Method for blending combustion of hydrogen in coal-fired boiler and boiler

Abstract

The invention relates to the technical field of coal-fired boilers, and discloses a method for blending combustion of hydrogen in a coal-fired boiler and a boiler, the method comprises the following steps: S1, primary air is fed into a flame area of the boiler, and the primary air conveys pulverized coal into the flame area of the boiler for combustion; s2, secondary air is fed into a flame area of the boiler, and over-fire air is fed into an after-fire area of the boiler; s3, the air is fed into the middle of a burnout area of the boiler and ignited, the total air inlet amount of the boiler is 1.13-1.30 times of the air content needed by complete combustion of pulverized coal and complete combustion of hydrogen, the air volume of primary air is 10%-40% of the total air inlet amount of the boiler, the air volume of secondary air is 20%-75% of the total air inlet amount of the boiler, and the total air inlet amount of the secondary air is 10%-20% of the total air inlet amount of the boiler; the air volume of the over-fire air is 10%-50% of the total air inlet amount of the boiler, and the balance is surrounding air; according to the method, hydrogen blending combustion can be met on the premise that the staged combustion mode of the coal-fired boiler is maintained. Meanwhile, the invention discloses a boiler for implementing the method.

Description

Technical Field

[0001] The invention relates to the technical field of coal-fired boilers, and in particular to a method for blending hydrogen into a coal-fired boiler and a boiler. Background Art

[0002] One of the ways to reduce carbon dioxide emissions from coal-fired boilers is to mix low-carbon or zero-carbon fuels. Hydrogen produced from renewable energy is a globally recognized fuel with zero carbon emissions. Mixing hydrogen in a coal-fired boiler at a certain ratio, while the total output energy remains unchanged, can reduce carbon dioxide emissions from the source by replacing part of the coal with hydrogen. However, due to the large difference in the combustion of hydrogen and pulverized coal, there are various problems when adding hydrogen directly to coal for combustion.

[0003] Coal-fired boilers are mainly designed according to the combustion characteristics of coal. If the input fuel characteristics are greatly different, it will affect the safe operation of the boiler. Since hydrogen ignites quickly, the burner needs to be designed with a very high hydrogen outlet velocity to prevent flame flashback or nozzle overheating. The outlet velocity of the hydrogen burner is much higher than the design velocity of the coal-fired boiler burner, which easily causes the problem of interference between the flow fields of the two adjacent burners. In addition, hydrogen combustion has the characteristics of high local flame temperature and weak radiation. When a boiler designed for coal-fired combustion is mixed with hydrogen in a large proportion, it is easy to cause local overheating of the boiler, causing excessive nitrogen oxides and overheating of the heating surface in the furnace. When hydrogen is input into the boiler as pure fuel and mixed with the coal-fired boiler, whether it is an independent burner or mixed with coal powder, because the hydrogen combustion rate is much higher than that of coal powder, it consumes the surrounding oxygen very quickly, making it difficult for coal powder to ignite, that is, the so-called "wind grabbing" phenomenon, making it difficult for coal powder to burn normally. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for blending hydrogen into a coal-fired boiler and a boiler for implementing the method, which can meet the requirements of blending hydrogen into a coal-fired boiler under the premise of maintaining a graded combustion mode of the coal-fired boiler.

[0005] In order to solve the above technical problems, the present invention provides a method for mixing hydrogen with a coal-fired boiler, comprising the following steps:

[0006] S1: primary air is sent to 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: Supply secondary air to the flame zone of the boiler and supply burnout air to the burnout zone of the boiler;

[0008] S3: hydrogen is introduced into the middle of the burnout zone of the boiler and ignited, wherein the hydrogen blending ratio is less than or equal to 30%;

[0009] Among them, the total air intake of the boiler is 1.13 times to 1.30 times the air content required for complete combustion of coal powder and complete combustion of hydrogen, the air volume of primary air is 10% to 40% of the total air intake of the boiler, the air volume of secondary air is 20% to 75% of the total air intake of the boiler, the air volume of burnout air is 10% to 50% of the total air intake of the boiler, and the rest is peripheral wind.

[0010] As a preferred embodiment of the present invention, in S3, the proportion of hydrogen added to the combustion is gradually increased.

