Abstract: The present invention relates to a method for the transference, cooling and compression of nitrogen oxide-containing gases. In critical sections of a unit for such processes the formation of salt deposits can be removed or prevented by maintaining a water vapor pressure which lies above the equilibrium water vapor pressure of the salt deposits at the existing temperatures. The prescribed water vapor pressure is maintained by dividing the gas into at least two separate streams, cooling at least one of the streams solely by directly injecting water thereinto, cooling the remaining streams by indirect cooling, forming condensate in indirect coolers, and then joining the directly and indirectly cooled streams prior to introduction thereof into the critical sections. The condensate from the indirect coolers can be utilized for direct cooling. Salt deposits can be removed/prevented without the supply of extra energy, water vapor or liquid.

Abstract: Gas mixtures from a urea plant, particularly such mixtures containing dust and especially off-gases from prilling towers or granulation units are cleaned. In order to prevent precipitation and accretion in the cleaning unit, there is applied an aqueous washing solution to which formaldehyde is added before it is brought in contact with the gas mixture. Formaldehyde is preferably added in the form of formaline, and the addition of formaline is regulated by pH-measurements in the washing solution such that pH is maintained at pH=6-8.5. The pH of the washing solution is preferably kept at pH=about 7, especially in order to obtain optimal removal of ammonia. The method is carried out during application of standard scrubbers in which aqueous washing solutions can be used.