US3618332A

US3618332A - Evaporation of potentially explosive residue of oxygen containing gas fractionation process

Info

Publication number: US3618332A
Application number: US745218A
Authority: US
Inventors: Lothar Setzpfandt; Josef Stockner
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 1967-07-19
Filing date: 1968-07-16
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09
Also published as: FR1571842A; DE1551588C3; DE1551588B2; DE1551588A1; ES356797A2; GB1198228A

Abstract

LOW-BOILING POINT LIQUIDS ARE EVAPORATED IN AN EVAPORATING STREAM FORMED BY ENTRAINING AMBIENT AIR IN A JET OF PROPELLANT GAS. THE LIQUID TO BE EVAPORATED IS ATOMIZED BY INJECTION INTO THE JET AND AN AEROSOL IS THEREBY FORMED. THE ATOMIZED LIQUID IS CONTINUOUSLY EVAPORATED IN THE THUS FORMED AEROSOL STREAM BY HEAT DERIVED FROM THE CHANGE OF ENTHALPY OF THE AMBIENT AIR AND PROPELLANT GAS.

Description

Nov. 9, 1971 L. SETZPFANDT ETA!- Filed July 16. 1968 CONTAINING GAS FRACTIONATION PROCESS 3 Sheets-Sheet l Air 7 E 5 71' r/ i FRACTIONATION COLUMN 74 Potentially explosive fractionation residue 10 Air Gaseous Propellant INVENTORS LOTHAR SETZPFANDT J 0581' STOCKNER iliiwfi ad ATTORNEY NOV. 9, 1971 SETZPFANDT EIAL 3,618,332

EVAPORATION OF POTENTIAL-LY EXPLOSIVE REsmuE 0F OXYGEN CONTAINING GAS FRACTIONATION PROCESS Filed July 16, 1968 5 Sheets-Sheet 2 INVKNTORS LOTHAR .SETZI' PANIYI JOSE!" STOCKNKR ATTORNEY Nov. 9, 1971 1 zp -r ETAL 3,618,332

EVAPORATION OF POTENTIALLY EXPLOSIVE RESIDUE 0F. OXYGEN CONTAINING GAS FRACTIONATION PROCESS 3 Sheets-Sheet 5 Filed July 16, 1968 F I G 3 INVENTORS LOTHAR SETZPFAND'I' JOSEF STOCKNER ATTORNEY United States Patent ice 3,618,332 Patented Nov. 9, 1971 US. CI. 62-18 5 Claims ABSTRACT OF THE DISCLOSURE Low-boiling point liquids are evaporated in an evaporating stream formed by entraining ambient air in a jet of propellant gas. The liquid to be evaporated is atomized by injection into the jet and an aerosol is thereby formed. The atomized liquid is continuously evaporated in the thus formed aerosol stream by heat derived from the change of enthalpy of the ambient air and propellant gas.

This invention relates to a process and apparatus for the evaporation of low-boiling point liquids.

Low-boiling point liquids can be evaporated without danger if they are free from explosive substances, such as hydrocarbons. However, during the separation of gaseous mixtures containing even minor quantities of explosive substances admixed therewith which are enriched during rectification, there is the constant danger of explosions in terfering with the operation of the process at the points where solid depositions of the explosive gases can collect. Acetylene accumulated in liquid oxygen during the separation of atmospheric air is an example of such a substance.

When shutting down low-temperature gas separation plants, e.-g., air separation plants, or the individual components of such plants, low-boling point liquids or solidliquid suspensions also remain in the apparatus as a residue. Such residue must be rapidly removed, safetly evaporated and conducted away. One known method of disposing of such residue is to pass the liquid or suspension into a cement pit, normally disposed in the ground near the plant. Under the influence of ground heat and heat from the surrounding atmosphere, the residual liquid gradually evaporates. The pit can also be filled with a heat-retaining mass for accelerating such evaporation. The low-boiling point liquid evaporates in the pit relatively slowly, and during this process is enriched in higher-boiling admixtures, particularly hydrocarbons. If the solubility of the hydrocarbons in the liquid is exceeded, then it is possible, for example, for acetylene to be precipitated in solid form in the liquid oxygen and to lead to an explosion. Furthermore, the area surrounding the pit is endangered by cold clouds of vapor, produced by evaporation, creeping along the ground. These clouds represent a grave danger since they have, in part, a high oxygen content and they persist for long periods of time, due to the slow evaporation process in the pit.

