Coal (석탄에너지)

백 성 현

Office : 2남 308, x7474

Email : shbaeck@inha.ac.kr

BET (Brunauer, Emmett & Teller) Equation

가스나 액체를 구체 표면에 등온흡착시켜 분말고체의

표면적을 측정하는 방법

P0 : 포화 증기압

c : 상수 (첫 단일층의 흡착에너지 상수)

v : 주어진 증기압에서 흡착된 증기의 부피

Vm : 단위 중량의 고체에서 단층으로 흡착된 증기의 부피

00

11)( P

Pcv

ccvPPv

Pmm

−+=

−

00

11)( P

Pcv

ccvPPv

Pmm

−+=

−

0 )(PvP- P

0PP

(C-1)/VmC

1/VmC

Y X

P/P0 = 0.05~0.35

일반적

)(10023.6)/(400,22),/()/( 123

3

32 − σ×××= mol

molcmSTPgcmVmgmS

Example Calculation of Surface Area from BET Equation

P/P0 Adsorbed N2 (cc/g)0.1090.1990.309

4.2144.8235.593

P/P0 (X) P/V(1-P/P0) (Y)0.1090.1990.309

0.029030.051510.07995

0.10 0.15 0.20 0.25 0.300.02

0.03

0.04

0.05

0.06

0.07

0.08

Y = 0.0011 + 0.2548 X 1/VmC = 0.0011

(C-1)/VmC = 0.2548

C = 231.64

Vm = 3.92 cc/g

S = (3.92 / 22400) x 6.02 x 1023 x 0.162 x 10-18

= 17.1 m2/g

Trace metals: Lead, Cadmium, Manganese, Arsenic, Antimony, Copper, Mercury, Barium, Nickel, Selenium, Berylium, Thalium, Chromium, Cobalt, and Zinc.

Other: Chlorine, Fluorine, PAHs, Sulfur, Dioxins.

Polycyclic aromatic hydrocarbons

Lead (Pb)

Mercury (Hg)

Coal CompositionCoal is not pure carbon, even Anthracite has impurities.

Coal Cleaning – Removal of sulfur from coal.Scrubbers are used to trap SO2 when coal is burned

Plentiful. Resource ~ 500 years (vs. gas/oil: ~100 years).

Inexpensive. 1-1.5 $/GJ HHV (vs. gas at 2.5+ $/GJ).

Ubiquitous. Wide geographic distribution (vs. middle east).

Clean?! Gasification, esp. with sequestration, produces little gaseous emissions and a chemically stable, vitreous ash.

Coal is of great interest because it is:

Expensive pollution controls

Acid rain

Global warming

Disadvantages

CO2 Emission

Coal Sources

Coal is the world’s most plentiful fossil fuel.Recoverable world coal reserves are estimated at about 1X1012 tons.

32%

29%

12%

8%

7%

7% 5%United States

Russia

China

Australia

Germany

South Africa

Poland

65-95%C2-7%H<25%O<10%S1-2%N

20-70%Char5-15%Ash2-20%H2O20-45%VMPr

oxim

ate

Ana

lysis

Elem

enta

l Co

mpo

sition

From CHNOS Analysis

Coal Composition

Coal Combustion

C + ½ O2 CO

CO + ½ O2 CO2

CO2 + C 2CO

C + O2 => CO2

Carbon Reaction

S + O2 SO2

H2 + ½ O2 H2O

H2O + C CO + H2

CO + H2O => CO2 + H2

Non-Carbon Reaction

1st step : Combustion of Volatile Matter

2nd Step : Combustion of Char

Main Processes in Coal Combustion

Coal Particle

Volatiles

char

homogeneouscombustion CO2, H2O,

…

Devolatilization

heterogeneouscombustion

CO2, H2O, …

tchar=1-2sectvolatiles=50-100mstdevolatile=1-5ms

t

Coal Combustion: Air Pollutants

CO2

CONOxSOxParticulate matterTrace metalsOrganic compounds

Six Pollutants : CO, Pb, NO2, O3, SO2, PM (Particulate Matter)

Coal combustion emissions in Israel:71% of total SO2 emissions.62% of total CO2 emissions.39% of total NOx emissions.38% of total SPM emissions.1% of total CO emissions.

