A new mechanistic model for vertical spindle mills (VSM) has been developed by Julius Kruttschnitt Mineral Research Centre (JKMRC) at the University of Queensland. Unlike the previous work in the literature, which treats the VSM as a "black box", the present work incorporates two sets of variables in the model: (1) the coal specific property, and (2) the machine specific variables. The VSM model is presented in two parts/papers. The first part presents the sub-models for comminution and classification in the VSM. The second part describes the integration of the sub-models to simulate industrial scale E-Mill, MPS and CKP mills. The sub-models include mill power prediction, size specific energy calculation, size dependent breakage function, product size distribution estimation, elutriation classification and gas cyclone classification. The coal breakage property was measured with a JKFBC grinding device and modelled using a size-dependent breakage function. The machine specific variables include mill geometry, air classifier geometry, coal feed rate, primary air flow rate, air temperature, air pressure, grinding table rotational speed, mill spider hydraulic load and mill power draw. These variables are incorporated in the comminution and classification functions based on physical principles. (C) 2014 Elsevier Ltd. All rights reserved.