CN101915419B - A method and system for reburning biomass gasification gas in a coal-fired fluidized bed - Google Patents

Abstract

The present invention belongs to a coal-fired fluidized bed for reducing N₂The technical field of O emission, in particular to a method and a system for reburning biomass gasified gas in a coal-fired fluidized bed. Through arranging a plurality of biomass gasified gas nozzles on the wall of the fluidized bed boiler, biomass gasified gas is introduced into the hearth of the fluidized bed boiler, and the biomass gasified gas and pulverized coal in the hearth are combusted to generate N-containing gas₂The O flue gas reacts to realize multi-stage reburning, improve the combustion efficiency of the whole fluidized bed and reduce N₂And (4) discharging O. The invention utilizes the mixed combustion of biomass gasified gas and coal powder, and compared with pyrolysis and direct combustion, the invention is rich in H₂、CH₄The biomass gas of combustible substances such as CO and the like has low ash content and extremely low sulfur content, does not have the problem of desulfurization, is an ideal reburning fuel and can effectively reduce the emission of nitrogen oxides; because the content of alkali metal and chlorine in the gasified gas is lower, the problems of slag bonding and corrosion can be avoided, the utilization of the fly ash can not be influenced, and the efficient clean utilization of the biomass can be realized.

Description

A method and system for reburning biomass gasification gas in a coal-fired fluidized bed

technical field

The invention belongs to the technical field of reducing N ₂ O emissions in a coal-fired fluidized bed, and particularly relates to a reburning method and system of biomass gasification gas in a coal-fired fluidized bed, which can be used for mixed combustion of coal powder and biomass gasification gas, reducing N ₂ O emissions.

Background technique

Circulating fluidized bed power generation technology has developed rapidly in China in recent years. Many 300MW circulating fluidized bed (CFB) power stations have been put into operation. Compared with conventional pulverized coal boilers, circulating fluidized bed boilers have lower NO _x and SO _x emission concentrations. , but another pollutant N ₂ O emission concentration is generally 39 ~ 589mg/Nm ³ , sometimes even up to 786mg/Nm ³ , much higher than the traditional pulverized coal furnace N ₂ O emission level of less than 20mg/Nm ³ . N ₂ O, commonly known as laughing gas, is one of the six greenhouse gases stipulated in the Kyoto Protocol. The harm caused by its emission is mainly manifested in two aspects: strong greenhouse effect and ozone layer destruction. The annual N ₂ O produced by human activities accounts for 31% of the world's total annual production, and more than 80% of the N ₂ O produced by human activities comes from the combustion of fossil fuels. The annual N ₂ O emissions caused by human activities are increasing. Increased at an average rate of about 0.25% per year. The concentration of N ₂ O in the atmosphere has increased from 285ppbv before the industrial revolution to 310ppbv at present, and increases at a rate of 0.2-0.3% per year. N ₂ O can absorb long-wave infrared radiation with central wavelengths of 7.78 μm, 8.56 μm and 16.98 μm, and its contribution to the greenhouse effect is 2.5 times that of CH ₄ , and the warming potential of equimolar concentration N ₂ O is 150 times that of CO ₂ times, the impact on the earth's radiation is about 10-15% of CO ₂ , it can stay in the troposphere for as long as 120 years, and it can be converted into NO when it is transported into the stratosphere, thereby causing the destruction of the ozone layer. The harm of N ₂ O is higher than that of NO more serious. Therefore, while utilizing the advantages of circulating fluidized bed coal combustion technology, corresponding technical measures should be taken to reduce N ₂ O emissions.

Usually, methods to reduce N ₂ O emissions from coal-fired circulating fluidized bed boilers include:

1. The use of catalysts can reduce the decomposition activation energy of N ₂ O. Many metal oxides have a certain decomposition effect on N ₂ O. However, due to the large amount of dust in the flue gas of the fluidized bed, if the catalyst is used to reduce N ₂ O, it may be blocked. or damage the catalyst.

