WO2020259576A1

WO2020259576A1 - Forced internal flue gas circulation furnace

Info

Publication number: WO2020259576A1
Application number: PCT/CN2020/098075
Authority: WO
Inventors: 方振明; 陈勇强; 郑向阳; 陈伟
Original assignee: 浙江先创能源科技股份有限公司
Priority date: 2019-06-28
Filing date: 2020-06-24
Publication date: 2020-12-30
Also published as: CN210462982U

Abstract

A forced internal flue gas circulation furnace, comprising a combustion chamber (4), a forced internal flue gas circulation system, a flue gas exhaust pipe (5), a chimney (6), a fuel outlet (7), a combustion air channel (8), and a blower (10). The forced internal flue gas circulation system comprises a variable frequency fan (3), an electric regulation valve, a circulation flue gas inlet, and a circulation flue gas outlet (9). An air inlet of the variable frequency fan (3) communicates with the combustion chamber (4). An air outlet of the variable frequency fan (3) communicates with the circulation flue gas inlet. A hollow flared nozzle (1) is detachably installed at the flue gas outlet (9). The nozzle (1) comprises an air incoming end surface and a termination end surface that have a circular cross-sections. The air incoming end surface, the termination end surface, and a side surface enclose to from a hollow cavity. A series of apertures (2) are provided on the side surface for outputting a circulation flue gas. The air incoming end surface of the flared nozzle has an area smaller than that of the termination end surface. The air incoming end surface is a hollow circular pipe, and the termination end surface is a closed planar surface. The furnace enables adjustment of the amount of circulation of a flue gas, thereby reducing NOx in the flue gas.

Description

Forced internal circulation boiler for flue gas

Technical field

The utility model belongs to the technical field of environmentally friendly combustion, and particularly relates to a flue gas forced internal circulation boiler.

Background technique

With increasing environmental pollution and increasingly scarce energy, people are paying more and more attention to energy saving and emission reduction through new combustion methods. Among them, the flue gas recirculation technology has the advantages of reducing NOx emissions and improving combustion efficiency. It is widely used in industrial burners, boilers and other fields, and has achieved good energy-saving and emission-reduction effects. The reasonable design of the realization form of the flue gas recirculation, the circulation temperature, and the circulation volume can effectively improve the combustion, reduce the pollution emission and improve the combustion efficiency, and it is one of the important methods of energy saving and emission reduction.

Flue gas recirculation refers to taking a part of low-temperature flue gas before the air preheater of the boiler and directly sending it into the furnace, or mixing it with primary air or secondary air and sending it into the furnace. This can not only reduce the combustion temperature, but also Reduce the oxygen concentration, thereby reducing the emission concentration of nitrogen oxides.

The internal circulation of the flue gas of the existing domestic and foreign low-nitrogen burners is a passive circulation, and the supply and quantity cannot be adjusted according to the actual demand. The external circulation of the flue gas needed to dilute the oxygen content of the combustion-supporting air needs to be realized through the combustion-supporting air supply pipeline, thereby increasing about 20% of the incombustible medium in the air duct, burner, furnace, convection tube, and waste heat boiler , Air preheater, flue and air duct between the long flow cycle, the circulation flow will inevitably increase energy consumption.

Summary of the invention

In order to solve the disadvantages of the uncontrollable flue gas recirculation in the furnace in the prior art and the low energy consumption of the flue gas recirculation outside the furnace, the utility model discloses a gas-fired low-nitrogen combustion boiler with forced internal circulation. The traditional external circulation consists of Cycle substitutions.

The utility model sucks a part of the flue gas directly back to the fuel nozzle of the furnace burner by circulating in the middle flue gas temperature area inside the boiler, directly mixes with fuel, dilutes the fuel to reduce the concentration of mixing with oxygen, thereby reducing the combustion temperature. The outlet of the circulating flue gas is equipped with a horn-shaped nozzle, and the nozzle cavity is filled with a denitrification adsorbent to reduce the content of nitrogen oxides in the circulating flue gas. At the same time, the exhaust hole of the flue gas on the nozzle is designed to make the circulating flue gas uniform The ground is ejected in the form of a launching device, fully mixed with fuel, and the amount of circulating flue gas is controlled by adjusting the frequency of the circulating fan or adjusting the damper. Through online monitoring of the NOx concentration in the flue gas discharge pipe, the frequency of the circulating fan and the flow rate of the combustion-supporting wind are continuously adjusted to obtain the optimal parameters to reduce the NOx concentration in the exhaust flue gas.

