A technique to avoid two-phase flow in solar collector tubes of the direct steam generation system for a solar aided power generation plant

Abstract

In a traditional solar aided power generation (SAPG) plant, problematic two-phase flow may be present in the solar collector tubes which can lead to burst pipes. Within the SAPG plant, it is proposed that a flash tank be applied. By using a flash tank and mandating its inlet pressure by controlling the booster pump, the preheating and overheating collectors can each be ensured to have single-phase flow. To assess the economic and performance criteria of adding a flash tank, a simulation model using is developed and using a unified matrix equation technique. This method is used to assess the effect of the flash tank on a case study 300 MW SAPG plant. Two modes of SAPG operation are considered. In the ‘single-generation mode’ only steam is introduced to the fossil-fuelled plant. In the ‘co-generation mode’ both steam, from the overheating collector, and water, from the flash tank, are introduced to the fossil-fuelled plant. The ‘co-generation mode’ is found by the authors to be the marginally better performing mode. By applying a flash tank in the SAPG system, the problem of unstable two-phase flow in solar collector tubes can be effectively overcome thereby improving the viability of implementation of retrofitted solar aided power generation to fossil-fuelled plants.