Development of a solar-energy activated organic Rankine-cycle pilot power plant

摘要

with the development of a low-grade energy engine in theSchool of Mechanical Engineering at Cranfield, there begana venture towards utilizing the Sun's power to operate theengine via a thermodynamic cycle, in an Egyptian desertarea, i. e latitude 3Q0N. The derived mechanical power is todrive an irrigation pump at the site.The solar thermal system is to operate in a Rankine-cycleusing an organic working fluid. The engine is in the formof a multi-vane expander. The solar-energy collectorcomprises of an array of gravity-assisted heat- pipes eachenclosed within a cylindrical high-vacuum glass tube. Theirrigation water which is to be sucked from below groundlevel, is also to cool the shell-and-tube condenser.The first section(i. e. PART A) of this thesis is apresentation of some design optimization concepts in thedevelopment of the thermodynamically operated solar-energysystem.As in any desert area dust will constitute a problem,reducing the harnessing capability of the collector array.Regular cleaning would therefore be essential. However,cleaning a large array (1000) of such fragile tubes insitu is unlikely to be accomplished without cracks andbreakages occurring. This perhaps means that thehigh-vacuum which is essential for each collectorscontinued adequate thermal performance could be easilylost. The collectors are also considered expensive. Forexample, one tube with an effective aperture area of about0.102ml costs about twenty pounds Sterling. These and thefact that the maximum anticipated working temperature inthe organic Rankine-cycle would be about 1201 C, led to thestudy into a means other than evacuation of reducingthermal losses from the receiver of a flat-platesolar-energy collector in the second section (i. e. PART B).A flat-plate collector employing a simple slattedconvection suppression device was studied. It was shownthat a flat-plate collector employing an effectiveconvection suppression device and an initial cost of about£1o0/m`would be more cost effective than the evacuated-tubecollector, when employed to activate the pilot power plantfor operatinq temperaures of (80-X120)° C.The cost per peak watt could be reduced by an average valueof about 15% depending upon the'operating temperture.Whereas the break-even time against electricity could bereduced by about 4%. However, the overall efficiency of thepower plant could fall by an average value of about 23%,depending upon the operating temperature.