[0011] As a preferred embodiment of the present invention, hydrogen and inert gas are mixed and then sent into the burnout zone of the boiler. As the hydrogen blending ratio increases, the mixing ratio of inert gas and hydrogen gradually decreases, so that hydrogen and inert gas are mixed and sent into the burnout zone of the boiler at a set flow rate.

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

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

[0014] At the same time, the present invention also provides a boiler for realizing the above-mentioned method of blending hydrogen into a coal-fired boiler, comprising a boiler body, a furnace of the boiler body being provided with a flame zone and a burnout zone located above the flame zone, a pulverized coal burner, a secondary wind box and a burnout air nozzle being provided on one side of the boiler body, the output port of the pulverized coal burner being connected to the flame zone, the air outlet of the secondary wind box being connected to the flame zone, the air outlet of the burnout air nozzle being connected to the burnout zone, a plurality of the burnout air nozzles being provided and being arranged at intervals along the vertical direction, wherein a hydrogen burner is provided between two adjacent burnout sub-nozzles, and the gas output port of the hydrogen burner being connected to the middle of the burnout zone.

[0015] As a preferred embodiment of the present invention, the boiler further comprises a mixer, wherein the mixer is provided with an inert gas inlet, a hydrogen inlet and a gas outlet, and 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 a main air supply pipe, a first air supply branch pipe and a second air supply branch pipe, the main air supply pipe is respectively connected to the first air supply branch pipe and the second air supply branch pipe, the secondary air box is provided with a plurality of air inlets thereof are respectively connected to the first air supply branch pipe, and the air inlets of the plurality of 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 plurality and are arranged alternately.

[0018] The embodiment of the present invention provides a method for blending hydrogen into a coal-fired boiler and a boiler. Compared with the prior art, the beneficial effects of the present invention are as follows: the method of the present invention ensures that there is a certain distance between the hydrogen and the coal powder introduced by feeding and igniting the hydrogen into the middle of the burnout zone of the boiler, and the flow fields of the two fuels due to different flow rates interfere with each other, thereby ensuring the normal combustion of hydrogen and coal powder; wherein the total air intake of the boiler is 1.13 times to 1.30 times the air content required for complete combustion of coal powder and complete combustion of hydrogen, the air volume of the primary air is 10% to 40% of the total air intake of the boiler, the air volume of the secondary air is 20% to 75% of the total air intake of the boiler, and the air volume of the burnout air is 10% to 50% of the total air intake of the boiler, thereby realizing staged combustion of the coal-fired boiler. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a boiler of the present invention;

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

[0021] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0022] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like used in the present invention to indicate the orientation or position relationship is based on the orientation or position relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second" and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0023] A method for mixing hydrogen with a coal-fired boiler according to a preferred embodiment of the present invention comprises the following steps:

[0024] S1: primary air is sent 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 the ignition and initial combustion of the pulverized coal.

[0025] S2: secondary air is sent into the flame zone of the boiler and burnout air is sent into the burnout zone of the boiler to provide a part of air for the pulverized coal to continue to burn. During combustion, the pulverized coal and smoke in the flame zone will rise. The burnout air at the bottom of the burnout zone continues to supplement oxygen for the pulverized coal and smoke rising in the flame zone to maintain the continuous combustion reaction of the pulverized coal;

[0026] S3: hydrogen is fed into the middle of the burnout zone of the boiler and ignited, ensuring that there is a certain distance between the fed hydrogen and the fed coal powder, and the flow fields of the two fuels interfere with each other due to different flow velocities, wherein the hydrogen blending ratio is less than or equal to 30%, that is, the ratio of the amount of hydrogen to the total amount of hydrogen and coal powder, the hydrogen entering the burnout zone is quickly mixed with the flue gas, and the oxygen in the flue gas is used to complete the ignition, and at the same time, the burnout wind at the bottom of the burnout zone provides the hydrogen combustion with oxygen at the initial stage of combustion, the coal powder and hydrogen combustion tail gas are mixed and continue to rise, and then the burnout wind at the top of the burnout zone supplements it with oxygen, and finally completes the complete combustion of coal powder and hydrogen;

