Efficient Solution for Reducing Nitrogen Oxide (NOx) Emissions in the Semiconductor Industry
Acid rain and heavy smog — these threats to health and nature are caused by NOx (nitrogen oxides NO2 and NO). Dealing with harmful NOx produced during combustion processes is a real challenge in many industries.
DAS Environmental Experts has developed a turnkey solution for NOx treatment that is suitable for the semiconductor industry and other industries.
What are Nitrogen Oxides and what Effects do they have on the Environment and Health?
Nitrogen oxides, abbreviated to NOx, are gaseous compounds produced by the combustion of fossil fuels such as oil, gas, coal or wood. The group of nitrogen oxides includes nitrogen monoxide (NO) and nitrogen dioxide (NO2).
Nitric oxide (NO) is a colorless, bioactive substance that is used in the body as a messenger substance, among other things. It has a dilating effect on blood vessels and is therefore used in cardiology and heart surgery as well as for the treatment of pulmonary hypertension in newborns. NO can be easily oxidized to NO2 in the atmosphere. Nitrogen dioxide (NO2) is a reddish-brown, highly toxic, pungent-smelling gas that decomposes into nitrogen monoxide and oxygen at temperatures above 200 °C. It forms acid with water and leads to the formation of acid rain; both nitrogen oxides also contribute to the formation of summer smog. The health of humans and animals is endangered by these substances, as nitrogen oxides — especially nitrogen dioxide — irritate and damage the mucous membranes of the respiratory tract and eyes and impair lung function. Inhaling these nitrous gases in high concentrations is extremely dangerous; among other things, it can cause respiratory distress and pulmonary oedema.
A not insignificant proportion of air pollution is caused by traffic (approx. 37% of total emissions). The stationary sources of pollution, which account for around 30% of emissions, are mainly power stations, waste incineration plants, glass and cement production and oil refineries. Nitrogen oxides can be released not only during combustion processes, but also when working with nitric acid. In addition, the relevance of agriculture as a source of NOx emissions is increasing (approx. 10%).
For this reason, strict limits already apply to nitrogen oxides in many countries around the world. Governments and authorities around the world are endeavoring to further restrict the release of these air pollutants. National environmental regulations such as the TA-Luft in Germany or the EPA in the USA set strict limits for NOx emissions. This is why not only the large NOx emitters mentioned above, but also high-tech industries such as the semiconductor industry, require effective solutions to prevent, reduce or treat nitrogen oxides.
Source: https://www.epa.gov/
How are nitrogen oxides generated?
NOx is mainly formed by the oxidation of nitrogen during various combustion processes. A distinction is made between three formation mechanisms. Thermal NOx is formed at relatively high temperatures (over 1300°C) from the nitrogen and oxygen in the combustion air. Fuel NOx is formed from nitrogen chemically bound in the fuel at temperatures of 800°C and above. These complex chemical processes can be strongly influenced by the reaction conditions. It is also possible for nitrogen to be converted to nitrogen oxide, known as prompt NOx, under the influence of fuel radicals (CHx) in the flame front.
In normal combustion processes, 95% of NOx consists of NO. NO2 is mainly formed after combustion with the oxygen in the atmosphere. However, unfavorable process control can also lead to the formation of nitrous oxide (N2O), better known as laughing gas. This substance is used, for example, in medicine as an anesthetic and in the food industry as a propellant. Above all, nitrous oxide is considered a greenhouse gas with an impact 298 times greater than CO2.
Nitrogen is generally used as a protective gas or purge gas in the processing of silicon wafers in clean rooms because the gas is extremely inert under normal conditions — but at high temperatures it can produce thermal nitrogen oxides (NOx). This mainly affects point-of-use incinerators that are used for the removal of perfluorocarbons (PFCs) after etching processes. The temperatures required in the reactor for the decomposition of PFCs promote the formation of NOx as a side effect.
In the semiconductor industry, nitrogen compounds are also required for the deposition of nitride layers, for example. Nitrous oxide is normally used to form oxynitride layers in the chemical vapor deposition (CVD) process. Nitrogen trifluoride (NF3) is used to clean CVD chambers not only in microelectronics production, but also in the production of thin-film screens and thin-film solar cells, and ammonia (NH3) is also used in the production of crystalline silicon solar cells.
The unreacted residues of these nitrogen-containing compounds are usually disposed of thermally together with other process gases and are therefore considered to be the source of the nitrogen oxide emissions that arise according to the fuel-NOx mechanism.
DAS Environmental Experts offers innovative solution for secondary exhaust gas purification
As an innovation leader in the semiconductor industry, DAS Environmental Expert GmbH (DAS EE) has developed TSUGA, a solution for secondary purification for NOx-generating exhaust gas cleaning systems, such as burn-wet systems. This approach is an efficient and reliable option for high-tech fabs and other industrial applications.
The TSUGA point-of-use solution removes NOx in the concentration range up to 4000 ppm (NO2, NO), fine dust (PM1, PM2.5, PM10) and particles in high exhaust gas flows up to 5000 slm (standard liters per minute). This means that several exhaust gas purification systems can be connected to one TSUGA.
The DAS solution for NOx and dust reduction combines state-of-the-art technologies: a highly efficient DeDust filter system and the selective catalytic reduction technology for DeNOx. More than 99% of the particles (including SiO2) are demonstrably separated in the DeDust stage. This filtration prevents clogging of the downstream components and the downstream catalytic converter and thus also ensures the best catalytic activity over a long period of time.
In the subsequent DeNOx stage, a technology is used that demonstrably converts NOx into nitrogen (N2) and water (H2O): selective catalytic reduction (SCR). Thanks to the SCR catalytic converter, a NOx reduction of more than 95% and emission values in the range of 5 ppm can be demonstrably achieved. State-of-the-art DeNOx catalytic converters are used in TSUGA. Ammonia (NH3), which is used for the reduction of NOx, is added automatically. Internal sensors ensure precise control and low overall media consumption.
With our design, we can ensure the efficient treatment of fluctuating NOx concentrations over a very long period of time and long-term catalytic activity. TSUGA works with minimal energy consumption by recovering more than 75% of the process heat.
Real-time monitoring is also integrated into TSUGA: The system is equipped with online measurement of NOx emissions. This enables optimized control of all relevant parameters and ensures TA-Luft and EPA conformity. The data generated is available for official requirements and documentation purposes. Access for operation and maintenance of the system is only from the front.
Waste Gas Treatment Abatement TSUGA
Post Combustion Waste Gas Treatment for NOx
DAS EE is your partner for the reliable and efficient treatment of nitrogen oxides (NOx).
No matter what your requirements are, our experts will find the perfect solution for you!
Contact & Consulting
Your contact person for all questions about efficient solution for reducing nitrogen oxide (NOx) emissions
Dr. Christian Kuhne
Director Sales Global