A method and system for preventing and controlling tail heating surface contamination of a liquid slag discharge furnace

Abstract

The application discloses a method and system for preventing and controlling tail heating surface contamination of a liquid slag discharge furnace, and the system comprises a liquid slag discharge furnace and a sprayer; according to a flue gas flow process, a cold slag section is located downstream of a molten slag section and is a burnout zone of the liquid slag discharge furnace; a water wall is a boiler heating surface located in the cold slag section; a tail heating surface is located downstream of the cold slag section, and an exhaust passage is located downstream of the tail heating surface; the sprayer is installed on the water wall, an inlet of the sprayer is connected with a passage for conveying a contamination inhibitor and a medium, and a gas-solid mixture of the contamination inhibitor and the conveying medium enters the cold slag section through the sprayer, mixes with flue gas and coal fly ash, and then flows to the tail heating surface; the contamination inhibitor is sprayed into the cold slag section of the liquid slag discharge furnace; the contamination inhibitor used is in a solid powder state; the application can economically and effectively solve the problem of cold slag section contamination of the liquid slag discharge furnace when high-alkali coal is combusted, improve the adaptability to high-alkali coal quality fluctuation and extreme parameter high-alkali coal, and improve the operation safety of the liquid slag discharge furnace.

Description

Technical Field

[0001] This invention belongs to the field of pulverized coal boiler combustion technology, specifically relating to a safe operation technology for preventing fouling of the tail heating surface of a liquid ash discharge furnace, and particularly a method and system for preventing fouling of the tail heating surface of a liquid ash discharge furnace. Background Technology

[0002] Northwest my country possesses over one trillion tons of high-alkali coal reserves, and optimizing the utilization of this coal is crucial for ensuring regional energy security. High-alkali coal ash contains a high content of alkaline oxides, and its ash alkali-to-acid ratio is... R B / A =( W Fe 2 O 3+ W CaO + W MgO + W Na 2 O + W K 2 O ) / ( W SiO 2+ W Al 2 O 3+ W TiO 2) With a Na₂O content exceeding 2.5% and a concentration above 0.30%, these coal ash exhibits strong slagging and fouling properties, easily forming a fluid slag layer on water-cooled walls. Currently, most boilers burning high-alkali coal are solid-discharge pulverized coal boilers, with a few being solid-discharge fluidized bed boilers. Due to the high Na and K content in high-alkali coal ash, it forms low-ash-melting-point substances with silicon and aluminum materials. Furthermore, excess Na and K, with volatilization temperatures below 1000℃, readily escape from the solid material to form gaseous alkali metals. These gaseous alkali metals inevitably cool further, easily forming a sticky bottom layer on the boiler's heating surface, adhering to large ash particles or forming ultrafine particles. This significantly strengthens the adhesion between fly ash and the heating surface or fouling layer, resulting in fouling of the heating surface. Slagging and fouling in pulverized coal boilers are difficult to avoid, especially when high-alkali coal accounts for over 95% of the combustion. Controlling the slagging and fouling rate on the heating surface is challenging, affecting the safe operation and economic efficiency of the power plant and severely restricting the large-scale, high-quality utilization of high-alkali coal resources.

[0003] A liquid ash discharge boiler is a type of boiler that uses high-temperature pulverized coal combustion, where most of the coal ash is in a molten state and discharged from the furnace as a liquid ash flow. Structurally, a liquid ash discharge boiler is divided into a molten ash section and a cold ash section. The molten ash section is the pulverized coal combustion chamber and the coal ash melting and flowing section, with a high temperature, generally exceeding 1600℃. The cold ash section is the burnout section, with a large number of heating surfaces, and the flue gas temperature is generally below 1300℃. A liquid ash discharge boiler can capture and fix 50-80% of the coal ash entering the furnace through liquid ash discharge, significantly reducing the risk of slagging and fouling on the heating surfaces of the cold ash section, making it advantageous for burning low-ash-melting-point coals. Considering the characteristics of liquid ash discharge boilers, they hold promise for safe combustion applications. R B / A High-alkali coal with a Na2O content higher than 2.5% and a Na2O content higher than 0.30% has overcome the slagging and fouling characteristics of high-alkali coal. In recent years, the technology route of using high-alkali coal in liquid ash discharge furnaces has received attention from the industry.

[0004] The coal quality parameters of high-alkali coal resources in Xinjiang are widely distributed. In some regions or some coal seams of the same mining site, the coal ash content is high. R B / A High-alkali coal with a Na2O content exceeding 5.0% is extremely difficult to utilize. Even when using a liquid ash discharge furnace for pure combustion, there is still a serious problem of fouling on the heating surface of the cold ash section. This is because the excess Na and K prevents a large amount of alkali metals from being reliably captured by the liquid ash, and they still enter the cold ash section in gaseous form with the flue gas, threatening boiler safety. The problem of fouling on the tail heating surface of the liquid ash discharge furnace has been proven by laboratory tests (Zhou Guangqin et al. Combustion and fouling characteristics of high-sodium coal from Zhundong in a liquid ash discharge cyclone furnace [J]. Thermal Power Generation, 2018, 47(11): 40-45). Therefore, when burning high-alkali coal with extreme coal quality parameters, the fouling problem in the cold ash section of the liquid ash discharge furnace remains a very prominent challenge.

