This system is designed as a final washer to further clean primarily cleaned and cooled gas to the degree necessary for use in gas engines. The principle of this system consists in creating in a vertical tower a very fine spray or mist of water by means of an injector of the Korting type, in which water under pressure is atomized by means of compressed blastfurnace gas, the spray being produced by the expansion of the compressed gas. An intimate mixture of the spray so formed, with the dirty gas entering the apparatus, is obtained by the arrangement of the apparatus.

"A separator is provided in connection with this apparatus, which consists substantially of a cone arranged in the lower part of the tower in such a way as to leave between the base of the cone and the walls of the tower a very narrow passage, through which the gases are forced over the surface of a water seal, where the dust and water vapor are deposited.

"In the accompanying drawing, Fig. 202, A is the vertical tower, the lower end of which terminates a short distance above the surface of the water seal D. Within the lower end of the tower is arranged a conical deflector, C, and near the top of the tower is the gas inlet, B. The lower section of the tower A is surrounded by a casing which is open at the bottom and extends beneath the surface of the water in the seal. A gas outlet, E, is provided in connection with the outer casing. The Korting injector is located at F and the feed water for same is supplied through the pipe G. The pressure is supplied by withdrawing a portion of the purified gas from the outlet pipe E and forcing this by the compressor K through the pipe H into the injector simultaneously with a stream of water.

Final Dry Cleaning

(Some of the following systems can also be applied to primary cleaning).

Halberger-Beth Gas-Cleaning System

The principle of the Halberger-Beth system, shown in Fig. 203, is based primarily on filtering the gas through canvas bags. The gas coming from the blast-furnace passes through the usual dust catchers and gas mains to a cooling tower, where the temperature of the gas is reduced to about 175° Fahr. The cooling tower is arranged so that the necessary amount of cooling can be accomplished either by air or by direct contact with water, depending on the temperature of the gas entering the cooler, which temperature is naturally variable, in accordance with blast-furnace conditions.

"From the cooler, the raw gas, by means of the suction of a fan placed beyond the filters, or without a fan when the pressure of the gas issuing from the furnace is sufficient, passes into and through the canvas filtering bags, depositing its impurities on the surface of the bags. These canvas filters are contained in a series of double compartments, each usually holding twelve canvas bags in rows of three by four. Each bag is about 8 in. in diameter by 9 ft. 9 in. long, and is equipped with a ring at each 18 in. of its length to prevent entire collapse of the bag when cleaning. The bags are fastened into a stationary header at the bottom, this bottom end being open, while the top is closed by a steel plate. Each bag is connected with a shaking mechanism located outside and above the filter compartment, and at regular intervals, usually about every four minutes, these bags are automatically shaken, a compartment at a time, for a period of from fifteen to twenty seconds. By means of a butterfly valve, the uncleaned gas is shut off from the compartment while the shaking is in progress, and cleaned gas, superheated to the proper temperature of about 1750 Fahr., is forced under pressure into the compartment. This causes a partial collapse of the canvas bags, which, in conjunction with the simultaneous shaking, allows the dust to fall from the canvas. The separated dust drops into a hopper beneath the sacks, whence it is transferred by means of a spiral conveyor to a bin, from which it is loaded into cars. At the end of the cleaning period the butterfly valve automatically returns to its original position and filtering commences again.

Fig. 202. Sepulchre gas washer.

Fig. 203. Halberger-Beth gas-cleaning system.

"It is quite necessary to keep the temperature of the gas at about 175° Fahr., as if much higher than this there is danger of scorching the bag, while if lower the water vapor in the gas is deposited on the canvas and prevents proper filtration. In case the gas becomes cooled below 175° Fahr. in the cooling tower it is superheated by means of steam or by waste heat from the hot-blast stoves to about this temperature before entering the filtering bags. After leaving the canvas bags, the gas requires no further cleaning for gas engines and is cooled down to the proper temperature in cooling towers of various designs.

"The degree of cleanliness of the gas is indicated by the clearness of the effluent water from these towers and no settling basins are required. Consequently, this water can be used over and over again, which is a material item in districts where water is scarce. A further advantage lies in the non-pollution of streams, the laws relating to which are very strict in certain districts.

"This system utilizes the basic principle employed in the "bag house" system, which has been used for the last twenty years in connection with recovering zinc dust from the gas issuing from zinc-oxide furnaces and collecting dust from lead smelters.