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ScienceDirect Energy Procedia 105 (2017) 1467 – 1472
The 8th International Conference on Applied Energy – ICAE2016
System design and thermodynamic analysis of a sinteringdriven organic Rankine cycle Yan Liu, Zhilong Cheng, Jingyu Wang, Jian Yang, Qiuwang Wang* Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, P.R. China
Abstract By reviewing development of waste heat utilization in sintering process and sinter cooling process , two major difficulties are more and more apparent. A system of low temperature waste heat utilization based on organic fluids is proposed, which is composed of flue gas waste heat utilization heat exchanger, thermal storage subsystem and organic Rankine cycle (ORC) subsystem. The sintering flue gas and the sinter cooling air are adopted as the heat source. And on this basis, we establish the simulation analysis platform for the whole thermodynamic system. From a comprehensive perspective, the low temperature waste heat utilization could run well when the sintering heat source fluctuates within a certain range. It means that, the ORC-based system could overcome difficulties in utilizing waste heat in sintering process. © Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ©2017 2016The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.
Keywords: Sintering process; Intermittent heat source; System design; Organic Rankine cycle; Heat storage
1. Introduction In 2010, the crude steel production in China represented 44.3 % of the global steel production and accounted to 717 million tons in 2013. Iron and steel production consumes lots of energy and the energy consumption accounting for 10 % the total energy consumption of nat ional economy in the country. Sintering plants occupy about 18 % o f the total energy consumption in iron and steel industry and generally consist of two moving beds: the sintering bed and the sinter cooling bed. Waste heat of the sintering bed and the sinter cooling bed are about 13-23 % and 19-35 % o f the total sintering energy consumption. Therefo re, rational waste heat utilizat ion of sintering bed and sinter cooling bed plays an important role in energy conservation in the steel-making process. Recently, several researchers are focusing on heat transfer, chemical reaction and waste heat utilizat ion in sintering process and sinter cooling process. Pahlevaninezhad et al.  studied the effects of kinetic parameters on combustion characteristics in sintering bed. Cheng et al.  investigated characteristics of charcoal combustion and its effects on iron o re sintering performance. Wang et al.  evaluated combustion characteristic of a flue gas recirculation iron ore sintering process .
* Corresponding author. Tel.: +86-029-82665539; fax: +86-029-82665539. E-mail address: [email protected]
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.436
Yan Liu et al. / Energy Procedia 105 (2017) 1467 – 1472
In order to investigate waste heat utilizat ion of sinter cooling process based on the mechanis m level and the unit level, flow and heat transfer in randomly packed of sinter part icles, nu merical study and mu lti-objective optimization on waste heat cascade utilization in sinter cooling bed were conducted in our recent study, as reported by Liu et al. [4, 5]. According to the authors ’ knowledge, few researches have been conducted on the design and thermodynamic analysis of a sintering-driven system. Therefore, it is necessary to review develop ment of waste heat utilizat ion in sintering p rocess first. After that, a waste heat utilization system could be designed and analysed. 2. Current Development 2.1. Current development on waste heat utilization system of sint er process Presently, there are three approaches to utilize waste heat in sintering process . The first approach is to purify flue gas and be adopted as combustion-supporting air for ignit ion furnaces or be used to preheat sinter mixture. The second approach is to generate steam by heat pipes and waste heat boiler to merge into steam pipe system of whole steel plants. The last approach is to generate steam using waste heat boiler to drive a turbine. Fro m the perspective of cascade waste heat utilization and economy, waste heat power generation is a most effective way to utilize waste heat. Currently, the main waste heat power generation technologies in iron and steel industry are coke dry quenching (CDQ) waste heat power generation technology, sintering waste heat power generation technology, blast furnace top gas recovery turbine (TRT) technology, combined cycle power plant (CCPP) technology, and so on. In China, sintering waste heat power generation technology adopting s team waste heat boiler has become mature. The power units are classified into four groups, single pressure technology, dual pressure technology, flash of waste heat power generation technology and complementary combustion waste heat power generation technology. 2.2. Current development of low temperature waste heat utilization Recently, there are various developed technologies for low temperature waste heat utilizat ion : Organic Rankine cycle (ORC), Stirling cycle, thermoelectric power generation of semiconductor material, ammon ia water mixture Kalina cycle and thermoacoustic, etc. Co mpared with other technologies, turbine and expender (the heart of ORC technology) have been deeply investigated. The results show that, Organic working mediu m has low boiling point, the cycle has higher efficiency and could be work in low temperature. Based on above discussion, ORC is adopted to utilize waste heat in sintering process. 3. System Description The sintering-driven ORC system consists of an intermittent heat source of sintering process , a thermal storage subsystem and an organic Ran kine cycle subsystem. Fig. 1 illustrates the schematic diagram of the entire system. The intermittent heat source could be from the sintering machine and the sinter cooler. After dusting, the flue gas heats water in flue gas heat exchange. Next, the flue gas is adopted to preheat sinter mixture and be hot air ignition. The booster heater is installed as the backup energy source to boost the temperature of thermal storage tank to the allowable temperature when the temperature of thermal storage tank drops below the reference temperature. Water is used in both the flue gas heat exchanger and the thermal storage system. 3.1. Intermittent heat source of sintering process Based on results fro m field measurements, relat ionship between downtime o f s intering machine and shutdown of generator is illustrated in Fig. 2. It could be found that, time interval fro m sintering mach ine starting to unit connecting to grid is much larger than downtime of sintering machine. Therefore, waste heat in sintering process is difficult to be utilized.