[0005] Furthermore, the thickness of high-alkali coal seams in Xinjiang reaches 20–80 meters, and coal quality parameters frequently fluctuate during the mining process. Even with the overall combustion of liquid ash discharge furnaces... R B / A High-alkali coal with a pH less than 0.8 may still exhibit Na₂O and K₂O contents exceeding 8.0% at certain times. The fouling development of high-alkali coal can lead to very serious accidents within hours. Furthermore, the current inability to accurately detect the composition of coal ash entering the furnace beforehand makes it impossible to accurately predict fouling risks. Therefore, fouling problems in the cold ash section are likely to significantly hinder the safe and reliable operation of liquid ash discharge furnaces burning high-alkali coal from Xinjiang. Summary of the Invention

[0006] To address the problem of fouling in the cold ash section of a liquid ash discharge boiler when burning high-alkali coal, this invention provides a method and system for preventing fouling on the tail heating surface of the boiler. By using a fouling inhibitor, fouling on the tail heating surface is suppressed, thereby improving the safety and reliability of boiler operation.

[0007] This invention provides a system for preventing fouling of the tail-end heating surface of a liquid slag discharge furnace to solve the aforementioned problem. The system includes a liquid slag discharge furnace and an ejector. The liquid slag discharge furnace includes a cold slag section, a water-cooled wall, a tail-end heating surface, a flue gas passage, and a molten slag section. According to the flue gas flow, the cold slag section is located downstream of the molten slag section and is the burnout zone of the liquid slag discharge furnace. The water-cooled wall is the boiler heating surface located in the cold slag section. The tail-end heating surface is located downstream of the cold slag section, and the flue gas passage is located downstream of the tail-end heating surface. The ejector is installed on the water-cooled wall, and its inlet is connected to a channel for conveying fouling inhibitors and a medium. The gas-solid mixture of the fouling inhibitor and the conveying medium enters the cold slag section via the ejector, mixes with the flue gas and fly ash, and then flows to the tail-end heating surface.

[0008] The injectors are of the single-layer multi-nozzle type or arranged in more than one layer, and the injectors are distributed on two pairs of water-cooled walls or on four water-cooled walls.

[0009] The injector is either a single-channel DC nozzle or a dual-channel nozzle with internal DC and external swirl.

[0010] Some or all of the injectors are burnout air nozzles in the cold slag section.

[0011] It also includes a storage silo, a feeder, a grinding mill, a media supply unit, and a powder silo; the storage silo, feeder, and grinding mill are connected in sequence; the media supply unit is connected to the grinding mill; the air-powder outlet of the grinding mill is connected to the ejector through a pipeline, and the discharge port of the powder silo is connected to the channel of the conveying medium. The conveying medium carries the contamination inhibitor to the ejector and the cold slag section. The grinding mill is a steel ball grinding mill.

[0012] This invention provides a method for preventing fouling on the tail-end heating surface of a liquid slag discharge furnace to solve the aforementioned problem. A fouling inhibitor is sprayed into the cold slag section of the liquid slag discharge furnace. The fouling inhibitor is a solid powder with an average particle size of less than 50 μm. According to industrial analysis methods for coal, the fouling inhibitor meets the following mass content limits:

[0013] 1) M t ≤15%;

[0014] 2) A ar ≥60%;

[0015] 3) S ar, t ≤1%;

[0016] According to the coal ash composition analysis method, the ash composition detection index of the contamination inhibitor meets the following mass content limits:

[0017] 1) 40%≤ w (SiO2)≤80%;

[0018] 2) 15%≤ w (Al2O3)≤50%;

[0019] 3) w (Fe2O3)≤10%;

[0020] 4) w (Na2O)≤2%;

[0021] 5) w (K2O)≤3%;

[0022] 6) w (SiO2) +w (Al2O3) +w (TiO2)≥75%;

[0023] 7) w (Fe2O3) +w (CaO) +w (MgO) +w (Na2O) +w (K2O)≤20%;

[0024] Furthermore, when the contamination inhibitor is a coal-bearing clay mineral, the clay mineral's detection index meets the following mass content limits according to the industrial analysis methods for coal:

[0025] 1) M t ≤8%;

[0026] 2) A ar ≥80%;

[0027] 3) S ar, t ≤0.7%;

[0028] According to the coal ash composition analysis method, the ash composition detection index of the clay minerals meets the following mass content limits:

[0029] 1) 55%≤ w (SiO2)≤80%;

[0030] 2) 15%≤ w (Al2O3)≤35%;

[0031] 3) w (Fe2O3)≤8%;

[0032] When the contamination inhibitor is kaolin, bentonite, or ceramic clay, the detection index of the contamination inhibitor shall meet the following mass content limits according to the industrial analysis methods for coal:

[0033] 1) M t ≤6%;

[0034] 2) A ar ≥85%;

[0035] 3) S ar, t ≤0.5%;

[0036] According to the coal ash composition analysis method, the ash composition detection index of the contamination inhibitor meets the following mass content limits:

[0037] 1) 40%≤ w (SiO2)≤60%;

[0038] 2) 25%≤ w (Al2O3)≤50%;

[0039] 3) w (Fe2O3)≤5%;

[0040] When the contamination inhibitor is coal gangue, the coal gangue detection index meets the following mass content limits according to the industrial analysis methods for coal:

[0041] 1) M t ≤15%;

[0042] 2) A ar ≥60%;

[0043] 3) S ar, t ≤1%;

[0044] 4) V daf ≥35%;

[0045] According to the coal ash composition analysis method, the ash composition detection index of the contamination inhibitor meets the following mass content limits:

[0046] 1) 40%≤ w (SiO2)≤60%;

[0047] 2) 25%≤ w (Al2O3)≤50%;

[0048] 3) w (Fe2O3)≤10%;

[0049] 4) w (Na2O)≤1.5%;

[0050] 6)w (SiO2) +w (Al2O3) +w (TiO2)≥80%;

[0051] 7) w (Fe2O3) +w (CaO) +w (MgO) +w (Na2O) +w (K2O)≤15%.

