燃燒源排放氣相汞與其他污染物之 多重控制研發

Graduate Institute of

Environmental Engineering

Air Pollution &

Environmental Material Lab.

Hsing‐Cheng Hsi (席行正)

Graduate Institute of Environmental Engineering National Taiwan University

2015/10/22

環保署2015年持久性有機污染物及汞管理研討會

燃燒源排放氣相汞與其他污染物之 多重控制研發

1

Outline

1. Why should we concern about Hg

contamination? Especially low-concentration Hg emissions (ppb level)?

2. How to control low-concentration Hg

emissions? Do we have chances? What are the challenges?

3. Does catalysis and absorption a solution?

2

MERCURY: WHY IS IT OF INTEREST?

• Unique physical and chemical properties

• Hg⁰: melting point = -39 °C, boiling = 357 °C, high saturation vapor pressure (0.246 Pa at 25 °C), easily vaporized at > 150

°C, low water solubility (6.0×10^-5 g/L H₂O at 25 °C) 。

• Existing in gaseous form in flue gases, difficult to be removed by conventional air pollution control devices.

• Highly toxic

− Attack neuro-system

− After absorption of mercury in the body, mercury circulates in the blood stream and accumulates in the spleen, liver, kidneys and bones.

• Bioaccumulation and Biomagnification

− Mercury, especially organic mercury that had greatest toxicity, can bioaccumulate in aqueous species (e.g., fish) and affect human and wildlife health via food chain.

3

Minamata Disease ( 水俣病 )

• First discovered in 1956 in certain villages around Minamata Bay, Japan. In 1965, breakout again.

• Attributed to the consumption of fish or shellfish contaminated by methylmercury compounds, which were discharged from chemical plants.

• In March 1997, the Japan government certified 2,952 Minamata disease patients.

• The victims certified as Minamata disease could receive compensation from the

companies responsible for the pollution. A

lump-sum payment of ~24,000,000 Japanese Yen had been paid to each of the 2,952 certified patients, and a total payments amount to

approximately 136 billion Japanese Yen.

The crippled hand of a Minamata disease victim

(photo: W. E. Smith)

4

Hg has caused emerging concerns

5

6

MERCURY SOURCES

• The total global mercury input to the atmosphere from natural and anthropogenic sources was estimated at 4,400−7,500 metric ton/yr .

• The main natural emission sources are the oceans, volcanoes and soil weathering.

• Global anthropogenic mercury emissions are estimated to be 1,960 (1,010-4,070) metric ton/yr , with 50-100%

error

(Global Mercury Assessment 2013, UNEP)

.

• The total anthropogenic Hg emission of Taiwan was about 1.5~15 metric ton/yr, mainly from utility boiler

(26%), waste combustor (20%), cement kiln (14%) and other sources such as smelters.

7

REGULARTIONS

• The Minamata Convention on Mercury by United Nations in January 19, 2013 has set a goal to develop an international treaty to curb mercury emissions and discharges.

• Mercury and Air Toxics Standards (MATS) were finalized by USEPA in December 2011 for coal-and oil-fired electric

generating units.

• (Supreme Court Rules Against EPA Mercury And Air Toxics Standards For US Coal Plants)

• 中國《火电厂大气污染物排放标准》（GB13223-2011）中，规 定燃煤电站汞污染排放标准为30 μg/m³，自2015年1月1日起开 始执行。

• Taiwan also set Hg emission standards in January 22, 2013 for utility boiler (< 5 μg/Nm³ for existing and < 2 μg/Nm³ for new sources).

8

Control strategies for Hg removal

Wet Scrubber

Hg⁰ NOx SOx PCDD/Fs

>2500 °F Flue Gas

700 °F

SCR ESP or FF Coal & Air

Ash Residue

Ammonia

Stack

Other options?

