Process for pneumatically conveying a powdery material

Abstract

Process and device for pneumatically conveying a powdery material comprising the steps of Pneumatically conveying a powdery material in a pneumatic conveying pipeline (first) and into said recipient by a flow generated by a blower, A powdery material dosing step, A fluctuation step of pressure drop in said pneumatic conveying pipeline or up to said recipient,
wherein a sonic device generates sonic waves inside said pneumatic conveying pipeline or up to said recipient and provides a counteraction on the fluctuation step of the pressure drop in said pneumatic conveying pipeline or up to said recipient.

Claims

1. Device for improving capture of polluting compounds from flue gases comprising a furnace or combustion chamber provided for burning fuel and/or a material to be burned or heated or melted and producing flue gases, said furnace or combustion chamber being connected to a flue gas duct where flue gases generated in said furnace or combustion chamber are directed, a powdery sorbent storage tank connected to said flue gas duct by means of a first pneumatic conveying pipeline, said first pneumatic conveying pipeline being further connected to a blower provided for pneumatically conveying said powdery sorbent from said powdery sorbent storage tank in said first pneumatic conveying pipeline to said flue gas duct, said first pneumatic conveying pipeline comprising a pipeline wall and being connected to said flue gas duct, said blower being provided to generate a flow of conveying fluid inside said first pneumatic conveying pipeline in which particles of said powdery sorbent are transported, a powdery sorbent dosing means provided for dosing an amount of said powdery sorbent when entering from said powdery sorbent storage tank into said first pneumatic conveying pipeline, said first pneumatic conveying pipeline being connected to said powdery sorbent storage tank through said dosing means, a controlling device for adjusting said amount of powdery sorbent in response to a first signal, characterized in that it further comprises a sonic device connected to said first pneumatic conveying pipeline and provided to generate sonic waves inside said first pneumatic conveying pipeline and/or up to said flue gas duct, said sonic device being further provided to counteract on a fluctuation step of the pressure drop in said first pneumatic conveying pipeline and/or up to said flue gas duct, wherein the sonic device provided to generate sonic waves is an infrasound device provided to generate infrasonic waves; wherein said infrasound device comprises a first and a second chamber, both first and second chamber being connected to each other by a tube, said first chamber comprising an exciter located inside said first chamber, provided to generate said infrasonic waves by providing infrasound pulses to a first portion of said conveying fluid which is blown inside said first chamber, said generated infrasonic waves being transported through the tube acting as a resonance pipeline to reach the second chamber; and wherein the device further comprises a flowrate distributor pipe which is provided for deriving a second portion of said conveying fluid blown by said blower and introducing said second portion of said conveying fluid inside said second chamber while said first portion of said conveying fluid is transported through said tube from said first chamber to said second chamber.

2. Device for improving capture of polluting compounds from flue gases according to claim 1, further comprising a mixing or connecting device located between said dosing means and said first pneumatic conveying pipeline, provided to mix said powdery sorbent in said conveying fluid.

3. Device for improving capture of polluting compounds from flue gases according to claim 1, further comprising a cooling device located between said blower and said first pneumatic conveying pipeline.

4. Device for improving capture of polluting compounds from flue gases according to claim 1, wherein said sonic device is connected to said blower and to the first pneumatic conveying pipeline.

5. Device for improving capture of polluting compounds from flue gases according to claim 1, wherein said sonic device is connected to a second blower and to the first pneumatic conveying pipeline between the powdery sorbent storage tank and the flue gas duct.

6. Device for improving capture of polluting compounds from flue gases according to claim 1, wherein said sonic device is connected to a second blower and to the first pneumatic conveying pipeline between the powdery sorbent storage tank and the blower.

7. Device for improving capture of polluting compounds from flue gases according to claim 1, further comprising an adjustable flowrate distributor pipe connected at a first end either to the blower, between the blower and the first chamber or to the first chamber, preferably to the first compartment of the first chamber and at a second end to the second chamber, said adjustable flowrate distributor pipe being provided for deriving a portion of said conveying fluid blown by the blower and introducing it inside the second chamber.

8. Device for improving capture of polluting compounds from flue gases according to claim 1, wherein the powdery sorbent storage tank is a powdery sorbent storage tank of powdery sorbent selected from the group consisting of hydrated lime, hydrated or semi-hydrated dolime, limestone, dolomite, quick lime, quick dolime, sodium carbonate or bicarbonate, sodium sesquicarbonate dihydrate, halloysite, sepiolite, a carbonaceous organic compound selected from active carbon and lignite coke, fly ash or a mixture of any of these compounds.

9. Device for improving capture of polluting compounds from flue gases according to claim 1, wherein said conveying fluid is air, inert gas, exhaust gases, or mixture thereof.

10. Device for improving capture of polluting compounds from flue gases according to claim 1, further comprising an Helmholtz bass trap connected to said first chamber or preferably on the pipeline between the blower and the first chamber, provided to prevent infrasonic waves transported inside said first pneumatic conveying pipeline during said transport of powdery sorbent to reach the blower.

11. Device for improving capture of polluting compounds from flue gases according to claim 1, comprising an emergency device having a first position being an emergency position and a second position being an operating position, said emergency device comprising a switch connected to an emergency pipe connecting directly the blower to the first pneumatic conveying pipeline, downstream the infrasound device, said emergency position being a position wherein the switch prevents the blown conveying fluid from entering said first chamber and diverting it directly to said first pneumatic conveying pipeline, downstream the infrasound device and wherein the operating position is a position wherein the blown conveying fluid is provided at least partially to said first chamber.

12. Device for improving capture of polluting compounds from flue gases according to claim 1, wherein said first signal is such as wind speed of environment at the outlet of the chimney, atmospheric pressure of environment at the outlet of the chimney or outside said flue gas duct, temperature of the flue gas, nature of the fuel, sulfur content of the fuel, sulfur content of the flue gas, chloride content of the flue gas, mercury content of the flue gas, chloride content of material to be burned or to be heated or melted, sulfur content of material to be burned or to be heated or melted, mercury content of material to be burned or to be heated or melted, and their combination.

13. Device for improving capture of polluting compounds from flue gases according to claim 1, wherein said dosing means is selected from a dosing screw, a rotating valve with a vertical shaft or an horizontal shaft, an air slide, a jet feeder, a screw-feeder, an airlock-feeder, a screw pump, a pressure vessel, an air lift, said dosing means being located between said powdery sorbent storage tank and said first pneumatic conveying pipeline being provided to be contacted by sonic waves transported inside said first pneumatic conveying pipeline during said transport of powdery sorbent.

