abstract
Flue gas desulfurization is the only large-scale commercial desulfurization method in the world at present, and it is the main technical means to control acid rain and sulfur dioxide pollution in thermal power plants. The investment of flue gas desulfurization device will cost a lot of money. Most of the flue gas desulfurization projects in domestic thermal power plants are imported from abroad, and only domestic installation is responsible. The use of foreign technology and equipment will inevitably make the project very expensive. If the technology and equipment are localized, the cost of flue gas desulfurization project can be greatly reduced, thus making it possible for large-scale application of flue gas desulfurization devices in China.
This design aims at the flue gas content and desulfurization requirements given in the graduation design task book, and combines the technical status of flue gas desulfurization in China to design a relatively complete flue gas desulfurization system. The purpose of this design is to actively prepare for the localization of flue gas desulfurization technology.
The main work of this design is:
The existing flue gas desulfurization technology is introduced and analyzed, and the wet limestone-gypsum method is determined as the desulfurization method of this system.
Some main desulfurization devices and types are introduced. After comparison and selection, the type and process of absorption tower are determined.
Each subsystem of limestone-gypsum wet flue gas desulfurization process is introduced, and the processing technology, devices and equipment of each subsystem selected for this process are roughly determined.
The ventilation diagram of the system is designed, including flue, equipment and chimney. On this basis, the pressure loss, flow rate and temperature drop of the pipeline are calculated step by step, and the desulfurization fan and limestone slurry circulating pump are selected according to the above data.
The technical and economic analysis of the designed flue gas desulfurization process is carried out.
Finally, the general conclusion is drawn, and the main problems and some suggestions in the process are put forward.
Keywords: limestone-gypsum wet flue gas desulfurization system composition, technical and economic analysis of pipeline calculation
abstract
Flue gas desulfurization is the only large-scale commercial desulfurization method in the world. This is the main technical measure to control acid rain and sulfur dioxide pollution. F GD equipment costs a lot of money. Most of the equipment of flue gas desulfurization project in thermal power plants in China is imported. We are only responsible for installation. Foreign technology and equipment are too expensive, and if it is localized, the cost of flue gas desulfurization project will be greatly reduced, thus making it possible for flue gas desulfurization equipment to be widely used in China.
According to the composition of flue gas and desulfurization requirements, combined with the existing flue gas desulfurization process in China, a suitable flue gas desulfurization system is designed. The purpose of this paper is to make some preparations for the design process of flue gas desulfurization device in China.
The main work of this paper is as follows:
The existing flue gas desulfurization technologies at home and abroad are analyzed and compared, and the limestone-gypsum wet flue gas desulfurization technology is selected.
The main equipment of desulfurization is introduced, and the type and process flow of absorption tower are determined.
The layout of the system is designed, including machines and related equipment.
The pressure loss, smoke volume and temperature drop of these chimneys are calculated.
The economic and technical analysis of the flue gas desulfurization system designed by the author is carried out.
The conclusion of this paper is drawn, some problems existing in practical application are pointed out, and some suggestions are given.
Key words: technical and economic analysis of limestone-gypsum wet desulfurization system.
catalogue
Preface to chapter 1- 1.
1. 1 current situation of flue gas desulfurization technology -2.
1. 1. 1 classic flue gas desulfurization process -2.
1. 1.2 Development of new technologies -4
1.2 introduction of flue gas desulfurization technology abroad -6.
1.3 development trend and prospect of flue gas desulfurization technology -6
1.3. 1 new technology development trend -6
1.3.2 development prospect of flue gas desulfurization technology -7.
Chapter II Determination of System Desulfurization Scheme and Selection of Purification Equipment -8
2. 1 Determination of system desulfurization scheme -8
2. 1. 1 Characteristics of various flue gas desulfurization technologies -8.
2. 1.2 factors to be considered when selecting process scheme -9.
2. 1.3 FGD process comparison-10.
2. 1.4 Selection of absorption tower process mode-12
2. 1.5 Comparison and selection of oxidation processes-13
2.2 Limestone-gypsum wet desulfurization process principle-14
2.2. 1 desulfurization mechanism-14.
2.2.2 SO2 absorption-15.
Formation of sulfate-15
2.2.4 gypsum crystallization-16.
