Air Emission Treatment Technologies

NOx Overview

Nitrogen Oxides represent a group of seven similar compounds consisting of Nitrogen and Oxygen often referred to as NOx. Nitrogen Oxides are released into the air from the burning of hydrocarbon based fuel sources. Nitrogen Oxides can cause damage to the environment including tropospheric ozone (O3) formation, acidic rain, atmospheric particulate formation, and nutrient pollution in aquatic ecosystems. Nitrogen Oxides, Nitrogen Dioxide (NO2) in particular, can also irritate or damage the respiratory system in humans and cause or aggravate respiratory conditions. Due to the damage Nitrogen Oxides can cause, there is an effort in all industries to minimize the atmospheric release of Nitrogen Oxides during any activity. Hydrocarbon based burning processes typically produce mainly NOx in the form of Nitric Oxide (NO) and secondarily Nitrogen Dioxide (NO2). As such both species are of interest since they are typically generated during abatement of chemical process exhaust streams produced during industrial manufacturing. Nitrogen Oxides can be produced in the manufacturing process or in the exhaust treatment process by combustion abatement units. Supplementally, other EPA regulated compounds such as sulfur dioxide and sulfur trioxide are also produced in these same manufacturing processes. These sulfur-based compounds are referred to as SOx and cause similar negative impacts to the environment as NOx emissions.

Most commonly, NOx and SOx emissions are treated in high temperature applications through Selective Catalytic Reduction (SCR) processes which utilize urea-based chemistry at high process temperatures to treat NOx and SOx emissions in order to comply with regulatory requirements. There are however low temperature manufacturing processes that cannot economically utilize SCR based technology due to the required energy input needed to complete the treatment process. Furthermore, many of these low temperature manufacturing processes have organic contamination which can foul traditional SCR process equipment. As a result, there is an industry need for treating low temperature produced NOx and SOx emissions. The most common industry process for treating low temperature NOx and SOx is the utilization of multi-stage scrubbing processes where the first stage employs an oxidation chemistry to convert Nitric Oxide to Nitrogen Dioxide, then the produced Nitrogen Dioxide is absorbed in the subsequent scrubbing process thus being released into the atmosphere as Nitrogen. Additional scrubbing equipment may be employed to address odors from the chemical reactions produced in the first two steps of the treatment process. While effective at treating NOx and SOx emissions, multi-stage scrubbing requires more equipment, a larger physical footprint, increased water utilization, and subsequently increased chemical use. Retrofitting existing facility exhaust systems to a multistage scrubbing system can present significant structural engineering and CAPEX challenges. As a result, operating and capital equipment costs of multi-stage scrubbing solutions can be expensive and in some cases cost prohibitive. For these reasons, there is an industry need for a novel solution to cost effectively treat low temperature NOx and SOx abatement applications.

ApHinity exhaust gas abatement treatment technology involves the utilization of a newly patented simplified process where nonionic gaseous phase chlorine dioxide is combined with an organic scrubber additive used to remove nitrogen oxides and sulfur oxides from fume exhaust systems. Pure nonionic gas phase chlorine dioxide produced by single precursor electrolytic generation reacts with NOx compounds more chemically efficient versus traditional wet scrubber water phase chemical oxidant reactions. The process is unique in that the first step of gas phase chlorine dioxide reaction with nitric oxide is performed in existing ductwork as opposed to reacting in a wet scrubber. This saves the cost of adding scrubber equipment for the first stage of the process. The second step of the reaction employs the organic catalyst which occurs in a single stage scrubber equipment thus, no additional scrubber or scrubbers are required resulting in lower capital cost as well as lower operational cost. Water footprint and chemical utilization is kept to a minimum. Typically, 95% or greater NOx DRE is achieved when treated with this gas phase plus organic catalyst treatment approach. The end result is a simple, effective, and economical removal process. NOx treatment levels between 10 ppm and 60,000 ppm can be efficiently and economically achieved.