Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-04-03
2002-03-12
Warden, Sr., Robert J. (Department: 1744)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S400000, C204S431000, C205S786500
Reexamination Certificate
active
06355150
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an analyser for continuously measuring the H
2
S contained in a gas. It also relates to a device including the said analyser for regulating the flow rate of air injected into a reactor for oxidizing H
2
S to sulphur.
BACKGROUND OF THE INVENTION
In order to recover the H
2
S present in low concentration, especially a concentration of less than 5% by volume, in gases of various origins, it is common practice to use processes involving oxidation, especially catalytic oxidation, of H
2
S to sulphur according to the reaction H
2
S+{fraction (
1
/
2
)} O
2
→S+H
2
O.
In such oxidation processes, the gas to be treated containing H
2
S in the presence of a controlled amount of a gas containing free oxygen is made to come into contact with a catalyst for selective oxidation of H
2
S to sulphur, the said contact being achieved at temperatures either above the dew point of the sulphur formed, in which case the sulphur formed is present in the vapor state in the gaseous effluent resulting from the reaction, or at temperatures below the dew point of the sulphur formed, in which case the said sulphur is deposited on the catalyst, thereby requiring the sulphur-laden catalyst to be periodically regenerated by purging, by means of a non-oxidizing gas having a temperature of between 200° C. and 500° C. The gas containing free oxygen used for oxidizing the H
2
S to sulphur is usually air, but it may also consist of oxygen, oxygen-enriched air or else mixtures, in various proportions, of oxygen and an inert gas other than nitrogen. In the following, “air” is used to denote the said gas containing free oxygen.
The amount of air, with which the gas to be treated containing H
2
S is combined, is continuously adjusted in response to a parameter resulting from the superposition of a prediction parameter, representative of an air flow rate corresponding to an amount of oxygen proportional to the amount of H
2
S present in the gas to be treated and injected into the oxidation reactor, and of a correction parameter (a feedback parameter), representative of a corrective air flow rate for bringing the H
2
S content present in the gaseous effluent coming from the oxidation back to a set value.
The oxidation is carried out in a reactor having an upstream end and a downstream end which are advantageously separated by a bed of a catalyst for selective oxidation of H
2
S to sulphur, the said upstream end being equipped with a first line and a second line for the injection of the gas to be treated and of air into the reactor, respectively, and the said downstream end being equipped with an output line for the gases, in order to discharge the gaseous effluent resulting from the oxidation, and the flow rate of air injected into the oxidation reactor is adjusted with the aid of a regulating device combining (i) a prediction unit, which comprises a prediction computer receiving a signal from a flow meter and a signal delivered by a first H
2
S-content analyser, these being mounted in the first line at the upstream end of the oxidation reactor and generating, from the said signals, a signal representative of an air flow rate corresponding to an amount of oxygen proportional to the H
2
S content entering the oxidation reactor with (ii) a feedback unit, which comprises a correction computer receiving a signal delivered by a second H
2
S-content analyser, mounted in the output line of the oxidation reactor and generating, from the said signal, a signal representative of a corrective air flow rate in order to bring the H
2
S content present in the gaseous effluent passing through the said output line back to a given set value and with (iii) a flow regulator, which receives the signals generated by the prediction and correction computers and the signal delivered by a flow meter, mounted in the air injection line at the upstream end of the oxidation reactor and applying, to a valve with an adjustable opening, mounted in the said air injection line downstream of the flow meter, a control signal for adjusting the opening of the said valve, the said control signal being the resultant of the signals generated by the prediction and correction computers.
The analysers, which are mounted in the line for injecting the gas to be treated into the oxidation reactor and on the output line of the said reactor, respectively, may be, for example, gas chromatography analytical units (U.S. Pat. No. 3,026,184 and FR-A-2,118,365), differential spectrometry analytical units (FR-A-2,420,754) or infrared absorption analytical units, after selective transformation of the H
2
S into SO
2.
The analysers of the aforementioned types, used for measuring the H
2
S content in gases containing this compound, do not always deliver continuous signals or do not always provide adequate sensitivity or adequate reliability, nor satisfactory operating simplicity.
SUMMARY OF THE INVENTION
The present invention provides an analyser for continuously measuring the H
2
S content of a gas containing it, which has a high sensitivity and the response of which shows no significant drift over time.
The analyser according to the invention, for continuously measuring the H
2
S content of a gas sample containing it, is characterized in that it comprises:
a dry-operating module for drying the gas sample, comprising an inlet, connected to a nozzle for taking and injecting the said sample, and an outlet for the dried sample;
a compressor module having a suction port, connected via a line to the outlet of the drying module, and a discharge port extended by a flow line for the compressed sample, the said line being equipped with an indicating and/or regulating primary flow meter;
a system for diluting the compressed sample, comprising an air intake line, which is mounted as a branch off the flow line for the compressed sample, downstream of the primary flow meter, and which is equipped with a regulating secondary flow meter adjusting the degree of opening of a valve having an adjustable opening, mounted in the air intake line downstream of the secondary flow meter, and a regulating module connected to each of the primary and secondary flow meters and slaving the secondary flow meter to the primary flow meter; and
an electrochemical sensor for measuring H
2
S, which is mounted in the flow line for the compressed sample, downstream of the air intake line, and delivers a signal proportional to the concentration of H
2
S in the said sample.
Advantageously, the nozzle for taking and injecting the gas sample, connected to the inlet of the dry-operating module for drying the gas sample, may be provided, at its remotest end from the said inlet, with a primary filter. Optionally, a finer filter may be provided at the other end of the said nozzle, located on the same side as the said module. If required, this nozzle may be surrounded by a jacket equipped with means for maintaining the temperature, for example by electrical heating or by the circulation of a heat-transfer fluid.
The dry-operating module for drying the gas sample may consist, in particular, of a dryer comprising permeation membranes such as the “SEC” dryer sold by Environnement SA.
The compressor module may be chosen from various miniaturized compressors having the required performance. Particularly suitable are diaphragm compressors.
The indicating and/or regulating primary flow meter mounted in the flow line for the compressed sample, as well as the regulating secondary flow meter mounted in the air intake line are, in particular, mass flow meters. In this case, the regulating module which is associated with them is a mass-regulating module.
The electrochemical sensor for measuring the H
2
S concentration is of the electrochemical transducer type for measuring the partial pressure of the compound measured. This sensor comprises a measurement cell, which contains a liquid electrolyte, in which a measurement electrode, a comparison electrode and a reference electrode are immersed, and which is separated, by a membrane, from the flow space for the gas sample on
Becourt Pierre
Pepy Andre
Savin-Poncet Sabine
Elf Exploration Production
Olsen Kaj K.
Townsend and Townsend / and Crew LLP
Warden, Sr. Robert J.
LandOfFree
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