Description

(1) In the drawings, FIG. 1A is a schematic representation of a heating process where pneumatic conveying of a powdery material according to the present invention is performed.

(2) FIG. 1B is another schematic representation of a heating process where pneumatic conveying of a powdery material according to the present invention is performed.

(3) FIG. 1C is another schematic representation of a heating process where pneumatic conveying of a powdery material according to the present invention is performed at different possible locations.

(4) FIG. 1D is another schematic representation of a heating process where pneumatic conveying of a powdery material according to the present invention is performed.

(5) FIG. 2 is a schematic representation of a pneumatic conveying of a powdery material, where the sonic device is located in line with the pneumatic conveying pipeline.

(6) FIG. 3 is a schematic representation of a pneumatic conveying of a powdery material, where the sonic device is located in parallel with the pneumatic conveying pipeline.

(7) FIG. 4 is a schematic representation of a pneumatic conveying of a powdery material, where the sonic device is located in parallel with its own blower with the pneumatic conveying pipeline.

(8) FIG. 4A is a schematic representation of a multilines pneumatic conveying of a powdery material.

(9) FIG. 5 is a Jenicke flow diagram for powdery material showing the cohesive behavior of the powdery material when it is hydrated lime.

(10) FIG. 6 is a graph showing the pressure trends in the first pneumatic conveying pipeline where the first curve shows the pressure drop over time in one pneumatic conveying pipeline 13′ without an infrasound device and the second curve shows the pressure drop over time in another pneumatic conveying pipeline 13 without infrasound device.

(11) FIG. 6 A is a graph showing the pressure trends in the first pneumatic conveying pipeline where the first curve shows the pressure drop over time in one pneumatic conveying pipeline 13′ WITH an infrasound device and the second curve shows the pressure drop over time in another pneumatic conveying pipeline 13 without infrasound device.

(12) FIG. 7 illustrates schematically the plants where the example was carried out.

(13) In the drawings, the same reference numbers have been allocated to the same or analog element.

(14) As it can be seen in FIG. 1A, a heating process typically comprises a heating unit such as a heat exchanger (for example a boiler), an incinerator or a furnace 8 which is followed by a filtering unit and/or a scrubber 9. In the heating unit 8, flue gases are contained in a flue gas duct (not illustrated) and exit the heating unit 8 to enter the filtering unit and/or a scrubber 9 from which the flue gas is passing through a blower (fan) 11 and evacuated to the chimney 10. It is obvious that even if only one item is represented as equipment 9, there can be consecutive filter and scrubber units, in whatever order, connected by a duct, depending of the flue gas treatment facility of the plants.

(15) The heating process illustrated in FIG. 1 can be a burning process where a furnace 8 is present such as coal, lignite or biomass furnace, cement furnace, lime furnace, glass furnace, metal ore, in particular iron ore, furnace, recycling material furnace or even an incinerator 8 burning for example garbage.

(16) The heating process as illustrated here can also be a process comprising a boiler 8 recovering heat energy from a former step. The boiler 8 can recover the energy from a former burning step in a furnace or in a burner (see FIG. 1C) or from another burning step.

(17) The flue gases can come from the combustion or heating or smelting of the material (garbage, iron ore is a steel plant, limestone, silica) to be burned or from the fuel (coke, coal, gas, lignite, petroleum liquid fuels, . . . )

(18) For this reason, industries, called herein after “burning industries” using burners such as garbage incinerator, but also industries using furnaces are more and more controlling polluting compounds emission in flue gas treatment to stick with environmental requirements.

(19) The treatment of gases, in particular flue gases, requires abatement of acid gases, notably HCl, SO.sub.2 and/or HF, which reduction may be carried out under dry conditions, by injecting a substance, often mineral, dry and powdery into a flue gas flow or through a filter-bed comprising solid particles either fixed or in motion. In this case, the powdery compound generally comprises a calcium-magnesium compound, in particular lime, preferably slaked or hydrated lime or a sodium compound like a sodium carbonate or bicarbonate. Other compounds may also be used notably those used for reducing dioxins, furans and/or heavy metals including mercury, for example carbonaceous substance like active carbon or lignite coke or mineral substance, like those based on phyllosilicates, such as sepiolite or halloysite or the like.

(20) As flue gas contains polluting compounds which have to be removed, very often powdery material, in particular powdery sorbent is injected in the flue gas duct to capture a certain level of polluting compounds.

(21) To inject a powdery material, for example a powdery sorbent, the process plant comprises a blower 1 which is connected to a first pneumatic conveying pipeline 13 and blows conveying fluid, such as for example air, inert gas, exhaust gases, or mixture thereof in the first pneumatic conveying pipeline 13.

(22) A powdery material, in particular a powdery sorbent storage tank 2 is connected to the first pneumatic conveying pipeline 13 through a dosing means 3. The first pneumatic conveying pipeline 13 comprising a pipeline wall is connected to said powdery material, in particular said powdery sorbent storage tank 2 and to the flue gas duct of the heating unit 8 and pursue downstream of the heating unit 8.

(23) The conveying fluid has a flow comprising boundary layer along said pipeline wall, but also the particles of said powdery material have a boundary layer around them inside said conveying flow.

(24) The powdery material, in particular the powdery sorbent is therefore pneumatically conveyed in the first pneumatic conveying pipeline 13 from the powdery material, in particular a powdery sorbent, storage tank 2 to the flue gas duct of the heating unit 8 and pursue downstream of the heating unit 8 by a flow of conveying fluid generated by the blower 1 and blowing conveying fluid inside said first pneumatic conveying pipeline 13 in which particles of said powdery material, in particular said powdery sorbent are transported.

(25) The dosing means 3 doses an amount of said powdery material, in particular said powdery sorbent when entering from said powdery material, in particular said powdery sorbent storage tank 2 into said first pneumatic conveying pipeline 13.

(26) The dosing means 3 are preferably selected from a dosing screw, a rotating valve with a vertical shaft or an horizontal shaft, an air slide, a jet feeder, a screw-feeder, an airlock-feeder, a screw pump, a pressure vessel, an air lift or the like.

