Category:Models

Models

This are two principal types of models in SAGMILLING.COM:

• Specific energy consumption models are used to estimate the amount of grinding energy required to grind a particular ore, and what throughput can be achieved by passing that ore through a particular set of grinding mills.
• Mill power draw models are used to estimate how much grinding energy can be generated by a particular mill geometry and charge.

History of Power Models

A systematic relationship between energy consumed in grinding and size reduction was proposed by Peter von Rittinger in 1867, yielding the first Power Model and beginning of comminution as a science ^{Lynch & Rowland, 2005}. This was followed in 1885 by the theory of Friedrich Kick who proposed a much different power model. Instruments of that age did not allow accurate enough measurements to test the theories ^{Lynch & Rowland, 2005}, so the difference between the models was largely of academic interest. It was not until instruments for motor power measurement and laboratory grinding mills were standardized (late 1930's to 1940's) that attempts were made to bench-mark the theories of von Rittinger and Kick to operating grinding plants (one such attempt was Myers, Michaelson & Bond, AIME 1947. The failure of these bench-mark studies in the rod mill and ball mill size range to validate either model led to the development of a "Third Theory" by Fred Bond ^{Bond 1952}. Hukki, 1962 showed that all three theories may be special cases of a spectrum of a larger, more generalized, theory where Kick best characterized the coarsest particles (blasting), Bond the middle size ranges (rod and ball milling), and von Rittinger the finest size classes (fine and ultra-fine grinding).

Theory of Power Models

Authors such as Taggart and Bond noted several properties of common size reduction processes that allows modelling as a process of energy consumption by and ore^1,2. The underlying observations (and assumptions) of Power Models are:

• Any particle size distribution can be modelled by a single value. Generally, it is the 80% passing size that is used as being indicative of the entire size distribution.
• Particle size distributions of "normal" size reduction processes

In general, the mill power draw models are independent of the ore being processed (ore density matters, but feed and product sizes should not affect power draw if the mill is run properly). The specific energy model uses the ore grindability test results to estimate energy requirements to achieve a particular size reduction, then it calls on the mill power draw model to determine how much energy is actually available. Dividing the energy available by the specific energy consumption results in the throughput.