DUCT

Field of the invention

The present invention relates generally to a sorbent injection assembly and method for injecting a sorbent into an exhaust gas duct for reducing the amount of noxious compounds in effluent gas streams from industrial processes, energy production, and the like.

Description of the prior art

As is well known, fuel combustion in industrial processes and in energy production generates a number of potential pollutants including fly ashes and acid gas. The release of these pollutants into the atmosphere needs to be minimized. Reducing the acidic gas content of the effluent gas prior to discharging the gas to the ambient air is one way to reduce air pollution. In particular, reducing the SO ₂ , SO _3, H ₂ SO _4, HC1, HF, etc., content as well as the heavy metals, e.g., Sb, As, Be, Cr, Mn, Hg, Se, etc., content of such effluent gases provides a number of advantages such as reducing unsightly gas plumes, reducing corrosive by-products, and reducing the risk of harmful human exposure. One area in which these problems are prevalent is in the area of coal-fired power plants which produce significant amounts of SO ₂ and/or SO ₃ . There are also other industrial processes that involve formation of gaseous effluents that contain acidic gases including, for example, sulfuric acid plants and other industrial chemical plants, waste incinerators, non-coal fired power plants such as oil-fired plants, large-scale diesel generators, boilers, brick and ceramic furnaces, as well as lime and cement kiln operations.

Common elements of various combustion systems of this general type include a combustion chamber and a burner for igniting fuel located in the combustion chamber. Fuel (e.g., coal or biomass) is fed into the combustion chamber, were it is rapidly ignited and stabilized on burners. Any of a number of the previously mentioned undesirable components included in the fuel, e.g., acid components or metal components, may enter the environment via the flue gas exiting the exhaust stack and may cause undesirable consequences. The prior art is replete with various flue gas desulfurization ("FGD") processes which have been developed to reduce the amount of acidic gases in the effluent gas, particularly with respect to the previously mentioned SO ₂ , SO ₃ and/or H ₂ SO ₄ . A commonly practiced method uses a dry alkaline sorbent such as hydrated lime, i.e., Ca(OH) ₂ ,with the sorbent being introduced into an exhaust duct of the particular industrial process of concern. Flue gases from such industrial process pass through the exhaust duct where they react with the sorbent. The resulting reaction of the sorbent with the acid compound forms a particulate solid, e.g., CaSCb or CaS0 ₄ . These solid reaction products can subsequently be removed in a downstream bag house or other collection system.

Prior art has taught that improved dispersion and homogeneity of injected dry powders in sorbent injection systems can be achieved by combining the sorbent with large volumes of supplemental air, e.g., on the order of 2000 scfm, within the device prior to ejection from the respective outlet into the duct. However, there are disadvantages associated with using very high peripheral air flow rates, in some cases, even disturbing the overall operation of the facility for treating the flue gases.

The present inventive method provides one solution to these and other longstanding needs in the industry in a manner that is simple to implement as well as being cost effective, and yet which does not require the use of large volumes of supplemental air, as was sometime used in the past.

Summary of the invention

The present invention is directed to an improved apparatus and method for reducing the acidic gas content of effluent gas, e.g., flue gases produced from coal-fired power plants, which use a sorbent composition such as hydrated lime, in which increased dispersion of the sorbent particles is achieved. This increased dispersion of particulate reduces the mean free path for the effluent gas molecules to diffuse to the sorbent surface, thereby increasing the overall efficiency of the process.

The principle aim of the device of the invention and of the method of using such device is thus to introduce a well-dispersed dry powder (e.g. hydrated lime, powdered activated carbon, various clays and other modified or unmodified minerals, trona, sodium bicarbonate etc.) into the exhaust duct of an industrial process for remediation of one or more pollutants including acid gases (e.g. SO ₂ , SO ₃ , HC1, HF etc.) and heavy metals (e.g. Sb, As, Be, Cr, Mn, Hg, Se etc.) from combustion fumes. As will be described more fully in the written description which follows, the device and method of the invention can be designed to provide the pollution mitigation sorbents with both tangential (side to side) dispersion as well as with lateral (depth) penetration in to the duct to provide enhanced sorbent homogenization with the process gas and with the target pollutants.

According to the principles of the invention, a method is shown for reducing the noxious compounds, such as but not limited to acidic gas, in an effluent mixture passing through a duct, the duct having an inner wall which defines a flow path for the passage of the effluent gases. In accordance with the method, a sorbent composition, such as but not limited to hydrated lime, is introduced into a specially designed sorbent dispersion device, also referred to herein as sorbent injection assembly.

The present disclosure describes a sorbent injection assembly for injecting a sorbent into an exhaust gas duct, the sorbent injection assembly comprising: a sorbent injection pipe having an inner bore with a longitudinal axis, an inlet and an outlet, which outlet is in particular configured to be positioned within the exhaust gas duct, the sorbent injection pipe being configured for conveying a sorbent there through by a carrier gas such that the sorbent is injected into the exhaust gas duct such that a flow of sorbent exits the outlet with an axial component parallel to the longitudinal axis of the sorbent injection pipe; and at least one nozzle coupled to a dispersing gas, such as air, supply line, in particular by having an inlet configured to be coupled thereto, and having an outlet provided in the vicinity of the outlet of the sorbent injection pipe, the nozzle being oriented towards the longitudinal axis of the sorbent injection pipe such as to project a flow of dispersing gas onto the flow of sorbent exiting the outlet of the sorbent injection pipe, wherein the sorbent injection assembly is effective to provide increased dispersion of sorbent within the exhaust gas duct.

