arsenic and selenium distribution in coal-fired plant samples

Western Kentucky UniversityTopSCHOLAR®

Masters Theses & Specialist Projects Graduate School

5-2009

Arsenic and Selenium Distribution in Coal-FiredPlant SamplesPauline Rose Hack NorrisWestern Kentucky University, [email protected]

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Recommended CitationNorris, Pauline Rose Hack, "Arsenic and Selenium Distribution in Coal-Fired Plant Samples" (2009). Masters Theses & SpecialistProjects. Paper 52.http://digitalcommons.wku.edu/theses/52

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ARSENIC AND SELENIUM DISTRIBUTION IN COAL-FIRED PLANT SAMPLES

A Thesis

Presented to

The Faculty of the Department of Chemistry

Western Kentucky University

Bowling Green, Kentucky

In Partial Fulfillment

Of the Requirements for the Degree

Master of Chemistry

By

Pauline Rose Norris

May 2009


Date Recommended___1/20/2009______

__Wei-Ping Pan____________________

Director of Thesis

__Cathleen Webb___________________

__Rui Zhang_______________________

________________________________________________

Dean, Graduate Studies and Research Date

i

Table of Contents

Chapter Page

1. Introduction……………………………………………………………… 3

1.1 Objective………………………………………………………. 3

1.2 Regulatory Requirements……………………………………… 3

1.3 Health Effects………………………………………………..… 4

1.4 Environmental Distribution ………………………………..….. 5

1.5 Previous Work ……………………………………………........ 7

1.6 Digestion Methods…………………………..………………… 10

1.7 Analysis Methods ………………………………………………12

1.8 Air Pollution Control Devices Overview……………………… 15

2. Experimental ………………………………………………………...…. 20

2.1 Power Plant Specifications …………………………………. 20

2.2 Sample Collection and Preparation ………………………….. 23

2.3 Sample Digestion ……………………………………………….24

2.4 Arsenic & Selenium Analysis………………………………….. 26

2.5 Proximate & Ultimate Analysis of Coal………………………. 26

3. Results…………………………………………………………………… 28

3.1 Plant A…………………………………………………………. 28

3.2 Plant B…………………………………………………………. 34

3.3 Plant C ………………………………………………………… 40

3.4 Plant D ………………………………………………………… 45

4. Discussion……………………………………………………………….. 56

ii

5. Bibliography…………………………………………………………….. 62

Appendix…………………………………………………………………... 64

iii

List of Tables

Table 1. Typical Arsenic and Selenium Concentrations in Common

Power Plant Residues …………………………………………………………….. 5

Table 2. Digestion Methods Outline………………………………………………. 10

Table 3. Analysis Methods Outline ………………………………………………. 13

Table 4. Sample Collection and Preparation Methods ……………………………. 18

Table 5. Proximate and Ultimate Coal Analysis Methods ……………………….. 27

Table 6. Plant A Coal Proximate and Ultimate Analysis Data …………………… 28

Table 7. Trace Elements in Plant A Coal …………………………………………. 29

Table 8. Trace Elements in Plant A Fly Ash ……………………………………… 30

Table 9. Trace Element Concentrations in Plant A Gypsum …..…………………. 31

Table 10. Trace Element Concentrations in Plant A Blow Down Water ………… 32

Table 11. Trace Element Concentrations in Plant A Make Up Water …………….. 32

Table 12. Trace Element Concentrations in Plant A Flue Gas ..………….……….. 33

Table 13. Power Plant Provided Parameters for Plant A…………………………... 34

Table 14. Arsenic & Selenium Results per Kg of Coal Burned for Plant A ……….34

Table 15. Plant B Coal Proximate and Ultimate Analysis Data ……..…………… 35

Table 16. Trace Elements in Plant B Coal ………………………………………. 36

Table 17. Trace Elements in Plant B Fly Ash …………………………………… 37

Table 18. Trace Element Concentrations in Plant B Economizer Ash……………. 38

Table 19. Trace Element Concentrations in Plant B Bottom Ash……………..…. 39

Table 20. Trace Element Concentrations in Plant B Gypsum …..………………. 40

Table 21. Trace Element Concentrations in Plant B Blow Down Water ………… 40

iv

Table 22. Trace Element Concentrations in Plant B Flue Gas ..………….……….. 41

Table 23. Power Plant Provided Parameters for Plant B…………………………... 41

Table 24. Arsenic & Selenium Results per Kg of Coal Burned for Plant B ………. 42

Table 25. Plant C Coal Proximate and Ultimate Analysis Data ……..…………… 43

Table 26. Trace Elements in Plant C Coal ………………………………………. 44

Table 27. Trace Elements in Plant C Fly Ash …………………………………… 45

Table 28. Trace Element Concentrations in Plant C Gypsum …..………………. 46

Table 29. Trace Element Concentrations in Plant C Blow Down Water ………… 46

Table 30. Trace Element Concentrations in Plant C Make Up Water …….……… 47

Table 31. Trace Element Concentrations in Plant C Flue Gas ..………….……….. 48

Table 32. Power Plant Provided Parameters for Plant C…………………………... 48

Table 33. Arsenic & Selenium Results per Kg of Coal Burned for Plant C ………. 49

Table 34. Plant D Coal Proximate and Ultimate Analysis Data ……..…………… 50

Table 35. Trace Elements in Plant D Coal ………………………………………. 51

Table 36. Trace Elements in Plant D Fly Ash …………………………………… 52

Table 37. Trace Element Concentrations in Plant D Gypsum …..………………. 53

Table 38. Trace Element Concentrations in Plant D Blow Down Water ………… 53

Table 39. Trace Element Concentrations in Plant D Flue Gas ..………….……….. 54

Table 40. Power Plant Provided Parameters for Plant D…………………………... 55

Table 41. Arsenic & Selenium Results per Kg of Coal Burned for Plant D ……….55

Table 42. Plant Boiler Type & Coal Information …………………………………. 56

v

List of Figures

Figure 1. Arsenic Distribution in the Combustion Process ……………………….. 5

Figure 2. Selenium Distribution in the Combustion Process ……………………… 6

Figure 3. Trace Element Distribution in the Environment ………………………... 7

Figure 4. Trace Element Volatility………………………………………………… 9

Figure 5. FGD System Diagram…………………………………….……………. 16

Figure 6. Comparison of As Concentrations in Flue Gases With and Without

Limestone Addition as presented in an article by Senior, C.L. …………………… 17

Figure 7. SCR System Diagram……………………………………………………. 18

Figure 8. Electrostatic Precipitator System Diagram ……………………………… 19

Figure 9. Plant A ………………………………………………………………… 20

Figure 10. Plant B………………………………………………………………… 21

Figure 11. Plant C ………………………………………………………………… 22

Figure 12. Plant D ………………………………………………………………… 22

Figure 13. EPA Method 29 Sampling Train.......………………………………….. 24

Figure 14. Comparison of Arsenic Removal in Plants A-D ……………………… 59

Figure 15. Comparison of Selenium Removal in Plants A-D ……………………. 59

Figure 16. Arsenic in Solid Phase and Gas Phase………………………………… 60

Figure 17. Selenium in Solid Phase and Gas Phase………………………………. 61

vi

Abbreviations or Term Name

A Ash content in coal

a excess air ratio

AAS Atomic Absorption Spectroscopy

AFS Atomic Fluorescence Spectroscopy

C ba Concentration of the selected element in bottom ash

C blowdown Concentration of the selected element in the blowdown

C econ Concentration of the selected element in economizer ash

C fa Concentration of the selected element in fly ash

C flue gas Concentration of the selected element in the flue gas.

C gypsum Concentration of the selected element in the gypsum

C makeup Concentration of the selected element in the makeup water

C reagent Concentration of the selected element in the reagent

C Stack Concentration of the element at the stack

EPA Environmental Protection Agency

EPRI Electric Power Research Institute

ESP Electrostatic Precipitator

FGD Flue Gas Desulfurization

h esp Particulate collecting efficiency of the ESP

ICP-AES Inductively Coupled Plasma Emission Spectroscopy

ICP-MS Inductively Coupled Plasma Mass Spectrometry

MACT Maximum Achievable Control Technology

MAPH Mass of selected element exiting the system in APH ash

vii

MAs out Mass of Arsenic (or selected element) exiting the system

M ba Mass of selected element exiting the system in bottom ash

M blowdown Mass of blowdown water

M econ Mass of selected element exiting the system in econ ash

M flue gas Mass of the selected element in the flue gas

M fa Mass of selected element exiting the system in fly ash

M FGD Slurry Mass of selected element exiting the system in FGD slurry

M gypsum Mass of gypsum

M makeup Mass of makeup water

M reagent Mass of reagent

M stack Mass of selected element exiting from the stack

MW Megawatt

PC Pulverized Coal

SCR Selective Catalyst Reduction

SNCR Selective Non-Catalyzed Reduction

TVA Tennessee Valley Authority

Vo

Air volume required for complete combustion

V CO2 Volume of carbon dioxide produced by the combustion of

one unit of coal

V DF3% Dry flue gas volume generated by firing one unit of coal,

corrected to 3% oxygen

Vodf Dry flue gas volume

VH2O Water vapor in the flue gas

VoN2 Volume of nitrogen gas produced by the combustion of one

unit of coal

viii

V SO2 Volume of sulfur dioxide produced by the combustion of

one unit of coal

XAFS X-ray Absorption Fine Structure Spectrometry

Yaph Fraction of total ash that is air pre heater ash

Yba Fraction of total ash that is bottom ash

Yecon Fraction of total ash that is economizer ash

Yfa Fraction of total ash that is fly ash

ix


Pauline Rose Norris May 2009 68 pages

Directed by: Wei-Ping Pan

Department of Chemistry Western Kentucky University

Arsenic and selenium distributions in coal-fired plant samples are studied. This

research includes arsenic and selenium concentrations in samples of coal, fly ash, bottom

ash, economizer ash, Flue Gas Desulfurization (FGD) slurry and flue gas taken from four

power plants with the goal being to examine the distribution of these metals in these

materials and calculate a materials balance for the system. All samples were analyzed

using ICP-ES.

This research shows that 60-80% of the arsenic in coal-fired plant samples will be

associated with the fly ash. Approximately 35-55% of the selenium will be associated

with the fly ash and approximately 30-40% will be associated with the FGD slurry

materials. The amount of arsenic and selenium present in the flue gases escaping the

stack is very little, 6-7% or less.

Hopefully, research in this area will be helpful when setting emissions limits,

identifying and disposing of hazardous wastes and improving air pollution control

devices for maximum metal removal.

