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A. TEKNOLOGI PENGOLAHAN SUSU BUBUKPrinsip pengolahan susu bubuk
: penghilangan air dengan biaya sekecil mungkin, pada kondisi
higienis dgn mempertahankan semaksimal mungkin sifat alami susu yg
dikehendaki - warna, flavour, kelarutan, dan nilai nutrisi.
Whole (full cream) milk mengandung air 87% dan skim milk
mengandung 91% air. Selama pengolahan susu bubuk air dihilangkan
dgn mendidihkan susu pada tekanan rendah yg dikenal dgn proses
evaporasi.
Hasil evaporasi adalah susu kental yg selanjutnya disem-protkan
dalam bentuk tetesan kecil ke arah udara panas utk penghilangan air
lebih lanjut shg menghasilkan bubuk.
Sekitar 13 kg whole milk powder (WMP) atau 9 kg skim milk powder
(SMP) dapat diperoleh dari 100 L susu segar.
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KOMPOSISI RATA-RATA SUSU BUBUK
PRODUKProteinLemakLaktosaAbuAirWhole milk26,026,738,06,02,3Skim
milk36,00,751,08,13,0Butter
milk34,55,048,08,03,0Cream11,072,014,02,40,6Whey12,90,367,08,53,5
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Susu bubuk
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Proses konvensional untuk produksi susu bubuk dimulai dgn
penerimaan susu, pasteurisasi dan separasi menghasilkan susu skim
dan krim menggunakan centrifugal cream separator.
Jika diproduksi Whole Milk Powder (WMP) sejumlah krim
ditambahkan kembali kepada susu skim menghasilkan produk susu
dengan kadar lemak sesuai standar tertentu (umumnya 26-30% lemak
dalam bubuk).
Krim yg berlebih digunakan untuk membuat butterSEPARASI /
STANDARIATION
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Efek pemanasan:Perlindungan thd lemak dari enzim perusakTimbul
cooked flavorKelarutan turun karena denaturasi proteinPEMANASAN
PENDAHULUAN (PREHEATING)/ PASTEURISASI (lanjutan)Tujuan
pemanasan:Inaktivasi semua mikroba patogen, menurunkan total
bakteriInaktifasi enzym, terutama lipaseMengaktifkan gugus SH
groups dlm -Lacto-globulin shg meningkatkan stabilitas bubuk thd
oksidasi selama penyimpanan.
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Suhu dan waktu pemanasan
Suhu antara 75-120oC dipertahankan pd waktu tertentu mulai dari
beberapa detik sampai bbrp menit (contoh: pasteurisasi 720C, 15
detik).
Metode pemanasan "High-short" lebih disukai karena dapat
mencapai efek yg dikehendaki dan pembentukan senyawa antioksidan
lebih banyak
Kelarutan bubuk meningkat jika dilakukan metode high-short.
Pemanasan dgn metode ini selama 15-30 detik pada 88-95C, bahkan
sampai 1300C
PEMANASAN PENDAHULUAN (PREHEATING)/ PASTEURISASI
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Waktu dan suhu pemanasan bergantung tipe produk dan
penggunaannya. Produk whole milk powder pemanasan lbh tinggi utk
meningkatkan kualitas mikrobilogis dan memper-panjang umur simpan
tetapi mengurangi kelarutan.
Preheating dapat secara tidak langsung (melalui heat
exchangers), atau langsung (melalui steam injection atau infusi ke
dalam produk), atau campuran dari dua cara tersebut. Pemanasan
tidak langsung umumnya menggunakan limbah panas dari bagian proses
yang lain utk menghemat energi.PEMANASAN PENDAHULUAN (PREHEATING)/
PASTEURISASI (lanjutan)
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Tahap ini dilakukan sebab lbh ekonomis karena jika pengeringan
langsung:
kebutuhan steam lbh besar memerlukan space lbh besarwaktu
pengeringan lebih panjangukuran partikel kecil shg loss lbh
besarketahanan flavor lbh kecil sebab lbh mudah oksidasipenanganan
lebih sulitEVAPORASI
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Tujuan:Memekatkan susu, yang awalnya memiliki total padatan
sekitar 9.0% (skim milk) dan 13% (whole milk), menjadi total
padatan 33-35% (drum drying) atau 40-50% (spray drying)
Prosedur: Susu dididihkan di bawah kondisi vakum pada suhu
45-750C, umumnya di bawah 720C di dalam falling film yg terletak di
dalam tabung vertikal dan air dikeluarkan sebagai uap EVAPORASI
(lanjutan)
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Uap yg dihasilkan dapat di compress secara mekanis atau
pemanasan, selanjutnya dpt digunakan utk memanaskan susu pada
effect dari evaporator yg berikutnya yg mungkin beroperasi pada
tekanan dan suhu lebih rendah dibandingkan sebelumnya.
