Measuring H2S And SO2in Flue Gas - Applied Analytics

Introduction

Power plants and refineries are required to monitor and regulate the flue gas released from the burning of fossil fuels because this gas is released directly into the environment. A certified CEMS (Continuous Emissions Monitoring System) is enormously expensive to implement and maintain, so many operators choose to install affordable emissions analyzers and have the results audited yearly by a government agency.

H2S and SO2 are two highly controlled pollutants which are commonly found in flue gas from hydrocarbon fuel combustion. H2S occurs naturally in many fossil fuel reserves as well as biogas, and oxidizes to SO2 in combustion. Legal requirements for monitoring the emissions of both chemicals are growing increasingly stringent with increasingly severe punitive measures for exceeding the required limits. As the world energy industry delves deeper into sour gas reserves, the emphasis on regulating these specific emissions is bound to grow.

The OMA system provides fast response measurement of H2S and SO2 in the flue gas stream for tight emissions control. Providing excellent detection limits in a solid state package, the OMA is a highly practical solution for a facility that needs reliable emissions monitoring but lacks an astronomical budget for analyzers and maintenance.

OMA Benefits: H2S and SO2 in Flue Gas

• Measures sulfur compound concentration using solid state, consumable-free technology
• Close-coupled sample conditioner provides fast response with easier maintenance than cross-stack
• Scalable measurement allows later addition of analytes and modified concentration ranges
• Decades of field-proven performance in demanding flue gas applications

H2S and SO2 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:

The figures above demonstrates how the OMA ‘learns’ the absorbance curve structure of each analyte through a full-spectrum calibration on a standard concentration mixture. Using the measurements from each photodiode (each circle in the curve represents a single photodiode providing a data point at an integer wavelength), the OMA knows the expected relation of each point in the absorbance curve and automatically eradicates erroneous results.

This full-spectrum measurement also allows the OMA to easily de-convolute the overlapping absorbance curves of H2S and SO2 to accurately isolate the absorbance of each. This capability is unique to spectrophotometers and ensures that there will be no false positive sulfur compound readings, while also preventing cross-interference between the two components.

Close-Coupled Sample Conditioner Design

The OMA flue gas analyzer is paired with a close-coupled sample conditioner which is mounted directly on the stack via a sintered metal probe which extracts the sample. This design has extremely fast response due to the minimal sample route, yet is far easier to install and maintain than a cross-stack method (no issues with optical alignment or span gas validation).

Example system: close-coupled SCS for measuring H2S in flue gas.

Schematic: close-coupled mounting.

Example Installation: close-coupled OMA system analyzing flue gas at a manufacturing site.

The specifications below represent performance of the OMA-300 Process Analyzer in a typical flue gas application.

For technical details about the OMA-300 Process Analyzer, see the data sheet: DS-001A: OMA-300 Process Analyzer

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.

Application Data
Performance Specifications
Accuracy	Custom measurement ranges available; example ranges below.
	H2S	0-10 ppm: ±1 ppm0-100 ppm: ±1% full scale or 1 ppm*0-10,000 ppm: ±1% full scale
	SO2	0-100 ppm: ±1% full scale or 1 ppm*0-10,000 ppm: ±1% full scale
	*Whichever is larger

Note: Subject to modifications. Specified product characteristics and technical data do not serve as guarantee declarations.

Further Reading

Subject	Type
OMA-300 CEM System	Data Sheet
Advantage of Collateral Data	Technical Note
Multi-Component Analysis	Technical Note

OMA H2S Analyzer