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AB_C.3_EGAT_ENVIRONMENTAL IMPACT ASSESSMENT OF MERCURY FROM

COAL POWER PLANT: CASE STUDY OF MAE MOH POWER PLANT UNIT 4-7

REPLACEMENT

Jittakarn Sintusek, Coal Power Plant and Mines Environment Section

Electricity Generating Authority of Thailand (EGAT)

53 Moo 2 Bangkruai, Nonthaburi, 11130, Thailand

Tel: +662 436 1114 Fax: +662 436 1190 Email: jittakarn.s@egat.co.th

ABSTRACT

The Mae Moh Power Plant Units 4-7 Replacement Project (MMRP) is lignite-fired thermal power

plant, 600 MW installed capacity. EGAT has strictly adopted the relevant environmental laws and regulations

including Environmental and Health impact Assessment (EHIA) process in accordance with the Enhancement

and Conservation of National Environmental Quality Act 1992. Mercury, a kind of heavy metal, is impurity

contaminated in lignite. It was found that the mercury content in lignite is trace in concentration. The

Concentration of mercury from the stack is not exceed the regulated standard. The Concentration of mercury

from the bottom ash and fly ash are classified as non-hazardous waste. According to the anticipation of mercury

in the operation period around the project site through model reveals that it is very low concentration.

Concentration of mercury in soil, underground water, surface water, sediment and fish showing they are not

exceed the regulated standards. According to risk assessment for 30 years consumption and respiration of

Mercury found that health effect on people living nearby is low. Therefore, the environmental impact of

Mercury from the MMRP is trace in concentration, However the suitable preventive and mitigation measures as

well as monitoring measures for mercury impact are established.

Key Words: Environmental and Heath Impact Assessment (EHIA), Mercury, Lignite-fired, Coal-fired

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1. INTRODUCTION

A coal fired power plant concerns source of toxic mercury air emissions contaminated in land and

water. Mercury in the atmosphere can be deposited onto the soil or water. Mercury in water can be sedimented.

Mercury in water, soil and sediment can be methylated and demethylated. Methymercury in water can

bioaccumulate in aquatic organisms. So the environment impact assessment of mercury from MMRP had been

studied.

The Mae Moh lignite-fired thermal power plant, total 2400 MW installed capacity, consisting of

Units 4-7, 600 MW installed capacity(150 MW each), and Units 8-13, 1800 MW installed capacity(300 MW

each). Units 4-7 have been used for electricity generating for 25 years in 2009-2010. The Electricity Generating

Authority of Thailand (EGAT), as a consequence, considered construction of new generating units to replace the

existing Units 4-7. The replacement units will have a total installed capacity of 600 MW which is equal to those

of the existing ones. Lignite is utilized to produce the cost-efficient electricity to enhance the power generating

capacity and to strengthen the national power grid system.

EGAT has not only strictly adapted all of the relevant regulation including EHIA process, the Rule of

the Office of the Prime Minister and Public Consultation 2005 and the National Public Health Act 2007 but also

the Public Involvement and Participation throughout the EHIA process, which provide opportunities for all

concerned stakeholder to express their views on the environmental and social issues.

2. MAIN CONTENTS

2.1 Project Detail and Air Pollution Control

The Mae Moh Power Plant Units 4-7 Replacement Project is located in Mae Moh sub-district, Mae

Moh district, Lampang province (Figure 1). Encompassing about 63 rai of land (Figure 2) within the boundary

of the Mae Moh Power Plant, the project site consists of the power generating unit and switchyard (51 rai),

transmission system and power station (6 rai), water production unit (2 rai), and cooling system (4 rai). Major

components in the power generating process comprise the following:

Supercritical Pressure Steam Generator with a capacity of 1,435.90 tons/hr. at the maximum

pressure of 260 Bar(a) and the temperature of 566 °C

Steam turbine generators with three levels of pressure: high-pressure turbine, intermediate-pressure

turbine, and low-pressure turbine

Condenser: The exhaust steam from steam turbine is condensed for reuse in the steam generating

system.

