FR2477239A1 - Turbo-compressor oil return line - has intermediate reservoir and dip pipe to isolate compressor from return tank - Google Patents

Abstract

The oil return lines of a turbocompressor in a gas synthesis plant (1,8) join in a common return line (3) which connects to an oil reservoir. The reservoir is hydrostatically isolated from the line pressure by an intermediate tank (4) and a dip pipe (5). The return pipes are submitted to a small vacuum by one or several pumps (7). The compressor bearings are also put under a small vacuum, but this does not affect sealing.

Description

 The present invention relates to a lubricating oil return circuit of a turbo-compressor group for gas synthesis, in particular of a turbo-compressor group for ammonia synthesis.

 We know the turbo-compressor groups used in ammonia synthesis installations and used to compress the synthesis gas. Such groups are groups with high characteristics and also include a lubricating oil circuit common to the turbine and the compressor. Currently in conventional manner, the lubricating oil circuits returning from the turbine and compressor bearings are combined in the same manifold in a single pipe going to the oil tank. From this reservoir, the oil is then recycled, in the direction of the turbine and the compressor.

 For safety reasons, a light sweep of the oil tank is commonly carried out using an auxiliary gas, such as nitrogen in the case of ammonia synthesis, so as to remove the traces synthesis gas which could exist in the tank. There is therefore, due to this sweeping using the auxiliary gas, a slight overpressure in the oil tank, and consequently, in the oil return line to this tank, this line being conventionally put at tank pressure.

With the devices currently known, this overpressure is reflected through the oil return pipes inside the bearings of the turbine. However, it is not possible, as is the case for the compressor bearings, to make seals on the shaft outputs of the bearings using sealed covers to prevent oil leakage to the outside, because such watertight covers cannot be installed between the oil parts and the steam parts which are at very high temperature.

Consequently, the overpressure created inside the turbine bearings is liable to cause oil leaks outwards, which, as a result of the very high rotational speeds of the turbine, are projected onto the hot parts of that -this, and can therefore cause fire risks.

 The device of the invention does not have the drawbacks of the devices known at present, being of a design such that the danger of oil leaking from the turbine to the outside due to the overpressure in the oil tank is eliminated. I1 is characterized in that the connection of the lubricating oil return pipes is carried out using an intermediate hydrostatic pressure isolation tank, with respect to the oil tank, of at least the return of oil from the turbine. Furthermore, in the event that this arrangement proves to be insufficient, it is also possible, in accordance with the invention, to connect the pipes thus isolated in pressure by the intermediate tank to a depression, such as an electric fan or a venturi ejector.

The invention will be better understood using the following description of two exemplary embodiments with reference to the accompanying drawings in which
- Figure 1 schematically shows a first embodiment of the invention, in which the turbine bearings are isolated and placed under vacuum without the compressor bearings being.

 - Figure 2 schematically shows a second embodiment of the invention, in which the turbine bearings and the bearings of the compressors are isolated and put under vacuum simultaneously.

In Figure 1, there is designated by the reference 1, the lubricating oil return pipe immediately at the outlet of the turbine bearings, and by the reference 2, the lubricating oil return pipe immediately at the outlet of the bearings In a manner known per se, the pipes 1 and 2 meet in a single pipe 3 for the return of oil to the common oil tank, this oil tank being placed at a slight overpressure due to circulation in this one from a stream of cleaning nitrogen
In accordance with the invention, the junction of the pipes 1 and 2 is effected by means of a small tank 4 in which the pipe 1 plunges fully, so as to be always completely submerged, the pipes 2 and 3 constituting on the other hand an inlet and outlet piping respectively. A convenient arrangement as shown in FIG. 1 consists for example in using for piping 1 and 2 a common piping having a lower bulge 4 constituting the small intermediate tank, of sufficient depth so that the piping 1 can always be totally submerged therein, the tank 4 of course always being. filled with oil. As can be seen in the drawings, hydrostatic isolation of the communicating vessel type of the piping 1 is thus carried out relative to the piping (2, 3). The level of return oil 5 shown in the drawing is therefore due of this overpressure slightly higher than common level 6 of the pipes
(2, 3).

 It will be noted that if this arrangement makes it possible not to put the piping 1 at the tank overpressure, on the other hand the piping 2 is indeed at this overpressure. The slight overpressure which.

the result in the compressor bearings does not, however, matter a great deal, since the seals on the shaft outlets of the compressor bearings are made using airtight covers, so that this overpressure does not cause leaks. oil outside.

 In the event that the arrangement according to the invention does not.

not provide sufficient security against oil leaks at the turbine bearings, it is also possible, according to the invention, to create one. bearing pressure. turbines by placing the piping 1 under vacuum, for example as shown diagrammatically in FIG. 1 using an electric fan 7.

 As a variant, it is obviously possible in the case where it is also desired to isolate the compressor oil return pipe 2 from the common return pipe 3, as well. that possibly put this pipe 2 in slight depression, as we did in the example considered for the pipe 1, to isolate the pipe 2 in the same way and possibly to put it under pressure using 'a second electric fan for example. It would simply suffice for this. to join the pipe 2 with the tank 4 using a pipe completely submerged in this tank.

The embodiment of FIG. 2 resembles that of FIG. 1, but, in the latter, it is the piping 8, common to the oil return circuits of the turbine and of the compressor, which is isolated by means hydrostatic of the return pipe 3 to the oil tank, this pipe being - conventionally put under pressure from this tank. In a similar manner to the previous one, for example for this hydrostatic pressure isolation, a small intermediate tank 4 is used in which the pipe 8 ends, by means of a wall 9, so as to be always completely submerged in that -this. As previously, there is shown schematically in the drawing an optional depression of the pipe 8 using an electric fan 7.

The arrangement of FIG. 2 has the advantage of isolating and possibly putting in-depression both the turbine bearings and the compressor bearings by means. particularly simple.

In FIG. 2, the intermediate tank 4 is also produced in a particularly simple manner, thanks to a practical bulge in the common return piping (8, 3). This kind of realization is easy because it is practiced on the still horizontal part of the oil return piping. In the case where the junction according to the invention would be carried out on the vertical part, one could use an intermediate tank of any shape, in which the piping- such as 8 would be completely submerged, while the starting piping such as 3 would only be partially so.

 The invention finds its industrial application for the synthesis of gases, in particular for the synthesis of ammonia gas.

Claims (3)

 1. Lubricating oil return circuit of a gas synthesis turbo-compressor group, of the type according to which the oil return pipes of the turbine and of the compressor are combined in a common oil return pipe towards the oil tank, said common piping being put under pressure from said tank and said tank may be subjected to a slight overpressure due to the circulation therein of an auxiliary cleaning gas, characterized in that the junction of said return piping is carried out using an intermediate hydrostatic pressure isolation tank (4), relative to the oil tank, of at least the oil return pipe (1) of the turbine.  2. Oil return circuit according to claim 1, characterized in that the pipe or pipes (1, 8) insulated (s) by pressure by said intermediate tank (4) is / are also connected (s) to a or more vacuum devices (7). 3. Oil return circuit according to claim 1 or claim 2, characterized in that said intermediate tank is produced by means of a bulge (4) of the common oil return pipe (3).