OCR Text |
Show The quench cools the hot combustion gas to full saturation by direct contact with water. If the quench does not fully saturate the gas, then scrubbing liquid will be evaporated and possibly re-entrain previously captured particulate or dissolved solids. Although the quench will remove much of the larger particulate and some of the soluble acid gas, the majority of the scrubbing takes place in the scrubber section. The liquid separator removes entrained liquid from the gas stream. Any liquid which is not removed and allowed to carry through to the stack may be collected in the emissions sampling equipment. In the sampling equipment, the suspended and dissolved solids contained in the liquid will be reported as particulate emissions. For this reason, high efficiency chevron mist eliminators are normally chosen for the liquid removal. Typical Emission Results Particulate matter emissions from a free-jet scrubber are related to the particulate characteristics (size distribution, wettability, etc.), correction factors (for gas moisture, temperature, 02, CO2) and scrubber energy input. When compared with conventional wet scrubbers, free-jet scrubbers are less sensitive to increases in particulate matter quantity. In general, outlet particulate matter emissions decrease with: 1) Increasing particulate size 2) Favorable correction factors 3) Increasing scrubber energy input For design purposes and energy estimates, combustion processes can be grouped into categories based on the similarity of particulate matter. Experience has show that these processes can be divided into four (4) groups, listed below in order of increasing difficulty: 1) Sludges and contaminated soils 2) Solids and liquids (with low total dissolved solid (IDS)) 3) Aqueous liquids with high IDS 4) Processes that generate metal chloride particulate matter Within these groupings, particulate matter emissions are strongly influenced by scrubber energy input. Figure 8 indicates the general relationship between average particulate matter emissions and scrubber energy input for the Tandem Nozzle scrubber. Energy input for the Tandem Nozzle scrubber is expressed as gas side static pressure drop, while energy input for the Steam Ejector scrubber would be expressed as the ratio of steam mass flow to wet gas mass flow. Unusual applications may require a demonstration test. This can be accomplished either at the user site or at the John Zink International Research Center. At the user site a slip stream of the process off-gas is taken through a portable skid-mounted scrubber which is transported to the user site via motor freight. At the International Research Center, various combinations of combustion equipment are assembled to model the user's process and the off-gas is taken to a dedicated free-jet scrubber. 7 |