Skip to main content

Biomass heat pipe reformer—design and performance of an indirectly heated steam gasifier


Indirectly heated dual fluidized bed (DFB) gasifiers are a promising option for the production of syngas, in particular in the small- and medium-scale range. The application of so-called heat pipes solves the key challenge of indirectly heated gasifiers—the heat transfer into the gasifier's reformer part. Performance, technical challenges, and solutions for the so-called biomass heat pipe reformer are discussed, and the development of the last 10 years is summarized. An equation for the heat pipe reformer's cold gas efficiency is presented. The equation applies for any dual fluidized bed gasifier and indicates that the efficiency of the combustion process dominates the cold gas efficiency of any directly or indirectly heated allothermal steam gasification system.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10


a, a min :

(Stoichiometric) air demand (kilogramsair/kilogramfuel)

b :

Fuel-to-bed material ratio (kilogramsbed material/kilogramfuel)

c p :

Specific heat (kilojoules per kilogram per Kelvin)

H l :

Lower heating value (kilojoules per kilogram)

H i :

Molar enthalpy (kilojoules per kilomole)

ΔH r :

Heat of reaction (kilojoules per kilomole)

ΔH v :

Heat of evaporation (kilojoules per kilomole)

\( \overset{\cdot }{m} \) :

Mass flow (kilograms per second)

\( \overset{\cdot }{n} \) :

Molar flow (kilomoles per second)

\( {\tilde{M}}_{{}_i} \) :

Molar mass (kilograms per kilomole)

m, n :

Molar fraction of hydrogen and oxygen in the fuel (–)

\( \overset{\cdot }{Q} \) :

Energy flow, heat demand, heat flux (kilowatts)

\( \overset{\cdot }{q} \) :

Specific heat demand (–)

\( \varDelta {\overset{\cdot }{Q}}_{\varDelta \mathrm{h},\mathrm{r}} \) :

Heat of reaction for the endothermal gasification reactions (kilowatts)

\( \varDelta {\overset{\cdot }{Q}}_{\varDelta \mathrm{h},\mathrm{v}} \) :

Heat of evaporation for the evaporation of the fuel's moisture (kilowatts)

\( \varDelta {\overset{\cdot }{q}}_{\varDelta \mathrm{h},\mathrm{r}} \) :

Specific heat of reaction for the endothermal gasification reactions (–)

\( \varDelta {\overset{\cdot }{q}}_{\varDelta \mathrm{h},\mathrm{v}} \) :

Specific heat of evaporation for the evaporation of the fuel's moisture (–)

s, s min :

(Stoichiometric) steam demand (kilogramssteam/kilogramfuel)

t :

Temperature (Kelvin)

w :

Moisture content of fuel (kilogramswater/kilogramfuel)

x char :

Char content (kilogramschar/kilogramfuel)

η cg :

Cold gas efficiency (–)

η comb :

Combustor efficiency (–)

λ :

Excess air ratio (–)

σ :

Excess steam ratio (–)

ν I :

Stoichiometric coefficient (–)

φ char :

Char conversion rate (–)




Bed material




Combustion chamber




Flue gas


Heat pipe






Sensible heat




Dual fluidized bed


Combined heat and power


Absorption enhanced reforming


Heat pipe reformer


Biomass heat pipe reformer


Moving bed gasification


Substitute natural gas


  1. Hofbauer H, Rauch R, Bosch K, Koch R, Aichernig C (2003) Biomass CHP plant guessing—a success story. In: Bridgwater AV (ed) Pyrolysis and gasification of biomass and waste. CPL Press, Newbury, pp 371–383

    Google Scholar 

  2. Pfeifer C, Koppatz S, Hofbauer H (2011) Steam gasification of various feedstocks at a dual fluidised bed gasifier: impacts of operation conditions and bed materials. Biomass Conversion and Biorefinery 1(1):39–53

    Article  Google Scholar 

  3. Kern S, Pfeifer C, Hofbauer H (2012) Synergetic utilization of biomass and fossil fuels: influence of temperature in dual fluidized bed steam co-gasification of coal and wood. International Journal of Environmental Science and Development 3(3):294–299

    Article  Google Scholar 

  4. Paisley MA, Overend RP (2002) The SILVAGAS process from future energy resources—a commercialization success. In Biomass for energy, industry and climate protection, Proceedings of the 12th International Conference on Biomass, Amsterdam, The Netherlands, pp 975–978

