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  • 1.
    Blasiak, Wlodzimierz
    et al.
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Yang, Weihong
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Rafidi, Nabil
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Physical properties of a LPG flame with high-temperature air on a regenerative burner2004In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 136, no 4, p. 567-569Article in journal (Refereed)
  • 2.
    Mörtberg, Magnus
    et al.
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Rafidi, Nabil
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Blasiak, Wlodzimierz
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Measurements of temperature, heat flux and flue gas composition in HTAC flame2002In: Proceedings of IOM conference, 2002Conference paper (Other academic)
  • 3.
    Rafidi, Nabil
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Thermodynamic aspects and heat transfer characteristics of HiTAC furnaces with regenerators2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Oxygen-diluted Combustion (OdC) technology has evolved from the concept of Excess Enthalpy Combustion and is characterized by reactants of low oxygen concentration and high temperature. Recent advances in this technology have demonstrated significant energy savings, high and uniform thermal field, low pollution, and the possibility for downsizing the equipment for a range of furnace applications. Moreover, the technology has shown promise for wider applications in various processes and power industries.

    The objectives of this thesis are to analyze the thermodynamic aspects of this novel combustion technology and to quantify the enhancement in efficiency and heat transfer inside a furnace in order to explore the potentials for reduced thermodynamic irreversibility of a combustion process and reduced energy consumption in an industrial furnace. Therefore, theoretical and experimental investigations were carried out.

    The 2nd law of thermodynamics analyses of OdC systems have been carried out for cases in which the oxidizer is either oxygen (Flameless-oxy-fuel) or air (High Temperature Air Combustion, HiTAC). The analyses demonstrate the possibilities of reducing thermodynamic irreversibility of combustion by considering an oxygen-diluted combustion process that utilizes both gas- and/or heat-recirculation. Furthermore, the results showed that an oxygen-diluted combustion system that utilizes oxygen as an oxidizer, in place of air, results in higher 1st and 2nd law efficiencies.

    Mathematical models for heat regenerators were developed to be designing tools for maximized heat recovery. These models were verified by heat performance experiments carried out on various heat regenerators.

    Furthermore, experiments were performed in a semi-industrial test furnace. It was equipped with various regenerative burning systems to establish combustion and heat transfer conditions prevailing in an industrial furnace operating based on HiTAC. The tests were carried out at seven firing configurations, two conventional and five HiTAC configurations, for direct and indirect heating systems.

    Measurements of energy balance were performed on the test furnace at various configurations in order to obtain the 1st law efficiency. Moreover, local measurements of temperature, gas composition, and heat fluxes in the semi-industrial test furnace were performed to find out the main characteristics of HiTAC flame and the effects of these characteristics on the heating potential, i.e., useful heating in the furnace. In the case of HiTAC, these measurements showed uniformities of chemistry, temperature, temperature fluctuation, and heat fluxes profiles. The values of fluctuations in temperature were small. The high speed jets of the fuel and air penetrated deep into the furnace. The fuel gradually disappeared while intermediate species gradually appeared in relatively high concentrations and at broader regions inside the furnace. These findings indicate: a large reaction zone, low specific combustion intensity in the flame, low specific fuel energy release, and high heat release from this large flame. In addition to the thermodynamic limitations to the maximum temperature of the Oxygen-diluted Combustion, the low specific energy release of the fuel and the high heat release from the flame to its surroundings cause this uniform and relatively moderate temperature profile in a HiTAC flame, consequently suppressing thermal-NO formation.

    Heat flux and energy balance measurements showed that heating potential is significantly increased in the case of HiTAC compared to that in the conventional case, implying much more energy savings than the apparent heat recovery from the heat regenerators, and consequently much less pollutants emissions. Therefore, it is certain that this large HiTAC flame emits more thermal radiation to its surroundings than the conventional flame does, in spite of the moderate-uniform temperature profile of the flame. This intense heat flux was more uniform in all HiTAC configurations, including the indirect heating configuration, than that of the conventional-air combustion configuration.

