Device and Method for Treating Flue Gases

Abstract

Device (10) for injecting powders into a furnace pipe (500), comprising a chamber (230) connected to a peripheral pipe (220) and, on the other hand, to the said furnace pipe via the said peripheral pipe (220), which comprises a first part (221) of diameter DP1, and a second part (222) of diameter DP2, having a downstream end (222a) and intended to be in communication with the furnace pipe, and a powder conveying pipe (120) which has a diameter DT and a downstream end (121), characterized in that the second part of the peripheral pipe has a length Lthe diameter (DP2) of the second part of the peripheral pipe, and in that the diameter (DT) and the diameter (DP2) are connected by the relationship 0<DP2DT< DT.

Claims

1: Device (10) for injecting a powdered compound for abatement of pollutants of flue gases into a furnace pipe (500), said device comprising: a chamber (230) connected to a peripheral pipe (220) and arranged to be connected to a first blowing element (200) arranged to blow a peripheral gas (210) into said chamber and into said peripheral pipe, and to said furnace pipe via said peripheral pipe, said peripheral pipe (220) comprising a first portion (221) having a diameter DP1, connected to the chamber, and a second portion (222) having a diameter DP2, opposite the first portion, having a downstream end (222a), and intended to be in communication with the furnace pipe, a pipe (120) for transporting powdered compound, intended to be connected to a second blowing element (100) arranged to blow a transportation gas (110) into said transportation pipe, simultaneously to the jet of peripheral gas, said transportation pipe having a diameter DT and a downstream end (121), said transportation pipe (120) passing through said first portion (221) of the peripheral pipe concentrically and longitudinally, in such a way that the downstream end (121) of said transportation pipe is located in a secant plane between the first and the second portion of the peripheral pipe, characterized in that the second portion of the peripheral pipe has a length L greater than or equal to the diameter (DP2) of the second portion of the peripheral pipe and in that the diameter (DT) of the transportation pipe (120) and the diameter (DP2) of the second portion of the peripheral pipe (222) are linked by the following relationship:
0DP2DT<DT.

2: Device for injecting a powdered compound according to claim 1, wherein the downstream end (222a) of the second portion of the peripheral pipe is arranged to be directly connected to the furnace pipe.

3: Device for injecting a powdered compound according to claim 1, wherein the peripheral pipe further comprises' a third portion (223) comprising an upstream portion (224) provided with an upstream end (224a) and a downstream portion (225) provided with a downstream end (225a), having a diameter DP3 less than the diameter DP2, said upstream end being intended to be connected to the downstream end of the second portion of the peripheral pipe, said downstream end being intended to be connected to the furnace pipe.

4: Device for injecting a powdered compound according to claim 3, wherein the downstream end (225a) of the third portion of the peripheral pipe is arranged to be directly connected to the furnace pipe.

5: Device for injecting a powdered compound according to claim 3, wherein said upstream portion (224) of the third portion of the peripheral pipe has the shape of a truncated cone.

6: Device for injecting a powdered compound according to claim 1, further comprising: a first blowing element (200) connected to the chamber (230) and arranged to blow a peripheral gas (210) into said chamber and into the peripheral pipe (220), a second blowing element (100) connected to the transportation pipe (120) and arranged to blow a transportation gas (110) into said transportation pipe, a dosing apparatus (130) for dosing powdered compound, connected to a tank of powdered compound and to the transportation pipe, downstream of said second blowing element with respect to a direction of flow of the transportation gas, arranged in order for the transportation gas to drive the dosed powdered compound.

7: Device for injecting a powdered compound according to claim 6, wherein said first blowing element (200) and the second blowing element (100) allow the adjustment of flow rates in such a way that the flow rates of the first blowing element (200) and of the second blowing element (100) can be adjusted separately.

8: Furnace pipe provided with at least one device for injecting a powdered abatement compound according to claim 1.

