ITP330-Evaporasi 2016-pha-handout ready
Transcript of ITP330-Evaporasi 2016-pha-handout ready
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EVAPORATION
Baca
• http://www.nzifst.org.nz/unitoperations/evaporation.htm• Landasan Teknik Pangan (Buku Bacaan ITP330)
EVAPORATION
• Frequently in the food industry a raw material or a potential foodstuff contains more water than is required in the final product.
• When the foodstuff is a liquid, the easiest method of removing the water, in general, is to apply heat to evaporate it.
• Evaporation is thus a process that is often used by the food technologist.
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The basic factors that affect the rate of evaporation are the:
• rate at which heat can be transferred to the liquid,
• quantity of heat required to evaporate each kg of water,
• maximum allowable temperature of the liquid,
• pressure at which the evaporation takes place,
• changes that may occur in the foodstuff during the course of the evaporation process.
EVAPORATION
PROSES ………..??
• Evaporasi : 1. Atmosferik
2. Vakum
EVAPORATION
Vakum• Boling Pt lbh rendah• Disain: Vacuum system• Energi: Lebih efisien• Single & Multiple effect• Cocok untuk pangan
sensitif thd panas
Atmosferik :- Boiling pt lb tinggi- Disain: Sederhana- Energi: kurang efisien (- Single & Multiple effect- Tidak cocok untuk pangan
sensitif thd panas : off flavor
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PROSES ………..??
• Evaporasi : 1. Atmosferik
2. Vakum
EVAPORATION
Mass and energy transfer phenomena
An evaporator has 2 functions:
1. Heat exchange the evaporating section, where the liquid boils and evaporates,
and
1. Separate vapor formed from liquid (leaves the liquid and passes off to the condenser or to other equipment)
EVAPORATION
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EVAPORATION
Open kettle or pan evaporator:
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EVAPORATION
Concentrate
Condensate
Pan
Boiler
Jacket
Steam
Open kettle or pan evaporator:
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EVAPORATION
Open kettle or pan evaporator:
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EVAPORATION
Open kettle or pan evaporator:
• Simplest form of evaporators
• Inexpensive
• Simple to operate
• Very poor heat economy
• In some cases paddles and scrapers for agitation are used
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EVAPORATION
Horizontal-tube evaporator:
Dilute feed
Condensate
Concentratedproduct
Vapour
Steam inlet
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EVAPORATION
Horizontal-tube evaporator:
- Relatively cheap
- Used for non-viscous liquids having high heat-transfer coefficients and liquids that do not deposit scales
- Poor liquid circulation (and therefore unsuitable for viscous liquids)
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EVAPORATION
Vertical-type short-tube evaporator:
Dilute feed
Condensate
Concentratedproduct
Vapour
Steam inlet
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EVAPORATION
Vertical-type short-tube evaporator:
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EVAPORATION
• Liquid is inside the tubes
• Steam condenses outside the tubes
• Used for non-viscous liquids having high heat-transfer coefficients and liquids that do not deposit scales
Vertical-type short-tube evaporator:
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Factors effecting evaporation:Concentration in the liquid:
• Liquid feed to an evaporator is initially at a very dilute condition;
• Viscosity is low heat-transfer coefficient high.
• As evaporation proceeds, the solution becomes concentrated.
• Viscosity increases heat-transfer coefficient drops.
• Density and the boiling point of solution also increase.
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Factors effecting evaporation:Solubility
As evaporation progress
concentration of the solute increases
when solubility limit of the solute in solution is exceeded, then crystals may form.
Solubility of the solute: determines the maximum concentration of the solute in the product stream.
Generally: the solubility of the solute increases with temperature.
When a hot concentrated solution from an evaporator is cooled to room temperature crystallization may occur.
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• Functional products/foods componens may be damaged when heated to moderate temperatures for relatively short times.
• Special techniques are employed to reduce temperature of the liquid and time of heating during evaporation
Factors effecting evaporation:Heat Sensitivity of compounds
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Foaming and frothing:- Solutions like organic compounds tend to foam and froth during vaporization.
- The foam is carried away along with vapor leaving the evaporator.
- Entrainment losses occur.
