Presses – With additional treatment of material – Separating materials
Patent
1988-06-03
1992-04-28
Hornsby, Harvey C.
Presses
With additional treatment of material
Separating materials
100112, 100121, 210386, 210391, B30B 900, B30B 920
Patent
active
051077574
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a press type dewatering method and apparatus for separating liquid and solid contents from various kinds of suspension and solid-liquid mixture containing various kinds of substances such as organic and inorganic substances, for example, industrial waste water, human waste, sewage sludge, raw materials for pulp, waste liquors, spent grains or the like.
BACKGROUND ART
Examples of machines for dewatering suspensions which contain substances whose particles are so fine that it is difficult to dewater them, such as sewage sludge, generally include various kinds of dehydrators such as vacuum dehydrators, centrifugal dehydrators, filter presses and belt presses. However, the dewatering performances of vacuum dehydrators, centrifugal dehydrators and the like are limited to a water content of about 80%, dehydrators for suspensions which are difficult to dewater there are now generally used filter presses and belt presses.
Belt presses are arranged such that about ten or more rolls are combined to stretch two filter, cloths having a mesh size of about 0.5 mm or less in such a manner that the filter cloths are able to travel, and a suspension which is passed between the filter cloths is pressed so as to be dewatered by means of a tensile force of the belts. However, such belt presses suffer from the problem that the filter cloths become clogged, thus involving troublesome maintenance.
In dehydration of suspensions which are difficult to dewater, it is general practice for improving the dewatering performance to add a polymeric flocculating agent or the like to a suspension, thereby flocculating particles therein and thus effecting dehydration. But still the water content after the dehydration is said to be generally limited to 70%.
In countries, particularly those which have limited land spaces, disposal of various kinds of sludge now becomes a problem, and there is a question as to how the use of reclaimed lands can be ensured in several years' time. For this reason, the disposal of sewage sludge is gradually being carried out more frequently by the volume reduction treatment in which the volume of sewage sludge is reduced by thermal disposal.
In the case of thermal disposal of sludge, the water content at which self-burning can take place, that is, at which sludge itself can burn without the need of an assisting fuel oil such as heavy oil, is from 65% to 70% for sewage sludge, although such water content depends on the kinds of sludge. However, since existing dehydrators do not have the capacity for dewatering sewage sludge to a water content at which it is able to self-burn, the fact is that sludge is subjected to thermal disposal with an assist from an oil such as heavy oil (about 100 l per ton of sludge), which means that disposal of sludge involves high costs. Because of the desire to conserve energy, those skilled in the art set the goal at incinerating sludge without using any oil, and various kinds of sludge incinerating systems have already been developed for the purpose of saving and creating energy. Principal examples of such systems include those wherein pulverized coal is added to sludge in order to obtain a higher heating value, those which utilize waste tires, and those which involve thickening by evaporation, drying, high-concentration dehydration, etc., and the sludge drying system has gradually become the most commonly used of the sludge incinerating systems. The sludge drying system is arranged such that a waste heat boiler is installed to dry sludge by means of steam so that the sludge becomes able to self-burn, but the system has the disadvantage that the installation cost is gigantic. Therefore, the appearance of a dehydrator which has a simple system arrangement and is still able to perform highly efficient dehydration is eagerly awaited, and dehydrators obtained by variously improving the above-described belt press which is the simplest system have already appeared.
One example of the above-described conventional dewatering apparatus is sc
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Asai Kiyoshi
Hirose Tetsuhisa
Ishikawa Ryuichi
Ohshita Takahiro
Ebara Corporation
Gerrity Stephen F.
Hornsby Harvey C.
Ibiden Co. Ltd.
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