21.03.2013 Views

a study on fine grinding process in jet mill - ePrints@USM

a study on fine grinding process in jet mill - ePrints@USM

a study on fine grinding process in jet mill - ePrints@USM

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Mechanochemical effect normally takes place when batch <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> is carried out for<br />

l<strong>on</strong>ger <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> period <strong>in</strong> high <strong>in</strong>tensity <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s (Kanno, 1985; G<strong>on</strong>zalez et. al.,<br />

2000). Jet <strong>mill</strong> is a c<strong>on</strong>t<strong>in</strong>uous type <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong> with <strong>in</strong>ternal classificati<strong>on</strong> which means<br />

size reducti<strong>on</strong> and classificati<strong>on</strong> will take place simultaneously. In <strong>jet</strong> <strong>mill</strong> the retenti<strong>on</strong><br />

time of particles <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber is very short because the particles will be<br />

classified out as so<strong>on</strong> as it reaches the desired size.<br />

Not much attenti<strong>on</strong> is given <strong>on</strong> the mechanochemical effect <strong>in</strong> c<strong>on</strong>t<strong>in</strong>uous <strong>gr<strong>in</strong>d<strong>in</strong>g</strong><br />

<strong>process</strong> especially when the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and classificati<strong>on</strong> <strong>process</strong> occur simultaneously<br />

<strong>in</strong> short <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> period. Although <strong>in</strong> <strong>jet</strong> <strong>mill</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> and classificati<strong>on</strong> <strong>process</strong><br />

occurs simultaneously and the retenti<strong>on</strong> time of the particles is believed to be very<br />

short, but the energy <strong>in</strong>tensity delivered to the particle is huge which may result <strong>in</strong><br />

mechanochemical effect <strong>in</strong> short <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> period. Chung et. al. (2003) and Choi et. al.<br />

(2004) reported that significant structural changes did not take place when<br />

ursodeoxycholic acid was ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong> where the reducti<strong>on</strong> of crystall<strong>in</strong>ity was <strong>on</strong>ly<br />

2%. C<strong>on</strong>tradict<strong>in</strong>g to Chung et. al. (2003) and Choi et. al. (2004), Juhacz and Opoczky<br />

(1990) reported that cement cl<strong>in</strong>ker, dolomite, limest<strong>on</strong>e and silica ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong><br />

showed the highest reactivity due to the feed which suffered deep-seated changes <strong>in</strong><br />

its crystal structure <strong>in</strong>duced by high velocity impact.<br />

1.2 Problem Statement<br />

Besides size reducti<strong>on</strong>, <strong>f<strong>in</strong>e</strong> <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>process</strong> <strong>in</strong>duces mechanochemical effect that<br />

changes physicochemical characteristics of particles <strong>in</strong> energy <strong>in</strong>tensive <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> <strong>mill</strong>s<br />

(Venkataraman and Narayanan, 1998). The amount of energy delivered to the particles<br />

and breakage mechanism c<strong>on</strong>trols the <strong>in</strong>tensity of mechanochemical effect of particles<br />

ground <strong>in</strong> <strong>jet</strong> <strong>mill</strong>. These two factors are c<strong>on</strong>trolled by the operat<strong>in</strong>g parameters and<br />

<strong>in</strong>side <strong>mill</strong> c<strong>on</strong>diti<strong>on</strong>s of the <strong>jet</strong> <strong>mill</strong>. The <strong>in</strong>side <strong>mill</strong> c<strong>on</strong>diti<strong>on</strong>s such as <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber<br />

pressure and amount of holdup <strong>in</strong> the <strong>gr<strong>in</strong>d<strong>in</strong>g</strong> chamber which will <strong>in</strong>fluence the<br />

6

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!