Factors effecting evaporation:
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Pressure and temperature:- The boiling point of the solution is related to the pressure of the
system.
- The higher the operating pressure of the evaporator, the higher the temperature at boiling.
- Also, as the concentration of the dissolved material in solution increases by evaporation, the temperature of boiling may rise (a phenomenon known as boiling point rise/elevation).
- To keep the temperatures low in heat-sensitive materials, it is often necessary to operate under atmospheric pressure (that is, under vacuum).
Factors effecting evaporation:
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Scale deposition:- Some solutions deposit solid materials (called scale) on the
heating surfaces.
- The result is that the overall heat-transfer coefficient (U) may drastically decrease, leading to shut down of the evaporators for cleaning purposes.
Factors effecting evaporation:
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Materials of construction:- Evaporators are made of some kind of steel.
- However many solutions attack ferrous metals and are contaminated by them.
- Copper, nickel, stainless steels can also be used.
Factors effecting evaporation:
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Method of operation of evaporators
- When a single evaporator is used ,the vapor from the boiling liquid is condensed and discarded. This is called single effect evaporation.
- It is simple but utilizes steam ineffectively.
- To evaporate 1 kg of water from the solution we require 1-1.3 kg of steam.
- Increasing the evaporation per kg of steam by using a series of evaporators between the steam supply and condenser is called multiple effect evaporation
Single-effect evaporation:
Multiple-effect evaporation:
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mf, mp : Aliran cairan (liquid) (kg/jam)mv : Aliran uap (kg/jam)x : Konsentrasi padatan (kg padatan/kg total)T : Suhu (0 C)
MASS & ENERGY BALANCE
Uap (mv, Ti)
Produk (mp, xp, Ti)
Steam (ms,Ts)
Kondensat (ms,Ts)
Heat Exchanger
Feed (mf, xf, Tf)
Interface uap-cairan (liquid)
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ASUMSI :
• Umpan yg masuk (Tf) langsung mencapai titik didih (Ti) dan uap (mv)
serta produk (mp) meninggalkan evaporator pada suhu tersebut
• Uap (steam) masuk heat exchanger sbg uap jenuh (ms) pada suhu Ti
meninggalkan H.E sebagai kondensat cairan (ms)
MASS & ENERGY BALANCE
Uap (mv, Ti)
Produk (mp, xp, Ti)
Steam (ms,Ts)
Kondensat (ms,Ts)
Heat Exchanger
Feed (mf, xf, Tf)
Interface uap-cairan (liquid)
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MASS BALANCE
• Material balance keseluruhan :
mf = mv + mp …………………………………………(1)
• Kesetimbangan padatan larut
xf mf = xp mp …………………………………………(2)
• O.K.I :
mv = mf (1- (xf / xp))………………………………….(3)
MASS & ENERGY BALANCE
Uap (mv, Ti)
Produk (mp, xp, Ti)
Steam (ms,Ts)
Kondensat (ms,Ts)
Heat Exchanger
Feed (mf, xf, Tf)
Interface uap-cairan (liquid)
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ASUMSI : Heat loss Negligible
Maka panas yg disuplai steam yang berkondensasi = panas yg diperlukan untuk memanaskan danmenguapkan
MASS & ENERGY BALANCE
Uap (mv, Ti)
Produk (mp, xp, Ti)
Steam (ms,Ts)
Kondensat (ms,Ts)
Heat Exchanger
Feed (mf, xf, Tf)
ENERGY BALANCE
Interface uap-cairan (liquid)
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mf Hf + ms Hvs = mv Hvi + mp Hpi + ms Hcs
Dimana : H = entalpi (kJ/kg) : Lihat Tabel UapHvs = entalpi uap jenuh pada Ts
Hvi = entalpi uap jenuh pada Ti
Hcs = entalpi kondensat
MASS & ENERGY BALANCE
Uap (mv, Ti)
Produk (mp, xp, Ti)
Steam (ms,Ts)
Kondensat (ms,Ts)
Heat Exchanger
Feed (mf, xf, Tf)
ENERGY BALANCE
Interface uap-cairan (liquid)
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MASS & ENERGY BALANCE
Uap (mv, Ti)
Produk (mp, xp, Ti)
Steam (ms,Ts)
Kondensat (ms,Ts)
Heat Exchanger
Feed (mf, xf, Tf)
ENERGY BALANCE
Hf = cpf (Tf – 0oC)cpf = panas jenis (kJ/kgoC)
Hpi = cpp (Ti -0oC)
Hvs dan Hvi dari Tabel Uap pada saturated vaporHcs dari Tabel Uap pada saturated liquid
Interface uap-cairan (liquid)
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Laju Pindah Panas
q = UA (Ts-Ti) = ms Hvs - ms Hcs
Dimana: U =Overall heat transfer coefficient (W/m2K)A = Luas permukaan pindah panas (m2)q = Laju pindah panas (W)
MASS & ENERGY BALANCE
Uap (mv, Ti)
Produk (mp, xp, Ti)
Steam (ms,Ts)
Kondensat (ms,Ts)
Heat Exchanger
Feed (mf, xf, Tf)
Interface uap-cairan (liquid)
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Example 1:
A continuous single-effect evaporator concentrates 9072 kg/h of a 1.0 wt % salt solution entering at 38ºC to a final concentration of 1.5 wt %.
