| 摘要 |
<p>Prodn. of urea by the double isobaric recycle method comprises reacting NH3 and CO2 at high mole ratio and thermal treatment of the synthesis product formed at about synthesis pressure in presence of an entraining gas. Improvement is that (a) thermal treatment is in two consecutive isobaric steps with virtually all residual carbamate decomposed in the first step and displacement of decompsn. products with a part of the excess NH3; and in the second the remaining NH3 is displaced by additional heat and injection of a current of CO2; and (b) gases from the first stage are recycled directly while those from the second subjected to condensation and purging with residual gas before recycling as liq. The urea prd. soln. is virtually free of CO2 and NH3 yet excessively large heat inputs are not necessary. Temp. fluctuations in the process can be avoided by controlling the two recycle streams.</p> |