2.2.5 limestone dissolution-16
2.2.6 Summary-17
2.3 Selection of limestone-gypsum wet flue gas desulfurization and purification device-17
2.3. 1 desulfurization tower type and selection-17
2.3.2 Further determine the spray absorption tower process-18
2.3.3 Summary-19
Chapter III Composition of limestone-gypsum flue gas desulfurization system -2 1
3. 1 limestone slurry preparation system -2 1.
3.2 flue gas reheat system -23.
3.2. 1 regenerative gas-gas heat exchanger (GGH)-24
3.2.2 Flue gas discharged from cooling tower-24
3.2.3 bypass flue gas method -25
3.2.4 Regeneration and Reheating Methods -25
3.2.5 Summary -26
3.3 SO2 absorption system -26.
3.4 Gypsum Preparation and Treatment System -27
3.5 Desulfurization Fan -29.
3.6 wastewater treatment -30.
3.7 public * * * system -3 1.
3.8 Summary -3 1
Chapter 4 Design, Calculation and Selection of Distribution Facilities -33
4. 1 overview -33
4.2 Design Calculation -33
4.2. 1 basic data -33
4.2.2 Determine the position of absorption tower, reheater and chimney and the arrangement of pipes -34
4.2.3 Section Calculation -35
4.3 Selection of Fan, Motor and Circulating Pump -43
4.3. 1 Selection and calculation of fans and motors -43
4.3.2 Selection of circulating pump of absorption tower -45
Chapter 5 Technical and Economic Analysis of the System -47
5. 1 Purpose and significance of technical and economic analysis -47
5.2 System Technical Analysis -47
5.2. 1 System technical indicators and their analysis -47
5.2.2 Influence of flue gas desulfurization device on boiler and flue gas system -48
5.2.3 The area of flue gas desulfurization device is -49.
5.2.4 Process complexity of flue gas desulfurization device -49
5.2.5 Maturity of flue gas desulfurization device -49
5.3 Economic evaluation -49
5.4 Summary -50
Chapter VI Conclusions and Suggestions -5 1
6. 1 conclusion -5 1.
6.2 Problems and suggestions -52
6.2. 1 question -52
Some suggestions -52
Graduation Design Summary -54
Thank you.-55.
References-56
Preface to chapter 1
With the rapid development of China's economy, the consumption of coal is increasing, and the emission of sulfur dioxide is increasing day by day, which has caused serious sulfur dioxide pollution and acid rain harm. The latest report [1] shows that the total sulfur dioxide emission in China in199 was18.57 million tons, of which industrial source14.6 million tons and domestic source was 3.97 million tons. The acid rain area accounts for 30% of the national territory, mainly distributed in the south of the Yangtze River, east of the Qinghai-Tibet Plateau and the vast areas of the Sichuan Basin. 106 Statistics of monitoring results of urban precipitation pH value show that there are 43 cities with annual precipitation pH value lower than 5.6, accounting for 40.6% of the statistical cities. In 59 southern cities, the annual precipitation pH of 465,438+0 (69.5%) is lower than 5.6.
Acid rain withered forests, acidified soils and lakes, destroyed vegetation, reduced grains, vegetables and fruits, and corroded metals and building materials [2]. Sulfur dioxide in the air also seriously affects people's physical and mental health [3], and it can also form sulfuric acid fog, which is even more harmful.
In order to prevent sulfur dioxide and acid rain pollution, in February, the the State Council Environmental Protection Committee adopted the Opinions on Controlling the Development of Acid Rain at its 1990 and 19 meetings. Since 1992, the pilot work of collecting sulfur dioxide sewage charges has been carried out in nine cities including Guizhou and Guangdong provinces, Chongqing and Yibin. 1In August 1995, the National People's Congress Standing Committee (NPCSC) passed the newly revised Law on the Prevention and Control of Air Pollution. 1998 February 17, the state environmental protection bureau held a conference on comprehensive prevention and control of acid rain and sulfur dioxide pollution. This shows that our government attaches great importance to the prevention and control of acid rain and sulfur dioxide pollution.
Xie Zhenhua, director of the State Environmental Protection Bureau, pointed out [4]: "Mature sulfur dioxide pollution control technology and equipment are the key factors to achieve the control objectives of the two control areas." He also pointed out that in order to achieve the goal of acid rain and sulfur dioxide pollution control, it is necessary to speed up the research, development, popularization and application of domestic desulfurization technology and equipment. Therefore, it is an urgent task to research and develop flue gas desulfurization technologies and devices suitable for China's national conditions, and to absorb and digest foreign advanced desulfurization technologies.
