An anti-blocking two-way sampling system and sampling method for a reducing atmosphere of a water-cooled wall

Abstract

The present invention discloses a blocking-proof water-cooled wall reducing atmosphere bidirectional sampling system and sampling method. The bidirectional sampling system is installed on the outer side of the water-cooled wall of a coal-fired boiler. A first sampling port and a second sampling port are provided on the fins of the water-cooled wall. The two ends of a primary sampling pipeline are respectively connected to the first sampling port and the second sampling port. The primary sampling pipeline is provided with a first pneumatic conveyor and a second pneumatic conveyor arranged opposite to each other. One end of a first compressed air pipeline and a second compressed air pipeline are respectively connected to a compressed air source and the other end are respectively connected to the first pneumatic conveyor and the second pneumatic conveyor. A first compressed air control valve is provided on the first compressed air pipeline and a second compressed air control valve is provided on the second compressed air pipeline. A secondary sampling pipe is cross-connected with the primary sampling pipe between the first pneumatic conveyor and the second pneumatic conveyor, and a sampling probe is inserted into the secondary sampling pipe. The sampling system of the present invention has a simple and reliable structure and solves problems such as blockage and inconvenient installation.

Description

Technical Field

[0001] The invention relates to an anti-blocking water-cooled wall reducing atmosphere bidirectional sampling system and a sampling method, belonging to the technical field of power station coal-fired boiler monitoring. Background Art

[0002] In recent years, as boilers have evolved toward larger capacities and higher parameters, the temperature of the boiler water-walls has correspondingly increased, leading to a growing problem of high-temperature corrosion. To reduce NOx generation, most power plants currently employ staged air supply or low-oxygen combustion, which creates a reducing atmosphere near the water-walls. This, in turn, leads to high-temperature corrosion of the water-walls. A certain degree of water-wall thinning can cause boiler tube bursts, posing a serious threat to the safe and economical operation of boiler units.

[0003] Boiler high-temperature corrosion is primarily categorized as sulfate and sulfide. Sulfate corrosion primarily occurs in superheaters and reheaters, while sulfide corrosion primarily occurs in furnace water walls. Sulfide corrosion is primarily caused by the combustion of pulverized coal in anoxic conditions, which produces H2S and free sulfur [S]. These react with the iron metal and iron oxides on the tube walls to form iron sulfides, further corroding the boiler water walls and causing the oxide film to loosen, crack, or even fall off.

[0004] A study shows that when a reducing atmosphere appears near the water-cooled wall of the furnace, the proportion of sulfur in the coal released in the form of H2S gas is more than 75%; when CO / (CO+CO2) increases from 8% to 24%, the H2S gas concentration increases from 0.02% to 0.07%, causing severe corrosion of the water-cooled wall.

[0005] Extensive operational analysis has revealed that in severely corroded furnace water-cooled walls, reducing atmospheres and high concentrations of H2S gas are found in the flue gas composition of the corresponding corrosion areas. H2S gas has a penetrating effect, penetrating the loose Fe2O3 and reacting with the FeO in the denser magnetic iron oxide Fe3O4 to form FeS. After the FeO protective film is destroyed, H2S gas can also react with the Fe on the tube wall to form FeS and H2. Because the corrosion products FeS and FeO have a loose and porous structure, they cannot prevent the intrusion of corrosive media. At the same time, as the furnace smoke washes away, corrosion continues to spread to the base metal, gradually progressing from the outside in. Oxidizing and reducing atmospheres alternate near the tube wall, and the generated corrosion products are reoxidized into iron oxides, which can continue to react with the corrosive medium, causing the corrosion to continue to intensify.

[0006] The mechanism of high-temperature corrosion of the water-cooled wall shows that a reducing atmosphere is a necessary condition for high-temperature corrosion. Therefore, reducing atmosphere monitoring of areas of the water-cooled wall prone to high-temperature corrosion (generally, small holes are opened on the water-cooled wall fins and gas samples are directly extracted for detection and analysis) helps operators to promptly identify problems and resolve them through combustion adjustments. However, the flue gas temperature near the boiler water-cooled wall is very high, contains a large amount of dust, and requires measurement at multiple points. It is difficult to ensure continuous and reliable monitoring using conventional flue gas sampling and analysis systems, and the sampling ports are also prone to coking and clogging. In addition, there may be equipment such as bellows and burners arranged on the outside of the water-cooled wall. Directly placing the flue gas sampling probe in situ may cause difficulties in installation and operation. Summary of the Invention

[0007] The present invention provides a blocking-proof water-cooled wall reducing atmosphere bidirectional sampling system, which is used to solve the problems of high cost and low reliability caused by the excessive complexity of the flue gas sampling and analysis system in the prior art, as well as the problems of easy clogging of the sampling port and inconvenient installation of the sampling probe.

