Problem 3: Material and heat balance

A zinc concentrate of composition  and rest inert is roasted continuously with dry air. Assume  converts to  and all S to , the gases leaving the system analyses  (volume basis)

Calculate:

a) Rate of blowing of air (m3⁄min) when 100 ton concentrate is roasted in24 hrs

b) Excess air

c) Analysis of flue gases.

d) Perform heat balance of the roasting/ton of concentrate. The reactants enter at 298K

e) The products leave at 1100K. Roasting is carried out at 1100K.You may assure heat loss is 10% of total heat input.

(All the thermo chemical data are given at the end of lecture 19.)

Solution:

Basis 1000kg concentrate

Several problems on material balance are illustrated.

To perform heat balance, material balance is a pre-requisite

Material balance results are given

Rate of blowing of air/100 Ton concentrate 

Excess air

Flue gas 



Complete material balance in terms if input and output of material is required for heat balance reference temperature 298 K

This problem is solved in video lecture 19 in materials and heat balance in metallurgical processes

To complete the solution of the problem:  From heat of formation values, heat of reaction can be calculated.From the sensible heat of gases, heat taken by the gas can be calculated.

Total heat output = 853199 kcal


Analysis

1) In roasting large amount of heat is generated

In this problem there is 583557 kcal is surplus which is 40.6% of heat input. This heal will raise the temperature within the reactor, if  surplus  heat is unutilized.

2) Around 33% of heat input is carried by  in flue gas. One may think to utilize this heat. Flue gas   contains large amount of dust particles, ash particles. Hence utilization of heat in fluegas is a problem.