• Sebastian Ravn
Pig production is a large industry in Denmark. Unfortunately, it is also an industry which results in significant odour problems to its surroundings. Due to an increase in both numbers and size of Danish pig farms and also urbanisation of land areas, the odour problems are increasing. Solutions to the problem have to be found, in orders to preserve the opportunity for increases in pig productions for the future and just to overcome the problem. One of the solutions to the problem is to clean the ventilation air using a bio filter, but the impact on the odour is still not optimal and there is major cost involved because of the large amounts of air that have to be cleaned. This project will focus on the effect of gas velocity, surface area and particle size distribution on mass transfer coefficients in the gas phase.

Experiments are made in a constructed model of a bio filter where the gas phase used is CO2 in atmospheric concentration and the liquid phase is water added sodium hydroxide to a 1 M concentration. The filter medium used is 36 LECA fractions with uniform particle size distribution and different surface area and a Munter's cellulose filter. Experiments are performed to study the effect of gas velocity, surface area and the particle size distribution on the mass transfer in the gas phase.

Result for experiments with LECA as filter medium showed that in the studied area of gas velocity 1000 - 4000 m/, there are no significant effect on the mass transfer. Result for Munter's filter showed that the gas velocity in the range 0 - 1000 m/t had an increasing effect on the mass transfer with an increasing velocity. Above 1000 no significant effect was observed.
Experiments with 36 LECA fractions have shown that the mass transfer can be described on the basis of the surface area with a linear regression. Results have also shown that the mass transfer can be described from the Range and particle diameter in the form of Deq, equivalent particle diameter, with the model kGaw = 157.85 * Deq^-0.75. The models are only valid for uniform particle size distribution and with LECA as filter medium.
Experiments with LECA as filter medium show that the smallest fractions, 2-4 mm have the highest mass transfer. In a bio filter, not only a good mass transfer describes a good filter medium, but also a low pressure drop across the filter. If the mass transfer as well as the pressure drop is taken into account, there is no significant difference between the 36 fractions in proportion to be the best fraction for filter medium.

A model is constructed to describe the most cost effective construction of a bio filter with LECA as filter medium with regards to kr./year during a 10 year period. The model takes the removal efficiency, constructions cost and running costs into account and it shows that the most cost efficient filter can be made from LECA with a minimum diameter of 2 mm and a range above 6 mm. The model is only valid for LECA with uniform particle size distribution and for compounds with the resistance in the gas phase. There are also uncertainties related to the constructions costs and running costs.
Publication date21 May 2012
Number of pages65
ID: 63235112