Olive cake
Olive cake is a by-product of the second extraction of olive oil. First extraction is done in the olive oil factories by mechanical squeezing of the olives. As a result of it, so called virgin olive oil is received. Remaining brown mass, called pomace, has a moisture of about 60% and oil content of about 7-8%. After the first extraction of olive oil, pomace is then transported to specialized factories, where the second extraction of oil by hexane is completed. As a result of this process, the second extraction oil is produced and the residue consisting of olive meat, olive skin, whole and crushed olive stones with the moisture of around 13-14% is received. This material is called olive cake and it is a biofuel.
In majority of cases, olive stones are separated from olive cake, but even after this process about 30% of the crushed olive stones still remain in the material.
During several years, starting from 2001, olive cake was widely used in Belgium, UK and later in Poland for co-firing with coal. Usually, about 4-7% of olive cake was admixed to coal before entering the boiler. Later, most of the coal-fired power plants in Europe were converted to wood pellets. Nowadays, olive cake is not used so widely anymore by big power plants. Though, it is still utilized for co-combustion in some smaller power stations. It can also be used in biomass dedicated power plants as a single fuel or in combination with other biomass products.
Olive cake’s usual specification:
| Parameter | Value | Parameter | Value |
| Moisture | 12-17% | Cr. (Chromium) | 4-8 mg/kg |
| Ash | 6-8% | Cu. (Copper) | 10-20 mg/kg |
| Net calorific value | 15-16 Gj/mt | Zn. (Zinc) | 16-19 mg/kg |
| Bulk density | 650-680 kg/m3 | Cl. (Chlorine) | <0,4% |
| K. (Potassium) | <3% | S. (Sulphur) | <0,12% |
| As. (Arcenic) | 0,1-0,9 mg/kg | Ni. (Nickel) | 4,5 mg/kg |
| Hg. (Mercury) | <0,1 mg/kg | V. (Vanadium) | <1,0 mg/kg |
Oil content is usually about 1,5% and it should not exceed 4%. Combination of moisture and oil in the biomass cargo over 20% (for example, 16% of moisture and 4% of oil) is regarded to be dangerous for transportation, as it can cause self-combustion.
Learn more:
