Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1990-04-02
1991-10-29
Spitzer, Robert
Gas separation
Means within gas stream for conducting concentrate to collector
55 68, 55158, B01D 5322
Patent
active
050612972
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of, and apparatus for, providing improved separation of gases in a gas mixture using particularly, but not exclusively permeable membranes.
The membrane gas separation technique consists of passing a mixture of gases over a semi-permeable membrane with a pressure difference (or at least partial pressure difference) across the membrane. Gases with low diffusivity tend to stay on the high pressure side, while those with higher diffusivity tend to pass through. Diffusivity itself is a function of molecular size and solubility in the membrane.
Membranes are currently manufactured either as bundles of small diameter plastic tubing, or as spiral-wound plastic sheets sealed at three sides with a collecting tube in the middle, with spacers to hold the plastic apart. For the tubing, the high pressure side can be either the inside or the outside, depending on the manufacture.
The current method of using permeable membranes to separate gases has certain disadvantages. If the orientation of the element is chosen so the gas flow is horizontal, gas stratification can occur. Stratification may be best explained with reference to the following example which concerns the separation of a binary gas mixture such as helium and nitrogen.
In the boundary layer near the membrane wall the permeable gas, helium, diffuses through the membrane and leaves a layer of relatively dense nitrogen. This layer of nitrogen separates from the wall and falls through the lighter mixture, with little or no mixing, and "puddles" on the bottom of the membrane cylinder. If the gas velocity between the membrane surfaces is too low, the dense "puddle" will remain there, reducing the effective membrane area, and causing an area of high partial pressure of residual gas on the high pressure side of the membrane.
The current method of overcoming this separation problem is to increase the gas velocity between the membrane surfaces until the velocity is high enough to entrain the gas that tends to "puddle" on the bottom. Because there needs to be a flow of mixture to entrain the separated gas this implies that there will be a significant amount of permeable gas in the residual gas so that complete separation of the gases is restricted and is inefficient. Also special equipment is necessary to provide high flow rates which increases the cost and complexity of the gas separation procedure.
An object of the present invention is to provide an improved gas separation apparatus and method which obviates or mitigates at least one of the aforesaid disadvantages.
This is achieved by recognising and making use of the fact that in passing over a membrane, a portion of a gas mixture in intimate contact with the membrane wall experiences a change in density as components of the gas selectively diffuse through the membrane. When the density of the gas at the surface of the conduit is changed (via diffusion), the gas is subjected to a buoyancy-induced acceleration in the direction of flow, it forms coherent cells which peel away and interchange with cells of the adjoining gas, thus edging away from the membrane surface and out into the open space. Because of its density and the nature of laminar flow, gas already exposed to the membrane will end up in the centre away from the two membrane surfaces and will have the highest velocity in the stream. In particular, the present invention uses gravity to act on the density difference created by diffusion to assist in a) `peeling` (away from the membrane wall) the gas which has already undergone substantial diffusion; b) keeping this gas away from the diffusion surface, once it has left; c) removing the gas from the membrane more quickly; and d) slowing gas which has had less exposure to the diffusion process and moving it toward the membrane wall.
In a preferred arrangement, the membrane element is mounted vertically. The direction of flow is oriented to use the effect of gravity on gases of different density and the velocity of gases is controlled to be sufficiently low to prevent or
REFERENCES:
patent: 2734592 (1956-02-01), Jones
patent: 2961062 (1960-11-01), Hunter et al.
patent: 3144313 (1964-08-01), Pfefferle
patent: 3246449 (1966-04-01), Stern et al.
patent: 3397790 (1968-08-01), Newby et al.
patent: 4152093 (1979-05-01), Germain
patent: 4342723 (1982-08-01), Sado et al.
patent: 4367135 (1983-01-01), Posey Jr.
patent: 4397661 (1983-08-01), King et al.
patent: 4427424 (1984-01-01), Charpin et al.
patent: 4671809 (1987-06-01), Taketomo et al.
patent: 4704139 (1987-11-01), Yamamoto et al.
patent: 4789480 (1988-12-01), Bruschke
W. A. Bollinger et al., "Separation Techniques: Separation Systems for Oil Refining and Production", CEP Oct. 1982, pp. 27-32 (Copy in 55/158).
W. J. Schell et al., "Separation Techniques: Spiral-Wound Permeators for Purification and Recovery", CEP Oct. 1982, pp. 33-37 (Copy in 55/158).
"Chemical Engineering"; vol. 88, No. 14, July 13, 1981; pp. 63, 65 and 67.
LandOfFree
Apparatus for and method of providing improved gas separation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for and method of providing improved gas separation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for and method of providing improved gas separation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1397615