WO2024053250A1

WO2024053250A1 - Boiler system

Info

Publication number: WO2024053250A1
Application number: PCT/JP2023/026068
Authority: WO
Inventors: 聡吉本; 伸章林本; 将貴菅井; 裕人田中
Original assignee: 株式会社日本サーモエナー
Priority date: 2022-09-09
Filing date: 2023-07-14
Publication date: 2024-03-14

Abstract

A boiler system 100 includes: a boiler 10 that combusts fuel gas GF to heat supply water W1; an exhaust line 16 that exhausts exhaust gas GE from the boiler; a circulation line 20 that branches from the exhaust line, has connected thereto an oxygen supply line 30 and an air supply line 26, and supplies air or oxygen gas together with the exhaust gas GE to the boiler as combustion-supporting gas GS. The oxygen supply line 30 includes a main line 30A provided with an ON/OFF valve 32, and a sub line 30B provided with an adjustable opening value 34, and is configured to be capable of adjusting an oxygen concentration in a mixed gas of the oxygen gas and the exhaust gas and supplying the mixed gas to the boiler.

Description

boiler system

The present invention relates to a boiler system, and particularly to a boiler system that can increase the CO ₂ concentration in exhaust gas discharged from a small boiler.

In recent years, there has been a demand for a significant reduction in CO ₂ (carbon dioxide) gas emissions, which are considered to be a cause of global warming. To this end, various systems have been developed for separating and recovering _CO2 in exhaust gas exhausted from combustion devices such as boilers by chemical adsorption methods, solid absorption methods, and the like. However, since the CO ₂ concentration in the exhaust gas is usually as low as about 10%, there is a problem that the recovery efficiency of the CO ₂ separation and recovery device is low.

In response, a method has been proposed to increase the _CO2 concentration in exhaust gas by performing oxy-combustion instead of conventional air-combustion in the boiler of a coal-fired power plant. Demonstration tests have also been conducted on carbon dioxide capture and storage (Non-Patent Document 1 and Patent Document 1).

Oxygen combustion is a method of burning fuel by supplying oxygen gas instead of air as an oxidizing agent or combustion-supporting gas. In the case of oxyfuel combustion, the exhaust gas contains almost no nitrogen component, so the main component of the exhaust gas (for example, 90% or more in the case of coal combustion) can be CO ₂ gas. Therefore, if oxyfuel combustion is used, it becomes easier to separate and recover CO ₂ by cooling the exhaust gas.

However, if oxygen combustion is performed using highly concentrated oxygen gas, the flame temperature will become too high, which may damage the burner or boiler. For this reason, in the oxyfuel combustion boiler equipment described in Non-Patent Document 1 and Patent Document 1, a part of the exhaust gas is circulated and the produced oxygen is mixed with recirculated gas (mainly CO ₂ gas) to reduce the oxygen concentration. The combustion supporting gas is supplied to the boiler.

In addition, in the above-mentioned coal-fired power plant, in order to perform oxy-combustion, an oxygen production device is installed near the boiler to produce high-purity oxygen from the taken in air using a cryogenic separation method or the like. However, if electric power is required to produce oxygen, it is conceivable to take in atmospheric air and perform air combustion as in the past until the start of power generation.

Patent Document 2 discloses a boiler plant for coal-fired power generation that can switch between oxygen combustion and air combustion. In this boiler plant, air combustion can be performed by supplying atmospheric air instead of oxygen gas and circulating exhaust gas when the boiler is started before shifting to oxyfuel combustion. After it became possible to produce oxygen gas using the electricity obtained by air combustion, the air supply system was closed and oxygen gas and circulating exhaust gas were supplied to the boiler, which led to the oxy-combustion of coal. Can be easily migrated.

Further, Patent Document 2 describes a technique for controlling the oxygen concentration in combustion-supporting gas by adjusting the flow rate of circulating exhaust gas, and controlling the ratio of the amount of oxygen to the amount of fuel to a desired setting. The oxygen concentration can be calculated from each gas flow rate command value as a ratio of the oxygen flow rate to the total gas flow rate. Furthermore, by setting the feed water temperature based on the calculated oxygen concentration, it is also possible to control the temperature of water or steam flowing through the heat exchanger within an allowable range for safe operation.