(27) The powdery material, in particular the powdery sorbent contained in the powdery material storage tank 2 is selected from the group consisting of hydrated lime, hydrated or semi-hydrated dolime, limestone, dolomite, quick lime, quick dolime, sodium carbonate or bicarbonate, sodium sesquicarbonate dihydrate (also known as Trona), halloysite, sepiolite, a carbonaceous organic compound selected from active carbon and lignite coke, fly ash or a mixture of any of these compounds.

(28) In the illustrated embodiment, a drying device 14 is provided to dry the conveying fluid before entering in the blower 1. A cooling device 4 is also provided to cool the conveying fluid after being blown by said blower into the first pneumatic conveying pipeline 13 to further convey in the first pneumatic conveying pipeline 13 a dried conveying fluid. A mixing or connecting device 5 is also present in the process plant allowing the mixing of the conveying fluid blown by said blower 1 and the powdery material, in particular the powdery sorbent dosed by said dosing means 3.

(29) More specifically, a mixing device comprises a first feeding tube where the conveying fluid in the first pneumatic conveying pipeline is entering a mixing chamber to which the first feeding tube is connected and a second feeding tube connected to said dosing means 3 and to said mixing chamber for feeding the powdery material. During feeding of powdery material and the conveying fluid, an homogeneous mixture of the powdery material and the blown conveying fluid is performed, which leaves the mixing chamber to pursue its transport through said first pneumatic conveying pipeline 13 to said flue gas duct in the furnace or blower 8. In the first pneumatic conveying pipeline, downwards the mixing chamber, the particles are conveyed and spread properly in the conveying fluid. The particles of the powdery material in the conveying fluid are fed in the bottom of the furnace or boiler 8, especially, in the flue gas duct.

(30) A sonic device 12 is located or connected at any location between the blower and the flue gas duct, preferably, as shown herein, between the blower and the mixing device 5. The sonic device 12 generates sonic waves inside said first pneumatic conveying pipeline and/or up to said flue gas duct. In this illustrated preferred embodiment, the blower 1 connected to said first pneumatic conveying pipeline 13 is blowing conveying fluid inside said first pneumatic conveying pipeline 13 but also blows said conveying fluid at least partially through said sonic device 12.

(31) In this illustrated embodiment, said dosing means 3 located between said powdery sorbent storage tank 2 and said first pneumatic conveying pipeline 13 is also contacted by sonic waves transported inside said first pneumatic 13 conveying pipeline during said transport of powdery sorbent.

(32) By the terms “connected to”, it is meant that one element is connected to another element directly or indirectly, meaning that the elements are in communication one to each other but other elements can be inserted in between.

(33) By the terms pneumatic conveying of powdery material, it is meant within the scope of the invention pneumatic conveying by negative pressure or by positive pressure, pneumatic conveying of powdery material as a dense or strand phase or dilute phase, in particular dilute phase, in conveying fluid, or as a discontinuous phase in conveying fluid.

(34) During pneumatic conveying of a powdery material, pressure drop fluctuations occurs at any time, very frequently and are difficult to control. The fluctuations in pressure drop may be due to a number of intrinsic factors of the pneumatic conveying process or to external event.

(35) Such fluctuations of pressure drop are disturbing the entire pneumatic conveying of the powdery material, in particular the powdery sorbent, to be conveyed, causing different kind of perturbations. Amongst other perturbations, one can found the fact that the fluctuations in pressure drop is causing a modification of the conveying velocity of the powdery sorbent.

(36) As explained in the beginning, powdery sorbent flows have a saltation velocity under which the powdery material, in particular the powdery sorbent, starts settling in the pneumatic conveying pipe while conveying fluid blown by blowers is given a safe nominal value of velocity, greater than the saltation velocity to prevent the powdery material, in particular the powdery sorbent, settling inside the pneumatic conveying pipe.

(37) Indeed blowers are characterized by a curve between pressure drop and flowrate. The pressure drop is the one imposed by the plant inside which pneumatic conveying shall be performed and the characterizing curve of the blower impart a flowrate to the pneumatic conveying of the powdery material, in particular the powdery sorbent depending on the value of the pressure drop occurring inside the plant.

(38) As soon as there is a small fluctuation in pressure drop, the pressure drop start decreasing or increasing without it being possible to control it enough quickly for non-disturbing the pneumatic conveying of the powdery material. As a consequence, for example, without again being limited thereto, when the pressure drop increases, the pneumatic velocity or flowrate of the conveying fluid is reduced causing possibly the velocity of the conveying fluid to reach a value lower than the safe nominal value velocity, causing therefore the powdery material, in particular the powdery sorbent, pneumatically conveyed to sediment inside the pneumatic conveying pipeline.

(39) The powdery material starts therefore to accumulate inside the pneumatic conveying pipeline causing on its turn fluctuations of the pressure drop as the passing diameter of the pipeline available for pneumatic conveying is reduced, causing an increase in pressure drop having on its turn consequence on the pneumatic conveying.

(40) As one can understand, the smallest single fluctuation in the pressure drop, which occur whatever the level of optimization of the pneumatic conveying will have strong consequence in the efficiency of the pneumatic conveying of the powdery material, in particular the powdery sorbent, inside the pneumatic conveying pipeline.

(41) This phenomena of fluctuation is occurring in any conveying fluid when blown, but is of course further amplified when a powdery material, is conveyed as the powdery material itself cannot recover easily the right regimen of pressure drop as soon as it starts accumulating inside the pneumatic conveying pipeline.

(42) In the process according to the present invention, the sonic device 12 generates sonic waves inside said first pneumatic conveying pipeline 13 up to said flue gas duct in the furnace or in the boiler 8 and provides a counteraction on the fluctuation step of the pressure drop in said first pneumatic conveying pipeline up to said flue gas duct.

(43) It has been indeed surprisingly realized that when sonic waves generates an increase of pressure, the increase of pressure has the capability to counteract on the fluctuation step of the pressure drop in said first conveying pipeline and/or in said flue gas duct.

(44) The sonic device preferably creates a pressure drop increase in the first pneumatic conveying pipeline close to the sonic generator of between 20 and 200 mbar, in particular of at least 30 mbar, in particular of at most 150 mbar.

(45) Preferably, when said sonic device provides a counteraction on the fluctuation step of the pressure drop in said first pneumatic conveying pipeline and/or up to said recipient zone, said sonic device provides a smoothing action and/or a masking action on the fluctuation step of the pressure drop in said first pneumatic conveying pipeline and/or up to said flue gas duct.

