RECENT DEVELOPMENTS OF THE COTTRELL ELECTRICAL PRECIPITATION PROCESSES IN CONNECTION WITH FUEL TECHNOLOGY IN JAPAN

In the first portion of the paper, the physical natures of suspended particles in gases or of the disperse system, the so-called "Aerosol, " as well as a brief outline of the electrical precipitation processes are set forth; and then various fields of application of the processes and the percentages of elimination or collection of dust and fume, i.e., the efficiencies of precipitation for various kinds of gases to be treated, are described and tabulated. Furthermore, the author has described two examples of the actual operation of the Cottrell plants other than those relating to fuel technology, -one pertaining to the scientific treatment of Cottrell-dust at he Asio Copper Smelter of the Furukawa Mining Company, which has resulted in a wonderful gain and profit from the collected metallurgical dust, formerly not only thrown away in vain but which caused severe troubles due to smoke-nuisance; the other the precipitation of cement dust escaping from rotary kilns at the Osaka Ceramic and Cement Company, Osaka City, where an enormous tonnage of semi-calcined cement dust is being collected every day, running from about 250 to 300 tons per day. In regard to the application of the processes in the field of fuel technology, the author describes the following in good detail : - No.1. The collection of escaping powdered coal ashes from a pulverized coal fired steam-power generating plant; No.2. The cleaning of iron blast-furnace gases for the purpose of using the cleaned gases; (a) for boiler and hot-stove firing, and (b) for gas-engine driving. No.3. Detarring of carbonized or gasified combustible gases. No.4. The recovery of concentrated sulphuric acid from sludge acid waste in oil refining industries. In No.1, showing the micro-photographs of the pulverized coal ashes collected by the Cottrell processes and their sizing test results, the author has theoretically elucidated that, owing to the extraordinary fineness of the pulverized coal-ashes, the dimension being of an order of 10^<-3> cm. in diameter, the mechanical means usually adopted, such as the gravitational or centrifugal methods, i. e., uses of the expanded chambers or cyclones, cannot meet the requirements of getting rid of the dust nuisance which causes complaints to be made from the inhabitants in the vicinity of the plant, by satisfactorily eliminating the dust-discharge from the stack. He has also given an outline of the Cottrell plant at the Oura pulverized coal steam power plant, belonging to the Miike Dye-stuff Factory of the Mitsui Kozan K.K., where the exhaust steam from a 9,000Kw. back-pressure steam turbine, driving a 11,250KVA generator is utilized as process-steam for various chemical departments of the works. In No.2, the author has shown the constructional features and some novel devices used for the primary and the secondary precipitators built and put into operation at the Kamaishi Iron & Steel Works. The primary Cottrell has a capacity to clean the whole gases liberated from the two blast-furnaces, the maximum output of pig iron of which runs to about 750 tons per 24 hours, and consists of four independent compartments, each having an ample capacity to clean the raw blast-furnace gases amounting to 42,500cbm. per hour at an average temperature of 75℃., minimizing the dust from about 1 to 1.5gms. per cbm. to less than 0.1gm. per cbm., the cleaned gases being burnt under steam-boilers and hot-stoves, while the secondary is a twin-type precipitator cleaning the primarily cleaned gases of 17,000cbm. per hr. at an average temperature of 25℃., i.e., an amount of gas required for driving two 2,820 H.P. Demag gas-engine blowers under fully loaded conditions, the dust content in the secondary cleaned gases being less than 0.01gm. He also relates in full the actual operating results of the above plants, such as (a) the degree of cleanliness of the treated gases, which shows much higher figures than those of the sim ilar installations in the United States of America and Europe, (b) the gains in potassium chlorides of about 95% purity from the primary Cottrell precipitates by lixiviating the same, (c) the saving of a considerable amount of boiler fuel due to the rise of combustibility of the gases by the effective elimination of dust, (d) the results of firing cleaned gases under power plant boilers, the amount of coal replaced by the blast-furnace gases being clearly shown, (e) the distribution of the blast-furnace gases consumed at the works, &c., &c. Finally, based upon actual operating data at the Kamaishi Works, he has concluded that it is quite possible, in general, that the whole electrical power demanded for full plant operation at any iron and steel works can be generated from their own blast-furnace gases, provided that the means of generating power of reasonable high effciency combined with a rationalized method of cleaning the blast-furnace gases, such as the electrical precipitation processes, are employed; that is to say, the employment of the Cottrell processes for cleaning the blast-furnace gases would surely play a part in the rationalization of the iron and steel industry. In this paragraph, an outline in brief is given of the primary Cottrell precipitator installed and put into operation in the spring of this year at the Imperial Iron and Steel Works, Yawata. In No.3, the author defines the advantages of using the Cottrell processes for detarring combustible gases, such as carbonization gases, water gases, blue or carburetted, producer gases, low-temperature carbonization gases, &c., and refers to the installation cost of the Cottrell plants. In No.4, brief schemes relating to the Cottrell processes as applied to a sulphuric acid recovering plant for oil refineries and installation costs of the plant are described. More than a dozen illustrations and twenty-six tables showing Cottrell installations and some operating data accompany the paper, and t he whole operating outcome is described in comparative detail.