SCREENING TECHNOLOGY
HAZEMAG and the HRS roller screen
HAZEMAG offers a unique screening solution in the form of its scalping device , a roller screen design which mainly competes in the market with products such as large vibrating grizzly screens and conventional wobblers . One advantage is that the HRS has cleaning scrapers underneath the rotating shafts which help in handling sticky material , which grizzlies often cannot cope with and which frequently show clogging . In addition , the HRS screens reduce the amount of fishy ( flaky and elongated ) material passing the screen . Another difference is in the vibration and dynamic loads on the structure . The roller screen is not vibrating at all . This , in combination with being able to handle difficult material makes the advantage of the HRS even higher according to HAZEMAG . In terms of TCO the company says the HRS is very attractive when it comes to investment cost , power consumption and maintenance cost .
The separation surface is formed by rotating disc-fitted rollers , which transport the material , circulate and loosen it . The separation of the fines is effected in the gap between the individual rollers whilst the coarse material is transported via the screen into the overflow . The polygonal shape of the discs supports the material conveyance . Erik Bach , HAZEMAG Managing Director told
IM : “ Furthermore the downstream crusher whether that is an impactor or sizer or other design is relieved through a roller screen which has removed finer material eg < 100 mm so obviously results in reduced wear , a reduced energy consumption and – at best – in being able to use a smaller crusher with less installed power . In general , roller screens entail reduced energy and operational costs and / or an increased operational reliability . Transporting the material is effected horizontally so that the subsequent crusher is fed gently and constantly . The compact design , resulting from the horizontal material flow , as well as a multitude of options permit the application in many ranges – above as well as underground . The HRS is capable of up to 3,000 t / h which has already been achieved at several projects . This is definitely not the limit .”
Stefan Ernsting , HAZEMAG Team Leader added : “ It is also worth remembering that the
HRS is modular so you could in theory use 30 or 40 shafts for very high throughput . The design can be single or multi deck ie stepped on different levels , with which you achieve cleaning in different stages for greater screening efficiency .”
One additional variant is the socalled VARIOwobbler where the gap setting between the individual shafts and thus the separation is adjustable at the push of a button and without any tools . This leads to a distinct extension of the field of application and a solid increase of flexibility by being able to very quickly respond to changing requirements where the nature of the ore changes from summer to winter or where there is ore variability within the same pit . The distance between the individual shafts is adjusted by a mechanic-hydraulic system . In the front part of the machine the roller distance is fixed in most cases at the smallest required gap , whilst the rear part is correspondingly adjustable .
Most HRS installations have been in fixed crushing stations , whether primary or secondary . Some have been put in as mobile units within the open pit , and there have also been some underground applications .
On mining specifically , Bach said it has had a lot of success with softer materials such as limestone quarried for cement but a big focus now is to increase the use of the HRS in harder materials where it is just as capable . He commented : “ The HRS has been used to some extent in mining for specific applications such as at a gold mine in PNG , apatite ore processing in Russia , plus some coal and salt mining applications , including underground . In coal , they are removing fines in mines in Indonesia , Russia and South Africa and others . The PNG example was chosen specifically for its ability to handle clay-rich gold ore . They weren ’ t getting the required thoughputs for the crusher so the HRS now cleans out the material prior to crushing .”
Bach said the HRS has already been proven in harder rock both in tests and through several project examples , one of which being Hammerfall Dolomit ( see right ). HAZEMAG has also developed over time special discs with hardened surfaces as well as upgrading shafts to cope with increasing hardness and abrasivity .
The HAZEMAG roller screen ( HRS ) has further potential in mining due to its unique design & capabilities
The HRS was part of a solution for Hammerfall Dolomitt A / S in Røsvik , Norway , for the delivery and setting up of a processing plant with a feeding capacity of 600 t / h . Top priority is given the minimisation of the fines ahead of secondary crushing . A final grain size as cubic as possible is also a requirement . The processing plant includes the field-tested HAZEMAG chain conveyor HCF 1500 as feeding unit for the primary crusher , the HAZEMAG centre sizer HCS 1020 , a HAZEMAG three stage HRS and the HAZEMAG centre sizer HCS 0820 as secondary crusher . In addition a stockpile belt conveyor with belt weigher and a dedusting plant were part of the scope of supply .
The dolomite which is extracted underground by means of blasting has cubical feed sizes of up to 1,200 mm and is conveyed by truck to the 30 m 3 feed hopper . The chain conveyor HCF 1500 with a length of 24.5 m conveys the material to the primary crusher HCS 1020 . The crushed fraction with maximum sizes of 250 mm is transported via two belt conveyors to the secondary crushing plant . For the protection against metallic foreign bodies the second conveyor has permanent magnets and a metal detector .
The HRS is in front of the secondary crusher . The first and second screening stage separates the < 16 mm fraction from the material flow . This fraction gets to a reversing belt conveyor which permits the material to be conveyed to a stockpile during the winter months or – in summer – to the end product . The opening width of the third screening stage is 70 mm . Due to this pre-screening the feed quantity and the size of the secondary sizer were reduced . performance while reducing maintenance and attendant costs . In some applications , run times without periodic cleaning cycles have extended beyond 18 months . And while initial cost is higher than wedge wire , due to its significantly lower maintenance costs , the G-Vault has been shown to produce a favourable return on investment ( ROI ) for mine management . Jeremy Rozelle , Senior Metallurgist at OceanaGold ’ s Haile Gold Mine explains his experience with the Derrick G-Vault screens . “ After the first checkup at six weeks , the determination was made to replace all interstage screens at our operation with the Derrick G-Vault baskets . This decision was based mainly on performance . During the first six weeks of the trial , neither basket had to be pulled by operations for any reason . Performance in the circuit went up , while also allowing operators to focus on other tasks . The wear on the screen panels tested was minimal to none over the trial .”
48 International Mining | OCTOBER 2020