(46) The sonic waves are used to increase the pressure drop, meaning that the sonic waves according to the present invention are used in such a way that they are able to counteract the fluctuation step of the pressure drop, thereby minimizing perturbations causing the accumulation of powdery material, in particular powdery sorbent, in said pneumatic conveying instead of curing or retro-acting on the accumulation of particles.

(47) In the illustrated preferred embodiment, the counteraction on the fluctuation step of the pressure drop in said first pneumatic conveying pipeline 13 causes the improvement of the polluting compounds capture by reducing fluctuations in powdery sorbent, in particular powdery mineral sorbent, fed in the flue gas duct by sonic waves transported inside said first pneumatic conveying pipeline 13 during said pneumatic conveying of powdery sorbent.

(48) Indeed, it has been found surprisingly that sonic waves transported inside said first pneumatic conveying pipeline during said pneumatic conveying of powdery sorbent has a direct impact on fluctuations in pneumatic conveying of powdery sorbent fed in the flue gas duct.

(49) The appropriated use of circulating sonic waves, creating an increase of the pressure drop inside said first pneumatic conveying pipeline 13 during said transport of powdery sorbent, can solve the fluctuations in the powdery material, in particular the powdery sorbent injected inside the flue gas duct.

(50) The sonic waves transported inside said first pneumatic conveying pipeline during said transport of powdery sorbent have been shown to prevent deficiencies in the pollutants capture inside the flue gas duct by counteracting very quickly on fluctuations in the pressure drop, thereby preventing particles not having enough speed to settle and enabling them to be conveyed by the pneumatic transport and as a consequence to still reach the flue gas duct. Indeed, sonic waves are colliding with the particles having a tendency to settle against the wall of the first pneumatic conveying pipeline when they did not have enough speed to be pneumatically conveyed as a result of the existence of boundary layer.

(51) Indeed, the combination of the proper use of the sonic waves creating an increase of pressure drop in the first pneumatic conveying pipeline together with the collision between the particles of the powdery sorbent and the sonic waves having fluctuating frequency of the waves that change the location of the antinodes and the vibration nodes of the sound in the pipe.

(52) Therefore, according to the present invention, the sonic waves transported inside said first pneumatic conveying pipeline 13 during said conveying of powdery sorbent have been shown to improve the level of pollutants capture by counteracting fluctuations in the pressure drop in the first pneumatic conveying pipeline 13 and thereby ensuring adequate/optimizing flowrate of powdery sorbent to the flue gas duct in the furnace or boiler 8.

(53) In some cases, fluctuations of pressure drop in the first pneumatic conveying pipeline are due to the operating conditions or to regulation loop due to a first signal given by the process in itself or by a measure or a data.

(54) More and more, burning industries use analyzer at the exit of the flue gas duct to measure level of polluting compounds (example of first signal) and have put in place over time regulation loop in order to retroact on the amount of powdery sorbent used to capture those pollutants. For example, if the level of SO.sub.2 starts to increase, the amount of powdery sorbent will be increased to improve the capture of this pollutant. If the level of SO.sub.2 starts to decrease, the amount of powdery sorbent will be decreased.

(55) Other “burning industries” are not using continuous analysis but as a precautionary measure, they adjust the amount of powdery sorbent based on several criteria and measurement (first signal), such as the level of sulfur in the fuel which will be used, pre-analysis or data regarding the level of chloride or sulfur present in the garbage to be burned or the material to be heated (metal ore, recycling material . . . ), based on the combustion or the heating step, the turnaround of people conducting the furnace, the primary air level introduced in the furnace to do the combustion of the material to be burned, based on temperature, atmospheric pressure, . . . . The amount of powdery sorbent is then fixed manually for a predetermined period of time and changed when a new condition (first signal) arises.

(56) More particularly, when a first signal arises from exhaust gases from the combustion of fuel and/or material to be burned, such as an increase in pollutants level, a decrease of pollutants level, the response to be given is to change the amount of powdery sorbent to be introduced inside the flue gas duct. The change in the amount of powdery sorbent which is blown inside the first pneumatic conveying pipeline by the blower yields to a change in the weight ratio between said conveying fluid and said powdery sorbent which creates fluctuations in the pressure drop of the pneumatic transport, thereby causing fluctuations in the powdery material, in particular the powdery sorbent injected inside the flue gas duct.

(57) Indeed, the change in the amount of powdery sorbent causes fluctuations in the operating of the pneumatic conveying system causing itself fluctuations of the conveying fluid flow rate to adapt itself to the counter-pressure as the blowing rate stays quite stable at the exit of the blower in the first pneumatic conveying pipeline.

(58) In response to a first signal, changes occur in the weight ratio between said powdery sorbent and said conveying fluid. The particles of the powdery sorbent are conveyed with fluctuating speed in the first pneumatic conveying pipeline which can increase or decrease.

(59) In other cases, said first signal is such as wind speed of environment at the outlet of the chimney, atmospheric pressure of environment at the outlet of the chimney or outside said flue gas duct, temperature of the flue gas, nature of the fuel, sulfur content of the fuel, sulfur content of the flue gas, chloride content of the flue gas, mercury content of the flue gas, chloride content of material to be burned, sulfur content of material to be burned or to be heated, mercury content of material to be burned or to be heated, and their combination.

(60) FIG. 1B illustrates a variant embodiment according to the present invention, where the particles of the powdery material in the conveying fluid are fed in a duct entering the heating unit 8.

(61) FIG. 1C, as mentioned earlier, illustrates a process where the heating process comprises a boiler 31 recovering heat energy from a furnace or from a burner 15.

(62) Hot flue gases are produced more specifically in the furnace or burner 15 and are conveyed to a boiler 31 for recovering the contained calories, before being transferred to a filtering device and/or a gas scrubber 9. It is obvious that even if only one item is represented as equipment 9, there can be consecutive filter and scrubber units, in whatever order, connected by a duct, depending of the flue gas treatment facility of the plants.

(63) The powdery material can be injected as illustrated in different locations, such as in the furnace 15, including in its after combustion chamber or post-combustion zone (option A), in the boiler 31 (option B), or at the entrance of the filtering device and/or gas scrubber 9 (option C) or in the gas duct in between all those equipment (dashed line) or any combination thereof. It is obvious that in case of multiple equipment 9, the powdery material can be injected in between the various equipment 9, in the duct between or at the entrance of one or more of the units 9.