2. Change the combustion conditions, such as staged combustion, staged air intake, excess air coefficient, bed temperature, fuel properties, bed residence time, etc.

等，这些原子、原子团、气体之间的相互作用可能会影响N₂O的生成和分解。而其N₂O分解的反应在窄脉冲电晕放电的条件下和放电的频率、电压和持续时间有关。3. Narrow pulse corona discharge, narrow pulse corona discharge can generate many atoms and atomic groups, like NO ⁺ , O ⁺ ,

etc. The interaction between these atoms, atomic groups, and gases may affect the generation and decomposition of N ₂ O. The N ₂ O decomposition reaction is related to the frequency, voltage and duration of the discharge under the condition of narrow pulse corona discharge.

4. The biomass molding fuel is directly passed into the furnace and mixed with coal powder for combustion. The alkali metal salt and phosphate compound produced by the biomass combustion will cause corrosion and coking to the internal structure of the fluidized bed.

5. It is a simple and easy way to reduce N ₂ O by introducing combustible gas (such as methane) to increase the flue gas temperature, but it needs a special gas pipeline, and its application is affected by the gas grade and economic constraints.

Patent 2501564 discloses a device for denitrification by reburning biomass pyrolysis gas. The device mainly includes a gasifier, a pulverized coal furnace and the connection between them. The air inlet pipe of the gasifier is connected with the tail flue of the pulverized coal furnace, and the air outlet pipe of the gasifier is connected with the hearth of the pulverized coal furnace. The device is mainly used for reducing NO _X emissions of pulverized coal furnaces, and is not suitable for circulating fluidized beds.

Patent 1963299 discloses a method and a boiler system for reducing NO _X emissions by mixing and reburning pulverized coal and biomass. It is characterized in that the reburning zone is divided into a primary reburning zone and a secondary reburning zone, and pulverized coal is sent to the primary reburning zone, and the biomass is sprayed to the secondary reburning zone after drying and grinding pretreatment; in the primary reburning zone It mainly completes the process of pulverized coal pyrolysis and coke generation, and realizes the NO _X reduction reaction in the secondary reburning zone, and utilizes the anoxic condition to favor the combustion of volatile matter and the catalytic reduction effect of coke on the reaction of CO and NO to further reduce the formation in the main combustion zone. NO _X , to achieve the purpose of low emission. The device directly burns biomass, which will cause problems such as coking and corrosion.

Patent 101021316 discloses a method and device for direct biomass reburning and flue gas recirculation. This device also directly utilizes biomass for reburning, which also has problems such as blockage and coking corrosion.

Contents of the invention

The purpose of the present invention is to provide a reburning method of biomass gasification gas in a coal-fired fluidized bed in view of the pollutant N ₂ O emission of the coal-fired circulating fluidized bed in the prior art is much higher than that of ordinary coal-fired boilers.

The technical solution adopted in the present invention is: feed biomass gasification gas into the furnace of the fluidized bed boiler, and ensure that the temperature of the fluidized bed combustion chamber is in a state of 800-980°C; the biomass gasification gas and the coal in the furnace The N ₂ O-containing flue gas produced by powder combustion reacts to realize multi-stage reburning, which improves the combustion efficiency of the entire fluidized bed on the one hand, and improves the emission reduction efficiency of N ₂ O on the other hand.

The biomass gasification gas is combustible gas produced by pyrolysis or gasification of biomass fuel.

The combustible gases include H ₂ , CH ₄ , CO and C _n H _m .

The heat generated by burning coal in the furnace accounts for 85-99%, and the calorific value of biomass gasification gas accounts for 1-15%.

The flow velocity of the biomass gasification gas injected into the furnace is 30-70m/s, and the temperature is 100-700°C.