Fuel cleaning &

Waste management

Enhancement of oxidation

Sorbent injection

Removal of soluble Hg²⁺

Lime

9

SCR是還原劑在催化劑作用下選擇性將 NO_x 還原為 N₂ 的方法。對於固定 源脫硝來說，主要是採用向溫度約為280 ~ 420 ℃的煙氣中噴入尿素或氨，

將NO_x 還原為N₂ 和H₂O。

如果尿素作還原劑，首先要發生水解反應：

選擇性催化還原的工作原理

( ^異氰酸 )

HNCO NH

NH CO

NH

₂

− −

₂

→

₃

+

2 3

2

O NH CO

H

HNCO + → +

氨選擇性還原 NOx 的主要反應式為：

O H N

O NO

NH

₃

4

₂

4

₂

6

₂

4 + + → +

O H N

NO

NH

₃

6 7

₂

12

₂

8 + → +

O H N

NO NO

NH

_{3 2}

2

₂

3

₂

2 + + → +

10

在 SO

₂

和 H

₂

O 的存在條件下，在催化劑表面還會發生如下的 副反應：

反應中形成的(NH

₄

)

₂

SO

₄

，和 NH

₄

HSO

₄

很容易沾污空氣預熱器，

對空氣預熱器損害很大。

SO

₃

轉換與使用之觸媒種類有明顯關係

3 2

2

2

2 SO + O → SO

4 4

2 3

3

SO H O NH HSO

NH + + →

(

₄

)

_{2 4}

2 3

2 NH

3

+ SO + H O → NH SO

4 2

2

3

H O H SO

SO + →

11

Hg removal with adsorbents and catalysts

•

1990-1995: Carbon-based adsorption processes, such as

activated carbon injection (ACI), have shown to possess the potential to remove very low concentrations (e.g., μg/m

³

or ppb levels) of mercury species that occur in coal combustion flue gas streams.

•

1995-2005: Activated carbons with large mercury adsorption capacities can be prepared by impregnating the samples with sulfur or halogen compounds at various temperatures.

•

Little attention has, however, been paid to the adsorbent modification using metal salts, such as copper salts.

•

Photocatalysts, such as TiO

₂

, may be possibly applied to enhance the oxidation of Hg

⁰

and increase the adsorption.

•

SCR catalyst can be a good material for multipollutant

control. 12

Studies in our lab

• Preparation and characterization of metal-

impregnated SCR and metal-doped activated carbon.

• Gaining a better understanding on the control of multipollutant (i.e., Hg

⁰

, SO

₂

, NO) using the metal- impregnated materials.

13

• A commercial honeycomb SCR catalyst (V

₂

O

₅

-

WO

₃

/TiO

₂

-SiO

₂

) was obtained from Taiwan Power Company.

• V, Mn, and Cu oxides are chosen to modify the SCR surface with 100

^o

C hydrothermal process and then 300

^o

C calcination.

• MnO

_x

surface-modified honeycomb SCR catalysts with a targeting Mn content of 1, 3, 5, and 10 wt% as the precursor Mn(NO

₃

)

₂

were impregnated onto the SCR surface using a 100

^o

C hydrothermal process followed by 300

^o

C calcination.

(part 1) SCR catalysts preparation

14

Hg ⁰ Oxidation and SO ₂ /NO _x Removal Tests

• Hg

⁰

oxidation tests were carried out using a simulated

coal-combustion flue gas as a carrier gas containing 30±5 μg Nm

^-3

Hg

⁰

at 350 °C. Experiment was performed for 900 min.

• The simulated flue gas also contained 14 vol% CO

₂

, 10 vol% H

₂

O, 6 vol% O

₂

, 50 ppmv HCl, 200 ppmv SO

₂

, 200 ppmv NO, 200 ppmv NH

₃

and balanced N

₂

.

• The mercury concentrated on the gold was then thermally desorbed and sent as a concentrated mercury stream to a cold-vapor atomic fluoresce spectrophotometer (CVAFS;

Brooks Rand Lab Model III) for analysis.

• The removal of SO

_x

and NO

_x

were continuously monitored with a flue gas component analyzer (Sick Maihak S710).

