Petroleum Coke
Petroleum coke (petcoke or pet coke) is a carbonaceous solid produced from oil refinery coker units or other cracking processes. Common coking methods include delayed coking, fluid coking, flexicoking, and contact coking. During these processes, heavy residual oils are converted into a high-carbon solid fuel.
Unlike calcined petroleum coke, fuel-grade petcoke does not undergo high-temperature calcining. It is primarily used as an industrial and energy fuel rather than for anode production.
Raw Petcoke Specifications
| Parameter | Value |
|---|---|
| Gross Calorific Value | 8,200 kcal/kg |
| Moisture Content | < 3% |
| Ash Content | 0.1 – 1% |
| Sulphur | < 3% (max) |
| Volatile Matter | 12 – 17% |
| Fixed Carbon | > 80% |
| Size | < 25 mm |
Petcoke Grades by Sulphur Content
Sulphur content significantly affects pricing and end-use applications. Buyers typically classify petcoke into three grades:
| Grade | Sulphur Level | Typical Application |
|---|---|---|
| Low Sulphur (LS) | < 1.5% | Blending & limited combustion |
| Medium Sulphur (MS) | 1.5% – 4.0% | Cement & industrial use |
| High Sulphur (HS) | > 4.5% | Power plants & kilns |
Types of Petroleum Coke
There are two primary commercial categories:
- Anode-grade (Green / Calcinable) Petcoke – Low in sulphur and metals. Suitable for further processing into calcined petroleum coke (CPC) for aluminium and steel anodes.
- Fuel-grade Petcoke – Higher in sulphur and metals. Used mainly as a fuel.
The coke exiting the coker unit is called green coke (unprocessed). Calcining green coke in a rotary kiln removes residual volatile hydrocarbons. The resulting calcined petroleum coke can be further baked into anodes used in aluminium and steel production.
Morphological types include:
- Needle coke (acicular coke) – Highly crystalline; used for electrodes in steel and aluminium industries. Produced from FCC decant oil or coal tar pitch.
- Honeycomb coke – Intermediate structure with uniformly distributed ellipsoidal pores; lower coefficient of thermal expansion than needle coke.
- Sponge coke and Shot coke – Common fuel-grade morphologies. Lower temperatures and higher pressures favour sponge coke formation.
Fuel-Grade Petroleum Coke – Typical Specifications
| Parameter | Value |
|---|---|
| Ash content | 1.0% max |
| Volatile matter | 12.0% max |
| Sulphur content | 5.0% max |
| Moisture content | 8.0% max |
| Size (< 8 mm) | 90% max |
| Net Calorific Value (ARB) | 7,500 kcal/kg min |
| Hardgrove Grindability Index (HGI) | 50 min |
Calcined Petroleum Coke (CPC) Specifications
Option 1
| Parameter | Specification |
|---|---|
| Size | 1–5 mm / 1–3 mm / 3–5 mm |
| Fixed Carbon | 98.5% min |
| Sulphur | 0.5% max |
| Moisture | 0.5% max |
| Ash | 0.5% max |
| Volatile Matter | 0.7% max |
Option 2
| Parameter | Specification |
|---|---|
| GCV (ADB) | 8,500 kcal/kg |
| Total Moisture (ARB) | 1% |
| Inherent Moisture (ADB) | 0% |
| Ash (ADB) | 0% |
| Size | 0–20 mm |
Environmental & Combustion Notes
Petcoke is typically over 90% carbon. On a per-unit-of-energy basis it emits 5–10% more CO₂ than coal. On a weight basis, emissions can be 30–80% higher due to its higher energy density. High sulphur content requires appropriate flue-gas treatment (e.g., SNOX or other desulphurisation systems). Fluidised-bed combustion and gasification are commonly employed.
Applications
| Category | End Uses |
|---|---|
| Fuel / Feedstock | Cement kilns, lime kilns, industrial boilers, gasification units, power generation |
| Carbon Source | Aluminium anodes, steel electrodes, synthetic graphite, TiO₂ pigments, carbon raiser, silicon carbide, foundries, coke ovens |
Cement industry note: Green delayed petcoke is the most commonly used type, though blends with fluid or flexicoke are also employed.
Advantages of Fuel-Grade Petcoke over Coal
- Significantly higher calorific value (typically > 7,800 kcal/kg vs 3,500–4,500 kcal/kg for coal)
- Hydrophobic nature (advantageous in rainy seasons compared with hydrophilic coal)
- Low volatile matter → minimal evaporation losses
- Higher density → lower transportation cost relative to liquid fuels
- Very low ash content
