High-stability biomass oxygen-enriched combustion circulating fluidized bed vertical partition pressure and CO concentration control method

Abstract

The invention relates to the technical field of biomass circulating combustion, and discloses a high-stability biomass oxygen-enriched combustion circulating fluidized bed vertical partition pressure and CO concentration control method.The system comprises a flue gas pretreatment unit, a hearth, a cyclone separator, a preheater and a dust remover, and the flue gas pretreatment unit comprises an induced draft fan, a flue gas cooler and a flue gas separator; a carbon monoxide monitoring device is arranged on the flue between the induced draft fan and the dust remover, and an oxygen concentration monitoring device is arranged on the flue between the hearth and the cyclone separator; the interior of the hearth is set to be micro-positive pressure, the pressure P1 of the lower middle portion of the hearth is 50-200 Pa, and the pressure P2 of the upper middle portion of the hearth is P1-alpha * H-100 Pa. According to the technical scheme, the internal pressure of the hearth is controlled to be micro-positive pressure, external air is reduced or prevented from leaking into the hearth, and the air leakage problem of the hearth is solved; the problem that the concentration of carbon monoxide in smoke is too high is solved in the mode that oxygen is injected into the flue to increase the smoke oxygen concentration and the hearth temperature, and the problems of energy loss and potential safety hazards existing in the biomass oxygen-enriched combustion process are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass circulating combustion, and particularly relates to a method for controlling the vertical partition pressure and CO concentration in a high-stability biomass oxy-fuel combustion circulating fluidized bed. Background Art

[0002] BECCS (Bioenergy with Carbon Capture and Storage) technology refers to the process of capturing, utilizing, or storing CO2 generated during the combustion or conversion of biomass. Since the carbon in biomass is derived from carbon dioxide in the air fixed by photosynthesis, BECCS technology, like direct air capture (DAC) technology, is a process that can achieve negative carbon emissions. Under new application scenarios and deep emission reduction requirements, the connotation and extension of CCUS technology are continuously enriched and expanded. The capture sources have gradually expanded from traditional energy / industrial facilities to neutral carbon sources such as biomass and air, and BECCS technology has also become a necessary means to achieve climate goals.

[0003] Oxy-fuel combustion is a highly potential carbon capture technology. It uses pure oxygen to replace air as the combustion-supporting gas in the combustion system, and part of the flue gas generated after combustion is recycled and mixed with oxygen to enter the furnace as boiler air supply to support combustion, so that the carbon dioxide in the flue gas is continuously concentrated, thereby greatly increasing the carbon dioxide concentration in the combustion flue gas. For the boiler oxy-fuel combustion system, in order to maximize the carbon dioxide concentration in the flue gas after combustion, it is necessary to strictly control the air leakage rate of the combustion system and reduce the amount of air leakage.

[0004] In addition, although oxy-fuel combustion technology has been developed for decades and demonstration projects have been built, the current research on oxy-fuel combustion technology still mainly focuses on pulverized coal boilers, and there is still relatively little research on oxy-fuel combustion technology for biomass boilers, especially for biomass circulating fluidized bed boilers. There is still a lack of technology in this field. On the one hand, due to the relatively low combustion temperature of biomass, incomplete combustion is likely to occur, and the carbon monoxide concentration in the flue gas is often relatively high. During oxy-fuel combustion, since the carbon monoxide concentration in the flue gas circulation will further increase, in addition to causing energy waste, there are also potential safety hazards. On the other hand, the feeding method of biomass boilers often adopts open feeding, and it is difficult to control the air leakage rate. Therefore, it is necessary to carry out innovative transformation on the existing oxy-fuel combustion technology, take necessary measures to improve the airtightness of the system, reduce the air leakage rate, and solve problems such as carbon monoxide enrichment to adapt to the characteristics of circulating fluidized bed biomass boilers.