[0052] Furthermore, the mass-weighted average particle size of the fouling inhibitor is less than 15 μm; the amount of fouling inhibitor added is 2.0~5.0% of the amount of coal fed into the boiler.

[0053] Furthermore, the amount of fouling inhibitor added is controlled according to the elemental composition of fly ash in the boiler tail flue gas. Specifically, this is achieved by configuring a fly ash sampling device and an online elemental analysis system for solid matter in the boiler tail flue gas, and adjusting the amount of fouling inhibitor added in real time based on the following element mass content limits:

[0054] 1) w (Si)≥20%;

[0055] 2) w (Al)≥8%;

[0056] 3) w (Na)≤2.4%;

[0057] 4) w (Si)+ w (Al)≥34%.

[0058] Furthermore, a portion of the boiler's hot primary air, hot secondary air, or hot flue gas is extracted to dry the fouling inhibitor, and the fouling inhibitor, ground into fine particles, is sent to the cold slag section of the liquid slag discharge furnace.

[0059] Compared with the prior art, the present invention has at least the following beneficial effects:

[0060] ①This invention addresses the problem of fouling of the tail heating surface in liquid ash discharge furnaces when burning high-alkali coal with extreme alkali-acid ratios or high-alkali coal with frequent fluctuations in coal quality parameters, which has not been addressed in existing research, and proposes a solution.

[0061] ② This invention proposes to spray a fouling inhibitor in the cold slag section of a liquid slag discharge furnace and specifies the quality indicators of the fouling inhibitor, thus forming an innovative solution for fouling of the tail heating surface of a liquid slag discharge furnace.

[0062] ③ The fouling inhibitor of this invention, when introduced into the boiler within a suitable temperature range and location, can strongly interact with gaseous alkali metals. Firstly, the fouling inhibitor utilizes the pores created during heating to adsorb and capture large quantities of gaseous alkali metals, with some reacting with them to form solids, thereby reducing the concentration of gaseous alkali metals in the flue gas and lowering the rate at which dust-laden flue gas enters the tail heating surface and causes fouling. Secondly, as a high-melting-point substance, the fouling inhibitor has a significant dilution effect on molten ash in the flue gas and the sticky ash formed during the condensation of gaseous alkali metals, greatly reducing the adhesion of flue dust when it contacts the tail heating surface and significantly reducing the fouling rate. Thirdly, after significantly reducing the adhesion of flue dust, the resulting fouling layer has weak adhesion, is relatively loose, and is easily detached or blown away, thus greatly reducing the safety threat to the boiler.

[0063] ④ This invention can solve the problem of fouling on the tail heating surface of a liquid slag discharge furnace. By using a fouling inhibitor, fouling on the tail heating surface can be effectively suppressed, improving the safety and stability of boiler operation, and thus improving the operating efficiency of the power plant.

[0064] ⑤ This invention can suppress fouling of the tail heating surface of the liquid slag discharge furnace, thereby enhancing the adaptability of the liquid slag discharge furnace to frequent fluctuations in the coal quality parameters of high-alkali coal, greatly expanding the range of combustible coal types, and promoting the reduction of coal procurement costs.

[0065] ⑥ This invention provides an easy-to-implement system and equipment configuration scheme. The technical solution of this invention is simple, economical, and easy to implement. The contamination inhibitor can be selected from natural substances found in coal mines or geological deposits, which are readily available and low in cost.

[0066] ⑦ At excessively high temperatures (slag section), the fouling inhibitor easily sintersects into a low-porosity material, significantly reducing its reactivity with gaseous alkali metals. Conversely, at excessively low temperatures (the area where the tail heating surface is located), the fouling inhibitor cannot be rapidly dehydrated, failing to form abundant pores, and the temperature range is unfavorable for the chemical reaction between the fouling inhibitor and gaseous alkali metals. The fouling inhibitor of this invention is injected into the cold slag section of the liquid slag discharge furnace, rather than at other locations, which facilitates obtaining a highly active fouling inhibitor and maximizes its effectiveness. Attached Figure Description

[0067] Figure 1 This is a simplified diagram of a system for preventing fouling of the tail heating surface of a liquid slag discharge furnace according to the present invention.

[0068] Figure 2 This is a schematic diagram of the structure of a liquid slag discharge furnace with multiple layers of contamination inhibitor nozzles according to the present invention.

[0069] Figure 3 This is a schematic diagram showing the nozzles arranged in a two-wall water-cooled configuration.

[0070] Figure 4 This is a schematic diagram showing the nozzles arranged in a water-cooled wall configuration on all four sides.

[0071] Figure 5 This is a schematic diagram of a single-channel DC nozzle.

[0072] Figure 6 This is a schematic diagram of a dual-channel nozzle with an internal DC and external swirling flow.

[0073] Figure 7 This is a schematic diagram of a system equipped with a powder silo to prevent fouling of the tail heating surface of a liquid slag discharge furnace.

[0074] 1-Storage bin; 2-Feeder; 3-Grinding mill; 4-Media supply unit; 5-Injector; 6-Cold slag section; 7-Water-cooled wall; 8-Tail heating surface; 9-Flue gas exhaust channel; 10-Pulverized coal burner; 11-Slag melting section; 12-Slag discharge port; 13-Slag collection pipe; 14-Inner direct current channel; 15-Outer vortex channel; 16-Pulverized coal bin. Detailed Implementation

[0075] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the present invention are shown in the accompanying drawings.

