JP2010264400A - Denitrification apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a denitrification apparatus which prevents massive ashes from flying to a denitrification catalyst and further which is capable of causing ammonia to efficiently react with NOx by properly arranging the distribution of ammonia. <P>SOLUTION: The denitrification apparatus is provided with an exhaust gas passage 16 constituting a part of a flue, an ammonia injection device 23 having a plurality of ammonia injection nozzles which have been dispersively arranged within the cross section of the exhaust gas passage, a denitrification catalyst 28 for promoting the reaction between the nitrogen oxide in the exhaust gas and ammonia injected from the ammonia injection nozzles, which is arranged at the downstream side of the ammonia injection device 23, a rectification member 18 which rectifies the stream of the exhaust gas within the exhaust gas passage and is uniformly distributed within another cross section of the exhaust gas passage different from within the exhaust gas passage, and which includes many exhaust gas circulation parts to make the circulation of the massive ashes included in the exhaust gas possible, and a recovery opening 21a arranged at the downstream side of the rectification member 18, which is connected with a passage 21 for dust collection to recover the massive ashes that passed the rectification member 18. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a denitration apparatus disposed in a flue gas treatment facility of a boiler unit.

  In coal fired oil or oil fired boilers, massive ash (popcorn ash) or scales may be contained in the boiler exhaust gas. In particular, when low quality fuel such as subbituminous coal is burned, massive ash having a diameter of about 1 cm may be generated due to a calcium (Ca) component in the coal fuel. Since the massive ash has a low specific gravity, it will fly to the denitration device together with the exhaust gas, which may cause clogging of the denitration catalyst, resulting in problems such as increased differential pressure and catalyst wear damage in the denitration device. As one of the causes that such massive ash is scattered on the denitration catalyst, the influence of the unbalance of the exhaust gas flow rate in the exhaust gas flow path in the denitration device inlet duct after the boiler outlet can be considered. If a situation in which the flow velocity distribution becomes larger in the cross section of the exhaust gas flow path occurs, there is a concern that massive ash is carried to the denitration reactor together with the exhaust gas in the high flow velocity portion. As a measure against massive ash, there is a method to collect massive ash by installing a metallic mesh at the boiler outlet, but the metallic mesh may be broken due to the influence of the exhaust gas high flow rate section mentioned above in the denitration equipment, and so on. It was difficult to achieve stable operation with forced wire mesh repair.

  Patent Document 1 discloses an exhaust gas dust removing device for collecting such massive ash and its operation method. This device has a partition plate in the duct, a damper in the divided duct, and controls the opening and closing of the damper according to the differential pressure value between the upstream and downstream sides of the dust screen disposed in the vertical duct. The dust is collected in the hopper at the lower end of the vertical duct. However, in the apparatus and method of Patent Document 1, the structure for collecting massive ash is complicated, and further, the differential pressure must be measured, so that control is also required, and it takes time to collect massive ash. It is troublesome.

On the other hand, in the denitration device, the NOx distribution in the exhaust gas generated from the boiler is adjusted by adjusting the injection amount from the ammonia (NH ₃ ) injection nozzle for injecting ammonia as a reducing agent, and at the denitration device outlet. By adjusting the ammonia distribution to achieve a uniform NOx concentration in the exhaust gas, the injected ammonia reacts efficiently with NOx. However, in a situation where an excessive exhaust gas flow velocity distribution occurs at the boiler outlet, ammonia distribution adjustment may not be successful even if ammonia injection balance adjustment is performed. That is, when the above-described imbalance in the exhaust gas flow velocity at the boiler outlet occurs, the distribution of the injected ammonia also becomes non-uniform accordingly, resulting in an unbalance in the exhaust gas NOx concentration at the denitration apparatus outlet. At this time, if the residual ammonia concentration distribution becomes larger due to the unbalance of the NOx concentration distribution at the outlet of the denitration device, the ammonia concentration locally in the gas air heater (GAH) for residual air heat disposed in the alternating current of the denitration device. Is generated, which becomes acidic ammonium sulfate, that is, ammonium hydrogen sulfate (NH ₄ HSO ₄ ) and ammonium sulfate, that is, ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), and clogging in the middle to low temperature layer elements of the gas air heater proceeds. End up. In addition, due to the imbalance of ammonia injected into the flue upstream of the denitration catalyst, the NH ₃ / NOx molar ratio balance distribution at the catalyst inlet is also affected, and the denitration reaction does not proceed efficiently. This will increase the amount of ammonia input.

