System and method for stable combustion and low nitrogen based on primary air pulverized coal semi-gasification ultra-low load

Abstract

The application discloses a system and method for stable combustion and low-nitrogen based on semi-gasification of primary air pulverized coal, and belongs to the technical field of low-load peak shaving of coal-fired boilers. The system comprises a furnace, the lower part of the furnace is communicated with a primary air main line, the primary air main line is connected with a primary air bypass, a semi-gasification device of pulverized coal is installed on the primary air bypass, the primary air bypass is connected back to the primary air main line through a mixing port, and the mixture of coal gas and unreacted residual carbon after the semi-gasification of the primary air through the semi-gasification device of pulverized coal is mixed into the primary air main line. The system enables the semi-gasification of the pulverized coal in the primary air bypass, generates high-temperature reducing semi-coal gas (including coal gas, generated coke powder and unreacted pulverized coal) and sends the semi-coal gas into the bottom of the boiler, so that the stable combustion and low-nitrogen combustion are realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of low-load peak shaving of coal-fired boilers, and particularly relates to a system and method for semi-gasification of pulverized coal in primary air for ultra-low load stable combustion and low nitrogen. BACKGROUND

[0002] The statements herein merely provide background technology related to the present application, and do not necessarily constitute prior art.

[0003] At present, new energy power generation is developing by leaps and bounds, but the volatility and intermittency of new energy are relatively large, which is in conflict with the requirement of stable power output of the power grid. Coal-fired power generating units play a "bottom" role in power supply. In order to improve the accommodation capacity of the power grid to new energy and ensure the safe and stable operation of the power system, flexible transformation of coal-fired units and improvement of deep peak shaving capacity have become one of the key tasks of the current coal power industry.

[0004] Among them, the implementation scheme of coal power unit transformation and upgrading puts forward clear requirements for the flexible transformation of new units and active units: the general requirement for peak shaving capacity under pure condensing conditions is that the minimum power output reaches 35% of the rated load, and the heating and power generating unit should strive to achieve a minimum power output of 40% of the rated load for 6 hours a day during the heating period, and other types of units should take measures to reduce the minimum power output as much as possible. Unit flexibility transformation involves boilers, steam turbines and thermal control, and the first is the low-load stable combustion technology of the boiler.

[0005] Common stable combustion technologies include micro-oil stable combustion, natural gas stable combustion and plasma ignition, among which, the micro-oil stable combustion has problems such as easy blockage of the oil gun nozzle, ignition not limited by the output of the gasification oil gun, and competition for air between fuel and coal; the natural gas stable combustion has safety hazards; the plasma ignition has problems such as frequent start-stop ignition, limited service life of plasma, and high maintenance cost. At the same time, the minimum load of the existing low-load stable combustion technology is usually 30-40% of the rated load, but in actual operation, power plants will encounter deep peak shaving demand below 30% or even as low as 20% of the rated load. In addition, when the boiler is running at low load, the denitration system is not running at rated conditions, the denitration efficiency is low, and the NOx emission is high. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a system and method for semi-gasification of pulverized coal in primary air for ultra-low load stable combustion and low nitrogen, which makes the pulverized coal semi-gasify in the primary air bypass for pre-combustion, generates high-temperature reducing semi-coal gas (including coal gas, generated coke powder and unreacted pulverized coal) and sends it into the bottom of the boiler to play a role in stable combustion and low nitrogen combustion. The use of the system not only can realize deep low-load stable combustion of coal-fired units below 30% of the rated load, but also can effectively reduce the generation of NOx in the combustion process.

[0007] To achieve the above object, the present application is realized by the following technical solutions:

[0008] In the first aspect, the present application provides a system for stable combustion and low nitrogen based on semi-gasification of pulverized coal by primary air under ultra-low load, comprising a furnace, the lower part of the furnace being in communication with a primary air main line, the primary air main line being connected with a primary air bypass line, the primary air bypass line being provided with a semi-gasification device for pulverized coal, the primary air bypass line being connected back to the primary air main line through a mixing port, and the coal gas and unreacted residual carbon mixture generated after the primary air is gasified by the semi-gasification device for pulverized coal being mixed into the primary air main line.

[0009] As a further technical solution, the primary air main line and the primary air bypass line are both provided with valves to adjust the proportion of the primary air distributed by the primary air main line and the primary air bypass line.

[0010] As a further technical solution, the valves of the primary air bypass line are arranged on the front and back sides of the semi-gasification device for pulverized coal, and the valves of the primary air bypass line and the primary air main line are arranged in parallel.

[0011] As a further technical solution, the distance between the mixing port of the primary air main line and the primary air bypass line and the furnace ranges from 0 to 10 m.