3

1. Introduction

1.1 Objective

More research needs to be done to clearly identify how much arsenic and

selenium is released each year from stationary sources in the form of stack gases and

waste by-products. Knowing the amount and distribution information could help

politicians pass needed legislation to regulate these materials; coal-fired plants could

choose their air pollution control devices for maximum pollution control and safely

dispose of dangerous waste or remove dangerous portions of waste to produce a useful,

marketable by-product. This research specifically looks at arsenic and selenium

concentrations in coal, fly ash, bottom ash, FGD slurry, limestone and gaseous samples

collected via EPA Method 29 from four different coal-fired plants with the goal being to

quantify how much arsenic and selenium are going into the coal-fired plant system from

the coal and how much is leaving the system in the form of solid, liquid and gaseous

wastes and calculating a mass balance.

1.2 Regulatory Requirements

Both arsenic and selenium are gaining importance in the combustion community.

They are included in the list of hazardous air pollutants in section 112 b of the Clean Air

Act and in the group of Total Selected Metals in the Industrial Boiler MACT (Maximum

Achievable Control Technology) regulations. Unlike mercury, the Federal EPA has yet to

impose limitations on the amount of arsenic or selenium specifically emitted from

stationary sources. As coal-fired plants are coping with exceedingly stringent regulations

regarding what they are releasing into the air, they must also be concerned with

contaminated waste removal and what might be getting into water sources. A good

4

example of the problem is the recent incident at the TVA Kingston Fossil Plant in

Harriman, Tennessee. On December 22, a retention wall failed releasing approximately

1.1 billion gallons of fly ash slurry waste into surrounding areas including water systems

such as the Emory and Clinch River systems and residential areas. This spill affects water

sources including fish and other wildlife. The amount of air particulate resulting from the

spill is also a cause for alarm. The total effect that this spill will have on the environment

is yet to be determined. Current analysis of the sediment in the spill area shows elevated

levels of arsenic, however, analysis of drinking water in the area indicates that arsenic

concentrations are below regulatory limits. The current EPA regulation specifies a

maximum containment level of 10 ppb arsenic and 50 ppb selenium in drinking water. If

these metals continue to get into our water sources, it could negatively affect our drinking

water and our food supply.

1.3 Health Effects

Long term exposure to arsenic is responsible for skin problems such as keratosis

and melanosis and can lead to skin and other cancers such as kidney, bladder and lung

cancer. Exposure to high levels of arsenic can be fatal. In the environment arsenic can

form compounds with oxygen, chlorine and sulfur. In animals, arsenic forms organic

compounds with carbon and hydrogen1.

Exposure to small amounts of selenium is actually healthy; however, exposure to

large doses of selenium can result in a condition called selenosis. Selenosis causes

nausea, nail brittleness and neurological problems. Inhalation of selenium can cause

respiratory problems. Selenium in the environment exists usually as selenium sulfide or

with minerals such as copper and silver2.

5

1.4 Environmental Distribution

Arsenic and selenium can be released from coal-fired plant sources in the form of

gaseous emissions from the stack, bound to solid combustion residues such as fly ash

particles and FGD gypsum and through liquid wastewaters. The concentrations of these

trace elements in these materials can vary greatly. Table 1 shows typical arsenic and

selenium concentrations found in common coal-fired plant residues. Figure 1 shows the

typical distribution of arsenic during the combustion process. Figure 2 shows the typical

distribution of selenium during the combustion process.

Table 1. Typical Arsenic and Selenium Concentrations

0.1-20.4-8N.D.-1600.1-100.2-130Se

1-500.5-1060.8-3860.02-1682-1385As

SoilCoalFGD materialBottom AshFly ash

Concentration (mg/kg)Element

Cheng et al., 2005, Tishmack and Burns 2004, Laperche and Bigham 2002, Taerakul et al. 2005, Eary et al. 1990

Figure 1. Arsenic Distribution in the Combustion Process

6

Figure 2. Selenium Distribution in the Combustion Process

Arsenic and selenium get into the environment from industrial sources, but they

can also come from other man-made sources such as vehicular & domestic sources as

well as from volcano eruptions and forest fires. Once in the environment, they can travel

through several pathways including ground deposition (from air to the ground), surface

runoff (from the ground to the water), wet deposition (from rain to water on the ground),

etc. Once in the environment, arsenic and selenium will exist in the soil, water and

atmosphere. Figure 3 illustrates the sources of emission and pathways through which

arsenic and selenium travel in the environment.

7

Figure 3 Trace Element Distributions in the Environment

1.5 Previous Work

Some research has already been done to determine arsenic and selenium in power

plant residues; Diaz-Somoano et al. measured sequestration of arsenic and selenium in

flue gases by limestone in a laboratory scale reactor3. Limestone reacts with arsenic and

selenium to produce Ca(AsO2)2 and CaSe. In this study they found that limestone had

good trapping ability (~17 mg As/g and ~64 mg Se/g) in the temperature region of 350 to

750oC and in a atmosphere free of H2S. Maximum retention for arsenic occurred at

550oC and at 750

oC for selenium. The study suggested that H2S in the atmosphere

decreased retention of arsenic due to competition with sulfur. Staudt, Engelmeyer,

Weston and Sigling studied the relationship between CaO and arsenic in a 45 MW boiler

and found that if sufficient CaO is present it will react with arsenic to form calcium

arsenide [Ca3(AsO4)2]. This compound is stable and usually becomes bottom or fly ash4.

Sources

1. Industrial Sources

2. Vehicular Emissions

3. Domestic Emissions

4. Volcanic Eruptions

5. Forest Fires

Pathways

6. Ground Deposition

7. Surface Runoff

8. Dry Deposition

9. Air/Water Gas Exchange

10. Water/Air Gas Exchange

11. Wet Deposition

12. Groundwater Runoff

Reservoirs

13. Soil/Bedrock

14. Water

15. Atmosphere

8

Loäpez-antoän, Diaz-Somoano and Spears measured arsenic and selenium capture by fly

ash in a quartz reactor at low temperatures5. In this study they found that fly ash could

capture as much as 5 mg/g arsenic and 17 mg/g selenium. Shah, Strezov and Nelson

measured coal, fly ash and bottom ash from four different power plants, labeled as A-D,

and analyzed samples for a semi-quantitative result using X-ray absorption fine structure

spectrometry (XRFS) 6

. They found that for the coal from the first power plant, Coal A,

90 % of the arsenic was in the arsenite (As3+

) form and only 10 % existed as arsenate

(As5+

). Coal B was approximately 60 % arsenate, 25 % arsenite & 15 % associated with

pyrite. Coal C was approximately 70 % arsenate and 30 % arsenite. Coal D was

approximately 45 % associated with pyrite, 45 % arsenite and 10 % arsenate. Selenium

existed primarily in the elemental form for all of the coals. In the fly ash, greater than 85

% of the arsenic existed as arsenate. The selenium in the fly ash is a mixture of selenite

(Se4+

) and selenate (Se6+

). Unfortunately, insufficient information was provided in the

article to calculate a materials balance for the samples. Huggins, Senior and Chu

measured arsenic and selenium speciation in fly ash samples taken from power plants

burning bituminous and sub-bituminous coals. He found that arsenic and selenium

species typically are in As (V) and Se (IV) forms7. Wang and Tomita performed a

laboratory study where they measured the volatility of various trace elements including

arsenic using a slow burning rate, a fast burning rate and in a nitrogen atmosphere

(pyrolysis)8. The slow burning rate consisted of heating 1.5 grams of coal sample from

room temperature to 950oC at 10

oC/min and then to 1150

oC at 5

oC/min in an air

atmosphere. The fast burning condition consisted of pushing the sample boat into a

furnace already preheated to 1150oC. The remaining residue was digested and the

9

solution ran on ICP AES. They found that arsenic had a high volatility and was

significantly lost at the high burning rate, only slightly lost at the low burning rate and

remained associated with the char during the pyrolysis step. Trace element volatility was

also studied in a 1992 IEA Coal Research report by Clarke and Sloss. The report lists

selenium as more volatile than arsenic as shown in Figure 4.

Increasing

volatility

HgBr Cl F

B Se I

As Cd Ga Ge Pb Sb Se Te Ti ZnBa Be Bi Co

Cr Cs Mo Ni Sr Ta Ti U V W

Eu Hr La Mn RbSc Sm Tb Zr

Class III

Class II

Class I

Group I Involatile or low volatility. be retained in all ash streams at broadly the

same concentration,(Ba, Ce, Cs, Mg, Mn, Th).Group II

Limited volatility and tend to show slight enrichment in particulate that has been exposed to flue gas

compared with the coarse slag and bottom ash, (As, Cd, Cu, Pb, Sb, Se,

Zn).Group III

Volatilise most readily. in the vapourphase even at flue gas exit

temperatures of just over 100°C and are depleted in all solid phases, ( Hg,

Br, I).

Increasing

volatility

HgBr Cl F

B Se I




HgBr Cl F

B Se I




Class III

Class II

Class I

Group I Involatile or low volatility. be retained in all ash streams at broadly the

same concentration,(Ba, Ce, Cs, Mg, Mn, Th).Group II

Limited volatility and tend to show slight enrichment in particulate that has been exposed to flue gas

compared with the coarse slag and bottom ash, (As, Cd, Cu, Pb, Sb, Se,

Zn).Group III

Volatilise most readily. in the vapourphase even at flue gas exit

temperatures of just over 100°C and are depleted in all solid phases, ( Hg,

Br, I).

Figure 4. Trace Element Volatility

Shoji, Huggins and Huffman measured arsenic concentrations in 7 different coal

ash residues using XAFS9. The residues were divided into less than 2.5 um and greater

than 2.5 um portions and the arsenic concentration was measured for each. For all 7

coals, more arsenic was captured by the smaller particles. In addition, the ashes with

larger loss on ignition values had higher capturing ability. Finally, they indicated that

only arsenic (V) was present in the ash samples and that arsenic (III) was not detected.

Sandelin and Backman measured trace elements at two pulverized coal-fired stations,

with the goal being to compare actual values for a variety of trace elements including

10

arsenic and selenium with predicted values from a “reactor model”10

. In this study they

measured arsenic and selenium values in flue gas, fly ash, bottom ash and FGD slurry

materials. They found that for arsenic, the largest portion was associated with the fly ash

with smaller portions associated with the gypsum materials and the bottom ash. Due to

selenium’s volatility, the model predicted that all the selenium would be in the gas phase.

However, they found a significant portion of selenium to be associated with fly ash. They

also indicated that the trace elements were soluble in the FGD solutions.

1.6 Digestion Methods

Several digestion methods for solid samples are available. Some considered for

this research are outlined along with their advantages and disadvantages in Table 2. A

more detailed description of the methods is presented below.

