Ammonia is a compound of nitrogen and hydrogen that serves as a foundational building block for fertilizer production, industrial chemicals, and increasingly, as a potential fuel source. Because the global demand for this chemical is immense, its manufacturing process is a significant contributor to industrial carbon emissions. Blue ammonia is a term used to classify ammonia produced from fossil fuels, typically natural gas, where the resulting carbon dioxide (\(\text{CO}_2\)) emissions are captured and permanently stored or utilized. The “blue” designation refers to the application of carbon capture technology to the production process, not to the color of the final product, which is a colorless liquid or gas. This approach aims to provide a low-carbon alternative while leveraging the existing infrastructure of conventional ammonia plants.
The Standard Method of Ammonia Production
The vast majority of the world’s ammonia is produced by reacting nitrogen gas with hydrogen gas under high pressure and temperature in a process known as the Haber-Bosch synthesis. Nitrogen is readily available, sourced directly from the air, but the hydrogen component is what drives the carbon emissions in the standard method. This hydrogen is overwhelmingly derived from natural gas, which is primarily methane.
The first step in conventional production is Steam Methane Reforming (SMR), where methane reacts with steam to produce hydrogen and carbon monoxide. The carbon monoxide then reacts with more steam in a water-gas shift reaction, yielding additional hydrogen and a concentrated stream of \(\text{CO}_2\). This process is highly energy-intensive, and when no carbon capture is applied, it results in what is known as “grey” ammonia.
Integrating Carbon Capture Technology
The production of blue ammonia maintains the established chemical processes but incorporates Carbon Capture and Storage (CCS) or Carbon Capture, Utilization, and Storage (CCUS) technology. This integration focuses on capturing the \(\text{CO}_2\) stream generated during production. Because this \(\text{CO}_2\) is produced in a relatively pure, high-pressure stream before the synthesis stage, it is more straightforward and cost-effective to capture than emissions from burning fuel.
The effectiveness of blue ammonia as a low-carbon solution is directly dependent on the capture rate achieved by the CCS technology. Modern designs aim for a capture efficiency of 90% or more, with some advanced technologies promising recovery rates exceeding 99%. Once captured, the \(\text{CO}_2\) is compressed for transport and either used in industrial applications, such as enhanced oil recovery, or permanently injected deep underground into suitable geological formations. These formations include depleted oil and gas reservoirs or deep saline aquifers.
Compared to the high emissions of the conventional method, blue ammonia production with a high capture rate can reduce life-cycle greenhouse gas emissions by 55% to over 90%. The process still requires energy, and any emissions associated with that energy or with methane leakage from the natural gas supply chain must also be minimized to realize the full environmental benefits.
Applications in the Energy Transition
Beyond its traditional use as a fertilizer, blue ammonia is gaining prominence as a versatile energy commodity that can aid in the global energy transition. Its primary utility is serving as an efficient carrier for hydrogen. Pure hydrogen is difficult to transport over long distances because it must be cooled to an extremely low temperature to be liquefied. Ammonia, however, can be liquefied and stored at a much warmer temperature or at moderate pressures, making its handling and shipping easier and less energy-intensive.
Blue ammonia can be shipped using the world’s established infrastructure for ammonia, including ports, pipelines, and storage facilities. Upon arrival at its destination, the ammonia can either be “cracked” back into hydrogen for use in fuel cells or industrial processes. Alternatively, ammonia can be used as a fuel itself, particularly in the maritime shipping industry, where it is being explored as a zero-carbon marine fuel.
It also holds potential for decarbonizing power generation, especially in countries with high energy demands. Blue ammonia can be co-fired alongside coal or natural gas in existing power plants, or it can be used in specialized gas turbines designed to run on a high percentage of ammonia. This fuel flexibility and the ability to leverage existing supply chains position blue ammonia as an important element for sectors that are difficult to electrify.
Comparison to Green and Grey Ammonia
Ammonia is commonly categorized by a color spectrum that indicates its carbon intensity, with grey, blue, and green being the most recognized types. Grey ammonia represents the conventional production method using fossil fuels without any \(\text{CO}_2\) capture, resulting in the highest carbon emissions, typically around 2.73 tons of \(\text{CO}_2\) per ton of ammonia. This method currently has the lowest production cost, which makes it the dominant form in use globally.
Blue ammonia is produced from the same fossil fuel feedstock as grey ammonia but with the crucial addition of \(\text{CO}_2\) capture and storage. This process drastically reduces the carbon footprint, bringing emissions down to approximately 0.28 tons of \(\text{CO}_2\) per ton of ammonia, depending on the capture rate. The production cost of blue ammonia is higher than grey due to the added expense of the capture and storage infrastructure, estimated to be around 1.3 times the cost of grey ammonia.
Green ammonia represents the lowest-carbon pathway, produced by using renewable electricity to split water into hydrogen through electrolysis, which is then combined with nitrogen. This method results in near-zero \(\text{CO}_2\) emissions, but it is currently the most expensive option, with costs potentially two to three times higher than grey ammonia. Blue ammonia is therefore viewed as an important option, offering a significant and immediate reduction in emissions at a lower cost and higher scalability than green ammonia, which remains a developing technology.