Weinheim/ Wuhan (China). August 1, 2011. China’s activities in the raw material business are on the increase, and energy demand is growing. In order to remain independent of energy imports, the government is systematically boosting its own energy reserves and building new power plants at a breathtaking pace. Wuhan Iron & Steel Group, for example, has built China’s first full-scale blast furnace gas-fired (BFG) combined-cycle power plant in Wuhan. EagleBurgmann, a member of the NOK Freudenberg Group, supplied the dry gas seals for the 240 megawatt combined-cycle plant. Weighing in at some 150 kilograms and with an internal diameter of over 350 millimeters, these are not only the largest dry gas seals in the world but, with an average seal chamber temperature of 250°C, they also have the highest heat tolerance, topping the previous limit of 230°C.
Steel plants are enormous power guzzlers so their operators are extremely interested in using blast furnace gas in combined-cycle power plants. That helps improve energy efficiency and save costs – while at the same time reducing emissions. BFG is a by-product of coal combustion during the smelting of iron ore in the blast furnace and is normally simply flared. In Wuhan, though, the blast furnace gas is treated and used to fuel the gas and steam turbines of the combined-cycle plant. The turbines at the Wuhan plant have a maximum capacity of 185,000 kilowatt. While industrial heat and power generation is in itself nothing new, using this technology in extremely large power plants fueled by blast furnace gas still presents a major technical challenge – for sealing technology provider EagleBurgmann, too.
Long-standing expertise in designing “super-sized” seals
Dry gas seals (DGS) are one of the most technically challenging sealing solutions. They play a crucial role in compressor availability and efficiency. In principle, large dry gas seals are nothing new for EagleBurgmann: The sealing technology provider already cooperated with leading compressor manufacturers in the past. Right from the outset, though, developing a version of the dry gas seal for the high-temperature environment of the furnaces in Wuhan posed a particular challenge in terms of design, production and testing. Design had to cater for all aspects of operation. Dry gas seals are usually designed for temperatures of between -20 and +160°C. Temperatures at the power plant in Wuhan, on the other hand, can be much higher, so the seal had to be designed to withstand temperatures of up to 250°C.
Testing and validation
Large or super-sized seals are especially challenging as regards production and testing because exactly the same tolerances apply for them as for smaller seals. The Wuhan design was subjected to all test procedures – including static and dynamic tests at full load, start/stop cycles, low-speed running and operation as well as a high-temperature test to prove stable tightness performance in a temperature range of 20 - 250°C. The world’s largest dry gas seal passed all tests carried out in a special test rig with flying colors.
“We spent almost six months working on developing and manufacturing this product. One of the difficulties was the large number of individual components,” Daniel Goebel, an engineer with EagleBurgmann and directly involved in production along with a team of 15, said. Everything was finally brought together in a complex process. The result is the largest dry gas seal in the world and the first reference for a seal of this type on an operational plant.
About the Wuhan project
Wuhan Iron & Steel Group is one of the world’s largest steel producers and ranks third in China. A project to build a 240 MW blast furnace gas-fired combined-cycle power plant at the largest blast furnace complex in Wuhan City kicked off in 2007. The new combined-cycle plant has two 120 MW turbines fueled with noncooled gas from two compressor trains, each comprising a specially designed mega-compressor – the largest of its kind in the world – and a standard size compressor. EagleBurgmann developed the world’s largest dry gas seal (390 millimeters) ever used to date for this installation.