Carbon Dioxide, CO2

C + O2 CO2

Almost 99% of C in coal is converted to CO2.CO2 sequestration is being tested.

Carbon monoxide, CO

C + ½O2 CO

air/fuel ratio residence time temperature turbulence

Hemoglobin (헤모글로빈)

적혈구 속에 존재하는 색소 단백질

철 함유 (4 Fe / Hemoglobin)

산소 운반 (1.36mL O2 / g Hemoglobin)

Coal-S (CS, S2, S, SH)

char

COS, CS2H2S

SO SO2 SO3

O2, M-SO4

SO2 molecule

radicals

SOx

Sources of sulfur in coal: Seawater sulfates, Limestone

Sulfur in Coal (<10%)

Organic sulfur (40%)Chemically bonded to the hydrocarbon matrix : thiophene, thiopyrone, sulfides and thiol.

Inorganic sulfur (60%)Imbedded in the coal, as loose pyrite - FeS2 or marcasite, and calcium/iron/barium sulfates.

H2S : H-S-H

Mercaptan : H-S-R

Nitrogen Oxides (NOx)

Thermal NOxN2 + O ↔ NO + NN + O2 ↔ NO + O

Strong temperature-dependence: >1300-1500°CNot a major source of NO in coal utility boilers.

ZeldovichZeldovich mechanismmechanism

Thermal NOx, Prompt NOx, Fuel NOx

Thermal NOx 생성 조건

(1) 연소온도가 높을때

(2) 연소영역에서 산소농도가 높을때

(3) 고온영역에서 연소가스의 체류시간이 길때

Prompt NO (Hydrocarbon + N2)N2 + CHx ↔ HCN + N + …

N + OH ↔ NO + H

Prevalent only in fuel-rich systems.

Not a major source of NO in coal utility boilers.

Fuel NO (Char-N, Volatile-N)1. Char-N

Char-N + ½O2 → NO

2. Volatile-NVolatile-N HCN/NH3HCN/NH3 + O2 NO

The major source of NO in coal utility boilers (>80%).

[Char-NO = ~25%] < [volatiles-NO = ~75%]

Name Structure ~ Relative amount Stability

Pyridine1

Pyrrole1

Aromatic amines

15-40% More stable

60% Less stable

6-10% Stable

N

NH

NH2

SCR (Selective Catalytic Reduction)SCR (Selective Catalytic Reduction)

* 선택적 촉매환원법(SCR)

NOx와 NH3를 촉매에 접촉시켜 NOx를 N2와 H2O로 생성하는 방법

주반응

4NO + 4NH3 + O2 ↔ 4N2 + 6H2O

2NO2 + 4NH3 + O2 ↔ 3N2 + 6H2O

경제성, NOx 제거 효율, 공정 특성 등 비교시 가장 우수한 공정

* SCR 촉매

금속산화물(Fe2O3, Pt, CuO, WO3)부터 zeolite에 이르기까지 다양

바나듐계(V2O5) 촉매가 우수한 것으로 알려짐

자세한 촉매의 특성은 알려지지 않음

전체 운전비의 약 70% 차지

NOx control options(from AP-42, EPA)

Control Technique NO Reduction Potential(%)

Overfire air (OFA) 20-30Low NOx Burners (LNB) 35-55

LNB + OFA 40-60Reburn 50-60SNCR 30-60SCR 75-85

LNB with SCR 50-80LNB with OFA and SCR 85-95

Particulate Matter

Bottom Ash, Fly Ash

Electrostatic precipitator (ESP)

99% (for 0.1>d(μm)>10)<99% (for 0.1<d (μm)<10)

Fabric filter (or baghouse) As high as 99.9%

Wet scrubber 95-99%

Cyclone 90-95% (d(μm)>10)

1) Bag House

2) Electrostatic Precipitator

효율이 좋다.

운영비, 설치비가 비싸다.

