Energy Management

Usage of Cheaper Fuels for Calciner Firing

Background

The Kiln and the Calciner are major consumers of fuel in a Cement plant. The fuel cost amounts to nearly 20 % of the manufacturing cost. The increasing cost of fuel and the competition among the units have made the Cement units to take up many thermal energy saving projects. The plants are also looking for avenues for reducing the cost by replacing the costly fuels with cheaper fuels. The possible fuels that have been tried by the Cement units include Lignite, Rice husk and Ground-nut shell.

Previous status

In a million tonne dry process pre-calciner plant, Coal was being used as fuel for firing in both the Kiln and Calciner. The Coal was having a Calorific value of about 5900 kCal / kg with a cost of about Rs. 2000 / MT.

Energy saving project

A provision was made to utilise Rice husk in the Calciner. With the new system it was possible to replace part of the coal fired in the Calciner with Rice husk.

Implementation methodology & time frame

A hopper was installed by the side of the pre-heater building for storing the Rice husk. The rice husk was fed to this hopper with the help of front end loaders.

The Rice husk was conveyed to the Calciner with the help of a Rotary blower of 32 m³ / hour capacity. The whole system was fabricated with the waste material available in the plant. The system was hooked up with the main system during a brief stoppage of the plant. The system could be operated for about 8 months of non- rainy dry season.

Benefits of the project

The implementation of the project resulted in the reduction of the cost of fuel used in the Calciner. The cost comparison of Coal and Rice husk are as below;

Parameter -- Coal – Rice husk

Cost – Rs.2000/MT – Rs.750/MT

Calorific Value – 5900 kCal/kg – 2900 kCal/kg

Energy Cost – Rs.340/MMKCal – Rs. 260/MMKcal

The rice husk was used for replacing about 10% of the total coal used for firing in the calciners. This resulted in reduction of the total thermal energy cost, with the other conditions such as output, temperature, pressure etc. remaining the same. There was also a marginal reduction of the power consumption in the coal mill, as the rice husk was used directly without grinding. The rice husk becomes wet and handling becomes difficult during the rainy season. Hence, the usage of rice husk was restricted to the non-rainy and dry season (about 8 months in a year).

Financial analysis

The annual benefits (in the form of reduction in thermal energy cost) was about Rs. 35 lakhs. The equipment required for conveying and firing in the pre-heater was fabricated in-house with available material and hence the investment was negligible.

Benefits of using cheaper fuel