[0012] As a further technical solution, the gasification temperature of the semi-gasification device for pulverized coal ranges from 800 to 1000℃.

[0013] As a further technical solution, a boiler bottom burner is arranged between the primary air main line and the furnace.

[0014] As a further technical solution, the boiler bottom burner is also in communication with a secondary air line.

[0015] As a further technical solution, a plurality of boiler upper burners are arranged on the side of the furnace to burn the materials in the furnace.

[0016] As a further technical solution, the top of the furnace is in communication with a flue gas passage to discharge the generated flue gas.

[0017] In the second aspect, the present application also provides a working method of the system for stable combustion and low nitrogen based on semi-gasification of pulverized coal by primary air under ultra-low load, comprising the following steps:

[0018] The primary air enters the primary air bypass line through the primary air main line, and in the semi-gasification device for pulverized coal, the primary air is ignited and semi-gasification occurs under an oxygen-deficient atmosphere to generate coal gas and unreacted residual carbon, and after the primary air bypass line is mixed with the primary air main line, the high-temperature reducing semi-coal gas carrying the unreacted residual carbon enters the bottom of the boiler furnace for secondary combustion, thereby realizing stable combustion under low load.

[0019] As a further technical solution, when the high-temperature reducing semi-gasification carries the unreacted residual carbon into the bottom of the boiler furnace for secondary combustion, the reducing atmosphere is beneficial to the reduction of NOx to N2, thereby realizing low-nitrogen combustion.

[0020] In a third aspect, the application further provides a system for stable combustion and low-nitrogen based on semi-gasification of pulverized coal by primary air at ultra-low load, comprising a furnace, wherein the lower part of the furnace is in communication with a primary air main line, the primary air main line is provided with a semi-gasification device for pulverized coal, and the front end of the semi-gasification device is provided with a pulverized coal shunt device to realize shunting of the primary air.

[0021] As a further technical solution, the gasification temperature of the semi-gasification device for pulverized coal ranges from 800 to 1000℃.

[0022] As a further technical solution, a boiler bottom burner is arranged between the primary air main line and the furnace.

[0023] As a further technical solution, the boiler bottom burner is further in communication with a secondary air line.

[0024] As a further technical solution, a plurality of boiler upper burners are further arranged at the side of the furnace to burn the materials in the furnace.

[0025] As a further technical solution, the top of the furnace is in communication with a flue gas passage to discharge the generated flue gas.

[0026] In a fourth aspect, the application further provides a working method of the system for stable combustion and low-nitrogen based on semi-gasification of pulverized coal by primary air at ultra-low load, comprising the following steps:

[0027] The primary air enters the semi-gasification device for pulverized coal through the primary air main line, and the shunting of the primary air is realized by the pulverized coal shunt device arranged at the front end of the semi-gasification device for pulverized coal, and the shunted primary air is preheated in the high-temperature semi-gasification gas by the cyclone entrainment of the pulverized coal shunt device, and then enters the furnace for secondary combustion, thereby realizing stable combustion and low-nitrogen effect.

[0028] The beneficial effects of the application are as follows:

[0029] The system of the application is provided with a primary air bypass line, the primary air bypass line is provided with a semi-gasification device for pulverized coal, the primary air contains pulverized coal, the pulverized coal is semi-gasified and pre-combusted by the semi-gasification device for pulverized coal in the primary air bypass line, the temperature of the fuel is increased, the physical space and reaction time of the combustion reaction of the pulverized coal are increased, the stable combustion at low load and complete combustion are facilitated, and the stable operation of the coal-fired boiler at ultra-low load (20% of the rated load at the minimum) can be realized.

[0030] The system of the present application, the primary air is bypassed through the coal powder semi-gasification device to carry out semi-gasification, can produce strong reducing gas, creates a local strong reducing atmosphere in the boiler, is beneficial to the reduction of NOx into N2, and can realize low NOx emission requirement when the coal-fired boiler is operated at ultra-low load.

[0031] The system of the present application, the primary air is bypassed through the coal powder semi-gasification device to carry out semi-gasification, can produce strong reducing gas, creates a local strong reducing atmosphere in the boiler, is beneficial to the reduction of NOx into N2, and can realize low NOx emission requirement when the coal-fired boiler is operated at ultra-low load. BRIEF DESCRIPTION OF DRAWINGS

[0032] The drawings constituting a part of the specification of the present application are used to provide further understanding of the present application, the illustrative embodiments of the present application and the description thereof are used to explain the present application, and do not constitute improper limitation on the present application.

