Equipment to control particulates part 2

equipment to control particulate matter
air pollution and control
control of air pollution
control of particulate matter

1. Equipment to Control Particulate Metter [part-2] Ravi Kumar GARRE

2. Contents covered Introduction Settling chambers Inertial separators Cyclones Filters Electrostatic precipitators Scrubbers/ wet collectors [ Note: settling chambers , inertial separators, cyclones are not covered in this presentation ]

3. Introduction To remove particulate matter from gaseous streams various types of equipments are in practice. Settling chambers Inertial separators Cyclones Filters Electrostatic precipitators Scrubbers/ wet collectors

4. Introduction The data to keep in mind in the selection of proper equipment is: Quantity of gas to be treated and its variation with time Nature of particulate matter Concentration of particulate matter Temperature and pressure of gas stream Nature of gas stream (i.e. solubility, corrosivity, ignitability, etc.) Desired quality of treated effluent

5. Introduction Objectives of control equipment Prevention of nuisance Prevention of physical damage to property Recovery of valuable waste product Minimization of economic losses Efficiency of separating device η = (quantity of particulates collected from gas) / (quantity of particulates present initially)

6. Filters Filters (or) fabric filters, also called as fabric collectors/ cloth filters/ bag filters/ bag house. Fabric collectors use filtration to separate particulates from polluted gas streams.

7. Filters Polluted gases enter the bag house and pass through fabric bags that act as filters. The bags can be of woven, cotton, synthetic or glass-fibre material in either a tube or envelope shape. In this system, the entered gas allowed to pass through these bags, which filters out the particulate matter and allows the gas to escape.

8. Fabric filters Small particles are retained on the fabric, later on when the dust mat will be formed. Frequently the bags/ filter material should be cleaned or replaced. Small particles can retain in the bags. Fabric filters can remove particle of size about 1µm.

9. Fabric filters Fabric filters are 99 % efficient in removing particles of size 1µm to 10 µm The factors affecting efficiency is: Improper selection of filter media Temperature of gaseous stream Particle size of particulate matter

10. Fabric filters Advantages Higher collection efficiency It collects particles smaller than 10µm Requires normal power consumption Disadvantages High temperature gases need to be cooled High initial and maintenance cost High fabric replacement cost Large size equipment Fabric is liable to chemical attack

11. Fabric filters Applications Metallurgical industry Foundries Cement industry Ceramic industry Flour mills Brick works

12. Electrostatic precipitators Electrostatic precipitator is a device that removes suspended dust particles from a gas or exhaust by applying a high-voltage electrostatic charge and collecting the particles on charged plates Electrostatic precipitators can remove particles of size less than 1µm Efficiency – 95 to 99%

13. Electrostatic precipitators In this method two electrodes are fitted inside a chamber. When high voltage is applied an electric discharge takes place in between these two plates as a result a strong electromagnetic field will be created. The air in the strong electromagnetic field get ionised. The ionised air consists of ions and free electrons.

14. Electrostatic precipitators

15. Electrostatic precipitators If the polluted gas allowed to pass through the strong electromagnetic filed, the particulate matter get negatively charged and attracted to positively charged electrodes. Therefore, the particulate matter settle down on the surfaces of electrode plates. These can be dislodged by vibrating the electrodes.

16. Electrostatic precipitators

17. Electrostatic precipitators C omponents of ESP A Source of high voltage Electrode plates Inlet and outlet for the gas A hopper for disposal of collected gases A cleaning system An outer casing to form an enclosure around the electrodes

18. Electrostatic precipitator Advantages Particles may be collected wet or dry Even small particles can be removed They can be operated at high temperatures up to 450 ˚C Maintenance is nominal Disadvantages Higher initial costs Sensitive to variable dust loadings and flow rates Collection efficiency reduces with time

19. Electrostatic precipitator Applications Cement factories Pulp and paper industries Steel plants Non-ferrous metal industry Chemical industry Petroleum industry Power plants

20. Scrubbers Scrubbers are also called as wet collectors. Scrubbers utilise liquids (generally water) to assist in the removal of particulates from the carrier gas stream. In wet collectors, the particulate matter is agglomerated with water and then separated from the gas with water. Scrubbers can separate particles even smaller than 0.2µm.

21. Spray towers Spray tower is the simplest type of wet scrubber. In this scrubber, gas is passed counter current to falling drops of liquid from a series of nozzles. The impingement and interception of particles with liquid droplets cause settlement of particles along with liquid droplets. Spray towers are used to separate coarser particles.

22. Cyclone scrubbers Cyclone scrubbers are another types of wet collectors. High pressure nozzle sprays located inside the chamber generate a fine spray that intercepts particles entrained in the swirling gases. The particulate matter is thrown on to the walls by centrifugal action and then drained to the bottom.

23. Scrubbers/ wet collectors Advantages Simultaneously remove particulates as well as gaseous pollutants Hot gases can be cooled down Corrosive gases can be recovered and neutralised Disadvantages Lot of waste water produced Maintenance cost is high

24. Choice of equipment Particulate size Particulate loading Required efficiency Properties carrier gas: Composition, Temperature, Pressure, Viscosity, Density, Humidity, ignitability, reactivity, electrical property, etc. flow characteristics of carrier gas Capital and operating cost of equipment Ease of maintenance and reliability

25. Economic aspects

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