Title of Invention

AN APPARATUS FOR TREATING FLUE GASES

Abstract

An apparatus comprising a reactor for treating flue gases such that the feed flue gas is mixed with ammonia and irradiated with electron beams to be freed of nitrogen oxides and/or sulfur oxides, characterized by means for adding ammonia within the reactor at a position in the flow of the flue gas that is upstream of the center of the electron beams being applied within the reactor by a distance no more then 2.5 times the range of the electron beams. PRICE: THIRTY RUPEES

Full Text

This invention relates to an apparatus for treating flue gases such that the feed flue gas is mixed with ammonia and irradiated with electron beams to be freed of nitrogen oxides and/or sulfur oxides. Conventionally, the diffusion and mixing of ammonia in a flue gas has been improved either by injecting ammonia at a position upstream of or near the inlet to the reactor so that it will stay within the flue gas for a prolonged time or by using a punching metal for mixing with the gas. It is generally held that denitration and desulfurization reactions proceed almost simultaneously and the low efficiency of denitration has primarily been ascribed to insufficient mixing and diffusion of ammonia and this is why nobody has ever thought of adding ammonia at a position closer to the region of 1 madiation with electron beams. With the recent enforcement of more rigorous regulations in respect to the concentration of leak ammonia in flue gases, it has been necessary to control the leak ammonia. In fact, however, ammonia has been supplied in excessive amounts in the prior art in order to ensure that denitration and desulfurization reactions proceed in the desired direction. But then the excessive addition of ammonia causes an increased amount cf ammonia to remain in the flue gas. Since the current regulations on..._the_.emission . of flue gases'requires that not L"only'"N"Ov,~'"S'0X and., dust but also .leak ammonia be controlled on the emission, it has be-on necessary for the ammonia to- be o.rejected a;: an opu imal posi. i .'on in the necessary minimum amount which ensures the desired efficiency of denitration and desulfurization reactions. . An object of the invention is to provide an apparatus for treating flue gases by irradiation with electron beams that reduces the addition of ammonia to the necessary minimum amount to meet two requirements simultaneously: one for improving the efficiency of denitration and the other for reducing the amount of leak ammonia to several tens c£ ppm. To attain this objective, the position where ammonia is added is specified by the distance from the zone of irradiation with electron beams and brought closer to, rather than farther from, the irradiation zone within the reactor. This is also effective in reducing the concentration of leak ammonia to a low.level. If ammonia is added at the conventional position, desulfurization reaction will first take place, followed then by denitration reaction, in a temperature range of about 60 - 803C; hence, before the supplied flue gas reaches the irradiation zone, part of the ammonia added is spent in the thermochemical desulfurization reaction. On the other hand, the greater the excess of ammonia, the higher the efficiency cf denitration but, in fact, part of the added ammonia is spent in the desulfurization reaction and the progress cf denitration reaction will not be as thorough as it is desired. This would be the cause of the lower efficiency cf denitration than that of desulfurization. Accordingly the present invention provides an apparatus for treating flue gases comprising a reactor (4) for treating flue gases such that the feed flue gas is mixed with ammonia and irradiated with electron beams to be freed of nitrogen oxides and/or sulfur oxides, characterized in that means (12) for adding ammonia within the reactor is provided at a position in the flow of the flue gas that is upstream of the center of the electron beams being provided within the reactor.^ a distance no more than 2.5 times the range of the electron beams. With reference to the accompanying drawings, in which: Fig. 1 is a flow chart of the facilities used to test the performance of the apparatus of the invention; Fig. 2 is a graph showing the relationship between the position of ammonia addition and each of the denitration and desulfiirization efficiencies; Fig. 3 is a graph showing the relationship between the position of ammonia addition and the concentration of leak ammonia; Fig. 4 is a diagram showing the positions of ammonia addition that were adopted in the performance test; Fig. 5 is a diagram showing an exemplary position of ammonia addition according to the invention; Fig. 6 is a front view showing the positions of- ammonia addition that were adjusted to contour the divergence of electron beams emitted in the invention; and Fig. 7 is a plan view corresponding to Fig. 6. DETAILED DESCRIPTION OF THE INVENTION: In the invention, ammonia is added at a position in the direction of the flue gas stream that is upstream of the center of electron beams applied within the reactor and which is not more than 2.5 times the range of electron beams, preferably not more than 2.0 times, more preferably not more than 1.5 times, most preferably from one half to a value equal to said range. Considering various factors such as the conditions of the flue gas, the desired denitration and desulfurization, efficiency and the limitations of the processing apparatus, ammonia is supplied in any one of the following ways; (1) only ammonia is supplied; (2) both ammonia and air are supplied; (3) both ammonia and water are supplied; and (4) ammonia, air and water are all supplied. From an operational viewpoint, ammonia is preferably supplied as diluted in the form of a mixture of heated ammonia and dry air (having preferably a dew point of 15CC or less at o: en atmosphere). It is also effective to supply ammonia through pipes that are arranged to contour the spherical divergence of electron beams. As already mentioned, ammonia has conventionally been added at a position upstream the flue gas stream in the reactor in order to enhance the diffusion and mixing of ammonia in the flue gas. However, this has caused the desulfurization reaction to proceed faster than the denitration reaction and part of [the added ammonia is spent to retard the progress of the la titer reaction thereby reducing -its- efficiency. L The present inventio.n solves this prcblem by adding ammonia at positions which," as shown in Fig. 4, are f upstream, ir, the direction of the} flue gas sure:;;:, of five center of electron beams applied iwithin the reactor and which are no more than 2.5 times (.the range of electron beams, preferably not more than 2.0 