The Austrians opting for biogas - Food scraps sorted with innovative QZ machine
In Germany, more than 4000 biogas plants are producing sustainable energy, and technology is becoming increasingly sophisticated. A piece of German shredding equipment – the MeWa Querstromzerspaner – has been in use in rural Austria where a cattle farmer has assumed an unusual and ground-breaking recycling role, as Harold Pandl explains
You will get a warm welcome by Josef Kröll at his biogas plant near the village of Schlitters, east of Innsbruck in Austria. The family-friendly holiday village at the bottom of the Zillertal valley is usually popular because of its sunny position surrounded by meadows and overlooked by impressive hills and mountains. But this is where Mr Kröll, a Tyrolean farmer, runs his cattle-breeding farm and operates a composting plant, and, since the beginning of 2008, a state-of-the art biogas plant.
The combination of farming, tourism and environmental protection plays a special role in the new energy project. The plant is fed with organic waste from the local area and with food waste from the numerous tourist hotels, guesthouses, taverns and restaurants in the Zillertal and Inn valleys. It also takes in food with an expired use-by date and packaged deep-frozen food.Rural waste disposal
The Zillertal region had been looking for an alternative means of disposing of its waste. ‘A farmer’s heart aches when waste food ends up on the waste site,’ Josef Kröll lets on. ‘This is why the Mayors encouraged me to do something.’| |
The Querstromzerspaner
For this purpose Finsterwalder Umwelttechnik GmbH (Fitec) from Bernau in Bavaria drew up a concept whereby the recycling machinery plays an ingenious role. They chose the patented ‘Querstromzerspaner’ (QZ) machine, produced by German company MeWa Recycling Maschinen und Anlagenbau GmbH, which ‘has qualities which original shredding methods do not offer.’ This is how planning engineer Klemens Finsterwalder describes the unusual choice.
| |
The machine has two big advantages. In contrast to conventional blade shredding technologies, the MeWa QZ is fitted with chains with which the machine efficiently processes foreign materials (such as cutlery in the organic waste produced by tourist facilities). Recycling specialist MeWa, based in Gechingen, Germany, had originally designed the QZ for metals and composite materials, but this dismantling version of the machine efficiently separates food with an expired use-by date, including packaged and frozen food.
A second advantage of the QZ is the method used for feeding materials into the machine. In addition to organic waste, public park and private garden waste can also be fed into the system. Conventional recycling machinery chops up the plant matter, but processing the waste with chains gives a far larger surface area – a similar principle to a pestle and mortar which mashes instead of cutting. This gives bacteria maximized contact during the fermentation stage – as proved by the measurably higher yields of methane gas in the QZ. Readings taken in a retrofitted plant showed 30% higher yields of methane gas.
A second advantage of the QZ is the method used for feeding materials into the machine. In addition to organic waste, public park and private garden waste can also be fed into the system. Conventional recycling machinery chops up the plant matter, but processing the waste with chains gives a far larger surface area – a similar principle to a pestle and mortar which mashes instead of cutting. This gives bacteria maximized contact during the fermentation stage – as proved by the measurably higher yields of methane gas in the QZ. Readings taken in a retrofitted plant showed 30% higher yields of methane gas.
Feeding the machine
Nowadays specially cultivated energy crops are the raw ingredients in biogas plants. These renewable raw products can be cultivated locally every year and supply energy which is virtually carbon-neutral. Silage corn is proving to have the highest yield, but since it does not grow everywhere, farmers adapt their own plant mix depending on their locality. Fodder, beet, sunflowers and rapeseed are also suitable for biogas production. But modern facilities can process almost any plant matter, it is only wood that cannot be digested by the bacteria.
The key to achieving an optimal yield of methane gas lies in a high level of biomass processing: the QZ breaks down the substance in a matter of seconds – much quicker than conventional machinery with blades. It only takes one manoeuvre to homogenize the substrate and prepare for it bacterial digestion.
