NEW TREATMENT PROCESS FOR OIL AND WATER EMULSION ON OFFSHORE PLATFORMS [PHASE 1]

Objectif

The quantity of water associated to the crude generally represents a significant part of the well effluents. This water must be separated as early as possible from the commercial part of the output. Specifications of the maximum water and salt concentration in the crude are stipulated by the refiners. In addition, the waste waters are subjected to environmental contraints covering their hydrocarbon concentrations.
Since the efficiency of primary separation process is not sufficient, heavy and cumbersome equipments are generally set up in order to achieve the required specifications.
The objectives of this study are both :
- to find out means of reducing the volumes and the fineness of the oil and water emulsions to be treated on offshore platforms,
- to develop smaller and lighter equipments for the settling of these emulsions.
a) HYPO-EMULSIFYING CHOKES AND VALVES
The three types of valves were initially tested on low concentration oil in water emulsions. The efficiency of each type of valve was quantified and the validity of the theoretical experiments initially set up was confirmed. These results were checked in the case of oil in brine emulsions, higher concentration emulsions an finally in the presence of gas. The relationship between the parameters being defined a conceptual design of two types of valves/chokes was completed. Although no potential problem was identified in the technical development of these equipments, the difficulties anticipated in the marketing approach of the customers in conjunction with the uncertainties of the oil industry linked to the low oil price level, have made necessary to cancel this project.
b) DE-OILING CYCLONE
Testing of the conventional type scale model has enabled first to optimize the general set up of the cyclone. Then an adjustable injection head was definedin order to improve the flexibility in flow rate. The efficiency of the cyclone was then improved furthermore by the addition of internal devices increasing the hydraulic stability of the stream. Two patent applications were filed. The cyclone performances were then comparable to those of a tilted plate separator but a much smaller weight and volume. However the results were much lower than what was anticipated from the theoretical calculations.Therefore the laboratory studies were resumed in order identify the origin of this problem. Based on this study a new concept was defined leading to a different type of hydrocyclone. An industrial prototype has been built and tested on an offshore field. Excellent results were obtained but some minor improvements are still required in order to reduced the pressure drop requirement. Further scale model testing are currently outstanding.
c) ELECTROSTATIC DEHYDRATOR/DESALTER
The sampling/blistering procedure studies lead to the development ofa method which has been patented. However, this system can only be used on laboratory fluids and attempts to extend it to the field conditions have failed.
Testing of newly available process have shown some possibilities of reduction in the sizes of the equipments. However the work on these pilots was stopped when studies on a new concept of equipment have revealed that larger progress could be achieved. A scale pilot is being tested resulting in significant improvement in performance and residence time. In the future it will be possible to prove that the weight and volume could be reduced yet further by optimizing this new technology.
Three types of equipment capable of bringing about significant gains, were initialy selected :
a) HYPO-EMULSIFYING CHOKES AND VALVES
The formulas defining the droplet size distribution of a liquid dispersed in another liquid by turbulent dissipation show that it is possible to increase the diameter of the droplets dispersed :
- by reducing the pressure drop, which is achieved by dividing this into several stages instead of a single stage,
- by increasing the energy dissipation volume, which corresponds to increasing the frictional surface areas that generate the turbulence,
- by increasing the concentration of the phase dispersed, resulting in partial local separation and in subsequently applying the pressure drop to each of the roughly separated phases.
Models applying the above processes :
- a multi-port stage valve,
- a rotating flow diode,
- a long pipe type valve.
were developed for parallel testing with a single diaphragm representing valves that already exist, thus providing a reference for comparison with other systems.
b) DE-OILING CYCLONE
Second a de-oiling cyclone (emulsion of oil in water) capable of accommodating to wide variations in flow (1 to 4) and oil concentrations whilst at the same time reducing in a proportion of 1 to 10 the overall dimensions and weights of existing equipments fulfilling the same functions.
This device, working on a segregation principle, will multiply the difference in specific gravity between the oil and the water phases by the huge centrifugal acceleration developed in a vortex flow.
On the basis of a mathematical model initialy set up, a plexiglass scale of a conventional cyclone was built first. After extensive testing of this model a new concept of hydrocyclone has emerged and a modified scale model was developed. Finally an industrial prototype was built and has been tested in an offshore field.
c) ELECTROSTATIC DEHYDRATOR/DESALTER
Design improvements and increases in efficiency of the electrostatic dehydratorwas found possible, which should result in significant reduction in the size and volume of the existing equipments. the initial analysis of the problem has focussed on the following axis of research :
- the design and the development of a sampling/blistering procedure enabling to clot the droplet size distribution of the emulsion for future characterization,
- the analysis by means of radioacive tracers of the flow of the different phases in refinery desalter,
- the pilot testing of the new developments available on the market like the three electrode technology (Bielectric from Petrolite) or of the horizontal flow type (HTI from Hydrotech).

Programme(s)

ENG-HYDROCARB 1C - Programme (EEC) of Community projects in the hydrocarbons sector, 1973-1985

Thème(s)

1.9 - PRODUCTION SYSTEMS

Appel à propositions

Data not available

Régime de financement

DEM - Demonstration contracts

Coordinateur

GERTH

Contribution de l’UE

Aucune donnée

Adresse

232 AV. NAPOLEON BONAPARTE
92500 Rueil Malmaison
France

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