//Progress in the Greek demo: Production of solid biofuels from olive tree prunings

Progress in the Greek demo: Production of solid biofuels from olive tree prunings

18 December 2019

The main goal of AGROinLOG is the demonstration of Integrated Biomass Logistic Centres (IBLC) for food and non-food products. In Greece, the study to evaluate the potential implementation of the IBLC model was performed on an agroindustry in the olive oil sector.

The agro-industry where the concept of the IBLC was investigated in Greece is NUTRIA. NUTRIA is an olive oil refinery plant that produces standardized olive oil, pomace oil and seed oils. The company is planning the installation of a pomace milling facility, which will provide several opportunities for its transformation into an IBLC, especially considering the use of olive tree prunings as a supplementary feedstock for the production of solid biofuels (e.g. pellets).

The main activity of an IBLC in the olive sector is the exploitation of the untapped biomass resources around it, that of olive prunings, mainly for energy means. The main equipment that can offer synergies is that of a dryer of a pomace mill that could be used also for drying olive tree prunings before their pelletization. Despite the fact that NUTRIA has not installed one yet, the concept of drying both olive tree prunings and two-phase pomace in the same dryer was investigated. From contacts made with pomace dryer manufacturers, a green-field dryer is able to dry both materials. A drawing plan and an offer of such a dryer along with its technical characteristics was retrieved, scaled at the needs of NUTRIA as an IBLC. Furthermore, the option of using existing pomace dryers was investigated. From contacts with several pomace mill owners and dryer manufacturers, it has been concluded that olive tree prunings can be also dried by existing pomace dryers if they further reduce the size of harvested prunings through an extra chipping step.

Moreover, the storage of olive tree prunings is a crucial step in the value chain of pruning exploitation. In this light, a 6 months storage test of harvested olive tree prunings from the IBLC area was performed. For comparison reasons, two piles of 3 meters height and 5.5 meters diameter were built at NUTRIA’s premises. One pile was stored as-is in open space and the other one was covered with a fleece, specialized in wood chips storage. Sample bags were used for determining the dry matter and energy variations of the olive tree prunings after two, four and six months of storage. Finally, thermocouples were used to measure the inside temperatures of the piles. After six months of storage, the covered pile showed a steady average weight loss of the retrieved sample bags. On the other hand, the sample bags retrieved from the uncovered bags had fluctuations on the weight losses due to their dependency on the weather conditions. Finally, the covered pile recorded a pretty much stable average temperature, whereas the uncovered pile recorded more violent temperature fluctuations throughout the storage period.

Figure 1: Pile A (without coverage) to the right and pile B (with fleece) to the left 

Continuously, the production of pellets from the harvested olive tree prunings was demonstrated. The harvested olive tree prunings was transported to a Greek pellet plant, subcontracted by NUTRIA. The production of around 63 t of olive tree prunings pellets was monitored. The pelletization of harvested olive tree prunings was supervised in order to assess the energy demands and production costs related to the pelletization of the harvested olive tree prunings. Finally, a fuel analysis of the produced olive tree prunings was performed for every shift during the pelletization process.

Figure 2: Pellet produced from harvested olive tree prunings

In overall, the main activity of an IBLC in the olive sector, that of the upgrading of harvested olive tree prunings into added value biofuels (pellets), along with their treatment and storage, has been demonstrated and monitored. Several parameters that influence such value chain were evaluated in order that each agroindustry willing to implement the IBLC concept, to be able to design its best strategy towards that concept.


2020-05-06T11:05:26+00:00 December 18th, 2019|