Transcript Unit Operation and Process Material and Energy Balance

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Unit Operation and Process
Material and Energy Balance
Widelia Ika Putri, S.T.P., M.Sc.
Basic Principles
The mass and energy going into
the box must balance with the
mass and energy coming out.
The law of mass conservation
states that mass can’t be created
nor destroyed.
The law of energy conservation
states that energy can’t be created
nor destroyed.
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Mass Conservation
Milk
X kg
Centrifugal
separator
Skim milk
A kg
Cream milk
B kg
So:
Milk mass = skim milk mass + cream milk mass
X kg/minute = A kg/minute + B kg/minute
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Energy Conservation
Food
(chemical
energy)
Body
Mechanical
energy
So:
Chemical energy entering body =
mechanical energy leaving body
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Energy Conservation
Heating water
Heat
exchanger
Milk
cool water heat lost
Heating milk
So:
The heat lost by the heating water = the heat
gained by the milk + the heat lost from heat
exchanger to its surroundings
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Soal
1. Berapa air yang harus diuapkan dari
pemekatan lar. Garam 5% menjadi
lar. Garam 20%?
2. Berapa penurunan berat yang terjadi
jika bahan dikeringkan dari kadar air
80% menjadi kadar air 50%?
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Soal
1. Tentukan jumlah daging sapi tidak
berlemak (lean beef), daging babi
berlemak (fat pork), dan air yang harus
ditambahkan untuk membuat adonan sosis
sebanyak 100 kg. dengan syarat :
 Lean beef => lemak 14%, protein 19%, air
67%
 Fat pork => lemak 89%, protein 3%, air
8%
 Sosis => lemak 20%, protein 15%, air
65%
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Soal
2. Pada pembuatan jam buah-buahan digunakan
perbandingan 45 buah : 55 gula. Untuk
mendapatkan konsistensi jam yang baik, jam harus
mengandung padatan terlarut 65%. Pada proses
pembuatan jam terdiri atas pencampuran buah dan
gula dengan perbandingan tersebut, penambahan
pektin, pemekatan campuran dalam evaporator
vacum sehingga kandungan padatan terlarut
minimal 65%. Jumlah pektin yang diperlukan
dipengaruhi oleh jumlah gula yang ditambahkan
(untuk 100 kg gula diperlukan pektin 1kg). Apabila
buah yang digunakan mengandung padatan terlarut
10%. Hitung berat buah , gula dan pektin yang
diperlukan? Untuk membuat jam 100 kg, dianggap
bahwa padatan terlarut yang dimaksud berasal dari
buah dan gula (pektin tidak dianggap).
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Energy
consumed
Direct energy
Indirect energy
Fuel and
electricity used on
the farm, in
transport, in
factories, in
storage, selling,
etc.
Energy which is
used to build the
machine, to make
the packaging, to
produce the
electricity, etc.
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Btu
Energy
unit
joule
kilocalories
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Heat
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1
2
Latent Heat
Sensible Heat
Is the heat
required to
change the
physical state of
material, at
constant
temperature.
The heat which
when added or
subtracted from food
materials changes
their temperature
and thus can be
sensed .
Latent Heats (phase changes)
Vapourisation (L to V)
Melting (S to L)
Sublimation (S to V)
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Sensible heat
‘Sensible’ heat – heat/enthalpy that must
be transferred to raise or lower the
temperature of a substance or mixture of
substances.
Heat capacities/specific heats (solids,
liquids, gases,vapours)
Use of mean heat capacities/specific
heats over a temperature range
Use of simple empirical equations to
describe the variation of Cp with T
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Uses
Heat required for a process
Rate of heat removal from a process
Heat transfer/design of heat exchangers
Process design to determine energy
requirements of a process
Pump power requirements (mechanical
energy balance)
Pattern of energy usage in operation
Process control
Process design & development
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Soal
1. Pengering casein mengkonsumsi gas
alam 4m3/h dengan nilai kalori
800kJ/mol. Jika input pengering
adalah 60 kg casein basah per jam,
pengeringan dari kadar air 55%
menjadi kadar air 10%, hitung
keseluruhan efisiensi panas
pengering (hanya menggunakan
panas latent)?
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Soal
2. Autoclave berisi 100 kaleng sop.
Dipanaskan mencapai suhu 100oC.
Kaleng didinginkan mencapai 40oC
sebelum meninggalkan autoclave. Berapa
air dingin yang dibutuhkan jika air masuk
pada suhu 15oC dan keluar suhu 35oC?
ket: Panas spesifik sop 4,1 kJkg-1oC-1 &
kaleng 0,5 kJkg-1oC-1 . Berat setiap kaleng
60 g & berisi sop 0,45 kg. diasumsikan
panas di dinding autoclave1,6 x 104 kJ
dan tidak ada panas yang hilang melalui
dinding.
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Soal
1. Sebuah pabrik minuman, menghasilkan
produk dengan kadar alkohol 16% dan
kadar gula 3%. Untuk membuatnya
diperlukan campuran:
 Anggur 1 => kadar alkohol 14,6% & kadar
gula 0,2%
 Anggur 2 => kadar alkohol 16,7% & kadar
gula 1,0%
 Anggur 3 => kadar alkohol 17,0% & kadar
gula 12,0%
bila diinginkan membuat 100 kg produk,
berapa berat masing2 minuman yang
diperlukan?
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