After reading the Chalmer's studies, a nagging question I have is in this issue in my header.
I decided to ask it here to see if Peter can add some light to this subject and assuage my curiosity about the subject matter.

Do we know the acceptable level of Nitrogen Oxide the Iron Ore Pelletization companies are willing to accept? Can we contol it by the level of wattage used to minimize it?

Could this issue be a major impedement for these company's not to select the Plasma methodology?

Is it possible that we are seeing a delay because this is part of the data set that needs to be done to find the sweet spot to minimize the Nitrogen Oxidation? (See two methods described below)

If so, it makes sense. I mean modeling can only do so much right? Once put in line with the fossil fuel burners, the picture comes to life so-to-speak? 

I know many are impatient with the contracts not coming forth but the above could be a logical reason as fine tuning is litterally happening in real time.

If anyone with any knowledge about this could add there two cents, that would be appreciated.


Forgive the long text from Chalmers below but it is essential to understand the question of where we may or may not be. I brought the paragraphs with stars up from further in the study as it seems to point to two solution methods in my Nitrogen Oxide question.

******Two methods for NO reduction were studied through simulations, reburning (staged combustion) and reduction of the oxygen content of the mixing air through combustion.

In the reburning simulations, different amounts of methane (CH4) was added into the mixing zone at a distance of 10 cm from the end of the plasma zone in order to destroy NO through reactions with hydrocarbon radicals. In the oxygen reduction simulations, the composition of the mixing air was changed assuming complete combustion of methane before mixing with the plasma gas.

These simulations were performed with a defined temperature profile according to the MixEE case. However, in practice, the additional combustion would cause a temperature increase, which might affect the NO reduction.

Conclusions

For plasma torches, there are some important details that can not be simulated with the process model. One example is the mixing process of the plasma and the recirculated air.

Since the plasma is much hotter than a combustion flame it becomes more important for the process gas to be homogeneous before reaching the pellet bed. This could otherwise lead to uneven oxidation of the pellets.

Due to this, the mixing process should be studied further through fluid dynamics simulations or practical experiments. When finally implementing plasma torches in the real process, it will be a good idea to begin by replacing only one pair of burners.

In this way, the investment cost can be spread out and changes in pellet quality can be evaluated. If no major changes are observed, more burners can be replaced until eventually the process operates with plasma torches only.

It is also important to remember that there are many uncertainties regarding the NO simulations. First of all, reaction modelling might not be able to accurately describe the behaviour of plasma. At extremely high temperatures the particles become ionized which affects the chemical reactions.

However, to which degree this would affect the results compared to normal gas-phase reaction kinetics is still unclear and needs to be studied further.

Secondly, more data of different types of plasma torches including dimensions, mass flows and plasma temperatures would allow for simulations that can be used to better predict the absolute amounts of NO formation.

Due to these uncertainties, it would be a good idea to measure the production of nitrogen oxides from plasma torches in a test rig before implementation. The NO formation could then be measured for different operating conditions to find out what works best in practice. ******

The methane flow rate was varied between 0-5 g/s for both reduction strategies. The maximum amount of methane that could be combusted was around 5.8 g/s based on the amount of oxygen available.

2.5 Nitrogen oxides Nitrogen oxides are molecules that are composed of nitrogen and oxygen atoms. The nitrogen oxides that contribute to atmospheric pollution are nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O). The term "NOx" is used to describe NO and NO2, while N2O is generally not included.

Anthropogenic activities are the main cause of increased levels of NOx in the atmosphere. Most of the NOx is formed in combustion processes where nitrogen from the air or the fuel reacts with oxygen and forms NOx.

A majority of the NOx emissions in developed countries originate from the transport sector and the industrial sector. [34] The emissions of NOx is considered to be a global problem. NOx is considered to be toxic and can cause lung diseases in humans. However, the main problems with NOx are the secondary effects, including acid deposition and formation of tropospheric ozone. [35] Acid deposition can be in the form of wet deposition (acid rain) or dry deposition (gas and particles). When released to the atmosphere, NOx will react with water vapor to form nitric acid (HNO3). This can be transported over long distances before being deposited as acid rain, resulting in acidification of land and water.

Acidification is harmful to vegetation and wildlife and has caused severe environmental problems in many parts of the world. [36] Ozone (O3) can be formed through a reaction between an oxygen molecule and an oxygen radical. The levels of oxygen radicals are increased by decomposition of NO2 by sunlight, thereby increasing the formation of ozone.

