CN107461742B

CN107461742B - Graded flameless low-nitrogen combustion head

Info

Publication number: CN107461742B
Application number: CN201710673565.XA
Authority: CN
Inventors: 王磊
Original assignee: Suzhou Boehmer Thermal Energy Products Co ltd
Current assignee: Suzhou Boehmer Thermal Energy Products Co ltd
Priority date: 2017-08-09
Filing date: 2017-08-09
Publication date: 2020-04-28
Anticipated expiration: 2037-08-09
Also published as: CN107461742A

Abstract

A graded flameless low-nitrogen combustion head belongs to the technical field of industrial combustors and boilers. The invention comprises an air pipe, a gas pipe, a connecting flange, an ignition device and an ion induction needle; the gas pipe is arranged inside the air pipe and is connected with the air pipe through a connecting flange; an ignition device and an ion induction needle are also arranged between the air pipe and the gas pipe. The graded flameless low-nitrogen combustion head prepared by the invention can effectively reduce the emission of NOx and CO to below 10ppm during combustion, and can maintain the stability of combustion.

Description

Graded flameless low-nitrogen combustion head

Technical Field

The invention relates to a combustion device with low nitrogen oxide emission, in particular to a graded flameless low-nitrogen combustion head, and belongs to the technical field of industrial combustors and boilers.

Background

According to the detection statistical analysis result of the national gas industrial boiler in 2014, the mass concentration of NOx emission is less than or equal to 200mg/m³The boiler only accounts for 35 percent, and the detection of NOx emission of 37 burners (dual-purpose for both oil and gas) with different models sold in China by China Special Equipment detection research institute discovers that the NOx emission concentration of the burners in a reasonable use state is 54-184 mg/m³Mean concentration of 116 mg/m³. The industrial boiler burner mostly adopts the traditional, forced air supply and diffusion type combustion mode, the main purpose of the type of burner is burnout and safety, and corresponding measures for NOx emission are rarely taken.

Some modifications to the burner head, such as the addition of gas nozzles perpendicular to the air flow, may be used in countries in europe and the united states to achieve NOx emissions below 80 mg/m.

Today, major technical routes that have emerged and adopted for environmental protection requirements for NOx emissions below 30mg/m in some regions include staged combustion, premixed combustion, flue gas recirculation, porous media catalytic combustion and flameless combustion:

(1) fuel staged combustion or air staged combustion:

air staged combustion (as shown in fig. 2) is carried out with fuel rich combustion in the first stage and air excess in the second stage, lean combustion, with air cooling between the stages to ensure that the combustion temperature is not too high. Staged combustion of fuel (as shown in fig. 3) is the exact opposite of staged combustion of air, with the first stage being fuel lean phase combustion and the second stage being fueled to achieve the desired equivalence ratio. Both methods will eventually maintain the excess air ratio of the entire system at a constant value. This technical system is complex and does not eliminate the high temperature zone of the flame.

(2) Lean premixed combustion technology:

premixed combustion refers to complete mixing of fuel and oxidant at the molecular level before ignition of the mixture, and the process flow is shown in fig. 4. An advantage of this technique for controlling NOx production is that control of combustion temperature can be achieved with full control of equivalence ratio, thereby reducing the rate of thermal NOx production, and in some cases premixed combustion and partial premixed combustion can reduce NOx production by 85% -90% over non-premixed combustion. In addition, complete premixing may also reduce the reduction in NOx generation control due to excess air ratio non-uniformity.

If the lean premixed burner is added with the wire mesh burner to form surface combustion, the flame is more dispersed, and the NOx emission is further reduced.

However, the premixed combustion technology still has unsolved technical difficulties in safety control: firstly, the premixed gas may cause backfire due to its high flammability; secondly, the excessive air excess coefficient can cause the increase of the exhaust smoke loss, and the heat efficiency of the boiler is reduced; thirdly, the combustion head of the wire mesh is easily adhered by the melted fine dust, and the maintenance period is short. Today's lean premixed combustors typically do not exceed 2MW in power.

(3) External flue gas recirculation and internal flue gas recirculation techniques: the reduction of the combustion temperature can be achieved by adding flue gas in the flame zone, which absorbs heat and thereby reduces the combustion temperature. Combustion products of the flue gas are added into the combustion area, so that the combustion temperature is reduced, and the generation of NOx is reduced; meanwhile, the added flue gas reduces the partial pressure of oxygen, which weakens the process of generating thermal NOx by oxygen and nitrogen, thereby reducing the generation of NOx. According to different application principles, the flue gas recirculation has two application modes, namely external flue gas recirculation and internal flue gas recirculation.