As described in more detail below, such a sorbent injection assembly allows increased dispersion of sorbent within the exhaust gas duct. In particular, by impinging the sorbent stream, after it has been ejected from the sorbent injection pipe, with a dispersing gas, such as air, the particles of the sorbent stream are spread further apart, thereby achieving greater dispersion and, in turn, reducing the mean free path for the effluent gas molecules to diffuse to the sorbent surface.

In an embodiment of the sorbent injection assembly, the nozzle is fixed to the sorbent injection pipe.

In another embodiment of the sorbent injection assembly, the nozzle is spaced apart from the sorbent injection pipe.

In another embodiment of the sorbent injection assembly, the nozzle is fixed on a sleeve surrounding the sorbent injection pipe and comprises a bore extending from a first extremity connected to the air supply line, to at least a second extremity forming the outlet.

In another embodiment of the sorbent injection assembly, the sorbent injection pipe is surrounded by a sleeve which forms an annular chamber with an external wall of the sorbent injection pipe, wherein the sleeve carries the at least one nozzle connected to the annular chamber and the annular chamber is connected to the air supply line.

In a preferred embodiment of the sorbent injection device, at least two nozzles are provided around the outlet of the sorbent injection pipe.

In another embodiment of the sorbent injection pipe, a circular duct carrying a plurality of nozzles surrounds the sorbent injection pipe, the duct being connected to the air supply line.

One preferred sorbent injection device includes a plurality of specially arranged and oriented air nozzles or injectors which are mounted about and extend outwardly from a conventional dry sorbent lance. As has been previously described above, the lance has a central passageway for conveying sorbent. A sorbent, such as but not limited to hydrated lime, is introduced into the central passageway of the lance by means of a carrier gas stream. The injectors or nozzles are curved tubes having an exterior surface and an interior passageway or bore. Each of the injectors also has an inlet end and an outlet end which serves as the air nozzle. It will be appreciated by those skilled in the relevant arts that various other nozzle configurations could be used, the nozzles or injectors having any other shape, provided that the outlets of the air nozzles are angled towards an axial center line of the lance, in particular by an angle comprised between 0 to 120 degrees. The nozzles may be in communication with each other via a central air line running adjacent to the lance that is connected to a source of compressed air. Depending upon the angular orientation, the particular arrangement of the injectors relative to the centrally located lance can provide tangential (side to side) dispersion as well as lateral (in depth) dispersion. The sorbent is discharged from the central passageway of the lance into the duct to react with pollutants of exhaust gases being conveyed in the exhaust duct, thereby reducing the concentration of noxious components in the effluent gas.

It is desirable to maintain the carrier gas velocity in the sorbent injection duct at reasonable velocity. A high velocity can result in wall build-up by impinging particles. For this reason, increasing the flow rate of the carrier gas to improve sorbent dispersion into the exhaust gas duct is not a desirable option. According to the invention, the sorbent is dispersed into the exhaust duct by the dispersion gas flowing through the at least one nozzle arranged at the vicinity of the outlet of the sorbent injection pipe without requiring excessive carrier gas velocities.

To explain further, the prior art has taught that improved dispersion and homogeneity of injected dry powders can be achieved by combining the sorbent with large volumes of supplemental air (-2000 scfm) within the sorbent injection lance prior to ejection from the respective outlet into the exhaust duct. However, the method of the present invention achieves improved sorbent dispersion by impinging the sorbent stream, after it has been ejected from a lance, with relatively low volumes (i.e., < 400 scfm) of pressurized air. Under normal FGT operation conditions, sorbent powder is supplied to the lance component of the device at a mass flow rate of 1 to 20,000 pounds per hour. Simultaneously, compressed air, supplied at 1 to 400 scfm and pressurized to 0.5 to 200 psig, is delivered to the central air line of the sorbent injection pipe. The resultant impingement air, also referred to as dispersing gas in the present disclosure, from the air nozzles, directed at the effluent sorbent stream, increases the dispersion of the sorbent particles, thereby increasing the total volume within the duct occupied by the injected dry powder. As a result, exposure of effluent gas to particulate sorbent is increased improving the overall performance of the process of pollutant removal from exhaust gas using the particulate sorbent. Increasing the sorbent dispersion allows further penetration into the duct and improved pollutant mitigation and/or neutralization.

In one configuration the device used in practicing the method of the invention is comprised of (1) a cylindrical dry sorbent lance of length 6 to 240 inches, and an inner diameter of 1 to 10 inches, and (2) up to 20 interchangeable cylindrical air nozzles (injectors) of length 0.25 to 6 inches and an inner diameter of 0.1 to 2 inches. The outlets of these air nozzles may be angled towards the axial center of the lance by 0 to 120 degrees. The nozzles are in communication with each other via a central air line running adjacent to the lance that is connected to a source of compressed air.

Various refinements exist of the features noted in relation to the above-mentioned aspects of the present disclosure. Further features may also be incorporated in the above-mentioned aspects of the present disclosure. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present disclosure may be incorporated into any of the above-described aspects of the present disclosure, alone or in any combination.

Brief description of the drawings

Figure 1 is a side view of one embodiment of the improved sorbent lance of the invention showing the cylindrical lance body being surrounded by a pair of injector tubes, the injector tubes being fed, in this case, by a common manifold which is itself connected to an air source by a main air supply line.

Figure 2 is a partial side, cross sectional view of the lance of Figure 1.

Figure 3 is a perspective view of an alternate embodiment of the improved lance of the invention in which the cylindrical lance body is surrounded by a plurality of injector tubes which are themselves connected by a common line which is fed by the main air supply line. Figure 4 is a simplified illustration of a flue gas treatment installation carrying out the flue gas treatment process of the invention with the improved lance configuration as shown in Figure 1.