By performing oxygen combustion in this manner to increase the CO ₂ concentration in the exhaust gas and then recovering CO ₂ , it is possible to recover and store CO ₂ more efficiently. Patent Documents 3 and 4 describe specific exhaust gas CO ₂ separation/recovery devices. Furthermore, Patent Document 5 describes a technique for adjusting the CO ₂ concentration in exhaust gas in a relatively small boiler. However, this exhaust gas is used to neutralize the boiler effluent, and the _CO2 concentration is simply adjusted by adjusting the amount of air mixed before being introduced into the boiler effluent. .

Patent No. 6471485 Patent No. 5130145 Patent No. 5351816 Patent No. 3025566 Japanese Patent Application Publication No. 11-244654

As mentioned above, in large-scale equipment such as coal-fired power generation equipment, by performing oxy-combustion using oxygen gas produced from the atmosphere and recirculated exhaust gas, the _CO2 concentration in the exhaust gas is significantly increased, and even more Attempts have been made to efficiently capture and store _CO2 . In such a system, since nitrogen is removed from the combustion-supporting gas in advance, there is also the advantage that the generation of nitrogen oxides (NO _x ) during boiler combustion can be suppressed.

However, rather than large equipment such as power plants, small boilers such as small once-through boilers and hot water boilers require larger changes in output during use, and the combustion control speed must be controlled at an order of magnitude faster than in large equipment. must be done. For this reason, even if exhaust gas CO ₂ concentration can be increased by simply adopting the same oxyfuel combustion boiler configuration as in conventional large-scale equipment, there is a risk that malfunctions such as misfires will occur in small-sized boiler equipment.

The present invention has been made to solve the above problems, and even when using a small boiler that requires relatively high response in combustion control, it is possible to achieve oxy-fuel combustion while achieving stable combustion. The purpose of the present invention is to provide a boiler system that can improve the CO ₂ concentration in exhaust gas.

A boiler system according to an embodiment of the present invention includes a boiler that heats feed water by burning fuel gas, an exhaust line that exhausts exhaust gas from the boiler, and a circulating gas line that branches from the exhaust line, a circulating gas line to which a supply line and an atmospheric supply line are connected and capable of supplying the exhaust gas to the boiler as a combustion supporting gas together with at least one of atmospheric air and oxygen gas; A damper for controlling suction is provided, and the oxygen supply line includes a main line provided with an on/off valve and a subline provided with a variable opening valve, and the oxygen supply line includes a main line provided with an on/off valve and a subline provided with a variable opening valve. Adjusting the oxygen concentration in the mixed gas of the oxygen gas from the oxygen supply line and the exhaust gas by closing the damper and controlling the opening/closing of the on/off valve and the opening degree of the variable opening valve of the oxygen supply line. It is configured such that it can be supplied to the boiler as a combustion-supporting gas.

In one embodiment, the boiler system includes a combustion-supporting gas fan provided near the boiler for delivering the combustion-supporting gas from the circulating gas line to the boiler; The fuel cell further includes an oxygen sensor that measures the oxygen concentration in the combustion-supporting gas sent to the boiler, and the variable opening valve is configured to be feedback-controlled based on the output of the oxygen sensor.

In one embodiment, the outlet of the combustion-supporting gas fan is connected to a burner wind box provided in the boiler, and the oxygen sensor measures the oxygen concentration of the gas inside the burner wind box. Based on the output of the oxygen sensor, the variable opening valve is controlled so that the oxygen concentration of the gas inside the burner wind box is maintained at 20 to 22%.

In one embodiment, the main line of the oxygen supply line is configured by a plurality of lines connected in parallel, each of which is provided with the on/off valve, and by controlling each on/off valve of the plurality of lines, the main line is It is configured so that oxygen gas can be supplied from the line at multiple flow rates.

In one embodiment, a manual valve is provided on at least one of the primary side and the secondary side of the variable opening valve provided in the subline of the oxygen supply line, and a manual valve is provided on at least one of the primary side and secondary side of the variable opening valve provided in the subline of the oxygen supply line, and ~90% of oxygen can be supplied through the main line, and 0~50% of the theoretical combustion oxygen amount required for combustion can be supplied through the subline. .

In one embodiment, the boiler system further includes an economizer that preheats water supplied to the boiler using the heat of exhaust gas from the boiler, and a gas cooler that cools the exhaust gas downstream of the economizer, and the exhaust line includes: The gas cooler is provided to exhaust the exhaust gas cooled by the gas cooler, and the gas cooler is configured to be able to cool the outlet temperature of the exhaust gas to 30°C to 50°C.

