CROSS-REFERENCE TO RELATED APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSERED OR DEVELOPEMENT

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BACKGROUND OF THE INVENTION The present invention relates to clean up of soil or other media contaminated by manufactured gas plant coal tar, or other organic contaminants such as petroleum products, solvents and chemicals. The invention additionally relates to removal of particulates from the vaporized organic stream prior to oxidizing the vapors in a utility boiler furnace.

Manufactured gas plant (MGP) coal tar contaminated soil and other media have been burned in utility boilers in the prior art. The contaminated soil or other media was screened, ground and mixed with pulverized coal prior to conventional firing in a utility boiler furnace or mixed with sized coal and fired in a stoker or grate furnace.

The prior art methods succeeded in destroying the coal tar, but the amount of contaminated material as a percentage of the total coal fed was severely limited. Wear on grinding mills was accelerated, feed system blockages occurred, and slagging,

fouling and erosion of the furnace as well as boiler components also occurred. These feed system blockages have occurred due to the fact that the soil has a high moisture content and, therefore, tends to be "stickier" thereby creating blockages in systems which had previously worked well for coal. Fouling of the furnace and boiler components occurs due to soil having a different chemistry than coal. For example, clays may have a high sodium content which causes the fly ash to slag and melt at lower temperature than expected. Erosion occurs because there is a higher ash content traveling through the system. This results in high costs, reduced reliability and interference with standard equipment and operating procedures.

In addition to burning contaminated soil and other media in utility boilers, the prior art has also utilized high temperature, stand alone transportable kilns and low temperature, mobile desorbers. Most have utilized a secondary combustion chamber to destroy the vaporized coal tar compounds. Low temperature direct-fired desorbers have used burners directly mounted to the desorber faceplate. This has allowed flame impingement on the soil and concomitant quenching of the flame, thereby producing products of incomplete combustion. In addition, the use of such burners promotes oxidation of desorbed organics in the desorber drum, which is an undesirable occurrence.

Other low temperature desorbers have used retorts and similar means of desorption to reduce the volume of the gas stream sent to a condenser or to activated carbon for removal of desorbed organics. These systems have been high in cost and low in capacity. Further, the condensed waste and water must

be treated and is normally shipped off-site for further processing, which results in higher costs. The waste is only separated and is not destroyed in this type of system.

BRIEF SUMMARY OF THE INVENTION

The present invention involves a system for cleaning contaminated media, such as soil, which utilizes a utility boiler furnace as the control device to destroy coal tar vapors produced in the system. The present process also uses the boiler's air pollution control system, thereby eliminating the capital and operating costs for a secondary combustion chamber, air pollution control system and stack. By utilizing a utility boiler furnace to destroy coal tar vapors and by utilizing the boiler's air pollution control system, the net result is reusing what typically already exists on site rather than a duplication of the entire system.

Another feature of this invention is that it recycles coal tars. The invention recycles the coal tars by utilizing their heat value for steam production in the boiler. The heat from the desorber burners is also available for steam production.

This invention also addresses a major deficiency in prior attempts to use utility boilers for treatment of manufactured gas plant waste, in that the inorganic fraction (typically about 90% by weight of contaminated soil) is precluded from entering the boiler furnace. Problems with blockages, slagging, fouling, erosion and the like previously discussed are thus eliminated.

Yet another feature of this invention is that the amount of contaminated media that may be processed is not limited by the boiler's bottom ash and fly ash handling capability. Coal is approximately 90% fuel and 10% ash. Contaminated soil is the

inverse being approximately 90% ash and 10% contaminants and other volatiles. To burn large quantities of contaminated soil in a standard boiler overwhelms the ability of the ash handling system and air pollution control system to take it back out. 5 Still another feature of this invention is that the processed soil does not intermingle with coal ash. Therefore, this processed soil can be used for multiple purposes such as road fill, daily cover in land fills and fill for the excavation that the contaminated soil is derived. The prior art systems resulted

10 in an end product of commingled coal ash and processed soil, subject to government regulations.

The present invention thus provides a low cost, method to clean contaminated media, especially soil in connection with utility boiler operation while avoiding problems caused by

1 5 inorganic material entering the boiler furnace.

In order to accomplish the above features and advantages, the present invention provides a method of cleaning media contaminated with organic contaminants, comprising the steps of separating contaminated media into oversized particles and 0 undersized particles; separating the undersized particles into a gaseous fraction containing volatile contaminants and a solid fraction containing treated material; removing particulate matter from said gaseous fraction to form a light gaseous stream and a heavy dust stream; and burning said gaseous fraction.