Figures 5A and 5B are photographs made with a high temperature camera installed into a port of an exhaust duct, comparing sorbent dispersion (A) in the absence of impingement air; and (B) when 25 scfm of air, pressurized to 75 psig, is supplied to the curved injector tubes of the device of the invention.

Figure 6 is a schematic cross sectional view of another embodiment of a sorbent injection assembly according to the invention which is provided to an exhaust gas duct and wherein the sorbent injection assembly comprises a flange carrying a sorbent injection pipe having a longitudinal axis and a nozzle directed to the longitudinal axis of the sorbent injection pipe, wherein the nozzle is at a short distance away from the sorbent injection pipe.

Figure 7 is a schematic cross sectional view of another embodiment of a sorbent injection assembly according to the invention which is provided to an exhaust gas duct and wherein the sorbent injection assembly comprises a flange carrying a sorbent injection pipe having a longitudinal axis and a nozzle directed to the longitudinal axis of the sorbent injection pipe, wherein the nozzle is fixed along the sorbent injection pipe.

Figure 8 is a schematic cross sectional view of another embodiment of a sorbent injection assembly according to the invention which is provided to an exhaust gas duct and wherein the sorbent injection assembly comprises a flange carrying a sorbent injection pipe having a longitudinal axis and a nozzle directed to the longitudinal axis of the sorbent injection pipe, and a sleeve forming an annular chamber around the sorbent injection pipe and having a side wall on which is mounted the nozzle and an opposite side wall attached to the flange.

Figure 9 is a schematic cross sectional view of another embodiment of a sorbent injection assembly according to the invention which is provided to an exhaust gas duct and wherein the sorbent injection assembly comprises a flange carrying a sorbent injection pipe having a longitudinal axis and a nozzle directed to the longitudinal axis of the sorbent injection pipe, and a sleeve having two opposite side walls fixed to the sorbent injection pipe, forming an annular chamber around the sorbent injection pipe and wherein the nozzle and an air supply line are connected to the annular chamber.

Figure 10 is a schematic cross sectional view of another embodiment of a sorbent injection assembly according to the invention which is provided to an exhaust gas duct and wherein the sorbent injection assembly comprises a flange carrying a sorbent injection pipe having a longitudinal axis and a nozzle directed to the longitudinal axis of the sorbent injection pipe, wherein the nozzle is fixed along the sorbent injection pipe, the sorbent injection assembly further comprising an air supply line intersecting a side wall of the sorbent injection pipe, the assembly further comprising a nozzle within the said sorbent injection pipe, the said nozzle being directed towards the outlet of the said sorbent injection pipe.

Figure 11 is a graph showing measurements of SO ₂ concentrations after passage of an effluent gas through a duct without any flue gas treatment device, after flue gas treatment using a conventional sorbent injection device and after flue gas treatment using a sorbent injection device according to the present invention, respectively.

Detailed description of the invention

The present invention provides an improved sorbent injector system, also referred as sorbent injection assembly, which meets the foregoing objectives. The invention described herein, and the various features and advantageous details thereof are explained more fully with reference to the non-limiting examples which are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processes and manufacturing techniques are omitted so as to not unnecessarily obscure the workings of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the invention herein may be practiced and to further enable those of skill in the art to practice the invention. Accordingly, the examples should not be construed as limiting the scope of the claimed invention. Turning first to Figure 4, there is shown a simplified representation of a sorbent injection system which is the subject of the present inventive method. The injection system includes a lance 11, also referred to as a sorbent injection pipe, which is mounted in a sidewall 13 of an exhaust duct 15 of the type used to convey exhaust gases from an industrial or energy process. The process could be, for example, a coal-fired power plant, which plants often produce significant amounts of SO2 and/or SO3. However, many other types of industrial processes also involve the formation of gaseous effluents that contain acidic gases including, for example, the previously mentioned sulfuric acid plants and other industrial chemical plants, waste incinerators, non-coal fired power plants such as oil-fired plants, large-scale diesel generators, boilers, brick and ceramic furnaces, as well as lime and cement kiln operations.

The effluent gas stream that is treated according to the method of the invention may include any number of acidic compounds such as, for example, SO ₂ , SO ₃ , H ₂ SO ₄ , HC1, and/or HF. Further the concentration of these gases before treatment may be on the order from about 50 ppm to about 3000 ppm, but these concentrations are not limitative for the present invention. The temperature of the effluent gas in the duct will typically range from about 250°F to about 800°F (about 121 °C to about 427 °C), by way of example only. In other applications, for example in the case of Furnace Sorbent Injection (FSI), temperatures up to about 2200°F can be envisioned.

Any number of sorbent compositions, including combinations thereof, may be utilized in the sorbent injection system of the invention. These materials include, for example, hydrated lime, pulverized quicklime, powdered activated carbon, clays and other modified or unmodified minerals, trona, and sodium bicarbonate. In this general context, calcium oxide, CaO, is often referred to as "quicklime", while calcium hydroxide, Ca(OH)2, is referred to as "hydrated lime", both sometimes being informally referred to as "lime". Quicklime is usually in the form of lumps or pebbles but it can also be a powder. Dry hydrated lime is usually a powder. In the meaning of the present invention,“powder” means a solid substantially made of particles lower than about 2 mm, in particular lower than 1 mm or even lower than 500 pm and notably greater than 0.1 pm, in particular 0.5 pm. A particularly preferred sorbent composition is powdered hydrated lime. However, as mentioned, other compounds such as a carbonate or a bicarbonate of sodium or the compounds used for the abatement of dioxins, furans, and/or heavy metals, including mercury, for example, such as those containing phyllosilicates, like sepiolite or halloysite or the equivalent may also be utilized. Powdered hydrated lime, also called slaked lime as used herein, will be understood to mean a set of solid particles mainly consisting of Ca(OH)2 _, i.e., calcium hydroxide.

