Method and apparatus for the destruction of volatile organic compounds

Abstract

A system for the destruction of volatile organic compounds while generating power. In a preferred embodiment the system comprises a combustor and a reaction chamber connected to an exit of the combustor. A primary inlet to the combustor supplies a primary fuel to the combustor. A secondary fuel, comprising air and an amount of one or more volatile organic compounds, is supplied to a compressor, which compresses the secondary fuel and directs the secondary fuel to the combustor and the reaction chamber. The system is suitably configured to enable the stoichiometric reaction of the two fuels in a manner sufficient to destroy the volatile organic compounds contained in the secondary fuel and power a turbine engine connected to an exit of the reaction chamber.

Description

This application is a division of application Ser. No. 08/538,692, filed Oct. 3, 1995, now U.S. Pat. No. 5,592,811.

TECHNICAL FIELD

This invention relates generally to a method and apparatus for the destruction of hazardous materials, such as volatile organic compounds, and more particularly, to the destruction of volatile organic compounds through the use of a turbine engine in order to produce power.

BACKGROUND OF THE INVENTION

Increasingly over the past half century, air quality has become an issue of public concern. Over this period, the scientific community has steadily improved its understanding of the origins of the air pollution that is apparent over most major U.S. cities. A large part of this air pollution is attributable to the release of volatile organic compounds into the atmosphere. As a result, the reduction of the releases of volatile organic compounds has become an increasingly important part of the overall strategy to improve air quality.

The most familiar volatile compound reduction technique is the control of fuel vaporization by vapor recovery techniques, first on automobiles and now on gasoline stations located in nonobtainment areas. As a result, the steady year over year increase in U.S. releases of these compounds has leveled off and is now even declining.

Manufacturing sites are responsible for approximately 8.5 million tons of volatile organic compound emissions annually. Solvent vaporization or in some cases, hydrocarbon byproducts, are key to the manufacturing process of many of the items used regularly in daily life. The manufacture of familiar consumer products results in the release into the atmosphere of significant amounts of organic compounds such as pentane, ethanol, methanol, ethyl acetate, and many others. The control of volatile organic compounds is essential to the environmentally friendly manufacture of these products, and thus, there remains a struggle with the cost of control versus the loss of competitiveness.

The most common control method in use today is the thermal oxidizer. In connection with this method, the volatile solvent is released in amounts generally less than a few thousand parts per million into the plant air system. This air is then selectively collected and fed into a combustion chamber where it is mixed with enough natural gas to sustain combustion. It is then ignited in a large chamber that incinerates the volatile solvent, as well as, the natural gas, thereby producing carbon dioxide and water vapor as the primary products of combustion. These oxidizers are large, complicated devices that represent a major capital expense and require significant amounts of electricity and gas to operate. While heat can sometimes be recovered, generally speaking, thermal oxidizers represent a significant economic loss to the businesses using them. In a typical U.S. industrial plant, the cost of operating this type of device easily adds 25%, and often much more, to the yearly energy bill.

Another current control technology uses solvent recovery methods that pass the air from the plant through an activated charcoal filter. Periodically, the charcoal is heated, driving off highly concentrated volatile compounds into a chilled condensing system. The output is a liquid organic compound often requiring hazardous waste treatment. The cost of operation, as well as the initial capital costs, are significantly higher than the thermal oxidizer, thereby making this control technology less attractive for the majority of industrial sites.

Accordingly, an efficient and cost effective device for the destruction of volatile organic compounds is needed.

SUMMARY OF THE INVENTION

A system for the destruction of volatile organic compounds according to the present invention addresses the shortcomings of the prior art.

In accordance with one aspect of the present invention, a system for the destruction of volatile organic compounds comprises a power generator, such as a gas turbine engine, which is provided with a reaction chamber driven by a combustion device. The system further comprises a primary inlet to the combustor for supplying a primary fuel. A secondary fuel is also supplied to the combustor and to the reaction chamber. The secondary fuel comprises air and an amount of a volatile organic compound. The system further includes a compressor, typically the compressor of the power generator, for compressing the secondary fuel. The reaction chamber is preferably connected to an exit of the combustor to allow for stoichiometric reaction of the two fuels after they are mixed together.

