Method of and apparatus for the separation of components of...

Gas separation: processes – Sound waves used

Reexamination Certificate

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C095S032000, C095S034000, C096S389000

Reexamination Certificate

active

06372019

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a method of and apparatus for the separation of the components of gas mixtures by liquefaction, and can be applied in various areas of technology, including application to liquefaction of a gas, for example for use in gas and petroleum processing including, metallurgy, chemistry and other areas of technology.
BACKGROUND OF THE INVENTION
A widely used method for the liquefaction of gas indudes compression of gas in a compressor, preliminary cooling in a heat exchanger and further cooling in an expander with subsequent expansion of the gas through a throttle valve to cause cooling and condensation. Subsequently the liquid phase is selected and separated (see Polytechnic Dictionary, 1989, Moscow, “Sovetskaya Entsiklopediya”, p. 477, Ref. 1). A disadvantage of this known method is the implementation complexity in operation, and sensitivity to liquid drops in the inlet gas flow.
A known method for the separation of the components of gas mixtures by means of liquefaction includes cooling of the gas mixture in stages to the condensation temperature of each of the components and the separation of the corresponding liquid phase at each stage (see Japanese patent application No. 07253272, F 25 J 3/06, 1995, Ref. 2). A disadvantage of this known method is its small efficiency while requiring a large amount of energy.
Another known method for the separation of the components of gas mixtures by means of their liquefaction includes adiabatic cooling of the gas mixture in a supersonic nozzle and the separation of the liquid phase (see U.S. Pat. No. 3,528,217, U.S. Cl. 55-15, Int. Cl. V 01 D 51/08, 1970, Ref. 3). In this known method, the separation of the liquid phase is performed by passing the gas-liquid mixture around a perforated barrier by deflection of the flow from a simple linear flow. As a result, centrifugal forces arise due to the deflection of the flow, and under the action of these centrifugal effects, drops of liquid are displaced radially outwards. The liquid drops then pass through the perforated barrier, so as to be separated, and are collected in a container. A disadvantage of this known method is its low efficiency. The reason for this low efficiency is that under the deflection of the gas flow that moves with supersonic speed, shock waves occur, which raise the temperature of the gas, and this leads to the unwanted vaporization of part of condensed drops back into the gaseous phase.
Among the known methods, a method that is the closest to the present invention consists of the separation of gas components by their liquefaction (as disclosed in U.S. Pat. No. 5,306,330, U.S. Cl. 95-29, Int. Cl. V 01 D 51/08, 1994, Ref. 4). This known method can be used to separate the components of a gas mixture. (See column 1, lines 5-10, Ref. 4).
The method in Ref. 4 includes cooling of a gas in a supersonic nozzle and the separation of the liquid phase. A shock wave is present at the nozzle, and the invention relies on droplets, already formed, having a greater inertia. Hence, the droplets maintain a higher velocity downstream, facilitating their separation by centrifugal effects. To separate the liquid phase, the cooled gas flow, which contains already drops of a condensed liquid phase, is deflected through a curve, away from the initial axis of the nozzle. As a result of the deflection of the flow, under the action of the inertia, and centrifugal forces, the droplets with a higher velocity are displaced radially outwards from the axis of the flow. The flow is then divided into two channels, and one portion of the flow containing the droplets is passed along one channel, and another portion of gas flow, substantially dry and free of liquid droplets, passes along another channel. This technique bears some similarities with Ref. 3, in that the gas is effectively rotated or caused to turn about an axis perpendicular to the original axis and flow direction of the nozzle.
A disadvantage of this known method is its low efficiency. This is due to the fact that under such a deflection of the gas flow, shock waves again occur, and thus the temperature of the flow increases, which leads to the unwanted evaporation of part of the condensed droplets.
Moreover, when liquefying a selected component, the partial pressure of the remaining gas phase is reduced. Hence, for a more complete (subsequent) liquefaction, one must provide for a decrease of the static temperature of the flow. This can be achieved by means of an increase of the rate of the adiabatic expansion of the flow, and hence by the corresponding increase of its Mach number. This requires a substantial reduction of the output pressure of the flow, which drastically reduces the efficiency of this technology, in terms of power requirements.
There is yet another known device for the separation of the components of gas mixtures and isotopes that contains an evaporator, a curvilinear supersonic nozzle, a separator in the form of a cooled knife, and receivers for the separated components (see the description to the patent pending of Russian Federation No. 2085267, V 01 D 59/18,1997, Ref. 5). Disadvantages of this known device are the complexity of the construction and low efficiency with respect to both the energy efficiency of the process and to the extent of the separation.
All the above methods of Ref. 2-5 have a common disadvantage that significantly reduces their efficiency and that results from the existence of a shock wave due to the change of the gas flow direction. These shock waves both heat the gas, leading to vaporization of the drops, and significantly decrease the total head at the outlet of the apparatus.
The present invention is intended to improve the efficiency of the separation of gas mixtures by means of their liquefaction and of the liquefaction of a gas, and is intended to provide separation of gas components at the instant of liquefaction.
This desired result is accomplished, in the present invention, by the provision of a method for the liquefaction, which includes adiabatic cooling of a gas mixture or a gas in a supersonic or subsonic nozzle and the separation of the liquid phase. Moreover, the present invention modifies the partial pressure of the gas or each component in the mixture. Then, in one aspect of the invention, the partial pressures in the initial mixture can be modified in the device so as to provide a higher temperature of condensation of one component, that has a lower temperature of condensation at atmospheric pressure than the temperature of condensation of another component with a higher temperature of condensation at atmospheric pressure. The geometry of the nozzle is chosen to preserve in the gaseous phase, in the course of cooling, the other component with the higher temperature of a condensation at atmospheric pressure and the liquefaction of the one component that has a lower temperature of a condensation at atmospheric pressure is in an amount that is sufficient to dissolve in it the gaseous phase of the bulk of the component that has a higher temperature of condensation at atmospheric pressure.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided a method of liquefying a gas, the method comprising the steps of:
(1) applying a swirl velocity to the gas;
(2) passing the gas, with the swirl velocity, through an expansion nozzle;
(3) permitting the gas flow to expand adiabatically downstream from a nozzle in a working section having a wall, whereby the gas cools and at least a portion of the gas flow condenses to form droplets;
(4) permitting centrifugal effects generated by the swirl velocity to drive the droplets towards the wall of the working section; and
(5) separating condensed liquid gas droplets from remaining gas in the gaseous state at least adjacent the wall of the working section.
Preferably, the method includes separating condensed liquid from the gas flow downstream from the nozzle at a location spaced a distance L from the dew point, where L=V&tgr;, where V is the speed of the gas fl

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