Performance calculation for inertial-type gas cleaners

Abstract

Working formulas are given for the diameters of suspended particles trapped with 0.5 efficiency for dry centrifugal dust traps, wet dust traps (cyclones with wet film, scrubbers), and high-speed mist traps.The particle deposition performance in any dust trap can be represented as a function of dimensionless parameters or criteria [1, 2], each of which characterizes a corresponding deposition mechanism, together with the Re number, which defines the hydrodynamic conditions. Performance calculations for a particular apparatus should be done on the basis of the most important mechanisms while excluding the minor ones.That approach greatly simplifies methods of calculating gas cleaning plant. If the inertial mechanism predominates, the main effect on the performance comes from the Stokes number, whose formalized expression iswhere d p is the diameter of the suspended particles (droplets) in µm; ρ p is their density in kg/m 3 ; v is the gas flow speed in the active section in m/sec; µ is the dynamic viscosity of the gas in Pa·sec; and l is a linear parameter characterizing the deposition surface in m. The particular case of the inertial mechanism is centrifugal deposition. Then formula (1) can be put aswhere D is the diameter of the apparatus in m. The centrifugal mechanism is predominant for most designs of dust and mist traps that are assigned on the generally accepted classification as gas-cleaning equipments [3] in various groups: dry, centrifugal, and inertial dust traps; virtually all types of wet dust trap (scrubbers); and high-speed fibrous filter mist traps.The performance of a dust or mist trap with a predominant inertia mechanism may be considered on the criterial dependence η = ƒ(Stk, Re).The technical literature gives several such formulas, mainly of theoretical character. For example, there are the equations for the performance in the deposition of a single drop in a potential (turbulent) flow mode in a gas [4,5] or on a