Question

How can a mass and energy balance of a cement ball mill be written/expressed?

Answer 1

For any process, Material balance is written as

In case of Ball Mill, there is no generation and accumulation of mass

Hence

In general, there are two out streams from Ball mill, one goes to the scrubber and one goes to the separator

Heat Balance for Ball Mill can be written as

We know that griding is a very inefficient process, only around 5% of the energy supplied to the mill is actually utilized for size reduction and remaining is utilized to overcome frictions which get dissipated in the form of heat.

Now, heat input to the system is the summation of heat calculated by following formulae

(Answers are in kcal)

...............................heat added from energy supplied to the mill

heat Out from the system is the summation of heat calculated by following formulae

(Answers are in kcal)

Where,

M= heat generated by grinding (kcal)

N= power absorbed at motor terminals (kW)

F= heat associated with Feed (kcal)

f = fresh feed rate (kg/h)

t_f = Temperature of fresh feed (⁰C)

C_f = Circulating factor (A/F)

t_R = Outlet temperature of product (⁰C)

A = heat associated with air (kcal)

t_A = Temperature of air entering to the mill (⁰C)

V = Volumetric flow rate of dry air (Nm³/h)

W_w = Weight of water in material (moisture and added) (liter)

W = Heat associated with water (kcal)

t_w = Temperature of water (⁰C)

S = Heat loss due to convection and radiation (kcal)

S_s = Shell surface area of ball mill (m²)

C = heat loss from material at discharge (kcal)

t_c = Temperature of product at discharge (⁰C)

A₀ = Heat loss from air at discharge (kcal)

W_v = Heat loss in form of water vapor at discharge (kcal)