Application of semi dry desulfurization filter bag in ultra clean emissions
2016-02-03 09:35:38
Author: Yang Jiajun
Abstract: In the semi-dry desulphurization system , the originally conventional baghouse can no-t meet the strict emission requirements,optimization and upgrade are needed. This paper completel-yintroduce various aspects. form the filtration velocity, updraft speed, material selection,air dist-ribution of baghouse，and so on.
Keywords：clean emissions；baghouse； filtration velocity
1、survey
With countries of flue gas of thermal power units achieve 50355+53 ultra clean emissions requirements, semi dry circulating fluidized bed desulfurization technology with covers an area of province, craft by-product dry state convenient transportation processing, the investment cost is saved, low operation cost, no secondary discharge of pollutants, such as a series of obvious advantages, is city thermoelectric unit ultra clean emissions of the best choice. Subsequently configuration of bag type dust collector in order to adapt to the characteristics of flue gas and more stringent dust emission concentration requirements (less than or equal to 5mg / Nm3) and need for ordinary cloth bag dust remover for the optimization and upgrading of the design.
The special design of bag precipitator mainly is composed of a box body, air distribution system, filtering system and Qing ash system, gas supply system composed of the following characteristics: high dust removal efficiency, especially for fine powders and PM2.5 has a very high collecting efficiency can generally be 99.999% to, ensure that the dust emission concentration is less than or equal to 5mg / Nm3; II adaptability, it can adapt to different flue gas load and different types of particulate pollutants; (3) large elasticity of operation, the inlet gas containing dust concentration change is large, the impact on the dust removal efficiency is not.
2、Special ultra clean emissions in semi dry flue gas desulfurization
In the ultra clean emissions of circulating fluidized bed semi dry desulfurization system, and before the conventional semi dry flue gas desulfurization system has a very different place, the conventional desulfurization tower outlet dust concentration usually are in the range of 800 ~ 1000mg/Nm3, and super net emissions desulfurization tower outlet dust concentration to above 1000mg/Nm3, particularly large dust concentration; desulfurization tower outlet flue gas temperature is very low, only about 70 DEG C, and need long-term stable operation in this temperature range, the most direct is a reflection of the flue gas moisture content, especially refuse incinerator flue gas, moisture capacity can be reached 15%.
The special design of desulfurization filter bag three, ultra clean emissions in the
1) than the selected gas
Conventional semi dry desulphurization matching bag precipitator gas cloth is relatively high, generally between the 0.75~0.80m/min. But in super net emissions, due to the cloth inlet flue gas containing dust high volume, dust particle viscosity, humidity is very large, the baghouse filter area needs to be large enough to achieve a good filtering effect. At the same time, in order to increase the fine powder and PM2.5 trapping efficiency, the surface of the filter bag should be some dust cover, clear ash frequency can not be too high. After the test, the resistance of bag filter can be controlled at 1800 ~ 2000Pa, the frequency of dust cleaning and not too frequent and affect the service life of the equipment. The gas Bubbe are low, after repeated tests, the value should be between 0.70 ~ 0.75m/min.
2) select the rising speed of airflow
The box body bag updraft speed is a key control parameter. In the design process, should ensure that the airflow speed rise less than the settling velocity of dust particles, if the updraft velocity is too large, cause bag cleaned off the dust suspended in midair, and even secondary entrainment into the bag. As a result, the bag type dust collector resistance ranks high, making the ash cleaning system in a state of paralysis. After that a large number of engineering cases, the upper part of the body when the airflow speed control is less than 0.80m/s, the cleaning system can work in a normal state.
3) selection of filter material
Bag as the core component of the bag dust collector, has a pivotal role, choice of filter material naturally became the top priority. For coal-fired boilers and waste incineration furnace, PPS is the preferred media, PPS filter material, the price is very high, strong acid, strong hydrolysis resistance, stability and fire resistance, good tensile strength, abrasion resistance, folding resistance, the shortcomings of PPS filter is weak antioxidant properties; for garbage incineration furnace, due to garbage furnace flue gas containing oxygen and humidity are relatively high, typically reaching 10% and 16%, P84 and PTFE can be as the preferred material, the utility model has the advantages of is very strong antioxidant. But no matter what kind of filter was used, in order to meet the requirements of ultra clean emissions standards, the filter must be blended superfine fiber, surface coating processing, waterproof put oil treatment before the filter surface gram weight shall not be less than 630g/ square meters.