Table 2. Digestion Methods Outline

Digestion Method Advantages Disadvantages

ASTM Method D 6357 Hydrofluoric acid is boiled off Time intensive

Unlimited sample size Higher probability of

loosing volatile elements

Incomplete dissolution

ASTM Method D 6349 No hydrofluoric acid is used Time intensive

Complete dissolution Higher probability of

Unlimited sample size loosing volatile elements

Microwave Digestion Quick Hydrofluoric acid resistant

Low probability of analysis system required

loosing volatile elements Incomplete dissolution

Complete dissolution

ASTM D 6349 Standard Test Method for Determination of Major and Minor

Elements in Coal, Coke, and Solid Residues from Combustion of Coal and Coke by

Inductively Coupled Plasma—Atomic Emission Spectrometry consists of an initial

11

ashing step, a fusion with lithium tetraborate to form a pellet and then the subsequent

dissolution of that pellet in a dilute nitric acid solution. The major advantage to this

method is that the entire sample completely goes into solution. There is no undigested

portion of sample. However, the procedure is time consuming, the ashing step takes

several hours and the fusion/dissolving step can take up to 30 minutes. In addition, the

method requires a rather expensive platinum dish for fusing the sample, meaning that

unless several of these dishes are purchased, samples must be done one at a time. The

major disadvantage is the high temperature (1050oC) required to fuse the lithium

tetraborate pellet. The method is listed for major and minor elements such as iron and

calcium and the high temperature might affect the recovery of trace metal analytes.

ASTM Method D 6357 Standard Test Methods for Determination of Trace

Elements in Coal, Coke, and Combustion Residues from Coal Utilization Processes by

Inductively Coupled Plasma Atomic Emission Spectrometry, Inductively Coupled

Plasma Mass Spectrometry, and Graphite Furnace Atomic Absorption Spectrometry is a

hot plate method. It has a variety of possible problems, with one major advantage over

the microwave digestion method; the first problem is the volatility of arsenic and

selenium. Overheating the sample, either in the initial ashing step in the furnace or in the

Teflon digestion beaker on the hot plate could have the potential to cause analyte losses if

the sample is not digested carefully. In addition, complete digestion of the sample using

this method is very difficult. Finally, this method is very time consuming; it requires an

initial ashing step that takes several hours, a digestion that takes several hours and then

time to filter the samples. The benefit to this method is that the amount of sample can be

increased if necessary. This method calls for the digestion of 0.2-0.5 grams of the ashed

12

sample, but that could be increased if the concentration in the sample was extremely low

and could not be detected.

With the microwave digestion method, the amount of sample digested is limited

by the amount of pressure that the vessel can withstand and how much digestion solution

must be added to the vessel to ensure complete digestion. The advantages to the

microwave digestion method is that the volatility of analytes is not a problem since the

vessel is closed throughout heating and that there is no need to ash the samples prior to

analysis nor do the samples require filtering since the microwave digests the samples

almost completely. The omission of these steps aid in preserving data quality since fewer

calculations are done to get the final result and the solution comes in contact with fewer

containers, thus decreasing the possibility of contamination. The disadvantage to the

microwave method is that the hydrofluoric acid is not evaporated necessitating the use of

a hydrofluoric acid resistant sample introduction system.

Samples from Plant A were digested using the hot plate digestion method because

a microwave for digesting samples was not available at that time. Samples from plants B,

C and D were digested using the microwave digestion method because of the closed

digestion vessel and more complete digestion of samples.

1.7 Analysis Methods

There are several methods for measuring arsenic and selenium concentrations.

Several of these techniques along with advantages and disadvantages are presented in

Table 3 with a more complete description given below.

13

Table 3. Analysis Methods Outline

The ICP emission spectroscopy instrument, used in this research, atomizes liquid

samples using a plasma torch. Surrounding the torch is a water cooled coil that is

powered by a radio-frequency generator. An initial spark ionizes the argon flowing into

the torch. The sample is pumped to the nebulizer first which produces a very fine mist.

Then, the sample travels to spray chamber and the torch. The torch atomizes the sample

and a fraction of these atoms are excited to higher electronic states. The subsequent

relaxation of these atoms produces ultraviolet and visible line spectra. The advantages to

using ICP would be better quantitative results with a low detection limit and

simultaneous analysis of arsenic and selenium. The major disadvantage to using ICP is

the necessary sample digestion procedure that can contribute to analyte losses or

contamination and prevents the determination of speciation information. In addition,

accurate analysis using ICP can be difficult due to numerous possible interference

Analysis Method Advantages Disadvantages

ICP-ES Detection Limit 8 ppb for arsenic Interferences from other elements

(ASTM Method D 6357) & 10 ppb for selenium Digestion required

Multi element technique No speciation data

Expensive, complex equipment

ICP-MS Detection Limits at ppt level Digestion required(ASTM Method D 6357) Multi element technique No speciation data

Less interference problems Expensive, complex equipment

Graphite Furnace Detection Limits at sub-ppb levels Digestion requiredAtomic Absorption No interference problem Single element technique

(ASTM Method D 6357) Relatively easy to operate No speciation data

Atomic Fluorescence 0.01 ppb Arsenic, 0.002 ppb Selenium Digestion required

Instrument Manufacturer No interference problem Additional sample preparation Method Relatively easy to operate No speciation data

XAFS No digestion required Semi-quantitative

(No standard method) Speciation data possible

Detection Limits were obtained from instrument manufacturers, from an article11

and EPA methods12

14

problems from other elements present in the sample.

ICP-mass spectrometry has similar sample introduction features mentioned for the

emission spectrometry instrument above; however, the method of detection is different.

The torch produces ions characteristic of each element which are separated and detected

using the mass spectrometer. The ion masses for arsenic and selenium are 75 & 8211

. The

advantages and disadvantages to this technique are similar to the emission spectroscopy

instrument; however the detection limit for the mass spectrometer detection method is

superior to the emission spectroscopy method.

Similarly to ICP systems, atomic absorption/fluorescence spectroscopy techniques

also require sample digestion; therefore, negating speciation information and possibly

introducing errors from the digestion step. Atomic absorption/fluorescence spectroscopy

involves the absorption of energy by the electrons in the element at specific wavelengths

or the emission of energy at specific wavelengths. In fluorescence, the emitted energy

will not be at the same wavelength as what was absorbed. The sample is excited to a

higher state by a flame, a graphite furnace or hydride generation sample introduction

system. The system is equipped with a lamp containing the element of interest which,

when subjected to an electrical current, produces energy at a known wavelength

characteristic of the element. The major advantage to atomic fluorescence is a superior

detection limit, better than ICP-ES or atomic absorption. Additional advantages include

instrumentation that is easier to operate and fewer problems with interferences. The

disadvantage to both absorption and fluorescence techniques is that only one element can

be analyzed at a time.

Atomic absorption or emission systems typically use either a flame produced by

15

an air/acetylene fuel mixture or a graphite furnace in which the sample is heated inside of

a small tube. With some elements, including arsenic and selenium, it is preferable to

create a volatile hydride by mixing the sample with sodium borohydride and dilute

hydrochloric acid. The decomposition of the hydride produces the elemental form of the

element.

X-ray Absorption Fine Structure spectroscopy uses x-rays to probe the physical

and chemical structure of matter. The x-rays are chosen to be at and above a particular

binding energy for a specific electronic level of a specific element. The major advantage

for using XAFS is the ability to analyze the sample itself without any pretreatment and

obtain speciation information. However, like other x-ray techniques, the sensitivity is not

as good as ICP.

ICP-ES was used for this research because for most samples, the concentration

levels were high enough to be detected using this method and because a hydrofluoric acid

system was necessary to analyze the microwave digested samples and the available

atomic fluorescence system was not equipped with a hydrofluoric acid resistant system.

1.8 Air Pollution Control Devices Overview

Power plants commonly utilize air pollution control devices for removing excess

sulfur, excess nitrogen and excess particulate matter. This is necessary since these

elements can form sulfur and nitrogen oxide pollutants that can contribute to acid rain.

These pollution control devices can have additional positive benefits such as the removal

of particulate bound mercury or soluble mercury in Flue Gas Desulfurization liquids as

demonstrated in the work done by Senior et al 13

. Ideally, evaluation of arsenic and

selenium concentrations in various media would provide information as to what

16

techniques could be used to remove these elements.

Flue gas desulfurization systems function in removing excess sulfur by a reaction

between sulfur dioxide and calcium carbonate. The product is calcium sulfite which can

then be further reacted to form gypsum, a marketable product. Since the calcium

carbonate is typically added in the form of wet slurry, the possibility to remove arsenic

and selenium in both the waste water and the solid product exists. This theory is further

supported by the research of Diaz-Somoano and Sandelin as mentioned above. Major

components of FGD system are represented in Figure 5.

Figure 5 FGD System Diagram

Selective catalyst reduction systems function in removing excess nitrogen oxides

via a reaction with ammonia on typically a vanadium or tungsten catalyst to form

quencher

Circulating

loop

AbsorberFeed tank

ReagentFeed tank

4

7

5

Disposal

Hydro-clone

5

D

Wet well

Vacuum

drum

E

3

3

AbsorberHydroclone

1

A

1: Flue gas in (available)

2: Absorber hydroclone underflow+ Reagent feed3: Returned waste water (available)

4: process makeup water (available)5: Disposal hydroclone overflow (Calculated)

6: Absorber feed to spray tower (available)7: Desmister water

8: Reagent Feed (available)

2

6

A: Flue gas out (Available)

B: Absorber feed to quencher (calculated)C: Quencher Discharge (Tower) (Available)

D: Disposal hydroclone underflow (Available)E: Gypsum (Available)

F: Wastewater Discharge (Available)

B

C

8

6

F

Inflow Outflow

quencher

Circulating

loop

AbsorberFeed tank

ReagentFeed tank

4

7

5

Disposal

Hydro-clone

5

D

Wet well

Vacuum

drum

E

3

3

AbsorberHydroclone

1

A

1: Flue gas in (available)

2: Absorber hydroclone underflow+ Reagent feed3: Returned waste water (available)

4: process makeup water (available)5: Disposal hydroclone overflow (Calculated)

6: Absorber feed to spray tower (available)7: Desmister water

8: Reagent Feed (available)

2

6

A: Flue gas out (Available)

B: Absorber feed to quencher (calculated)C: Quencher Discharge (Tower) (Available)

D: Disposal hydroclone underflow (Available)E: Gypsum (Available)

F: Wastewater Discharge (Available)

B

C

8

6

F

Inflow Outflow

17

nitrogen gas and water vapor. Typically these systems operate between 300 and 450oC in

high dust atmospheres. Arsenic is a problem in these systems because of the formation of

gaseous arsenic oxide (As2O3). This compound “poisons” the catalyst in the SCR system

by reacting with oxygen to form As2O5 on the catalyst surface thereby consuming the

active sites14

. Arsenic and its association with fly ash at SCR temperatures and conditions

is already being studied as well as the use of limestone injection into the SCR to form

stable Ca3(AsO4)2 with good results, as shown in Figure 315

.

