Comparison of dust-collecting systems
Mechanical dry cleaning in cyclones, cleaning using cloth filters and electrical precipitation and wet scrubbing are used to remove solid particles from gases, including air, and to prevent environmental pollution.
Centrifugal cyclones are used for purifying gases at 200 to 400 g/m3 dust content and 5 to 10 µm minimum precipitable particle size. Capacity of cyclones in terms of dust air mixture, depending on their capacity, is 1500 to 15,000 m3/h.
Dusty air is fed into the upper cylindrical part of the housing tangentially. In the cyclone the air moves down spirally which is facilitated by a guide – a fixed helical blade (or the cylinder cap is installed on the helical surface). Under the action of centrifugal forces the particles are thrown to the external walls, slide down and are removed from the cyclone through a special gate. The purified air is escapes upwards through the central pipe. The air mixture speed at the cyclone inlet is 15 to 25 m/s.
Coefficient of purification in centrifugal cyclones is 70 to 90%.
Small diameter cyclones ensure better purification. Therefore, to achieve high purification degree and increase capacity, they are integrated into groups (batteries).
The air mixture is fed through a pipe to the distributor from where it is fed into cyclones. The purified air exits through the tubes into the collector and is fed through the pipe into the next purification stage. The extracted material is precipitated in the collector from where it is removed through special gates.
A more thorough gas purification is achieved in cloth filters. Gases are purified in such filters when passing porous partitions on which small particles precipitate. Usually partitions are made as thick cloth bags. When gas temperature is over 100 °С, the bags are made of glass cloth.
The polluted air is fed through the pipe to the housing in which bags are installed on special bags. Having passed through the bag walls, air is purified of the dust which settles on them, then it is removed through a pipe. To ensure operation of the filter, its bags are periodically shaken by a special mechanism.
During shaking the outlet lines are closed with a damper interlocked with the shaking mechanism. The material settled in the collector is fed by the auger through the rotary discharger into the bins. To enhance the cloth cleaning, fresh air is periodically blown through the filter in the reverse direction.
The purification degree in bag filters is as high as 96 to 98% if dry gases are purified.
The most efficient gas purification method is electric one.
The method is based on ionisation of the particles suspended in gas when the latter is exposed to high voltage electric field. The particles being charged move to the electrode the charge of which is opposite in sign and settle on it. The electric filters catch up to 5 µm particles with up to 99% purification degree. Such filters are successfully used for purification of hot (up to 350° С). The aerodynamic resistance is low in them, and that what differs them from cloth filters. Power consumption is about 0.3 kW per 1000 m3 of gas.
High-voltage (up to 75,000 V) direct current is used for creation of the electric field. The dust particles are electrified in the electrostatic field induced by electrodes, are repelled from the corona-producing electrode and settle on electrode 1 connected with the housing.
The contaminated gas is fed through the inlet distributor to the chamber of the filter divided into two parallel sections. Each section is equipped with three electric filter stages through which passes successively. Each stage consists of several rows of precipitation plate gauze electrodes and corona-producing electrodes consisting of rods, electrodes installed on isolators.
The precipitation electrodes are periodically shaken by a cam gear for removal of the dust settled on it. The dust collected in the receivers is removed through gates. The collected gas is removed through a gathering manifold.
The above discussed equipment is designed for air and gas de-dusting, and so it is equipment for the environmental protection and improvement of personnel working conditions. However, there are specific operation peculiarities to which special attention should be paid.
Compressed gas is used in separators, cyclones and bag filters, so these vessels and lines are explosion hazardous is proper modes of their operation are not observed. It is necessary to monitor the correct condition of instrumentation and protection devices (pressure gauges, relief valves, etc.). Monitoring and emergency devices shall be tested and sealed by a special service.
Only specially trained personnel having respective certificates shall be allowed to operate the pressurised equipment. High voltage is used in electric filters and the electric shock hazard is increased. Therefore the filter should be installed in a way precluding any direct contact of the personnel with live equipment. A disadvantage of the electric filter is impossibility to re-use the settled dust due to its residual electricity.
Thus, the following conclusion can be made as a summary: bag filters feature the best combination of purification and cost efficiency. Naturally, the use of a particular type of purifying equipment depends upon the specific process task and capacity of the enterprise. However, the new generation bag filters allow achieving high air purification degree (up to 99%) and using them as a non-waste production component.
The bag filters are widely used in construction material industry in closed-cycle grinding plants, in gypsum, lime, cement production, etc. In these cases the output increases significantly, and mill power consumption is reduced significantly due to continuous selection of finished product.
The Samara Strommashina plant is a producer and supplier of dust removal equipment for industrial enterprises in Russia and all over the world. Available cyclones and bag filters for sale offered for saleare highly reliable and reasonably priced.