Gas analysis supports a wide range of cleaner air initiatives in hydrocarbon processing. Plant operators are becoming increasingly sensitive to their contribution to greenhouse gas emissions, with this awareness driven by ever stricter environmental regulations and pressing international action, such as the 2016 Paris Agreement, designed to reduce industry’s impact on the climate.
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Many plants are turning to gas analysis systems to support efforts to operate in an ecologically responsible way and reduce emissions.
Plants must leverage a combination of combustion efficiency, gas cleanup, and emissions monitoring solutions in order to achieve these goals. This approach not only ensures that air remains clean, but it is also key to optimizing processes, reducing fuel consumption, and achieving higher yields in hydrocarbon processing.
Effective Combustion Control
Combustion is central to many hydrocarbon processing applications, and there are currently no tangible alternatives to generating the extremely high temperatures required. The combustion reaction sees fuel mixed with oxygen (from air) in a fired heater, delivering heat energy that can then be transferred to different parts of the process.
This reaction generally requires a considerable amount of fuel, as well as generating harmful emissions and creating potential safety hazards.
Optimizing the ratio between air and fuel is key to ensuring the most efficient reaction. Fired heaters were generally run in high excess air conditions before the advent of gas analyzer technology, but this approach was inefficient and led to increased fuel consumption. It did avoid the unsafe conditions that could potentially lead to an explosion, however.
Excess oxygen (O2) can also combine with nitrogen and sulfur present in the fuel, producing undesirable emissions including oxides of nitrogen (NOx) and sulfur (SOx). Accurate gas analysis of oxygen and combustibles like carbon monoxide (CO) has enabled an improved approach to balancing the air-to-fuel ratio and managing the combustion reaction.
Effectively controlling combustion offers a wide range of benefits, especially for plants seeking to meet requirements set by environmental standards. It also ensures reduced fuel consumption, resulting in fewer emissions, less NOx, SOx, and CO, and a reduction in the greenhouse gas carbon dioxide (CO2).
Zirconia-based sensing technology has long been a popular solution for O2 monitoring in combustion, providing accurate, reliable results with a rapid response to shifting conditions.
A combustibles sensor can be added inexpensively and with ease, offering an all-in-one combustion control solution. Servomex’s SERVOTOUGH FluegasExact 2700 combustion analyzer is an example of such a system.
Tunable Diode Laser (TDL) technology has recently emerged as an ideal solution for this application, offering even quicker measurement, especially for carbon monoxide. TDL technology also delivers an average measurement across the measurement path, as opposed to the result at a single point.
TDL sensing is highly specific to the gas being measured, meaning that separate analyzers will be required for O2 and CO.
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Servomex’s SERVOTOUGH Laser 3 Plus Combustion TDL analyzer has been specifically designed for this application, providing a rapid-response measurement for safety in natural gas-fired heaters and boilers. It is possible to configure this analyzer to measure either O2 or CO, or for a joint measurement of CO and CH4.
Gas analysis is also employed in a wide range of applications to improve process efficiency and help ensure cleaner air. The more efficient a process reaction is, the less harmful emissions tend to be generated.
For instance, the fluid catalytic cracking (FCC) unit is one of the most significant sources of air emissions in a refinery. The FCC unit requires multiple gas measurements across the process, typically requiring a process control oxygen measurement in the regenerator off-gas, where low O2 results in incomplete combustion (and, therefore, removal) of the catalyst coke, and excess O2 lowers the lifespan of the catalyst.
Measuring CO and CO2 in the same off-gas helps plant operators to calculate catalyst coke formation, enabling the determination of catalyst regeneration efficiency.
Excess O2 and CO levels must also be monitored in the regenerator flue gas, and ammonia slip must be measured at the selective catalytic reduction (SCR) outlet in order to manage the NOx removal process.
The application of an appropriate technology will benefit each point of this process. For instance, the off-gas measurements for O2 and NH3 slip benefit from the use of TDL open-path measurements, which reduce issues with catalyst particulates experienced by in situ or simple extractive systems.
The FluegasExact 2700 and other close-coupled extractive systems represent reliable and cost-effective means of measuring O2 and combustibles (COe) in flue, while the SERVOTOUGH SpectraExact 2500 is ideally suited to measuring off-gas CO and CO2.
Cleaning Process Gases
The second phase of Servomex’s clean air strategy is focused on gas cleaning. Gas cleaning is the removal of harmful substances from process gases that would otherwise be emitted by the plant. Ammonia slip treatment and flue gas desulfurization are common applications within this area.
Ammonia Slip Treatment
Ammonia or urea is used to suppress the harmful NOx emissions from combustion, either via SCR or a selective non-catalytic reduction (SNCR) process. Both of these methods necessitate accurate ammonia dosing in order to reduce NOx levels. The use of insufficient NH3 will result in NOx emissions not being sufficiently suppressed, while the use of too much NH3 can eventually lead to the formation of ammonium bisulfate.
Ammonium bisulfate is a white powder with the potential to plug the catalyst in SCR processes, reducing the value of the fly ash by-product, and resulting in equipment damage. It is, therefore, essential that plants efficiently manage NOx removal processes in order to maintain a level of ammonia slip of 2-3 ppm ammonia.
It is possible to monitor ammonia via extractive sampling, but this is challenging because it is necessary to keep the sample above 290 °C to prevent the formation of sulfuric acid and ammonium bisulfate.
Measurement can also be impacted by inlet NOx concentration, catalyst performance, and fuel composition, while infrared-based extractive systems may also be affected by signal interferences from high levels of dust and from gases formed by the process.
A TDL analyzer is a more effective solution for these types of applications. The SERVOTOUGH Laser 3 Plus Environmental can be installed directly into process ducts to provide an average signal across the duct, delivering a more accurate NH3 reading even when flow conditions are uneven.
Flue Gas Desulfurization
A flue gas desulfurization (FGD) system removes sulfur compounds (SOx, primarily SO2) from exhaust gases. This process is typically employed by fossil fuel power plants and operators in other SOx-emitting processes.
Acknowledgments
Produced from materials originally authored by Sangwon Park Servomex Group Limited.
This information has been sourced, reviewed and adapted from materials provided by Servomex.
For more information on this source, please visit Servomex.