  Patent Document 2 discloses a denitration reactor ammonia injection apparatus and method for efficiently operating a denitration apparatus while suppressing the amount of leaked ammonia as much as possible. In this apparatus and method, the exhaust gas flow velocity distribution at the duct outlet is provided with a gas recirculation fan, the exhaust gas flow velocity distribution in the ammonia injection section is obtained in consideration of the boiler load, and an appropriate ammonia injection amount is obtained and introduced. It is. However, the configuration of Patent Document 2 requires a device for arithmetic processing and control, the structure is complicated, and the operation load of the boiler must be taken into consideration, and it is troublesome to obtain an appropriate ammonia injection amount. Is troublesome.

JP 2005-152746 A JP-A-11-179155

  The present invention is based on the above prior art, and provides a denitration apparatus that prevents massive ash from flying up to a denitration catalyst and that can efficiently react with NOx by aligning the distribution of ammonia. For the purpose.

  In order to achieve the above object, according to the first aspect of the present invention, a denitration apparatus is provided in a flue for guiding exhaust gas discharged from a boiler to remove nitrogen oxides in the exhaust gas, and is a part of the flue. An exhaust gas passage through which the exhaust gas flows in the denitration device, an ammonia injection device having a plurality of ammonia injection nozzles distributed in the exhaust gas channel cross section, and a downstream side of the ammonia injection device A denitration catalyst for promoting a reaction between nitrogen oxides in the exhaust gas and ammonia injected from the ammonia injection nozzle, and a rectifying member that rectifies the flow of the exhaust gas in the exhaust gas flow path. A rectifying unit that includes a large number of exhaust gas distribution portions that are uniformly distributed in a cross section of the exhaust gas flow channel different from the cross section of the exhaust gas flow channel and that allow the flow of massive ash contained in the exhaust gas. If, disposed downstream of the rectifying members, to provide a denitration apparatus characterized by comprising a collecting aperture which is connected to the dust collecting passage for recovering the bulk ash that has passed through the rectifying member.

According to a second aspect of the present invention, in the first aspect of the present invention, the rectifying member is provided with a wear-resistant coating.
The invention of claim 3 is characterized in that, in the invention of claim 1 or 2, a mesh member having a mesh smaller than that of the massive ash is disposed downstream of the collection opening.
According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the ammonia injection device is disposed downstream of the rectifying member.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, the exhaust gas flow path includes an inclined portion extending obliquely upward from the boiler outlet, a vertical rising portion extending vertically upward from the inclined portion end, and It comprises a horizontal portion extending in the horizontal direction from the end of the vertically rising portion and a vertically descending portion extending vertically downward from the end of the horizontal portion, the ammonia injection device is attached to the horizontal portion, and the denitration catalyst is the vertically descending The rectifying member and the dust collecting flow path are attached to the inclined portion.

  According to the first aspect of the present invention, since a rectifying member including a large number of exhaust gas circulation portions having a diameter through which the ash contained in the exhaust gas can be distributed is provided, which is uniformly distributed with respect to the cross section of the exhaust gas flow path, The exhaust gas flow velocity distribution in the exhaust gas passage can be made uniform. Therefore, even if the massive ash passes through the exhaust gas circulation part of the rectifying member, since the high flow rate part does not exist in the exhaust gas flow path, the massive ash can be prevented from flying to the denitration catalyst. Further, since the dust collecting flow path is provided on the downstream side of the rectifying member, the massive ash that has passed through the rectifying member flows into the dust collecting flow path without flowing through the exhaust gas flow path, and collects the massive ash. be able to.

