EP0614525A1 - Procede et dispositif servant a controler une alimentation en gaz - Google Patents

Procede et dispositif servant a controler une alimentation en gaz

Info

Publication number
EP0614525A1
EP0614525A1 EP92923905A EP92923905A EP0614525A1 EP 0614525 A1 EP0614525 A1 EP 0614525A1 EP 92923905 A EP92923905 A EP 92923905A EP 92923905 A EP92923905 A EP 92923905A EP 0614525 A1 EP0614525 A1 EP 0614525A1
Authority
EP
European Patent Office
Prior art keywords
gas
volume
chamber
hydrocarbon
collected
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP92923905A
Other languages
German (de)
English (en)
Inventor
Patrick John Reynolds
John Keith Bartington
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Essex Enterprises Ltd
Original Assignee
University of Essex Enterprises Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University of Essex Enterprises Ltd filed Critical University of Essex Enterprises Ltd
Publication of EP0614525A1 publication Critical patent/EP0614525A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0047—Organic compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00—Biological treatment of water, waste water, or sewage
    • C02F3/006—Regulation methods for biological treatment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00—Biological treatment of water, waste water, or sewage
    • C02F3/28—Anaerobic digestion processes
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M21/00—Bioreactors or fermenters specially adapted for specific uses
    • C12M21/04—Bioreactors or fermenters specially adapted for specific uses for producing gas, e.g. biogas
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M41/00—Means for regulation, monitoring, measurement or control, e.g. flow regulation
    • C12M41/44—Means for regulation, monitoring, measurement or control, e.g. flow regulation of volume or liquid level
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/38—Diluting, dispersing or mixing samples
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0011—Sample conditioning
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N7/00—Analysing materials by measuring the pressure or volume of a gas or vapour
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/03—Pressure
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/28—CH4
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/42—Liquid level
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/44—Time
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00—Technologies for the production of fuel of non-fossil origin
    • Y02E50/30—Fuel from waste, e.g. synthetic alcohol or diesel