[0008] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0009] A blocking-proof water-wall reducing atmosphere bidirectional sampling system is installed on the outside of the water-wall of a coal-fired boiler and includes a primary sampling pipeline, a first pneumatic conveyor, a second pneumatic conveyor, a first compressed air pipeline, a second compressed air pipeline, a compressed air source, a first compressed air control valve, a second compressed air control valve, a secondary sampling pipe and a sampling probe;

[0010] The first sampling port and the second sampling port are provided on the water-cooled wall fins. The flow cross-section of the first sampling port and the second sampling port is not less than 3cm. 2 ; One end of the primary sampling pipeline is connected to the first sampling port, and the other end is connected to the second sampling port. The first pneumatic conveyor and the second pneumatic conveyor are both installed on the primary sampling pipeline, and the first pneumatic conveyor and the second pneumatic conveyor are arranged back to back; One end of the first compressed air pipeline is connected to the compressed air source, and the other end is connected to the first pneumatic conveyor. The first compressed air control valve is arranged on the first compressed air pipeline; One end of the second compressed air pipeline is connected to the compressed air source, and the other end is connected to the second pneumatic conveyor. The second compressed air control valve is arranged on the second compressed air pipeline; The secondary sampling pipe is cross-connected with the primary sampling pipeline between the first pneumatic conveyor and the second pneumatic conveyor, and the sampling probe is inserted into the secondary sampling pipe to extract and analyze the sample gas.

[0011] The above-mentioned first pneumatic conveyor and second pneumatic conveyor both use compressed air as the power source and are used to convey dust-laden flue gas. They have no moving parts and are maintenance-free. Whether they generate suction force is controlled by the on-off of the first compressed air control valve and the second compressed air control valve respectively.

[0012] The first and second pneumatic conveyors are arranged in opposite directions, which means that "when the first pneumatic conveyor is in suction operation, the second pneumatic conveyor is located upstream of it" or "when the second pneumatic conveyor is in suction operation, the first pneumatic conveyor is located upstream of it." The direction from upstream to downstream is consistent with the direction of gas flow.

[0013] When the first compressed air control valve is open and the second compressed air valve is closed, flue gas flows from the second sampling port to the first sampling port, and the analytical gas sample extracted by the sampling probe originates from the second sampling port. When the first compressed air control valve is closed and the second compressed air valve is open, flue gas flows from the first sampling port to the second sampling port, and the analytical gas sample extracted by the sampling probe originates from the first sampling port. When both the first compressed air control valve and the second compressed air valve are open, the system is in a compressed air backflush state. When both the first compressed air control valve and the second compressed air valve are closed, the system is in a stopped state.

[0014] After the above-mentioned sampling probe extracts the analytical sample gas, it is sent to the flue gas analysis cabinet for component analysis. The analyzed components include but are not limited to O2, CO, CO2, H2S, etc. The analyzer uses infrared method, ultraviolet method or laser method.

[0015] After research, the applicant found that the anti-blocking water-cooled wall reducing atmosphere bidirectional sampling system, through a two-stage sampling design, and the flow rate design of the first-stage sampling is relatively large, can greatly reduce the risk of coking and blockage at the sampling port; through the bidirectional sampling design, the sampling probe can be arranged at a suitable position outside the water-cooled wall, which is easy to install, and a set of sampling probes can be used to sample the flue gas from two sampling ports, which improves the utilization efficiency of the system, and is also conducive to reducing the system failure rate and improving the system operation reliability.

[0016] In order to further improve the anti-blocking effect, the inner diameter of the primary sampling pipeline shall not be less than 30mm.

[0017] The distance between the first sampling port and the second sampling port is not less than 1m.

[0018] The sampling method using the above-mentioned anti-blocking water-cooled wall reducing atmosphere bidirectional sampling system includes the following:

[0019] Sampling method 1: Open the first compressed air control valve and close the second compressed air valve. The flue gas inside the water-cooled wall flows out from the second sampling port, passes through the primary sampling pipeline, and returns to the inside of the water-cooled wall from the first sampling port. The end of the sampling probe is inserted into the intersection of the primary sampling pipeline and the secondary sampling pipe to complete the sampling of the second sampling port and simultaneously complete the backflush of the first sampling port. The backflush gas is a mixture of air and flue gas.

[0020] Sampling method 2: Open the second compressed air control valve and close the first compressed air valve. The flue gas inside the water-cooled wall flows out from the first sampling port, passes through the primary sampling pipeline, and returns to the inside of the water-cooled wall from the second sampling port. The end of the sampling probe is inserted into the intersection of the primary sampling pipeline and the secondary sampling pipe to complete the sampling of the first sampling port and simultaneously complete the backflush of the second sampling port. The backflush gas is a mixture of air and flue gas.