In accordance with a further aspect of the present invention, the power generator drives a recovery system that generates electricity.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The present invention will hereinafter be described in conjunction with the appended drawing figures, wherein like designations denote like elements, and:

FIG. 1 is a simplified schematic drawing of a destruction device in accordance with the present invention;

FIG. 2 is a schematic drawing of a device of the type shown in FIG. 1 as utilized in an exemplary plant layout;

FIG. 3 is a cross-sectional view of a combustor used in connection with the destruction device of FIG. 2;

FIG. 4 is a partial cross-sectional view of the combustion device and reaction chamber of the destruction device of FIG. 2;

5 8, compressor 24 preferably comprises alternate respective sets of rotating blades 56 and stationary blades 58 . Rotating blades 56 are suitably rotated through rotation of shaft 28, which is briefly noted above, is initially activated by generator 20. In accordance with a preferred aspect of the present invention, compressor 24 comprises a multi-stage compressor, more preferably a two stage compressor, i.e. there are at least 2 rotating blades (impellers) 56 within the body of compressor 24 .

As will be recognized by those skilled in the art, inlet air A drawn into compressor 24 is suitably compressed to pressures ranges from about 4 to about 30 atmospheres, and preferably to about 9 atmosphere. This compression raises the temperature of inlet air A, and thus the secondary fuel, to ideally about 600° F., but suitably within the range of about 550° F. to about 650° F. The compressed air B then exits compressor 24 through outlets 57A, 57B and preferably enters reaction chamber 18 through inlets 59A, 59B.

With continued reference to FIG. 1, compressed air B is suitably directed to a flow valve 50 which is provided with a monitor 52. Valve 50 suitably controls the amount of compressed air B which is provided to reaction chamber 18 and combustor 16.

As shown best in FIG. 1, a primary fuel inlet 70 provides primary fuel C to combustor 16 through a flow valve 72. Flow valve 72 preferably includes a monitor 74 to monitor the volume of fuel which is provided to combustor 16. As will be described in greater detail hereinbelow, fuel C and a limited amount of compressed air B (including the secondary VOC fuel) is suitably provided to combustor 16, the remaining portion of the secondary fuel being provided to reaction chamber 18. In accordance with a particularly preferred aspect of the present invention, the combination of combustor 16 and reaction chamber 18 is effective to substantially destroy the VOC within compressed air B and provide a mixed combustion gas stream D having a temperature suitable to activate the nozzle and turbine stages of gas turbine 26. In accordance with a preferred aspect of the present invention, the mixed-out temperature of mixed stream D provided to turbine 26 is in the range between about 1500° F. and about 2300° F., preferably about 1850° F.

In a conventional fashion, mixed stream D is directed to turbine 26. Turbine 26 of the type generally described above, is initially started by cranking it over with a starter (not shown) to produce air flow through the compressor. At the appropriate speed, fuel C is permitted to flow into combustor 16. However, once device 10 is in operation, mixed stream D suitably powers turbine 26 in a manner such that the output E from turbine 26 is suitably harnessed and utilized in subsequent operation of device 10, as well as in connection with the production of power for other applications.

With reference to FIGS. 3 and 4, the way in which reaction chamber 18 and combustor 16 cooperatively work to effectively destroy the VOC's in the VOC laden air in a manner to suitably drive power generator 12 will now be described in greater detail.

