Petroleum Refining, Fluid Catalytic Cracking (FCC) & Heat Balance
FCC Regenerator Coke Burn, Catalyst Circulation & Air Rate Formula
Calculate Zeolite Catalyst Circulation Rate (t/hr), Regenerator Coke Burn Rate (kg/hr), Exothermic Regenerator Heat Duty (MWth), and Main Air Blower Mass Flow (t/hr).
An FCC unit is a self-balancing thermal flywheel—burning catalytic coke in the regenerator powers endothermic riser cracking!
In a refinery Fluid Catalytic Cracking (FCC) unit upgrading heavy vacuum gas oil (VGO) into high-octane gasoline and propylene, hot regenerated zeolite catalyst circulates up the riser reactor at Catalyst-to-Oil Mass Ratio (C/O, typically 5–8 t catalyst / t oil), depositing spent hydrocarbon coke during cracking and returning to a fluidized-bed Regenerator at 700°C! Burning off Delta Coke = Wt%_Spent_Coke - Wt%_Regen_Coke (typically 0.70–1.00 wt% on circulating catalyst!) releases Coke_Burn_kg_hr = Oil_Feed_t_hr * CO_Ratio * 1,000 * (Delta_Coke_Pct / 100)! In real refinery operations, the Main Air Blower (MAB) limit (~12.0–13.0 kg dry air per kg CH_x coke burned at 2%–3% flue-gas O2) is the #1 bottleneck capping refinery gasoline throughput on heavier resid feeds!
Verify on a 250.0 t/hr (~42,000 bbl/d) VGO FCC Unit—Gas_Oil_Feed = 250.0 t/hr (B2), Catalyst_to_Oil_Ratio C/O = 6.0 (B3 -> Catalyst Circulation = 1,500.00 t/hr = 25 t/min! in E2), Delta_Coke_on_Catalyst = 0.80 wt% (B4), Coke_Combustion_Enthalpy = 31.0 MJ/kg coke (full-burn CO2 mode, B5), and Specific_Air_Requirement = 12.5 kg air/kg coke (B6): Regenerator Coke Burn hits 12,000.00 kg/hr (12.0 t/hr, E3), Regenerator Thermal Duty equals (12,000 * 31.0) / 3,600 = 103.33 MWth (E4), and Main Air Blower Demand equals (12,000 * 12.5) / 1,000 = 150.00 t/hr (E5)!
| FCC Riser-Regenerator KPI (250 t/hr VGO, C/O = 6.0, dCoke = 0.80 wt%) | Formula | Verified Output |
|---|---|---|
| Catalyst Circulation Rate (t/hr) | Gas_Oil_Feed_t_hr * Cat_to_Oil_Ratio | 1,500.00 t/hr |
| Regenerator Coke Burn (kg/hr) | Cat_Circ_t_hr * 1000 * (Delta_Coke_Pct/100) | 12,000.00 kg/hr (15,000 @ 1.0% dC) |
| Regenerator Heat Duty (MWth) | (Coke_Burn_kg_hr * Heat_MJ_kg) / 3600 | 103.33 MWth (129.17 @ 1.0% dC) |
| Main Air Blower Flow (t/hr) | (Coke_Burn_kg_hr * Air_kg_per_kg) / 1000 | 150.00 t/hr (187.50 @ 1.0% dC!) |
FCC Regenerator Coke Burn & Main Air Blower Capacity Formula
Validate Oil_Feed > 0, Cat_to_Oil_Ratio in [2, 15], Delta_Coke_Pct in (0.10, 2.50], Heat_MJ_kg in [15, 36] (partial CO vs full CO2 burn), and Air_per_Coke in [8, 18]!
=LET(ol_f, B2, co_r, B3, dc_p, B4, dh_c, B5, ar_k, B6, IF(OR(ol_f <= 0, co_r < 2, co_r > 15, dc_p <= 0.1, dc_p > 2.5, dh_c < 15, dh_c > 36, ar_k < 8, ar_k > 18), "Invalid FCC Input", LET(ck_b, ol_f * co_r * 1000 * (dc_p / 100), ROUND((ck_b * dh_c) / 3600, 2))))Heavier Conradson Carbon Resid Feed Blower Bottleneck Check (Set Delta Coke = 1.00 wt%)
Blend atmospheric resid into VGO raising Delta_Coke B4 from 0.80% to 1.00 wt%: Coke Burn E3 jumps to 15,000.00 kg/hr, Regenerator Heat Duty E4 surges to 129.17 MWth (requiring a catalyst cooler!), and Main Air Blower Demand E5 spikes 25% to 187.50 t/hr!
=IF(ISTEXT(E4), E4, ROUND((B2 * B3 * 1000 * (B4 / 100) * B6) / 1000, 2))Try the example
Use the original values or change them to test your understanding.