Ammonia production

Ensure safe and reliable operation

There are various valves present in the ammonia synthesis loop, controlling the flow of synthesis gas into the converter and ensuring proper recycling of the unreacted synthesis gas. Valmet offers a good selection of suitable valves for ammonia synthesis loop – ensuring safe and reliable operation plus long service life.

Ammonia synthesis process overview

Ammonia synthesis is used to produce ammonia from nitrogen and hydrogen. The produced ammonia can then be used as a fertilizer, or it can be further processed into urea or nitric acid. A mixture of hydrogen and nitrogen, usually originating from a steam reformer, is admitted to the synthesis loop and then compressed in two stages into the synthesis pressure of 150-300 bar (2200-4400 psi). The stream is preheated by heat exchange with the hot effluent coming out of the converter before entering the ammonia converter.

The ammonia conversion process is a compromise between temperature and pressure. For the catalyst to be efficient a temperature of at least 400 °C (750 °F) is needed, but since the reaction is exothermic a higher temperature negatively affects product yield. To counter this issue, the pressure is increased to push the reaction equilibrium toward ammonia (thus increasing product yield). Heat is recovered from the effluent by generating steam and by pre-heating the incoming feed. The effluent is then sent to refrigeration before the product is separated from the medium and unreacted gas is recycled to the start of the synthesis loop.

Process challenges

High temperature, between 200 °C and 450 °C (400- 840 °F)
Very high pressure (130-220 bar / 1900-3200 psi)
Presence of hydrogen and ammonia make for a challenging environment as both hydrogen attack and nitriding may occur
Emission control is important due to toxicity of the media being handled
Since pressure is a very expensive commodity, efficiency in the synthesis loop is important to keep the operating costs down

Valves in ammonia synthesis loop

The role of valves in the ammonia synthesis loop is to control the flow of synthesis gas into the converter and to ensure the recycling of the unreacted synthesis gas.

Converter inlet valve

This valve is used to adjust the flow of synthesis gas into the converter. The flow may need to be adjusted to cope with temperature fluctuations in the converter.

Converter outlet valve

This valve is located after the reactor and is used to regulate the flow of effluent to the boiler.

Boiler bypass valve

This valve is used to control the flow of reactor effluent that bypasses the boiler, allowing the amount of pre-heating by the synthesis gas heat exchanger to be controlled.

Valmet's solution

Neles™ butterfly valves provide the optimal solution for ammonia synthesis loop isolation and control valves. Their wide design options make them suitable for all on-off/control applications in the ammonia synthesis loop. Triple offset design reduces wear and provides extended operational life in control and shut-off applications.

Pressure classes ASME 150-2500
Temperatures up to 600 °C (1110 °F), higher with special constructions
Wide selection of body & trim materials, ensuring a lasting design in the harshest of conditions
Standard seat leakage class ISO 5208 rate C / FCI 70.2 class V. ISO 5208 Rate A / FCI 70.2 Class VI available
No resilient parts exposed to the medium
Interchangeable seats, without needing to disassemble
the disc and shaft
Live-loaded stem seal as standard, ISO 15848 and
TA-Luft/VDI 2440
Fire-tested per API 607, 6th edition
Certified up to SIL 3, with select designs

Efficiency

The solid metal seat allows highest possible flow velocities without damaging the seat. The unique two-piece shaft gives the valve a higher flow capacity and reduces the torque requirements for operating the valve. The unique two piece-shaft gives the following advantages:

Lower pressure drop across the valve, reducing operation costs, due to the higher flow capacity
Use smaller valve size for the same flow amount, reducing capital costs
Smaller actuator due to lower torque requirements, further decreasing capital costs
Lower pipe stress as less torque is applied by the actuator
Less torque also allows better controllability of the valve

For example, a flow 2000 m3/h (8800 US gal/min) through a valve giving a pressure drop of 2 bar vs 3 bar (30 psi vs 45 psi) allows potential energy savings of about $45 000 per year in pump operations.

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Ammonia production

Ensure safe and reliable operation

Ammonia synthesis process overview

Process challenges