Method for removing ammonia and dust from a waste gas that results during the production of fertilizers

#Applicants claim priority under 35 U.S.C. §119 of German Application No. 103 46 519.7 filed Oct. 2, 2003. Applicants also claim priority under 35 U.S.C. §365 of PCT/EP2004/009886 filed Sep. 4, 2004. The international application under PCT article 21(2) was not published in English.

#The invention relates to a method for removing ammonia and dust from a waste gas that occurs during the production of fertilizers, preferably urea, in which method the waste gas is introduced into a first washer, and a cooling gas is introduced into a second washer, and additional water is introduced into the one washer and an aqueous solution is introduced into the other washer, whereby both the waste gas and the cooling gas pass through at least one mist collector before exiting from the washer, in each instance.

#In the production of fertilizers that contain ammonia, i.e. fertilizers that can split off ammonia, e.g. fertilizers that contain urea, ammonia and waste air streams that contain dust occur in various process steps, which must be purified before being passed into the environment or recycled back into the process. Such waste gases occur, in particular, during granulation and cooling.

#The invention will be explained in greater detail below, using the drawing. This shows, in:

#FIG. 1 a fundamental schematic for implementing the method, and in

#FIG. 2 a detail of FIG. 1 in a special embodiment.

#A system for implementing the method first has a first washer 1 and a second washer 2. A pre-purification stage 3 precedes the first washer 1. A mist collector 4 (demister) is disposed in the upper area of the first washer 1, just like a mist collector 5 in the second washer 2. The first washer 1 is divided into two washing areas, whereby a liquid-impermeable but gas-permeable partition bottom 12 (e.g. bell-shaped bottom) as well as an outlet 11 are disposed below the mist collector 4, forming a fine-washing area 14. Below the partition bottom 12, there is the main washing area 21 of the first washer 1.

#The system parts described above are preferably components of a system for the production of fertilizers, preferably urea, and are connected with a granulator, not shown, and a cooler. Waste gas charged with ammonia and dust is passed out of the granulator, not shown, specifically at first into the pre-purification stage 3, as indicated by an arrow 6. The waste gas passes through the pre-purification stage 3 and is introduced into the main washing area 21 of the first washer 1. Cooling gas, which is also charged, is passed directly to the second washer 2, as indicated by an arrow 7.

#Additional water, preferably purified or non-purified process water, is supplied directly to the fine-washing area 14 of the first washer 1, whereby the water feed line is indicated with arrows 8, 9. The water feed line ends within the washer 1, below the mist collector 4, in spray heads 10 that are directed upward, in such a manner that additional water is sprayed against the mist collector 4 and thereby cleans it off. The additional water mixes with the droplets that pass through the partition bottom 12, and results in a great dilution in the urea concentration of the droplets, so that the droplets have a remaining urea concentration of only 1 to 4%, for example, even if the urea concentration in the main washing area 21 is 55 to 60%. The additional water thereby accumulates urea, and exits from the discharge 11, to which a line 13 that opens into the second washer 2 is connected, as an aqueous solution, whereby the aqueous solution is passed into the second washer 2.