Method for blending hydrogen into a coal-fired boiler and boiler

Abstract

The present application relates to the technical field of coal-fired boiler, and discloses a method for mixing hydrogen into a coal-fired boiler and the boiler, the method comprising the following steps: S1: sending primary air into a flame zone of the boiler, the primary air delivering coal powder into the flame zone of the boiler for combustion; S2: sending secondary air into the flame zone of the boiler and sending burnout air into a burnout zone of the boiler; S3: sending and igniting the burnout air into the middle of the burnout zone of the boiler, wherein the total air volume of the boiler is 1.13-1.30 times the air volume required for complete combustion of the coal powder and complete combustion of the hydrogen, the air volume of the primary air is 10-40% of the total air volume of the boiler, the air volume of the secondary air is 20-75% of the total air volume of the boiler, the air volume of the burnout air is 10-50% of the total air volume of the boiler, and the rest is peripheral air; the method can meet the requirement of mixing hydrogen under the premise of maintaining the staged combustion mode of the coal-fired boiler. Meanwhile, the present application discloses the boiler for realizing the method.

Description

Technical Field

[0001] This invention relates to the field of coal-fired boiler technology, and in particular to a method for co-firing hydrogen in a coal-fired boiler and the boiler itself. Background Technology

[0002] One way to reduce carbon dioxide emissions from coal-fired boilers is by blending them with low-carbon or zero-carbon fuels. Hydrogen, produced from renewable energy sources, is a globally recognized carbon-free fuel. By blending hydrogen in a certain proportion in a coal-fired boiler, hydrogen can replace some coal while maintaining the same total energy output, thus reducing carbon dioxide emissions at the source. However, due to the significant differences in combustion between hydrogen and pulverized coal, directly adding hydrogen to coal for combustion presents various problems.

[0003] Coal-fired boilers are primarily designed based on the combustion characteristics of coal. Significant differences in the characteristics of the input fuel can affect the safe operation of the boiler. Because hydrogen ignites quickly, the burner needs a very high hydrogen outlet velocity to prevent flame backfire or nozzle overheating. The outlet velocity of the hydrogen burner is much higher than the design velocity of the coal-fired boiler burner, easily causing interference between the flow fields of adjacent burners. Furthermore, hydrogen combustion is characterized by high local flame temperature and weak radiation. When boilers designed for coal combustion blend with a large proportion of hydrogen, localized overheating can easily occur, leading to excessive nitrogen oxide emissions and overheating of the furnace heating surfaces. When hydrogen is introduced into a boiler as pure fuel and co-fired with coal, regardless of whether a separate burner is used or it is mixed with pulverized coal, the hydrogen combustion rate is much higher than that of pulverized coal, rapidly consuming surrounding oxygen and making it difficult for the pulverized coal to ignite—a phenomenon known as "air rush"—resulting in poor pulverized coal combustion. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for hydrogen co-firing in a coal-fired boiler while maintaining the staged combustion mode of the coal-fired boiler, and a boiler for implementing the method.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for co-firing hydrogen in a coal-fired boiler, comprising the following steps:

[0006] S1: Primary air is introduced into the flame zone of the boiler, and the primary air transports the pulverized coal to the flame zone of the boiler for combustion.

[0007] S2: Secondary air is supplied to the flame zone of the boiler and burnout air is supplied to the burnout zone of the boiler;

[0008] S3: Hydrogen is introduced into the middle of the combustion zone of the boiler and ignited, wherein the proportion of hydrogen in the combustion is less than or equal to 30%;

[0009] The total air intake of the boiler is 1.13 to 1.30 times the air content required for the complete combustion of pulverized coal and hydrogen. The primary air volume is 10% to 40% of the total air intake of the boiler, the secondary air volume is 20% to 75% of the total air intake of the boiler, the burnout air volume is 10% to 50% of the total air intake of the boiler, and the remainder is perimeter air.

[0010] As a preferred embodiment of the present invention, in S3, the proportion of hydrogen co-firing gradually increases.

