SYSTEM NAME: "DOUBLE HEADSPACE"

MEASUREMENT(S):
hydrogen sulfide (0-7,000 ppm)
ammonia (0-7,000 ppm)

DESIGN CHALLENGE:
The process stream at this site consisted of dirty (opaque) wastewater. The light signal could not transmit through an as-is sample.

SYSTEM CONCEPT:
This opaque process stream required use of the "headspace" technique, which exploits Henry's Law to force part of the liquid sample into the gas phase. The measurement is performed on the representative vapor-phase sample. This principle only works when the compounds of interest have a significantly lower boiling point than other compounds in the mixture (true for hydrogen sulfide and ammonia). To simultaneously measure two stream chemicals, this system uses two parallel headspace columns, each temperature-controlled for the boiling point of a designated analyte.

Read more: Headspace SCS Brochure [pdf]

SYSTEM NAME: "OFFSHORE"

MEASUREMENT(S):
hydrogen sulfide (0-20 ppm)

DESIGN CHALLENGE:
Offshore environments are highly corrosive due to moisture. Additionally, destructive sulfur compounds may leak into the analyzer site on deap sea oil platforms. An unprotected system will have a short lifetime due to severe corrosion.

SYSTEM CONCEPT:
This offshore sytem was specifed to withstand long-term oceanic stress. Wetted materials are super duplex stainless steel; the high chromium and molybdenum content of this steel makes it extremely resistant to corrosion/erosion.

SYSTEM NAME: "MULTI-STREAM"

MEASUREMENT(S):
hydrogen sulfide (0-20 ppm)
dimethyl sulfide

DESIGN CHALLENGE:
A brewery needs to monitor low hydrogen sulfide and DMS concentrations in the recycled CO₂ used for bottling. To increase system value, multiple streams need to be monitored using a single analyzer unit. This requires a multiplexed sample conditioning system.

SYSTEM CONCEPT:
This system uses physical stream multiplexing, whereby the sample stream entering the flow cell is physically alternated by valves. Only one flow cell/spectrophotometer pair is required, as all multiplexing is performed by the sample conditioning system.

SYSTEM NAME: "CLOSE-COUPLED"

MEASUREMENT(S):
hydrogen sulfide (0-20 ppm)

DESIGN CHALLENGE:
In continuous emissions monitoring (CEM), a continuous sample is drawn from the stack. A fully extractive system has the benefit of easy measurement validation, but has slow response due to sample transport as well as maintenance due to sample line plugging; conversely, the cross-stack in situ method has excellent response time but is virtually impossible to validate and requires disassembly for maintenance. An elegant solution would strike a balance between these two designs to capitalize on the benefits of each.

SYSTEM CONCEPT:
The close-coupled system is mounted directly on the stack via a sintered metal probe which draws the sample from the process. It provides the ease of maintenance/validation of a typical extractive system while approximating the response time of a true in situ system. Read more...

SYSTEM NAME: "FEED FORWARD"

MEASUREMENT(S):
hydrogen sulfide (high level)

DESIGN CHALLENGE:
In a sulfur recovery unit (SRU), the incoming feed gas can have highly variable levels of hydrogen sulfide. The key parameter to control in terms of process efficiency is the air demand (i.e., the amount of air required to combust the current concentration of H₂S in the feed gas). The process gas can also fluctuate dramatically in pressure and temperature, requiring a rugged sampling method.

SYSTEM CONCEPT:
The feed forward sample conditioning system is designed to handle the highly corrosive process gas with extremely resistant wetted parts. The temperature in the system is held high to prevent condensation of hydrocarbons or water. Since the pressure in the process can drop without warning, the system has a nitrogen-driven aspirator (since introducing air would create a volatile sample).

SYSTEM NAME: "OIL IN POND WATER"

MEASUREMENT(S):
trace petroleum

DESIGN CHALLENGE:
Since "oil" describes a complex mixture of hydrocarbons and other compounds, it is critical to establish an absolutely oil-free sample to use as the background reference. Specific deviations from the absorbance spectrum of this reference sample are registered as oil absorbance.

SYSTEM CONCEPT:
Since the pondwater composition can vary, the system had to continuously produce an oil-free background sample. For this objective, part of the incoming sample is routed through a special filtration clay that extracts all petroleum and subsequently directed to a dedicated vessel for oil-free sample. During the auto-zero procedure, the system automatically fills the flow cell from this continuously replenished "background" vessel, and reverts back to the real sample once the 60-second zero task is complete.

SYSTEM NAME: "BUFFER VESSEL"

MEASUREMENT(S):
hydrogen sulfide (0-2%)

DESIGN CHALLENGE:
The customer had various specifications for this SCS, including:

• NACE MR-0175
• ATEX zone 2 approval
• Flow switch
• Pressure relief valve
• Numerous ball valves for sample isolation

SYSTEM CONCEPT:
The system was designed to fulfill all the above requirements. Additionally, the system had to be held at high temperature to prevent condensation of water in the sample (dew point).

SYSTEM NAME: "TOTAL SULFUR LIQUID"

MEASUREMENT(S):
total sulfur compounds in liquid process

DESIGN CHALLENGE:
The diesel fuel process stream contains various sulfur compounds, some of which are unknown. An accurate total is required to know sourness level, but there is no feasible way to measure each contaminant separately.

SYSTEM CONCEPT:
The system continuously creates a precise air:sample ratio and flows this mixture into an industrial pyrolyzer. Through combustion, any and all sulfur compounds in the sample are converted to sulfur dioxide. The SO₂ concentration in the resultant sample is measured by a UV fluorescence detector. This value is directly correlated to the present total sulfur level in the diesel stream.

SYSTEM NAME: "HEADSPACE"

MEASUREMENT(S):
hydrogen sulfide in crude oil

DESIGN CHALLENGE:
The customer needed to measure H₂S directly in the crude. The light signal could not transmit through an as-is sample due to the opacity of the crude oil stream.

SYSTEM CONCEPT:
This opaque process stream required use of the "headspace" technique, which exploits Henry's Law to force part of the liquid sample into the gas phase. A carrier gas is flowed up through the temperature-controlled headspace column to carry a representative vapor-phase sample up to the flow cell for measurement. This principle only works when the compound of interest (in this case, H₂S) has a lower boiling point than other compounds in the crude. This gap in volatility makes headspace an excellent solution for H₂S-in-crude analysis.

Read more: Headspace SCS Brochure [pdf]