Cooling tower

Electrical equipment: transformer, circuit breaker and switchgear

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Figure 1: Location of Mae Moh Power Plant Units 4-7 Replacement Project in Mae Moh Sub-District, Mae Moh

District, Lampang Province, Thailand

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Figure 2: General Layout Plan of Mae Moh Power Plant Units 4-7 Replacement Project within The Mae Moh

Power Plant Boundary

MMRP, which will use lignite to produce electricity will have a generating unit with a gross capacity

of 600 MW, and a net capacity of 540 MW. The net plant heat rate (new & clean) efficiency will be 41.77%

whereas the average net efficiency throughout the lifetime of 30 years will be 40.95%. The maximum fuel

consumption per unit will approximate to 8,504 tons/day and a total raw water of 45,084 m3/day will be required

from Mae Kham and Mae Jang reservoirs. (The reservoir simulation result based on the 54-year statistical data

revealed that the existing water supply system will have sufficient capacity to cope with the demand of all

power plant units without shortage. The two reservoirs will supply raw water in a total amount of 148,000

m3/day.) The effluent will be 6,121 m

3/day. The pollutant emission rates are as follows: sulfur dioxide (SO2) of

3,246 tons/year, nitrogen oxide (NOX) of 2,799 tons/year, and total suspended particulates of 376 tons/year. The

waste generated during the operation period comprises bottom ash (455 tons/day), fly ash (1,057 tons/day), and

gypsum (1,691 tons/day).

The following air pollution emission control devices will be installed.

Electrostatic Precipitator (ESP) will collect the particulates and fly ash with the efficiency of

99.48%.

NOX control system:

(1) Low NOX Burner (LNB) and Over Fired Air (OFA) technologies

(2) Selective Catalytic Reduction system is used to control NOX arising from exhaust by using the

reaction between NH3 and NOX. The NOX control efficiency is about 50%.

Wet Limestone Flue Gas Desulfurization (FGD) system has the efficiency of 97.9%.

The air pollution emission control criteria established for the project is presented below.

Pollutant Unit EGAT Criteria Standard

SO2 ppmvd 100 180

NO2 ppmvd 120 200

Particulates mg/m3 30 80

Regarding effluent management, effluent originated from the project operation and treatment methods

can be summarized as follows.

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Effluent from general use, including wastewater from consumption, will be treated in the sewage

treatment plant whereas oil contaminated effluent will be treated by the oil separator. Effluent from coal stock

pile will be collected in the settling pond, and effluent from the steam generation system will be discharged into

two settleable solid and oxidation ponds with a combined storage capacity of 32,000 m3 (20,000 m

3 and 12,000

m3). Settleable solids and oil will be removed.

Effluent from electricity generating process, such as effluent contaminated by chemicals, will be

drained into the neutralization basin. Effluent from the cooling tower blow down and from demineralization

plant will be collected in the waste ash water basin (ZQ-1) before releasing into the ash water lake of 50,000 m3

in storage capacity where waste ash will be separated from water. The effluent from the lake will be pumped

back and sprayed onto the bottom ash on submersible scrapper conveyor.

Effluent from two sources will be treated by using the bio-treatment pond to meet the effluent quality

standards for industrial factory and industrial estate. Since the new Units 4-7 will have the same installed

capacity as and more efficiency than the existing ones, the present wastewater treatment system of the Mae Moh

Power Plant will be able to cope with the effluent from the new power plant units.

Solid waste management method will be similar to that used with the existing Units 4-13. An ash

dump site is located about 4 km north of the existing Units 4-13. The ash dump which was built by compacted

clay has been used for 25 years. Coal ash and gypsum are carried from the power plant by conveyor system and

disposed of by layering on the dump site. Covering an area of about 700 rai, the ash dump site is about 390 m

MSL with a storage volume of 8.5 million m3. EGAT has planned to increase the dump site’s elevation by

heightening the earth embankment and uplift the conveyor belt in order to sufficiently cope with the amount of

coal ash, gypsum, and refuses from the power plant and surrounding communities until 2047. Since the dump

site was built on clay, no seepage into underground water is found. EGAT has implemented measures to control

and oversee the environment, particularly quality of surface water and underground water. Wastewater

collection and treatment system was installed. Quality of surface and underground water around the project site

is regularly monitored to ensure ash water will not cause impacts on environment. The monitoring result

revealed that all environmental parameters meet the standard criteria

2.2 Environmental Contamination by Mercury

Natural transformations and environmental pathways of mercury are very complex and are greatly

affected by local conditions. To assess the environmental fate and the impacts of anthropogenic mercury

emissions, researchers must examine a range of biogeochemical interactions affecting mercury in its different

physical states and chemical forms. Understanding the relationships between local conditions and mercury

levels in various environmental media and living organisms is critical to predicting changes in concentration and

form.

