PT87042B - PROCESS AND APPARATUS FOR THE TREATMENT OF TOXIC SUBSTANCES FROM THE ESCAPE OF AN INCINERATOR WHICH BURNS SOLID MUNICIPAL RESIDUES - Google Patents

Abstract

A waste material incinerator (10) which produces an exhaust (20), containing trace amounts of a toxic organic substance, includes a flue (28) containing a refractory filter (60). The refractory filter (60) is heated by the exhaust (20) produced by the incinerator (10) to a temperature above 700 DEG C to destroy the toxic organic substance in the exhaust (20). The refractory filter (60) preferably includes a plurality of ceramic cylinders (62) and is periodically cleaned to remove accumulated solid particles on the upstream surface of the cylinders (62) by injecting high pressure air into the cylinders (62).

Description

WESTINGHOUSE ELECTRIC CORPORATION

PROCESS AND APPARATUS FOR THE DEPURATION OF

TOXIC SUBSTANCES OF THE EXHAUST OF AN INCINERATOR

BURNS SOLID MUNICIPAL WASTE

A. The present invention relates to an incinerator for burning waste material and more particularly, an apparatus and a process for the destruction of small amounts of toxic organic substances that may be present in the exhaust gases produced by the incineration of municipal waste. .

The proper removal of solid waste has become an increasingly serious problem, as the existing places to discharge the waste are nearing the end of their capacity and it is becoming increasingly difficult to obtain new locations, while the quantities of waste municipalities seem to grow. Incineration of combustible solid waste has long been used to reduce the amount of solid matter that needs to be disposed of. However, in recent decades, it has been widely recognized that when solid waste from municipal waste is incinerated, trace residues of toxic chemicals such as dioxins and furans, can be broken down by the exhaust gases.

In the past two decades, plasterwork by the U. S. Environmental Protection Agency, other foreign environmental protection agencies and other groups has shown that such toxic chemicals are decomposed at comprehensive temperatures. between 600 ° C and values slightly above 1 300 ° C during

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during an exposure period that lasts something like a tenth (0.1) and two and a half (2.5) seconds. The most recent studies indicate that more than 99% of some substances, such as biphenyl, dibenzofuran, dibenzo-p-dioxin and tetrachlorobiphenyl, are destroyed at temperatures slightly above 700 ° C, with residence times (period of exposure) of approximately 1 s. These values are based on a study by Duvall and Rubey, done in 1977 and published in Laboratory Evaluati on of High-Temperature Destruction of Polychlorinated Biphenyls and Related Compounds, U.S. EPA Eeport EPA-600-2-77-223. More recent studies, including one done by the Banisk National Environmental Protection Agency with results published in 1934 under the title MILJO-RAPPORT Bilag rapporten om Dannelse og spredning af Dioxiner isaer i forbindinelse med affaldsforbraending, which translates to Dioxin formation and dispersion, particularly in conjunction with the combustion of waste, indicate that the exposure of the exhaust gases at a temperature of approximately 1 000 C for a period of time of at least two seconds results in the destruction of substantially all dioxins and furans.

The results of these studies are contradictory with practical experience, since temperatures are usually much higher than 1 000 ° C in the municipal waste incineration process, however it is known that potentially toxic materials are present in the exhaust gases from the incineration of municipal waste. To elucidate the nature or origin of this problem, reference was made to US Patent No. 4,515,233, which illustrates a type of incinerator

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commonly used, known as a water-cooled rotary burner.

object of the present invention is to remove toxic organic substances from the exhaust gases produced in the incineration process of municipal waste by destroying the toxic organic substances in the exhaust gas material by incinerating waste by using the heat produced by incinerating the material and removing the solids from the exhaust gases produced by a waste incinerator in order to minimize the deposition of solids in the refrigerator areas to prevent the reforming of the toxic organic substances there.

