JPS60207803A - Boiler device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a boiler device equipped with a denitrification device, and the present invention relates to a boiler device equipped with a denitrification device. This invention relates to a boiler device that removes .

[Background of the invention]

In recent years, as the demand for power generation has increased, boilers that use fossil fuels as their main fuel have become larger, and the influence of power generation boilers on air pollution is also increasing.

Emission regulations for NOx, which accounts for a large proportion of the pollutants that increase air pollution, are becoming stricter year by year.

On the other hand, as boilers become larger, boiler operations such as starting, stopping, and partial load operation are repeated on a daily basis in order to frequently change load according to power generation demand in order to reduce power generation costs. .

As a feature of recent electricity demand, with the growth of nuclear power generation, the difference between maximum and minimum loads has also increased, and there is a tendency for boilers for thermal power generation to shift their operating range from base load to load adjustment. To achieve this, thermal power generation boilers are operated at variable pressure by changing the pressure according to the load, so-called variable pressure boilers that operate in a supercritical pressure region at full load and in a subcritical pressure region at partial load. This is because the power generation efficiency can be improved by several orders of magnitude.

However, although it is convenient for the boiler to frequently start, stop, and change the load on a daily basis,
This is not preferred in the case of a denitrification device.

The reason is that the denitrification medium in the denitrification equipment usually shows high activity at temperatures above 300°C, and the denitrification equipment is generally installed between the boiler's economizer and the air preheater, and the reaction takes place at a temperature of around 350°C. However, due to fluctuations in the boiler load before and after the boiler, the exhaust gas temperature at the exit of the economizer is around 3500C during full load operation, while it is around 350°C during 1/2 load operation, and 1/4
This is because during load operation, the temperature decreases at about 270'C and the denitrification performance deteriorates.

In addition, if the exhaust gas temperature drops too much, NHs in the exhaust gas
reacts to form acidic ammonium sulfate (NH4I S 04 ), ammonium sulfate ((NH4)2 SO4), ammonium sulfite C (NH42S
Oa ) j, etc. are produced, and these adhere to the catalyst surface and reduce the denitrification performance.

Figure 1 is a schematic system diagram of a conventional boiler. superheater, reheater and economizer, 6 is inlet flue, 7f'
i, outlet flue, 8, denitrification device, 9, bottom of furnace 1, 10
is an exhaust gas recirculation duct), 11 is an exhaust gas recirculation fan, 1
2 is a water supply pump, 13 is a water supply heater, 14 is a water supply pipe, 1
5f'i ammonia injection pipe.

In such a structure, exhaust gas generated in the furnace I of the boiler flows to the convection heat transfer section 2, and then to the superheater 3, reheater 4, and energy saver 5.

Ammonia injection pipe work 5 is installed between the superheater 3 and the economizer 5.
is arranged, and while the ammonia and exhaust gas from the ammonia injection pipe 15 pass between the tube groups of the economizer 5, they are uniformly mixed by the tube group itself or the Karman vortex generated on the downstream side of the tube group. The denitrification reaction occurs through the inlet flue 6 to the denitrification device 8, where a denitrification reaction occurs due to the action of the catalyst 1, and after the denitrification reaction is rendered harmless, the heat is recovered through the outlet flue 71 by an air preheater (not shown). Released into the atmosphere.

On the other hand, in this type of power generation boiler, it is necessary to maintain the steam temperature at the outlet of the superheater 3 and reheater 4 constant over the widest possible load range in order to maintain the efficiency of the power generation plant. For this reason, exhaust gas recirculation is performed to suppress the amount of heat absorbed in the furnace 4 and to increase the amount of heat absorption in the convection heat transfer section 2.

That is, when entering low load operation, the exhaust gas recirculation duct from the inlet flue 6 to the bottom 9 of the furnace 4)10. Exhaust gas recirculation fan 1
1, when a part of the exhaust gas is introduced into the furnace 1, the amount of heat absorbed in the furnace 1 of the boiler is reduced, and the temperature of the exhaust gas flowing in the convection heat transfer section 2 is increased, which increases the temperature of the exhaust gas flowing through the convection heat transfer section 2.
Therefore, this is because the amount of heat absorbed by the superheater 3 and reheater 4 is increased to keep the steam temperature constant.

On the other hand, the water supplied to the boiler is supplied to the energy saver 5 and the furnace 1 via a water supply pump 12, a water supply heater 13, and a water supply pipe 14.

The above is an explanation of the general flow state of boiler exhaust gas, water supply, etc. However, as mentioned above, boiler systems that start, stop, and change the load on a daily basis have the following drawbacks.

That is, since the ammonia injection pipe 15 is arranged at the inlet of the economizer 5 to inject ammonia, a part of the ammonia passes through the exhaust gas recirculation duct 10 to the furnace 1 together with the circulating exhaust gas, and is recycled in the furnace 1. Some ammonia is decomposed into nitrogen and water, but some is oxidized to form nitrogen oxides (
NOx) and are consumed.

However, if the amount of furnace feed fleas supplied to the furnace 1 is constant, even if the amount of circulating 411 gas is changed, only ammonia will be circulated even though the amount of exhaust gas from the inlet flue 6 to the denitrification device 8 is constant. Since the ammonia flows into the furnace 1 together with the exhaust gas and is consumed, it is necessary to change the amount of ammonia injected from the ammonia injection pipe 15 as the number of recirculated exhaust gas bombs increases or decreases, which poses a control problem.