According to the second aspect of the present invention, since the rectifying member is provided with the wear-resistant coating, it is possible to suppress the resistance of the ash contained in the exhaust gas as much as possible, and hinder the boiler operation. Can be prevented.
According to the invention of claim 3, since the mesh member having a mesh smaller than the massive ash is disposed on the downstream side of the rectifying member, most of the massive ash that has passed through the rectifying member is collected by the mesh member. Can do. Therefore, it is possible to reliably prevent the massive ash from scattering on the denitration catalyst. At this time, since the flow rate of the exhaust gas flow path is made uniform by the rectifying member, the mesh member is not damaged due to wear due to the local high-speed flow rate portion.

  According to the invention of claim 4, since the ammonia injection device is disposed on the downstream side of the rectifying member, the rectified exhaust gas flow channel is uniformly (uniformly) arranged in the flow channel cross section. Since ammonia is injected from the ammonia injection nozzle, the NOx distribution in the exhaust gas becomes uniform. Further, ammonia is uniformly injected into this flow velocity distribution, so the ammonia distribution is also uniform, and NOx and ammonia are reacted efficiently. be able to.

  According to the invention of claim 5, the flow rate distribution of the exhaust gas in the cross section of the exhaust gas flow path is provided by attaching the ammonia injection device to the horizontal part, the denitration catalyst to the vertical descending part, and the rectifying member and the dust collecting flow path to the inclined part. Becomes uniform, and the distribution of ammonia becomes uniform. This is confirmed by the present inventors through simulation.

1 is a schematic view of a flue to which a denitration apparatus according to the present invention is applied. 1 is a schematic view of a denitration apparatus according to the present invention. It is a schematic front view of a rectifying member. It is the schematic of an ammonia injection apparatus. It is a graph which shows the flow-velocity distribution in an exhaust gas flow path. It is a distribution map of ammonia.

FIG. 1 is a schematic view of a flue to which a denitration apparatus according to the present invention is applied.
As shown in the figure, the flue 1 has a boiler 2 at the start and a chimney 3 at the end. Between the boiler 2 and the chimney 3, a denitration device 4, an electrostatic precipitator 5, and a desulfurization device 6 are arranged from the upstream side. The entrance of the boiler 2 is equipped with an FDF (Forced Draft Fan) which is an indentation fan 7. An APH (Air Pre Heater) that is an air preheater 8 is provided between the pushing fan 7 and the boiler 2 and between the denitration device 4 and the electrostatic precipitator 5. Between the electric dust collector 5 and the desulfurization device 6, an IDF (Induced Draft Fan) which is an incentive ventilator 9 for blowing the boiler exhaust gas after combustion is provided. Between the desulfurization device 6 and the chimney 3, a BUF (Boost Up Fan) which is a boosting fan 10 is provided. A GGH (Gas Gas Heat exchanger), which is a heat exchanger 11 for recovering thermal energy, is provided between the incentive ventilator 9 and the desulfurizer and between the booster fan 10 and the chimney 3.

The exhaust gas discharged from the coal fired boiler is subjected to denitration, dust collection and desulfurization treatment, and is discharged from the chimney 3 to the outside. The present invention relates to a denitration apparatus used in this exhaust gas discharge process.
FIG. 2 is a schematic view of a denitration apparatus according to the present invention. 3 is a schematic front view of the rectifying member, and FIG. 4 is a schematic view of the ammonia injection device.

  As shown in FIG. 2, the outlet side of the boiler 2 (the inlet side including the combustion part of the boiler 2 is omitted in the figure) is separated by the partition wall 12 and the reheat gas channel 13 and the superheated gas channel 14. It is divided into. A reheater (RH) (not shown) is disposed in the reheat gas flow path 13, and a superheater (SH) (not illustrated) is disposed in the superheated gas flow path 14. An STC damper 15 is disposed on the outlet side of the reheat gas channel 13 and the superheated gas channel 14. The STC damper 15 adjusts the flow rate of the respective flow paths 13 and 14, and when the boiler 2 becomes a low load, on the other hand, control such as closing the damper is performed to actively perform heat recovery. Is done. An economizer (ECO) (not shown) is disposed upstream of the STC damper 15.

