Dryer

Dryer – is an equipment used in removing moisture or solvents from a wet material or product.

Hygroscopic Substance – a substance that can contained bound moisture and is variable in moisture content which they posses at different times.

Weight of Moisture – amount of moisture present in the product at the start or at the end of the drying operation.

Bone Dry Weight – it is the final constant weight reached by a hygroscopic material when it is completely dried out. It is the weight of the product without the presence of moisture.

Gross Weight – it is the sum of the bone-dry weight of the product and the weight of moisture.

Moisture Content – it is the amount of moisture expressed as a percentage of the gross weight or the bone dry weight of the product.

A) Wet Basis – is the moisture content of the product in percent of the gross weight.

B) Dry Basis 0r Regain – it is the moisture content of the product in percent of the bone dry weight.

Continuous Drying – is that type of drying operation in which the material to be dried is fed to and discharge from the dryer continuously.

Batch Drying – is that type of drying operation in which the material to be dried is done in batches at definite interval of time.

CLASSIFICATION OF DRYERS

1. Direct Dryers – conduction heat transfer

2. Indirect Dryers – convection heat transfer

3. Infra-red Dryers – radiation heat transfer

PRODUCT SYMBOLS

1. GW = BDW + M

2. Xm = [M/GW] x 100% (wet basis)

3. Xm = [M/BDW] x 100% (dry basis or regain)

where:
GW – gross weight

BDW – bone dry weight

M – weight of moisture

Xm – moisture content

HEAT REQUIREMENT BY THE PRODUCT

Q = Q1 + Q2 + Q3 + Q4

Q1 = (BDW)Cp(tB – tA) kg/hr

Q2 = MBCpw(tB – tA) kg/hr

Q2 = MB(hfB – hfA) kg/hr

Q3 = (MA – MB)(hvB – hfA) kg/hr = MR(hvB – hfA)

Q4 = heat loss

Q1 – sensible heat of product, KJ/hr

Q2 – sensible heat of moisture remaining in the product, KJ/hr

Q3 – heat required to evaporate and superheat moisture removed from

the product in KJ/hr

Q4 – heat losses, KJ/hr

A,B – conditions at the start or at the end of drying operation

t – temperature in C

hf – enthalpy of water at saturated liquid, KJ/kg

hv – enthalpy of vapor, KJ/kg

Cp – specific heat of the product, KJ/kg-C or KJkg-K

Cpw – specific heat of water, KJ/kg-C or KJ/kg-K

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