15

Hg Removal and Oxidation Test Parameters

Catalyst weight Quartz sand Testing T Flow rate 10 mg 0.5 g 150 and 350 °C 1.5 L/min

N

₂

gas condition

Gas condition N₂ only

Flue gas condition

Flue gas condition

O₂ HCl SO₂ NO NH₃ H₂O CO₂ N₂

6 vol% 50 ppm_v

200 ppm_v

200 ppm_v

200 ppm_v

10 vol%

12

vol% balanced

Hg

⁰

concentration = 30±5 μg/Nm

³

16

(1) Gas mixing chamber-1 (2) Gas mixing chamber-2 (3) Hg⁰vapor generator

(4) Temperature-controlled; a adsorption fixed-bed (5) Gold/amalgamation/CVAFS\

(6) Computer system (7) Cooler/condenser

(8) SO₂/NO continuous monitoring system

EXPERIMENTAL APPARATUS

17

Physical properties of SCR

• BET area of SCR catalyst slightly increased after modification.

• The results also shows that the catalysts lacked of microporosity.

Sample

S_BET S_micro V_t V_micro

(m² g^-1) (m² g^-1) (cm³ g^-1) (cm³ g^-1)

Raw catalyst 63.7 0 0.28 0

VO_x-impregnated catalyst 89.7 0 0.24 0

MnO_x-impregnated catalyst 66.7 0 0.26 0

CuO_x-impregnated catalyst 96.4 0 0.25 0

18

SEM results

SEM images indicated that the raw and treated catalysts had a similar morphology, presenting as bean-shaped nanoparticles within 10-30 nm.

Raw catalyst VO_x-impregnated catalyst

MnO_x-impregnated catalyst CuO_x-impregnated catalyst

19

XRD examination

• After transition metal oxides (V/Mn/Cu) loadings, all of samples had similar activated component. It can be concluded that VO_x, MnO_x and CuO_x were evenly dispersed in the SCR catalysts.

2θ (degrees)

20 30 40 50 60 70 80

Intensity (a.u)

★

★ ★

★★ ★ ★★ ★

★ Anatase TiO₂

(a) (b) (c) (d) (a) Raw catalyst

(b) VO_x-impregnated catalyst (c) MnO_x-impregnated catalyst (d) CuO_x-impregnated catalyst

20

XPS atomic concentration examination (1)

Sample

Atomic concentration of elements by XPS（at%）

O_1s Si_2p Ti_2p W_4f V_2p Mn_2p Cu_2p

Raw catalyst 76.00 7.17 13.65 3.10 ━ ━ ━

VO_x-impregnated catalyst 68.69 6.99 16.29 3.07 4.93 ━ ━

MnO_x-impregnated catalyst 70.45 9.15 15.53 2.54 ━ 2.34 ━

CuO_x-impregnated catalyst 68.55 8.99 18.06 2.64 ━ ━ 1.75

• The table shows surface compositions of the SCR catalysts based on XPS results.

• The analyzed results indicated that have transition metal oxides contain W、Ti、Si、V、Mn、Cu in the SCR catalyst.

21

XPS atomic concentration examination (2)

Sample Valence state Position

(eV)

Peak area (%)

VO_x-impregnated catalyst

V⁴⁺ 516.0 57.2

V⁵⁺ 517.2 42.8

MnO_x-impregnated catalyst Mn⁴⁺ 642.0 100 CuO_x-impregnated catalyst Cu²⁺ 933.3 100

• XPS results showed that V⁴⁺ and V⁵⁺, Mn⁴⁺ and Cu²⁺ were the major valence states presenting in the VO_x-, MnO_x-, and CuO_x-impregnated SCR catalysts, respectively.

22

Hg

⁰

Oxidation Percentage under N

₂

/flue gas condition

Oxidation time (min)

0 200 400 600 800

Hg0 oxidation percentage (%)

0 20 40 60 80 100

Raw catalyst

VOx-impregnated catalyst MnOx-impregnated catalyst CuOx-impregnated catalyst

Oxidation time (min)

0 200 400 600 800 1000

Hg0 oxidation percentage (%)

0 20 40 60 80 100

Raw catalyst

VOx-impregnated catalyst MnOx-impregnated catalyst CuOx-impregnated catalyst

• After metal oxide impregnation, the Hg⁰ oxidation of VO_x, MnO_x, and CuO_x- impregnated catalysts was between 0.5 and 44% under N₂ condition.

• The Hg⁰ oxidation percentages of VO_x, MnO_x, and CuO-impregnated samples were markedly enhanced to > 64% under flue gas condition.

