Page 236 - Chemical and process design handbook

Speight_Part II_C 11/7/01 3:08 PM Page 2.176

2.176 MANUFACTURE OF CHEMICALS

Ammonia gas
Ammonia liquor
(1% ammonia)

Free still

Liquid level
Milk of lime
Steam
Steam

Waste
FIGURE 2 An ammonia still.

The vapors, steam distilled and superheated, pass overhead from the top
of the tray-type distillation column, enter the bottom of the bubble-cap
fractionating column, and are separated into four fractions and a residue,
leaving the residue at the bottom of this fractionating column. The pitch
cascades from the top of the distillation column down through the super-
heated steaming section to establish the desired pitch hardness and to strip
this pitch of the higher-boiling volatile oils. It is then withdrawn from
above the middle of the distillation column and conducted through the
pitch-tar heat exchanger to storage. The products are:

o
Product Boiling point, C

Light oil To 170
Carbolic oil 170–205
Naphthalene oil 205–240
Creosote or wash oil 240–280
Residue or anthracene 270–340
Residuum or pitch 325–400

The gaseous mixture leaving the oven is made up of permanent gases
that form the final purified coke-oven coal gas for fuel, along with con-