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Reducing waste with residual solid fuels

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World Cement,

Cristian Muriel, Satarem, reviews a low-CAPEX project to adapt a vertical milling circuit to take advantage of solid fuel residues.

In the last 20 years, there has been a global phenomenon in terms of economic growth, especially in the expansion of Asian markets, namely India and China, in both electricity and cement production.

This growth in energy demand has been accompanied by a considerable increase in the price of coal. This price increase occured even though China, India, and the USA (the second largest energy generator in the world) have guaranteed local production and politically protected reserves; the impact has been even more significant in countries without major local coal extraction sectors, such as Brazil.

Given this context, the Brazilian cement industry, which has shown constant growth in demand since the 2000s, has been making a migration in the type of fuel used for cement production from coal and natural gas to varying alternatives. The large cement manufacturers in Brazil have found in petcoke an interesting and accessible alternative to conventional fuels. This is due it to being a by-product of heavy oil extraction and the Brazil’s significant oil production, which makes it readily available.

Currently, the use of this petroleum by-product is attractive due to its high calorific value. However, it is a very volatile market and depends on environmental regulations, as well as petcoke prices relative to those of natural gas. When natural gas prices increase, petcoke becomes an economically attractive energy source.

The use of petcoke has become a key ally to cement producers in Brazil, however, some cement plants have grinding circuits that are ill-equipped to process this material due to the material’s hardness (grindability index between 35 – 42 HGI), and in many occasions stone and sand sediment can be found in the mixture, making it difficult to grind.

The project

For this reason, one cement producer in Brazil invited Satarem to design and implement a project taking advantage of petcoke residues generated in the vertical milling circuit of the plant, given Satarem’s extensive experience in designing and implementing projects focussing on waste utilisation and the uses of alternative fuels in the cement sector.

When grinding using vertical Raymond mills, any material that the mill is not able to process is rejected, an outcome that becomes more frequent if the fuel has a higher hardness index.

For this project, the plant had a grinding circuit composed of two Raymond mills in parallel with a total capacity of 24 tph, rejecting between 8 and 10 tph, that is, 41% of the material being discarded, generating a significant economic impact on the kiln operation.

To solve this problem and take advantage of this rejected petcoke, which is composed of approximately 50% petcoke (HGI 35 – 42) and 50% silica, an open circuit grinding system was proposed, that would allow processing of the material to a fineness of 10% retained in mesh #170 and reincorporated into the ground coal silos to feed the main burner of the kiln. To ensure the economic viability of the project, Satarem offered a solution that involved supplying high quality equipment under the banner of being a BCC (Best Cost Country) supplier, with a delivery time of less than 16 weeks under the restricted conditions of the pandemic and the subsequent logistical crisis.

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