(64) The first pneumatic conveying pipeline shall be depending on the several options connected to the furnace or its after combustion chamber or post-combustion zone (option A), to the boiler (or any other heat exchanger) 31 (option B), or to the filtering (or scrubbing) device 9 (option C) or in the gas duct in between all those equipment or any combination thereof.

(65) In a specific variant according to the present invention, it is also foreseen that multiple conveying pipelines are present, each containing their own sonic device or even that downstream of the sonic device a multiway connector is present and the first multiple conveying pipeline is spread into a bundle of pneumatic conveying pipelines, optionally provided with a closing/opening mechanism to provide more flexibility to the device according to the present invention.

(66) FIG. 1D represent the embodiment A illustrated in FIG. 1C where the sonic device generating sonic waves being an infrasound device generating infrasonic waves is detailed. It is to be noted that the sonic device can be integrated in both variants B and C.

(67) In the infrasound device, infrasonic waves are generated inside an infrasound device 12 comprising a first chamber 16 and a second chamber 17, both first and second chamber being connected to each other by a tube 18, said infrasonic waves being generated by an exciter 19 inside the first chamber 16 providing infrasound pulses to said conveying fluid blown at least partially inside said first chamber 16, said generated infrasonic waves being transported through the tube to reach the second chamber 17 wherein the first chamber is divided into a first compartment 20 and a second compartment 21. The first compartment 20 is connected to the second compartment 21 through a passing hole 22 and comprises an internal channel inside which a moving piston is moved from a first position to a second position and from said second position to said first position by a power source 23, located externally with respect to the first chamber 16 and forming the exciter. The internal channel is concentrically installed inside said first compartment 20.

(68) Infrasonic waves are generated by the moving piston and transported by said conveying fluid from said first compartment 20 to said second compartment 21, through the passing hole 22 before being transported through the tube 18 to reach the second chamber 17.

(69) The conveying fluid blown by said blower 1 reaches the first compartment of the first chamber to enter the infrasound device through feed line 24. The first chamber 16 is followed by a tapered section 16a to the connection with the tube acting as a resonance tube 18. The conveying fluid follows the tube 18 to reach a second expansion tapered section 17a having a widening section in the direction of the second chamber 17 to which it is connected.

(70) In a preferred embodiment, further comprising an adjustable flowrate distributor pipe 25 connected at a first end either to the blower 1, between the blower 1 and the first chamber 16 or to the first chamber 16, preferably to the first compartment 20 and at a second end to the second chamber 17. Said adjustable flowrate distributor pipe 25 is provided for deriving a portion of said conveying fluid blown by the blower 1 and introducing it inside the second chamber 17.

(71) In another preferred embodiment, the device according to the present invention further comprises an Helmholtz bass trap (not illustrated) connected to said first chamber 16 or preferably on the pipeline between the blower and the first chamber. The Helmholtz bass trap is provided to prevent infrasonic waves transported inside said first pneumatic conveying pipeline 13 during said transport of powdery sorbent to reach the blower 1.

(72) In another preferred embodiment as shown in FIG. 1D, the device according to the present invention comprises an emergency device 26 having a first position being an emergency position and a second position being an operating position, said emergency device comprising a switch 27 connected to an emergency pipe 28 connecting directly the blower 1 to the first pneumatic conveying pipeline 13, downstream the infrasound device 12. The switch 27 can be a 3-Way valve installed in connection point as drawn and so all the blown conveying fluid go through emergency pipe 28 or can be a 2-ways valve inserted in any position in pipe 28 allowing the blown conveying fluid to be conveyed (totally or partially depending of the position of the moving piston in the internal channel) downstream the infrasound device 12.

(73) The emergency position being a position wherein the switch 27 prevents the blown conveying fluid from entering said first chamber 16 and diverting it directly to said first pneumatic conveying pipeline 13, downstream the infrasound device 12 and wherein the operating position is a position wherein the blown conveying fluid is provided at least partially to said first chamber 16.

(74) The infrasonic device operates at low pressure, meaning that the pressure inside the infrasonic device is oscillating around the atmospheric pressure but stays lower that 1.5 absolute bar.

(75) The generated infrasonic waves are high power waves between 150 and 170 dB. The entering conveying fluid is fed at a pressure around 1.25 bar. The piston 23 propels the conveying fluid from the entry for the conveying fluid 24. The power source drives the piston for ensuring its movement. The preferred diameter of the piston is comprised between 50 and 150 mm. The piston moves from a first position to a second position inside a jacket connected to the first compartment 20. The jacket comprises holes of a first type allowing the jacket to be in fluid connection with the conveying fluid entry 24. In addition, the piston 23 comprises a head also provided with holes of a second type.

(76) The jacket is located inside a the first compartment 20 in fluid connection with the conveying fluid entry 24. During the displacement of the piston 23 from the first position to the second position, the holes of the second type moves gradually in front of the holes of the first type, allowing gradually the conveying fluid to travels from the first compartment 20 to the second compartment 21. When the piston 23 is in the first position, the holes of the first type co-channel with the holes of the second type, fully allowing the passage of the conveying fluid (open position). When the piston 23 is in the second position, the holes of the first type does not co-channel with the holes of the second type, preventing therefore the passage of the conveying fluid (closing position).

(77) The generator of infrasonic pulses generates downstream the oscillation of the conveying fluid at a sonic frequency, which is in the case of infrasonic waves, lower than 30 Hz, preferably around 20 Hz. The generation of the pulse, i.e. the moving of the piston 23 generates a fluctuation of the pressure in the conveying fluid at a sonic frequency which propagates through the piping of the device.

(78) The first chamber causes a reduction of the power of the oscillations, but increases the bandwidth. Indeed, because a resonance tube is provided, the frequency may vary from +0.5 to −0.5 Hz which changes the location of the antinodes and the vibration nodes of the sound in the first pneumatic conveying pipeline.

(79) Preferably the diameter of the basis of the tapered section 16a is comprised between 350 to 500 mm and the diameter of the top of the tapered section 16a is comprised between 150 and 219 mm. The resonance tube 18 has a diameter comprised between 150 and 300 mm and a length of X/4 where X is the wavelength of the infrasonic signal. The resonance tube 18 allow the conveying fluid to start resonance. The basis of the tapered section 17a is comprised between 150 and 300 mm and the top of the tapered section 17a has a diameter comprised between 400 and 600 mm. The second chamber 17 allows to propagate the oscillations for ensuring the transmission to the powdery material. The length of the second chamber 17 is about 750 mm and the diameter is comprised between 400 and 600 mm.