Figure 6 Comparison of As Concentrations in Flue Gases With and Without Limestone

Addition as presented in an article by Senior, C.L.

Major components of the SCR system are represented in Figure 7.

18

Figure 7. SCR System Diagram

Electrostatic precipitators function in removing excess particulate matter from

flue gas using the force of an induced electrostatic charge. The particles are collected in

hoppers. Fly ash serves an important function in trace element removal. Serre, Lignell,

Sarofim and Meht discuss how the unburned carbon in fly ash can help to capture

mercury16

. Fly ashes with more unburned carbon tend to have larger concentrations of

associated trace elements than fly ashes with less unburned carbon. Major components of

the electrostatic precipitator are represented in Figure 8.

19

Figure 8. Electrostatic Precipitator System Diagram

20

2. Experimental

2.1 Power Plant Specifications

Plant A, shown in Figure 9, specifications consisted of a 200 MW pulverized coal

boiler equipped with a Selective Catalyst Reduction (SCR) system, an Electrostatic

Precipitator (ESP) and a Flue Gas Desulfurization (FGD) system. Plant A burns

bituminous coal.

Figure 9. Plant A

Similarly, Plant B specifications consisted of an 800 MW pulverized coal boiler

equipped with a SCR system, an ESP and a FGD system. Plant B burns bituminous coal

and is shown in Figure 10.

21

Figure 10. Plant B

Plant C specifications consisted of two units. Unit 1 is a 151 MW cyclone boiler

equipped with a SCR system and an ESP. Unit 2 is a 290 MW pulverized coal boiler

equipped with a Selective Non-Catalyzed Reduction (SNCR) system and an ESP. The

two units share a FGD system and stack. Plant C burns bituminous coal and is shown in

Figure 11.

22

Figure 11. Plant C

Plant D specifications consisted of a 176 MW cyclone boiler equipped with a

SCR system, an ESP and a FGD system. Plant D burns bituminous coal and is shown in

Figure 12.

Figure 12. Plant D

FGD

Sta

ck

IDF

Unit 4

Cyclone

Boiler

ESP

APH

SCR

APH

StackFGD

ESPSCRSCR

A-side 1st

Sampling

Location

4th Sampling

Location5th Sampling Location

A side 3rd Sampling

Location

A-side 2nd

Sampling

Location

APH ESPSCRSCR

IDF

FGDFGD

Sta

ck

IDFIDF

Unit 4

Cyclone

Boiler

ESPESP

APH

SCR

APHAPH

StackStackFGDFGD

ESPESPSCRSCRSCRSCR

A-side 1st

Sampling

Location

4th Sampling

Location5th Sampling Location

A side 3rd Sampling

Location

A-side 2nd

Sampling

Location

APHAPH ESPESPSCRSCRSCRSCR

IDFIDF

23

2.2 Sample Collection and Preparation

Methods for sample collection and preparation are provided in Table 4 with a

more complete description given below.

Table 4. Sample Collection and Preparation Methods

Method Description

ASTM D2013-86 Standard Method of Preparing Coal Samples for Analysis

EPRI Method A1 FGD Chemistry and Analytical Methods Handbook

Method A1 Reagent and Slurry Sampling

EPA Method 29 Metals Emissions from Stationary Sources

Coal samples were collected so that the mass of arsenic and selenium going into

the system could be measured. Basic proximate and ultimate analysis of the coal is also

necessary to calculate the dry flue gas produced per kg of coal burned, which is used in

the metals flue gas calculations. Coal samples taken from Plants A, B, C & D were

collected from multiple feeders. To make a composite coal sample, the samples from

individual feeders were dried together, crushed together, riffled to representatively reduce

the sample amount and finally pulverized to an analysis size of 60 mesh according to

ASTM Method 2013. Fly ash samples from individual hoppers were blended to make a

composite. Bottom, Economizer & Air Pre-heater Ash was collected, dried (if necessary),

and crushed using an 8500 Shatterbox from Spex CertiPrep. FGD sludge was collected

and filtered to separate solid and liquid portions. The liquid portions were preserved with

nitric acid. The solid portions were allowed to air dry prior to digestion.

Flue gas was sampled according to EPA Method 29 Determination of Metals

Emissions from Stationary Sources. In this method, gas samples are withdrawn from the

collection site and flowed through a series of impingers. The first impinger is empty and

24

is used as a water knock-out. The second and third impingers contain acidified hydrogen

peroxide. Hydrogen peroxide is a more useful oxidizer than potassium permanganate in

this case since the use of potassium permanganate would negate any manganese

measurements and would be less likely to produce interference problems. The final

impinger contains silica gel and is used as a final moisture removal step prior to the gases

entering the gas meters. At least 1 m 3 of flue gas was collected. The impinger solutions

are recovered and acid digested. The sampling train for EPA Method 29 is shown in

Figure 13. The method was modified slightly during sampling to remove small

particulate in the fly ash that could erroneously contribute to the flue gas measurements.

That modification is illustrated in Figure 13 also.

Figure 13. EPA Method 29 Sampling Train

2.3 Sample Digestion

Plant A solid samples were digested according to ASTM Method D 6357. In this

method, samples are ashed to a constant weight at 500oC in a furnace. Then, 0.2-0.5

25

grams of the ashed sample, 20 ml of aqua regia and 20 ml of hydrofluoric acid are added

to a Teflon beaker and heated to dryness. Then, 1 ml of nitric acid and 20 ml of water are

added to the beaker and the sample is heated at just below boiling for an hour. After

heating, the sample is filtered and diluted to a total volume.

Plant B, C & D coal samples were acid digested using a Milestone Ethos

Microwave digestion system with Teflon beakers. All chemicals used were trace metal

grade. Approximately 0.2 grams of coal and 8 ml of concentrated nitric acid were added

to each Teflon beaker. The temperature program was set to increase the temperature

inside the Teflon beaker to 180oC in the first 5 minutes and then hold at that temperature

for an additional 10 minutes. After cooling, the vessels were opened and 2 ml of

hydrofluoric acid was added to each vessel. For the second part of the digestion, the

temperature increased to 230oC in the first 5 minutes and then held at that temperature for

an additional 10 minutes. This digestion method was taken from the acid digestion

system’s manufacturer. Fly ash and FGD solids were acid digested using the same acid

digestion system, but a different digestion method was used due to the sample matrix.

Approximately 0.2 grams of sample, 10 ml of water, 6 ml of concentrated nitric acid, 2

ml of concentrated hydrochloric acid and 2 ml of hydrofluoric acid was added to the

Teflon digestion vessel. The temperature program was set to increase the temperature

inside the Teflon beaker to 230oC in the first 8 minutes and then hold at that temperature

for an additional 40 minutes.

EPA Method 29 requires the liquid samples to be acid digested prior to analysis.

The acid digestion involves adding 30 ml of 50 percent nitric acid to 20 ml of sample and

heating for 30 minutes on a hot plate at just below boiling. Then, 10 ml of 3 percent

26

hydrogen peroxide is added and heated for 10 more minutes. Finally 50 ml of hot water

is added and the solution is heated for a final 20 minutes. The final volume of solution

should be the same as the initial volume of solution digested.

2.4 Arsenic & Selenium Analysis

Samples were analyzed using a Leeman ICP Prodigy system. Plant A samples

were analyzed using a glass dual view torch. The flow rate was set at 1.2 ml/min. The

power was set to 1.1 kW. The nebulizer was set to 36 psi, the auxiliary was set to 0.6 psi

and the coolant was set to 19 psi. Plants B, C & D samples contained hydrofluoric acid

from the microwave digestion so the ICP was equipped with a hydrofluoric acid resistant

nebulizer and torch. The settings were modified due to the different sample introduction

system and the highly acidic nature of the samples. For samples containing hydrofluoric

acid, the sample solution was pumped at a flow rate of 1.4 ml/min. The power for the

instrument was set to 1.2 kW. The nebulizer was set to 37 psi, the auxillary was set to 0.4

psi and the coolant was set to 20 psi. The instrument was calibrated using standards from

Spex Certiprep and diluted with a solution similar to the sample matrix to minimize

interference effects. The arsenic 197 nm, 193 nm & 189 nm and the selenium 196 nm

lines were used for quantitation.

2.5 Proximate & Ultimate Analysis of Coal

For the purposes of calculating arsenic and selenium concentrations in the Method

29 flue gas samples, it is necessary to include Proximate and Ultimate analysis of the coal

from Plants A, B, C & D. Standard methods for the proximate and ultimate analysis of

coal are presented in Table 5 with a more detailed description given below.

27

Table 5. Proximate and Ultimate Coal Analysis Methods

Method Description

ASTM Method D 5142 ASTM D 5142 Standard Test Methods for Proximate

Analysis of the Analysis Sample of Coal and Coke by

Instrumental Procedures

ASTM Method D 5373 ASTM D 5373 Instrumental Determination of Carbon,

Hydrogen, and Nitrogen in Laboratory Samples of Coal

and Coke

ASTM Method D 4239 ASTM D 4239 Sulfur in the Analysis Sample of Coal and

Coke Using High-Temperature Combustion and Infrared

Absorption

Moisture, ash and volatile matter were measured using a LECO 701

Thermogravimetric Analyzer according to ASTM Method D 5142. In this method,

samples are heated to 104oC under a nitrogen atmosphere and the weight loss is equal to

the moisture. Then, the sample is heated to 950oC under a nitrogen atmosphere. The

weight loss in this step is equal to the volatile matter. Finally, the samples are heated to

750oC in an oxygen atmosphere. Any material remaining after this step is the unburned

or ash portion. The carbon, hydrogen, nitrogen and sulfur values were measured using a

LECO Truspec CHNS Analyzer according to ASTM Method D 5373 & 4239. In this

method, the sample is burned to produce carbon dioxide, nitrogen oxides, water vapor

and sulfur dioxide. All are analyzed using infrared detection except for the nitrogen

oxides, which are detected using a conductivity cell.

28

3. Results

3.1 Plant A

For Plant A, coal, fly ash, FGD slurry materials and flue gas samples were

collected. All samples except for the FGD make-up water were collected from three

separate sampling periods from the same day and averaged to make a composite for that

day.

Proximate & Ultimate Analysis

Results for proximate and ultimate analyses are given in Table 6.

