Systems and related methods for analyzing a gas

Systems and methods for analyzing a gas are provided. In some embodiments, the system includes: at least one scrubber including a scrubber material that removes at least one sulfur compound from the gas to produce a scrubbed gas; at least one gas sensor in fluid communication with the at least one scrubber, the at least one gas sensor sensing at least one remaining sulfur compound in the scrubbed gas. In some embodiments, the systems and methods disclosed herein may be used to analyze individual odorants in a hydrocarbon gas such as natural gas.

FIELD OF TECHNOLOGY

The following relates to gas analysis. More particularly, the present disclosure relates to systems and methods for analyzing sulfur compounds in hydrocarbon gas.

BACKGROUND

Hydrocarbon gases including natural gas, liquid petroleum gas, and propane are colorless and odorless. Organosulfur compounds are typically used to odorize hydrocarbon gases, allowing humans to detect leakage of these hydrocarbons before they reach their lower explosion limit. Organosulfur compounds commonly used as gas odorants include tetrahydrothiophene (THT), tert-butyl mercaptan (TBM), ethyl mercaptan (EM), sec-butyl mercaptan (SBM), methyl ethyl sulfide (MES), n-propyl mercaptan (NPM), isopropyl mercaptan (IPM), diethyl sulfide (DES), and dimethyl sulfide (DMS). In North America, a widely used natural gas odorant is a blend of TBM and MES.

Natural gas distributors typically analyze and maintain the concentration of the odorants throughout their distribution network on a regular basis. This process is conventionally done by sampling natural gas samples from the field and sending each sample to a gas chromatography laboratory for analysis. An example of natural gas odorant analysis method with gas chromatography can be found in Macak et al. “Determination of sulphur compounds in natural gas by gas chromatography with a flame photometric detector”, Journal of Chromatography, 286 (1984), pp. 69-78. However, such methods can be time-consuming and expensive.

U.S. Pat. No. 4,526,755 to Vincent et al. teaches an alternative approach to natural gas odorant analysis in which natural gas passes through bubblers followed by analysis by coulometric titrators. The bubblers contain aqueous solutions to remove specific compounds from the natural gas: e.g., a 1.0% CdSO4and 2.0% H3BO3solution (to remove H2S), a 10.0% NaOH solution (to remove mercaptans), and a 0.5% AgNO3water solution (to remove sulfides). Although this approach may be suitable for laboratory use, it is not suitable for field deployment as the aqueous bubbling solutions may freeze if the environmental temperature drops below their freezing point. The concentration of the bubbling solutions may also need to be frequently compensated due to evaporation. Furthermore, additional moisture in the processed gas can also influence the performance of the sensors positioned downstream of the bubblers.

Another possible approach for the analysis of odorants in natural gas involves the use of electrochemical cell gas sensors, also known as electrochemical sensors. Electrochemical sensors are widely used and their selectivity has improved greatly over in recent years (Guth et al. “Recent developments in electrochemical sensor application and technology—a review”, Measurement Science and Technology, 20 (2009), 042002); however, they still suffer from cross-sensitivity issues. For example, an electrochemical sensor designed for sensing methyl mercaptan (MM) will also respond to other sulfur-containing molecules (including TBM, MES, and H2S), triggering a false positive when MM is not present. Thus, electrochemical gas sensors alone are not able to analyze the concentrations of individual odorants when two or more sulfur compounds are present in an analyte gas. As a result, commercial electrochemical gas sensors designed for natural gas odorant analysis typically only provide estimated total odorant concentration. In addition, these sensors may be affected by cross-sensitivity to H2S that naturally exists in natural gas.

European Patent Publication No. EP0445927 to Willance et al. describes an odorant analyzer system to address the cross-sensitivity issue. The system utilizes a gas chromatography column to separate the sulfur compounds present in a natural gas sample before analysis by an electrochemical gas sensor. However, this system is large and complex with considerable electronic requirements, which would be difficult to implement for field deployment in hazardous locations.

SUMMARY

An aspect relates to a system for analyzing a gas, the system comprising: at least one scrubber comprising a non-aqueous scrubber material that removes at least one sulfur compound from the gas to produce a scrubbed gas; and at least one gas sensor in fluid communication with the at least one scrubber, the at least one gas sensor sensing at least one remaining sulfur compound in the scrubbed gas.

In some embodiments, the scrubber material comprises an alkali metal hydroxide, an alkaline earth metal hydroxide, a carbonate salt, a bicarbonate salt, an iodate salt, a metal oxide, an amine, or a combination thereof.

In some embodiments, the at least one scrubber comprises a first scrubber and a second scrubber, the first scrubber comprising a first scrubber material and the second scrubber comprising a second scrubber material.

In some embodiments, the first scrubber material is a liquid-phase scrubber material and the second scrubber material is a solid-phase scrubber material.

In some embodiments, the first scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the second scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt.

In some embodiments, the at least one gas sensor comprises a first gas sensor and a second gas sensor, the first gas sensor fluidly connected to the first scrubber and the second gas sensor fluidly connected to the second scrubber.

In some embodiments, the system further comprises a valve in fluid communication with the first and second scrubbers and the at least one gas sensor, the valve selectively movable between a first position in which a first gas stream flows from the first scrubber to the at least one gas sensor and a second position in which a second gas stream flows from the second scrubber to the at least one gas sensor.

In some embodiments, the system further comprises at least one pump operable to move the scrubbed gas from the at least one scrubber to the at least one gas sensor.

In some embodiments, the system further comprises a processor that processes sensor output of the at least one gas sensor to determine a concentration of the at least one remaining sulfur compound.

In some embodiments, the at least one gas sensor comprises one or more electrochemical cells.

In another aspect, there is provided a method for analyzing a gas, the method comprising: contacting the gas with a non-aqueous scrubber material that removes at least one sulfur compound to produce a scrubbed gas; and sensing at least one remaining sulfur compound in the scrubbed gas.