In one embodiment, the on-off valve provided in the main line of the oxygen supply line is a solenoid valve, and the variable opening valve provided in the subline of the oxygen supply line is an electric valve.

In one embodiment, the fuel gas is either city gas or LP gas, and the boiler is either a once-through boiler or a hot water boiler.

According to the boiler system according to the embodiment of the present invention, even when using a small boiler such as a once-through boiler or a hot water boiler, it is possible to increase the CO ₂ concentration in exhaust gas while achieving stable combustion.

1 is a schematic diagram showing a boiler system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating one aspect of an oxygen supply line according to an embodiment of the invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

FIG. 1 shows a boiler system 100 according to an embodiment of the invention. The boiler system 100 includes a combustion boiler 10 having a burner 11 that burns fuel gas GF, an economizer 12 through which exhaust gas GE from the boiler 10 passes, and a cooling system for cooling the exhaust gas GE that has passed through the economizer 12. A gas cooler 14 and an exhaust line 16 for exhausting the exhaust gas GE cooled by the gas cooler 14 are provided.

The boiler 10 used in this embodiment is a relatively small once-through boiler or a hot water boiler, for example. Further, the fuel gas GF used is, for example, city gas (or gas containing methane as a main component) or LP gas (or gas containing propane or butane as a main component). The boiler system 100 is configured to generate and provide steam or hot water using a relatively small boiler 10, and is installed in various factories, residences/accommodations, hot bath facilities, etc., depending on the purpose. It is possible to provide hot water or steam at an appropriate temperature.

The boiler 10 can heat the water supply W1 to the boiler 10 by burning the fuel gas GF with the burner 11, and can generate hot water and steam. The economizer 12 can preheat the feed water W1 before supplying it to the boiler 10 using the heat of the exhaust gas GE from the boiler 10, and can save the amount of fuel gas GF consumed.

Furthermore, in the present embodiment, the gas cooler 14 exchanges heat with the supplied cooling water W2 using various heat exchangers (for example, a plate heat exchanger or a tube heat exchanger), thereby reducing exhaust gas GE. is configured to cool the The gas cooler 14 is configured to be able to cool the exhaust gas until the outlet temperature T1 reaches, for example, about 30 to 50°C, particularly about 40°C. Thereby, steam contained in the exhaust gas can be converted into drain in the gas cooler 14, and dry exhaust gas can be obtained.

Blow water from the boiler 10, drain from the economizer 12, and drain from the gas cooler 14 are sent to the neutralization device 18. The neutralization device 18 neutralizes wastewater using various methods, adjusts the pH value to meet industrial wastewater standards, and discharges the wastewater to the outside.

The exhaust line 16 is provided to discharge the cooled exhaust gas GE from the flue 16A into the atmosphere or to transfer it to the CO ₂ recovery facility via the CO ₂ recovery line 16B. As will be described later, in the boiler system 100, the CO ₂ concentration in the exhaust gas can be increased by performing oxygen combustion, so it is possible to efficiently recover CO ₂ from the exhaust gas sent through the CO ₂ recovery line 16B. It is. Although not shown, the exhaust line 16 may be provided with any exhaust gas treatment device such as a bag filter, if necessary.

In the boiler system 100 of this embodiment, a circulating gas line 20 branching from the exhaust line 16 is connected to the exhaust line 16. The circulating gas line 20 is configured to be able to circulate the exhaust gas GE cooled by the gas cooler 14 to the boiler 10 using a forced fan (combustion-supporting gas fan) 22 provided near the boiler. There is. The circulating gas line 20 is provided with a damper 24 for drawing in circulating gas driven by a motor M, and by adjusting the opening degree of the damper 24 for drawing in circulating gas, exhaust gas GE is supplied to the boiler 10 at an arbitrary flow rate. be able to.

Further, an atmosphere supply line 26 and an oxygen supply line 30 are connected to the circulating gas line 20. Thereby, atmospheric air AIR, oxygen gas O ₂ and/or exhaust gas GE drawn from the exhaust line 16 can be supplied to the boiler 10 as the combustion-supporting gas GS. In this configuration, the boiler 10 is capable of performing both air combustion and oxygen combustion.