Effect adalah unit tunggal dalam evaporator yg ber-operasi pada
tekanan dan suhu tertentu. Evaporator umumnya memiliki tiga sampai
tujuh effects shg panas digunakan kembali beberapa kali.EVAPORASI
(lanjutan)
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Diagram of a falling film evaporator (Source: GEA Niro Inc.)
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HOMOGENISASITujuan: mencegah pengelompokan lemak selama proses
shg mencegah creamingMengurangi lemak bebas yang tdk memiliki
protective membrane shg mudah menggumpal dan menyebabkan
oksidasiTahap ini harus dilakukan utk proses drum drying krn hasil
berupa lempengan shg harus homogenSpray drying tidak harus melewati
homogenisasi krn hasil berupa partikel-partikel shg mudah bercampur
Homogenisasi dilakukan pada tekanan 50-150 bar.
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Dua metode pengeringan yg umum digunakan adalah drum drying dan
spray drying. Drum drying lapisan tipis dari konsentrat susu
didistribusikan pada permukaan panas, menyebabkan sejumlah besar
air teruapkan dalam beberapa detik. Spray drying konsentrat susu
dibuat menjadi droplet kecil dan dikenakan udara panas sehingga air
teruapkan dari dropletPENGERINGAN (Drying)
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Lapisan tipis konsentrat susu (30-35% bahan kering)
didistribusikan pada pengering drum berputar. Di dalam drum tdp uap
panas sampai suhu 1450C. Dalam waktu kurang dari 3 detik kadar air
yang tersisa mencapai 4% dan susu yang kering dikerok (scraped)
dari drum menggunakan pisau (blade). Serpihan bubuk (powder flakes)
jatuh ke atas conveyor, dipecah oleh hammer mill, didinginkan, di
ayak selanjutnya dikemas. PENGERINGAN - Drum drying
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Karena pemanasan tidak langsung, perlu suhu sangat tinggi yg dpt
berakibat pada:
penurunan kelarutan karena denaturasi protein,diskolorasi
(pencoklatan) karena karamelisasi laktosa dan reaksi Maillard,
perubahan rasa dan aroma
Proses drum drying menghasilkan partikel datar (flat atau
flake-like)PENGERINGAN - Drum drying (lanjutan)
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PENGERINGAN - Drum drying (lanjutan)Diagram roll dryerPartikel
bubuk hasil drum dryer
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Unit Operations. Spray drying consists of the following unit
operations: Pre-concentration of liquid Atomization (creation of
droplets) Drying in stream of hot, dry air Separation of powder
from moist air Cooling Packaging of product
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Relatively high temperatures are needed for spray drying
operations. However, heat damage to products is generally only
slight, because of an evaporative cooling effect during the
critical drying period and because the subsequent time of exposure
to high temperatures of the dry material may be very short. The
typical surface temperature of a particle during the constant
drying zone is 45-50 C. For this reason, it is possible to spray
dry some bacterial suspensions without destruction of the
organisms. The physical properties of the products are intimately
associated with the powder structure which is generated during
spray drying. It is possible to control many of the factors which
influence powder structure in order to obtain the desired
properties.
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Typical Spray Drying Systems. The diagram shows a schematic
representation of a typical spray drying system for milk powder.
For spray drying, it is usual to pump a concentrate of the liquid
product to the atomizing device where it is broken into small
droplets. These droplets meet a stream of hot air and they loose
their moisture very rapidly while still suspended in the drying
air. The dry powder is separated from the moist air in cyclones by
centrifugal action. The centrifugal action is caused by the great
increase in air speed when the mixture of particles and air enters
the cyclone system. The dense powder particles are forced toward
the cyclone walls while the lighter, moist air is directed away
through the exhaust pipes. The powder settles to the bottom of the
cyclone where it is removed through a discharging device. Sometimes
the air-conveying ducts for the dry powder are connected with
cooling systems which admit cold air for transport of the product
through conveying pipes. Cyclone dryers, such as shown here have
been designed for large production schedules capable of drying
ton-lots of powder per hour.