[0076] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The technical solution of this invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0077] Unless otherwise stated, the exemplary embodiments / exemplifications shown are to be understood as providing exemplary features of various details that provide ways in which the technical concept of the invention can be implemented in practice. Therefore, unless otherwise stated, the features of the various embodiments / exemplifications may be additionally combined, separated, interchanged and / or rearranged without departing from the technical concept of the invention.

[0078] When a component is referred to as being "on" or "above" another component, "connected to," or "joined to" another component, the component may be directly on, directly connected to, or directly joined to the other component, or there may be intermediate components. However, when a component is referred to as being "directly on" another component, "directly connected to," or "directly joined to" another component, there are no intermediate components. Therefore, the term "connection" can refer to a physical connection, an electrical connection, etc., and may or may not have intermediate components.

[0079] First, the basic characteristics of liquid slag discharge furnaces are described: Liquid slag discharge furnaces come in various types. The boiler body of a liquid slag discharge furnace generally includes at least a pulverized coal burner 10, a slag melting section 11, a slag discharge port 12, a cold slag section 6, a water-cooled wall 7, a tail heating surface 8, and a flue gas passage 9.

[0080] The pulverized coal burner 10 is a device that sends air and pulverized coal into the molten slag section 11 for combustion. In some liquid slag discharge furnaces, the pulverized coal burner 10 is injected into the molten slag section 11 for combustion after the high-temperature air and pulverized coal have been ignited and pre-combusted.

[0081] This invention also provides a system for preventing fouling of the tail heating surface of a liquid slag discharge furnace, including a liquid slag discharge furnace and an injector 5; the liquid slag discharge furnace includes a cold slag section 6, a water-cooled wall 7, a tail heating surface 8, a flue gas passage 9, and a molten slag section 11; according to the flue gas flow, the cold slag section 6 is located downstream of the molten slag section 11 and is the burnout zone of the liquid slag discharge furnace; the water-cooled wall 7 is the boiler heating surface located in the cold slag section 6; the tail heating surface 8 is located downstream of the cold slag section 6, and the flue gas passage 9 is located downstream of the tail heating surface 8; the injector 5 is installed on the water-cooled wall 7, and the gas-solid mixture of fouling inhibitor and conveying medium enters the cold slag section 6 through the injector, mixes with the flue gas and fly ash, and flows to the tail heating surface 8.

[0082] As an optional implementation, the injector 5 is designed as a single-layer, multi-nozzle type, with the nozzles distributed on two opposite water-cooled walls or on four water-cooled walls; the injector 5 can be arranged in double or multiple layers, and other implementation methods are the same as in specific implementation method one; some or all of the injectors 5 are designed as burnout air nozzles for the cold slag section 6, as shown in the reference. Figure 3 and Figure 4 .

[0083] Furthermore, the injector 5 described in this invention is designed as a single-channel DC nozzle or an internal DC and external swirling dual-channel nozzle. When the injector 5 is designed as a single-channel DC nozzle, the nozzle velocity is designed to be 30~60m / s, which can significantly enhance the jet penetration and improve the efficiency of uniform mixing of the contaminant and the flue gas. When the injector 5 is designed as an internal DC and external swirling dual-channel nozzle, the DC channel is used to transport the medium and the contaminant, while the external swirling channel only contains the medium. The expansion cone design of the internal DC and external swirling dual-channel nozzle is 20~30°, which enhances the rigidity of the rotating jet and strengthens the mixing of the contaminant and the flue gas. (Refer to...) Figure 5 and Figure 6 .

[0084] The slag melting section 11 is the main combustion zone of the liquid slag discharge furnace. Because the furnace wall of the slag melting section 11 is lined with refractory insulation material, the highest furnace temperature reached by pulverized coal combustion (generally 1500~1800℃) is much higher than that of conventional pulverized coal boilers (generally 1250~1450℃). Most of the ash in the coal melts directly at high temperatures and flows to the slag pool at the bottom of the slag melting section 11 under gravity. A slag discharge port 12 is located at the bottom of the slag pool. The excess air coefficient in the slag melting section 11 is generally 0.85~0.95, and 40%~90% of the ash in the coal becomes liquid slag in the slag melting section 11. The flue gas generated by combustion in the slag melting section 11, including fly ash and gasified coal components, flows downstream to the cold slag section 6.

[0085] The water-cooled wall 7 of the cold slag section 6 is not lined with refractory insulation material, thus enabling efficient heat transfer and steam production. The overall flue gas temperature in the cold slag section 6 is generally below 1300℃, lower than the ash melting point of coal ash, and the flue gas continues to cool, so most of the coal ash remains solid, while the gasified alkali / alkaline earth metal compounds also begin to condense in this area. The cold slag section 6 is generally equipped with burnout air nozzles to provide air that ensures complete combustion of gaseous and solid combustibles. The overall excess air coefficient of the molten slag section 11 and the cold slag section 6 in the boiler liquid slag discharge furnace is generally 1.10~1.25. Some of the large particles or slag lumps generated by continued combustion in the cold slag section 6 fall to the bottom of the furnace and are discharged from the boiler, or are guided by relevant structural components into the slag pool at the bottom of the molten slag section 11. The total slag discharged from the molten slag section 11 and the cold slag section 6 in the liquid slag discharge furnace can account for 50%~90% of the coal ash content entering the furnace. The flue gas from the cold slag section 6 flows downstream to the tail heating surface 8.

