ASSIGNMENT-3

1. Natural gas containing CH4 = 83% and C2H6 = 17% was burnt with an excess of dry air.

The analysis of the flue gas was CO2 = 6.76% ; CO = 2.77% ; O2 = 5.63% ; N2 = 84.84%.

Calculate the following:

i. percentage excess air supplied

ii. percentage completion of oxidation of carbon

iii. Amount of fuel gas produced per 100 m3 of fuel at 500

oC and 1 atmosphere

pressure.

2. A storage tank of demineralised (DM) water has a holding capacity of 1500m3 upto an

overflow point. The DM water having silica (SiO2) content of 0.005 mg/l is flowing into

a tank at a rate of 25 l/s. the outflow from tank to high pressure boilers is 25 l/s. with

time, quantity of DM water deteriorates and the silica content in the feed DM water

increased to 0.02 mg/l. Assuming that the inflow into and the outflow from the tank

remains constant at 25 l/s. calculate the time required for the silica content in the storage

tank to increase to 0.01 mg/l.

3. Heptane is burnt with 10% excess air calculate

A) air/fuel ratio by weight

B) air/fuel ratio by volume.

C) Weight of dry exhaust gas formed per unit weight of fuel.

D) Moles of O2 in the exhaust per unit weight of fuel.

E) Moles of water vapour in exhaust per unit weight of fuel.

F) Volume of exhaust gas at 1atm and 2600C per unit weight of fuel. Specific gravity of

Heptane is 0.7.

4. Fresh juice contains 15% solids and 85% water by weight and is to be concentrated to

contain 40% solids by weight. In a evaporator system it is found that volatile constituents

of juice escape with water leaving the concentrated juice with a flat taste. To overcome

this problem part of the fresh juice bypasses the evaporator. Calculate

(a) The fraction of juice that bypasses the evaporator.

(b) The concentrated juice produced (containing 40% solids) per 100 kg of fresh juice fed

to the evaporator.