MazerRR wrote: Look, it’s another Thesis paper from our friends at Chalmers University in Sweden… this time evaluating the use of Plasma Torches in cement production :D
https://odr.chalmers.se/bitstream/20.500.12380/257463/1/257463.pdf Key points:
This work developed and evaluated a heat transfer model for the cement production process, focusing on the rotary kiln but also including the cyclone tower.
The purpose of the model is to evaluate the implementation of new heat sources, in this case plasma torches. The model is validated against two distinctive cases of operational conditions of production line 8 at Cementa in Slite.
Worldwide cement production emits around 2.8 billion tonnes of CO2 annually, equivalent to 8% of the global total, which is a greater amount than any given country apart from China or the US. [2] The floor area of the world’s buildings is projected to double in the next 40 years, meaning that the cement production is set to increase by approximately 5 billion tonnes by 2030, an expected yearly production rate increase of 25% compared to today’s level [3]. It is therefore important to reduce the emissions from this industry.
Considering the emissions from the process, approximately 35-40% of the total CO2 emissions in the cement industry is associated with combustion of fossil fuels in order to heat the raw material to temperatures high enough for the calcination and clinker processes [4]. The remaining 60-65% of the CO2 emissions is due to the calcination reaction itself [5] and cannot be decreased but the emissions could be managed by Carbon Capture and Storage (CCS) or other methods [1].
According to Cementa’s preliminary investigations report, electrification of the system is a better economical alternative with less energy consumption to reduce their CO2 emissions than other CO2 extraction methods, e.g. amine extraction. The heating technologies they have considered are plasma, electrical flow heaters, microwave heating, resistive electrical heating, inductive heating, direct separation reactors and hydrogen combustion.
Based on the results of the investigation the preferred alternative for heating in the kiln is plasma torches, with CO2 as the preferred working gas. An advantage of replacing conventional burners with plasma torches, other than decreased greenhouse gas emissions from replacing combustion, is that the
operating costs can decrease, according to a comparison performed by L. Rao, F. Rivard and P. Carabin [17] on a 2 MW fuel oil burner and a 2 MW air plasma torch. They state several reasons why the operating costs are lower, including decreased costs of heat production due to fuel consumption being replaced by cheaper electricity. Secondly, no more handling and extraction of fuels would be necessary, meaning less process equipment utilisation and manpower. Thirdly the volumetric flow of gas could decrease which means that the cost of off-gas treatment decreases. The preferred working gas of the implemented plasma torches is CO2 . The reason for CO2 being the preferred working gas is that CO2 will still be produced from calcination, and to prepare for future implementation of CCS it is desirable to have as pure gas flows as possible.
The CO2 can be acquired by recirculating the CO2 from calcination, which is another advantage of using CO2 as working gas. The results of modelling plasma torches indicated that it is feasible to replace the fuel burners with plasma torches in the rotary kiln. To validate this result, calculations on the gas temperature profile in the kiln need to be performed to investigate if the required temperatures can be reached.