In order to preclude the aforedescribed danger of acetylene precipitating in solid form, it is known from German Pat. 1,033,689 to concentrate liquid oxygen containing hydorcarbons from, for example, the external chamber of the main condenser of a double rectification column, by evaporation in the second evaporator only to such an extent that the concentration of hydrocarbons in the residual liquid remains below the explosion or solubility threshold. The residual liquid, rich in hydrocarbons, is separated from the gas after evaporation in the second evaporator, in a separator, and is either withdrawn or purified in adsorbers. This process, however, is very expensive from the standpoint of equipment cost. Furthermore, the liquid oxygen cannot be completely evaporated in the second or additional evaporator, since, upon total evaporation, the solubility threshold of the acetylene is certain to be exceeded, and acetylene would precipitate in solid form. The use of an additional evaporator, as well as the subsequent purification of the residual acetylene-rich liquid in regenerative adsorbers is also cumbersome and dangerous, since, in both methods, a relative enrichment of acetylene occurs.

SUMMARY OF THE INVENTION A principal object of this invention therefore is to provide a process and apparatus therefor wherein low-boiling point liquids, particularly liquids having hydrocarbons admixed therewith, can be evaporated in a rapid, safe, and complete manner.

Upon further study of the specification and claims, other objects and advantages of the present invention will become apparent.

The objects are attained in accordance with this invention, by drawing in atmospheric or ambient air by means of a jet or propellant gas and simultaneously atomizing the liquid to be evaporated, whereupon the atomized liquid is continuously evaporated in a predetermined concentration in the thus-formed aerosol.

In accordance with the process of this invention, the kinetic energy of a jet propellant gas exiting from a nozzel is utilized to simultaneously atomize the liquid to be evaporated and form an aerosol and to draw in and entrain a limited quantity of atmospheric or ambient air to form an evaporating stream. Thereafter, the atomized liquid is continuously evaporated in a predetermined concentration in the thus-forming aerosol, while the propellant gas and the drawn-in air is cooled. For producing the evaporating stream, the aerosol is conducted through an evaporation chamber restricted in its lateral dimensions.

This process exhibits the advantage that, due to the atomization, the low-boiling liquid evaporates rapidly and completely, and therefore admixed hydrocarbons present are not enriched in the liquid to be evaporated. The changes in enthalpy level of the entrained air and of the propellant gas provide the heat required to evaporate the atomized liquid. In accordance with the invention, the aerosol has imparted to it a high flow velocity and turbulence in the evaporation chamber, and the improved heat transfer rate from the propellant gas and the entrained air to the atomized liquid allows the latter to evaporate quickly without residue.

When evaporating an oxygen-rich liquid, the propellant gas and the drawn-in air decrease the oxygen concentration of the aerosol, which decrease is enhanced when the evaporated liquid leaves the evaporation chamber and mixes intimately with the surrounding air as a result of the continuing high kinetic energy of the exhausted vapors. Danger to the surroundings of the site is thereby made impossible.

The liquid to be evaporated is introduced into the evaporation chamber under pressure to atomize the liquid. The amount of liquid atomized by the jet of propellant gas in increased with increasing liquid pressure.