In some embodiments, the scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine.

In some embodiments, sensing the at least one remaining sulfur compound comprises sensing a first sulfur content of the scrubbed gas.

In some embodiments, further comprising sensing a second sulfur content of an unscrubbed stream of the gas and determining an H2S concentration based on the difference between the first sulfur content and the second sulfur content.

In some embodiments, the scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt.

In some embodiments, sensing the at least one remaining sulfur compound comprises sensing at least one of MES, DMS, DES, and THT.

In some embodiments, the at least one remaining sulfur compound is sensed by at least one gas sensor, the at least one gas senor comprising one or more electrochemical cells.

In another aspect, there is provided a method for analyzing a gas, the method comprising: separating the gas into a first gas stream and a second gas stream; contacting the first gas stream with a first non-aqueous scrubber material to produce a first scrubbed gas stream; contacting the second gas stream with a second non-aqueous scrubber material to produce a second scrubbed gas stream; sensing at least one first remaining sulfur compound in the first scrubbed gas stream; and sensing at least one second remaining sulfur compound in the second scrubbed gas stream.

In some embodiments, the first scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the second scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt.

Other aspects and features of the present disclosure will become apparent, to those ordinarily skilled in the art, upon review of the following description of the specific embodiments of the disclosure.

DETAILED DESCRIPTION

Generally, the present disclosure provides a system for analyzing a gas. In some embodiments, the system comprises: at least one scrubber comprising a non-aqueous scrubber material that removes at least one sulfur compound from the gas; at least one gas sensor in fluid communication with the at least one scrubber, the at least one gas sensor sensing at least one remaining sulfur compound in the scrubbed gas. Related methods for analyzing a gas are also provided.

As used herein, “upstream” and “downstream” refer to the direction of flow of a gas stream through embodiments of the systems described herein. Under normal operating conditions, the gas stream flows from an upstream position to a downstream position.

The systems and methods disclosed herein may be used to analyze a gas. In some embodiments, the gas is a hydrocarbon gas. As used herein, the term “hydrocarbon gas” refers to any gas comprising at least one hydrocarbon component. Non-limiting examples of hydrocarbon gases include natural gas, liquefied petroleum gas, and propane. In some embodiments, the gas further comprises one or more native sulfur compounds that are naturally present in the gas. In some embodiments, the native sulfur compounds comprise hydrogen sulfide (H2S) and/or one or more mercaptans.

The gas may further comprise one or more odorants. In some embodiments, one or more of the odorants comprises a sulfur compound. In some embodiments, the sulfur compound is an organosulfur compound. Non-limiting examples of organosulfur compounds include (THT), tert-butyl mercaptan (TBM), ethyl mercaptan (EM), sec-butyl mercaptan (SBM), methyl ethyl sulfide (MES), n-propyl mercaptan (NPM), isopropyl mercaptan (IPM), diethyl sulfide (DES), and dimethyl sulfide (DMS). In some embodiments, the gas comprises a blend of two or more odorants including, but not limited to, an organic sulfide and a mercaptan (e.g., TBM/MES blends or TBM/THT blends). In some embodiments, the gas to be analyzed comprises between about 0 and about 10 ppm of each odorant.

FIG.1Ais a schematic diagram of an example system100for analyzing a gas, according to some embodiments. The system100may comprise at least one scrubber and at least one gas sensor. The system100in this embodiment comprises a scrubber102and a gas sensor104. The system100may therefore also be referred to herein as a “one-scrubber-one-sensor” system.

As used herein, “scrub” or “scrubbing” refers to removing at least one chemical component of the gas and a “scrubber” refers to an apparatus or device that comprises a material capable of scrubbing (the “scrubber material”). The scrubbing may involve one or more physical and/or chemical processes to remove the chemical component(s) from the gas. Physical processes may include adsorption and/or absorption. Chemical processes may include one or more chemical reactions between the chemical component and the scrubber material that convert the chemical component into one or more different chemical entities. Scrubbing may fully or partially remove the chemical component(s) from the gas.

The scrubber material may have selectivity for at least one pre-defined chemical component of the gas. As used herein, “selectivity” or “selective removal” refers to relatively strong physical or chemical interaction with the pre-defined chemical compound(s) and relatively weak interaction (or no interaction) with any other components of the gas. In some embodiments, the scrubber material has selectivity for at least one sulfur compound.

The scrubber material may be a non-aqueous material. As used herein “non-aqueous” refers to a material that is substantially free of water, although it may contain trace amounts of water as an impurity. In some embodiments, the scrubber material may also be substantially free of other solvents, carriers, and the like. In some embodiments, the scrubber material comprises a substantially pure chemical compound. As used herein, “purity” refers to the amount of a chemical compound in a given substance and a “substantially pure” chemical compound refers to a substance in which at least about 50% of the total composition of the substance is the compound of interest. In some embodiments, the purity of the chemical compound of the scrubber material is at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 98%, or at least about 99%. In some embodiments, the scrubber material may be a single substantially pure chemical compound or a mixture of two or more substantially pure chemical compounds. In other embodiments, the scrubber material may have a lower purity if none of the other components interfere with the interaction between the scrubber material and the sulfur compounds in the gas being analyzed.

In some embodiments, the scrubber material is a solid material that selectively removes at least one chemical component of the gas (a “solid-phase scrubber material”). The solid-phase scrubber material may be in the form of powder, pellets, or any other suitable solid form.

In some embodiments, the solid-phase scrubber material comprises a solid form of a carbonate salt, a bicarbonate salt, a metal oxide, or a combination of one or more carbonate salts, bicarbonate salts, and/or metal oxides. In some embodiments, the carbonate salt, bicarbonate salt, or metal oxide is substantially pure. Non-limiting examples of carbonate and bicarbonate salts include Na2CO3, CaCO3, K2CO3, NaHCO3and KHCO3. Non-limiting examples of metal oxides include CaO and ZnO. The solid-phase scrubber material may selectively remove H2S from the gas. In some embodiments, H2S reacts with the scrubber material. Non-limiting examples of possible reactions between H2S and the scrubber material are provided below:
xH2S+M2(CO3)x=M(HS)x+M(HCO3)x
xH2S+2M(HCO3)x=M2Sx+2xH2O+2xCO2
xH2S+M2Ox=M2Sx+xH2Owhere M is a metal atom and x is equal to its oxidation number.

