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M e a s u r e m e n t of D u s t - R e l e a s e P o t e n t i a l of C o t t o n ROY V. BAKER U.S. Department of Agriculture, Agricultural Research Service, Southern Plains Cotton Research Laboratory, Lubbock, TX 79401
Measurable quantities of cotton dust were extracted from small cotton l i n t samples by means of high-velocity air jets. Dust removed in this manner was sized by a wire-mesh screen that restric ted the flow of particles larger than the openings in the screen. Particles smaller than the openings in the screen were collected for gravimetric analysis. The weight of dust extracted by this technique rep resented an estimate of the dust-release potential of raw cotton l i n t . Equipment was designed, constructed, and evaluated for extracting dust particles smaller than 100, 50, and 17 micrometers from 20-gram, ginned lint-cotton samples. The development of experimental equipment and the operating procedures for preparing lint samples and for extracting, sizing, and collect ing particulates are discussed. Representative dust level measurements for three cotton cultivars and for three particle sizes are presented. R e s p i r a b l e dust escaping from c o t t o n during processing becomes airborne and lowers the q u a l i t y o f the working atmosphere i n a t e x t i l e m i l l . This problem i s c u r r e n t l y a source o f c o n s i d erable concern i n the t e x t i l e i n d u s t r y . The amount of dust escapi n g from cotton during p r o c e s s i n g i s i n f l u e n c e d by many f a c t o r s , i n c l u d i n g the d u s t - r e l e a s e p o t e n t i a l o f the cotton being processed (1). Experimental-card-room t e s t i n g procedures have been developed i n recent years f o r determining the d u s t - r e l e a s e p o t e n t i a l o f v a r i o u s types o f cotton (2_). These procedures, although r e l i a b l e , are time consuming and r e q u i r e r e l a t i v e l y l a r g e amounts of c o t t o n f o r t e s t i n g . A method by which dust-release p o t e n t i a l could be determined more r a p i d l y and w i t h only s m a l l cotton samples would be extremely u s e f u l t o the research community and might b e n e f i t t e x t i l e m i l l s i n s e l e c t i n g c o t t o n f o r t h e i r manufacturing needs.
This chapter not subject to U.S. copyright. Published 1982 American Chemical Society.
Montalvo; Cotton Dust ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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DUST
Background Anderson and Baker (3) demonstrated the f e a s i b i l i t y of removing measurable q u a n t i t i e s of cotton dust from s m a l l (10-g) l i n t samples by means of h i g h - v e l o c i t y a i r j e t s . Dust removed by t h i s technique was conveyed by a i r through a s i z i n g screen cont a i n i n g 100- x 100-micrometer openings. Dust s m a l l e r than the openings i n the screen was c o l l e c t e d on a g l a s s - f i b e r f i l t e r f o r g r a v i m e t r i c a n a l y s i s . These p r i n c i p l e s were used to develop a prototype cotton-dust analyzer f o r measuring the d u s t - r e l e a s e p o t e n t i a l of l i n t cotton. (A). The cotton-dust analyzer was used to measure the d u s t - r e l e a s e p o t e n t i a l of cotton that had been subjected to v a r i o u s h a r v e s t i n g and c l e a n i n g treatments. R e s u l t s of the measurements were compared w i t h corresponding measurements w i t h a v e r t i c a l e l u t r i a t o r i n an experimental card room. G e n e r a l l y , the cotton-dust analyzer detected s i g n i f i c a n t d i f f e r e n c e s i n the d u s t - r e l e a s e p o t e n t i a l of l i n t , and the d i f f e r e n c e s were s i m i l a r to the d i f f e r e n c e s i n card room dust l e v e l s as measured by the v e r t i c a l e l u t r i a t o r . However, l i n e a r c o r r e l a t i o n a n a l y s i s of the two measurement techniaues produced a r e l a t i v e l y low c o e f f i c i e n t of determination (r2=69%). These s t u d i e s i n d i c a t e d that the cotton-dust a n a l y z e r was a p o t e n t i a l l y u s e f u l t o o l f o r studying the e f f e c t s of v a r i o u s mecha n i c a l treatments on the d u s t - r e l e a s e p o t e n t i a l of a given cotton. However, whether the cotton-dust a n a l y z e r would a c c u r a t e l y measure the d u s t - r e l e a s e p o t e n t i a l of cotton from a broad range of growth and production c o n d i t i o n s was not determined. The prototype cotton-dust analyzer used i n the i n i t i a l study was designed to measure dust s m a l l e r than 100 ]im, whereas a v e r t i c a l e l u t r i a t o r i n a card room measures only the dust that i s s m a l l e r than about 15 ym. Differences i n p a r t i c l e size d i s t r i b u t i o n s of dust from v a r i o u s types of cotton would l i k e l y a f f e c t the r e l a t i o n s h i p between the two dust measurements. Therefore, we deemed i t necessary to i n v e s t i g a t e the use of s i z i n g screens w i t h s m a l l e r openings; i . e . , openings whose s i z e approximated the maximum s i z e of p a r t i c l e s c o l l e c t e d by a v e r t i c a l e l u t r i a t o r . The purpose of t h i s report i s to d e s c r i b e a d d i t i o n a l m o d i f i c a t i o n s to the cotton-dust analyzer and to present data on the performance of the machine when 17-, 50-, and 100-ym s i z i n g screens were used. Machine M o d i f i c a t i o n s A new model of the cotton-dust analyzer was constructed to overcome some of the shortcomings of the prototype. I t was more compact and e a s i e r to operate than the o r i g i n a l machine. The s i z i n g - s c r e e n arrangement i n the new model was more a c c e s s i b l e than i n the o r i g i n a l machine t o f a c i l i t a t e the e v a l u a t i o n of v a r i o u s screen s i z e s . I t was a l s o equipped w i t h an a i r r e g u l a t o r to maintain a constant a i r pressure on the spray bar f o r improved airflow characteristics. Also, a high-efficiency particulate a i r
Montalvo; Cotton Dust ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
5.
