Comprehensive selection of ultra low emission technology route of 1050MW ultra supercritical coal fired power generation units

2016-04-01 16:31:42

1 Overview
With the increasing demands of environmental protection, the flue gas of coal-fired power plant has been highly valued at all levels. Through thirty years of development, our country in the field of coal dust emission control, dust removal equipment and technology to reach the international advanced level, the smoke and dust emissions have been effectively controlled.
In order to strengthen the protection of the environment, to achieve energy-saving emission reduction targets, State Environmental Protection Department of the implementation of the new emission standard of environmental protection, the thermal power plant emission standard of air pollutants "(GB 13223-2011), permitted in the standard emission limits in 2003 compared to the second revision of the limit values for strictly.
Some of the power companies to seek a broader space for development, and actively with the design units, environmental protection enterprises cooperation, research or the introduction of some to further reduce pollutant emission levels of technology, such as wet desulfurization increased wet electric dust collector. Through the application and implementation of some power plants, emission concentrations to achieve a lower effect, or even better than the combustion engine emission standards, "ultra low emission" technology has been highly appreciated by the industry. For further promotion and development of ultra low emission technologies, three ministries and commissions under the national development and Reform Commission, the National Energy Bureau sent the coal energy-saving emission reduction upgrade and transformation plan of action (2014 - 2020) ", for thermal power units to conditional execution of burning engine emission standards (also known as super ultra low emission standards). Namely the pollutant emission limit value in accordance with the sulfur dioxide 35 mg/m3 (superscript, 6%O2), nitrogen oxide 50 mg/m3 (superscript, 6%O2), smoke and dust 10 mg/m3 (superscript, 6%O2) implementation.
From the environmental point of view, the "ultra low emission" of the flue gas pollutants is an important issue and new development requirements for coal-fired generating units. Shenhua Group as the central enterprises, take the lead in doing environmental work is an unshirkable social responsibility, in the construction of the project strictly in accordance with the ultra low emission standards for the construction, power plant in Chongqing Wanzhou Shenhua two 1050MW unit as the project put into operation in 2015 group company in accordance with the requirements, the flue gas emissions of environmental protection facilities are provided effective transformation, achieve ultra-low emissions units must be.
2 ultra low emission technology route selection
2.1 the status of dust treatment facilities
Shenhua Shendong power Wanzhou power plant phase of the project construction of 2 * 1050MW ultra supercritical coal-fired generating units, every unit boiler with low nitrogen burners and simultaneously supporting the construction of two sets of three rooms five electric field, electric dust collector, a limestone gypsum wet flue gas desulfurization device and a set of SCR de denitrification system. Among them, desulfurization system in the design to the maximum sulfur content coal-fired, boilers checked coal for sulfur content was 0.8%) as the design of the desulfurization of coal design, design desulfurization efficiency is greater than or equal to 96%, SO2 emissions concentration is less than or equal to 76mg/Nm3. Desulfurization absorption tower by the national fresh green technology Limited by Share Ltd to design supply, the use of limestone - gypsum wet flue gas desulfurization process spin exchange coupling technology, no GGH. Project implementation in the process of considering changes in the sulfur content of coal, desulfurization system and according to the amount of sulfur was 1.2% of capacity expansion design, design desulfurization efficiency is more than or equal to 96.5%.
In this project, the smoke emission concentration is less than 20 NOx, and the concentration of 47mg/Nm3 emission is less than 27mg/Nm3, and the concentration of SO2 emission is less than mg/Nm3. In addition to the desulfurization and dust removal facilities outside the facility design indicators and ultra low emission requirements, the choice of a reasonable technical route for the transformation of flue gas treatment facilities is no time to delay.
2.2 measures to improve the dust removal efficiency of conventional electrostatic precipitator
In order to improve the efficiency of the dust collector, in the design phase of the dust collector, the design optimization seminar was held several times to determine the design of electrostatic precipitator many details, focusing on the following aspects of the work:
1. increase the section, reduce the flow rate of flue gas, improve the efficiency of dust removal.
Wanzhou power plant dust collector design of flue gas velocity 0.817m/s, residence time of 24.46s, reduction of flue gas velocity, mean a flue gas volume, the length of the electric field in the same situation, flue gas in the electric field treatment time prolonged, dust removal efficiency to improve. Sectional area was can reduce the wind speed, prolong flue gas in the electric field in the residence time, reduces the vibration secondary dust, improving the dust collecting efficiency of the electrostatic precipitator; can reduce the dust on the plate, polar erosion wear, prolong the service life of the electric dust collector internals.
2. larger than the dust collection area, improve the efficiency of dust removal, reduce export emissions.
Wanzhou power plant than the dust collecting area design data for the 126.62m2/m3/s, compared with the domestic conventional dust collector, larger than the area of dust collection. In general, the dust removal efficiency is increased with the increase of the area ratio, and the area of a certain amount of dust collection is a necessary condition to ensure the efficiency of dust collection. Therefore, this is a certain amount of dust collection area is based on a large number of similar projects, based on the scientific theory derived. At the same time, the dust collecting area can overcome the harm caused by the bad working conditions caused by the high specific resistance dust.
3.power supply technology:
In every field is divided into technical measures taken within about three power supply area, each dust collector consists of 15 power supply area, effectively diminishes the power supply unit, improve the reliability of equipment operation.
4 .using a mixed polar proportion, eliminate field dead, increase coal applicability.
This project uses the mixed polar matching form. This polarity type, one is the intensity of electric field distribution, the plate on the corona current density distribution is uniform, thus inhibiting the back corona generation; second, under the premise of guaranteeing the efficiency of proper increase of electrostatic precipitator range for the coal, can eliminate the electric field and dead zone of dust collection efficiency is increased.
At the end of the 5 electric field using fishbone needle plus auxiliary electrode, the smoke outlet box equipped with groove plate system.
At the end of the electric field by fish bone needle for the auxiliary electrode, and the outlet of the smoke box installation of double-layer labyrinth groove plate system in the electrostatic precipitator to guarantee the electric dust collector on the practical condition of the adaptation performance and long-term effective dust removal efficiency.
6. the power-off rapping and intermittent power supply and other measures to effectively control the anti corona phenomenon.
In view of the need to strengthen the vibration cleaning requirements, "reducing vibration power play" and "power-off rapping" function, the function and vibration beat controller closely, playing in the field vibration period, which corresponds to a high-voltage power supply automatically enter set minus power "or" off "power supply, decrease the deposition on the electrode electric adhesion, effectively improve the vibration beating dust removing effect. According to the actual need, also can adjust the power frequency vibration to get the best results.
7 . three electric field using three-phase power supply, four to five electric field using domestic high frequency power supply, more conducive to improve the efficiency of dust removal.
Wanzhou project of the original five field design used in all specifications for 72KV high frequency power supply, 1800mA power supply, after the transformation, one to three electric field to the specifications for the 82KV, 2200mA three-phase power supply. The two main factors determining the efficiency of electrostatic precipitator is: size and operating voltage of the body height. The electric dust index can effectively reflect the two aspects, and it meets the electric dust removal efficiency as shown in the equation relationship:
The size of the electric dust index reflects the level of electrostatic energy storage in the electrostatic precipitator, and the higher the storage energy, the higher the efficiency of dust removal. Through the design and application of the electrostatic precipitator technology optimization, ensure the Wanzhou power plant conventional electric precipitator outlet dust concentration is less than or equal to 15mg/Nm3. On February 5, 168 during, according to local environmental monitoring station monitoring data: precipitator inlet dust 6.22g/Nm3, dust outlet for 7.7mg/Nm3 data demonstrating, precipitator efficiency raising and reform success, further dust removal desulfurization absorption tower lay a better foundation.