[0033] Figure 1 is a schematic diagram of the system for ultra-low load stable combustion and low nitrogen based on primary air coal powder semi-gasification according to one or more embodiments of the present application;

[0034] Figure 2 is another schematic diagram of the system for ultra-low load stable combustion and low nitrogen based on primary air coal powder semi-gasification according to one or more embodiments of the present application;

[0035] In the drawings, the mutual distance or size is exaggerated for showing the position of each part, and the schematic diagram is only used for illustration;

[0036] Wherein, 1, primary air main road; 2, coal powder semi-gasification device; 3, valve; 4, secondary air wind road; 5, furnace; 6, boiler bottom burner; 7, boiler upper burner; 8, flue gas passage; 9, coal powder shunt device. DETAILED DESCRIPTION

[0037] It should be pointed out that the following detailed description is exemplary, and is intended to provide further description of the present application. Unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0038] As introduced in the background, the existing coal powder combustion boiler has the problems of difficult stable combustion at low load and high NOx emission. In order to solve the above problems, the present application proposes a system and method for ultra-low load stable combustion and low nitrogen based on primary air coal powder semi-gasification.

[0039] Example one:

[0040] In a typical embodiment of the present application, as shown in Figure 1 A system for stable combustion and low nitrogen based on semi-gasification of primary air pulverized coal at ultra-low load is proposed, which improves the original combustion system and semi-gasifies the primary air of the lowermost combustion system to achieve stable combustion and low nitrogen sensitive regulation and control of the boiler at ultra-low load.

[0041] Specifically, the system comprises a furnace 5, the lower part of which is communicated with a primary air main line 1, the primary air main line 1 is additionally provided with a primary air bypass, a pulverized coal semi-gasification device 2 is installed on the primary air bypass, and the primary air main line 1 and the primary air bypass are both provided with valves 3.

[0042] The primary air main line and the primary air bypass are connected, and the primary air bypass is connected back to the primary air main line through a mixing port; the primary air bypass is provided with valves 3 on both sides of the pulverized coal semi-gasification device 2, and the valves 3 of the primary air bypass and the primary air main line are connected in parallel, that is, the valve of the primary air main line is arranged between the two connection points of the primary air bypass and the primary air main line. The pulverized coal semi-gasification device can use the commonly used pulverized coal gasification device, and does not need to pursue the requirement of high conversion rate parameter, after gasification, the coal gas and unconverted residual carbon are sent into the furnace for secondary combustion together, and the secondary combustion in the reducing atmosphere (mainly CO and H2) can effectively reduce the generation of NOx.

[0043] Through the additionally installed primary air bypass, part of the primary air enters the pulverized coal semi-gasification device, and the semi-gasification of the pulverized coal is completed in the gasification chamber after ignition, that is, without the requirement of high carbon conversion rate, the gasification temperature is controlled at 800-1000℃, so that it can be stably operated without coking / sludging, and after gasification, the mixture of coal gas and unreacted residual carbon is mixed into the primary air main line, and then enters the furnace for secondary combustion by the burner.

[0044] The valves installed on the primary air main line and the primary air bypass are used to adjust the proportion of the primary air distributed by the main line and the bypass, so as to realize flexible regulation and control during low load operation in the furnace, and even realize deep low load (about 20% of rated load) operation.

[0045] A boiler bottom burner 6 is arranged between the primary air main line 1 and the furnace 5, and the boiler bottom burner 6 is also communicated with a secondary air line 4; a plurality of boiler upper burners 7 are arranged on the side of the furnace 5 to burn the materials in the furnace 5.

[0046] The top of the furnace 5 is communicated with a flue gas passage 8, and the flue gas generated after combustion is discharged from the flue gas passage 8.

[0047] The air of the primary air carries the coal powder, and the temperature of the coal gas and the unreacted residual carbon after the gasification of the primary air bypass is high, about 800-1000 DEG C. When the primary air partially semi-gasifies, the primary air mixed into the main road will cause the pyrolysis of the coal powder in the main road. In order to avoid the problem of tar blockage caused by the pyrolysis of the coal powder, the mixing port of the primary air main road and the primary air bypass is closer to the furnace, and the distance range is 0-10 m.

[0048] The system improves the temperature of the fuel into the furnace by the partial / total semi-gasification of the primary air, increases the coal powder combustion reaction space and time, and realizes the stable operation of the coal-fired boiler at an ultra-low load (the lowest 20% of the rated load), and can realize the sensitive regulation and control of the low-load operation of the boiler. In addition, due to the reducing atmosphere generated by the semi-gasification of the primary air, when entering the furnace for secondary combustion, it is beneficial to the reduction of NOx into N2 under the reducing atmosphere, and the low-nitrogen combustion of the boiler at a low load is realized.

[0049] The system is stable in operation and can realize the stable operation of the boiler at an ultra-low load, and meets the flexible peak regulation demand of the power plant.

