Environmental problems on mercury is not dominant in Japan at present, although we experienced the pollution problem of Minamata disease. However, many developing countries, especially in the Asian region, are not yet able to take measures against mercury and are concerned about serious environmental pollution. From these global perspective, attention has been focused on mercury as a global environmental pollutant from local environmental problems. The Minamata Convention on mercury was issued on August 16, 2017. In this chapter, trends of domestic and foreign regulations on atmospheric emissions from coal-fired power generation facilities as anthropogenic sources and guidance contents of the BAT/BEP experts’ meeting of the United Nations Environment Program is described.

In up-to-date coal fired power plants, flue gas treatment equipment consists of deNOX, dust removal and desulfurization facilities in series downstream of the coal combustion boiler. As a result of many researchers works, these facilities have been found to control mercury emissions to the air, too. In general, mercury exists as gaseous elemental mercury in the flue gas just after the boiler outlet. Since elemental mercury is highly volatile and water-insoluble, it is very difficult to be captured in either solid or liquid phases. Meanwhile, a typical SCR (selective catalysis reduction) reactor for deNOX converts gaseous elemental mercury to oxidized mercury, which is water-soluble. Oxidized mercury is easy both to be captured by EP (Electrostatic Precipitator) as particulate mercury trapped in fly-ash, and to be dissolved in wet FGD (flue-gas desulfurization) solutions. Therefore, the combination of SCR, EP and wet FGD considerably contributes for gaseous mercury removal in coal fired power plants. In this report, recent studies of mercury emission behaviors in coal fired power plants and contributions of flue gas treatment system to gaseous mercury removal are reviewed in detail.

In Japan, impinger method is established for measuring gaseous mercury in flue gas. On the other hand, particulate mercury is collected on the filter by isokinetic sampling and analyzed by Cold Vapor Atomic Absorption Spectroscopy (CVAAS). In addition to this method, various methods such as dry measurement method using sorbent trap and continuous measurement method are provided for measuring gaseous mercury in JIS method and US EPA method etc. In Japanese methods, gaseous and particulate mercury are sampled separately. In many countries, the methods sampled gaseous and particulate mercury simultaneously with an isokinetic sampling system are used for the measurement of total mercury in a flue gas. Gaseous mercury in a flue gas exists elemental and oxidized forms and these forms of gaseous mercury have great influence on the behavior in plants. So, speciation methods of mercury are developed and used to study on mercury behavior in a combustion process. Although the accuracy of these measurement methods has been examined, there are many points to be noted for the measurement with high accuracy. In this paper, various measurement technologies of mercury in a flue gas and points of attention for mercury measurement are explained.

MITSUBISHI HITACHI POWER SYSTEMS, LTD. (MHPS) has supplied technologies to remove NOX, SOX and so on in flue gas in thermal power plant over a period of time. In addition to advancement of the technologies to remove them, in recent years, MHPS has developed Air Quality Control System (AQCS) technology to remove harmful trace substances actively. Countries have ratified Minamata convention on mercury and a worldwide interest in mercury emission among harmful trace substances has been growing. MHPS’s mercury removal technology uses high functional SCR (Selective Catalytic Reduction) system, Gas-GasHeater (GGH), ESP and wet-flue gas desulfurization system in an integrated manner. High removal performance of mercury has already proven in pilot demonstration facilities (1.5 MW in Japan and 5 MW in the US) and in actual coal-fired thermal power plant (720 MW in the US).

This paper reviews an overview of Regenerative Activated Coke Technology (ReACT), which is a multipollutant control technology that achieves simultaneous reduction in SO_X, NO_X, particulates and mercury in one vessel. Activated coke (AC) is a formed carbonaceous material that is designed for the dry DeSO_X-DeNO_X process. The surface functionality of microporous AC in regenerated use is believed to be an important factor influencing both adsorption and catalytic activities for SO_X, NO_X, and mercury removal.