In accordance with the invention, a preferred apparatus for conducting the process comprises an evaporating chamber consisting of a mixing tube having centrally disposed at one end a propellant gas nozzle of substantially smaller cross section, (e.g. 1.5 to 12%) than the tube. At least one liquid conduit is disposed substantially normal to the mixing tube and extends at its open end proximate the propellant gas nozzle. In the tube, turbulent flow and high flow velocity, e.g. about 19 to 300, preferably 65 to 230 meters/sec. of the aerosol are produced, due to the large amount of atmospheric air which is entrained by the srteam of propellant gas, and the stream of both gases together is driven through the mixing tube. The turbulent flow, in the mixing tube acts to rapidly transfer the heat of the propellant gas and the entrained air to the atomized, cold liquid. The mixing tube should be of great enough length to provide substantial evaporation of the liquid before exhaust thereof. Tubes of a length between and 30 meters have been found suitable for this purpose.

The attached drawings depict the preferred embodiment of the apparatus of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a longitudinal section through an evaporating device by means of which the process of this invention for the evaporation of low-boiling liquids is con ducted, and

FIGS. 2 and 3 show modified arrangements of the apparatus shown in FIG. 1.

The device according to FIG. 1 consists substantially of a vertically disposed mixing tube 1. A propellant gas nozzle 2 having a nozzle end 3 substantially smaller in cross-sectional area than the inside diameter of the mixing tube 1 is centrally disposed at the lower end of the tube so that there is formed an annular opening 4 between the nozzle 2 and the mixing tube 1. A liquid conduit 5 is disposed substantially normal to the propellant gas nozzle 2 penetrating the lower end of the mixing tube 1 at 6. The conduit has an open end 7 vertically coincident with the inner wall 8 of the nozzle end 3 adjacent the point of penetration 6. The propellant gas employed can be low-pressure air since such is available without cost and need only be brought to a higher pressure by means of a blower, which is, for example, usually present in air separation plants. It should be understood, however, that under certain circumstances, other fluids such, for example, as, preferably superheated, steam can be advantageously employed as the propellant gas.

The evaporation of a low-boiling liquid is conducted in accordance with the invention, by drawing in a limited amount of atmospheric air, indicated by arrows 10, under the influence of a low-pressure air jet, shown by arrows 9, exiting the nozzle end 3; atomizing liquid-to-be-evaporated, indicated by arrow 11; and continuously evaporating the atomized liquid in an aerosol which is formed in the mixing tube 1. Vapors, free of atomized liquid llezave the upper end of the mixing tube 1 shown by arrow The inside diameter and the length of the evaporation chambenor mixing tube must be adapted to the required evaporation rate of the atomized liquid. An annular space is formed between the centrally disposed propellant gas nozzle, and the inner wall of the end of the mixing tube is of such a size that a suflicient amount of atmospheric air is entrained into the mixing tube in order to evaporate the atomized liquid. The size of the annular opening is dictated by a requirement for an air velocity therethrough greater or equal to the entrainment velocity for the atomized liquid. The volume of air drawn-in is a multiple of the volume of propellant gas, so proportioned that the change in enthalpy level of the drawn-in air supplies the larger part of the heat of evaporation of the atomized liquid.

Preferably, the mixing tube is disposed vertically and the propellant gas nozzle is arranged in the lower end of the mixing tube, so that the atomized liquid is carried in the aerosol flow from the bottom to the top through the mixing tube. Dry gas exits at the upper end of the mixing tube to be safely blown into the atmosphere at a great height from the ground. The mixing tube, however,

4 can also be disposed horizontally, if so desired, in which case the end of the tube is turned upwardly. With such an arrangement, the horizontally positioned tube requires more floor space than a vertically disposed tube.

The lower end of the mixing tube can be straight or can have a flared section, preferably conical in shape. The flared construction of the end of the mixing tube will considerably enhance the intake of atmospheric air under the influence of the jet of propellant gas. A tube end of conical configuration is also easily produced from the viewpoint of manufacturing technology.

The propellant gas nozzle is in the configuration of a Laval nozzle 2, thereby making supersonic flow possible.

