Evaporator design

INDIAN INSTITUE OF TECHNOLOGY ROORKEE

HEAT TRANSFER ASSIGMENT REPORT EVAPORATOR DESIGN

By SAURAB DEVANANDAN Enrollment ID: 15514023

MTECH 1st Year, CAPPD

AIM: To Evaluate the Performance of a Quadruple Effect sugar Evaporator for different Feed Temperatures and studying the effect on steam Economy. PROBLEM STATEMENT: Calculate The Area of Heat Transfer in each effect on Basis of Equal Area and Calculate the overall steam economy and plot Steam Economy Vs Temperature GIVEN DATA: Feed Mass Flowrate = 70000 kg/hr Concentration of Solute in Feed = 18 oBx Final thick Liquor Concentration = 60 oBx Feed Temperatures Considered are 70oC, 75oC, 80oC, 85oC, 90oC, 95oC, 100oC, 105oC Saturation Temperature of Steam entering the 1st Effect = 115oC Saturation Temperature of Steam Entering The Final Effect =55 oC Specific Heat = 2.508 kJ/(kg oC) Overall Heat Transfer Coefficient EFFECT 1 2 3 4

U(W/(m2 oC) 3200 2500 2000 1400

ASSUMPTIONS:    

The Boiling Point Rise due to solute concentration is considered negligible. The Specific Heat of all Liquid Streams is assumed to be constant. The steam entering each effect is considered to be saturated, i.e., the steam only transfers its latent heat of vaporization. There is no heat loss while moving between effects.

GOVERNING EQUATIONS: For the first effect, L0Cp(τ0 - T1) + V0λ0 - (L0 – L1)λ1 = 0 U1A1(T0 – T1) – V0λ0 = 0

…(1) …(2)

For remaining effects, LiCp(Ti-1 – Ti) + (Li-2 - Li-1)λi-1 - (Li-1 – Li)λi = 0 UiAi(Ti-1 – Ti) – (Li-2 – Li-1)λi-1 = 0 i=2,3,4.

…(3) …(4)

where, V0 = steam flow rate entering first effect, Li = liquid flow rate leaving ith effect, Ti = temperature of steam in ith effect, λi = latent heat of evaporation in ith effect, Ui = overall heat transfer coefficient of ith effect, Ai = area of ith effect. These equations are solved simultaneously taking λi = λ = 2040 (kJ/kg.oC) at T0=115 oC , for all i, and with the requirement that A1 = A2 = A3 = A4. Program Considerations: The Program for design of Evaporator was performed using C++. Gauss Elimination is used to solve the Multivariable system. The Program solves for any N effect

Results and Conclusions: The heat transfer area of each effect is calculated to be around 780 m2. The Steam Economy is found to increase gradually with increase in Feed Temperature. The Heat Transfer Surface Area requirement and Steam requirement reduces with the Increase in FEED temperature. The steams Economy for Different Feed Temperatures are in the following Table. Feed Temperature (oC) 70 75 80 85 90 95 100 105

Steam Economy

Steam Requirement(In Kg/hr)

Area Req(m2)

3.2935 3.43617 3.51963 3.76182 3.94894 4.15566 4.38521 4.6416

10371.5 9911.78 9510.96 9080.66 8650.37 8220.07 7789.78 7359.48

790.064 783.432 780.92 776.348 771.776 767.204 762.633 758.01

Graph Steam economy vs Temperature.

STEAM ECONOMY vs FEED TEMPERATURE 4.8 4.6

STEAM ECONOMY

4.4 4.2 4

Steam Economy

3.8 3.6 3.4 3.2 3 65

70

75

80

85

90

95

FEED TEMPERATURE

100

105

110

(oC)

Graph Steam Requirement vs Temperature.

Steam Requirement 12000

Steam Requiremt (in kg/hr)

10000 8000 6000 Steam Requirement 4000 2000 0 65

70

75

80

85

90

FEED TEMPERATURE

95 (oC)

100

105

110

Graph Area Requirement vs Temperature.

Area Req 795 790

Area Required (in m2)

785 Area Req

780 775 770 765 760 755 65

70

75

80

85

90

FEED TEMPERATURE

95 (oC)

100

105

110