[0050] In another typical embodiment of the present application, a method for stable combustion and low-nitrogen at an ultra-low load based on the semi-gasification of the primary air coal powder is provided, which adopts the above system, and the specific process is as follows:

[0051] The primary air enters the primary air bypass through the primary air main road. In the coal powder semi-gasification device, the primary air is ignited and semi-gasified under the oxygen-deficient atmosphere to generate coal gas and unreacted residual carbon. After the primary air bypass and the primary air main road are mixed, the high-temperature reducing semi-coal gas carrying the unreacted residual carbon enters the bottom of the boiler furnace for secondary combustion.

[0052] The raw material into the boiler is changed from the mixture of the low-temperature (<100 DEG C) air and powder to the high-temperature (800-1000 DEG C) semi-coal gas and the high-temperature (800-1000 DEG C) residual carbon, which can obviously strengthen the combustion at a low load, so as to realize the stable combustion at a low load. In addition, the secondary combustion is beneficial to the reduction of NOx into N2 under the reducing atmosphere, so as to realize the low-nitrogen combustion.

[0053] Example two:

[0054] In another typical embodiment of the present application, as Figure 2As shown, a system based on primary air pulverized coal semi-gasification ultra-low load stable combustion and low nitrogen is proposed. Compared with the first embodiment, in the present embodiment, the primary air bypass is no longer arranged, the pulverized coal semi-gasification device 2 is directly installed on the primary air main road 1, the pulverized coal shunting device 9 is arranged at the front end in the pulverized coal semi-gasification device 2, the shunting of the primary air is realized through the pulverized coal shunting device 9 arranged at the front end of the pulverized coal semi-gasification device 2, the primary air shunted to the center is ignited to realize the semi-gasification state through the ignition device, and the primary air shunted to the periphery without gasification is sucked into the high-temperature semi-gasification gas to realize preheating through the cyclone entrainment of the pulverized coal shunting device 9, and then enters the furnace together for secondary combustion, so as to realize the stable combustion and low nitrogen effect.

[0055] The pulverized coal shunting device 9 adopts the existing technology, adopts a conical bluff body structure to realize the shunting of the pulverized coal, and the end is a tooth ring structure to realize stable combustion.

[0056] The other parts are the same as those in the first embodiment.

[0057] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A system based on primary air pulverized coal semi-gasification ultra-low load stable combustion and low nitrogen, characterized in that, The present application relates to a coal-fired boiler, which comprises a furnace, and a primary air main path connected with the lower part of the furnace, wherein a coal powder semi-gasification device is installed in the primary air main path, a coal powder flow distribution device is arranged at the front end of the coal powder semi-gasification device, the primary air is distributed by the coal powder flow distribution device, the primary air distributed to the center is ignited by an ignition device to achieve a semi-gasification state, and the primary air distributed to the periphery is sucked into the high-temperature semi-gasification gas by the cyclone entrainment of the coal powder flow distribution device to achieve preheating, and then enters the furnace together to realize secondary combustion, thereby achieving stable combustion and low-nitrogen effect.

2. The system for stable combustion and low nitrogen based on primary air pulverized coal semi-gasification ultra-low load according to claim 1, characterized in that, The gasification temperature of the coal powder semi-gasification device is 800-1000 ℃, and a boiler bottom burner is arranged between the primary air main path and the furnace, which is also connected with a secondary air path.

3. The system for stable combustion and low nitrogen based on primary air pulverized coal semi-gasification ultra-low load according to claim 1, characterized in that, A plurality of boiler upper burners are arranged on the side of the furnace to burn the materials in the furnace.

4. The system for stable combustion and low nitrogen based on primary air pulverized coal semi-gasification ultra-low load according to claim 1, characterized in that, The top of the furnace is connected with a flue gas passage to discharge the generated flue gas.

5. The method for operating the system based on the primary air pulverized coal semi-gasification ultra-low load stable combustion and low nitrogen of claim 1, characterized in that, The present application relates to a coal-fired boiler, which comprises a furnace, and a primary air main path connected with the lower part of the furnace, wherein a coal powder semi-gasification device is installed in the primary air main path, a coal powder flow distribution device is arranged at the front end of the coal powder semi-gasification device, the primary air is distributed by the coal powder flow distribution device, the primary air distributed to the center is ignited by an ignition device to achieve a semi-gasification state, and the primary air distributed to the periphery is sucked into the high-temperature semi-gasification gas by the cyclone entrainment of the coal powder flow distribution device to achieve preheating, and then enters the furnace together to realize secondary combustion, thereby achieving stable combustion and low-nitrogen effect. The primary air enters the coal powder semi-gasification device through the primary air main path, and the primary air is distributed by the coal powder flow distribution device arranged at the front end of the coal powder semi-gasification device.

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