WTE incinerator, Spittelau, Austria

Waste-processing technologies transform the town of Gussing

E&T on a set of pioneering waste-processing technologies which have changed the face of a formerly unremarkable Austrian town.

It was literally the end of the road - the little Austrian village of Güssing, population 4,000, situated up against the rusted barbed wire separating Hungary from Austria - the 'Iron Curtain'. In 1988, Güssing was one of the most economically depressed regions of Austria, with no through-transportation and no job base. As much as 70 per cent of its workforce had to commute out of the area to find jobs. Young people were emigrating to the metropolitan centres of Vienna or Graz. Economically, the community was almost entirely dependent upon imported energy for transportation, heating, and electrical needs, while local forest resources, comprising 45 per cent of the region, went largely unused.

Today, just 20 years later, Güssing stands as a model of energy self-sufficiency for Austria, Europe and the world. This is the story of that remarkable transformation. A rags-to-relative riches tale - of adaptation and evolution overcoming economic hardships to the benefit of the little town of Güssing and its surrounding communities, bringing jobs and new prosperity - a true Cinderella tale of great importance for the modern world as we contemplate civilisation after the age of oil and fossil fuels.

Toward energy independence

In the early 1990s, the visionary Mayor of Güssing, Peter Vadasz, contemplated what to do about the dire situation of his small town. How to create jobs and turn around the sagging economy that Güssing and the surrounding region were labouring under? Together with a young engineer, Reinhard Koch, he embarked on an ambitious plan: to stop the bleeding of the local economy for imported fossil energy supplies by becoming energy independent using local resources. Those resources were essentially made up of agricultural crops and residues, and wood/forest biomass.

The first steps toward energy independence were realised by reducing local energy demand. This was achieved primarily by optimisation of energy efficiency of buildings and dwellings - reducing energy demand in existing structures in the town centre by as much as 50 per cent through better insulation, more energy-conserving windows, and other energy-saving construction measures. Further steps involved construction of a district heating system for the town, initially powered by a simple wood biomass incineration plant, and of a small biodiesel production plant using rape seed oil.

The flagship of the Güssing energy innovation, however, is its biomass gasification plant. The Biomasse Kraftwerk Güssing employs fluidised bed steam gasification technology. On line since 2002, it is the first utility-scale power plant of its kind in the world, with a rated capacity of 8MW, producing on average about 2MW of electricity and 4.5MW of heat per hour. Gasification is a thermochemical conversion process that converts carbonaceous material into 'producer gases' - hydrogen and carbon monoxide - that can be combusted at the plant for combined heat and power (CHP) or processed further into synthetic natural gas (SNG), hydrogen fuel cells, or even liquid fuels.

Operating at 8,000 hours per year for the last several years, the Güssing facility, together with a network of smaller district heating plants and other renewable energy units, produces more energy than the town consumes on an annual basis. Güssing has gone from completely energy-dependent to an independent power producer in just ten years.

Waste-to-energy Austrian style

Biomass combustion - basically, burning wood or other organic materials - is the most ancient of renewable energy technologies, warming caves and homes since the dawn of humanity. It is 'renewable' as long as the amount of biomass burned does not exceed the amount of carbon taken up by plants through photosynthesis per unit area over time.

Besides woody biomass, municipal solid waste (MSW) is perhaps the most abundant biomass resource. Containing roughly 50-70 per cent organic, combustible material, MSW represents a potential gold mine for energy production. In the past, waste was simply burned to reduce the volume in landfills. Waste incineration power plants have been burning biomass to produce steam to generate electricity for more than a century, but with increasingly stringent air and water quality regulations, modern-day waste incineration is a highly technical engineering process.

Biomass combustion power plants can use a variety of feedstocks, including wood waste (wood chips, sawdust, branches and other waste from wood milling operations), agricultural crop residues, MSW, and sewage sludge. The caloric energy of the biomass is converted by combustion to heat water to produce steam, which can then be used to generate electricity and, if one has the means of distributing it, useable heat, but the energy efficiency is still relatively low, at less than 50-60 per cent - that is, only half of the caloric energy of the feedstock is converted into useful energy.

Austria is a world leader in waste-to-energy technology. It begins in the country's homes and businesses, where consumers separate recyclable materials into coloured and clear glass, cans and metal containers, plastic, paper, and green yard waste. Without complaint and with a high degree of compliance, the Austrian population does this as a routine way of life; reducing its MSW generation by about 50 per cent. The recyclables are picked up separately, and the remaining waste is delivered to landfill, or in the case of larger Austrian cities - to the Kraftwerk - or power plant.

Once delivered to the power plant, the MSW goes through a four-step process of heating/drying, devolatilisation, gasification, and combustion. The first two steps are endothermic - requiring heat input to get the reactions started. Between 500 C and 1,000 C, gasification reactions take place, converting the organic material into their component 'producer' gases, comprised of carbon, hydrogen, and oxygen compounds; and above these temperatures complete oxidation of the organic material occurs.

One of the problems of standard biomass waste incineration is that, by using air as the gasification agent (79 per cent nitrogen, 21 per cent oxygen), the product gas is comprised of carbon monoxide (CO) plus nitrogen compounds (NOx), the latter being a primary constituent of photochemical smog and harmful air pollutants. Thus modern waste incinerators must treat their flue gas through a long train of electrostatic precipitators, scrubbers, dust separators, and finally a dioxin/de-NOx treatment process to remove and neutralise their emissions.

