GB2352812A

GB2352812A - Detecting components present in a liquid or solid phase

Info

Publication number: GB2352812A
Application number: GB0018873A
Authority: GB
Inventors: Etienne Werlen; Dioron Raymond Le; Claire Szulman; Frederic Crayssac; Philippe Fraysse
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 1999-08-04
Filing date: 2000-08-01
Publication date: 2001-02-07
Also published as: DE10035410A1; JP2001083051A; FR2797325A1; GB0018873D0; FR2797325B1

Abstract

Detection and analysis of a component(s) in a liquid or solid phase is carried out in a fixed volume chamber and comprises lowering the temperature of the chamber to bring the component(s) into it's liquid or solid phase then hermetically sealing the chamber and increasing the temperature therein to volatilise the component(s) whilst continuously measuring the pressure and temperature in the chamber and deducing from these measurements the nature and quantity of the volatilised component(s). The process and it's associated apparatus can be used to monitor air fed to a distillation unit.

Description

2352812 The present invention relates to the detection and analysis of at

least one compound present in liquid or solid phase in a chamber, particularly volatile crystals, and more particularly for the detection and analysis of at least one pollutant likely to be present in a flow circulating in an industrial installation.

Conventional solutions for detecting and analyzing such compounds consist in vaporizing the compound and for transferring the gas obtained into conventional analyzers, of the chemical cell type or, by sampling, of the chromatographic type. So as not to lose the compounds present in the chamber, there can be used an analyzer of the infrared spectrometer type, which works on a specimen in a closed cell. The size and cost of such equipment are often prohibitive. Moreover, for tiny quantities of compounds, they cannot be measured as to mass, the precision of the balances being insufficient.

The present invention has for its object to provide a process and an apparatus for precise, simple and efficacious detection and analysis,. that will be easy to use and reproducable and of low cost of production and use, suitable for controlling and following industrial processes.

To do this, the invention provides a process according to claim 1.

The invention has for another object to provide a process and apparatus for detection and analysis permitting carrying out a cumulative material balance of impurities or I pollutants circulating in at least one flow of fluid over time, without interrupting the operation of the installation in which said flow circulates.

To do this, the invention provides a process according to claims 2 and 6, 7.

By practicing such processes, the invention provides an apparatus according to claim 14.

The invention thus has for another object the use of such an apparatus and of such a method for monitoring and controlling a distillation unit, particularly a mixture of liquids to be vaporized in an air distillation column.

Other characteristics and advantages of the present invention will become apparent from the following description of embodiments, given by way of illustration but in no way limiting, with respect to the accompanying drawings, in which:

Figure I is a schematic cross-sectional view of an embodiment for apparatus for detection and analysis according to the invention; Figure 2 is a schematic view of the incorporation of another embodiment of an apparatus of the invention in a distillation column; and Figure 3 shows graphs of the readings taken according to the process of the invention for two quantities of crystals of nitrous oxide deposited in the chamber of the apparatus.

In Figures 1 and 2 there is schematically shovm an apparatus for detection and analysis according to the inven- 2 0 tion, generally designated by the numeral 1, comprising essentially an internal chamber 2 of reduced fixed volume disposed in an aluminum block 3 provided with heating means controlled by a regulation block 4, typically a network of electrical resistances 5, and a cooling circuit 6. The block 3 is typically enclosed in a thermally insulating envelope 7.

Chamber 2 is connected to an inlet conduit 8 and an outlet conduit 9 each provided with a valve, respectively 10 and 11, for sealing against pressure, permitting selectively closing the chamber 2 and cutting any fluid communication with the exterior.

The temperature and pressure in the chamber 2 are measured continuously by a temperature detector 12 and a pressure detector 13 supplying signals recorded and processed in an electronic monitoring and control unit 14. In the embodiment of Figure 2, the chamber 2 is in the form of a straight tubular section. In the particular embodiment shown in Figure 1, the chamber 2 has a U-shape configuration. In both cases, the chamber is constituted typically by one or several sections of stainless steel tubing internally electropolished, embedded in an aluminum block formed. by moulding about the tube and the cooling coil. The arrangement of Figure 1 permits the provision, in the open ends of the U and before casting the aluminum, of glass rods hermetically sealing the U and permitting, by one of them (15), a direct view into the chamber illuminated by the waveguide effect from a lamp 16 via the other glass rod 17. As a modif ication, to 3 0 permit homogenization of the fluids within the chamber 2, the latter can be provided with a mini-turbine 18 actuated by an electric motor 19 via a magnetic drive 20 through a wall of the amagnetic block 3.

