almost 100%, minimizing the amount of dissolved aromatics components: table 2 shows the excellent separation results obtained in the treatment of produced water from AGIP Oil Centre in Cavone , where the average particle size of the suspended solids was around 7 microns.

An improved Techno floc system allows also the removal of heavy metals and bacteria from the treated water

The system can be efficiently integrated with the water wall to obtain a final treatment for production water for: discharge into environment, re-injection or direct delivery to R.O. for steam production purposes.

Conclusions

Water wall has been exhibited at the offshore Technology Conference in Huston (Texas) on may 1996. Afterwards, the European Commission has sponsorised the validation of this technology with the funding of a validation programme on a pilot . the programme has been done jointly with AGIP and ELF Most of the trials were carried out last 1999 in Pau at ELF Research Centre.

The conclusion of the trials given to the European Commission said that “the project demonstrated the viability of the innovative technologies for the treatment of the oily water either collected as wastes or separated from produced oil. The wastewater prototype has satisfactory worked over one year in both configurations and the monitoring data support the advise for the reduction of the system complexity eliminating the solid separation unit, obtaining economical advantage without reducing the water treatment performances . The production water plant showed excellent performance in terms of oil separation , thus demonstrating the good potential of the technology. The validation programme was successfully completed on may 2001 with final report to the European commission.