Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1991-10-11
1994-03-15
Schwadron, Martin P.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34180, 34183, F26B 2106
Patent
active
052936961
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method and a device for the dehydration of sewage sludge, in particular the sludge which accumulates in municipal sewage plants.
BACKGROUND OF THE INVENTION
The fresh or decayed sludge which accumulates in large volumes in such sewage plants consists of less than 10% solid matter. To be utilized or eliminate, this sludge must first be dehydrated. Through mechanical dehydration methods, such as suction cell filtering, sludge is reduced to a consistency of about 30% solid matter; thus it is still composed mainly of water.
SUMMARY OF THE INVENTION
What is required is an improved apparatus for dehydrating sewage sludge.
The process which has been developed to meet the need outlined above is as follows: radiant heat and hot air are produced simultaneously through the combustion of heating oil or gas. Then the radiant heat acts on the sewage sludge while it is being conveyed mechanically. At the same time, the sewage sludge undergoes an indirect heat exchange with the hot air.
According to another aspect of the invention there is provided an apparatus for dehydration of sewage sludge, which is comprised of a dehydration chamber having an intake opening and a discharge opening. Mechanical conveyance means is used to convey sewage sludge from the intake opening to the discharge opening. A plurality of radiant heaters with burners disposed in side by side relation, each of the radiant heaters having heat radiation surfaces disposed within the dehydration chamber which radiate heat at temperatures in excess of 850 degrees centigrade, whereby sewage sludge is heated to convert moisture in the sewage sludge to steam and most harmful organic compounds contained in the sewage sludge are broken down. A condenser adjoining the dehydration chamber, means being provided to draw steam from the dehydration chamber into the condenser, whereby the steam is condensed to form hot water and gases. A gas vent pipe diverting gases from the condenser to one of the burners of the radiant heaters, whereby the gases are heated to temperatures in excess of 1700 degrees centigrade thereby breaking down harmful dioxins contained in the gases.
In the thermal sludge dehydration process described polluted air is drawn through the incineration zone so that the pollutants can be burned and wet sewage sludge, whether free or decayed, is reduced to a solid-matter consistency of more than 95%. Further advantages in this new process and device can be seen from the following description.
The process which has been developed to meet the need outlined above is as follows: radiant heat and hot air are produced simultaneously through the combustion of heating oil or gas. Then the radiant heat acts on the sewage sludge while it is being conveyed mechanically. At the same time, the sewage sludge undergoes an indirect heat exchange with the hot air which has been generated. The vapours produced from the sludge are then suctioned off from the space above the sludge and are condensed. As a result of the effect of heat radiation and the simultaneous transfer of heat from the hot air to the wet sewage sludge, considerable dehydration is already taking place, e.g. from less then 10% solid content to between 50 and 90%. In the process, a considerable volume of steam is produced. The volatile organic pollutants, such as hydrocarbons and dioxins, given off by the sludge as it is being mechanically moved, are cracked or broken down due to the influence of heat radiation during the steam phase. The products of cracking or disintegration are on the whole harmless and therefore--so long as they condense with the vapours--do not pollute the condensate. Disintegration of the sludge through oxidation is not possible, the steam thus generated being almost completely free of oxygen, so that the sludge does not come into contact with oxygen.
In the recommended method of carrying out the process, the sludge which has been partially dried by means of radiant heat in the first stage undergoes a second, and possibly further, drying stages, by mean
REFERENCES:
patent: 3800865 (1974-04-01), Onarheim et al.
patent: 3997406 (1976-12-01), Arvanitakis
patent: 4156392 (1979-05-01), Bayeh
patent: 4176465 (1979-12-01), Murray et al.
patent: 4685220 (1987-08-01), Meenan et al.
patent: 4756092 (1988-07-01), Anderson
Schmidt Gerhard
Schmidt Heinz
Axbridge Holdings Ltd.
Lee Kevin L.
Schwadron Martin P.
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