A method for extending the life of a pulverized coal entrained flow gasifier

Abstract

The application discloses a method for prolonging the service life of a pulverized coal entrained-flow gasification furnace. The method uses a molten slag surface tension mathematical model, a molten slag viscosity-temperature model and a mixed coal technology, strictly controls the content of silicon oxide, aluminum oxide, calcium oxide and iron oxide in the ash composition of the coal entering the furnace, reduces the surface tension of the high-temperature molten slag, promotes the molten slag to completely cover the silicon carbide refractory material, forms a dense molten slag layer on the surface of the refractory layer as a protective layer, and achieves the purpose of prolonging the service life of the silicon carbide refractory material. Moreover, the method realizes the "molten slag resistance", and the remaining ash can be normally discharged and used as a building material raw material such as cement.

Description

Technical Field

[0001] This invention relates to a method for extending the lifespan of a gasifier, specifically a method for extending the lifespan of a pulverized coal fluidized bed gasifier, belonging to the field of pulverized coal gasification technology. Background Technology

[0002] The gasification temperature of a pulverized coal fluidized bed gasifier reaches as high as 1400–1700℃, making refractory brick insulation unsuitable; water-cooled wall insulation is essential. Generally, a layer of amorphous silicon carbide refractory material, 10–30 mm thick, is cast onto the fire-facing surface of the water-cooled wall, with embedded metal pins 10–18 mm high. This amorphous silicon carbide refractory material has a heat resistance of 1500℃ and can withstand temperatures of 1400–1700℃ for short periods. For example, during the initial 8 hours of coal feeding into the gasifier, a complete slag layer has not yet formed on the fire-facing surface of the water-cooled wall, necessitating protection with silicon carbide refractory material.

[0003] However, silicon carbide refractories cannot be exposed to high temperatures for extended periods, otherwise their lifespan will be reduced, eventually damaging the water-cooled walls. In other words, the silicon carbide refractories themselves also require protection. Effective protection of the water-cooled walls, pins, and silicon carbide refractories is achieved, thereby protecting the water-cooled walls from hydrogen and sulfur corrosion from syngas, high-temperature ablation, and slag abrasion. The ash melting point of the coal fed into the furnace is generally <1450℃, and the pulverized coal gasification temperature is generally between 1400-1700℃. The high temperature melts the ash in the coal, forming tiny molten slag droplets in the crude gas. These droplets are affected by centrifugal force within the gasifier and the backflow effect around the high-speed coal burner flames, causing the tiny molten slag particles in the crude gas to be thrown onto the inner surface of the water-cooled walls, forming a slag layer. This slag layer consists of two parts: a fixed slag layer close to the water-cooled wall with a relatively constant thickness; and a liquid slag layer on the fire-facing side with a significantly varying thickness, flowing downwards under gravity. Studies have shown that covering silicon carbide refractories with slag can effectively slow down their erosion rate. However, complete slag coverage is an ideal situation, difficult to achieve with current technology. During the operation of pulverized coal gasifiers, localized areas such as the bottom cone and slag outlet often experience difficulty in slag adhesion or lack of a slag layer on the water-cooled walls, leading to damage to the silicon carbide refractories. In severe cases, this can damage the water-cooling pipes and cause unplanned shutdowns due to overheating in the annular space. Therefore, ensuring complete slag coverage of silicon carbide refractories is of paramount importance for protecting the inner walls of the gasifier. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a method for extending the lifespan of a pulverized coal fluidized bed gasifier. This method utilizes a mathematical model of slag surface tension, a slag viscosity-temperature model, and coal blending technology to strictly control the content of silicon oxide, aluminum oxide, calcium oxide, and iron oxide in the coal ash composition fed into the furnace. This reduces the surface tension of the high-temperature slag, allowing the slag to completely cover the silicon carbide refractory layer on the inner wall of the gasifier, forming a dense slag layer on the surface of the refractory layer. This achieves the goal of extending the lifespan of the silicon carbide refractory material, thereby realizing the technical objective of "using slag to resist slag." At the same time, the remaining ash can be discharged normally and used as raw materials for building materials such as cement.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for extending the service life of a pulverized coal fluidized bed gasifier, comprising the following steps:

[0006] 1) Calculate the surface tension value of the raw coal slag based on the mathematical model of slag surface tension;

[0007] 2) Classify raw coal according to the surface tension value of molten slag;

[0008] 3) Blend raw coal with different slag surface tension values ​​to obtain blended raw coal;

[0009] 4) The mixed raw coal is fed into the pulverized coal gasifier for reaction, and the molten slag is applied to the surface of the silicon carbide refractory material on the furnace wall.

