Study of a Single Effect Evaporator

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ChE 30

Chemical engineering laboratory - II

Experiment No. Group No. 03 (A2)

Name of the experiment:

STUDY OF A SINGLE EFFECT EVAPORATOR

Submitted by:

Md. Hasib Al Mahbub

Student Id: 0902045

Level: 3; Term: 2

Section: A2

Date of performance:28/01/2014

Date of submission:11/02/2014

Partners Student Id.0902041

0902042

0902043

0902044

Department of Chemical Engineering.

Bangladesh University of engineering and technology, Dhaka.


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Summary

The main objective of this experiment was to study, operate and obtain characteristics, to

perform material and energy balance and to determine steam economy which denotes the

efficiency of the whole evaporating operation of a single effect evaporator. This process

involved evaporation of only water in a still and steam at 10 psig is supplied to the still to heat

the water for evaporating. The vapor produced in the column goes to condenser and in a

condensate collected tank it was collected to find out the total amount of vapor formed with

time. Using the observed experimental data cumulative steam economy as well as overall steam

economy was calculated .The values of cumulative steam economy range was 0-0.19548 and

steam economy range for each observation was 0-0.960837and the overall steam economy was

0.1955 .The overall heat loss was 131.902 MJ. A graph between vapor condensation rates vs.

cumulative time was plotted. The graph shows that the time required to reach steady state

condition was high. There were some discrepancies in the experiment. The possible cause of

other discrepancies discussed in discussions.


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Temperature

of Vapor

Steam Pressure

EvaporatorPressure

Temperature

of Still

Steam In

Feed In

Drain

Stream Trap

Steam Chest

Evaporator

Water Level

Entrain

Separator

Condenser

CondensateDrum

Cooling

Water Temp.

Figure 1: Experimental setup of a single effect evaporator

ExperimentalSetup

2


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Flow Diagram

Figure 2: Flow diagram of the system


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Observed Data

Steam pressure = 10 Psig

Weight of bucket1=0.65 Kg

Weight of bucket2= 0.70 KgTime interval = 180 Sec

Condensate tank perimeter = 76 inch

Cooling water flow rate = 0.23 Kg/Sec

Cooling water inlet temperature = 74 oF

Cooling water outlet temperature = 80 oFTable-1: Observed data for study of single effect evaporator.

Obs.

No.

Vapor space

Temperature

( oF )

Still

Temperature

( oF )

Steam

condensate

Time (Sec)

Level of

vapor

condensate

( cm)

Steam

condensate

+

Bucket1

(kg)

Steam

condensate

+

Bucket2

(kg)1 68 100 180 91.9 6.5 -

2 72 122 180 91.9 - 5

3 76 144 180 91.9 4.35 -

4 84 160 180 91.9 - 3.95

5 96 174 180 91.9 3.3 -

6 108 180 180 91.9 - 2.87 120 186 180 91.9 2.75 -

8 130 190 180 91.9 - 2.5

9 146 196 180 91.9 2.3 -

10 188 206 180 91.9 - 2.5

11 210 206 180 91.9 2.25 -

12 212 206 180 91.3 - 2.55

13 212 206 180 91.1 2.45 -

14 212 206 180 90.9 - 2.4

15 212 206 180 90.7 2.5 -

16 212 206 180 90.5 - 2.6

17 212 206 180 90.3 2.3 -18 212 206 180 90.0 - 2.3

19 212 206 180 89.8 2.6 -

20 212 206 180 89.5 - 2.6

21 212 206 180 89.2 2.72 -

22 212 206 180 88.9 - 4.15

23 212 206 180 88.6 3.5 -

24 212 206 180 88.2 - 4

25 212 206 180 87.9 2.6 -


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Calculated DataTable-2: Calculated data for study of single effect evaporator.

Obs.

No.

Time

(sec)

Cumulative

height ofvapor

condensate(m)

Water

evaporated(Kg)

Water

condensationrate

Kg/Sec

Steam

condensate(Kg)

Rate of steam

condensation(Kg / Sec )

1 180 0 0 5.85 0.0325

2 180 0 0 0 4.30 0.0238

3 180 0 0 0 3.70 0.0205

4 180 0 0 0 3.25 0.0180

5 180 0 0 0 2.65 0.0147

6 180 0 0 0 2.10 0.0116

7 180 0 0 0 2.10 0.0116

8 180 0 0 0 1.80 0.01009 180 0 0 0 1.65 0.0091

10 180 0 0 0 1.80 0.0100

11 180 0 0 0 1.60 0.0088

12 180 0.006 1.7775 0.0098 1.85 0.0103

13 180 0.008 0.5925 0.0033 1.80 0.0100

14 180 0.010 0.5925 0.0033 1.70 0.0094

15 180 0.012 0.5925 0.0033 1.85 0.0103

16 180 0.014 0.5925 0.0033 1.90 0.0106

17 180 0.016 0.5925 0.0033 1.65 0.0092

18 180 0.019 0.8887 0.0049 1.60 0.0088

19 180 0.021 0.5925 0.0033 1.95 0.010820 180 0.024 0.8887 0.0049 1.90 0.0105

21 180 0.027 0.8887 0.0049 2.07 0.0115

22 180 0.030 0.8887 0.0049 3.45 0.0191

23 180 0.033 0.8887 0.0049 2.85 0.0158

24 180 0.037 1.1850 0.0065 3.30 0.0183

25 180 0.040 0.8887 0.0049 1.95 0.0108


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Table-3: Calculated data for study of single effect evaporator.