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  • 4.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Heat transfer characteristics of HiTAC heating furnace using regenerative burners2006In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 16, p. 2027-2034Article in journal (Refereed)
    Abstract [en]

    The aim is to experimentally study the various modes of heat transfer and to investigate the effect of the HiTAC flame characteristics on the heat transfer intensity and uniformity inside a setni-industrial test furnace using various industrial regenerative burners and various flame configurations namely; single-flame, twin-flame counter. twin-flame parallel and twin-flame stagger. Measurements of local instantaneous and average temperatures, heat fluxes and gas composition at several locations inside the furnace were carried out. It was observed that the HiTAC flame with highly reduced temperature fluctuations. turbulent intensity and combustion intensity have a larger reaction zone than a conventional flame. This large flame emits more thermal radiation in spite of its uniform and reduced temperature. Furthermore, the convective heat transfer was found to be uniform and as high as 30% of the total heat transfer to an object surface in the furnace. On the other hand, the very high reduction of NOx emission is a consequence of the low temperature and temperature fluctuation levels of the HiTAC flames. The above findings are valid to a similar extent in all burners and configurations but to less extent in the twin-flame counter configuration.

  • 5.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Thermal performance analysis on a two composite material honeycomb heat regenerators used for HiTAC burners2005In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 25, no 17-18, p. 2966-2982Article in journal (Refereed)
    Abstract [en]

    Honeycomb heat regenerators do not only reduce the fuel consumption in a high temperature air combustion (HiTAC) burning system but also provide the necessary high temperature of combustion air. A two-dimensional simulation model was developed to numerically determine the dynamic temperature and velocity profiles of gases and solid heat-storing materials in a composite material honeycomb regenerator. Consequently, the energy storage and the pressure drop are calculated and the thermal performance of honeycomb heat regenerator is evaluated at different switching times and loading. The model takes into account the thermal conductivity parallel and perpendicular to flow direction of solid and flowing gases. It considers the variation of all thermal properties of solid material and gases with temperature, Moreover, the radiation from combustion flue gases to the storage materials was considered in the analysis, The results are presented in a non-dimensional form in order to be a design tool as well, These analyses were applied on a regenerator made of two layers of ceramic materials, one is pure alumina and other is cordierite. This regenerator is contained in a. 100 kW twin-type regenerative-burning system used for HiTAC. The effectiveness and the energy recovery rate were 88% and 72% respectively at nominal operating range of the regenerator and the pressure drop across the twin regenerator system wits 1.16 kPa. The periodic steady state condition is reached after about 11 min and it takes only 2 min of operation until the temperature of combustion air remains above the self-ignition temperature that is required for HiTAC. Furthermore. these mathematical analyses show good agreement with experiments made on the same regenerator. In the experiments, the dynamic behavior of the heat regenerator operation was considered in order to compensate measurement readings for this effect.

  • 6.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Thermodynamic aspects of oxygen-deficient2005In: Archives of Thermodynamics, ISSN 1231-0956, Vol. 26, no 2, p. 29-44Article in journal (Refereed)
    Abstract [en]

    The oxygen deficient combustion (ODC) is characterized by reactants of low oxygen concentration and high temperature. This work is devoted to analysis of such combustion process from the thermodynamic point of view. It demonstrated the possibilities for reducing thermodynamic irreversibility of combustion by considering the oxygen-deficient combustion process that utilizes both gas- and heat-recirculation. Furthermore, an ODC system utilizes oxygen as oxidizer has higher 1st and 2nd low efficiencies compared to an ODC system using air as oxidizer. This study is a technical guidance for further efficiency-improvement in combustion process especially because the temperature increase due to the reaction in an ODC system is mild.

  • 7.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology. Alstom Switzerland Ltd., Baden, Switzerland .
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Gupta, Ashwani K.
    High temperature air combustion (HITAC) phenomena and its thermodynamics2014In: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 2014, Vol. 6AConference paper (Refereed)
    Abstract [en]

    The fundamentals and thermodynamic analysis of High Temperature Air Combustion (HiTAC) technology is presented with focus on industrial furnaces as they are amongst the major energy users. The HiTAC is characterized by high temperature of combustion air having low oxygen concentration. This study provides a theoretical analysis of HiTAC a process from the thermodynamic point of view. The results demonstrate the possibilities of reducing thermodynamic irreversibility of combustion by considering an oxygen-deficient combustion process that utilizes both gas- and heat-recirculation. Furthermore, combustion with the use of oxygen (in place of air) is also analyzed. The results showed that a system which utilizes oxygen as an oxidizer results in higher 1st and 2nd law efficiencies as compared to the case with air as the oxidizer. This study is aimed at providing technical guidance to further improve efficiency of a combustion process which show very small temperature increases due to mild chemical reactions. The significant of these findings are now widely used in industrial furnaces with singular successes on energy savings, pollution reduction and reduced size of the equipment. The exergy analysis too can be used as a technical tool to improve efficiency in combustion processes.