[0010] This invention achieves precise proportioning of raw coal using a mathematical model of slag surface tension. While ensuring normal operation of the gasifier, it strictly controls the content of silicon oxide, aluminum oxide, calcium oxide, and iron oxide in the coal ash fed into the furnace, reducing the surface tension and contact angle of the slag. This allows the slag to wet and spread on the surface of the silicon carbide refractory layer, forming a uniform slag layer that completely covers the silicon carbide refractory layer, avoiding difficulties in slag adhesion and slag-free conditions on the surface. Furthermore, to verify the accuracy of this method, this invention also records the viscosity changes of the slag at various temperatures during gasification based on a slag viscosity-temperature model, ensuring the slag maintains fluidity in the working section of the gasifier.

[0011] As a preferred embodiment, the raw coal includes at least one of silicon oxide, iron oxide, aluminum oxide, and calcium oxide.

[0012] In the technical solution provided by this invention, the sum of the mass percentage concentrations of silicon oxide, iron oxide, aluminum oxide, and calcium oxide in the ash component of the raw coal is between 82% and 95%, while the sum of the mass percentage concentrations of other components such as sodium oxide, potassium oxide, magnesium oxide, phosphorus pentoxide, titanium oxide, and sulfur trioxide is between 5% and 18%. According to the Pareto principle (80 / 20 rule), the mass percentage concentrations of silicon oxide, iron oxide, aluminum oxide, and calcium oxide are considered the key components affecting the surface tension of the molten slag, while the influence of other components on the surface tension of the molten slag is ignored. Furthermore, among these four components, silicon oxide has the lowest surface tension, aluminum oxide has the highest, and the surface tensions of iron oxide and calcium oxide are in between and relatively close. Therefore, based on the differences in the surface tensions of these four components, the surface tension of the molten slag mixture can be adjusted by adjusting the mass percentage concentrations of silicon oxide, iron oxide, aluminum oxide, and calcium oxide.

[0013] As a preferred embodiment, the calculation process for the surface tension value of the slag in the raw coal is as follows: after converting the weight percentage concentration of each ash component in the raw coal into molar concentration, normalization is performed and weighted summation is performed.

[0014] The surface tension of the slag from raw coal mainly comes from the surface tension of its ash components. Therefore, the first step is to collect the weight percentage concentration data of silicon oxide, aluminum oxide, calcium oxide, and iron oxide in the raw coal ash, convert them into molar concentrations, and then normalize them to obtain the normalized molar concentrations of silicon oxide, aluminum oxide, calcium oxide, and iron oxide, denoted as A, B, C, and D, respectively. A weighted summation is then performed to obtain the final molar concentrations. The summation formula is as follows:

[0015] σ=A*0.286+B*0.630+C*0.586+D*0.560

[0016] In the formula: σ is the surface tension, with units of N / m.

[0017] As a preferred embodiment, the raw coal is classified into raw coal with high surface tension value and raw coal with low surface tension value.

[0018] As a preferred embodiment, the high surface tension raw coal is one in which the slag surface tension is between 0.400 < σ ≤ 0.800 N / m at a temperature of 1500℃.

[0019] As a preferred embodiment, the low surface tension raw coal is raw coal with a slag surface tension of 0.200≤σ≤0.400N / m at a temperature of 1500℃.

[0020] This invention also provides a simple method for classifying the surface tension of raw coal slag. Since the calculation process of slag surface tension is relatively complex, and the calcium oxide content in raw coal has a high weight in relation to the surface tension of raw coal slag, generally speaking, raw coal with a calcium oxide content ≥15wt% in the ash is considered high surface tension raw coal, while raw coal with a calcium oxide content <15wt% in the ash is considered low surface tension raw coal.

[0021] As a preferred embodiment, the mass ratio of high surface tension raw coal to low surface tension raw coal in the blended raw coal is 1-67:1-97.

