JP5187730B2 - Boiler and power generation system - Google Patents

Description

  The present invention relates to a boiler and a power generation system, and is particularly useful when applied to operating a boiler that burns liquid fuel.

  Some thermal power plants, for example, generate electricity using a boiler that burns liquid fuel. FIG. 3 is a schematic configuration diagram of a liquid fuel-fired boiler according to the prior art. As shown in the figure, the boiler includes a furnace 1, and a plurality of burners 2 are attached to the furnace 1. Each burner 2 is supplied with liquid fuel such as heavy oil from the liquid fuel supply means. The burner 2 burns liquid fuel in the furnace 1, and exhaust gas generated when the liquid fuel is burned is discharged to the outside of the furnace 1. The furnace 1 is provided with a water pipe and a steam pipe 7. Water and steam in the pipe collect heat from the combustion gas and drive a steam turbine to generate electricity.

  In general, nitrogen oxides discharged from the furnace 1 are often generated by a thermal NOx generation mechanism (also called a Zeldovich NO mechanism) that has a very high temperature dependency of the generation rate. Are known.

  In such a boiler, various measures are taken to reduce nitrogen oxide (NOx) contained in the exhaust gas as much as possible in order to cope with environmental influences and various regulations.

  For example, a part of the exhaust gas is mixed with the combustion air via the exhaust gas circulation blower 3 to lower the oxygen concentration of the air supplied to the burner 2 so that the flame formed by the burner 2 is locally heated. An operation method (exhaust gas recirculation) that prevents this from occurring is put into practical use.

  In addition to exhaust gas recirculation or simultaneously with exhaust gas recirculation, a two-stage combustion method is also employed in many boilers (see, for example, Patent Document 1). In the two-stage combustion method, first, fuel is burned in an atmosphere having a low oxygen concentration and a strong reducibility (hereinafter referred to as “low oxygen concentration atmosphere”), and then additional air is supplied to remain unburned. It burns fuel. For example, in the burner zone 4 which is the flame periphery of the burner 2 in the furnace 1, a small amount of air is supplied to the burner 2 so that a low oxygen concentration atmosphere is obtained. On the other hand, above the burner zone 4, the two-stage combustion air is injected from the two-stage combustion air injection port 5. As a result, the burner zone 4 is highly reducible, so that the exhausted NOx can be reduced. Above the burner zone 4, the unburned fuel can be reduced by the two-stage combustion air.

  However, if the amount of air supplied to the burner 2 is too small, the fuel combustion rate in the burner zone 4 decreases, and the amount of dust (unburned fuel and ash) increases. In this way, there has been a problem in that waste of fuel is generated when reducing NOx emission.

Japanese Patent Laid-Open No. 5-203108

  In view of such circumstances, an object of the present invention is to provide a boiler and a power generation system that can reduce exhaust NOx without increasing the amount of dust.

In order to achieve the above object, a first aspect of the present invention includes a furnace for burning liquid fuel, a fuel supply means for supplying liquid fuel to the furnace, and a high-temperature gas that is equal to or higher than a temperature at which the liquid fuel evaporates. High temperature gas supply means for supplying, the liquid fuel supply means is connected to the furnace through a pre-evaporator that makes liquid fuel into droplets by spraying, the hot gas supply means from the furnace is an exhaust gas at a high temperature gas discharged to supply to the pre-vaporizer, said by spraying the liquid fuel from the liquid fuel supply means to the exhaust gas supplied to the pre-vaporizer The liquid fuel droplets are evaporated and supplied to the burner attached to the furnace, and a mixture of combustion air and the exhaust gas is supplied to the burner separately from the evaporated liquid fuel. Shi Configuration wherein the furnace is configured to burn the liquid fuel and the mixture injected from the burner is mixed with the burner zone, so that by supplying air to the upper of the burner zone to improve the combustion rate of the liquid fuel The liquid fuel is burned in a low oxygen concentration atmosphere in which the amount of air supplied is smaller than the amount of air required for complete combustion of the fuel in the burner zone.

In the first aspect, the liquid fuel supplied from the fuel supply means evaporates with the high-temperature gas before being supplied to the furnace. As a result, since the liquid fuel in an evaporated state is supplied to the furnace, the fuel can be efficiently burned even in a low oxygen concentration atmosphere for suppressing the generation of nitrogen oxides. Moreover, liquid fuel can be evaporated using the high temperature exhaust gas from a furnace. That is, it is not necessary to prepare a special heat source such as a heater, and energy can be efficiently used in the entire boiler. Furthermore, since the unburned fuel that has not been burned by the burner is further burned by supplying air, the combustion rate of the fuel can be improved.

According to a second aspect of the present invention, in the boiler according to the first aspect, an exhaust gas pipe for connecting a middle portion of the furnace and the pre-evaporator is provided .

In the second aspect, the exhaust gas is supplied to the pre-evaporator without being cooled and has a sufficiently high temperature, so that the liquid fuel can be evaporated.