The aforementioned objective is achieved by providing an apparatus and a process described in the claims for purifying exhaust gases containing toxic organic substances, produced by an incinerator in the process of combustion of waste material. The apparatus comprises means for directing the exhaust gases to transport these exhaust gases, produced by the incinerator, to a discharge port to discharge them into the atmosphere. The apparatus also comprises filter means, arranged in means of exhaust gas routing, to absorb heat from the exhaust gases to reach a temperature above 700 ° C and to hold all exhaust gases at the outlet for a sufficient time to destroy substantially all toxic organic substance in the exhaust gases. In an area form. In which the incinerator has an inlet end to receive the waste material and an outlet end to discharge the exhaust gases, the exhaust gas containment means comprise a flue pipe, with a longitudinal axis a

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an inner surface, tightly surrounding the exit end of the incinerator; the filter means comprise a porous ceramic filter for gases, disposed inside the flue, therefore downstream of the outlet end of the incinerator, and sealed throughout in relation to the inside surface of the flue.

Preferably, the filter is heated to a temperature of approximately 1000 ° C, with all exhaust gases at the outlet heated to that temperature. Preferably, the apparatus furthermore includes means for periodically cleaning the filter to remove solid particles accumulated on the outer surface thereof.

The apparatus preferably also includes means for detecting a pressure drop through the filter so that the cleaning means can automatically clean the filter when the pressure drop detected by the sensing means falls below a predetermined pressure differential.

These objects, together with other objects and other advantages that will be highlighted in the following, reside in the details of construction and operation, as more fully described and claimed below, with reference to the attached drawings, which are part of the same , in which the same reference numbers always refer to the same parts in all drawings. Figs.

drawings represent:

Fig. IA, a cross-section and an elevation in an electrochemical view of a rotary burner incorporating the present invention.

Fig. 1B, a schematic plan view of the rotary burner illustrated in fig. IA;

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- 5 Fig. 1C, a schematic view of a conventional exhaust gas cleaning system;

Fig. 2, a schematic elevational view with a cross-sectional view, the cut being made by a plane perpendicular to the axis of a rotary burner of the prior art, for example, the rotary burner illustrated in fig. IA;

Fig. 3, a side elevation view in cross section of a portion of a filter according to the present invention; and

Fig. 4 is a schematic top view of a portion of the filter according to the present invention.

apparatus according to the present invention is capable of destroying toxic organic substances without the need for auxiliary energy sources. In the illustrated embodiment, the present invention is used in conjunction with color. the rotary burner shown in figs. IA, IB and 2 described below. However, the present invention is not limited to the illustrated embodiments, but can be used like any municipal incinerator that produces exhaust gases at temperatures above 700 ° C and preferably 1,000 ° C or more.

rotary burner cooled by water as shown in figs. 1A and 1C comprise a combustion cylinder (10) with a side view (23) with a cylindrical shape formed by longitudinally arranged cooling tubes (24) and porous interconnections (36) for gases, for example perforated ribs in fig. IA only a few of these ribs (J6) between adjacent cooling tubes (24) J. The combustion cylinder (10) has a central axis of rotation that is slightly tilted

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relative to the horizontal, descending from the input end (16) to the output end (18). Thus, the cooling tubes (24) and the perforated ribs (31) are also slightly angled from the inlet end (16) until the tubes (24) fold into the smoke tube (28). The cooling tubes (24) have first and second ends located near the outlet end (18) and the inlet end (16), respectively, of the cylinder (10). Combustion is typically initiated in the cylinder (10) using an auxiliary fuel, such as oil or natural gas, which can be supplied through the inlet end (16) of the combustion cylinder (10).

The perforated ribs (36) are preferably formed by steel bars which have openings (37) for supplying combustion air into the combustion cylinder (10). The ribs (36) extend from the inlet end (16) and along the mostly straight portions of the tubes (24) to a section (24a) angled at the inside of the smoke tube (23). The ribs (36) are then included in the angled bent section (24a), in which the cooling tubes (24) extend in a somewhat convergent relationship to the outlet end (18) of the cylinder (10), thus allowing that the exhaust gases (20), which include gases and solid particles such as non-current fly ash and solid combustion products (22), for example ash and slag, escape more easily from the cylinder (10).

