Page 176 - Advances In Productive, Safe, and Responsible Coal Mining

156 Advances in Productive, Safe, and Responsible Coal Mining

9.1.2 Impacts of dilution

As shown in Fig. 9.1, dilution has a pervasive impact on each step of the coal produc-
tion process. Not only does OSD have an obvious impact on face production costs due
to extracting extra material, but also it negatively impacts the cost of all downstream
processes. Roof rock is typically much harder than coal and mining; it results in higher
power costs and increased maintenance and wear on extraction equipment. Materials
handling costs are affected by the dilution material, which decreases conveyor belt life
and increases power costs. Processing costs are also impacted as a result of the added
waste material flowing through the processing plant. The OSD material is eventually
rejected, where it adds to the costs of constructing, maintaining, and reclaiming a suit-
able waste disposal area.
Some less obvious, but nevertheless significant, impacts of dilution on coal
processing are related to clays removed from the mine floor and to carbonaceous black
shale removed from the mine roof. Floor clay impacts the processing system in the
following three ways:
1. It completely breaks down in solution leading to increases in the viscosity of the medium in
dense media circuits. This might improve media stability at the low end of the gravity spec-
trum; however, for the more common higher separation gravities, increased viscosity is
detrimental as it decreases separation efficiency leading to lower clean coal quality.
2. Increased clay implies higher thickening and dewatering cost along with correspondingly
higher flocculant costs for water clarification.
3. Higher clay content impairs the ability of flotation cells to clean and dewater ultrafine coal,
which can be as much as 5% of raw coal production.
Another major impact of OSD, which is frequently ignored because it is not very well
understood, is its influence on clean coal quality. If preparation plants were 100%

Plant size Transportation
Plant recovery cost
Product quality Freeze-thaw
Dewatering Customer
Water reuse penalties

Material transport
Mining face Rotary Processing Product
area breaker plant transport
In-mine Waste
disposal management

Equipment cycle Transportation
times cost Disposal cost Land, water, air
Equipment Belt life Environmental issues
maintenance Transfer point issues of in- Management cost
Equipment jams mine disposal Environmental
supplies Dust control issues
Dust Monitoring and
Visibility control
Product quality
Fig. 9.1 Impact of dilution on various components of the coal-mining system [2].