High Pressure and Low Pressure Selective Catalytic Reduction Systems

Technical Management
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What are the differences between HP and LP SCR systems?

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Hello @AndreasTravlos!
Both are quite popular NOx reduction methods for Tier III compliance.

In a HP (high pressure) Selective Catalytic Reduction System (SCR) the SCR reactor is placed before the turbocharger. Please refer to the below sketch (source MAN ES):
image

In a LP (low pressure) Selective Catalytic Reduction System (SCR) the SCR reactor is placed after the turbocharger. Please refer to the below sketch (source MAN ES):

image

The HP SCR is a more compact installation (it requires less space, less piping length) compared to the LP SCR. In addition to the above, the proximity of the HP SCR to the M/E turbocharger is beneficial because of the higher exhaust gas temperatures. It is known that high exhaust gas temperatures increase the efficiency of the SCR catalyst inside the reactor.

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