As shown in fig. IA, the cooling tubes (24) are fixed on annular support bands (13) which are received on rollers (12). The rollers (12) can be driven to rotate the cylinder (10) around its longitudinal axis, or else an ORIGINAL tamBAD

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toothed edge (not shown) can be fixed to the side wall (23) and driven by a pinion.

As noted above, temperatures above 1000 ° C are reached in the combustion cylinder (10), with the residues (14) being introduced at the generally open inlet end (16) and incinerated by the air supplied through the wind (38).

combustion cylinder (10) is able to withstand so high through periods because a cooling medium circulates refrigerant tubes (24), which is discharged from (10) through an annular gland (17) and from the temples of the supply tube cylinders (26). The discharge through the supply pipes (26) circulates by means of a pump (32) through a rotating union (30), to the heat exchanger equipment (34) that makes the return of the refrigerant medium with a low level of energy for the ring fitting (17), through the pump (32), the connection (30) and the supply pipes (26). The annular fitting (17) distributes the cooling medium with low energy level to a first set of cooling pipes (24) that carries the cooling medium along the cylinder (10) to return means, such as U tubes (39) at the extreme. inlet pressure (16) of the cylinder (10). The U tubes (39) connect the first set of cooling tubes (24) to a second set of cooling tubes (24) which return the cooling medium to the annular fitting (17) to be discharged to The heat exchanger equipment (34). The heat exchanger equipment (34) may include a steam generator (40) (fig. 10), a condenser, connection to a steam powered electricity generating system, etc. (all of which is not represented), as it is known

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in art.

As illustrated in fig. 2, air is supplied to the combustion cylinder (10) through an air duct (3θ) that is connected to wind boxes (38) via individual control ducts (35) · There are a total of six boxes wind turbines (33) arranged under the combustion cylinder (10). The windboxes (33) are arranged in three zones from the inlet end (16) to the outlet end (18), as shown in fig. 1A, with a lower fire wind box (58 _u ) and a wind box in each zone, as shown in fig.

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starter (59) to illustrate the connection of the lower fire wind box (38) to the control duct (35 _u ) - The fire boxes (38) receive the combustion air under pressure from a fan (not shown). The pressure is maintained by means of sealing strips (54) that extend longitudinally along the outside of the combustion cylinder (10) and have a cross-section in the shape of a dog's paw, as illustrated in fig. sealing strips (54) are contiguous at least in the axial length of a windbox (38) and help to form a pressure seal against the edges of the windbox (56) in addition to the combustion air coming out of the windboxes (33) enter the combustion cylinder (10).

A housing (57), shown in fig. 2, but excluded from fig. LA to simplify the design, is supported on a suitable surface by supports (58). The housing (57) surrounds the pair. side of the combustion cylinder (10) so that the combustion air is driven from the inlet (16) and the windboxes (38) by an induced draft fan (50) (fig. 10). The fan

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- 9 induced draft (5θ) is coupled to the smoke pipe (28) downstream of the rotary burner to keep the smoke pipe (28) slightly below atmospheric pressure. Thus, substantially all of the exhaust gases at the outlet (20) of the combustion cylinder (10) come out through the smoke pipe (28).

The rotary burner described above produces exhaust gas temperatures of up to 1100 ° C. However, the side wall (23) of the combustion cylinder (10) is maintained at a temperature of approximately 275 ° C by the circulating refrigerant. The smoke pipe walls (28) are typically lined with steam generating tubes (not shown) connected to the heat exchange equipment (JA) and are thus kept at approximately 275 ° 0. However, the heat distribution in municipal solid waste incinerators is so uneven that not all exhaust gas molecules are exposed to 1 000 ° C for a sufficient time to destroy trace organic substances, such as dioxins and furans.

