selective catalytic reduction

Combined Cycle Journal: “Consider the impact of new operating regimes on your SCR”

Incorporating real world operating data analysis into your SCR management plan is a topic that is gaining some well-deserved traction within the power industry. Combined Cycle Journal posted an article on November 8th, 2017 highlighting Environex Senior Engineer Andrew Toback’s presentation at the 2017 Combined Cycle Users Group Conference, “Impact of Real-World Operation on Catalyst Performance”. The article focuses on case studies that show the need to revise performance and lifecycle expectations based on actual operating conditions instead of original design parameters, particularly given the challenges and variability imposed by GT upgrades for higher output and lower turndown operation. Deeper knowledge of actual operating conditions and how they impact catalyst system performance sets the foundation for optimizing plant emissions performance.

With over 25 years of power industry experience, Environex understands the importance of evaluating catalyst performance at real world operating conditions, and that is why Full SCR System Evaluations provide the best value to our clients. Full SCR System Evaluations include a combination of catalyst testing, operating data analysis, and physical system inspection that enables us to distinguish system problems from catalyst problems. Laboratory testing of the catalyst across the range of plant operating conditions in conjunction with the data analysis allows us to identify the limiting operating case for your system and evaluate design and operating adjustments that can improve plant emissions performance.

Click here to read the article on ccj-online.com
Operating Data Analysis: Before and After Upgrade

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Why should I test multiple SCR samples?

Taking multiple samples ensures accurate and actionable results.

In the real operating environment of an SCR catalyst, exhaust gas temperatures, flows, and other factors vary across the catalyst cross-section. These differences cause non-uniform wear and tear on the catalyst. Uncontrolled thermal events and poisons entrained in the exhaust can cause irreversible damage to the catalyst which cannot be seen by the naked eye. Furthermore, as-manufactured variability in catalyst activity may cause single-sample testing to misrepresent the bulk catalyst activity level.

For these reasons, Environex recommends a full system evaluation which includes testing multiple samples from the inlet and outlet sides of the catalyst. This ensures that the catalyst test results are representative of the actual condition of the bulk catalyst in a way that single-sample testing cannot. These results, particularly when combined with operating data analysis, provide a secure foundation from which to make future catalyst maintenance and replacement plans. This level of analysis minimizes the risk of unplanned catalyst maintenance or replacement, which can help you avoid costly environmental fines, forced plant downtime, and expensive expediting costs.

There are some instances when single sample testing may be appropriate. Baseline testing of a new catalyst, interim testing between full system evaluations, and post-mortem failure analysis of a spent catalyst are the most common cases where single sample testing is acceptable.

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What is Selective Catalytic Reduction (SCR) Catalyst?

Selective catalytic reduction is a catalytic reaction which uses ammonia to reduce oxides of nitrogen (NOx) into harmless nitrogen (N2) and water. Because of this function, the SCR catalyst is sometimes referred to as a NOx catalyst in the industry. It has been used in many industrial facilities including power plants and chemical refineries to reduce NOx emissions since the 1980’s. It has been used in automotive applications since the mid 2000’s to reduce NOx emissions from heavy duty and light duty diesel vehicles.

Industrial Selective Catalytic Reduction Catalyst

The active component of the catalyst itself can be one of several different materials; vanadium pentoxide is frequently used in industrial settings while copper and iron zeolites are frequently used in automotive applications. Different materials are used because of differences in operating conditions, temperatures, and resistance to impurities in the fuel and environment.

On industrial installations, SCR catalysts are installed along with an Ammonia Injection Grid, or AIG for short. The AIG sprays ammonia, typically stored as aqueous ammonia, anhydrous ammonia, or a urea solution, into the exhaust stream. The ammonia adsorbs onto the SCR catalyst, where it reacts with NOx and oxygen to form nitrogen and water. In a vehicle, onboard urea, known as Diesel Exhaust Fluid (DEF) or AdBlue, is sprayed into exhaust gas upstream of the catalyst brick and diffused using a mixer to optimize airflow and ensure thorough vaporization and even distribution in the exhaust prior to entering the catalyst.

If an Industrial SCR catalyst NOx removal efficiency declines or ammonia usage increases significantly, it could signal a serious problem with the catalyst and inspection and performance testing by a qualified company should be scheduled. See Environex’s SCR System Evaluation page for more information on our services.

In an industrial facility, the AIG may need to be tuned periodically to ensure proper distribution of ammonia into the SCR catalyst. If there are areas of high and low ammonia flow entering the system, the catalyst will not be used effectively and higher NOx emissions and ammonia may result. See AIG Tuning for more information.

Posted by eking in industrial catalyst services, NOx, selective catalytic reduction, 2 comments