Table 6. Plant A Bituminous Coal Proximate and Ultimate Analysis data

As Determined Dry As Received

Moisture % 11.09 -- 18.60

Ash % 9.03 10.16 8.27

Volatile Matter % 25.35 28.51 23.21

Carbon % 62.81 70.64 57.50

Hydrogen % 5.65 4.96 6.12

Nitrogen % 1.06 1.19 0.97

Sulfur % 3.92 4.40 3.58

Oxygen % 17.54 8.65 23.556

Air Dry Loss = 8.44 %

Coal

The concentration of arsenic in coal was measured to be 0.139 +/- 0.02 mg/Kg.

The concentration of selenium was 0.991 +/- 0.30 mg/Kg. The concentrations of all trace

elements in coal are provided in Table 7.

29

Table 7. Trace Elements in Plant A Coal

Average (ug/g) Std Dev. (ug/g)

Arsenic 0.139 0.024

Barium 1.352 0.234

Beryllium 1.322 0.558

Cadmium 0.174 0.025

Cobalt 4.102 2.600

Chromium 3.962 0.543

Copper 3.329 1.078

Manganese 28.007 7.661

Molybdenum 0.232 0.206

Nickel 6.943 0.616

Lead 1.180 0.393

Selenium 0.991 0.301

Strontium 0.124 0.025

Thorium 0.131 0.042

Thallium 0.335 0.141

Uranium 2.525 1.298

Vanadium 0.241 0.229

Zinc 8.990 3.202

Fly Ash

The concentration of arsenic in fly ash was measured to be 1.188 +/- 0.004

mg/Kg. The concentration of selenium was 3.763 +/- 2.491 mg/Kg. The concentrations of

all trace elements in fly ash are provided in Table 8. The mass of arsenic and

selenium/Kg of coal is equal to the product of the concentration of the element in fly ash,

the collecting efficiency of the ESP, the fraction of fly ash and the percentage of ash in

coal, Eq 1. This equation is provided in the Appendix.

30

Table 8. Trace Elements in Plant A Fly Ash


Arsenic 1.188 0.004

Barium 102.319 60.457


Cadmium 6.059 3.800

Cobalt 13.280 2.212

Chromium 53.212 32.398

Copper 39.292 7.085

Manganese 162.308 56.748


Nickel 76.208 19.073

Lead 11.837 8.036



Thorium 1.586 0.400


Uranium 33.664 32.216


Zinc 169.474 11.510

FGD Slurry

The concentration of arsenic and selenium in gypsum was measured to be 0.933

+/-0.082 mg/Kg and 2.518 +/- 0.506 mg/Kg, respectively. The concentration of arsenic

and selenium in blowdown was measured to be 0.074 +/- 0.010 mg/L and 0.184 +/- 0.026

mg/L, respectively. The trace element concentrations for gypsum, blowdown water and

make up water are provided in Tables 9-11. The masses of arsenic & selenium/Kg of coal

burned are equal to the sum of the masses of the element in the waste water and the

gypsum less the sum of the masses of the elements in the make-up water and the reagent,

as shown in Eq 2. This equation is provided in the Appendix. The mass of arsenic and

selenium per Kg of coal burned is equal to 0.037 mg/Kg coal burned and 0.393 mg/Kg

coal burned, respectively.

31

Table 9. Trace Element Concentrations in Gypsum


Arsenic 0.933 0.082

Barium 4.616 1.609


Cadmium <1.5

Cobalt <1.5

Chromium 18.188 4.658

Copper 2.751 0.354



Nickel 1.632 0.530

Lead <1.5


Strontium <1.5

Thorium <1.5

Thallium <1.5

Uranium 29.737 18.931

Vanadium <1.5

Zinc 5.362 0.347

32

Table 10. Trace Element Concentrations in Blowdown Water

Average (mg/L) Std Dev. (mg/L)

Arsenic 0.074 0.010

Barium 0.604 0.025


Cadmium 0.006 0.001

Cobalt 0.049 0.003


Copper <0.006


Molybdenum <0.006

Nickel 0.989 0.026

Lead 0.061 0.001



Thorium <0.006

Thallium <0.006

Uranium 37.867 0.948


Zinc 0.142 0.004

Table 11. Trace Element Concentrations in Make Up Water

Average (mg/L)

Arsenic <0.006

Barium 0.055

Beryllium 0.011

Cadmium <0.006

Cobalt <0.006

Chromium <0.006

Copper 0.010

Manganese <0.006

Molybdenum <0.006

Nickel <0.006

Lead <0.006

Selenium <0.006

Strontium <0.006

Thorium <0.006

Thallium <0.006

Uranium 0.381

Vanadium 0.046

Zinc <0.006

33

Flue Gas

The flue gas concentration was 10.297 +/- 1.915 ug arsenic/dscm of flue gas and

37.536 +/-14.390 ug selenium/dscm of flue gas. The other trace element concentrations

are provided in Table 12. The masses of arsenic and selenium/ Kg of coal are equal to the

product of the concentration of the element in flue gas and the volume of dry flue gas

corrected to 3% oxygen, shown in Eq 3. This equation is provided in the Appendix. The

equations for calculating the dry volume of flue gas corrected to 3% oxygen are also

provided in the Appendix.

Table 12. Trace Element Concentrations in Flue Gas

Average

(ug/dscm)

Std Dev.

(ug/dscm)

Arsenic 10.297 1.915

Barium <4.0

Beryllium <4.0

Cadmium <4.0

Cobalt <4.0

Chromium <4.0

Copper <4.0

Manganese 42.077 34.868

Molybdenum <4.0

Nickel 5.164 6.289

Lead <4.0

Selenium 37.536 14.390

Strontium <8.0

Thorium <4.0

Thallium <4.0

Uranium 8.110 1.670

Vanadium <4.0

Zinc 23.050 7.791

34

Power Plant Provided Information

The fraction of fly ash, the collecting efficiency of the ESP, the mass of gypsum,

wastewater, make-up water and reagent/Kg of coal burned were provided by the power

plant and are shown in Table 13.

Table 13. Parameters Provided Power Plant

parameter unit value

Yfa= 0.75

Yba= 0.20

Yecon= 0.03

YAPH= 0.03

hesp % 99.50

m blowdown kg/kg coal 0.55

m gypsum kg/kg coal 0.14

m makeup kg/kg coal 0.37

m reagent kg/kg coal 0.22

Mass Balance

The mass balance for a system is represented by a ratio that is equal to the mass of

the element coming out of the system divided by the mass of the element going into the

system, as shown in Equation 4 in the Appendix. For Plant A, that ratio is equal to 1.75

for arsenic and 1.10 for selenium. The masses of arsenic and selenium/Kg of coal burned

for each of the materials tested used to calculate the mass balance ratio is shown in Table

14.

Table 14. Arsenic & Selenium Results per Kg of Coal Burned

Arsenic Removal Selenium Removal

mg/ Kg of Coal % mg/ Kg of Coal %

Coal 0.14 0.99

Fly Ash 0.11 79.86 0.35 35.52

FGD Slurry 0.04 26.62 0.39 39.66

Flue Gas 0.10 68.35 0.35 34.91

Total 174.82 110.09

35

3.2 Plant B

For Plant B, coal, fly ash, economizer ash, FGD slurry materials and flue gas

samples were collected. Only one sample was collected per day for this plant.



Table 15. Plant B Bituminous Coal Proximate and Ultimate Analysis Data


Moisture % 1.60 -- 3.04

Ash % 11.42 11.61 11.26


Carbon % 76.21 77.45 75.10

Hydrogen % 5.16 5.06 5.25

Nitrogen % 1.38 1.40 1.36

Sulfur % 2.02 2.05 1.99

Oxygen % 3.80 2.41 5.04

1.46Air Dry Loss Moisture (ADL) %

Coal

The concentration of arsenic in coal was measured to be 3.763 +/- 1.645 mg/Kg.

The concentration of selenium was 7.859 +/- 0.958 mg/Kg. The concentrations of all

trace elements in coal are provided in Table 16.

36

Table 16. Trace Elements in Coal


Arsenic 3.763 1.645

Barium 50.706 15.275


Cadmium 4.433 0.639

Chromium 24.185 2.402

Cobalt 27.079 1.251

Copper 13.236 0.179

Lead 31.605 10.514


Molybdenum <1.5

Nickel 14.333 0.532


Thallium <1.5

Vanadium 38.872 1.833

Fly Ash

The concentration of arsenic in fly ash was measured to be 26.909 +/- 2.460

mg/Kg. The concentration of selenium was 36.876 +/- 0.607 mg/Kg. The concentrations

of all trace elements in fly ash are provided in Table 17. The equation for calculating the

mass of the element in fly ash/Kg of coal burned is in the Appendix and was described

above for Plant A.

37

Table 17. Trace Element Concentrations in Fly Ash


Arsenic 26.909 2.460

Barium 248.289 39.290


Cadmium 11.596 0.127

Chromium 102.355 3.726

Cobalt 104.509 7.169

Copper 81.815 3.262

Lead 142.354 8.744

Manganese 131.314 2.391


Nickel 84.444 2.188

Selenium 36.876 0.607

Thallium <1.5

Vanadium 158.145 3.839

Economizer Ash

The concentration of arsenic in economizer ash was measured to be 22.242 +/-

5.201 mg/Kg. The concentration of selenium was 28.169 +/- 2.170 mg/Kg. Other trace

element concentrations for the economizer ash are given in Table 18. The mass of the

element in the economizer ash/ Kg of coal burned is equal to the product of the fraction

of economizer ash, the concentration of the element in the ash and the amount of ash in

coal, Eq 5. This equation is provided in the Appendix.

38

Table 18. Trace Element Concentrations in Economizer Ash


Arsenic 22.242 5.201

Barium 147.950 52.568


Cadmium 13.011 0.500

Chromium 99.705 0.897

Cobalt 101.647 9.793

Copper 56.475 3.877

Lead 110.737 1.613

Manganese 112.704 23.600

Molybdenum <1.5

Nickel 68.992 11.951

Selenium 28.169 2.170

Thallium <1.5

Vanadium 137.878 18.719

Bottom Ash

The concentration of arsenic in bottom ash was measured to be 10.191 +/- 0.593

mg/Kg. The concentration of selenium was 25.293 +/- 2.997 mg/Kg. Other trace element

concentrations for the bottom ash are given in Table 19. The mass of the element in the

bottom ash/ Kg of coal burned is equal to the product of the fraction of bottom ash, the

concentration of the element in the ash and the amount of ash in coal. This equation is

provided in the Appendix.

