CN107606603A - A kind of combustion system for the combustion of pulverized-coal fired boiler ultra-low load steady - Google Patents

Abstract

The invention provides a combustion system for ultra-low-load stable combustion of pulverized coal boilers. The pulverized coal pipelines at the outlets of at least two pulverizers are divided into conventional pulverized coal pipelines and pulverized coal pipelines for low load; conventional pulverized coal pipelines Connect the primary air burner, and the primary air burner is set on the boiler body; the low-load pulverized coal pipeline is equipped with a thick-lean separator, and the outlet of the thick-lean separator is equipped with thick and light pulverized coal pipelines, and the thick and light pulverized coal pipelines are respectively connected Thick and light pulverized coal burners, the thick and light pulverized coal burners are arranged above the main burner of the boiler body. At normal load, pulverized coal enters the furnace for combustion through conventional pulverized coal pipelines and primary air burners; at ultra-low loads, pulverized coal enters the furnace for combustion through pulverized coal pipelines for low loads and thick and light pulverized coal burners. The pulverized coal concentration of the dense pulverized coal airflow can reach the pulverized coal concentration of the pulverized coal airflow at the rated load. The present invention can make the pulverized coal boiler burn stably under the ultra-low load of 15% to 20% without combustion-supporting equipment.

Description

A combustion system for ultra-low load stable combustion of pulverized coal boilers

technical field

The invention relates to a combustion system for ultra-low-load stable combustion of a pulverized coal boiler, which can realize stable combustion of the boiler under an ultra-low load of 15% to 20%, and belongs to the technical field of combustion systems for pulverized coal boilers.

Background technique

In recent years, renewable energy sources such as wind power and photovoltaics have developed rapidly in China. However, the instability of renewable energy such as wind power and photovoltaics requires the power grid to have stronger peak-shaving capabilities. In addition, the instability of the power load on the power consumption side also puts forward higher requirements on the peak-shaving capability of the power grid. Insufficient peak shaving capacity has led to frequent and serious "abandoned wind and solar" phenomena in northern my country.

Thermal power units are currently the main units in my country, with installed capacity accounting for about 65% of the national installed capacity, and power generation accounts for more than 70% of the national power generation. To improve the peak-shaving capability of the power grid, the peak-shaving capability of thermal power units must be greatly improved. The flexibility transformation of thermal power units is imperative. The minimum stable combustion load of conventional bituminous coal boilers is about 30%, and the minimum stable combustion load of lean coal and anthracite boilers is about 40% to 50%. As the load continues to decrease, on the one hand, the temperature in the furnace decreases; on the other hand, the stable combustion characteristics of the burner also decrease. Continuing to reduce the boiler load may cause unstable combustion.

Take a 600MW class quadrangular tangentially fired boiler as an example. As shown in Figure 1, the combustion system of the entire boiler consists of a boiler body 1, a primary fan 2, a coal mill 3, a pulverized coal pipeline 4, a primary air burner 5, a secondary fan 6, a large wind box 7, and a secondary air nozzle 8 and so on. The primary air generated by the primary fan 2 passes through the coal mill 3, carrying pulverized coal, and enters the furnace for combustion through the pulverized coal pipeline 4 and the primary air burner 5, and the secondary air formed by the secondary fan 6 enters the large wind box 7, and passes through the secondary air The secondary air nozzle 8 enters the furnace to assist combustion.

In this example, the boiler is provided with six coal mills, and one coal mill is equipped with a deck of four primary air burners 5 . Coal mills are "five uses and one standby", and five coal mills are put into operation at rated load. Each coal mill bears 20% of the coal consumption of the rated load of the boiler. The air-to-coal ratio of the primary air is around 1.8 to 2.2. Among them, the air volume of the primary air is determined by the ventilation volume of the coal mill, and the coal feeding volume is determined by the boiler load. For a certain coal mill, when the coal supply decreases, the ventilation rate also decreases. But when the ventilation rate drops to a certain level, generally around 70% of the maximum ventilation rate of the coal mill, the ventilation rate will no longer drop. Continued decline may lead to too low wind speed in the pulverizer and pulverized coal pipeline, and then pulverized coal clogging.

When the boiler is running at an ultra-low load of 15% to 20%. In order to ensure the safe operation of the boiler, the regulations require that the boiler must be put into operation with two coal mills. At this time, the coal consumption of the boiler is only about 15% to 20% of the rated load, and the coal grinding capacity of each coal mill is only about 7.5% to 10% of the rated load boiler coal consumption. The coal grinding capacity is about 37.5% to 50%, while the ventilation rate of the coal mill is about 70% of the rated load. At this time, the air-to-coal ratio of the primary air is 1.4 to 1.8 times the rated load, which is far beyond the range of the air-to-coal ratio that the burner can burn stably, and the stable combustion characteristics of the burner decline. Boilers cannot achieve stable combustion under 15% to 20% load, and can only support combustion through oil injection guns and plasma equipment.

