experiment # uo1 double effect evaporator - KFUPM Open ...

EXPERIMENT # UO1
DOUBLE EFFECT EVAPORATOR
OBJECTIVE:
The objective of this experiment is to study the performance of a double effect
evaporator. Mass and energy balances will be carried out to determine steam
economy and heat transfer coefficients.
INTRODUCTION
Evaporation is a process whereby a solution consisting of a volatile solvent and
a non-volatile solute is concentrated by vaporizing the solvent. Common types
of evaporators used in the industry include i.) forced circulation evaporators,
ii.) natural circulation evaporators (thermosiphon), iii.) falling film
evaporators, and iv.) rising film evaporators. Drying differs from evaporation
in that the product in this case is solid.
In many industrial applications, water is used as the solvent while steam is
utilized as heating medium for the vaporization process. In such cases, given
efficient heat exchange, one kilogram of water may be evaporated per kilogram
of steam condensed.
To improve steam economy, multiple evaporators are used. The basic
principle involved is to utilize steam generated in one effect as the source of
heat for the subsequent evaporator. In this way, multiple effect evaporators
have the capacity to significantly reduce steam consumption.
THEORETICAL BACKGROUND
Steam economy, which is defined as the mass of water vapor generated per
mass of steam is the process parameter most significant in evaluating the
performance of multiple effect evaporators (Equation 1). The other important
parameter upon which both the evaporation and condensation process depend
is the heat transfer coefficient (Equation 2).
Steam Economy :
m
m
v
E = (1)
s
Heat Transfer Rate: q = UAΔT (2)
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ΔT for both effects should be considered. For U 1 , ΔT=T s – T 1 , and for U 2 ,
ΔT=T 1 – T 2 .
MASS AND ENERGY BALANCES
Assuming that the stream entering the effect is saturated and that the
condensate resulting from the steam is not sub cooled, then the total heat
transfer in the effect is obtained as :
q = m s .λ s
-(3)
The heat given up by the condensing steam is absorbed by the process fluid and
used for partial vaporization. From mass and enthalpy balance,
q = ( m − m ) H + m H − m H
-(4)
f p v p p f f
Values of enthalpies at the experimental conditions of temperature and pressure
should be obtained from literature. The flow rates of various streams are
determined from experimental data.
PROCESS DESCRIPTION AND EXPERIMENTAL PROGRAM
The double effect evaporator unit is shown schematically in Figure 1.The two
effects are initially filled to desired operating levels. Steam is supplied to the
first effect where heat transfer takes place causing partial evaporation of water
in the effect. The vapor generated is then supplied to the second effect where it
is used to vaporize some of the liquid water in the evaporator. Vapor produced
in the second effect is subsequently condensed and collected in the receiving
tank.
The entire experimental unit is to be operated at steady state for analysis. At
steady state, process parameters such as pressures, temperatures, mass flow
rates and tank level are measured and recorded as shown in the log sheet. The
measurements are repeated three times at regular intervals for reproducibility.
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P2
m v1
P4
m v2
T3
P5
T1
FIRST
EFFECT
CYCLONE
I
T2
SECOND
EFFECT
CYCLONE
II
CONDENSER
T4
C3
Steam
P1
P3
CONDENSATE
TANK
T5
Feed Water F1
m p1
m p2
C1
FIGURE 1 : DOUBLE EFFECT EVAPORATOR
C2
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Data:
Condensate Tank Diameter D = 50 cm
Evaporator Heat A = 0.51m 2
Transfer Area
C : Condensate
P : Pressure Indicator
T : Temperature Indicator

EXPERIMENTAL PROCEDURE
1. Start the unit and let it reach steady state (to be done with the help of
technician).
2. After the unit reaches steady state, record the temperature and pressure at
various points as shown in the log sheet.
3. Measure the flow rate of condensate from the first effect by collecting a
quantity of the condensate in a given time.
4. Repeat steps (3) for the second effect.
5. Measure the flow rate of the condensate flowing into the receiving tank by
monitoring the rise in the level in the tank.
6. Repeat steps (3) to (5) two more times.
7. Shut down the unit. (To be done with the help of technician).
DATA ANALYSIS
The following items must be covered in the data analysis and the analysis sheet
filled in accordingly:
1) Tabulate all enthalpies used in analysis from literature.
2) Carry out a mass and energy balance for the two effects.
3) Determine the steam economy of the process.
4) Determine the overall heat transfer coefficients for thde two effects.
Notations:
A Surface area of heat transfer , m 2
E
Steam Economy
Hv, Hf , Hp Enthalpies of the vapor, the feed and the product, W/m 2 .K
m f , m p , m s mass flow rate of the feed, product and steam supplied
kg/hr
m v1
mass flow rate of vapor from first effect, (= C2) kg/hr
m v2
mass flow rate of vapor from second effect, (= C2) kg/hr
q heat transfer rate, W.
T p
temperature of the process fluid, K
T s
temperature of the steam supplied, K
U overall heat transfer coefficient, W/m 2 .K
λ
Latent heat of vaporization, J/kg
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References:
1.) Kern, D. Q., Process Heat Transfer, McGraw Hill, (1965)
2.) Perry, R.H. and Chilton, C.H., "Chemical Engineers' Handbook", 5th
Edition, McGraw-Hill Book Company NY, chap 20 (1973).
3.) Thompson, E.V., and Ceckler, W.H., "Introduction to Chemical
Engineering.", McGraw-Hill Book Company, NY, chap.17 (1977).
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TABLE 1. LOG SHEET FOR EXPERIMENT UO1
Date :
Name of students: 1)
2)
3)
Signature of Instructor:
Tag Description Units Set 1 Set 2 Set 3
PI-1 Fresh steam pressure Psig
PI-2 Vap. pr. in the 1 st effect "
PI-3 Steam pr. in the 2nd effect "
PI-4 Vapor pr. in the 2nd effect In. Hg
PI-5 Shell side pr. in the cond. "
TI-1 Vap temp in the 1st effect oF
TI-2 Vap temp in the 2nd effect "
TI-3 Vap temp at cond. Inlet "
TI-4 Temp at condenser outlet "
TI-5 Feed temperature "
FI-1 Feed flow rate LPM
Weight of cond (1st effect)
Flow time (1st effect)
Weight of cond (2nd effect)
Flow time (2nd effect)
kg
min.
kg
min.
LI-3 Rise in tank level cm
Diameter of Tank cm 50
Total Time
Weight of empty bucket
Weight of empty bucket
with condensate
min.
kg
kg
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TABLE 2. ENTHALPY TABULATION
Temperature Pressure Enthalpy Ref.
T1 P2 H v1 =
" " H p1 =
T5 1 atm. H f1 =
T2 P4 H v2 =
" " H p2 =
T sat P1 λ1 =
T sat P3 λ2 =
TABLE 3. CALCULATION SUMMARY
(Details to be shown elsewhere)
Parameter Value Units
Feed flow rate to 1st effect
kg/h
Vapor flow rate from 1st effect "
Condensate flow rate from 1st effect "
Steam Economy of 1st effect
Vapor flow rate from 2nd effect
kg/h
Condensate flow rate from 2nd effect "
Steam Economy of 2nd effect
Heat transfer area of H01,H02 0.51 m2
Overall heat transfer coefficient of 1st effect
W/m2.K
Overall heat transfer coefficient of 2nd effect "
Overall Steam Economy of process
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