Study on desulfurization and denitrification process of coal fired power plant in thermal power plant

2016-05-14 12:00:45

0 Introduction
The development of modern industry is a double-edged sword, on the one hand, it brings unprecedented material civilization to mankind, on the other hand, it also

brings serious environmental problems. The haze problem caused by air pollution emissions has become a major environmental problem in China. Waste gas emitted from the

use of coal as fuel in industrial production is the main cause of air pollution. The SO2 and NOx, NOx and, which will be discharged after coal combustion, will form a

photochemical smog, which seriously harm human health. SOx and NOx are the main factors to form acid rain. China is a big country of coal production is also a big

country with coal, since the founding of new China, coal occupies a very important position in China's power generation and industrial activities, about half of the

annual amount of coal used to power generation. Research shows that the thermal power plant is a major atmospheric pollutant emission in china. Under such background,

it is urgent to control the SO2 and NOx of the boiler flue gas in thermal power plant [1].
1 thermal power plant desulfurization process
Reduce SO2 emissions, can start from two aspects: A in the coal combustion process control SO2 generation; B using flue gas desulfurization technology, eliminating the

generated SO2.
There are hundreds of desulfurization technology at home and abroad, the effect is good, and is often used to industrial practice, including the following: wet

limestone (lime) - gypsum flue gas desulfurization process, rotating spray drying method (SDA), furnace Calcium Spraying and tail increased wet activation (LIFAC),

fluidized bed combustion desulfurization, electron beam irradiation method, reflux circulating fluidized bed flue gas desulfurization method, the NID method, mobile

bed of activated carbon adsorption method, seawater desulfurization method and so on [2]. This paper focuses on the first two kinds of technology.
1.1 wet limestone gypsum flue gas desulfurization process
This process in the reaction tower (absorption tower) in the use of limestone (CaC03) or lime (CaO) slurry washing coal flue gas, in order to remove the flue gas in

the SO2. The specific process is: first through the precipitator eliminate dust, from the bottom into the reaction tower (absorber) upward mobility, limestone or lime

slurry from the top of the reaction tower is sprayed downward are in contact with the flue gas to produce chemical reaction, with generation of sediment, namely CaSO3

and CaSO4, the desulfurization of flue gas through the chimney discharged.
The principle of this process can be expressed as:
Lime method: 2SO2+2CaO+H2O, 2CaSO3, H2O?
Lime stone method: 2SO2+2CaO+H2O, 2CaSO3, H2O?
In the cyclic oxidation groove on the bottom of the desulfurization reaction tower blown O2 can precipitate CaSO3 oxidation generated by-product gypsum, to make full

use of resources. Using this process, coal flue gas desulphurization rate reaches as high as 90% ~ 98%, large capacity units, coal type adaptability, reliable work

performance, cheap detergent, by-products can be recycled, but need larger area and water consumption, the initial commissioning and operation cost is high, strength

and less space in the thermal power plant is not suitable for the.
1.2 rotary spray drying method
Rotating spray drying method (SDA) with lime as desulfurizer. First of all, the lime made of lime mortar, again through the top of the reaction tower of high-speed

centrifugal spray to spray, and self to the flue gas full contact, contact produces chemical reaction, in the flue gas SO2 and lime reaction, with the dust together

into precipitator is collected can be recycled, can be properly handled.
The chemical reaction of this process is:
Lime digestion and pulping: CaO+H2O=Ca (OH) 2
SO2 absorption: Ca (OH) 2+SO3=CaSO4+H2O
Using this technique, the thermal power plant desulfurization rate of 85%, although the desulfurization rate than the wet limestone (lime) - gypsum slightly lower, but

the advantage of mature technology, the unit system reliable operation, technological process is simple, covers an area of and less water consumption, process without

any sewage and waste acid discharge. The process was put into use in 1980 by the United States a power plant, soon to be welcomed and applied by the European and

American fire power plant, Huangdao, China Shandong thermal power plant and Sichuan since the horse power plant is the use of this process.
2 power plant denitrification process
There are two ways to reduce the emission of NOx in thermal power plants: A in the coal combustion process to reduce the generation of B; NOx) as far as possible to

eliminate the generated NOx[3].
2.1 low NOx combustion technology
Low NOx combustion technology is to control the coal combustion conditions and methods to control the conversion of N to NO in flue gas to reduce the production of NO

technology. In the combustion process control NOx production should be in accordance with the following requirements: a) reduce combustion process in air and O2

content, so that the coal in the combustion state of hypoxia; b) control of boiler combustion temperature, beware of local temperature is too high; c) maintain boiler

and flue unobstructed, shortening the stay in the environment of high temperature of flue gas.
2.2 flue gas denitrification technology
After the coal combustion has been produced NOx, you can take the wet or dry elimination, the specific common method is: the meteorological reaction method, liquid

absorption method, adsorption method, etc..
Gas phase reaction method of A. The method also includes three kinds: electron beam irradiation and pulsed corona plasma method; selective catalytic reduction method,

selective non catalytic reduction method and hot carbon reduction method; low temperature atmospheric pressure plasma decomposition method. (a) electron beam

irradiation method and pulse corona plasma method is using high-energy electrons produce free radical oxidation of no to NO2, and H2O and NH3 generation of sediment,

fertilizer; (b) selective catalytic reduction, selective non catalytic reduction method and hot carbon reduction method, with the help of catalytic or non catalytic

conditions under, NH3 and C reducing agent the NOx is reduced into harmless N2; (c) at atmospheric pressure and low temperature plasma decomposition method is the use

of ultra high voltage and narrow pulse corona discharge to produce high-energy active particle collisions with NOx molecules and the chemical chain cleavage of O2 and

