Experimental Investigation on a New Axial Separator for Oil–Water with Small Density Difference

Hydrocyclones play an important role in pre-separation downhole to decrease the water content of produced liquids. While the structural feature of tangential inlet limits the further improvement of separation efficiency. Therefore, the axial separator has emerged as the potential alternative due to its low swirl turbulence, easy installation, and low energy consumption. Since the first proposition of axial separators, several designs have been introduced. They are used for two fluids with more than a 100 kg/m3 density difference. However, there are some situations where the oil density is above 900 kg/m3 and their densities are closer. In this paper, a new axial separator was introduced, and the separation performance was investigated experimentally using gear oil with 920 kg/m3 density and tap water. The results show that the separator keeps high separation efficiency, and the oil concentration in heavy phase outlet is below 500 mg/L in experimental conditions where water flow rate ranges from 3 to 7 m3/h and oil fraction ranges from 1 to 10%. Additionally, higher inlet flow rate and larger oil fraction lead to an increase of oil concentration. Also, the split ratio should be kept in a reasonable range to acquire the best separation performance.