Cooling nitrogen for ammonia production plant

Producing ammonia requires a precise hydrogen/nitrogen feedrate ratio of 3:1. Mess with these ratios and ammonia production crawls to a standstill. 

Nitrogen comes from outside air and is fed into the reactor via a large compressor, but in summertime the outside air is less dense, hence reduced flow, hence less ammonia production.

One way of getting the rate back up is to cool the air as it goes into the compressor. The producers had already tried this but the cooling system was unreliable and couldn't maintain the airflow rates required. With peak temperatures hitting 105°F (40°C), could we come up with a cooling system that would get the flowrates back to wintertime levels?

Our Aggreko Process Service (APS) engineers, who specialise in temperature control, went through a couple of different scenarios and decided that the most effective way to combat the high summer temperatures and the consequent reduction in flowrate was to build a two-stage system that cooled the outside air.

We designed an air conditioning unit that cooled the outside air in filter housings. Once the air in the filter housings dropped to 50-55°F it was passed into the compressors. The design made special provisions to avoid a drop in pressure after the compressor took in the cooled air.

The two-stage system increased air mass flow to approximately 5,550-7,500 lbs/hr, which increased the flow rate to wintertime levels of around 48,000-50,000 lbs/hr, even when outside temperatures soared. 

The customer was very happy with the service provided by our engineers, who bought process knowledge and expertise together with the right equipment. The integrated package got ammonia production up to 38 tonnes per day, a significant contribution to the plant’s bottom line profit. 

The cooling units were put in place with minimal disruption or down time to the plant.