[0086] The tail-end heating surface 8 generally includes tube-type heating surfaces such as superheaters, reheaters, and economizers. The main heat exchange mechanism of the tail-end heating surface 8 is convective heat transfer, with significant radiative heat transfer potentially occurring in the area near the upstream cold slag section 6. The flue gas from the tail-end heating surface 8 flows downstream through the exhaust duct 9. Severe fouling of the tail-end heating surface 8 has a significant impact on the boiler. If the fouling layer is thick and blocks the flue, it may directly lead to the boiler's flue gas flow failing to meet load requirements, significantly reducing the generator unit's ability to respond to grid dispatch commands. Soot blowers are generally installed in the tail-end heating surface 8 to periodically remove adhering ash. If the fouling layer is too tightly adhered, the soot blowers cannot clean the heating surface, and the underlying deposits will accelerate fouling development. Therefore, in principle, properly controlling the adhesion of coal ash and the growth rate of fouling is crucial for controlling fouling of the tail-end heating surface 8. The flue gas from the tail-end heating surface 8 flows downstream through the exhaust duct 9.

[0087] In addition, some liquid slag discharge furnaces, especially closed liquid slag discharge furnaces, are equipped with a slag collection pipe 13 between the molten slag section 11 and the cold slag section 6. The slag collection pipe 13 is a partition device with a cooling medium and a heating surface tube inside and refractory material on the outside. It has two functions: first, to collect ash and slag, especially molten slag, in the flue gas; and second, to separate the molten slag section 11 from the cold slag section 6, which helps to maintain the high temperature of the molten slag section 11.

[0088] The described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Specific implementation method one:

[0090] A contamination inhibitor is injected into the cold slag section of a liquid slag discharge furnace; the contamination inhibitor is a solid powder with an average particle size of less than 50 μm; according to the industrial analysis methods for coal, the contamination inhibitor meets the following mass content limits:

[0091] 1) M t ≤15%;

[0092] 2) A ar ≥60%;

[0093] 3) S ar, t ≤1%;

[0094] According to the coal ash composition analysis method, the ash composition detection index of the contamination inhibitor meets the following mass content limits:

[0095] 1) 40%≤ w (SiO2)≤80%;

[0096] 2) 15%≤ w (Al2O3)≤50%;

[0097] 3) w (Fe2O3)≤10%;

[0098] 4) w (Na2O)≤2%;

[0099] 5) w (K2O)≤3%;

[0100] 6) w (SiO2) +w (Al2O3) +w (TiO2)≥75%;

[0101] 7) w (Fe2O3)+w (CaO) +w (MgO) +w (Na2O) +w (K2O)≤20%.

[0102] This implementation method addresses the issue of fouling on the tail heating surface of liquid ash discharge furnaces, which has not been addressed in existing research when using high-alkali coal with extreme alkali-acid ratios or high-alkali coal with frequent fluctuations in coal quality parameters. It proposes to spray fouling inhibitors in the cold ash section of the liquid ash discharge furnace and specifies the quality indicators of the fouling inhibitors based on scientific principles and boiler characteristics, thus forming an innovative solution for fouling on the tail heating surface of liquid ash discharge furnaces. The fouling inhibitor in this scheme enters the boiler within a suitable temperature range and location (cold slag section). It can strongly interact with gaseous alkali metals. First, the fouling inhibitor utilizes the pores created during the heating process to adsorb and capture a large amount of gaseous alkali metals, and some of it reacts with the gaseous alkali metals to form solids, thereby reducing the concentration of gaseous alkali metals in the flue gas and lowering the rate at which dust-laden flue gas enters the tail heating surface and causes fouling. Second, as a high-melting-point substance, the fouling inhibitor has a significant dilution effect on molten ash in the flue gas and the sticky ash formed during the condensation process of gaseous alkali metals, greatly reducing the adhesion of flue dust when it comes into contact with the tail heating surface, and significantly reducing the fouling rate. Third, after the flue dust adhesion is greatly reduced, the resulting fouling layer has weak adhesion and is relatively loose, making it easy to fall off or be blown away, thus greatly reducing the safety threat to the boiler. Specific Implementation Method Two:

[0104] Based on Implementation Method 1, coal-bearing clay minerals are selected as contamination inhibitors. According to the industrial analysis methods for coal, the selected clay mineral detection indicators need to further meet the following mass content limits:

[0105] 1) M t ≤8%;

[0106] 2) A ar ≥80%;

[0107] 3) S ar, t ≤0.7%;

[0108] According to the coal ash composition analysis method, the ash composition detection indicators of the selected clay minerals need to further meet the following mass content limits:

[0109] 1) 55%≤ w (SiO2)≤80%;

[0110] 2) 15%≤ w (Al2O3)≤35%;

[0111] 3) w (Fe2O3)≤8%.

[0112] In this implementation method, readily available coal-bearing clay minerals are selected, the process is easy to implement, and the cost is low and economical. The sedimentary rocks from which coal-bearing clay minerals have undergone geological changes are mainly composed of silica and aluminum, and are common geological strata in large coalfields. Therefore, the clay minerals meeting the requirements in this implementation method are widely available. Within the above-mentioned index range, the clay's activity is highly suitable for capturing gaseous alkali metals, diluting viscous substances, and inhibiting fouling of the tail heating surface 8. Specific implementation method three:

[0114] Based on Specific Implementation Method 1, kaolin, bentonite, or ceramic clay are selected as contamination inhibitors. According to the industrial analysis methods for coal, the selected contamination inhibitor detection indicators need to further meet the following mass content limits:

[0115] 1) M t ≤6%;

[0116] 2) A ar ≥85%;

[0117] 3) S ar, t ≤0.5%;

[0118] According to the coal ash composition analysis method, the ash composition detection index of the selected contamination inhibitor meets the following mass content limits:

[0119] 1) 40%≤ w (SiO2)≤60%;

[0120] 2) 25%≤ w (Al2O3)≤50%;

[0121] 3) w (Fe2O3)≤5%.