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Spray Dryerdiagram of a typical spray drying operation utilizing
a centrifugal atomizer and a cyclone separator
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Pre-Concentration of Liquid Feed. For operation of a spray dryer
it is usual practice to pre-concentrate the liquid as much as
possible. There are several reasons for this :
Economy of operation (evaporation is less expensive) Increased
capacity (amount of water evaporation is constant) Increase of
particle size (each droplet contains more solids) Increase of
particle density (reduction of vacuole size) More efficient powder
separation (related to increased density) Improved dispersibility
of product (reduction in surface area)
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First, it must be recognized that water removal in a vacuum
evaporator and in a spray dryer are two very different processes.
Evaporation under vacuum is a process which takes place at a much
lower temperature than spraydrying. Generally, the temperature of
the first stage is only 65 C and subsequent stages even less. For
this reason, vacuum evaporation in multiple stages permits the use
of low-cost energy and regeneration of the energy contained in the
vapor removed from the product. In principle, very little heat
energy is used or lost during vacuum evaporation.In contrast, spray
drying takes place at atmospheric pressure; therefore, the drying
air needs to be heated to high temperatures, generally around
150-175 C. This requires high-cost fuel in the form of gas or oil.
Besides, there is almost no opportunity to regenerate the energy
from the vapor phase. Thus, for efficient industrial spray drying
operation, it is usual to combine the two processes.
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Next, it must be recognized that the performance of a spray
dryer is rated according to the maximum amount of water which can
be removed per hour by that system. For example, a spray dryer
rated at 1000 kg/hr water evaporation will produce only 111 kg/hr
of bone-dry powder from a liquid of 10% total solids. If that
liquid is concentrated to 45% total solids, the powder production
increases to 818 kg/hr of bone-dry powder.
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Finally, the powder structure and, therefore, the physical
properties of a powder is very dependent upon the total solids
concentration of the liquid which is being dried. If the droplets
are maintained at a constant size, then, the amount of solids will
affect both the size and the density of the dry particles. The
structure of a spray-dried particle is a hollow sphere, with the
solids being a shell which surrounds a central vacuole. As the
total solids of the feed increases, the shell becomes thicker and,
as a consequence, the particle does not shrink as much during
drying. Similarly, as the air-filled vacuole decreases in size, the
particle density increases.
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The increase in particle density has a pronounced influence on
the efficiency of powder separation/collection by the cyclones,
because these operate on the principle of a difference in the
buoyant density difference between air and particles. It is
well-known in the spray-drying industry that drying a liquid of low
solids content is the cause of very fine particles which are
difficult to collect. This results in product losses as well as
environmental pollution when they are discharged into the
atmosphere.
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Konsentrat susu disemprotkan ke atas menara pengering
menggunakan spray nozzle atomizer ber-tekanan tinggi atau rotary
atomizer tower menghasilkan droplet (tetesan) kecil dgn diameter
50-80 m (tahap atomization)
Tahap atomization dilakukan dlm chamber pengering besar yang
dialiri udara panas bersuhu 150-300C
Konsentrat dipanaskan sebelum atomization utk menurunkan
viskositasPENGERINGAN - Spray drying
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Droplet yg terbentuk selama atomization memper-tahankan bentuk
selama proses pengeringan shg partikel bubuk hasil spray-drying
berbentuk spherical.
Udara yg terperangkap dlm partikel menghasilkan densitas yg
rendah.
Air dlm droplet yg sangat kecil akan teruapkan dengan
cepatPENGERINGAN - Spray drying (lanjutan)
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Suhu maksimum partikel selama pengeringan sekitar 65-75C.
Air diuapkan dalam drying chamber, menghasilkan bubuk halus dgn
kadar air 6% dan ukuran diameter partikel rata-rata < 0.1
mm.
Pengeringan akhir atau "sekunder" dilakukan dlm fluid bed yang
mengalirkan udara panas melalui lapisan bubuk yang dialirkan utk
menghilangkan air shg produk memiliki kadar air 2-4%.
Selanjutnya bubuk dipisahkan dr udara pengeringan dgn bantuan
cyclone dan didinginkan dgn udara dinginPENGERINGAN - Spray drying
(lanjutan)
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Limitations on Pre-Concentration. The limit on the extent of
pre-concentration of the feed is dictated by the viscosity of the
liquid, which must not be so high, that the product cannot be
pumped or atomized. For milk powder manufacture, it is common to
pre-concentrate the milk (9% total solids in skim milk; 13% total
solids in whole milk) to 45% in an evaporator. For many protein
isolates, such a high concentration cannot be used, because most
protein solutions are very viscous. In this case, spray drying must
be done with a concentrate of about 25% total solids concentration.
This practice, however, causes the powder particles to have a lower
density. Therefore, these products are typically very light and
fluffy and the unit cost of operation increases dramatically.