  The denitration device 4 is provided downstream of the boiler 2. That is, the exhaust gas passage 16 formed in the denitration device 4 communicates with the outlet side of the boiler 2. The exhaust gas flow channel 16 constitutes a part of the above-described flue 1. The exhaust gas channel 16 includes an inclined portion 16a extending obliquely upward from the outlet of the boiler 2, a vertical ascending portion 16b extending vertically upward from the end of the inclined portion 16a, and a horizontal portion extending horizontally from the end of the vertical ascending portion 16b. 16c and a vertically descending portion 16d extending vertically downward from the end of the horizontal portion 16c.

  A hopper 17 is formed on the inlet side of the inclined portion 16 a and below the boiler 2. This hopper 17 is for collecting dust. A straightening member 18 is disposed on the inclined portion 16a. As shown in FIG. 3, the rectifying member 18 has a perforated plate made of a punching metal. More specifically, a plurality of punching metals are fitted into the frame body 19. This porous distribution is formed to be uniform with respect to the cross section of the inclined portion 16a. Depending on the opening degree of the STC damper 15 described above, the flow velocity distribution of the exhaust gas becomes uneven on the inlet side of the inclined portion 16a. More specifically, the gas flow is concentrated on the lower side of the inlet of the inclined portion 16a due to the change in the direction of the exhaust gas flow from the vertical direction to the inclined portion 16a at the outlet of the STC damper 15, and on the upper side of the inlet. Occurrence of the exhaust gas flow occurs, which is a circulation region. That is, the flow velocity on the lower side of the inlet of the inclined portion 16a is higher than that on the upper side. The flow velocity distribution in the cross section of the inclined portion 16a can be made uniform by disposing the rectifying member 18 in the inclined portion 16a. In other words, the flow velocity that has been dispersed in the cross section of the inclined portion 16a is blocked to some extent by the rectifying member 18, the flow direction is determined by a large number of exhaust gas flow portions (punching metal holes in the figure), and as a result, the flow rates are made uniform. Therefore, it is possible to prevent the massive ash contained in the exhaust gas from the boiler 2 from coming down to the downstream as it is along the high flow velocity portion. The rectifying member 18 may be formed by intricate pipes as long as the rectifying member 18 has a certain amount of resistance of the exhaust gas flow channel 16 and has a large number of exhaust gas circulation portions uniformly distributed with respect to the cross section of the exhaust gas flow channel 16. It may be like a heat exchanger.

  The rectifying member 18 is provided with a wear-resistant coating such as a heat-treated aluminum alloy. Thereby, it can suppress as much as possible that it becomes the resistance of the ash contained in waste gas, and it can prevent that it impedes boiler operation. When a porous plate as shown in the figure is used as the rectifying member 18, for example, it is preferable that the hole diameter is 40φ, the aperture ratio is 65%, and the plate thickness is 9 mm. This is because the rectifying member can be formed with a simple structure. However, numerical values such as the hole diameter of the perforated plate are determined each time within the allowable pressure loss range.

  A wire mesh (mesh member) 20 is attached to the downstream side of the rectifying member 18. The mesh of the metal mesh 20 employs about 4 to 5 mesh, which is the same as the opening size of the denitration catalyst. Accordingly, lump ash having a diameter of 10φ or more cannot pass through the wire mesh 20 and is collected by the wire mesh. Thereby, it is possible to reliably prevent the massive ash from scattering to the downstream side. At this time, since the flow velocity of the exhaust gas flow path is made uniform by the rectifying member 18, the wire net 20 is not damaged due to the presence of the high-speed flow velocity portion locally.

