Flow regulation in green ammonia production

Ammonia and the Haber-Bosch process 

In the 20th century, ammonia (NH₃) was used primarily for fertilizer development. In the 21st century, ammonia is finding new use as a hydrogen energy carrier because hydrogen can easily be converted to and from ammonia. Because ammonia requires less pressure to liquefy and is easier to move or store than hydrogen within existing infrastructure, as hydrogen is prone to leakage, ammonia is a potential solution for hydrogen transportation.  

The Haber-Bosch process to produce ammonia invented at the beginning of the 20th century brought about the green revolution within agriculture, allowing for the manufacturing of nitrogen fertilizers in bulk to exponentially increase the food supply for humans and animals. However, the Haber-Bosch process is also extremely energy intensive, requiring high pressure and temperature. Globally, the Haber-Bosch process produces more than 1% of all carbon dioxide emissions, classifying it as a major contributor to global climate change. 

Replacing Haber-Bosch 

As global fertilizer and hydrogen use will rise rapidly as global population and energy demand grows, the expected demand for ammonia will also increase. Due to this expanding interest in ammonia, researchers have developed new methods to produce ammonia more affordably than using the Haber-Bosch process.  

One such method developed by UC Berkeley chemists uses metal-organic frameworks, or MOFs, that are able to adsorb and release ammonia at temperatures around 175 °C. As these MOFs don’t bond to any of the reactants, the capture and release of ammonia can be accomplished with smaller temperature swings to save energy.  

Another method recently developed by the Korea Institute of Machinery and Materials (KIMM) requires even less energy to produce ammonia by using a plasma catalyst-integrated system that reacts with H₂O and N₂ at atmospheric pressure. In this process, nitrogen plasma splits water that reacts with the nitrogen to create NOx and H₂. In the presence of a catalyst heated to 100-110 °C, these intermediaries turn into roughly 85% ammonia at a 95% selectivity.  Since the energy required is low enough to be powered by renewable sources such as solar or wind energy, this process can be classified as a “green” ammonia production method.

KIMM’s green ammonia production method 

In the KIMM method, plasma is first generated from nitrogen gas at a flow rate of 20 L/min and then sent into a chamber. Simultaneously, water flows into the nitrogen discharge region of the chamber as a water film at a rate of 50 mL/min. The water film is split by the nitrogen plasma into H₂ and NO. After this, NO is reduced via H₂ to ammonia via noble-metal catalysts heated between 100−110 °C (Pd/γ-Al₂O3 catalysts on a ceramic monolith connected to the plasma chamber).  

Implementing gas and liquid mass flow controllers allows for more repeatable, precise, accurate flow control and automation of the nitrogen plasma, water, and heated catalyst within the chamber.  

Gas flow regulation

For gas flow regulation, Alicat’s MC-Series provides nitrogen and catalyst gas flow (before plasma generation or catalysts heating) with useful specs and features such as: 

• 0.5 SCCM full scale to 5,000 SLPM full scale with a turndown of 0.01% – 100% of full scale 
• NIST-traceable accuracy up to ±0.5% of reading or ±0.1% of full scale 
• Repeatability of ±0.1% of full scale + 0.02% of full scale 

Because the KIMM green ammonia generation process requires temperature control of the catalyst via gas heating, a PLC or computer can automate the gas flow control of the heating gas, adjusting flow based on communication with temperature sensors within the chamber. 

Alternatively, for gas flow regulation, Alicat’s CODA KC-Series can provide nitrogen and catalyst gas flow (before plasma generation or catalysts heating) with attributes discussed in the next section since CODA KC-Series can also provide liquid flow regulation.  

Liquid flow regulation

Moreover, for liquid flow regulation of the water into the chamber, either Alicat’s LC-Series or CODA KC-Series can be used with attributes such as: 

LC-Series  

• 0.5 CCM to 10 LPM full scale with a turndown of 2% – 100% of full scale 
• NIST-traceable accuracy up to ±2% of full scale 
• Repeatability of ±2% of full scale 

CODA KC-Series  

• 40 g/h full scale to 100 kg/h full scale with a turndown of 2% – 100% of full scale 
• NIST-traceable liquid accuracy up to ±0.6% of reading or ±0.2% of full scale, whichever is greater 
• Repeatability of ±0.1% of full scale 

As CODA KC-Series can be suitable for both liquids and gases, it can be used as an all-in-1 solution for both the gas and liquid flow control in this process.

All device options also include totalization, batching, and automation customization through a PLC or computer using various communication options.