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Blue Circle Southern Cement
Cleaner Production - Limestone Mine sells dust as by-product

A technical modification at the Marulan South Limestone Mine involving the addition of a chute and a second rotary valve to the collection hoppers of the primary and secondary crusher baghouses has enabled the removal of fine dusts from the process and the collection of the limestone dust for sale as a by-product.

Background

The Marulan South Limestone Mine is part of the Blue Circle Southern Cement company. It is situated on the edge of the Shoalhaven River gorge adjoining the Morton National Park 380 km south west of Sydney.

Marulan

The Marulan Site Limestone Mine and the surrounding environment

The company supplies limestone to cement plants at Berrima and Maldon as well as the BHP steelworks at Port Kembla. The mine has a total production of three million tonnes per year. The mine has been in existence since 1929 with some of the original plant still in operation.

Pre-excisting Process

The limestone rock is drilled, blasted, loaded and hauled from the opencut mine to a processing plant where it is crushed and then dispatched in railtrucks. The crushing plant consists of primary, secondary and tertiary crushers. The limestone is transported between crushing stations and to dispatch silos by conveyors.

As a result of the crushing and conveying processes a significant amount of dust is generated. The primary and secondary crushers are connected to baghouses to minimise direct dust emissions to the atmosphere. Both baghouses have collection hoppers which hold up to 6 tonnes of fine limestone dust. The collected dust is discharged periodically back onto the conveyor system via an automatically controlled rotary valve and chute.

Conveyor unit

However as the collected dust is very fine a large portion of it becomes airborne again. Additional dust is generated from this fine material at conveyor transfer points or at conveyor return rollers, where material that has become lodged in small indentations in the conveyor surface is shaken off.

This dust either settles on the plant floor and equipment, which requires regular cleaning, or is discharged to the atmosphere. The airborne dust also poses a health hazard to employees.

Cleaner Production Initiative

The cleaner production initiative implemented at Blue Circle was relatively simple. A bypass chute and second rotary valve were fitted to the collection hoppers on the primary and secondary crusher baghouses. The bypass chute was then connected to one tonne capacity bulker bags. This enabled the collected fines to be discharged directly to a contained system and has eliminated the substantial generation of dust associated with the former practice. In addition the collected material is now sold as a lime fertiliser.

Advantages of the Process

Bulker bags

The three main benefits from this cleaner production initiative are:

Sale of the dust as lime fertiliser generates income of $25,000 per year (1997).

The costs of the modifications were only $3,500, giving a payback period of approximately two months.

Cleaner Production Incentive

The initial motivation came from the staff on the plant floor who wanted to reduce the hours involved in plant and equipment cleaning. 

Barriers

An initial obstacle encountered was the occasional difficulty experienced by customers in unloading the bulker bags due to moisture retention which caused the limestone dust to set hard. This problem was overcome through bulk transport of the dust in specially designed trucks.

Further Developments

An upgrade of Marulan Works occurred in early 2001 encompassing the principles of cleaner production. The upgrade involved the installation of a limestone feed pre-heater which has improved the plant's energy efficiency and capacity in line with customer demand whilst improving product quality and enhancing Blue Circle Southern Cement's continual commitment to the environment. 

The limestone treatment process involves the conversion of limestone (calcium carbonate) into quicklime (calcium oxide) by heating the crushed limestone in a kiln. 

Prior to the installation of the pre-heater, the limestone feed entered the kiln at ambient temperature. The pre-heater, which is fuelled by waste gases from the kiln raises the temperature of the limestone to 800 degrees Celsius prior to its entering the kiln. 

The benefits are that:

The Pre-heater equipment and inside the kiln

The Pre-heater equipment and inside the kiln

Blue Circle Southern Cement implemented numerous environmental initiatives in addition to those documented here and in particular has established Community Liaison Committees who help to prepare the company's environmental improvement plans. Blue Circle Southern Cement is also a Greenhouse Challenge participant.

Contact

Trevor Kemp
Lime Operations Manager
Blue Circle Southern Cement
Marulan Works
MARULAN  NSW 2579
Ph: (02) 4820 3031
Fax: (02) 4841 1617
Email: trevor.kemp@boral.com.au
Internet: www.bluecirclesoutherncement.com.au (preferred)

Implementation: 1997
Further initiatives: 2001
Casestudy initially prepared: June 1997 by the Australian Centre for Cleaner Production

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Last modified: May 2001