Waste products from the olive oil production process are used to fuel a 30 MWe gas turbine-based cogeneration system in southern Spain, delivering significant economic and environmental benefits to the area. Marco van Schaik reports.

The European regulations on the disposal of agricultural waste and the associated cost of this disposal can have a big impact on the economics of the olive oil production process – costs that are ultimately passed on to end-users. Therefore it is essential to find solutions for the utilization and valorization of the olive oil waste.

The use of biomass for drying, incineration and power generation is economically feasible and can be easily integrated into a factory’s existing equipment. The technology has great economic and environmental benefits compared with open combustion of the waste. With the world producing about 2 million tonnes of olive oil per year (including 660,000 tonnes in Spain alone, 500,000 tonnes in Italy, and 360,000 tonnes in Greece), there is a large potential for this well proven technology.


Residues from the olive oil production process serve as biomass feedstock for the on-site cogeneration plant at an olive mill
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In early 2003 Bioenergía Santamaría, a Spanish company which uses olive oil production residues for the generation of power, awarded Turbomach the contract for the engineering, procurement and construction (EPC) of the biomass-fired power plant in Lucena, Córdoba. The plant is based on a 14.3 MWe gas turbine generator package, an olive oil residue incinerator and heat recovery system, and a 14.8 MWe steam turbine generator package. Turbomach has been acting as the main contractor and O&M contractor for the plant. The gas turbine and steam turbine generator packages are products from Turbomach.

THE OBJECTIVE

The plant aims to recycle in the most economic way the residues from olive oil mills, specifically the solid/liquid mixture by-product, or alperujo, coming from Hermanos Santamaría, a producer of olive oil and pomace oil. (Pomace is the by-product of the first phase oil production. Pomace is often sent to reprocessors where (often with steam) more oil (secondary) is removed. This oil is called pomace oil.)

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After analyzing several possible processes, and on the basis of previous experience, Bioenergía Santamaría decided to undertake a project in the town of Lucena to process the alperujo from several of the region’s olive oil mills, extract the pomace oil it still contains, and produce electrical energy.

THE PROCESS

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Phase I: Production of pomace oil

The alperujo from various olive oil mills within a 70 km radius of Lucena (which includes the provinces of the Community of Andalusia, such as Córdoba, Jaén, Málaga, Seville and Granada) is stored in two new evaporation ponds with a total capacity of 170,000 tonnes. The pond-filling process is known as campana (referring to the annual harvest) and lasts approximately five months, which is the length of the olive oil production period in the mills. The stored product is processed in some six months.

The alperujo is then put through a physical process using decanters, or horizontal centrifuges, to extract pomace oil and further alperujo. An annual production of some 2000 tonnes of pomace oil is expected, which will be sent to the refineries before being used for human consumption.

The alperujo has good heating value but also contains a high level of moisture, rendering it unviable for combustion. Therefore this residue must be dried before being used as fuel.

Phase II: drying the alperujo

About 240,000 tonnes/year of olive oil residue (orujo) is available. This residue has a moisture level of 65% – 70% and must be dried before it can be recycled. The drying system consists of a horizontal drier (trommel-type) which uses hot gases from a combustion chamber for drying.

In the past, the dried pulp residue (orujillo), normally with the stones removed, was combusted in a chamber to generate hot gases of 500°C. The drying process consisted of two phases. In the first phase, approximately 48% of the moisture was driven out. Then the material went into a second dryer where its moisture was reduced to 10% – 12%. Some of the dried orujillo obtained was used as fuel for the drying process itself and the remainder sold to industrial facilities such as brick factories.

However, the introduction of natural gas in Spain has considerably decreased the demand for orujillo.

In view of the special characteristics of the dryer, the heat required appeared very well in line to the latent heat in a gas turbine generator package which produces gases at a temperature of around 500°C. This led to the development of a drying phase along with the use of the TBM-T-130 gas turbine generator, which is able to supply heat for the dryers while producing electrical energy. The special combustion characteristics of the gas turbine generator package ensure that the exhaust gases are clean, without any traces of lubrication oil or pollutants.

At the end of the process, two different products with a high specific value are obtained. Of these, orujillo with a moisture content of 10% – 12% is suitable for direct combustion. It is also recyclable, either for sale to third parties or for use in the new cogeneration plant which is connected to the Endesa grid. The dried orujillo, the other product, is stored in a silo in an area near the cogeneration plant.