[0122] In this embodiment, the selected kaolin, bentonite, or ceramic clay are common and inexpensive minerals with excellent composition. After dehydration or heat treatment, they have a strong adsorption effect on alkaline / alkaline earth metal gaseous compounds such as Na and K, thereby significantly inhibiting the contamination of the tail heating surface 8. Specific implementation method four:

[0124] Based on Implementation Method 1, coal gangue is selected as a contamination inhibitor. According to the industrial analysis methods for coal, the selected coal gangue testing indicators need to further meet the following mass content limits:

[0125] 1) Mt ≤15%;

[0126] 2) A ar ≥60%;

[0127] 3) S ar, t ≤1%;

[0128] 4) V daf ≥35%;

[0129] According to the coal ash composition analysis method, the ash composition detection index of the selected contamination inhibitor needs to further meet the following mass content limits:

[0130] 1) 40%≤ w (SiO2)≤60%;

[0131] 2) 25%≤ w (Al2O3)≤50%;

[0132] 3) w (Fe2O3)≤10%;

[0133] 4) w (Na2O)≤1.5%;

[0134] 6) w (SiO2) +w (Al2O3) +w (TiO2)≥80%;

[0135] 7) w (Fe2O3) +w (CaO) +w (MgO) +w (Na2O) +w (K2O)≤15%.

[0136] In this embodiment, the selected coal gangue is a common byproduct of coal mining, some of which are even solid wastes with extremely low calorific value that cannot be reused. However, its ash composition shows that it can interact with alkaline / alkaline earth metal gaseous compounds such as Na and K, thus inhibiting fouling of the tail heating surface 8. Therefore, coal gangue powder is injected into the cold slag section 6 of the liquid slag discharge furnace. The combustible components in the coal gangue can burn and burn out under the action of flue gas temperature, releasing heat. On the other hand, the lime content of the coal gangue can inhibit fouling of the tail heating surface 8. Specific implementation method five:

[0138] The mass-weighted average particle size of the contamination inhibitor is controlled to be less than 15 μm, and other implementation methods are the same as any of the specific implementation methods one to four. Generally, a ball mill is used for heating and drying to grind the contamination inhibitor and obtain powder with the specified particle size.

[0139] In this embodiment, the contamination inhibitor is maximally pulverized, exposing the largest specific surface area, which greatly reduces the heat and mass transfer resistance between the contamination inhibitor, gaseous alkali / alkaline earth metals, and flue gas components. This can significantly accelerate the capture of alkali / alkaline earth metal gaseous compounds such as Na and K by the contamination inhibitor and the dilution and viscosity reduction effect on sticky particles, thus suppressing contamination of the tail heating surface 8. Specific implementation method six:

[0141] The amount of the fouling inhibitor added is 2.0-5.0% of the amount of coal fed into the boiler. Other implementation methods are the same as any one of the specific implementation methods one to four.

[0142] This implementation method establishes an appropriate dosage of fouling inhibitor. Generally, the dosage of fouling inhibitor is related to factors such as the quality of the coal fed into the boiler, the slag collection rate of the molten slag section of the liquid slag discharge furnace, the structural type of the tail heating surface, and the arrangement and operation mode of the sootblower. If the boiler itself has strong anti-fouling capabilities, the dosage of fouling inhibitor can be lower; conversely, the dosage should be increased. However, from a practical and economic perspective, the optimal dosage of fouling inhibitor is 2.0% to 5.0% of the boiler's coal feed rate. Adjusting the dosage within this range according to the boiler load level and slagging fouling situation can effectively suppress the deterioration of fouling and achieve the best economic benefits.

[0143] To further illustrate the additive ratio, Tables 1 and 2 provide the process settlement results for adding fouling inhibitors to extremely high-alkali coal and common medium-to-high-risk high-alkali coal, respectively. The tables show that by adding an appropriate proportion of typical fouling inhibitors, the alkali-to-acid ratio of fly ash at the inlet of the tail heating surface 8 can be adjusted to below 0.36, the mass content of silicon and aluminum oxides is greater than 70%, the mass content of silicon is greater than 20%, the mass content of aluminum is greater than 8%, and the mass content of silicon and aluminum is greater than 34%. This significantly inhibits fouling of the tail heating surface 8.

[0144] Table 1. Calculation Table for Controlling Flue Dust Composition at Tail Heating Surface Inlet (Extreme Coal Quality)

[0145]

[0146] Table 2. Calculation Table for Controlling Flue Dust Composition at Tail Heating Surface Inlet (Common High-Alkali Coal)

[0147] Specific implementation method seven:

[0149] The dosage of fouling inhibitor is adjusted according to the elemental composition of fly ash in the boiler tail gas. Specifically, this is achieved by configuring a fly ash sampling device and an online elemental analysis system for solid matter in the boiler tail gas, and adjusting the dosage of fouling inhibitor in real time based on the following element mass content limits:

[0150] 1) w (Si)≥20%;

[0151] 2) w (Al)≥8%;

[0152] 3) w (Na)≤2.4%;

[0153] 4) w (Si)+ w (Al)≥34%.

[0154] The remaining implementation methods are the same as any of the specific implementation methods described above.