Reaction chamber 18 preferably comprises a double walled vessel having a main, inner wall 60 and an outer wall 62 that envelopes inner wall 60. The chamber 64 defined by walls 60 and 62 is suitably configured and positioned in proximity to compressor 24 to receive compressed air B. Preferably, and with reference to FIGS. 4 and 5, chamber 64 receives compressed air B (containing the secondary fuel) from outlets 57A, 57B of compressor 24. Chamber 64 extends about the periphery of reaction chamber 18. Further, in accordance with a preferred aspect of the present invention, chamber 64 also suitably communicates with combustor 16 in the region of respective openings 67A and 67B by way of a plurality of inlets 69, as well as wall 60 by way of tube outlets 124, 126. Thus, compressed air B is, in accordance with at least one aspect of the present invention, suitably provided to the combustor 16 and also directly to chamber 64 by way of tubes 116, 118, as will be discussed in further detail below.

With reference to FIG. 3, combustor 16 preferably comprises a hot wall type thermally insulated combustor. Preferably, combustor 16 comprises an outlet wall 80 within which a conventional combustion device 82 is suitably orientated. An inlet 84 communicates with combustion device 82 to advantageously effect combustion of fuel C. As previously briefly mentioned, fuel inlet C is preferably directed from fuel supply 70 through fuel control valve 74 and compressed air B is provided to combustion device 82 through inlets 69. In accordance with preferred aspects of the present invention, fuel supply C is suitably controlled by a control system 150 such that a sufficient amount of primary fuel C is provided to combustion chamber to effectively maintain an appropriate equivalence ratio (ER) thereby enabling stoichiometrically correct combustion. As shown best in FIGS. 3 and 4, the outlet 86 of combustor 16 suitably communicates with the interior of reaction chamber 18.

Combustor 16 may be attached to reaction chamber 18 in any convenient manner. For example, combustor 16 can be fixably attached to chamber 18 such that outlet 86 of combustor 16 directly communicates with an opening of reaction chamber 18 in an in-line manner. However, in accordance with a preferred aspect of the present invention and as shown best in FIGS. 3 and 4, combustor 16 is attached to reaction chamber 18 such that combustor 16 is orthogonal to the central axis X of reaction chamber 18. In this manner, as will be described in greater detail below, the combination gases exit outlet 86 of combustor 16 tangentially to reaction chamber 18 thereby tending to create a substantially cyclonic flow of the resulting fuel mixture within reaction chamber 18. While combustor 16 is shown in FIG. 4 as being attached to reaction chamber 18 tangentially near an end of reaction chamber 18 opposite inlets 59a, 59b, it should be appreciated that combustion chamber 16 may be attached in any convenient fashion. For example, combustor 16 may be attached at any angle from about 0° to about 90° from the central axis X of reaction chamber 18 and at any point along a side or the top of reaction chamber 18.

Combustion within combustor 16 takes place in a generally conventional manner, with the exception that compressed air B, i.e. the VOC laden air introduced into the system, is permitted to mix with the primary fuel C within the later stages of combustor 16. As will be appreciated by those skilled in the art, near inlet 84, primary fuel C is relatively rich such that it burns under near stoichiometric conditions, typically at a temperature in the range of about 2500° F. to about 3200° F., preferably between about 2800° F. and about 3000° F. and optimally 3000° F. In this region denoted in FIGS. 3 and 4 as “P”, often referred to as the “primary zone”, a minor portion of secondary fuel, which is contained within the compressed air is suitably mixed with primary fuel thereby creating a fuel mixture of primary and secondary fuels. The minor portion of secondary fuel introduced into the primary-zone P via inlet 69 is about 10% to about 30% of the secondary fuel. If the portion falls much below 10%, the fuel will become too rich and thereby cause “rich blowout.” While the amount of secondary fuel introduced into combustor 16 will vary, in general preferably from about 0 to about 70%, and more preferably from about 0 to about 50% of the fuel necessary to drive power generator 12 is provided by the secondary fuel.

