Prompted by questions from a GBHE C2PT Customer who wanted to know how much “dust” will be retained by fixed bed catalyst and absorbents. - Dust Retention by Vulcan Series VGP Catalyst and Absorbents - PD Rise versus Available Voidage - Assessment of Bed Protection Media

1. GBHE C2PT Catalyst Process Technology
Vulcan VGP Series Purification Catalyst and Absorbents
Gerard B. Hawkins
Managing Director

2.  Information contained in this publication or as otherwise supplied to Users
is believed to be accurate and correct at time of going to press, and is given
in good faith, but it is for the User to satisfy him/herself of the suitability of
the Product for his/herself own particular purpose. GBH Enterprises,
C2PT, Catalyst Process Technology gives no warranty as to the fitness of
the Product for any particular purpose and any implied warranty or condition
(statutory or otherwise) is excluded except to the extent that exclusion is
prevented by law. GBH Enterprises, C2PT accepts no liability for loss or
damage caused by reliance on this information. Freedom, under Patent,
Copyright and Designs cannot be assumed.

3.  Prompted by questions from a GBHE C2PT
Customer who wanted to know how much “dust”
will be retained by fixed bed catalyst and
absorbents.

4.  Difficult to quantify
◦ Depends on the nature of the foulant
◦ Depends on operating conditions
◦ Depends on the nature of the bed
◦ protection medium
 General information on foulant effects
◦ Available from arguments around hydrotreating fouling

5.  Assume a reactor of set dimensions has a given
gas flow rate, composition, pressure and
temperature through a given installed
catalyst/absorbent volume
 Pressure drop is then related to
voidage and particle equivalent
Diameter.

6.  Ergun equation defines
PD = k. {(1-e)/e3}.{1/d[eq]}
◦ where e = voidage and d[eq] is equivalent diameter
 Also: d[eq] = 6/gsa
 So PD = k’. {(1-e)/e3}.{gsa}
gsa = geometric surface area

7.  Bed fouling blocks available voidage
 Thus, as fouling increases, PD rises
 Rate of PD rise accelerates as e decreases
◦ e3 term
 Rate of PD rise becomes exponential once a
limiting voidage is reached
 Limiting value is eexp ~ 0.21

9.  Voidage in excess of the limiting value, eexp, is
defined as “useful voidage”, euseful
 euseful is the available voidage for fouling before
PD becomes unacceptable
 Thus, euseful = efresh – eexp
= efresh – 0.21

10.  Foulant will tend to accumulate at the bed top
 Voidage and HGSA of hold down (top) layer is
critical
 Spheres usual hold down medium
◦ Voidage depends on sphere packing
 Cubic 0.476
 Ortho-rhombic 0.395
 Tetragonal 0.302
 Rhombohedral 0.260
◦ Best view for poured balls = voidage ~ 0.36

11.  Other shapes
◦ Tablets: efresh ~ 0.44
◦ HGSA Support : efresh ~ 0.54 – 0.57 (16x10x7; 16x16x7)
 Useful voidage
◦ Spheres: euseful = 0.36 - 0.21 = 0.15
◦ Cylinders: euseful = 0.44 - 0.21 = 0.23
◦ HGSA Support 16x10x7: euseful = 0.54 - 0.21 = 0.33
◦ HGSA Support 16x16x7: euseful = 0.57 - 0.21 = 0.36
 Data on other shapes available
 HGSA = High Geometric Surface Area

12.  Relative PD also relates to GSA
◦ Higher GSA means
 lower SOR pressure drop
 more absolute PD margin
 a slightly lower eexp before a limiting
absolute PD value is reached
◦ Relative SOR PD
 1" dia spheres: 100%
 HGSA Support 16x10x7: 63%
 HGSA Support 16x16x7: 58%