Thermodynamic and economic investigation of a screw expander-based direct steam generation solar cascade Rankine cycle system using water as thermal storage fluid

Li, Jing; Li, Pengcheng; Gao, Guangtao; Pei, Gang; Su, Yuehong; Ji, Jie

Abstract

Solar electricity generation system (SEGS) which employs cascade steam-organic Rankine cycle (SORC) and steam screw expander (SE) is promising due to the high efficiency at moderate heat source temperature. This paper puts a special emphasis on heat storage and thermo-economic evaluation. Preferable operating temperature of the system is first clarified on the basis of SE characteristics. The temperature-dependent permissible stress of steam accumulator is modelled and the capital cost is investigated. Comparison between the direct steam generation (DSG) SEGS and an indirect one using thermal oil is made at a power capacity of 1 MW and storage of 6.5 h. The results indicate the DSG system has both thermodynamic and economic superiorities. The hot side temperature (THTH) of SORC generally does not exceed 250 °C to achieve an optimum solar thermal power efficiency. Given radiation of 750 W/m2, the maximum efficiency (ηT,mηT,m) is 14.3% with a corresponding THTH around 240 °C. The material cost of pressure vessels is 2.55 million RMB. For the indirect system, the optimal THTH is about 230 °C and ηT,mηT,m approximates to 13.2% and the estimated oil cost is 7.92 million RMB. It is recommended to adopt steam accumulators in the SE-driven SEGS.

Citation

Li, J., Li, P., Gao, G., Pei, G., Su, Y., & Ji, J. (2017). Thermodynamic and economic investigation of a screw expander-based direct steam generation solar cascade Rankine cycle system using water as thermal storage fluid. Applied Energy, 195, https://doi.org/10.1016/j.apenergy.2017.03.033

• Journal Article Type: Article
• Acceptance Date: Mar 9, 2017
• Online Publication Date: Mar 17, 2017
• Publication Date: Jun 1, 2017
• Deposit Date: May 9, 2017
• Publicly Available Date: May 9, 2017
• Journal: Applied Energy
• Print ISSN: 0306-2619
• Electronic ISSN: 0306-2619
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 195
• DOI: https://doi.org/10.1016/j.apenergy.2017.03.033
• Keywords: Solar thermal power generation; Screw expander; Thermal storage; Steam accumulator; Part-load behavior
• Public URL: https://nottingham-repository.worktribe.com/output/863167
• Publisher URL: http://www.sciencedirect.com/science/article/pii/S0306261917302568