Results are given on cleaning diesel exhaust gases by means of a system containing ceramic filters, which show that high-temperature filtration provides effective cleaning.Much attention is being given to ecological cleanliness of diesel engines, as the exhausts from diesel engines contain soot, CO 2 , CO, NO x , SO x , hydrocarbons, aldehydes, acids, benzpyrene, and so on [1]. To reduce the ecological risks from diesel engines, various processes have been introduced: additives in the hydrocarbon fuel, liquid and plasma neutralization of exhaust components, catalytic aftercombustion, filtration, electrofiltration, and so on [2]. However, such cleaning systems cannot be used for maintaining backup diesels, which are usually installed mainly in underground rooms.It has been proposed to treat engine gases by high-temperature filtration with ceramic components developed by the Keramikfil'tr Company (patent RF No. 2164444).A ceramic filter element (CFE) is a close-packed bundle of tubes, whose ends are open on one side and closed on the other. The gases enter the open end, filter through the walls, and pass into the space between the tubes.These CFE tubes are fitted with membranes and are made from ceramic mass based on classified electrocorundum powders. The material also includes refractory bentonite clay, carboxymethylcellulose, and water. It is prepared in a mixer with Z-shaped blades and extruded in a vacuum press into tubes with the required outside and inside diameters, and is then dried and fired at about 1300°C. The total open porosity, no matter what the grain size of the electrocorundum, is ε = 0.38-0.42 m 2 /m 2 , which is close to theoretical close packing of spheres (α = 1 -ε).The CFE are used under the following conditions: gas temperature not more than 500°C, gas pressure not more than 1.0 MPa, and pH 1-12.The CFE may be chemically regenerated by alternating acid-alkali treatment; one cycle of alkali treatment lasts not more than 10-15 min at a temperature of not more than 80°C and an alkali concentration of not more than 0.08 mass %.We tested an experimental specimen of a filter containing CFE as developed by the Keramikfil'tr Company on a 6Ch12/14 diesel of nominal power 50 kW (exhaust output not more than 500 m 3 /h, exhaust gas temperature up to 500°C).The soot concentration (smoke) in the exhaust was determined by the methods described by the NAMI organization [3] and the NIIOGAZ Company [4], which before the apparatus containing the CFE constituted respectively 0.15 g/m 3 and 0.114-0.148 g/m 3 for a maximum permissible concentration of soot in air 0.115 mg/m 3 .

The filtering characteristics (air permeability, efficiency) of porous permeable ceramic materials with different microstructures are determined. The requirements on ceramic filter elements are formulated; specifications for a module-type plant with ceramic filter elements are prepared. The use of these elements for cleaning hot gases from dust, apart from the ecological effect, yield an economic effect manifested as additional energy produced due to recovery of waste gas heat.

The design is based on empirical formulas proposed for determining the bulk heat-transfer coefficient. Results are given on the height of the scrubber as indicated by various models: volume heat-transfer coefficient (empirical model), evaporation time given by an interval iteration method (iteration model), and without allowance for the time needed for the droplets to attain the suspension velocity (simplified model).A method has been given [1] for designing a direct-flow hollow spray scrubber involving complete evaporation of the irrigating liquid, which enables one to determine all the input and output parameters of the two-phase gas-liquid system in the apparatus.The second part deals with designing the geometrical parameters, particularly the height H. The simplest way of solving this is based on empirical formulas [2] proposed for the bulk heat-transfer coefficient K in kW/(m 3 ·K).In that case, the working volume V of the scrubber in m 3 is defined byin which Q is the thermal load (kW), whose calculation has been given in [1], and ∆t is the temperature difference in K. For the forward flow,in which t g ′ and t g ″ are the gas temperatures at the inlet and outlet in °C; while t w is the wet-bulk thermometer temperature in °C. This t g ′ is given, while t g ″ and t w are determined during the calculations [1]. Thus one determines V and defines the diameter of the apparatus D in m to derive quite simply the working height H in m.The literature has no clear-cut recommendations on gas speed in an evaporative scrubber, but a choice must be made in order to determine D, and the literature gives only the recommended ratio of the diameter and height H/D ≈ 2.5.More accurate calculation on the working height requires one to determine the time for complete evaporation of droplets of the irrigating liquid (water).

