The activity aimed at the design, construction and testing of a test plant to simulate some operating conditions of trickle bed reactors (TBRs) for biological methanation and in particular for the estimation of the liquid holdup parameter.
The experimental apparatus consists of a packed bed column of commercial elements (Hel-X biological substrate), crossed, from top to bottom, by a flow of atomized liquid with a full cone nozzle and by a countercurrent air flow.
The report describes the experimental apparatus, then it discusses the results of an experimental campaign aimed at investigating the influence of the different operating conditions of trickle bed reactors on the liquid holdup parameter, defined as the ratio between the volume of the liquid phase and the volume of the bed, also referring to what is reported in the literature. In particular, the liquid flow rate, the bed spraying time and the air flow rate were considered, using full cone nozzles with different opening angles.
The liquid holdup parameter, measured experimentally for Hel-X elements, stood in a range between 8% and 10.61% depending on the operating conditions.
It was also observed that: i) the trend over time of the liquid holdup parameter is almost stable after a few minutes (static holdup) and increases with the overall volume of water sprayed on the bed; ii) the maximum value of 10.61% was found in the test with a water flow rate of 57 l/h for 6 minutes in the absence of gas flow using nozzle H (opening angle 120°); iii) the countercurrent air flow reduces the quantity of liquid deposited on the filling elements in line with what has been found in the literature.
In the future, the experimental facility is planned to continue to be used to test new filling elements with a view to improving the efficiency of the process and to use the results for the development of mathematical models for simulating trickle bed reactors for biological methanation.