Nox Oxidation
Nox Oxides Of Nitrogen

Nitrogen Oxides (NOx) Emissions. NOx refers to both nitric oxide (NO) and nitrogen dioxide (NO 2 ). The environmental effects of releasing too much NOx into the atmosphere are listed below. NOx is a main constituent in the formation of ground-level ozone which causes severe respiratory problems. Respiratory problems may result from. Nox works seamlessly on mac based machines including iMac and macbooks. Android is an highly customizable OS and supports hundreds and thousands of games and apps and this is why it is loved by even apple lovers. If you are a mac user but want to play android games on your mac then Nox is absolutely for you.

The NOX System control panel software is now also available for download on macOS from the Mac App Store (free of charge)

In addition to Windows PCs, Android and iOS devices, the NOX control panel software is now also available for macOS.

The full range of functions is implemented:

Arming and disarming of areas
Alarm handling
Floor plans (additional license)
Temperature display with statistics
User administration
Time profiles and holidays
Video camera integration

System requirements: macOS Catalina or macOS BigSur

With the passage of the 1990 Clean Air Act Amendments, many chemical and metal industries and utility producers will now be required to further limit the amount of NOx (Nitrogen Oxides) produced. NOx is a precursor to ozone in the atmosphere, and is believed to be a major contributor to acidic deposition (acid rain).

Formation of ozone: NOx is produced in a variety of different processes, including combustion equipment, gas turbines, incinerators, kilns and power plants. NOx also is emitted as by product from many metal treatment processes where nitric acid is used as an oxidant. Plating or catalyst recovery involves the reaction of nitric acid and transition metals also forming NOx. Substantial amounts of NOx also can be generated in the specialty chemical industry when nitric acid is used as a reagent.

The denitration processes for removal of NOx are classified into two groups: in one, NOx is absorbed by means of solutions, and in the other NOx is reduced to N2 by means of a reducing gas under the presence of a catalyst.

Selective catalytic reduction (SCR) is a chemical process that changes the oxides of nitrogen into N2 and H2O. The reactions take place at a temperature of 600-750 F in the presence of a catalyst. Ammonia is injected into the exhaust gases prior to their passing into the SCR. NOx removal efficiencies with SCR range from 80 to 90% [2]. An NH3/NOx mole ratio of 1.0 to 1.5 is normally used although the theoretical ratio is about 0.67. Although a portion of the excess ammonia decomposes in the reactor, a considerable amount of it would remain in the treated gas and may cause problems. For example, ammonia may combine with SO3, which is present in a small amount even after the wet scrubbing, to form ammonium bisulfate which condenses in a heat exchanger. However, catalysts are affected by dust and most are poisoned by sulfur and chlorine compounds.

For treatment of contaminated gas, a wet removal process may be carried out first to remove dust and poisonous chemicals, but in this case, the gas temperature drops to 120-150 and must then be reheated to 600-750 F, a large heat exchanger and a considerable amount of fuel are needed. In addition, mists from the scrubber may cause corrosion of the heat exchanger and contamination of the catalyst. Over a period of time, the materials in the catalyst-ceramics and zeolites degrade and must be replaced depending upon the industrial sources of the gases. Because the catalysts are made up of heavy metals, disposal of spent catalysts can also be a problem.

In recent years, many wet processes for NOx removal have been developed with the aim of removing NOx and SOx simultaneously. Scrubbing process also used to remove NOx from NOx rich gases is produced in a relatively small amount at metal-dissolving, nitric acid and chemical plants, etc.

This article describes the NOx chemical reaction associated with wet removal processes. The aim, then, is to provide a reasonably clear and uncomplicated basis for evaluation of potential treatment methods to help determine which may be practically applicable in a given situation.

Several oxides of nitrogen are found in the atmosphere but only nitric oxide (NO) and nitrogen dioxide (NO2) are important as air pollutants. The symbol NOx is frequently used to represent the composite of the two. The other nitrogen oxides seldom occur in appreciable quantities and then only under special conditions.

Essentially, NOx contains nitric oxide and nitrogen dioxide in varying proportions. This fluctuating ratio, and the fact that these compounds exhibit quite different properties when contacted with water (as would occur in a wet scrubber) complicate the treatment of NOx.

NO2 gas has fairly high solubility and reactivity to water and in aqueous solutions or alkalis as compared with NO, and can be removed by wet scrubbing. On the other hand, gaseous NO is only slightly soluble in water and is not very reactive with typical aqueous solutions. Nitric oxide does react with oxygen as follows:

2NO+O2 = 2NO2

This equation implies the coexistence of NO and NO2. Calculated equilibria indicates that the stability of NO2 decreases with increasing temperature. Nevertheless, from an equilibrium standpoint, the absolute concentration of NO2 increases with temperature while the ratio of its concentration to that of NO decreases with increasing temperature. The equilibrium concentration of NO varies with temperature; it is negligible below 1000 F but quite significant above 2000 F. (Table 1)

The oxidation of NO is concentration dependent to a marked degree as illustrated in Table 2, which shows the time required for half the NO present in air at various concentrations to be oxidized to NO at ambient temperature. This reaction proceeds more rapidly at a lower temperature than at raised temperatures.

It may then be concluded that it is impossible to reduce effluent concentration below a few hundred parts per million NOx in absorption equipment of practical dimensions when the entering concentration is in the low percent range. The slow oxidation rate for NO in air can be greatly improved by adding an oxidant such as ozone (O3) or chlorine dioxide (ClO2). The oxidation of NO in the gas phase by ozone or chlorine dioxide occurs much more rapidly than oxidation in the liquid phase because the rate of absorption of NO in the aqueous solution is slow. Ozone is capable of oxidizing NO not only to NO2 but also to N2O5 which rapidly reacts with water or alkaline solutions to form nitric acid or nitrates. Ozone, however, is fairly costly making it usually uneconomical.

It has been shown that the use of stoichiometric amounts of ClO2 eliminates approximately 95 percent of the NO in the gas in concentrations of up to at least 24 ppm in less than 2 seconds [4]. Chlorine dioxide is less costly than ozone, but there are inherent difficulties involved in its storage or recovery in terms of equipment maintenance. This is due to its reactive and hazardous nature.

For all practical purposes it is impossible to remove NO gas by wet scrubbing in the situation in which the gas does not contain NO2. It is also known that gaseous NO present in amounts approximately equal to or less than that of gaseous NO2 in a waste gas, when brought into contact with an alkali solution, forms a nitrite and is thereby absorbed as indicated by the formula (2)

If in this case NO2 is present in excess to NO, it reacts with an alkali solution to form nitrate and nitrite and is thereby absorbed as indicated in (3):

where NO and NO2 are present in equal volumes (NO2:NO mole ratio is 1) reaction (2) will principally proceed, while reaction (3) will become secondary. If the ratio by volume of NO to NO2 is greater than 1 the NO equal in volume to NO2 will react to the nitrite, but the excess NO will essentially remain unchanged. Therefore, the reaction between an alkaline solution and NO/NO2 is optimal at a 1:1 molal ratio of the oxides.

It has been determined that the controlling mechanism of NOx absorption

2021.09