rimes, more preferably not more than 1.5 times, most prdferably from one half to a value equal to said range. If this arrangement is adopted, the amount of ammonia that would otherwise be spent in the desulfurization reaction is reduced and the amount of ammonia that contributes to the denitration reaction is increased, accordingly, thereby accomplishing an improvement in the denitration efficiency. However, the intended effect of the invention is not attained if ammonia is added at a position more than 2.5 times the range of electron beams. If, on the other hand, ammonia is added at a position that is unduly close to the zone of irradiation with electron beams, part of the applied electron beams will impinge on some of the ammonia feed pipe and this not only results in the loss of electron beam's energy but also the ammonia feed pipe that is being struck by electron beams will become so hot that a need arises to employ a special provision that inquires safety. The following example is provided for the purpose of further illustrating the invention but is in no way to be taken as limiting. Example .1 A flue gas was treated in a reactor L, (see Fig. 4) having a cross section of 1,100 mm" x 1,000 mm" by irradiation with electron beams applied from an electron beam generator 11. Ammonia diluted about 100 folds with dry air (having a dew point of -I5°'C at one atmosphere) was supplied through a feed pipe 12 and added at three positions that were upstream the flow of the flue gas by distances of 1,100 mm (equal to the range of electron beams that is indicated by 14 in Fig. 4 and which is determined considering the loss of electron beams that is caused by- the L window in che zone of irradiation with electron beams as they are generated rroni the electron beam generator 1 i at an acceleration voltage of 0. '5 Mevj)-, 1 , 5C0 mm and 4,000 mm, with the conditions for irradiation with election beams being her.: constant. The denitration and desulfurization efficiency that could be achieved was calculated. The test .conditions are listed in Table 1 and a flow-sheet for the general layout of the test facilities is shown in Fi.g. 1. Referring to Fig. 1, a flue gas containing S0X and/or N0X that has been generated in a boiler 1 is cooled in a cooling tower 2 and introduced to a reactor 4, which is also supplied with ammonia through a feed pipe 3. The flue gas is irradiated with electron beams from an electron beam generator 5 so that S0X and N0X are converted to ammonia sulfate and ammonia nitrate, respectively, in a solid form, which are subsequently trapped by an electric precipitator 6 and a bag filter 7. The clean gas is thereafter discharged into the atmosphere via a suction fan 8 and a stack 9. The test results are shown in Table 2 and in Figs. 2 and 3. Obviously, the denitration efficiency improved and yet I.!:?? amount of leak a?mmonia decreased when ammonia i'as added in positions that were upstream the center of electron beams by the distances within the reactor no more than 2.5 times the range of electron beams, preferably not more than 2.0 times, more preferably not more than 1.5 times, most preferably from 0.5 to 1.0 times the range of electron beams. In the test range, the desulfurization efficiency was comparable to the values achievable in the prior art. The maximum thickness of a given medium that can be penetrated by an electron accelerated at a voltage of E (0.01 MeV <..-_e_- _2. mev is called the of the.. ..> electron, which is expressed by -the- following empirical formula: [ where R is the range (cm) of an electron, E is the Acceleration voltage (MeV) and pf_ is the density of a, medium ( g/cmJ) . ...... The results of range calculation for acceleration . voltages of 0.5 - 1.0 MeV are shown in Table 3 without taking into account the energy loss caused by the window through which electron beams were applied from the electron beam generator. In the example, the range of electron beams was assumed to be 1,100 mm at an acceleration voltage of 0.5 MeV considering the scattering of electron beams and the energy loss caused by the window. According "to "the invention, ammonia xs added at a position in the direction of a flue gas stream that is upstream of the center of electron beams being applied within a reactor by a distance no more than 2.5 times the range of electron beams., preferably not more than 2.0 times, more preferably not more than 1.5 times, most preferably from 0.5 to 1.0 times the range of the electron beams and this is effective in imr/roving the denitration efficiency and yet reducing the concentration of leak ammonia to several tens of ppm. As a result, the denitration efficiency which was no more than 80% in-the prior art.can be Increased to as high as 85 - 90% in the invention if the electron beam generator used produces the same output. This means a comparable denitration efficiency to the prior art apparatus can be accomplished even if the output of the electron beam generator is reduced. Further, the operating cost of utilities in ths treatment "of flue gases by irradiation with electron beams is reduced and this adds the advantage of lower energy to the existing benefits of treating flue gases by irradiation with electron beams. WE CLAIM: 1. An apparatus for treating flue gases comprising a reactor (4) for treating flue gases such that the feed flue gas is mixed with ammonia and irradiated with electron beams to be freed of nitrogen oxides and/or sulfur oxides, characterized in that means (12) for adding ammonia within the reactor is provided at a position in the flow of the flue gas that is upstream of the center of the electron beams being provided within the reactor by a distance no more than 2.5 times the range of the electron beams. 2. The apparatus according to claim 1, wherein said distance is less than 2.0 times the range of the electron beams. 3. The apparatus according to claim 1, wherein said distance is less than 1.5 times the range of the electron beams. 4. The apparatus according to claim 1, wherein said distance is from one half to a value equal to the range of the electron beams. 5. The apparatus according to any one of the preceding claims, wherein ammonia is added through pipes that are disposed to contour the spherical divergence of the applied electron beams. 6. An apparatus comprising a reactor for treating flue gases substantially as herein described with reference to the accompanying drawings.

Documents:

1045-mas-1995 abstract.pdf

1045-mas-1995 claims.pdf

1045-mas-1995 correspondence-others.pdf

1045-mas-1995 correspondence-po.pdf

1045-mas-1995 description (complete).pdf

1045-mas-1995 drawings.pdf

1045-mas-1995 form-1.pdf

1045-mas-1995 form-26.pdf

1045-mas-1995 form-4.pdf

1045-mas-1995 others.pdf

1045-mas-1995 petition.pdf