39

Table 19. Trace Element Concentrations in Bottom Ash


Arsenic 10.085 0.593

Barium 169.108 17.531


Cadmium 13.500 0.757

Chromium 101.526 0.146

Cobalt 42.240 0.510

Copper 60.858 0.139

Lead 148.958 27.188

Manganese 109.551 2.819


Nickel 78.442 0.443

Selenium 25.293 2.997

Thallium <1.5

Vanadium 234.890 3.557

FGD Slurry Materials

The concentration of arsenic in the FGD slurry materials was measured to be

2.802 +/- 0.865 ug/g for the solid gypsum material and 1.172 +/- 0.053 ppb for the

blowdown liquid. The concentration of selenium in the FGD slurry materials was

measured to be 17.674 +/- 4.534 ug/g for the solid gypsum material and 0.301 +/- 0.039

ppm for the blowdown liquid. Concentrations for other trace elements in gypsum and

blowdown liquid are provided in Tables 20 and 21. The equation for calculating mass of

arsenic and selenium in FGD slurry materials/Kg of coal burned is provided in the

Appendix and was described above for Plant A.

40

Table 20. Trace Element Concentrations in Gypsum


Arsenic 2.802 0.865

Barium 6.153 1.588

Beryllium <1.5

Cadmium <1.5

Chromium <1.5

Cobalt 2.655 0.179

Copper 1.931 0.054

Lead 2.606 0.367


Molybdenum <1.5

Nickel 3.623 0.249

Selenium 17.365 4.998

Thallium <1.5

Vanadium <1.5

Table 21. Trace Element Concentrations in Blowdown Liquid


Arsenic * 1.172 0.053

Barium 0.091 0.008


Cadmium 0.018 0.002


Cobalt 0.054 0.005

Copper 0.020 0.007

Lead 0.214 0.027

Manganese 64.462 13.292

Molybdenum <1.5

Nickel 0.256 0.041


Thallium <1.5

Vanadium <1.5

*value in ug/L

Flue Gas

The concentration of arsenic and selenium in the flue gas was measured to be

0.119 +/- 0.130 ug/dscm and 0.037 +/- 0.020 mg/dscm, respectively. Trace element

41

concentrations in flue gas are given in Table 22. The equation for calculating the mass of

arsenic and selenium in flue gas/Kg of coal burned is in the Appendix and was described

above for Plant A.

Table 22 Trace Element Concentrations in Flue Gas

Average

(ug/dscm)

Std Dev.

(ug/dscm)

Arsenic 0.120 0.130

Barium 1.892 0.207

Beryllium <2.5

Cadmium <2.5

Chromium <2.5

Cobalt <2.5

Copper 5.509 0.208

Lead <2.5


Molybdenum <2.5

Nickel <2.5

Selenium 37.283 20.020


Vanadium <2.5


The fractions of fly ash, bottom ash, economizer ash, the collecting efficiency of

the ESP and the mass of blowdown and gypsum produced per kilogram of coal burned

were provided by the power plant and are shown in Table 23.

Table 23. Power Plant Provided Parameters


Yfa= 0.85

Yba= 0.10

Yecon= 0.03

hesp % 99.50



42

Mass Balance



system. For Plant B, that ratio is equal to 0.99 for arsenic and 0.94 for selenium. The

masses of arsenic and selenium/Kg of coal burned for each of the materials tested used to

calculate the mass balance ratio is shown in Table 24.

Table 24 Arsenic & Selenium Results per Kg of Coal Burned


mg/Kg of Coal % mg/Kg of Coal %

Coal 3.76 7.86

Fly Ash 2.64 70.15 3.62 46.03

Flue Gas 0.00 0.03 0.35 4.47

Econ Ash 0.06 1.71 0.08 1.04

FGD Slurry 0.89 23.56 3.06 38.90

Bottom Ash 0.12 3.14 0.29 3.73

Total 98.59 94.18

43

3.3 Plant C

For Plant C, coal, fly ash, FGD slurry materials and flue gas samples were

collected. Sampling took place over several different days.



Table 25. Plant C Bituminous Coal Proximate and Ultimate Analysis Data


Moisture % 5.23 - 12.40

Ash % 15.38 16.23 14.22


Carbon % 65.62 69.24 60.65

Hydrogen % 4.98 4.64 5.45

Nitrogen % 1.26 1.33 1.16

Sulfur % 3.81 4.02 3.52

Oxygen % 8.91 4.50 14.96

Air Dry Loss = 7.57 %

Coal

Arsenic and selenium in the coal was measured at 24.943 +/- 4.359 mg of

arsenic/Kg of coal and 10.585 +/- 4.967 mg of selenium/Kg of coal. Average trace

element concentrations in coal for Units 1 and 2 are given in Table 26.

44

Table 26. Trace Element Concentrations in Coal


Arsenic 24.943 4.359

Barium 81.797 26.631

Beryllium <1.5

Cadmium 7.753 1.293

Cobalt 60.868 8.600

Chromium 20.554 1.547

Copper 14.575 2.324

Manganese 68.954 22.139


Nickel 11.550 3.379

Lead 22.636 7.316

Selenium 10.585 4.967

Thorium 5.231 1.776

Thallium <1.5

Uranium 32.042 4.074

Vanadium 33.380 5.362

Zinc 107.787 46.377

Fly Ash

Arsenic and selenium in the fly ash was measured to be 195.607 +/- 29.162 mg of

arsenic/Kg of fly ash and 52.319 +/- 6.257 mg of selenium/Kg of fly ash. The average

concentrations for all the trace elements in fly ash from Units 1 and 2 are given in Table

27. This would mean a concentration of 20.532 mg of arsenic/Kg of coal burned and

5.491 mg of selenium/Kg of coal burned.

45

Table 27. Trace Elemental Concentrations in Fly Ash


Arsenic 195.607 24.990

Barium 674.529 43.951


Cadmium 26.198 4.829

Cobalt 48.226 5.133

Chromium 117.362 12.592

Copper 92.771 13.128

Manganese 560.868 45.094


Nickel 63.697 16.206

Lead 44.467 6.278

Selenium 52.319 6.257

Thorium 9.020 2.573

Thallium <1.5

Uranium 222.382 22.482

Vanadium 287.760 24.156

Zinc 769.184 106.213


The concentration of arsenic and selenium in the FGD slurry materials was

measured to be 5.603 +/- 0.55 mg of arsenic/Kg of gypsum and 11.418 +/- 5.34 mg of

selenium/Kg gypsum. The concentrations of arsenic and selenium in the make-up and

blowdown waters are 0.814 +/- 0.855 ug arsenic/L make-up water, 0.036 +/- 0.007 mg

selenium/L make-up water, 0.612 +/- 0.376 ug arsenic/L blowdown water and 0.219 +/-

0.090 mg selenium/L blowdown water. Trace element concentrations in gypsum,

blowdown water and make-up water are shown in Tables 28-30.

46

Table 28. Trace Elements in Gypsum


Arsenic 5.603 0.550

Barium 3.095 0.944

Beryllium <1.5

Cadmium 0.445 0.126

Cobalt 2.914 1.904

Chromium 14.576 3.831

Copper 2.660 1.022


Molybdenum <1.5

Nickel 2.320 0.347

Lead 4.303 0.537

Selenium 11.418 5.338

Thorium 3.073 0.931

Thallium <1.5

Uranium 26.262 18.738


Zinc 19.589 5.363

Table 29. Trace Elements in Blowdown Water


Arsenic * 0.612 0.376

Barium 0.038 0.023


Cadmium 0.012 0.006

Cobalt 0.009 0.001


Copper 0.020 0.003



Nickel 0.019 0.017

Lead <0.006


Thorium 0.043 0.014

Thallium <0.006

Uranium 0.182 0.011

Vanadium <0.006

Zinc 0.029 0.021

*values in ug/L

47

Table 30. Trace Elements in Make-Up Water


Arsenic * 0.814 0.855

Barium 0.047 0.007


Cadmium <0.006

Cobalt 0.014 0.011


Copper 0.020 0.004



Nickel 0.010 0.004

Lead <0.006


Thorium 0.021 0.008

Thallium <0.006

Uranium 0.031 0.008

Vanadium <0.006

Zinc 0.033 0.015

*value in ug/L

Flue Gas

The concentration of arsenic and selenium in the flue gas was measured to be 0.21

+/- 0.28 ug/dscm and 96.28 +/- 49.38 ug/dscm, respectively. The average trace element

concentration in the flue gas is given in Table 31. The equation for calculating the mass

of arsenic and selenium in flue gas/Kg of coal burned is in the Appendix and was

described above for Plant A.

48

Table 31. Trace Elements in Flue Gas

Average

(ug/dscm)

Std Dev.

(ug/dscm)

Arsenic 0.212 0.279

Barium 4.912 1.354

Beryllium <4.0

Cadmium 4.937 1.379

Cobalt 7.187 5.007


Copper 7.990 2.338



Nickel 5.213 1.458

Lead 5.708 1.020

Selenium 96.285 49.375

Thorium 18.471 2.123

Thallium <4.0

Uranium 15.990 1.194


Zinc 32.823 8.993


The fraction of fly ash, the collecting efficiency of the ESP and the mass of

blowdown, mass of make-up water and gypsum produced per kilogram of coal burned

were provided by the power plant and are shown in Table 32.



Yfa= 0.65

hesp % 99.50

m makeup kg/kg coal 0.99



Mass Balance



49

system. For Plant C, that ratio is equal to 0.83 for arsenic. The selenium mass balance

ratio was 0.76. The masses of arsenic and selenium/ Kg of coal burned for each of the

materials tested used to calculate the mass balance ratio is shown in Table 33.



mg/ Kg of Coal % mg/ Kg of Coal %

Coal 24.94 10.59

Fly Ash 20.53 82.32 5.49 51.88

FGD Slurry 0.31 1.24 1.87 17.65

Flue Gas 0.00 0.01 0.73 6.91

Total 83.56 76.43

50

3.4 Plant D

For Plant D, coal, fly ash, FGD slurry materials and flue gas samples were

collected. Sampling took place over several different days.



Table 34. Plant D Bituminous Coal Proximate and Ultimate Analysis Data


Moisture % 2.94 -- 10.61

Ash % 13.60 14.01 12.53


Carbon % 73.92 76.16 68.08

Hydrogen % 4.85 4.66 5.35

Nitrogen % 1.39 1.43 1.28

Sulfur % 3.46 3.56 3.19

Oxygen % 2.77 0.16 9.57

Air Dry Loss Moisture (ADL) 7.90 %

Coal

Arsenic and selenium in the coal was measured at 5.719 +/- 0.978 mg of

arsenic/Kg of coal and 10.703 +/- 2.892 mg of selenium/Kg of coal. Average trace

element concentrations in coal for Plant D are given in Table 35.

51

Table 35. Trace Element Concentrations in Coal


Arsenic 5.719 0.978

Barium 58.136 19.600


Cadmium 1.977 0.310

Cobalt 5.101 0.933

Chromium 18.400 3.584

Copper 10.005 1.907

Manganese 57.630 21.178


Nickel 15.967 3.367

Lead 25.426 5.725

Selenium 10.703 2.892

Thorium 10.140 3.644

Thallium <1.5

Uranium 31.295 9.933

Vanadium 36.164 10.208

Zinc 83.945 27.871

Fly Ash

Arsenic and selenium in the fly ash was measured to be 124.563 +/- 36.830 mg of

arsenic/Kg of fly ash and 62.766 +/- 13.435 mg of selenium/Kg of fly ash. The average

concentrations for all the trace elements in fly ash from Plant D are given in Table 36.

