Design of a phase separation system for a Direct Steam Generation Parabolic Trough Collector Field

Kurzfassung

The direct steam generation in parabolic troughs is a promising option to further reduce levelised electricity costs of solar thermal power plants. The operation of the field in recirculation mode offers advantages concerning the control and stability of the system. Due to the large dimensions of the field compact phase separators installed in each collector row are discussed as an alternative to a central drum-type separation vessel. This paper deals with the design of a distributed phase separation system composed of the separation devices themselves and a common drainage line to the central buffer tank. As a reference configuration for this analysis the collector field developed within the INDITEP project is chosen. In a first step transient numerical simulation of the collector loop is used to define the loads on the separation system especially under transient conditions caused by cloud coverage. It is found that peak liquid flow rates can exceed the steady-state values by a factor of 10. Based on these results a model for the required separation efficiency is suggested and the drainage system is dimensioned. In order to guarantee sufficient draining even under transient conditions the separators have to be equipped with additional buffer volumes. Finally the distributed separation system is compared to the configuration with a central buffer tank considering the criteria materials consumption, thermal inertia, parasitic losses and controllability. The results of the presented analysis are of vital importance for the layout of future DSG-collector fields.