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Bahan kuliah ini di ambil dari

berbagai sumber baik dari teks

book maupun internet

Gaseous Fuels

• Natural gas

• Refinery gas

Liquid Fuels

• Kerosene

• Gasoline, diesel

• Alcohol (Ethanol)

• Oil

Solid Fuels

• Coal (Anthracite, bituminous, subbituminous, lignite)

• Wood

Something can burn

Why hydrocarbons?

Many are liquids - high density, easy to transport

Lots of it located at Middle East, Saudi Arabia,

Iran, Iraq

Relatively non-toxic fuel & combustion products

Relatively low explosion hazard

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Covalent Bonds and Radicals

Chemical bonds result from a mutual sharing of electrons between atoms,

the shared electrons are in the outermost shell, known as valence electrons

Lewis notation:

Hydrogen Atomic # 1 1 valence electron

Carbon Atomic # 6 4 valence electrons

Oxygen Atomic # 8 6 valence electrons

H

C

O

Atoms like to have electron configuration like noble gas, usually eight valence

electrons, an octet.

H H C H

H

H

H H2 CH4

Atoms and molecules with unpaired valence electrons are called radicals

e.g. O, H, OH, N, C

Most common hydrocarbon fuels are Alkyl Compounds and are

grouped as:

Paraffins (alkanes): single-bonded, open-chain, saturated (no more

hydrogen can be added)

CnH2n+2 n= 1 CH4 methane n= 4 C4H10 butane

n= 2 C2H6 ethane n= 8 C8H18 n-octane and

n= 3 C3H8 propane isooctane

C

H

H

H

C

H

H

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

C

H

H

H

H

C

H

H

C

H

H

methane propane n-octane

H H

H

C

H

For alcohols one hydroxyl (OH) group is substituted for one hydrogen

e.g. methane becomes methyl alcohol (CH3OH) also known as methanol

ethane becomes ethyl alcohol (C2H5OH) also known as ethanol

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Olefins (alkenes): open-chain containing one double-bond,

unsaturated (break bond more hydrogen can be added)

CnH2n n=2 C2H4 ethene

n=3 C3H6 propene

propene

Note: n=1 yields CH2 is an unstable molecule

H

C

H

H C C

H

H

H

(not very stable -lots of strain in C-C bonds) H - C - C - H

H H

H H

C Napthenes – Alkanes with cyclo structure Cyclopropane

C C

C C

C

C

H

|

H

|

H

H

H

H

Benzene

Aromatics - contains one or

more six-sided ring structures

(benzene structure)

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Olefins (alkenes): open-chain containing one double-bond,

unsaturated (break bond more hydrogen can be added)

CnH2n n=2 C2H4 ethene

n=3 C3H6 propene propene

Acetylenes (alkynes): open-chain containing one C-C triple-bond

unsaturated

CnH2n-2 n=2 C2H2 acetylene

n=3 C3H4 propyne

H C C H

acetylene

Note: n=1 yields CH2 is an unstable molecule

H

C

H

H C C

H

H

H

More Fuels : hydrogen, carbon monoxide, ammonia

Hydrocarbon

Alkena C = C

Alicyclic

Aromatic

Aliphatic

Alkana C - C

Alkuna C C

Cyclo-alkana

Cyclo-propana Cyclo-butana

Toluene Benzene

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Anthracite (hard)

Bituminous (soft)

Mixture of C, H2, S, O2, N2, water and non-combustibles (e.g. Ash)

Macro-organism

Peat (gambut)

Brown coal Lignite

Sub-bituminous

Bituminous Semi-anthracite

Anthracite

Meta Anthracite Grapite

COAL (others : wood, coke)

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65-95% C

2-7% H

<25% O

<10% S

1-2% N

20-70% Char

5-15% Ash

2-20% H2O

20-45% VM

• Inhomogeneous organic fuel formed

mainly from decomposed plant

matter.

• Over 1200 coals have been

classified.

Time, Temperature

Coal Rank

• Coalification forms different coal

types:

(Peat)

Lignite

Bituminous coal

Anthracite

(Graphite)

Pro

xim

ate

An

aly

sis

E

lem

en

tal C

om

po

sitio

n

Coal

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0 500 1000 1500 2000

Anthracite

Bituminous

Lighite

Burned energy (1,000 calories per kg)

0 20 40 60 80 100

Carbon content (%)

Energy

Carbon

Anthracite

– Highest grade; over 85% carbon.

– Most efficient to burn.

– Lowest sulfur content; the least polluting.

– The most exploited and most rapidly depleted coal resource in many areas.

Bituminous

– Medium grade coal, about 50-75% carbon content.

– Higher sulfur content and is less fuel-efficient.

– Most abundant coal found in the USA.