Note that in the illustrated embodiment, the atmospheric supply line 26 is connected to the upstream side of the oxygen supply line 30, but on the contrary, the oxygen supply line 30 may be connected to the upstream side. In addition, the atmospheric supply line 26 and the oxygen supply line 30 do not necessarily need to be connected to different places, but are connected using a common line at the same connection point of the circulating gas line 20, and are branched on the upstream side of the common line. may be arranged in parallel.

The atmospheric supply line 26 and the oxygen supply line 30 may be connected in any manner as long as they communicate with the circulating gas line 20 between the circulating gas drawing damper 24 and the boiler 10. Further, in this embodiment, the forced fan 22 as a combustion-supporting gas fan provided near the boiler is used to form the gas flow in the circulating gas line 20 toward the boiler, but instead of this, Alternatively, in addition to this, another blower (such as a forced fan or an induced fan) may be provided in the circulating gas line 20. Further, an arbitrary blower may be provided in the exhaust line 16 as well, if necessary.

Hereinafter, a more detailed configuration of the circulating gas line 20 will be described.

The atmosphere supply line 26 connected to the circulating gas line 20 is provided with an atmosphere suction damper 28 driven by a motor M. By adjusting the opening degree of this atmospheric suction damper 28, atmospheric air (air) AIR can be supplied to the boiler 10 at an arbitrary flow rate.

In this way, air whose flow rate can be controlled can be supplied to the boiler 10 as the combustion-supporting gas GS via the circulating gas line 20, so that oxy-fuel combustion can be performed stably, such as when starting up the boiler. When this is difficult, boiler operation using air combustion can be performed. During the period when air combustion is being performed, air is supplied to the boiler 10 at a controlled flow rate via the atmospheric suction damper 28 whose opening degree is adjusted, while the circulating gas suction damper 24 and the oxygen Supply line 30 remains closed.

When city gas 13A is used as the fuel gas, in air combustion using air from the atmospheric supply line 26, the combustion exhaust gas contains about 10 vol% _CO2 , and most of the remainder is composed of nitrogen gas and water vapor. . For this reason, when trying to separate and recover CO ₂ from exhaust gas in air combustion, there is a problem that efficiency is poor and the equipment on the recovery device side becomes excessively large, so that no cost advantage can be expected. Therefore, after the boiler is started and combustion becomes stable and stable circulating supply of exhaust gas GE becomes possible, it is preferable to switch from air combustion to oxyfuel combustion to improve the CO ₂ concentration in the exhaust gas.

The oxygen supply line 30 used for oxygen combustion is composed of a main line 30A and a subline 30B connected in parallel. In the illustrated embodiment, the main line 30A and the subline 30B are connected to the same oxygen supply source, but they may be connected to different oxygen supply sources. As the oxygen supply source, for example, oxygen gas generated from air by pressure swing adsorption (PSA) can be used.

The main line 30A of the oxygen supply line 30 is provided with an on/off valve 32, while the subline 30B is provided with a variable opening valve (typically a proportional valve) 34. In this embodiment, the on-off valve 32 is constituted by a solenoid valve (solenoid valve S), and the variable opening valve 34 is constituted by an electric valve driven by motor M. The on-off valve 32 may be configured by, for example, an air-operated valve (AOV).

In this embodiment, the main line 30A can supply 80 to 90% of the theoretical combustion oxygen amount required for combustion that matches the composition and flow rate of the fuel gas GF, and the subline 30B can supply oxygen that is 80% to 90% of the theoretical combustion The flow rate of oxygen gas in each line is controlled so that 0 to 50% of the amount of oxygen can be supplied. The oxygen gas supplied from the oxygen supply line 30 is mixed with the exhaust gas GE introduced by opening the circulating gas intake damper 24, and is supplied to the boiler 10 as a combustion-supporting gas GS with an adjusted oxygen concentration.

Further, in this embodiment, the sub-line 30B is composed of one line provided with a single variable-opening valve 34, whereas the main line 30A is composed of a single line provided with an on-off valve 32, respectively. Consists of multiple parallel lines.

FIG. 2 shows an example in which the main line 30A is composed of three lines. As shown in FIG. 2, a main line 30A is composed of

lines

301, 302, and 303 connected in parallel, and each

line

301, 302, and 303 is connected to an on-off valve (here, a solenoid valve) 321, 322, and 323. are provided for each. The rated flow rate (or CV value: the flow rate coefficient of the fluid passing through the open valve when the inlet pressure and outlet pressure values are the specified values) of each on-off

valve

321, 322, and 323 when open is the same. It may be different, or it may be different.