[0011] As a preferred embodiment of the present invention, hydrogen is mixed with an inert gas and then fed into the combustion zone of the boiler. As the proportion of hydrogen co-firing increases, the mixing ratio of inert gas and hydrogen gradually decreases, so that the hydrogen and inert gas are mixed and fed into the combustion zone of the boiler at a set flow rate.

[0012] In a preferred embodiment of the present invention, the inert gas is the flue gas after boiler combustion.

[0013] As a preferred embodiment of the present invention, the flow velocity of hydrogen mixed with inert gas and fed into the burnout zone of the boiler is 60 m / s to 120 m / s.

[0014] Meanwhile, the present invention also provides a boiler for implementing the above-mentioned method of co-firing hydrogen in a coal-fired boiler, comprising a boiler body, wherein the furnace of the boiler body is provided with a flame zone and a burnout zone located above the flame zone, and a pulverized coal burner, a secondary air box and a burnout air nozzle are provided on one side of the boiler body, the output port of the pulverized coal burner is connected to the flame zone, the air outlet of the secondary air box is connected to the flame zone, the air outlet of the burnout air nozzle is connected to the burnout zone, and a plurality of burnout air nozzles are provided and arranged at vertical intervals, wherein a hydrogen burner is provided between two adjacent burnout air nozzles, and the gas output port of the hydrogen burner is connected to the middle of the burnout zone.

[0015] As a preferred embodiment of the present invention, the boiler further includes a mixer, which is provided with an inert gas inlet, a hydrogen inlet, and a gas outlet, wherein the gas outlet is connected to the gas inlet of the hydrogen burner.

[0016] As a preferred embodiment of the present invention, the boiler further includes an air supply main pipe, a first air supply branch pipe, and a second air supply branch pipe. The air supply main pipe is connected to the first air supply branch pipe and the second air supply branch pipe respectively. The secondary air box is provided with multiple air inlets, and the air inlets of the multiple burnout air nozzles are respectively connected to the second air supply branch pipe.

[0017] As a preferred embodiment of the present invention, the pulverized coal burner and the secondary air box are provided in multiple and alternately arranged.

[0018] This invention discloses a method for co-firing hydrogen in a coal-fired boiler and a boiler in general. Compared with the prior art, the advantages of this method are as follows: The method of this invention ensures that there is a certain distance between the hydrogen and the pulverized coal by feeding and igniting hydrogen into the middle of the combustion zone of the boiler. The flow fields of the two fuels interfere with each other due to the different flow velocities, thereby ensuring the normal combustion of hydrogen and pulverized coal. The total air intake of the boiler is 1.13 to 1.30 times the air content required for complete combustion of pulverized coal and hydrogen. The primary air volume is 10% to 40% of the total air intake of the boiler, the secondary air volume is 20% to 75% of the total air intake of the boiler, and the combustion air volume is 10% to 50% of the total air intake of the boiler, thereby realizing staged combustion in the coal-fired boiler. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the boiler structure of the present invention;

[0020] In the diagram, 1 is the boiler body; 11 is the flame zone; 12 is the burnout zone; 2 is the pulverized coal burner; 3 is the secondary air box; 4 is the burnout air nozzle; 5 is the hydrogen burner; 51 is the mixer; 6 is the main air supply pipe; 61 is the first air supply branch pipe; and 62 is the second air supply branch pipe. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0022] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., used to indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] A preferred embodiment of the present invention provides a method for co-firing hydrogen in a coal-fired boiler, comprising the following steps:

[0024] S1: Primary air is introduced into the flame zone of the boiler. The primary air transports the pulverized coal to the flame zone of the boiler for combustion. The primary air serves as the combustion air for pulverized coal ignition and the initial combustion stage.