25 In accordance with a preferred embodiment of the invention, soil or other contaminated media is screened to two inch top size. It then enters a rotary flighted drum where a direct-fired burner with external furnace provides heat in a co- current mode of operation. The soil is heated as it passes

3 _. 0 through the drum vaporizing water and organic material. After

exiting the drum, the vapors pass through one or more cyclones to remove entrained inorganic particulate. The vapors may also pass through a baghouse to provide additional particulate removal. The vapors then enter an induced draft fan which keeps the treatment system under draft and provides the increase in pressure necessary to transport the vapors to the utility boiler furnace.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Figure 1 is a schematic illustration of the MGP coal tar treatment system embodying the present invention.

DETAILED DESCRIPTION OF THE INVENTOIN Referring now to the drawing, Fig. 1 illustrates an apparatus and method for remediation or cleanup of MGP (manufactured gas plant) coal tar contaminated media. As used herein, the term "media" preferably refers to different types of common soil, but may also include wood chips, iron filings, sediments from harbors or rivers, sludges from sewage or other waste byproducts, sand, gravel, clays, and the like, which are typically found at MGP sites and other contaminated sites. The term "media" refers to any type of material having the ability to be contaminated with undesirable organic constituents that also has the ability to be treated to remove the contaminates so that the base material may be recycled or reused. As noted above, this media is preferably MGP coal tar contaminated soil, and the following description will be directed toward the cleanup or treatment of such soil.

The preferred media for use in the system of the present invention is soil contaminated with organic materials such as coal tar which is typically found in MGP (manufactured gas plant) sites. The soil is typically contaminated with coal tar from coal- fueled gas works and is a byproduct of the coal gasification process. Contamination of soil typically occurred from various plant operations, leaks and demolition where coal tar was simply buried with other debris. Typically, treatment or cleanup of contaminated soil from MGP sites first begins by excavating the contaminated soil and feeding the contaminated soil via line 1 to a hopper or bin 2. From hopper 2 the raw soil is metered onto a conveyer 3 which in turn feeds the soil at a constant rate to an inclined conveyor 4 which uniformly distributes the soil to a screening apparatus, preferably a shaker screen 5. Screen 5 separates the contaminated soil into oversized particles and undersized particles. The oversized particles are those materials greater than approximately 2 inches in diameter and the undersized particles are those typically less than about 2 inches in diameter. The oversized particles are fed via line 6 to a conveyor 7 which in turn feeds the oversized particles via line 8 to be crushed and recycled to shaker screen 5. Alternately, the oversized particles could be cleaned mechanically, or washed in a soil washing process. It should be noted that screening of contaminated soil can be more than the above mentioned 2 inch particle size if the material handling system hereinafter to be described is designed to accommodate the larger size particles. However, particles of 2 inches or less in diameter may be accommodated by standard equipment designs, and is therefore preferred.

The undersized particles from screen 5 are fed via line 9 to a constant speed belt 10. Belt 10 receives the contaminated undersized particles from screen 5 and monitors tonnage flow to the system while feeding the undersized particles to the thermal treatment stage of the process.

Contaminated soil typically includes 0-4% coal tars by weight with most contaminated soil averaging 1 -2% coal tar by weight. Contaminated soil is thus fed to a rotary desorber 11 from belt 10 via line 12 and chute 13. Desorber 11 is a well- known device which is sized and rotated at a suitable speed for the volume of material to be processed. Preferably, desorber 1 1 is a co-current, direct fired, rotating flighted drum which, as shown in Fig. 1 uses an external furnace 14 and burner 15 to prevent the flame from direct contact with soil to thereby preclude quenching of the flame. Desorber 1 1 heats the contaminated soil to a temperature sufficient to cause water and organic contaminates from coal tar contained in the soil to vaporize into a gas leaving a treated solid soil material. Typically, soil temperatures of between 600°F and 900°F are achieved, but soil temperatures of up to 1000°F and as low as 450°F are possible if desired. Desorber 11 may be co-current or counter- current in operation, but is preferably co-current to avoid the possible condensation of coal tar in the cyclones, the baghouse or in the baghouse fines which may occur with counter-current designs. As an alternate means for heating contaminated soil, rotary desorber 1 1 may be replaced by a retort, paddle dryer and/or hollow flight augers with hot oil or molten salts pumped through the shafts and jackets thereof. Each of these devices are well known in the art and function to separate the undersized

particles in the contaminated soil into a gaseous fraction containing volatile organic contaminates and a soil fraction containing treated material.

Heating the soil is the key to removing organic contaminates. Coal tar and other high boiling point organics can be removed at temperatures between 600°F and 900°F with appropriate residence time. As a result, virtually all organics can be removed from the soil to produce treated material having organic contaminants below a one part per million level. The soil matrix is a major factor in setting the required temperature.

