Measuring H2S in Scrubber Outlet Gas

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Application Summary

Analytes H2S (hydrogen sulfide)
Detector OMA-300 H2S Analyzer
Process Stream scrubber outlet gas
Typical Range 0-10 ppm

Introduction

Removing toxic, corrosive H2S from hydrocarbon fuels is a universal undertaking to protect environment, equipment, and humans. Myriad technologies exist for this purpose, ranging by parameters like throughput and H2S level in the feed.

While any such removal operation can benefit from validation of the H2S-free ‘sweetened’ stream, the amine scrubber is a specific technology where online H2S measurement is highly cost-effective. In this process, an amine solution absorbs H2S from the sour gas feed, producing a sweetened gas stream which exits the absorber.

Over time, the amine solution becomes saturated (rich) with H2S and can no longer effectively sweeten the incoming gas. At this point, the amine needs to be sent to the regnerator to be converted back to lean amine. H2S breakthrough in the scrubber outlet gas can result from scrubbing with a rich amine or other problems with the process. Measurement of H2S at this sampling point is necessary to monitor breakthrough.

The OMA H2S Analyzer provides this continuous measurement with fast response and automated reliability. This system allows the operator to maximize the amine lifetime between regeneration cycles (saving power costs of reboiling) and ensure that H2S breakthrough is rapidly addressed.

Applied Analytics also offers the OMA H2S Analyzer for the following applications within the amine scrubber process:

H2S Absorbance Curve

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:

Measuring H2S in Scrubber Outlet Gas--spectra

In the figures above, each diamond represents a single photodiode and data point. The nova II registers absorbance at each integer wavelength within the 210-250 nm measurement range and produces an H2S absorbance curve. After being calibrated on a full spectrum of pure H2S, the OMA knows the absorbance-concentration correlation for each measurement wavelength; the system can average the modeled concentration value from each wavelength to completely eradicate the effect of noise at any single photodiode.

The OMA visualizes the H2S absorbance curve in this manner and knows the expected relation of each data point to the others in terms of the curve’s structure. This curve analysis enables the OMA to automatically detect erroneous results at specific wavelengths, such as when a single photodiode is saturated with light. The normal photometer, with a single data point, is completely incapable of internally verifying its measurement.

Example Installation

The systems below measure H2S at the inlet (0-5,000 ppm) and outlet (0-50 ppm) of a desulfurization process in Colombia:

Measuring H2S in Scrubber Outlet Gas--Field-Photo-desulfurization-process

Measuring H2S in Scrubber Outlet Gas--Field-Photo-desulfurization-process

The specifications below represent performance of the OMA-300 Process Analyzer in a typical scrubber 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 (@10 bar): ±0.1 ppm
0-10 ppm: ±1 ppm
0-100 ppm: ±1% full scale or 1 ppm*
0-10,000 ppm: ±1% full scale
*Whichever is large.

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

Further Reading

SubjectType
OMA-300 H2S AnalyzerBrochure
OMA-300 Process AnalyzerData sheet
AN-025: Lean Amine / Rich Amine AnalysisApplication Note
Advantage of Collateral DataTechnical Note