In other embodiments, the solid-phase scrubber material comprises a hydroxide-based scrubber material. In some embodiments, the hydroxide-based scrubber material comprises a solid form of an alkali metal hydroxide, an alkaline earth metal hydroxide, or a combination of one or more alkali metal hydroxides and/or one or more alkaline earth metal hydroxides. In some embodiments, the alkali metal hydroxide and/or alkaline earth metal hydroxide is substantially pure. The alkali metal hydroxide may comprise NaOH, LiOH, KOH, RbOH, or CsOH. The alkaline earth metal hydroxide may comprise Ca(OH)2, Ba(OH)2, and Sr(OH)2. The hydroxide-based scrubber material may selectively remove H2S and mercaptans (e.g., TBM) from the gas. Where the gas to be analyzed comprises natural gas, the scrubber material may also remove other mercaptans that are naturally present in the natural gas. In some embodiments, H2S and mercaptans reacts with the scrubber material. Non-limiting examples of possible reactions between H2S and mercaptans and the scrubber material are provided below:
xH2S+2M(OH)x=M2Sx+2xH2O
xRSH+M(OH)x=M(SR)x+xH2Owhere M is an alkali metal atom or alkaline earth metal atom, x is equal to the oxidation number of the metal atom, and R is an alkyl group

In other embodiments, the solid-phase scrubber material comprises an iodate-based scrubber material. In some embodiments, the iodate-based scrubber material comprises a solid form of an iodate salt, or a combination of one or more iodate salts and one or more alkali metal hydroxides or alkaline earth metal hydroxides. In some embodiments, the iodate salt is substantially pure. The iodate salt may comprise NaIO3, KIO3, Ca(IO3)2, or Mg(IO3)2. The iodate-based scrubber material may selectively remove H2S and mercaptans (e.g., TBM) from the gas. Where the gas to be analyzed comprises natural gas, the scrubber material may also remove other mercaptans that are naturally present in the gas.

In other embodiments, the solid-phase scrubber material comprises any other suitable solid material that is capable of scrubbing at least one sulfur compound from a gas.

In other embodiments, the scrubber material is a liquid material that selectively removes at least one chemical component of the gas (a “liquid-phase scrubber material”). The liquid-phase scrubber material may comprise an organic, non-aqueous liquid. In some embodiments, the liquid-phase scrubber material comprises an amine or a mixture of two or more amines. In some embodiments, the amine is substantially pure. Non-limiting examples of amines include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA), and diglycolamine (DGA). The amine-based scrubber material may selectively remove H2S from the gas. In some embodiments, H2S reacts with the scrubber material. Non-limiting examples of possible reactions between H2S and the scrubber material are provided below:
RNH2+H2S═RNH3++HS—
RR′NH+H2S═RR′NH2++HS—
RR′R″N+H2S═RR′R″NH++HS—where R, R′, and R″ are alkyl or alkanol groups.

In embodiments in which the scrubber material is solid-phase, the scrubber102may comprise a dry scrubber, a filter, or any other suitable apparatus configured to contain the solid-phase scrubber material. In embodiments in which the scrubber material is liquid-phase, the scrubber102may comprise a wet scrubber. The wet scrubber may comprise a bubbler, a spray tower, or any other suitable apparatus configured to contain the liquid-phase scrubber material. As used herein, a “bubbler” refers to any system in which a stream of gas is directed (i.e., “bubbled”) through the liquid-phase scrubber material, while a “spray tower” is any system in which the liquid-phase scrubber material is sprayed through or into the gas.

The gas sensor104is configured to sense at least one remaining sulfur compound in the gas scrubbed by the scrubber102. In this embodiment, the gas sensor104comprises an electrochemical sensor having one or more electrochemical sensor cells (hereafter also referred to as simply “electrochemical cells”). Electrochemical sensors have several advantages including low cost, low power consumption, and high sensitivity. Electrochemical sensor cells operate by reacting an analyte on the surface of a working electrode, generating an electrical signal that is linearly proportional to the concentration of the analyte. Each sensor cell may comprise a working electrode and a counter electrode (two electrode cell) and optionally a reference electrode (three electrode cell). In some embodiments, the gas sensor104comprises two or more electrochemical sensor cells placed in series or parallel with one another.

In other embodiments, the gas sensor104comprises a portable gas chromatograph, a UV-Visible spectrophotometer, a stain tube detector, or any other suitable gas sensing device. In alternative embodiments, the gas sensor104may be replaced by an individual performing a “sniff” test.

The gas sensor104may be in fluid communication with the scrubber102. In this embodiment, the gas sensor104is positioned downstream of the scrubber102and fluidly connected to the scrubber102by a first fluid conduit103. As used herein, “fluid conduit” will be understood to include one or more pipes, hoses, ducts, tubes, channels, or the like, in any suitable size, shape, or configuration. Embodiments are not limited to any specific type, number, or structure of fluid conduit.

The system100may further comprise a pump106. The term “pump” in this context refers to any device that moves fluids, including but not limited to pumps, aspirators, etc. The pump106may be any suitable type of pump capable of pumping a gas stream. In this embodiment, the pump106is positioned upstream of the scrubber102and is fluidly connected to the scrubber102by a second fluid conduit105.