The process according to the invention is as follows:

For each analysis of the contents as to compounds in solid or liquid phase in the chamber 2, first introduced via the inlet conduit 8, the block 3 is brought to a f irst low temperature Tbj and to a f irst pressure P, at which at least one particular compound potentially present in the chamber will be in liquid or solid phase. The shutoff valves 10 and 11 are then closed and the temperature of the block 3 is raised to a high temperature Th higher than the temperature of vaporization of the particular compound in the range of pressures in question. The block 3 is sufficiently massive to guarantee that the temperature will be perfectly uniform on the walls and in the interior volume of the chamber 2. The temperature increase is fairly slow to ensure that thermal equilibrium is achieved for each temperature level. During this temperature rise, there are registered in the unit 14, via the detectors 12 and 13, the temperature and the pressure at each instant and they are correlated. Then, the temperature is lowered again to the initial temperature Tb, before opening the valves 10 and 11 so as to maintain in the chamber 2 the compounds previously again vaporized, in a solid or a liquid phase.

4 The analysis of the temperature/pressure curves permits knowing the total quantity of compounds vaporized between the initial temperature and the final temperature. Associated with the knowledge of the curves of vapor pressure of the bodies that it is sought to detect and quantify, this analysis permits knowing the nature and quantit-ative distribution of the solid or liquid compounds initially present in the chamber. Thus, the volume of the chamber being constant, the application of Mariotte's Law (PV = nRT) permits deducing from the instantaneous values P and T the number of moles of a particular compound undergoing vaporization at a given temperature. There is thus shown in Figure 3 the diagrams I and II obtained automatically from the unit 14 for two quantities (respectively 0.052 g and 0.135 g in the given example), of nitrous oxide present in the chamber before closing the valves 10 and 11, the number of moles in the reference volume giving directly the quantity of the compound present in the chamber.

For a minimum analysis threshold corresponding to a number of moles nj, the volume V of the chamber 2 is, -according to the invention, typically less than 2200 n, (which gives a pressure response equal to 10 X 102 Pa), preferably below 220 n- (which gives a pressure response equal to 100 X 102 Pa).

According to another aspect of the invention, the process described above is more particularly applicable to the continuous monitoring and detection and analysis of at least one pollutant in a fluid. of an installation, for example for the detection and analysis of volatile organic compounds in gaseous effluents of industrial installations or -for the detection and analysis of pollutants in mixtures of liquids to be vaporized in a distillation column, particularly for the distillation of air, in particular pollutants present in air and likely to be deposited dry in the form of crystals such as nitrous oxide and various hydrocarbons.

There is shown such an arrangement in Figure 2, in which will be seen, shown very schematic-ally, by way of example, a section of a distillation column 21 enclosing an open film type vaporizer 22 receiving by gravity, from a pourer schematically shown at 23, a flow F of fluid or mixture of liquids to be vaporized, the non-vaporized liquid accumulating at 24 in the bottom of the section 21. Acccrding to the invention, the inlet conduit 8 is connected to a branch conduit 25 above the pourer 23. There can thus be caused, selectively, through the chamber 2, a very small portion of the flow F. To detect and analyze a pollutant suspected of being present in the flow F, the chamber 2 is brought at a predetermined time to to a very low temperature Tb21 lower than Tb,, and the valves 10 "and 11 are opened lully to cause a controlled flow of the liquid (typically liquid oxygen i n an air distillation column) to circulate for a given time to+LT; said liquid is thus totally vaporized in the chamber under a small temperature difference (less than 100C), the pollutant for its part being cryotrapped at the temperature Tb, on the walls of the chamber. The temperature is then increased to 6 Tb, and the valves 10 and 11 are then (time t1, closed and, as before, the temperature is slowly raised, to a time t2, to the high t-emperature Th while continuously measuring the pressure and the temperature in the chamber thereby to trace the curves P/T cr n/T showing the steps of vaporization of the compound or compounds being studied, after which, at a temperature t3l the temperature in the chamber is permitted to stabilize and the valves 10 and 11 are reopened.

In use for the surveillance of pollutants in air to be distilled, with a chamber 2 of a volume of 50 cm3, Tb2 'S of the order of 900 K, for a pressure in the chamber adjacent atmospheric pressure, and Th is generally the ambient temperature at a pressure not exceeding 4 x 105 Pa. Among the pollutants to be monitored, particularly in air to be distilled, with substantially identical quantities in the chamber, the temperature increase will permit detecting successively the vaporization of C2H41 then N20, then C3H,'.