• These experimental results suggest that flue gas components play a key role in heterogeneously oxidizing Hg⁰ into Hg²⁺.

N₂ condition Flue gas condition

23

Enhancement of SO ₂ /NO removal for SCR catalyst

Experimental time (min)

0 200 400 600 800 1000

SO2 removal enhancement (%)

0 20 40 60 80 100

Raw catalyst

VOx-impregnated catalyst MnOx-impregnated catalyst CuOx-impregnated catalyst

Experimental time (min)

0 200 400 600 800 1000

NO removal enhancement (%)

0 20 40 60 80 100

Raw catalyst

VOx-impregnated catalyst MnOx-impregnated catalyst CuOx-impregnated catalyst

• Metal oxide impregnation resulted in 6 to 29 % increase in SO₂ removal.

• The raw and surface-impregnated SCR catalysts exhibited strong and steady NO reduction activity.

• After metal oxide impregnation, the NO removal significantly increased.

24

Sample

N₂ condition Coal-combustion flue gas condition Average Hg⁰

oxidation (%)

Average Hg⁰ oxidation

(%)

Average SO₂ removal

(%)

Average NO removal

(%)

Raw catalyst 20.1±9.0 48.3±11.3 6.1±2.4 77.6±1.8

VO_x-impregnated catalyst 20.0±12.2 96.4±1.5 20.8±4.6 91.8±1.8 MnO_x-impregnated catalyst 13.2±6.8 81.6±11.1 10.4±2.4 90.2±1.3 CuO_x-impregnated catalyst 3.2±1.5 95.2±1.4 20.0±2.0 89.0±2.2

• These observations support the importance of flue gas components on enhancing Hg⁰ oxidation.

• That various impregnated metal oxides can cause different effects on Hg⁰ oxidation, SO₂ and NO removal efficiency.

• The MnO_x-modified catalyst had the greatest potentials for the Hg⁰/SO₂/NO control.

Average Hg ⁰ /SO ₂ /NO oxidation/removal efficiency

25

(Part 2) Influence of flue gas components on MnO

_x

-impregnated SCR catalysts

26

Physical properties of SCR

Sample S_BET S_micro V_t V_micro

m² g^-1 m² g^-1 cm³ g^-1 cm³ g^-1

Raw-catalyst 63.7 0 0.3 0

MnO_x-1%/catalyst 66.0 0 2.4 0

MnO_x-3%/catalyst 69.7 8.2 2.5 0

MnO_x-5%/catalyst 66.7 0 0.3 0

MnO_x-10%/catalyst 32.8 4.7 1.9 0

• When MnO_x content increased from 0 to 5 wt%, all of the resulting catalysts had a similar surface area as the untreated sample.

• When the MnO_x-doped amount was up to 10 wt%, the surface area was decreased due to the blockage of pores with MnO_x doping.

27

Although the irregular bean-shaped nanoparticles within 10‒30 nm on the raw catalyst supporter were still presented in the treated samples.

SEM results

Raw catalyst MnO_x-1%/catalyst

MnO_x-3%/catalyst MnO_x-5%/catalyst MnO_x-10%/catalyst

28

2θ (degrees)

20 30 40 50 60 70 80

Intensity (a.u)

★

★ ★ ★★ ★ ★★ ★

★ Anatase TiO2

(a) (b) (c) (d) (a) Raw catalyst

(b) MnO_x-1%-impregnated catalyst (c) MnO_x-3%-impregnated catalyst (d) MnO_x-5%-impregnated catalyst (e) MnO_x-10%-impregnated catalyst

(e)

XRD examination

• Significant changes in crystal phases were not observed after MnO_x

impregnation at various contents, except for that the intensity of the diffraction peaks denoting anatase TiO₂ became slightly weaker.

