System REITHER A Patented Venturi Scrubber Demonstrated efficiencies with fine particles, aerosols, mists and gases. ALTECH Technology Systems Inc. 12 Banigan Drive, Toronto, Ontario, Canada M4H 1E9 Tel: (416) 467-5555 Fax: (416) 467-9824 www.altech-group.com
Introduction Of all the air pollution abatement technologies, wet scrubbing systems remain the most versatile and cost efficient. New, patented advances in venturi scrubbing of air particulate, aerosols and gases achieves removal efficiencies greater than 99% for particulate and aerosols down to 3µm. Sub-micron particles present a special concern because they cause irritation of the breathing passages and may, more importantly, include toxic and/or odorous compounds. Benefits of Venturi Scrubbing Venturi scrubbers are one of the most common forms of wet scrubbing, extensively used in industry. Venturi scrubbers are particularly effective at removing particles from 1 µm to 100 µm at very high efficiencies. Because of the low mass of these small particles, inertial separation is not satisfactory. At the sub micron size, the principle of the venturi scrubber is to force the contact of the particle with fine water droplets. This is done by using a constricting orifice, creating a venturi throat, that forces the intimate contact between the water and the particulate or aerosol. There are various designs of venturi scrubbers available. System REITHER TM, a new generation of venturi scrubber, is profiled in this poster presentation. Some of the advantages of this new venturi scrubber design include; Simple and compact design, able to fit in existing flue gas ducting; High removal efficiencies for sub-micron dusts and aerosols; Flexibility to handle any mass flow rate especially at smaller flows; High and constant reliability; Easy to control by simply using pressure drop; Potential to absorb gaseous contaminants; Can handle corrosive streams through corrosion resistant materials; Modular design capability and can be easily expanded. Venturi scrubbers are not without disadvantages. Performance and removal efficiencies are difficult to control when mass loading and variations in flow rate are experienced. The basis for maintaining removal efficiencies is by controlling the pressure drop at a set rate. The key to reliable performance, then is the ability to vary the throat size to maintain a constant pressure drop as the gas flow rate fluctuates. This ensures that the removal efficiencies stay constant as the flow varies. System REITHER has this important feature.
Design Principles New advances in throat design has led to significant improvements in removal efficiencies, the ability to respond to variability in flow, and the ability to remove very small particles, aerosols and some gases. The principle of the design is illustrated in Figure 1 where the gas stream flows through the duct, passes by the water spray heads, and is forced by two outside cylinders into the middle region. By adding a third cylindrical displacer on a lifting rod, a double split is formed creating two venturi throats. The vertical movement of the displacer can vary the split to the optimum width for maximum efficiency even during variations in flow. There are several important innovations with the System REITHER approach. The water or scrubbing solution is sprayed across the air stream at right angles as the flow bends around the first constriction and is forced to the middle. This will maximize contact with the fine particulate. The scrubbing solution is sprayed at low pressure but, due to the high sheer effect of the gas stream in the throat - velocities between 50 and 150 m/sec. - the liquid aerosols are further atomized into very fine drops or mists. This is the key to the performance of this design. The high gas acceleration in the throat, and the high relative velocity between particles and scrubbing aerosols provides for excellent opportunity for contact and, therefore, separation efficiencies with this venturi scrubber. Figure 1. Venturi throat design
Performance Characteristics Figures 2, 3 and 4 show that the efficiency improved with decreasing split width and with increasing throat velocity. The scrubbing water volumes remained constant. Particle size (microns) Figure 2: Collection efficiency curves for the gas flow rate of 45 m 3 /h and a water flow of 200 l/h at various split widths. Collection Efficiency Collection Efficiency Particle size (microns) Figure 3: Collection efficiency curves for the gas flow rate of 100 m 3 /h and a water flow of 200 l/h at varying split width.
Particle size (microns) Figure 4: Comparison of collection efficiency at different water loadings at split width of 1.5 mm; the gas flow rate is 100 m 3 /h The volumes of scrubbing water used has an important influence on the collection efficiency. The maximum scrubbing water volumes is 200 l/h with nozzle pressure of 4 bar. Figure 4 demonstrates the impact of water volume on the same split width and Figure 5 shows the effect of different split widths. Collection Efficiency Collection Efficiency Particle size (microns) Figure 5: Comparison of collection efficiency at same water loadings and split widths of 1.5 to 3.3 mm; the gas flow rate is 100 m 3 /h
Collection Efficiency Particle size (microns) Figure 6: Comparison of collection efficiency at different water loadings and split widths of 1.5 to 2.0 mm; the gas flow rate is 100 m 3 /h It is evident that the efficiency of the particle removal is most effected by water loading and split width. The value 2 l/m 3 is optimum for the water loadings but the split width which intern is reflected in the pressure drop across the venturi scrubber is to be optimized for each system.
System REITHER Venturi Scrubber design variations
Typical Applications for Venturi Scrubbing Chemical manufacturing Metal smelting Metal finishing and plating Electronic equipment manufacturing Iron and steel Drum filling operations Pharmaceutical manufacturing Fertilizer production Pulp and paper Textiles Incineration/boiler flue gas Petrochemical refining Food and beverage Paint and coatings Drying systems
Continuing Research Research continues with the system including the optimization of collection efficiency and performance results. For example, the effect of humidification and condensation on sub micron particles is showing that sub micron particles lower that 0.1 µm can be separated with high efficiency. Aerosol growth techniques can be incorporated with System REITHER TM to achieve efficiencies at 0.1-0.5 µm of 99% with less pressure drop, resulting in energy savings. As well, testing has begun on gases such as SO 2 demonstrating a removal efficiency of 99%. The adsorption of gaseous contaminants is based on the solubility of the gas and the scrubbing liquid. However, the intimate contact of the gas and scrubbing medium can result in surprising efficiencies. ASK US FOR MORE INFORMATION....... ALTECH Technology Systems Inc. 12 Banigan Drive, Toronto, Ontario Canada M4H 1E9 Phone: (416) 467-5555 Fax: (416) 467-9824 Website: www.altech-group.com President Mr. Alex R. Keen