Although the N2, which exists in the air with a rate of 78%, is a harmless and inert gas, nitrogen oxides that this gas is formed with oxygen are among the most important parameters which cause air pollution to increase.
Nitrogen oxides (nitrogen monoxide, nitrogen dioxide and di nitrogen oxide), which are indicated as NOx, emerge with high temperature during the combustion of fossil fuels. In these gases, especially NO2 (nitrogen dioxide) and N2O (nitrous oxide) are at the forefront in the calculation of air quality and greenhouse gas index.
In the calculation of air quality index, it takes place among the top 5 along with NO2 gas, carbon monoxide (CO), particulate matter (PM10), Ozone (O3) and Sulfur dioxide (SO2). N2O gas is a factor causing the global warming 310 times more than carbon dioxide in the calculation of carbon footprint for greenhouse gas.
Most gas derivatives released into the atmosphere are reversed by the atmosphere cycle. Nitrogen oxide derivatives released into the air complete the natural transformation by turning into the form of nitric acid (HNO3). The nitric acid in the atmosphere is combined with the water vapor in the air and from time to time return to the surface with acid rain. Acid rains directly affect the entire life of humans, animals and plants. In addition, material damage is the result of its effects on objects.
Decreased air quality due to increased air pollution triggers asthma and similar respiratory disorders, especially on children. According to the World Health Organization (WHO), air pollution causes direct or indirect impacts on the death of more than 600.000 children and 1 out of every 8 deaths in the general population.
Industrial plants are the biggest source of formation of nitrogen oxides. The combustion of fossil fuels and the production of nitrogen oxides (such as glass and fertilizer production) are released into the atmosphere according to the limit values determined by laws and regulations. In recent years, nitrogen oxide limit values have been reduced by 75% depending on the industrial establishment. Parallel to these changes, the nitrogen oxide limit values are gradually reduced also in our country.
Most industrial establishments in our country do not own a purification system for nitrogen oxides. Only new installations, facilities that are not capable of releasing emissions below their limit values, and installations that wish to take precautionary measures based on revisions to the limit values with the new regulation amendment, have or install such and similar treatment/washing facilities.
Common systems for reducing nitrogen oxide emissions are SNCR (selective non-catalytic reduction), SCR (selective catalytic reduction) and Hybrid systems.
SNCR and SCR systems generally follow the principle of applying ammonia (NH3)- water or urea (CO(NH2) 2) -water mixture as a reagent to the combustion chamber and nitrogen oxides retention based on the following basic reactions.
NH3 + NOx N2 + H2O
CO(NH2)2 + NO N2 + CO2 + H2O
Checking the efficiency of the installed system and whether the emissions are at the desired level are determined by continuous measurements after SNCR / SCR units.
These analyzes are basically performed in 3 ways as follows;
• Measurement of the NOx parameter at outlet of the SNCR/SCR unit,
• Measurement of the NOx parameter at the chimney level, (CEMS)
• And the measurement of the NH3 parameter at outlet of the SNCR
/ SCR unit.
In the companies that have to establish a continuous emission measurement system, the NOx parameter is followed by the chimney level in accordance with the communiqué. However, in order to improve the follow-up quality, nitrogen oxides can also be monitored at the unit outlet.
Ammonia is an expensive chemical that increases operating costs. In SNCR/SCR units, ammonia consumption will exist as long as the plant is in operation. In order to minimize this consumption and to avoid unnecessary ammonia emission in the process, the NH3 parameter is continuously monitored at the SNCR unit outlet.
For this measurement, the extractive infrared types or in-situ laser analyzers that we explain in our blog titled “Continuous Emission Monitoring Systems” Regulation and their necessity in the sectors are widely used. Generally, in-situ laser analyzers are preferred because of the short response time and the need for less maintenance.
Siemens LDS6 Gas Analyzer Process Application
The Siemens LDS6 model laser NH3 analyzer delivers high efficiency and precision and continuous measurement results at the SNCR outlet. Instead of taking point measurements like extractive systems do, it can provide the ammonia value of the entire channel axis where it is installed. In this way, the measurement result is more stable and accurate.
LDS6 analyzers that can operate effectively in areas with high dust (up to 100g/m3) and temperature (up to 1000°C), according to the region and process provide the fastest measurement results in measurement systems with a response time between 1 …100 s.
In this technology, the expansion of the measuring range, in contrast to extractive technologies, does not lead to a reduction in measurement accuracy. Thanks to its wide measuring range and high precision, it can measure high measurement values and reliably analyze very small concentrations such as 1 ppm.
The LDS6 analyzer consists of 3 main parts. The system, which works with 2 measuring heads connected to 1 electronic unit, can be designed to be capable of sampling from 3 different measuring points thanks to the headers that can be attached to the single electronic unit.
Instrument air connection to measuring heads is available. This keeps the optical surfaces away from the sample gas and dust particles, as well as continuously performing zero calibration, eliminating the shifts in the measurement results of the device.
A reference cell for the relevant sample gas is available in the analyzer. Thanks to this cell, the measurement value is continuously corrected against transmission effects that may occur at high dust levels.
Thanks to the EN14181 KGS1 certificate, with the LDS6 analyzers available in Continuous Emission Measurement, parameters other than NH3 such as O2, HCI, HF, CO, CO2 and H2O can be measured separately or together.