3) Cyclone

5 μm 이상의 입자제거

가장 일반적으로 쓰임

Organic CompoundsVolatile Organic Compound(VOC) Semivolatile Organic CompoundCondensable Organic Compounds

Polynuclear Aromatic Hydrocarbon (PAH)

Napthalene Benzopyrene

Coal Gasification

Reaction ΔH (kcal/mol)

Coal H2 CmHn, C 131.418.238.2

- 17.9- 9.8

- 49.0C + O2 CO2 - 97.0 Combustion

- 58.8

Coal Pyrolysis

C + H2O CO + H2 Steam Reforming

C + 2H2O CO2 + 2H2 Steam Reforming

C + CO2 2CO Boudouard Reaction

C + 2H2 CH4 Methanization

CO + H2O CO2 + H2 Water-Gas Shift Reaction

CO + 3H2 CH4 + H2O

2C + O2 2CO Combustion

Thermodynamic Equilibrium

•Step 1: Treat heated, crushed coal with superheated steam:

• C + H2O → CO + H2

Step 2: CO reacts with H2 to produce methane and water:

CO + 3H2 → CH4 + H2OOr reacts with water:

CO + H2O → CO2 + H2

•Step 3: Purification & Removal of CO2

Energy

< 3000 kcal/Nm3

5000 ~ 6000 kcal/Nm3

8500 ~ 10000 kcal/Nm3

Coal

Gasification

Oxygen or Steam

Gas Cleaning

CO Conversion

CO + H2

H2

Fuel cell Industrial fuel Household fuelCity gas For coal liquefaction

Transpotation fuel

AmmoniaAmmonia Synthesis

Chemical Synthesis

Power Generation

High Energy Density

Low Pollution

국내의 화력발전 환경규제치 강화 추세

Integrated Coal Gasification Cycle : IGCC

Year ‘91-‘94 ‘95-‘98 ‘99-SOx (ppm) 700 500 270 NOx (ppm) 350 350 350

Particulates(mg/m3) 250 100 50

2003년이후신규발전소NOx 80 ppm으로규제

“가스화”는 근본적으로 “연소”에 기초한 기존 화력발전과는 화학반응 자체가 틀림.

산소가 부족한 환원분위기 반응 : No SOx / NOx

석탄내 황성분 : H2S로 발생, 황산/유황으로 회수, 판매가능

석탄내 질소성분 : NH3 로 발생, 세정 편이

석탄내 회분 : 중금속 침출문제 없는 slag으로 발생, 도로포장재등으로 재활용

IGCCSOx : 25 ppm 이하

NOx : 60 ppm 이하

CO2 : 15 ~ 30% 감소

PM : 5 mg/m3 이하

30 40 50 60

0.1

0.2

0.3

Power generation efficiency(%)

CO 2

emis

sion

s (k

g/kW

h)

Coal

Crude oil

Natural gas

Pulverized coal combustionPFBC

IGCCMCFC

Combined Cycle

Combined CycleMCFC

0.0

,

IGCC (Integrated Coal Gasification Combined Cycle)

“Chemical conversion of coal to synthetic gas for combustion in a modified gas turbine”

30% increase in efficiency over brown coal steam power plantCorresponding 30% reduction in CO2 emissionsPower costs 30% less than conventional steam plantSuitable for high moisture fuels including biomass

Cf) ICFC (Integrated Coal Gasification Fuel CellCombined Cycle)

http://www.lanl.gov/projects/cctc/factsheets/wabsh/images/wabsh_schematic.jpg

Comparative SO2 Emissions

1.85

0.160.00

New Coal Current IGCC New Natural gasEmis

sion

s in

Pou

nds

per M

WH

Comparative NOx Emissions

New Coal Current IGCC New Natural gas

Emis

sion

s in

Pou

nds

per M

WH

1.11

0.160.07

Carbon Capture and SequestrationCarbon Capture and Sequestration

Sequestration of Carbon in the OceansEnhancement of the Natural Terrestrial CyclesSequestration of Carbon in Underground Geologic RepositoriesManagement of Carbon by Sequencing Micro-organisms

Cost of Electricity in $/MWh

Conventional Coal

IGCC Conventional Coal

IGCC

Bituminous 46.6 45.8-48.3 75.4 61-67

Subbituminous 44 48-54 64-97 61

Without CCS With CCS

Clean Coal Technique

Coal Gasification

ICGC, ICFC

Coal Liquefaction

Coal To Liquid

석탄

가스화기가스 정제(CO+H2)

F-T합성

생성물분리/정제

디젤휘발유

수소공여 용매

산소수증기

액화반응기 upgrading refining

촉매

수소

석탄간접액화

석탄직접액화

Coal LiquefactionCoal LiquefactionDirect Method

Indirect Method1) Direct Method (Hydrogenation)