[0022] As a preferred embodiment, the blended raw coal also contains limestone; the mass of the limestone is less than 5% of the total mass of the raw coal in the blended raw coal.

[0023] As a preferred embodiment, the blended raw coal comprises the following components by mass percentage: 25-50% high surface tension raw coal, 50-75% low surface tension raw coal, and 0.5-2.0% limestone powder.

[0024] As a preferred embodiment, the operating temperature of the raw material in the gasifier is 160–370°C, and the ash melting point of the raw material in the gasifier is 1300–1450°C. The gasification reaction temperature must be higher than the ash melting point of the raw coal to melt the solid ash in the raw coal into liquid slag. The liquid slag flows on the surface of silicon carbide, and the influence of slag viscosity and surface tension on slag flow behavior must be considered simultaneously. If the slag viscosity is too high, the slag flow will be difficult, easily clogging the slag outlet. If the slag surface tension is too high, the slag flow behavior is similar to mercury on a tilted glass plate, which is not conducive to uniform spreading on the surface of the silicon carbide refractory layer, and may result in the silicon carbide refractory layer not being able to adhere to slag or having no slag, thus damaging the silicon carbide refractory layer. By changing the composition of the raw coal ash and reducing the surface tension of the slag, the slag flow behavior is changed from being similar to mercury on a tilted glass plate to being similar to water on a tilted glass plate. The slag is evenly spread on the surface of the silicon carbide refractory layer, avoiding the inability to adhere to slag or having no slag, thus protecting the silicon carbide refractory layer.

[0025] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0026] 1) The technical solution provided by this invention uses a mathematical model of slag surface tension, a slag viscosity-temperature model and coal blending technology to strictly control the content of silicon oxide, aluminum oxide, calcium oxide and iron oxide in the coal ash composition fed into the furnace, reduce the surface tension of high-temperature slag, and promote the slag to completely cover the silicon carbide refractory material, thereby extending the service life of the silicon carbide refractory material.

[0027] 2) This invention ensures that the surface tension (1500℃), operating space, ash melting point and other indicators of the coal ash slag meet the quality requirements of the feed material of the fluidized bed pulverized coal gasifier through reasonable mixing of raw materials. While producing high temperature and high pressure crude coal gas in the pulverized coal gasifier, the slag completely covers the silicon carbide refractory layer, thereby extending the service life of the inner wall of the gasifier and achieving the technical goal of "using slag to resist slag". At the same time, the remaining ash slag can be discharged normally and can be used as raw material for building materials such as cement.

[0028] 3) The technical solution provided by this invention uses common materials for coal gasification reaction in gasifiers. No additional raw materials are needed, nor is it necessary to set up waste recycling and treatment processes or modify equipment. The overall process is simple, easy to operate, and low in cost, making it suitable for large-scale industrial application. Attached Figure Description

[0029] Figure 1 The viscosity-temperature curve of the slag of the mixed raw materials obtained in Example 1 is shown. Detailed Implementation

[0030] To facilitate understanding of the present invention, the following description will be more comprehensive and detailed in conjunction with preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Surface tension data for silicon oxide, iron oxide, aluminum oxide, and calcium oxide at 1500°C are shown in Table 1.

[0031] The coal used in the following examples and comparative examples was purchased from Shenhua Group Co., Ltd.

[0032] Example 1

[0033] Low surface tension raw coal A, low surface tension raw coal B, high surface tension raw coal and limestone were mixed at 24.75%, 24.75%, 49.5% and 1%, respectively, to obtain the mixed raw materials. The results of raw material ash analysis and surface tension calculation at a gasifier temperature of 1500℃ during the operation process are shown in Table 2.

[0034] When the gasifier temperature is 1500℃, the surface tension of the high surface tension raw coal is 0.425N / m, which does not meet the requirements. After adding low surface tension raw coal A and 187A, low surface tension raw coal B and limestone in proportion, the surface tension of the mixed raw materials is reduced to 0.399N / m.

[0035] Example 2

[0036] Low surface tension raw coal A, low surface tension raw coal B, high surface tension raw coal and limestone were mixed at 25.25%, 25.25%, 48.5% and 1%, respectively, to obtain the mixed raw materials. The results of raw material ash analysis and surface tension calculation at a gasifier temperature of 1500℃ during operation are shown in Table 3.