9: Method for treating flue gases in a furnace pipe with a powdered compound for abatement of pollutants of flue gases, comprising: injection of a jet of transportation gas having a mass flow rate Q.sub.T, said jet of transportation gas being intended to transport said powdered abatement compound into said flue gases having a flue gas flow rate Q.sub.F, simultaneously, injection of a jet of gas, peripherally with respect to the jet of transportation gas, forming a jet of peripheral gas having a mass flow rate Q.sub.P, characterized in that said mass flow rate of peripheral gas in relation to said mass flow rate of the flue gases forms a ratio Q.sub.P/Q.sub.F between 0.05% and 0.25%.

10: Method for treating flue gases in a furnace pipe according to claim 9, wherein said transportation gas has a speed V.sub.T and said peripheral gas has a speed V.sub.P, the speed of peripheral gas V.sub.P being between two times and twenty times the speed of the transportation gas V.sub.T according to 2V.sub.TV.sub.P20V.sub.T.

11: Method for treating flue gases in a furnace pipe according to claim 9, wherein the mass flow rate of the transportation gas Q.sub.T added to the mass flow rate of the peripheral gas Q.sub.P in relation to the mass flow rate of the flue gases Q.sub.F forms a ratio (Q.sub.T+Q.sub.P)/Q.sub.F between 0.1 and 0.5%.

12: Method for treating flue gases in a furnace pipe according to claim 9, wherein the powdered compound is injected at a mass flow rate Q.sub.A, the mass flow rate of the transportation gas Q.sub.T in relation to the mass flow rate of powdered compound forming a ratio Q.sub.T/Q.sub.A between 5 and 10.

13: Method for treating flue gases according to claim 9, characterized in that the injection of the jets of transportation gas and of peripheral gas occurs at the inner face of the furnace pipe.

14: Method for treating flue gases according to claim 9, wherein the temperature of the flue gases to be treated is between 850 C. and 1150 C.

15: Method for treating flue gases according to claim 9, wherein the speed of the flue gases to be treated is between 2 m/s and 150 m/s, preferably between 3 and 50 m/s, in particular between 5 and 30 m/s.

16: Method for treating flue gases according to claim 9, wherein the speeds of the jets of transportation gas and of peripheral gas are adjusted independently of each other.

17: Method for treating flue gases according to claim 9, wherein the transportation gas and/or the peripheral gas is air, independently of one another.

18: Method for treating flue gases according to claim 9, wherein the flue gases comprise pollutants selected from the group consisting of the acidic gases, said acidic gases including those which are sulphurated and/or halogenated, the heavy metals, the furans, the dioxins and their mixtures.

19: Method for treating flue gases according to claim 18, wherein the acidic gases comprise pollutants selected from the group consisting of SO.sub.2, SO.sub.3, HCl, HF, HBr, and their mixtures.

20: Method for treating flue gases according to claim 9, wherein the powdered abatement compound comprises a carbonate, a hydroxide and/or an oxide of an alkaline earth metal selected from the group consisting of calcium and magnesium, or a mixture thereof.

21: Method according to claim 9, wherein the powdered abatement compound comprises a calcium-magnesium compound having the formula aCaCO.sub.3.bMgCO.sub.3.xCaO.yMgO.zCa(OH).sub.2.tMg(OH).sub.2.ul, where l represents impurities, a, b, x, y, z, t and u being mass fractions each between 0 and 100%, with u55%, with respect to the total weight of said calcium-magnesium compound, the sum of the mass fractions a+b+x+y+z+t+u being equal to 100% of the total weight of said calcium-magnesium compound.

22: Method for treating flue gases according to claim 9, wherein the powdered abatement compound comprises over 50% by weight, in particular over 90% by weight, Ca(OH).sub.2.

Description

[0084] Other features, details and advantages of the invention will be clear from the description given below, in a non-limiting manner and in reference to the examples and to the appended figures.

[0085] FIG. 1 shows a functional diagram of an embodiment of an injection device allowing the method according to the invention to be implemented.

[0086] FIG. 1A shows a cross-sectional view along the cutting line A-A in FIG. 1.