[0005] At present, the oxy-fuel combustion of biomass circulating fluidized bed boilers generally follows the oxy-fuel combustion technology scheme of pulverized coal boilers. The current general oxy-fuel combustion scheme is to adopt the method of recirculating flue gas + pure oxygen injection. By changing the composition of the boiler combustion-supporting gas (from O2 / N2 to O2 / CO2), the oxy-fuel combustion of the fuel is realized, and then combined with the airtightness control of the boiler system, the CO2 concentration in the flue gas is finally increased. In terms of air leakage control, the method of physical sealing of holes and slightly positive pressure in the whole furnace is generally adopted. In terms of carbon monoxide concentration control, no relevant literature reports on the carbon monoxide control scheme for biomass oxy-fuel combustion have been found. At present, to solve this problem, the combustion is usually promoted by optimizing the air distribution. Chinese Patent CN113187571 A discloses a biomass pure oxygen combustion power generation system and method, which realizes the biomass pure oxygen combustion by mixing the oxygen produced as a by-product of electrolyzing water with the recirculating flue gas. Although the method provided by this patent realizes the biomass pure oxygen combustion, it does not consider the control of the ratio of oxygen to flue gas, and does not conduct quality control on the recirculating flue gas, which may cause the problem of unstable boiler combustion. Summary of the Invention

[0006] The present invention aims to provide a method for controlling the vertical partition pressure and CO concentration of a high-stability biomass oxy-fuel combustion circulating fluidized bed, so as to solve the problems of too high carbon monoxide concentration in the flue gas during the oxy-fuel combustion of biomass circulating fluidized bed boilers in the prior art and the unstable boiler combustion caused by the physical sealing and positive pressure methods.

[0007] To achieve the above object, the present invention adopts the following technical scheme: A high-stability biomass oxy-fuel combustion circulating fluidized bed vertical partition pressure and CO concentration control system, including a flue gas pretreatment unit, a furnace, a cyclone separator, a preheater and a dust collector. The flue gas pretreatment unit includes a induced draft fan, a flue gas cooler and a flue gas separator. A carbon monoxide monitoring device is arranged on the flue between the induced draft fan and the dust collector, and an oxygen concentration monitoring device is arranged on the flue between the furnace and the cyclone separator; The inside of the furnace is set to be slightly positive pressure, and the pressure P1 in the middle and lower part of the furnace is 50 - 200 Pa, and the pressure in the upper part of the furnace is P2 = P1 - α×H - 100 Pa, where α is the control coefficient = 5 - 8, and H is the effective height of the furnace combustion area in m.

[0008] Preferably, as an improvement, it further includes an oxygen supply module. The oxygen supply module is connected with an oxygen injection fan. An air inlet is arranged on the flue between the top outlet of the furnace and the cyclone separator, and an oxygen injection pipeline is arranged between the oxygen injection fan and the air inlet.

[0009] Preferably, as an improvement, a reduced diameter part is arranged in the middle of the furnace. The cross-sectional area of the reduced diameter part is smaller than the cross-sectional areas at both ends of the furnace. The relationship between the cross-sectional area A2 of the reduced diameter part in the middle of the furnace and the cross-sectional area A1 at both ends of the furnace is A2 = βA1, where β is the reduced diameter coefficient, and the value range of β is 0.65 - 0.9.

[0010] Preferably, as an improvement, the relationship between the vertical height H2 at the reduced diameter of the furnace and the effective combustion height H of the furnace is H2 = δH, where δ is a control coefficient, and the value range of δ is 0.05 - 0.1.

[0011] Preferably, as an improvement, a method for controlling the vertical partition pressure and CO concentration in a high-stability biomass oxy-fuel combustion circulating fluidized bed includes the following steps:

[0012] I. After the biomass completes oxy-fuel combustion in the furnace, the generated flue gas enters the cyclone separator under the action of the induced draft fan. The unburned fuel is separated and returned to the furnace from the return feeder at the bottom of the cyclone separator. The flue gas enters the tail flue from the top of the cyclone separator, is cooled by the preheater, and then enters the dust collector to remove most of the dust.

[0013] II. A part of the flue gas at the outlet of the induced draft fan enters the chimney for emission, and the other part enters the flue gas cooler for cooling. After reducing the temperature and water content of the flue gas, it enters the flue gas distributor.

[0014] III. The flue gas distributor distributes the cooled flue gas into four parts:

[0015] The first part enters the fluidizing fan, is pressurized by the fluidizing fan, and then enters the return feeder at the bottom of the cyclone separator for fluidizing the returned material.

[0016] The second part enters the carbon capture device, and carbon dioxide products are obtained through separation and purification.

[0017] The third part is mixed with pure oxygen from the oxygen supply module, pressurized by the primary fan, heated by the preheater first, and then enters the primary air chamber at the bottom of the furnace as the fluidizing air of the circulating fluidized bed boiler. The flow ratio of the flue gas to oxygen is 4.5 - 5.0.