[0025] S2: Secondary air is supplied to the flame zone of the boiler and burnout air is supplied to the burnout zone of the boiler to provide some air for the pulverized coal to continue burning. During combustion, the pulverized coal and flue gas in the flame zone will rise. The burnout air in the lower part of the burnout zone will continue to replenish the oxygen of the rising pulverized coal and flue gas in the flame zone to maintain the continuous combustion reaction of pulverized coal.

[0026] S3: Hydrogen is introduced into the middle of the combustion zone of the boiler and ignited. Ensure that there is a certain distance between the introduced hydrogen and the introduced pulverized coal. The flow fields of the two fuels interfere with each other due to the different flow rates. The proportion of hydrogen co-firing is less than or equal to 30%, which is the ratio of the amount of hydrogen to the total amount of hydrogen and pulverized coal. The hydrogen entering the combustion zone quickly mixes with the flue gas and uses the oxygen in the flue gas to complete the ignition. At the same time, the combustion air at the bottom of the combustion zone also provides oxygen for the initial combustion of hydrogen. After the pulverized coal and hydrogen combustion exhaust gas mix, they continue to rise. Then the combustion air at the top of the combustion zone replenishes oxygen for it, and finally completes the combustion of pulverized coal and hydrogen.

[0027] The total air intake of the boiler is 1.13 to 1.30 times the air content required for the complete combustion of pulverized coal and hydrogen, meaning the oxygen content is greater than that required for the complete combustion of hydrogen and pulverized coal to ensure complete combustion. The primary air volume is 10% to 40% of the total boiler air intake, and the secondary air volume is 20% to 75%, resulting in an air chemical equivalent of 0.6 to 0.9 supplied to the fuel in the flame zone during the initial combustion phase. This means the total volume of primary and secondary air is 60% to 90% of the air required for the complete combustion of hydrogen and pulverized coal (not the total boiler air intake), causing incomplete combustion and creating a locally reducing atmosphere, where nitrogen (N) produces oxygen. The combustion is suppressed, and a burnout zone is set above the flame zone. In this zone, the air required for the complete reaction of fuel (burnout air) is added. Since the temperature of the burnout zone is lower than that of the flame zone, the amount of nitrogen oxides generated is limited. By introducing air in stages, the two necessary conditions for the oxidation of nitrogen element, namely high temperature and excess oxygen, are not simultaneously met, thus achieving the purpose of low nitrogen combustion. The volume of burnout air is 10% to 50% of the total air intake of the boiler. There is a part of burnout air below the hydrogen. The oxygen content can be adjusted in real time according to the hydrogen blending ratio and operating condition feedback to maintain stable combustion. There is also a part of burnout air above the hydrogen. Overall, the combustion organization scheme of air staged combustion in coal-fired boiler is maintained.

[0028] The rest is perimeter air. It is understandable that the perimeter air delivery channel is independent of the primary air, secondary air and burnout air channels. It is mainly used to cool the burner and generally accounts for 5% of the total air intake.

[0029] The above method can meet the requirement of hydrogen co-firing in coal-fired boilers while maintaining the staged combustion mode of coal-fired boilers.

[0030] For example, in S3, the proportion of hydrogen co-firing gradually increases to ensure stable boiler operation. It should be noted that the air volume of primary air, secondary air, and burnout air is adjustable. The air volume is adjusted according to the proportion of hydrogen co-firing. The higher the proportion of hydrogen co-firing, the larger the air volume of burnout air, while the air volume of primary air and secondary air decreases accordingly. However, the total air intake of the boiler is maintained at 1.13-1.30 times the air volume required for complete combustion of pulverized coal and hydrogen to ensure complete combustion of hydrogen and pulverized coal.