There are many ways to control sulfur dioxide, which can be divided into three categories:
(1) Desulfurization before combustion, such as coal washing [5].
(2) Desulfurization in the combustion process, such as briquette sulfur fixation and calcium injection in the furnace.
(3) Flue gas desulfurization (FGD) is the most widely used and efficient desulfurization technology at present.
1. 1 Present situation of flue gas desulfurization technology
1. 1. 1 classic flue gas desulfurization process
Flue gas desulfurization is the only large-scale commercial desulfurization method in the world, and it is also the most economical and practical method. Up to now, it is estimated that more than 200 FGD technologies have been developed all over the world, and there are more than 10 mature and feasible technologies at present. Generally, it is divided into wet method, semi-dry method and dry method according to the wet and dry state of desulfurizer and desulfurization products [7].
1.1.1.1wet desulfurization
This is a mature and stable method at present. Because it is a gas-liquid reaction, the desulfurization reaction is fast and efficient, and the utilization rate of desulfurizer is high. However, its wastewater treatment capacity is large and its operating cost is high.
It is also relatively high.
(1) limestone-lime method
It is a method that limestone or lime slurry is used as desulfurizer, and SO2 flue gas is washed and absorbed in an absorption tower, and its products are CaSO3 and CaSO4.
(2) Limestone-gypsum method
Air is blown into the absorption tower to oxidize CaSO3 into CaSO4 (gypsum). Because of the blown gas, the feed liquid is more uniform, the desulfurization rate is higher, and the probability of blockage and scaling is greatly reduced.
(3) Double alkali method
There are many kinds of this method, mainly the double alkali method of sodium and alkali. That is, NaCO3 or NaOH solution is used as the first absorption solution, and then limestone or lime solution is used as the second alkali solution for regeneration, and the regenerated solution continues to be recycled. SO2 obtained by this method still precipitates in the form of CaSO3 and CaSO4.
(4) sodium-alkali absorption method
In this method, aqueous solutions of NaOH, Na2CO3 and Na2SO3 are used as absorbents to absorb SO2 in flue gas. Wellman-Lord method is one of the most widely used desulfurization methods in the United States and Japan. In fact, this method uses the mixed solution of Na2CO3 and NaHSO3 as absorbent. When the concentration of NaHSO3 in the absorbent reaches 80%-90%, it is necessary to regenerate the absorbent to obtain higher concentrations of SO2 and Na2CO3. The regenerated Na2CO3 can be recycled, and SO2 can be used to produce sulfuric acid. The smoke absorption efficiency can reach more than 90%.
In addition to the above methods, wet methods include magnesium oxide absorption method, ammonia method and basic aluminum sulfate method.
Wait a minute. These methods have low absorption efficiency and narrow application scope.
1. 1. 1.2 semi-dry desulfurization
(1) calcium injection activation in furnace (LIFAC)
On the basis of the traditional calcium spraying method in the furnace, an activation reactor is added, and water spraying humidification is promoted. The desulfurization efficiency can reach about 75%-80%.
(2) Spin spray drying (SDA) method
This method uses the principle of spray drying to spray absorbent (such as lime slurry) into the absorption tower, so that the absorbent reacts with SO2 in flue gas. The obtained solid is discharged in the form of waste residue.
1. 1. 1.3 dry desulfurization
Traditionally, lime soda (CaO-Na2CO3) dry powder is used to remove SO2 contained in flue gas. So as to obtain a mixed product of dry powdery calcium salt and sodium salt and unreacted dry dust.
1. 1.2 Development Status of New Technologies
Due to the low efficiency and complicated operation of traditional technology, many countries are not limited to traditional classic technology under the requirements of scientific and technological development and environmental protection. Therefore, new technologies are constantly being researched and developed.
(1) charged dry jet desulfurization (CDSI) method.
This method is a patented technology developed by ALANCO company in the United States. Its technical core is that the absorbent passes through the high-voltage electrostatic corona charging area at high speed to obtain strong electrostatic charge, which is sprayed into the flue gas and diffused to form a uniform suspension state. The investment and land occupation of this method is only 10%~27% of that of the traditional wet method. But the desulfurization efficiency is relatively low.
