Refiners’ heavy choice: coker or FCC as specs tighten

Refineries start by splitting crude into light gases (C₁–C₄), LPG (liquefied petroleum gas), light/heavy naphtha, kerosene/jet, diesel (gas oil), heavy vacuum gasoil, and vacuum residue. From there, each stream takes a different path: light naphtha is usually processed in a reformer (or isomerizer/alkylation unit) to make high‑octane gasoline; middle distillates (kerosene/diesel) are hydrotreated (hydrogen-based cleanup) to remove sulfur and improve cetane; heavy vacuum gasoil often heads to an FCC (fluid catalytic cracking) unit or a hydrocracker. The heaviest cuts (vacuum residue) either become fuel oil—now subject to strict sulfur limits—or are upgraded.

Product specs are setting the tone. In Indonesia today, diesel must meet two grades — CN48 (cetane number 48) with ≤3,500 ppm S now, tightening to 500 ppm by 2021 and 50 ppm by 2025 (transportpolicy.net) (transportpolicy.net) — and CN51 (cetane number 51) with ≤500 ppm S. Gasoline must be unleaded with RON≥90 (Research Octane Number; Indonesia phased out RON88 fuel in 2023, qcintel.com) and ≤500 ppm S (transportpolicy.net). These specifications drive refiners to maximize hydroprocessing and conversion of heavy residues into clean fuels.

Vacuum residue conversion routes

Delayed coking (DCU). Vacuum resid is thermally cracked (furnace 482–516 °C, moderate pressure) into hydrocarbons and solid coke. Typical DCU product yields (wt%) can be ~10–15% C₅–360°F naphtha, ~20–27% 360–650°F gasoil, ~20–38% >650°F gasoil, ~7–9% dry gas (C₁–C₄), and ~20–26% coke (refiningcommunity.com). In one commercial test at 910°F heater outlet, dropping the coker drum pressure from 48 to 23 psia shifted yield from 15.4% to 11.1% naphtha and from 26.5% to 22.0% coke (refiningcommunity.com). In practice, delayed coking produces roughly ≥30 wt% petroleum coke (fliphtml5.com). More severe variants — fluid coking or flexicoking — partial‑gasify the coke and yield much less solid carbon (~20% or as low as 2%, fliphtml5.com). Coker naphtha and gasoil are low‑quality (low RON, high aromatics and sulfur) and are always hydrotreated before blending into gasoline or diesel.

Fluid catalytic cracking (FCC). An FCC unit (riser reactor) cracks heavy gas oils (roughly 316–566 °C) over zeolite catalysts to maximize gasoline. “The FCC…cracks heavy desulphurized feedstock into lighter, mainly high octane gasoline,” and produces C₃–C₄ olefins and LPG (fliphtml5.com). Typical yields: 45–60 vol% gasoline (C₅–C₁₀), ~10–20 vol% LPG, ~10–20 vol% light cycle oil (diesel‑range), and ~5–10 wt% coke, depending on conversion. FCC gasoline is high‑octane (90–100 RON) and readily meets blend specifications after hydrotreatment of the feed. FCC light cycle oil (LCO) is high in aromatics (low cetane) and usually goes to hydrocrackers or hydrotreaters for diesel blending. Overall, FCC prioritizes gasoline and petrochemical feed (LPG/propylene) production, whereas coking maximizes distillate plus residue rejection (as coke). Global trends show gasoline demand growth slowing (due to EVs), while LPG/naphtha for petrochemicals is rising (asiandownstreaminsights.com), so many refiners find higher margin in FCC units when converting resid.

Feed quality and pretreatment

Coking accepts very heavy, metal‑rich feeds (vacuum resid, CCR ~20–30%, Ni+V in the thousands ppm) with minimal pretreatment. Its drawback is high coke yield — up to ~30% of feed weight (fliphtml5.com). FCC requires cleaner feeds: vacuum gasoil or hydrotreated coker gasoil with low Conradson carbon and low metals. Feeds are often hydrotreated (and even deoiled) first (fliphtml5.com). A specialized Resid FCC (RFCC) can intake vacuum resid, but only if it’s first desulfurized/deasphalted; otherwise metal‑rich coke poisons the catalyst (fliphtml5.com).

Gasoline pool requirements

Gasoline in Indonesia must be unleaded; RON ≥ 90 (Indonesia raised the minimum to 90 RON from January 2023, qcintel.com). Sulfur ≤ 500 ppm nationwide (transportpolicy.net) with a target of 50 ppm by 2025 (transportpolicy.net). Other typical specs (not Indonesia‑specific) include Reid vapor pressure ~45–60 kPa, benzene ≤ 1 vol%, and aromatics ≤ 35 vol% (EU standards). FCC gasoline usually meets these after proper blending and hydrotreating of the feed (fliphtml5.com).

Diesel and middle distillates

Diesel grades include CN48 (“BioSolar”) and CN51 (“Pertamina Dex”); sulfur is ≤ 500 ppm for CN51 and currently ≤ 3,500 ppm for CN48 (transportpolicy.net) (transitioning to 500 ppm by 2021 and 50 ppm by 2025, transportpolicy.net

Kerosene and jet fuel specs

Per IMO 2020, sulfur in fuel oil (residue/bunker) must be ≤ 0.5 wt% (manifoldtimes.com). Indonesia’s official bunker fuel spec (ISO MFO 180 and MFO 380) sets S ≤ 0.5% (manifoldtimes.com), density ≤ 991 kg/m³, and viscosity ≤ 180 or 380 cSt at 50 °C (manifoldtimes.com). Other limits include vanadium ≤ 350 ppm and carbon residue ≤ 18% (manifoldtimes.com). These tight specs mean any heavy fractions from residue cracking must be desulfurized (or blended) if sold as bunker fuel.

LPG fractionation and sweetening

Contract LPG (mostly C₃/C₄) for domestic supply or petrochemicals must be dry (H₂O < 10 ppm) and sulfur‑free (H₂S typically < 5–10 ppm). LPG from FCC or coker is fractionated and sweetened to meet these requirements.

Blending control and hydrotreating

Every product pool is monitored: gasoline pool sulfur is blended to meet the 500 ppm spec, often requiring undercutting the heavy tail of the FCC gasoline cut if sulfur creeps above market limit (ogj.com). Diesel pool cetane and sulfur are similarly managed by blending hydrotreat products. In practice, all cracked naphtha and gasoil streams are hydrotreated to meet these product specs. For instance, coker naphtha (rich in olefins) is saturated and desulfurized to become reformer feed or alkylation feedstock, while FCC LCO is often hydrocracked into diesel.

Margin logic and sources

Overall, the choice of coking vs. FCC heavily influences the refinery’s product slate and the downstream quality adjustments needed. Coking can handle cheaper, heavier feed (tolerating metals) but requires large hydrotreating of its liquid products, whereas FCC yields more gasoline/LPG (requiring catalytic pretreatment or hydrotreat of feed) (fliphtml5.com). The data above — e.g., FCC’s 50% gasoline vs. coker’s ~25% coke yields (fliphtml5.com) (refiningcommunity.com) — help refiners decide which path yields the best margin under current market and regulatory conditions.

Industry studies and reports underpin the yields and specs cited here: one plant’s delayed coker data (refiningcommunity.com) and tabulated coking processes (fliphtml5.com) quantify yields; Indonesian fuel regulations are summarized by TransportPolicy (transportpolicy.net) (transportpolicy.net) and recent news (qcintel.com) (manifoldtimes.com), among others. Data‑backed insights (e.g., trends in residual cracking) are drawn from published reviews (fliphtml5.com) (asiandownstreaminsights.com).