Process for the Preparation of a Urea-Comprising Aqueous Stream
The invention relates to a process for the preparation of a urea-comprising aqueous stream, that is suitable for use in a unit for the reduction of NO x in combustion engine exhaust gases, wherein the urea-comprising aqueous stream is separated directly from or after a recovery section in a urea production process and is thereafter diluted with water until the urea-comprising stream comprises 30-35 wt % urea.
1 . Process for the preparation of a urea-comprising aqueous stream, that is suitable for use in a unit for the reduction of NO x in combustion engine exhaust gases, characterized in that the urea-comprising aqueous stream is separated directly from or after a recovery section in a urea production process and is thereafter diluted with water until the urea-comprising stream comprises 30-35 wt % urea.
2 . Process according to claim 1 , wherein at least one of the recovery sections comprises a dissociation unit, in which dissociation is promoted by the addition of a stripping medium, characterized in that the urea-comprising aqueous stream is separated after the dissociation unit.
3 . Process according to claim 1 or 2 , characterized in that the urea-comprising aqueous stream is separated after the recovery section(s).
4 . Process according to any one of claims 1 - 3 , wherein a urea storage tank is present after the recovery section(s) and, when a shaping section is present, before the shaping section, characterized in that the urea-comprising aqueous stream is separated from the urea storage tank.
5 . Process according to any one of claims 1 - 4 , characterized in that the urea-comprising aqueous stream comprises 60-90 wt % urea.
6 . Process according to claims 1 - 5 , characterized in that the urea-comprising aqueous stream is subjected to dissociation before or after dilution with water.
7 . Process according to claim 2 or 6 , characterized in that the dissociation is preformed by steam stripping at a pressure of 0.001-0.2 MPa.