This would mean a concentration of 3.47 mg of arsenic/Kg of coal burned and 1.75 mg of

selenium/Kg of coal burned.

52

Table 36. Trace Elemental Concentrations in Fly Ash


Arsenic 124.563 36.830

Barium 517.070 103.044


Cadmium 25.903 5.426

Cobalt 54.774 1.913

Chromium 212.480 23.851

Copper 190.528 22.181

Manganese 311.745 19.987


Nickel 174.191 14.850

Lead 557.953 91.028

Selenium 62.766 13.435

Thorium 45.258 10.590

Thallium <1.5

Uranium 329.881 22.351

Vanadium 361.127 50.516

Zinc 2592.227 307.052


The concentration of arsenic and selenium in the FGD slurry materials was

measured to be 2.800 +/- 1.394 mg of arsenic/Kg of solid slurry and 6.917 +/- 2.651 mg

of selenium/Kg solid slurry. The concentrations of arsenic and selenium in the blowdown

waters are 0.185 +/- 0.034 mg arsenic/L blow down water and 0.609 +/- 0.124 mg

selenium/L blowdown water. Trace element concentrations in the solid slurry and

blowdown water are shown in Tables 37-38.

53

Table 37. Trace Elements in Solid Slurry


Arsenic 2.800 1.394

Barium 3.395 0.717

Beryllium <1.5

Cadmium <1.5

Cobalt <1.5


Copper 4.856 0.281



Nickel 3.174 0.471

Lead 0.819 0.637


Thorium 6.291 1.559

Thallium <1.5

Uranium 7.408 1.265


Zinc 40.075 6.085

Table 38. Trace Elements in Blowdown Water


Arsenic 0.185 0.034

Barium 0.082 0.019

Beryllium <0.006

Cadmium <0.006

Cobalt 0.010 0.001


Copper 0.010 0.005



Nickel 0.236 0.066

Lead 0.014 0.004


Thorium 0.012 0.001

Thallium <0.006

Uranium 3.586 0.276

Vanadium <0.006

Zinc 0.719 1.585

54

Flue Gas

The concentration of arsenic and selenium in the flue gas was measured to be

4.690 ug/dscm and 4.310 ug/dscm, respectively. These measurements were made using

an atomic fluorescence instrument since the levels were below the ICP detection level.

The average trace element concentration in the flue gas is given in Table 39. The

equation for calculating the mass of arsenic and selenium in flue gas/Kg of coal burned is

in the Appendix and was described above for Plant A.

Table 39. Trace Elements in Flue Gas

Average

(ug/dscm)

Std Dev.

(ug/dscm)

Arsenic 4.690 1.437

Barium <4.0

Beryllium <4.0

Cadmium <4.0

Cobalt <4.0

Chromium <4.0

Copper <4.0

Manganese 45.333 13.831

Molybdenum <4.0

Nickel <4.0

Lead <4.0


Thorium <4.0

Thallium <4.0

Uranium <4.0

Vanadium <4.0

Zinc 39.865 24.536


The fraction of fly ash, fraction of bottom ash, the collecting efficiency of the

ESP, the mass of blowdown, and gypsum produced per kilogram of coal burned were

provided by the power plant and are shown in Table 40.

55



Yfa= 0.20

Yba= 0.75

hesp % 99.50



Mass Balance



system. For Plant D, that ratio is equal to 1.02 for arsenic. The selenium mass balance

ratio was 0.96. The masses of arsenic and selenium/Kg of coal burned for each of the

materials tested used to calculate the mass balance ratio is shown in Table 41.



mg/Kg of Coal % mg/Kg of Coal %

Coal 5.72 10.70

Fly Ash 3.47 60.76 1.75 16.35

Flue Gas 0.03 0.52 0.03 0.28

FGD Slurry 0.87 15.22 2.24 20.95

Bottom Ash 1.51 26.43 6.27 58.54

Total 102.93 96.12

56

4. Discussion

Mass Balance

A summary of boiler type and coal for each power plant is given in Table 42.

Comparison data for each of the plants are shown in Figures 14 and 15.

Table 42. Plant Boiler Type & Coal Information

Boiler Type Coal Type

Plant A PC Boiler Bituminous

Plant B PC Boiler Bituminous

Plant C PC Boiler Bituminous

Plant D Cyclone Bituminous

The data for Plant A indicates that approximately 80% of the arsenic leaves the

system in the form of fly ash, 27% leaves the system in the form of FGD slurry and 68%

leaves the system in the form of flue gas. The total arsenic mass balance for Plant A

indicates much more arsenic is exiting the system than what was put in. This indicates

that there is error in the measurements. The most likely source for the error is the flue gas

measurement. Arsenic present in the flue gas at that high a concentration would be very

highly improbable. Sources of error associated with the flue gas measurement that might

bias the results high would be possible contamination during the digestion or analysis

steps or a problem with the ICP measurement due to interference, more sources of

possible errors in measurements will be discussed in the following section on quality

assurance. The distribution of selenium is fairly even throughout the ash (36%), slurry

(40%) and flue gas (35%). Although the overall material’s balance for selenium in Plant

A is not high enough for the values to be considered suspect, again, the concentration in

the flue gas is much higher than what would be considered probable. The selenium 196

nm line does have an iron and aluminum as interfering lines, however, since both the

arsenic and selenium results in flue gas seem to be high that would tend to favor the

57

possibility of contamination or a calculation problem. The flue gas measurements for

arsenic and selenium from Plant A are considered suspect and are provided here as

reference, however, Figures 14 and 15 are shown with this data omitted.

The data for Plant B indicates that approximately 70 % of the arsenic leaves the

system in the form of fly ash, 24 % leaves the system in the form of FGD slurry and

0.03% leaves the system in the form of flue gas. Approximately 46 % of the selenium

leaves the system in the form of fly ash, 39% leaves the system in the form of FGD slurry

and 4% leaves the system in the form of flue gas. Economizer and bottom ash represent a

very small portion of the arsenic and selenium removal.

The data for Plant C indicates that approximately 82% of the arsenic leaves the

system in the form of fly ash, 1% leaves the system in the form of FGD slurry and 0.01%

leaves the system in the form of flue gas. Approximately 54% of the selenium leaves the

system in the form of fly ash, 18% leaves the system in the form of FGD slurry and

almost 7% leaves the system in the form of flue gas. The FGD slurry values are

considerably less than both plants A and B. The pulverized coal boiler for Plant C, Unit

2, shares an FGD system with the cyclone boiler, Unit 1, at the plant. As shown in the

Plant D data, discussed below, the FGD materials from cyclone systems did not contain

as high a percentage of metal due to the amount present in the bottom ash. Therefore, it is

likely that gases entering the FGD from the cyclone boiler did not possess arsenic and

selenium concentrations as large as those entering from the pulverized coal boiler.

The data for Plant D indicates that approximately 61% of the arsenic leaves the

system in the form of fly ash, 15% leaves the system in the form of FGD slurry, 26 %

leaves the system in the form of bottom ash and 0.52 % leaves the system in the form of

58

flue gas. Approximately 16% of the selenium leaves the system in the form of fly ash,

21% leaves the system in the form of FGD slurry, 59% leaves the system in the form of

bottom ash and 0.28 % leaves the system in the form of flue gas.

Fly ash data for all 4 plants is in good agreement, showing that 60-80% of the

arsenic will be removed in fly ash and 35-55% of the selenium will be removed with the

fly ash, with the exception being for Plant D which had a substantial amount of selenium

in the bottom ash, leaving a smaller portion of metals available for the fly ash.

FGD slurry data for Plants A and B are in fairly good agreement, showing that

approximately 25% of the arsenic and approximately 30-40% of the selenium will leave

the system in the slurry materials.

Flue gas data for Plants B, C & D are similar in that both plants show very little

arsenic and selenium escaping with the flue gas, 6-7% or less.

Figure 14. Comparison of Arsenic Removal in Plants A-D

0

20

40

60

80

100

120

Plant A Plant B Plant C Plant D

Ars

enic

Rem

ova

l in

Mat

eri

al (

%)

Econ. Ash

Bottom Ash

Flue Gas

FGD Slurry

Fly Ash

59

Figure 15. Comparison of Selenium Removal in Plants A-D

0

20

40

60

80

100

120


Sele

niu

m R

em

ova

l in

Mat

eri

al (

%)

Econ. Ash

Bottom Ash

Flue Gas

FGD Slurry

Fly Ash

The trace metals concentration associated with the fly ash, bottom ash and

economizer ash are trace metals associated with the solid phase. The calculation for

determining the trace metal concentration per kilogram of coal burned is similar for all

components of the solid phase. After the ESP, trace metals measured in the FGD slurry

come from the flue gas and, of course, trace metals in the stack come from the flue gas. It

is therefore relevant to look at the trace metals in plant residues in terms of metals

associated with the solid phase and those associated with the flue gas. Figures 16 and 17

show the arsenic and selenium concentrations for the individual plants in terms of solid

phase and gas phase. Approximately 80% of the arsenic removal in a system will be

through the solid phase with the remainder being with the flue gas. Most of the selenium,

almost 80%, in the cyclone boiler will be removed in the solid phase, but the selenium in

the pulverized coal boilers is only removed at about 50% or less in the solid phase. The

selenium in the gas phase is removed at 20-40 %, whereas the arsenic in the gas phase is

approximately 20%. The larger portion of selenium in the gas phase as compared with the

60

arsenic is in good agreement with selenium being the more volatile element as discussed

in the previous work section.

Figure 16. Arsenic in Solid Phase and Gas Phase

0

20

40

60

80

100

120


Ars

enic

Rem

ova

l (%

)

Gas Phase

Soild Phase

Figure 17. Selenium in Solid Phase and Gas Phase

0

20

40

60

80

100

120


Sele

niu

m R

em

ova

l (%

)

Gas Phase

Soild Phase

Implications for Arsenic and Selenium Regulations

The EPA has already invested a great deal of time and attention addressing mercury

emission and control. Due to the toxicity of arsenic, setting specific emissions limits for

that metal should be of paramount interest; however, this research indicates that selenium

61

is not as easily captured and that more selenium escapes into the environment through

emitted flue gas. One must examine the information carefully to determine which

element presents a greater threat, a minuscule amount of the more toxic element or a

greater amount of the less toxic element. Implications in dealing with hazardous waste

disposal are equally important. Currently, a large portion of fly ash is put into landfills

while some is sold to be used in concrete and cement products. The EPA already has

regulations in place to determine how much arsenic and selenium can leach out of a

material under landfill conditions before it has to be disposed of as hazardous waste. The

concentrations of arsenic and selenium that leach out of the materials such as those

studied in this research will have to be closely monitored to make sure that they meet

these EPA requirements. Meeting these EPA restrictions might also necessitate a limit on

the amount of arsenic and selenium that can be captured by fly ash depending on the

leaching characteristics of the selected element in this material.