In fig. 1C illustrates a conventional exhaust gas cleaning system (41) for a rotary burner. In a typical rotary burner installation, the refrigerant outlet from the combustion cylinder is supplied through pipes (33s) θ (531) to a steam generator (40) before it is supplied to other elements of the heat exchanger equipment ( 34). The steam generator (40) extracts heat from the exhaust gases (42) at high temperature and transfers the heat to the refrigerant. Thus, the exhaust gas outlet (44) of the steam generator (40) has a considerably lower temperature than the exhaust gas (42), as a result of its passage through the steam generator (40). The gases

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exhaust pipes (44) with reduced temperature pass through a sepa. cyclone generator (46) to remove the larger particles and will pass through a gas cleaning station (48) which is typically a baghouse filter or an electrostatic precipitator. An induced draft fan (50) assists the flow of exhaust gases (42) and (44) through the steam generator (40), the separating cyclone (46) and the gas scrubbing station (48), and finally , the exhaust gases (44) at low temperature are discharged in the form of emissions (53) from an exhaust port (51) in a chimney (52).

Conventionally, when additional gas purification is desired, in addition to that provided by the cyclone (46) and the bag filter station (48), complementary elements such as electrostatic precipitators, pod columns or catalysts are added, to the gas purification station (48), or inside or at the top of the chimney (52).

As schematically illustrated in fig. IA, according to the present invention, a refractory filter (60) is inserted, which removes particulate materials from the exhaust gases (20), in a zone of you. boiler (23) at high temperature. The filter (60) is preferably lined with ceramic materials which are heated by the exhaust gases (20) to temperatures of approximately 1000 ° C. run any filter that is able to withstand such temperatures and that represents a sufficient barrier to dioxins and furans in order to block its passage for a time sufficient to heat all exhaust gases. The porosity of the filter, the volume of the smoke pipe (28) used by the filter (60) and the capacity of the induced draft fan (50) must be equal

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I ί> released in such a way that the flow of exhaust gases produced by the induced draft fan (5O) (fig. 1C) is sufficient to maintain a combustion speed in the combustion drum (10) that completely incinerates the material, while an induced draft fan comparable to that used in the prior art is used.

In the embodiment illustrated in fig. 3, the filter (60) comprises porous ceramic filter elements for the gases (62), arranged in the exhaust gas outlet flow (63), as shown in fig. 3 and schematically in fig. IA. The filter elements (62) made of porous ceramic for gases can consist of a filter plug with flanges, known by the designation SCHUMACEL HTHP 60/40, which has a cylindrical portion (64) with an inner diameter of 40 mm and an outer diameter of 60 mm and a base (66) coarsely annular with an outer diameter of 74 mm · The length of the cylinder is 15C0 num (approximately 3 feet), thus providing a large surface area. The SCrfJKACEL is formed by porous silicon carbide for gases. SCHUTCACELs are manufactured by Schumacher-Sche Fabrik GmbH from Bietigheim, Federal Republic of Germany, and have been used to filter exhaust gas solids from coal burners in law. so fluidized.

In the filter (60) used in the patent, the bases (66) of the filter elements (62) are connected and sealed to li media. section provided by a support structure (68a, 68b) which in turn is sealed on the wall of the smoke pipe (28), as shown in fig. 3- As a consequence, all gases that pass. sam through the smoke pipe (28) must pass through the bad elements ORIGINAL

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- 12 / filter units (62) and out through the opening (70) in the support structure (6Sa, 68b) as exhaust gases (44 '). In the embodiment illustrated in fig. 5, two pieces (63a) and (68b) of sheet steel provide support for the filter elements (62) · As shown in fig. 4, to the left of the axis line (65), fig. 3 θ a cross section made by a plane that passes between the filter elements (62), while to the right of the axis line (65) the view is along a plane that passes through a row of the filter elements ( 62). As shown in fig.3, the bases (66) with flange are flushed between the two parts (68a) and (681) of the steel plate. In the upper plate (68a) openings (70a) are formed with a skin diameter less as large as the inner diameter of the filter elements (62) but smaller than the outer diameter of the bases (66). In the lower plate (68b) similar openings are formed with a diameter slightly larger than the outer diameter of the main cylindrical portion (64) of the filter elements (62). The steel plate parts (68a) and (68b) are then fixed and sealed on the smoke pipe wall (28) by means of fixing devices, such as rivets (72) ·

