| Organic Rankine cycle（ORC）is an important technical means of industrial waste heat recovery.The research on ORC system mainly focuses on these aspects of the screening of organic working medium,the protection of key heat exchange equipment and the optimization of system structure and operating parameters under different heat source conditions.The sensible heat of blast furnace slag is an excellent remaining heat resource with high energy level because of its high temperature,which can be utilized sufficiently to avoid energy wasting.For iron and steel enterprises,in order to improve the quality of slag making products,the method of INBA slag is usually to use the recovered sensible heat of blast furnace slag.However,due to its low temperature of flushing water,the efficiency of ORC system is generally low.Thus,focusing on these issues,in this paper,it is proposed that the radiant sensible heat in the slag ditch can be recovered by cold air without affecting the fluidity of slag,and then use INBA method to obtain the heat source from blast furnace slag flushing water.According to the two heat source conditions,a Double Organic Rankine Cycle（DORC）power generation system is established.The thermodynamic performance of the optimal operating parameters is determined by genetic algorithm,and compared with the basic ORC system with a single blast furnace slag flushing water source.Under different system heat source conditions and evaluation indexes,the optimal circulating working medium is different,or even just the opposite in terms of physical properties for the working medium.In this work,ORC thermodynamic models are established for the research of medium temperature air heat source and low temperature slag flushing water heat source respectively.The influence of system parameters on system performance is explored,and the optimal working medium is achieved.The heat sources are mostly corrosive and easy to scale for industrial waste heat recovery ORC power generation system,which can easily cause corrosion and blockage to ORC heat exchange equipment.In order to avoid that problem,the anti-corrosion coating is adopted in our work through spraying it on the heat exchange surface,and the influences of the thermal conductivity of the coating on the heat transfer performance were explored for the heat exchangers.The ORC condenser has a large heat exchange area due to its small heat transfer temperature difference.Thus,spraying hydrophobic coating on the heat exchange surface of the condensation side can not only prevent the occurance of scaling,but also improve the condensation heat transfer coefficient through the conversion of film condensation to bead condensation.The liquid film formed by the medium condensation in the condenser constitutes the main thermal resistance of the condensing side.By discharging the film in time,the condensing heat transfer performance can be effectively improved.In this paper,the performance of water vapor in the intermediate drainage cooling is studied experimentally.In order to study the condensation characteristics of organic working medium in new plate heat exchanger,the condensation and heat transfer correlation formula of R245fa in plate heat exchanger was obtained through numerical simulation and experimental verification,which provides reference for the design of condenser.The main research contents and conclusions are as follows:1.According to the production conditions of iron-making blast furnace with a volume of 4038 m3,the blast furnace slag flushing water ORC system and medium temperature air ORC system are established,respectively.The changes of thermodynamic performance of ORC system with evaporation temperature,condensation temperature and superheat under specific heat source conditions are explored.The results showed that the circulating net work of all pure refrigerants in the blast furnace slag flushing water ORC system exhibited a tendency of increasing at the first and then decreasing with the evaporation temperature,which reached the maximum value at 60℃of evaporation temperature,in which R227ea exhibited the best performance.The R227ea/R245fa（0.5/0.5）is the best for binary non azeotropic mixtures.When the condensation temperature is 38℃,the maximum net work reaches4336 k W.Compared with R227ea and R245fa,its efficiency increased by 18.24%and26.41%with the exergey efficiencies of 56.37%,which increased by 20.5%and 14.18%,respectively.In the ternary non azeotropic mixtures,the maximum cycle net work of R227ea/R134a/rc318（0.1/0.2/0.7）showed the best level of 4049 k W,which is increased by 10.42%,13.07%and 13.39%,respectively,compared with pure refrigerants R227ea,R134a and RC318.In the medium temperature air heat source ORC system,R601 working medium has the largest net work and is better than its other mixed working mediums,indicating that the improvement of performance of ORC system by mixed working medium could change due to the different heat source temperatures.The obtained net work contour map of ternary mixed working medium cycle provided a reference for analyzing the physical properties of multivariate mixed working medium and determining the best working medium,which can expand to make the thermal efficiency,exergey efficiency and other value maps of multivariate mixed working mediums,and provided guidance for the calculation of thermal performance of Organic Rankine cycle.2.For the new corrugated plate condenser,the appropriate mathematical model and physical model are selected for numerical simulation.After building the experimental platform of ORC system,the parameters of temperature,flow and differential pressure are measured to verify the simulation results,which exhibited a good agreement with the experiment.The effects of working medium inlet flow rate,inlet superheat and condensate side inlet flow rate on the heat transfer factor j,friction factor F and overall factor j·f-1 of the condenser are discussed,combined with the orthogonal design test.For the plate condenser in ORC system,the greater the inlet flow rate,the smaller the undercooling,and the better the overall performance.Furthermore,according to the classical condensation heat transfer correlation,the heat transfer correlation of R245fa in the new plate condenser is fitted by linear regression combining with the numerical simulation results.3.Anti corrosion coating sprayed on the heat exchange surface of ORC evaporator was to prevent the corrosion from waste heat medium.The coating increases the thermal resistance in the heat transfer process of heat exchanger when the coating thickness is200μm,in the process of gas-liquid heat transfer,when the thermal conductivity of the coating is 0.1 W·（m·K）-1,under the heat transfer conditions of different cold fluid Re number,the proportion of coating thermal resistance to the total is 13%,and the main thermal resistance is distributed on the side of gaseous hot fluid.In the process of liquid-liquid heat transfer,when the thermal conductivity of the coating is increased from 1 W·（m·K）-1 to 30 W·（m·K）-1,the proportion of thermal conductivity and thermal resistance of the coating is reduced from 52%-53%to 4%under different cold fluid Re number heat transfer conditions.The condensation can be changed from membrane condensation to droplet condensation by spraying hydrophobic coating on the heat transfer surface of ORC condenser.The visual condensation experiment showed that the heat transfer coefficient increased with the water contact angle.When the water contact angle is 153°,it is 6.9 times higher than film condensation.In order to meet the thermal conductivity and hydrophobicity at the same time,the coating ratio is optimized by neural network and genetic algorithm.The water contact angle gets164.24°and the thermal conductivity gets 14.19 w·（m·K）–1 by optimization.4.The condenser adopts the way of segmented condensation and intermediate drainage,which can reduce the thermal resistance of the liquid film formed by the condensed liquid on the condensation surface and improve the heat exchange efficiency to a great extent.Through the condensation experiment of water vapor in corrugated plate heat exchanger,it is found that the intermediate discharge mode is more conducive to liquid condensation than the undivided condenser.At the same time,liquid separation condensation reduces the steam condensation pressure loss,increases the steam flow and improves the heat exchange.The experimental results show that the heat transfer coefficient of liquid separation condensation is doubled when the heat transfer areas are equal and the air outside the plate is flowed by natural convection.5.In this chapter,it is proposed to use air to pre-cool the slag in the ditch,recovering the radiant sensible heat of the blast furnace slag on the premise of ensuring the fluidity.Then use INBA to make the cooled blast furnace slag to obtain the waste heat resource of blast furnace slag flushing water,so as to establish a dual loop Organic Rankine cycle power generation system.At the same time,genetic algorithm is used to optimize the evaporation temperature,condensation temperature and superheat of the two cycle systems with the system cycle network as the objective function.The operation results are compared with the Simple Organic Rankine Cycle of single blast furnace slag flushing water heat source.It is found that the network of the dual loop system is increased by 48.8%and the exergy recovery efficiency of the system is improved by 20.3%. |
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