[0155] This embodiment employs an easily implemented method for determining the proportion of fouling inhibitors. Common fly ash sampling devices (such as compressed air ejector isokinetic sampling devices) and online elemental analysis systems for solid materials (such as X-ray fluorescence spectrometry) are installed in the flue gas channel 9 of the liquid slag discharge furnace. By detecting the composition of the flue ash, the appropriate amount of fouling inhibitor to add is determined. The addition amount is then adjusted according to the target, thus achieving closed-loop control. Furthermore, this embodiment primarily detects silicon and aluminum, which have relatively high content, effectively reducing detection errors, obtaining more accurate and reliable results, enhancing the utilization efficiency of fouling inhibitors, reducing dosage, and saving costs. Detailed implementation method eight:

[0157] The primary air, hot secondary air, or hot flue gas pipeline is connected to the fouling inhibitor delivery pipeline. A portion of the hot primary air, hot secondary air, or hot flue gas from the boiler is extracted to dry the fouling inhibitor. The fouling inhibitor, which is then ground into fine particles, is sent to the cold slag section of the liquid slag discharge furnace. The remaining implementation methods are the same as any of the aforementioned specific implementation methods.

[0158] This implementation method, by equipping the boiler with drying and grinding devices, can effectively control the moisture content and fineness of the fouling inhibitor in the process, thereby enhancing the effectiveness of the fouling inhibitor. Specific implementation method nine:

[0160] Combined with appendix Figure 1This embodiment describes a system for preventing fouling of the tail-end heating surface of a liquid slag discharge furnace, provided by the present invention to solve the aforementioned problem. The system includes a liquid slag discharge furnace and an injector 5. The liquid slag discharge furnace includes a cold slag section 6, a water-cooled wall 7, a tail-end heating surface 8, a flue gas passage 9, and a molten slag section 11. According to the flue gas flow, the cold slag section 6 is located downstream of the molten slag section 11 and is the burnout zone of the liquid slag discharge furnace. The water-cooled wall 7 is the boiler heating surface located in the cold slag section 6. The tail-end heating surface 8 is located downstream of the cold slag section 6, and the flue gas passage 9 is located downstream of the tail-end heating surface 8. The injector 5 is installed on the water-cooled wall 7. A gas-solid mixture of fouling inhibitor and conveying medium enters the cold slag section 6 through the injector, mixes with the flue gas and fly ash, and then flows to the tail-end heating surface 8. Other embodiments are based on the process methods described in specific embodiments one to eight.

[0161] This implementation method clarifies the equipment configuration and structure of the method described in the foregoing specific embodiments, fully considering the characteristics of liquid slag discharge and the risk of fouling, and is simple and economical to arrange. It can flexibly and effectively control the fouling of the heating surface. Specific Implementation Method Ten:

[0163] This embodiment is based on specific embodiment nine, and further configures the storage silo 1, feeder 2, grinding mill 3, and media supply unit 4; the storage silo 1, feeder 2, and grinding mill 3 are connected in sequence; the media supply unit 4 is connected to the grinding mill 3; the air-powder outlet of the grinding mill 3 is connected to the ejector 5 through a pipeline, see reference. Figure 1 .

[0164] This implementation introduces a drying and grinding device for the boiler, which can effectively control the moisture content and fineness of the fouling inhibitor in the process, enhance the effectiveness of the fouling inhibitor, and is simple and economical to implement. Detailed Implementation Method Eleven:

[0166] Combined with appendix Figure 1 This embodiment describes a single-layer nozzle based on any of the aforementioned embodiments. It can utilize the existing burnout air nozzle of the boiler or create a separate single-layer nozzle.

[0167] This implementation method is simple and economical. When using the boiler's existing burnout air nozzles, the amount of modification work is small and the initial investment is low. Detailed Implementation Method Twelve:

[0169] Combined with appendix Figure 2 This embodiment is described below. Based on specific embodiment eleven, a multi-layered fouling inhibitor nozzle 5 is further provided. This allows fouling inhibitors to be sprayed in different temperature ranges, and the addition position of the fouling inhibitor can be adjusted according to the load and operating parameter characteristics, thereby improving the overall utilization efficiency of the fouling inhibitor and reducing costs.

[0170] The present invention discloses a system for preventing fouling of the tail-end heating surface of a liquid slag discharge furnace, which also includes a central storage pulverizing system for drying, grinding, and storing fouling inhibitors. The central storage pulverizing system includes at least a powder silo 16, the outlet of which is connected to a channel for conveying medium. The conveying medium carries the fouling inhibitors to the injector 5 and the cold slag section 6. Because the fouling inhibitor powder is stored, the reliability of operation is significantly increased, preventing downtime due to mill failure. Furthermore, the pulverizing process of the central storage pulverizing system can be flexibly adjusted according to boiler load and other actual operating conditions, and it also allows multiple boilers to share a single fouling inhibitor grinding system and powder silo 16. (See reference...) Figure 7 .

[0171] The above technical solutions may be flexibly applied and implemented within the scope described, according to actual needs.

[0172] This invention is generally used in liquid slag discharge boilers that burn high-alkali coal. It can solve the problem of slagging and fouling on the boiler tail heating surface 8, and ensure that the growth rate of fouling is suppressed under the condition of frequent fluctuations in boiler operating parameters and coal quality parameters, thus ensuring the safety of power plant boilers.

