Biozone Manufacturing

nitrous oxide abatement

NOx Nitrous Oxide Abatement

A carbon credit opportunity to investors

It has been universally accepted that  the existence of man-made climate change is beyond doubt, and that there should be a global  system  of  emission  caps  and  carbon  emissions  trading  applying  to  both industrialised nations and developing countries. 

The Kyoto Protocols have now been superseded with new and projected emissions in place. 

In 2009 emission limits set for Nitrogen Oxides (NOx) was 50 – 150 mg/m³ with the intention to reach the lower limit by 2012. It was anticipated that more stringent emission targets will be used in the years beyond 2012.  

Currently (2008) the World Bank set the emission limits for nitrogen oxides based on NO2 and is 200 mg/m3.

Yet many if not all Nitric acid, smelter, coal fired, municipal waste, blast furnace, cement kilns and paper mill plants exceed these every day.

The World Bank lists the Best Available Technology (BAT) as Selective Catalytic 

Reduction  (SCR)  which  presents  many  problems  because  it  has  an  optimum temperature operating range of 300 to 400 ºC. 

Many gas streams will have to be heated to this temperature and therefore have high energy costs associated with the process. 

In addition, the heating process will create thermal NOx and is therefore limited and would probably not achieve the near zero NOx emissions envisaged by the IEA Clean Coal Centre in the United Kingdom. 

This organisation is of the opinion that near zero NOx emissions will be in place for new plants over the next five to ten years. 


The system introduced here is a NOx removal system that uses ozone, injected into the flue gas stream, at low temperature, to oxidize NO to oxidised compounds that can be more easily processed. Ozone can be produced on site and on demand by passing oxygen through an ozone generator. 


•    Needs ammonia 

•    High energy cost 140kJ/g NOx removed 

•    Needs Catalyst 

• NOx reduction 75 – 90 % 

•    Ammonia slip 

•    CO2 produced during heating 


  • Needs oxygen 
  • Cooling water
  • Energy cost 52 kJ/g NOx removed
  • NOx reduction estimate 90+%


  • NOx is one of the major pollutants in the air. It is directly related to acid rain, smog, ozone depletion, and global warming (N2O). 

At the same time, high NOx can lead to severe damage to the human 


NOx includes N2O, NO, NO2, N2O3, N2O4, NO3 and N2O5, among which NO and NO2 are the most steady forms. 

These compounds trigger a series of chain reactions that lead to smog and ozone depletion.

The Ozone Oxidation Denitration process is a wet scrubbing process. 

NO is indissoluble in water, but both NO2 and N2O5 are soluble, and react with alkaline to form steady inorganic salts. 

After oxidizing NO to a higher valence state with ozone, it is easy to remove NOx with alkaline solution. This process does not require high temperatures. 

This method has the following merits:

  •  No requirement for high temperature
  • High and consistent efficiency (>90%)
  • The oxidation and scrubbing process is consistently effective and predictable in removing NOx. 
  • Small footprint

The reaction of ozone with NO occurs in a scale of 0.1s, thus a small reaction chamber is enough for the reaction to finish. An air scrubber is needed to finish the process. 

Therefore, it is easier to integrate the system into an existing facility.

  •  Simple automation.

Nowadays, large ozone generators are controlled by precise automation, and the ozone production can be finely tuned in a quick manner. 

This, combined with the fact that the ozone reaction with NO is a fast reaction, makes the Ozone Oxidation Denitration process an easily automated one.

 It is thus possible to fine tune the ozone production according to the NO concentration measured at the outlet of the treatment system.

Potential market 

It is difficult to measure the size of the environmental markets because the legislation is anticipated and not yet enforced. 

The size of the NOx abatement market in the USA was estimated at $ 3.5 billion USD in 2009 without the stringent controls on other pollutants such as SOx. 

Environmental Market Magazine February 2007 indicated the SOx abatement market is $ 41 billion USD. 

Fortune Magazine reported in 2002 that over 2000 SOx abatement systems were installed at power plants in the USA since the legislation came into effect ten years earlier. 

South Africa, as one of the five top emerging economies and a participant in the Washington Climate Change Dialogue will need to get tougher on its major polluters.  

