Results from A1

Laboratory pilot scale experiments for the BABIU process were conducted within the project UPGAS-LOWCO2 in June of 2010. The ability of bottom ash from Italy to remove CO₂ and H₂S from landfill gas has been investigated at the Institute of Waste Management, BOKU University, Vienna. The experimental apparatus was similar to a previous report (MOSTBAUER et al., 2008), but in addition a pressure gauge was used to measure the pressure loss in compacted bottom ash. The bottom ash fraction < 100 mm was compacted in three layers in the lab-scale carbonation tank, stored overnight therein, and flushed with nitrogen and treated with the synthetic gas (CH₄ + CO₂ or CH₄ + CO₂ + H₂S) on the next day. Other experimental conditions are shown in Table A1-1.

Table A1-1: Input mass, initial water content, initial temperature and other experimental conditions

It has been demonstrated that with an input flow rate of ≈ 2.0 m³ landfill gas per hour and ton of bottom ash the process performance is still excellent. As an example, the composition of the upgraded gas is shown in Figure 1. The temperature increase observed in the laboratory test runs was 18 to 21^oK. Using an estimation of the heat loss of the lab-scale carbonation tank, it is expected that the temperature increase in pilot scale and industrial scale will be in the range between 21 and 26^oC in the case of the bottom ash from Italy.

Figure A1-1: Results from experiment 2

At a flow rate of 1.97 m³/h/tBA (input gas) the CO₂ fixation capacity of the bottom ash from Italy was 10.5 to 11.3 kgCO₂/tBA, which is rather low compared to bottom ash from Germany and Austria, where values up to 39 kgCO₂/tBA have been observed previously. Due to higher ratio of height: area, lower heat losses and expected higher tortuosity, the CO₂ uptake should be higher at the semi-industrial pilot scale and field scale. A CO₂ uptake of approximately 12 kgCO₂/tBA is expected.

The H₂S fixation capacity of the bottom ash from Italy is high (37 g H₂S/t BA). In the lab-scale experiments the H₂S content of the raw gas was 237 ppm in average, whereas the H₂S content of the landfill gas ranges frequently ranges from 10 to 1000 ppm. The breakthrough time was more than 45 h at flow rate of 1.97 m³/h/tBA (input gas) and with 237 ppm H₂S in input gas.  No breakthrough of H₂S is expected for the up-scaled BABIU process as long as the bottom ash reacts with CO₂. Additionally, the high H₂S fixation capacity leads to the suggestion, that bottom ash could be used as a H₂S trap within a new process design, with a realistic potential to compete with conventional biological desulphurization processes as long as the H₂S content of the raw landfill gas / biogas is small or moderate.

Mostbauer, P; Lenz, S; Lechner, P, 2008; MSWI bottom ash for upgrading of biogas and landfill gas. Environ. Technol. 2008; 29(7): 757-764.