The Laval nozzle, well known to those skilled in the art, is characterized by a converging-diverging nozzle wall, configured to provide acceleration of fluids flowing therethrough into the supersonic region. This ensures that, due to the high velocity of the propellant gas, as much atmospheric air as possible is entrained into the mixing tube and that the liquid to be atomized is converted in the mixing tube into an extremely fine, rapidly evaporating mist.

In the preferred embodiment, in order to impart supersonic speed to the pressurized air stream 9, the propellant gas nozzle 2 is constructed as a Laval nozzle with entrance and

exit portions

16 and 17 respectively.

The liquid conduit 5 preferably enters the lower end of the mixing tube 1. The annular opening 4 for drawing in atmospheric air between the propellant gas nozzle and the mixing tube is only slightly reduced by the liquid conduit. The conduit can readily be attached to the wall of the mixing tube 1, such for example as by welding.

Advantageously, the liquid conduit 5 extends in as far as the inner wall 8 of the nozzle end 3 at a point adjacent the point of penetration 6 of the conduit. In this manner, the jet of propellant gas exiting from the nozzle end is undisturbed by the liquid conduit. Since the jet of propellant gas 9 conically widens after leaving the nozzle 2, the end of the liquid conduit 7 is beveled. In this connection, the angle of the end with respect to the nozzle center line is larger than the angle of the jet cone, to facilitate the feeding of the liquid. The kinetic energy of the boundary layer of the gas jet is thus eflective over the entire width of the liquid conduit to atomize the liquid.

A suitable space 14, e.g. about 0.3 to 3 cm. is provided between the nozzle end 3 and the end 7 of the liquid conduit 5, since, when atmospheric air is employed as propellant gas, water vapor and carbon dioxide can freeze out of the air in the zone of the propellant gas nozzle, due to the cold of the liquid to be atomized. Such freezing is avoided by providing this heat-insulating spacing between the nozzle end and the liquid conduit.

In a particularly advantageous embodiment, several liquid conduits can be arranged around the propellant gas nozzle so that the kinetic energy of the boundary layer of the gas jet can be utilized throughout its entire circumference for the atomization of the liquid. Furthermore, in this manner, a very evenly distributed gasliquid mixture is provided in the mixing tube, so that the atomized liquid evaporates rapidly and completely.

The amount of atmospheric air drawn in by the jet of propellant gas can be additionally increased, if so desired, by providing the upper section of the mixing tube with a diffuser 18 and a cylindrical, enlarged tube 19 arranged thereafter, as it is shown in FIG. 2. The total length of tube 1, diffuser 18 and tube 19 approximately corresponds to the length of tube 1 in FIG. 1. The length of diffuser 18 and tube 19 is about 70 to of that total length, and the angle of the diffuser 18 with respect to diffuser centerline is about 5 to 7. The area of the cross section of the tube 19 is given by the demand the velocity at the end of the tube 19, indicated by the arrow 20, is about 15 to meters/sec.

According to FIG. 3, the propellant gas nozzle, if so desired, can be of a continuously tapering shape. With such a nozzle 21, the maximum velocity will be the velocity of sound reached in the mouth of the nozzle. The exit diameter of the nozzle 21 is about 10 to 30% of its entrance diameter. It is advantageous, if the length of the nozzle 21 corresponds to the length of the nozzle 2. Then the nozzles can easily be exchanged. The exchangeability of the nozzles makes it possible to use one and the same apparatus in spite of different conditions, e.g. pressure, of the propellant gas.

In general, this invention is applicable to the rapid evaporation of any liquid, but is particularly useful for the evaporation of liquids having a temperature of 180 to 200 C., and especially those having a concentration of potentially explosive hydrocarbons, such as acetylene. Consequently, liquid oxygen streams containing any acetylene therein (in practice usually about to 2.l0 parts by weight of actylene in 100 parts by weight of oxygen) are advantageously treated by this invention to remove the explosive hazard.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not lirnitative of the remainder of the specification and claims in any way Whatsoever.