[0031] For example, the total air intake of the boiler is designed to be 1.15 times the air required for the complete combustion of pulverized coal and hydrogen. When the boiler starts operating, hydrogen is not initially added. At this time, the primary air volume is 22% of the total boiler air intake, the secondary air volume is 32.7%, the burnout air volume is 40.3%, and the perimeter air volume is 5%. As the proportion of hydrogen added increases, the burnout air volume gradually increases, while the primary and secondary air volumes gradually decrease. When the hydrogen added ratio reaches the set 20%, due to the reduction in pulverized coal, the primary air volume decreases to 19% of the total boiler air intake. The air volume is determined by the air volume corresponding to the change in load of the coal mill. The secondary air volume is also reduced accordingly to 29.6% of the total air volume of the boiler as the pulverized coal decreases. This air volume is determined by the combustion ratio controlled by staged combustion. The burnout air volume is increased to 41.4% of the total air volume of the boiler. Among them, the burnout air in the lower part of the burnout zone accounts for 23.4% of the total air volume of the boiler (5.4% is to provide the air required for the continued combustion of hydrogen, and the other 18% is to provide some air for the unburned pulverized coal). The burnout air in the lower part of the burnout zone accounts for 23% of the total air volume of the boiler, providing the final air required for the combustion of pulverized coal and hydrogen. The perimeter air volume is maintained at 5% of the total air volume of the boiler.

[0032] For example, hydrogen is mixed with inert gases (such as water vapor, carbon dioxide, nitrogen, and flue gas after combustion) before being fed into the burnout zone of the boiler (through the nozzles of the hydrogen burner). This ensures the flow rate of hydrogen when it is delivered to the burnout zone, especially when the actual amount of hydrogen added during operation is lower than the rated design value. This helps maintain the flow rate of hydrogen to the burnout zone and prevents burner backfire. As the proportion of hydrogen added increases, the mixing ratio of inert gas and hydrogen gradually decreases, so that the hydrogen and inert gas are fed into the burnout zone of the boiler at a set flow rate. That is, when hydrogen and inert gas are mixed, the amount of hydrogen increases and the amount of inert gas decreases, thereby keeping the total amount of hydrogen and inert gas constant. This helps keep the flow rate of the mixed gas into the burnout zone within the set range.

[0033] For example, the inert gas is the flue gas after boiler combustion, which effectively utilizes the flue gas.

[0034] For example, the hydrogen gas mixed with an inert gas is fed into the burnout zone of the boiler at a flow rate of 60 m / s to 120 m / s, and is injected into the furnace at a high flow rate to prevent backfire.

[0035] At the same time, such as Figure 1 As shown, the present invention also provides a boiler for implementing the above-mentioned method of co-firing hydrogen in a coal-fired boiler, comprising a boiler body 1, the furnace of the boiler body 1 having a flame zone 11 and a burnout zone 12 located above the flame zone 11, a pulverized coal burner 2, a secondary air box 3 and a burnout air nozzle 4 on one side of the boiler body 1, the output port of the pulverized coal burner 2 being connected to the flame zone 11, the air outlet of the secondary air box 3 being connected to the flame zone 11, the air outlet of the burnout air nozzle 4 being connected to the burnout zone 12, and multiple burnout air nozzles 4 being provided and arranged vertically at intervals, wherein a hydrogen burner 5 is provided between two adjacent burnout air nozzles, generally, the hydrogen burner 5 is located in the middle of the multiple burnout air nozzles, and the gas output port of the hydrogen burner 5 is connected to the middle of the burnout zone 12.

[0036] The working principle of this boiler is as follows: Primary air and pulverized coal (conveyed via primary air) are delivered to flame zone 11 through pulverized coal burner 2. Primary air serves as the combustion air for pulverized coal ignition and initial combustion. Then, secondary air is delivered to flame zone 11 through secondary air box 3 to provide additional air for the continued combustion of pulverized coal. During combustion, the pulverized coal and flue gas in flame zone 11 rise. Simultaneously, burnout air is delivered to burnout zone 12 through burnout air nozzle 4. The burnout air in the lower part of burnout zone 12 (the burnout air delivered by burnout air nozzle 4 located below hydrogen burner 5) continues to replenish oxygen for the rising pulverized coal and flue gas in flame zone 11, maintaining the pulverized coal combustion reaction. Continuing; Hydrogen is delivered to the burnout zone 12 via hydrogen burner 5. The hydrogen is injected into the furnace at a high flow rate (60-120 m / s) to prevent backfire in the hydrogen burner 5. The hydrogen injected into the furnace uses its high flow rate to quickly mix with the flue gas and uses the oxygen in the flue gas to complete the ignition. At the same time, the burnout air in the lower part of the burnout zone 12 also provides oxygen for the initial combustion of hydrogen. After the pulverized coal and hydrogen combustion exhaust gas mix, they continue to rise. Then, the burnout air in the upper part of the burnout zone 12 (the burnout air delivered by the burnout air nozzle 4 located above the hydrogen burner 5) replenishes oxygen for it, and finally completes the combustion of pulverized coal and hydrogen.

