Electricide CDE-10 electrochemical chlorine dioxide generator for gas phase NOX destruction
NOx Destruction Chlorine Dioxide Systems

Are you looking for NOx reduction strategies to reduce charges or obtain license compliance? We can help.

NOx is a term representing nitrogen oxide compounds: primarily nitric oxide (NO) and nitrogen oxide (NO2). NO and NO2 are considered atmospheric pollutants as they contribute to smog and acid-rain. Many State and Federal environmental authorities throughout the world impose strict regulations on the maximum concentration (ppmv) and mass (kg per day/year) that sites can discharge into the air. In some cases, there are fines for exceeding concentration limits and taxes on mass discharge.

NOx destruction with chlorine dioxide is efficient, fast and cost effective.

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:

Treatment Type Advantages Disadvantages
Chlorine Dioxide Destruction using patented system
  • Very quick reaction with high reaction efficiency
  • Low capital and running cost
  • Flexible process for varying contaminant concentration in air. The process can ramp up and down to meet demand quickly and automatically.
  • Small footprint
  • Can be combined with existing wet scrubbing to reduce running cost
  • Also removes SO2
  • Rugged with respect to other presence of other contaminant gases
  • Low temperature process – maximum 40ºC. May require pre-cooling if application is from a thermal process
Wet Scrubbing
  • Single, 2 or 3 stage versions can be used and they are relatively simple to install
  • Well known technology
  • NO2 is very soluble and easily reacts with sodium hydrosulfide and caustic
  • NO is sparingly soluble in water so difficult to remove in a scrubber
  • Large footprint
  • Storage and handling of different types of chemicals – some Dangerous Goods
  • TDS bleed from scrubbers must go to waste
SCR (Selective Catalytic Reduction)
  • When operating, running cost is low
  • Requires proprietary catalysts and reducing agents (methane or ammonia)
  • Capital cost is high
  • Requires high temperature for efficient operation
  • Solid particulates in air discharge
  • Catalyst can become fouled or destroyed in presence of some compounds
Adsorption using GAC (activated carbon), zeolites, copper or zinc oxide
  • Simple installation
  • Low capital cost
  • Media can become quickly saturated, requiring media replacement or regeneration with heat or chemicals. High running cost for large air and NOx flows

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.

Do you have an application in mind or want further information? Complete the form at our Contact Us page.