The key to achieving an optimal yield of methane gas lies in a high level of biomass processing: the QZ breaks down the substance in a matter of seconds – much quicker than conventional machinery with blades. It only takes one manoeuvre to homogenize the substrate and prepare for it bacterial digestion.
 |
| The delivery of organic waste from the surrounding area |
The bacteria live in airtight sealed fermenters. By sealing it off from oxygen biogas develops as the biomass decomposes – like in a cow’s stomach. The process of fermentation is natural, but also controlled. Biogas plants utilize the natural behaviour of bacteria to generate low-cost, climate-neutral electricity and heat. The individual plant components are perfectly co-ordinated to achieve this: the feed, the individual pumps, the hygiene procedures, each mixer, and the temperatures in the fermenters (which can be monitored and controlled with measuring equipment and viewed on-screen).
The organic material is broken down in batches before transportation by pumps to the fermenters. The type and composition of material delivered to the plant in Schlitters changes every day and the operators are able to react to these varied compositions with different settings. A separator sorts anomalies such as pieces of bone or wood, metal or foil-wrapping material. The biomass is then hygienized and transported to the fermenter. Liquid manure from farming is also added. The remaining unusable waste which floats to the top of the fermenter or sinks down to the bottom is removed from the tanks by specially-developed systems.
The increased yield of methane gas was taken into account at the beginning of the design process – a CHP plant converts this yield into heat and electricity, so it does not escape directly into the atmosphere. The 330 kW generated is fed direct into the public grid and supplies electricity to about 600 households. The waste heat is used immediately to heat the fermenters to a consistent 37°C. In the future Josef Kröll wishes to use the residual heat to operate a woodchip and hay bale drying system and to supply his neighbouring houses with heat.
Machines operate around the clock, but hardly any noise can be heard outside as a special lining inside absorbs most of the sound.
The build-up of odours is also significantly reduced in the plant. The MeWa QZ is a closed system from which few odours escape, the liquid manure fed into the fermenter also alleviates the effects of odours. The liquid ‘mineralizes’ the nutrients in the biogas plant and what remains is a fermented residue which ‘not only smells better than liquid manure, it is also a better plant fertilizer,’ says Josef Kröll. The fermented residue is composted next to the plant and is returned to the soil as a fertilizer by the local farmers. The ecological balance in biogas production is therefore complete.
The organic material is broken down in batches before transportation by pumps to the fermenters. The type and composition of material delivered to the plant in Schlitters changes every day and the operators are able to react to these varied compositions with different settings. A separator sorts anomalies such as pieces of bone or wood, metal or foil-wrapping material. The biomass is then hygienized and transported to the fermenter. Liquid manure from farming is also added. The remaining unusable waste which floats to the top of the fermenter or sinks down to the bottom is removed from the tanks by specially-developed systems.
Paving the way
Fitec initially retrofitted the MeWa unit into a plant and conducted exhaustive tests: ‘Decomposition with the Querstromzerspaner replaces the organic pre-treatment procedure that would, for example, need to be carried out in a process of hydrolization,’ explains plant design engineer Klemens Finsterwalder. This paved the way for use in the new biogas plant in Schlitters.The increased yield of methane gas was taken into account at the beginning of the design process – a CHP plant converts this yield into heat and electricity, so it does not escape directly into the atmosphere. The 330 kW generated is fed direct into the public grid and supplies electricity to about 600 households. The waste heat is used immediately to heat the fermenters to a consistent 37°C. In the future Josef Kröll wishes to use the residual heat to operate a woodchip and hay bale drying system and to supply his neighbouring houses with heat.
Machines operate around the clock, but hardly any noise can be heard outside as a special lining inside absorbs most of the sound.
The build-up of odours is also significantly reduced in the plant. The MeWa QZ is a closed system from which few odours escape, the liquid manure fed into the fermenter also alleviates the effects of odours. The liquid ‘mineralizes’ the nutrients in the biogas plant and what remains is a fermented residue which ‘not only smells better than liquid manure, it is also a better plant fertilizer,’ says Josef Kröll. The fermented residue is composted next to the plant and is returned to the soil as a fertilizer by the local farmers. The ecological balance in biogas production is therefore complete.
