Total Sulfur Gas Analyzers

Application Summary: Total Sulfur Direct

• Measurement: Total Sulfur (up to 5 sulfur compounds)
• Detector: OMA-300 Process Analyzer
• Process Stream: hydrocarbon fuels

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Technology: Total Sulfur Direct

The ASTM method for total sulfur analysis calls for oxidation of all present sulfur compounds to sulfur dioxide for straightforward measurement. When a stream contains many different sulfur species, or unknown exotic sulfur compounds, this method is usually the only option.

The OMA-300 Total Sulfur Direct Analyzer takes a different approach, measuring up to 5 sulfur compounds directly in the unaltered sample using powerful multi-component analysis software and a high-resolution UV-Vis spectrophotometer.

The OMA-300 Total Sulfur Direct has compelling benefits for the process operator:

• Richer data through individual concentration measurement of each constituent sulfur species
• Decades of proven reliability measuring multiple sulfur compounds simultaneously
• Highly suitable for natural gas applications (e.g. pipeline gas)

Sulfur Compound Absorbance Curves

Any single photodiode measurement is vulnerable to noise, signal saturation, or unexpected interference. This susceptibility to error makes a lone photodiode data point an unreliable indicator of one chemical’s absorbance.

As accepted in the lab community for decades, the best way to neutralize this type of error is to use collateral data in the form of ‘confirmation wavelengths,’ i.e. many data points at many wavelengths instead of a single wavelength:

In the figures above, each diamond represents a single photodiode and data point. The OMA measures absorbance at each integer wavelength within the measurement wavelength range and produces analyte absorbance curves. This use of ‘confirmation wavelengths’ instead of simple peak absorbance measurement serves to eradicate the effect of noise at any single photodiode, allowing for much more accurate analysis free from cross-interference with light.

Multi-Component Total Sulfur Analysis

Each photodiode supplies one data point of absorbance information at an integer wavelength. The OMA’s ECLIPSE software continuously solves a matrix of equations from all these data points simultaneously to de-convolute each compound’s absorbance curve from the total sample absorbance:

In the analysis, we use a 4-component equation:

A’_(w+x+y+z) = A’_w + A’_x + A’_y + A’_z = e’_wbc_w + e’_xbc_x + e’_ybc_y + e’_zbc_z

where A’ is the absorbance at wavelength ‘, e’ is the molar absorptivity coefficient at wavelength ‘, c is concentration, and b is the path length of the flow cell. In the image above, four such equations (at 216nm, 217nm, 218nm, and 219nm) are shown. In reality, the matrix includes one equation from every single integer wavelength in the measurement wavelength range.

This matrix of data from many wavelengths provides far more accurate multi-component analysis within a spectral region that has heavily overlapping absorbances from each analyte.

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Specifications: Total Sulfur Direct

Note: All performance specifications are subject to the assumption that the sample conditioning system and unit installation are approved by Applied Analytics. For any other arrangement, please inquire directly with Sales.

• General
• Performance
• Certifications

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Resources: Total Sulfur Direct

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Applications: Total Sulfur Combustion

Sulfur compounds--particularly hydrogen sulfide--in natural gas carry with them a host of problems and considerations for both producer and consumer. Sulfur content is known to:

• Cause pipeline corrosion, jeopardizing distribution networks and necessitating complex maintenance regimens
• Officially reduce the quality of sales gas; natural gas quality assurance involves monitoring of sulfur content, e.g. at custody transfer points
• Contribute directly to SO₂ emissions from gas-burning plants; SO₂ is a widely regulated pollutant and a necessary concern for avoiding fines and fulfilling social responsibility
• Introduce unpleasant odors to gas-dependent industrial and domestic environments; mercaptans are added to natural gas to make leaks noticeable by smell, but uncontrolled sulfur content turns the odor from useful to intolerable

Avoiding these chronic sulfur-related issues requires reliable online monitoring of total sulfur load in gaseous hydrocarbon streams. The only way to verify the efficiency of sulfur removal processes and ensure satisfaction of customer and environmental needs is to proactively analyze stream composition.

The TSA-200 is a fully integrated monitoring solution driven by UV-Vis diode array detection. This solid state instrument is much more practical than the consumable-laden designs that have historically dominated the market.

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Technology: Total Sulfur Combustion

Principle of Operation

The TSA-200 uses an ultraviolet-visibile (UV-Vis) spectrophotometer to measure the resultant SO₂ concentration after pyrolysis. This method is known to be highly resistant to false positives; full-spectrum analysis quickly removes erroneous data using averaging algorithms.

The TSA-200 uses a long-life xenon light source to transmit a signal through the sample fluid in the flow cell. The signal is carried by fiber optic cables from the analyzer to the flow cell, where the chemical mixture of the sample has unique interactions with the light based on its current composition.

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Sampling: Total Sulfur Combustion

The TSA-200 sample conditioning system is designed primarily for controlled combustion of the sample.

Upon entering the TSA-200, the sample is split via tee into a bypass loop and a sample loop. In the sample loop, two mass flow controllers are used to accurately mix the sample with air, ensuring an optimal air/fuel ratio for combustion.

The sample/air mixture flows through a pyrolysis furnace, where all present sulfur compounds are converted to sulfur dioxide:

R-S + R-H + O₂ > SO₂ + CO₂ + H₂O

The fully oxidized sample then enters the measurement flow cell where SO₂ absorbance is monitored (via fiber optic cables). Finally, the sample exits the system as waste.

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Specifications: Total Sulfur Combustion

Note: All performance specifications are subject to the assumption that the sample conditioning system and unit installation are approved by Applied Analytics. For any other arrangement, please inquire directly with Sales.

• General
• Performance
• Certifications

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Resources: Total Sulfur Combustion

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