Definitions

  • This invention relates to a method and apparatus for monitoring a supply of gas.
  • gas is to be understood to extend to pure gas, vapours, or mixtures of gases and/or vapours, unless the context dictates otherwise.
  • anaerobic degradation for example to determine, for a given material or materials, how much methane is produced, at what rate, and whether and to what extent production is affected by conditions such as temperature or the presence of other materials e.g. pollutants.
  • the gases produced in anaerobic degradation are not all methane but contain, perhaps 20%, carbon dioxide.
  • One conventional procedure for monitoring the production of methane is to use a pressure lock syringe to withdraw a sample periodically from a sealed vial containing the matter being tested and to analyse the sample using a gas liguid chromatograph to determine the amount of methane in the sample. The amounts produced in successive samples are recorded and added to produce a total.
  • the procedure is time consuming, involves the use of expensive equipment, in the form of the chromatograph, and being invasive is liable to operator error.
  • the percentage of methane in the gas produced is assumed and the volume of the total gas produced is monitored by letting the pressure in the vial build up to a small predetermined degree and then releasing the pressure and logging the event.
  • the assumption of the percentage methane which relies on knowing the composition of the sample to be tested, can be inaccurate.
  • a method of monitoring a supply of one or more first gas with a gas sensor comprising the steps of: a) collecting a volume of gas containing the one or more first gas mixed with one or more gas to which the sensor is insensitive; b) diluting the collected volume in a chamber to a predetermined volume with one or more second gas to which the sensor is insensitive; and c) exposing the sensor to the diluted one or more first gas to provide a signal indicative of the concentration of the diluted one or more first gas.
  • the method is applied to monitoring a supply of, e.g. the production of, methane.
  • a convenient sensor is a catalytic gas sensor which produces an electrical output signal dependent on the concentration of hydrocarbon gas or vapour in the range 0 to about 1%. Since the gases produced by anaerobic degradation contain, typically, about 80% methane, the gas sensor cannot be used to measure such concentrations direct.
  • the dilution step at a predetermined ratio of preferably about 100:1, permits use of such a gas sensor. All the methane burns on the gas sensor which gives an output signal which rises to a peak and then dies away as the combustion reduces the concentration.
  • the integral of the output signal against time thus represents the total volume of methane in the sensor chamber, scaled by the known and constant volume of the chamber.
  • Adding together the amounts of methane calculated in each collection provides the total amount of methane produced. Logging the time of or for each collection enables the rate of methane production to be calculated. The accuracy of the volume of gas collected in each cycle is not important unless it is also required to know the total volume of gas produced, since this is diluted to a known volume in which the concentration of methane is measured and from that the volume of methane can be calculated.
  • gas sensors may be used for the same or other gasses.
  • the value of the method lies in the dilution step which allows a sensor, which is only effective to sense relatively low gas concentrations, to be used to monitor a supply of a relatively concentrated gas .
  • the procedure may be automated, saving time compared with the known procedure.
  • the preferred use of a catalytic gas sensor instead of a liquid gas chromatograph represents a great saving in capital outlay and enables the concentration of methane in each sample collected to be monitored thus improving the accuracy.
  • the process is non invasive so that the procedure is not so liable to operator error.
  • the gas may be collected at atmospheric pressure so removing the alteration in the conditions which exists in the known procedure so that there is no increase in the amount of carbon dioxide dissolved in the matter being tested and thus in the acidity thereof.
  • the catalytic gas sensor is responsive to the presence of other gaseous or vaporous hydrocarbons, e.g. butane and ethane, and in other applications the procedure may be used to monitor the supply of these.
  • apparatus for monitoring a supply of one or more first gas comprising: a) means for collecting a pre-set volume of gas containing the one or more first gas and for diluting the collected gas to a predetermined volume with one or more second gas; and b) a gas sensor sensitive to the diluted one or more first gas but not to the one or more second gas, to provide a signal indicative of the concentration of the diluted one or more first gas.
  • the means for collecting and diluting a volume of the one or more first gas comprises: valve means selectively operable to direct a supply of the first one or more gas to a manometer or to direct said one or more first gas from the manometer to a chamber; means to detect manometer liquid above a first relatively high level; means to detect manometer liquid below a second relatively low level; and control means to operate the valve to direct the one or more first gas to the manometer when the liquid is detected above the high level and to direct the one or more first gas from the manometer to the chamber when the manometer liquid is detected below the low level.
  • the manometer may have a wide section at least on the side open to atmosphere so that a substantial volume of gas is collected for a small change in liquid level. Additionally or alternatively, the liquid in the manometer may have a low density, e.g. water.
  • an arrangement to purge the chamber In order to permit the apparatus to be used repetitively, there is preferably included an arrangement to purge the chamber.
  • the gas sensor is operative to combust hydrocarbon gases to provide said signal indicative of concentration and thus to purge the chamber of said hydrocarbon gases.
  • the chamber is most preferably constructed so that oxygen can permeate or diffuse thereinto to replace that used in combusting the hydrocarbon(s) .
  • the chamber may be vented by a solenoid valve, or purged by supply of a gas, e.g. oxygen, via a solenoid valve.
  • the apparatus preferably includes computer means for integrating the signal indicative of concentration to give a signal indicative of the volume of the collected hydro- carbon(s).
  • the control means is preferably arranged to operate the valve to direct the gas to the manometer when the liquid is detected above the high level and to direct the gas from the manometer to the chamber when the liquid is detected below the low level, repetitively.
  • the computer means is preferably arranged for adding the integrated signals to provide a signal indicative of the total volume of the hydrocarbon(s) collected.
  • the computer means is preferably arranged for measuring the time over which the hydrocarbon(s) are collected to produce a time indicative signal; and from the volume indicative signal and the time indicative signal, producing a signal indicative of the rate of collection of the hydrocarbon(s) .