[0027] Among them, 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 complete combustion of hydrogen, that is, the oxygen content is more than the amount required for complete combustion of hydrogen and pulverized coal to ensure that they can be burned out; the air volume of the primary air is 10% to 40% of the total air intake of the boiler, and the air volume of the secondary air is 20% to 75% of the total air intake of the boiler, so that the air chemical equivalent of the fuel supplied to the flame zone at the initial stage of combustion is 0.6 to 0.9, that is, the total air volume of the primary air and the secondary air is 60% to 90% of the air volume required for complete combustion of hydrogen and pulverized coal (not the total air intake of the boiler), so that the fuel cannot be completely burned and a local reducing atmosphere is presented, and the oxidation of the N element is suppressed. A burnout zone is set above the flame zone, and fuel is added in this area for complete reaction. The required air (burnout air) should be used. Since the temperature in the burnout zone is lower than that in the flame zone, the nitrogen oxides generated are limited. The air is delivered in batches so that the two necessary conditions of high temperature and excess oxygen required for the oxidation of the N element will not be met at the same time, ultimately achieving the purpose of low-nitrogen combustion. The volume of the burnout air is 10% to 50% of the total air intake of the boiler. There is part of the burnout air below the hydrogen, and 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 part of the burnout air above the hydrogen, which maintains the air-staged combustion organization plan of the coal-fired boiler as a whole. The rest is boundary air. It can be understood that the transmission channel of the boundary air is independent of the channels of the primary air, secondary air and burnout air. It is mainly used to cool the burner and generally accounts for 5% of the total air intake.

[0028] The above method can meet the requirement of hydrogen blending in a coal-fired boiler under the premise of maintaining the staged combustion mode of the coal-fired boiler.

[0029] For example, in S3, the hydrogen blending ratio is gradually increased to ensure stable operation of the boiler. It should be noted that the air volumes of the primary air, secondary air and burnout air are adjustable, and the air volumes are adjusted according to the hydrogen blending ratio. The higher the hydrogen blending ratio, the larger the burnout air volume, while the primary air and secondary air volumes are reduced accordingly. However, the total air intake of the boiler is maintained at 1.13-1.30 times the amount of air required for complete combustion of pulverized coal and hydrogen to ensure complete combustion of hydrogen and pulverized coal.

[0030] For example, the total air intake of the boiler is designed to be 1.15 times the amount of air required for complete combustion of pulverized coal and hydrogen; when the boiler starts working, hydrogen is not mixed at first. At this time, the air volume of the primary air is 22% of the total air intake of the boiler, the air volume of the secondary air is 32.7% of the total air intake of the boiler, the air volume of the burnout air is 40.3% of the total air intake of the boiler, and the air volume of the peripheral air is 5% of the total air intake of the boiler; as the proportion of hydrogen blending increases, the air volume of the burnout air gradually increases, while the air volumes of the primary air and the secondary air gradually decrease. When the proportion of hydrogen blending reaches the set 20%, the air volume of the primary air is reduced to 19% of the total air intake of the boiler due to the reduction in the amount of pulverized coal. The air volume is determined by the air volume corresponding to the variable load of the pulverizer. The secondary air is also reduced to 29.6% of the total air intake of the boiler as the pulverized coal decreases. The air volume is determined by the combustion ratio controlled by the staged combustion. The burnout air volume is increased to 41.4% of the total air intake of the boiler. Among them, the burnout air in the lower part of the burnout zone is 23.4% of the total air intake of the boiler (5.4% provides the air required for continued combustion of hydrogen, and the other 18% provides part of the air for unburned pulverized coal). The burnout air in the lower part of the burnout zone is 23% of the total air intake of the boiler, providing the final air required for the combustion of pulverized coal and hydrogen. The boundary wind is maintained at 5% of the total air intake of the boiler.

[0031] For example, hydrogen is mixed with an inert gas (such as water vapor, carbon dioxide, nitrogen, flue gas after combustion, etc.) and then fed into the burnout zone of the boiler (through the nozzle of the hydrogen burner), thereby ensuring the flow rate of hydrogen when it is transported to the burnout zone, especially when the hydrogen added in actual operation is lower than the rated design value, the flow rate of hydrogen when it is transported to the burnout zone can be maintained to prevent burner flashback; as the hydrogen blending ratio increases, the mixing ratio of inert gas to hydrogen gradually decreases, so that after the hydrogen and inert gas are mixed, they 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 unchanged, which helps to keep the flow rate of the mixed gas into the burnout zone within a set range.

