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Heat transfer characteristics of HiTAC heating furnace using regenerative burners
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
2006 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 16, 2027-2034 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2006. Vol. 26, no 16, 2027-2034 p.
Keyword [en]
heat transfer, combustion, furnace, regenerative burner
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-8881DOI: 10.1016/j.applthermaleng.2005.12.016ISI: 000238798200031Scopus ID: 2-s2.0-33744970679OAI: oai:DiVA.org:kth-8881DiVA: diva2:14357
Note
Uppdaterad från "In press" till published: 20101011. QC 20101011Available from: 2005-12-06 Created: 2005-12-06 Last updated: 2010-10-11Bibliographically approved
In thesis
1. Thermodynamic aspects and heat transfer characteristics of HiTAC furnaces with regenerators
Open this publication in new window or tab >>Thermodynamic aspects and heat transfer characteristics of HiTAC furnaces with regenerators
2005 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. xiv, 68 p.
Keyword
Combustion, flameless, oxy-fuel, heat-recirculation, gas-recirculation, heat transfer, furnace, radiant-tube, regenerative burner, honeycomb, fixed-bed
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-541 (URN)91-7178-223-0 (ISBN)
Public defence
2005-12-15, F4/Sem and F3, Lindstedtsvägen 26, KTH Main Campus, 10:00
Opponent
Supervisors
Note
QC 20101011Available from: 2005-12-06 Created: 2005-12-06 Last updated: 2010-10-11Bibliographically approved

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