2.3 scheme selection of wet electrostatic precipitator and tube bundle type dust removal device
Brief introduction of 2.3.1 wet electrostatic dust removal technology
Wet electrostatic dust removal device is additionally arranged in the tail of the desulfurization system, traditional dry electrostatic precipitator (ESP) on high specific resistance and fine particle removal rate is not high; wet electrostatic dust removal device processing is saturated wet flue gas, dust particle charging performance, corona current, on wet flue gas dust specific resistance is not required, especially for in wet removal in flue gas of fine particles and aerosols, dust collection effect is very good.
Currently wet electrostatic precipitator technology mainly in the metal plate, the flexible plate type, non metal pipe type different genres, from an engineering example, can really achieve the ultra low emission requirements for the first two techniques, however, its investment is large, on-site reconstruction covers an area of, construction difficult, wastewater is difficult to treat such problems were prominent.
Technical introduction of 2.3.2 tube bundle dust removal device
Tube bundle type dust removing device is a patent product developed by Beijing state electric fresh environmental protection technology company in 2013-2014. Use environment containing a number of liquid droplets of 50 DEG C saturated clean gas, which is characterized by large amount of droplet, droplet size distribution of a wide range, by the slurry droplets and condensate droplets and dust particles; dust is mainly removing slurry droplets and dust particles.

