TOPIC 2-COAGULATION AND CHEMICAL FLASH MIX

SP2C - FLASH MIX DESIGN

Design a chemical flash mix facility given the following design criteria:

Total plant design capacity = 45,000 m³/hr

Two flash mix basins, each ½ plant capacity

A turbine mixer will be used, but do not design the mixer speed or impeller etc.

G = 1000 sec-1, minimum

Hydraulic Retention Time = 8 seconds

Width = Depth of water = Length, i.e., a "cube"

Water Temperature = 10°C

Power transfer efficiency of mixer to water = 0.85

a) Determine the volume of each flash mix basin, m³ and the dimensions, nearest 0.1 m

b) Determine the power, kW, which must be introduced into the water, i.e., without transfer

efficiency

c) Determine the mixer power requirement, KW

d) If one of the flash mixers had to be taken out of service because of mechanical failure and

of the plant design capacity must go through one basin, determine the hydraulic retention

time and the G value. Any comment?

e) Considering the coagulation process is charge neutralization which occurs in milliseconds,

will the reduction in HRT in part d) be problematic?