Contents of the invention

The technical problem to be solved by the invention is how to make the pulverized coal boiler burn stably under the ultra-low load of 15%-20% without combustion-supporting equipment.

In order to solve the above technical problems, the technical solution of the present invention is to provide a combustion system for ultra-low load stable combustion of pulverized coal boilers, including at least two coal mills, the primary fan is connected to the air inlet of the coal mill, and the outlet of the coal mill A pulverized coal pipeline is provided, which is characterized in that: the pulverized coal pipeline at the outlet of at least two pulverizers is bifurcated into a conventional pulverized coal pipeline and a pulverized coal pipeline for low load;

The conventional pulverized coal pipeline is connected to the primary air burner, and the primary air burner is installed on the boiler body;

The pulverized coal pipeline for low load is equipped with a dense-lean separator, and the outlet of the denser separator is equipped with a pulverized-concentrated pipeline and a pulverized-coal pipeline. The pulverized-coal pipeline is connected to the pulverized-coal burner and the pulverized-coal pipeline is connected to the pulverized-coal burner , The thick pulverized coal burner and the light pulverized coal burner are arranged on the boiler body.

Preferably, valves are provided on the conventional pulverized coal pipeline and the pulverized coal pipeline for low load.

More preferably, during normal load, the valve on the conventional pulverized coal pipeline is opened, and the valve on the pulverized coal pipeline for low load is closed; The valve on the pulverized coal pipeline is open.

Preferably, the pulverized coal pipelines at the outlets of at least two coal mills are bifurcated to form at least two layers of concentrated primary air burners and at least two layers of light primary air burners. An area that concentrates the heat load and is conducive to the stable combustion of the boiler.

Preferably, the dense pulverized coal burner and the light pulverized coal burner are arranged above the main burner of the boiler body.

Preferably, at normal load, pulverized coal enters the furnace for combustion through conventional pulverized coal pipelines and primary air burners; at ultra-low loads of 15% to 20%, pulverized coal passes through pulverized coal pipelines for low loads, concentrated pulverized coal burners, light The pulverized coal burner enters the furnace for combustion.

More preferably, when the 15% to 20% ultra-low load, the pulverized coal flow is divided into two streams of pulverized coal, thick and light, by the thick-lean separator, and enters the furnace for combustion through the thick and light pulverized coal burners respectively; The pulverized coal concentration of the pulverized coal airflow is improved compared with the unseparated pulverized coal airflow concentration before the thick-lean separator, and the pulverized coal concentration of the pulverized coal airflow reaches the rated load.

The combustion system provided by the present invention overcomes the deficiencies of the prior art. Without combustion-supporting equipment, it can make the pulverized coal boiler burn stably under the ultra-low load of 15% to 20%. The system has simple structure, reliable performance and low cost. It is suitable for large-scale promotion and use.

Description of drawings

Figure 1 is a schematic diagram of the combustion system of a conventional pulverized coal boiler;

Fig. 2 is a schematic diagram of a combustion system for ultra-low-load stable combustion of a pulverized coal boiler provided in this embodiment.

detailed description

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Figure 2 is the layout of the ultra-low load stable combustion combustion system of a 600MW boiler. The boiler adopts the four-corner tangential combustion method, and is equipped with 6 coal mills 3, numbered A, B, C, D, E, and F respectively. Each pulverizer is equipped with a layer of pulverized coal burner 5. Among them, the outlet pulverized coal pipelines of A, B, C, and D pulverizers are consistent with the conventional combustion system, and the outlet pulverized coal pipelines of E and F coal pulverizers are divided into conventional pulverized coal pipelines 41 and low-load pulverized coal pipelines 42 . The conventional pulverized coal pipeline 41 and the pulverized coal pipeline 42 for low load are respectively equipped with shut-off valves 411 and 421. A thick-lean separator 422 is installed on the pulverized-coal pipeline 42 for low load, so that the pulverized-coal gas flow is divided into two streams, thick and light, and enters the thick and light pulverized-coal burners 501, 502 through the thick and light pulverized-coal pipelines 423, 424 respectively. Two layers of thick and light pulverized coal burners 501 and 502 are arranged above the original main burner. When the ultra-low load is put into operation, it is beneficial to increase the height of the furnace flame, increase the temperature of the smoke at the furnace outlet and the temperature of the main and reheated steam.