For external flue gas recirculation techniques, flue gas is reintroduced into the furnace from the outlet of the boiler through an external duct. External flue gas recirculation can reduce NOx generation by 70%. The external circulation proportion also has a larger influence on the NOx control effect, the reduction range of NOx is more obvious along with the increase of the external circulation proportion, but the power consumption of the circulating fan is also increased.

For internal flue gas recirculation, the return of flue gas to the combustion zone is primarily through the gas dynamics of the burner. Internal flue gas recirculation is achieved by rotating the gas stream mainly through entrainment of high velocity jet flames or swirl burners. The external flue gas recirculation system (fig. 5) adds a recirculation cup to the burner head, with high velocity gas flow in between, which re-introduces the flue gas into the combustion zone due to pressure differentials. The internal flue gas recirculation system (figure 6) achieves the recirculation effect through the high-speed airflow nozzles.

By creating an annular recirculation zone in the center of the flame, the hot gases will return to the burner throat, which ensures ignition of the cold, unburned gases, while reducing NOx production by lowering flame temperature and lowering oxygen partial pressure.

The external circulation and the internal circulation of the flue gas have larger size requirements on a combustion hearth, and after the technology is adopted, the manufacturing cost of the boiler is greatly improved.

(4) Catalytic combustion with porous media:

another way to reduce the flame temperature is to enhance the heat transfer from the flame to the outside as quickly and as much as possible. A porous medium (PIM) is added to the burner such that the combustion reaction occurs within the porous medium such that radiant and convective heat transfer from the burner to the surrounding environment is enhanced. Experiments show that the combustion temperature of the PIM burner is lower than 1600K, and the NOx generation amount is about 5-20 ppm.

PIM burners may also add a catalyst at the burner inlet so that the fuel molecules and oxidant molecules react at the catalyst surface with a relatively low activation energy. So that the reaction temperature is lower than in the case of combustion of the same type. Since the reaction process is only carried out on the surface of the catalyst, no NOx is generated, so that the generation of NOx in catalytic combustion can be reduced to 1 ppm.

The defects of catalytic combustion are that the active surface is not oxidized or evaporated at a relatively low temperature, the cost of the catalyst is relatively high, and the catalyst has a poisoning phenomenon in long-term application, so that the combustor is difficult to be applied in a large scale.

(5) Flameless combustion:

the traditional flame combustion is divided into premixed combustion and diffusion combustion, and the main characteristics of the traditional flame combustion comprise that ① fuel reacts with oxygen at high temperature, the higher the temperature is, the more the stability of the flame is facilitated, ② flame peak surface is visible (the flame of methane combustion is generally blue, and yellow when soot is generated), and ③ most of the fuel completes combustion in a very thin flame layer, but the combustion reaction can be completed in a downstream invisible area.

Typically, the flame after ignition generally acts as an igniter itself to ignite the incoming flow. This requires a high enough flame temperature to achieve the minimum ignition energy, but high flame temperatures can lead to increased NOx production.

The flameless combustion of the fuel is realized under the conditions that the temperature in the furnace is 1000 ℃, the air is preheated to 650 ℃ and the flow rate of the air flow is high. And a large amount of backflow high-temperature flue gas is formed by mixing with fresh air by utilizing the position relation between the main combustion nozzles uniformly arranged in an annular mode and the cylindrical backflow structure arranged in the center and the shearing effect of viscous fluid, the temperature of the air is increased, the air is diluted, the diluted high-temperature air is subjected to spontaneous combustion when meeting the fuel, a highly dispersed reaction zone is formed, and accordingly flameless combustion is achieved. For such flameless combustion, flue gas recirculation occurs before combustion, and possibly even during combustion, such recirculated flue gas heats the premixed fuel and air and lowers the combustion temperature, expanding the reaction zone. Flameless combustion flames are evenly distributed and the combustion temperature is low, which results in less NOx production.

This type of flameless combustion generally requires special means or measures for preheating the air.

Disclosure of Invention

The invention aims to overcome the defects and provide the graded flameless low-nitrogen combustion head, which solves the problem of high NOx emission in gas combustion and simultaneously ensures that the NOx emission meets the low emission requirement under the conditions of low load and low air excess coefficient.

According to the technical scheme provided by the invention, the graded flameless low-nitrogen combustion head comprises an air pipe, a gas pipe, a connecting flange, an ignition device and an ion induction needle; the gas pipe is arranged inside the air pipe and is connected with the air pipe through a connecting flange; an ignition device and an ion induction needle are also arranged between the air pipe and the gas pipe.

The air pipe comprises an outer air pipe and an inner air pipe, and a baffle is arranged on one side of the inner air pipe; and a hollow wind cylinder is formed between the outer wind pipe and the inner wind pipe.