In operation, the pump106receives a gas stream via an inlet107and pumps the gas stream through the second fluid conduit105to the scrubber102. As the gas stream passes through the scrubber102, one or more sulfur compounds are removed from the gas. The gas sensor104then receives a stream of scrubbed gas via the first fluid conduit103and the gas sensor104senses one or more of the remaining sulfur compounds in the scrubbed gas. In this embodiment, the electrochemical cell of the gas sensor104outputs an electrical signal linearly proportional to the concentration of the one or more remaining sulfur compounds.

In some embodiments, the system100further comprises a control module108. The control module may be operatively connected to one or both of the pump106and the sensor104. As shown inFIG.1B, the control system108may comprise at least one processor110, a memory112, a transceiver114, and a user interface116.

The processor110is operatively connected to the memory112, the transceiver114, and the user interface116. The memory112stores processor-executable instructions therein that, when executed, cause the processor110to implement one or more methods described herein.

The transceiver114may be configured to send and receive communications over a communication network such as the Internet. The communication network may be a wired or wireless network. In some embodiments, the transceiver114comprises both a transmitter and receiver sharing common circuitry. In other embodiments, the transceiver114comprises a separate transmitter and receiver.

In some embodiments, the control module108is in communication with one or more remote devices via the communication network. The remote device may comprise, for example, a client computer or server. In some embodiments, the remote device comprises a mobile communications device such as a smartphone or tablet.

The user interface116may be configured to display information to a user and/or to receive user input. In some embodiments, the user interface116comprises at least one output component and at least one input component. The output component may comprise, for example, at least one of a display screen, a display panel, one or more lights, an audio output device, etc. The input component may comprise, for example, one or more buttons, a touchscreen, keyboard, keypad, trackpad, mouse, microphone, etc.

The processor110may be operatively connected to the sensor104and may be configured to receive and process sensor output therefrom. For example, the processor110may calculate the concentration of one or more sulfur compounds based on the electrical signal generated by the sensor104. The calculated concentration(s) may be displayed to the user via the user interface116and/or may be transmitted to a remote device via the communication network.

The processor110may also be operatively connected to the pump106, for example, via the pump's power source (not shown). The processor110may run a program stored in the memory112to control the operation of the pump106. Alternatively, or additionally, the processor110may receive user input via the user interface116to start, stop, or adjust the operation of the pump106. In some embodiments, the processor110is operable to receive input via a remote device via the communications network. In other embodiments, the pump106may be operated manually and the connection between the processor110and the pump106may be omitted.

In some embodiments, the system100further comprises one or more additional components. For example, one or more valves (not shown) may be provided in fluid communication with one or more of the fluid conduits103,105,107to control the flow of fluid therethrough. In some embodiments, the processor110of the control module108is operatively connected to the valve(s) to control their operation.

In embodiments in which the gas sensor104comprises an electrochemical sensor cell, the system100may further comprise an air pump (not shown) and an air purging line (not shown) upstream and in fluid communication with the gas sensor104. Although electrochemical sensor cells operate normally in hydrocarbon gas (generally a low-humidity and low-oxygen environment) for a short period of time (several minutes to hours), maintaining the cells in a humid (e.g., approximately 10-90% relative humidity) and oxygen-rich environment may improve performance. In these embodiments, ambient air may be pumped through the gas sensor104, via the air pump and air purging line, to purge the gas sensor104between readings and thereby maintain a suitable humid and oxygen-rich environment. Optionally, the system100may further comprise a humidity and temperature sensor (not shown) to monitor the gas flowing into or out of the gas sensor104. In other embodiments, where the gas sensor104comprises a different type of sensor (e.g., a portable gas chromatograph, a UV-Visible spectrophotometer, or a stain tube detector), the air pump, air purging line, exhaust line, and humidity and temperature sensor may be omitted.

In some embodiments, the system100comprises a single housing (not shown) that encloses all of the components described above. In other embodiments, the system100may comprise two or more separate housings, each housing enclosing one or more individual components.

FIG.2is a schematic diagram of another example system200for analyzing the gas. The system200is an alternative embodiment of a one-scrubber-one-sensor system. As shown inFIG.2, the system200comprises a scrubber202, a gas sensor204, and a pump206. In this embodiment, the gas sensor204is positioned downstream of the scrubber202and the pump206is positioned downstream of the gas sensor204.

FIG.3is a schematic diagram of another example system300for analyzing a gas. The system300is another alternative embodiment of a one-scrubber-one-sensor system. As shown inFIG.3, the system300comprises a scrubber302, a gas sensor304, and a pump306. In this embodiment, the pump306is positioned between the scrubber302and the gas sensor304.

The system200and300may each further comprise a control module (not shown) similar to the control module108of the system100ofFIGS.1A and1B. The systems200and300may also comprise any of the other optional components of the system100as described above.

FIG.4is a flowchart of an example method400for analyzing a gas, according to some embodiments, that may be implemented using the systems100,200, and300ofFIGS.1A-1B,2, and3. The method400may be used to analyze a gas containing one odorant such as, for example, THT, TBM, MES, NPM, IPM, DMS, SBM, DES, or EM.

At block402, a gas is contacted with a scrubber material. The term “contact” in this context is intended to include any means by which the gas is brought into contact with the scrubber material. For example, in embodiments in which the scrubber material is solid-phase, the gas may be flowed through the scrubber material. In embodiments in which the scrubber material is liquid phase, the gas may be bubbled through the scrubber material, or the scrubber material may be sprayed into or through the gas. As discussed above, at least one sulfur compound in the gas may react with the scrubber material. In some embodiments, the reaction is instantaneous or near instantaneous such that there is little to no retention time of the gas in the scrubber material.

Contacting the gas with the scrubber material scrubs the gas to remove at least one sulfur compound and thereby produce a scrubbed gas. The gas may be contacted with the scrubber material in the scrubber102,202, or302of the system100,200, or300described above. In some embodiments, at least one sulfur compound is completely removed from the gas by the scrubber material such that the compound(s) are no longer present in the scrubbed gas. In other embodiments, at least one sulfur compound is partially removed from the gas such that the concentration of the compound(s) in the scrubbed gas is significantly reduced but small quantities may still be present.

