EP0453478A1 - Ejector with peripheral supply of propellent gas - Google Patents

Abstract

The ejector described, which is intended for a pneumatic conveyor system and which is provided with nozzles for the propellant gas which open at the periphery of the ejector, comprises a housing (4) containing a conical insert (6). Recesses in the insert and in the surrounding surface of the ejector housing form a channel (10) having a cross section (diffuser) which gradually decreases from an inlet (10a) for the propellant, where the propellant gas expands and reaches high speed. These channels (10) open at the periphery into the ejector flow channel and form the nozzles of the ejector.

Description

Ejector with peripheral supply of propellent gas

TECHNICAL FIELD

The invention relates to an ejector intended for a pneuma_¬ tic transport device for particulate material, especially erosive material. The diffusor is formed with nozzles 5 through which propellent gas is supplied peripherally in the flow channel of the ejector.

BACKGROUND ART

An ejector with peripheral supply of propellent gas in a pneumatic conveying pipe for particulate material is known TO from UK Patent Specification 2 002 312 A. Ejectors with peripheral supply of propellent gas in nozzles for blasting and surface coating are known from European Patent Specifi¬ cation 0 189 709 and International Patent Application 0 86/02587, respectively.

15 SUMMARY OF THE INVENTION

--- One object of the invention is to provide an ejector with high power and low consumption of propellent gas. Another object is to give an ejector such a design that the erosion therein becomes insignificant.

20 According to the invention the ejector is provided with a number of peripherally arranged nozzles around a central flow channel. These nozzles are formed from an ejector housing and and insert forming part of the flow channel in the ejector. Suitably, the ejector housing is formed with

25 a conical seat and the insert with an outer conical surface contiguous to the seat. Suitably, recesses in the conical surface of the insert and the surrounding surface in the conical seat in the ejector housing form a nozzle channel. The recess can be made in the seat of the ejector housing, which, however, is more complicated from the manufacturing point of view. From an inlet for propellent gas, the nozzle channel has a continuously increasing cross section and forms a diffusor where the propellent gas expands and attains a very high velocity which provides a great driving power.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 shows a longitudinal section through an ejector,

Figure 2 a section according to A-A in Figure 1 ,

Figure 3 shows a section at B-B in Figure 1,

Figure 4 shows on an enlarged scale a portion of the sec_¬ tion according to Figure 1 , and

Figure 5 shows an extension of a conical insert, included in the ejector, with milled-out portions forming nozzles and diffusor channels.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the figures, 1 designates an ejector in a pneumatic transport device between an upstream suction pipe 2 and a downstream conveying pipe 3. The ejector comprises an ejector housing 4 with a propellent gas inlet 5 and a sleeve-formed insert 6. The housing 4 is formed with a conical seat 7 and the insert 6 with an external conical portion 6a adapted to the insert 6. The sleeve or insert 6 is fixed with its flange 6b in the housing 4 by the suc- tion pipe 2. The propellent gas channel 8 of the inlet 5 opens out into an- annular space 9 formed by an annular tur_¬ ned cavity in the housing 4 and by the flange 6b of the sleeve/insert 6.

In the outer surface of the conical part 6a of the sleeve 6 milled grooves are provided which together with the housing 4, which surrounds the sleeve 6, form flow channels 10. The inlet 10a communicates with the annular space 9 and the outlet with the opening 11 in the housing 4. These channels 10 have a cross section increasing from the inlet 10a towards the outlet 10b and form Laval nozzles where the gas, after the smallest cross section at the inlet, is accelerated by expansion to a very high velocity in the channel serving as a diffusor and provided downstream of the inlet. This channel opens out at the periphery of the flow channel 11. The high velocity of the propellent gas gives a very high driving power with a small quantity of gas. Since the propellent gas is supplied peripherally in the ejector, particles are prevented from hitting the wall in the ejector passageway 11 and the wall in the pipe nearest the diffusor where the particle velocity may become very high. To achieve a better mixing between propellent gas and particulate material to be transported, the channels are suitably formed such that their centre line makes a certain angle of with a plane extending through the longitudinal axis of the ejector.

Claims

1. An ejector for a pneumatic transport system, especially intended for erosive particulate material such as ashes, bed material or the like in a combustion plant for combus_¬ tion of a solid fuel such as coal, c h a r a c t e r i _¬ z e d in that it comprises an ejector housing (4) with a tubular insert (6) forming part of the flow channel (11) in the ejector (1), and that flow channels (10) are provided between the ejector housing (4) and the insert (6), said flow channnels (10) having a cross section (diffusor) which continuously increases from a propellent gas inlet (10a) and form nozzles opening out at the periphery in the flow channel (11) through the ejector (1).

2. An ejector according to claim 1, c h a r a c t e r i _¬ z e d in that recesses inside the seat (7) of the ejec¬ tor housing (4) and the insert (6) or recesses externally in the insert (6) and the seat (7) form the flow channels or the nozzles (10).

3. An ejector according to claim 2, c h a r a c t e r i _¬ z e d in that the housing (4) is formed with a conical seat (7) for an externally conical insert".