  • the means to detect liquid in the manometer above a first relatively high level and the means to detect liquid in the manometer below a second relatively low level preferably comprise optical sensors. If the liquid used in the manometer is, say, water, the optical sensors detect the meniscus, so that when the upper optical sensor detects the presence of the meniscus, the liquid is detected to be above the first predetermined level, and when the lower optical sensor detects the presence of the meniscus, the liquid is detected to be below a second predetermined level.
  • the total number of operations of the valve means represents the total volume of gas collected (for example methane and carbon dioxide) and the rate at which operations of the valve means occur represents the rate of total gas production.
  • a serum vial 2 contains a sample of material, of which it is desired to study the anaerobic degradation.
  • the vial is inoculated with bacteria which is active in anaerobic conditions to degrade the sample.
  • the vial is closed by a butyl rubber or Teflon bung which has an opening through which a tube 4 is connected to the vial to collect gas produced in the process of decomposition of the sample by the bacteria.
  • a further hole through the bung enables a tube 6 to be connected to purge the vial of air with, for example, nitrogen or carbon dioxide.
  • the further hole may also be used to inject with a syringe other substances into the vial in order to assess their effect on the production of methane. After the tube 6 or the syringe has been withdrawn from the further hole, it closes so as to seal the vial against the ingress of air.
  • the tube 4 connects the vial 2 to a valve 8 which is operated by a solenoid 10.
  • the vial is connected to one arm 12 of a manometer 14 via the valve 8 and a tube 16.
  • the valve is operable selectively to open an exhaust port to connect the tubes 4 and 16 to a chamber 18 within which the valve is located.
  • the solenoid 10 is located outside the chamber, a plunger 20 passing through a flexible membrane 22 forming one wall of the chamber 18, to operate the valve.
  • the chamber has an impermeable cylindrical wall 24 closed at one end by the membrane 22 and at the other by a porous plug 26 the purpose of which will be explained below.
  • the manometer 14 is constructed of a transparent material, e.g. plastics or glass.
  • Two optical sensors 28 and 30 are located adjacent the arm 12 of the manometer to sense whether or not there is fluid at two levels.
  • the output signals from the optical sensors are connected to a logic and solenoid driver unit 32 in a control unit 34.
  • the optical sensors detect the interruption of light caused by the meniscus of the fluid in the manometer.
  • the logic causes the unit 32 to activate the solenoid to operate the valve 8 so as to close the exhaust port to the chamber 18.
  • the vial produces gases as a result of the bacterial activity on the sample
  • the meniscus in arm 12 of the manometer is depressed.
  • the logic in unit 32 causes the solenoid driver to activate the solenoid to operate the valve to connect the tubes 4 and 16 to the interior of the chamber 18.
  • the slight pressure head in the manometer causes gas collected therein to be exhausted to the chamber 18.
  • the pressure head which can be quite small (typically as little as 3mm) , has no significant effect on the degradation process in the vial 2.
  • the vial When the valve is open, the vial is connected to the chamber 18, but as the rate of production of gas by the culture is very low compared with the rate at which the gas collected in the manometer is discharged into the chamber, any error produced thereby is insignificant.
  • the collection of the gas in the manometer may take several hours, but the discharge into the chamber 18 may take only a second or so. It is thus possible to use a simple open/closed exhaust valve instead of a change ⁇ over valve which would otherwise be necessary, but a change-over valve may be used when high gas production rates are to be measured.
  • the valve When the meniscus reaches the level of the upper optical sensor 28, the valve is operated again to close the exhaust port to the chamber 18 and the cycle is repeated indefinitely.
  • a catalytic gas sensor 36_ This comprises a platinum bridge network, one side of which is treated to burn hydrocarbon gases better than the other. The combustion causes the one side of the bridge thus to become hotter than the other, resulting in an increase in the resistance and consequent unbalancing of the bridge which thus produces an electrical signal indicating the concentration of a combustible hydrocarbon gas or vapour, methane in the present example, since that is the only such gas present. Provided the concentration of methane is not more than about 1%, the output of the sensor is indicative of the concentration. Since the anaerobic fermentation in the vial will usually produce a concentration of about 80% methane, the volume of the chamber 18 is about 100 times greater than the volume of the manometer swept by the meniscus, to give an appropriate dilution for the sensor.
  • the output signal from the sensor 36 is received by a bridge circuit 38 in the control unit 34, amplified by an amplifier 40 and transmitted to an analogue to digital convertor (not shown) to produce a digital signal representative of the concentration of methane in the chamber 18, which digital signal is transmitted to a computer (not shown) for processing.
  • the concentration of methane in the chamber varies as the volume collected in the manometer is introduced into the chamber and as it is then burned on the sensor 36.
  • the digital concentration-representative signal varies correspondingly and is processed in the computer to produce a value representative of the integral of the concentration with respect to time. Since the volume in which this concentration exists is known and fixed, being that of the chamber 18, the value produced to represent the integral of the concentration is also representative of the total amount of methane in the chamber, and thus in the volume collected in the manometer, and may be scaled accordingly.
  • the computer is arranged to add successive values so producing a value representative of the total volume of methane produced.
  • the computer is also arranged to time the interval between successive cycles of operation, e.g. between successive output pulses from the gas sensor, and from that and the successive integral values to produce a value representative of the rate of production of methane.
  • the plug 26 serves to prevent draughts from disturbing the mixture of air and collected gases but to allow the oxygen in the chamber to be replenished by diffusion therethrough between successive releases of collected gases into the chamber.
  • the methane combusts relatively quickly on the sensor 36 so that no substantial amount diffuses through the porous plug 26, almost all being combusted.
  • the plug may be replaced with a small hole in the wall of the chamber. Such a hole would need to be large enough to permit oxygen to diffuse into the chamber but small enough to prevent draughts disturbing the combustion of the methane.
  • the number of cycles of operation of the valve 8 represents the total volume of gas produced and this too may be recorded. Indeed, the apparatus is useful to record just that and no more in other applications. For example, by adapting the apparatus so that the gas exhausted from the valve 8 can. be delivered to a serum vial, the volume of oxygen used by an aerobic process could be monitored.

