Biogas

Pergamon

Chemical Enyineerin0 Science, Vol. 51, No. 17, pp. 4065 4073, 1996 Copyright ~c3 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved PII: S0009-2509(96)00264-3 ooo9 2509/96 $15.00 + 0.00

MODELLING THE HYDRODYNAMICS A N D THE LIQUID-MIXING BEHAVIOUR OF A BIOGAS TOWER REACTOR*
G E O R G R E I N H O L D , t S T E F A N M E R R A T H , +"F R I E D R I C H L E N N E M A N N t a n d H E R B E R T M)i, R K L *'~ *Technische Universit~it Hamburg-Harburg, Bioprozel3 und Bioverfahrenstechnik, Denickestr. 15, D-2107 l Hamburg, Germany *+Preussag Noell Wassertechnik GmbH, Robert-Hooke-Str. 5, D-28359 Bremen, Germany

(First received 5 April 1995; revised manuscript received and accepted 20 November 1995)
Abstraet--A new concept of a biogas reactor for anaerobic waste water treatment is presented. The characteristic features of this type of reactor are the tower shape, its modular structure and the internal installations. Gas-collecting devices are installed at different levels along the height of the reactor to withdraw the gas produced and to avoid gas accumulation in the upper zones of the reactor. The remaining gas causes a fluid circulation along baffles similar to airlift-loop reactors. A settler is integrated at the top of the reactor. As the reactor is built in a tower shape, the mixing behaviour is strongly linked to two questions: (1) how to supplement the microorganisms in the upper zones of the reactor with substrate and (2) whether there is a toxic concentration due to insufficient mixing near the inlet of the substrate. The scale-up of the biogas tower reactor, as far as the liquid mixing is concerned, was based on the knowledge of the mixing within a module and the intermixing between two modules. Two mathematical models are proposed to describe liquid mixing within the reactor. Model A describes the intramixing within one module as well as the intermixing between neighbouring modules. Model B describes only the global