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Atomization. The size and uniformity of droplets are determined
by the atomization. Karel (1975) has described this operation as
the most important feature of a spray dryer. Two different
principles are illustrated in the following diagrams.Centrifugal
Atomizer. This is a spinning disk assembly with radial or curved
vanes which rotates at high velocities (2000-20,000 rpm). The feed
is delivered near the center and spreads between the two plates and
is accelerated to high linear velocities before it is thrown off
the disk in the form of thin sheets, ligaments or elongated
ellipsoids. However, the subdivided liquid immediately attains a
spherical shape under the influence of surface tension. The
atomizing effect is dependent upon centrifugal force but also must
depend upon the frictional influence of the external air.
Centrifugal atomizers have the great advantage of less tendency to
become clogged. For this reason, they are preferred for spray
drying of non-homogeneous foods.
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Centrifugal Atomizer for Cyclone Spray Dryers.A. Top view. B.
Side view.High Pressure Spray Jets. High pressure jets are
alternative atomizing systems in which a fluid acquires a
high-velocity tangential motion while being forced through the
nozzle orifice. The fluid emerges with a swirling motion in a cone
shaped sheet, which breaks up into droplets.
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Faktor yg Menentukan Sifat Susu Bubuk Spray DryingKondisi
preheating dan derajat pengentalan yg me- nentukan TS setelah
penguapanDesain pengering (metode atomizing)Temperatur operasi
(inlet & outlet temperature)Umumnya spray drying tdk
menyebabkan denaturasi protein Penurunan kelarutan disebabkan oleh
stabilitas komplek kasein-fosfatPENGERINGAN - Spray drying
(lanjutan)
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Susu bubuk perlu dilindungi dari kelembapan, oksigen, cahaya,
dan panas untuk menjaga mutu dan umur simpan
Susu bubuk mudah menyerap uap air dari udara menyebabkan
turunnya mutu dan penggumpalan
Kandungan lemak dalam WMP dapat bereaksi dgn oksigen di udara
menyebabkan off-flavours, terutama pada penyimpanan suhu tinggi
(> 30C)
Susu bubuk dikemas dalam kantong plasti multi-layer atau kaleng.
PENGEMASAN DAN PENYIMPANAN
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WMP sering dikemas dengan aliran gas Nitrogen utk melindungi
produk dari oksidasi dan mempertahankan flavour dan umur
simpan.
Pemilihan kemasan harus melindungi produk dari kelembapan,
oksigen dan cahaya. Umumnya berupa kantong yg tdd beberapa lapis
utk menyediakan kekuatan dan perlindungan.
Transportasi susu bubuk harus menghindari paparan sinar matahari
langsung.
Beberapa jam transportasi pada suhu tinggi (> 40C) dapat
mengurangi mutu yg dipertahankan selama bbrp minggu penyimpanan dlm
kondisi yg baik.PENGEMASAN DAN PENYIMPANAN
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B. TAHAP PENGOLAHAN SUSU BUBUK FORMULASusu Bubuk
FormulaMerupakan susu bubuk rekonstitusi dari susu skim yang
ditambah lemak susu atau lemak nabatiFormula lebih mudah ditentukan
tergantung tujuan atau permintaan pasarSumber lemak dapat berasal
dari minyak nabatiPengkayaan zat gizi lebih mudah dilakukanProses
lebih sederhana, tidak menggunakan unit evaporasi
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Proses pembuatan tdd 3 (tiga) tahap: Pembuatan susu bubuk inti
Formulasi dan pencampuran Pengepakan / pengalenganTAHAP PENGOLAHAN
SUSU BUBUK FORMULA
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TAHAP PENGOLAHAN SUSU BUBUK FORMULA (lanjutan)Pembuatan susu
bubuk intiTerdiri dari beberapa tahap sbb:a. Pencampuran: minyak,
bubuk skim, lesithin (stabilizer), airb. Penyaringanc. Pemanasan d.
