ดาวน์โหลด All Proceeding - AS Nida

Fig.1 Process Flow Diagram of Ethanol Process
The ethanol process consists of 4 major unit operations:
2.1.1. Liquefaction & Saccharification
Heat up the mash to 90 o C, liquefying the starch. And
enzymes are added to the mash to convert the starch to dextrose.
2.2.2.Fermentation
Yeast is added to the mash to ferment the sugars. During this
process, the yeast eats the sugars, and in the process produces heat,
ethanol 10%v/v and carbon dioxide.
2.2.3.Distillation
After fermentation the mash is called beer. The beer contains
approximately 10% alcohol by volume and still has many impurities.
These impurities are removed during the distillation phase until pure
alcohol with at least 95% alcohol by volume is obtained. The alcohol
moves on to dehydration. The stillage is processed into distiller grains.
2.2.4.Dehydration
The alcohol circulates through a molecular sieve to capture
the last bit of water. At the end of this process, the ethanol obtains at
least 99.5% v/v.
2.2.5.Storage
Finally, the ethanol is pumped into storage tanks. It is then
ready for shipment to gasoline terminals or retailers.
2.2 Heat distribution in distillation section
For conventional distillation column
Conventionally supplied at the bottom reboiler to evaporate
a liquid mixture and is lost when liquefying the overhead vapor at the
reflux condenser. Actually, heat is added at the highest temperature (T B)
in the column, whereas that is removed at the
157
F, Z F
Heat source
T D1
Tray 1
Feed tray
Tray n
T B1
CW
R 1
Steam
Q C1
Q R1
D 1, x D1
B 1, x B1
Tray 1
Feed tray
Tray n
TB2 Steam
Mash column Rectifying column
T D2
CW
R 2
Q C2
Q R2
D 2, x D2
Fig. 2 Simplified conventional distillation flowsheet
B 2, xB2
lowest temperature (T D). Interestingly, the thermal energy
recovered at the condenser cannot be reused for heating other flows in
the same distillation unit since the temperature of the coolant is usually
sufficiently lower than that of the flows inside the column. Heat is
added at the reboiler and thrown away at the condenser. Actually the
energy is degraded over the temperature range of T B-T D and this is the
prime reason of thermodynamic inefficiency of the conventional
distillation technology [2].
For heat integrated distillation column
Fig. 3 Simplified heat integrated distillation flowsheet
In the HIDiC scheme, the overhead vapor of the rectifying
column enters the reboiler of mash column as heat source. The mash
feed is preheated by vapor of mash column before entering to mash
column. So steam and cooling water consumption can be saved.