Page 89 - Advances In Productive, Safe, and Responsible Coal Mining

74 Advances in Productive, Safe, and Responsible Coal Mining

Fig. 5.15 Average cycle times 10.60
(RHS). 10.50
Cyle time (min) 10.40

10.30

10.20
11 13 15 17 19 21
Number of entries

Fig. 5.16 Production rate. 560
Production rate (tph) 550
555

545

540
11 13 15 17 19 21
Number of entries

spotting time resulting in long wait times and bunching; however, expanding panel
width beyond 17 entries results in inadequate haulage unit capacity and underutiliza-
tion of the CM. This is confirmed by Figs. 5.14 and 5.16, which show that the haulage
unit cycle time increases when the panel width exceeds 17 entries. Initial expansion of
the panel reduces the haulage unit cycle time (minimizes waiting time). However, fur-
ther expansion of the panel increases haulage unit cycle times because haul distances
become longer, leading to an operation constrained by haulage unit capacity. Adding
more haulage units will increase production and CM utilization but will also increase
the unit cost of operation. These trends (cycle time and CM loading times) directly
result in the observed trend in production rate (Fig. 5.16), with a panel width of
17 entries generating the maximum production rate.
Fig. 5.16 provides the information needed to generate production rate indexes,
which can be used in the optimization model to account for the relationship between
production rate and panel width.

5.3 Maximizing recovery as a cutting stock problem

5.3.1 Modeling coal recovery as a cutting stock problem
The cutting stock problem (CSP) is the problem faced by someone who seeks to cut
smaller pieces of material, given the customer demand, from a larger piece of stock
material in such a way as to minimize waste [8, 11]. The problem is one-dimensional if
cuts differ in only one dimension (width or length). Higher dimensional problems