According to one aspect of the invention, the compounds to be analyzed will remain trapped in solid or liquid state in the chamber 2, such that there can be carried out a continuous quantiiication and the evolution of their accumulation can be followed at regular intervals over time whilst surveying, through the rod 15, with illumination 16, the presence and/or accumulation of non-volatile compounds accumulating in the chamber. In the case o-f large accumulation of such non-volatile compounds, one can, at regular intervals, carry out the analysis and quantification of them 7 by disconnecting the apparatus 1 of the installation supplying the fluid to be analyzed, by washing and rinsing the chamber with a solvent, and by analyzing and characterizing the nature and content of the various pollutants in the solvent, after which the apparatus is returned to operating condLtion in fluid communication with the installation.

Although the present invention has been described in relation to particular embodiments, it is not thereby limited but is susceptible to modifications and variations which will be aDparent in the scope of the following claims.

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Claims

I Process for the detection and analysis of at leasz one compound present in liquid or solid phase in a chamber of fixed volume, comprising the following successive steps:

a) bringing the chamber to a first low temperature Tb,. and a first pressure (P,) at which at least the compound to be analyzed is in solid or liquid phase in the chamber, b) hermetically sealing the chamber, c) progressively increasing the temperature of the char.ber to a high temperature (Th) while continuously measuring the pressure and temperature in the chauber, d) deducing from these measurements the nature and quantity of the volatilized compounds.
2. Process according to claim 1, for the detection and analysis of at least one pollutant in a f luid in an installation, comprising the following successive steps:

e) bringing the chamber to a second low temperature (Tb,) and a second pressure (P2) at which at least said pollutant to be analyzed is cryotrapped in the chamber, f) placing the chamber in communication with the installation, to cause to circulate therein a controlled flow rate of the fluid for a given time, and 9 performing the detection and analysis of pollutants acccrding to steps a) to d).
3. Process according to claim 2, comprising the final step:

g) of restoring the temperature cf the chamber to the second low temperature (Tb2) whilst maintaining it hermetically sealed.
4. Process according to one of claims 1 to 3, characterized in that Tb2 < Tbj.
5. Process according to claim 2 or claim 3, in which the sequence of steps 'e), f) and g) are carried out at regular intervals.
6. Process according to one of claims 1 to 5, comprising the steps of visually detecting, near the high temmerature, the non-volatile pollutants deposited in the chamber.
7. Process according to claim 6, comprising the stens of disconnecting he chamber from the installation, washing the chamber with a solvent and analyzing the nature and content of the different non-volatile pollutants in the solvent.
8. Process according to one of the preceding claims, in which the content of compounds i.:ithin the chamber is homogenized during at least a portion of step c)
9. Process according to one of claims 2 to 8, characterized in that the fluid is a gas.
10. Process according to one cf claims 2 to 8, characterized in that the fluid is a liquid that is -vaporized under a small temperature difference in the chamber.
Ii. Process according to claim 9 or claim 10, characterized in that the pollutants present in the gas in the chamber are cryotrapped on the walls of the chamber.
12. Process according to claim 10, characterized in that the fluid is liquid oxygen.
13. The use of a process according to one of the preceding claims for the i nspection and surveillance of a distillation unit.
14. Apparatus for practicing a process according to one of claims I to 11, comprising:

- a section of a line for the passage of fluid (8, 9) comprising a chamber (2) of reduced volume disposed in a metallic block (3) and, on opposite sides of the chamber, at least two valves (10, 11) for isoiating the chamber, - means (5, 6) to modify in a controlled manner the temperature of the chamber, - a pressure detector (13) and a temperature detector (12) to measure the pressure and the temperature in the chamber, and - means for visualizing the interior of the closed chamber.
15. Apparatus according to claim 14, characterized in that it comprises means (16) for illuminating the interior of the closed chamber.
16. Apparatus according to claim. 14 or 15, characterized in that it comprises, in the chamber, means (20) for homogenization of the contents of the compou. nds within the interior of the hermetically closed chamber.
17. Apparatus according to one of claims 14 to 16, characterized in that the chamber is constituted by, at least one section of a stainless steel tube embedded in a block of aluminum.
18. Apparatus according to claim 17, characterized in that the tube comprises at least one U-shaped portion.
19. Apparatus according to one cf claims 14 to 18, characterized in that the interior volume (V) of the chamber does not exceed 2.200 n,, nj being the threshold for the detection of the number of moles to be measured.
20. Distillation unit comprising at least one apparatus according to one of claims 14 tc 19 connectable to a fluid flow into the unit.

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21. Distillation unit according to claim 20, in which said fluid is a mixture of hquids to be vaporized.
22. Distillation unit according to one of claims 20 and 21 for the separation of air gases.
23. A process for detection and analysis of at least one compound, substantially as hereinbefore described with reference to the accompanying drawings.
24, Apparatus for practising a process according to any of claims 1 to 11, substantially as hereinbefore described with reference to the accompanying drawing.
25. A distillation unit, substantially as hereinbefore described with reference to the accompanying drawings.

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