Quench Cooling Research Articles

Simulations and experiments on the formation of ammonium chloride particles in wet scrubbers

The formation of aqueous ammonium chloride aerosols has been investigated both experimentally and by simulation. The considered process is a flue gas cleaning plant in which hot gases containing gaseous ammonia and hydrogen chloride at 200 °C enter a quench cooler in which they are brought in intense contact with water and chilled down. The processes of absorption, cooling and nucleation occur simultaneously. The simulations are based on a description of the process according to the film model combined with homogeneous nucleation theory. The experiments were done at a semi-technical flue gas cleaning plant. It is found that the proposed model is able to predict the qualitative behaviour of the system, especially its sensitivity to a change of the concentrations of the two pollutants at its entry. However, to get quantitative coincidence an adjustment is necessary. In this, the governing parameter is the surface tension of ammonium chloride.

Aerosol formation by heterogeneous nucleation in wet scrubbing processes

The phenomenon of aerosol formation is often watched in industrial wet scrubbing processes especially if strong acid gases are absorbed in aqueous solutions. Although the basic principles of aerosol formation are well known in general, there exist nearly no specific rules for the design of industrial processes in which aerosol formation can be expected. There are two reasons for the fragmentary knowledge concerning aerosol formation in wet scrubbing processes. Firstly, it is a very complex task to describe the formation and the growth of aerosols theoretically under typical conditions of industrial processes. Secondly, no reliable experimental data, especially for the validation of theoretical work, has been available to date. To bridge this gap, a semi-technical wet scrubbing plant has been developed and erected in which the formation and the growth of aerosols under realistic conditions can be studied and the characteristic aerosol parameters can be measured in situ. It is shown that HCl-aerosols are formed in a quench cooler for hot flue gases of about 200°C even at low HCl feed concentrations of about l000 mg m −3, but only in the presence of foreign nuclei. The aerosol droplets in the quench cooler grow up to 1–1.5 μm and can be enlarged in a direct-contact-cooling column up to about 2.5 μm. Furthermore, a strategy for aerosol evaporation is discussed.