[0018] The fourth part is mixed with pure oxygen from the oxygen supply module, pressurized by the secondary fan, heated by the preheater first, and then enters the secondary air distributor in the middle of the furnace after being evenly distributed, and then enters the furnace. The flow ratio of the flue gas to oxygen is 3.0 - 3.5.

[0019] IV. In the furnace, the biomass completes combustion in an oxy-fuel atmosphere to generate flue gas, which enters the subsequent device to form a cycle.

[0020] Preferably, as an improvement, in step I, there is a flue gas outlet in the tail flue. Part of the high-temperature flue gas is extracted after the economizer in the tail flue of the furnace, and the high-temperature flue gas is introduced into the primary air chamber of the circulating fluidized bed by the high-temperature circulating fan.

[0021] Preferably, as an improvement, in step II, after being cooled by the flue gas cooler, the temperature of the flue gas is 30 - 60 °C, and the water content is 7 - 8%.

[0022] Preferably, as an improvement, in step three, the flow rate ratios of the four parts of the flue gas distributed by the flue gas distributor are respectively: <1%, 20 - 30%, 40 - 50%, 20 - 40%.

[0023] Preferably, as an improvement, based on the value displayed by the carbon monoxide monitoring device as the control basis, when the carbon monoxide concentration exceeds 500 ppm, start the oxygen injection fan to inject oxygen into the flue to promote the oxidation reaction of carbon monoxide, thereby reducing the carbon monoxide concentration in the flue gas.

[0024] Preferably, as an improvement, the oxygen injection volume Q = γ × N × C × 10-6 m 3 / h, where:

[0025] γ is the excess coefficient, and the value range is 0.55 - 1.1;

[0026] N is the boiler flue gas volume m 3 / h;

[0027] C is the carbon monoxide concentration in the flue.

[0028] The principle and advantages of this solution are: In practical applications, in this technical solution, aiming at the problems existing in biomass combustion in the prior art, the inventor has comprehensively optimized the biomass circulating fluidized bed oxy-fuel combustion system and control method: Solve the problems of high air leakage rate and difficult air leakage control existing in the oxy-fuel combustion of biomass circulating fluidized bed boilers through pressure management and seal air replacement; Solve the problem of excessive carbon monoxide concentration in the flue gas existing in the oxy-fuel combustion of biomass circulating fluidized bed boilers through the decentralized air distribution method.

[0029] Specifically, for the problem of air leakage in the system, this solution reduces or avoids the leakage of external air into the furnace by controlling a slightly positive pressure inside the furnace. Both the primary air blower and the secondary air blower are optimized into variable-frequency blowers. The outlet pressure head can be adjusted through the variable-frequency blowers. At the same time, multiple pressure sensors are arranged vertically downward in the furnace to monitor the pressure inside the furnace, and the sectional pressure inside the furnace is adjusted by regulating the air output intensity of the primary air blower and the secondary air blower. In addition, to facilitate the differential and precise control of the pressures at the upper and lower parts of the furnace, the furnace is designed in a structure with a smaller middle part and larger ends. In this way, when the flue gas at the lower part passes through the reduced-diameter part in the middle and then enters the upper space, the gas expansion pressure decreases, making it easier to achieve the control goal of a higher pressure at the lower part and a lower pressure at the upper part. This technical solution combines the structural characteristics of the furnace. There are relatively large air leakage holes such as the feed inlet at the bottom of the furnace. Maintaining a slightly positive pressure at the bottom of the furnace can effectively reduce the air leakage through the holes. There are fewer air leakage holes at the upper part of the furnace, and the upper part is closer to the induced draft fan, with a lower pressure itself. Moreover, the gas temperature at the upper part of the furnace is higher. If the same positive pressure level as the bottom is maintained, on the one hand, it requires a large output of the secondary air blower, which is too difficult to achieve and has a high energy consumption, resulting in energy waste. On the other hand, a relatively high positive pressure does not actually need to be controlled at the upper part, and there is a greater risk of high-temperature gas leakage under a relatively high pressure. Through vertical sectional pressure control, the boiler characteristics and the actual operating conditions are precisely matched, and the boiler air leakage rate is reduced under the conditions of lower control difficulty and energy consumption. In addition, using recirculated flue gas as fluidizing air in this technical solution is also one of the key control points for reducing the air leakage rate.

