REPORT

Raw material:-

Sugarcane Steam Lime

Process description:-

Manufacturing of sugar from the sugar cane also helps to generate electricity by burning of bagasse which is the by-product of sugar-cane.

Initially when the cane are introduced as the feed in the plant it passes through the crushing unit. Crushing unit consists of chopper and fibrizer.

When the canes are passed through choppers it evens out the cane and cut into small pieces.

This small pieces of sugar cane is then converted into fibers by putting crushed sugar canes in fibrizer.

In this unit the sugarcanes are crushed and then send to mills to extract the juice from the crushed canes.

This process of cutting canes and converting into fibers is called as cane preparation.

These fibers are send to mills through rake elevator type of conveyors. There are in total 5 numbers of mills which extract juice from the sugarcane fibers.

This mills are driven by A.C. motors having an rpm of 1000 and 750HP. After the extraction of the juice is done then the juice is send for further

processing and the residue is send to the storage which is adjacent to the boiler in boiler section.

This residue which is left after extracting the juice is known as bagasse. Bagasse is used as a fuel in the boiler to generate steam.

When the steam is generated it is having a temperature of 500⁰C and a very high pressure of 84Kg/cm2.

Since this steam is superheated the heat transfer coefficient of the steam is less which can’t be directly used in the evaporation sections.

Therefore we have two options available with us one is sent the steam to a MP Saturator and another is used the high pressure steam to rotate turbine which will help in generating electricity.

If we use in MP Saturator then there will be no electricity generated only the superheated steam will convert to MP Steam which will give high heat transfer coefficient.

So the high pressure steam is used to generate the electricity by running turbine.

This section is known as power generation section. In this section the high pressure steam is used to rotate turbine, this

turbine is connected to a rotor through a shaft. When the turbine rotates this shaft also rotates due to which there is a

magnetic flux generated this cause the current in the coils of the armature, thus electricity is generated.

After the steam is passed through the turbine the high pressure steam is converted in to mild pressure steam and some amount of condensate is produced.

The outlet of the turbine is divided into two lines one is the feed line which is going to the evaporation section and another is the recycle line going to the boiler.

This MP Steam from the feed line is send to the evaporation section at a flowrate of 17 Tons per hrs of condensate at a temperature of 119⁰C and 1.03Kg/cm2 pressure is reused in the boiler.

The remaining steam which is at a temperature of 264⁰C and 10kg/cm2 is send to the evaporators through feed line.

Products:-

Sugar crystals Electricity generation

Before:-

The flue gas exiting from the boiler goes to the economiser where it

preheats the entering boiler feed water. This flue gas is then used to

preheat the air entering the boiler and then goes to the ESP.

Suggestion:

If this flue gas exiting from the air preheater is used to dry the Bagasse

in a Rotary drum drier, before it enters the boiler, energy can be saved.

As some heat is lost in vaporising the moisture content of the Bagasse.

Hence the efficiency of boiler increases, which leads to huge savings.

Rotary Drier Calculations:-

Data:

1) The moisture content of bagasse is 0.44 and the equilibrium

moisture content is 0.02.

2) The flue gas temperature from the Boiler is 4500C and this is sent to

Economizer to heat the boiler feed water before it enters the boiler.

The temperature of flue gas coming out from Economizer is 250 0C and

here after the flue gas goes to Air heater.

3) Air heater inlet is 2050C and outlet temperature of the flue gas is 120

to 1250C.

4)The inlet temperature of flue gas entering ESP is 120 to 1250C

5) The flow rate of the bagasse entering the boiler is 42 MT/Hr.

