Pictures of the Future    Spring 2006

More Power, Lower Emissions

Population growth and economic development continue to drive up energy consumption, particularly in urban centers. To meet the world’s demand for electricity in an environmentally compatible way, it will be necessary to exploit fossil fuels more efficiently and make greater use of renewable energy sources. Four Siemens projects illustrate how this can be accomplished.

By the time the UN Climate Change Conference in Montreal ended on December 9 of last year, the delegates —10,000 from 189 countries —had every reason to be satisfied with the outcome. After all, they had just resolved to extend the Kyoto Protocol for reducing greenhouse gases. Their resolution calls for continuing Kyoto beyond 2012, with even more stringent limits. Given global population growth and increasing economic development, however, energy use worldwide will be climbing to unprecedented levels. This means the only effective way to limit emissions of greenhouse gases is for governments to maximize the efficiency of fossil fuel use and rely more on renewable energy sources (see Pictures of the Future, Spring 2004, Main Focus "Natural Resources").

Politicians also will have to be joined by industry in finding innovative solutions in this area —a job Siemens has been taking on for quite some time. In Montreal, the international Climate Group even singled out the company as a pioneer in climate protection over the last decade.

To illustrate Siemens’ commitment to environmental protection, this article takes a look at four of the company’s most recent projects in environmentally compatible power generation, including the gas-and-oil-fired power plant operated by E.ON Kraftwerke GmbH in the town of Irsching in Bavaria.

Since 1995, high gas prices have meant running the steam turbines at this facility for only a few days a year to cover peak loads. "Germany’s generating capacity is by no means as lavish as it once was, especially now that even more nuclear power plants are to be decommissioned," warns Alfred Beck of E.ON. That’s why, starting this summer, Siemens will be building a new power unit at the Irsching plant that will set new standards in economy and performance. With an output of 340 megawatts (MW) for a single gas turbine, this new unit will be unsurpassed worldwide. Following a test phase, the turbine will be upgraded to combined-cycle operation, and will generate additional power with the hot exhaust from the gas turbine (see graphic above). The overall rating of the unit will then increase to 530 MW and its overall efficiency will hit 60 % —1.6 percentage points higher than the current world-record holder, the Mainz-Wiesbaden power plant, also built by Siemens. "In terms of technology, we’re entering new territory with this gas turbine plant," explains Dr. Johannes Teyssen, CEO of E.ON Energie AG. "And we fully expect the higher efficiency to cut our generating costs."

Following completion in 2011, the Irsching plant will also set a new record in climate protection: an annual 40,000-t reduction in emissions of carbon dioxide compared with today’s conventional plants. This is the result of technological advances such as computer-enhanced turbine-blade design and new materials that can bear greater mechanical loads, which makes it possible to use larger blades. Furthermore, the blades have a ceramic coating to withstand higher combustion and exhaust-gas temperatures. This in turn makes the facility more efficient, because a power plant’s efficiency is basically determined by the difference in the temperature of the gas when it enters the gas turbine and the temperature of the steam when it exits the steam turbine as condensation.

More Energy from Cooling. In the Norwegian town of Kårstø, north of Stavanger, Siemens is building a 420-MW combined-cycle power plant that’s scheduled to be completed in summer 2007. The plant will draw cooling water from the icy North Sea. "That alone nudges up overall efficiency by up to one percentage points compared to a plant using the warmer water from rivers like the Danube or the Rhine," explains Dr. Martin von Hassel, project manager at Siemens Power Generation. "At the same time, we’ve also made a lot of technical improvements."

For example, the rotor disk for the gas turbine can be moved along its axis to provide a better seal, ensuring that less hot gas escapes through the gap between the turbine blades and the housing. The plant also features a low-pressure turbine that makes more efficient use of steam pressure. And like the facility in Irsching, Kå>rstø has two steam turbines connected in series, which together extract energy from the hot exhaust gases, boosting overall efficiency to almost 60 %. Another highlight is the plant’s catalytic converter, which reduces emissions of nitrogen oxides in the exhaust gases to only two parts per million (ppm) —comparable plants in the U.S. with emissions four or five times as high are considered very clean.

The use of modern technology also brings improvements in many areas of coal-fired generation. The average efficiency of coal-fired power plants in Germany today is about 37 %. By comparison, the Waigaoqiao III coal-fired plant near Shanghai —Siemens is to supply a generator and the main components for the plant’s two 1,000-MW steam turbines —will operate at 45-% efficiency. The plant is to be completed in 2009. China is eager to improve its generating efficiency, not least because two-thirds of the country’s power consumption is covered by domestically produced coal.

Waigaoqiao III will operate with steam pressurized and heated to the ultra-supercritical range (as high as 270 bar at 600 °C), which makes it possible to better use energy and achieve higher efficiency. But that also demands a lot of high-temperature components such as the shaft, blades and housing of a high- and medium-pressure turbine —a situation that in turn requires innovative design concepts and the very latest in materials technology. What’s more, research is already under way to boost operating temperatures to as high as 700 °C.

Deep Power. Exploiting geothermal energy —the earth’s internal heat —neither produces emissions nor uses fossil fuels. Those are two very good reasons why Siemens Industrial Solutions and Services (I&S) is building an ultramodern geothermal power plant in Unterhaching, near Munich, Germany. The town is fortunate enough to be 3,300 m above a water-bearing stratum, or aquifer, that runs through rock that has a temperature of 122 °C. The water from this depth immediately vaporizes at atmospheric pressure, but it still isn’t hot enough to drive a turbine efficiently —for that, it needs to be at least 180 °C. So a heat exchanger is used to transfer the water’s thermal energy to a medium that vaporizes at a much lower temperature. The resulting vapor is then used to drive a turbine.

This plant will be the first in Germany to use the Kalina principle (see box) for the heat exchanger. "This is renewable energy in the truest sense," says Roland Lutz of I&S. "All we do is drill a hole in the earth and tap the heat that’s always available inside." Engineers predict the facility will have an output of 3.36 MW, enough to supply about 6,000 German four-person households with electricity. Commercial operation is due to start in mid-2007.

German legislation in this field stipulates a dependable level of financial support for renewable energy, including a guaranteed price of 0.15 €/kWh for electricity generated in this way, which should help the plant remain commercially viable over the long-term. And 25 of the 150 l of thermal water pumped to the surface every second will be diverted to a district-heating distribution system to supply about half of Unterhaching’s 20,000 inhabitants. The plant will mean an annual reduction in emissions of 12,000 t of CO₂, seven tons of sulfur dioxide and almost 100 t of nitrogen oxides.
                                                                                                                  Bernhard Gerl