[0030] For the problem of excessive carbon monoxide concentration in the flue gas during oxy-fuel combustion of a fluidized bed boiler, this solution mainly solves the problem of excessive carbon monoxide concentration in the flue gas by monitoring and injecting a certain amount of oxygen into the flue duct in a timely manner to increase the oxygen concentration in the flue gas and the furnace temperature. Specifically, an on-line carbon monoxide monitoring device is installed on the flue duct between the dust collector and the induced draft fan for real-time monitoring of carbon monoxide. At the same time, an oxygen concentration monitoring device is installed on the flue duct between the furnace and the cyclone separator for real-time monitoring of the oxygen concentration in the flue gas. An air inlet is set on the flue duct between the outlet at the top of the furnace and the cyclone separator. Oxygen in the oxygen supply module is led out through an oxygen injection fan and injected into the set air inlet through an oxygen injection pipeline to be mixed with the flue gas to increase the oxygen concentration in the flue gas. Based on the value displayed by the carbon monoxide monitoring device as the control basis, when the carbon monoxide concentration exceeds 500 ppm, the oxygen injection fan is started to inject oxygen into the flue duct to promote the oxidation reaction of carbon monoxide, thereby reducing the carbon monoxide concentration in the flue gas. A part of the high-temperature flue gas is extracted after the economizer in the boiler tail flue, and the high-temperature flue gas is introduced into the primary air chamber of the circulating fluidized bed by using a high-temperature circulating fan. Introducing the high-temperature flue gas can increase the temperature at the bottom of the furnace and the average furnace temperature, thereby enhancing the fuel oxidation reaction and further reducing the generation amount of carbon monoxide.

[0031] During the technology R & D stage, the inventor tried to reduce the air leakage rate by enhancing the airtightness of the system. For example, key air leakage points such as the furnace body, economizer, air preheater, and dust collector were blocked to reduce the air leakage rate by physical blocking. However, in the actual implementation process, it was found that the boiler system was huge, and there were numerous leakage points such as measurement ports, process interfaces (such as feed ports and other interfaces that could not be blocked), and damaged ports. Through the method of combining slightly positive pressure and pressure zoning in this technical solution, the air leakage rate of the system can be controlled within 3.5%, which is much lower than the air leakage rate of 15% - 20% of traditional circulating fluidized bed boilers. In addition, through experiments, it was also found that by increasing the oxygen supply volume and furnace combustion temperature, the carbon monoxide concentration in the flue gas can be stably maintained within 200 ppm. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 FIG. is a schematic structural diagram of a high - stability biomass oxy - fuel combustion circulating fluidized bed vertical - zone pressure and CO concentration control system of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following is a more detailed description through specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well - known to those skilled in the art; the experimental methods used are all conventional methods; the materials, reagents, etc. used can all be obtained through commercial channels.

[0034] The reference numerals in the accompanying drawings of the specification include: furnace 1, cyclone separator 2, preheater 3, dust collector 4, induced draft fan 5, flue gas cooler 6, flue gas distributor 7, fluidization fan 8, carbon capture device 9, primary air fan 10, secondary air fan 11, oxygen injection fan 12, oxygen supply module 13, tail flue 14, secondary air distributor 15, primary air chamber 16, loop seal 17, oxygen concentration monitoring device 18, carbon monoxide concentration monitoring device 19.

[0035] As Figure 1 shown, a high - stability biomass oxy - fuel combustion circulating fluidized bed vertical - zone pressure and CO concentration control system includes a flue gas pretreatment unit, furnace 1, cyclone separator 2, preheater 3, and dust collector 4.

[0036] The flue gas pretreatment unit is used to pre - treat the flue gas, adjust its temperature, flue gas volume, and water content, and distribute the pre - treated flue gas. The flue gas pretreatment unit includes an induced draft fan 5. One end of the induced draft fan 5 is connected to a chimney. A part (0 - 20%) of the flue gas at the outlet of the induced draft fan 5 enters the chimney for discharge. The other end of the induced draft fan 5 is connected to a flue gas cooler 6, and another part enters the flue gas cooler 6 and is cooled to 30 - 60 °C by water spray cooling, reducing the flue gas volume to 150000 Nm 3 / h, reducing the water content to 7 - 8%, and increasing the CO2 concentration to 70 - 75%.