A third aspect of the present invention includes the boiler described in the first or second aspect, and a generator driven by a steam turbine that recovers heat from a high-temperature gas generated in the boiler. It is in the power generation system.

In the third aspect, a power generation system is provided that can reduce the unburned residue of liquid fuel such as dust and the like and reduce the generation of nitrogen oxides.

  According to the present invention, the liquid fuel supplied from the fuel supply means evaporates with the hot gas before being supplied to the furnace. As a result, since the liquid fuel in an evaporated state is supplied to the furnace, the fuel can be efficiently burned even in a low oxygen concentration atmosphere for suppressing the generation of nitrogen oxides.

  Hereinafter, the best mode for carrying out the present invention will be described. The description of the present embodiment is an exemplification, and the present invention is not limited to the following description.

<Embodiment 1>
FIG. 1 is a schematic configuration diagram of a boiler according to the first embodiment. The boiler of this embodiment includes a furnace 1, and a plurality of burners 2 are attached to the furnace 1. Each burner 2 is connected via a pre-evaporator 6 to liquid fuel supply means (not shown) constituted by a fuel tank, a pump and the like.

  Moreover, the boiler of this embodiment performs what is called exhaust gas recirculation and a two-stage combustion method simultaneously. That is, the exhaust gas exhausted from the furnace 1 is supplied to each burner 2 via the exhaust gas circulation blower 3 in order to perform exhaust gas recirculation. As a result, the oxygen concentration of the combustion air supplied to the burner 2 is lowered, so that the liquid fuel is burned in the burner zone 4 under a low oxygen concentration atmosphere. Further, in order to perform the two-stage combustion method, a two-stage combustion air injection port 5 for injecting air into the furnace 1 is provided above each burner 2.

  More specifically, in the furnace 1, the liquid fuel from the liquid fuel supply means is burned by each burner 2, and the unburned residue at this time is further burned by the supply of the two-stage combustion air from the two-stage combustion air injection port 5. The The exhaust gas generated by the combustion of the liquid fuel is discharged outside the furnace 1. A part of the exhaust gas is configured to be supplied to the burner 2 and the pre-evaporator 6 through the exhaust gas circulation blower 3.

  The pre-evaporator 6 is formed such that exhaust gas is supplied from the furnace 1 through the exhaust gas circulation blower 3 to the inside. Further, the pre-evaporator 6 is formed so that the liquid fuel from the liquid fuel supply means can be sprayed into droplets in the exhaust gas supplied to the inside thereof. Since the exhaust gas is a high-temperature gas having a temperature sufficient to evaporate the liquid fuel, the liquid liquid droplets sprayed into the exhaust gas by the pre-evaporator 6 is supplied to the burner 2 in an evaporated state. . Alternatively, even if the liquid fuel in the form of droplets does not completely evaporate, most of the liquid fuel is accelerated and supplied to the burner 2. Since the exhaust gas has a low oxygen concentration, only the liquid fuel evaporates in the pre-evaporator 6 and there is no possibility that a combustion reaction occurs.

  The burner 2 is configured such that combustion air and exhaust gas from the furnace 1 are mixed and supplied, and the combustion air and the exhaust gas are injected into the furnace 1. The burner 2 is also configured to be supplied with an air-fuel mixture of the liquid fuel evaporated by the pre-evaporator 6 and the pre-evaporation exhaust gas, and to inject the air-fuel mixture into the furnace 1. The mixture of combustion air and exhaust gas and the mixture of liquid fuel and exhaust gas evaporated in the pre-evaporator 6 are mixed in the burner zone 4 and burned.

  Here, the general combustion of liquid fuel goes through a process in which the liquid fuel first evaporates and then burns in the gas phase. On the other hand, in the boiler having the above-described configuration, evaporation of the liquid fuel is promoted by the heat of the exhaust gas in the pre-evaporator 6 before the liquid fuel is supplied to the burner 2. That is, since the liquid fuel is evaporated by the pre-evaporator 6, the vaporized liquid fuel is supplied to the burner 2. Therefore, in the burner zone 4, the fuel vaporized in advance burns, so that the combustion reaction proceeds rapidly and there is little unburned residue. As a result, the boiler according to the present embodiment can perform combustion in a low oxygen concentration atmosphere to reduce exhaust NOx, and can efficiently burn by reducing generation of soot and dust.

  Further, since the boiler according to the present embodiment employs a so-called two-stage combustion method, even if the fuel does not burn in the burner zone 4, the remaining fuel is burned by the air injected from the two-stage combustion air injection port 5. Combustion is also promoted. In general, in the two-stage combustion method, the higher the two-stage combustion rate (the ratio of air from the two-stage combustion air injection port 5 to the total amount of air supplied to the furnace 1), the lower the exhaust NOx. However, the temperature of the burner zone 4 is lowered, the progress of the combustion reaction is lowered, and the amount of unburned fuel is increased, so that the amount of dust tends to increase. On the other hand, the boiler having the above-described configuration is operated without increasing soot by burning the fuel previously vaporized in the burner zone 4 even under a high two-stage combustion rate for reducing exhaust NOx. Can do.