A number of suitable sorbent compositions are commercially available in the marketplace. For example, products of the above types are commercially available from Lhoist North America, 5600 Clearfork Main Street, Fort Worth, Tex. 76109, or from Lhoist Operations worldwide. One such product is sold commercially as“SORBACAL ® SP”. This sorbent composition has the following product characteristics: purity (content of Ca(OH)2) of greater than 90%; a BET Specific Surface Area of more than 18 m ² /g; a Total Pore Volume (90-1000 Angstrom) of more than 0.10 cm ³ /g; and a dso in a range comprised between 5 and 15 pm.

The hydrated lime, or other sorbent, may be stored in a bulk lime storage silo and may be transferred into a pneumatic conveying line, for example, by a variable rotary airlock. Where multiple injection units are used (i.e. multiple sorbent injection assemblies are arranged at distinct locations of the exhaust gas duct), the pneumatic conveying sorbent line may be divided into a plurality of sorbent feeder lines by use of one or more line splitters. Each sorbent feeder line is in fluid communication with a respective sorbent injection pipe or lance. An air supply line for the nozzles used in the method of the invention may also be comprised of a main conveying line divided into a plurality of air feeder lines. Each air feeder line is in fluid communication with one or more nozzles of a respective sorbent injection assembly.

As briefly discussed in the Background portion herein, sorbent injection processes of the above general type pose a number of challenges in practical operation in terms of transportation flow rate, injection flow rate and radial dispersion of the powdered compound in the exhaust duct. For example, the injection of the powder (sorbent composition) into the exhaust duct should be carried out at a pressure greater than the pressure of the flue gases present in the exhaust duct, in order to prevent the powder from dispersing poorly therein and, in certain cases, agglomerating against the walls of the duct. However, too great a pressure can lead to such problems as friction/attrition and/or clogging of the powder in the transportation pipe, and the latter phenomenon can also lead, when the powder contains slaked lime, to carbonatation of the lime powder.

Also, in order for the treatment to be most effective, the powdered sorbent should be dispersed homogeneously over the entire transverse cross-section of the exhaust duct (with respect to the flow of the flue gases in the exhaust duct) in order to allow homogeneous and efficient abatement of the gaseous pollutants. This dispersion is dependent on a number of factors, such as the size of the duct and on the flow rate of the gases that pass through it. In order to overcome problems associated with effective dispersion of the sorbent, many of the prior art systems have utilized "penetrating nozzles" or“lances” as they are often referred to in the industry. These“lances” penetrate the sidewall of the exhaust duct and are therefore entirely subjected to the flow of the flue gases. In particular, the prior art used“shaped lances” together with a high volume of transport air.

Even the use of such "penetrating nozzles" or“lances” presents certain problems in practice, however. For example, the desired lance design must be relatively simple in construction and yet be sturdy enough to resist the temperature and acidity conditions to which they are exposed in the exhaust duct. Where lances require frequent replacement, operating costs are increased since it may be necessary to stop the associated furnace, sometimes for several days. Restarting the combustion after each stoppage of the furnace, in order to replace the penetrating nozzles, is problematic when these furnaces do not rapidly and easily reach their equilibrium during combustion.

Most significantly for purposes of the present invention, the "penetrating nozzles" previously used in the industry, although allowing for a certain degree of dispersion of the powder in the exhaust duct, failed to achieve superior dispersion of the particulate sorbent in the exhaust duct and thus lacked in terms of maximum efficiency.

Because of problems with lance type injection systems, certain“lanceless” systems have also been developed. However, these“lanceless” injection systems require the very high peripheral air flow rates previously discussed. As has been mentioned, such flow rates are generally undesirable and may even disturb the overall operation of the facility for treating the flue gases. For example, with peripheral air flow rates that are so high, compared to the flow rate of the flue gases, the quantity of air added to the flue gases is non-negligible and leads in particular to undesired cooling of these flue gases, thus reducing the overall energy performance of the furnace. Such a device also has the effect of increasing the total flow rate and the oxygen concentration of the flue gases located downstream of said device, thus forcing the operator to modify the line for treating the flue gases accordingly.

The present inventive method has as its aim to overcome problems of the above type associated with the prior art sorbent injection systems through the use of an improved“lance” injector type device which achieves improved sorbent dispersion by impinging the sorbent stream, after it has been ejected from the lance, with relatively low volumes (< 400 scfm) and relatively high pressure air, e.g., 0.5 to 200 psig, in one case to be further described, 75 psig of pressurized air. The nozzle arrangement used in the improved lance design of the invention impinges upon the sorbent stream to spread the particles of sorbent further apart, thereby achieving greater dispersion and, in turn, a greater surface area for contact with the effluent gases.

Figure 4 is a simplified representation of a sorbent injector system featuring the improved sorbent injector device or sorbent injection assembly of the invention. As shown in Figure 4, a portion of the injector, in this case lance 11, extends through the exhaust duct wall 13. The distance to which the injector 11 extends in the duct should be selected such that sorbent becomes well distributed in the duct and may vary depending on a number of system factors including the size of the duct, the respective effluent gas and sorbent flow rates. This distance may be, for example, on the order of 4 to 5 feet. The duct 15 defines a flow path, generally at 17 in Figure 4, for the effluent gases leaving the industrial process, as previously described. The duct 15 is represented in Figure 4 as having a rectangular cross section, but one skilled in the art can easily adapt the sorbent injection assembly to match with a duct having another cross section shape such as a circular cross section.