THE COGENERATION PLANT

As discussed, the heat requirement for the drying process, on the basis of operating more than 8200 hours/year, permitted the installation of a 14.3 MWe gas turbine generator package based on the Solar Titan 130 industrial gas turbine which generates more than 100,000 MWhth/year. The exhaust gases are supplied directly and in parallel to two tram-mel-type dryers. Gases exit the gas turbine generator at 45 kg/s at about 495°C. About 10% of the exhaust gases from the gas turbine is conducted to the biomass boiler to increase the plant efficiency by pre-heating the boiler’s combustion air, which will be regulated to minimize the formation of NOx and CO.


The gas turbine cogeneration package achieves about 90% fuel efficiency
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The fuel efficiency of the cogeneration plant is close to 90%, whereas the electrical efficiency is 34%. Approximately 1.5 MWe is used for the plant’s own consumption.

The gas turbine is fed with LNG stored at the site. In the future the plant will connect to the gas pipeline at the town of Lucena in Córdoba.

Out of the approximately 92,600 tonnes/year of orujillo with 10% – 12% moisture and around 4000 kcal/kg of heating value, around 77,000 tonnes are burnt per year in the biomass plant. The rest will be provided as fuel to the Hermanos Santamaría plant.

Orujillo is combusted in the biomass boiler that produces steam at highpressure and temperature. The biomass boiler will produce superheated steam at about 65 bars and 450°C, at about 55 tonnes/hour. The boiler has a high heat output so that the efficiency of the biomass plant surpasses 30%. The flue gas from the boiler is filtered to prevent the emission of particles into the atmosphere.

The steam produced is expanded up to 0.08 bar in a Turbomach-TV2 steam turbine generator package. The steam turbine is a MARC4C01 system manufactured by B+V Industrietechnik. It is equipped with an intermediate bleed to feed the thermal de-aerator.

The steam turbine generator package has a capacity of about 14.8 MWe, with the export of some 104,000 MWh/year of electrical energy.

The electrical power generated by the plant at 11 kV will be connected to the Sevillana-Endesa grid at 66 kV via a step-up transformer station. The plant is furthermore provided with its own utilities for compressed air and low-voltage power (400 V). Both the gas turbine generator package and the steam turbine generator package are installed outdoor with their own individual weatherproof and sound-attenuating enclosures. The electrical substations are also located outdoor. The plant is provided with one main building where the auxiliary services and control room is located.

In order to increase plant efficiency and taking into account the climate of the site (high temperature and low humidity in summer), an evaporative cooler system is installed in the gas turbine combustion air inlet system to reduce the temperature of the combustion air to a maximum of 20°C. This increases the power output of the gas turbine generator from 12,400 kW to 12,800 kW in periods of extreme heat. This cooler will be fed by osmotized water from the biomass plant. The steam will be condensed in a condenser, which will be cooled by water from cooling towers.

The incineration of biomass can be considered CO2-neutral as the CO2 captured during the growth of the olives (via photosynthesis) is being released again to the atmosphere. In comparison to a coal-fired power plant, biomass incineration at the plant reduces the emission of CO2 by about 110,000 tonnes per year.


About 1.5 MW of electricity generated at the 30 MW plant is used on-site, while much of the rest is sold to the grid.
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The facility has been designed to work non-stop and at 100% load for some 7800 hours per year. Virtually all of the olive oil plant’s auxiliary services will be shared with the cogeneration plant.

OPERATION AND MAINTENANCE

Together will the turnkey supply agreement, Turbomach has signed a contract for the operation and maintenance of the cogeneration and biomass plant for a period of 20 years. The plant is being operated in three shifts with two operators and a supervisor. Furthermore there are two maintenance engineers and two plant managers. The project provides 19 jobs in total.

Marco van Schaik is responsible for new business development at Turbomach SA, Switzerland. marco_vanschaik@turbomach.com

The players

  • Bioenergía Santamaría was founded in 2002 by Hermanos Santamaría SA and SIIF Ibérica, whose business goal is to look for economic ways of recycling the residues from olive oil mills, specifically the solid/liquid mixture by-product or alperujoas as it is called in Spanish. The power generated by the plant is sold to the utility Sevillana-Endesa.
  • Hermanos Santamaría SA is a family enterprise located in Lucena, Córdoba. Its main activity is the production of olive oil and pomace oil. It also has a 1.7 MW biomass electric plant.
  • SIIF Ibérica (70% of Bioenergía Santamaría) is the 100%-owned subsidiary of the French group SIIF Energies (EDF group, a national electricity company), specialized in renewable energies. Apart from this project, SIIF Ibérica is developing other similar plants in Spain.
  • Turbomach SA is a well established name in the world power market. The company is wholly owned by Caterpillar (USA). The company has accumulated more than 25 years of knowledge and experience in technical design, application engineering, and manufacturing of power plants based on its gas and steam turbine packages.