Section 3 - Purification

Question 1

Draw a purification system

Answer 1

(page 25, figure 10)

Question 2

What is the purification aim?

Answer 2

Specialised process of removing fine branny fragments from the graded semolina and middlings stocks

Question 3

What is the basic principle of purification

Answer 3

passing the stock down a vibrating sieve through which currents of air are drawn upwards

Question 4

What is a purifier made up of

Answer 4

2 side-by-side longitudinal, slightly sloped sieves above separate receiving hoppers
Each sieve has 2-3 super-imposed screening decks
Longitudinal exhaust chamber above each sieve divided into 4 components along its length
Exhaust port to each compartment can be adjusted to regulate amount of air drawn

Question 5

How does separation happen in a purifier

Answer 5

Reciprocating action and upward moving air stratify the stocks, floating coarse stocks and heavy bran over the sieve, and lifting beeswing and other light bran. Light particles pass out of the machine with air to dust collector
Purified throughs fall into hoppe beneath
Collecting worm or shaker conveyor is arranged so throughs are spouted off separately and passed to appropriate rolls
Bran is lifted by air and spouted off separately for further treatment

Question 6

Can germ particles be removed by pruification?

Answer 6

No, unless they have pieces of bran attached

Question 7

In modern purifiers what are the separations made by

Answer 7

Sifting, shaking, gravity and aspiration

Question 8

What are the 3 elements that purification separated stock into

Answer 8

Pure endosperm to be fed to reduction rolls free of bran
Composite particles of endosperm and bran to be broken down further on scratch rolls
Particles of poorer quality that are sent to break system or direct to wheatfeed

Question 9

What conditions must be followed for purifiers to work at max efficiency

Answer 9

Stock must be graded and thoroughly dusted before purification
Sieve covers have a range of meshes appropriate to the feed
Stock must cover the sieve evenly and completely
Correct ratio must be maintained between horizontal and vertical movement of the sieve
Air pressure differential must be uniform within each aspiration section

Question 10

What are the sieve widths in europe?

Answer 10

30.5-45.7cm

Question 11

What are the sieve widths in the UK

Answer 11

38.1-45.7cm

Question 12

What does the number of double sieve machine required depend on

Answer 12

The size of the plant
The wheat being milled
Complexity of the flow sheet

Question 13

How many purifiers would a 200 tonnes/day plant require?

Answer 13

6

Question 14

Where do most purifier throughs go to

Answer 14

Reduction rolls

Question 15

Where do bran particles from a purifier go

Answer 15

Disposed as a co-product

Question 16

Where are pieces of endosperm with adhering bran sent to after purifiers

Answer 16

Scratch rolls

Question 17

Do reduction rolls work better on uniform particle sizes or a mixture?

Answer 17

Uniform

Question 18

What are the 2 advantages of grading stocks for purification?

Answer 18

The purifiers work better on graded stocks
The pure endosperm that emerges is already graded into stock sufficiently uniform in particle size to allow the rollermills to do good work

Question 19

Where may purifierless mills be used

Answer 19

Only soft wheats are milled for biscuits and other speciality flours

Question 20

Where is a purifierless mill not advisable?

Answer 20

Where a high percentage of top patent flour is required
Where semolina is required as a separate product