The ammonia molecule (NH₃) can help reduce carbon footprints and step forward net zero emission goals in multiple ways. It can function as a carrier of low-carbon hydrogen, making it suitable for facilitating international trade of renewable energy and storage. Ammonia can also be burned, carbon free, as a fuel for power generation or for transportation fuel for the maritime shipping industry.

Co-firing with ammonia is currently undergoing testing for its feasibility and effectiveness in reducing carbon emissions. Although this technology holds potential, it is just one of several strategies being explored to reduce carbon emissions. The effectiveness and sustainability of ammonia co-firing remain under scrutiny as part of broader efforts to identify solutions for reducing carbon emissions.

In Japan alone, annual demand for ammonia is expected to reach 3 million tons by 2030 and 30 million tons by 2050, up from 1 million in 2022. The global supply chain being built by Japanese companies aims for market capture of 100 million tons of ammonia annually by 2050.

Likewise, the global market for ammonia is expected to triple in the decades ahead, according to an analysis by S&P Global Commodity Insights. Driven by decarbonization policies and economic incentives, nearly all this growth will be in low-carbon blue and green ammonia, which is expected to represent two-thirds of the total ammonia market by 2050, up from less than 2% today.

Future of Ammonia

Accomplishing the global transition to low-carbon ammonia will require a major effort to decarbonize the ammonia industry and deploy new infrastructure utilizing emerging technologies. Today’s ammonia industry emits about 620 million metric tons of CO₂ annually, or 1.6% of total global CO₂ emissions. More than 70% of the emissions occur in the production process; the remainder are associated with energy and fertilizer use. Today’s ammonia production processes are also energy-intensive, accounting for 2% of global energy consumption in 2020.

Multiple industries are already using electrolysis and renewable energy to produce carbon-free green hydrogen. With advancements in electrolyzer technology, the deployment of green hydrogen infrastructure is increasing. Another emerging technology that offers a route to green hydrogen is methane pyrolysis, a process that involves breaking down methane molecules into hydrogen and solid carbon. In both cases, this hydrogen can be synthesized with nitrogen (N₂) under high pressure and temperature to produce NH₃.

For the time being, the cost of producing green ammonia remains high, especially compared to the cost of traditional ammonia production. A more economical and immediate path to low-carbon ammonia may lie in the production of blue ammonia.

A Closer Look at Ammonia Carbon Capture  

Like traditional ammonia, blue ammonia is produced from hydrogen derived from natural gas or other fossil fuels. In the ammonia synthesis process, the hydrogen required for the ammonia synthesis loop is produced when CO₂ is removed from the shift reactor process gas using chemical or physical solvents. When traditional ammonia production facilities are not integrated with fertilizer units, the CO₂ is removed from the process gas and emitted. Unlike traditional ammonia production, blue ammonia is produced by capturing CO₂ from water gas shift reactor (WGSR) process gas and sequestering or utilizing it in downstream processes.

Ammonia is produced by combining hydrogen and nitrogen at high pressure and moderate temperature. The hydrogen required for ammonia synthesis is produced by either steam methane reforming (SMR) process or autothermal reforming (ATR). The SMR process has two primary sources of CO₂ emissions: precombustion and postcombustion emissions. Precombustion emissions originate from CO₂ present in the product gas from a WGSR. Postcombustion emissions come from flue gas generated during the combustion of fossil fuels for heating. ATR has no post-combustion flue gas; all CO₂ is captured in one place from the syngas in precombustion emissions.

Costs of Carbon Capture

There are costs associated with carbon capture, including the cost of compressing the captured CO₂ gas to pipeline pressure, then for the transporting and sequestering it. Other factors impacting carbon capture’s cost and feasibility can include process conditions, bulk and trace contaminants and resource availability, utilization of the captured CO₂, and location and depth of sequestration sites.

Some of these costs can be offset by government funding and incentives, including those available through section 45Q and 45V of the U.S. tax code for carbon capture and clean hydrogen production, respectively, along with offsets from process intensification and CO₂ utilization.

Applying Ethanol Industry Experience

To better understand how carbon capture, utilization and storage (CCUS) technologies can be adapted to reduce greenhouse gas emissions in ammonia production, look no further than the ethanol industry, which has a strong track record for carbon capture.

As of 2021, three of the 12 facilities with integrated commercial-scale CCUS operating in the U.S. were ethanol plants. However, the U.S. Government Accountability Office reports that CCUS projects at another 34 ethanol plants are in advanced development — triple the existing number of commercial CCUS projects across all sectors. In addition to integrated commercial-scale CCUS, there are more than 50 ethanol facilities already capturing CO₂ for sale in the food-grade CO₂ market.

A review of CCUS infrastructure at existing ethanol facilities reveals opportunities to improve the feasibility and economics of building CCUS systems for ammonia and other sectors.

Comparing CCUS in Ethanol and Ammonia Production

The primary difference between applying CCUS in the ethanol industry and in ammonia production lies in the carbon capture process. In an ethanol plant, CO₂ comes from a high-purity source containing more than 99.5% CO₂ in a moisture-free state, requiring little or no purification. The water-based scrubbers found in some ethanol plants can be used to remove any traces of volatile organic compounds (VOC) and particulate present in fermenter exhaust before the CO₂ is compressed to pipeline pressure and transported to a sequestration site or utilized for food or industrial processing facilities.

In comparison, capturing CO₂ from WGSR product gas in ammonia production is more complex. It requires a CO₂ capture plant and specialized equipment that must be integrated with existing operations. Helpfully, ammonia plants already possess CO₂ capture systems that separate CO₂ from hydrogen. The high-purity off-gas from these units is more than 99.5% CO₂ in a moisture-free state, similar to that from an ethanol plant. However, an ammonia plant’s gas is at a slightly higher pressure — approximately 12 to 15 pounds per square inch gauge (psig) — compared to the atmospheric vent from an ethanol plant’s fermenter scrubber. Consequently, an ammonia plant may not require a dedicated blower before the compression unit.

In an ammonia plant, CO₂ is removed from water-gas shift reaction (WGSR) process gas by using a chemical solvent such as an activated methyl diethanolamine or hot potassium carbonate solution or a physical solvent such as Selexol, depending on the process conditions and the composition of process gas from the WGSR. These units are already installed in traditional ammonia production facilities. The difference is that the CO₂ removed is sometimes released into the atmosphere. To reduce carbon intensity in ammonia production, the CO₂ can be treated and compressed to pipeline pressure for sequestration or other industrial utilization, as is done in ethanol plants.

Once captured, the CO₂ is compressed to pipeline pressure using methods like those employed in ethanol plants. Depending on the plant’s footprint and CO₂ capacity, the captured CO₂ is compressed in up to eight compressor stages.

In every case, compressor selection is guided by multiple considerations, including source and discharge pressures, capacity, efficiency and reliability.

Leveraging Efficiencies

The carbon capture process used for ammonia production is high on the maturity scale for technology readiness assessments. Although capture plant technology can vary significantly from one ammonia plant to the next, compression unit design can be standardized based on compression capacity, footprint and pipeline pressure requirements.

As demonstrated in ethanol industry applications of CCUS, designs can be replicated on multiple plant sites with minimal engineering cost using a plug-and-play construction strategy.

This cloned approach to design is one of many ways to reduce both carbon emissions and the cost of CCUS in ammonia production. Further application of ethanol industry experience will undoubtedly yield many more.