The vapor space of the evaporator is at 101.325 kPa (1.0 atm abs) and the steam supplied is saturated at 150 kPa. The overall coefficient U = 1704 W/m2.K.
Calculate the amounts of vapor and liquid products and the heat-transfer area required. Assumed that, since it its dilute, the solution has the same boiling point as water.
MASS & ENERGY BALANCE
Uap (mv, Ti)
Produk (mp, xp, Ti)
Steam (ms,Ts)
Kondensat (ms,Ts)
Heat Exchanger
Feed (mf, xf, Tf)
Interface uap-cairan (liquid)
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Data provided:
F = 9072 kg/h
xF = 1 wt % = 0.01 kg solute / kg feed
TF = 38ºC
xL = 1.5 wt %
= 0.015 kg solute / kg liquid product
P = 101.325 kPa (1.0 atm abs)
PS = 150 kPa
U = 1704 W/m2.K
T1 = saturated temperature at P (= 101.325 kPa) = 100ºC
TS = saturated temperature at 150 kPa = 111.4ºC
Steam, SPS, TS, HS
Feed, F
xF, TF, hF
Condensate, S
PS, TS, hS
Vapour, V
yV, T1, HV
Concentrate, L
xL, T1, hL
P
T1
Calculation methods for single-effect evaporators(taken from http://www.nzifst.org.nz/unitoperations/evaporation.htm)
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Overall material balance:
F = L + V
Solute balance:
F xF = L xL (no solute in the vapour)
Heat balance:
F hF + S λ = L hL + V HV
where λ = HS – hS
Data provided:
F = 9072 kg/h
xF = 0.01 kg solute / kg feed
TF = 38ºC
xL = 0.015 kg solute / kg liquid product
P = 101.325 kPa; T1 = 100ºC
PS = 150 kPa; TS = 111.4ºC
U = 1704 W/m2.K
q = S λ = U A ∆T = U A (TS – T1
Amounts of vapor and liquid products = ?
F, xF and xL are known, and therefore
L = 6048 kg/h and V = 3024 kg/h
Available equations:
Calculation methods for single-effect evaporators(taken from http://www.nzifst.org.nz/unitoperations/evaporation.htm)
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Heat balance:
F hF + S λ = L hL + V HV
where λ = HS – hS
Data known:
F = 9072 kg/h; L = 6048 kg/h, V = 3024 kg/h
TF = 38ºC
P = 101.325 kPa; T1 = 100ºC
PS = 150 kPa; TS = 111.4ºC
U = 1704 W/m2.K
q = S λ = U A ∆T = U A (TS – T
Available equations:
S λ = L hL + V HV – F hF
= (F – V) hL + V HV – F hF
= F (hL – hF) + V (HV – hL )= F Cp (T1 - TF) + V (Latent heat of vapourization at 101.325 kPa )
Calculation methods for single-effect evaporators(taken from http://www.nzifst.org.nz/unitoperations/evaporation.htm)
Heat transfer area A = S λ / U (TS – T1) = ?