In some embodiments, the scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine. In these embodiments, the scrubbing (or “pre-treatment”) step removes H2S from the gas. In other embodiments, the scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt. In these embodiments, the scrubbing step removes H2S and one or more mercaptans (e.g., TBM). Where the gas to be analyzed comprises natural gas, the scrubbing step may also remove one or more native mercaptans that are naturally present in the natural gas.

The scrubbing step at block402may be performed under any suitable conditions. In embodiments in which the scrubber material is one of the solid-phase scrubber materials, the scrubbing step may be performed at any ambient temperature, including a wide range of temperatures in the field such as between about −50° C. and about 50° C. In embodiments in which the scrubber material is a liquid-phase material, the scrubbing step may be performed at suitable temperature to maintain the viscosity of the liquid. For example, a scrubbing step with an amine-based scrubbing material may be performed at about 0° C. or higher.

At block404, at least one remaining sulfur compound in the scrubbed gas is sensed. As used herein, “sensing” refers to detecting, measuring, or otherwise acquiring data or information related to at least one sulfur compound in the gas. The sulfur compound(s) may be sensed using any embodiment of the sensors104,204, or304described above. In some embodiments, the sulfur compound(s) are sensed by an electrochemical sensor that generates an electrical signal, which is linearly proportional to the concentration of the sulfur compound(s).

In some embodiments, the method400further comprises calculating a concentration of at least one sulfur compound based on a sensor output. In embodiments in which the sensor is an electrochemical sensor, the sensor output is an electrical signal (I), and the concentration of the sulfur compound can be calculated by dividing the signal by a linear coefficient as shown in Equation 1:
C=I/a(Eq. 1)where a is the linear coefficient.

The concentration may be expressed in ppm or any other suitable unit. In some embodiments, the calculation step is performed by the processor110of the control module108(or similar control modules of the systems200or300). In other embodiments, the sensor output is transmitted to an external device to perform the calculation or to display the sensor output to a user to perform the calculation manually.

As one specific example of the implementation of the method400, the gas to be analyzed is natural gas containing TBM as an odorant along with native H2S. At block402, the scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the scrubbing step removes H2S from the gas. At block404, the TBM in the gas is sensed by an electrochemical sensor and the sensor output is used to determine the concentration of TBM in the gas. THT, MES, NPM, IPM, DMS, SBM, DES, or EM can also be analyzed in a similar manner.

As another example, the gas to be analyzed is natural gas containing THT as an odorant along with native H2S and one or more mercaptans. At block402, the scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt, and the scrubbing step removes H2S and one or more mercaptans. At block404, the THT in the gas is sensed by an electrochemical sensor and the sensor output is used to determine the concentration of THT in the gas. MES, DES, and DMS can also be analyzed in a similar manner.

FIG.5is a schematic diagram of another example system500for analyzing a gas, according to some embodiments. The system500in this embodiment comprises a first scrubber502A, a second scrubber502B, a first gas sensor504A, and a second gas sensor504B. The system500may therefore be referred to herein as a “two-scrubber-two-sensor” system.

The first scrubber502A may comprise a first scrubber material and the second scrubber502B may comprise a second scrubber material. In this embodiment, the first scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the second scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt.

In this embodiment, the first and second sensors504A and504B each comprise an electrochemical sensor comprising one or more electrochemical cells. In other embodiments, the first and second sensors504A and504B comprise any other suitable type of sensor including any of the sensors described above for the sensor104of the system100. The first and second sensors504A and504B may be the same type of sensor or different types of sensors.

The first sensor504A may be in fluid communication with the first scrubber502A and the second sensor504B may be in fluid communication with the second scrubber502B. In this embodiment, the first sensor504A is downstream of the first scrubber502A and is fluidly connected to the first scrubber502A by a first fluid conduit503A. The second sensor504B is downstream of the second scrubber502B and fluidly connected to the second scrubber502B by a second fluid conduit503B.

The system500may further comprise at least one pump. In this embodiment, the system500comprises a pump506upstream of both the first and second scrubbers502A and502B. The pump506may be fluidly connected to the first and second scrubbers502A and502B via a branched fluid conduit505. The fluid conduit505may comprise a junction508that splits the fluid conduit505into a first branch509A and a second branch509B. The first branch509A may fluidly connect to the first scrubber502A and the second branch509B may fluidly connect to the second scrubber502B.

The system500may operate as follows. The pump506receives a gas stream via an inlet507and pumps the gas stream through the branched fluid conduit505, where it is split at the junction508into a first gas stream and a second gas stream. The first gas stream flows through the first branch509A to the first scrubber502A and the second gas stream flows through the second branch509B to the second scrubber502B.

As the first gas stream passes through the first scrubber502A, one or more sulfur compounds are removed from the gas to produce a first scrubbed gas. The first scrubbed gas is received by the first gas sensor504A via the first fluid conduit503A and the first gas sensor504A senses one or more of the remaining sulfur compounds in the first scrubbed gas. In this embodiment, the electrochemical cell of the first gas sensor504A outputs an electrical signal linearly proportional to the concentration of the one or more remaining sulfur compounds.

As the second gas stream passes through the second scrubber502B, one or more sulfur compounds are removed from the gas to produce a second scrubbed gas. The second scrubbed gas is received by the second gas sensor504B via the second fluid conduit503B and the second gas sensor504B senses one or more of the remaining sulfur compounds in the second scrubbed gas. In this embodiment, the electrochemical cell of the second gas sensor504B outputs an electrical signal linearly proportional to the concentration of the one or more remaining sulfur compounds.

The system500may comprise a control module (not shown) similar to the control module108of the system100ofFIG.1B. In some embodiments, where at least one of the gas sensors504A and504B comprises an electrochemical sensor cell, the system500may comprise an air pump, air purging line, exhaust line and, optionally, a humidity and temperature sensor (all not shown) as described above with respect to the system100.

