Fig. 1 Wall ring retrofit
Retrofitting an absorber tray into an open spray tower is an effective way to maximize the contact between the flue gas and the slurry. The tray maximizes the contact between the gas and the slurry due to the vigorous frothing action that occurs on the tray. The absorber tray also evenly distributes the flue gas flow across the absorber cross-section, promoting optimum contact as the flue gas passes through the absorber spray levels. Figure 2 illustrates gas velocity profiles of the flue gas at the spray levels in an open spray tower compared to an absorber tower with a tray. As can be seen, the addition of a tray eliminates the high-velocity areas along the absorber wall.
Fig. 2 Gas velocity profiles of the flue gas at the spray levels in an open spray tower (left) compared to an absorber tower with a tray (right).
The use of an absorber tray can eliminate the need for the addition of a spray level in the absorber. The additional fan power required from the increased gas-side system pressure drop of the tray is typically offset by a reduction in pumping power associated with the lower L/G required to achieve a given SO2 removal efficiency. For moderate SO2 removal improvements, the absorber tray retrofit can allow the plant to use one less spray level and spray pump per absorber. This results in decreased operating and maintenance costs. Figure 3 shows a tray installed above the gas inlet of an absorber.
Fig. 3 Wet FGD absorber tray installed just above the flue gas inlet.
Depending upon the target removal efficiency and configuration of the existing wet FGD module, installing two trays may also be considered as an option to achieve the most optimized upgrade to the system. Full-scale field tests have shown the benefit of adding an absorber tray to an open spray tower. Figure 4 illustrates the SO2 removal efficiency increase in the same absorber tower with and without an absorber tray.
Fig. 4 SO2 removal efficiency increase in the same absorber tower with and without an absorber tray.
