Promoting the penetration of agrobiomass heating in European rural areas

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Combustion of solid biofuels from olive tree prunings

Main interest of an Integrated Biomass Logistic Centre (IBLC) in the olive sector is the exploitation of olive prunings. Olive prunings are treated as agricultural residues and mostly burned in open fires or less frequently mulched into soil. However, they can be exploited in various ways and offer added value. One main exploitation method of harvested olive tree prunings (OTP) is that for energy purposes. Olive tree prunings can be used either in hog fuel or in chip or pellet form for the production of bioenergy.

In this light, AGROinLOG investigated the combustion efficiency of fuels derived from olive tree pruning and their validation at industrial boilers.

The olive tree prunings that were harvested during the demo actions -implemented in the area of Agios Konstantinos, Greece, and the respective solid biofuels (pellets) that were produced form these prunings, were used in various industrial facilities with biomass boilers in order to validate their suitability as solid biofuels.

Combustion of OTP pellets (left) vs sunflower husk pellets (right) at industrial boiler: combustion chamber inspection (first row) and ash formation inspection (second row)

All industrial facilities that tested the produced biofuels, both in pellet and hog fuel form, were very satisfied with their performance. However, a few domestic users that tried the OTP pellets stated that they encountered problems due to the high ash content of the OTP pellets.

In the case of a greenhouse in Northern Greece, where emission measurements were also performed, OTP pellets slightly decreased the boiler’s efficiency compared to the reference fuel (sunflower husk pellets). Nonetheless, the loss of efficiency is mostly related to the increased energy density of the OTP. The higher energy density led to the decrease of the feeding rate by the boiler operator. However, the setting of the boiler was not optimum, thus higher losses were observed (high flue gas temperature). Apart from the slightly decreased efficiency, the emissions for OTP pellets were lower for CO, NOx and CO2. On the other hand, OGC emissions were much higher with OTP pellets compared to sunflower husk pellets. With both fuels, the boiler emissions were within the MCPD limits for NOx and SO2 emissions. The dust emissions however were much higher than the limits. More validation tests of OTP fuels at industrial boilers will be performed later on.

Consequently, OTP pellets can compete with well-established industrial fuels, in terms of combustion efficiency and emissions. The vast amount of untapped biomass of olive tree prunings along with cost-effective harvesting configurations and logistics constitute OTP pellet a solid biofuel with great potential and future.

Source: Agroinlog H2020 project

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