Читайте также:
|
1. The equipment for starch production is the same as for flour milling. 2. Usually in starch production the flash type of dryer is used.
3. In wet milling, grains are first steeped in warm water and then dry-cleaned.
4. The operation principle of centrifuges and hydrocyclones is based on gravitational force. 5. The dried starch does not contain water.
Exercise 6. Match the starch production stages with their objectives. Make up the sentences adding words if necessary.
Steeping 2. Cleaning
Degerminating 4. Washing
Milling
a) to remove the germ
b) to get the finely ground flour c) to soften the grain
d) to remove any impurities
e) to refine the starch milk
Exercise 7. Check your grammar.
Fill in the gaps with the necessary prepositions.
1. Modern mills are usually equipped ___ control units. 2. The grains are steeped ___ warm water.
3. The steeping is carried ___ ___ a continuous counter-current process. 4. ___ the cleaning the corn is divided ___ portions ___ weight.
5. The germs are separated ___ the slurry ___ hydrocyclones. 6. The grain is ground ___ different mills.
7. There is a need of fresh water ___ the last stage.
8. The cleaning is normally done ___ wet-processing. 9. The starch is screened ___ ___ the fibre washing. 10. The germs are washed ___ a three-stage screen.
Part 2. Centrifuges and hydrocyclones. Exercise 1. Read and translate the following words without a dictionary.
Accelerate - acceleration, pneumatically, transport - transportation, position, centrifuge – centrifugal, hydrocyclone, limit – limitation, balance, technology – technological, separate – separation, concentrate – concentration, adequate, filtrate.
Reading. Read the text and say what physical principles are in the basis of the centrifuges and hydrocyclones operation and what are the similarities and the differences between centrifuges and hydrocyclones.
The centrifuge obtains its gravitational force by spinning the bowl and the output concentration is controlled through a balance between feed and output. The feed is adjusted so that an adequate concentration in the overflow is obtained. The number and capacity of nozzles adjust the output. Output and wash water is particularly subject to acceleration, thereby limiting the overall capacity of the centrifuge.
A disc stack forming narrow channels, shortening the distance particles have to travel in a free liquid space, divides the inner bowl. The hydrocyclone has no moving parts and the separation is totally dependent on the pressure difference over the cyclone. The technological development and quality demands have forced centrifuges to give way for hydrocyclones in corn starch refining, but centrifuges still hold a defensive position in primary separation and gluten concentration.
The purified starch milk is via an overhead tank discharged to a peeler centrifuge for dewatering. The peeler filtrate is recycled to the primary separator or to the starch refining. The dewatered starch is batch-wise peeled off and discharged by gravity to the moist starch hopper.
From the moist starch hopper the starch is fed by a metering screw conveyor into a flash dryer and dried in hot air. The inlet air temperature is moderate. The dried starch is pneumatically transported to a starch silo ready for screening and bagging. The moisture of cornstarch after drying is normally 12-13 %.
Before delivery the starch is screened on a fine sieve in order to remove any scale formed in screw conveyors etc. A coarse screen with larger openings may protect the fine screen.
Exercise 2. Translate the following word-combinations.
A balance between feed and output, the inner bowl, to be recycled to the primary separator, the technological development and quality demands, a metering screw conveyor, the inlet air temperature, the number and capacity of nozzles.
Exercise 3. Complete each sentence with a word or phrase from the box. Use each word or phrase only once.
centrifuge flash dryer hydrocyclone peeler centrifuge fine sieve
1. The rapidly rotating machine designed to separate liquids from solids is called the ___. 2. The ___ has no moving parts and it depends only on the pressure difference over it.
3. Before delivery the starch is screened on a ___. 4. Usually the starch is dried in the ___.
5. Dewatering of the purified starch milk is done in ___.
Exercise 4. There are some more operations in starch production. Put them in the right order. a) germ separation
b) steeping
c) germ drying
d) starch dewatering e) fibre drying
f) cleaning
104 
g) starch drying
h) fine grinding and screening i) fibre drying
j) starch refining
k) crude oil extraction
l) steepwater evaporation
m) starch and fibre primary separation n) fibre concentration and dewatering
Exercise 5. Match the verbs with their meanings.
1) to discharge 2) to peel
3) to dry 4) to meter 5) to feed
a) to put into practice b) to unload
c) to make free from moisture d) to streep the skin
e) to measure by recording instrument
6) to carry out 7) to screen on 8) to dewater 9) to spin
f) to supply a material to the machine g) to turn round quickly
h) to sieve
i) to make free from water
10)to refine j) to make free from detect or impurities
Exercise 6. Word building.
Explain the meaning of the following complex adjectives as in the pattern or in your own way.
Pattern. A right-angled figure is a figure with right angles.
An air-operated device, a five-sided building, an oval-shaped body, a parallel-sided figure, a three-legged chair, a dry-cleaned grain, a wet-milled corn, a steam-heated radiator, a gas-fired oven, a starch-derived sweetener.
Exercise 7. Sentence building.
Join each of the following pairs of sentences in two ways with so or because.
1. The great number of hydrocyclone refining steps may increase water savings. Multistage hydrocyclones are used.
2. The stone grinding mills cut and tear the grain.
They have found a wide application in modern milling industry. 3. Each reduction roll increases flour output.
There are usually four or five reduction rolls in the flour milling process. 4. Very fine sieves remove any impurities.
They are applied at the last processing stage. 5. Hot water softens the grain.
The corn is soaked in hot water for up to fifty hours.
Дата добавления: 2015-11-16; просмотров: 79 | Нарушение авторских прав
| <== предыдущая страница | | | следующая страница ==> |
| Part 1. Essential stages in starch production. | | | Exercise 8. Translate in the written form. |