The residence time of the gas mixture of primary fuel and secondary fuel within reaction chamber is enhanced due to the preferred configuration of combustor 16 relative to reaction chamber 18. Specifically, and in accordance with a preferred aspect of the present invention, as the combustion gases exit the combustor at outlet 86, such gases are directed toward the opposing wall of reaction chamber 18. The flow pattern which results in the interior of reaction chamber 18 tends to be cyclonic, i.e. creating a spiral pattern.

In accordance with a preferred aspect of the present invention, the fuel mixture, comprising primary fuel and secondary fuel is retained in reaction chamber 18 for a sufficient time to effectively burn, i.e. combust the VOC's contained within the secondary fuel B. Typically, the residence time of the gas mixtures within reaction chamber 18 is on the order of about 0.25 seconds or more. In accordance with a preferred design of the present invention, the tangential orientation of the combustor relative the reaction chamber has been found to not only enhance residence time, but also to cause a degree of recirculation within reaction chamber 18 thus further enabling substantially complete destruction of the VOC's within reaction chamber 18.

In practice, the present invention generally results in an excess of 90%, and typically from between about 95 and 99.5% of the VOC contained within secondary fuel B being effectively broken down into water vapor and carbon dioxide. As will be appreciated, and as will be discussed in greater detail below, through effective operation of device 10, substantially all of the VOC's contained within the inlet air A, and thus compressed air B, are thus effectively destroyed within reaction chamber 18 and/or combustor 16.

Preferably, flow channels 112, 114 of system 110 each comprise respective tubes 116 and 118. Preferably, tubes 116 and 118 are suitably attached to reaction chamber 18 at 116A, 118A and are in fluid communication with chamber 64 at outlets 124 and 126. Tubes 116 and 118 each preferably include respective valves 120 and 122, which may comprise any conventional flow control valve, such as a general poppet-type valve or the like. Tubes 116, 118 are in fluid communication with duct 65, which is in fluid communication with chamber 64, such that when valves 120, 122 are opened, the pressure differential between chambers 18 and 64 pushes a portion of the compressed air B out of chamber 64 through duct 65 and into tubes 116, 118. This portion of compressed air B then travels through the tubes 116, 118 and exits through outlets 124, 126 directly into chamber 60, causing air B to thereby bypass the combustor 16. In a preferred embodiment, when the valves 120, 122 are closed, all of compressed air B enters combustor 16 in the region of openings 67A and 67B via inlets 69.

Preferably, as shown, channels 112 and 114, as well as duct 65, each comprise a single tube that allow for the adequate bypass of compressed air B from chamber 64 directly into reaction chamber 18. However, other arrangements for accomplishing this objective easily can be devised and employed in the context of the present invention. Due to size considerations, generally the number of channels 112, 114 are minimized to two or three, and preferably even one; however, additional channels may be employed as desired.

Inlet air control system 110 can be activated manually or through the computer control associated with control system 150, which will now be described.

Preferably, control system 150 is a computer based system suitably configured and arranged to control, among other things, power generator 12 and fuel supply C, as well as inlet and outlet air from device 10. In general, control system 150 operates in a conventional manner to control power generator 12 including, among other things, compressor 24 and turbine 26. Further, in a conventional fashion, control system 150 operates to start device 10 initially and monitor operation of device 10 as device 10 begins to operate due to the burning of primary fuel A and secondary fuel C.

Control system 150, however, differs from conventional gas turbine and other industrial engine controls in that system 150 operates to monitor and, as necessary, adjust fuel supplies A and C, as well 25 air control system 110 to achieve optimum levels of efficiency and ensure that device 10 safely and effectively remains operative. Any suitable electronic means that is well known in the art may be utilized for control system 150. As previously noted, and with momentary reference to FIG. 1, control system communicates and utilizes information received from sensors 42, 48, 52, and 72. In addition, one or more sensors 152 may be utilized which are incorporated in proximity to or within reaction chamber 18 or combustor 16. (While sensor 152 is shown in FIG. 1 as being outside of both chamber 18 and combustor 16, its location is only illustrative of its position (or the positions) somewhere within fuel control system 14). In cooperation, these sensors provide information reflective of, among other things: VOC level in inlet air (e.g. sensor 48); temperature and flow rate of inlet air A, compressed air B, fuel C, mixed stream D and the like; fuel content and volume (e.g. sensor 74); power output from device 10; and speeds of turbine 26, with this and other information, control system suitably controls the operation of device 10.