  5. van der Meijden CM, Veringa HJ, Rabou L (2010) The production of synthetic natural gas (SNG): a comparison of three wood gasification systems for energy balance and overall efficiency. Biomass Bioenergy 34(3):302–311

    Article  Google Scholar 

  6. Göransson K, Söderlind U, Zhang W (2009) Preliminary test on the allothermal gasifier at Mid Sweden University, 17th European Biomass Conference and Exhibition, Hamburg, Germany

  7. Poboß N, Swiecki K, Charitos A, Hawthorne C, Zieba M, Scheffknecht G (2012) Experimental Investigation of the absorption enhanced reforming of biomass in a 20 kWth dual fluidized bed system. Int J Thermodyn (IJoT) 1:53–59. doi:10.5541/ijot.321

    Google Scholar 

  8. Fang M, Wang Q, Yu C, Shi Z, Luo Z, Cen K (2005) Development of gas steam and power multi-generation system. In Proceedings of the 18th International Conference on Fluidized Bed Combustion, Toronto, Ontario, Canada

  9. Corella J, Toledo M, Molina G (2007) A review on dual fluidized-bed biomass gasifiers. Ind Eng Chem Res 46:6831–6839

    Article  Google Scholar 

  10. Jüntgen H, van Heek KH (1975) Gasification of coal with steam. Nucl Eng Des 34:59–63

    Article  Google Scholar 

  11. Jüntgen H, van Heek KH (1981) Kohlevergasung. Verlag Karl Thiemig, München (in German)

    Google Scholar 

  12. Gokarn AN, Mühlen H-J (1995) Catalysis of coal gasification by Na lignosulfonate. Fuel 74(1):124–127

    Article  Google Scholar 

  13. Lee JM et al (1998) Catalytic coal gasification in an internally circulating fluidized bed reactor with draft tube. Appl Therm Eng 18:1013–1024

    Article  Google Scholar 

  14. Kubiak H, Schröter H, Sulimma A, van Heek K-H (1983) Application of K2CO3 catalysts in the coal gasification process using nuclear heat. Fuel 62(2):242–245

    Article  Google Scholar 

  15. Mansour M (1989) et al. Pulse-enhanced indirect gasification for black liquor recovery. In: Preprints of the 1989 International Chemical Recovery Conference, Ottawa, Canada, pp. 217–221

  16. Metz T (2000) Betriebsverhalten eines Pulsbrenners, dipl. th., TU München (in German)

  17. Williams RH, Larson ED, Katofsky RE, Chen J (1995) Methanol and hydrogen from biomass for transportation. Energy Sustain Dev 1(5):18–34

    Article  Google Scholar 

  18. Karl J, Schmitz W, Hein D (2001) Allothermal gasification in fluidized bed gasifiers. In M. Kwauk, J. Li, W.-Ch. Yang (Ed.) Fluidization X, Proc. of the 10th Eng. Found. Conf on Fluid., UEF, New York, 2001

  19. Dunn PD, Reay DA (1994) Heat pipes, 4th edn. Pergamon-Press, Oxford

    Google Scholar 

  20. European Patent, Device for the gasification of carbonaceous feedstock, EP000001187892B1

  21. Metz T (2007)Allotherme Vergasung von Biomasse in indirekt beheizten Wirbelschichten, Fortschr.-Ber. VDI Reihe 6, Nr. 554, VDI-Verlag, Düsseldorf

  22. Metz T, Kuhn S, Karellas S, Stocker R, Karl J, Hein D (2004) 10.05.2004 Experimental results of the biomass heatpipe reformer. 2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, Rome, Italy

  23. Gallmetzer G et al (2012) The agnion heatpipe-reformer—operating experiences and evaluation of fuel conversion and syngas composition. Biomass Convers and Biorefinery 2(3):207–215

    Article  Google Scholar 

  24. Ahrenfeldt J, Thomsen T, Henriksen U, Clausen L (2013) Biomass gasification cogeneration—a review of state of the art technology and near future perspectives. Appl Therm Eng 50:1407–1417

    Article  Google Scholar 

  25. Lettner F, Haselbacher T, Timmerer H, Leitner P, Suyitno, Rasch B (2007) Latest results of Cleanstgas—clean staged biomass CHP. 15th European Biomass Conference & Exhibition, Berlin, Germany 1035–1039

