This invention relates to a method and apparatus for dehydrating sludge, and more particularly to an apparatus for continuously dehydrating metal hydroxide metal sludge.
Metal hydroxide sludges containing approximately 60-80% water, most of which is in the form of water of hydration, are produced as waste products in metal finishing processes. Typically, the waste metal hydroxide sludge is concentrated by a centrifuge, a vacuum filter, a pressure filter, or a filter press. The disposal of the concentrated metal hydroxide sludge is facilitated by the removal of water from the sludge to create a chemically more stable sludge and to reduce both the volume and weight of the sludge, thereby minimizing disposal costs.
Water is typically removed from metal hydroxide sludge in a batch process. A large volume of wet sludge is deposited into the drying chamber or oven in which the large mass of sludge is subjected to relatively small volumes of hot air, the air must be forced rapidly into surface contact with the sludge in order to adequately dry the sludge. Ideally, the air flow must be greater at the beginning of the batch drying process than at the end, gradually decreasing as the volume of water is removed from the sludge. As a practical matter, some intermediate constant air flow rate is utilized during the drying process. After the large volume of sludge is dried, material handling equipment, such as a forklift, is required to load and unload the drying oven.
If a constant air flow is applied to the batch of sludge, excessive drying toward the end of the cycle produces an increasing amount of dust. Accordingly, a dust removal system is required, such as a filter system or centrifuges.
Various types of drying apparatus incorporating elongated tubular chambers through which the treated material is moved by a spiral conveyer and through which heated air or hot gases are passed to dry the material are shown in the following U.S. patents:
______________________________________ 245,274 Byerly Aug. 9, 1881 676,165 Wacker Jun. 11, 1901 1,371,546 Bollmann Mar. 15, 1921 1,459,923 Nagel Jun. 26, 1923 1,478,347 Mitchell Dec. 18, 1923 1,538,385 Daman May 19, 1925 2,067,506 Silva Jan. 12, 1937 2,122,857 Carlson Jul. 5, 1938 3,347,533 Mauldin Oct. 17, 1967 3,678,596 Kubo Jul. 25, 1972 4,156,392 Bayeh May 29, 1979 4,176,465 Murray, et al. Dec. 4, 1979 ______________________________________
The Bylerly U.S. Pat. No. 245,174, discloses a feed hopper having a feed auger in combination with the dryer chamber.
However, none of the above patents discloses the specific process and apparatus of this invention for deydrating metal hydroxide sludges continuously, and particularly do not teach the utilization of a feed hopper for breaking up concentrated wet metal hydroxide sludge before it is introduced into the dehydrater chamber.