FIGS.6A,6B,6C, and6Dare schematic diagrams of additional example systems600,620,630, and640, respectively, for analyzing the gas. The systems600,620,630, and640are alternative embodiments of two-scrubber-two-sensor systems

As shown inFIG.6A, the system600comprises a first scrubber602A and a second scrubber602B, a first gas sensor604A and a second gas sensor604B, and a pump606. The first and second scrubbers602A and602B and the first and second gas sensors604A and604B may be similar to the first and second scrubbers502A and502B and the first and second gas sensors504A and504B, respectively, of the system500as described above. A first branched conduit605may be fluidly connected to the first scrubber602A and the second scrubber602B.

In this embodiment, the pump606is positioned downstream of the first and second gas sensors604A and604B. The pump606is fluidly connected to the first and second gas sensors604A and604B by a second branched conduit610.

The system600may operate in a similar manner to the system500as described above. Briefly, the gas may be received by the first branched fluid conduit605and split into a first fluid stream and a second fluid stream. The pump606may draw the first gas stream through the first scrubber602A to the first gas sensor604A and draw the second gas stream through the second scrubber602B to the second gas sensor604B. The first and second scrubbed gas streams may be combined downstream of the first and second gas sensors604A and604B in the second branched conduit610, from which they are pumped out of the system600.

As shown inFIG.6B, the system620comprises a first scrubber622A, a second scrubber622B, a first sensor624A, and a second sensor624B. In this embodiment, the system620further comprises a first pump626A and a second pump626B. The first pump626A is positioned downstream of the first sensor624A and the second pump626B is positioned downstream of the second sensor624B.

As shown inFIG.6C, the system630comprises a first scrubber632A, a second scrubber632B, a first sensor634A, a second sensor634B, a first pump636A, and a second pump636B. In this embodiment, the first pump636A is positioned between the first scrubber632A and the first sensor634A and the second pump636B is positioned between the second scrubber632B and the second sensor634B.

As shown inFIG.6D, the system640comprises a first scrubber642A, a second scrubber642B, a first sensor644A, a second sensor644B, a first pump646A, and a second pump646B. The first pump646A is positioned upstream of the first scrubber642A and the second pump646B is positioned upstream of the second scrubber642B.

The systems620,630, and640may otherwise operate in a similar manner to the systems500and600as described above.

FIG.7is a schematic diagram of another example system700for analyzing a gas. The system700in this embodiment comprises a first scrubber702A, a second scrubber702B, a gas sensor704, and a pump706. The system700may also be referred to herein as a “two-scrubber-one-sensor” system. The system700is a simplified embodiment of the two-scrubber-two-sensor systems described above.

The first and second scrubbers702A and702B may be similar to the first and second scrubbers502A and502B, respectively, of the system500as described above. In this embodiment, the pump706is upstream of the first and second scrubbers702A and702B and is fluidly connected to the first and second scrubbers702A and702B via a branched fluid conduit705.

The system700in this embodiment further comprises a three-way valve712. The valve712is in fluid communication with the first and second scrubbers702A and702B and the gas sensor704and is positioned downstream of the first and second scrubbers702A and702B and upstream of the gas sensor704. The valve712in this embodiment is fluidly connected to the first scrubber702A via a first fluid conduit711, to the second scrubber702B via a second fluid conduit713, and to the gas sensor704via a third fluid conduit714.

The system700may operate as follows. The pump706receives a gas stream via an inlet707and pumps the gas stream through the branched fluid conduit705where it is split into a first gas stream and a second gas stream. The first gas stream flows through the first scrubber702A and the second gas stream flows through the second scrubber702B. A first scrubbed gas flows through the first fluid conduit711and a second scrubbed gas flows through the second fluid conduit713.

The valve712may be selectively movable between a first position and a second position. When the valve712is in the first position, the first fluid conduit711is in fluid communication with the third fluid conduit714and the gas sensor704receives the first scrubbed gas. When the valve712is in the second position, the second fluid conduit713is in fluid communication with the third fluid conduit714and the gas sensor704receives the second scrubbed gas. Thus, the gas sensor704may alternate between sensing one or more sulfur compounds in the first scrubbed gas and one or more sulfur compounds in the second scrubbed gas.

Alternatively, instead of a three-way valve712, the system700can comprise two one-way valves (not shown). A first one-way valve may be in fluid communication with the first fluid conduit711to control the flow of the first scrubbed gas and a second one-way valve may be in fluid communication with the second fluid conduit713to control the flow of the second scrubbed gas. In other embodiments, the three-way valve712(or two one-way valves) may be positioned upstream of the first and second scrubbers702A and702B to alternate the flow of gas into the first scrubber702A and the second scrubber702B, thereby alternating the generation of the first gas stream and the second gas stream.

The system700may further comprise a control module (not shown) similar to the control module108of the system100ofFIG.1B. The control module may be operatively connected to the three-way valve, or two one-way valves, to control operation thereof.

FIG.8is a flowchart of an example method800for analyzing a gas, according to some embodiments. The method800may be implemented by embodiments of the systems500,600,620,630,640, and700ofFIGS.5,6A,6B,6C,6D and7, respectively. For simplicity, only systems500,600, and700will be referred to in the description of the method800below. The method800will be described using natural gas as the gas to be analyzed, wherein the natural gas contains two odorants (TBM and MES) along with native H2S and mercaptans. However, it will be understood that the method800may be adapted to analyze any other gases comprising two or more odorants such as sulfur compounds.

At block802, the gas is separated into a first gas stream and a second gas stream. In some embodiments, the gas is separated by pumping the gas through a branched fluid conduit such as the branched fluid conduit505,605, or705of the system500,600, or700.

At block804, the first gas stream is contacted with a first scrubber material. Contacting the first gas stream with the first scrubber material scrubs the gas to remove at least one sulfur compound and thereby produce a first scrubbed gas stream. The first gas stream may be contacted with the first scrubber material by the first scrubber502A,602A, or702A of the system500,600, or700. In this embodiment, the first scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the scrubbing step removes H2S from the first gas stream.

