The double sodium-calcium method of FGD means that the adoption of the NaOH and limestone as the desulphurization agents whereas the main desulphurization agent is the limestone. This technique is characterized by the low operation cost and small investment. The process principle is that the circulation pump transmits the sodium alkali into the desulphurization tower, and then the desulphurized slurry in the tower reacts with the flue gas and next the purified flue gas discharges into the chimney. The loaded desulphurization fluid enters into the regeneration pool through the back water ditch of the desulphurization tower bottom and after that reacts with the injected limestone slurry.
Then displaces the sodium hydroxide, calcium sulfite and the calcium carbonate into the sediment pool. The sodium alkali fluid of the upper layer overflows into the circulation pool to be circulated to using. The calcium slat dissoluble into the water sediment into the bottom of the sedimentation pool and then is transmitted into the sludge pump and subsequently is conveyed into the sludge treatment system.
The Wet limestone-gypsum method of FGD adopts the cheap limestone/lime as the absorbing agent of the desulphurization. The limestone/lime power is stirred with water and then is made as the absorption slurry fluid after the digestion treatment. Within the absorption tower, the absorbed slurry fluid is mixed with the flue gas and the sulfur dioxide in the flue gas reacts with the calcium-base desulphurization agent and the blow air and the final reaction product is the gypsum. At the same time it removes part of other contaminants in the gas such as the dust, HCL, HF. The flue gas after desulphurization passes through the demister to remove the accompanying fine fluid particles and then discharge into chimney. The desulphurized gypsum slurry dehydrates though the dehydration device and then is recycled. This technology adopts the circulation spraying frog empty tower structure. It has features including the mature technology, wide scope of application, high efficiency of desulphurization, high reliability of operation and high usable rate.
The purpose of the mist eliminator is to eliminate the carrying water in the flue gas to avoid the dew deposit due to the cooling of flue gas.
The materials used for the mist eliminator reinforcement PP. It can bear the high speed of water current flushing in the tube and the abrasion of the outside flue gas. Its dehydration mist elimination principle is the following; when the flue gas with the fluid drip enters into the cannel of the mist eliminator, due to the biased folding of the current line, it achieves the separation of the gas and fluid under the effect of the inertia and part of the fluid drip impacts with the mist eliminator and then it captured.
The capture efficiency of the mist eliminator increases with the speed of gas flow. This gives rise to the high flow speed and the big inertia acted on the drip, which is beneficial to the separation of the gas and fluid. But the acceleration of the flow speed causes the increase of the system resistance and causes the energy consumption to increased as well. At the same time the increasing of the flow speed has some limit. If the flow speed is too high, it causes the secondary water carrying and therefore decreases the efficiency of the mist elimination.
Two kinds of the mist eliminator
The horizontal eliminator provides high efficiency and big strength and lower cost. It can be a single stage or multi-stage arrangement. The standard space of the vane plates is 20mm-45mm. The horizontal mist eliminator not only can be used in newly built projects, but also can be used in retrofit project to improve the performance of given structures. This demister is made of reinforced PP.
The herringbone type of mist eliminator is applied in the conditions where very high flow speeds prevail. It can’t easily bring about the secondary entertainment. This demister made of reinforced PP.
The purpose of spraying layer is to evenly vaporize the desulphurization slurry into small droplets and then have it fully react with the flue gas to remove the sulfur oxide. The spraying layer generally adopts the glass steel (FRP) material. The slurry fluid spraying tube is usually manufactured in section components for easy transportation. It uses threaded assembly for the site installation. At present, the connection between the slurry fluid spraying nozzle and the glass steel (FRP) spraying tube is transformed basically from the previous flange connection to threaded joint. The threaded connection has the advantage of high strength of connection, avoidance of leakage and easy construction at low cost.