[0037] Example 3

[0038] Low surface tension raw coal A, low surface tension raw coal B, high surface tension raw coal and limestone were mixed at 26.5%, 26.5%, 46.4% and 0.6% respectively to obtain mixed raw materials. The results of raw material ash analysis and surface tension calculation at gasifier temperature of 1500℃ during operation are shown in Table 3.

[0039] Comparative Example 1

[0040] Table 3 shows a comparison of the analysis results of ordinary raw coal from Shenhua Group, the raw material for gasification furnaces, and the calculated surface tension results when the gasification furnace temperature is 1500℃.

[0041] Comparative Example 2

[0042] Low surface tension raw coal A, low surface tension raw coal B, and high surface tension raw coal were blended at 10%, 10%, and 80% respectively to obtain blended raw coal. The results of raw ash analysis and surface tension calculation at a gasifier temperature of 1500℃ during operation are shown in Table 3.

[0043] Table 1. Surface tension of silicon oxide, iron oxide, aluminum oxide, and calcium oxide at 1500℃

[0044]

[0045] Table 2. Analysis results of raw material ash and surface tension at a gasifier temperature of 1500℃

[0046]

[0047] Table 3. Analysis results of raw materials for the gasifier and surface tension at a gasifier temperature of 1500℃

[0048]

[0049] As shown in Table 3, when the surface tension of the raw materials fed into the furnace using the blended raw materials obtained in Examples 2 and 3 is controlled within 0.400 N / m, the water-cooled wall of the gasifier operates normally. In Comparative Example 1, the surface tension of the raw materials fed into the furnace using ordinary raw coal that has not been blended increases to 0.412 N / m, resulting in a water-cooled wall burn-out accident. In Comparative Example 2, although the raw coal was blended, the blending ratio was not in accordance with the requirements set by this invention, and the surface tension of the raw materials fed into the furnace was as high as 0.413 N / m, resulting in a water-cooled wall burn-out accident.

Claims

1. A method for extending the service life of a pulverized coal fluidized bed gasifier, characterized in that: Includes the following steps: 1) Calculate the surface tension value of the raw coal slag based on the mathematical model of slag surface tension; 2) Classify raw coal according to the surface tension value of molten slag; 3) Blend raw coal with different slag surface tension values ​​to obtain blended raw coal; 4) The mixed raw coal is fed into the pulverized coal fluidized bed gasifier for reaction, and the molten slag is covered on the surface of the silicon carbide refractory material on the furnace wall. The raw coal is classified into high surface tension value raw coal and low surface tension value raw coal; The calculation process for the surface tension value of the slag in the raw coal is as follows: after converting the weight percentage concentration of each ash component in the raw coal into molar concentration, normalization is performed and weighted summation is performed. The high surface tension raw coal is the raw coal with a slag surface tension between 0.400 < σ and 0.800 N / m at a temperature of 1500℃. The low surface tension raw coal is defined as raw coal with a slag surface tension of 0.200≤σ≤0.400 N / m at a temperature of 1500℃. The mass ratio of high surface tension raw coal to low surface tension raw coal in the blended raw coal is 1~67:1~97.

2. The method for extending the service life of a pulverized coal fluidized bed gasifier according to claim 1, characterized in that: The raw coal includes at least one of silicon oxide, iron oxide, aluminum oxide, and calcium oxide.

3. The method for extending the service life of a pulverized coal fluidized bed gasifier according to claim 1, characterized in that: The blended raw coal also contains limestone; the mass of the limestone is less than 5% of the total mass of the raw coal in the blended raw coal.

4. A method for extending the lifespan of a pulverized coal fluidized bed gasifier according to claim 1, characterized in that: The blended raw coal comprises the following components by mass percentage: 25-50% high surface tension raw coal, 50-75% low surface tension raw coal, and 0.5-2.0% limestone powder.

5. The method for extending the service life of a pulverized coal fluidized bed gasifier according to claim 1, characterized in that: The operating temperature of the raw material in the gasifier is 160~370℃, and the ash melting point of the raw material in the gasifier is 1300~1450℃.

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