In this configuration, by controlling the opening and closing of the on-off

valves

321, 322, and 323, it is possible to immediately control the oxygen flow rate in multiple stages that match the combustion pattern of the boiler. For example, in the case of 4-position control that controls the combustion pattern at 0%-20%-50%-100%, 0% control is performed with all on-off valves closed, and 20% control is performed with only the on-off valve 321 open. 50% control can be performed with the on-off

valves

321 and 322 open, and 100% control can be performed with all the on-off

valves

321, 322, and 323 open. In each combustion pattern, the total amount of oxygen supplied via each line is adjusted according to the fluctuation of the fuel gas flow rate so that the amount of oxygen is 80 to 90% of the theoretical combustion oxygen amount as described above. ing.

In addition, although the embodiment in which three lines with on/off valves are used to perform four-position control has been described above, depending on the combustion pattern, two or four or more lines with on/off valves may be used. Needless to say. In addition, if the flow rate control in the main line 30A is sufficient with two-stage control from 0% to 100%, the main line 30A is also configured with one line, as in the subline 30B, as shown in Fig. 1. may have been done.

In the main line 30A, each electromagnetic valve constituting the on-off valve 32 has sufficiently high responsiveness compared to a motor-driven electric valve (opening variable valve 34). Therefore, opening control of each electromagnetic valve can be performed at high speed to match the combustion pattern, and thereby oxygen gas can be supplied at a flow rate that can prevent occurrence of combustion defects. Furthermore, since the on/off valves 32 are provided in a plurality of lines and the flow rate is controlled by controlling the opening and closing of the valves, instantaneous switching between a large flow rate and a small flow rate can be realized relatively easily.

In particular, the output adjustment of small boilers is often switched in a very short time (for example, 2 to 3 seconds, often within 5 seconds) in accordance with the demands of the heat demand side, and the output is high for a narrow combustion chamber. Since combustion is performed using a burner, the amount of oxygen required for fuel combustion may change in a short period of time each time the output is switched. For this reason, if there is even a slight delay in the supply of the required amount of oxygen, it will instantly lead to incomplete combustion, oscillating combustion, and even misfire. In contrast, although the flow rate is controlled in stages, oxygen is supplied from the main line 30A, which is highly responsive and can control the flow rate from small to large. It is possible to reliably supply a limited amount of oxygen. Therefore, the boiler system 100 can prevent misfires and poor combustion even when used as a small boiler with severe output fluctuations.

Furthermore, in the subline 30B of the oxygen supply line 30, a manual valve 38 may be provided on at least one of the primary side and the secondary side of the variable opening valve 34. FIG. 1 shows an example in which a manual valve 38 is provided on the primary side of the variable opening valve 34, and FIG. 2 shows an example in which a manual valve 38 is provided on the secondary side of the variable opening valve 34. An example is shown. Manual valve 38 arranged in this manner can be used to adjust the maximum control flow rate in subline 30B. By using the manual valve 38 to previously set the amount of oxygen to be introduced with respect to the set opening degree of the damper 24 for drawing in the circulating gas, it is possible to adjust the ratio of the circulating gas amount.

In order to finely adjust the amount of oxygen, a subline 30B having a variable opening valve 34 is used. As a result, the oxygen concentration in the combustion-supporting gas GS formed by the mixture of oxygen gas O ₂ from the oxygen supply line 30, exhaust gas from the exhaust line 16, and GE is equivalent to, for example, the oxygen concentration in the atmosphere. The overall flow rate of oxygen gas can be fine-tuned so that it remains stable at a ratio of about 21% (eg, 20-22%).

In addition, in order to reduce the amount of exhaust gas itself, in consideration of oxygen-enriched combustion in which the oxygen concentration is set to 21% or more, the variable opening valve 34 has a CV value (CV value) that can supply up to about half of the required amount of oxygen. or rated flow rate value).

Here, as shown in FIG. 1, the boiler system 100 of this embodiment includes an oxygen sensor 36a for measuring the oxygen concentration of the combustion-supporting gas GS supplied to the burner 11. More specifically, the oxygen sensor 36a is attached to the burner wind box 13 to which the outlet of the forced fan 22 is connected, and is installed to measure the oxygen concentration of the gas inside the burner wind box 13. . As the oxygen sensor 36a, for example, a galvanic cell type sensor is suitably used, but various types of sensors can be used as long as they can measure the oxygen concentration.