The present invention also provides a biomass gasification gas reburning system in a coal-fired fluidized bed. The air entering the boiler can be evenly distributed; the feeder connected to the boiler feed port realizes the transportation and feeding of pulverized coal particles through a screw feeder or a belt feeder; the cyclone separator connected to the boiler exhaust port, And a return system connected by a standpipe between the cyclone separator and the boiler return port; 1 to 12 burner nozzles are arranged on the furnace wall along the height of the fluidized bed boiler, and multiple burner nozzles are arranged on the top of the fluidized bed furnace Supplementary combustion air nozzle; a plurality of biomass gasification gas nozzles are arranged between the burner nozzle and the supplementary combustion air nozzle of the fluidized bed boiler wall, and a biomass gasification gas nozzle is arranged at the entrance of the cyclone separator spout.

The biomass gasification gas nozzles are evenly arranged in layers along the furnace height, a total of 1 to 4 layers, and each layer is arranged with four biomass gasification gas nozzles, and the biomass gasification gas nozzles of each layer are cut into circles at four corners Arrangement, so that the flue gas in the boiler is rotated and burned, and the mixing is strengthened; the bottom layer of the biomass gasification gas nozzle is 1.5-3m away from the air distribution plate at the bottom of the fluidized bed boiler.

The burners are evenly arranged in layers along the furnace height, and four burner nozzles are arranged in each layer, and the burner nozzles in each layer are arranged in a manner of cutting circles at four corners.

The supplementary combustion air nozzles are evenly arranged in layers along the furnace height, and four supplementary combustion air nozzles are arranged in each layer, and the supplementary combustion air nozzles in each layer are arranged in a manner of tangential circle at four corners.

The beneficial effects of the present invention are: because the biomass has different shapes and is not easy to be broken, the mixing before combustion and direct co-combustion will cause problems such as blockage of the fuel bin; Slagging and corrosion are likely to occur during internal high-temperature combustion, which may affect the utilization of co-combustion ash, and may also affect the service life of subsequent denitrification system catalysts. The present invention provides a biomass gasification gas reburning system in a coal-fired fluidized bed, which is a system that processes biomass to generate biomass gasification gas and then sends it to the furnace combustion zone of a coal-fired fluidized bed to reduce NO _X way of burning. Using the mixed combustion of biomass gasification gas and coal powder, compared with pyrolysis and direct combustion, the biomass gas rich in combustible substances such as H ₂ , CH ₄ and CO has low ash content and extremely low sulfur content, so there is no desulfurization problem , is an ideal reburning fuel, which can effectively reduce the emission of nitrogen oxides; due to the low content of alkali metals and chlorine in the gasification gas, it can avoid slagging and corrosion problems, and will not affect the utilization of fly ash, and can realize production Efficient and clean utilization of materials. This technology can gasify and burn biomass such as agricultural and forestry waste near the power plant in the power plant, which not only utilizes the energy in the biomass, but also reduces nitrogen oxide emissions and flue gas treatment costs, and realizes the reuse of agricultural and forestry waste. .

Description of drawings

Fig. 1 is a schematic structural view of the present invention.

Labels in the figure:

1-air chamber, 2-fluidized bed boiler, 3-feeder, 4-burner nozzle, 5-biomass gasification gas nozzle, 6-combustion air nozzle, 7-cyclone separator, 8-return material system.

Detailed ways

The present invention provides a method and system for reburning biomass gasification gas in a coal-fired fluidized bed. The present invention will be further described below through the description of drawings and specific implementation methods.