[0037] The flue gas cooler 6 is connected to a flue gas distributor 7, and the flue gas distributor 7 is respectively connected to a fluidizing fan 8, a carbon capture device 9, a primary fan 10 and a secondary fan 11. Both the primary fan 10 and the secondary fan 11 are variable-frequency fans with high pressure heads. An oxygen injection fan 12 is further included. The oxygen injection fan 12 is connected to an oxygen supply module 13, and oxygen injection pipelines are connected to the pipelines where the oxygen supply module 13 is connected to the primary fan 10 and the secondary fan 11.

[0038] In this way, the flue gas distributor 7 distributes the cooled flue gas into four parts:

[0039] The first part (with a proportion < 1%) enters the fluidizing fan 8, and after being pressurized by the fluidizing fan 8, it enters the return feeder 17 at the bottom of the cyclone separator 2 for fluidizing the returned material. Since ordinary circulating fluidized bed return uses air, using the circulating gas as the return air can reduce a certain amount of air leakage;

[0040] The second part (with a proportion of 20 - 30%) enters the carbon capture device 9, and carbon dioxide products are obtained through separation and purification;

[0041] The third part (with a proportion of 40 - 50%) is mixed with pure oxygen from the oxygen supply module 13, pressurized by the primary fan 10, heated by the preheater 3 first, and then enters the primary air chamber 16 at the bottom of the furnace chamber 1 as the fluidizing air of the circulating fluidized bed boiler. The flow ratio of the flue gas to oxygen is 4.5 - 5.0;

[0042] The fourth part (with a proportion of 20 - 40%) is mixed with pure oxygen from the oxygen supply module 13, pressurized by the secondary fan 11, heated by the preheater 3 first, and then enters the furnace chamber 1 after being evenly distributed by the secondary air distributor 15 in the middle of the furnace chamber 1. The flow ratio of the flue gas to oxygen is 3.0 - 3.5.

[0043] In this embodiment, the furnace chamber 1 is used for the combustion of biomass, and the inside of the furnace chamber 1 is under slightly positive pressure to reduce or avoid external air leakage into the furnace chamber 1. The pressure P1 in the middle and lower parts of the furnace chamber 1 = 50 - 200 Pa, and the output of the primary fan 10 is adjusted to maintain the pressure in the middle and lower parts of the furnace chamber 1 within the control value; the pressure in the upper part of the furnace chamber 1 is controlled to be P2 = P1 - α×H - 100 Pa (α is a control coefficient taken as 5 - 8, and H is the effective height of the combustion area of the furnace chamber 1 in m), and the output of the secondary fan 11 and the induced draft fan 5 is adjusted to maintain the pressure in the middle and lower parts of the furnace chamber 1 within the control value.

[0044] In order to facilitate the differential and precise control of the pressures in the upper and lower parts of the furnace 1, the furnace 1 is designed in a structure with a smaller middle part and larger ends. In this way, when the flue gas in the lower part passes through the reduced-diameter part in the middle and then enters the upper space, the gas expansion pressure decreases, thus facilitating the achievement of the control goal of a higher pressure in the lower part and a lower pressure in the upper part. The relationship between the cross-sectional area A2 at the reduced-diameter part in the middle of the furnace 1 and the cross-sectional area A1 at other positions of the furnace 1 is A2 = βA1, where β is the reduced-diameter coefficient, and the value range of β is 0.65 - 0.9. The relationship between the vertical height H2 at the reduced-diameter part and the effective combustion height H of the furnace 1 is H2 = δH, where δ is the control coefficient, and the value range of δ is 0.05 - 0.1.

[0045] A primary air chamber 16 is provided at the bottom of the furnace 1, and a high-temperature circulating fan is connected to the primary air chamber 16; a secondary air distributor is provided at the upper part of the furnace 1, and an air inlet is provided on the flue between the top outlet of the furnace 1 and the cyclone separator 2. Oxygen in the oxygen supply module 13 is led out through the oxygen injection fan 12 and injected into the set air inlet through the oxygen injection pipeline to be mixed with the flue gas, so as to increase the oxygen concentration in the flue gas.

[0046] An on-line carbon monoxide monitoring device 19 is installed on the flue between the dust collector 4 and the induced draft fan 5 for real-time monitoring of carbon monoxide. At the same time, an oxygen concentration monitoring device 18 is installed on the flue between the furnace 1 and the cyclone separator for real-time monitoring of the oxygen concentration in the flue gas.