The effect of dust properties, parameters and composition of gases for cleaning on the choice of synthetic filter materials for bag filters with pulsed regeneration is considered. Particular attention is devoted to cleaning high-temperature moist gases containing corrosive components. Recommendations are proposed for calculating the temperature of the acid dew point of gases being cleaned. Comparative characteristics are provided for synthetic materials produced overseas and used in gas filtration.One of the most efficient methods for cleaning industrial gas discharges from dust is filtration through cloth barriers. Of the numerous items of equipment operating on this principle, recently the most extensively used is bag filters with pulsed regeneration of the filtering cloth surface by compressed air. These filters are characterized by a high degree of capture due to the use of needle-punched filter materials, servicing simplicity as a result of the absence of moving parts (apart from the dust discharge system), compactness and correspondingly small area occupied.The operating reliability and efficiency of bag filters depends to a considerable extent on physicomechanical properties of the dust being captured (dispersed composition, abrasiveness, adhesiveness, hygroscopicity, electric properties of dust particles; tendency of dust particles towards coalescence, etc.), and also the main parameters of the gas stream being cleaned (temperature, moisture content, chemical composition).A careful study of production processes that are accompanied with emission of harmful substances; analysis of the qualitative and quantitative characteristics of the medium for cleaning in a bag filter; and the correct choice of synthetic filter materials for bag filters are all necessary conditions for achieving highly efficient and prolonged operation of this equipment.Recently in domestic practice of dust capture the most widely used filter materials are produced by well-known firms: Dupont (USA), Webron (Great Britain), BVF (Germany). Main Dust PropertiesDispersed composition. This is an original parameter in designing filtration equipment, that commences with a choice of specific gas flow (ratio of the volume of gas being cleaned in a unit time to the filtration surface area), expressed numerically as a rule by m 3 /(m 2 ·min), which corresponds to the gas filtration rate. The specific gas load should not exceed an optimum value, with which a sufficiently effective degree of cleaning and a not very high hydraulic resistance for the filter are provided.

The paper discusses a hollow sprayer scrubber and cooler involving complete evaporation of the irrigating liquid. It is shown to be possible to use an empirical model to calculate the geometrical parameters. Technical characteristics are given of a standard series of scrubbers of SOI type with complete evaporation of irrigating liquid.Calculations have been performed [1, 2] on the evaporation time for a polydisperse flow of droplets (diameter of the large droplets d d , mass proportion not more than 10%, equal to 553 µm) in a hollow scrubber based on three mathematical models (empirical, iterative, and simplified), and values have been obtained for the necessary active height * (Table 1) in relation to the initial parameters of the evaporative cooling, gas temperature at the inlet to the apparatus 750°C, at the outlet 400°C, mean gas speed in apparatus 4.5 m/sec, and initial water content 0.35 kg/kg of dry gas.We consider the evaporative cooling in a standard scrubber (Fig. 1), in which there are mechanical sprayers of centrifugal type (nozzle diameter 4 mm) working at a pressure of 0.68 ± 0.01 MPa. For these devices at this pressure, the diameter of the large droplets constituted by mass not more than 10%, is 314 µm, i.e., almost half of that assumed in calculations in [1,2]. Use has been made in [1, 2] of calculation models, and the height of a scrubber has been determined required to provide complete evaporation, and the evaporation time.The calculations have been performed for the air-water system with the following initial parameters: gas temperature at the inlet 750°C, and that at the outlet 400°C; mean gas speed in apparatus 4.5 m/sec; initial water content 0.35 kg/kg of dry gases; and initial temperature of irrigating liquid (water) 20°C. Table 2 gives the results.Calculations from the iterative model (Fig. 2) show that as the size of the large droplets is reduced from 553 to 314 µm, the time needed for the droplets to attain the floating velocity is approximately 0.1 sec, which is much less than was obtained in [1, 2] (about 0.4 sec). In the standard apparatus, the smaller droplet diameter means that the evaporation is much more rapid.At the same time, the practical data were analyzed, ** which had been obtained on testing a plant for destruction of wastes by incineration, in which the hollow scrubber (Fig. 3) was installed before the sleeve filter.The water pressure ahead of the sprayers was up to 2.5 MPa, and the size of the mass-largest drops (10%) was approximately 151 µm.