In order to achieve the above objectives, the technical solutions adopted by this utility model are as follows:

A flue gas forced internal circulation boiler, which is characterized by comprising a furnace, a flue gas forced internal circulation system, a flue gas discharge pipe, a chimney, a fuel outlet, a combustion-supporting air passage, and a blower. The flue gas forced internal circulation system includes a frequency conversion fan , Electric regulating valve, circulating flue gas inlet and circulating flue gas outlet, the frequency conversion fan is fixedly installed on the outer side wall of the furnace, the air inlet of the frequency conversion fan is connected with the furnace, and the air outlet of the frequency conversion fan is connected with the circulating smoke inlet. The outlet of the circulating flue gas is in the furnace, the electric regulating valve is installed on the pipe between the inlet of the circulating flue gas and the outlet of the circulating flue gas, the inlet of the flue gas discharge pipe is in the upper part of the furnace, and the outlet is connected to the chimney outside the furnace. The inlet of the combustion-supporting air channel is connected to the blower outside the furnace, and the outlet of the combustion-supporting air channel is in the furnace;

The flue gas outlet is detachably installed with a hollow trumpet-shaped nozzle. The nozzle includes an air inlet end face and a terminal end face with a circular cross section. The air inlet end face, the end section and the side face enclose a hollow cavity, so A series of small holes for outputting circulating flue gas are opened on the side.

Further, the area of the air inlet end face of the horn-shaped nozzle is smaller than the area of the end end face, the air inlet end face is a hollow round tube, and the end section is a closed plane.

Further, the side surface of the nozzle is provided with a series of small holes along the circumferential direction, and the small holes are distributed on the mutually parallel cross sections of the horn-shaped nozzle, and the shape is a circle or an ellipse.

Further, the horn-shaped nozzle is filled with particulate denitrification adsorbent, and the particles are spherical and have a particle size of 0.5-3 cm. The adsorbent is one or more of molecular sieve, activated carbon, activated coke, natural zeolite or peat.

Further, the frequency conversion fan is used to adjust the inhalation of the circulating flue gas, and the frequency of the frequency conversion fan is set to 10-50HZ.

Further, the electric regulating valve is used to regulate the outflow of circulating flue gas, and the valve opening of the electric regulating valve is set to 5-95%.

Further, a NOx online monitoring instrument is provided on the flue gas discharge pipe to detect the content of NOx in the flue gas discharged through the chimney.

Further, a flow controller is provided on the combustion-supporting air passage for adjusting the flow of the combustion-supporting air.

The beneficial effects of the utility model are as follows:

Part of the flue gas is sucked in the middle flue gas temperature area inside the boiler by the induced draft fan and returned directly to the fuel nozzle of the furnace burner, mixed with the fuel, and diluted the fuel and oxygen concentration, thereby reducing the combustion temperature and reducing the NOx production.

(1) The recirculated flue gas of the present invention is directly mixed with fuel, which is highly targeted, has a simple pipeline structure, and reduces equipment costs;

(2) The circulating flue gas is forced to circulate by the fan, and the flue gas circulation volume can be controlled by the fan motor frequency or the air regulating valve. According to the NOx content in the flue gas discharged by the boiler, the flue gas circulation volume is adjusted, under the condition that the boiler is satisfied , To maximize the flue gas circulation and reduce the NOx in the emitted flue gas as much as possible;

(3) The recirculated flue gas circulates in the furnace and the flue gas forced internal circulation system. Due to the short flow and low resistance, the power consumed by the motor is small.

(4) The outlet of the circulating flue gas is equipped with a horn-shaped nozzle, so that the circulating flue gas is evenly ejected in a launching device. The nozzle cavity is filled with a denitrification adsorbent to reduce the nitrogen oxide content in the circulating flue gas .