Further, an oxygen concentration control circuit 36b is connected to the oxygen sensor 36a. The oxygen concentration control circuit 36b is configured to feedback control the variable opening valve 34 provided in the subline 30B of the oxygen supply line 30 based on the output of the oxygen sensor 36a.

For example, when the set oxygen concentration is 20 to 22%, and the oxygen concentration output by the oxygen sensor 36a is lower than 20%, the variable opening valve 34 is opened with a manipulated variable according to the difference. Increase oxygen concentration. Further, when the oxygen concentration output by the oxygen sensor 36a is higher than 22%, the opening degree of the variable opening valve 34 is closed with a manipulated variable according to the difference to lower the oxygen concentration. In this way, by feedback-controlling the variable opening valve 34 using the oxygen concentration control circuit 36b so that the difference between the set concentration and the measured concentration approaches 0, a desired set oxygen concentration is set for the burner 11. It is possible to continue supplying the combustion-supporting gas GS having the following properties. Note that it goes without saying that the set oxygen concentration may be a constant value (for example, 21%).

In this way, the boiler system 100 can supply the combustion-supporting gas GS, which is a mixture of oxygen gas and exhaust gas (mainly CO ₂ ), to the boiler 10 via the circulating gas line 20. Oxygen combustion can be performed stably. During the period of oxy-combustion, exhaust gas mixed with oxygen gas is supplied to the boiler 10 as the combustion-supporting gas GS, while normally the atmosphere suction damper 28 is closed and the atmosphere supply line 26 is closed. remains closed.

When switching from air combustion to oxygen combustion, the circulating gas suction damper 24 and the on/off valve 32 in the main line 30A are opened in synchronization with the closing operation of the atmospheric suction damper 28. At the same time, an oxygen concentration adjustment operation by adjusting the opening of the variable opening valve 34 in the sub-line 30B is also started. The boiler system 100 closes the damper 28 of the atmospheric supply line 26 and controls the opening/closing of the on/off valve 32 and the opening degree of the variable opening valve 34 of the oxygen supply line 30, thereby removing oxygen gas O ₂ from the oxygen supply line. After adjusting the oxygen concentration in the mixed gas of the exhaust gas GE and the exhaust gas GE, this is configured to be able to be supplied to the boiler 10 as a combustion-supporting gas GS to perform oxy-fuel combustion.

Therefore, in the boiler system 100, it is possible to smoothly transition from air combustion to oxyfuel combustion when the boiler is started, and after switching to oxyfuel combustion, the oxygen supply amount can be quickly switched to match the output change characteristics of the small boiler. By doing so, it is possible to discharge exhaust gas with a high concentration of CO ₂ while preventing the occurrence of combustion defects such as incomplete combustion and misfire.

Next, the configuration of the gas cooler 14 will be explained. As described above, the gas cooler 14 in this embodiment is configured to lower the exhaust gas outlet temperature T1 to, for example, 30° C. to 50° C. to obtain dry exhaust gas. In particular, in the case of a small boiler 10 that uses city gas or LP gas as fuel gas, although water vapor is generated by combustion, the exhaust gas GE does not contain corrosive gases such as sulfur, so it is cooled to near room temperature. However, there will be no major problem. Therefore, it is possible to easily obtain dry exhaust gas with increased CO ₂ concentration by converting the water vapor contained in the exhaust gas into drains through cooling. Since the boiler system 100 performs combustion by mixing dry exhaust gas with combustion-supporting gas in oxy-combustion, it is also possible to avoid adverse effects of moisture in the recirculated gas on burner combustion.

The cooling water W2 used in the gas cooler 14 is typically provided using a cooling water circulation line that includes a cooling system such as a cooling tower that is provided as a separate system from the supply system for the boiler feed water W1. However, it is also possible to introduce a part of the cooling water W2 from the outlet of the gas cooler 14 to the softening device and use it as the boiler feed water W1.

Further, in the gas cooler 14, a large amount of drain is generated during cooling of the exhaust gas. In order to efficiently move and drip this drain to the bottom of the gas cooler 14, it is preferable that the exhaust gas GE flows downward from the top of the gas cooler 14 toward the bottom. On the other hand, it is preferable that the cooling water W2 be allowed to flow upward in order to prevent the formation of air pockets. Further, since the drain absorbs CO ₂ and the like in the exhaust gas and becomes acidic, it is preferable that the gas cooler 14 be constructed using an acid-resistant material. Note that it is preferable that the gas cooler 14 be constructed using a material having an appropriate heat-resistant temperature, taking into consideration the inlet exhaust gas temperature when the economizer 12 is operated by bypass.