[0087] FIG. 2 shows a functional diagram of another embodiment of an injection device allowing the method according to the invention to be implemented.

[0088] FIG. 3 shows a comparison of the desulphurisation performance of a pilot facility and of the industrial tests carded out either with a penetrating metal nozzle of the prior art or with the injection device of the present invention.

[0089] FIGS. 4, 5A and 5B show results of digital CFD (Computational Fluid Dynamics) simulations of the distribution of powdered abatement compound in the same furnace pipe, with a device and its corresponding method, according to the present invention (FIG. 4), in comparison to the prior art US 2013/0125749 (FIGS. 5A and 5B).

[0090] FIG. 1 is an example of a first embodiment of a device 10 for injection of a powdered compound according to the invention. A furnace (not shown) produces flue gases comprising gaseous pollutants that are transported by a furnace pipe 500 to a chimney (not shown) in order to evacuate them into the atmosphere.

[0091] During operation, the injection device according to the invention generates two flows of gas: [0092] a flow of gas called transportation gas 110, created by a blower 100 having an adjustable flow rate, (lateral blower in the example illustrated); this flow of transportation gas circulates in a transportation pipe 120 connected to the blower; on the path of this transportation flow, there is a system 130 for dosing powdered compound, connected to a tank of powdered compound (not shown), in such a way that the transportation flow is loaded with powdered compound; [0093] a flow of gas called peripheral gas 210 created by a blower 200 having an adjustable flow rate; this flow of peripheral gas is delivered into a chamber 230 and then circulates in a peripheral pipe 220 connected to this chamber.

[0094] The transportation pipe 120 passes through the chamber 230 impermeably and exits therefrom concentrically to the peripheral pipe 220 inside said pipe. It is interrupted at its upstream end 121 located in a secant plane between the first portion 221 and the second portion 222 of the peripheral pipe 220.

[0095] As illustrated by the cross-section A-A of FIG. 1A, there is therefore an annular space 170, between the axial transportation pipe 120 and the first portion 221 of the peripheral pipe, in which the flow of peripheral gas 210 circulates, the flow of transportation gas 110 circulating in the transportation pipe 120. The device thus provides two jets of gas in the furnace pipe, an axial jet of transportation gas 110, loaded with powdered compound, and a jet of peripheral gas 210 that surrounds the jet of transport gas.

[0096] In a particular embodiment of the present invention, illustrated in FIG. 2, the peripheral pipe 220 further comprises a third portion (223) comprising an upstream portion (224) provided with an upstream end (224a) and a downstream portion (225) provided with a downstream end (225a), having a diameter DP3 less than the diameter DP2, said upstream end being intended to be connected to the downstream end of the second portion of the peripheral pipe, said downstream end being intended to be connected to the furnace pipe.

[0097] Advantageously, said upstream portion (224) of the third portion of the peripheral pipe has the shape of a truncated cone.

[0098] The shrinking of the diameter of the peripheral pipe 220 in its third portion 223 causes, via conservation of mass, a second Venturi effect allowing an additional acceleration of the flows of the transportation gas and peripheral gas and thus an additional improvement of the penetrability of the powdered compound in the furnace pipe.

[0099] In general, the peripheral pipe 220 is connected to the furnace pipe 500 radially. The flow of peripheral gas 210, peripheral to the flow of transportation gas 110, maintains the shape of and guides this flow of transportation gas 110 until they penetrate the furnace pipe 500, allowing the central vein of the furnace pipe 500 to be reached without the need for a penetrating nozzle.

[0100] Moreover, since the flow rates of the blowers 100 and 200 can be adjusted separately, the device allows adaptation to a large variety of conditions of use, namely in terms of speed of the flue gases, concentration of acidic gases, diameter of the pipe, . . .