Loss on Ignition vs. Calcium Content

As shown previously in the environmental distribution section, the concentration

of calcium in the coal can help to trap arsenic in the form of Ca3(AsO4)2. It is also well

known that the unburned carbon in fly ash can help to trap mercury. It is relevant here to

provide a brief discussion on the relationship between loss on ignition and calcium

concentration in the fly ash and the capturing ability of the fly ash. The most arsenic was

captured in Plant C, with less being captured in Plant A and the least being captured by

Plant B. Plant D is not being compared here due to the significant portion already

captured by the bottom ash. The calcium oxide concentrations were 5.437 %, 4.828% and

1.6% for Plants C, A and B, respectively. The amount of arsenic associated with the fly

62

ash increases with increasing calcium concentration. For comparison, Plant B had the

highest loss on ignition value, 4.01%. Plant C had the second highest, 2.65% and Plant A

had the least, 0.79%. This data would indicate that calcium content will be a better

indicator of arsenic capturing ability than loss on ignition value. In addition, Plant C

captures more selenium in the fly ash than plant B, again indicating that unburned carbon

may not be the major factor for selenium capture.

Quality Assurance

The possibilities for error when conducting research are always present. In

research involving many steps and calculations, such as this, impediments to quality data

exist at every level. Initially, problems can exist with the sample itself and the non-

homogeneous nature of coal-fired plant materials. Utilizing the procedures outlined in

established methods for processing the sample to make it homogenous, such as the

ASTM D 2013 method mentioned previously, can help, but not completely eliminate this

problem. Problems digesting the sample are of extreme importance also. Scrupulous

cleaning of vessels that come into contact with the sample, purity of reagents and

measurement errors such as those associated with weight are some problems common to

many analytical techniques. Additional problems specific to the analysis of arsenic and

selenium in coal and coal by-product matrices are the low concentrations of these

elements present in the samples, the volatility of selenium, the low intensity of these

elements in comparison with other elements and the difficulty in digesting these samples

completely.

Problems specific to ICP analysis include improper wavelength alignment, poor

background placement, varying torch conditions throughout the analysis causing possible

63

drift and, most importantly, interfering elements. The arsenic 193 nm quantitation line

has an iron interferent visible to the left of the arsenic peak in the spectra. This interferent

can often produce a sloping baseline, which makes proper positioning of the background

bars for quantitation difficult. This could easily cause a result to be biased higher than

actual. The arsenic 197 nm line also has an interferent line that, when present, emits at a

wavelength so close to arsenic that it is almost indistinguishable from the arsenic line.

Even if arsenic wasn’t present at high concentrations, it would be possible to mistakenly

use the intensity from this interfering element for quantitating arsenic and calculate a

result that was biased high. The selenium 196 nm line has iron and aluminum interfering

lines.

Additional sources of error include the parameters provided by the power plant.

Parameters such as the fraction of fly ash, fraction of bottom ash, masses of blowdown

and gypsum produced per kilogram of coal are typically general estimates.

64

5. Bibliography

1. Agency for Toxic Substances and Disease Registry (ATSDR). 2007.

Toxicological Profile for Arsenic (Update). Atlanta, GA: U.S. Department of

Public Health and Human Services, Public Health Service.

2. Agency for Toxic Substances and Disease Registry (ATSDR). 2003.

Toxicological Profile for Selenium (Update) Atlanta, GA: U.S. Department of

Health and Human Services, Public Health Service.

3. Diaz-Somoano, M.; Martinez-Tarazona, M.R., Environ. Sci. Technol., 2004, 38,

899-903.

4. Staudt, J.; Engelmeyer, T.; Weston, W.; Sigling, R. The Impact Of Arsenic On

Coal Fired Power Plants Equipped With SCR– Experience At OUC Stanton. 2002

Conference on Selective Catalytic Reduction (SCR) and Selective Non-Catalytic

Reduction (SNCR) for NOx Control. 2002 Conference Proceedings

5. López-Antón, M.A; Diaz-Somoano, M.; Spears, D.A., Environ. Sci. Technol,

2006, 40, 3947-3951.

6. Shah, P.; Strezov, V.; Stevanov, C.; Nelson, P., Energy & Fuels, 2007, 21, 506-

512.

7. Huggins, F.E.; Senior, C.L.; Chu P., Environ. Sci. Technol. 2007, 41, 3284-3289.

8. Wang, J; Tomita, A, Energy & Fuels, 2003, 17, 954-960.

9. Shoji, T.; Huggins, F.E.; Huffman, G. P.; Linak, W.P.; Miller, C.A., Energy &

Fuels, 2002, 16, 325-329.

10. Sandelin, K.; Backman, R., Environ. Sci. Technol. 2001, 35, 826-834.

11. Thomas, R.; Today’s Chemist at Work. 8, 10, 42-48.

12. EPA Method 200.8. Determination Of Trace Elements In Waters And Wastes By

Inductively Coupled Plasma - Mass Spectrometry

13. Senior, C.; Helble, J.; Sarofim, A., Predicting the Speciation of Mercury

Emissions from Coal-Fired Power Plants. Proceedings of the Conference on Air

Quality II: Mercury, Trace Elements and Particulate Matter, McLean, VA,

September 19-21, 2000.

14. Sakulpitakphon, T.; Hower, J. C.; Trimble, A. S.; Schram, W. Nalbandian, H.;

Carpenter, A. M. Prospects for Upgrading Coal-Fired Power Plants; Reference

65

No. CCC/41; International Energy Agency Coal Research: London, 2000.

15. Senior, C.; Lignell, D.; Sarofim, A.; Meht, A. Combustion and Flame, 147, 3,

2006, 209-221.

16. Serre, S.; Silcox, G.; Ind. Eng. Chem Res. 2000, 39, 1723-1730.

17. Steam: Its Generation and Use. Babcock & Wilcox Company.

18. Criterion 304 A Arsenic and Clarifications to Compliance and New Source

Contaminants Monitoring Final Rule Federal Register (66 FR 6976) January 22,

2001. 401 KAR 64:005

66

Appendix

Calculations

1. The mass of the selected element in fly ash/Kg of coal burned, M fa, is calculated

by Equation 1

M fa = Y fa x A x h esp x C fa Equation 1

Where h esp is equal to the particulate collecting efficiency of the ESP provided by

the power plant, Y fa is the fraction of fly ash provided by the power plant. A is

the ash content in coal. C fa is the concentration of the selected element in fly ash.

2. The mass of the selected element in the FGD slurry material/Kg of coal burned,

M FGD Slurry, is calculated by Equation 2.

M FGD Slurry = C blowdown x m blowdown + C gypsum x m gypsum – C makeup x m makeup – C

reagent x m reagent

Equation 2

Where C blowdown, C gypsum, C makeup, C reagent are the element concentrations and m

blowdown, m gypsum, m makeup, m reagent represent the amount of material produced or

consumed when one unit of coal is fired.

3. The mass of the selected element in the flue gas, M flue gas, is calculated by

Equation 3.

M flue gas= V DF3% x C flue gas Equation 3

Where V DF3% is the dry flue gas volume generated by firing one unit of coal,

corrected to 3% oxygen and C is the concentration of the metal in the flue gas.

4. The ratio of Arsenic or Selenium at the stack is given by the equation

R = M out/ M in Equation 4

MAs out = Mstack+Mfa+Mba+Mecon+MAPH+MFGD Slurry

Where M in is the amount of arsenic or selenium into the process when one unit

of coal is fired. M out is equal to the sum of the masses of the elements in the

different power plant samples.

5. The mass of the selected element in economizer ash/Kg of coal burned, M econ, is

calculated by Equation 5.

M econ = y econ x A x C econ Equation 5

67

Where Y econ is the fraction of economizer ash provided by the power plant. A is

the ash content in coal. C econ is the concentration of the selected element in the

economizer ash.

6. The mass of the selected element in the bottom ash/ Kg of coal burned, Mba, is

calculated by Equation 6

Mba = y ba x A x Cba Equation 6

Where Y ba is the fraction of bottom ash provided by the power plant. A is the ash

content in coal. Cba is the concentration of the selected element in bottom ash.

7. The mass of the selected element at the stack, Mstack, is calculated by Equation 7.

Mstack= V DF3% x C Stack Equation 7

Where V DF3% is the dry flue gas volume generated by firing one unit of coal,

corrected to 3% oxygen and C Stack is the concentration of the element at the stack.

8. The dry flue gas volume generated by firing one unit of coal, corrected to 3%

oxygen, V DF3%, is calculated by Equation 8

V DF3% =Vodf + VH2O + (a-1)V

o Equation 8

Where Vodf ,VH2O , a, V

o represent the dry flue gas volume, water vapor in the flue

gas, excess air ratio and air volume required for complete combustion.

9. The dry flue gas volume,Vodf , is calculated by Equation 9.

Vodf = V CO2 + V SO2 + V

oN2 Equation 9

Where V CO2 is equal to the volume of carbon dioxide produced by the

combustion of one unit of coal, V SO2 is equal to the volume of sulfur dioxide

produced by the combustion of one unit of coal and VoN2 is equal to the volume of

nitrogen gas produced by the combustion of one unit of coal.

10. The volume of carbon dioxide produced by the combustion of one unit of coal is

equal to

VCO2 = 0.01866 x Carbon Content in coal Equation 10

11. The volume of sulfur dioxide produced by the combustion of one unit of coal is

equal to

VSO2 = 0.007 x Sulfur Content in coal Equation 11

12. The volume of nitrogen produced by the combustion of one unit of coal is equal

to

68

VoN2 = 0.79 V

o + 0.008 x Nitrogen Content in coal Equation 12

13. The air volume required for complete combustion, Vo, is calculated by

Vo = 0.0889 (Carbon Content + 0.375 x Sulfur Content) + 0.265 x Hydrogen

Content – 0.0333 x Oxygen Content Equation 13

14. Water vapor in the flue gas, VH2O, is calculated by

VH2O = 0.111 x Hydrogen Content + 0.0124 x Water Content +

0.0161 x a x Vo Equation 14

15 The excess air faction, a, is calculated by

a = 1 + Vodf x O2/ (V

o x (21-3)) Equation 15

arsenic and selenium distribution in coal-fired plant samples

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