SCR solutions for the cement industry

In today’s world, regardless of the industry, emission regulations are getting stricter. In the cement industry there is a drive to reduce NOx emissions. Plants are now considering the use of a selective catalytic reduction system (SCR) to accomplish this task. When designed and operated properly, an SCR system can reduce NOx emissions by up to 97%.

An SCR system is an add-on device that injects a reagent such as ammonia or urea, into the gas stream with the presence of catalyst to start a chemical reaction. At the right temperature (570 – 750°F) the reagent and the catalyst convert NOx to nitrogen and water.

Urea + 2NO + ½O2 → 2N2 + 3H2O, or

2NH3 + 2NO + ½O2 → 2N2 + 3H2O

SCR systems have been used successfully in various industries for several years. In the US they are frequently installed in the power, industrial, oil, gas, and petrochemical industries. The use of SCR systems in the US to control NOx emissions in the cement industry is uncommon. In Europe and China, however, SCR systems are more commonly used in cement plants to reduce NOx pollution.

Global push to reduce NOx emissions

Regulations for the harmful pollutant NOx are becoming stricter across the globe. Perhaps the best example is the ‘Good Neighbor Provision’ recently passed in the US. This regulation has set specific goals and targets for stricter NOx emissions in 23 states. This regulation specifically addresses air pollution that crosses state boundaries that affects neighbouring states. It is believed the new stronger emission regulations will increase cement production costs and offer new operational challenges. To meet the new regulations new NOx removal equipment is expected to be required.

The most proven solution is the addition of an SCR system. Many plants have used SNCR systems to combat NOx emissions, but the efficiency will not meet the new regulations. New SCR systems in the cement industry can reduce NOx emissions by 90% and in some cases 97%.

Many of the SCR units installed in the cement industry have suffered from buildup issues which reduces NOx removal and operational time. Buildup has been a challenge which can be overcome.

Buildup prevents the reagent from interfacing with the catalyst and has a deep impact on NOx removal and pressure drop across the system. It is not uncommon for plants to be forced into downtime to manually clean the SCR system.

This system operates continuously and requires a boiler tube bank ahead of the system to heat the air. This is an expensive and unreliable system to operate and in most cases does not clean the catalyst. Indeed, it has proven effective at plugging the catalyst.

These types of systems have failed to keep the SCR unit free from buildup and are often the cause of damage to the catalyst. Buildup is one of the greatest challenges in good SCR system operation in cement plants. Buildup that is evenly spaced across a reactor is often a sign that the gas flow velocity is too low. This reactor is located after the baghouse was not expected to suffer from buildup.

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Read the article online at: https://www.worldcement.com/special-reports/30102023/scr-solutions-for-the-cement-industry/