Other means may be used to support the filter elements (62), provided that they retain the filter elements (62) securely in their lugs, so that the filter elements do not receive vibrations and strike against each other. , so that an effective seal is formed to ensure that substantially all of the gases of type pass through the filter elements (62) · For example, a single sheet of steel, or other material, having openings (? 0a) appropriate, it can be fixed to the filter elements (62) by an adhesive capable of resisting temperatures

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- 13 ζ between room temperature and 1,200 ° C. Similarly, and support structure (68a, 68b) can be attached to the flue pipe (28) by any known means that provide a good seal. In fig. 3, the bases (66) of the filter elements (62) are illustrated as being in top-to-top contact, which is preferable from the point of view of minimizing pressure drop across the filter (60) providing an area of large surface. On the other hand, when the filter elements are packed so close together, the stiffness of the support structure (68a, 68b) must be sufficient to ensure that that tension does not cause the bases (66) to damage each other . Other types of refractory filters (60) can also be used, as long as the material is able to withstand the temperatures present in the smoke pipe and has such a porosity as the material. al holds the exhaust gases for a sufficiently long time to destroy the toxic organic substances contained therein, while requiring a volume and pressure drop through them comparable to that of prior art filters.

In addition to destroying the toxic organic substances in the exhaust gases, the filter (60) removes solid particles, such as fly ash, which together with the exhaust gases, are pre. at the outlet (20), thus producing clean exhaust gases (44 '). Therefore, it is expected that the toxic organic substances present in the solid particles removed from the exhaust gases (20) by the filter (60) will also be destroyed. It is shown that the gas cleaning equipment illustrated in fig. 10 and other known devices for removing particulate material from the lower temperature zone after the steam generator, works

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inefficiently for the removal of organic substances. In addition to these points, considerable external heat sources are required if toxic organic substances are to be destroyed by heating in the purification station (48) (52).

In addition, delaying the removal of solids until after the exhaust gas leaks through the steam generator (40) re deposits in the steam generator (40) degrading the heat transfer from the exhaust gases to the refrigerant sent through the steam generator (40) and the particulate material sows the formation of dioxins in the zone downstream of the ge. steam generator (40) where the temperature is in the range of at 400 ° C. When using a filter according to the present invention, the cleaning and maintenance of the steam generator (40) is reduced and the conventional gas scrubbing equipment (48) can be removed (fig. 10), so that the total pressure drop between the combustion cylinder (10) and & induced draft fan (50) can be compared to that of the prior art system. Otherwise, a more powerful induced draft fan (50) may be necessary, partly because the solid particles in the exhaust gases (20) will accumulate on the upstream surface of the filter elements (62) · If using such equipment, the particulate material would again be supplied to the system upstream of the filter elements and in such a place that the organic substances are removed by heating them.

Therefore, means must be provided for cleaning the filter elements (62). For this, as illustrated in fig. IA, a high pressure air source (721 ·.

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(74), which are best seen in fig. 3, are connected to the high pressure air source (72) by a pressure tube (73) · Periodically, air is injected through the injectors (74) to reverse the flow of gases through the cylinders (64) , dislodging accumulations of solid particles from the surface, which then fall through the smoke pipe (28) and can be discarded by the conventional method used to remove solid products from combus. so (22). The high pressure air (72) can be provided from any conventional source and the pressure tube (73) and the injectors (74) can be formed from any non-porous material capable of withstanding temperatures above 1000 ° C . The injectors (74) do not need to be constructed as shown, but may have any suitable shape in order to reverse the flow of gases through the filter elements (62).