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  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Biochemistry (AREA)
  • Microbiology (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Wood Science & Technology (AREA)
  • Pathology (AREA)
  • Immunology (AREA)
  • Bioinformatics & Cheminformatics (AREA)
  • Zoology (AREA)
  • Molecular Biology (AREA)
  • Genetics & Genomics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Sustainable Development (AREA)
  • Biotechnology (AREA)
  • Food Science & Technology (AREA)
  • General Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Water Supply & Treatment (AREA)
  • Medicinal Chemistry (AREA)
  • Combustion & Propulsion (AREA)
  • Biodiversity & Conservation Biology (AREA)
  • Hydrology & Water Resources (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • General Chemical & Material Sciences (AREA)
  • Sampling And Sample Adjustment (AREA)

Abstract

Procédé et dispositif servant à contrôler une alimentation en gaz, telle que la production de méthane au moyen de la dégradation anaérobie de matières organiques et utilisant un manomètre (14), afin de mesurer avec précision des volumes prédéterminés dudit gaz. Chaque volume mesuré est introduit dans une chambre (18) possédant également un volume prédéterminé et contenant un deuxième gaz, de façon à obtenir une dilution connue avec précision de la production de gaz à contrôler. La chambre (18) contient un détecteur de gaz catalytique (36) sensible au gaz à contrôler et produisant une sortie indiquant la concentration du premier gaz à l'intérieur de ladite chambre (18), ce qui permet de déterminer le débit de production et le volume dudit premier gaz.
EP92923905A 1991-11-26 1992-11-25 Procede et dispositif servant a controler une alimentation en gaz Withdrawn EP0614525A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9125125 1991-11-26
GB9125125A GB9125125D0 (en) 1991-11-26 1991-11-26 Method and apparatus for monitoring a supply of gas
PCT/GB1992/002170 WO1993011421A1 (fr) 1991-11-26 1992-11-25 Procede et dispositif servant a controler une alimentation en gaz

Publications (1)

Publication Number Publication Date
EP0614525A1 true EP0614525A1 (fr) 1994-09-14

Family

ID=10705267

Family Applications (1)

Application Number Title Priority Date Filing Date
EP92923905A Withdrawn EP0614525A1 (fr) 1991-11-26 1992-11-25 Procede et dispositif servant a controler une alimentation en gaz

Country Status (3)

Country Link
EP (1) EP0614525A1 (fr)
GB (1) GB9125125D0 (fr)
WO (1) WO1993011421A1 (fr)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9420481D0 (en) * 1994-10-11 1994-11-23 Taylor Research & Dev Ltd Analysis of gas emissions
ES2268925B1 (es) * 2004-03-08 2008-02-16 Universidad De Valladolid Equipo y procedimiento para la determinacion de actividad metanogenica de fangos, biodegradabilidad de muestras solidas y liquidas y toxicidad/inhibicion de compuestos.
CN100368790C (zh) * 2005-07-07 2008-02-13 吴伟祥 多层取样型生活垃圾生态填埋反应器
US8168121B2 (en) 2006-12-05 2012-05-01 Elkins Earthworks, Llc Portable gas monitor
US11504754B2 (en) 2006-12-05 2022-11-22 Elkins Earthworks, Llc Portable gas monitor
US20110231099A1 (en) 2006-12-05 2011-09-22 Charles Elkins Portable gas monitor
CN108469499B (zh) * 2018-03-22 2020-11-03 郑州轻工业学院 一种堆肥气体智能检测装置及系统

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2799561A (en) * 1954-11-17 1957-07-16 Monarch Logging Company Inc Method and apparatus for determining hydrocarbon content of solid earth formation samples
US3531980A (en) * 1967-04-14 1970-10-06 Nashua Corp Method and apparatus for measuring volatile content
US4270381A (en) * 1979-10-01 1981-06-02 Demaray David E Recording instrument to measure microbal gas production
EP0120882A1 (fr) * 1982-09-28 1984-10-10 W.W. Engineering A/S Procede et systeme de decomposition de dechets organiques par action bacterienne de fa on a former un gaz combustible
KR890004163A (ko) * 1987-08-12 1989-04-20 고마쯔 신 유중용존 가스측정장치

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9311421A1 *

Also Published As

Publication number Publication date
GB9125125D0 (en) 1992-01-22
WO1993011421A1 (fr) 1993-06-10

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