At block806, a second gas stream is contacted with a second scrubber material. Contacting the second gas stream with the second scrubber material scrubs the gas to remove at least one sulfur compound and thereby produce a second scrubbed gas stream. The second gas stream may be scrubbed by the second scrubber502B,602B, or702B of the system500,600, or700. In this embodiment, the second scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt, and the scrubbing step removes H2S, TBM, and native mercaptans from the second gas stream.

At block808, at least one remaining sulfur compound in the first scrubbed gas stream is sensed. The sulfur compound(s) may be sensed by the first sensors504A or604A of the systems500or600, respectively, or by the sensor704of the system700when the valve712is in the first position. A first sensor output may be generated by the first sensor504A or604A or the sensor704. In this example, both TBM and MES are sensed in the first scrubbed gas stream and the first sensor output is a total electrical signal (IA) induced by TBM and MES.

At block810, at least one remaining sulfur compound in the second scrubbed gas stream is sensed. The sulfur compound(s) may be sensed by the second sensors504B or604B of the systems500or600, respectively, or by the sensor704of the system700when the valve712is in the second position. A second sensor output may be generated by the second sensor504B or604B or the sensor704. In this example, MES is sensed in the second gas stream and the second sensor output is an electrical signal (IB) induced by MES.

In some embodiments, the steps at blocks804and808are performed approximately simultaneously as the steps of blocks806and810. In other embodiments, the steps at blocks804and808can be performed before or after the steps of blocks806and810.

The method800may further comprise calculating a concentration of at least one sulfur compound based on the first and second sensor output. In this example, the concentrations of TBM (CTBM) and MES (CMES) can be computed by Equation 2 as follows:
CMES=IB/a
CTBM=(IA−IB)/b(Eq. 2)where a and b are the linear coefficients.

Thus, the method800can be used to determine the concentrations of two different sulfur-based odorants within a hydrocarbon gas. It will be understood that the method800may be adapted for other types of gases and other combinations of odorants. For example, the method800may be adapted to determine the concentrations of an odorant blend comprising an organic sulfide and a mercaptan (e.g., TBM/MES blends or TBM/THT blends). Embodiments are not limited to the specific odorants described herein.

FIG.9is a schematic diagram of another example system900for analyzing a gas, according to some embodiments. The system900comprises a scrubber902, a gas sensor904, and a pump906. The system900is an alternative embodiment of a one-scrubber-one-sensor system that may be used to determine H2S content in a hydrocarbon gas.

The scrubber902may comprise a scrubber material that selectively removes H2S from the gas. For example, the scrubber material may comprise at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine. The gas sensor904in this embodiment comprises an electrochemical sensor comprising one or more electrochemical cells. In other embodiments, the gas sensor904comprises any other suitable type of gas sensor.

The system900may further comprise a three-way valve912between the scrubber902and the sensor904. The valve912may be fluidly connected to the scrubber902by a first fluid conduit908and fluidly connected to the sensor904by a second fluid conduit909. The system900may further comprise a control module (not shown) operatively connected to the three-way valve912to control operation thereof.

The pump906in this embodiment is positioned upstream of the scrubber902and is fluidly connected to the scrubber902via a branched fluid conduit905. The branched fluid conduit905may comprise a first branch910and a second branch911. The first branch910may be fluidly connected to the scrubber902and the second branch911may be fluidly connected to the three-way valve912.

In operation, the pump906receives a gas stream via an inlet907and pumps the gas stream through the branched fluid conduit905, where it is split into a first gas stream and a second gas stream. The first gas stream flows through the first branch910to the scrubber902where it is scrubbed to produce a scrubbed gas stream. The scrubbed gas stream flows through the first fluid conduit908to the valve912. The second gas stream is an “unscrubbed” stream of the gas that flows through the second branch911directly to the valve912.

The valve912may have a first position and a second position. When the valve912is in the first position, the first fluid conduit908is in fluid communication with the second fluid conduit909and the gas sensor904receives the scrubbed gas stream from the scrubber902. When the valve912is in the second position, the second branch911of the branched fluid conduit905is in fluid communication with the second fluid conduit909and the gas sensor904receives the unscrubbed gas stream from the pump906. Thus, the gas sensor904may alternate between sensing total sulfur content of the unscrubbed gas and sensing total sulfur content of the scrubbed gas (from which H2S has been removed) depending on the position of the valve912. As described in more detail below with respect to the method1000, the system900may thereby be used to determine the H2S concentration of the hydrocarbon gas.

In some embodiments, the system900may be integrated with one of the systems100,200,300,500,600,700described above by connecting a fluid conduit for unscrubbed gas to one of the sensors in the system and providing a valve in fluid communication with the fluid conduit to control the flow of unscrubbed gas therethrough.

FIG.10is a flowchart of an example method1000for analyzing a gas, according to some embodiments, that may be implemented using the system900. The method1000may be used to analyze H2S in a hydrocarbon gas.

At block1002, a first sulfur content of the gas is sensed. As used herein “sulfur content” refers to the total content of sulfur compounds in the gas. The first sulfur content may be sensed by the sensor904of the system900when the valve912is in the second position such that unscrubbed gas is received by the sensor904. A first sensor output may be generated by the sensor904. In this example, the first sensor output is a total electrical signal (IC) induced by the sulfur compounds in the unscrubbed gas.

At block1004, the gas is contacted with a scrubber material. Contacting the gas with the scrubber material scrubs the gas to remove H2S and thereby produce a scrubbed gas. The gas may be scrubbed through the scrubber902with a scrubber material comprising at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine.

At block1006, a second sulfur content of the scrubbed gas is sensed. The second sulfur content may be sensed by the sensor904when the valve912is in the first position such that scrubbed gas is received by the sensor904. A second sensor output may be generated by the sensor904. In this example, the second sensor output is a total electrical signal (IA) induced by the remaining sulfur compounds in the scrubbed gas.