[0021] After the sampling is completed, the first compressed air control valve and the second compressed air valve are closed. The above-mentioned sampling method 1 and sampling method 2 are operated alternately, or sampling method 1 and sampling method 2 are operated selectively.

[0022] In actual application, bidirectional sampling is selected according to needs. This application has two sampling modes, which can obtain two streams of gas, while only using one set of sampling probes.

[0023] Open both the first and second compressed air valves, and the sampling probe takes air as the sample to calibrate the zero position of the rear-end instrument. Of course, opening both the first and second compressed air valves also has a certain back-blowing and anti-blocking effect.

[0024] The technologies not mentioned in this invention are all referred to the prior art.

[0025] The anti-blocking water-cooled wall reducing atmosphere bidirectional sampling system of the present invention is provided with a two-stage sampling structure of a primary sampling pipeline and a secondary sampling pipe, and a pneumatic conveyor with compressed air as the power source is provided on the primary sampling pipe, which can greatly reduce the risk of coking and clogging of the sampling port; at the same time, through the bidirectional sampling design, the sampling probe can be arranged at a suitable position outside the water-cooled wall, which is easy to install, and the flue gas from two sampling ports can be sampled through a set of sampling probes, which improves the utilization efficiency of the system, is also conducive to reducing the system failure rate, and improves the reliability of the system operation; the structure is simple, the reliability is high, and the maintenance cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of the anti-blocking water-cooled wall reducing atmosphere bidirectional sampling system of the present invention.

[0027] In the figure, 1 is the first sampling port, 2 is the second sampling port, 3 is the first pneumatic conveyor, 4 is the second pneumatic conveyor, 5 is the first compressed air control valve, 6 is the second compressed air control valve, 7 is the secondary sampling pipe, 8 is the sampling probe, 9 is the primary sampling pipeline; 10 is the water-cooled wall fin, 11 is the compressed air source, and 12 is the flue gas analysis cabinet. DETAILED DESCRIPTION

[0028] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0029] like Figure 1 As shown, a blocking-proof water-wall reducing atmosphere bidirectional sampling system is installed on the outside of the water-wall of a coal-fired boiler, comprising a primary sampling pipeline, a first pneumatic conveyor, a second pneumatic conveyor, a first compressed air pipeline, a second compressed air pipeline, a compressed air source, a first compressed air control valve, a second compressed air control valve, a secondary sampling pipe and a sampling probe;

[0030] The first sampling port and the second sampling port are provided on the water-cooled wall fins. The interval between the first sampling port and the second sampling port is 1.5m. The flow cross-section size of the first sampling port and the second sampling port is 1.2×5cm, and the cross-sectional area reaches 6cm. 2 ; The inner diameter of the primary sampling pipeline is 32mm, one end of the primary sampling pipeline is connected to the first sampling port, and the other end is connected to the second sampling port. The first pneumatic conveyor and the second pneumatic conveyor are both installed on the primary sampling pipeline, and the first pneumatic conveyor and the second pneumatic conveyor are arranged back to back; one end of the first compressed air pipeline is connected to the compressed air source, and the other end is connected to the first pneumatic conveyor, and the first compressed air control valve is arranged on the first compressed air pipeline; one end of the second compressed air pipeline is connected to the compressed air source, and the other end is connected to the second pneumatic conveyor, and the second compressed air control valve is arranged on the second compressed air pipeline; the secondary sampling pipe is cross-connected with the primary sampling pipeline between the first pneumatic conveyor and the second pneumatic conveyor, and the sampling probe is inserted into the secondary sampling pipe to extract and analyze the sample gas.

[0031] Sampling method using the above-mentioned anti-blocking water-cooled wall reducing atmosphere two-way sampling system:

[0032] Sampling method 1: Open the first compressed air control valve and close the second compressed air valve. The flue gas inside the water-cooled wall flows out from the second sampling port, passes through the primary sampling pipeline, and returns to the inside of the water-cooled wall from the first sampling port. The end of the sampling probe is inserted into the intersection of the primary sampling pipeline and the secondary sampling pipe to complete the sampling of the second sampling port and the backblowing of the first sampling port. After the sampling is completed, close the first compressed air control valve and the second compressed air valve at the same time.

[0033] Sampling method 2: Open the second compressed air control valve and close the first compressed air valve. The flue gas inside the water-cooled wall flows out from the first sampling port, passes through the primary sampling pipeline, and returns to the inside of the water-cooled wall from the second sampling port. The end of the sampling probe is inserted into the intersection of the primary sampling pipeline and the secondary sampling pipe to complete the sampling of the first sampling port and the backflush of the second sampling port. After the sampling is completed, close the first compressed air control valve and the second compressed air valve at the same time.