(80) FIGS. 2 to 4 illustrate, without being limited thereto preferred location of the sonic device in a pneumatic conveying system.

(81) In other embodiment, the sonic device can also be located downstream the storage tank

(82) In those embodiment illustrated in FIGS. 2 to 4, the first pneumatic conveying pipeline can be connected to, as in FIGS. 1A to 1D to a furnace, an incinerator, a boiler, a filter, a scrubber or even to a silo. This has been mentioned in the following a recipient zone.

(83) According to the present invention, by the terms recipient zone, it is meant a silo for collecting the powdery sorbent, a channel where the powdery material, in particular the powdery sorbent shall be injected through pneumatic conveying, such as a flue gas duct, a pipeline inside a plant, gas scrubbers, filters devices, such as electrostatic precipitator, bag filters, . . . .

(84) FIG. 2 illustrates schematically a pneumatic conveying system to convey a powdery material, for example a powdery sorbent.

(85) The pneumatic conveying system comprises a blower 1 is connected to a first pneumatic conveying pipeline 13 and blows conveying fluid, such as for example air, inert gas, exhaust gases, or mixture thereof in the first pneumatic conveying pipeline 13.

(86) A powdery material, in particular a powdery sorbent storage tank 2 is connected to the first pneumatic conveying pipeline 13 through a dosing means 3. The first pneumatic conveying pipeline 13 comprising a pipeline wall is connected to said powdery material, in particular said powdery sorbent storage tank 2 and the recipient zone

(87) The conveying fluid has a flow comprising boundary layer along said pipeline wall, but also the particles of said powdery material have a boundary layer around them inside said conveying flow.

(88) The powdery material, in particular the powdery sorbent is therefore pneumatically conveyed in the first pneumatic conveying pipeline 13 from the powdery material, in particular a powdery sorbent storage tank 2 to the flue gas duct in the recipient zone (not illustrated) by a flow of conveying fluid generated by the blower 1 and blowing conveying fluid inside said first pneumatic conveying pipeline 13 in which particles of said powdery material, in particular said powdery sorbent are transported.

(89) The dosing means 3 doses an amount of said powdery material, in particular said powdery sorbent when entering from said powdery material, in particular said powdery sorbent storage tank 2 into said first pneumatic conveying pipeline 13.

(90) The dosing means 3 are preferably selected from a dosing screw, a rotating valve with a vertical shaft or an horizontal shaft, an air slide, a jet feeder, a screw-feeder, an airlock-feeder, a screw pump, a pressure vessel, an air lift.

(91) The powdery material, in particular the powdery sorbent contained in the powdery material storage tank 2 is selected from the group consisting of hydrated lime, hydrated or semi-hydrated dolime, limestone, dolomite, quick lime, quick dolime, sodium carbonate or bicarbonate, sodium sesquicarbonate dihydrate (also known as Trona), halloysite, sepiolite, a carbonaceous organic compound selected from active carbon and lignite coke, fly ash or a mixture of any of these compounds.

(92) In the illustrated embodiment, a drying device 4 is also provided to dry the conveying fluid after being blown by said blower to in the first pneumatic conveying pipeline 13 to further convey in the first pneumatic conveying pipeline 13 a dried conveying fluid. A mixing or connecting device 5 is also present in the process plant allowing the mixing of the conveying fluid blown by said blower 1 and the powdery material, in particular the powdery sorbent dosed by said dosing means 3.

(93) More specifically, the mixing device comprises a first feeding tube where the conveying fluid in the first pneumatic conveying pipeline is entering a mixing chamber to which the first feeding tube is connected and a second feeding tube connected to said dosing means 3 and to said mixing chamber for feeding the powdery material. During feeding of powdery material and the conveying fluid, an homogeneous mixture of the powdery material and the blown conveying fluid is performed, which leaves the mixing chamber to pursue its transport through said first pneumatic conveying pipeline 13 to said recipient zone. In the first pneumatic conveying pipeline, downwards the mixing chamber, the particles are conveyed and spread properly in the conveying fluid.

(94) A sonic device 12 is located or connected at any location between the blower and the flue gas duct, preferably, as shown herein, between the blower and the mixing device 5. The sonic device 12 generates sonic waves inside said first pneumatic conveying pipeline and/or up to said recipient zone. In this illustrated preferred embodiment, the blower 1 connected to said first pneumatic conveying pipeline 13 is blowing conveying fluid inside said first pneumatic conveying pipeline 13 but also blows said conveying fluid at least partially through said sonic device 12.

(95) In this illustrated embodiment, said dosing means 3 located between said powdery material storage tank 2 and said first pneumatic conveying pipeline 13 is also contacted by sonic waves transported inside said first pneumatic 13 conveying pipeline during said transport of powdery material.

(96) By the terms “connected to”, it is meant that one element is connected to another element directly or indirectly, meaning that the elements are in communication one to each other but other elements can be inserted in between.

(97) By the terms pneumatic conveying of powdery material, it is meant within the scope of the invention pneumatic conveying by negative pressure or by positive pressure, pneumatic conveying of powdery material as a dilute phase in conveying fluid, or as a discontinuous phase in conveying fluid.

(98) During pneumatic conveying of a powdery material, pressure drop fluctuations occurs at any time, very frequently and are difficult to control. The fluctuations in pressure drop may be due to a number of intrinsic factor of the pneumatic conveying process or to external event.

(99) Such fluctuations of pressure drop are disturbing the entire pneumatic conveying of the powdery material to be convey causing different kind of perturbations. Amongst other perturbations, one can found the fact that the fluctuations in pressure drop is causing a modification of the conveying velocity of the powdery material.

(100) As explained in the beginning, powdery material flows have a saltation velocity under which the powdery material, in particular the powdery sorbent start settling in the pneumatic conveying pipe while conveying fluid blown by blowers are given a safe nominal value of velocity, greater than the saltation velocity to prevent the powdery material, in particular the powdery sorbent settling inside the pneumatic conveying pipe.

(101) Indeed blowers are characterized by a curve between pressure drop and flowrate. The pressure drop is the one imposed by the plant inside which pneumatic conveying shall be performed and the characterizing curve of the blower impart a flowrate to the pneumatic conveying of the powdery material, in particular the powdery sorbent depending of the value of the pressure drop occurring inside the plant.