[0101] Of course, the invention covers different shapes of the device, provided that at the inlet of the furnace pipe, a jet of transportation gas 110 loaded with powdered abatement material and a jet of peripheral gas 210 are obtained. For example, in FIGS. 1 and 3 of the present application, the peripheral pipe 220 is connected to the furnace pipe 500 perpendicularly, in other words with an angle of 90 between the axes of the two pipes. Alternatively, this peripheral pipe 220 could obviously be connected to the furnace pipe 500 with an angle between the axes of the two pipes that is greater than or less than 90.

[0102] Digital Simulations

[0103] In order to demonstrate the effectiveness of the device and of the method according to the present Invention, digital simulations of distribution of powdered slaked lime in a furnace pipe containing flue gases were carried out while considering various injection devices. More precisely, the distribution of the lime obtained using the device according to the present invention and its method was compared to that obtained with the device and the method of document US 2013/0125749, with comparable operating parameters (in other words, by setting the geometry of the furnace pipe, the composition and the speed of the flue gases that pass through it, the position and the cross-section of the duct for transporting lime, as well as the flow rate of transportation air and of lime, which is calculated theoretically with respect to the quantity of pollutants present in the flue gases, according to the performance in terms of trapping lime).

[0104] The distribution of the lime in the furnace pipe is evaluated via CFD (Computational Fluid Dynamics) using a distribution factor Phi that corresponds to the concentration of lime in the flue gases, at a given point of said pipe, when the lime Is Injected transversely.

[0105] This distribution factor is dependent in particular on the geometry of the furnace pipe and is defined as follows:

[00001]$\mathrm{Phi}=\frac{\mathrm{Vi}}{\mathrm{Vtot}}$

[0106] Where

[0107] V.sub.i corresponds to the volume of the powdered lime;

[0108] V.sub.tot corresponds to the sum of the volume of the powdered lime and of the volumes of all the gases present in the flue gases.

[0109] In the digital simulations carried out, the furnace pipe considered is in the shape of an Inverted U (see FIGS. 4 and 5) and has a square cross-section 4 m long.

[0110] In order to be able to compare the efficiency of the device of the present invention to that of the device of the prior art US 2013/0125749, the optimal distribution factor Phi.sub.opt must first be determined. This factor corresponds to the concentration of lime in the flue gases to be reached in order for this lime to be distributed optimally in such a way as to cover the entirety of the cross-section of the furnace pipe considered.

[0111] In the present case, this optimal distribution factor was determined by simulating a device comprising a penetrating nozzle (and thus not containing peripheral gas), at present considered to be the most efficient device in terms of distribution of powdered compound. The nozzle is inserted into the furnace pipe at a depth of 1 m.

[0112] In this configuration and for the furnace pipe considered, the optimal distribution factor Phi.sub.opt is approximately 7.10.sup.3. Indeed, for this value of Phi, the distribution of the lime in this furnace pipe is optimal and is in the form of a transverse screen, covering the entirety of the cross-section of a leg of the inverted U, 50 cm above the injection point. This situation (Phi.sub.opt=7.10.sup.3) has therefore been considered to be the optimal distribution factor to be achieved.

[0113] Devices Studied:

[0114] a) Device and method according to the present invention.

[0115] b) Device and method according to document US 2013/0125749.

[0116] The results of this simulation are indicated in FIGS. 4 (the present invention) and 5 (prior art US 2013/0125749).

[0117] As can be observed in FIG. 4, when a flow of peripheral gas with a mass flow rate of 0.1 to 0.2% with respect to the flow rate of flue gases is used, according to the invention, a distribution factor identical to the optimal distribution factor (Phi.sub.d=7.10.sup.3) is obtained in a transverse plane located 50 cm above the injection point. The present invention is therefore capable of injecting powdered slaked lime with the same penetrability as the penetrating nozzle but without using an invasive device.

[0118] However, when using the device and the method according to the patent application US 2013/0125749, a flow of peripheral gas having a very high flow rate with respect to the flue gas (mass flow rate of peripheral gas 10 times greater than that of the present invention) is generated, which creates great turbulence that is moreover desired by document US 2013/0125749. In this case, the zone in which the lime is uniformly distributed is very small, requiring, in order to achieve an optimal distribution factor of lime in the furnace pipe, at least three devices according to this prior art to be placed.

