Скачать или смотреть Ensuring Uniform Gas Injection Using CFD Modeling

Ensuring uniform gas injection using CFD modeling . A short video by Dr Kevin Linfield

This video is brought to you by Airflow Sciences Corporation. For all your flow modeling and testing needs, since 1975.

Many engineers make a simplification by assuming a uniform mass flow distribution emanating from pipes or lances featuring multiple holes. Sometimes this can be a good assumption, depending on the relative size of the header, manifold, lances, and orifices. Handbook calculations can be used to approximate the size requirements of each component, but a detailed CFD model of the internal piping from the manifold through the lance and out the nozzle will help ensure that the system has been designed properly for flow uniformity, temperature, and flow discharge angle.

Tempering, or cooling air is often used to mix gases that are too hot for a component (such as a catalyst) or to cool a product quickly (such as bread or meat). This figure shows pathlines colored by total velocity. In this case, due to the high velocity inside the supply duct the area to the left in the figure does not receive cooling air and hence the product line cools non-uniformly.

A properly designed lance should feature pressure driven flow, not velocity driven flow. Results from a detailed lance model are often used to produce boundary conditions inside a larger model, where the velocity, temperature, and density of the flow from each nozzle is mapped into the full CFD model.

Most injection system are designed for a uniform distribution of gas, whether tempering air or chemical species such as ammonia or natural gas. Variations of up to 5% are often tolerated, but designing blind and assuming a uniform profile may result in major headaches once the system is built and operational.

A case study involving a Heat Recovery Steam Generation unit featuring ammonia injection is presented in this and the following slides. In the "before" situation, mapping the ammonia from a separate detailed lanced model resulted in a very non-uniform ammonia distribution at the SCR catalyst face with an RMS of 59%.

After modifications including tweaking the AIG geometry and respacing the injection nozzles, the redesigned system featured a significantly reduced ammonia RMS of only 8% at the SCR catalyst face.

For more information on CFD modeling for uniform gas injection, please visit www.airflowsciences.com

Have a wonderful day.

Thank you

Copyright Airflow Sciences Corporation. With content provided by Dr. Kevin Linfield, P.Eng., P.E.