[0047] A high-stability biomass oxy-fuel combustion circulating fluidized bed vertical partition pressure and CO concentration control method includes the following steps:

[0048] 1. After the biomass completes oxy-fuel combustion in the furnace 1, the generated flue gas enters the cyclone separator 2 under the action of the induced draft fan 5. The unburned fuel separated is returned to the furnace 1 from the return feeder 17 at the bottom of the cyclone separator 2, while the flue gas enters the tail flue 14 from the top of the cyclone separator 2, is cooled by the preheater 3, and then enters the dust collector 4 to remove most of the dust.

[0049] 2. A part (0 - 20%) of the flue gas at the outlet of the induced draft fan 5 enters the chimney for emission, and the other part enters the flue gas cooler 6 to be cooled to 30 - 60 °C. After reducing the water content of the flue gas, it enters the flue gas distributor 7.

[0050] 3. The flue gas distributor 7 distributes the cooled flue gas into 4 parts:

[0051] The first part (with a proportion < 1%) enters the fluidizing fan 8, and after being pressurized by the fluidizing fan 8, it enters the return feeder 17 at the bottom of the cyclone separator 2 for fluidizing the returned material. Since the return material of a general circulating fluidized bed uses air, using the circulating gas as the return air can reduce a certain amount of air leakage;

[0052] The second part (accounting for 20 - 30%) enters the carbon capture device 9, and carbon dioxide products are obtained through separation and purification;

[0053] The third part (accounting for 40 - 50%) is mixed with pure oxygen from the oxygen supply module 13, pressurized by the primary air blower 10, first heated by the preheater 3, and then enters the primary air chamber 16 at the bottom of the furnace 1 as the fluidizing air of the circulating fluidized bed boiler.

[0054] The fourth part (accounting for 20 - 40%) is mixed with pure oxygen from the oxygen supply module 13, pressurized by the secondary air blower 11, first heated by the preheater 3, and then enters the secondary air distributor 15 in the middle of the furnace 1, and is evenly distributed and then enters the furnace 1.

[0055] IV. In the furnace 1, the biomass is burned in an oxygen-rich atmosphere to generate flue gas, which enters the subsequent device to form a cycle.

[0056] V. A flue gas outlet is provided in the tail flue 14. Part of the high-temperature flue gas is extracted after the economizer in the tail flue 14 of the furnace 1, and the high-temperature flue gas is introduced into the primary air chamber 16 of the circulating fluidized bed by the high-temperature circulating fan. Introducing the high-temperature flue gas can increase the temperature at the bottom of the furnace 1 and the average temperature of the furnace 1, thereby enhancing the fuel oxidation reaction and reducing the generation amount of carbon monoxide.

[0057] Taking the value displayed by the carbon monoxide monitoring device 19 as the control basis, when the carbon monoxide concentration exceeds 500 ppm, the oxygen injection blower 12 is started to inject oxygen into the flue to promote the oxidation reaction of carbon monoxide, thereby reducing the carbon monoxide concentration in the flue gas.

[0058] The oxygen injection amount is calculated as Q = γ × N × C × 10-6 m 3 / h. (γ is the excess coefficient, with a value range of 0.55 - 1.1, N is the boiler flue gas volume m 3 / h, and C is the carbon monoxide concentration in the flue). During the injection process, observe the top oxygen concentration monitoring device, and judge the increase or decrease of the injection amount according to the change of the oxygen concentration. If the oxygen concentration rises rapidly, the injection amount can be reduced; if the oxygen concentration remains stable or decreases, the injection amount can be increased.

[0059] Example 1

[0060] A certain domestic power plant is equipped with a biomass circulating fluidized bed boiler with an evaporation capacity of 150 t / h, designed for air combustion. Using the system and method provided by the present invention, the boiler is technically transformed to achieve oxygen-rich combustion, and the oxygen content in the flue gas is increased to 71% (Vol, wet basis). The specific implementation process is as follows:

[0061] After the biomass fuel completes oxygen-rich combustion in the furnace 1, it generates approximately 185000 Nm 3The flue gas with a flow rate of / h, a moisture content of 25.3%, and a CO2 concentration of 57.91% is cooled to approximately 140°C successively through heat exchange equipment such as the economizer and air preheater under the action of the induced draft fan 5, and then enters the dust collector 4 to remove most of the dust. The flue gas at the outlet of the induced draft fan 5 is divided into two paths. One path is connected to the chimney for direct flue gas discharge. In this embodiment, in order to maximize the carbon capture amount, this gas path is closed, and all the flue gas passes through the other path and is introduced into the flue gas cooler 6.

