Urea is a key component in nitrogen-rich fertilizers. Typically, the urea production process begins with hydrogen from natural gas and nitrogen in the air to produce ammonia. Urea is produced from the combination of ammonia and carbon dioxide. Urea producers must balance throughput with efficiency and the quality of the urea produced.In a new whitepaper, 4 Solutions for Urea Automation Challenges, Emerson’s James Gremillion shares ways that additional measurements and insights can help to improve overall reliability and operational performance.
He cites four challenges in meeting production targets:
- Highly corrosive ammonium carbamate causes equipment degradation and failure
- Variable feedstock characteristics affect conversion and equipment efficiency
- Cyclical market prices of feedstock and urea require plants to adjust throughput
- Missing measurement capabilities make it difficult for operators to get a comprehensive view of process problems and develop plans to overcome them
James provides an overview of the urea production steps:
In the urea synthesis step, the ammonium carbamate (H2N-COONH4) formed is highly corrosive, so the equipment handling it must be specially designed and constructed of materials able to withstand the environment and provide a long service life. In the recirculation and recycle phase, turning ammonium carbamate into water and urea is a slow endothermic reaction occurring in the reactor until a certain equilibrium has been reached.
The evaporation phase removes the water from the urea melt to change it into the solid state. Finishing produces the particle sizes, quality and chemical composition required by the customer specifications.
James notes how the production capacity and productivity of a plant is determined by precise measurements of ammonia and carbon dioxide coming into the plant and urea leaving the plant. Coriolis and Vortex flow measurement devices are corrosion resistant to measure the incoming ammonia flow. Coriolis technology measures mass flow and also provides insight into feedstock quality.
For the incoming carbon dioxide, differential pressure (dP) flow measurement provides accurate measurement of this feedstock usage. For the flow and temperature measurement of urea melt, magnetic flow meters (magmeters) work well. Controlling the temperature is critical to prevent pipe plugging and/or quality issues.
You’ll want to read the whitepaper for the importance of pressure and level measurements in preventing crystallization, erosion and corrosion, monitoring carbon dioxide compression efficiency, and monitoring hydrogen vent monitoring.