Obs. No. Cumulative

wt. of steam

cond.(Kg)

Cumulative

Steam

economy

Steam

economy

for each

observation

Heat

recovered

by

steam(MJ)

Heat

absorbed

by

water(MJ)

Heat

loss(MJ)

1 5.850 0 0 15.789 0 15.789

2 10.15 0 0 27.394 0 27.394

3 13.85 0 0 37.380 0 37.380

4 17.10 0 0 46.152 0 46.152

5 19.75 0 0 53.304 0 53.304

6 21.85 0 0 58.972 0 58.972

7 23.95 0 0 64.640 0 64.640

8 25.75 0 0 69.498 0 69.498

9 27.40 0 0 73.952 0 73.952

10 29.20 0 0 78.810 0 78.810

11 30.80 0 0 83.128 0 83.128

12 32.65 0.05444 0.960837 88.121 4.755 83.365

13 34.45 0.06879 0.329176 92.979 6.341 86.638

14 36.15 0.08195 0.348539 97.568 7.926 89.641

15 38.00 0.09355 0.320279 102.56 9.511 93.049

16 39.90 0.10395 0.311851 107.68 11.09 96.592

17 41.55 0.11408 0.359101 112.14 12.68 99.460

18 43.15 0.13044 0.555484 116.46 15.06 101.40

19 45.10 0.13794 0.303854 121.72 16.64 105.07

20 47.00 0.15128 0.467776 126.85 19.02 107.82

21 49.07 0.16301 0.429359 132.43 21.40 111.03

22 52.52 0.16922 0.257616 141.75 23.77 117.9723 55.37 0.17656 0.311851 149.44 26.15 123.28

24 58.67 0.18683 0.359101 158.34 29.32 129.02

25 60.62 0.19548 0.455782 163.61 31.70 131.90

Table-4: Calculated data for study of single effect evaporator.

Overall steam

economy

Overall heat

released from

steam (MJ)

Overall heat

recovered by

water(MJ)

Overall Heat loss

(MJ)

0.1955 163.612 31.705 131.902


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Sample CalculationFor Observation no. 16

Steam condensate flow rate = {(2.60.7) / 180} kg /sec= 0.011 kg /sec

Perimeter of storage tank = 76 inch = 1.9304 m

Inner radius of storage tank, r = {1.9304 / (2)} m

= 0.3072 m

Level of water vapor storage tank, h12= 90.3 cm =0.903 m

Level of water vapor storage tank, h13= 90.0 cm =0.90 m

Volume of water vapor condensate = r2h

= { (0.3072)2 (0.903-0.90)} m3

= 8.8943x 10-4m3

Water vapor condensed in the condenser = Water evaporated in the feed tank

From Franzini (Table: A-1)

Density of water, = 1000 kg /m3

Mass of water evaporated, m = (8.8943 10-41000) kg

= 0.88943 kg

Total mass of steam condensate, m1= 60.62 kg

Total mass of water evaporated, m2 = 11.85 kg

Overall steam economy = (Total mass of water evaporated / Total mass of steam consumed)

= (11.85 / 60.62)

= 0.1955

Cumulative mass of water evaporate = 4.1476 kg

Cumulative mass of steam condensate= 39.9 kg

Cumulate steam economy= (Cumulative mass of water evaporated / Cumulative mass of

steam)


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Cumulate steam economy = (4.1476/39.9)

= 0.1039

Calculation of steam economy for Observation no. 15

Mass of water evaporate = 0.5925 Kg

Mass of steam condensate = 1.9 Kg

Steam economy = (Mass of water evaporated / Mass of steam consumed)

= (.5925/1.9)

= 0.3118

Enthalpy balance

Steam pressure = 10 psig = 24.7 psia

At 24.7 psia , Tsat= 115.203oC

Enthalpy of evaporation, Hv1= 2698.985 KJ /Kg

Cumulative heat released from steam, Q1= m13 Hv1

= (39.9 x 2698.985) KJ

= 107.69 MJ

Overall heat released from steam, Q1,ov= mtotalHv1

= (60.62 2698.985) KJ

=163.612 MJ

At, condenser pressure= 14.7 Psia , Tsat=100oC

Enthalpy of evaporation, Hv2= 2675.57 kJ/ kg

Cumulative heat recovered by water, Q2= m13 Hv2

= (4.1476 2675.57) KJ

= 11.097MJ


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Overall heat recovered by water, Q2 ov= mtotal Hv2

= (11.85 2675.57) KJ

= 31.705 MJ

Cumulative heat loss , H = Q1Q2

= (107.6911.097) MJ

= 96.586 MJ

Overall heat loss, H = Q1 ovQ2 ov

= (163.61231.705) MJ

= 131.902 MJ


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Results and Discussions

Table-5: Range of result for various observation of single effect evaporator.

Ranges of steam

economy for

each observation

Range of

cumulative heat

loss (MJ)

Range of

cumulative

steam economy

Overall heat

loss(MJ)

Overall steam

economy

0-0.960837 15.789-131.90 0-0.19548 131.902 0.1955

From vapor condensation rate Vs. cumulative time curve, it was observed that at beginning rate

increases with time and go through the pick point its to a steady state condition. This state arrived after

40 minutes.

In this experiment, the steam economy is very low because of single effect evaporator. Steam economy

would be greater if multiple effect evaporator was used. Heat loss is very high .The possible reasons for

this high heat loss are discussed below

In this experiment, we converted a double effect evaporator to a single effect evaporator byclosing some valves. The total unit of heat exchanger was too old to perform and lost its actual

insulation. Therefore, energy could be lost in the surroundings.

The inlet steam was collided at the steam chest and thus condensed and lost its energy. The evaporator, condenser, other apparatus used, and the internal pipe network could absorb

some energy.

Moreover, the result could be varied due to the error reading of the mass of condensed steamand height of condensed vapor.

Study of a Single Effect Evaporator

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