Patent EA-000374-B1 (EA)
Title: Flue gas scrubbing and waste heat recovery system
Inventor: HINKE THOMAS V
IPC: B01D53/77
Filed: 1996-05-29
Abstract: 1. A process for reducing the NCx content of a flue gas, comprising the steps of: preparing an emulsion (39) of liquid P4 in water having a selected P4/water ratio; finely dispersing a metered amount of the emulsion in the flue gas at a location of injection, the location of injection being selected such that the temperature of the flue gas after injection of the metered amount is between about 180 degree C and about 280 degree C to initiate oxidation of P4 and NO in the vapour phase of the flue gas; removing NO2 from the flue gas at a selected distance downstream from the location of injection by subjecting the flue gas to a wet scrubbing step, the distance being selected such that the oxidation of P4 and NO is substantially separated in time and space from the wet scrubbing step. 2. The process of Claim 1, wherein the step of preparing the emulsion comprises the steps of heating solid P4 (14) in a water bath (18) (to prevent contact of the phosphorus with air) to a temperature above the melting point of phosphorus and below 280 degree C, and admixing the liquefied P4 with water in the preselected ratio and under a N2 atmosphere. 3. The process of Claim 1, wherein the emulsion is dispersed in the form of microdroplets having an average diameter of 60 mkm or less. 4. The process of any preceding Claim, wherein the metered amount or the emulsion (39) and the selected P4/water ratio are adjusted such that the volume flow of O3 in the flue gas, generated by oxidation of the P4 in the vapour phase is at least equal to the volume flow of NO in the flue gas. 5. The process of Claim 4, wherein the selected P4/water ratio is 1/100. 6. The process of any preceding Claim, wherein the flue gas temperature in the location of the emulsion injection is about 200 degree C. 7. Apparatus for reducing the N0x content of a flue gas in a flue gas manifold (51), which includes: means for preparing an emulsion (39) of liquid P4 in water having a selected P4/water ratio; means for finely dispersing a metered amount of the emulsion (39) in the flue gas manifold (51) at a location of injection; means for adjusting the temperature of the flue gas, (if required), in an upstream portion of the manifold (51) immediately upstream of the location of injection such that the temperature of the flue gas after injection of the metered amount of emulsion is in the range of about 180 degree C to about 280 degree C to initiate oxidation of P4 and NO in the vapour phase of the flue gas; and wet scrubbing means connected to the manifold (51) for removing NO2 from the flue gas at a distance downstream from the location of injection, the length of the manifold (51) between the location of injection and the means for removing NO2 being selected such that the oxidation of P4 and NO is substantially separated in time and space from the wet scrubbing step. 8. The apparatus of Claim 7, wherein the means for removal is a wet scrubbing tower (52) and the means for injecting is an atomizer nozzle (41) positioned in the flue gas manifold (51), which is shaped and constructed to disperse the emulsion (39) as microdroplets having an average diameter of 60 mkm or less and to disperse the emulsion (39). 9. The apparatus of Claim 7 or 8, further comprising monitoring means for detecting the temperature and NO content of the flue gas at the point of injection, the means for preparing the liquid emulsion (39) including a mixing control means for controlling the P4/water ratio, and a central controller (82) for automatically operating the mixing control means and the means for dispersing to optimise the P4/water ratio and the metered amount of emulsion (39) according to the temperature and NO content detected by the monitoring means. 10. The apparatus of Claim 9, further comprising exhaust monitoring means for detecting the P4 and O3 content of the flue gas at an exhaust of the scrubber, the exhaust monitoring means being connected to the central controller for automatic adjustment of the P4/water ratio and/or the metered amount when P4 and/or O3 is detected at the exhaust. 11. The apparatus of any Claim 7-10, wherein the means for preparing the P4 in water emulsion (39) comprises a heated water bath (18) for melting solid phosphorus stored in a container, the container being completely submersible in the bath to prevent contact of the phosphorus with air, an emulsion tank (34) sealed from ambient, a means for supplying liquefied phosphorus from the container to the emulsion tank, and means for admixing the liquefied phosphorus with water at the preselected ratio and in the emulsion tank (34). 12. The apparatus of Claim 11, wherein the means for preparing the P4 in water emulsion (39) further includes means for washing the liquefied P4 with a solution of an acid-dichromate to remove trace contaminants. 13. The apparatus of Claim 9, wherein the scrubbing tower (52) includes a sump (62) for collecting spent scrubbing liquid and a scrubbing liquid conditioning circuit for recovering from the scrubbing liquid heat energy taken up from the flue gas and from the evapourated water phase of the emulsion (39). 14. The apparatus of Claim 13, wherein scrubbing tower (52) includes a flue gas treatment chamber, a flue gas entry port for introducing the flue gas into the treatment chamber, a spray assembly for introducing scrubbing liquid into the stream of flue gas in the treatment chamber, a scrubbing liquid sump (62) for collecting used scrubbing liquid, a scrubbing liquid conditioning circuit for reconditioning of the scrubbing liquid and recirculating the scrubbing liquid to the scrubbing tower (52), and a heat exchange for removing from the scrubbing liquid in the conditioning circuit heat energy taken up by the scrubbing liquid from the flue gas.