[0119] Indeed, as can be seen in FIG. 5A, the zone in which the lime is uniformly distributed is very concentrated. In this case, a single nozzle does not allow a Phi=7.10.sup.3 to be achieved in a transverse plane located 50 cm above the injection point Indeed, in this transverse plane, the distribution factor Phi is equal to 4.10.sup.3 (FIG. 5B), which makes the dispersion of the lime 1.75 times less effective in comparison to the present invention.

[0120] Indeed, three devices according to the prior art US 2013/0125749 must be used in order to obtain a distribution equivalent to that of a single penetrating nozzle of the prior art.

EXAMPLES

[0121] In order to evaluate the efficiency of the dispersion obtained according to the present invention, the abatement of the SO.sub.2 at a very high temperature by a powdered slaked lime as obtained according to the method described in document WO2007000433 has been studied.

[0122] In the temperature range between 850 and 1150 C., the Ca(OH).sub.2 hydrated lime reacts with SO.sub.2 in order to form CaSO.sub.4 according to the following equations:

Ca(OH).sub.2.fwdarw.CaO+H.sub.2O

CaO+SO.sub.2+O.sub.2.fwdarw.CaSO.sub.4

[0123] In this temperature range, the reaction between the calcium hydroxide and the SO.sub.2 is selective and fast.

[0124] Selective because besides the SO.sub.2, none of the other compounds present in the flue gases (such as CO.sub.2) have a stable reaction product in the aforementioned temperature range. Indeed, for the needs of the experiment, even if the calcium hydroxide allows other acidic gases to be abated, only the neutralization of SO.sub.2 by the calcium hydroxide is of interest in order to be able to dose the product of the reaction namely CaSO.sub.4 and thus achieve the efficiency of the method studied, namely with respect to the stoichiometric ratio RS.

[0125] Fast because the speed of the reaction between the slaked lime and the SO.sub.2 increases exponentially with the temperature according to the Arrhenius law. Thus, at 900 C., the time of contact between the acidic gases and the slaked lime can be less than 0.5 seconds.

[0126] Below, the results obtained under the following three conditions have been compared: [0127] Comparative example 1: Pilot facility that can be considered to represent a situation of perfect mixture. [0128] Comparative examples 2 and 3: Industrial facilities with injection of powdered slaked lime carried out via a metal penetrating nozzle according to the prior art. [0129] Example: Industrial facility with injection of slaked lime carried out using the device of the present Invention.

[0130] The comparison was carried out for an abatement of 70% of the SO.sub.2, which represents the average abatement desired for this type of method.

Comparative Example 1: Pilot Facility

[0131] The pilot facility allowed the change in the conversion of the SO.sub.2 according to the stoichiometric ratio RS (number of moles of calcium hydroxide/number of moles of SO.sub.2 at the input) in a perfect case, that is to say, in the absence of dust, to be measured, with a temperature perfectly distributed over the entire reaction zone and without a dead or turbulent zone. Such a pilot facility is also described in document WO2007000433.

[0132] The parameters of the flue gases present in the pilot facility are the following: [0133] Total flow rate: 2 Nm.sup.3/h [0134] Temperature: 950 C. [0135] SO.sub.2 concentration: 1500 ppm [0136] CO.sub.2 concentration: 10% vol [0137] O.sub.2 concentration: 6% vol

[0138] For the pilot facility, the stoichiometric ratio (RS) measured is 1.5 in order to obtain 70% conversion of the SO.sub.2. It can thus be concluded therefrom that in the context of abatement of the SO.sub.2 at a temperature between 850 and 1150 C., the RS of a perfect mixture will be close to 1.5 for 70% conversion of the SO.sub.2.

[0139] Numerous industrial tests have been carried out using metal penetrating nozzles aimed at maximising the efficiency of the dispersion of the solid particles in the flow of flue gas.

[0140] The two comparative examples presented below use the highest conversion/RS ratios obtained up to now.

