How to control ammonia in Selective Catalytic Reduction?

February 14, 2023 Chris King
Ammonia Control for NOx reduction

NOx Reduction through Mass Flow Control

As a technique to reduce the level of Nitrogen Oxides (NOx) in boiler or furnace exhaust gases, Selective Catalytic Reduction has been around for years. Selective Catalytic Reduction is a technology which converts Nitrogen Oxides (NOx) with the aid of a catalyst into diatomic Nitrogen and water. A reductant agent is injected into the exhaust stream through a special catalyst. A typical reductant used here is anhydrous ammonia.

A customer of Bronkhorst, who has been selling and servicing boilers and pumps for commercial and industrial applications all over the world, had been using a mass flow controller. Unfortunately this mass flow controller was not reliable and robust enough for the application and thus their customers were suffering from poor ammonia measurement and control.

Ammonia flow meter for Selective catalytic reduction
Selective Catalytic Reduction example

Why use mass flow measurement in ammonia control?

Some NOx reduction systems are liquid ammonia based, and others are gas based ammonia.  Whatever the state of the ammonia in the NOx reduction system, Bronkhorst can offer accurate ammonia measurement and control. Systems in the field today are using the MASS-STREAM flow controller (gas), IN-FLOW flow devices (gas) and mini CORI-FLOW instruments (liquid) to accurately control the ammonia being injected into the exhaust gas stream. This way proper reaction takes place without ammonia slip.  Ammonia slip is when too much ammonia is added to the process and it is exhausted, un-reacted, from the system; effectively sending money out the exhaust stack...

There are very strict federal and state air quality regulations that specify the allowable level of NOx which can be released into the atmosphere and there can be very heavy fines if those levels are exceeded. The company needs to provide their customers with a reliable and robust solution. The application demands a robust and repeatable mass flow controller that is at home in industrial environments.

Which ammonia flow meter can be used here?

In the NOx reduction system serviced by our customer the mass flow controllers are used to control the flow of anhydrous ammonia (ammonia in gas state) into the exhaust gas of a boiler or furnace. Here it is adsorbed onto a catalyst. The exhaust gas reacts with the catalyst and ammonia which converts the nitrogen oxides into nitrogen and water.

Bronkhorst recommended an ammonia flow controller from the MASS-STREAM series. This model flow controller measures the flow ‘in line’ which makes it less sensitive to clogging in polluted industrial gas applications.

Check out our knowledge base section to learn more about the ‘inline’flow measurement principle.

Find your MASS-STREAM model

Need help?

Working principle of 'inline' ammonia flow meters

Let us know how we can help you

Want to stay up-to-date which our products and trends in the market? Sign up for our mailing list. 

Please let us know! Sign up