Proving that ammonia is a viable, cost-effective renewable fuel for large energy users off the mains gas grid

Project programme

Amburn Phase 1

Phase 1 of the Amburn project consisted in completing a feasibility study to determine the viability of using Ammonia as an alternative fuel. The study was part of the Industrial Fuel Switching Competition (IFS) phase 1.

The study found that from an economic point of view, boilers fuelled with Ammonia have a significant advantage over other low carbon solutions:

Technology

Comparison

Hydrogen

Hydrogen requires very low temperatures (-253°C) or high pressures (>500 bar) to achieve reasonable volumetric energy density. This means that Hydrogen cannot compete with Ammonia on a total cost of ownership basis.

In addition to this, there is a lack of existing hydrogen distribution infrastructure, which makes storage and distribution costs exceedingly high, in particular for remote sites.

Biofuels

Biofuels may offer an attractive transitional solution for off-grid heating, however competition for from higher value sectors such as aviation and plastics for a finite sustainable biomass resource, means that they likely do not offer a long-term scalable solution.

Direct electrification

Direct electrification necessitates significant grid updates , which can be costly and has long lead times.

Heat pumps

Heat pumps are a viable alternative to ammonia-fuelled boilers, however, low coefficient of performance or high temperature operations (>150°C) makes them more suitable for low temperature applications such as domestic heating.

During phase 1 of the project, consortium partners developed an innovate ammonia burner design which addressed two key challenges associated with ammonia combustion:

Low flame speed and flame stability

Ammonia has a lower burning velocity than hydrocarbon fuels, which can lead to unreliable ignition and unstable combustion. The Amburn design mitigates this by integrating an ammonia cracker unit inside the combustion chamber. The ammonia cracker decomposes a fraction (5% by mass) of the ammonia to produce highly flammable hydrogen (and nitrogen). The resultant fuel mixture has a flame speed of a similar order to fossil fuels (e.g., propane). This was proven by laboratory tests at Cardiff University for a small-scale prototype system at 25 kW.

NOx emissions

Ammonia combustion has the possibility of increased NOx emissions, primarily from the presence of nitrogen atoms in the ammonia molecule (‘fuel NOx’). Testing at Cardiff University’s laboratory suggested that NOx emissions are minimised when ammonia is burned rich. However, rich burning leads to ammonia slip, which both wastes fuel and is dangerous, as ammonia is toxic at very low concentrations. Therefore, the Amburn burner utilises a two-stage combustion process, whereby the bulk of the fuel is burned rich in Stage 1 (to minimise NOx). This is followed by a post-combustion zone where hot unburned ammonia traces reduce the remaining NO. The process is then followed by lean combustion stage (Stage 2), minimising any fuel residue in the exhaust gases.

Figure 1 shows a simplified diagram of the innovative design developed by the consortium partners to address the two key challenges associated with ammonia combustion.

Industrial Fuel Switching Competition

Amburn Phase 2