(102) As soon as there is a small fluctuation in pressure drop, the pressure drop start decreasing and increasing without it being possible to control it enough quickly for non-disturbing the pneumatic conveying of the powdery material. As a consequence, for example, without again being limited thereto, when the pressure drop increases, the pneumatic velocity or flowrate of the conveying fluid is reduced causing possibly the velocity of the conveying fluid to reach a value lower than the safe nominal value velocity, causing therefore the powdery material, in particular the powdery sorbent pneumatically conveyed to sediment inside the pneumatic conveying pipeline.

(103) The powdery material starts therefore to accumulate inside the pneumatic conveying pipeline causing on its turn fluctuations of the pressure drop as the passing diameter of the pipeline available for pneumatic conveying is reduced, causing an increase in pressure drop having on its turn consequence on the pneumatic conveying.

(104) As one can understand, the smallest single fluctuation in the pressure drop, which occur whatever the level of optimization of the pneumatic conveying will have strong consequence in the efficiency of the pneumatic conveying of the powdery material, in particular the powdery sorbent inside the pneumatic conveying pipeline.

(105) This phenomena of fluctuation is occurring in any conveying fluid when blown, but is of course further amplified when a powdery material, is conveyed as the powdery material itself cannot recover easily the right regimen of pressure drop as soon as it starts accumulating inside the pneumatic conveying pipeline.

(106) In the process according to the present invention, the sonic device 12 generates sonic waves inside said first pneumatic conveying pipeline 13 up to said recipient zone and provides a counteraction on the fluctuation step of the pressure drop in said first pneumatic conveying pipeline up to said recipient zone.

(107) It has been indeed surprisingly realized that when sonic waves generates an increase of pressure, the increase of pressure has the capability to counteract on the fluctuation step of the pressure drop in said first conveying pipeline and/or in said recipient zone.

(108) The sonic device preferably creates a pressure increase in the first pneumatic conveying pipeline close to the sonic generator of between 20 and 200 mbar, in particular of at least 30 mbar preferably of at most 150 mbar.

(109) Preferably, when said sonic device provides a counteraction on the fluctuation step of the pressure drop in said first pneumatic conveying pipeline and/or up to said recipient zone, said sonic device provides a smoothing action and/or a masking action on the fluctuation step of the pressure drop in said first pneumatic conveying pipeline and/or up to said recipient zone.

(110) The sonic waves are used to increase the pressure drop, meaning that the sonic waves according to the present invention are used in such a way that they are able to counteract the fluctuation step of the pressure drop, thereby minimizing perturbations causing the accumulation of powdery material in said pneumatic conveying instead of curing or retro-acting on the accumulation of particles.

(111) In the illustrated preferred embodiment, the counteraction on the fluctuation step of the pressure drop in said first pneumatic conveying pipeline 13 causes the improvement of the pollutant compounds capture by reducing fluctuations in powdery material, in particular powdery mineral material, fed in the flue gas duct by sonic waves transported inside said first pneumatic conveying pipeline 13 during said pneumatic conveying of powdery material.

(112) Indeed, it has been found surprisingly that sonic waves transported inside said first pneumatic conveying pipeline during said pneumatic conveying of powdery material has a direct impact on fluctuations in pneumatic conveying of powdery material fed in the recipient zone.

(113) The appropriated use of travelling sonic waves, creating an increase of the pressure drop inside said first pneumatic conveying pipeline 13 during said transport of powdery material, can solve the fluctuations in the powdery material, in particular the powdery sorbent injected inside the recipient zone.

(114) The sonic waves transported inside said first pneumatic conveying pipeline during said transport of powdery material have been shown to prevent deficiencies in the pollutants capture inside the flue gas duct by counteracting very quickly on fluctuations in the pressure drop, thereby preventing particles not having enough speed to settle and enabling them to be conveyed by the pneumatic transport and as a consequence to still reach the flue gas duct. Indeed sonic waves are colliding with the particles having a tendency to settle against the wall of the first pneumatic conveying pipeline when they did not have enough speed to be pneumatically conveyed as a result of the existence of boundary layer.

(115) Indeed, the combination of the proper use of the sonic waves creating an increase of pressure drop in the first pneumatic conveying pipeline together with the collision between the particles of the powdery material and the sonic waves having fluctuating frequency of the waves that change the location of the antinodes and the vibration nodes of the sound in the pipe.

(116) FIG. 3 illustrates another possible location of a sonic device in a pneumatic conveying system according to the present invention.

(117) As it can be seen, in this embodiment, the sonic device is not located in the first pneumatic conveying pipeline 13 but instead is placed in parallel and is connected to the first pneumatic conveying pipeline 13 through an exit duct 29 reaching the first pneumatic conveying pipeline before the mixing device. The sonic device is a dead-end device.

(118) FIG. 4 illustrates another possible location of a sonic device in a pneumatic conveying system according to the present invention.

(119) As it can be seen, in this embodiment, the sonic device is not located in the first pneumatic conveying pipeline 13 but instead is placed in parallel and is connected to the first pneumatic conveying pipeline 13 through an exit duct 29 reaching the first pneumatic conveying pipeline before the mixing device. The sonic device 12 is a blow through device and is connected by an entry duct 30 to another blower 6.

(120) FIG. 4A is showing a multiline pneumatic conveying system wherein one sonic device 12 is located upstream of the dosing means 5 of both illustrated pneumatic conveying pipelines.

(121) FIG. 5 is a Jenicke flow diagram for powdery material showing the cohesive behavior of the powdery material when it is hydrated lime.

(122) As it has been said previously, the problem of adhesion to solid objects is increasingly important for particles of decreasing particle diameter because of the increased contribution of electrostatic forces in comparison with friction, impulse and gravitation forces.

(123) Hydrated lime particles with diameter (<100 μm) are generally classified as cohesive according to the Geldart classification and their flow properties can be evaluated in detail using the flow function classification according to Jenicke.

(124) With the Jenicke flow function the internal cohesion of the powder is measured and this can be regarded as a good indicator for the adhesion properties of a powder.

(125) In FIG. 5, the cohesiveness of two hydrated lime powders are shown. Powder A has a particle size of d.sub.p=10 (μm) while Powder B has a particle size of d.sub.p=3 (μm). It is clear that Power B is more cohesive and is classified by the flow function by “very cohesive”. As a result, Powder B, will be much more sensitive to adhesion to rigid pipe walls than Powder A. Powder C is an easy flowing powder, Powder D is a free flowing powder, while powder E is a sticky powder.

