Superheated Steam From CLFR Solar Steam Generators

Abstract

AREVA Solar has designed, constructed and demonstrated the first successful Once Through Solar Steam Generator (SSG) to deliver superheated steam without intermediate heat transfer fluids. Deployed at the Kimberlina Solar Thermal Power Station, SSG4 represents the state of the art for solar steam production, for stand-alone power generation and augmentation of fossil fueled steam cycles. The ASME Section I boiler was designed, constructed, stamped and commissioned during 2010, and includes a novel Model Predictive Control system capable of maintaining any two of three steam conditions (flow, pressure, temperature) under varying solar input. During field trials in September 2010, exit steam conditions were maintained at 60 +/− 3 bar and 370 +/− 20C during steady and transient conditions, while steam flow consistently exceeded predictions. In a “lights-out” test, simulating complete instantaneous cloud cover, SSG4 had sufficient thermal inertia to supply more than 18 minutes of superheated steam. AREVA Solar’s SSGs incorporate a 400m long tube bundle within an elevated insulated cavity receiver, onto which sunlight is concentrated by reflectors. The multi-pass tube bundle arranges superheater tubes in the high flux regions, and economizer/evaporator tubes in lower flux regions. This assures sufficient heat flux to sustain superheated steam temperatures throughout the operating day, and also reduces the average bundle temperature to reduce radiant heat losses. Boiler tubes were prepared in AREVA Solar’s factory to improve their absorption of solar energy and reduce radiant heat losses. The inverted cavity maintains a stagnant air layer between the tube bundle and a glass cover below the boiler tube supports, to reduce convective heat loss. SSG4 was designed for a Maximum Allowable Working Pressure of 105 bara, and a Maximum Mean Wall Temperature of 482C in the superheater section. AREVA Solar is the first Concentrated Solar Power provider with an ASME “S” Stamp and National Board authorization. Following the initial trials at 370C, the SSG is expected to operate at 450C superheated steam temperature. This paper describes the design, construction, commissioning, and testing of the Compact Linear Fresnel Reflector (CLFR) SSG4.

Control systems for direct steam generation in linear concentrating solar power plants – A review

“…The Compact Linear Fresnel Reflector is a concept of linear Fresnel collector originally proposed in the work of Mills and Morrison [42], and later used as the design basis of Areva Solar DSG plants [43]. This latter reference presents the SSG4 direct steam generation collector operated in once through mode with a two pass arrangement at the Kimberlina solar thermal plant.…”

Linear Fresnel reflector (LFR) technology

“…In early 2010, Ausra was bought outright by the French nuclear giant Areva and was renamed Areva Solar. Performance is said by the company to have met or exceeded modelling predictions (Conlon, 2011). In early 2010, a $105 million 18 line 44 MWp(e) steam booster project was secured with the utility CS in Queensland to go online in 2013.…”

“…Areva has stated that it is developing a 482°C version available for 2011 with 165 bar operation (Areva, 2012) , which may be the 13 refl ector line version described by Conlon (2011), who cites a design operational temperature of 450°C and pressure of 165 bar with a maximum pipe wall temperature of 482°C. Areva has also suggested a version 2.0 to be under development, so it is possible that the next version could be designed for maximum steam temperature of more than 500°C, but that is not clear at the time of writing.…”

“…On the other hand, a scale drawing (fi g. 2 in Conlon, 2011) shows a widening gap between refl ectors with greater distance from the receiver, which would reduce shading and blocking at normal incidence and allow a closer-packed fi eld. Something favouring Areva in the calculation is that this is a peak calculation with the sun essentially overhead; the Areva refl ectors are larger relative to the aperture with potentially greater off-angle astigmatism, but this would not affect the zenith angle fi gure used.…”

The feasibility of hybrid solar-biomass power plants in India

“…Thus, hybrid solar-biomass power plants will require high-quality control systems which should be the focus of further work. One manufacturer of an LFR system claims that they have already developed a predictive control system that is capable of maintaining pressure, temperature and flow for varying solar inputs [59]. By implementing suitable control strategies a fast boiler response time, and constant pressure, temperature and flow should also be achievable.…”