David Salazar, Aerzen Americas Application Manager, Cement - Lime – Concrete, writes about selecting the right technology and machine size for fuel conveying, combustion air and air cooling systems to optimise fuel efficiency in the kiln for lime production plants.
- Article Size actually matters
Amount of air in the limestone production
According to the data available from the USGS (U.S. Geological Survey), in 2018, the quicklime and hydrate lime market value in the Americas exceed the USD 3 Billion and an estimated of 32 million tons were produced all over the region from over 120 production plants located from Canada to Argentina, the market growth expectations worldwide are about 7.5%, and the Americas expects to reach a constant CAGR of 7% from 2018 to 2022, mainly driven by the need of improved processes in the mining industry, sugar cane market by the increased demand of biofuels and the industrialisation for wastewater treatment facilities in Latin American Countries. These good market expectations for the near future require serious process optimisations in the production facilities to look for the best fuel efficiency in the kiln process. The efficiency in the burning process is closely related to the availability of certain types of fuel and the proper selection of the fuel conveying, combustion air and cooling air technologies that includes low pressure oil free rotary lobe compressors and turbo blowers.
Kiln technologies
Currently in the limestone production processes, there are two main kiln technologies used: vertical kilns and rotary kiln systems. Both technologies require a large amount of low pressure oil free air for fuel conveying and cooling processes to guarantee the proper quality of the calcium oxide, according to a specific research on lime production process in the USA from RTI (Research Triangle Institute). Vertical kilns are the preferred technology for lime producers as less capital investment is required, and the fuel efficiency is greater. However, in the U.S., vertical kilns have been largely replaced by rotary kiln systems, mainly because they require less labor and have the highest output by reducing the amount of spalls. A summarised analysis of the two technologies is shown in the table.
Air supply for the kiln
As shown in table, the amount of air required for both vertical and rotary kiln in the combustion process is large enough to consider it as critical application for the production process. AERZEN application specialists have identified some common improving opportunities at different plant locations that involve the following main aspects:
- Appropriate selection and design of the machine that provides the combustion air to efficiently burn the fuel. In total, AERZEN offers with positive displacement blowers, rotary lobe compressors, screw compressors and turbo blowers, an extensive range of products and technologies in order to be able to offer tailor-made process air solutions for the most diverse requirements.
- Design of the pipe diameter through which the air for the cooling lances (vertical kilns) flows. There is the danger that the air speed is too low, which can lead to clogging of the lances.
- Initial investment for the low pressure air compressors, without considering the TCO for the project, which in the medium term may lead to a reduction of MTBR and an increase of the total cost of ownership.