The boiler system according to the embodiment of the present invention is suitably used in, for example, a small steam boiler or a water heater to increase the CO ₂ concentration in exhaust gas while continuing stable combustion.

10 Boiler 12 Economizer 14 Gas cooler 16 Exhaust line 18 Neutralization device 20 Circulating gas line 22 Forced fan (combustion-supporting gas fan)
24 Damper for drawing in circulating gas 26 Atmospheric supply line 28 Damper for atmospheric suction 30 Oxygen supply line

30A Main line

30B Sub line 32 On-off valve (electromagnetic valve)
34 Adjustable opening valve (motorized valve)
36a Oxygen sensor 36b Oxygen concentration control circuit 38 Manual valve 100 Boiler system GE Exhaust gas GF Fuel gas GS Combustion supporting gas

Claims

a boiler that heats feed water by burning fuel gas;
an exhaust line for exhausting exhaust gas from the boiler;
A circulating gas line branching from the exhaust line, to which an oxygen supply line and an atmosphere supply line are connected, and which can supply the exhaust gas to the boiler as a combustion-supporting gas together with at least one of atmospheric air and oxygen gas. A boiler system comprising a gas line,
The atmospheric supply line is provided with a damper for controlling atmospheric suction,
The oxygen supply line includes a main line provided with an on-off valve and a subline provided with a variable opening valve,
Mixing of the oxygen gas from the oxygen supply line and the exhaust gas by closing the damper of the atmospheric supply line and controlling the opening/closing of the on/off valve and the opening degree of the variable opening valve of the oxygen supply line. A boiler system configured to adjust the oxygen concentration in the gas and supply it to the boiler as a combustion-supporting gas.
a combustion-supporting gas fan provided near the boiler for sending the combustion-supporting gas from the circulating gas line to the boiler; and a combustion-supporting gas fan that sends the combustion-supporting gas from the combustion-supporting gas fan to the boiler. It further includes an oxygen sensor that measures the oxygen concentration in the gas,
The boiler system according to claim 1, wherein the variable opening valve is configured to be feedback-controlled based on the output of the oxygen sensor.
The outlet of the combustion-supporting gas fan is connected to a burner wind box provided in the boiler, and the oxygen sensor is configured to measure the oxygen concentration of the gas inside the burner wind box. 3. The variable opening valve is controlled based on the output of the oxygen sensor so that the oxygen concentration of the gas inside the burner wind box is maintained at 20 to 22%. boiler system.
The main line of the oxygen supply line is composed of a plurality of lines connected in parallel, each of which is provided with the on/off valve, and by controlling each on/off valve of the plurality of lines, a plurality of lines can be connected from the main line to the main line. 4. The boiler system according to claim 1, wherein the boiler system is configured to be able to supply oxygen gas at a flow rate of stages.
A manual valve is provided on at least one of the primary side and the secondary side of the variable opening valve provided in the subline of the oxygen supply line, and the oxygen supply line contains 80 to 90% of the theoretical combustion oxygen amount necessary for combustion. According to claim 1, the fuel cell is configured to be able to supply oxygen through the main line, and to supply oxygen in an amount of 0 to 50% of the theoretical combustion oxygen amount necessary for combustion through the sub-line. 3. The boiler system according to any one of 3.
The system further includes an economizer that preheats water supplied to the boiler using the heat of exhaust gas from the boiler, and a gas cooler that cools the exhaust gas downstream of the economizer, and the exhaust line exhausts the exhaust gas cooled by the gas cooler. It is set up so that
The boiler system according to any one of claims 1 to 3, wherein the gas cooler is configured to be able to cool the outlet temperature of the exhaust gas to 30°C to 50°C.
Any one of claims 1 to 3, wherein the on-off valve provided in the main line of the oxygen supply line is a solenoid valve, and the variable opening valve provided in the subline of the oxygen supply line is an electric valve. Boiler system described in Crab.
The boiler system according to any one of claims 1 to 3, wherein the fuel gas is either city gas or LP gas, and the boiler is either a once-through boiler or a hot water boiler.