Thermal gasification technology

Professor Hermann Hofbauer is one of the world leaders in thermal gasification technology. At Professor Hofbauer's laboratory at the Technical University of Vienna, one can view several cold-flow gasification models and the 'fluidisation' reaction through the clear reactor vessels.

The gasification process begins with a fixed bed of silica or olivine sand and organic biomass at the bottom of the reactor. The biomass and bed material are fed into the reactor by means of a screw conveyor. As the steam is injected upwards through the bed material, it begins to boil and the bed behaves like a liquid. Particles are conveyed upwards and down again, depending on their specific gravity, like a bubbling pot. Non-combustible particles sink down into the bed material and can be discharged. Lighter materials begin to float upwards to the top of the 'fluidised' bed.

A circulating fluidised bed reactor, such as the Güssing plant, consists of the bed vessel, a combustion cyclone, and a valve connecting the cyclone standpipe back to the gasification reactor. Heavier particles sink in the bed vessel and are conveyed into the cyclone. The heated particles rise in the combustion cyclone and the flue gas is removed. The precipitated particles are carried back into the gasifier through the connecting valve where they are fluidised again. In this way, the bed material cycles from the gasifier to the combustion cyclone, where the smaller ash particles are given off with the flue gas and the heavier particles are recirculated back to the gasifier for further pyrolysis.

The flue gas is separated at the top of the cyclone stack, and the heat contained in it is transferred to the district heating system. The product gas, released in the gasifier, is also removed, cleaned of ash and other particulates and cooled for use in a gas engine to produce electricity. The heat transferred in the cooling process is conveyed to the district heating system, and the waste heat from the gas engine itself is also conveyed to the district heating system. By this means, almost no energy is wasted, with electric energy efficiencies of 25-28 per cent, and overall efficiencies, including usable heat energy, of 80-85 per cent, as opposed to the 50 per cent energy efficiencies achieved through standard waste-to-energy incineration.

At the International Conference on Polygeneration Strategies, held in Vienna in September, 2009, Professor Hofbauer's graduate students fired up a fluidised bed popcorn maker and coffee roaster to demonstrate the process. At first the popcorn kernels begin to bounce and circulate in the 'gasifier' and then through the cyclone and back, and in due course, as the kernels expand and their specific gravity becomes lighter, the popped corn is given off, like producer gas, to the waiting popcorn hopper - with almost perfect 'pop' per kernel results - no unpopped kernels and zero emissions.

Because the gasification reactor uses steam instead of ambient air as its gasification agent, the product gas is nitrogen-free, low in tar, and of high energy content. The flue gas must still be cleaned, as with a waste incineration facility, but it contains very low levels of nitrogen compounds (NOx) and, with wood biomass, low levels of sulfur compounds (SOx) as well. The small amounts of potentially problematic emissions can be treated and removed, resulting in a zero-emissions, carbon-neutral suite of energy products.

Gasification energy production is considered to be carbon-neutral in that whatever carbon is released in the flue gas is equal to the carbon originally taken up by the plants that comprise the feedstock through photosynthesis in the first place. The rule of carbon neutrality does not apply to plastics in municipal waste feedstock, as these are largely derived from fossil fuels in the first place. However, even here, the high energy-efficiencies, achieved by modern utility-scale gasifiers, equate to approximately one-eighth of the carbon dioxide per kilowatt of energy produced in comparison to fossil fuel-generated energy.

Green jobs

The successful operation of the Güssing CHP biomass plant has spawned several new energy research projects in the region under the umbrella of the koEnergieland (eco-energy-land) programme. The 'Energy Systems of Tomorrow' sub-programme investigates a suite of other renewable energy products.

Research on generation of methane from syngas is underway in conjunction with the Paul Scherrer Institute of Switzerland. A 1MW demonstration plant producing up to 100m3 of Bio-SNG per hour has been in operation since 2009. A Fischer-Tropsch refinery was recently installed at the plant to produce diesel fuel and gasoline from the producer gas, and will go online in 2010. Other research projects include wood gas and biogas fuel production, combining thermal and biological gasification technologies; research on increasing the CHP efficiencies; and fuel cell technology.

Cinderella stories have happy endings and the Güssing story is no exception. The availability of abundant, locally-produced energy has attracted approximately 50 new businesses to the district, creating more than 1,000 new jobs. Manufacturing companies that can use the heat energy, such as a wood flooring company, have located in the village where they use the district heat to dry their parquet-laminated flooring materials. Several photovoltaic and solar thermal companies have relocated here, installing new demonstration facilities in the district. The little village of Güssing has become a net energy producer - generating more energy from renewables than it uses.

Altogether, there are more than 30 renewable energy sites within 10km of the village; and now the goal is to become energy-independent and sustainable in the district as a whole. Researchers have analysed the total energy resources against the overall demand, and calculated that there is more than enough land and forest area to create a completely energy self- sufficient, sustainable community within the Güssing District.

According to the study, a complete shift to renewable energies would reduce CO2 emissions by as much as 85 per cent; and with the potential economic multiplier effects of new businesses and an improved job market, the shift from fossil fuels to a renewable energy economy could create added value on the order of €39m to the region.

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