Cleaning of the filter (60) can be done periodically, at fixed time intervals, or when necessary. Preferably However, the pressure drop through the filter (60) should not be greater than approximately 4 mm of mercury. For this purpose, pressure sensors are inserted (75) ^No fumes inside the tube (28), one upstream and one downstream of the filter (60). The pressure sensors (75) produce signals that are supplied to a cleaning control unit (76) which determines the pressure differential between the two signals and provides a control signal for the high pressure air source (72) when the pressure differential exceeds the predetermined level, for example 4 mm: of mercury. Pressure sensors can be of any conventional type, such as the 1151 series sensor, manufactured by Kosemount of Minneapolis, Minnesota, which is capable of withstanding temperatures above

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000 ° C. The cleaning control unit (76) can comprise a conventional microprocessor, such as an INTEL 88/40.

The many important features and advantages of the present invention are evident from the minor specification and therefore, the attached claims are intended to cover all such features and advantages of the device that fall within the true spirit and scope of the present invention. Furthermore, as numerous modifications and changes can easily occur to those skilled in the art, it is not desired to limit the present invention to the exact construction and operation illustrated and described. Accordingly, all appropriate and equivalent modifications may be considered to fall within the scope and spirit of the present invention.

Claims (5)

1 · ~ Process for the purification of exhaust gases (20), containing gases, toxic organic substances and material in. particles produced by an incinerator (10) in the process of burning solid waste material from municipal waste (1M), the incinerator (10) having an inlet end (16) to receive the waste material (1U) and an outlet end (18) for exhaust gas discharge (20), with the left end (18) placed in a chimney flue (28) lined with steam generators to transport the scale gases (20) out of the exhaust end. outlet (18) of the incinerator (10), characterized by understanding the phases of: direct the exhaust gases (20) through a porous filter (80) of the gases, arranged in the flue pipe lined with steam generating tubes (28) downstream of the outlet end (1E) with ORIGINAL 3AD incinerator (10) so that the particulate material is removed from the exhaust gases (20); heat the filter (60) using the heat from the exhaust gases (20) to a temperature above 700 ° C; controlling the flow of exhaust gases (20) through the filter (60) to expose substantially all exhaust gases (20) to a temperature of at least 700 ° C for a time sufficient to destroy substantially all toxic organic substance in the exhaust ( 20); detecting the pressure drop through the filter (60); compare said pressure drop with a predetermined pressure drop to automatically clean said filter (60) by removing the accumulated particulate material when the detected pressure exceeds the predetermined pressure drop and thereby operating the incinerator (10) so that the effluent exhaust gases (42) are substantially free of toxic chronic substances. 2. The process according to claim 1, further characterized in that said predetermined pressure drop is generally in the range of 4 η ~ Hg. 3. - Exhaust gas purification apparatus (20) containing gases, toxic organic substances and particulate material produced by an incinerator (10) in the process of burning T ORIGINAL 3AD 'solid waste material from municipal waste (14.), the incinerator (10) having an inlet end (16) to receive the waste material (14) and an outlet end (16) disposed in a flue (26) lined with steam generating tubes to transport the exhaust gases (20) from the outlet end (18) of the incinerator (10), characterized by comprising a porous filter (60) of the gases disposed in the pipe chimney (28) lined with steam generating tubes in a sealing relationship with it, downstream of the outlet end (18) of the incinerator (10) in order to absorb heat from the exhaust gases (20) so that the filter (60 ) reaches a temperature above 700 ° C to raise the total exhaust gas (20) to at least 700 ° C; means (72,73 and 74) for cleaning the porous gas filters (60) disposed adjacent to them; means (75) for detecting the pressure drop through the gas porous filter (60); and means (76) for operating the cleaning means (72,73 and 74) when the pressure drop detection means (75) detects a higher pressure drop and a predetermined value, in order to remove the material in exhaust gas particles (20) and keep all exhaust gas (20) at a temperature of 700 ° C near the porous filter (60) so that the effluent exhaust gases (42) are substantially free of organic substances. ORIGINAL SAQ toxic. 4.- Apparatus according to claim 3, further characterized in that the gas porous filter (60) is made of a ceramic material. 5.- Apparatus according to claim 4, further characterized in that the predetermined pressure drop is generally in the range of 4 mm Hg,