1. Lizeth Ortiz Advisor: Dr. Ben Church Materials Science and Engineering
Performance of alumina forming alloys under repeated coking and de-coking cycles
Lizeth Ortiz
Advisor: Dr. Ben Church
Materials Science and Engineering

2. Ethylene production Steam crackers are made of alloys that provide:
High temperature mechanical strength
Chemical resistance to attack under the aggressive carbon-rich conditions
Production facilities are periodically taken off-line
Reactor systems can be “de-coked”
Loss of production efficiency (~2-8% of annual capacity)
Blockages of coke formed inside a serpentine furnace tube.*
Steam crackers
Ethane
Propane
Ethylene

3. Alloy composition in wt%.
Cyclic test
Pre-Oxidation
100% Steam
12 hours at 850 °C
1 hour at 915 °C
Coking
30:1 H2:C2H6
Temp: 950 °C
Time: 12 hours
Decoking
Temp: 850 °C
Finish cycle 10
Alloy composition in wt%.

4. RESULTS: Cyclic Test G3606 – 3.2% Al G3610 – 3.9% Al HP-Nb Coking
De-Coking
HP-Nb
Average of 3 samples/material
All mass changes are relative to the mass after pre-oxidation

5. This work is sponsored by ARPA-E; DE-AR0000690
SUMMARY
Mass changes showed that the HP-Nb alloy had the highest gain in mass compare to the AFA alloys both for pre-oxidation and coking/de- coking cycles.
AFA alloys showed an stabilization on their change in mass after the 4th cycle while HP-Nb continued gaining mass.
Oxide layer and coke layer are seen in SEM pictures for each alloy.
Overall, alumina-forming alloys are showing better resistance to cyclic conditions than chromia-forming alloy.
Future work will focus on:
Cyclic conditions with alloys of different Aluminum content
Study of longer cyclic effects as well as thermogravimetric analysis.
Comparative studies of alloy behavior of alternative feedstocks.
This work is sponsored by ARPA-E; DE-AR
Electron microscopy conducted in the UW-Milwaukee Advanced Analysis Facility