Description of the drawings

Figure 1 is a schematic structural diagram of a boiler with forced internal circulation of flue gas;

Figure 2 is a top view of a circulating flue gas outlet nozzle of a flue gas forced internal circulation boiler;

In the figure, 1 is the flue gas outlet nozzle, 2 is the small hole of the nozzle, 3 is the frequency conversion fan, 4 is the furnace, 5 is the flue gas discharge pipe, 6 is the chimney, 7 is the fuel outlet, 8 is the combustion air channel, 9 is Circulation outlet, 10 is a blower.

Detailed ways

The embodiments of the present invention will be further described below in conjunction with the drawings.

Example 1

A flue gas forced internal circulation boiler, including a furnace 4, a flue gas forced internal circulation system, a flue gas discharge pipe 5, a chimney 6, a fuel outlet 7, a combustion-supporting air channel 8, a blower 10, and the flue gas forced internal circulation system includes a frequency conversion fan 3. Electric regulating valve, circulating flue gas inlet and circulating flue gas outlet 9, frequency conversion fan 3 is fixedly installed on the outer side wall of furnace 4, the air inlet of frequency conversion fan 3 is connected to furnace 4, and the air outlet of frequency conversion fan is connected to the circulating flue gas inlet Connected, the frequency conversion fan sucks a part of the flue gas from the middle flue gas temperature area inside the boiler and directly returns to the fuel nozzle of the furnace burner. The frequency of the frequency conversion fan is set to 10-50HZ. The circulating flue gas and fuel are evenly mixed and then burned, which is beneficial to reduce the fuel concentration, thereby reducing the temperature in the furnace and reducing the generation of nitrogen oxides. An electric regulating valve is installed on the pipe between the circulating flue gas inlet and the circulating flue gas outlet to control the inhalation of the circulating flue gas. The valve opening of the electric regulating valve is set to 5-95%. When the temperature in the furnace is too high When it is detected that the nitrogen oxide content emitted by the chimney is increased, the inhalation of the circulating flue gas is increased, and the fuel concentration is further diluted; when the temperature in the furnace is low and the boiler power is insufficient, the inhalation of the circulating flue gas is reduced. The fuel concentration increases, the flame range increases, and the temperature increases. The inlet of the flue gas discharge pipe 5 is in the upper part of the furnace, and the outlet is connected to the chimney outside the furnace, which is used to directly discharge part of the flue gas in the furnace from the chimney. The flue gas discharge pipe is provided with an online NOx monitoring instrument for detecting passing Describe the NOx content in the flue gas emitted by the chimney. The inlet of the combustion-supporting air channel is connected to the blower outside the furnace, and the outlet of the combustion-supporting air channel is in the furnace, and is used to provide an oxygen source for the fuel in the furnace.

The flue gas outlet is detachably installed with a hollow horn-shaped nozzle 1. The nozzle includes an air inlet end face and a terminal end face with a circular cross section. The air inlet end face, the end section and the side face are enclosed in a hollow cavity. There are a series of small holes 2 for the output of circulating flue gas. The area of the air inlet end face of the horn-shaped nozzle is smaller than the area of the end end face, the air inlet end face is a hollow round tube, and the end end face is a closed plane. When the circulating flue gas flows in quickly from the nozzle inlet, it quickly reaches the closed end surface. After the air flow is turned back, the momentum is reduced, and it is sprayed out from the small holes on the side. The flue gas is uniformly output from around the nozzle. The flue gas is dense and uniform, and the impact force is weak. , It is conducive to mixing with fuel under stable conditions, reducing the impact of air flow in the furnace.

A series of circular or elliptical small holes are opened on the side of the nozzle along the circumferential direction. The small holes are distributed on each parallel cross section of the horn-shaped nozzle, which is equivalent to the spiral distribution of the nozzles on the side of the nozzle, which is beneficial to smoke. Uniform and stable output.

The detachable horn-shaped nozzle is filled with granular denitrification adsorbent, and the granules are spherical and have a particle diameter of 0.5-3 cm. The adsorbent is one or more of molecular sieve, activated carbon, activated coke, natural zeolite or peat. The flue gas passing through the nozzle is used to remove nitrogen oxides with an adsorbent. Because the nozzle is detachable, the adsorbent with saturated adsorption capacity can be easily replaced. In addition, the cost of the adsorbent is low, and the recovered adsorbent can be reused after treatment.

The following examples further illustrate the use of the burner with low nitrogen oxide emissions.