Homogenisasie. Spray dryingf. Pengepakan
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2. Komposisi Formula- Komposisi formula disesuaikan tujuan atau
permintaan pasar - Komponen utama dalam formulasi:* Susu bubuk
inti* Susu skim untuk mencapai jumlah protein yg diinginkan* Gula,
vitamin, mineral- Komponen lain: zat anti kempal, antioksidan,
dllTAHAP PENGOLAHAN SUSU BUBUK FORMULA (lanjutan)
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Susu Bubuk Instan Susu bubuk yg mudah larut jika diberi air
dingin.Merupakan partikel yang besar dan bersifat porous
Prinsip pengolahan ACRSAglomerasi : menyebabkan terjadinya
aglomerasi susu bubuk dengan mencampurkan airRe-dries : setelah
pencampuran dengan air, dikering-kan kembali shg terbentuk partikel
yg besar dan porousCools : pendinginan Sizes : penyeragaman
ukuranC. PENGOLAHAN SUSU BUBUK INSTAN
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AglomerasiSusu bubuk dari loading hopper dimasukkan dalam
aglomerating tube (AT)Uap dimasukkan AT dgn kecepatan tinggi shg
membasahi partikel susu bubuk dan menggabungkannya menyebab-kan
terbentuknya kluster (kesatuan partikel yg volumenya lbh besar =
0,1-0,3 mm) dlm btk tak beraturan (aglomerat)Bubuk aglomerat
terdispersi dlm air lbh cepat dan tidak mudah berhamburan shg lbh
mudah ditangani.Kluster yg lebih besar dipisahkan dari aliran udara
ke dalam wet collector. Selama pembasahan laktosa akan mengkristal
sebagian oleh krn itu susu bubuk instan lebih tidak
higroskopisTAHAP PENGOLAHAN SUSU BUBUK INSTAN (lanjutan)
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PROSES INSTANISASI DAN AGLOMERASI PARTIKELA is a representation
of regular powder. B represents aggregates from drying a rewetted
powder
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As the development went on, the concentration was carried out in
forced recirculation evaporators. In this evaporator the milk
streams upwards through a number of tubes or plates. On the outside
the heating medium, usually steam, is applied. The heating surface
is thus increased in this system, but the evaporation surface is
still limited, as the tubes and plates remain filled with product,
which therefore becomes superheated in relation to the existing
boiling temperature. Not until the product leaves the top of the
tubes, are the vapours released and the product temperature
decreases. For the separation of liquid and vapours, centrifugal
separators were preferred. In order to obtain the desired degree of
evaporation the product was recycled in the system. The
concentration was thus controlled by the amount of concentrate
discharged from the plant. Fig. 1 shows a diagram of a forced
recirculation evaporator.
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Falling Film Evaporators
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In order to make the evaporator work as an integral unit the
following auxiliary equipment is needed:Separators Product
distribution system Preheaters Pasteurization/holding equipment Low
thermophilic heating/pasteurizing equipment Condensation and vacuum
equipment Cooling towers High-concentrators Flash coolers Sealing
water equipment Instrumentation and automation
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EVAPORATION OF LIQUID The liquid to be evaporated is evenly
distributed on the inner surface of a tube (see page 39). The
liquid will flow downwards forming a thin film, from which the
boiling/evaporation will take place because of the heat applied by
the steam. See Fig. 3. The steam will condense and flow downwards
on the outer surface of the tube. A number of tubes are built
together side by side. At each end the tubes are fixed to tube
plates, and finally the tube bundle is enclosed by a jacket, see
Fig. 3a. The steam is introduced through the jacket. The space
between the tubes is thus forming the heating section. The inner
side of the tubes is called the boiling section.
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EVAPORATION OF LIQUID Together they form the so-called
calandria. The concentrated liquid and the vapour leave the
calandria at the bottom part, from where the main proportion of the
concentrated liquid is discharged. The remaining part enters the
subsequent separator tangentially together with the vapour. The
separated concentrate is discharged (usually by means of the same
pump as for the major part of the concentrate from the calandria),
and the vapour leaves the separator from the top. The heating
steam, which condenses on the outer surface of the tubes, is
collected as condensate at the bottom part of the heating section,
from where it is discharged by means of a pump.
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Fig. 3 Evaporation in a falling film evaporator tubeFig. 3a
Evaporator calandria
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In order to understand the heat and mass transfer, the basis for
the evaporation, it is necessary to define various specific
quantities. From a given quantity of feed (A) part of the solvent
is evaporated (B) leaving the concentrate or the evaporated product
(C). And thusA = B + C(1)
See Fig. 4, showing specific quantities and the corresponding
heat flow diagram. The evaporation ratio (e) is a measure for the
evaporation intensity and can be defined either as the ratio
between the amount of feed and concentrate or the ratio between the
solids percentage in the concentrate and in the feed.e =A/C =
C-Concentrate/C-Feed(2)
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The principle of all spray dryers is to transform the
concentrate into many small droplets which are then exposed to a
fast current of hot air. Because of the very large surface area of
the droplets (11 of concentrate will be atomized to 1.5 x 1010
particles of 50 with a total surface of 120 m2) the water
evaporates almost instantaneously and the droplets are transformed
into powder particles.