Power station supplies valuable raw materials
Scientists are examining the use of alkaline metals and alkaline earth metals as potential fuels for power station processes. As an example, they have constructed a laboratory reaction chamber for burning lithium. The experimental lithium burner achieved a thermal capacity of 30 kilowatts. It atomises and burns melted lithium in a carbon dioxide atmosphere to produce lithium carbonate. Carbon monoxide is also produced.
The scientists' idea is to use excess electrical energy for the electrochemical production of metals such as lithium, sodium or magnesium. When electricity is needed, the metal is used as fuel in special power stations. The burning of metal in a carbon dioxide or nitrogen atmosphere occurs at a similar thermal level to conventional burning of fossil fuels. The highlight is that in contrast to carbon-based fuels, the burning of metals results in various different products, depending on the reaction partners, that can be used as valuable raw materials in the chemical industry. This compensates for energy losses in the process chain, meaning that the process can provide energy balance rewards and also financial rewards. Re-using the combustion product lithium carbonate for the manufacture of lithium results in a closed cycle.
Industrially valuable combustion products
"We utilise the high reactivity of the electropositive alkaline metals, which can also be reduced by poorly reactive gases such as carbon dioxide or nitrogen," says the project leader Dr. Dan Taroata, who then added: "In a nitrogen atmosphere we obtain lithium nitrite, which can be used to synthesise ammonia." Carbon dioxide and ammonia are used as raw materials in many chemical industry production processes.
The scientists initially examined a number of different reactor concepts for burning lithium. The assessment criteria were:
- Complete combustion
- Temperature level corresponding to an energy decoupling process for electricity generation
- System for extracting the lithium-based reaction processes from the reactor, at the highest possible recovery rate
The lithium must be atomised into small droplets or particles to ensure complete combustion. The researchers proved that it is possible to burn atomised lithium in typical combustion chambers. The burner is designed in a similar manner to coal dust or oil burners.
Pilot plant experiments
When burning in carbon dioxide, the preferred solid reaction product lithium carbonate liquefies in a temperature range of 700 to 1,000 degrees Celsius and can be drawn off from the combustion chamber in molten form. This means that a reactor concept based on the tried and true melting chamber principle is the most suitable approach.
Lithium is sprayed into the upper end of a reaction chamber and reacts with CO2 injected at multiple different points. The carbonate reaction product is extracted as slag from the lower end of the chamber and the gas flow escapes to the right.
Numerical simulations of the flow field in the plant show that the plant is large enough for a high degree of burnout. This method was also used to optimise the positions of the secondary CO2 jets for influencing the flow to suit the process requirements.
Burning alkaline metal in a spray reactor
Once the researchers had mastered the controlled atomisation of liquid lithium and had examined the various atomisation types with single-substance and twin-substance jets, they were then able to maintain a controlled lithium metal flame in a laboratory reactor for the first time.
The solid reaction products resulting from the burning of lithium in CO2 confirm the expected reaction process, with the production of lithium carbonate. The reduction of carbon dioxide to carbon monoxide also occurred as expected.
The scientists also analysed the reaction products resulting from the burning of liquefied, atomised lithium in a nitrogen atmosphere. After hydrolysis of the reaction products, the presence of ammonia was also wet-chemically verified. In addition to the pure aspect of the storage and later recovery of electrical energy, the burning of lithium in a nitrogen atmosphere also provides access to ammonia. From a purely commercial perspective, ammonia is one of the most commonly produced raw materials used in the chemical industry.
The commercial utilisation of these results has been completely secured by twelve patents.