Ammonia plants are normally measured in thousands of tonnes a day, because the economics favour size. A feasibility proposal prepared with a university partner asked whether a lower-pressure catalyst could make 10 to 100 tonnes a day viable, powered by renewable electricity and located near its customers. This article sets out the idea, the process and what the feasibility study needed to prove. It is a proposal and has not been proven at scale.

The challenge: ammonia is global, large and carbon-heavy

The world market was close to 200 million tonnes in 2019. Conventional production from natural gas, coal or oil accounts for roughly 1.4% of global energy-related greenhouse gas emissions, according to the source application. Because plants are large, ammonia travels long distances to users. Small plants have existed, but as scaled-down versions of large designs they tended to serve niches such as storing wind and solar energy.

The idea: cut the cost of the reactor

The Haber-Bosch reaction combines nitrogen and hydrogen over a catalyst at high pressure. The core of the proposal was a catalyst developed at the university that:

• operates at a lower pressure, aiming at up to 100 bar rather than the usual 150 to 200 bar, which cuts reactor and pipeline cost (a 30 to 50% reduction in pressure);
• tolerates oxygen-containing contaminants, so feed gas purification can be simpler and cheaper.

The process

The main components in the outline list, at a demonstration scale of tens of kilograms a day, were:

1. A pressure swing adsorption unit making nitrogen from air.
2. An electrolyser splitting water into hydrogen and oxygen using renewable electricity.
3. Gas storage for nitrogen and hydrogen, sized to smooth intermittent supply from wind or solar.
4. Compressors and a gas purification filter to bring oxygen down to about 10 ppm so the catalyst is not poisoned.
5. A packed-bed ammonia reactor with heat removal.
6. A condensing column to separate liquid ammonia, a secondary purification flash and ammonia storage.

The product is liquid anhydrous ammonia. When burned, it releases nitrogen and water, not carbon dioxide.

The staged plan

1. Laboratory work to refine catalyst use at small scale.
2. A pilot rated at 50 kg of ammonia a day to confirm the full process.
3. A 10 tonne-per-day demonstrator, followed by units up to 100 tonnes a day.

Why the sponsor’s experience is relevant

The company has spent about twenty years removing and recovering ammonia from wastewater, already converting it into ammonium hydroxide and salts such as ammonium sulphate and phosphate. A green ammonia plant would serve similar markets, but at much larger volumes than the 2 to 10 tonnes a day of ammonia a large wastewater plant may produce.

What to consider if you are exploring local ammonia

1. Demand first. Identify buyers such as fertiliser, nitric acid or ammonium product makers who would pay a premium for low-carbon product.
2. Power supply. Renewable electricity cost and intermittency drive the economics.
3. Storage. Gas buffers smooth variable generation.
4. Safety. Ammonia is toxic and needs proper hazard management under UK regulations such as COMAH where thresholds are met. See the HSE COMAH guidance.

FAQ

What is green ammonia?

Ammonia made from hydrogen produced by electrolysis with renewable power, and nitrogen from air.

Why not make it at large scale only?

Large plants are efficient but ship product long distances. Local plants avoid transport and serve local demand.

Has the process been proven?

The source describes a feasibility proposal. Proof at scale was still to be shown.

Interested in local ammonia?

Get in touch to discuss ammonia recovery and production.