BAKER
Measurement of Dust-Release Potential
55
f i l t e r (HEPA) was used f o r improved f i l t e r i n g of the a i r introduced i n t o the a n a l y z e r by the high-pressure f a n . F i g u r e s 1 and 2 i l l u s t r a t e the e s s e n t i a l components of the new model of the cotton-dust a n a l y z e r . The a i r j e t spray bar c o n s i s t e d of 6.4-mm copper t u b i n g t h a t contained 17 openings of 1.6-mm diameter spaced at 9.5 mm along i t s a x i s . The spray bar was p o s i t i o n e d 2.2 cm above the l i n t b a t t and was moved back and f o r t h by a s m a l l r o l l e r chain powered by an e l e c t r i c r e v e r s i n g d r i v e . T h i s arrangement produced a spray bar movement across the e n t i r e b a t t surface once every 8 s. A i r from an 827-kPa c o n v e n t i o n a l compressed-air source was p r e c o n d i t i o n e d before d e l i v e r y to the spray bar by a combination p r e f i l t e r / w a t e r trap and a secondary a i r f i l t e r r a t e d at 0.01 micrometer. An a d j u s t a b l e a i r r e g u l a t o r i n the compressed-air l i n e maintained a constant pressure on the spray bar. L i n t specimens were contained between two wire-mesh screens. The top screen was 10 x 10 mesh (per cm) and h e l d l i n t b a t t s i n p l a c e during p r o c e s s i n g . The bottom screen served as a s i z i n g screen by c o l l e c t i n g p a r t i c l e s l a r g e r than the screen's openings and a l l o w i n g s m a l l e r p a r t i c l e s to move downward to the g l a s s - f i b e r c o l l e c t i n g f i l t e r . Another 10 x 10 mesh screen (per cm) below the s i z i n g screen was used to support the g l a s s - f i b e r f i l t e r . A high-pressure fan d i r e c t l y under the g l a s s - f i b e r f i l t e r provided s u f f i c i e n t a i r f l o w to convey d i s l o d g e d dust from the l i n t b a t t s through the s i z i n g screen to the c o l l e c t i o n f i l t e r . Room a i r , induced i n t o the top of the cotton-dust a n a l y z e r by the f a n , passed through the HEPA f i l t e r , l i n t b a t t , screens, and c o l l e c t i o n f i l t e r before e n t e r i n g the fan. The a i r was then exhausted back to the room through a port near the botton of the machine enclosure. The fan had an o p e r a t i n g c a p a c i t y of 0.03 m3/s a g a i n s t a s t a t i c pressure of 5 kPa. An aluminum enclosure housed the working components of the cotton-dust a n a l y z e r . The upper s e c t i o n of the e n c l o s u r e , which was hinged to the lower s e c t i o n , contained the HEPA f i l t e r , the spray bar assembly, and the t o p , hold-down screen f o r the l i n t b a t t . The botton s e c t i o n housed the s i z i n g screen, f i l t e r support, fan, and the e l e c t r i c a l and pneumatic c o n t r o l s . The e n t i r e enclosure was 60 cm wide, 46 cm deep, and 72 cm t a l l . F i g u r e 3 i s a schematic of the e l e c t r i c a l c o n t r o l system. The e l e c t r i c a l system provides power f o r the o p e r a t i o n of the fan motor, the gear motor and magnetic c l u t c h e s i n the r e v e r s i n g drive, the timer motor, and the a i r s o l e n o i d v a l v e . The manually i n i t i ated timer was a d j u s t a b l e f o r p r o c e s s i n g times up to 15 min. Operating
Procedures
C o l l e c t i o n F i l t e r s . The cotton-dust a n a l y z e r r e q u i r e s 20.3cm x 25.4-cm g l a s s - f i b e r f i l t e r s f o r c o l l e c t i o n of dust p a r t i c l e s . These f i l t e r s are b i n d e r - f r e e and s p e c i a l l y designed f o r g r a v i m e t r i c a n a l y s i s of a i r p o l l u t a n t s . The f i l t e r s are r a t e d at 99.9%
Montalvo; Cotton Dust ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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DUST
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Figure 1. Schematic of cotton dust analyzer. 1, high efficiency particulate air filter; 2, reversing drive; 3, chain drive; 4, spray bar; 5, top screen; 6, lint batt; 7, sizing screen; 8, glassfiberfilter;9, high-pressure fan; 10, pressure gages; 11, compressed-air entrance; 12, prefilter/watertrap; 13, air-pressure regulator; 14, solenoid valve; 15, secondary airfilter;16, hose to spray bar.
Montalvo; Cotton Dust ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
5.
BAKER
Figure 2.
Measurement of Dust-Release Potential
57
Cotton dust analyzer showing top holding screen, sizing screen, and front control panel.
Montalvo; Cotton Dust ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
58
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DUST
LI -I20VAC10 AMP
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I20VAC/90VDC
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Reversing-Drive Latching
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SPRAY BAR LIMIT SWITCHES
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