A first version of the improved sorbent injector device of the invention is shown in perspective in Figure 1. The injector includes the lance 11 which comprises a cylindrical pipe having an inlet 19, an outlet 21 an exterior 23, and interior 25, the interior comprising a central passageway for the sorbent injector and defining an axial center line 27 of the lance 11. The previously described sorbent composition (e.g., hydrated lime) is conveyed through the interior of the sorbent lance by a pressurized carrier gas, as is customary in the industry.

As also shown in Figures 1 and 2, two curved injector tubes or curved nozzles 29, 31, are mounted about the exterior of the sorbent lance 11 and extend in a longitudinal direction generally parallel to the axial center line 27 for a major portion (“1” in Figure 2) of their respective lengths, terminating in a curved end region (“e” in Figure 2). The curved injector tubes each have an inlet 33, 35, a central bore 37, 39, and an outlet 41, 43, for dispensing pressurized air. As will be appreciated with respect to Figure 2, the curved nozzles 29, 31, are angled toward the axial center line 27 of the sorbent lance 11 by a preselected angle which may range from about 0 degrees to about 120 degrees in most cases. In the example shown in Figure 2, the two nozzles 29, 31, are directed exactly toward the center line 27 and toward each other, forming a 0 degree angle, whereby the nozzles directly impinge upon one another. However, it will be appreciated that the outlet 41, 43 of the nozzles 29, 31, could also be oriented in one direction or another with respect to the central axis 27 to provide a tangential or partially tangential flow of air with respect to the central axis 27 and thus into the flow path of the sorbent passing through the central passageway (25 in Figure 1) of the lance. It should also be noted that the curved shape of the nozzle is not limitative for the present invention and that other nozzles of different shapes can be provided, as long as the outlets of such nozzles is directed towards the projected longitudinal axis 27 of the lance 11.

Each of the air nozzles 29, 31, is in communication with an air supply line, such as line 45 in Figure 2, which is, in turn, in communication with a source of compressed air (not shown). The arrangement of the curved injector tubes or curved nozzles 29, 31, causes air being discharged from the outlets 41, 43, thereof to be dispersed into the flow path of the sorbent exiting the central passageway (25 in Figure 1) of the sorbent lance 11. The sorbent composition being discharged from the outlet end of the injectors and passing into the interior of the duct (17 in Figure 4) reacts with the acidic gases or other noxious compounds in the exhaust gas, thereby reducing the concentration of acidic gas or these noxious compounds in the effluent stream. As discussed above, the sorbent composition can be, for example, selected from the group consisting of hydrated lime, pulverized quicklime, powdered activated carbon, clays and other modified or unmodified minerals, trona, and sodium bicarbonate or a mixture thereof.

The sorbent composition will generally have a mass flow rate in the range from about 1 to 20,000 lbs/hr for a typical installation. The sorbent composition in the central passageway of the sorbent lance will generally be subjected to a compressed air flow rate in the range from about 5 to 500 scfm and a compressed air pressure in the range from about 0.5 to 200 psig for the typical industrial installation.

It will be appreciated from Figures 1 and 2, that the first version of the injector device of the invention has the curved nozzles 29, 31, extending from a common manifold 47. The dotted lines in Figure 2 show the bores 37, 39, of the tubes being joined in the manifold 47 to the common air supply line 45. The nozzles 29, 31 can be pressed- fit within the bores 37, 39 of the manifold or fixed to the bores 37, 39 by welding or threads. However, as shown in Figure 3, it is not strictly necessary that a manifold be present. In the version of the injector device shown in Figure 3, there are four curved tubes 49, 51, 53, 55, equidistantly spaced about the cylindrical lance 57. The tubes are joined by a common conduit portion 59, which is, in turn, in communication with the air supply line 61.

The curved tubes 49, 51, 53, 55, are attached to the lance body 57, as by tack welding, or by any other convenient means. The material for the curved tubes can be any metal strong enough to withstand the environment of the exhaust gases in the duct 17.

In any of the embodiments of the sorbent injection assembly presented in the present disclosure, the materials used for the nozzles, the lance, the manifold or any other part of the sorbent injection assembly, should generally be resistant to corrosion in the environment in which they are used and, in particular, should be resistant to corrosion when exposed to acidic gases. Suitable materials of construction include any material (e.g., metals) that can reliably withstand the temperatures and pressures used within the exhaust duct environment, such as carbon steel, stainless steel or brass, by way of example. In one case, the curved tubes and air supply line were constructed from stainless steel grade 316 tubing. The maximum temperature rating for the particular material selected should be up to about 1200° F. In one installation, the sorbent lance has a cylindrical body with a length in the range from 6 to 240 inches and an inner diameter in the range of 1 to 6 inches. Although only two injector tubes are shown in Figures 1 and 2, for ease of illustration, it will be understood that more tubes might be present, e.g., four equidistantly spaced tubes. In some installations up to about 20 interchangeable curved injector tubes may be mounted about the cylindrical sorbent lance body, the curved injector tubes having a length in the range from about 0.25 to 6 inches and an inner diameter in the range from about 0.1 to 2 inches. In some situations, it may be desirable to temporarily or permanently cap selected ones of the outlets of the injector tubes to thereby further adjust the impingement angle achieved.

