subject: Ejector Venturi Scrubber - China Project Case - Marble Texture [print this page] Particle collection Particle collection
Ejector venturis are effective in removing particles larger than 1.0m in diameter. These scrubbers are not used on submicrometer-sized particles unless the particles are condensable [Gilbert, 1977]. Particle collection occurs primarily by impaction as the exhaust gas (from the process) passes through the spray.
The turbulence that occurs in the throat area also causes the particles to contact the wet droplets and be collected. Particle collection efficiency increases with an increase in nozzle pressure and/or an increase in the liquid-to-gas ratio. Increases in either of these two operating parameters will also result in an increase in pressure drop for a given system. Therefore, an increase in pressure drop also increases particle collection efficiency. Ejector venturis operate at higher L/G ratios than most other particulate scrubbers (i.e., 7 to 13 l/m compared to 0.4-2.7 l/m for most other designs).
Gas collection
Ejector venturis have a short gas-liquid contact time because the exhaust gas velocities through the vessel are very high. This short contact time limits the absorption efficiency of the system. Although ejector venturis are not used primarily for gas removal, they can be effective if the gas is very soluble or if a very reactive scrubbing reagent is used. In these instances, removal efficiencies of as high as 95% can be achieved [Gilbert, 1977].
Maintenance problems
Ejector venturis are subject to abrasion problems in the high-velocity areas - nozzle and throat. Both must be constructed of wear-resistant materials because of the high liquid injection rates and nozzle pressures. Maintaining the pump that recirculates liquid is also very important. In addition, the high gas velocities necessitate the use of entrainment separators to prevent excessive liquid carryover. The separators should be easily accessible or removable so that they can be cleaned if plugging occurs.
Summary
Because of their open design and the fact that they do not require a fan, ejector venturis are capable of handling a wide range of corrosive and/or sticky particles. However, they are not very effective in removing submicrometer particles. They have an advantage in being able to handle small, medium and large exhaust flows. They can be used singly or in multiple stages of two or more in series, depending on the specific application.
Multiple-stage systems have been used where extremely high collection efficiency of particles or gaseous pollutants was necessary. Multiple-stage systems provide increased gas-liquid contact time, thus increasing absorption efficiency.
Table 1 lists the operating parameters for ejector venturis.
Table 1. Operating characteristics of ejector venturis
Pollutant
Pressure drop (p)
Liquid-to-gas ratio (L/G)
Liquid-inlet pressure (pL)
Removal efficiency
Applications
Gases
1.313cm of water
7-13 l/m3
100-830 kPa
95% for very soluble gases
Pulp and paper industry
Chemical process industry
Food industry
Metals processing industry
Particles
0.5-5 in of water
50-100 gal/1,000ft3
15-120 psig
1m diameter
Bibliography
Bethea, R. M. 1978. Air Pollution Control Technology. New York: Van Nostrand Reinhold.
Gilbert, J. W. 1977. Jet venturi fume scrubbing. In P. N. Cheremisinoff and R. A. Young (Eds.), Air Pollution Control and Design Handbook. Part 2. New York: Marcel Dekker.
Richards, J. R. 1995. Control of Particulate Emissions (APTI Course 413). U.S. Environmental Protection Agency.
Richards, J. R. 1995. Control of Gaseous Emissions. (APTI Course 415). U.S. Environmental Protection Agency.
References
^ *US EPA Air Pollution Training Institute developed in collaboration with North Carolina State University, College of Engineering (NCSU)
Categories: Pollution control technologies | Air pollution control systems | Wet scrubbers | Liquid-phase contacting scrubbersHidden categories: Wikipedia articles needing context from October 2009 | All Wikipedia articles needing context | Wikipedia introduction cleanup from October 2009
