Coal power plants emit not only CO2 but also various kinds of pollutants. Coal contains heavy metals including mercury and emit these pollutants to the air when it is burned at power plants. Also, heavy metals remain in coal ash. Mercury is discharged into the environment in various forms.
According to the estimates of the Ministry of the Environment, the amount of mercury emissions in the atmosphere was 16µg/Nm3 at the maximum and less than 0.1µg/Nm3 at the minimum (among 139 data from 76 facilities), and an inventory data in 2014 indicated that the mercury emission amount from coal-fired power plants was 1.3tHg per year and the total amount in Japan reached 18tHg per year.
Japan’s regulation of mercury emissions
In 2013, the “Minamata Convention on Mercury” was adopted for the purpose of limiting the worldwide mercury emissions. Coal power plants are subject to this convention’s control [*1]. Following to this agreement, Japanese government revised the Air Pollution Control Act in June 2015, and the mercury emissions into the atmosphere became a subject of regulation for the first time. In addition, in December 18th 2015, the government commissioned the Central Environmental Council to examine the implementation of measures against atmospheric mercury emissions, and in January 6th 2016, the Expert Committee on Regulations for Atmospheric Emissions was set up under the Subcommittee on Air, Noise and Vibration. After having four meetings, the expert committee completed an initial report regarding types and scales of mercury emitting facilities, emission standards, coverage of discharge control facilities and measuring methods of mercury emissions.
The mercury emission standards for coal-fired power plants are listed as below.
The emission standard in the United States is 0.3lb/TWh (equivalent to 0.5µg/Nm3). That in EU is 2µg/Nm3 for new facilities and 4µg/Nm3 for existing facilities, but then it is criticized as lax standard which possibly could be 1µg/Nm3. On the other hands, the standard in Japan is 8 – 15µg/Nm3, comparatively higher than other countries’. Existing Japanese coal power plants have not installed equipment specifically to eliminate mercury from exhaust air. They have NOx remover as a part of smoke ventilation system, but not Hg remover. Even though new emission standard has been established considering reality of conditions that other equipment (denitration, dust exhaustion and desulfuration) :are secondarily removing mercury, it seems going along with the status quo which is not actually controlling mercury emissions. In addition, this lax standard does not prescribe total emission reduction targets, a schedule for achieving and restrictions to whom violate this emission control. Coal is, according to what the government‘s statement, the cheap fuel, but that is only achieved by ignoring huge external costs.
In this way, coal power plants continuously emit a certain amount of mercury in the environment and remains as the most “dirty” power generation. Japan has experienced hardships of Minamata disease in our history. Isn’t it so dishonorable for us?
Emission standards for coal combustion boilers (Corrected value (oxygen reference value = 6%))
|1. coal-fired boilers (exclude 2.)||Boilers with more than 10㎡ of boiler heating surface area, or with more than 50L/h (in heavy oil equivalent) of burner’s fuel combustion capacity.||8||10|
|2.small coal-mixed combustion boilers||Boilers with more than 10㎡, of boiler heating surface area, or with more than 50L/h (in heavy oil equivalent) but less than 100,000L of burner’s fuel combustion capacity.||10||15|
In order to set this emission standard, criteria for small coal-mixed combustion boilers specifically employed low emission standard level which had applied to waste incinerators because small coal-mixed combustion boilers often show higher mercury concentration than other (larger) coal plant boilers. Coal used for waste incinerators contain certain amount of mercury but relatively unstable. Considering amount of mercury in fuels used for small power plants, it is judged to set a level of emission criteria as same as for waste incinerators. Value in above table was corrected with oxygen reference value = 6%.
An amendment to the “Order for Air Pollution Control Act”
The draft proposal for amendment to the “Order for Air Pollution Control Act” was approved at the Subcommittee on Air, Noise and Vibration in June 7th after getting public comments, and it was discussed in early July at the joint committee of the Subcommittee and the Ministry of Economy, Trade and Industry. The “Order for Air Pollution Control Act” will be revised in August, and the details of act, such as type and scale of facilities, emission limits, measuring methods, process of various paper works will be decided. Then, it will be enforced within two years from the issue date of the treaty.
After September in 2016, the Expert Committee on Regulations for Atmospheric Emissions is planning to examine how to follow up the independent efforts of facilities which needed emission control, and make a second report.
*1 In the Minamata Convention on Mercury (Annex D), coal-fired power plants (for power generation) and coal-fired industrial boilers (for industrial use) were in different categories. While coal-fired power plants generate electric power generation, many industrial coal-fired boilers also generate electric power for business operators as private power generator, so it was hard to distinguish coal-fired power plants and industrial boilers. Thus, the mercury emissions standard has categorized these two coal-fired utilities into one same group as “boilers use coal as fuel (including blast boilers)”.
The Subcommittee on Air, Noise and Vibration of the Central Environmental Council
Data for the 11th meeting on June 7, 2016 (Japanese 2016/6/7)
“Results of investigation into the actual conditions of mercury emissions in the atmosphere”
“Inventory of mercury emissions in the atmosphere (2014 covered)” (Japanese 2014)
“About measures to restrain mercury emissions in the atmosphere (the initial report)” (Japanese 第一次報告書)