Example 2

A boiler with forced internal circulation of flue gas, the blower is turned on, the combustion-supporting air is input into the furnace through the combustion-supporting air channel, the fuel outlet is ignited, the frequency conversion fan is turned on, and the flue gas in the furnace is sucked into the circulating flue gas inlet, and the smoke is discharged through the circulating flue gas outlet. Gas and fuel are mixed, and the NOx content in the flue gas discharged through the chimney is detected under the premise of meeting the strength of the boiler. When the NOx in the discharged flue gas is greater than 30mg/Nm ³ , the cycle is increased through the electric control valve and the motor frequency For the outflow of flue gas, the maximum valve opening is 95%, and the motor frequency is between 10 and 50 Hz.

The application of the utility model can save energy consumption and save about 50% of the motor power consumption compared with the existing flue gas external circulation technology. Taking a certain type of boiler (25t/h) as an example, when the same flue gas recirculation volume is reached, the flow resistance of flue gas recirculation is only 2000Pa, which only needs to consume about 15kw of power. At the same time, the required circulation cross-sectional area of all equipment (boiler host, waste heat boiler, flue, air duct, air preheater) can be reduced by 20%, which can save about 20% of equipment cost. And the NOx emission index of the gas heat conduction oil boiler can reach <30mg/m3.

Claims

A flue gas forced internal circulation boiler, which is characterized by comprising a furnace, a flue gas forced internal circulation system, a flue gas discharge pipe, a chimney, a fuel outlet, a combustion-supporting air passage, and a blower. The flue gas forced internal circulation system includes a frequency conversion fan , Electric regulating valve, circulating flue gas inlet and circulating flue gas outlet, the frequency conversion fan is fixedly installed on the outer side wall of the furnace, the air inlet of the frequency conversion fan is connected with the furnace, and the air outlet of the frequency conversion fan is connected with the circulating smoke inlet. The outlet of the circulating flue gas is in the furnace, the electric regulating valve is installed on the pipe between the inlet of the circulating flue gas and the outlet of the circulating flue gas, the inlet of the flue gas discharge pipe is in the upper part of the furnace, and the outlet is connected to the chimney outside the furnace. The inlet of the combustion-supporting air channel is connected to the blower outside the furnace, and the outlet of the combustion-supporting air channel is in the furnace;

The flue gas outlet is detachably installed with a hollow trumpet-shaped nozzle. The nozzle includes an air inlet end face and a terminal end face with a circular cross section. The air inlet end face, the end section and the side face enclose a hollow cavity, so A series of small holes for outputting circulating flue gas are opened on the side.
The flue gas forced internal circulation boiler according to claim 1, wherein the area of the inlet end face of the horn-shaped nozzle is smaller than the area of the termination end face, the inlet end face is a hollow round tube, and the termination end face is a closed Plane.
The flue gas forced internal circulation boiler according to claim 1, characterized in that a series of small holes are formed on the side of the nozzle along the circumferential direction, and the small holes are distributed on each parallel cross section of the horn-shaped nozzle.
The flue gas forced internal circulation boiler according to claim 3, wherein the shape of the small hole is a circle or an oval.
The flue gas forced internal circulation boiler according to claim 1, wherein the horn-shaped nozzle is filled with particulate denitrification adsorbent, the particles are spherical and have a particle size of 0.5-3 cm.
The flue gas forced internal circulation boiler according to claim 5, wherein the adsorbent is one or more of molecular sieve, activated carbon, activated coke, natural zeolite or peat.
The flue gas forced internal circulation boiler according to claim 1, wherein the frequency conversion fan is used to adjust the inhalation amount of the circulating flue gas, and the frequency of the frequency conversion fan is set to 10-50HZ.
The boiler for forced internal circulation of flue gas according to claim 1, wherein the electric regulating valve is used to regulate the outflow of circulating flue gas, and the valve opening of the electric regulating valve is set to 5-95%.
The flue gas forced internal circulation boiler according to claim 1, wherein the flue gas discharge pipe is provided with a NOx online monitoring instrument for detecting the content of NOx in the flue gas discharged through the chimney.
The flue gas forced internal circulation boiler according to claim 1, wherein a flow controller is provided on the combustion-supporting air passage for adjusting the flow of the combustion-supporting air.