Tube type dust removing device is the desulfurization tower, in addition to dismantle the mist eliminator, use except the mist eliminator bracket installation, the flue gas into the desulfurization tower first after the speed increaser ensure to minimum resistance conditions of gas lift the rotating speed, a large number of fine droplets and particles under the condition of high speed collision probability increased significantly, easy to aggregate, aggregation into large particles, so as to realize the separation from the gas phase. Dust remover cylinder wall surface film will collector noted come into contact with the surface of fine droplets, especially in growth and splitter blade surface of the thick film, "Apron" phenomenon occurred in under the action of high-speed airflow, a lot of large droplets from the blade surface was spilled out, on the blade forming a large droplets of liquid droplet layer, through the liquid droplet layer of fine droplets arrested noted, large droplets change after fall back to the surface of the blade back into the liquid drop, of small droplets catching noted.
After the accelerator to speed up after high-speed rotating airflow upward movement, airflow in small droplets, dust particles under the action of centrifugal force and gas separation, to the surface of the cylinder body direction. The film layer and the high-speed airflow rotating force drops entrapped form a rotary motion in the cylinder wall. From the gas separation of small droplets, dust particle in film after contact with arrested noted, the realization of small droplets and dust particles from flue gas removal.
Rotating gas flow rate increases, centrifugal separation effect is better, collector noted droplet quantity is big, the formation of liquid film thickness greater, running resistance is greater, more prone to formation of secondary droplets; so the multi-stage separator, respectively under different velocity of droplet removal to ensure low running resistance of high efficiency dust removing effect.
Comparison of technical performance of 2.3.3 Wanzhou power plant dust removal retrofit scheme selection (single stage furnace)

Rotating gas flow rate increases, centrifugal separation effect is better, collector noted droplet quantity is big, the formation of liquid film thickness greater, running resistance is greater, more prone to formation of secondary droplets; so the multi-stage separator, respectively under different velocity of droplet removal to ensure low running resistance of high efficiency dust removing effect.
Comparison of technical performance of 2.3.3 Wanzhou power plant dust removal retrofit scheme selection (single stage furnace)
Based on the above analysis, considering an investment, energy consumption, maintenance cost and the equipment maintenance convenient maintenance, reduce renovation work, the compact layout and the factors, the project take tube type dust removing device as soot ultra low emissions reconstruction scheme.
3 the implementation of the reform of the tube bundle type dust removal device in Wanzhou power plant
3.1 removal and reconstruction of the original absorber unit

1) to cancel the original absorption tower of tertiary demister (2 layer roof type + 1 layer tube type), for the transformation of the new tube type dust removing device and corresponding washing water system.
2) in fog is supported girder construction transformation selection demolition original except sprayer, the second floor girder, the original except the fog the first layer beam, and the demolition of the existing of the second layer beam (two) to strengthen in the first layer is arranged on the beam.
3) in addition to the fog device flushing water interface has been constructed, the transformation of the choice of cutting plugging the existing flushing water interface, re design, construction and flushing water interface opening position.
1) 4 absorption tower in addition to the fog device washing operation and maintenance platform has been constructed, the selection of the existing platform to transform to meet the transformation after the operation and maintenance requirements of the mist.
3.2 efficient tube type dust removing device in the installation and operation of absorption tower
1), tube type dust removing device adopts modularization design, which is arranged in the upper part of the spraying layer is in addition to the location of the mist eliminator, instead of conventional except the use function of the mist and dust removing fog effect is far superior to the common roof type demister.
2) for the reconstruction of desulfurization unit, in the top of the absorption tower to set aside more than two-story roof type in addition to low mist eliminator installation space, and design and ridge type except the mist eliminator is a considerable strength of support beam, directly to the module tube type dust removing device is installed on the beam.
3) set the flushing water can meet the requirement of the toilet flushing, than the conventional roof in addition to save the installation space of the mist eliminator, reduce the quantity of water for flushing, reduce the electric valve configuration. According to the running resistance of tube bundle dust removal device, set and adjust the frequency of washing washing water and washing effects.
The original 2.3 other system reform
Original system, flue gas SO2 absorption system, slurry preparation system, gypsum dewatering system, process water systems, emptying system and wastewater treatment system completely satisfies the performance requirement of the system output, without changing, only the original absorption tower internal turbulator and demister to transform, original except the mist eliminator flushing water and flush water pump parameters unchanged.
The effect of the internal flow field design optimization on the dust removal in the 4 absorption tower
4.1 effect of flue gas desulfurization tower set uniform facilities

