Mill Material Balance
CHAPTER XI
MILL POWER REQUIREMENT
Furthermore an approximate calculation could be made for the power required in a mill from the material balance. The power required by the mill and should be developed by the mill drive to press the cane or bagasse between the rollers. First we have to know the coefficient of friction between the cane or bagasse and the roller surface. The mill balance calculation has determined the value for each mill, but then we need the data of the hydraulic rams diameter respectively. If the diameter of hydraulic ram = d cm, and the hydraulic pressure = p kg/cm 2, then the total hydraulic force is: 2
Ph = Ph =
2π . d . p 4 π .
kgs; or
2
d .p 2
kgs
It is to be noted that the hydraulic pressure is the actual pressure where the top roller really works actively up and down, even when an unstable feed of cane / bagasse occurred. The total force received by the cane / bagasse at the work openings is equals to: P = Ph + Wr kgs
Where:
Wr = the top roller weight, in kgs.
Therefore the circumferential force due on the top roller is: Pk = µ .P
Where:
Pk = the circumferential / tangential force, in kgs. kgs. µ
= coëficient of friction
P = Ph + Wr; same as mentioned above being the total hydraulic and top roller weight forces, in kg unit. The coefficient of friction value calculated by the material balance defined from the following formula: µ
= 0.43 -
.Dk .n 6000 x 1,524 π
........…............………………..………............. (22)
Where: Dk = mean diameter of the top roller in mm, and:
n
= the actual roller rotation per hour.
This formula is derived into metric system from an empirical test made by Bullock in Australia1).
1)
Hugot, Emil (1972), Handbook of Cane Sugar Engineering, page 188.
Power Requirement
XI-1
Mill Material Balance
Originally the formula was:
where:
µ
= 0.43 – 0.002 v
v
= circumferential velocity of the roller surface in feet per minute.
The coëficient of friction occurred in each mill normally have not the same value in a tandem. Logically for the first mill is the lowest, and then increasing to the ensuing mills (the bagasse becomes dryer). Identical condition applied for the hydraulic pressures, which are increasing from the first to the ensuing mills. The hydraulic pressures should not be determined only by calculation, but should be best defined by actual condition where it can actually move freely depending on the feeding layers. Henceforth, the calculation for approximate power required by each mill could be determined by the following formula: Ne =
π .
D k . n . Pk
2700000 . η
HP ……………………………..….…………… (23)
Whereas: Dk = mean diameter of of the top roller, in mm. n
= the actual rotation rotation per hour of the top roller.
Pk = circumferential force of the top roller, due on the middle of work opening gaps, in kg. η
= mechanical efficiency of the transmission between the mill and the mill drive, in %.
Further, when the result of the above formula (23) divided by the weight of fiber per hour, then we will have the specific power required by each mill in the tandem. When: Q = the mill capacity or the cane crushed crushed per day day (24 hours), in tons (metric). f
= fiber content of cane, in % (percent).
Then the weight of fiber per hour will be: Gs
=
10 Q x f 24
kg/hour
And the specific power is: SpP =
Power Requirement
24 π . Dk . n . Pk 27000. Q . f . η
HP/tons fiber ……………………………….(24)
XI-2
