Electrification of Rotary Kiln Processes

At IBU-tec, we have years of experience with thermal processes in rotary kilns gained from a wide range of customer trials - both in directly heated systems with a gas burner directly in the rotary kiln, the reaction chamber; indirect gas-fired rotary kilns, in which the gas burner heats the kiln from the outside, and indirectly heated rotary kilns with electric heating elements. Alongside traditional gas-fired systems, these have long been a cornerstone of thermal process engineering in many industries. Now, however, it is more attractive than ever to convert gas-fired processes to electric heating elements. This is also possible in previously indirectly heated rotary kilns, where the gas burner is also located outside the reaction chamber. However, converting directly heated rotary kilns to electric heating is anything but simple. Here, the burner in the reaction chamber is an elementary part of the process, its presence and effects an integral part of the process control, the reaction atmosphere and the required material treatment. Converting a direct-fired rotary kiln process to electrical indirect heating is a major intervention that requires a great deal of technical and process engineering understanding, if it is possible at all. IBU-tec's extensive experience in process development is extremely useful here.

Before converting a gas-powered process to electric heating, a few important questions need to be clarified: What is the availability and reliability of the power supply at your site? Thermal processes could place demands on this beyond the load limits, so it must be agreed with your supplier whether the existing infrastructure is suitable for electrification or whether it can be expanded.

If the conversion is being considered due to possible CO₂ savings, the question of the overall CO₂ balance must also be asked and answered: What source does the electricity at your location come from: What are the CO₂ emissions of your available electricity mix? What other changes to the process will be necessary? All of this is included in the overall CO₂ balance and will clarify whether retrofitting makes sense at all for the emissions considered as a whole.

There are two ways to convert a direct natural gas-fired rotary kiln process to electric heating:

One way is to convert the process from a gas burner to an electric hot gas generator, which is also in the reaction chamber or feeds the hot gas stream into the reaction chamber. Depending on how energy-intensive and on what scale the production is to take place, this approach can be viable. At IBU-tec, for example, we have already carried out such engineering and redesigned a combustion chamber with an electric hot gas generator, which was able to generate similar reaction conditions in the tube.

The other option is to develop the existing direct process into an indirect process, which is easier to implement in an electrically heated indirect rotary kiln. This requires a deep understanding of the process and not all processes can be realized in an indirect furnace.

A limiting factor for both options is often the technical and economic feasibility of the process. The larger the production and the more material is used, the more reliant you are on scaling effects for market-competitive production. These can often no longer be realized with electrically heated rotary kilns after a certain point.

Electrification is more interesting for processes with lower throughput volumes, which achieve higher prices per kilogram. Which material system is used tends to be less important in terms of process technology.

However, as indirectly or electrically heated rotary kilns can often only achieve lower temperatures than gas-fired direct rotary kilns, the required treatment temperature is very important in determining whether the electrification of a process is sensible or even possible.

In terms of temperature control, however, electrically heated rotary kilns have an advantage over gas-fired kilns: the treatment temperatures of electric kilns can be easily controlled across the entire temperature spectrum, even in lower temperature ranges where direct gas-fired kilns often only allow less precise temperature control.

Electrification of indirectly heated rotary kilns, on the other hand, is more straightforward: one heat source outside the reaction chamber must be replaced by another. Apart from supplying thermal energy, it plays no active role in the process, so the main question to be answered is whether electric heating elements are sufficient for the temperatures to be achieved.

At IBU-tec, we recently converted one of our own indirectly heated rotary kilns, which are available for customer projects, from gas firing to electric heating. The electrification was an important project for us and a showcase for prospective customers. By converting one of our furnaces to electric heating, we have not only improved our own security of supply, but have also gained further valuable experience for customers and prospective customers with which we can approach engineering for you.