  26. Neubauer Y (2011) Strategies for tar reduction in fuel-gases and synthesis-gases from biomass gasification. Journal of Sustainable Energy & Environment Special Issue 67–71

  27. Hauth M, Lerch W, König KH, Karl J (2011) Impact of naphthalene on the performance of SOFCs during operation with synthetic wood gas. J Power Sources 196(17):7144–7151

    Article  Google Scholar 

  28. Biollaz SMA, Hottinger P, Pitta C, Karl J (2009) Results from a 1200 hour test of a tubular SOFC with woodgas. 17th European biomass conference & exhibition, Hamburg: ETA Florence 635–638

  29. Karellas S, Karl J, Kakaras E (2008) An innovative biomass gasification process and its coupling with microturbine and fuel cell systems. Energy 33:284–291

    Article  Google Scholar 

  30. Karl J, Karellas S. Highly efficient SOFC systems with indirect gasification. Proceedings 6th European Solid Oxide Fuel Cell Forum, Lucerne, 2004, vol. 2, S. 534–545

  31. Pfeifer C, Puchner B, Hofbauer H (2009) Comparison of dual fluidized bed steam gasification of biomass with and without selective transport of CO2. Chem Eng Sci 64:5073–5083

    Article  Google Scholar 

  32. Karl J (2008) Distributed generation of substitute natural gas from biomass. In: Proceedings 16th European biomass conference and exhibition; Valencia p. 2515–2519

  33. Gröbl T, Walter H, Haider M (2012) Biomass steam gasification for production of SNG—process design and sensitivity analysis. Appl Energy 97:451–461

    Article  Google Scholar 

  34. Kienberger T, Mair S, Karl J (2010) Fixed-bed methanation of biogeneous syngas, ideas for the decentralized approach, from research to industry and markets: Proceedings of the 18th European Biomass Conference, S. 1840–1847

  35. Karellas S, Panopoulos KD, Panousis G, Rigas A, Karl J, Kakaras E (2012) An evaluation of substitute natural gas production from different coal gasification processes based on modeling. Energy 45:183–194

    Article  Google Scholar 

  36. Baumhakl C, Kienberger T, Karl J (2012) Substitute natural gas (SNG) from coal and lignite—methanation of synthesis gas from allothermal gasification. Proceedings of the 37th International Conference on Clean Coal & Fuel Systems, Clearwater, Florida, 3.6.2012-7.6

  37. Gomez-Barea A, Leckner B (2010) Modeling of biomass gasification in fluidized bed. Prog Energy Combust Sci 36:444–509

    Article  Google Scholar 

  38. Kuhn S (2007) Funktions- und Betriebssicherheit eines druckaufgeladenen Wirbelschichtvergasers. PhD thesis, TU München (in German)

  39. Karl J, Hein D (2002) Performance characteristics of the biomass heatpipe reformer. Proc. of the 12th European Conf. on Biomass for Energy, Amsterdam

  40. German patent (2011) DE 10 2008 055 947 84

  41. German patent application (2010) DE 10 2009 017 854 A1

  42. Basu P (2006) Combustion and gasification in fluidized beds. CRC Press, Boca Raton

    Book  Google Scholar 

  43. Karellas S, Karl J (2007) Analysis of the product gas from biomass gasification by means of laser spectroscopy. Opt Lasers Eng 45:935–946

    Article  Google Scholar 

  44. Reschmeier R, Karl J (2013) Kinetik der Pyrolyse von Holzwürfeln in Wirbelschichten, 26. Deutscher Flammentag - VDI Bericht Nr 2161:727–731 (in German)

    Google Scholar 

  45. Karellas S, Kakaras E, Papadopoulos T, Schäfer C, Karl J (2008) Hydrogen production from allothermal biomass gasification by means of palladium membranes. Fuel Process Technol 89:582–588

    Article  Google Scholar 

  46. de Atkins P, Paula J (2007) Physikalische Chemie, 4th edn. Willey-VCH, Weinheim

    Google Scholar 

Download references

Author information

Authors and Affiliations


Corresponding author

Correspondence to Jürgen Karl.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Karl, J. Biomass heat pipe reformer—design and performance of an indirectly heated steam gasifier. Biomass Conv. Bioref. 4, 1–14 (2014).

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


  • Biomass
  • Allothermal gasification
  • Heat pipes