METHOD FOR DESTRUCTING UNDESIRED ORGANIC SUBSTANCES

Abstract: Method for destructing undesired organic substances such as solvent vapours diluted with air, by supplying the air with substances entrained therein and passing said air through a reaction zone in an elongated combustion chamber (16) heated by burning supplementary fuel from one end thereof. At the other end, the combustion chamber is connected to a waste heat boiler or a gas turbine (10, 13). The air with substances entrained therein, in the reaction zone is maintained at a temperature within a predetermined temperature range for a time of flow the lower limit of which is within a predetermined time interval.

Description: The invention relates to a method for destructing, by oxidation, undesired organic substances diluted with air. It has been proposed particularly for destructing solvent vapours, e.g. such as occur in paint spraying and escape with the ventilation air from spraying chambers. The solvents then most frequently involved are toluene, methyl benzene, xylene (di-methyl benzene), ethyl acetate, butyl acetate, cyclohexane and octane. The solvents are present at low concentrations of the order of 20 to 220 ppm, which makes difficult to recover the solvents from the ventilation air. The best mode of neutralizing such substances therefore is to oxidize them, carbon dioxide and water being produced as the end product. However, it has been found that the temperature and period of the oxidation are critical factors and it is thus necessary to effect the oxidation within a predetermined temperature range and a predetermined time interval. Otherwise, the oxidation can be more or less incomplete. The purpose of the invention is to provide an effective and economic destruction of the solvents by oxidation, the final product being practically only carbon dioxide and water. In order to obtain this purpose the invention provides a method of the type disclosed in DE-A-2543761, for destructing, by oxidation, undesired organic substances diluted with air, and according to the invention this method has obtained the characterizing features of claim 1. By the method in the invention the heat energy is utilized which has to be supplied for the oxidation and, moreover, also the energy bound in the solvents will be utilized. Embodiments of the invention will be described in more detail below with reference to the accompanying drawings in which FIG. 1 is a diagram showing a turbine plant for practising the method of the invention, FIG. 2 is an elevational view illustrating the constructive embodiment of essential elements of the plant, FIG. 3 is an enlarged axial cross-sectional view of the combustion chamber, and FIG. 4 is a diagram showing a waste heat boiler plant for practising the method of the invention. The turbine plant shown in FIGS. 1 and 2 comprises a turbine unit including a high pressure turbine 10 connected to a high pressure compressor 11 and an electric generator 12 for recovering utility power from the unit, and a low pressure turbine 13 connected to a low pressure compressor 14. Between the high pressure turbine and the low pressure turbine a controllable connection is provided which in the present case comprises a circular array of adjustable (rotatable) vanes 15. This connection provides the power control means of the turbine unit. An elongated combustion chamber 16 formed as a tube is connected at the gas outlet thereof to the high pressure turbine to supply gas to said turbine and thus to the low pressure turbine connected in series therewith. The combustion chamber is shown in more detail in FIG. 3. At the left end thereof a burner 17 is provided for burning oil or gas. Around the burner, a primary air inlet 18 is provided having a turbulator, and outwardly thereof there is an inlet 19 for cooling air. In the shell of the combustion chamber, an inlet 20 for secondary air and an inlet 21 for diluting air are provided. The suction side of the low pressure compressor 14 is connected to a spraying chamber 22 via a particle filter 23 to draw the air from the spraying chamber with solvents entrained therein, particles carried by the air being separated in the particle filter 23. The pressure side of the low pressure compressor is connected to the suction side of the high pressure compressor 11 via an intermediate cooler 24, the high pressure compressor being connected to the combustion chamber 16 via a recuperator 25 for supplying the air with solvents entrained therein to the combustion chamber. Then, the air can be supplied as primary air through the air inlet 18, as cooling air through the air inlets 19, as secondary air through the air inlets 20 or as diluting air through the air inlets 21. The low pressure turbine 13 is connected to a chimney as indicated by an arrow 26, the recuperator 25 being located between the waste gas conduit of the low pressure turbine and the air inlet conduit of the combustion chamber, extending from the high pressure compressor, for heating the compressor air by heat exchange with the waste gas. Furthermore, in the waste gas conduit of the low pressure turbine, a waste heat boiler 27 is provided for generating steam or hot water. A shunt valve 28 is provided over the recuperator 25 for controlling the waste gas flow from the low pressure turbine 13, passing through the recuperator, and thus the ratio between the electricity production by means of the generator 12 of the turbine unit and the heat production by means of the waste heat boiler 27. By controlling the gas condition at the inlet side of the low pressure turbine 13 by means of the controllable connection 15 and by recovering utility power directly from the high pressure turbine 10 via the generator 12 substantially at a constant rotational speed the temperature of the gas to the high pressure turbine can be kept substantially constant independently of the utility power recovered from the gas turbine unit, i.e. electric power from the generator 12 and/or heat power from the waste heat boiler 27. This means that the temperature in a reaction zone in the burner 16, which extends from the inlets for secondary air to the waste gas outlet of the combustion chamber can be maintained within a predetermined temperature range. Moreover, the combustion chamber should be constructed such that the duration of stay of the air supplied to the combustion chamber, in the reaction zone will not decrease below a predetermined value. It is achieved as a consequence thereof that there can be maintained in the combustion chamber the prerequisites required for a complete oxidation of the solvents supplied, to carbon dioxide and water. This is promoted also by the turbulence of the air in the combustion chamber, which can be initiated by means of the turbulator in the air inlet 18 and by a suitable direction of the air supplied through the air inlets 19 to 21. If it is desired to keep the turbine unit operating also when the spraying chamber 22 is operating with a reduced ventilation flow or is taken out of operation, valve means 29 can be provided at the inlet side of the low pressure compressor 14 for the supply of fresh air. In FIG. 4, there is no turbine unit and the combustion chamber 16 supplies the waste heat boiler 27 only. In this case, the ventilation air with solvents entrained therein from the spraying chamber is transported by means of a fan 30 via the recuperator 25 to the combustion chamber 16. The predetermined temperature in the combustion chamber is maintained by controlling the additional amount of fuel supplied to the burner 17. The heat quantity recovered from the waste heat boiler 27 is controlled by controlling the waste gas flow through the recuperator 25 by means of the valve 28. Generally, the temperature in the reaction zone in the combustion chamber 16 should range from about 700°C to 900°C and the lower limit of the duration of stay in the reaction zone should range from about 0.3 s to about 0.4 s. For 99.9% destruction e.g. of benzene a temperature of 750°C and a duration of stay of 0.4 s will be required.