4) pre settlement room set
Because the dust concentration in desulfurization tower outlet net emissions in more than 1000mg/Nm3, especially high dust concentration. In order to reduce the load of the dust bag, shall be provided with pre settling chamber. In order to improve the efficiency of dust settling chamber, to do some special design of the settling chamber. Or in the box body installation of shutter and extended dust pass away at the same time, the dust under the action of gravity gradually subsided, or installed in the box body shaped baffle, some small vortex is produced in the air, dust by centrifugal force, separated from the gas containing dust and gas in the large particles dust natural sedimentation and after separation of diversion system directly into the hopper, the rest of the dust under the guidance of the diversion system, with the air into the filter box area. In the bag filter design can utilize the full section, the volume expansion of dust in the residence time to increase, improve the efficiency of pre settling chamber.
At the same time, increase the height of the bag in box, change from the traditional way of the intake of the ash hopper of the bag, optimized for from a bag in box inlet. In this way, so that the smoke into the bag filter after the rise to bag a certain space, but also to avoid the bag in the hopper in boiling like ash secondary dust deposit. After the settlement room so optimized, dedust efficiency can reach 60 ~ 70%.
5) air distribution system
Design for super net emissions of bag type dust collector, the use of modular structure design, interior is divided into a plurality of bag chambers, bags and bags, room independent of each other, in this way, the room the air intake evenness is critical, a direct impact on the bag dust removal effect. Therefore, through the CFD numerical simulation to verify the uniformity of the flow field, the following is the comparison simulation of flue gas flow field before and after the air distribution system settings.
No smoke flow into the air distribution system
Smoke flow set into the air distribution system of the
The flow field analysis, can be found very clear, in fabric air distribution system is not set, each bag room flue gas load is extremely uneven, near the tail of the bag chamber flue gas load is too large, it will lead to tail bag chamber overload operation, air to cloth ratio and airflow rising speed will seriously exceed the design value, leading to a differential pressure chamber, cleaning too frequently, can't even normal cleaning. Can be found in the near future, set the uniform air distribution system, flue gas load of each bag room than before there was a clear change, gas distribution is very uniform, provides a powerful guarantee for the normal operation of cleaning system.
6) design of ship ash hopper
Super net emissions, due to the absorption tower bed bed pressure differential large bag dust hopper must being inadequate circulation ash content to meet the absorption tower of the circulating ash system establishment. At this time, bag dust hopper can be set to ship type ash bucket and the bottom of the ash bucket set air chute, the setting angle of the air chute shall not be lower than 10 degrees. Only in this way can hopper to ensure continuity of ash, also reduce the mechanical fault of ash.
7) cancel bypass system
Bag filter routine set built-in bypass, when the boiler tube explosion, flue gas to switch to protect the bag. But in super net emission system, bag filter bypass seal and the important and normal operation, if the seal is not good, the raw gas easily leak, the net flue gas emission concentration impact, resulting in excessive dust emission concentration, and the bypass valve is very difficult to achieve the zero leakage. At the same time, the environmental protection agency has stipulated the desulfurization and dust removal system allowed to set any bypass system, therefore in the system of ultra clean emissions, consider the abolition of built-in bypass system, eliminate all possibility of leakage.
4、conclusion
In the super net emissions of semi dry flue gas desulfurization system, supporting the cloth bag dust remover bear pivotal role, only to conventional bag dust collector for optimization and upgrading, in order to meet the current strict emission standards for dust. In improving air quality and accelerate the haze to solve the problem of the moment, it has good popularization significance.
reference
[1] Liu Xuejun high concentration dust collector, thermal power generation application of reflux circulating fluidized bed flue gas desulfurization system. 2007（12）：53-55
[2]Luo Weiqiu special bag dedusting and desulphurization device design and application of chemical engineering and equipment2009:7：79-83