SUPER HEATED WASH WATER SYSTEM FOR CENTRIFUGAL MACHINE

 

Super Heated Wash Water | SHWW | system for centrifugal machines

Sugar washing :

Washing in a centrifugal is designed to remove the high color molasses layer adhering to crystal surface.

This is an important part of the cycle and needs careful attention to detail if the required sugar quality is to be achieved without excessive dissolution of sugar. The sprays must be set up to spread the water uniformly across the height of the inside of the sugar layer.

In Water washing, the water is applied in fine spray on the surface of sugar. The water washes the molasses film and removes it and at the same time it unavoidably dissolves small amount of sugar.

The sprays are set up in an empty basket, and allowance must be made for the thickness of the cake in setting the sprays.

To avoid harmful effects of purity drop, the amount of washing has to be kept minimum. It is theoretically given that wash water is to applied when 75 % of molasses has been eliminated.

Super heated wash water (SHWW):

For better washing and get good quality sugar, super heated wash water is used for washing. In case of self-discharge batch type centrifugal, both water and steam is adopted. The super heated wash water system heat the hot condensate water to 115 ± 5 ^oC  by steam. .  The supply of water to pump suction is from overhead condensate tank. And temperature is about 70-80^oC.   Water under pressure 5 to 6kg/cm² heated up to 115 – 120^oC is known as super heated water.

The steam required to get the temperature should be applied at pressure of 7 kg/cm² & 160^oC – 180^oC . The inlet hot water is supplied to suction side of pump.  The delivery side of pump is connected to inlet tube side of heater  the outlet  of heater is connected to main header of super heated wash water system running behind C/F machines the other end of main pipe should be constantly leaked out to hot water tanks or drain by means of spring loaded valves.

In present scenario for reducing steam consumption, few sugar mills are now using system Plate Type heat exchanger for heating the super heated wash water (SHWW). Here 2^nd body condensate heated by exhaust steam.

Gravity factor of Centrifugal machine has significant effect on washing water requirement.  High G.F. of machine will require less water and vice versa

Quantity of water & steam to the sugar washing :

As per Noel Deer values are

Water required for washing 10 % on weight of sugar or . 5 % on massecuite.

Steam required for washing 20 % on weight of sugar or . 10 % on massecuite.

But practically  SHWW only  is sufficient for washing  maximum 4 – 5% on sugar or 2 –2.5% on massecuite

SHWW requirement can be calculate in three ways:

While considering of Crushing Rate :

Data requirement (For better understanding purpose go through the some values in example)

Crushing rate  230TCH

A m/c % on cane = 30

A m/c quantity  per hour = Crushing rate x m/c %cane = 69 T/hr

SHWW quantity  on m/c = 5% on m/c (taken maximum value)

Water inlet temperature = 85^oC

SHWW temperature requirement=  120 ^oC

Heating media Temperature (Exhaust) =     125 ^oC (here consider PHE system and heating media is exhaust)

Calculation

Heating media latent heat = 522.5 Kcal/Kg (At 125^oC)

SHWW requirement   =       3.45    kg/ hr

Take 100% extra  =  6.9       T/hr (To overcome the stoppages)

Steam requirement  for SHWW system= SHWW requirement (Kg/hr) x ( Water O/L temp. – Water I/L temp.)/ Latent heat. = 0.46  T/hr

Steam % Cane for SHWW system = Steam requirement  for SHWW system x 100 / TCH = 0.20

While considering of centrifugal machines:

Data requirement

Machine Capacity = 1750  kg/charge

Water quantity on m/c = 5   % on m/c (taken maximum value)

No. of cycles per hour = 22

No. of machines = 3

Water inlet temperature =   85^oC

SHWW temperature requirement  = 120  ^oC

 Heating media Temp. (Exhaust) = 125 ^oC

Heating media Latent heat= 522.5  Kcal/Kg

Calculation

SHWW required per machine = Machine Capacity x Water quantity on m/c x No. of cycles per hour = 1925   kg/ hr

Total SHWW required for all machines =  SHWW required per machine  x No. of machines =   5775   kg/hr

Take 50% extra due to re circulation =  8.6625    T/hr

Steam requirement = 0.58    T/hr

While considering of centrifugal machines nozzle data

Here we can calculate requirement of SHWW can estimate  by the  No. of nozzles and its capacity per each machine,

Timing requirement for nozzle operation   ( Basket wash  + 1^st wash + 2^nd wash …..etc)

Now  we can calculate SHWW quantity requirement per cycle than easily find the total SHWW requirement.