Turbines

Application example: Espey® WKA400 for a steam turbine used in the manufacture of wood pellets

Issue and challenge:

In contrast to fossil fuel power stations, pellet power stations are CO2 neutral, and are becoming in­creas­ingly im­por­tant. If dry wood is used, the energy required to make the wooden pellets is only about 2.7 % of their total energy value. Wood pellets are in most cases man­u­fac­tured close to the source in forested areas. First, wood scrap or logs are chopped. The chopped material is pressed, under high pressure, in a pel­let­ing press through a steel grille con­tain­ing holes to create the desired pellet diameter. As it emerges from the grille, the strand is cut by a scraping knife to form pellets in the desired length. In this ap­pli­ca­tion, the pressure required to make the pellets is gen­er­ated by a three-stage steam turbine. For reasons of cost, the first two stages of the steam turbine are sealed by labyrinth seals. For the third stage, the ad­di­tional length of shaft would become too large to use a labyrinth. The seal needed here had to be compact and short. It had to provide fa­cil­i­ties for removing steam and leaking con­den­sate and had to with­stand both high pres­sures and high tem­per­a­tures while re­quir­ing minimal ser­vic­ing.

Solution from EagleBurgmann Espey:

To meet the needs of the operator, Espey chose the compact, short Espey® WKA400 chamber seal with steam and con­den­sate leakage removal fa­cil­i­ties and eight seal rings for a tem­per­a­ture of up to 500 °C (932 °F), a pressure of 23 bar (333.59 PSI), and rotation speeds of up to 8200 rpm. The seg­men­ta­tion of the seal rings means that they are easier to change if repair is needed. The seal solution has a long service life, is main­te­nance-free, and is designed for dry running.