Catalytic seawater flue gas desulfurization model.

A model of a seawater flue gas desulfurization process (SFGD) where oxidation of the absorbed SO(2) is catalyzed by activated carbon is presented. The modeled SFGD process is comprised of two main units, an absorption packed scrubber, where SO(2) absorption takes place, and an oxidation basin, where the absorbed SO(2) is catalytically oxidized to sulfate, a natural component of seawater. The model takes into account the complex physical-chemical features of the process, combining mass-transfer, kinetics and equilibrium equations, and considering the electrolyte nature of the liquid phase. The model was validated with data from a SFGD pilot plant and a sensitivity analysis was performed, showing its predictive capability. The model is a useful tool for designing industrial desulfurization units with seawater.

Catalytic seawater flue gas desulfurization process: an experimental pilot plant study.

In previous articles by the authors on seawater S(IV) oxidation kinetics, a significant catalytic effect was demonstrated by means of a commercially available activated carbon. The aims of this study carried out at pilot plant scale were to assess the use of high-efficiency structured packing and to validate the positive results obtained previously in laboratory studies. A comparison between a packed tower and a spray column was made by maintaining the same desulfurization efficiency. A 47% reduction in seawater flow can be obtained with a packed tower. This option seems to be more economical, with a reduction in operation costs of least of 33%. With the appropriate activated carbon, it is possible to reach a greater oxidation rate at a low pH level than by operating conventionally at a high pH level without a catalyst. A preliminary technical and financial comparison between the advanced seawater desulfurization process (equipped with a packed tower and a catalytic oxidation plant) and the conventional process (spray tower and noncatalytic oxidation) was carried out.

Catalytic oxidation of S(IV) in seawater slurries of activated carbon.

Flue gas desulfurization (FGD) by means of SO2 absorption in seawater is a well-known process with a main drawback; due to the low S(IV) oxidation rate at the low pH values of the absorption tower effluent, a large oxidation basin is required. Laboratory reactor tests, in which a commercially available activated carbon was used, showed a significant catalytic effect. It is shown that the kinetic equation for the catalytic oxidation of S(IV), in seawater slurries of activated carbon, is first-order with respect to S(IV) and zero-order with respect to oxygen. The dependence of the kinetic constant with respect to pH, temperature, and catalyst size particles were also obtained.

A kinetic study of the oxidation of S(IV) in seawater.

Flue gas desulfurization by means of SO2 absorption in seawater is a well-known process. However, it can be optimized if the oxidation kinetics of dissolved S(IV) is known. Laboratory reactor experiments in which the pH and temperature were controlled, determined the oxidation kinetics of S(IV) in seawater. This study conclusively shows that the order with respect to S(IV) is one and that the order with respect to oxygen is zero. The kinetic constant depends greatly on the temperature and on the pH; consequently, the activation energy and a relationship between the kinetic constant and the hydrogen proton concentration (2 < pH < 6) were also obtained.

A pilot plant technical assessment of an advanced in-duct desulphurisation process.

In-duct sorbent injection (DSI) is a well-known, low-cost desulphurisation technology handicapped by its moderate SO(2) removal capacity. Fortunately, there are some technical options for increasing the desulphurisation efficiency without eliminating its inherent advantages. In this experimental study, several improvement design options like the recirculation of reactivated sorbent, the pre-collection of the fly ash and the use of seawater for humidification have been analysed using an extensive parametric testing programme. The effect of the main operating variables directly related to the desulphurisation efficiency has been also tested following a fractional factorial design. These variables were the Ca/S ratio, the approach to the adiabatic saturation temperature and the recirculation ratio of the partially converted sorbent. Other important questions like the use of a high-BET-area lime and the impact of the DSI process on an ESP have been also included in this experimental assessment. More than 50 experimental tests were carried out in a 3-MWe equivalent pilot plant to assess the different improvement options for in-duct sorbent injection. The results of this study allow us to extract practical conclusions about the devices, equipment and operating conditions as a function of the target SO(2) efficiency, and even enable us to provide an economic assessment. Using the proposed improvement options to process a flue gas with 400-1000ppm of SO(2) concentration, a 90% sulphur removal with a lime utilisation of 45% was achieved.