And the gas pipe is arranged in the inner air pipe after penetrating through the connecting flange and the baffle.

The gas pipe is welded on the baffle.

The ignition device is positioned above the gas pipe and is fixed between the connecting flange and the baffle; the ion induction needle is positioned below the gas pipe and fixed between the connecting flange and the baffle.

The ignition device is a high-voltage pulse igniter.

A plurality of air jet holes are formed in the inner air pipe; the gas pipe is provided with a plurality of gas jet holes.

The aperture of the air jet hole is 10-40 mm, and the aperture of the fuel gas jet hole is 1-4 mm; the apertures of the air jet hole and the gas jet hole are adjusted in a stepped mode according to the air excess coefficient.

When the air jet type air conditioner runs, air with certain pressure is arranged between the inner air duct and the outer air duct, and the air with certain pressure can be jetted to the center through the air jet flow holes; the center of the combustion device is a gas pipe, and a plurality of gas jet holes are arranged on the gas pipe. When the gas jet nozzle runs, gas with certain pressure in the gas pipe is jetted out through the gas jet hole.

Before the operation, air supply of the air duct is started, then the ignition device is connected with high-voltage pulse electricity, the tip end of the ignition device excites electric sparks, then the gas pipe is connected with gas, and the gas sprayed from the gas spray hole is ignited by the electric sparks. When the gas turbine works normally, the sprayed gas firstly entrains the surrounding smoke at a high speed, and the diluted gas and the sprayed high-speed air which also entrains the smoke move oppositely and are fully mixed and combusted. After normal operation, the ion induction needle induces ion current, and then the ignition device is closed.

The gas ejected at high speed absorbs the smoke gas, so that the concentration of the gas is diluted. The air sprayed at high speed absorbs the smoke gas, so that the oxygen concentration is diluted. In an atmosphere of low fuel gas concentration and low oxygen concentration, the combustion reaction becomes slow. The inner layer of the air duct is in a high-temperature state due to heating, and air in the air duct is preliminarily preheated. The ejected air can be further heated and heated due to entrainment of high-temperature flue gas. The high temperature air-flue gas mixture, the high speed air flow and the slower combustion reaction can form the dispersive flameless combustion, the combustion coreless area and the high temperature area, and the generation of the thermal type and the rapid type nitrogen oxides is reduced.

In addition, the diameters of the jet holes in different areas can be designed to realize different proportions of air supply and fuel gas in different areas, so that staged combustion is formed.

The combustion in the region where the air excess coefficient is less than 1 (generally 0.7 to 0.9) lowers the combustion temperature due to the oxygen-deficient combustion, reducing the generation of nitrogen oxides of the thermal type and the rapid type. Meanwhile, the reducing gas carbon monoxide is generated in the area due to incomplete combustion, and the carbon monoxide can reduce nitrogen oxides generated by combustion into nitrogen and carbon dioxide, so that the emission of the nitrogen oxides is reduced. Meanwhile, the air excess coefficient of some areas is larger than 1.2, and the combustible gas which is not completely combusted in the area with the air excess coefficient smaller than 1 is re-distributed with air for combustion, so that the fuel gas can be completely combusted. Further reducing the emission of nitrogen oxides.

The invention has the beneficial effects that: the graded flameless low-nitrogen combustion head prepared by the invention can effectively reduce the emission of NOx and CO to below 10ppm during combustion, and can maintain the stability of combustion. But also has many advantages over other low NOx combustion technologies: compared with the common staged combustion, the method has the advantages of no obvious flame gathering area, uniform temperature distribution and low CO emission; compared with the lean premixed combustion, the flame-retardant premixed combustion does not cause the phenomenon of tempering or thermoacoustic oscillation and has good flame stability; compared with dilution diffusion combustion (flue gas recirculation), no additional equipment is required, the size of a hearth is not required to be increased, the complexity of a system is not increased, or the problems of unstable combustion and reduced combustion efficiency are caused; compared with the catalytic combustion technology, the cost is lower; compared with other flameless combustion technologies, the flameless combustion technology has the characteristics of staged combustion, lower NOx emission and wider stability interval of flameless combustion.

Drawings

FIG. 1 is a sectional view of the structure of the present invention.

Fig. 2 is a schematic diagram of air staged combustion.

FIG. 3 is a schematic diagram of fuel staging combustion.

FIG. 4 is a process flow diagram of a premixed combustion system.

Figure 5 is a schematic of an external flue gas recirculation system (recirculation hood).

Figure 6 is a schematic of an internal flue gas recirculation system (jet entrainment).