It will be appreciated from Figures 1-3 that the particular angular arrangement of the curved tubes and air outlets (such as outlets 41, 43, in Figure 2) determine the type of dispersion achieved. Thus, where the nozzles are oriented at a 0 degree angle, they will directly impinge upon one another. However, other angular orientations, i.e., more than a 0 degree angle, will cause air being discharged from the outlets thereof to be dispersed radially in to the duct in a tangential, side to side direction with respect to the sorbent composition exiting the central passageway of the sorbent lance. The particular arrangement of the air nozzles causes impingement air to be directed at the effluent sorbent stream at a particular selected angle, thereby allowing further penetration into the exhaust duct and improved pollutant mitigation and neutralization.

The flow rate of the carrier gas in the lance interior and the amount of sorbent introduced into the exhaust duct may vary depending on a number of system factors including, for example, throughput of the exhaust gas to be treated, the concentration of the acidic gases therein, the target acidic gas concentration of the treated gas, the sorbent type, the sorbent residence time and the like. Likewise, the number of sorbent injection assemblies used to supply sorbent (e.g., hydrated lime) into the exhaust duct may vary depending on the size of the gas duct. The number of sorbent injection assemblies should be selected to allow sorbent to sufficiently contact all acidic gas and/or noxious compounds in the exhaust duct to thereby neutralize the acidic gas and/or capture other noxious compounds such as heavy metals, mercury and/or dioxins. In addition to the size of the duct, the number of sorbent injection assemblies used may depend upon such factors as the flue gas temperature, acidic gas content and residence time of the exhaust gas within the exhaust duct.

As discussed in the Background portion, the effluent gas which is treated to reduce the pollutant content thereof may be formed in any number of industrial processes. The effluent gas may be a gas produced in operation of, for example, a waste incinerator, a sulfuric acid plant, a non-coal fired power plant (e.g., oil), a large-scale diesel generator, a boiler, a furnace (brick or ceramic) or a kiln (lime or cement). The sorbent injection assembly of the invention is particularly well suited for treating flue gas produced during coal-fired power generation. In coal-fired power plants, the exhaust duct to which the sorbent, such as for example hydrated lime, is introduced may be the boiler exhaust duct, ducts downstream of any catalytic processes (e.g., selective catalytic reduction), the pre-heater exhaust duct or ducts that are upstream of an electrostatic precipitator. The sorbent may alternatively be added at other process points. As used herein, the phrases "exhaust duct" and "effluent gas" should not be limited to any particular process or to any particular process point. Further, the term "duct" should not be limited to any particular duct shape or to any particular type of conveying apparatus. In some embodiments, sorbent (e.g., hydrated lime) may be added to one or more unit operations directly or to the discharge portions of the unit operations themselves (e.g., air pre -heater).

Figures 5A and 5B represent a photographic comparison of the sorbent dispersion (A) in the absence of impingement air; and (B) when 25 scfm of air, pressurized to 75 psig, is supplied to the air nozzles of the injector device according to the method of the invention. The sorbent used in this experiment is hydrated lime. The results shown below were obtained using (1) the injection device featured in Figures 1 and 2; (2) a high-temperature camera, and (3) a real-time flue gas analyzer. The injection device was installed into the port of a 8 x 8 foot rectangular duct supporting > 220,000 scfm of exhaust gas at temperatures in excess of 520° F. Approximately 300 feet downstream of the device was a flue gas analyzer that recorded temperature and gas composition. The high-temperature camera was positioned within 10 feet of the injector device. The photos show the normal plume (A) as compared to the modified plume (B) where the size of the plume is increased and spread out. As a result, the sorbent has a better dispersion in a certain volume to capture the acid gases or other noxious compounds. Initially the flue gas composition data was recorded for a minimum of 30 minutes in the absence of sorbent. Shortly thereafter, 1000 lbs /hr of hydrated lime was supplied a volumetric flow rate of conveying air of 5 - 500 scfm through the lance. The flue gas composition was recorded for a minimum of 30 minutes, and an in-duct image was captured (Figure 5A). Following the second step, 25 scfm of 75 psig compressed air (referred to as supplemental air in Table 1 below) was supplied through the nozzles. Data was recorded for 30 minutes and an in-duct image was captured (Figure 5B).

The results in Table 1 below confirm that hydrated lime, supplied at 1000 lbs/hr, with a volumetric flow rate of conveying air of 5 - 500 scfm effectively reduces the concentration of SO2 by 32%. Further, the 31% improvement of the sorbent plume length, afforded by the impingement air, resulted in an additional 18% reduction in SO2 concentration.

Table 1:

Other embodiments of the sorbent injection assembly according to the spirit of the invention are presented here below.

An embodiment of a sorbent injection assembly according to the invention is presented schematically in Figure 6. The sorbent injection assembly is provided to an exhaust gas duct 107 and comprises a flange 111 carrying a sorbent injection pipe 101 and a nozzle 108 arranged at a short distance away from the sorbent injection pipe. The flange 111 closes an opening provided along the exhaust gas duct 107 and is fixed to the exhaust duct by appropriate fixation means such as screws or threads and O-rings (not shown) to provide a sealed fastening. The sorbent injection pipe 101 has a bore 102 developed around a longitudinal axis 106, an inlet 103 connected to a feeding line 105 alimented by a carrier gas, e.g. air, itself connected to a conveying screw 115 providing powdered sorbent to the feeding line 105 such that the sorbent is conveyed by the carrier gas successively through the feeding line 105, the sorbent injection pipe 101 and the outlet 104 of the sorbent injection pipe 101 to the interior of the exhaust gas duct.

