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

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

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!