Lignite

– Lowest grade of coal, with about 40% carbon content.

– Low energy content.

– Most sulfurous and most polluting.

Carbon Volatile matter Moisture Ash Heating value

(%) (%) (%) (%) (106 J kg-1)

Anthracite (PA) 77.1 3.8 5.4 13.7 27.8

Bituminous (PA) 70.0 20.5 3.3 6.2 33.3

Subbituminous (CO) 45.9 30.5 19.6 4.0 23.6

Lignite (ND) 30.8 28.2 34.8 6.2 16.8

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Main Processes in Coal

Combustion

coal particle p-coal, d=30-

70m

devolatilization

volatiles

char

homogeneous combustion

heterogeneous combustion

CO2, H2O, …

CO2, H2O, …

tchar=1-2sec tvolatiles=50-100ms tdevolatile=1-5ms

t

Coke : adalah batu bara yang

dihilangkan moisture dan volatile

matter. Prosesnya disebut

karbonisasi pirolisa.

900 – 1200 C high temperatur coke

750 – 900 C medium temperatur coke

500 – 600 C low temperatur coke

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Coal Applications

Homes – heat and cooking

Transportation – steam engines

Industry – metal works

Electricity – power plants

A. Analisis PROXIMATE

Analisis yg paling sederhana, yaitu dgn memanaskan batu bara dgn cara2

tertentu, untuk memperoleh hasil analisa :

1. MOISTURE, M (water) : dipanaskan pada suhu 104 – 110oC dalam waktu

tertentu. Pengurangan berat dikalikan 100% = M

― Surface moisture : moisture karena sumber luar, mis : percikan air,

hujan, kondensasi udara dll

― Inherent moisture : moisture yg terikat dg batu bara dimana

menimbulkan kebasahan. Contoh : kadar IM ± 2 – 4 % u/ anthracite

& bitiminous

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2. VOLATILE MATTER , VM adl bahan yg mudah menguap : dipanaskan dalam ruang

tertutup pada 950oC selama ± 7 menit. VM terdiri dari Hidrogen, CO, CO2,

uap air

3. Kadar abu, A, (ash), caranya membakar sisa batu bara dalam dapur muffler pada

suhu 700 – 750oC.

4. FIXED CARBON, FC : dianggap sb kadar karbon tetap, ditentukan dg mengurangi

sisa M, VM dan A sehingga didapatkan :

Catatan : FC tsb bukan merupakan karbon murni, karena masih mengandung Si, Al, Fe,

Ti, Mg dll. Dan juga tidak mewakili total karbon dari batu bara krn ada C

dikeluarkan sebagai CO, CO2 dll

FC = 100 – ( M + VM + A )

A. Analisis ULTIMATE

Analisi ultimate adalah analisa kandungan unsur kimia bahan bakar secara

kimia, terutama unsur-unsur karbon (C), hidrogen (H), oksigen (O) dan sulfur (S).

Dari kedua analisa diatas dapat dibuat suatu hubungan antara analisa ultimate

dengan analisa proximate seperti dibawah ini :

% C = 0,97 + 0,7 ( VM - 0,1A ) – M ( 0,6 - 0,01M )

% H = 0,036 FC + 0,086 ( VM - 0,1A ) - 0,0035M2

%N2 = 2,10 – 0,020 VM

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Nilai kalor bahan bakar dapat dicari dengan :

1. Pengujian langsung dengan menggunakan CALORIMETER

- Padat & cair : bomb calorimeter

- Gas : gas calorimeter

2. Analisis dengan menggunakan rumus pendekatan yang dikembangkan oleh

DULONG – PETIT :

HHV = 8080 C + 3446 ( H – O / 8 + 2250 S ) ( kkal / kg bb )

8 O

Catatan : - diperlukan data analisa Ultimate

- Analisa tsb akan valid jika kadar karbon ≥ 76% dan kadar oksigen ≤ 10 %

- Jika kadar tsb memenuhi maka hasil yang didapat berbeda hanya 2% dari uji

laboratorium

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What is Petroleum?

Petroleum, also known as Crude Oil ,is

occurring brown to black flammable

liquid.

Mainly constituted of hydrocarbons mixed

with variable amount of sulfur, nitrogen,

oxygen and metal (such as V,Ni) compounds.

