1 Gas Suspension Absorber Description Following for guidance only

2 Introduction FLSmidth proudly offers our unique Gas Suspension Absorber (GSA) process. The FLSmidth GSA process means an extremely efficient use of the lime slurry, thus reducing requirements for fresh lime to a minimum. One of the reasons for the high efficiency of the FSmidth GSA is that the reactor has been based on gas suspension technology. This means that a very large concentration of fly ash, dust particles and lime builds up inside the reactor. The concentration is normally 50 to 100 times as high as in a conventional reactor. The effect is further enhanced by the fact that lime, fly...

3 Process description A standard FLSmidth GSA flue gas system comprises the following main components: - Flue gas duct system - Reactor - Cyclone - Re-circulation box - Dust filter - Lime slurry preparation system - Activated Carbon system - By-product system Reference is made to the flow sheet presented below. Flue gas duct system The flue gas duct system consists of all ducts required for transporting process flue gas to the reactor, from the cyclone to the dust filter, from the dust filter to the ID-fan and from the ID-fan to the stack. 1 Activated carbon silo 2 Reactor 3 Cyclone 4 Re-circulation...

4 Reactor The reactor system comprises an inlet bend, a venturi and a riser section as demonstrated in figure below. Flue gas is led through the venturi via the inlet bend, and into the reactor. In the reactor the pollutants are removed by chemical reactions with the injected lime. The only purpose of the inlet bend is to ensure proper distribution of the flue gas in the venturi. This is done by means of guide vanes placed in the bend. In the venturi the cross section of the duct is narrowed in order to increase the linear flue gas velocity. The increased velocity ensures that solid material...

5 A dual fluid nozzle is installed in the venturi, and through this nozzle fresh lime slurry and water are dosed into the riser section. The nozzle schematically displayed in the figure below, is developed by FLSmidth and is a pressurised-air atomizing nozzle, very sturdy, hard-wearing, and non-choking. The main part of the flue gas treatment takes place in the riser section due to the intimate contact between the lime and the flue gas. In this section the lime reacts with the acid constituents in the flue gases, thus capturing and neutralising them. Because of the very large reaction surface...

6 Cyclone In the riser section the flue gas velocity is relatively high, and some of the solid particles are transported by the flue gas to the top of the riser section and into the cyclone. In the cyclone the main part of the particles are separated from the flue gas. Approximately 99% are captured, and only the small particles are transported by the flue gas to the filter. The captured particles are returned to the reactor via the re-circulation box. Re-circulation box The purpose of the recirculation box is to have a buffer of reaction products with excess lime to maintain the absorption capacity...

7 The re-circulation box consists of a metal box provided with conveyors. Two screw conveyors are placed at the bottom of the box for transport of solid material back into the riser section, whereas the screw conveyor at the top bleeds out the excess of fly ash and material formed by the chemical reactions. The bottom screw conveyors are controlled by a frequency converter, whereas the one at the top operates at constant speed. Activated carbon system In order to capture mercury, dioxins, and other organic micro pollutants activated, carbon is injected into the flue gas in the duct leading to...

8 From the slaker the lime slurry is transferred to a slurry mixer tank. From the mixer tank lime slurry is dosed into the reactor by means of the dosing pumps. Ca(OH)2 lime preparation When hydrated lime is applied no preparation system is called for. The dry lime is simply blown dry into the venturi part of the reactor from a lime silo. Operation procedure Description of the control system The GSA system is equipped with an automatic control and monitoring system that serves the purpose of ensuring a safe, stable and at the same time an economically optimal operation by continuous control of...

9 Flow control of re-circulated media The amount of re-circulated media is controlled by the flue gas flow through the absorber via a flow-proportional measurement. Outlet temperature control The GSA outlet temperature is controlled by the water injected into the GSA venturi. The speed of the water pump is controlled by a temperature measurement of the outlet gas. It ensures that the flue gas is cooled down to a suitably low temperature - keeping a safety margin to the dew point - in order to minimize the consumption of lime. In addition, the inlet temperature is used partly as feed-forward during...