For example, sand and gravel release organics easily and have low moisture content and thus require lower temperatures. Clays have higher moisture content and the organics may bind tightly to clay particles thus requiring higher temperatures. As noted above, contaminated soil entering desorber 1 1 contains preferably anywhere from 0-4% concentration of MGP coal tars and due to the thermal treatment within desorber 11 the undersized contaminated soil particles are separated into a gaseous fraction containing volatile MGP coal tar contaminates which exit desorber 1 1 via line 16, and a solid fraction containing substantially clean treated soil which exits desorber 1 1 via line 17. However, this method, with certain modifications, will work with any percentage of contamination including pure coal tar. The solid fraction in line 17 is then fed to a cooler 18 which typically comprises a low RPM auger.

Cooler 18 may also be a pugmill, rotary drum, or other device depending upon the soil matrix or other treated material being fed to it. Cooler 18 reduces the overall temperature of the treated soil from between 600°F-900°F, which is the

temperature of the soil exiting desorber 1 1 , to approximately 200°F or less. This is accomplished by spraying water via line 19 to cool and consolidate the treated soil. Cooled, treated soil exits cooler 18 via line 20 and may be recovered for multiple purposes such as road fill, cover in land fills and other construction soil fill.

The gaseous fraction leaving desorber 11 via line 16 contains substantially all of the MGP coal tars driven off of the contaminated soil and forms a light gaseous stream which needs to be further processed to remove particulate matter therefrom. The typical composition of MGP coal tar gaseous fraction contained in line 16 is as follows:

Major Components of MGP Coal Tar Gas Fraction

Approximate

Component Percentage Boiling Point (°C)

Naphthalene 3.0 218

2 -Methylnaphthalene 1.2 241

1 -Methylnaphthalene 0.9 245

Biphenyl 0.8 256

Dimethylnaphthalenes 2.0 268

Acenaphthene 9.0 279

Dibenzofuran 5.0 287

Fluorene 10.0 293-295

Methylfluorenes 3.0 318

Phenanthrene 21.0 340

Anthracene 2.0 340

Carbazole 2.0 355

Methylphenanthrenes 3.0 354-355

Major Components of MGP Coal Tar Gas Fraction

Approximate

Component Percentage Boiling Point (°C)

Methylanthracenes 4.0 360

Fluoranthene 10.0 382

Pyrene 8.5 393

Benxofluorenes 2.0 413

Chrysene 3.0 448

Entrained within the gas stream is particulate matter which needs to be removed. In order to accomplish this, the light gaseous stream is fed to a cyclone dust collector 21. Cyclone 21 is a well-known device which centrifugally separates the particulate matter from the gaseous fraction in a known manner to create a light gaseous stream which exits cyclone 21 via line 22 and a heavy dust stream which exits cyclone 21 via line 23. If necessary, the volatile gasses in light gaseous stream 22 may optionally further be processed to remove additional particulate matter by being fed to a filter, typically a bag filter contained in baghouse 24, downstream of cyclone 21. The bag filters in baghouse 24 further separate particulate matter from the gaseous fraction and provides a light gaseous stream 25 exiting therefrom which is substantially clean ofx all particulate matter, and a heavy dust stream which exits baghouse 24 via line 26. As illustrated in Fig. 1 , the heavy dust stream 23 from cyclone 21 and the heavy dust stream 26 from baghouse 24 may

be combined and recycled with the treated soil in cooler 18 where it is simultaneously cooled with the soil leaving desorber 11.

The light gaseous stream 25 from baghouse 24 enters the inlet of an induced draft fan 27 which in turn feeds the volatile organic gasses to a boiler furnace via line 28 where the coal tar gasses are destroyed. The heat value of the volatile organic gases is thus being utilized to produce steam in the boiler.

Fan 27 also functions to reduce the presser in lines 16, 22 and 25 to aid in separating the undersized particles into gaseous and solid fractions in desorber 1 1 and to aid in removing particulate matter in cyclone 21 and baghouse 24, as is well known in the art. Also, it may be necessary to maintain the gas streams 16 and 22 above a predetermined temperature in order to prevent condensation of organic volatiles in the filter bags contained within baghouse 24. In order to accomplish this, lines 16 and 22 are typically insulated from the surrounding ambient air. However, it may be necessary to use heat tracing on lines 16 and/or 22 depending upon the circumstances and other factors well-known by those skilled in the art. Preferably, the temperature in lines 16 and 22 should be maintained at 600°F- 900°F.

An MGP coal tar separation and cycling system has been illustrated and described which permits the separation of MGP coal tar contaminants from soil or other media to enable both the volatile coal tar contaminants as well as the clean soil to be recycled and /or reused. It should be noted that control interlocks prevent system operation when the utility boiler is not in normal service. Also, the gasses produced in the process can be fed to a steel mill blast furnace or cupola as alternatives to

the utility boiler furnace. In addition, the coal tars can be from sources other than manufactured gas plant sites such as coke ovens and wood treating sites. The contaminates in the soil may also contain organics other than manufactured gas plant coal tars.