NOx Reduction Technologies
Environmental Compliance
Worldwide, emissions requirements are increasingly stringent, and in many areas regulations have sharply reduced allowable levels of nitrogen oxides and other greenhouse gas emissions from fired equipment.
A leader in environmental applications for the petrochemical and refining sectors, OnQuest has historically specialized in designing air pollution controls in conformance with the State of California's environmental compliance regulations. As a result, our professionals are highly aware of agency oversight; we have for years specialized in designing furnace applications that incorporate technologies to reduce NOx emissions, volatile organic compounds (VOCs), and hazardous air pollutants (HAPs).
A number of methods—including both pre- and post-combustion technologies—can be used to achieve lower emissions levels during start-up and operation of furnaces, heaters, kilns, and process plants, and in retrofitted equipment.
Burner Technology I: Efficiently Preventing Emissions
The designs for new and evolving ultra-low NOx burners largely rely on lower flame temperatures and longer flames to minimize the formation of thermal NOx while maintaining radiant heat transfer performance. These parameters need to be taken into account during design; the dimensions of fired compartments are frequently not the same as they were a few years ago.
Burner Technology II: Retrofits of Older Fired Equipment
Many existing heaters can be retrofitted with ultra-low NOx burners to achieve NOx levels as low as 25 ppm(v). In special cases, emission levels may be even lower. However, incorporating these technologies requires precise design engineering and construction oversight; retrofitting an existing burner design is rarely a straightforward one for one "change-out" of the burners.
Burner Technology III: Oxy-Fuel Burners
In some industries, it is economical to use oxygen for combustion instead of ambient air, for a hotter flame with minimal thermal NOx formation, and bare minimum volumes of combustion products. OnQuest's engineers are experienced with these situations, and the economical application of oxygen-fueled burners using either VPSA = 95% pure or cryogenic = 99.9% pure oxygen.
The Ultra-Low Alternative: Selective Catalytic Reduction
In some jurisdictions, regulatory constraints on allowable emissions are particularly tight. When requirements approach the single digit ppm(v), another method for effectively reducing NOx is to use a selective catalytic reduction unit, or SCR.
SCR can be applied in conjunction with selective non-catalytic reduction—the injection of ammonia or urea at a higher temperature to "shave" the NOx concentration peaks. When used upstream of an SCR unit, the emissions of un-reacted ammonia ("ammonia slip") are held to the absolute minimum.
OnQuest is also developing applications of a lower-temperature SCR unit, known as cold SCR or CSCR. This technology can have significant benefits for thermal efficiency, as flue gases can be treated after economizer or waste heat recovery units, with exhaust gas temperatures of about 200 - 300°F (95 - 150°C). The CSCR technology can be used to treat a flow made up from several process streams combined.
The key to success with these reduction techniques is the injection of the ammonia such that it gets evenly distributed throughout the flue gas stream. OnQuest's engineers have the experience to ensure the best results for your project.
OnQuest has a proven track record of designing innovative retrofits of existing heaters to accommodate SCR units. In cases where space is constrained, we have also successfully integrated pressure-drop requirements, and instrumentation and controls for ammonia injection.
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