Mercury is emitted to the atmosphere from volcanoes and industrial sources of pollution. Mercury in

the atmosphere can be deposited onto the soil or water. Mercury in water can be sedimented. Mercury in water,

soil and sediment can be methylated and demethylated. Methylmercury in water can bioaccumulate in aquatic

organisms. Conceptual biogeochemical mercury cycle is presented as figure 3

Figure 3: Conceptual Biogeochemical Mercury Cycle

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There are two main types of reactions in the mercury cycle that convert mercury through its various

forms: oxidation-reduction and methylation-demethylation. In oxidation-reduction reactions, mercury is either

oxidized to a higher valence state (e.g. from relatively inert Hg0 to the more reactive Hg

2+) through the loss of

electrons, or mercury is reduced, the reverse of being oxidized, to a lower valence state.

The oxidation of Hg0 in the atmosphere is an important mechanism involved in the deposition of

mercury on land and water. Elemental mercury (Hg0) can volatilize relatively easily and be emitted to the

atmosphere, where it may be transported on wind currents for a year or more and be re-deposited in the

environment for further cycling. In contrast, Hg2+

has an atmospheric residence time of less than two weeks due

to its solubility in water, low volatility and reactive properties. Hence, when (Hg0) is converted to Hg

2+, it can be

rapidly taken up in rain water, snow, or adsorbed onto small particles, and be subsequently deposited in the

environment through "wet" or "dry" deposition.

In the environment, mercury is transformed into methylmercury when the oxidized, or mercuric

species (Hg2+

), gains a methyl group (CH3). The methylation of Hg2+

is primarily a natural, biological process

resulting in the production of highly toxic and bioaccumulative methylmercury compounds (MeHg+) that build

up in living tissue and increase in concentration up the food chain, from microorganisms like plankton, to small

fish, then to fish eating species like otters and loons, and humans.

Understanding the variables influencing the formation of methylmercury is critically important due to

its highly toxic, bioaccumulative and persistent nature. A variety of microorganisms, particularly methanogenic

(methane producing) and sulfate-dependant bacteria are thought to be involved in the conversion of Hg2+

to

MeHg under anaerobic (oxygen poor) conditions found, for example, in wetlands and river sediments, as well as

in certain soils. Methylation occurs primarily in aquatic, low pH (acidic) environments with high concentrations

of organic matter.

In general, the form of mercury in the environment varies with the season, with changes in organic

matter, nutrient and oxygen levels and hydrological interactions within an ecosystem.

2.3 Environmental Impact Assessment of Mercury from MMRP

Environmental Impact Assessment of Mercury was carried out based on the suitable criteria and

technical methods which are acceptable to ONEP and related government offices, covering environmental

parameters in physical resources, biological resources, human use values, and quality of life values. Mercury

impacts on environment, natural resources, and social aspects were assessed during the operation periods. In

addition, the project impacts on ecological system were also evaluated using the systematic relationships

between humans and environment and inter specific interaction.

2.4 Mercury content in coal

MMRP uses lignite from Mae Moh mine as the fuel to generate electricity. Coal quality of Mae Moh

basin is presented as below. Coal quality show that mercury in Mae Moh basin is very low.

Analysis Percent by weight

Minimum Maximum Average Proximate Analysis

Volatile Matter 25.95 28.60 27.44

Ash Content 11.74 21.57 16.46

Moisture Content 30.15 37.77 31.98

Fixed Carbon 16.09 28.68 23.04

Total Sulfur 2.19 3.00 2.39

Ultimate Analysis

Sulfur 2.43 10.72 5.35

Mercury 1.0x10-7

(0.001 mg/Kg)

1.0x10-6

(0.01 mg/Kg)

5.1x10-7

(0.0051 mg/Kg)

Note : Analysis by Mae Moh Mines Labolatory,2012

2.5 Key Environmental Impacts

1) Air quality

The analysis of mecury in air from current Mae Moh Power Plant unit 4-5 Stack shows that mercury

contains 0.001 milligram/cubic metre or 0.014 lb/GWhr which not exceed the EPA standard. In the operation

period, the anticipation of air quality around the project site through CALPUFF model considering sulphur

dioxide, nitrogen dioxide, total suspended particulates, mercury, lead, and arsenic, reveals that Concentration of

mercury in 1-hour maximum average at the project site is at 5.610-5

microgram/cubic metre. The concentration

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of mercury in 1-hour average ranges 1.0810-6

- 1.0910-5

microgram/cubic metre (No standard is established

for the concentration of mercury in 1-hour average in the ambient.)

