Find

① 5NO + 2ClO₂ + 2H₂O → 2HCl + 5NO₂

② 5NO₂ + ClO₂ + 3H₂O → HCl + 5HNO₃

① + ② (combined) 5NO + 3ClO₂ + 4H₂O → 3HCl + 5HNO₃

On a molar basis, 5 moles NO reacts with 3 moles ClO₂. On a mass basis, 1 g of NO requires 1.35 g of ClO₂.

The reaction is more than 90% complete in 1-3 seconds.

Waste gas with NOx present flows through a duct. Dioxide Pacific will engineer a patented mixing device for installation into the duct to suit the gas mixture, flow and chlorine dioxide dose. Chlorine dioxide is generated using the Electricide^® electrochemical chlorine dioxide generator and dosed directly into the gas stream prior to the mixer. If the duct dosing point is under vacuum, the generated gas stream will suck through the generator into the duct. If there is a positive pressure in the duct, a vacuum pump is used to inject the ClO₂/air mix. Chlorine dioxide immediately reacts with NO and NO₂ according to reactions 1 and 2 above.

After injection and mixing, ClO₂, NO and NO₂ concentration are measured with online analyzers. The Electricide generator automatically regulates the mass of ClO₂ generated using PID or FPRT control using an entered setpoint for discharged NO. The aim is to control NO concentration to the lowest acceptable concentration and not have any ClO₂ slip.

If neutralisation of the HCl and HNO₃ is required, the treated gas can be directed to a caustic scrubber.

• The Electricide^® generator makes ClO₂ gas.  ClO₂ gas is generated and extracted using air to produce a very pure and safe ClO₂+air gas mixture. Since it already generates ClO₂ in air, this gas stream can be connected directly to the duct. No additional sparges or gas handling systems are required.
• Single precursor chemical. The Electricide^® generator produces chlorine dioxide from a single precursor chemical: Electricide-P1. The use of one precursor chemical makes it safe and simple for operators.
• All controls included with the generator. The PLC + HMI control for operation of the generator; monitoring ClO₂ and NOx concentration and remote access is included as part of the standard system.|
• Proven technology. It is proven for more than 5 years in successful operation.

This system of NOx destruction is protected under a number of US and international patents. The patents are licensed to Dioxide Pacific.

We can engineer a turnkey solution for NOx destruction to include chlorine dioxide generation and injection; measurement and control; chemical handling and chemical scrubbers if required. Our project quality management system ensures the plant will be installed on time, with the smallest possible interruption to your site. We have proven risk management protocols written specifically for chlorine dioxide systems to ensure that installation, commissioning, training and operation of the plant is extremely safe.

Dioxide Pacific supplied an Electricide^® CDE-150 chlorine dioxide generator to a metal finishing plant in California in 2012. The process periodically generates NO + NO₂ gas which is collected in a fume hood and treated in a chemical scrubber employing sodium hydrosulfide and sodium hydroxide. The scrubbing system was effective in treating NO₂ as this gas is very soluble. However, NO is quite insoluble and was not removed in the scrubber.

In order to comply with license conditions imposed by the AQMD for low discharge concentration of NOx, the chlorine dioxide system was installed under an R&D permit. Over 5 years, the chlorine dioxide system demonstrated the ability to reduce NOx to zero (if required) with zero ClO₂ slip. The requirement is for NOx reduction to less than 9 ppm, which is easily achieved. Gas flow is variable (12,000 – 38,000 cfm) and NOx concentration varies continuously 0 – 50 ppm. The chlorine dioxide generator control system includes a suitable algorithm to regulate ClO₂ dose to achieve the discharge NOx setpoint without over or under-dosing. The R&D permit was converted to a license permit in early 2018.

Typically, NO and NO₂ : (NOx) Reduction can be achieved using a variety of processes:

Typical applications for NOx destruction with chlorine dioxide include the following:

• Fuel combustion: Flue gas produced from the burning of fuels can contain 100-1500 ppm of nitrogen oxides.
• Nitric acid manufacture
• Metal finishing operations: Any surface treatment operations that use nitric acid, nitrites or nitrates can cause production of NOx. Examples: pickling, phosphatising, bright dipping.
• Chemical processes involving nitric acid, nitrites or nitrates such as manufacture of dyes, plastics and explosives can form nitrogen oxides as a by-product.
• High temperature processes such as boilers, furnaces and kilns can produce nitrogen oxides.