|A view of Revico’s cogeneration plant, which uses biogas derived from ‘vinasse’ waste from cognac production Source: Revico|
Farms across Europe are increasingly looking to cogeneration projects as they seek to marry green targets with sustainability. And while the industry is embryonic, pioneers in France and Italy are finding innovative ways to ramp up efficiency while keeping costs down, writes Tracey Colley.
Ferme d‘Arcy, run by the Quaak family, is a farm of the future. About 60 km from Paris near Chaumes-en-Brie, in an area famous for its cheese, the farm of about 400 hectares (ha) grows crops and pastures mainly to feed its 500 Limousine cattle. But things are changing down on the farm with the construction of a biodigester that will treat organic waste to produce biogas for upgrading to grid quality gas, the first of its type in France.
The feed streams to the biodigester include manure from the livestock sheds, some crop residues (subject to government regulations regarding sustainability), green mulch and liquid from a nearby cheese factory.
About 85% of the organic load entering the biodigesters is likely to be converted to gas, although gas production will vary according to season, with higher production in winter (up to 125 m3/hour) when livestock are in sheds and lower production during summer (50–60 m3/hour). The biodigester consists of three large tanks, one of which has the capacity to hold the digestate (liquid) over the winter period when irrigation is not needed. Some of the biogas will be used to maintain the required temperatures in the biodigester.
The site already has 1800 m2 of solar photovoltaic cells, with an installed capacity of 247 kW. Cogeneration generally works best when there is a heat and electrical need at the same time, but as this site has solar PV during daylight hours, a cogeneration plant would probably only need to operate during non-daylight hours, which tend to be lower tariff periods. Consequently, it makes more sense for the biogas generated in the biodigesters to be upgraded to grid quality. And if the ‘site’ concept is expanded to include the downstream users of the farm’s production, such as meat and dairy processing plants, then the gas produced really does help to reduce the overall carbon footprint of food production.
But the project is more than just bioenergy, it is also about improving the overall sustainability and resource efficiency of the farm. For example, the solids remaining after digestion are stabilised and can be used on the farm to augment soil quality without creating nutrient drawdown in the soil or problems with nutrient runoff into surface water streams. Meanwhile, the liquid digestate provides water for irrigation, reducing the farm’s reliance on bore water, which is heavily controlled and regulated due to the farm’s close proximity to Paris. The digestate also recycles the nutrients from livestock production, reducing the farm’s need to apply industrial fertiliser.
Selling biogas and electricity from solar PV could diversify the farm’s income with products that are connected but distinctly separate from produce such as grain and livestock. This could become increasingly important in the future, as climate change is expected to change agricultural production in ways not currently well understood. From an economic risk management perspective, it makes sense for farmers to have opportunities to mitigate some of the climate change risk that they cannot control, such as seasonal rain and temperature impacts, by diversifying into areas such as bioenergy production. As farms produce energy for humans by converting sunlight into grass or grain and then meat protein, producing renewable energy for other human needs is a natural extension of primary production.
Based on this farm’s production rates, gas can be generated at 0.14–0.34 m3/ha, and 3–7 ha are required to produce each cubic metre of gas. France’s arable land totalled about 18.4 million ha in 2009, which means 92–221 TJ of biogas could be available from farms like Ferme d’Arcy. But the extent to which the farming sector can realise this potential will depend in part on courageous pioneers like the Quaak family – who have taken on the project management challenges of the first project of its type in France – but, more importantly, on government support.
A farm in Italy
The Ospedaletto Lodigiano plant, owned by Inalca and located near Milan, Italy, is Europe’s largest beef processing plant. It consists of butchering, boning, processing and packing facilities on a 40 ha site, and processes about 350,000 head of cattle per year, many of which come from the nearby Po valley. The boning rooms process over 100,000 tonnes of product per year, and final products from the site include sides, quarters, fresh and frozen cuts, processed meats, mince and hamburgers.
Several reasons prompted Inalca and its parent company, the Cremonini Group, to adopt cogeneration. Cogeneration projects fitted with an overall objective of improving environmental sustainability. But Inalca also had an internal objective to produce 65% of its own energy requirements by 2012 through the use of cogeneration and renewable energy sources, including recycling organic wastes from livestock.
Since 2005 the plant has had two natural gas fired cogeneration sets, which each produce 1824 kW of electricity, 550 kW of steam (800 kg/h) and 1229 kW of hot water at 93°C (1229 kg/h), with an overall thermal efficiency of up to 87%. The system was designed by AB Energy to integrate with the existing hot water tanks and supply system, meaning that the steam generators are now only needed to cover peak thermal loads. The cogeneration plant is designed to operate in island mode in the event of the failure of grid electricity supply.