The Minamata Convention on Mercury which aims to protect the human health and the environment from anthropogenic emissions and releases of mercury entered into force on 16 August 2017. Many countries have been preparing for their early ratification and implementation of the Convention through the development of mercury inventory and material flow analysis of mercury. The government of Japan has been working on the development of mercury material flow since 2009. According to the latest report published in 2017, it is estimated that coals used in the coal-fired power plants in Fiscal Year 2014 contains 3.2 tons of mercury (t-Hg) on total. The amount of mercury emission into air from such plants is estimated to be 1.3 t-Hg, and the rest of the mercury is presumed to be contained in coal ash, desulfurized plaster, and sludge. Many of those substances are recycled in other industrial fields such as cement production.

The flue gas desulfurization (FGD) equipment deployed ins coal-fired power plants discharges FGD wastewater. Any coal-fired power plant equipped with FGD equipment is subject to regulation as a “Specific Facility” under Japan’s Water Pollution Control Law, and it is mondatory to treat wastewater to meet wastewater standards for various substances. To this date, FGD wastewater treatment technologies have evolved so that it can adapt to treat newly regulated substances, such as fluorine and selenium compounds. As a result, stable operations of power plants are possible while complying with water quality standards. Today, thermal power plants are working on reducing greenhouse gas emissions by improving power generation efficiency and other factors. Waste reduction and energy conservation are also required in wastewater treatment while complying with water quality standards. This report presents an overview of current wastewater treatment technologies introduces several issues related to the optimization of wastewater treatment facilities.

The online selenium monitor, a fully automated process monitor for aqueous selenium in desulfurization wastewaters, measures selenium concentration in process effluents with a Galvanic cell gas detector for hydrogen selenide. We added the function to humidify carrier gas onto the online selenium monitor, to prevent a decline in performance of the gas sensor. The improved selenium monitor was installed in a full-scale coal-fired power plant and monitored the selenium concentration in flue gas desulfurization effluents, i.e., the influent and effluent of the wastewater treatment facility for selenium removal. The concentration of selenium varied in the range of 0.05 and 1.06 mg/L for the influent, whereas the effluent remained almost below the effluent standard (0.1 mg/L). We had three months of measurement failure, but except those data a fairly good correlation (r² = 0.961 for n=326) was obtained in the measurements between the monitor and the official method (ICP-OES), which demonstrated the improved monitor serves as a useful tool for managing selenium emission in process effluents. The causes for the malfunction in the test were due to the sensor life, operational fraud in a stirrer and chemicals addition and so on. We established a protocol for the monthly maintenance to prevent operational malfunctions and criteria to evaluate the life of sensor.

Some thermal power plants experience an inexplicable increase in the COD of the desulfurization wastewater, making effective actions difficult. Although nitrogen-sulfur (NS) compounds could increase the COD, information on the subject is limited and the emission of NS compounds is not fully understood. In this paper, the analytical methods to determine the concentration of NS compounds as well as their treatment methods and chemical properties were reviewed. In addition, the results of the investigation on the emission of NS compounds were discussed. The study also assessed the removal of hydroxylamine trisulfonate (HATS) present in high levels in high COD wastewater. The results indicated that HATS could not be removed by activated carbon adsorption, coagulation, or biological denitrification. Moreover, negative correlation was found between the HATS concentration and the oxidation-reduction potential.

Gasification power generation of woody biomass is an ideal technology boasting a small scale and high energy efficiency, but there are technical problems such as removal of tar, generation of stable gas, long-term continuous operation of gas engines, etc. In Europe the technology which reached the commercial level is only a few. Under such circumstances, “Volter 40” (made in Finland) has a track record of introducing 110 aircraft in the world, boasting the oldest and most successful operation from 2009, and has a proven track record. Continuous operation has also been proved in facilities using chips that are sufficiently dry and of good quality even in Japan. It is a combined heat and power type that can be used on a compact scale with a power generation output of 40 kW and also with the use of waste hot water of around 80 °C. It is also easy to procure domestic fuel as compared with that of pellet type as it uses chips as fuel. Even as expectations for gasification power generation technology are increasing due to policy support by FIT, there are also many inquiries from the whole country, and it is a technology highly expected to promote popularization.