N2.
B) liquid absorption method. This is a common method of denitrification, liquid absorption in the so-called "liquid" including water, alkali solution, HNO3, H2SO4,

etc.. But because NOx is very difficult to dissolve in water or alkali solution, so this method has lower efficiency;
C) adsorption method. The use of molecular sieve, activated carbon, natural zeolite, silica gel and peat, as adsorbents for the removal of NOx, which some adsorption

agent and catalytic effect, the flue gas of no into NO2 adsorption in water or alkali recovery. The method has the advantages of high denitrification efficiency, but

requires the adsorbent dose, site, equipment, and therefore less used in actual production.
3 thermal power plant integrated desulfurization and denitrification process
3.1 typical flue gas desulfurization and denitrification process
Integrated desulfurization and denitrification process is the new direction of the current thermal power plant environmental protection project. Current comparison is

the Wet-FGD+SCR combination process, that is, wet flue gas desulfurization (Wet-FGD) and NH3 selective catalytic reduction (SCR) technology integration of the new

process.
Wet-FGD) a is the use of alkaline slurry or solution as absorbent, and SO2 reaction to produce sulfate products to remove SOx. The method of forced oxidation wet

desulfurization with limestone or lime as absorbent is a typical representative. Using this process desulfurization rate and absorbent utilization rate can be higher

than 90%, but the disadvantage of this process is: Equipment Engineering and a large, initial production costs are higher, the production process is easy to produce

two pollution;
NH3) B selective catalytic reduction process is the use of the catalyst in the oxygen environment in the coal waste gas NH3 NOx reduction to N2 and water. The

technology is mature and reliable, good condition for denitrification rate up to a maximum of 90%, widely used in developed countries, but the technology investment is

large, production increased preheating flue gas treatment process, required catalyst is expensive, and NH3 leakage and corrosion potential safety hazards. Patients. At

present, the industry is studying the CH4, C3H6, C3H8 and C8H18 and other organic compounds instead of NH3 as a catalyst for the production of process improvement

methods in low temperature, and has been put into practical use.
3.2 new flue gas integrated desulfurization and denitrification technology
In order to better simultaneous desulfurization and denitrification, in addition to the original process improvement, the invention also invented a new type of

technology, such as high energy radiation chemical method and pulse corona plasma method.
A) high energy radiation chemistry method is also called flue gas irradiation method. At present, there are mainly electron beam irradiation and pulsed corona plasma

method. Electron beam irradiation method (EBA) is the cathode emission and the electric field accelerates the formation of a high energy electron beam irradiation flue

gas, which can be used to generate free radicals, in NH3 into the environment and waste gas of Sox and NOx reaction, generating NH3NO3 and (NH4) 2SO4 can recycling

by-products.
(b) pulse corona plasma method (PPCP) is a process which is similar to the basic principle of high energy radiation chemistry method, but it is only used in the high-

energy electron irradiation. PPCP method of high-energy electron is from the corona discharge, and then use up front steep, narrow pulse high voltage power supply and

power load combination of a corona electrode system (corona reactor), streamer corona plasma in the corona and corona reactor electrode air gap, thereby of SO2 and no

oxidation removal.
4 Conclusion
Desulfurization and denitrification process in thermal power plant, a variety of practical processes have been developed at home and abroad, and the new technology is

also in the process of continuous improvement and development. Although the concentration of SOx and NOx in the coal-fired flue gas of thermal power plant is not high,

but because of the large amount of coal-fired power plant, the total amount of SOx and NOx is very huge, and the serious harm to the environment. For thermal power

plants, the use of two sets of equipment, respectively, for the treatment of two kinds of harmful substances, is bound to face high capital investment, covers an area

of large, high human capital, operation and management complex and other issues. In recent years, many countries have carried out the research and application of

simultaneous desulfurization and denitrification technology, but the technology is still not mature, there is no large-scale application. According to the actual

situation in China, now the thermal power plant desulfurization de NOx technology research and application of should pay attention to the reduced floor area, reduce

the technological process, reduce the amount of investment operation, improve production efficiency, enhance the level of industrial applications and focuses on the

integration of practical and feasible desulfurization denitration technology.
reference：
[1] Ge Rongliang. Technology and application of denitrification in thermal power plant and the integration development trend of desulfurization and denitrification

[J]. Shanghai electric power, 2007 (5): 458
[2] Wang Liping, Song Cenglin. Simultaneous desulfurization and denitrification technology of flue gas desulfurization in thermal power plant [J]. thermal power

generation, 2005 (2): 6
[3] Yang Qiaoyun. Review of desulfurization technology in thermal power plants [J]. environmental protection science, 2008 (6): 8-10.
Original title: coal-fired power plant integrated desulfurization and denitrification process research