Poly-stream Comminution Circuits

Övrigt konferensbidrag, 2015

Comminution and classification circuits consume significant amounts of energy. Some estimates show that comminution processes accounts for around 40 % of the total energy consumed in mining operations and 1.5-1.8 % of the total national energy consumption in mining intensive countries such as South Africa, Australia and Canada (Tromans, 2008). Apart from recent market fluctuations the global trend is that the demand for metals and minerals is increasing (Norgate and Haque, 2010). At the same time the ore competence generally increases as material is mined at greater depths and the grade is usually lower. The consequence is that increased amounts of raw material need to be processed in larger and larger comminution devices. The task of reducing the energy consumption in this context seems daunting. The conventional comminution circuit is usually based on a crushing and screening process followed by a tumbling milling process. HPGR machines and other new devices have also become more common during the last 20 years. Independent of what type on units that are used in the circuits the global trend is that larger and larger comminution devices are manufactured and installed. With this outlook as a foundation we propose an alternative mindset to think about circuits; poly-stream comminution circuits. A general trend in product development is that technologies transform from mono-systems to poly-systems. In this paper the concept is described and exemplified in a case study including a comparison with a conventional SABC circuit. In poly-stream circuits the material streams after one or several parallel primary crushing stages are split into 5-20 streams by using ore sorting and classification units. Each stream handles a proportional throughput capacity and the material passes through a dedicated set of smaller comminution and classification modular units with settings optimized to target the specific properties of the material in each stream. The results of this conceptual case study suggests that smaller, instead of larger, comminution and classification units open up for modularization, higher theoretical operational availability, better plant flexibility and expansion potential. Lower mass flow streams enable the use of ore sorting with separate treatment and early rejection of gangue. It is generally also easier to achieve higher energy efficiency performance for smaller comminution, classification and separation units. There are a number of apparent challenges and problems associated with the concept. It requires new solutions for stream rerouting, sensor technology, advance control systems and advanced maintenance management systems to name a few. However, the consequent conclusion of this hypothetical concept is that perhaps the focus of research and development efforts should target material handling, sensor technology and comminution unit modularization in order to meet the challenges of future comminution circuits.