The nozzle 108 and the sorbent injection pipe 101 are fixed to the flange 111 by welding or by press fit, or by appropriate threads and O-rings to provide a sealed fastening. The sorbent injection pipe 101 and the nozzle 108 may also extend through the flange. The nozzle 108 is connected to a dispersing gas supply line 109 which is preferably an air supply line. The nozzle 108, in particular the outlet 110 thereof, is directed towards the longitudinal axis 116 of the sorbent injection pipe and may form an angle relative to the longitudinal axis comprised between 0 and 120°. A plurality of nozzles may be arranged on the flange and may be connected to a respective air supply line or to a single manifold connected to an air supply line. The flow of dispersing gas passing through the nozzle and directed towards the flow of sorbent 106 carried by the carrier gas and injected into the exhaust gas duct provides dispersion of the sorbent particles within the exhaust gas duct, increasing the probability of sorbent particles to interact with the exhaust gas.

Another embodiment of a sorbent injection assembly according to the invention is described in combination with the Figure 7. The sorbent injection assembly differs from the one presented in relation with figure 6 in that the nozzle 108 is arranged against the sorbent injection pipe. The nozzle 108 may be welded to the sorbent injection pipe 101.

Another embodiment of a sorbent injection assembly according to the invention is described in combination with the Figure 8. The sorbent injection assembly is provided to an exhaust gas duct

107 and comprises a flange 111 carrying a sorbent injection pipe 101 a nozzle 108 and a sleeve 112 having an end wall 114 surrounding the sorbent injection pipe 101 such as to form an annular chamber 113. The flange 111 closes an opening provided along the exhaust gas duct 107 and is fixed to the exhaust duct by appropriate fixation means such as screws or threads and O-rings (not shown) to provide a sealed fastening. The flange 1 11 further closes the annular chamber 113 at an end opposite the end wall 114 of the sleeve 112. The annular chamber is connected to the nozzle

108 and to an air supply line 109. Preferably a plurality of nozzles 108 are arranged on the end wall 114 of the sleeve 112, whereby the annular chamber 113 functions as a manifold providing air from a single air supply line 109 to a plurality of nozzles 108. The nozzles can be fastened to the sleeve by welding or preferably by press-fit or by appropriate treads and O-rings such that they can be removed and replaced. Such an assembly construction allows easier machining of the separated pieces of the assembly and easier replacement of worn pieces. Alternatively, the end wall 114 may be machined on the external wall of the sorbent injection pipe instead of being machined on the inner wall of the sleeve.

The sorbent injection pipe 101 has a bore 102 developed around a longitudinal axis 106, an inlet

103 connected to a feeding line 105 supplied by a carrier gas and connected to a conveying screw 115 providing powdered sorbent to the feeding line 105 such that the sorbent is conveyed by the carrier gas successively through the feeding line 105, the sorbent injection pipe 101 and the outlet

104 of the sorbent injection pipe 101 to the interior of the exhaust gas duct. The sorbent injection pipe 101 is fixed to the flange 111 by welding or by press fit, or by appropriate threads and O-rings to provide a sealed fastening. The sorbent injection pipe 101 may also extend through the flange. The nozzle 108 is directed towards the longitudinal axis 106 of the sorbent injection pipe and may form an angle relative to the longitudinal axis comprised between 0 and 120°. The flow of dispersing gas passing through the nozzle(s) and directed towards the flow of sorbent 106 carried by the carrier gas and injected into the exhaust gas duct provides dispersion of the sorbent particles within the exhaust gas duct, increasing the probability of sorbent particles to interact with the exhaust gas.

Another embodiment of a sorbent injection assembly according to the invention is described in combination with the Figure 9. The sorbent injection assembly is provided to an exhaust gas duct 107 and comprises a flange 111 carrying a sorbent injection pipe 101 a nozzle 108 and a sleeve 112 and surrounding the sorbent injection pipe 101 and having two opposite end walls 114, 116 fixed to the external wall of the sorbent injection pipe such as to form an annular chamber 113. The flange 111 closes an opening provided along the exhaust gas duct 107 and is fixed to the exhaust duct by appropriate fixation means such as screws or threads and O-rings (not shown) to provide a sealed fastening. The annular chamber is connected to an air supply line 109 which passes through the flange 111 and terminates in a nozzle 108. Preferably a plurality of nozzles 108 are arranged on the end wall 114 of the sleeve 112 around the outlet 104 of the sorbent injection pipe and the annular chamber 113 has the function of a manifold providing air from a single air supply line 109 to a plurality of nozzles 108. The nozzles can be fastened to the sleeve by welding or preferably by press-fit or by appropriate threads and O-rings such that they can be removed and replaced. Such an assembly construction allows easier machining of the separated pieces of the assembly and easier replacement of worn pieces.

In this embodiment, the sleeve 112 does not extend along the full length of the sorbent injection pipe within the exhaust duct. Such a sleeve with a shorter length reduces the amount of metal needed for manufacturing the sleeve and also reduces the volume of the chamber 113 formed by the sleeve 112 and the external wall of the sorbent injection pipe 101. Alternatively, the opposite end walls 114, 116 may be machined on the sorbent injection pipe instead of being machined on the inner wall of the sleeve.

The sorbent injection pipe 101 has a bore 102 developed around a longitudinal axis 106, an inlet

103 connected to a feeding line 105 supplied by a carrier gas and connected to a conveying screw 115 providing powdered sorbent to the feeding line 105 such that the sorbent is conveyed by the carrier gas successively through the feeding line 105, the sorbent injection pipe 101 and the outlet

104 of the sorbent injection pipe 101 to the interior of the exhaust gas duct. The sorbent injection pipe 101 is fixed to the flange 111 by welding or by press fit, or by appropriate threads and O-rings to provide a sealed fastening. The sorbent injection pipe 101 may also extend through the flange. The nozzle 108 is directed towards the longitudinal axis 106 of the sorbent injection pipe and may form an angle relative to the longitudinal axis comprised between 0 and 120°. The flow of dispersing gas passing through the nozzle(s) and directed towards the flow of sorbent 106 carried by the carrier gas and injected into the exhaust gas duct provides dispersion of the sorbent particles within the exhaust gas duct, increasing the probability of sorbent particles to interact with the exhaust gas.

