It has been shown that mining processes, especially the comminution processes (grinding
and crushing) are some of the biggest consumers of electricity in the world where energy
management application would have a significant impact on the sustainability of both the
energy supply and demand sides. However, very little research has been done in this area.
Energy efficiency management in the mining industry can be done at four levels, namely
the technology level, equipment level, operational level and performance level. In this work,
operation energy management is considered for crushing circuits with the aim of minimizing
the total energy cost by accounting for the time-of-use (TOU) electricity tariff. The work is
limited to three types of crushing machines, namely the jaw crusher, vertical shaft impact
(VSI) crusher and high-pressure grinding rolls (HPGR) crusher. Firstly, the energy model
of each crusher is developed and expressed in terms of its control variables. Secondly, an
optimal energy control model is formulated, where both physical and technical/operational
constraints of the crushing process are taken into account. Thirdly, a case study is done in
order to evaluate the effectiveness of the developed models. Lastly, experimental results of
the performance model of the jaw crusher are presented.
Simulation results show that when TOU electricity tariff is applied there is potential for
achieving energy cost saving in all types of crushing processes, depending on the size of
storage systems and plant production requirement. However, achieving energy saving is not
always evident. When the throughput rate and product size distribution of the crusher are
both controlled by a unique variable, as in the case of the jaw crusher, it is shown that no
significant energy saving can be achieved. This is due to the trade-off between the throughput
rate, product size distribution and specific energy consumption of the jaw crushing machine.
Increasing the closed-side setting (unique control variable) of the jaw crusher with the aim
to decrease the specific energy consumption will result in coarse particles in the product.
However, there is a great opportunity for energy saving through optimal switching control
due to the high no-load power consumption of the jaw crusher. On the other hand, when the
throughput rate and product size distribution are controlled by more than one variable, as
in the case of the VSI and HPGR crushers, more energy saving can be achieved in presence
of varying feed size. In the VSI crushing process, for instance, the product size distribution
is controlled by the rotor speed while the throughput rate is controlled by the rotor feed
throttle. Hence, energy consumption reduction is achieved through any small decrease of the
crusher rotor speed whenever the feed size decreases. The same applies to the HPGR crushing
processes where the rolls operating pressure is used to control the product size distribution
and the throughput rate is controlled by the rotor speed.
The analysis of the performance model of the jaw crusher reveals that although the Bond
energy model presents larger prediction error compared to the throughput and product quality
index, this can still be used as performance indicator in jaw crushing energy optimization,
as it shows a strong linear correlation with experimental results. However, for actual energy
consumption and energy saving calculation, a field test should be conducted.
Daar is aangetoon dat mynbouprosesse, veral die vergruisingproses (maal en breek) een van
die grootste verbruikers van energie in die wêreld is, waar die toepassing van energiebestuur’
n beduidende impak sal hê op die volhoubaarheid van sowel die engergievoorsiening- as
aanvraagkant. Daar is egter nog min navorsing op hierdie gebied gedoen. Die bestuur
van energie-effektiwiteit in die mynbou-industrie kan op vier vlakke plaasvind, naamlik die
vlakke van tegniek, toerusting, werkverrigting en prestasie. In hierdie werk word werkverrigtingbestuur
oorweeg vir vergruisingkringlope, met die doel om die totale energiekoste
te minimeer deur die tyd-van-gebruik-elektrisiteitstarief in berekening te bring. Die werk
word beperk tot drie tipes vergruisingsmasjiene, naamlik die bekvergruiser, vertikaleskagimpakvergruiser
(VSI) en parallele hoëdruk- breekrollervergruiser (HDBR). Eerstens word die
energiemodel van elke vergruiser ontwikkel en uitgedruk volgens die kontrole-veranderlikes
daarvan. Tweedens word ’n optimale energiekontrolemodel geformuleer, waarin sowel die
fisiese as tegniese/operasionele beperkings van die proses in ag geneem word. Derdens word
’n gevallestudie gedoen om die effektiwiteit van die modelle wat ontwikkel is, te evalueer.
Laastens word die eksperimentele resultate van die werkverrigtingmodel van die bekvergruiser
aangebied.
Simulasies toon aan dat wannneer die tyd-van-gebruik-elektrisiteitstarief toegepas word, energiekostebesparings
potensieel in alle tipes vergruisingsprosesse bereik kan word, afhangend
van die grootte van die bergingstelsels en aanlegproduksievereiste. Die bereiking van energiebesparing
is nogtans nie altyd duidelik nie. Wanneer die toevoertempo en produkgrootteverspreiding
van die vergruiser albei deur een veranderlike beheer word, soos in die geval van
die bekvergruiser, word aangetoon dat geen beduidende energiebesparing bereik kan word nie.
Dit is die gevolg van die ruil tusen die toevoertempo, produkgrootteverspreiding en spesifieke
energieverbruik van die bekvergruisermasjien. Om die sluitsystelling (kontrole-veranderlike)
van die bekvergruiser te verhoog met die doel om die spesifieke engergieverbruik te verminder,
sal lei tot growwe deeltjies in die produk. Daar is nogtans goeie geleentheid vir energiebesparing
deur optimale skakelkontrole omrede die hoë geenlading-kragverbruik van die bekvergruiser.
Aan die ander kant, as die toevoertempo en produkgrootteverspreiding deur meer as
een veranderlike beheer word, soos by die VSI- en HDBR-vergruiser, kan groter energiebesparing
bereik word saam met veranderlike toevoergrootte. In die VSI-vergruisingproses
word die produkgrootteverspreiding byvoorbeeld deur die rotorspoed beheer, terwyl die toevoertempo
deur die rotortoevoerversneller beheer word. ’n Afname in energieverbruik word
gevolglik verkry deur enige klein afname in die vergruiserrotorspoed wanneer die toevoergrootte
afneem. Dieselfde geld in die HDBR-vergruisingprosesse, waar die operasionele druk
van die rollers gebruik word om die produkgrootteverspreiding te beheer en die toevoertempo
deur die rotorspoed beheer word.
Analise van die werkverrigtingmodel van die bekvergruiser toon dat alhoewel die Bondenergiemodel
’n groot voorspelfout lewer, dit steeds gebruik kan word as ’n aanduiding van
werkverrigting in energie-optimering vir die bekvergruiser, aangesien dit sterk lineêre korrelasie
toon met eksperimentele resultate. Nietemin sal veldwerktoetse uitgevoer moet word
om die werklike energieverbruik en energiebesparing te bepaal.