The ozone that is located close to the ground is called tropospheric ozone. Ozone in the upper atmosphere is vital for protecting the earth from harmful UV-radiation. However, tropospheric ozone is hazardous since it harms the human respiratory system and causes damage to vegetation and crops. Ozone is also a component of the so called "smog" that is a common problem in large cities.

[37] 2.5.1 Formation of thermal NO The formation of NOx is dominated by NO at high temperatures but the emitted NO usually converts to NO2 at lower temperatures. Therefore, the focus of this work will be the production and reduction of NO rather than NO2.

The formation of NO is a complex process and consists of many intermediate reactions but it is common to divide the reactions into three main mechanisms; thermal, fuel and prompt NO. Thermal NO is formed through the reaction between nitrogen and oxygen from the air which normally occurs at very high temperatures.

Fuel NO is formed by oxidation of nitrogen from the fuel with oxygen from the air. Finally, prompt NO is formed by the reaction between nitrogen from the air and hydrocarbon radicals from the fuel. 

Out of these three mechanisms, only thermal NO will be relevant to plasma torches since the other two mechanisms requires combustion of fuel. The formation of thermal NO can be described by the Zeldovich reactions [38], Reaction 2.6 - 2.8. N2 + O ↔ NO + N (2.6) N + O2 ↔ NO + O (2.7) N + OH ↔ NO + H (2.8)

These reactions are only important at high temperatures since N2 contains a triple bond that requires a large amount of energy to break. The rate of formation for thermal NO usually becomes important relative to the other NO reactions at a temperature of over 1500 °C. The reaction rate is also determined by the concentrations of O2, N2 and NO.

[35] The formation of NO is limited by reaction 2.6, where nitrogen molecules reacts with oxygen radicals producing NO and nitrogen radicals. The nitrogen radicals will then be consumed immediately by reaction 2.7, producing more NO and oxygen radicals. The activation energy of reaction 2.6 is approximately 318 kJ/mol.

The total amount of thermal NO produced also depends on the gas residence time at high temperatures. Strategies to reduce thermal NO will usually focus on reducing the O2 concentration and removing temperature peaks. 2.5.2 NOx emissions from iron ore pelletization The iron ore industry is a substantial emitter of NOx in Sweden.

Iron ore pelletization plants normally has a heat input of around 40 MW and will probably have to comply with emission limits for medium to large size combustion plants. However, very limited research has been carried out on NOx mitigation measures for these type of plants since the combustion conditions differ significantly from conventional combustion systems.

It is important to maintain high oxygen levels in the process gas to ensure a high degree of oxidation. Therefore, a large volumetric flow of air is required in the firing zones. Relating the air flow to the fuel flow, an air-to-fuel ratio of 4-6 is obtained.

This is significantly higher than in conventional combustion, where the air-to-fuel ratio is approximately 1. Implementation of flue gas cleaning systems such as selective catalytic reduction (SCR) is considered to be less efficient and more costly and the proportional cost for the environmental benefit is still being discussed in the industry. NOx mitigation is usually only considered in cases where environmental regulations are otherwise not likely to be met. There is therefore incentive to develop cost efficient measures to reduce NOx emissions from this type of plants.

[35] 22 2. Theory 2.5.3 NOx emissions from plasma torches One of the major technical issues with the use of thermal plasma torches is the nitrogen oxides that can be generated in the high temperature plasma which may limit the plasma torch in its various applications. An electric arc operating in an oxidizing gas atmosphere, in combination with high plasma temperatures, leads to formation of NOx.

The plasma bulk temperature is normally 5000 - 6000 K, while the maximum temperature in the plasma jet can be up to 10 000 K [39]. The NOx formation in plasma torches has not been studied extensively since most research has focused on NOx emissions from conventional fuel combustion, where temperatures usually are below 2000 °C. One study has been made on plasma torches applied to an electric arc furnace [40].

These trials did not confirm any influence of the electric parameters of the plasma torch on the formation of NOx. The influence was not detectable due to other more dominant parameters, including the composition of the furnace atmosphere. Two common methods for industrial NOx reduction are flue gas recirculation (FGR) and staged combustion.

FGR involves extracting flue gases and mixing it with combustion air in order to lower the oxygen content of the combustion air as well lowering the combustion temperature. Staged combustion is a reduction strategy that works by injecting additional fuel in a secondary combustion zone.

This creates a fuel rich reburning zone where NOx is destroyed through reactions with hydrocarbon radicals. These two reduction strategies could probably also be applied to plasma torches with some modifications. For example, a study by Uhm et al. [39] showed that NOx generated by a plasma torch can be disintegrated in a fuel-burning atmosphere with an exponential decrease in terms of methane flow rate.