Commissioning and Validation of the underlying model of a test rig analyzing rotation and expansion performing assemblies in parabolic trough collector power plants

Kurzfassung

One of the most critical parts of parabolic trough collector power plants are the Rotation and Expansion Performing Assemblies (REPAs), �exible tube connections, that link the absorber tubes in the focal lines of the parabolic mirrors and the �xed pipes on the ground, leading to the power block. In a typical solar �eld there are eight REPAs per collector loop with a cost of approx. 1000 Euro each. [2]. A report of the International Renewable Energy Agency (IRENA) states that for a 50 MW PTC power plant 2.6 Million USD or 0.7% of the Investment is needed for swivel joints (i.e. REPAs) [3]. But this is the investment only. Beyond the investments REPA wear requires maintenance during operation and often expensive replacements and repair. The latter require an operation stop and oil discharge of the whole loop which means costly production losses. REPA leakage due to spillage of potentially very toxic HTFs is a severe threat to the environment. REPA failures, which have to be avoided by all means, may also damage other parts of the power plant. It can therefore be concluded that REPAs are an important, expensive and safety relevant part that needs to be well understood. Currently there are two main types of REPAs: Rotary Flex Hose Assemblies (RFHAs) which consist of a �exible tube and a swivel joint, and Ball Joint Assemblies (BJAs) which are made from three swivel joints connected by two rigid pipes. Regardless of the type used, REPAs have to endure high temperatures and pressures while compensating for rotational and translational motion between the two pipes they connect. Improvements to the current designs are limited by the fact that the causes of wear and failure, i.e. the pressures, forces and temperatures are not really understood. In fact no test-rig exists yet that reproduces the interaction of all important parameters that occur in daily REPA life. To increase e�ciency and thus lower costs in PTC power plants, higher �uid temperatures and pressures are aimed for. This further in creases operational loads and the necessity of a better understanding of wear mechanisms. Against this background REPA manufacturers have approached the German Aerospace Center (DLR) to build a test-rig and further investigate REPA wear and failure mechanisms. The DLR and the Centro de Investigaciones Energéticas, Medioambientales y Tecnol ógicas (CIEMAT) are therefore currently building a new test rig at the Plataforma Solar de Almería (PSA) in Tabernas, Almería, Spain for investigating all di�erent types of REPAs under representative and complete operational conditions. This thesis documents e�orts undertaken to accompany the mounting and commissioning process of the test-rig. The main focus is on the validation of the principle behind the REPA-force measurements. A correct measurement of the static and dynamic forces acting on and in the REPA is the key to understanding REPA wear under authentic working conditions.