  On the downstream side of the rectifying member 18 and upstream of the wire mesh 20 is for reheater steam temperature control (GR control) by exhaust gas recirculation, NOx reduction and superheater steam control (GI control) by exhaust gas recirculation. The circulation flow path is provided. For example, in GR control, the rotation speed of an exhaust gas mixing fan 1 (GMF) (not shown) provided in the middle of the circulation flow path is controlled, and the temperature is controlled by changing the gas flow rate in the boiler. The massive ash that has passed through the rectifying member 18 flows into this circulation channel. Therefore, the circulation flow path also functions as the dust collection flow path 21 for collecting massive ash. In other words, the dust collecting flow path 21 is disposed with the recovery opening 21 a from which massive ash is recovered facing the exhaust gas flow path 16. A dust collector (such as a multi-cyclone) 22 is provided in the middle of the dust collecting flow path 21, thereby collecting massive ash. In order to collect the massive ash efficiently, the dust collecting flow path 21 is preferably provided as close to the downstream side of the rectifying member 18 as possible. Moreover, it is preferable to provide the wire mesh 20 mentioned above downstream of the collection | recovery opening 21a. The massive ash that has not passed through the flow regulating member 18 is collected by the hopper 17 described above.

An ammonia injection device (AIG (Ammonia-Injection-Grid)) 23 is disposed in the horizontal portion 16c. As shown in FIG. 4, the ammonia injection device 23 is configured such that the ammonia injection nozzles 24 are uniformly expanded with respect to the cross section of the exhaust gas flow path 16 and arranged in a grid pattern. That is, the ammonia injection device 23 includes a plurality of ammonia injection blocks 25 that traverse the exhaust gas flow path 16 (two blocks in the figure). The ammonia injection block 25 includes a branch pipe 27 branched from the ammonia supply mother pipe 26 (in the figure, four branches) and a large number of the branch pipes 27 (shown only in the three branch pipes 27 in the figure). An injection nozzle 24 is provided, and a plurality (three in the figure) of these are formed to overlap. The length of the branch pipe 27 branched from each mother pipe 26 differs depending on each mother pipe 26 (in the drawing, the upstream branch pipe 27 is the longest and becomes shorter toward the downstream side). As described above, the ammonia injection nozzle 24 is disposed uniformly with respect to the cross section of the flow path, so that ammonia is injected so as to be uniform with respect to the flow path and can be reacted efficiently with NOx. That is, ammonia injected so as to have a uniform distribution reacts with the NOx distribution in the exhaust gas that has been rectified and made uniform by the rectifying member 18 described above, and therefore ammonia (NH ₃ ) and nitrogen oxidation are reliably performed without leakage. A thing (NOx) can be made to react.

  A plurality of denitration catalysts 28 (two in the figure) are disposed in the vertically descending portion 16d. By passing ammonia and NOx through the denitration catalyst 28, it is promoted to decompose NOx into nitrogen and water. As the denitration catalyst 28, a honeycomb or plate shape having a mesh size of about 6 mm to 7 mm can be used, and a catalyst in which an oxide such as tungsten or vanadium is supported as an active component using titanium oxide as a carrier can be used.

FIG. 5 is a graph showing the flow velocity distribution in the exhaust gas passage.
In the graph, Case-0 shows a case where a rectifying member is not attached, and Case-1 shows a case where a rectifying member is attached. The horizontal axis of the graph indicates the flow velocity (m / s), and the vertical axis indicates the height (mm) in the cross section of the exhaust gas passage. That is, in the graph, the channel diameter is 4500 mm. The place where the flow velocity was measured is near the entrance of the inclined portion 16a. In Case-0, the flow velocity on the upper side of the channel is low, while the lower side from the center of the channel shows a large value of 20.0 (m / s) to 30.0 (m / s). This indicates that the NOx distribution in the exhaust gas is non-uniform. When the flow rate is 30.0 (m / s), even 1 cm-diameter massive ash is entrained by the exhaust gas and carried downstream. End up. If a flow straightening member is provided in the vicinity of the inlet of the inclined portion 16a in this state, the flow velocity becomes substantially constant and uniform in the flow path cross section as shown by Case-1. As a result, it has been found by simulation that the flow regulating member is arranged to equalize the flow velocity distribution of the exhaust gas flow path.