Wherein, two layers of thick pulverized coal burners 501 are arranged adjacent to each other, so that the heat load is concentrated, and the stability of the pulverized coal airflow on ignition is improved.

At normal load, the boiler operates in the same way as a conventional combustion system. The conventional pulverized coal pipeline 41 is put into operation at the outlet of E and F coal mills. When the load is ultra-low, the boilers put into operation the coal mills E and F, and the outlets of the coal mills E and F put into operation the low-load pulverized coal pipeline 42 . The pulverized coal airflow is divided into two streams, thick and light, by the thick-lean separator, and enters the furnace for combustion through the thick and light pulverized coal burners. Among them, the pulverized coal concentration in the dense pulverized coal airflow has been greatly improved, and can reach the pulverized coal concentration of the pulverized coal airflow at the rated load. The air dust ratio in the dense pulverized coal airflow is low, the ignition heat of the pulverized coal airflow is low, and it can be ignited quickly, which improves the stable combustion ability of the boiler under ultra-low load. At the same time, two layers of dense pulverized coal burners are arranged adjacent to each other to concentrate the heat load of the boiler, which can effectively improve the stable combustion capability of the boiler at low load, and can make the boiler stable at an ultra-low load of 15% to 20% without combustion-supporting measures. combustion.

Claims (7)

1. a kind of combustion system for the combustion of pulverized-coal fired boiler ultra-low load steady, including at least two coal pulverizers (3), primary air fan (2) coal pulverizer (3) air inlet is connected, coal pulverizer (3) outlet is provided with pulverized coal channel (4), it is characterised in that：At least two coal pulverizers (3) pulverized coal channel (4) bifurcated of outlet is conventional pulverized-coal pipeline (41) and underload pulverized coal channel (42)；

Conventional pulverized-coal pipeline (41) connects a wind combustor (5), and a wind combustor (5) is on boiler body (1)；

Underload is provided with dense-and-weak separator (422) with pulverized coal channel (42), and dense-and-weak separator (422) outlet is provided with thick coal culm pipe Road (423), thin powdered coal pipeline (424), thick coal culm pipeline (423) connection thick coal culm burner (501), thin powdered coal pipeline (424) Thin powdered coal burner (502) is connected, thick coal culm burner (501), thin powdered coal burner (502) are on boiler body (1).

A kind of 2. combustion system for the combustion of pulverized-coal fired boiler ultra-low load steady as claimed in claim 1, it is characterised in that：It is described Conventional pulverized-coal pipeline (41), underload are equipped with valve with pulverized coal channel (42).

A kind of 3. combustion system for the combustion of pulverized-coal fired boiler ultra-low load steady as claimed in claim 2, it is characterised in that：Normally During load, the valve on conventional pulverized-coal pipeline (41) is opened, and underload is closed with the valve on pulverized coal channel (42)；15%~ During 20% ultra-low load, the valve on conventional pulverized-coal pipeline (41) is closed, and underload is opened with the valve on pulverized coal channel (42).

A kind of 4. combustion system for the combustion of pulverized-coal fired boiler ultra-low load steady as claimed in claim 1, it is characterised in that：At least The pulverized coal channel (4) of two coal pulverizers (3) outlet has carried out bifurcated, forms an at least two layers dense wind combustor (501), at least Two layers of light wind combustor (502), each dense wind combustor (501) are adjacently positioned.

A kind of 5. combustion system for the combustion of pulverized-coal fired boiler ultra-low load steady as described in claim 1 or 4, it is characterised in that： The thick coal culm burner (501), thin powdered coal burner (502) are above the main burner of boiler body (1).

A kind of 6. combustion system for the combustion of pulverized-coal fired boiler ultra-low load steady as described in claim 1 or 3, it is characterised in that： During normal duty, coal dust enters hearth combustion by conventional pulverized-coal pipeline (41), a wind combustor (5)；15%~20% surpass During underload, coal dust is entered by underload pulverized coal channel (42) and thick coal culm burner (501), thin powdered coal burner (502) Enter hearth combustion.

A kind of 7. combustion system for the combustion of pulverized-coal fired boiler ultra-low load steady as claimed in claim 6, it is characterised in that：It is described During 15%~20% ultra-low load, breeze airflow is divided into dense, light two strands of breeze airflows by dense-and-weak separator (422), passes through respectively Dense, thin powdered coal burner enters hearth combustion；Wherein, the coal powder density of thick coal culm air-flow is compared to before dense-and-weak separator (422) Not separated breeze airflow concentration improve, the coal powder density of breeze airflow when reaching rated load.