Attractive options for reducing emissions

Urea dust

The air from the granulator and the fluid bed coolers contains some urea dust which is easy to catch in standard scrubbing equipment. Efficiencies of more than 99.5% are easily obtained using industrially proven scrubbers, with dust outlet concentrations of less than 0.1 kg per ton of urea produced being achieved.

Ammonia

The majority of the ammonia is carried with the urea solution from the urea synthesis plant. A small part is generated by the biuret formation occurring in the transfer line between the urea synthesis plant and the granulator in the urea granulation plant.

The ammonia is released into the exhaust air leaving the granulator when the urea solution is sprayed into the fluidized bed. The standard wet scrubbing system is unable to catch the ammonia as the solubility of ammonia in an aqueous urea solution under the prevailing operating conditions is limited.

The following options are available for reducing ammonia emissions:

Ammonia Abatement System

UFTs proprietary ammonia abatement system is based on the reversible gas phase reaction between ammonia and formaldehyde. The free ammonia is captured from the exhaust air leaving the granulator and is recovered in the urea synthesis. As a result, ammonia emissions are reduced by up to 40 %. No additional scrubbing agent is required and the additional investment and operating costs are negligible.

Acidic Scrubbing

Dilute sulfuric acid is used as the scrubbing agent in an acid scrubbing stage installed downstream of the dust scrubbing section. The gaseous ammonia is absorbed in the diluted acid, and an ammonium sulfate (AS) solution is obtained as an additional side stream. As a result, ammonia emissions are reduced by approx. 90 %.

Ammonia Convert Technology

UFTs proprietary Ammonia Convert Technology is based on an acid scrubbing stage and recycling of the ammonium salt obtained back into the final product.

By this special arrangement in the scrubbing system it is possible to recycle the ammonium salt and the washed out dust to a separate small vacuum evaporation section within the urea granulation plant. In this additional dedicated Ammonia Convert evaporation section the urea solution containing the ammonium salt is inspissated to achieve the concentration required for granulation without generating any side streams. The concentrated solution is subsequently mixed with the urea solution coming from the vacuum evaporation in the urea synthesis plant to be used as feed solution for the granulator.

As no recycle flow to the urea synthesis plant is required, investment and operating costs within the urea synthesis plant are reduced.

As a result, ammonia emissions are reduced by approx. 90%.

publication in nitrogen + syngas July/August 2008