(2) Electron beam radiation (EBA) method
The principle is that ammonia gas is added before the flue gas enters the reactor, and then the flue gas is irradiated by an electron beam generated by an electron accelerator in the reactor, so that molecules such as water vapor and oxygen are excited to generate free radicals with strong oxidizing ability, and these free radicals rapidly oxidize SO2 in the flue gas to generate sulfuric acid. And then react with ammonia to form ammonium sulfate. Its main characteristics are simple system, convenient operation and easy control of the process, and by-products can be used to produce chemical fertilizers. The desulfurization cost is lower than that of traditional methods. However, this method requires an electron gun with high power and long-term temperature and radiation shielding.
(3) Pulse Corona Plasma (PPCP) method.
It was put forward by Japanese expert Shinichi Masuda on the basis of EBA method. It is a pulsed high-voltage power supply, which forms plasma in a common reactor and generates high-energy electrons. The equipment and operation of this method are simple, and the investment is 60% of EBA method.
In addition to the above, the new processes developed in recent years include the new integrated semi-dry desulfurization (NID) method developed by ABB Company, which is suitable for seawater desulfurization process and normal temperature fine desulfurization process in seaside factories [8].
1.2 Brief introduction of several main flue gas desulfurization technologies abroad
(1) LIFAC desulfurization process [9]
(mentioned in 1. 1. 1.2 semi-dry desulfurization) IVO Company and Tampera Company of Finland developed LIFAC desulfurization process, which is an improved limestone injection process, further improving the desulfurization rate. Its main advantages are low energy consumption, high economic benefit, simple process equipment, obviously lower investment than wet and atomized dry desulfurization methods, and no wastewater discharge. At the same time, it is convenient to maintain and occupies a small area.
(2) Urea method [10]
Urea flue gas purification process is jointly developed by Mendeleev Institute of Chemical Technology and other units in Russia, which can simultaneously remove SO2 and nitrogen oxides. The removal rate of NOX and SO2 can reach 99% ~ 65%, and the removal rate of nitrogen oxides is more than 95%. It has no corrosive effect on equipment, and the removal rate of nitrogen oxides and SO2 has nothing to do with the concentration of nitrogen oxides and SO2 in flue gas. Tail gas can be directly discharged, and ammonium sulfate can be recovered from the absorption solution after treatment.
In addition, there are SNOX technology [9, 1 1] and microbial flue gas desulfurization technology developed by Denmark.
1.3 development trend and prospect of flue gas desulfurization technology
1. 3 1 development trend of new technology
According to various data, the latest research on desulfurization technology abroad mainly has the following characteristics.
(1) integration of dust removal, desulfurization and denitrification
Because sulfur oxides and nitrogen oxides are pollutants restricted by the state, separate treatment obviously increases the investment of equipment and the occupation of space.
(2) Automation technology is more obvious.
Most of the latest desulfurization processes are developing in the direction of dry desulfurization, which is the easiest way to realize automation. This is also the continuous development of electronic technology to society. Accordingly, its scientific and technological content will be higher and higher.
(3) The production cost is reduced.
The desulfurization cost of the new process is relatively low. In this era of paying attention to economic benefits, the lower the cost, the better.
1.3.2 development prospect of flue gas desulfurization technology
In the next decade, circulating fluidized bed flue gas desulfurization device has great potential and application prospect in power plant desulfurization in China, and seawater flue gas desulfurization device has irreplaceable advantages in coastal power plants and areas with convenient seawater resources in China.
The application of microbial method in flue gas desulfurization will have the characteristics of no need of high temperature, high pressure and catalyst, low operating cost, simple equipment requirements, low nutritional requirements and no secondary pollution. Therefore, microbial flue gas desulfurization is a bioengineering technology with strong practicability and novel technology, which has attractive application prospects and should be paid attention to and accelerated.
Progress of Flue Gas Desulfurization Technology in China The flue gas desulfurization technology in China is basically in the experimental stage. From the test results, several technologies are close to the world level, such as dry circulating fluidized bed flue gas desulfurization technology developed by Tsinghua University Coal Clean Combustion Engineering Research Center, liquid column jet flue gas desulfurization and dust removal integrated technology, etc., which have been widely valued.