For example, when the power output of power generator 12 drops below an expected level for the measured full consumption of fuel C, thus indicating, for example, that the fuel mixture within combustor 16 may be becoming too lean, control system 150 may activate control system 110. In such cases, valves 120, 122 will be opened thereby creating a pressure difference sufficient to draw compressed air B out of the chamber 64 and into the bypass flow channels 112, 114, which in turn, direct compressed air B into reaction chamber 18 thus preventing its flow into combustor 16. Operation of control system 150 in this manner prevents the fuel mixture within combustor 16 from becoming too lean, while still allowing for the VOC laden air to be reacted with the primary fuel within reaction chamber 18 to thereby destroy the VOC concentration and retain the VOC fuel value.

Stated another way, control system 150, by monitoring the varying VOC level in inlet air A, and thus the corresponding fuel valve of inlet air, adjusts device 10 for appropriate operation. For example, in the case where inlet air A has a fuel valve in excess of that necessary to drive power generator 12 at idle alone, control system 150 suitably reduces the flow of fuel C and as necessary, activates air control system 110 to prevent generator 12 from operating at excessive speeds and/or combustor from operating at excessively lean or such levels.

Control system 150 may also be employed to compensate for the relatively long lag time between fuel introduction and changes in conditions at inlet 90 to turbine 26 caused by reactions taking place within reaction chamber 18, as well as to monitor or control other aspects of device 10.

In accordance with a further embodiment of the present invention, and with reference to FIG. 6, in some cases, it may be desirable to initially treat VOC laden air from a typical plant prior to destroying the VOC's contained therein. In accordance with this aspect of the present invention, an air treatment system 200 is advantageously employed and communicates with one or more destruction devices, for example respective destruction devices 10A and 10B. Destruction devices 10A and 10B are in a form similar to device 10 described above. System 200 suitably comprises an inlet 202 which cooperates with, for example, inlet air duct 40. Inlet air A is thereafter drawn into chamber 203 where inlet air A is both cooled and sampled to determine the level of VOCs in inlet air A. Preferably, one or more sensors 206 are suitably carried within chamber 203 for the purpose of determining the VOC level within inlet air A.

In the event inlet air A is determined to be laden with an unacceptable level of VOC, an inlet bypass device 208 opens to allow fresh air into chamber 203. Preferably, bypass device 208 comprises a shutter valve of conventional design.

In addition, inlet air A is suitably cooled to a temperature within an acceptable range. Preferably, such cooling is effected through a heat exchanger system 205. Preferably system 205 comprises respective heat exchange elements 204, 218, outlet 210 and cooling fan 222. As will be appreciated by those skilled in the art, element 204 is suitably connected via outlet and duct elements (not shown) to cooling pump 211 and heat exchange element 218 such that cooling fluid is suitably recirculated between elements 204 and 218. In a conventional manner, system 205 allows for the cooling of inlet air A. Inlet air A once cooled, is passed through a centrifugal separator 212 separating the VOC laden air from any large particles. Once separated, the VOC laden air is communicated to devices 10A and 10B, preferably by respective conduits 214 and 216. As previously briefly mentioned, devices 10A and 10B operate in a fashion similar to that of device 10 described above to generate respective exhausts E1, E2 which are released into the plant to provide process heat through respective outlet 230, 232.