As shown in Figure 1, the air chamber 1 is arranged below the fluidized bed boiler 2, and the lower part of the furnace of the fluidized bed boiler 2 is equipped with an air distribution plate, so that the air entering the boiler can be evenly distributed; the feeder 3 is connected to the boiler feed port , through the screw feeder or belt feeder to realize the conveying and feeding of pulverized coal particles; arrange 1 to 12 burner nozzles 4 and 1 to 12 supplementary combustion air on the furnace wall along the height direction of the fluidized bed boiler 2 nozzle 6, and arrange 4 to 12 biomass gasification gas nozzles 5 between the burner nozzle 4 and the supplementary combustion air nozzle 6, the burner nozzle 4, the biomass gasification gas nozzle 5 and the supplementary combustion air nozzle 6 Evenly arranged in layers, each layer is arranged in a way of cutting circles at four corners, so that the flue gas in the boiler can be rotated and burned, and the mixing can be strengthened; the cyclone separator 7 is connected to the exhaust port of the boiler, and between the cyclone separator 7 and the boiler return port A feed-back system 8 is set up through a standpipe connection between them; a biomass gasification gas nozzle is arranged at the entrance of the cyclone separator 7 .

The biomass gas injected into the biomass gasification gas nozzle is biomass fuel (agricultural, forestry, animal husbandry waste and domestic garbage, etc.) through pyrolysis or gasification (air gasification, water vapor gasification, _H2 gasification and Combustible gases produced by composite gasification, etc.), including H ₂ , CH ₄ , CO and C _n H _m . The biomass gasification gas is injected from the biomass gasification gas nozzle 5, and mixed with the pulverized coal fuel injected from the fuel inlet 3 feeder in the fluidized bed boiler 2 under the action of the air volume provided by the combustion air chamber 1 Combustion, during the combustion reaction process, the fluidized bed combustion chamber is at a temperature of 800-980°C. The flue gas generated by combustion is discharged from the top of the furnace and flows into the cyclone separator 7, and the combustible gas is injected into the biomass gasification gas nozzle 5 at the entrance of the cyclone separator 7 to react with the N ₂ O in the combustion flue gas. Under the action of the air flow, part of the solid fuel is brought into the cyclone separator 7, and the cyclone separator 7 realizes gas-solid separation, the gas is discharged from the top of the cyclone separator 7, and the solid flows from the bottom of the separator 7 to the fluidized bed boiler 2 The connected feeder 8 realizes material circulation. Considering the characteristics of the actual circulating fluidized bed, other auxiliary reagents such as desulfurization agent calcium oxide can be injected into the fluidized bed combustion chamber of the device at the same time to ensure low emissions of NO _X and SO _X in the combustion products.

Example 1:

Biomass gasification gas reburning system in 135MW circulating fluidized bed boiler.

In this embodiment, the present invention is used to replace the original combustion method to reduce N ₂ O emissions. 135MW circulating fluidized bed boiler, fuel low calorific value is 12435kJ/kg, fuel consumption is 78230kg/h. Annual consumption of 200,000 tons of biomass, biomass gasification temperature 680 ℃. In this embodiment, 3m up from the air distribution plate to the top of the furnace, there are 7 stages of combustion nozzles arranged according to the four corners tangentially, of which the bottom 2 stages are burner nozzles, and the middle 3 stages are biomass gasification gas nozzles. The biomass gas flow rate is 42m/s, and the top two stages are supplementary combustion air nozzles.

The boiler uses a biomass gasification gas reburning system. The calorific value of biomass gas accounts for 13.22% of the total calorific value, and the biomass gas accounts for 8.89% of the flue gas, which can reduce coal consumption by 13.22% and make N ₂ O The removal efficiency reaches over 99%.

Example 2:

Biomass gasification gas reburning system in 300MW circulating fluidized bed boiler.

In this embodiment, by adding biomass gasification gas nozzles around the furnace, the combustion system is transformed into a combustion system for fuel graded biomass gasification gas reburning. 300MW circulating fluidized bed boiler, fuel low calorific value is 19887kJ/kg, fuel consumption is 148600kg/h. Annual consumption of 200,000 tons of biomass, biomass gasification temperature 690 ℃. In this embodiment, from 2.5m up from the air distribution plate to the top of the furnace, there are 6 stages of combustion nozzles arranged in accordance with the four-corner tangential circle, which are respectively 2-stage burner nozzles, 2-stage biomass gasification gas nozzles, and 2-stage supplementary combustion The air nozzle, the flow rate of the biomass flow into it is 40m/s.