The following test results are applicable to an evaporating device of the present invention having the following configuration and operating under the following conditions (see FIG. 1):

Length of mixing tube 1: 5.5 m. Inner diameter of mixing tube 1: 100 mm. Angle of flared portion 13: 40 Length of flared portion 13: 120 mm. Laval nozzle 2:

External diameter: 48.3 mm. Throat diameter: 14.5 mm. Length of:

Entrance portion 16: 10 mm. Exit portion 17: 21 mm. Angle with respect to nozzle centerline of:

Entrance portion 16: 60 Exit portion 17: 5 Liquid conduit 5:

Diameter: 8 mm. Angle of end 7 with respect to centerline of nozzle 2: 10 Distance across space 14: 3 mm. Ambient temperature: +5 C. to +10 C. Temperature in the Laval nozzle 2: C. to C.

EXAMPLE I Without liquid injection 150 Nm. /h. of propellant air, at a pressure of 0.5 atmosphere gauge injected through the nozzle 2 drew in and entrained in the mixing tube 1,630 Nm. /h. of atmospheric air 10. The velocity of the drawn-in air in the annular opening 4, immediately prior to liquid injection, was 25 m./sec. After injection of the liquid nitrogen into the stream through the liquid conduit 5, the weight ratio of drawn-in air to propellant air decreased to 3.1, and the air velocity in the annular opening 4 was reduced to 18 m./sec. The weight ratio of the evaporated liquid to the propellant gas was 2.9. At the upper end of the mixing tube 1, a flow rate of 19 m./ sec. was observed at a gas exit temperature of -130 to 140 C.

6 EXAMPLE 11 Without liquid injection 600 Mm. /h. of propellant air at a pressure of 5.5 atmospheres gauge drew in and entrained in the mixing tube 1,800 Nm. /h. of atmospheric air. The velocity of the drawn-in air in the annular crosssection, immediately prior to injection of liquid, amounts to 68 m./sec. After feeding liquid nitrogen into the stream through the liquid conduit 5, the weight ratio of drawn-in air to propellant air decreased to 2.3, and the air velocity in the annular cross-section to 47 m./sec. The weight ratio of evaporated liquid to propellant air was 2.5. A flow rate of 63 m./sec. and a gas exit temperature of l30 to C. resulted at the upper end of the mixing tube.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/ or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be within the full range of equivalence of the following claims.

What is claimed is:

1. In a process for the low temperature fractionation of an oxygen-containing gas wherein upon termination of said process, a potentially explosive low boiling point liquid is a residue of said process, said residue comprising liquid oxygen and hydrocarbon, the improvement which comprises evaporating said potentially explosive liquid by:

forming an evaporating stream by entraining ambient air in a jet of propellant gas;

simultaneously atomizing said potentially explosive liquid residue by injection into sad jet, thereby forming an aerosol;

whereby the atomized potentially explosive liquid residue is continously evaporated in the thus-formed aerosol stream.

2. Process according to claim 1, characterized in that the potentially explosive liquid to be evaporated is under pressure.

3. Process according to claim 1, characterized in that low-pressure air is employed as the propellant gas.

4. Process according to claim 1, characterized in that steam is employed as the propellant gas.

5. Process according to claim 1, characterized in that said potentially explosive liquid comprises oxygen and acetylene, and said oxygen-containing gas is air.

References Cited UNITED STATES PATENTS 471,361 3/1892 Rogers 431-211 728,140 5/ 1903 Spicer 43 l211 1,719,397 7/ 1929 Edwards 431-211 2,043,597 6/1936 Sloyan 431211 2,918,901 12/1959 First 62-18 2,975,606 3/ 1961 Karwat 62--18 NORMAN YUDKOFF, Primary Examiner A. F. PURCELL, Assistant Examiner US. Cl. X.R. 261-76; 431-211