[0032] Exemplarily, the inert gas is flue gas after boiler combustion, which effectively utilizes the flue gas.

[0033] Exemplarily, the hydrogen is mixed with an inert gas and fed into the burnout zone of the boiler at a flow rate of 60 m / s to 120 m / s, and is sprayed into the furnace at a higher flow rate to prevent flashback.

[0034] At the same time, if Figure 1 As shown, the present invention also provides a boiler for realizing the above-mentioned method of blending hydrogen into a coal-fired boiler, comprising a boiler body 1, a furnace of the boiler body 1 being provided with a flame zone 11 and a burnout zone 12 located above the flame zone 11, a pulverized coal burner 2, a secondary wind box 3 and a burnout air nozzle 4 being provided 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 wind 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, a plurality of burnout air nozzles 4 being provided and arranged at intervals along the vertical direction, wherein a hydrogen burner 5 is provided between two adjacent burnout sub-nozzles, generally, the hydrogen burner 5 is located in the middle of the plurality of burnout sub-nozzles, and the gas output port of the hydrogen burner 5 is connected to the middle of the burnout zone 12.

[0035] The working principle of this boiler is as follows: primary air and pulverized coal (transported by primary air) are transported to the flame zone 11 through the pulverized coal burner 2, and the primary air is used as the combustion-supporting air for the ignition and initial combustion of the pulverized coal; then the secondary air is transported to the flame zone 11 through the secondary air box 3, providing a part of the air for the continued combustion of the pulverized coal. During combustion, the pulverized coal and smoke in the flame zone 11 will rise, and at the same time, the burnout air is transported to the burnout zone 12 through the burnout air nozzle 4. The burnout air at the bottom of the burnout zone 12 (the burnout air transported by the burnout air nozzle 4 located below the hydrogen burner 5) continues to supplement the oxygen for the rising pulverized coal and smoke in the flame zone 11, so as to maintain the pulverized coal combustion reaction. Continue; hydrogen is transported to the burnout zone 12 through the hydrogen burner 5, and hydrogen is sprayed into the furnace at a relatively high flow rate (60-120 m / s) to prevent the hydrogen burner 5 from flashing back. The hydrogen sprayed into the furnace uses its own 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 wind at the bottom of the burnout zone 12 provides the hydrogen combustion with oxygen at the initial stage of combustion; the pulverized coal and the hydrogen combustion exhaust gas continue to rise after mixing, and then the burnout wind at the upper part of the burnout zone 12 (the burnout air delivered by the burnout wind nozzle 4 located above the hydrogen burner 5) supplements it with oxygen, and finally completes the complete combustion of the pulverized coal and hydrogen.

[0036] The boiler is provided with an independent hydrogen burner 5, which allows hydrogen to ignite independently, and is at a certain distance from the pulverized coal burner 2, and is separated by at least one burnout zone 12, so as to avoid mutual interference of the flow fields of the two burners due to the different speeds of the output gases; the hydrogen burner 5 is arranged between two burnout air nozzles 4, and the hydrogen enters the furnace and mixes with the flue gas, and the oxygen in the flue gas is used to complete the ignition and maintain the combustion, without the need for additional air inlet; the hydrogen burner 5 is arranged between two burnout air nozzles 4, on the one hand, the pulverized coal and flue gas coming up from the flame zone 11 can be properly oxygenated by the burnout air to maintain the combustion process, and on the other hand, according to The proportion of hydrogen blending controls the burnout air in the lower part of the burnout zone 12, and can adapt to a wider proportion of blending changes; the hydrogen burner 5 is arranged between two of the burnout air nozzles 4, which can enable the boiler as a whole to maintain an air-staged combustion organization scheme, and the oxygen supply at the hydrogen burner 5 has not yet reached the total oxygen required for complete combustion of hydrogen and pulverized coal from the flame zone 11, which can avoid the chemical equivalent of oxygen in this area being too high, otherwise under the high-temperature heating of the hydrogen burner, high oxygen content and high temperature conditions are simultaneously present to produce nitrogen oxides; in summary, this boiler can meet the requirements of a coal-fired boiler blending with hydrogen while maintaining the staged combustion mode of a coal-fired boiler.

