Saving coal for the sake of conservation

To conserve raw materials and reduce emissions, operators of coal-fired power plants are working to achieve ever-higher levels of efficiency. Bilfinger Berger is making a substantial contribution to this process and to protecting the environment.

(Text: Sara Mously, Photos: Eric Vazzoler)

One of the most modern lignite-fired power plant blocks in the world is being built in the Lausitz region of Germany. While the average efficiency levels of these plants is about 30 percent, the level in Block R of the Boxberg power plant will reach more than 43 percent. The pipes that direct steam to the turbines are a key component. Beginning in February, 2011, the steam will shoot through the piping at temperatures of over 600 degrees and at pressures that reach 280 bar – without causing any cracks or deformations.

Bilfinger Berger is one of just a handful of companies in the world that is up to the challenges presented by the P 92 special steel, an alloy with chrome, tungsten, molybdenum, vanadium and niobium. Using the €4 million inductive bending machine at the factory in Essen, Bilfinger Berger staff can take ten-centimeter thick steel and bend it with extreme precision.

“One piping segment can weigh up to 13 tons”, says project manager Arno Schulz. Cranes that are 150-meters high are required to maneuver the elements into the correct position once they reach the power plant. Using heavy steel hooks and chain hoists, workers then take over the final adjustments: “It’s a job that requires the combined efforts of eight men.”

Bilfinger Berger is researching new methods to further improve efficiency levels.

Piping specialists work day and night welding the segments together into a complete system. For particularly thick pipes, they employ an automated process, the computer-controlled orbital narrow-gap welder. “Mainly because it’s more accurate than doing it by hand”, explains welder Uto Kubitzki and wraps a metal track around one of the two pipe ends that he wants to connect. He leaves a one-centimeter gap between the pipes which will now gradually be filled with welding rod. Kubitzki approaches the metal track and attaches a 15-centimeter long pin which extends into the gap. At its tip, the welding electrodes are glowing and, with every rotation, welding one millimeter-thin layer over another. The work proceeds slowly and precisely. A single rotation takes 20 minutes and the segment has to be turned about 80 times before the 8.5-centimeter deep gap is filled and the two pipes are firmly connected.

The diameter of the pipes can reach to well over a half-meter; they wind their way from the floor to under the roof of the boiler house 135 meters above, twisting hundreds of meters through a maze of scaffolding, stairways, steel beams and chains. “There have been huge developments in power plant construction in recent years”, explains Arno Schulz. “Efficiency levels in particular have improved”. With P-92 piping, Bilfinger Berger is making an important contribution to climate protection, “because the more efficiently we use each and every gram of coal, the less CO2 is released.”

In order to achieve ever-greater levels of efficiency, Bilfinger Berger is constantly carrying out research on new methods. In Block R, for example, the Powerise process is being applied, an approach that was developed in the Group and by which residual heat from the up to 150-degree flue gas is used to pre-heat the feed water.

Further increases in the level of efficiency are achieved through the improved drying of the lignite. In a test facility at Vattenfall’s Schwarze Pumpe power plant, Bilfinger Berger is testing the pressure-charged fluid bed drying. Higher pressure in the plant allows for lower temperatures and, as a result, lower energy consumption than with traditional methods. The principle is similar to that of a pressure-cooker – the heat energy is used optimally and the water content of the lignite is similar to that of hard coal. The efficiency level of power plants equipped in this way can increase by up to 50 percentage points.

A test plant in Gelsenkirchen, Germany in which 700-degree steam shoots through the pipes is also aiming to achieve further efficiency improvements. Bilfinger Berger uses Alloy 617 for the pipes in this plant, a material that consists primarily of extreme heat-resistant nickel. After four years of test operations, metallurgists are now looking into the effect on the material. “In five to six years we will be able to provide power plants with pipes from nickel-based materials”, says Gerd Lesser, Managing Director of Bilfinger Berger Power Services. “With our coal drying processes and heat recovery, we will be able to achieve efficiency levels of 50 percent.”

Higher efficiency levels – lower emissions

The average efficiency level for coal-fired power plants around the world is 30 percent, in Europe it is 36 percent. The average efficiency level for plants in Germany is 38 percent which puts them among the most efficient in the world.

There is substantial potential to reduce the consumption of coal and CO2 emissions in the technology for coal-fired power plants. The target for development in the next ten years is an efficiency level of 55 percent.