Another embodiment of a sorbent injection assembly according to the invention is described in combination with the Figure 10. The sorbent injection assembly comprises a flange 111 carrying a sorbent injection pipe 101 having a longitudinal axis 116 and a first nozzle 108 directed to the longitudinal axis 116 of the sorbent injection pipe 101, wherein the first nozzle 108 is fixed along the sorbent injection pipe 101. The sorbent injection assembly further comprises an air supply line 109’ passing through the wall of the sorbent injection pipe 101 and terminating in an outlet which is located within the said sorbent injection pipe, the said nozzle being directed towards the outlet 104 of the said sorbent injection pipe.

In any one of the embodiments presented herein in combination with the Figures 7 to 9, the nozzles 108 were presented with a shape forming a straight angle. However, any other kind of shape of nozzle is possible provided that the nozzle is oriented such as to project a flow of dispersing gas encountering the flow of sorbent exiting the outlet of the sorbent injection pipe. The nozzles can also have for example a curved shape or a straight shape inclined towards the longitudinal axis of the sorbent injection pipe.

In any one of the embodiments presented with the figures, the nozzles have an outlet diameter narrower than the outlet diameter of the sorbent injection pipe. This is beneficial to provide a higher velocity outflow from the nozzle when compared to the outflow from the sorbent injection pipe without requiring a relatively high, in particular an uneconomically high, volume of air to flow from the nozzle.

A trial was conducted using a first prototype air-boosted lance of the type shown in Figure 1. The lance was specifically designed to enhance the dispersion of Ca(OH) 2 particles injected into a duct, and thus improve the efficiency of acid gas capture. The lance achieved this enhanced dispersion by impinging the resultant sorbent plume with secondary air, and despite relatively low quantities of boost air (< 30 scfm) being applied at the time, a noticeable increase (18%) in SO2 capture was achieved.

In order to improve upon this encouraging result and validate the observation, two additional prototypes were fabricated for testing: a 4-nozzle air-boosted lance and a 3-nozzle air-boosted lance. The nozzle air supply lines featured in these lances were designed with larger internal diameters in order to accommodate significantly more secondary air flow. Additionally, the 3- nozzle air-boosted lance enabled one to distinguish sorbent dispersion induced by (1) secondary air directed at the resultant sorbent plume from (2) secondary air applied from the interior of the resultant sorbent plume. In addition, the nozzles were modified with removable tips of various orifice sizes (ranging from 3/8” to 5/8”) so that the velocity of the secondary air could be fine - tuned. Figure 11 is a graphical representation of measurements of SO2 concentrations after passage of an effluent gas through an duct without any flue gas treatment device, after flue gas treatment using a conventional sorbent injection device and after flue gas treatment using a sorbent injection device according to the present invention. An embodiment of a sorbent injection device according to the invention comprising four air nozzles was connected to a flue gas pipe as previously described. Dimensions and parameters of the experiment are provided here below and in Table 2:

- diameter of the flue gas pipe of the plant : 60”

- exhaust gas flow rate 384 cubic feet per second (at injection location)

- exhaust gas temperature 828 degrees F (at injection location)

- length of the sorbent injection line within the flue gas pipe (from the flange to the outlet of sorbent injection line : 3 feet

- diameter of the sorbent injection line, Inner diameter - 2.5”, Outer diameter - 2.9”

- angle between the air nozzles axis and the longitudinal axis of the lance : 20 degrees

- air nozzle diameter 3/8 inches.

Table 2: Detailed Lance Performance Results

An invention has been provided with a number of advantages. The current invention is a versatile dry sorbent injection system comprised of a modified lance that disperses ejected sorbent particles using compressed air impinging on the sorbent/air mixture as it exits the lance tip. This method achieves an improvement in sorbent particle dispersion, and thus acid gas removal. One of the benefits of the current invention is that it accommodates a range of interchangeable air nozzles to enable one skilled in the art to select the appropriate nozzle geometry that affords optimal dispersion of the effluent dry sorbent. Both the number and type of nozzle can be changed depending on the FGT conditions. The presently existing prior art injector systems suffer from a number of disadvantages/drawbacks including high initial costs and the fact that they are costly to operate and maintain due to specialized moving parts. The existing systems often deliver sorbent at low pressures and air velocities and require large volumetric air flows to achieve adequate dispersion of particulates, which can be detrimental to particulate control device performance. The existing prior art systems also do not accommodate a broad range of duct conditions and dimensions

On the other hand, the method of the invention overcomes many of the disadvantages of the prior art systems and offers a number of unique advantages including the fact that: a. The injection device requires no moving parts or specialized materials, and therefore can be manufactured at a relatively low cost.

b. Improved sorbent dispersion is achieved with considerably lower volumes of air than such systems as the“lanceless” injector systems. A conventional air compressor is suitable to supply the compressed air.

c. The equipment occupies a small footprint, both inside and outside of the duct, to accommodate a wider range of duct dimensions.

d. The injector is compatible with commercially-available parts and fittings, and therefore does not require specialized components and expertise for routine maintenance.

While the invention has been shown in several of its forms, it is not thus limited but is susceptible to various changes and modifications within the scope of the appended claims.