Yan Liu et al. / Energy Procedia 105 (2017) 1467 – 1472 Booster Heater
Turbine Sintering Machine
Flue Gas Heat Exchanger
Heat Storage Tank
Preheat Sinter Mixture or Hot Air Ignition
Sinter Cooler Condenser
Fig. 1. Schematic diagram of the sintering-driven ORC system 300
Downtime of sintering machine Time interval from sintering machine stops to boiler splits Time interval from sintering machine starts to unit connects to grid
10 11 12 13 14 15 16 17 18
Fig. 2. Relationship between downtime of sintering machine and shutdown of generator
3.2. Thermal storage system The thermal storage tank is emp loyed to store the intermittent heat source of sintering process and to provide stable power output when sintering process breaks down. In the present work, a sensible heat storage system is adopted and waste is adopted as the heat storage mediu m. The energy balance equation in the tank is as follows: dT [( UVCp ) w ( UVCp ) t ] Qu Qload (UA) t (TL, in Ta ) (1) dt where (ρVCp )w and (ρVCp )t stand for the heat capacity of water in the tank and the heat capacity of tank material, respectively. Ta is amb ient temperature around the tank. (UA)t represents the product of the overall heat transfer coefficient and surface area of the tank. Qu and Qload are useful gain fro m the sintering process and the energy discharged to power subsystem, respectively. The equation could be integrated within a reasonably small interval of time to the following form: T T ( UVCp )e L, in Li Qu mw cpw TL, in Ti (2) 't where the sum of the two heat capacities is replaced by a single (ρCp V)e. TL,in is temperature of the heat storage tank at present. TLi is temperature of the heat storage tank at last moment. t is time interval. Ti is inlet temperature of the heat storage tank.
Yan Liu et al. / Energy Procedia 105 (2017) 1467 – 1472
3.3. Organic Rankine cycle system The organic Rankine cycle subsystem mainly consists of five components, namely, a vapour evaporator, a turbine, a condenser, a pu mp and a regenerator. The system could be simp lified based on several assumptions. The system runs on a steady state. The pressure drop in vapour evaporator, regenerator, condenser and the tubes are ignored. The wo rking fluid at the condenser outlet is saturated liquid, and there exists a temperature difference of condenser. The working fluid at the turbine inlet is overheated, and the degree of superheat is given. The pump and the turbine have a g iven isentropic efficiency, respectively. Schematic d iagram and temperature-entropy diagram o f ORC subsystem are illustrated in Fig. 3. L, in 3
Generator T Turbine
L, in La ƸTpinch
Fig. 3. (a) Schematic diagram of ORC subsystem; (b) T emperature-entropy diagram of ORC subsystem
4. Validation of Thermodynamic Model of ORC The present model is validated with the previously published data [6, 7]. The working conditions for the validation are same with the Refs. [6, 7]. The heat source is 90 ºC and the mass flow rate of the heat source is 1 kg·s -1 . The condensation temperature is 20 ºC, the isentropic efficiency of radial inflow turb ine is 0.85, and the isentropic efficiency of cycle pump is 0.75. The pinch temperature difference in the heat exchangers is 5 ºC. The thermophysical properties of working fluid are calculated by REFPROP, which is developed by the National Institute of Standards and Technology. All system is simulated on MATLAB. The comparison is shown in Fig. 4. As depicted in Fig. 4, the thermal efficiency of ORC system increased when the evaporating temperature was fro m 72 ºC to 84 ºC. The results show the thermodynamic model established in the present work is reliable. 11.0
Thermal efficiency of ORC/%
R245fa (Wang et al. ) R245fa (Zhang et al. ) R245fa (Present study)
10.0 9.5 9.0 8.5 8.0 7.5 7.0 70
R134a (Wang et al. ) R134a (Zhang et al. ) R134a (Present study)
R600a (Wang et al. ) R600a (Zhang et al. ) R600a (Present study)
Fig. 4. T hermal efficiency of ORC system varying with evaporating temperature
Yan Liu et al. / Energy Procedia 105 (2017) 1467 – 1472
5. Effects of Instability of Waste Heat in Sintering Process on Whole System Under a typical condition, N2 , O2 , CO and CO2 account for 79 %, 15.8 %, 0.2 % and 5 % in flue gas in sintering process. The temperature of heat source is 200 ºC in the stable state. Based on field measurements, a certain sintering mach ine goes down about 85 t imes within a quarter. Downtimes with in 30 minutes account for 75 %. It is assumed in present work that, the sintering machine goes down twice within 24 hours (every downtime is 5 hours). Useful gain energy fro m sintering process, energy discharged to power subsystem and temperature of heat storage tank are illustrated in Fig. 5 (the working flu id of the ORC system is R245fa). As depicted in Fig. 5, when the useful gain energy is larger than energy discharged to ORC system, the excess energy could be