is cumulative but dependent on the level of poison in the feed. Because poisoning rates depend on concentration, it should be apparent at the inlet in a short reaction zone and slowly progress through the bed. A way to forecast performance across the lifetime of a catalyst charge is provided in OGT’s proprietary SulphurPro simulator. Examples will illustrate application to field obser - vations to interpret operating system temperature profiles. Primary causes of deactivation and considerations for its mitigation are discussed further in Part 3. All ageing and poisoning mechanisms are implemented in SulphurPro as function declines, requiring the user to input service run-time and exposure to poisoning stresses. Different user-configurable poisoning factors include options to specify the use of a reducing gas generator (RGG) burner, refinery gas, and reformer hydrogen as fuel sources. There is also an option to specify whether the unit processes off-gas from acid gas recovery units. In addition, the interface allows for specifying conditions such as the percentage of excess air and the level of BTEX in the feed gas. Taken together, these options allow the construction of a poisoning factor that is built into the mathematical frame- work of the catalyst bed. The SulphurPro user interface for specifying the ageing and poisoning level is shown in Figure 4 . Model case study To study the usability of the model, a case study was done by running the hydrogenation reactor model on a typical tail gas reactor feed at various levels of catalyst ageing and poisoning. Figure 5 shows the temperature profiles in the bed as a function of catalyst age under various poisoning conditions. The x-axis denotes the time online in months,
the primary y-axis shows the percentage temperature rise that occurs in each quarter of the bed, and the sec- ondary y-axis gives the total temperature rise across the entire catalyst bed. Each plot refers to a different poisoning mechanism. Note: these profiles show four zones, but the bottom zone (lower bed-to-outlet) in most operating units is disregarded because heat losses accrue here, and DT is often negative. The poisoning situations that were studied include an idealised operating scenario, which has no poisoning sources, including the expected poisoning of a gas plant and a refinery operating with a clean source of hydrogen; units with an inline RGG burner; reformer hydrogen and a TGU processing the off-gas from an acid gas enrichment (AGE) unit. Figure 6 shows the outlet concentration of vari- ous sulphur species for the same runs. The Figure 6 curves represent the different poisoning cases, and each sulphur- bearing species is shown in the individual plots. Figure 4 OGT SulphurPro interface for specifying catalyst age and poisoning level
Ag e ing only, no poisoning
Reformer hydrogen
Nominal re nery
100
100
80
80
60
60
40
40
20
20
0
0
0
20
40
60
80
100
120
0
20
40
60
80
100
120
0
20
40
60
80
100
120
Time on-line, months
% DT top
% DT mid
% DT lower
% DT bot
DT overall deg C
Nominal gas plant
AGE o -gas
RGG burner
40
40
30
30
20
20
10
10
0
0
0
20
40
60
80
100
120
0
20
40
60
80
100
120
0
20
40
60
80
100
120
Time on-line, months
Figure 5 Reactor temperature profile as a function of catalyst age at various poisoning levels
57
PTQ Q2 2023
www.digitalrefining.com
Powered by FlippingBook