29

XPS atomic concentration examination

Sample

Atomic concentration of elements by XPS（at%）

O_1s Si_2p Ti_2p W_4f V_2p Mn_2p Cu_2p

Raw catalyst 76.0 7.17 13.7 3.10 ━^* ━ ━

MnO_x-1%-doped

catalyst 61.0 2.89 25.8 8.61 ━ 1.74 ━

MnO_x-3%-doped

catalyst 68.9 3.27 18.4 6.51 ━ 3.02 ━

MnO_x-5%-doped

catalyst 70.2 3.32 15.9 6.48 ━ 4.03 ━

MnO_x-10%-doped

catalyst 68.8 2.41 16.0 5.78 ━ 7.06 ━

• After MnO_x impregnation, the strength of the Mn_2p peak, standing for the presence of Mn, accordingly enhanced to 1.74–7.06 at% with increasing the impregnation amount from 1 to 10 wt%.

30

Hg

⁰

Oxidation Percentage under N

₂

/flue gas condition

Oxidation time (min)

0 200 400 600 800 1000

Hg0 oxidation percentage (%)

0 20 40 60 80 100

Raw catalyst

MnOx-1%-impregnated catalyst MnOx-3%-impregnated catalyst MnOx-5%-impregnated catalyst MnOx-10%-impregnated catalyst

Oxidation time (min)

0 200 400 600 800 1000

Hg0 oxidation percentage (%)

0 20 40 60 80 100

Raw catalyst

MnOx-1%-impregnated catalyst MnOx-3%-impregnated catalyst MnOx-5%-impregnated catalyst MnOx-10%-impregnated catalyst

N₂ condition Flue gas condition

• Hg⁰ oxidation of DeNO_x catalyst can be greatly improved after MnO_x doping in different contents.

• The Hg⁰ oxidation was inhibited under N₂ condition.

• The mercury oxidation of raw DeNO_x catalyst was approximately 50% and the MnO_x-5%-modified catalyst having the greatest oxidation to up to 84%.

31

Enhancement of SO ₂ /NO removal for SCR catalyst

Experimental time (min)

0 200 400 600 800 1000

NO removal enhancement (%)

0 20 40 60 80 100

Raw catalyst

MnOx-1%-impregnated catalyst MnOx-3%-impregnated catalyst MnOx-5%-impregnated catalyst MnOx-10%-impregnated catalyst

Experimental time (min)

0 200 400 600 800 1000

SO2 removal enhancement (%)

0 10 20 30 40 50 60

Raw catalyst

MnOx-1%-impregnated catalyst MnOx-3%-impregnated catalyst MnOx-5%-impregnated catalyst MnOx-10%-impregnated catalyst

• The raw catalyst caused small SO₂ removal of 6.1% and MnO_x impregnation increased SO₂ removal to 8.9–14.5%, with 10% MnO_x-impregnated catalyst having the greatest SO₂ removal enhancement.

• MnO_x impregnation improved the NO reduction from 77.6 to up to 91.4%

under flue gas condition and increasing the MnO_x amount was shown to

enhance the NO reduction.

32

Average Hg ⁰ /SO ₂ /NO oxidation/removal efficiency

Sample

N₂ condition Coal-combustion flue gas condition Avg. Hg⁰

oxidation (%)

Avg. Hg⁰ oxidation

(%)

Avg. SO₂ removal

(%)

Avg. NO removal

(%) Raw catalyst 25.2 ±3.3 49.6±3.9 6.12±2.4 77.6±1.8 MnO_x-1%/catalyst 28.0 ±3.2 52.0±3.6 8.94±0.9 84.2±0.8 MnO_x-3%/catalyst 36.9 ±1.4 63.0±2.7 9.36±2.0 87.0±0.6 MnO_x-5%/catalyst 32.6 ±1.1 83.8±3.0 10.4±2.4 90.2±1.3 MnO_x-10%/catalyst 47.4 ±2.0 53.7±3.7 14.5±1.7 91.4±0.6

N

₂

/simulated coal-combustion flue gas condition

• Hg⁰ oxidation efficiency at flue gas condition was mush greater than that under the N₂ condition.

• The MnO_x-5%-modified catalyst had the greatest potentials for the Hg⁰/SO₂/NO control.