[0037] Exemplarily, the boiler also includes a mixer 51, which is provided with an inert gas input port, a hydrogen input port and a gas output port. The gas output port is connected to the gas input port of the hydrogen burner 5. Hydrogen is transported to the mixer 51 from the hydrogen input port. Inert gas (such as water vapor, carbon dioxide, nitrogen, flue gas after combustion, etc.) is input into the mixer 51 through the inert gas. Hydrogen and inert gas are mixed in the mixer 51 and then transported to the hydrogen burner 5 through the gas output port, and then transported to the burnout zone 12, which helps to ensure the flow rate of hydrogen when it is transported to the burnout zone 12, thereby preventing flashback. When the hydrogen blending ratio increases, the mixing ratio of the 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, which helps to ensure that the flow rate of the gas delivered from the gas output port of the mixer 51 is within a set range.

[0038] Exemplarily, the boiler also includes a main air supply pipe 6, a first air supply branch pipe 61 and a second air supply branch pipe 62, the main air supply pipe 6 is respectively connected to the first air supply branch pipe 61 and the second air supply branch pipe 62, the secondary air box 3 is provided with multiple air inlets respectively connected to the first air supply branch pipe 61, the air inlets of multiple burnout air nozzles 4 are respectively connected to the second air supply branch pipe 62, the main air supply pipe 6 transports air to the first air supply branch pipe 61 and the second air supply branch pipe 62 respectively, so as to transport secondary air to the flame zone 11 through the secondary air box 3 and transport burnout air to the burnout zone 12 through the burnout air nozzle 4, the main air supply pipe 6 can be respectively connected to the first air supply branch pipe 61 and the second air supply branch pipe 62 through a three-way proportional valve, so as to adjust the proportion of air supply, that is, to control the air volume of secondary air and burnout air.

[0039] Exemplarily, multiple pulverized coal burners 2 and secondary air boxes 3 are respectively provided and are 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 and ensure that each burner can obtain sufficient oxygen, thereby improving the combustion efficiency and ensuring the stability of combustion.

[0040] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A method for mixing hydrogen with a coal-fired boiler, characterized in that: The following steps are involved: S1: primary air is sent to the flame zone of the boiler, and the primary air transports the pulverized coal to the flame zone of the boiler for combustion; S2: Supply secondary air to the flame zone of the boiler and supply burnout air to the burnout zone of the boiler; S3: hydrogen is introduced into the middle of the burnout zone of the boiler and ignited, wherein the hydrogen blending ratio is less than or equal to 30%; Among them, the total air intake of the boiler is 1.13 times to 1.30 times the air content required for complete combustion of coal powder and complete combustion of hydrogen, the air volume of primary air is 10% to 40% of the total air intake of the boiler, the air volume of secondary air is 20% to 75% of the total air intake of the boiler, the air volume of burnout air is 10% to 50% of the total air intake of the boiler, and the rest is peripheral wind.

2. The method for blending hydrogen into coal-fired boiler according to claim 1, characterized in that: In S3, the proportion of hydrogen added to the combustion gradually increases.

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

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

5. The method for blending hydrogen into coal-fired boiler according to claim 3, characterized in that: The flow rate of hydrogen mixed with inert gas and sent into the burnout zone of the boiler is 60m / s to 120m / s.

6. A boiler for implementing the method for blending hydrogen into a coal-fired boiler as claimed in claim 1, characterized in that: The boiler body comprises a boiler body, a furnace of which is provided with a flame zone and a burnout zone located above the flame zone, a pulverized coal burner, a secondary wind box and a burnout air nozzle are provided on one side of the boiler body, the output port of the pulverized coal burner is communicated with the flame zone, the air outlet of the secondary wind box is communicated with the flame zone, the air outlet of the burnout air nozzle is communicated with the burnout zone, a plurality of the burnout air nozzles are provided and are arranged at intervals along the vertical direction, a hydrogen burner is provided between two adjacent burnout sub-nozzles, and the gas output port of the hydrogen burner is communicated with the middle of the burnout zone.

7. The boiler according to claim 6, characterized in that: The invention also comprises a mixer, wherein the mixer is provided with an inert gas input port, a hydrogen input port and a gas output port, and the gas output port is connected to the gas input port 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 and the air inlets thereof are respectively connected to the first air supply branch pipe, and the air inlets of the multiple burnout air nozzles are respectively connected to the second air supply branch pipe.

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

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