Sleeve filters in explosion-protection use

Abstract

Designs and characteristics are given for sleeve filters with explosion-protected design which have been developed by the NIIOGAZ.Various technologies give rise to dusty gas flows containing suspended explosive particles: metal melting, making organic products, and many chemical and petrochemical processes.Sleeve filters have become used as dust traps in recent years in connection with tightened specifications for performance in cleaning gases.For an explosion to occur, one needs a certain concentration of the explosive dust exceeding the lower flame propagation concentration (LFPC) [1]. When the sleeve filter is used as a dust trap, it is not possible to produce a dust content below the LFPC in the volume of the apparatus because on regenerating the filter surface the dust concentration varies widely.In addition to a dust concentration exceeding the LFPC, explosion requires an ignition source of adequate temperature and power, and also an appropriate oxygen concentration. However, it is very expensive to prevent explosion in sleeve filters when large gas volumes are to be treated. Therefore, to prevent explosion in a sleeve filter, one uses various designs: special valves, protective membranes, and so on.Safety membranes are most widely used at present in explosion-protection devices, which form an especially weakened part of the body of the sleeve filter with an exactly calculated failure pressure.Calculations on safety membranes involve determining the necessary area of the discharge hole, as well as the thickness and other geometrical parameters of the membrane on the basis of rupture at a given pressure.One calculates the area of the discharge hole, i.e., the membrane area, in accordance with RTM 6-28-009-90 [2], according to which the most hazardous situation is when the pressure in the body of the sleeve filter increases at the maximum rate.The amount of dust-gas mixture G a (kg/sec) formed in an accident can be related to the corresponding pressure rise rate by where M is the molecular mass of the gas in the apparatus in kg/mol (for suspensions in air, it is taken that M = 0.029, as for air); V is the internal volume of the sleeve filter body, including the volume occupied by the sleeves, in m 3 ; R is the universal gas constant, which is 8.314 J/(mol·K); T is the absolute temperature of the gas within the filter in K; and (dp/dt) max is the maximum rate of pressure rise in an explosion in time t (sec), MPa/sec. When one calculates the area of the discharge hole, one incorporates the condition for compensation of the discharge of the dust-gas mixture G a through the hole after the membrane ruptures, i.e., G ≥ G a , in which G is the flow rate per second through the hole, kg/sec.

Modern tendencies in the development of dust collecting theory and practice

“…Filter structures have been created in explosive protection applications [10], cartridge (pocket) filters with a system of pulsed regeneration [11,12]. A considerable amount of work is carried out in selecting new filter materials.…”