Distillation: processes – thermolytic – Feed other than coal – oil shale or wood
Utility Patent
1998-06-15
2001-01-02
Dunn, Tom (Department: 1754)
Distillation: processes, thermolytic
Feed other than coal, oil shale or wood
C201S015000, C201S027000, C201S030000, C201S037000, C202S096000, C202S099000, C048S1970FM, C422S184100, C423SDIG001, C588S253000
Utility Patent
active
06168688
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a method and plant for treating by thermolysis solid waste products whose disposal is harmful to the environment.
2. Description of the Prior Art
Document EP-A-0 610 120 discloses a plant facility for treating solid waste products whose disposal is harmful to the environment including a dehydration area into which the solid products are fed, a thermolysis area downstream of the dehydration area, an outlet area in which the solid residues are cooled and a pumping station communicating via an extraction line with the thermolysis area to maintain it at a reduced pressure and to aspirate thermolysis gases from it.
The pump station communicate via a combustible gas feed line with a boiler for burning the thermolysis gases which are maintained at a temperature greater than the temperature of condensation of tars that can form in the gaseous state during thermolysis, before they are used as fuel in the boiler. The thermolysis gases are exploited directly to generate thermal energy that is transformed in the plant or fed to a turbine that converts it to electrical energy or used for any other function, possibly external to the plant facility.
The boiler can also use the fuel (coal) contained in the solid residues.
The flue gases from the boiler are used to heat the dehydration area.
To enable thermolytic transformation in the total absence of free oxygen the dehydration, thermolysis and cooling areas consist of chambers isolated from each other in a substantially airtight manner.
The dehydration and thermolysis chambers are provided with heating elements such as catalytic radiator panels or flame burners using the thermolysis gases and/or (low price) commercially available combustible gases.
In the case of burners the enclosures of the aforementioned chambers are heated by radiation from the inside wall of the chambers heated by the burner flames. In this case heating is also assured by convection of the gases in the charge of products to be treated which is assured by expansion of the gases generated in the corresponding chamber.
The catalytic radiant panels are fed with pure oxygen or with air and with thermolysis gases resulting from thermolytic decomposition. In this case the carbon dioxide and the steam generated by oxidation of the thermolysis gases in the catalytic radiant panels can contribute to heating by convection and radiation.
As mentioned above, the flue gases from the boiler can also be used to heat the aforementioned chambers.
Thus the temperature of the thermolysis chamber is maintained at around 600° C., for example, and that of the dehydration chamber is maintained at a lower temperature above 100° C., for example around 120° C.
The solution described in document EP-A-0 610 120 is satisfactory overall. However, the use of burners in the dehydration and thermolysis chamber generates hot spots exposing the chambers to non-negligible mechanical stresses. These mechanical stresses can give rise to sealing problems which can be particularly troublesome because the penetration of oxygen into the thermolysis chamber can cause an explosion in the presence of hydrogen in the thermolysis chamber.
This risk of explosion is also present when catalytic radiator panels are used because they employ oxygen as a combustion-supporting gas.
Moreover, heating the chambers consumes external energy when commercially available combustible gases are used.
Document U.S. Pat. No. 3,525,673 describes another method of treating organic waste and the corresponding plant facility. In this method the waste is reduced to basic carbon-containing products by superheated steam at a low positive pressure in a closed circuit. The steam recovered after passing through the waste is condensed and the uncondensed gases are separated from the water and the substances dissolved therein.
BRIEF SUMMARY OF THE INVENTION
This method is limited to the treatment of organic waste and consumes large quantities of water.
The present invention aims to alleviate these drawbacks.
An underlying objective of the present invention is a method of treating solid waste products, whose disposal is harmful to the environment, that is self-sufficient from the energy point of view.
To this end the present invention proposes a method of treating solid waste products, whose disposal is harmful to the environment, including a step of thermolysis of the solid products in a thermolysis area, wherein:
the gases are aspirated from the thermolysis area;
at least a portion of the aspirated gases is cooled to a temperature less than approximately 80° C.;
the condensed products from cooling the uncondensed gases are separated from this cooling;
a portion of the aspirated gases is heated by combustion of at least a part of the uncondensed gases; and
the heated portion of the gases is recycled by feeding it back into the thermolysis area.
The invention also teaches replacing the catalytic radiant panels or burners with direct injection of a flow of hot gases including recycled thermolysis gases into the thermolysis area.
This prevents the creation of hot spots and any possibility of an explosive reaction between oxygen and hydrogen.
In situ recycling of the thermolysis gases also renders the treatment method of the present invention self-sufficient.
Thermolysis effected in this way, by forced circulation of a flow of hot gas resulting from feeding the flow into the thermolysis area, direct contact with the charge and then aspiration of the gases from the thermolysis area, is found to be particularly regular but most importantly significantly faster than thermolysis carried out in accordance with the teaching of document EP-A-0 610 120.
Moreover, a maximum of solid products treated by the method of the present invention is converted into energy. In particular, the tars obtained on cooling can be mixed with the fuel (coal) from the solid residues from the thermolysis area, for example, to constitute a fuel for subsequent exploitation.
Cooling at least some of the gases from the thermolysis area facilitates exploitation of the thermolysis products. Converting some of the gases from the thermolysis area into condensed products minimizes the volume of the means for storing the products (tars, etc). Furthermore, the uncondensed gases are advantageously reused to heat the flow of gas to be fed into the thermolysis area.
Finally, this cooling protects the treatment plant facility and in particular the pump utilized in the process.
To improve further the efficiency of thermal transfer of this thermolysis process, in a relatively simple manner, the heated portion of the gas is advantageously injected in the immediate proximity of a static charge of solid products to be treated.
In one preferred embodiment the portion of the gas to be heated is a second part of the uncondensed gases obtained by cooling.
Thus a fraction of the uncondensed thermolysis gases is burned to heat a second part of the uncondensed gases which are recycled and returned to the thermolysis area to be enriched with thermolysis gases and in particular with hydrogen and hydrocarbons (methane, ethane, ethylene, etc).
In another embodiment, a first fraction of the aspirated gases is heated to approximately 60° C. to approximately 80° C. and a second fraction of the aspirated gases is heated to approximately 230° C. to approximately 330° C., at least some of the uncondensed gases from the first fraction are burned, the uncondensed gases from the second fraction are heated by means of the gases resulting from this combustion, the heated second fraction of the gases constituting the heated gas portion, and the condensed products obtained by cooling the first and second fractions are recovered.
In this embodiment, the gas fraction to be heated and recirculated into the thermolysis area in the form of a flow of hot gas is maintained at a higher temperature than the fraction to be burned. The fraction to be heated therefore requires less heating before it is fed back into the thermolysis area.
In this case
Clot Guy
Roure Jean
Dunn Tom
Societe Francaise De Thermolyse
Vanophem Meehan & Vanophem P.C.
Vanoy Timothy C
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