The olive bone, with a calorific value of 4,100-4,450 Kcal / kg, is an energy resource of great economic interest in olive-growing areas. Although its production is insufficient for energy self-sufficiency, its influence is important in olive growing areas.
As with the fatty yield of the olive, the percentage of olive bone varies. This depends mainly on the olive variety and the percentage of moisture present in the olives during the collection. We can consider that between 10 and 20% of the weight of olives ground corresponds to the bone.
Considering an average of 150 grams of bone per kg of olives. We can estimate the Spanish olive bone production between 1,000,000 and 1,500,000 tons per year.
To those who would have to add the energy coming from the pulp of the dried olive (orujillo). Once the olive pomace oil is extracted, another by-product known by the name of orujillo is obtained. Formed by skin, pulp and bone remains, the orujillo has an energy power lower than that of the bone. The orujillo (3,900 Kcal), is used to produce electricity in biomass plants and manufacture cheap pellets for boilers.
Separation of bone and alperujo
To take advantage of the economic value of the olive bone, machines designed to separate the bone from the alperujo are used.
Most mills and cooperatives have in their facilities machinery to separate crushed bone from the alperujo.
However, due to space and logistics, installation is not feasible in all oil mills. You have to take into account the storage and management of bone needs space and dedication of resources.
The density of the olive bone is about 1,200 kg / m3, however, to dimension the storage areas, the bulk density must be taken into account. The bulk density of the crushed bone is about 650 kg / m3, due to the cavities that occur.
The alperujo is a byproduct from the extraction by centrifugation of olive oil. It consists of pulp, skin, bone, vegetation water (alpechin) and a portion of oil that does not it is possible to extract with the machinery of the mill.
To separate the bone from the alperujo, centrifugation methods are usually used, with a mesh or sieve that prevents the passage of the bone from the olive.
Once extracted from the alperujo, the olive bone has a certain degree of humidity, which is an inconvenience for its immediate use. For a better use of energy, it is advisable to wait for it to dry. As with olive wood, over time the olive bone will lose moisture naturally. In this way it improves its combustion capacity and its value as an energy resource. Obviously, the olive bone dries at a faster rate than the firewood, since its surface of contact with the air is greater.
Price of olive bone
The price of the olive bone varies depending on its condition and the amount purchased, approximately in 2019:
- 70 euros per ton for the uncleaned bone from the oil mills. Taking into account that about 7,000 kg of olives are needed to obtain 1 ton of bone, the valuation of the olive bone is just € 0.01 / kg.
It may seem little, but it is an extra income of 1-3% that hardly means work to obtain and that should be taken advantage of.
- 110 € / t for bulk orders clean and dehydrated bones, suitable for use in boilers and stoves.
- 120 € / t in big bag format.
- 150 € ton when packaged in 15kg bags.
At these prices, 21% VAT and transport costs should be added.
On the other hand would be the olive pomace, the Pomace pellets, it sells for just € 40 / t. Its calorific value is only 5-15% lower than bone, however, the ash production is much higher than that of bone. Reason that explains its lower value as a fuel for boilers or stoves.
In general, the olive bone is cheap compared to other energy resources. The lower tax burden, abundance existing in olive-growing areas and its lower versatility as fuel, favor economic prices for consumers.
In Andalucía, it is estimated that biomass energy, with the olive bone at the head, employs more than 20,000 people considering the part destined to production electric and thermal energy (burners, stoves, ovens, boilers, supply…). Considering the volume of olive bone and pomace produced in Andalusia and the sales prices of the product, an approximate market of 150 million euros is observed.
Production of Jaén olive bone
In Jaén there are between 400,000 and 600,000 tons of olive bone at year. Equivalent to 750 kg of bone per capita, with an energy power comparable to 350 liters of oil. Taking into account the per capita consumption in Spain is approximately 10 barrels per person per year. It can be considered that 20-25% of the annual energy consumption for the province of Jaén can be sustained with the olive bone. In addition, olive groves produce more traces of usable biomass such as olive pomace and firewood from the pruning of the olive tree. Counting the use of all the by-products from the work to produce oil, we approach an energy equivalent to 50% of the province’s oil needs.
It is clear that many olive families have energy self-supply capacity. In fact, the use of biomass boilers and olive bone stoves in Andalusian homes is frequent.
Savings by having a stove or boilers of olive bone
We have translated the information on our website from Spanish to English. Note that some words may have seen their meaning altered during their translation.