33

MnO_x-5%-impregnated catalyst^*

Avg. Hg⁰oxidation (%)

Without HCl 26.6 ±1.7

25 ppm HCl 44.3 ±2.0

50 ppm HCl 83.8±3.0

6% O₂ 83.8±3.0

10% O₂ 90.3±1.9

Without NO 91.9±2.1

100 ppm NO 88.7±2.7

200 ppm NO 83.8±3.0

Without NH₃ 99.5±0.3

NH₃:NO = 0.5 96.7±0.5

NH₃:NO = 1 83.8±3.0

NH₃:NO = 2.5 62.3±1.7

Without SO₂ 30.3 ±2.5

100 ppm SO₂ 64.9 ±1.8

200 ppm SO₂ 83.8 ±3.0

500 ppm SO₂ 23.5±2.1

200 °C 73.6±1.6

250 °C 77.2±2.7

300 °C 82.8±1.0

350 °C 83.8±3.0

Effect of flue gas components and temperature on Hg

⁰

oxidation

The presence of HCl, O₂, and SO₂ at ≤200 ppm promoted Hg⁰ oxidation. However, increasing the NO and NH₃ concentrations reduced Hg⁰ oxidation. Elevating flue gas temperature enhanced Hg⁰ oxidation.

34

SEM results

VO_x-SiO₂

MnO_x-SiO₂ CuO_x-SiO₂

SEM results showed that the change in activated carbon surface

morphology was varied after various metal oxide surface modification.

CAC/raw VO_x/CAC

MnO_x/CAC CuO_x/CAC

35

Sample S_BET S_micro S_micro/

S_BET V_t V_micro V_micro/

V_t m² g^-1 m² g^-1 (%) cm³ g^-1 cm³ g^-1 (%)

Raw CAC 1230 1108 90 0.69 0.59 86

VOx/CAC 1223 1089 89 0.69 0.57 83

MnOx/CAC 1085 1003 92 0.61 0.53 87

CuO/CAC 1090 971.8 89 0.61 0.51 84

Physical properties of raw/modified activated carbon

• After transition metal oxides doped, the surface area and total pore

volume of activated carbon decreased due to the pore blockage or filling.

• The VO_x/CAC sample had the largest S_BET and S_micro of 1223 and 1089 m² g^-1, respectively.

36

XRD examination

After metal oxides-doped, all resulting samples showed similar XRD patterns. It can be concluded that VO_x, MnO_x, CuO_x were uniformly dispersed on the surface of activated carbon.

20 40 60 80

(a) (b) (c) (a) CAC/raw (b) VO_x/CAC (c) MnO_x/CAC (d) CuO_x/CAC

(d)

37

XPS examination (1)

Sample

Atomic concentration of elements by XPS

（at%）

C

_1s

O

_1s

V

_2p

Mn

_2p

Cu

_2p

Raw/CAC 76.74 23.26 ━ ━ ━

VO

_x

/CAC 71.53 28.47 * ━ ━ ━

MnO

_x

/CAC 60.96 29.55 ━ 9.49 ━

CuO

_x

/CAC 59.33 31.79 ━ ━ 8.87

*━: Not detected in XPS examination. However, acid digestion followed by ICP/AES measurements verifies the presence of V on the VOx/CAC surface..

38

XPS examination (2)

Sample Valance state Position（eV） Area（%）

MnO

_x

/CAC Mn

³⁺

641.0 18.04

Mn

⁴⁺

642.3 81.96

CuO

_x

/CAC Cu

⁺

931.8 40.36

Cu

²⁺

934.1 59.64

XPS results showed that Mn

³⁺

, Mn

⁴⁺

, Cu

⁺

and Cu

²⁺

were the major valence states presenting in the MnO

_x

-, and CuO

_x

-

doped activated carbon, respectively.

39

Sample

N₂ condition (150 °C)

Flue gas condition (150 °C)

Flue gas condition (350 °C)

C_i/C_o Avg. Hg⁰ removal (%)

C_i/C_o Avg. Hg⁰ removal (%)

C_i/C_o Avg. Hg⁰ removal (%)

Raw/CAC 0.81 44.8±6.7 0.81 35.8±15.1 0.68 34.8±1.0 VO_x/CAC 0.53 48.5±2.2 0.32 86.0±6.8 0.74 36.3±3.3 MnO_x/CAC 0.65 50.2±3.3 0.20 89.4±5.6 0.59 47.9±3.9 CuO_x/CAC 0.44 54.5±3.6 0.03 98.9±0.6 0.15 87.5±1.3

Hg ⁰ average removal efficiency

• Metal oxides-doped activated carbons had superior adsorption potential for Hg⁰, especially under flue gas condition.