2) Surface water quality

The Mae Moh Power Plant Units 4-7 Replacement Project have an effluent of about 6,121 cubic

metre/day released to Mae Moh reservoir. The effluent can be adequately managed by an existing system. As a

result, water quality in Mae Moh reservoir, which is the last catchment before discharging to natural waterway,

is affected in a low level.

The treated effluent of Mae Moh power plant will comply with industrial factory and industrial estate

effluent standards. The treated effluent will then be discharged to Mae Moh reservoir and Mae Change

watershed. The impact on water quality in Mae Moh reservoir and Mae Change watershed is in a low level.

3) Groundwater quality

In the operation period, the effluent from the power plant and other activities will be treated through

wastewater treatment process of Mae Moh Power Plant, which consists of settling pond, ash pit and bio-

treatment system, for compliance with industrial factory and industrial estate effluent standards. The treated

effluent will then be released to Mae Moh reservoir and Mae Chang watershed, respectively. As a result, the

effluent from the activities of Mae Moh Power Plant Units 4-7 Replacement Project will affect water quality in

Mae Chang watershed and Mae Moh reservoir in a low level. Furthermore, it will not affect groundwater

4) Soil resources

In the operation period, coal ash from coal combustion will be conveyed by the conveyor belt to be

collected in coal ash pond.

The analysis of heavy metals in coal ash from current power generating process of Mae Moh Power

Plant shows that coal ash at silo contains 23 milligram/kilogram of arsenic, 53 milligram/kilogram of lead, 39

milligram/kilogram of zinc, 24 milligram/kilogram of chromium, 27 milligram/kilogram of nickel, and less than

0.05 milligram/kilogram of mercury. Meanwhile, coal ash at coal ash pond has 23 milligram/kilogram of

arsenic, 56 milligram/kilogram of lead, 38 milligram/kilogram of zinc, 26 milligram/kilogram of chromium, 27

milligram/kilogram of nickel and 0.16 milligram/kilogram of mercury. The detected heavy metals do not exceed

Disposal Standard for Non-Hazardous Wastes or Unused Materials, B.E. 2548.

Also, the analysis of heavy metals in soil at the edge of coal ash pond which has been operated for

about 25 years shows that the detected heavy metals in soil was much less than the ones found in fly ash.

Furthermore, the detected heavy metals do not exceed the standard of soil quality for living and agricultural

purpose according to the Notification of the National Environment Board, Vol. 25, B.E. 2547. In addition, toxic

elements of heavy metals, such as mercury, lead, arsenic, cadmium and chromium detected in underground

water were less than maximum allowable concentration.

Chemical property of heavy metals in fly ash, chemical reaction, activities of soil microorganisms

and the environment of soil at a coal ash pond did not cause leaching of whole heavy metals in fly ash to the

soil. This can be concluded from the detection of small quantities of heavy metals with toxic elements which do

not exceed the standard whether in coal ash leachate, soil, and groundwater. Consequently, it is anticipated that

power plant operation will slightly affect surrounding soil resources.

5)Aquatic ecology and fisheries

Effluent from the power plant will be treated through wastewater treatment system, released in

sedimentation tank and aeration tank. Then it is treated by a bio-treatment system for compliance with standard

of waste water discharged from factory according to Notification of Ministry of Industry, No.2 (B.E. 2539) prior

to being discharged to holding pond, Mae Moh reservoir, and Mae Chang watershed. Therefore, the impact from

effluent release to Mae Moh reservoir on aquatic ecology and fisheries is low.

6) Waste management

In the operation period, wastes generated by Mae Moh Power Plant Units 4-7 Replacement

Project consist of bottom ash (approx. 455 tons per day), fly ash (approx. 1,057 tons per day), gypsum (approx.

1,691 tons per day), resin (0.5 cubic metre), solid waste (90 kg./day), filter (150 filters/year), lubricant (15

litres/month) and sedimentation from clear water treatment system (64.88 tons/year. These wastes are combined

with the ones of Mae Moh power plant at present.) The project provides efficient disposal method and

preventive, and mitigation measures for waste in the operation period to minimize environmental impacts.

