Oil-water separator for a high-pressure centrifugal compressor

Abstract

The oil system of a high-pressure centrifugal compressor for transportation of natural and petroleum gas is one of the important systems in the design of gas-pumping units of gas and petroleum and gas industry compressor stations. The basic plan of a high-pressure centrifugal compressor oil system is shown in Fig. 1. The basic functions of the oil system are delivery of oil to the annular and thrust bearings and the toothed coupling, sealing of the centrifugal compressor by delivery of oil to the end seals with a pressure somewhat higher than the gas pressure in the sealed cavities, removal of oil from the gas cavities of the centrifugal compressor under pressure with subsequent degassing of it, cooling and filtration of the oil, and elimination of leaks into the tank. To a significant degree the oil system of a centrifugal compressor determines the operating reliability of the unit as a whole. Design decisions made in the stage of development of the centrifugal compressor to a significant degree depend on the operating costs, which are influenced not only by the unplanned shutdowns of the unit but also by the irreversible losses of oil. Both the end seals and the system for removal of oil, the basic elements of which are the oil-water separators (Fig. 1) designed for removal of oil, condensate, and other liquids from the gas cavities under pressure in the whole range of operating pressures of compressors, have a substantial influence on the oil losses and operating reliability of the off system. As is known, in centrifugal compressors, oil-water separators in which the relief valve is made in the form of a needle, a ball, or a gate and connected by a system of levers with a float providing opening of it are most frequently used [1]. With an increase in operating pressure there is an increase in the force clamping the relief valve to the seat of the overflow valve, which in turn requires an increase in the lifting force of the float. The force of action of the float on the relief valve may be increased by increasing the float diameter or the amplification factor of the lever system. In this case there is an increase in the dimensions of the off-water separator and, consequently, in its metal content and also in its cost and, most importantly, a decrease in its reliability. The M. V. Frunze Sumy Machine Construction Scientific-Production Association (SMNPO) Joint-Stock Company (AO) has developed an off-water separator design (Fig. 2) providing high throughput and distinguished by simple and reliable operation at high operating pressures [2]. The oil-water separator consists of the welded housing 2 with the fittings 5 and 6, respectively, for supply of the liquid-gas mixture and removal of the gas and also the base 1, in which a channel is made for draining of the oil and a two-stage drain mechanism connected by the level system 3 to the float 4 is located. The two-stage drain mechanism (Fig. 3) includes a supplementary valve and the main slide valve located in the housing 5, in the bottom of which is the drain channel 6. The supports of the lever system 4 and 13 are fastened to plate 12, which in turn is fastened to the housing of the drain mechanism. To compensate the weight of the float and the lever system the relief device with spring 11 is located on the plate. The supplementary valve is located with a sliding fit i~ the guide sleeve 1, which is rigidly fastened to the housing 5. The main valve operating the internal cavity of the housing into the above-the-valve A and the drain B chambers is located in the holes of this housing with a sliding fit. The drain chamber is connected by holes with the inner cavity of the oil-water separator and the above-the-valve chamber by the guaranteed gaps 9 and 10, respectively, with the drain chamber and the internal cavity of the oil separator. The main valve is tightened by spring 7 and has an axial channel 8 shut off by the supplementary valve. In the general condition, that is, in the absence of oil and pressure in the cavity of the oil -water separator, under the action of the float and the lever system, spring 11 of the relief device is compressed and the supplementary valve covers the axial channel and, simultaneously compressing the spring under it, presses it to the seat of the drain channel. With an increase