In November 2010 the plant installed an anaerobic digester with biogas cogeneration plant – an Ecomax® 10 Bio Container Module plant, provided by Jenbacher. The unit produces 1063 kW of electricity, 603 kW of hot water and 423 kW of thermal power to two diathermic oil boilers. The waste heat is used to maintain the digester temperature at a constant working temperature of 40°C, for hot water production and drying digested material. The latter process significantly reduces the volume of material requiring disposal, substantially reducing disposal volumes and costs.
|Revico’s biogas plant region produces 3000 MWh of electricity over a nine-month operating period Source: Revico|
From an energy conversion perspective, the cogeneration plants consume 437 Nm3/h of gas and, if we assume that they operate the same hours per year as the Ecomax10Bio plant (7055 hours per year), this equates to 3,083,255 Nm3/year of gas consumed. Gas production from the farm ranged from 50–125 m3/day for 500 cows, or 0.1–0.25 m3 per head of cattle per day depending on the season (36.5–91.25 m3/year or about 70 m3/year on average). The meat plant processes 350,000 head of cattle per year, so if we assume the cattle are at least yearlings before being processed at the plant, the cattle for this plant could provide 24,500,000 m3/year, or nearly eight times the gas requirement of the cogeneration plant. At present, 48% of the Inalca group facilities are produced within their plants, so this data suggests that integrating onfarm biogas production with meat processing could produce more gas than is required, meaning gas would be available for dairy processing plants too. Biogas could be used for transport, as in Sweden, where gas grids are less available than in France and other areas of Europe.
Water of life
Cognac is produced through distilling white wine. The remaining liquid – vinasse – must be disposed of sustainably and since the 1970s the industry has overseen this. A company called Revico handles vinasse from France’s Cognac region in a process that produces electricity and tartaric acid.
Revico treatment plant receives 300 million litres (ML) of vinasse between November and July. After the tartaric acid is removed using distillation and evaporation, the remaining liquid is directed to four anaerobic biogas reactors, with a total volume of 17,500 m3. Primary energy from the four digesters totals about 20 GWh each year, or 67 MWh/ML of wastewater.
The biogas had been used in three boilers to produce steam for process heating at the Revico facility. But when Revico were looking to upgrade the boiler system it worked with SAS Verdesis (the European distributor of Capstone microturbines and a subsidiary of EDF Energies Nouvelles) to create the SAS Revico Energies Vertes (Green Energies) joint venture. As a result, one boiler was replaced with a C800 CHP microturbine power plant, commissioned in 2009.
Biogas conditioning prior to the microturbine involves a scrubber, dryer, a carbon filter to remove particulates, and compression to 6 bars from the starting pressure of 300 mbar. The plant consumes about 440 m3/h of biogas and the overall energy efficiency of the system is about 78%, with 2600 kWh of biogas producing 858 kWh of electricity and 1170 kWh of heat. The plant produces up to 3500 MWh of electricity during the nine-month operating period, which equates to using about 50% of the biogas from the digesters (the rest is used to produce steam for distillation).
Electricity is sold to the grid, but the ‘site’ concept can be expanded to include this plant and the cognac plants that supply it with vinasse. About 70% of the site non-steam heating demand is for tartaric acid evaporation, about 24% is used to maintain the digester temperature at 37°C and about 6% is used to warm a large greenhouse which grows flowers for the city of Cognac’s street decorations. The cogeneration plant produces 53% of the site’s non-steam heating demand, which equates to all the heat requirements for the greenhouses, digesters and some for the evaporation process. The availability of the microturbine has been 97%, one advantage of microturbine systems over gas engine systems.
But the plant not only produces bioenergy but reduces the organic load of the wastewater by 95% in the digester stage, so the subsequent aerobic (activated sludge) wastewater treatment stage has less work to do. Overall, 99% of organic load as measured by COD is removed. The sludge from the decanting stage after aerobic treatment is mixed with shredded green waste, composted for three to six months, and can then be recycled back to agriculture. Surplus wine and wine lees are processed on-site to produce ethanol for transport biofuels.
A sustainable feast
Each sector of the food industry has significant potential to optimise how waste or by-products are managed. The agribusiness and food industry contributes to sustainable energy supply, and in recycling stabilised nutrient and organic components back to farms, it can reduce the need for petroleum-derived inputs.
Many thanks to Mauritz Quaak at Ferme d’Arcy, Nicolas Pouillaude at Revico and the team at AB Gruppo for their assistance in writing this article.