  In addition, you may comprise the boiler of this embodiment, and the generator driven by the steam turbine which collect | recovered heat from the furnace 1, and may construct | assemble a power generation system. For example, a steam pipe 7 in which water, which is an example of a heat medium, is circulated is installed in the furnace 1, a steam turbine is operated with steam recovered from the furnace 1, and a generator is driven by the steam turbine. According to this, a power generation system capable of efficiently burning liquid fuel and reducing exhaust NOx is provided.

  Moreover, in the boiler which concerns on this embodiment, although it was a boiler which performs a two-stage combustion method and waste gas recirculation, it is not necessary to necessarily perform these. That is, the boiler of the present invention can be widely applied to boilers using liquid fuel as fuel. Further, although the exhaust gas from the furnace 1 is configured to be supplied to the pre-evaporator 6 as the high temperature gas supply means, the exhaust gas from the furnace 1 is not necessarily used. In short, the pre-evaporator 6 only needs to be supplied with a high-temperature gas having a temperature sufficient to evaporate the liquid fuel.

<Embodiment 2>
In the boiler described in the first embodiment, the exhaust gas is discharged from the furnace 1 and then supplied to the pre-evaporator 6 and the burner 2 via the exhaust gas circulation blower 3. However, the exhaust gas is limited to such a route. Instead, the exhaust gas may be supplied to the pre-evaporator 6 and the burner 2 from any place in the furnace 1.

  FIG. 2 is a schematic configuration diagram of a boiler according to the second embodiment. In addition, the same code | symbol is attached | subjected to the same thing as Embodiment 1, and the overlapping description is abbreviate | omitted.

  The boiler according to the present embodiment is provided with an exhaust gas pipe 8 that connects an intermediate portion of the furnace 1 and the pre-evaporator 6. More specifically, the exhaust gas pipe 8 is connected to the furnace 1 at a position where exhaust gas having a temperature sufficient to evaporate the liquid fuel by the pre-evaporator 6 can be taken. Thus, the exhaust gas is supplied to the pre-evaporator 6 without being cooled and having a sufficiently high temperature, and the liquid fuel can be evaporated.

  This is useful when applied to the following cases. For example, in a power generation system using a boiler, all the heat sources for power generation are usually recovered in the furnace 1, and exhaust gas whose temperature has been lowered to the extent that heat cannot be recovered is discharged from the furnace 1. Further, in a small boiler for industrial use or household use, exhaust gas at a lower temperature is discharged. In such a case, if the exhaust gas is taken in from the furnace 1 via the exhaust gas circulation blower 3, the exhaust gas whose temperature is too low is supplied to the pre-evaporator 6. Therefore, as described above, if exhaust gas having an appropriate gas temperature is taken from the middle part of the furnace 1 and is circulated to the pre-evaporator 6, the liquid fuel can be sufficiently evaporated.

1 is a schematic configuration diagram of a boiler according to a first embodiment. It is a schematic block diagram of the boiler which concerns on Embodiment 2. FIG. It is a schematic block diagram of the boiler which concerns on a prior art.

Explanation of symbols

1 Furnace 2 Burner 3 Exhaust gas circulation blower 4 Burner zone 5 Two-stage combustion air injection port 6 Pre-evaporator 7 Steam pipe 8 Exhaust gas pipe

Claims (3)

A furnace for burning liquid fuel;
Fuel supply means for supplying liquid fuel to the furnace;
Comprising high temperature gas supply means for supplying a high temperature gas that is at or above the temperature at which the liquid fuel evaporates,
The liquid fuel supply means is connected to the furnace via a pre-evaporator that makes liquid fuel into droplets by spraying,
The high temperature gas supply means is configured to supply exhaust gas that is high temperature gas discharged from the furnace to the pre-evaporator,
Together supplied to the burner attached to the furnace to evaporate the droplets of liquid fuel by spraying the liquid fuel from the liquid fuel supply means to the exhaust gas supplied to the pre-vaporizer, evaporation Separately from the liquid fuel, the mixture of combustion air and the exhaust gas is supplied to the burner ,
The furnace is configured to mix and burn the liquid fuel injected from the burner and the air- fuel mixture in a burner zone, and to supply air above the burner zone to improve the combustion rate of the liquid fuel. And
The boiler is characterized in that the liquid fuel is burned in a low oxygen concentration atmosphere in which the amount of air supplied in the burner zone is less than the amount of air required for complete combustion of the fuel. In the boiler according to claim 1,
An exhaust gas pipe for connecting an intermediate portion of the furnace and the pre-evaporator is provided. A boiler according to claim 1 or claim 2;
A power generation system comprising: a generator driven by a steam turbine that recovers heat from a high-temperature gas generated in the boiler.

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