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S λ = F Cp (T1 - TF) + V (Latent heat of vapourization at 101.325 kPa)F, T1 , TF and V are already known. Cp = 4.14 kJ/kg.K (assumed)Latent heat of vapourization at 101.325 kPa = 2256.7 kJ/kgTherefore, S λ = (9072) (4.14) (100 – 38) +(3024) (2256.7) kJ/h
= 9152862 kJ/h
Calculation methods for single-effect evaporators(taken from http://www.nzifst.org.nz/unitoperations/evaporation.htm)
Data known:
F = 9072 kg/h; L = 6048 kg/h, V = 3024 kg/h
TF = 38ºC
P = 101.325 kPa; T1 = 100ºC
PS = 150 kPa; TS = 111.4ºC
U = 1704 W/m2.K
Heat transfer area A = S λ / U (TS – T1) = ?
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S λ = 9152862 kJ/h = 9152862 * 1000 / 3600 WT1 and TS are knownU = 1704 W/m2.KTherefore, A = S λ / U (TS – T1)
= [9152862 * 1000 / 3600] / [1704 * (111.4 – 100)]= 130. 9 m2
Calculation methods for single-effect evaporators(taken from http://www.nzifst.org.nz/unitoperations/evaporation.htm)
Data known:
F = 9072 kg/h; L = 6048 kg/h, V = 3024 kg/h
TF = 38ºC
P = 101.325 kPa; T1 = 100ºC
PS = 150 kPa; TS = 111.4ºC
U = 1704 W/m2.K
Heat transfer area A = S λ / U (TS – T1) = ?
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Technical Problems of evaporation :
• Foaming losses, occupation hazards
• Fouling reduced Heat Transfer
• Increase viscosity
• Heat sensitive vs Boiling-point elevation (BPE)
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Problems of evaporation : Boiling Point Elevation (BPE)
Duhring plot for boiling point of
sodium chloride solutions
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Contoh:
Duhring Chart : tentukan titik didih awal & akhir suatu cairan pangan dengan komposisi yang menghasilkan tekanan uap air mirip dengan larutan NaCl. Tek.dlm evaporator 20 kPa. Produk dikonsentrasikan dari 5% ke 25 % total solids
Pendekatan :
Penggunaan Duhring Chart perlu titik didih air bisa diperoleh dg Tabel Uap
Next Duhring chart titik didih larutan
Problems of evaporation : Boiling Point Elevation (BPE)
Prosedur :
1. Steam Table 20 kPa ttk didih air, yaitu60oC
2. Duhring Plot: Tarik garis vertikal ke atasdari 333oK (60oC) titikdidih air
• 5% TS bp=61oC
• 25 % TS bp=66oC
Problems of evaporation : Boiling Point Elevation (BPE)
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Prosedur :
1. Steam Table 20 kPa ttk didih air, yaitu60oC
2. Duhring Plot: Tarik garis vertikal ke atasdari 333oK (60oC) titikdidih air
• 5% TS bp=61oC
• 25 % TS bp=66oC
Problems of evaporation : Boiling Point Elevation (BPE)
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Diagram of single-effect evaporator
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Susunan MEE:1. Searah (Forward)2. Berlawanan arah (Reverse)
feed product
steam
vapour
Diagram of multiple-effect evaporator
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Susunan MEE:1. Searah (Forward)2. Berlawanan arah (Reverse)
feedproduct
steam
vapour
Diagram of multiple-effect evaporator
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Double-effect evaporator-– forward feed
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Baca
http://www.nzifst.org.nz/unitoperations/evaporation.htm
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Selesai ….……….
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SELAMAT BERLIBUR
SELAMAT UAS
Prinsip Teknik Pangan (ITP330)
• Review Matematika• Satuan dan Dimensi
• Neraca Massa• Thermodinamika dan Neraca Energi
• Aliran Fluida• Transportasi Fluida
• Pindah Panas• Alat Penukar Panas
• Proses Thermal• Refrigerasi
• Pembekuan• Psikrometri
• Pengeringan• Evaporasi