EXAMPLE

(126) Tests have been performed on an industrial scale, in a power plant, to evaluate the effects of the present invention for pneumatically conveying of powdery hydrated lime sorbent, notably in terms of the fluctuation of the pressure drop inside the plant.

(127) The power plant used in these tests, which is illustrated in FIG. 7, comprises a burner (15), a furnace (31) for burning coal, said furnace being connected to a flue gas duct wherein flue gases generated in said furnace are directed to an electrostatic precipitator (9), followed by a scrubber (32) and further evacuated to a chimney (10).

(128) The hydrated lime is injected into the flue gas duct of this power plant, before the electrostatic precipitator and before the chimney, for capturing gaseous pollutants, in particular SO.sub.2. Such sorbent is a high specific surface area hydrated lime, as disclosed in WO9714650.

(129) The plant further comprises a storage tank (2) for said powdery hydrated lime, said tank being connected to the furnace through a hopper (3) having two outputs for directing said powdery hydrated lime in parallel into two pneumatic conveying pipelines (13, 13′) at an identical feedrate. The conveying pipelines (13, 13′) both present a diameter of 4 inches (10.2 cm). The feedrate of hydrated lime is periodically adjusted, based on the quantity of coal burned in the furnace and on the amount of sulfur contained therein.

(130) Both conveying pipelines are supplied by blowers (1, 1′) with air (15, 15′) as conveying fluid.

(131) Those conveying fluids (15, 15′) are first dried by drying devices (14, 14′) before entering the blowers (1, 1′) and then further cooled by cooling devices (4, 4′) after being blown by the blowers. The blowers (1,1′) present an initial pressure drop fixed at about 10 kPa.

(132) In order to illustrate the present invention, the conveying fluid (15′) is further transferred into a sonic device (12′), as previously described, before being in contact with hydrated lime.

(133) The pressures drops in both conveying pipelines (13, 13′) are continuously measured by the blowers (1, 1′).

(134) Consequently, with this plant, it is possible to compare in real time the fluctuation of pressure drop, notably generated by the variation overtime of the feedrate of hydrated lime injection, in a conveying pipeline where no sonic device has been implemented, compared to a conveying pipeline according to the present invention comprising a sonic device, as previously described.

(135) The results are illustrated in FIGS. 6 and 6A.

(136) FIG. 6 shows the pressure in the lines measured as a function of time for a period of five consecutive days of operation. FIG. 6 represents the reference case i.e. the sonic device is not in operation and the conditions for lines 13′ and 13 are similar. It is clear from FIG. 6 that large fluctuations occur in the pressure readings and that these pressure fluctuations are similar for both line 13′ and 13. Table 1 shows a statistical analysis of the pressure readings of FIG. 6.

(137) TABLE-US-00001 TABLE 1 Statistical analysis of the pressure signals of lines 13′ and 13 with the sonic device not in operation. Line 13′ Line 13 Without Sonic Without Sonic Average Pressure 1.82 2.43 (PSI) Pressure fluctuations 0.54 0.53 (PSI) Relative pressure fluctuation 29.6 21.7 (%)

(138) We can conclude from Table 1 that both lines 13′ and 13 are operating at similar average pressure with line 13′ operating at a lower average pressure. The pressure fluctuation of the two lines is represented in Table 1 as the standard deviation (1σ) of the pressure signal. It is clear that the pressure fluctuation is virtually identical for the two lines. This means that, with the sonic device not in operation, the pressure loss and the variation in pressure is similar. Finally we represent the relative pressure fluctuation in Table 1 which is the ratio of standard deviation and average pressure. Since the average pressure in line 13′ is a little lower, the relative effect of the pressure fluctuations is a little higher. The relative pressure fluctuation is 22-30% in the two lines. Such variation of pressure is very significant and will generate variations in the gas flow rate of the pneumatic conveying system. Note that the reported pressure fluctuation is an average number for the whole five days of operation, the instantaneous pressure fluctuations are significantly larger.

(139) FIG. 6A shows the pressure signal of lines 13′ and 13 in the case the sonic device is in operation in line 13′ over a period of five days. It is evident that the pressure in line 13′ is significantly higher than in line 13. Apparently operating line 13′ with the sonic device generates a higher pressure loss. Note that in the case of operation without sonic device line 13′ showed a slightly lower pressure than line 13, see FIG. 6. A statistical analysis of the pressure signal of FIG. 6A is given in Table 2.

(140) TABLE-US-00002 TABLE 2 Statistical analysis of th pressure signals of lines 13′ and 13 with the sonic device in operation. Line 13′ Line 13 With Sonic Without Sonic Average Pressure 4.96 2.91 (PSI) Pressure fluctuations 0.35 0.51 (PSI) Relative pressure fluctuation 7.0 17.7 (PSI/PSI)

(141) First, Table 2 shows that the average pressure is nearly a factor of two (1.7) higher in the line with the sonic device in operation (13′) than in the line without sonic device (13). The pressure fluctuations, represented in Table 2 as the standard deviation (1σ) of the pressure signal, show that the line with sonic device in operation (13′) is much more stable than the line without sonic device (13). The standard deviation of the pressure signal is nearly one and a half (1.45) times higher for the line without sonic device (13) than for the line with sonic device.

(142) For the line with sonic device in operation (13′) a consequence of the combination of a higher average pressure and a low standard deviation is that the relative pressure fluctuation (ratio of standard deviation and average pressure) is more than 2.5 times lower. Line (13), without sonic device, shows a relative pressure fluctuation of 18% which is similar to the 22% found in the time frame shown in FIG. 6 and Table 1. For the line with sonic device in operation (13′) the relative pressure fluctuation is only 7%. This lower pressure fluctuation, both absolute and relative, will result in a significantly improved stability of the pneumatic conveying system.

(143) It is clear from FIGS. 6,6A and the statistical analysis of Tables 1, 2 that the sonic device results in dampening of the pressure fluctuations and as a consequence improved stability of the pneumatic conveying system.

(144) In addition, the operation at an higher average pressure, in case the sonic device is in operation, will cause pressure perturbations in the flue gas duct to have smaller effect on the pressure in the conveying line and as a consequence a smaller impact on the pneumatic air speed. This results in a more stable pneumatic conveying operation.