The boiler uses a biomass gasification gas reburning system. The calorific value of biomass gas accounts for 4.35% of the total calorific value, and the biomass gas accounts for 2.8% of the flue gas, which can reduce coal consumption by 4.35% and make N ₂ O The removal efficiency reaches over 99%.

Claims (8)

1. a coal-fired fluidized bed middle biomass gasified gas re-burning mode is characterized in that, in the burner hearth of fluidized-bed combustion boiler, feeds biomass gasified gas, and biomass gasified gas is the fuel gas that biomass fuel produces through pyrolysis or gasification mode; Biomass gasified gas injects from the biomass gasified gas spout; With the coal dust fuel that injects from the fuel inlet feeder; Provide under the effect of air air quantity at burning wind air compartment, mixed combustion in fluidized-bed combustion boiler, and guarantee that fluidized bed combustion chamber is in 800～980 ℃ state of temperature; Burning produces flue gas and discharges from roof of the furnace and flow into cyclone separator, re-injects the N in biomass gasified gas and the combustion product gases at the biomass gasified gas spout of cyclone inlet ₂O reacts; The flow velocity that said biomass gasified gas sprays into burner hearth is 30～70m/s, and temperature is 100～700 ℃; Under the effect of air-flow, the part solid fuel is brought into cyclone separator, and cyclone separator is realized gas solid separation, and gas is discharged from the cyclone separator top, and down-comer flows to the material returning device that is connected with fluidized-bed combustion boiler to solid from the separator bottom, realizes the material circulation; Coal dust firing produces in this biomass gasified gas and the burner hearth contains N ₂The O flue gas reacts, and realizes multistage combustion again, improves the efficiency of combustion of whole fluid bed on the one hand, improves N on the other hand ₂The emission reduction efficiency of O.

2. a kind of coal-fired fluidized bed middle biomass gasified gas re-burning mode according to claim 1 is characterized in that said fuel gas comprises H ₂, CO and C _nH _m

3. a kind of coal-fired fluidized bed middle biomass gasified gas re-burning mode according to claim 2 is characterized in that said C _nH _mBe in particular CH ₄

4. a kind of coal-fired fluidized bed middle biomass gasified gas re-burning mode according to claim 1 is characterized in that the coal-fired heat that produces accounts for 85～99% in the said burner hearth, and the caloric value of biomass gasified gas accounts for 1～15%.

5. use the combustion system again of any one coal-fired fluidized bed middle biomass gasified gas re-burning mode of claim 1 to claim 4; It is characterized in that; Longshore current fluidized bed boiler height is arranged 1～12 burner on the furnace wall, and at the roof of the furnace of fluidized-bed combustion boiler a plurality of afterburning air ports is set; Between the burner nozzle of said fluidized-bed combustion boiler furnace wall and afterburning air port, a plurality of biomass gasified gas spouts are set, and arrange 1 biomass gasified gas spout at the cyclone inlet place.

6. the system of firing again according to claim 5; It is characterized in that: said biomass gasified gas spout is along the uniform layered arrangement of furnace height; Totally 1～4 layer, arrange four biomass gasified gas spouts for every layer, every layer of biomass gasified gas spout all arranged by the mode of quadrangle tangential circle; Make the interior flue gas of boiler be rotated burning, enhancing mixed; Air distribution plate 1.5～the 3m of undermost biomass gasified gas jet opening distance fluidized-bed combustion boiler bottom.

7. the system of firing again according to claim 5 is characterized in that: said burner nozzle is arranged four burner nozzles for every layer along the uniform layered arrangement of furnace height, and every layer of burner nozzle all arranged by the mode of quadrangle tangential circle.

8. the system of firing again according to claim 5 is characterized in that: said afterburning air port is arranged four afterburning air ports for every layer along the uniform layered arrangement of furnace height, and every layer of afterburning air port all arranged by the mode of quadrangle tangential circle.

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