Coal Production Method

A five step process to deliver a quality product.

At Griffin Coal, coal production takes place through a five step process to deliver a quality product with a focus on reducing long term environmental impact. 

The five steps of the coal production process include:

1. Exploration and Development

The first stage to any coal production operation is exploration and development. This takes place to locate and determine the most appropriate methodology to extract the mineral. 

Exploration and development involves the combined efforts of geologists, geotechnical engineers, mining engineers, coal technologists and surveyors. 

The geologist is responsible for defining the shape, size and quality of the coal reserves and for producing a computer model. 

This model is used by the mining engineers to plan and manage the mining process taking into consideration:

1. Mine wall stability.
2. Scheduling of coal production at a consistent rate and quality.
3. Controlling groundwater seepage and rainwater runoff.
4. Mining block and backfill designs for minimal possible overburden removal distance.
5. Optimising equipment deployment and productivity.
6. Minimising operational interruptions.
7. Optimising drill and blast practices.

Surveyors support both the geologists and mining engineers by ensuring that the data required for deposit modelling is correctly gathered in the first instance. Surveyors also confirm that the engineers' mine plans are accurately reflected in the mine development. 

As Griffin Coal's mining occurs in soft, saturated sediments, sometimes at great depth, Griffin Coal has had to achieve high standards of professionalism in the above disciplines. 

2. Mining

Mining can take place through open cut or underground mining methods. At Griffin Coal’s Collie mines open cut mining methods are used. The mining process involves the removal of overburden and extraction of coal but can be considered as four distinct operations: 

- Topsoil

Topsoil is removed ahead of mining and either spread directly on shaped rehabilitation areas or stockpiled for later use. This operation is performed using dozers, front end loaders and trucks.

- Laterite

The cap rock (up to 2 metres thick) is either ‘ripped’ by dozers or blasted and recovered for use as road surfacing material.

- Overburden

All overburden apart from the ‘Nakina Formation’ is drilled with rotary ‘blast hole’ drilling rigs and charged with bulk explosive, typically a mixture of ammonium nitrate and fuel oil (ANFO). 

After blasting, overburden is loaded by hydraulic excavator or front end loader into rear dump trucks and placed in overburden dumps. Initially these had to be placed out of the pit in order to create a large enough hole to work in. The worked over areas of the pit are now filled in, a process known as backfilling. 

When the mine gets to the back firing stage, the hole gets bigger and moves slowly across the deposit. Then overburden materials are removed from the operating faces and dumped into backfill on the other side of the mine. 

In its operations, Griffin Coal places all overburden into mined out areas and focuses on the rehabilitation of the newly created final land surface.

- Coal

When overburden has been removed from the coal seam, the roof of the seam is cleaned using bulldozers. The coal seam is then drilled and blasted. Bulldozers clean down to the floor of the coal seam and front end loaders and coal trucks transport coal to either the Ewington Crushing Facility or direct to Muja Power Station. 

In some areas, coal can be loaded directly into trucks using a large backhoe, without need for bulldozing. Once the coal has been extracted it is then processed.

3. Processing

Processing involves crushing, screening and beneficiation. 

Processing takes place at Griffin Coal's Ewington Mine. It is a process wherein coal is converted from Run of Mine to a product that meets the customer's requirement.

Crushing

Mined coal can include lumps up to a metre in size, so crushing to a manageable size is required. Coal crushing can include a two stage process dependant on deposit size.

Crush One: Feeder Breaker

Coal is crushed in a feeder breaker, a chain conveyor under a toothed drum that breaks the biggest lumps.

Crush Two: Sizer

Coal size is further reduced through a sizer, where each oversize particles are reduced to less than 75 millimetres.

Screening

Screening is used to separate different sizes of crushed coal. In this process coarse and fine coal is separated so to accommodate for specific markets and industrial usage. Screening takes place at a processing plant adjacent to Ewington Mine. 

Griffin Coal’s screened coal is ideal for burning in horizontal kilns. In these kilns uniform particle grading is used to create even combustion along the length of the kiln. Coarser coal is also required by customers who burn coal in grate–fired applications.

Beneficiation/Washing

Beneficiation has been trialled at Ewington. During beneficiation, coal is processed to remove impurities reducing ash and sulphur thereby improving the market value of the coal. Beneficiation can improve the quality of contaminated coal that would otherwise be wasted. 

Most cleaning processes involve washing the coal in order to separate coal particles from stone particles as coal is considerably lighter.

Charring

Coal can be charred, a process wherein hydrogen and oxygen are removed from the coal to make it purer form of carbon. Once processed according to specifications, coal is loaded and transported accordingly.

4. Loading and Transportation

At Muja, ROM coal is delivered directly to the adjacent Muja Power Station. 

Preparation of coal for sale to industrial customers is an integral aspect of Ewington operations. Coal preparation involves crushing, screening and loading trucks and trains. A variety of products are produced to specification for size and quality. 

All coal consignments are sampled to Australian and International Standards and analysis is undertaken by an independent NATA accredited laboratory. 

At this point it is important to rehabilitate the environment so as to return it to its natural state. 

5. Rehabilitation

Restoring the environment to it's natural state.

Mine site rehabilitation is important to environmental sustainability. Rehabilitation involves returning the land to it's natural state post mining through strict, well researched strategies of revegetation and the regeneration of natural ecosystems. Work to restore disturbed areas is carried out progressively as soon as practicable. 

Griffin Coal’s environmental commitment includes the progressive rehabilitation of its mining operations. The objective of mine rehabilitation is to create a structurally stable landform capable of future productive use. 

Rehabilitation also occurs to return land to a scale and morphology similar to that which exists elsewhere in the Collie Basin. 

Rehabilitation involves a comprehensive process of classifying overburden material, land recontouring, seeding and regeneration.

Overburden Material Classification 

Overburden material is classified according to its potential to cause geochemical impacts (acid rock drainage) on the environment. Dumping of waste material is undertaken so the best materials end up near the surface of waste landforms and the other material is encapsulated in the middle.

Land Recontouring 

When the landforms are no longer needed for mining or dumping purposes the slopes are recontoured to around 10 degrees to control surface runoff and to ensure a stable slope. Topsoil is then spread to a depth of 150 millimetres before the area is contour ripped, fertilised and seeded with local natives.

Seeding 

Rehabilitation areas are seeded at the break of the winter rainy season, and initially are susceptible to erosion damage until germination and root development has occurred. Historically dumps were rehabilitated to pasture species. This approach was chosen to stabilise the dump outslope quickly to prevent erosion. More recently efforts have been directed to the re-establishment of native flora.

Regeneration 

Native species do not germinate and develop until the following spring, therefore the potential for massive erosion is present during the winter. A strategy has been developed whereby native bush species comprising grasses, groundcovers, shrubs and trees, are sown together with a "nurse" crop of cereal rye. 

The cereal rye germinates quickly and stabilises the surface through the winter and the natives emerge the following spring. The seed mix includes Jarrah, Wandoo, Flooded Gum, numerous Acacias and understorey species.