6) The moisture content of the flue gas (Data given by the company) is

4.3 %

7) Mass of bagasse entering: 42Mt/hr

8) Inlet temperature of bagasse: 30°C & Inlet temperature of flue gases:

120°C

9) Wet bulb temperature of flue gases: 40°C

10) Outlet temperature of bagasse from dryer: 60°C (Assumption) &

Outlet temperature of flue gases from dryer: 60°C

11) Moisture Content of Bagasse: 40% (Found experimentally),

Moisture content in the dried bagasse: 2% (found experimentally)

12) Specific heat of bagasse (solid): 0.24 kcal/kg°C, Specific heat of

water: 1 kcal/kg°C, Specific heat of flue gases:0.43 kcal/kg°C.

Qt = amount of heat transfer, kcal/hr

Xa = kg moisture/kg dry solid (entry)

Xb = kg moisture/kg dry solid (entry)

Cps = sp.heat of solid kcal/kg°CCpl=sp.heat of liquid kcal/kg°C.

Cpv = sp.heat of vapour, kcal/kg°C

Tsa = Inlet solid temperature , °C

Tv = Vapourisation temperature, °C

Tvb = Final vapour (exit) temperature, °C

Mass of bone dry solid (bagasse): 42000×0.56= 23520 kg

Water content in dried bagasse: 840 kg

Xa = 42000×0.44= 0.785

23520

Xb = 470 = 0.019

23520

Ni = 120-40 = 4

60-40

Rate of mass transfer = ms(Xa-Xb)

= 23520(.785-.019) = 18016 kg / hr

Qr = Cps (Tsb-Tsa) + Xa Cpl (Tv – Tsa) + (Xa –Xb )λ +Xb Cpl

Ms (Tsb-Tv) + (Xa-Xb ) x Cpv x ( Tvb – Tv )

= .416(60-30) + .785 x 1 x ( 40-30 ) +( .785- .019 ) x 575 + .019 x 1( 60-

50 ) + (.785 - .019) .43 (60-50 )

= 465 kcal/ kg

Qt = 465 x 23520 = 10936800 kcal/hr

Flow rate of air entering is found from heat balance and humidity,

Csa = humid heat

Assuming sp.heat of air as 0.23 kcal/kg0C and of humid vapour as 0.44

kcal/kg0C we get,

= .23 + .44 x .43 = .429 kcal/kg0C

Qt = Mg ( 1 + Ha ) Csa (Tha – Thb)

10936800 = Mg ( 1 + Ha ) .429 ( 120-60)

Amount of wet air = Mg ( 1 + Ha )

= 10936800 = 424895 kg air / hr

.429 ( 120-60)

Mg = 424895 = 295066 kg dry air/hr

1.44

Outlet humidity of air = H1 + 18016/295066 = 0.061 kg water / kg dry air

T = ( 120-50 ) - ( 60-50 )/ Ln( (120-50 )/(60-50))

= 30.830C

Assuming mass velocity of 10000 kg/hr,

Area = 295066 / 10000 = 29.5 m2

A=π r2

D = 6.13 m

L = Qt / .21 x π x DG.67 x T

= 10936800/.21 x 3.14 x 29.5 x 10000.67 x 30.83

= 38.10m

AFTER :

After using the rotary drier the bagasse is drier and then use which gives the higher generation of the steam rate which increases the rate of generation of electricity. Hence rotary drier is preferred.

AIR PREHEATER Air from Blower

ROTARY DRYER WET BAGASSE FROM PLANT

T= 90 ºC

ESP

T= 43 ºC

DESIGNS FOR BAGASSE DRYERS :

1. ROTARY DRYER :

The Roatary drier is a MS pipe

(L=2000,dia-150) provided with 2 nos handler for manual rotation.

External insulation of 25mm glass wool (mineral wool) to be provided.

The feed hopper will have a capacity of about 100kgs of wet shredded baggase.

Hot air is to be generated by Hair dryer/Electrical heating coils + a small blower.

Feed the wet material (about 10kgs at a time) and observe the dried material composition ,temp etc at different RPM of drier .

Study efficieny of drying at different T1/T2, feed rates and speed of rotation.

Size of shredded bagasse to be noted.

1. STATIONARY DRYER :