[0037] This boiler is equipped with an independent hydrogen burner 5, allowing hydrogen to ignite independently. It is located at a certain distance from the pulverized coal burner 2 and separated by at least one burnout zone 12, thus avoiding mutual interference in the flow fields caused by the different velocities of the output gases from the two burners. The hydrogen burner 5 is positioned between two burnout air nozzles 4. Hydrogen enters the furnace and mixes with the flue gas, utilizing the oxygen in the flue gas to complete ignition and maintain combustion, eliminating the need for additional air intake. The placement of the hydrogen burner 5 between the two burnout air nozzles 4 allows for appropriate oxygen supplementation to the pulverized coal and flue gas from the flame zone 11 via burnout air, maintaining the combustion process. Furthermore, it allows for... The proportion of hydrogen co-firing, controlled by the burnout air in the lower part of the burnout zone 12, can adapt to a wide range of co-firing ratios. The hydrogen burner 5 is arranged between the two burnout air nozzles 4, which enables the boiler to maintain a staged combustion organization scheme. The oxygen supply at the hydrogen burner 5 has not yet reached the total amount of oxygen required for the complete combustion of hydrogen and pulverized coal from the flame zone 11, which can avoid excessively high stoichiometric oxygen levels in this area. Otherwise, under the high-temperature heating of the hydrogen burner, the simultaneous presence of high oxygen and high temperature conditions would lead to the production of nitrogen oxides. In summary, this boiler can meet the requirements of hydrogen co-firing in coal-fired boilers while maintaining the staged combustion mode of coal-fired boilers.

[0038] For example, this boiler also includes a mixer 51, which has an inert gas inlet, a hydrogen inlet, and a gas outlet. The gas outlet is connected to the gas inlet of the hydrogen burner 5. Hydrogen is delivered to the mixer 51 from the hydrogen inlet. Inert gases (such as water vapor, carbon dioxide, nitrogen, flue gas after combustion, etc.) are input into the mixer 51 through the inert gas inlet. Hydrogen and inert gases are mixed in the mixer 51 and then delivered to the hydrogen burner 5 through the gas outlet, and then to the burnout zone 12. This helps to ensure the flow rate of hydrogen when it is delivered to the burnout zone 12, thereby preventing backfire. When the hydrogen co-firing ratio increases, the mixing ratio of inert gas and hydrogen decreases. That is, when hydrogen and inert gas are mixed, the amount of hydrogen increases and the amount of inert gas decreases, thereby helping to ensure that the flow rate of the gas delivered from the gas outlet of the mixer 51 is within a set range.

[0039] For example, this boiler also includes an air supply main pipe 6, a first air supply branch pipe 61, and a second air supply branch pipe 62. The air supply main pipe 6 is connected to the first air supply branch pipe 61 and the second air supply branch pipe 62 respectively. The secondary air box 3 is provided with multiple secondary air boxes, and its air inlets are connected to the first air supply branch pipe 61 respectively. The air inlets of multiple burnout air nozzles 4 are connected to the second air supply branch pipe 62 respectively. The air supply main pipe 6 supplies air to the first air supply branch pipe 61 and the second air supply branch pipe 62 respectively, thereby supplying secondary air to the flame zone 11 through the secondary air box 3 and supplying burnout air to the burnout zone 12 through the burnout air nozzles 4. The air supply main pipe 6 can be connected to the first air supply branch pipe 61 and the second air supply branch pipe 62 respectively through a three-way proportional valve to adjust the air supply ratio, that is, to control the air volume of secondary air and burnout air.