[0062] In the flue gas cooler 6, the flue gas temperature is reduced to 40°C by spraying cooling water, and the flue gas volume is reduced to 150,000 Nm 3 / h, the water content is reduced to 7.47%, and the CO2 concentration is increased to 71.7%.

[0063] The cooled flue gas enters the flue gas distributor 7. The flue gas distributor 7 divides the flue gas into 4 paths. One path of approximately 36,000 Nm 3 / h enters the flue gas carbon capture device 9. Since the carbon dioxide concentration in the flue gas is relatively high, liquid carbon dioxide can be produced through a simple process of liquefaction - rectification and purification. Another path of approximately 2,000 Nm 3 / h is introduced into the fluidizing fan 8, pressurized, and then sent into the bottom pipeline of the cyclone separator to strengthen the fluidization of the cyclone separator 2. The remaining flue gas is divided into two paths and mixed with oxygen supplied by the oxygen supply module 13 in two paths as primary air and secondary air respectively. Among them, the primary air is composed of 66,500 Nm 3 / h of recycled flue gas and 13,700 Nm 3 / h of pure oxygen to form 80,200 Nm 3 / h of mixed air (with an oxygen content of approximately 21%). After being pressurized by the primary air fan 10 and heated in the air preheater, it enters the bottom air chamber of the furnace 1. The secondary air is composed of 43,500 Nm 3 / h of recycled flue gas and 13,000 Nm 3 / h of pure oxygen to form 56,500 Nm 3 / h of mixed air (with an oxygen content of approximately 26.4%). After being pressurized by the secondary air fan and heated in the air preheater 3, it is sent to the secondary air distribution device in the middle of the furnace 1 through the second stage, and the working frequency of the induced draft fan 5 is synchronously adjusted. Finally, the pressure at the bottom of the furnace 1 is maintained between 50 - 100 Pa, and the pressure in the upper and middle parts of the furnace 1 is maintained between 0 - 50 Pa.

[0064] By using recycled flue gas as the sealing air and fluidizing air, and the slightly positive pressure operation mode of the furnace 1, the air leakage rate of the boiler system is controlled within 4%. Compared with the air leakage rate of about 15% in the traditional circulating fluidized bed system, the air leakage rate is significantly reduced, and the carbon dioxide concentration in the flue gas is increased.

[0065] In addition, since the moisture content of biomass fuel fluctuates greatly with seasons, when the fuel has a high moisture content, due to the relatively low combustion temperature in the furnace 1, the carbon monoxide concentration in the flue gas is often on the high side, and the highest concentration of carbon monoxide in the flue gas can exceed 10,000 ppm. On the one hand, this causes energy waste, and on the other hand, there are significant safety risks. In this embodiment, injecting pure oxygen from the top of the furnace 1 can effectively reduce the carbon monoxide concentration in the flue gas, reducing energy loss and safety risks.

[0066] The above are only embodiments of the present invention, and common general technical solutions and / or characteristics in the solutions are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application shall be subject to the content of its claims, and the specific implementation manners and the like recorded in the specification can be used to interpret the content of the claims.

Claims

1. A high-stability biomass oxygen-enriched combustion circulating fluidized bed vertical partition pressure and CO concentration control system, characterized by: It includes a flue gas pretreatment unit, a furnace, a cyclone separator, a preheater and a dust collector. The flue gas pretreatment unit includes an induced draft fan, a flue gas cooler and a flue gas separator. A carbon monoxide monitoring device is arranged on the flue between the induced draft fan and the dust collector, and an oxygen concentration monitoring device is arranged on the flue between the furnace and the cyclone separator. The interior of the furnace is set to a slightly positive pressure, and the pressure in the lower part of the furnace is P1=50~200Pa, and the pressure in the upper part of the furnace is P2=P1-α×H-100Pa, α is the control coefficient=5~8, and H is the effective height m of the furnace combustion area.

2. A high stability biomass oxygen-enriched combustion circulating fluidized bed vertical partition pressure and CO concentration control system according to claim 1, characterized in that: It also includes an oxygen supply module, which is connected to an oxygen injection fan. An air inlet is arranged on the flue between the top outlet of the furnace and the cyclone separator, and an oxygen injection pipeline is arranged between the oxygen injection fan and the air inlet.

