Static mixers and spray nozzles and their effect on the spray pattern in an intensified biogas desulphurization by caustic scrubbing

For the process intensification of biogas desulfurization the improvement of the phase contact is of high importance. In the course of the development of a new approach for this treatment the usefulness of a combination of static mixers and spray nozzles should be investigated. The determining factors for phase contact are droplet size, the resulting droplet surface, contact time, as well as a sufficient mixing. The droplet size and surface are mainly dependent on the type of atomizer and the flow velocity of the components involved. The mixing of the phases depends on the type of flow and also on the flow velocity of the continuous phase. Based on the assumption that static mixers generally induce a positive effect on the turbulence of the system, their impact on the other relevant characteristics had to be investigated. The measurement of the droplet size and velocity was done using Phase Doppler Anemometry. Due to the fact that the flow velocities influence the atomization quality of the spray nozzles and the contact time, the experiments were carried out using three different gas velocities. To get similar velocities for empty tubes and tubes with static mixers the rotational speed of the fan had to be increased, which leads to higher energy costs that have to be considered for economical reasons. To accommodate for this fact the pressure drop for the static mixers used in this survey was measured. The results showed that the use of static mixers offers no improvement in this context. This leads to significant simplification in the layout and operation of the process, as well as a cost reduction. The choice of the atomizer can be made based on the requirements of each individual case as each of the tested systems has distinct advantages.