With reference to FIG. 7, a further alternative embodiment of the present invention is shown. With certain applications, it may be desirable to utilize a destruction device in accordance with the present invention in a relatively mobile fashion. As shown in FIG. 7, a mobile destruction system 300 suitably comprises a sled 302 upon which a destruction device 10C is suitably mounted. Destruction device 10C is suitably configured in a manner similar to that of device 10 described hereinabove. As so configured, device 10C includes power generator 12 to which reaction chamber 18 and combustor 16 are suitably attached. The output of device 10C, namely exhaust E3 is suitably communicated via outlet 303 into a heat recovery air-oil cooler 304. In accordance with this embodiment of the present invention, a voltage source 306 is suitably provided to provide startup power to device 10C, as well as power, at least initially, to the other aspects of system 300. A gas compressor 308 is also suitably mounted to sled 302 for raising gas pressure to levels required by device 10C. Respective ventilators 310, 312 may be also suitably mounted to sled 302. In addition, a water supply 320 with respective auxiliary units 322, 324, 326, 328 and pump 330 may also be utilized for purposes of water injection into the combustor 16 to control emissions of nitrous oxide.

System 300 is suitably controlled through operation of a control system 350 which may be optionally cooled through operation of a refrigeration device 352. Various other devices such as ventilators, switch and other electronic devices may be also employed, in a conventional fashion, for a effective use of device 10C in connection with mobile system 300.

Preliminary experimental tests of devices embodying the present invention have indicated that by using the VOC laden secondary fuel, the amount of primary fuel needed to operate the engine is reduced without a loss of energy content in the fuel supply. Accordingly, the use of this volatile organic compound destruction system 10 results in substantially complete destruction of the volatile organic compound while reducing the amount of primary fuel required to operate an engine for the generation of electricity.

Thus, it will be appreciated that device 10 provides significant advantages over prior art designs for destruction of VOCs. For example, in accordance with experiments preformed using devices embodying preferred aspects of the present invention, substantial destruction of VOC laden air efficiency (e.g. at rates above 99.5%) at a level of about 6200 ft³/min can be obtained with the production of a nominal 525 kw of electrical power.

To illustrate the overall impact of the present invention, consider a typical plant using 640,000 kw hours per month with a need to consume 12,000 cubic feet per minute of air laden with 3,500 parts per million of a VOC. Consider further that the plant consumes 97,000 therms of fossil fuel each month. Without control, over 800 metric tons per year of VOC's are released into the atmosphere.

While prior art techniques (e.g. use of a thermal oxidizer) may reduce the emission of less than 50 metric tons per year of VOC's, use of such devices increases the plant energy consumption to about 125,000 therms per month.

In contradistinction, through use of a device embodying the present invention, effective VOC control is enabled with less energy. Specifically, in this example, the energy consumed and therefore, total fossil fuels burned, falls to 81,000 therms per month. Not only are the total operating costs for the plant reduced, but there is also a net reduction in the emission of carbon dioxide, nitric oxide and sulfur oxide. The sum effect of use of the present invention to control volatile organic emissions is thus cleaner air, less fossil fuel consumption and resulting lower costs.

It will be understood that the foregoing description is of the preferred exemplary embodiments of the invention, and that the invention is not limited to the specific forms shown. Various modifications may be made in the design and arrangement of the elements set forth herein without departing from the scope of the invention as expressed in the appended claims.

Claims

1. A method of destroying volatile organic compounds (VOCs) comprising the steps of:

collecting air laden with the VOCs;

compressing said VOC laden air in a compressor;

providing a primary fuel stream;

combusting said primary fuel stream in a combustor to create a first stream of combustion gases;

directing said first stream of combustion gases to a reaction chamber;

directing said compressed VOC laden air into said reaction chamber to create a second stream of combustion gases;

reacting said first and second streams of gases for substantially destroy said VOC's and create a resulting stream of combustion gases;

directing said resulting stream of combustion gases to drive a power generator; and

recovering power from operation of said power generator.

2. The method of claim 1 further comprising the step of:

controlling the flow of said collected VOC laden air and said primary fuel stream to maintain a substantially stoichiometric reaction in said reaction chamber.