3. A high stability biomass oxygen-enriched combustion circulating fluidized bed vertical partition pressure and CO concentration control system according to claim 2, characterized in that: A diameter change point is provided in the middle of the furnace, and the cross section of the diameter change point is smaller than the cross section at both ends of the furnace. The relationship between the cross-sectional area A2 of the diameter change point in the middle of the furnace and the cross-sectional area A1 at both ends of the furnace is A2=βA1, wherein β is the diameter change coefficient, and the value range of β is 0.65~0.

9.

4. A high stability biomass oxygen-enriched combustion circulating fluidized bed vertical partition pressure and CO concentration control system according to claim 3, characterized in that: The relationship between the vertical height H2 at the furnace diameter change point and the effective combustion height H of the furnace is H2=δH, δ is the control coefficient, and the value range of δ is 0.05~0.

1.

5. A method for controlling vertical zone pressure and CO concentration of a high-stability biomass oxygen-enriched combustion circulating fluidized bed, characterized in that: The method is accomplished by using the system described in any one of claims 1 to 4, comprising the following steps:

1. After the biomass completes oxygen-enriched combustion in the furnace, the generated flue gas enters the cyclone separator under the action of the induced draft fan, and the unburned fuel is separated and returned to the furnace from the return device at the bottom of the cyclone separator. The flue gas enters the tail flue from the top of the cyclone separator, cools down in the preheater, and then enters the dust collector to remove most of the dust; 2. Part of the flue gas from the exhaust fan outlet enters the chimney for discharge, and the other part enters the flue gas cooler for cooling, reducing the water content of the flue gas thermometer before entering the flue gas distributor; 3. The flue gas distributor distributes the cooled flue gas into 4 parts: The first part enters the fluidizing fan, and after being pressurized by the fluidizing fan, it enters the return device at the bottom of the cyclone separator for fluidization return; The second part enters the carbon capture device and is separated and purified to obtain carbon dioxide products; The third part is mixed with the pure oxygen from the oxygen supply module, pressurized by the primary fan, heated by the preheater, and then enters the primary air chamber at the bottom of the furnace as the fluidizing air of the circulating fluidized bed boiler. The flow ratio of flue gas to oxygen is 4.5-5.0; The fourth part is mixed with the pure oxygen from the oxygen supply module, pressurized by the secondary fan, heated by the preheater, and then enters the secondary air distributor in the middle of the furnace for uniform distribution before entering the furnace. The flow ratio of flue gas to oxygen is 3.0-3.5; 4. In the furnace, the biomass is burned in an oxygen-rich atmosphere to generate flue gas which enters the subsequent device to form a cycle.

6. A method for controlling vertical zone pressure and CO concentration in a high stability biomass oxygen-enriched combustion circulating fluidized bed according to claim 5, characterized in that: In step one, a flue gas outlet is provided at the tail flue, part of the high-temperature flue gas is extracted after the economizer at the tail flue of the furnace, and the high-temperature flue gas is introduced into the primary air chamber of the circulating fluidized bed by a high-temperature circulating fan.

7. A method for controlling vertical zone pressure and CO concentration in a high stability biomass oxygen-enriched combustion circulating fluidized bed according to claim 6, characterized in that: In step 2, after being cooled by the flue gas cooler, the flue gas has a temperature of 30-60° C. and a water content of 7-8%.

8. The biomass direct combustion-gasification coordinated combustion control method under oxygen-rich conditions according to claim 7, characterized in that: In step three, the flow rates of the four parts of flue gas distributed by the flue gas distributor are respectively: <1%, 20-30%, 40-50%, and 20-40%.

9. A method for controlling vertical zone pressure and CO concentration in a high stability biomass oxygen-enriched combustion circulating fluidized bed according to claim 8, characterized in that: The value displayed by the carbon monoxide monitoring device is used as the control basis. When the carbon monoxide concentration exceeds 500ppm, the oxygen injection fan is started to inject oxygen into the flue to promote the oxidation reaction of carbon monoxide and thus reduce the carbon monoxide concentration in the flue gas.

10. A method for controlling vertical zone pressure and CO concentration in a high stability biomass oxygen-enriched combustion circulating fluidized bed according to claim 9, characterized in that: Oxygen injection amount Q = γ × N × C × 10-6m 3 / h, where: γ is the excess coefficient, ranging from 0.55 to 1.1; N is the boiler flue gas volume m 3 / h; C is the flue carbon monoxide concentration.

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