Claims: 1. Method for destructing, by oxidation, undesired organic substances diluted with air, wherein the air with substances entrained therein is supplied to and passed through a reaction zone in a combustion chamber (16) heated by burning supplementary fuel from one end of the chamber which is connected at the other end thereof to a gas turbine, and wherein the air with substances entrained therein is supplied to the combustion chamber (16) by means of a high pressure compressor (11) driven by the gas turbine being a high pressure turbine (10) of a gas turbine unit comprising in addition to the high pressure turbine (10) and the high pressure compressor (11) a low pressure turbine (13) driven by the waste gas from the high pressure turbine (10), and a low pressure compressor (14) driven by the low pressure turbine (13) and connected in series with the high pressure compressor (11) and wherein the temperature of the air with substances entrained therein is maintained at a temperature in the reaction zone within a predetermined temperature range extending from about 700 °C to about 900°C, characterized in that the gas condition at the inlet side of the low pressure turbine (13) is controlled by means of a controllable connection (15), and that the utility power of the gas turbine unit is recovered from the high pressure turbine (10) substantially at constant rotational speed thereof while maintaining the temperature of the gas to the high pressure turbine (10) substantially constant maintaining the air with substances entrained therein in the reaction zone for a time of flow the lower limit of which is within a time interval extending from about 0.3 to about 0.4 s, independently of the utility power recovered from the gas turbine unit. 2. Method as in claim 1 wherein heat exchange is provided between the air with substances entrained therein, which is supplied to the combustion chamber (16), and the waste gas discharged from the low pressure turbine (13). 3. Method as in claim 2 wherein the heat exchange is effected only with an adjustable portion of the waste gas or air flow. 4. Method as in claim 1 wherein the air with substances entrained therein is supplied to the combustion chamber (16) as primary air (18) and/or secondary air (20) and/or cooling air (19) and/or diluting air (21). 5. Method as in claim 1 wherein turbulence is imparted to the air with substances entrained therein, in the combustion chamber (16).

Inventors: STRAND, TORSTEN
Applicants: ABB STAL AB
Application year: 1988
Main classification: F02C3
IPC codes: F23R3, F23G7, F02C6, A62B15, B01D53, F02C7, F23G5, F02C3