At block1008, an H2S concentration of the gas is determined based on a difference between the first sulfur content and the second sulfur content. The H2S concentration may be calculated using Equation 3 as follows:
CH2S=(Ic−IA)/c(Eq. 3)
where c is the linear coefficient of H2S concentration to the first sensor output.

In some embodiments, the method1000may be combined or performed in parallel with the method400or800described above. Thus, the concentration of H2S in a gas can be determined along with the concentration of one or more odorants.

Therefore, embodiments of the systems and methods described herein may be used to analyze odorants in a gas with high accuracy and sensitivity, while reducing or eliminating the cross-sensitivity issues of conventional electrochemical sensor-based approaches. Some embodiments of the systems and methods allow the concentrations of individual odorants to be determined in a blend of two or more odorants.

The systems described herein may be relatively inexpensive and may be deployed as automated field sensors in some embodiments. This unmanned approach may also allow for faster sampling (e.g., on a daily or hourly basis) resulting in near real-time analysis of odorants in natural gas pipelines and substations.

Moreover, embodiments of the disclosed systems are compact and require few electronic parts and may therefore be suitable for analyzing odorants in hazardous locations. Further, by using non-aqueous material as the scrubber material, the systems may avoid the need for additional filtration or moisture trapping between the scrubber(s) and the sensors(s), while maintaining performance of the sensor(s). The non-aqueous scrubber materials may also allow the systems to be used in the field across a wide temperature range without risk of freezing the scrubber material and/or requiring the concentration of the scrubber material to be compensated due to evaporation.

Other variations of the systems and methods described herein are also possible. As discussed in the Examples below, when the hydrocarbon gas to be analyzed by the system is already pressurized, alternative embodiments may also be provided in which the pump(s) are omitted, and the system instead comprises a pressure regulator and flow meter. It will also be understood that although particular configurations of the systems100,200,300,500,600,620,630,640,700, and900are shown inFIGS.1A-1B,2,3,5,6A-6D,7, and9described above, other configurations are possible and embodiments are not limited to the specific configurations provided herein, including the specific number and placement of fluid conduits, valves, etc.

EXAMPLES

Experiments were performed using an experimental system10as shown inFIG.11. The experimental system10is similar to the system700ofFIG.7with two scrubbers and one electrochemical sensor.

As shown inFIG.11, the experimental system10comprises a first scrubber12A and a second scrubber12B in fluid communication with an electrochemical sensor14. The first scrubber12A contains CaCO3or MDEA as a first scrubber material (to remove H2S) and the second scrubber12B contains a mixture of NaOH and Ca(OH)2as a second scrubber material (to remove H2S and mercaptans). A first on/off valve16A is provided between the first scrubber12A and the sensor14and a second on/off valve16B is provided between the second scrubber12B and the sensor14.

In the experimental system10, a natural gas sample is drawn from a pressurized pipeline and the sensing tests are performed at ambient pressure. Thus, in the experimental system10, a combination of a pressure regulator18and a flow meter20is used instead of a pump. A coalescing filter22is provided between the pressure regulator18and the flow meter20.

In addition, the experimental system10includes an air pump24and an air purging line26to purge the electrochemical sensor14with ambient air between the sensing tests. A check valve28is in fluid communication with the air purging line26to control the flow of air therethrough.

In operation, a sample inlet30receives a pressurized natural gas stream, which flows through the pressure regulator18, coalescing filter22, and flow meter20before being split into a first gas stream and a second gas stream via a branched conduit32. The first gas stream flows through the first scrubber12A to produce a first scrubbed gas and the second gas stream flows through the second scrubber12B to produce a second scrubbed gas.

When the first on/off valve16A is on (i.e., open) and the second on/off valve is off (i.e., closed), the first gas stream will flow to the electrochemical sensor14to allow the sensor14to sense at least one remaining sulfur compound in the first scrubbed gas. When the first on/off valve16A is off (i.e., closed) and the second on/off valve is on (i.e., open), the second gas stream will flow to the electrochemical sensor14to allow the sensor14to sense at least one remaining sulfur compound in the second scrubbed gas. The air pump24and the air purging line26are used to purge the sensor14between readings and the purged air flows out of an exhaust line34.

Gas samples with varying concentrations of TBM and MES were tested using the experimental system. As shown inFIGS.12and13, the voltage signals from the electrochemical sensor are linearly proportional to the concentrations of TBM and MES, respectively.

FIGS.14A to14Cshow the sensor response (voltage) over time to gas samples containing TBM, H2S, and MES, respectively, with and without a scrubbing (pre-treatment) step with the NaOH and Ca(OH)2scrubber material. As shown inFIGS.14A and14B, both TBM and H2S are substantially removed from the gas by the scrubbing step. As shown inFIG.14C, MES remains in the gas following scrubbing and little to no MES is lost during the scrubbing step. Thus, the experimental system was able to provide an accurate concentration of the MES present in the gas.

FIGS.15A and15Bshow the sensor response (voltage) over time to a gas sample comprising H2S, with or without a scrubbing step with the CaCO3scrubber material and with or without the scrubbing step with the MDEA scrubber material, respectively. As shown inFIGS.15A and15B, the H2S is substantially removed by the scrubbing step with the CaCO3scrubber material and completely removed with the MDEA scrubber material.

FIG.16shows the sensor response (voltage) of the system described inFIG.11in sensing the TBM and MES content of a gas sample containing TBM, H2S, and MES. The sensing peak at 16-28 min is the MES response, where the sample gas is scrubbed with the NaOH and Ca(OH)2scrubber material, and the sensing peak at 36-50 min is the total response of MES and TBM, where the sample gas is scrubbed by the MDEA scrubber material. Thus, the experimental system10can be used to determine the concentrations of both MES and TBM in a gaseous mixture.