Existing opportunities in Africa

Anglo platinum started looking into the problem in 2007. The idea was to set-up an experimental system to see if the NOx emissions could be brought down to 6mg/m3. 

This was done by setting up an ozone based NOx abatement system at the PF Retief Laboratory  in  Rustenburg.

A  second  test  at  another  one  of  their  laboratories  in Potgietersrus was planned. All of the equipment (scrubber, feed tank, effluent tank, ozone generator, five pumps and three fans) was delivered to site but never connected. 

The opportunity to do the first local test still exists.  

Sasol’s Nitric Acid production plant wants to achieve a NOx emission of 90 mg/m3 by installing an SCR system supplied by NORAM.  


  • A  joint  development  program  between Biozone Manufacturing, a local gas ( oxygen supplier) and a Mechanical Engineering should be investigated. 
  • Attempt to secure a South African Project requiring a carbon friendly solution.
  •  Penetrate international markets using the South African Projects as reference. 
  • The development needs to be accelerated to have viable reference plants ahead of anticipated legislations. 


SCR technology 

The current technology used in all industries is SCR as mentioned in the introduction. 

In addition to the high energy costs associated with this technology there are several other  problems  associated  with  it.  

This  is  evident  when  looking  at  the  process of chemistry.  

The  SCR process  for  the  removal  of NOx  is based  on  the  following 


4NO + 4NH3 + O2  4N2 + 6H2O                                                    

NO + NO2 + 2NH3  2N2 + 3H2O                                                   

6NO2 + 8NH3  7N2 + 12H2O                                                          

2NO2 + 2NH3  N2 + H2O + NH4NO3(s)  

Ammonia slip

A variation in the quantity of NOx in the emissions presents problems for the SCR 

system. The reason is that for the system to be effective the ammonia reactant needs to be supplied in the exact stoichiometric amounts.

 If too much ammonia is fed the excess will be released into the environment. Ammonia is a very harmful substance and this should be avoided. If the ammonia is not supplied in excess the SCR system’s efficiency drops and near zero NOx emissions cannot be reached. 

Produces CO2

The optimum temperature range for the reaction to take place is 300 – 400ºC, as 

mentioned previously. In order to reach this temperature gas burners are used and large amounts of CO2 are generated. 

This process is simply exchanging one problem for a few others. 

Produces thermal NOx

One of the mechanisms by which NOx is created is during the burning of natural gas to generate heat. This process therefore creates NOx in order to remove it and the NOx removal efficiency will be limited.  

Ozone technology 

The system is a NOx removal system that uses ozone, injected into the flue gas stream to oxidize insoluble NOx to soluble oxidised compounds. 

Ozone can produced on site and on demand by passing oxygen through an ozone generator. Ozone rapidly reacts with insoluble NO and NO2 molecules to form soluble N2O5. The species N2O5 is highly water soluble and will rapidly react with moisture in the gas stream to form nitric acid.  The conversion of NOx into the aqueous phase in the scrubber is rapid and  irreversible,  allowing  nearly  complete  removal  of  NOx.    

It  is  based  on  the following reactions: 

NO + O3  NO2 + O2                                                                                                           

NO2 + O3  O2 + NO3                                                                                                         

NO3 + NO2  N2O5                   

The nitric acid can either be recovered for example in a nitric acid production facility or neutralised by simple alkaline scrubbing.  

Technology comparison  

The two technologies will be compared on the basis of equipment cost and energy costs. The environmental impact of the two systems was discussed in the previous sections. 

Equipment cost 

Based on the Sasol Nitric Acid Plant 95% NOx Removal 

2.3 kg/h NO & 1.4 kg/h NO2

• SCR (Selective Catalytic Reduction) system by NORAM 

Quoted price SCR unit R 3 900 000.00 

• Ozone generator required for the same removal efficiency 

Quoted by Biozone Manufacturing

Quoted price Ozone generator R 1 485 319.75 

The SCR unit costs 263% more than the equivalent Ozone system. 

Energy cost 

• SCR 

The energy cost to heat the gas stream to the catalyst operating requirements of 300ºC using a gas burner.  

140 kJ is required to remove 1 gram of NO  

• Ozone  

The electricity requirements of the ozone generator 52 kJ required to remove 1 gram of NO 

The SCR system requires 269% more energy than the equivalent ozone system.