How do you troubleshoot poor FCC unit performance?

FCC troubleshooting methodology: Symptoms analysis - low conversion, poor selectivity, high delta coke, equipment damage. Data gathering - compare current vs. baseline operation, review trends. Catalyst evaluation - activity (MAT), coke selectivity, particle size, metal content (Ni, V), physical properties. Feed analysis - CCR, metals, nitrogen, density changes. Operating conditions review - riser temperature, C/O ratio, regenerator temperature. Mechanical inspection - catalyst distribution, riser termination, cyclone performance, slide valve operation. Common problems and solutions: Low conversion - insufficient temperature, low activity catalyst, feed quality change; increase temperature or fresh catalyst addition. High coke - metal contamination, poor feed quality; passivate metals with Sb or Bi, improve feed. Poor selectivity - catalyst circulation issues, temperature maldistribution; check slide valves, distributor. Systematic approach: one variable at a time, validate with test runs, monitor response.