• The CuO_x/CAC have excellent removal potential for Hg⁰, especially under flue gas condition at high temperature.

40

SO ₂ and NO removal

Sample Flue gas condition (350 °C) Avg. SO₂

removal (%)

Avg. NO removal (%) Raw/CAC 1.3±0.9 1.2±0.4

VO_x/CAC 28.3±3.3 1.9±0.9 MnO_x/CAC 12.2±2.1 2.0±0.9 CuO_x/CAC 14.7±1.4 3.7±1.2

• After metal oxide doping, SO₂ removal of activated carbon can be greatly improved.

• NO removal with metal-oxide impregnated CAC is very low.

41

Hg

⁰

Removal Percentage under N

₂

condition (150 °C)

• CuO

_x

-doped-modified activated carbon had the greatest Hg

⁰

removal efficiency of approximately 54.5% at N

₂

condition.

Experiment time (min)

0 200 400 600 800 1000

Hg0 removal percentage (%)

0 20 40 60 80 100

Raw/CAC VO_x/CAC MnO_x/CAC CuO_x/CAC

42

Hg

⁰

Removal Percentage under flue gas condition

Experiment time (min)

0 200 400 600 800 1000

Hg0 removal percentage (%)

0 20 40 60 80 100

Raw/CAC(150 ^oC) VOx/CAC (150 ^oC) MnOx/CAC (150 ^oC) CuO_x/CAC (150 ^oC)

• CuO_x-doped-modified activated carbon had the greatest removal percentage to up to 98.9% at 150 °C .

• When the temperature increased to 350 °C, the surface-doped activated carbon still showed 34.8-87.5% Hg⁰ removal, suggesting that a strong chemical bonding

between Hg and the surface groups of surface-doped activated carbon were formed.

Experiment time (min)

0 200 400 600 800 1000

Mercury removal percentage (%)

0 20 40 60 80 100

Raw/CAC (350 ^oC) VO_x/CAC (350 ^oC) MnO_x/CAC (350 ^oC) CuO_x/CAC (350 ^oC)

43

SO

₂

removal efficiency of activated carbon (350 ° C)

• After surface doping, the SO₂ removal efficiency of activated carbon was enhanced at 350 °C.

• The VO_x-doped activated carbon had the highest SO₂ removal percentage of approximately 28.3% and the MnO_x-doped sample had the lowest SO₂ removal of approximately 12.2% at 350 °C.

Experiment time (min)

0 200 400 600 800 1000

SO 2 removal percentage (%)

0 10 20 30 40 50

Raw/CAC VO_x/CAC MnO_x/CAC CuO_x/CAC

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NO

_x

removal efficiency of activated carbon (350 °C)

• After metal oxide doping, the NO removal percentage was slightly improved to 1.9-3.7% at 350 °C.

• The NO removal efficiency of raw and metal-doped activated carbon is very small under flue gas condition, indicating that adsorption of NO may not be a suitable route for NO control.

Experiment time (min)

0 200 400 600 800 1000

NO removal percentage (%)

0 5 10 15 20

Raw/CAC VO_x/CAC MnO_x/CAC CuO_x/CAC

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MESSAGE TO TAKE HOME

1. Source control: can “fuel cleaning” or “cleaning fuel” a feasible approach in the future?

2. Multipollutant control can definitely a feasible approach;

a full scale demonstration/validation, however, are still missing to date.

3. Combining SCR/FGD system for Hg removal could cause new issues, such as Hg reemission into atmosphere,

which has been a problem in the US.

4. New approach for “Zero Hg emission” should be developed, examined, and verified.

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Concept of “zero Hg emission” approach in a seawater FGD system

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Graduate Institute of Environmental Engineering National Taiwan University

We greatly acknowledge funding support from the Ministry of Science and Technology, Taiwan under

grant no. 100-2221-E-027-009-MY3.