From the figure can be seen in no gas distribution device of flow, flue gas flow appeared obvious bias, in the vicinity of the desulfurization tower inlet the distal end of the tower wall appeared in the high velocity zone, this phenomenon has been to 12 spray layer in the middle section is still very obvious, on the one hand affected the efficient utilization of desulfurization slurry, on the other hand, the local higher gas velocity leads to smoke on the droplet carrying capacity enhancement, increased loading except the mist, in addition to mist eliminator is harmful. And in the flow field of a gas distribution device, although in the flue gas uniform the following facilities area is still a bias exists, but when after the flue gas through the gas distribution device (Venta a characteristic: in the bottom spray layer is a layer of turbulent layer), the gap between imports of proximal and distal flow field has been basically eliminated, indicating that the gas distribution facilities of flue gas produced a good effect. At the same time, to the uniformity of velocity of the flue gas demister, to ensure that besides the mist eliminator in fog give full play to have great effect.
4.2 effects of spraying layer on the desulfurization tower flow field
From the figure can be seen, no spray, although gas distribution device corrects a part of smoke drift, but flow distribution in the entrance of the proximal and distal to the uneven did not completely eliminate, after adding a spray, in turbulence, spray layer, drift completely disappeared, the flue gas flow field achieve good uniform distribution.

In the spray layer and put into operation, can be very good uniform turbulence to in addition to the flow field of the mist eliminator, making into the mist of smoke removal with uniform velocity distribution, so spray layer nozzle spray angle and direction also to the flow field in the desulphurization tower to very important role.
4.3 optimization uniform outlet flue effect on the flow field of the
According to the basic principle of fluid mechanics, in addition to the mist eliminator flue arrangement will of mist flow in addition to interfere, to ensure except for mist eliminator in optimal conditions, re on the flue outlet optimized is exit flue by "side" changed to "top out", and change the flue of the right angle bend curved arc, by constant cross-section pipe instead of gradually expanding shape pipeline decreases resistance loss measures such as.
As you can see from the above two figures in the desulfurization tower outlet flue after optimization, increase the export and in addition to the distance between the mist and smoke flow space more fully in deflection before flue gas have plenty of exercise time and space, the in area of the mist eliminator uniform flow field significantly expanded, but also reduce the export of resistance. Through the simulation can be seen that the optimization of desulfurization tower outlet flue is necessary and reasonable.

5 Summary and recommendations
Tube type dust removing device covers an area is small, the change less workload, construction and installation, short construction period and operation stability and saving investment, and post operation and maintenance costs low, for in new construction and renovation of unit of smoke ultra low emissions. For the unit, as in the original absorption tower can realize the transformation, absorption tower without heightening, superiority is more obvious.
The transformation unit 1 has completed 168 hours of trial operation in February 2015, successfully put into commercial operation. The filter method was used to detect the emission data of unit 1, and the average 3.1mg/Nm3 of the smoke and dust was measured. Which February 5th commissioned by the local environmental monitoring stations to monitor the chimney outlet 9.0mg/Nm3 for SO2, dust for 4.5mg/Nm3 (monitoring stations using the State universal filter tube method), NOX for 23.0mg/Nm3.
Shenhua Wanzhou power plant by conventional electrostatic precipitator design optimization and power transformation of desulfurization absorption tower internal flow uniformly and optimize the, and taken in the application of comprehensive technology of tube type dust collector, a better realization of the ultra-low emissions of pollutants, explores a new path for the ultra low emissions from thermal power industry.
reference
[1] "thermal power plant flue gas desulfurization technology standard";
[2] "coal fired flue gas desulfurization and denitrification technical standards";
Code for construction and acceptance of flue gas desulfurization absorption tower in thermal power plant [3];
[4] "guide for design of flue gas desulfurization unit in coal fired power plant";
[5] "fluid mechanics", Tongji University press;
[6] "Engineering Fluid Mechanics", University of Science & Technology China press;
[7] "characteristics and development direction of wet electrostatic precipitator" electric power environmental protection.
[8] "Wanzhou 2X1000MW unit electrostatic precipitator design scheme" Lanzhou electric power plant.
HJ2028-2013 "general technical specification for electrical dust removal engineering" [9]
JB/T "design, commissioning, operation and maintenance of electrical dust catcher" 6407-2007 [10]