Experimental investigation on the effect of liquid injection by multiple orifices in the formation of droplets in a Venturi scrubber.

Venturi scrubbers are widely utilized in gas cleaning. The cleansing elements in these scrubbers are droplets formed from the atomization of a liquid into a dust-laden gas. In industrial scrubbers, this liquid is injected through several orifices so that the cloud of droplets can be evenly distributed throughout the duct. The interaction between droplets when injected through many orifices, where opposite clouds of atomized liquid can reach each other, is to be expected. This work presents experimental measurements of droplet size measured in situ and the evidence of cloud interaction within a Venturi scrubber operating with multi-orifice jet injection. The influence of gas velocity, liquid flow rate and droplet size variation in the axial position after the point of the injection of the liquid were also evaluated for the different injection configurations. The experimental results showed that an increase in the liquid flow rate generated greater interaction between jets. The number of orifices had a significant influence on droplet size. In general, the increase in the velocity of the liquid jet and in the gas velocity favored the atomization process by reducing the size of the droplets.

Atomization of liquids in a Pease-Anthony Venturi scrubber. Part II. Droplet dispersion.

Droplet distribution is of fundamental importance to the performance of a Venturi scrubber. Ensuring good liquid distribution can increase performance at minimal liquid usage. In this study, droplet dispersion in a rectangular Pease-Anthony Venturi scrubber, operating horizontally, was examined both theoretically and experimentally. The Venturi throat cross-section was 24 mm x 35 mm, and the throat length varied from 63 to 140 mm. Liquid was injected through a single orifice (1.0 mm diameter) on the throat wall. This arrangement allowed the study of the influence of jet penetration on droplet distribution. Gas velocity at the throat was 58.3 and 74.6 m/s, and the liquid flow rate was 286, 559 and 853 ml/min. A probe with a 2.7 mm internal diameter was used to isokinetically remove liquid from several positions inside the equipment. It was possible to study liquid distribution close to the injection point. A new model for droplet dispersion, which incorporates the new description of the jet atomization process developed by the present authors in the first article of this series, is proposed and evaluated. The model predicted well the experimental data.

Atomization of liquids in a Pease-Anthony Venturi scrubber. Part I. Jet dynamics.

Jet dynamics, in particular jet penetration, is an important design parameter affecting the collection efficiency of Venturi scrubbers. A mathematical description of the trajectory, break-up and penetration of liquid jets initially transversal to a subsonic gas stream is presented. Experimental data obtained from a laboratory scale Venturi scrubber, operated with liquid injected into the throat through a single orifice, jet velocities between 6.07 and 15.9 m/s, and throat gas velocities between 58.3 and 74.9 m/s, is presented and used to validate the model.

Evaluation of the models available for the prediction of pressure drop in venturi scrubbers.

The major running cost derived from the operation of venturi scrubbers is pressure drop. In the present study, the predictions of different models are compared to experimental data from venturi scrubbers of different sizes (throat diameter from 1.9 to 16cm), geometries, operating variables and liquid injection arrangements. As a result, it is concluded that most of the models must be used with caution. Much attention must be paid to the validity of the assumptions employed in the mathematical models. The equations proposed by Calvert [Scrubbing, Air Pollution, 3rd Edition, Vol. IV, Academic Press, New York, 1982], Yung et al. [JAPCA 27 (1977) 348] or Hesketh [Atomization and cloud behaviour in wet scrubbers, in: Proceedings of the US-USSR Symposium Control Fine Particulate Emissions 1974, San Francisco, 15-18 January 1974] produce good results only in very specific situations. The model proposed by Boll [Ind. Eng. Chem. Fundam. 12 (1973) 40] is simple, easy to compute and agrees reasonably well with the experimental data. Unfortunately, it cannot predict the effect of different liquid injection arrangements. The model by Azzopardi and coworkers [Filtr. Sep. 21 (1984) 196; Trans. IchemE. 69B (1991) 237; Chem Eng. J. 67 (1997) 9] was the only one to give good predictions for all the range of variables studied. On the other hand, this model is not simple and requires from the engineer an additional effort in terms of computation. In order to apply this model to the rectangular geometry, the concept of hydraulic equivalent diameter was used.