In addition, as mentioned above, recirculating exhaust gas is carried out for the purpose of controlling the temperature of the air, and in order to avoid insufficient ammonia injection even when the amount of recycled exhaust gas is at its maximum, ammonia is always injected assuming the maximum amount of circulating exhaust gas. Although it is possible to completely control the amount of ammonia, there is a drawback that excess ammonia must be injected in any case.

[Purpose of the invention]

The present invention aims to eliminate all such conventional drawbacks,
The purpose of this is to obtain a boiler device that consumes less ammonia and has excellent heat recovery efficiency even in a boiler device that returns start, stop, and partial load operation f: hTh. [Summary of the Invention] In order to achieve the above-mentioned objective f, the present invention provides an exhaust gas recirculation duct from upstream of the ammonia injection pipe to the bottom of the furnace, and prevents water condensation and perforation in the exhaust gas recirculation duct. A heat exchanger was installed to exchange heat between the heated medium such as air and the exhaust gas.

[Embodiments of the invention]

Examples of the present invention will be explained below using drawings.

FIGS. 2 and 3 are schematic system diagrams of a boiler apparatus according to a practical example of the present invention.

In FIG. 2, numerals 1 to 15 indicate the same parts as the conventional ones, and 16 is a heat exchanger installed in the middle of the exhaust gas recirculation duct 10. The heat exchanger 16 in FIG. It is also an auxiliary economizer in which the circulating gas exchanges heat. In this structure, the difference from the conventional boiler device shown in FIG. The point is that all the exhaust gas is exhausted and a sub economizer 16 is disposed in this exhaust gas recirculation duct 10.

Therefore, since the recirculated exhaust gas is diverted into the exhaust gas recirculation duct 10 from the upstream side of the ammonia injection pipe 15, even when recirculation gas is being supplied, the exhaust gas recirculation duct 10
Since ammonia does not flow into the tank, the amount of ammonia consumed decreases accordingly.

゛Also, the water supplied from the water supply pump 12 is supplied to a water supply heater 13,
The water flows through the sub economizer 16 and the water supply pipe 14 to the economizer 5,
This auxiliary economizer 16 lowers the temperature of the recirculated exhaust gas in order to recover the exhaust heat of the recirculated exhaust gas in the exhaust gas recirculation duct lo. By increasing the temperature of the exhaust gas in the flue 6, the denitrification performance of the denitrification device 8 can be improved, and the heat recovery efficiency of the auxiliary economizer 16 can be increased.

FIG. 3 is a schematic system diagram of a boiler device showing another embodiment.

In FIG. 3, numerals 1 to 16 are the same as those in FIG. 2, 17 and 18 are inlet and outlet pipes for dilution air, 19 is an ammonia supply pipe, and 20 is a mixer.

In this structure, the difference from the one in Figure 2 is that the second
In the one shown, the heat exchanger 16 was used as a sub-economy device, whereas the 8r! In the one shown in FIG. 3, this heat exchanger 16 is used as a temperature riser for air for diluting ammonia.

The flow of water supply is the same as that in Figure 1, and the flow of recirculated exhaust gas in the exhaust gas recirculation duct 10 is the same as that in Figure 2, so explanations will be omitted. The tube 17 is heated by the temperature riser 16, and the outlet tube 18
It is mixed with ammonia from the ammonia supply pipe 19 in the mixer 20 and injected into the exhaust gas from the ammonia injection pipe 15.

In other words, the ammonia gas from the ammonia injection pipe 15 is used to dilute the ammonia gas to a concentration of about 5 cm or less in terms of safety (lower explosive limit of 15.6 cm) and diffusion into the exhaust gas. It is used diluted with
In the present invention, this dilution air can be obtained by recovering heat from the recirculated exhaust gas using the temperature riser 16, and there is no need to take the trouble to lower the temperature of combustion air that has been heated to a high temperature for dilution air. , heat recovery efficiency is also excellent.

〔Effect of the invention〕

In the present invention, an exhaust gas recirculation duct is provided from upstream of the ammonia injection pipe to the bottom of the furnace, and a heat exchanger for heating the medium to be heated is placed in this exhaust gas recirculation duct, so that startup, shutdown, and partial load operation are repeated. Even in a boiler device, the amount of ammonia consumed is reduced, and a boiler device with excellent heat recovery efficiency can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic system diagram of a conventional boiler system, and FIGS. 2 and 3 are schematic system diagrams of a boiler system 5' according to an embodiment of the present invention. 1...Boiler furnace, 2...Convection heat transfer section, 5...Coal economizer, 6...Inlet duct,
8...Denitrification device, 9...Bottom, 10.
... Exhaust gas recirculation duct, 15 ... Ammonia injection pipe, 16 ... Heat exchanger. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] An ammonia injection pipe and an economizer are arranged in the convection heat transfer section of the boiler, and an exhaust gas recirculation duct recirculates the exhaust gas from the economizer outlet to the bottom of the boiler furnace, and an exhaust gas recirculation duct recirculates the exhaust gas from the economizer outlet to the denitration equipment. In a device that denitrates nitrogen oxides in the exhaust gas, an exhaust gas recirculation duct is provided from upstream of the ammonia injection pipe to the bottom of the furnace, and the medium to be heated is heated in the exhaust gas recirculation duct. A boiler device characterized by the placement of a heat exchanger.