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
1. GW = BDW + M
2. Xm = [M/GW] x 100% (wet basis)
3. Xm = [M/BDW] x 100% (dry basis or regain)
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