1. Background
Obtaining fresh air is an important means to improve the air quality of the built environment. Controlling the pollution sources of air quality in the atmospheric environment can ensure that we can obtain gases that meet the ambient air quality standards.
However, in recent years, China’s heavy chemical industry (electricity, building materials, metallurgy, chemical industry, etc.) has developed rapidly in terms of resources and energy consumption. China has become the world’s largest producer of steel, cement, coal, and chemical fiber, and the second largest Electricity, non-ferrous metals, fertilizer producers. Accompanied by the serious environmental pollution problems, the economic losses caused by environmental pollution such as air, water, and industry amounted to 100 billion RMB or more per year. The investment for environmental protection in China during the tenth five-year period reached 2.2% of GDP (2004 GDP is 13.65 trillion RMB).
The atmospheric pollutants in the heavy chemical industry are characterized by high-temperature flue gas, and soot particles are one of the main control objects. As a control of the total amount of laws and regulations, the state has successively revised the emission values formulated by various types of boilers and furnaces in the industrial sector, and has strictly requested the reduction of emissions. As a high-temperature flue gas emission particulate (smoke) control technology will be rapidly transformed to the bag type dust removal technology. However, as the key to the application of bag type dust removal technology, high temperature dust filter materials, most of them are still relying on foreign products, domestic products are lacking in technical support for imitating use, and urgently need to change the situation.
Taking electric power as an example, China’s energy is mainly coal-fired. According to the new standards of the country, the emission value of coal-fired boiler fumes from the power plant must reach 50 mg/Nm3 or less, and electrostatic dust removal technology needs to be changed to the bag type dust removal technology. At present, the unit has a capacity of about 4.4 million KW (at the end of 2004), and in 2010 it has reached 60 million KW and by 2020 it will have reached 90 million KW. In terms of energy structure, more than 75% need to use coal-fired thermal power. According to the current project budget investment, 100 – 1.2 million yuan / 10,000 KW, filter material accounted for 1/4, replaced once every 4 years, namely: filter material investment 6 – 8 million / million KW / year operating costs. Completed the current unit dust removal transformation investment reached 300 – 32 billion, follow-up project reached 380 – 45 billion, that is: the market capacity reached 70 billion, about 20 billion filter material, annual operating replacement cost of about 5 billion. The use of bag type dust removal technology can reach 20 mg/Nm3 or less, achieving a total capacity increase of 1.25 times the unit, smoke and dust emissions fell by 50% (based on the current average emission value of 100 mg/Nm3) -75% (based on the current average emission value of 200 Mg/Nm3 calculation). By controlling the particulate pollution in atmospheric air, the new air purification pressure needed to improve the air quality in the building environment is reduced.
2. Current status
Most of coal-fired boiler bag filter bag material of power plants choose PPS needle felt filter (acupuncture felt filter material referred to as filter). There are also PPS+P84 composite filter media, P84 fiber content of about 20%. Mainly for boilers burning low sulfur coal.
PPS polyphenylene sulfide
P84 scientific name polyimide, P84 fiber cross-section and PPS fiber rod-like compared to a multi-lobed, its irregular fiber cross-section increases the surface area of the fiber, increasing the permeability of the filter material, with the effect of reducing resistance and increasing efficiency.
The application conditions of PPS filter media mainly depend on the properties of PPS fiber. The most suitable conditions for dust removal from coal-fired flue gas are: flue gas temperature 120-160°C, SO2 content in flue gas <1000mg/m3, NOx content <800mg/m3, Oxygen content <10%. Before the start of the boiler operation, it is necessary to precoat ash; when the fuel injection furnace, boiler explosion pipe, and flue gas are over temperature, it is not suitable to directly enter the bag filter, and a bypass flue is needed; the bag filter is designed to filter wind speed 1.0m/ Around min, dust collector design resistance 1500Pa. The normal operation of the bag filter bag guarantees a service life of 30,000 hours. In order to reduce the filter resistance and increase the temperature resistance, PPS+P84 composite fiber needled felt was used.
The use of PPS and PPS+P84 filter materials mainly depended on foreign imports. Nowadays, domestic fiber is used for production.
3. Application Condition Analysis
The requirements for bag filter used for dust removal from power plant boilers are synchronized with the overhaul period of boiler equipment, and 30,000 hours have become the basic service life required by thermal power plants. However, with the dust removal from coal-fired power station boilers, there are differences between the domestic application conditions and foreign countries, which are mainly manifested in:
(1) Coal types: The use of clean coal in foreign countries and the use of raw coal in China are different in calorific value, ash, and S content;
(2) Technical level: The degree of automation of equipment in developed countries is high, and domestic equipment is combined with manual and automation.
(3) Boiler equipment: Boiler equipment in developed countries is relatively advanced, and there are a large number of small and medium-sized equipment (especially early boilers) in China;
(4) Comprehensive utilization of energy: The use of blast furnace gas causes fluctuations in the volume of smoke and dust, changes in gas composition, and an increase in the temperature of flue gas.
As a result, the domestic application environment of filter media has resulted in a four-year high and a low one (high emission flue gas temperature, high content of SO2 and NOx in flue gas, high oxygen content in flue gas, high dust concentration, and low filter bag resistance; ). Due to the relatively poor flue gas emission from coal-fired boilers, the service life of filter media (filter bags) will be affected. Therefore, in the use of filter material bag filter, reference but do not blindly copy foreign experience, should consider the actual situation of domestic boilers, targeted technology improvements.
4. Technology research and development
In order to reduce the filter resistance, the filter material made of a single fine PPS fiber is further improved to a filter material with a fiber gradient structure (gradient filter material) made of PPS fibers of different fineness.