Superheated Steam From CLFR Solar Steam Generators

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 bar_a, 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.