Development and coalescence mechanism of an improved filter cartridge for oil mist separators

Abstract

Oil mist coalescence and filtering are extensively used in the fields of natural gas purification and chemical production. However, it remains technically challenging to capture high-concentration, small-sized, oil mist droplets under complex industrial field conditions. To solve this problem, three novel high-efficiency coalescence filter cartridges are proposed, which have improved filter material arrangements. The filtering performance of the cartridges was evaluated in the laboratory and at a natural gas pipeline pressure station under different working conditions to understand the mechanism by which high-concentration small-sized droplets are captured. According to the laboratory results, the filtration efficiency for droplets> 0.2 µm can reach 99.99% if the first layer in the cartridge has a small pore size (1.5 µm). The use of a filtering material with a large pore size can reduce the pressure drop. An arrangement of layers with increasing pore sizes can significantly improve the quality factor of the cartridges and decrease secondary entrainment. In the field test, the size distributions of the oil mist under compressor “hot standby” and operating conditions were gained for the first time. The median size of oil mist droplets was 1.2 µm during hot standby and 0.5 µm during operation. Under both compressor modes, the downstream oil mist concentrations of the proposed cartridges were> 95% lower than that of an existing commercial cartridge once filtering reached a steady state. In a long-cycle test under field conditions, the proposed cartridges showed more stable filtering performance than the existing product, with the filtration efficiency being about 40% higher after 15 days. Moreover, the oil mist coalescence mechanism was determined by microscopic characterization of liquid channels.