Pictures of the Future        Fall 2008

Flaming Scrap

A technology developed by Siemens makes it possible to convert biomass waste into energy with a high degree of efficiency.

Our little toy" is how engineers at the residual waste cogeneration plant in Böblingen, Germany, refer to their 20-m  tower, which is crammed into a hall located next to a residual waste and slag bunker. The engineers are used to large numbers—over 150,000 t of waste is burned here each year in order to produce electricity and heat. "When we say toy, we aren’t being derogatory," says plant manager Guido Bauernfeind. "On the contrary, the SIPAPER Reject Power facility is perfect for us." One reason for this is that since September 2008 another type of raw material has also been converted to energy here—garden and forest scrap that has fallen through the facility’s sieves.

The facility's tower, which is clad in silvery sheet metal, is itself a small power plant. Its furnace chamber looks like a giant pizza oven whose vaulted interior is lined with fire bricks and is additionally insulated by half a meter of concrete. The outside temperature thus remains hand-hot, even when the fire within reaches 950 °C.

The RBB Böblingen energy cooperative collects 16,000 t of sieve residues from clipping and forest thinning work each year. These are chopped into chips that are then used as fuel for cogeneration plants and wood-fired heating systems. The pieces that fall through the sieves are too small for this, however, as they would turn into slag after combustion and clog the furnace grates in large power plants. They also have a much lower calorific value, which would necessitate a specialized combustion procedure. "Our capacity would also preclude burning this material at our cogeneration plant," Bauernfeind added.

A solution was offered by SIPAPER Reject Power technology, which was originally developed by Siemens’ Industry Sector for the paper industry (see Pictures of the Future, Spring 2007, Energy from Waste). Up until a few years ago, the paper industry disposed of its waste in landfills. Today, it either avoids waste or converts it into energy. But the tiny particles of waste produced during paper production couldn’t be effectively burned, as they were simply too inhomogeneous and damp.

The answer came in the form of a wheel  that flings the particles at high speeds into the furnace chamber. This setup makes for a much better distribution of the particles and thus more effective combustion. It also eliminates the danger of slag buildup. The first SIPAPER Reject Power facility entered service nearly three years ago at a paper mill in Austria, where it produces heat and electricity for the factory’s own use. "This form of waste recycling cuts the factory’s primary energy use by up to a third," says Dr. Hermann Schwarz, a technology product manager at the Siemens Industry Solutions Division in Erlangen.

The technology, which is particularly suitable for burning damp biomass made up of different parts, "is ideal for medium-sized biomass facilities generating five to 25 megawatts," says Manfred Haselgrübler, Reject Power manager in Linz, Austria.

Larger systems are better served by conventional power plants that use either reciprocating grates or a constant air flow. But smaller facilities, such as Siemens’ cogeneration plant in Böblingen, which has a thermal output of 5 MW, can enjoy impressive efficiency. Indeed, the Böblingen facility has an energy yield of 85 %. An 800-kW generator delivers electricity to the grid; the remaining energy is heat, which is channeled into the plant’s existing district heating network.

The Böblingen biomass plant marks the beginning of what will be a series of applications. For instance, burning coarse colza meal is also being considered. "Organic waste from beer production would also be a possibility," says Schwarz, who adds that the required technical adaptations would not be all that difficult to implement. "Basically, what we always need is a fuel with a certain type of particle size distribution—but we create that ourselves when we process it. The water content during this process can be up to 40 %."

The key to efficient combustion involves determining the optimal fuel-air mixture—control is fully automatic. "SIPAPER Reject Power offers great potential for exploiting biomass," Schwarz says. The most interesting markets for the exploitation of biomass waste at the moment are in the European Union—especially in Germany and in the Eastern European EU member states—as well as in Brazil and Indonesia.

Biomass Boom. "Biomass harbors huge, largely untapped potential," says Dr. Martin Kaltschmitt of the Biomass Research Center (DBFZ) in Leipzig. According to the DBFZ, more than 30 biomass power plants that use scrap wood or forest wood went on line in Germany in 2007, and a total of more than 200 such facilities are currently operating in the country. The development of biogas facilities has been even more dramatic. Energy production in 2007 was 828 PJ (43 % as heat, 38 % as electricity, and 19 % transport), which corresponds to around 6 % of total primary energy use in Germany. "That figure could be almost doubled if all existing technological potential were to be harnessed," Kaltschmitt explains. Ín any case, Kaltschmitt says, we can expect the biomass boom to continue throughout Europe and around the world for the coming years at least.

It’s possible that bio-energy production could cover one-third of global energy requirements by 2050. This would require the exploitation of around one-fifth of arable land, according to the Copernicus Institute in Utrecht, Netherlands. However, Thomas Nussbaumer, a professor of Bio-energy at Lucerne University of Applied Arts and Sciences in Switzerland, believes such a development could exacerbate hunger in the Third World. To support his argument, he cites the negative results associated with first-generation agrofuels made from corn, rapeseed, soy, and sugar cane. But Nussbaumer admits that the potential to expand agricultural production in developing countries is still high. "Ideally," he says, "The edible portions of plants would be used for food and animal feed production, while the rest would be put to work in energy production."
                                                                                                                          Urs Fitze