[0034] The above sampling method 1 and sampling method 2 are run alternately.

[0035] After the sampling is completed, the first compressed air control valve and the second compressed air valve are closed;

[0036] After the above-mentioned sampling probe extracts the analytical sample gas, it is sent to the flue gas analysis cabinet for component analysis. The analyzed components include but are not limited to O2, CO, CO2, H2S, etc. The analyzer uses infrared method, ultraviolet method or laser method.

[0037] During sampling, the primary sampling flow rate reaches over 50L / min, while the sampling flow rate of the sampling probe is only 1-3L / min. The larger primary sampling flow rate can prevent clogging of the first and second sampling ports, and the secondary sampling flow rate meets the stable operation requirements of the flue gas analysis cabinet.

[0038] The above system was applied to the reducing atmosphere monitoring of the water-cooled wall of a 660MW ultra-supercritical coal-fired power generation unit. It has been running stably for one year and has been tested to have no coking or blockage problems. It has a simple structure, low cost, and extremely high reliability. The sampling probe can be installed in a suitable position, solving the problem of difficult in-situ installation.

Claims

1. A blocking-proof water-wall reducing atmosphere bidirectional sampling system, installed on the outside of the water-wall of a coal-fired boiler, characterized by: It includes a primary sampling pipeline, a first pneumatic conveyor, a second pneumatic conveyor, a first compressed air pipeline, a second compressed air pipeline, a compressed air source, a first compressed air control valve, a second compressed air control valve, a secondary sampling pipe and a sampling probe; The first sampling port and the second sampling port are provided on the water-cooled wall fins. The flow cross-section of the first sampling port and the second sampling port is not less than 3cm. 2 ; One end of the primary sampling pipeline is connected to the first sampling port, and the other end is connected to the second sampling port. The first pneumatic conveyor and the second pneumatic conveyor are both installed on the primary sampling pipeline, and the first pneumatic conveyor and the second pneumatic conveyor are arranged back to back; One end of the first compressed air pipeline is connected to the compressed air source, and the other end is connected to the first pneumatic conveyor. The first compressed air control valve is arranged on the first compressed air pipeline; One end of the second compressed air pipeline is connected to the compressed air source, and the other end is connected to the second pneumatic conveyor. The second compressed air control valve is arranged on the second compressed air pipeline; The secondary sampling pipe is cross-connected with the primary sampling pipeline between the first pneumatic conveyor and the second pneumatic conveyor, and the sampling probe is inserted into the secondary sampling pipe to extract and analyze the sample gas.

2. The anti-blocking water-wall reducing atmosphere bidirectional sampling system according to claim 1, characterized in that: The inner diameter of the primary sampling pipeline shall not be less than 30mm.

3. The anti-blocking water-wall reducing atmosphere bidirectional sampling system according to claim 1 or 2, characterized in that: The distance between the first sampling port and the second sampling port is not less than 1m.

4. A water-wall reducing atmosphere bidirectional sampling method, using the anti-blocking water-wall reducing atmosphere bidirectional sampling system according to any one of claims 1 to 3, characterized in that: These include: Sampling method 1: Open the first compressed air control valve and close the second compressed air valve. The flue gas inside the water-cooled wall flows out from the second sampling port, passes through the primary sampling pipeline, and returns to the inside of the water-cooled wall from the first sampling port. The end of the sampling probe is inserted into the intersection of the primary sampling pipeline and the secondary sampling pipe to complete the sampling of the second sampling port and simultaneously complete the backflush of the first sampling port. Sampling method 2: Open the second compressed air control valve and close the first compressed air valve. The flue gas inside the water-cooled wall flows out from the first sampling port, passes through the primary sampling pipeline, and returns to the inside of the water-cooled wall from the second sampling port. The end of the sampling probe is inserted into the intersection of the primary sampling pipeline and the secondary sampling pipe to complete the sampling of the first sampling port and simultaneously complete the backflush of the second sampling port. After the sampling is completed, close the first compressed air control valve and the second compressed air valve.

5. The water-wall reducing atmosphere bidirectional sampling method according to claim 4, characterized in that: Sampling method 1 and sampling method 2 are run alternately, or sampling method 1 and sampling method 2 are run alternatively.

6. The water-wall reducing atmosphere bidirectional sampling method according to claim 4, characterized in that: Open the first compressed air control valve and the second compressed air valve. The sample taken by the sampling probe is air to calibrate the zero position of the rear-end instrument.

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