Abstract: In order to measure for example the velocity of particles moving within various pipes or enclosures (1), such as catalyst balls circulating in continuous reforming plants, a channel (2) with a section suited to that of the particles, connected to a source of fluid of determined flow rate (4), opens therein and the pressure variations in this channel, resulting from the flow of the particles circulating past the end thereof, which modify the free flowing of the fluid towards the pipe, are measured. The particle velocity is notably determined through an auto-correlation of the signal translating the pressure variations by means of a processing system (6). Two fluid-fed channels (7, 8) may also open onto two different locations along the pipe and, through a crosscorrelation of the signals translating respectively the pressure variations, the velocity and the section of the circulating particles may for example be determined.

Abstract: A device for separating hydrogen from gaseous mixtures containing it or for purifying gaseous hydrogen, comprising an outer casing (2) fiIled with a plurality of tubes (3) made of a suitable palladium based alloy, which tubes are closed at one end (4). The tubes are fixed in substantially seal-tight manner, at the open end side (5), to a part at least of a base (6) made of a metal alloy, the composition of which is such that its expansion coefficient in hydrogen is substantially equal to that of the alloy of the tubes. The base can be integrally formed and made of the above-mentioned alloy, or it can comprise a ring of substantially the same composition as that of the tubes adhering thereto by way of an autogenous soldering.

Abstract: Process for the treatment of a hydrocarbon fraction containing metals and comprising the following stages: (a) the said hydrocarbon fraction is treated in the presence of mean density particles (d.sub.o) under conditions for eliminating at least partly the metals contained therein and deposits of said metals on at least one fraction of said solid particles; (b) at least part of the solid particles from stage (a), whose mean density is (d.sub.i) is drawn off; (c) said solid particles from stage (b) are magnetohydrostatically separated by introducing said solid particles into a ferrofluid placed in a non-uniform magnetic field and creating a vertical magnetic field, whose intensity is adjusted in such a way that the apparent mean density (d.sub.af) of the ferrofluid permits the separation of said solid particles into at least one mean density fraction (d.sub.i) below said apparent mean density (d.sub.af) of the ferrofluid and into at least one mean density fraction (d.sub.s) above said mean apparent density (d.