Issue 15/2014 - Progress in flue gas desulfurization and denitrification technology

Progress in flue gas desulfurization and denitrification technology

School of Architecture and Environment, Sichuan University Liu Yulu Yin Huaqiang, National Engineering Research Center for Flue Gas Desulfurization

With the rapid development of the economy, the rapid improvement of industrialization, the large increase in coal consumption, the air pollution caused by coal burning is becoming more and more serious, especially the SO2 and nitrogen oxides (NOx) in coal-fired flue gas are the main pollutants of air pollution, and are also the main causes of
acid rain and haze.
Therefore, flue gas desulfurization and denitrification is an inevitable trend
in controlling air pollution.
So far, there are more than 100 flue gas removal methods studied, but about 10 can be industrialized and applied, and most of the others are in the semi-industrial or experimental stage
.

Combined desulfurization and denitrification technology

Combined desulfurization and denitrification technology belongs to the traditional flue gas desulfurization and denitrification technology, and it is also the most widely used technology
today.
In this technology, a lime/limestone flue gas desulfurization system (FGD) is typically used to remove SO2 and a selective catalytic reduction process (SCR) to remove NOx, which can remove more than 90% of SO2 and more than 80% of NOX
。 The joint process has been widely used in industrial applications in Japan, Germany, Sweden, Denmark and other countries, but the disadvantage is that SO2 in the flue gas is oxidized to SO3, and SO3 reacts with free CaO and ammonia to form CaSO4 and ammonium salts to cause scaling on the catalyst surface, which reduces the efficiency of SCR denitration, and increases blockage and corrosion
in air preheaters and gas/gas heat exchangers.
This process flow is complex, the operating cost is high, and the widely used V2O5-TiO2 catalyst cannot be produced in China, and the performance recovery and disposal technology of the catalyst needs to be further studied
.

Simultaneous desulfurization and denitrification technology

At present, the technology is simple, the operating cost is low, and the desulfurization and denitrification process is attracting more and more attention
.
However, at the same time, desulfurization and denitrification technology is still in the research stage and has not yet been applied
to large-scale industry.
This technology can be divided into: simultaneous removal technology of combustion process and simultaneous removal technology after combustion, the latter will be widely used in industrial production, and the technical methods can be divided into wet and dry methods
.
At present, most international research institutions mainly focus on dry simultaneous desulfurization and denitrification technology, mainly including high-energy electron activation oxidation method and solid phase absorption/regeneration method
.

1.
High-energy electron activation oxidation method (1) Electron beam method The electron beam method is referred to as EBA method
, which mainly uses an electron beam containing electron energy of 800MeV-1MeV to irradiate the flue gas, and converts SO2 and NOX in the flue gas into ammonium sulfate and ammonium
nitrate in a very short time.
Finally, the by-products are recovered by electrostatic precipitator to achieve the purpose of
simultaneous denitrification and desulfurization.
This research work began in Japan in 1970, after more than 30 years of research and development, this technology has been industrialized, applied in many enterprises, and widely promoted
in China.
In June 1997, the world's first industrial demonstration device to treat the boiler flue gas of a 100MW power plant "electron beam irradiation method" was completed and put into operation by Sino-Japanese cooperation in Chengdu Thermal Power Plant, with an investment of 104 million yuan, and the actual desulfurization rate was 80% and denitrification rate was 18%.

At present, many countries have established a number of electron beam experimental facilities and demonstration workshops, Japan, Germany, the United States and Poland demonstration workshops show that the total efficiency of SO2 removal by using this system exceeds 95%, and the efficiency of NOX removal can also reach 80%~85%.


Although it has many advantages compared with the traditional process, there are still some problems: such as the high cost and technical requirements of high-power electron accelerators, it is difficult to operate stably for a long time, and the X-rays generated need to build concrete radiation protection devices to prevent hazards
.

(2) Pulse corona method The principle of desulfurization and denitrification of pulse corona method is generally consistent with the electron beam irradiation method, which uses high-energy electrons generated during corona discharge to activate, crack or ionize molecules in flue gas such as H2O, O2, etc.
, thereby producing strong oxidizing particles O, OH, HO2, etc
.
These particles undergo plasma-catalytic oxidation of SO2 and NO to produce SO3 and NO2 or corresponding acids, respectively, and in the presence of additives such as ammonia, generate ammonium salts that can be used as fertilizers to settle down
.

At present, a large number of experimental studies
have been carried out in various countries on this law.
The Italian company ENEL has built an industrial pilot plant with flue gas treatment capacity of 1000m3/h and 14000m3/h in the power plant, and obtained some experimental data
.
Korea has built an industrial test plant with a flue gas treatment capacity of 2000m3/h, and the SO2 and NOX removal rates are up to 95% and 85%.

In China's "Ninth Five-Year Plan" key scientific and technological research, it is arranged to build an industrial pilot plant with a flue gas treatment capacity of 12000m3/h~20000m3/h in the thermal power plant of Science City in Sichuan Province
.

Although the corona method is currently the most promising technology, its application also has certain difficulties, the main problem lies in the power supply: due to the poor output characteristics of the pulse power supply, the energy consumption of effective electrons is high; The power supply has low energy storage density, short life, low cost performance, and capacitor banks are not suitable for processing atmospheric flow and pulse generators for continuous and stable operation
.
Therefore, improving the performance of the power supply is the key to
realizing the industrial application of corona desulfurization and depinning.

2.
Solid phase absorption/regeneration method - activated carbon adsorption method solid phase absorption/regeneration method includes activated carbon adsorption method, Pahlman flue gas desulfurization and denitrification process and CuO adsorption method
, among which activated carbon adsorption desulfurization and denitrification technology is widely
used.

In 1984, a joint SO2/NOx device for coal-fired boilers with a flue gas capacity of 30,000m3/h began operation in Omuta, Japan, and the SO2 and NOx removal rates reached about
98% and 80%, respectively.
At present, Japan has gradually used this technology in various industrial plants, such as petrochemical industry, sintering equipment of steel mills and so on
.
In 1987, Germany successfully used the combined SO2/NOx process of activated carbon for desulfurization and denitrification
of units of the Arzberg coal-fired power plant.

The biggest disadvantage of this process is that the enriched SOx gas consumes a large amount of activated carbon
.
In addition, the long-distance pneumatic transport between the absorption tower and the desorption tower is easy to cause damage to activated carbon
.