Pictures of the Future    Spring 2007

Treasures in the Trash

Ripped plastic bags, videocassettes, an old yucca palm, and mountains of less identifiable objects can be found among the rancid-smelling trash in the olympic swimming pool-sized delivery bay at the ALBA waste processing plant in Berlin.

But the potential value of the garbage is a much more pleasant story. "There’s a huge amount of energy in this garbage," says engineer Michael Blöcher, technical director of the ALBA facility. Indeed, everything here that can be burned can also be converted into useful energy, including plastic, cellulose from paper, garden and kitchen waste, and textiles—which altogether account for more than half of the 640 t of garbage delivered to the facility every day.

What’s more, even the non-combustible substances have value. These are separated from other materials using a sophisticated sorting machine, after which they are sold to cement and coal power plants either as "fluff" (loose material) or as compressed cigar-shaped pellets. In all, the facility processes about 160,000 t of residential and commercial waste per year in this manner, with more than 60 % of this volume converted into replacement fuels whose calorific value is enough to cover the energy needs of tens of thousands of households. The process also spares taxpayers the expense of managing landfills, with their high associated fees.

Control systems from Siemens ensure the smooth operation of the ALBA facility, which is the most modern in Europe. "The systems include customized software as well as various types of measurement devices," says Jürgen Knöfel from Siemens Industrial Solutions and Services (I&S) in Berlin. Knöfel helped launch the partnership between ALBA and Siemens three years ago, and is therefore well aware of the challenges involved in coordinating the operation of such a huge facility. For example, as it moves through the plant, waste has to travel along 1.5 km of conveyor belts and pass through 25 machines before being transformed into concentrated fuel. It’s dried out in giant barrels using hot air, then ground into small pea-shaped particles, shaken through screens, winnowed with blasts of air, conveyed past magnets and exposed to infrared light and X-rays. Non-combustible metals, sand, earth and glass are sorted out during this process, after which they can be recycled for further use. Any problems that occur during processing are immediately displayed on monitors in the facility’s control center. Disruptions can take the form of videotape that gets stuck in the conveyor belt’s wheels, or overloaded motors in the processing system. In such cases, the system is shut down until the problem has been solved.

Paper Recycling with a Third Less Energy. Mayr-Meinhof Karton, one of the world’s leading suppliers of recycled cardboard, has been converting used paper into high-quality cardboard for decades. For the past two years, however, the company has been utilizing waste paper to generate electricity and heat at a factory it operates in Hirschwang, Austria. Using a Siemens technology called SIPAPER Reject Power, the plant has slashed its energy and waste disposal costs. "The waste processing system has reduced primary energy consumption by around one-third," says Dr. Hermann Schwarz from Siemens I&S in Erlangen, which, as the general contractor, was responsible for planning the facility and putting the components together for a turnkey system. Siemens also supplied all of the plant’s automation and control equipment.

In order to ensure optimal combustion, the calorific value of the waste used in the Hirschwang plant’s energy generation system has to be kept nearly constant. But the composition of the waste makes this a challenging task, as the garbage consists of everything from high-quality blank paper to colorful brochures containing filler materials. Foils, paper clips and sand can also be found in the mixture. This so-called coarse reject—along with low-grade fibers and paints—is separated by machines from the recyclable paper and processed into a fuel mixture along with the facility’s sludge. The trick here is to regulate the dosage of the individual components in order to achieve the desired calorific value.

The resulting mixture is then fed into a furnace by a chopper wheel. "The materials simply dry out in the air above the fire bed," Schwarz explains. Eventually, the waste ignites and the energy released heats up pipes containing steam that is used to drive a turbine. A generator converts the rotation into electricity. Later on downstream, the steam (which is now under much less pressure) is channeled into the heating unit for the production hall, where it is used to dry out webs of new cardboard. In addition, a flue gas cleaning system lowers emissions to a level that is well under the legal maximum. "The Hirschwang power plant is the largest facility of its kind anywhere," says Schwarz. Another reject power facility for woodchip screen residue is currently being built in Böblingen, Germany.

Austria is also home to a third example of environmentally friendly power generation from waste—a cogeneration unit in the town of Dornbirn-Stöcken that is the product of a partnership between I&S and environmental services company Wirkungsgrad Energieservice GmbH. The facility converts frying fat and cooking oils into electricity and heat, thus eliminating reliance on fossil fuels.

Siemens' I&S office in Vienna served as the general contractor for the construction of the Dornbirn-Stöcken facility as well as two similar plants in the region, which are the first of their kind in Europe.

Throwing Fat in the Fire. "We delivered the complete power supply system and the automation technology for everything from the power plant itself to the control system and associated services," says Harald Loos from Siemens. Siemens software controls the processing of oils and fats obtained from residential and restaurant wastes. Free fatty acids represent the biggest problem here, according to Loos. These acids arise through long periods of contact with moisture—and high concentrations of such fatty acids quickly corrode steel piping and other steel components in the facility’s motors. "But thanks to a process developed by our project partner Wirkungsgrad Energieservice, we’ve been able to hold down the content of the aggressive components to around five % of the total," says Loos.

The processed waste fat is used to feed the heart of the cogeneration plant, which consists of three giant eight-cylinder heavy-oil engines connected to three generators that together produce 4.5 MW of power. The electrical energy produced—and the heat emitted by the engines—can cover the needs of thousands of households. A planned residential complex and neighboring industrial facilities will benefit from this power and heat generation in the future.

Those organic cogeneration power plants have performed so well that similar facilities will soon be built in other countries, and Siemens and Wirkungsgrad Energieservice are already working on the plans. It’s clear to all involved that such plans definitely won’t end up as recyclable garbage—after all, the age of energy from waste has only just begun.
                                                                                                        Andrea Hoferichter