  • 8.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Gupta, Ashwani K.
    High-temperature air combustion phenomena and its thermodynamics2008In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 130, no 2, p. 023001-Article in journal (Refereed)
    Abstract [en]

    The fundamentals and thermodynamic analysis of high-temperature air combustion (HiTAC) technology is presented. The HiTAC is characterized by high temperature of combustion air having low oxygen concentration. This study provides a theoretical analysis of HiTA C process from the thermodynamic point of view. The results demonstrate the possibilities of reducing thermodynamic irreversibility of combustion by considering an oxygen-deficient combustion process that utilizes both gas and heat recirculations. HiTA C conditions reduce irreversibility. Furthermore, combustion with the use of oxygen (in place of air) is also analyzed. The results showed that a system, which utilizes oxygen as an oxidizer results in higher first and second law efficiencies as compared to the case with air as the oxidizer. The entropy generation for an adiabatic combustion process is reduced by more than 60% due to the effect of either preheating or oxygen enrichment. This study is aimed at providing technical guidance to further improve efficiency of a combustion process, which shows very small temperature increases due to mild chemical reactions.

  • 9.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Jewartowaski, Marcin
    Szewczyk, Dariusz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Increase of the Effective Energy from the Radiant Tube Equipped with Regenerative System in Comparison with Conventional Recuperative System2005In: IFRF Combustion Journal, ISSN 1562-479X, no 03, p. 1-17Article in journal (Refereed)
    Abstract [en]

    This paper presents the experimental results of High Temperature Air Combustion (HiTAC)investigations with the use of a radiant tube, in order to compare the Regenerative System (RS)with a conventional recuperative system.For this work a semi-industrial HiTAC test furnace was equipped with the W-shape RadiantTube. The working length of this tube was around 7,0 m and the diameter was 0,195 m. Theradiant tube was operated in sequence with a conventional recuperative system and aRegenerative System. The recuperative burner was mounted in the upper end of the tube. TheRS consisted of two burners, equipped with honeycomb ceramic regenerators, mounted to bothends of the radiant tube. The temperature profile of the tube wall was monitored by 74thermocouples located along the tube. Additional temperatures, flow rates and pressures weremeasured to assess and compare the energy balance of both systems. Pollutant emissions,including NOx and CO, as well as the exhaust gas composition were measured. The tests werecarried out over a wide range of parameters: firing power from 75 kW to 155 kW, furnacetemperature from 670°C to 950°C and an oxygen molar fraction in the exhaust gases set at 3%.LPG was used as a fuel in all tests.Test results show that the temperature profiles along the tube were more uniform when theregenerative system was used. The cross-sectional temperature distribution for the tube wasalso more uniform. Because of the relatively flat temperature distribution along the tube, moreenergy from the radiant tube can be emitted using RS in comparison with the conventionalrecuperative burner, for the same maximum temperatures of the tube. In certain conditions, theincrease of energy release can be up to 100%.Energy balance calculations show that the efficiency of the Regenerative System can be up to25% higher than that of the recuperative system, mainly due to very low temperature of fluegases for RS operation. Although, the preheated air temperature used for combustion wasmuch higher in the case of the regenerative system (in some tests as high as 960°C), the NOxemission was found to be almost the same in both cases.

  • 10.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Włodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Thermodynamic aspects of oxygen-deficient combustion2005In: Archives of Thermodynamics, ISSN 1231-0956, E-ISSN 2083-6023, Vol. 26, no 2, p. 29-44Article in journal (Refereed)
    Abstract [en]

    The oxygen deficient combustion (ODC) is characterized by reactants of low oxygen concentration and high temperature. This work is devoted to analysis of such combustion process from the thermodynamic point of view. It demonstrated the possibilities for reducing thermodynamic irreversibility of combustion by considering the oxygen-deficient combustion process that utilizes both gas- and heat-recirculation. Furthermore, an ODC system utilizes oxygen as oxidizer has higher 1st and 2nd low efficiencies compared to an ODC system using air as oxidizer. This study is a technical guidance for further efficiency-improvement in combustion process especially because the temperature increase due to the reaction in an ODC system is mild.

1 - 10 of 10
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