Comparative Example 2Industrial Test with Metal Penetrating Nozzle (According to the Prior Art)

[0141] A slaked lime similar to that used in the pilot facility was injected at a speed of 15 m/s using a metal penetrating nozzle in a post-combustion chamber (furnace pipe), in which the combustion of the combustion residues takes place.

[0142] The parameters of the flue gases are the following: [0143] Total flow rate: 46,750 Nm.sup.3/h [0144] Average temperature: 925 C. [0145] Average SO.sub.2 concentration: 450 ppm [0146] CO.sub.2 concentration: 15% vol [0147] O.sub.2 concentration: 10% vol

[0148] The residence time of the hydrated lime in the furnace pipe is approximately 1 to 1.5 seconds. In the case of comparative example 2, the stoichiometric ratio measured is 2 in order to obtain 70% conversion of the SO.sub.2.

Comparative Example 3.Industrial Test with Metal Penetrating Nozzle (According to the Prior Art)

[0149] A slaked lime similar to that used in the pilot facility was injected at a speed of 15 m/s using a metal penetrating nozzle in a post-combustion chamber (furnace pipe).

[0150] The parameters of the flue gases are the following: [0151] Total flow rate: 140,000 Nm.sup.3/h [0152] Average temperature: 925 C. [0153] Average SO.sub.2 concentration: 390 ppm [0154] CO.sub.2 concentration: 15% vol [0155] O.sub.2 concentration: 8% vol

[0156] The residence time of the hydrated lime in the furnace pipe is approximately 1 to 1.5 seconds. In the case of comparative example 3, the stoichiometric ratio measured is 2.3 In order to obtain 70% conversion of the SO.sub.2.

[0157] The average stoichiometric ratio for comparative examples 2 and 3 is 2.1 for 70% conversion of the SO.sub.2.

ExampleIndustrial Test Carried Out According to the Method of the Present Invention

[0158] A slaked lime similar to that used in the pilot facility was injected using the device of the present invention into a post-combustion chamber (furnace pipe).

[0159] The parameters of the flue gases are the following: [0160] Total flow rate: 82,000 Nm.sup.3/h [0161] Average temperature: 900 C. [0162] Average SO.sub.2 concentration: 395 ppm [0163] 02 concentration: 17% vol [0164] CO.sub.2 concentration: 15% vol

[0165] The parameters of the injection device are the following: [0166] Diameter DT of the transportation pipe: 88.9 mm, [0167] Diameter DP2 of the second portion of the peripheral pipe 222: 107.1 mm, [0168] Speed of the transportation air V.sub.T: 15 m/s, [0169] Speed of the peripheral air V.sub.P: 44 m/s, [0170] Flow rate of the transportation air Q.sub.T: 420 Nm.sup.3/h, [0171] Flow rate of the peripheral air Q.sub.P: 290 Nm.sup.3/h.

[0172] The residence time of the hydrated lime in the furnace pipe is 0.1 seconds.

[0173] The method according to the invention allowed stoichiometric ratios (RS) of 1.6 to be obtained for 70% abatement of the SO.sub.2.

[0174] FIG. 3 repeats all of the results obtained with the pilot facility (comparative example 1); using the device of the present invention (example); and using a metal penetrating nozzle of the prior art (average of comparative examples 2 and 3).

[0175] As can be noted in FIG. 3, the values obtained according to the method of the present invention are close to the values obtained with the pilot facility.

[0176] As mentioned above, when the efficiency of the dispersion of the solid particles increases, the values measured on site move closer to the values obtained with the pilot.

[0177] These results show that the device and the method according to the present Invention allow, with an identical conversion rate, approximately 23% less powdered slaked lime to be used than with the metal penetrating nozzles of the prior art.

[0178] The efficiency of the dispersion of the solid particles in the fluid mixture is therefore better according to the device and the method of the invention than with the use of metal penetrating nozzles of the prior art. Moreover, the latter pose other problems in terms of transportation of the powder, safety, and ease of installation, also solved by the device and the method according to the invention.