Claims

1. A system for preventing fouling of the heating surface at the tail end of a liquid slag discharge furnace, characterized in that: The system includes a liquid slag discharge furnace and an injector (5); the liquid slag discharge furnace includes a cold slag section (6), a water-cooled wall (7), a tail heating surface (8), a flue gas passage (9), and a molten slag section (11); according to the flue gas flow, the cold slag section (6) is located downstream of the molten slag section (11) and is the burnout zone of the liquid slag discharge furnace; the water-cooled wall (7) is the boiler heating surface located in the cold slag section (6); the tail heating surface (8) is located downstream of the cold slag section (6), and the flue gas passage (9) is located downstream of the tail heating surface (8); the injector (5) is installed on the water-cooled wall (7), and the inlet of the injector (5) is connected to the channel for conveying the fouling inhibitor and the medium. The gas-solid mixture of the fouling inhibitor and the conveying medium enters through the injector (5). The cold slag section (6) mixes with flue gas and fly ash from coal combustion and flows to the tail heating surface (8); the injector (5) is a single-layer multi-nozzle type or more than one layer arrangement, and the injector (5) is distributed on two pairs of water-cooled walls or on four sides of water-cooled walls; some or all of the injectors (5) are burnout air nozzles of the cold slag section (6); the injector (5) is an inner DC and outer vortex dual-channel nozzle, the DC channel is used to transport the medium and transport the contaminant inhibitor, and the outer vortex channel only contains the medium. The expansion cone design of the inner DC and outer vortex dual-channel nozzle is 20-30°, and the mass-weighted average particle size of the contaminant inhibitor is less than 15μm; the amount of contaminant inhibitor added is 2.0-5.0% of the amount of coal fed into the boiler.

2. The system for preventing fouling of the tail heating surface of a liquid slag discharge furnace according to claim 1, characterized in that: It also includes a storage bin (1), a feeder (2), a grinding mill (3) and a media supply unit (4); the storage bin (1), the feeder (2) and the grinding mill (3) are connected in sequence; the media supply unit (4) is connected to the grinding mill (3); the air-powder outlet of the grinding mill (3) is connected to the ejector (5) through a pipeline, and the conveying medium carries the contamination inhibitor to the ejector (5) and the cold slag section (6). The grinding mill (3) is a steel ball grinding mill.

3. A method for preventing fouling of the tail heating surface of a liquid slag discharge furnace, characterized in that: Based on the system for preventing fouling of the tail heating surface of a liquid slag discharge furnace as described in claim 1 or 2, a fouling inhibitor is sprayed into the cold slag section of the liquid slag discharge furnace; the fouling inhibitor is a solid powder with an average particle size of less than 50 μm; according to the industrial analysis method for coal, the detection index of the fouling inhibitor meets the following mass content limits: 1)M t ≤15%； 2)A ar ≥60%； 3)S ar ,t≤1%; According to the coal ash composition analysis method, the ash composition detection index of the contamination inhibitor meets the following mass content limits: 1) 40%≤w(SiO2)≤80%; 2) 15% ≤ w(Al2O3) ≤ 50%; 3) w(Fe2O3)≤10%; 4) w(Na2O)≤2%; 5) w(K2O)≤3%; 6)w(SiO2)+w(Al2O3)+w(TiO2)≥75%; 7)w(Fe2O3)+w(CaO)+w(MgO)+w(Na2O)+w(K2O)≤20%; The amount of fouling inhibitor added is controlled according to the elemental composition of fly ash in the boiler tail flue gas. Specifically, a fly ash sampling device and an online elemental analysis system for solid matter are configured for the boiler tail flue gas, and the amount of fouling inhibitor added is controlled in real time based on the following element mass content limits: 1) w(Si)≥20%; 2) w(Al)≥8%; 3) w(Na) ≤ 2.4%; 4) w(Si) + w(Al) ≥ 34%.

4. The method for preventing fouling of the tail heating surface of a liquid slag discharge furnace according to claim 3, characterized in that: When the contamination inhibitor is a coal-bearing clay mineral, the clay mineral's detection index meets the following mass content limits according to the industrial analysis methods for coal: 1)M t ≤8%； 2)A ar ≥80%； 3)S ar ,t≤0.7%; According to the coal ash composition analysis method, the ash composition detection index of the clay minerals meets the following mass content limits: 1) 55%≤w(SiO2)≤80%; 2) 15% ≤ w(Al2O3) ≤ 35%; 3) w(Fe2O3)≤8%; When the contamination inhibitor is kaolin, bentonite, or ceramic clay, the detection index of the contamination inhibitor shall meet the following mass content limits according to the industrial analysis methods for coal: 1)M t ≤6%； 2)A ar ≥85%； 3)S ar ,t≤0.5%; According to the coal ash composition analysis method, the ash composition detection index of the contamination inhibitor meets the following mass content limits: 1) 40% ≤ w(SiO2) ≤ 60%; 2) 25% ≤ w(Al2O3) ≤ 50%; 3) w(Fe2O3)≤5%; When the contamination inhibitor is coal gangue, the coal gangue detection index meets the following mass content limits according to the industrial analysis methods for coal: 1)M t ≤15%； 2)A ar ≥60%； 3)S ar ,t≤1%; 4)V daf ≥35%； According to the coal ash composition analysis method, the ash composition detection index of the contamination inhibitor meets the following mass content limits: 1) 40% ≤ w(SiO2) ≤ 60%; 2) 25% ≤ w(Al2O3) ≤ 50%; 3) w(Fe2O3)≤10%; 4) w(Na2O)≤1.5%; 6)w(SiO2)+w(Al2O3)+w(TiO2)≥80%; 7)w(Fe2O3)+w(CaO)+w(MgO)+w(Na2O)+w(K2O)≤15%.

5. The method for preventing fouling of the tail heating surface of a liquid slag discharge furnace according to claim 3, characterized in that: A portion of the boiler's hot primary air, hot secondary air, or hot flue gas is extracted to dry the fouling inhibitor, and the fouling inhibitor, ground into fine particles, is sent to the cold slag section of the liquid slag discharge furnace.

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