Description of reference numerals: 1. an air duct; 1-1, an outer air duct; 1-2, an inner air pipe; 1-3, a baffle; 2. a gas pipe; 3. a connecting flange; 4. an ignition device; 5. an ion-sensitive needle; 6. an air spout hole; 7. and a gas jet hole.

Detailed Description

As shown in fig. 1: the graded flameless low-nitrogen combustion head comprises an air pipe 1, a gas pipe 2, a connecting flange 3, an ignition device 4 and an ion induction needle 5; the gas pipe 2 is arranged inside the air pipe 1 and is connected with the air pipe through a connecting flange 3; an ignition device 4 and an ion induction needle 5 are further arranged between the air pipe 1 and the fuel gas pipe 2.

The air pipe 1 comprises an outer air pipe 1-1 and an inner air pipe 1-2, and one side of the inner air pipe 1-2 is provided with a baffle 1-3; and a hollow wind cylinder is formed between the outer wind pipe 1-1 and the inner wind pipe 1-2.

The gas pipe 2 penetrates through the connecting flange 3 and the baffle plate 1-3, is arranged in the inner air pipe 1-2, and discharges gas into the inner air pipe 1-2 through the gas jet hole 7.

The gas pipe 2 is welded on the baffles 1-3.

The ignition device 4 is positioned above the gas pipe 2 and is fixed between the connecting flange 3 and the baffle plates 1-3; the ion induction needle 5 is positioned below the gas pipe 2 and is fixed between the connecting flange 3 and the baffle plates 1-3.

The ignition device 4 is a high-voltage pulse igniter.

A plurality of air jet holes 6 are formed in the inner air pipe 1-2; the gas pipe 2 is provided with a plurality of gas jet holes 7.

The aperture of the air jet hole 6 is 10mm-40mm, and the aperture of the fuel gas jet hole 7 is 1mm-4 mm; the aperture of the air jet hole 6 and the aperture of the fuel gas jet hole 7 are adjusted in a stepped mode according to the air excess coefficient.

The classification method of the two is as follows: the rows of air outlet openings close to the connection flange 3 have a relatively small diameter, corresponding to an air excess factor of less than 1 (typically 0.7-0.9), while the rows of air outlet openings remote from the connection flange 3 have a larger diameter, corresponding to an air excess factor of more than 1.2.

It will be obvious to those skilled in the art that, in light of the foregoing description, other variations and modifications may be made without departing from the spirit or scope of the invention as defined by the appended claims. All obvious changes and modifications of the technical solution belonging to the present patent are covered by the protection scope of the present patent.

Claims

1. The graded flameless low-nitrogen combustion head is characterized in that: comprises an air pipe (1), a gas pipe (2), a connecting flange (3), an ignition device (4) and an ion induction needle (5); the gas pipe (2) is arranged inside the air pipe (1) and is connected with the air pipe through a connecting flange (3); an ignition device (4) and an ion induction needle (5) are arranged between the air pipe (1) and the gas pipe (2),

the air pipe (1) comprises an outer air pipe (1-1) and an inner air pipe (1-2), and a baffle (1-3) is arranged on one side of the inner air pipe (1-2);

a hollow wind barrel is formed between the outer wind pipe (1-1) and the inner wind pipe (1-2),

a plurality of air jet holes (6) are arranged on the inner air pipe (1-2); a plurality of gas jet holes (7) are arranged on the gas pipe (2),

the aperture of the air jet hole (6) is 10mm-40mm, and the aperture of the fuel gas jet hole (7) is 1mm-4 mm;

the aperture of the air jet hole (6) and the aperture of the fuel gas jet hole (7) are adjusted in a stepped mode according to the air excess coefficient, the aperture is close to the connecting flange (3), the diameter of the air jet holes (6) in a plurality of rows is relatively small, and the corresponding air excess coefficient is smaller than 1.

2. The staged flameless low nitrogen combustion head as defined in claim 1, wherein: the gas pipe (2) is arranged in the inner air pipe (1-2) after penetrating through the connecting flange (3) and the baffle (1-3).

3. The staged flameless low nitrogen combustion head as defined in claim 2, wherein: the gas pipe (2) is welded on the baffles (1-3).

4. A staged flameless low-nitrogen combustion head as defined in any one of claims 1 to 3, wherein: the ignition device (4) is positioned above the gas pipe (2) and is fixed between the connecting flange (3) and the baffle plates (1-3); the ion induction needle (5) is positioned below the gas pipe (2) and is fixed between the connecting flange (3) and the baffle plates (1-3).

5. The staged flameless low nitrogen combustion head as defined in claim 4, wherein: the ignition device (4) is a high-voltage pulse igniter.