Study On Slag As Energy Storage Material In Concentrate Solar Power Plants

Concentrated solar power(CSP)plants can use heat storage machine,which will improve efficiency of the CSP plants.The traditional molten salt heat storage equipment is expensive,accounting for 15-25%of the system cost.Slag is a by-product of steel production.Steel slag is mostly consist of oxides of aluminum,calcium,iron,magnesium and silicon,which has a good thermal conductivity.Revalorization of the remaining slag into TES material can lead to a cost-effective solution to the CSP plants and the industry waste recovery.Parabolic trough collectors(PTC)is the most used technologies for CSP plants.The work temperature range of PTC and SPT technologies is 20-400 0C.In this work,the thermal stability,phase composition,microstructure,specific heat capacity,thermal conductivity and friction of steel slag were studied,appliing in PTC power generation technology.Thermal gravimetric analysis was used in this paper to measure the thermal stability of two kinds of slags at 100 ?-1000 ?.X-ray diffraction analysis was used to examine the microstructure of steel slag before and after the thermal gravimetric experiment.Using laser flash analysis to measure the specific heat capacity,thermal diffusivity and thermal conductivity from room temperature to 500 0C.Slag as a heat storage material,due to the alternating hot and cold work environment,go through an expansion and basic friction.In this experiment,a high-temperature pin-plate rotating friction machine was used to simulate the friction generated by the steel slag in the heat storage process.The wear test in different environment,friction atmosphere was vacuum,at 400 ? and friction atmosphere was air,at 800 ? were studied.The friction experiment was carried out to evaluate the influence of temperature on the tribological properties of steel slag samples.The study found that c steel slag and s steel slag remained stable below 1000 ?.Before and after the thermal gravimetric experiment,the phase compositions of c steel slag and s steel slag changed into more stable.From room temperature to 500 ?,the specific heat capacity of the two slag increases with the temperature.The temperature of 500 ?,c slag specific heat capacity of 0.975 J/g·K,s steel slag specific heat capacity of 0.858 J/g·K.The thermal conductivity of the two kinds of slag showed different variation with the increase of temperature because of the complex composition.At 500 ?,the thermal conductivity of c steel slag was 1.753 W/(m K),of s steel slag was 1.736 W/(m-K).Compared with the thermal properties of thermal storage materials widely used or studied in solar thermal power stations,c steel slag and s steel slag have the advantages of high thermal conductivity and high specific heat capacity.When the friction atmosphere was vacuum,at 400 ?,the friction coefficient of c steel slag was 0.54 and the wear rate was 8.44 ×10-7g/N·m.The friction coefficient of s steel slag was 0.46 and the wear rate was 55.46×10-7g/N·m.Compared with the coefficient of friction of solid thermal storage materials such as ceramics and concrete which are widely used or researched by solar thermal power plants,c steel slag and s steel slag have lower friction coefficient and better frictional performance.When the friction atmosphere was air,at 800 ?,the friction coefficient of c slag was 0.343 and the friction coefficient of s steel slag was 0.312.Compared with the friction coefficient of the two kinds of steel slag when the frictional atmosphere was vacuum,at 400 ?,the friction coefficient of c steel slag and s steel slag in the working atmosphere was air,at 800 ? were lower,which may be due to the oxidation of the metal element in slag in the air environment.After the high-temperature friction test,pores,cracks and fragments can be observed on the worn surfaces of c steel slag and s steel slag,indicating that the high-temperature wear mechanisms of these two steel slag are adhesive wear and abrasive wear.A model was developed to predict the distribution of stress in static contaction between pin and disk using ANSYS.The pin surface was subjected to the maximum stress.