'Residence Time' in catalytic VOC removal

[AlexEss]

What would normally be the design 'residence time' for gas flow through Platinum coated, ceramic honeycomb, catalyzer blocks ?

My understanding is in order for the catalytic reaction to take place, the off-gas must reside in the catalyst bed for a certain length of time -
I have heard time values of 0.5 -> 1.5 seconds as being acceptable.

To give some physical characteristics:
Off-gas volume = 6000 m3/hr ( 212,000 ft3/hr )
Off-gas temp = 400 oC ( 750 oF )

Catalytic bed
Surface area = 0.36 m2 ( 3.89 ft2 )
Bed depth = 0.3 m ( 1.0 ft )

If I'm correct, the time required to pass through the bed is c. 0.06 seconds.
Does this give sufficient reaction time ?

All comments and observations gratefully received.

Thanks in advance,

AlexEss

 

[georgeverghese]

What are the units for this volume flow - actual m3/hr or standard m3/hr ( at 15degC, 1atm) or some other?
What about free pore voidage of the catalyst block - is this not in m3 of pore volume / m3 of block ? If so, what is the volume of catalyst in the reactor ?
Sometimes, residence time is more simply expressed in terms of the gross reactor volume occupied by catalyst, while you are assuming it is based on actual voidage of the catalyst - can you confirm with supplier?

 

[AlexEss]

George, thank you for your reply.

The units are actual m3/hr, not Nm3/hr

Regarding the catalyst block, the info I have from the 3rd party supplier is:
Matl = Cordierite monolith
Catalyst type = Platinum
Cell Density = 200 cpsi (cells per inch2)
Matrix = 150mmx 150mm x150mm
Design Temp = 320oC -> 420oC
Space Velocity = 37037 l/hr
Number of monoliths = 32 ( 2 layers of 4 rows of 4 blocks )

I think more information is required to determine the volume of catalyst in the reactor.

Thank you for any advice or comments.

 

[georgeverghese]

Space velocity usually is superficial space velocity, but the units you've stated are not correct. It should be in m/sec or similar. So this parameter gives you cross sectional area of the reactor.
Tr. Va = Vreac = Areact. Lreact
Lreact = Va. Tr / Areact

Where Tr = residence time required, Va = actual gas flowrate, Areact = cross sectional area of reactor, Lreact = length of reactor.

 

[AlexEss]

George, thanks once again for your help.

I will let you know what the outcome is.