FIG. 6 is a distribution diagram of ammonia.
As shown in the figure, according to the present invention, it can be seen that the ammonia distribution in the vertically descending portion 16d on the downstream side of the ammonia injection device 23 is substantially uniform (175 ppm (vol) to 200 ppm (vol)). This is the case when the ammonia injection device 23 is attached to the horizontal portion 16c, the denitration catalyst 28 is attached to the vertical descending portion 16d, and the rectifying member 18 and the dust collecting flow path 21 are attached to the inclined portion 16a as shown in FIG. This shows that the exhaust gas flow velocity distribution and the ammonia distribution in the exhaust gas channel cross section are uniform and optimal. Therefore, NOx and NH ₃ can be efficiently reacted without excess or deficiency in the denitration catalyst, and as a result, the residual NH ₃ concentration distribution at the denitration catalyst outlet is reduced, and so on, and this is a denitration downstream device. It is possible to reduce the influence on the element blockage caused by acidic ammonium sulfate in APH. In FIG. 6, the denitration catalyst is omitted.

DESCRIPTION OF SYMBOLS 1 Flue 2 Boiler 3 Chimney 4 Denitration device 5 Electric dust collector 6 Desulfurization device 7 Push-in fan 8 Air residual heat machine 9 Induction fan 10 Boosting fan 11 Heat exchanger 12 Partition wall 13 Reheat gas flow path 14 Superheated gas flow path 15 STC damper 16 Exhaust gas flow channel 16a Inclined portion 16b Vertical ascending portion 16c Horizontal portion 16d Vertical descending portion 17 Hopper 18 Rectifying member 19 Frame body 20 Metal mesh 21 Dust collecting channel 22 Dust collecting device 23 Ammonia injecting device 24 Ammonia injecting nozzle 25 Ammonia Injection block 26 Ammonia supply pipe 27 Branch pipe 28 Denitration catalyst

Claims (5)

A denitration device that is provided in a flue that guides exhaust gas discharged from a boiler and removes nitrogen oxides in the exhaust gas,
An exhaust gas flow path that constitutes a part of the flue and in which the exhaust gas flows in the denitration device;
An ammonia injection device having a plurality of ammonia injection nozzles dispersedly disposed in the cross section of the exhaust gas flow path;
A denitration catalyst disposed on the downstream side of the ammonia injection device and for promoting the reaction between nitrogen oxides in the exhaust gas and ammonia injected from the ammonia injection nozzle;
A rectifying member that rectifies the flow of the exhaust gas in the exhaust gas flow path, and is uniformly distributed in a cross section of the exhaust gas flow path different from the cross section of the exhaust gas flow path, and is included in the exhaust gas A rectifying member including a large number of exhaust gas circulation sections that enable the circulation of
A denitration apparatus comprising: a collection opening disposed downstream of the flow straightening member and connected to a dust collecting flow path for collecting massive ash that has passed through the flow straightening member.   The denitration apparatus according to claim 1, wherein the rectifying member is provided with a wear-resistant coating.   3. The denitration apparatus according to claim 1, wherein a net member having a mesh smaller than that of the massive ash is disposed downstream of the collection opening.   The denitration device according to any one of claims 1 to 3, wherein the ammonia injection device is disposed downstream of the rectifying member.   The exhaust gas flow path includes an inclined portion extending obliquely upward from the outlet of the boiler, a vertical ascending portion extending vertically upward from the end of the inclined portion, a horizontal portion extending horizontally from the end of the vertical ascending portion, The ammonia injecting device is attached to the horizontal portion, the denitration catalyst is attached to the vertical descending portion, the rectifying member and the dust collecting flow path. The denitration device according to claim 1, wherein the denitration device is attached to the inclined portion.

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