[0040] For example, multiple pulverized coal burners 2 and secondary air boxes 3 are provided and arranged alternately. Multiple pulverized coal burners 2 can meet the high-load combustion requirements, and multiple secondary air boxes 3 can ensure the air intake. The alternating arrangement of the two can better distribute the air volume, ensuring that each burner can obtain sufficient oxygen, thereby improving combustion efficiency and ensuring combustion stability.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for co-firing hydrogen in a coal-fired boiler, characterized in that: Includes the following steps: S1: Primary air is introduced into the flame zone of the boiler, and the primary air transports the pulverized coal to the flame zone of the boiler for combustion. S2: Secondary air is supplied to the flame zone of the boiler and burnout air is supplied to the burnout zone of the boiler; S3: Hydrogen is introduced and ignited between two adjacent burnout air nozzles in the middle of the burnout zone of the boiler, wherein the proportion of hydrogen in the combustion is less than or equal to 30%; The total air intake of the boiler is 1.13 to 1.30 times the air content required for the complete combustion of pulverized coal and hydrogen. The primary air volume is 10% to 40% of the total air intake of the boiler, the secondary air volume is 20% to 75% of the total air intake of the boiler, the burnout air volume is 10% to 50% of the total air intake of the boiler, and the remainder is perimeter air.

2. The method for co-firing hydrogen in a coal-fired boiler according to claim 1, characterized in that: In S3, the proportion of hydrogen co-firing gradually increases.

3. The method for co-firing hydrogen in a coal-fired boiler according to claim 2, characterized in that: Hydrogen is mixed with inert gas and then fed into the combustion zone of the boiler. As the proportion of hydrogen co-firing increases, the mixing ratio of inert gas and hydrogen gradually decreases, so that the hydrogen and inert gas are fed into the combustion zone of the boiler at a set flow rate.

4. The method for co-firing hydrogen in a coal-fired boiler according to claim 3, characterized in that: The inert gas is the flue gas produced after combustion in the boiler.

5. The method for co-firing hydrogen in a coal-fired boiler according to claim 3, characterized in that: The flow velocity of the hydrogen mixed with the inert gas and fed into the combustion zone of the boiler is 60 m / s to 120 m / s.

6. A boiler for implementing the method of co-firing hydrogen in a coal-fired boiler as described in claim 1, characterized in that: The boiler includes a boiler body, the furnace of which has a flame zone and a burnout zone located above the flame zone. A pulverized coal burner, a secondary air box, and burnout air nozzles are provided on one side of the boiler body. The output port of the pulverized coal burner is connected to the flame zone, the air outlet of the secondary air box is connected to the flame zone, and the air outlet of the burnout air nozzles is connected to the burnout zone. Multiple burnout air nozzles are provided and arranged at vertical intervals. A hydrogen burner is provided between two adjacent burnout air nozzles, and the gas output port of the hydrogen burner is connected to the middle of the burnout zone.

7. The boiler according to claim 6, characterized in that: It also includes a mixer, which has an inert gas inlet, a hydrogen inlet, and a gas outlet, the gas outlet being connected to the gas inlet of the hydrogen burner.

8. The boiler according to claim 6, characterized in that: It also includes a main air supply pipe, a first air supply branch pipe, and a second air supply branch pipe. The main air supply pipe is connected to the first air supply branch pipe and the second air supply branch pipe respectively. The secondary air box is provided with multiple air inlets, and its air inlets are connected to the first air supply branch pipe respectively. The air inlets of the multiple burnout air nozzles are connected to the second air supply branch pipe respectively.

9. The boiler according to claim 6, characterized in that: The pulverized coal burner and the secondary air box are provided in multiple and are arranged alternately.

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