storage and the water temperature at outlet of heat storage tank increases. When the sintering mach ine goes down from 6 to 11 and fro m 16 to 21, the useful gain energy is 0 and the water temperature of heat storage tank decreas es. On this occasion, energy discharged to ORC subsystem is provided by the heat storage tank. Effects of turbine inlet temperature, turbine inlet pressure and condensing temperature on the system performance are also carefully investigated. It is found that, under the actual constrains, increasing turbine temperature and pressure or lowering condensing temperature could improve the system performance. We also found that, R245fa and R123 are the most suitable working fluids for the system established in the present study. 140000
120000 110 100000 100
Fig. 5. Useful gain from sintering process, energy discharged to power subsystem and tempreture of heat storage tank
6. Conclusions In present work, development of waste heat utilizat ion in sintering process and sinter cooling process are rev iewed firstly. We found the defect of existing technology is more and more h ighlighted . Then, a system of low temperature waste heat utilization based on organic fluids is proposed, which is composed of intermittent heat source, flue gas waste heat utilization heat exchanger, thermal storage system and organic Rankine cycle (ORC) system. And on this basis, the simu lation analysis platform for the thermodynamic system is established and validated with published data. The results obtained fro m present work are in good agreement with prev iously published data. Effects of instability of waste heat in sintering process on whole system are investigated when the sintering machine goes down. Fro m a comprehensive perspective, the waste heat utilization system of sintering process could run well when the heat source fluctuates within a certain range. It means that, the ORC-based system proposed in present work could overco me difficulties in utilizing waste heat of sintering flue gas. The approach introduced in present work offers some co mmon guidance for waste heat utilization in sintering process , which could also be applied to other related processes of industrial production.
Yan Liu et al. / Energy Procedia 105 (2017) 1467 – 1472
Acknowledgements We would like to acknowledge financial supports for this work provided by National Basic Research Program o f China (973 Program, No. 2012CB720402) and National Natural Science Foundation of Ch ina (No. 51536007). References  Pahlevaninezhad M, Davazdah Emami M, Panjepour M, The effects of kinetic parameters on combustion characteristics in a sintering bed, Energy 2014; 73: 160-176.  Cheng ZL, Yang J, Zhou L, Liu Y, Wang QW, Characteristics of charcoal combustion and its effects on iron-ore sintering performance, Applied Energy 2016; 161: 364-374.  Wang G, Wen Z, Lou GF, Dou RF, Li XW, Liu XL, Su FY, Mathematical modeling and combustion characteristic evaluation of a flue gas recirculation iron ore sintering process, International Journal of Heat and Mass Transfer 2016; 97: 964-974.  Liu Y, Yang J, Wang J, Cheng ZL, Wang QW, Energy and exergy analysis for waste heat cascade utilization in sinter cooling bed, Energy 2014; 67: 370-380.  Liu Y, Yang J, Wang JY, Ding XG, Cheng ZL, Wang QW, Prediction, parametric analysis and bi-objective optimization of waste heat utilization in sinter cooling bed using evolutionary algorithm, Energy 2015; 90: 24-35.  Wang X, Liu XM, Zhang CH, Parametric optimization and range analysis of Organic Rankine Cycle for binary -cycle geothermal plant, Energy Conversion and Management 2014, 80: 256-265.  Zhang SJ, Wang HX, Guo T, Performance comparison and parametric optimization of subcritical Organic Rankine Cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation, Applied Energy 2011; 88: 2740-2754.
Biography Yan Liu is a Ph.D. student in School of Energy and Power Engineering, Xi’an Jiaotong University, Ch ina. He received his bachelor’s degree in the School of Science fro m Xi’an Jiaotong University, Ch ina, in 2010. His main research interests are flo w and heat transfer in packed beds, waste heat recovery and building energy savings. Qiu wang Wang is a professor in the School of Energy and Power Engineering, Xi’an Jiaotong University, China. He received his Ph.D. in Eng ineering Thermophysics fro m Xi’an Jiaotong University, China, in 1996. He then joined the faculty of the university and took the professor post in 2001. His main research interests include Co mputational Flu id Dynamics and Nu merical Heat Transfer (CFD&NHT), heat transfer enhancement, transport phenomena in porous media, co mpact heat exchangers, building energy savings, and indoor air quality, etc. He has also been authors or co-authors of 4 books and more than 100 journal papers, and his H-index is 24. He has obtained 16 China Invent Patents and 2 US patents.