Furnaces – Process – Incinerating refuse
Patent
1994-09-12
1996-07-02
Bennett, Henry A.
Furnaces
Process
Incinerating refuse
110238, 110260, F23G 700
Patent
active
055311695
DESCRIPTION:
BRIEF SUMMARY
The present invention relates generally to a method and apparatus for treating liquid waste material by combustion. More particularly, the present invention relates to a method for treating contaminated acid, especially contaminated sulfuric acid, by the application of heat to thermally and oxidatively dissociate the acid.
The production of waste by-product materials is a common problem with many industrial processes. For example contaminated or spent acid is produced in the course of a number of industrial processes. Particular mention may be made of contaminated sulfuric acid which is produced in large quantities during the manufacture of methyl methacrylate by the so-called ACH process.
The sulfuric acid which is generated during the production of methyl methacrylate by the ACH process is contaminated with water, ammonium sulphate, ammonium bisulfate and various organic species. The treatment of such waste sulfuric acid by combustion has been described in various patents, especially when the furnace is part of a sulfuric acid recovery facility.
In one such sulfuric acid recovery facility, the contaminated sulfuric acid is introduced into a furnace along with fuel. The fuel/air mixture is combusted to generate the necessary heat to both vaporize the contaminated sulfuric acid and dissociate the acid and its associated contaminants to form water, carbon dioxide and sulfur dioxide. These gaseous combustion products, together with the nitrogen contained in the air, exit the furnace and are passed firstly through a waste heat boiler to recover waste heat and then through a gas cleaning unit to remove water. Following water removal, the gas stream containing the sulphur dioxide is passed through a catalytic converter where the sulphur dioxide is reacted with oxygen to produce sulphur trioxide. The resulting product is then passed through an absorption tower in which the sulphur trioxide is reacted with water to produce sulfuric acid and/or oleum by the contact process.
However, the use of air to support the combustion process carries with it certain problems. The inert gases (predominantly nitrogen) contained in air contribute significantly to the heat load, since they must also be heated to the appropriate temperature in the combustion process. In effect, a significant proportion of the heat generated in the combustion of the fuel is wasted by having to heat up the inerts contained in the air. In consequence, air burners are significantly less thermally efficient. Furthermore, where the furnace is part of a unit dedicated to sulfuric acid recovery (hereinafter SAR), the inerts in the air dilute the concentration of sulfur dioxide in the converter (where sulphur dioxide is reacted with oxygen to form sulfur trioxide) thereby limiting the conversion dioxide to sulphur trioxide. The inerts also reduce the residence time of the reactants in the converter, for a given throughput rate, making it necessary to use large volumes of catalyst to implement the desired reaction. A further problem with SAR plants in which the furnace utilizes air to support the combustion is that the processing rate of the furnace is less than the processing rate of the gas cleaning and the converter units. Moreover, the heat generated within the furnace may not effectively vaporize and dissociate sufficient sulfuric acid to produce an adequate concentration of sulphur dioxide for effective downstream treatment. In such circumstances, additional sulfur may need to be supplied to the furnace and combusted in order to generate additional sulphur dioxide. This contributes significantly to the cost of the SAR treatment.
In general, using air as the oxidizing medium necessitates the use of a large furnace, and as the inerts contained in the air are carried forward into the subsequent stages of the SAR process, large equipment sizes are needed here too, together with a large turbine compressor to draw the product gases generated in the furnace through the various stages of the process with consequent large usage of energy.
The use of oxygen or
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patent: 4890562 (1990-01-01), Gitman
Garrido Guillermo
Mole James
Queille Philippe
Bennett Henry A.
Imperial Chemical Industries plc
L'Air Liquide Societe Anonyme pour l'Etude et, l'Exploitation de
Tinker Susanne C.
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