100,000 to 1,000,000 different compounds

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Mainly properties of petroleum

API gravity

Most commonly crude oil in the rang 20~45

Higher API, more paraffine, higher yields of gasoline

Sulfur, wet % Sour is S% > 1, Sweet is <0.5

Viscosity at 100°F

131.5 S G

141.5 AP I

C1 5

g rav ity

Skematik

Distilasi

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Technical features to make/improve fuels

Convert heavier products into lighter ones into gasoline, Such as thermal cracking,coking, viscosity breaking, catalytic cracking, and hydrocracking

C16H34 C8H16 + C5H10 + C3H8

Combining lighter products into heavier ones, such as butane and propylene into alkylate , a high-octane gasoline component,such as alkylation and polymerization

C CH2

CH3

CH3

C

CH3

CH3

CH3

H + C C CH2 CH3

CH3

H CH3

CH3

CH3

Rearranging the molecular structure to improve desirable

qualities,such as reforming low-octane gasoline into high octane,

such as catalytic reforming and isomerization

Treating, to remove contaminants such as sulfur and nitrogen

CH2 CH2 CH3 CH3 H C CH3

CH3

CH3

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– A fuel designed for SIE’s

– Mixture of Hydrocarbon, (over 500)1, plus additives.

1. 1 B. Hamilton, FAQ: Automotive Gasoline

Coal tar distillates: Late 19th century.

Gasoline from Petroleum: Early 20th century.

Typical mid-1920s gasoline was 40 - 60 Octane.

1950s: compression ratio increase, requiring higher octane fuels: Leaded was introduced.

1970s: leaded was prohibited.

1970-1990: slow changes in gasoline as lead was phased-out.

1990 + : the US Clean Air Act started forcing major compositional changes on gasoline.

These changes will continue into the 21st Century.

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The sound of abnormal combustion.

Detonation (1 of 2)

Ketika terjadi detonasi, flame front merambat

mendekati kecepatan suara.

Ketika terjadi detonasi, tekana di dalam ruang

bakar terbentuk dengan cepat, sehingga bisa

merusak mesin dan menimbulkan spark knock

(suara)

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Octane

Bahan bakar terbakar dalam ruang bakar dalam

hitungan beberapa millisecond, tetapi

diharapkan sebagai suatu pembakaran yang

terkontrol, bukan sebuah ledakan.

Flame merambat pada kisaran 50 – 250 m/s.

Octane number : kecenderungan suatu bahan

menahan detonasi/knock pada kondisi operasi

tertentu.

Semakin besar octane number, semakin besar

dia mampu menahan detonasi

Cara mengukur octane number :

• normal heptane (n-C7H16) = 0

• isooctane (C8H18) = 100.

• campuran dari dua hydrocarbon diatas

menunjukkan nilai octane suatu bahan bakar. Mis:

campuran dari 10% n-heptane dan 90% isooctane

mempunyai nilai octane = 90.

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Octane Number Measurement

Dua methode telah dibuat untuk mengukur nilai octane, dengan

sebuah mesin standar satu cylinder dibawah pengawasan Cooperative

Fuel Research (CFR) Committee th. 1931.

Mesin CFR engine yang dipakai adalah 4-langkah dgn 3.25” bore and

4.5” stroke, compression ratio dapat divariasi dari 3 to 30.

Research Motor

Inlet temperature (oC) 52 149

Speed (rpm) 600 900

Spark advance (oBTC) 13 19-26

(varies with CR)

Coolant temperature (oC) 100

Inlet pressure (atm) 1.0

Humidity (kg water/kg dry air) 0.0036 - 0.0072

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Knock Characteristics of Various Fuels

Formula Name Critical r RON MON

CH4 Methane 12.6 120 120

C3H8 Propane 12.2 112 97

CH4O Methanol - 106 92

C2H6O Ethanol - 107 89

C8H18 Isooctane 7.3 100 100

Blend of HCs Regular gasoline 91 83

n-C7H16 n-heptane 0 0

Suatu baha bakar dg antiknock lebih tinggi dr octane, ON disetarakan

dg:

mT adalah jumlah tetraethyl lead per U.S. gallon

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Natural Gas :

1. Low pressure Natural Gas : yang biasanya digunakan langsung untuk

memasak atau memanaskan rumah tangga. Umumnya disalurkan dalam pipa

dalam tanah.

2. CNG ( Compressed Natural Gas ) : adalah gas alam yang di compress

pada tekanan tinggi sehingga bisa di bawa dengan kendaraan misalnya

truck.

3. LNG ( Liquid Natural Gas ) : Gas alam yang di dinginkan sehingga

menjadi cair. LNG lebih padat dari CNG karena berbentuk cair sehingga

lebih mudah diangkut. LNG dibuat dengan proses refrigerasi – 260 F.

Pendinginan tersebut akan menghilangkan uap air, butane, propane dan

beberapa gas lain, sehingga komponen utama LNG adalah 98 adalah

methane

LPG ( Liquid Petrolium Gas ) : Gas yang terutama terdiri dari propane

dan beberapa gas lain yang di compress dengan tekanan tinggi ( 200 psi)

sehingga mencair dan disimpan dalam tangki bertekanan.