Coal quarry simulation model

An indispensable part of fossil fuel quarrying is overburden removal - a draw rock which covers mineral deposits. The plan execution on the overburden transportation is a mandatory condition when executing the production schedule.

Planning is generally done by means of analytical instruments such as Microsoft Excel. Excel is good at many tasks, but has a number of disadvantages. It allows modeling only processes and logical connections which can be expressed with the help of mathematical formulae. It's difficult to take into account time and place, as well as deal with uncertainty in Excel. As a result, one has to use rather high level of abstraction or simply neglect some parameters and processes of the analyzed system.

One of the Excel alternatives is simulation modeling - a technology which allows creating a digital copy (double) of the analyzed system. If a standard model implies that we should show all the simulated connections as mathematical formulae, but in a simulation model we set the state of the system and its separate elements and how they should act.

NFP specialists have developed a simulation model of the overburden transportation for one of coal quarries which belong to a big international company.

The model allows simulating the quarry activity taking into account more than 100 adjustable parameters of work.

The modeling horizon can last from a few months to several years, depending on the User tasks.

Work and stoppage are modeled regarding five kinds of machines: dump trucks, excavators, pebble crushers, conveyors и stackers. Besides that, the mechanisms of breakage monitoring and purchase management have been implemented.

The fact that different breakage types of fundamental units of equipment can affect the productivity of the whole complex is taken into account in the simulation model.

«Ased on the results of the realized experiments, we can see whether it's possible or impossible to transport the declared volume of overburden, moreover, receive a predicted rank value of the environmental liabilities of the complex and each of its extractions.

The input data menu of the model allows us to vary in a flexible way a lot of initial parameters and assess their impact on the complex productivity in general.

One of the main advantages of simulation modeling is that a user can watch online how the modeled system works and track how these or those events influence the statistics.

Moreover, right in the middle of the simulation a user can make decisions if it's needed to place in and take off particular units of equipment – in the described model the following things are envisaged: the possibility to place in the conveyors of the second line, purchase new excavators and dump trucks, and pull out particular excavators and dump trucks for standby.

The model also identifies which extraction is a bottle-neck for a complex, calculates the maximum sustainable yield of each extraction and decomposes lost productivity (for example, actual extraction yield is 37% from the maximum, lost productivity caused by emergency repairs is 20%, lost productivity while waiting for the replacement parts -4% and etc.). This information can be used during making organizational and investment decisions aimed at improving the quarry operation.

One of the most significant features of the model is that it has become possible to calculate the time when the equipment is off-line as a result of some defected elements of the complex. For example, if one of the conveyors has broken, and there're no other ways to deliver the overburden to the disposal area, as a result not only the broken conveyor, but all the rest equipment will be off-line. Such a dynamic analysis is impossible to be done by means of standard instruments, such as Excel.

The developed model clearly demonstrates expansive opportunities of the simulation modeling and its advantages in comparison to standard analytical tools. Speaking about this model, its functionality has allowed a client to reduce risks significantly by analyzing various configurations:

• The launch of the conveyors of the second line and the second overburden stacker (in the current configuration the breakage of the only overburden stacker or any conveyor leads to the complete freeze of the complex.
• There is a choice of the optimal policy on the spare part purchase («when required», «as per schedule» or «the required level maintenance»).