Therefore, there will be low impact from wastes.

7) Communities around the power plant

The evaluation of respiratory system is done calculating acute health effect from exposure to nitrogen

dioxide and sulphur dioxide in the short run (1-hour average), which is the worst case. In the event that the

existing Mae Moh Power Plant operates concurrently with the Mae Moh Power Plant Units 4-7 Replacement

Project, health effect on people living in the nearby areas is low.

8) Mae Moh power plant’

The evaluation of respiratory system is done calculating acute health effect from exposure to nitrogen

dioxide and sulphur dioxide in the short run (1-hour average), which is the worst case. In the event that the

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existing Mae Moh Power Plant operates concurrently with the Mae Moh Power Plant Units 4-7 Replacement

Project, health effect on people living in the nearby areas is low

3. Conclusion

Although the environmental impact of mercury from the MMRP is low, However the suitable

preventive and mitigation measures as well as monitoring measures for mercury impact are established. Preventive and Mitigation measures of mercury for the environment are established as follow

1) Monitor the quality of air emitted from stack and in the atmosphere of power plant. If it exceeds

the standard or tends to be higher, immediate inspection and correction are needed.

2) Perform maintenance of 11 air monitoring stations around Mae Moh power plant.

3) Install a closed coal ash conveyer belt of Mae Moh Power Plant Units 4-7 Replacement Project

which is newly constructed.

4) Control the quality of effluents which are treated by the bio-treatment system. These effluents are

caused by activities of Mae Moh Power Plant Units 4-7 Replacement Project. These effluents are produced by

office, cleaning of machines and equipment, chemical contamination, water treatment plant, demineralization

system and cooling system. Control on effluents must comply with the standard of waste water discharged from

factory according to Notification of Ministry of Industry, No. 2 (B.E. 2539) on important effluent quality indices

prior to discharging to Mae Moh reservoir and Mae Chang watershed.

5) Check if the shield of coal ash that prevents coal ash blowing, which is installed on the conveyer

belt, is a close system for efficient prevention of coal as blowing.

6) Improve sprinkler system for thorough sprinkle in coal ash pond and perform maintenance of

sprinkler system for effective operation all the times.

7) If it is detected that fish in Mae Moh reservoir are contaminated with mercury of greater than the

standard for contaminants in food, suitable action should be performed. For instance, spoil dredging should be

excuted to reduce accumulation of heavy metals. Spoil must be removed to a suitable place. The operation will

be under supervision of monitoring and environmental development committee of communities around Mae

Moh power plant

8) Closely monitor heavy metals in fish in Mae Moh reservoir.

9) Train on villagers about risk factors and causes of mercury accumulation in fish in several

reservoirs in the project site and adjacent areas.

10) Take a continuous random sampling of fish focusing on fish that eat plants and benthic animals.

Monitoring measures of mercury for the environment are established as follow

1) Monitoring of mercury at stack twice a year.

2) Monitoring of mercury in ambient air twice a year at the same time of stack monitoring of power

plant.

3) Monitoring of mercury in coal, bottom ash, fly ash and gypsum twice a year at the same time of

stack monitoring of power plant.

4) Monitoring of mercury in surface water twice a year : 1 in the rainy season and 1 in the dry season.

5) Monitoring of mercury in the groundwater twice a year : 1 in the rainy season and 1 in the dry

season.

6) Monitoring of mercury in the soil resources once a year in the dry season.

7) Monitoring of mercury in fish at Mae Moh reservoir twice a year : 1 in the rainy season and 1 in

the dry season.

8) Monitoring of mercury in silt at Mae Moh reservoir twice a year : 1 in the rainy season and 1 in

the dry season.

9) Monitoring of mercury in human blood of communities around the power plant once a year.

10) Monitoring of mercury in vegetables planted and beef once a year in dry season.

REFERENCES

[1] Enhancement and Conservation of the National Environmental Quality Act, B.E. 2535 (1992)

[2] Types and Sizes of Projects or Activities which may seriously affect community with respect to Quality of

Environment, Natural Resources and Health, 2012

[3] The Environmental and Health Impact Assessment for The Mae Moh Power Plant Unit 4-7 Replacement

Project, May, 2014

[4] Environmental and climate Change CANADA (2013), The Biogeochemical Cycle.,

https://www.ec.gc.ca/mercure-mercury