Protection method for low-temperature corrosion of high-sodium coal pyrolysis gas

Abstract

The invention discloses a protection method for low-temperature corrosion of high-sodium coal pyrolysis gas. The protection method comprises the following steps: cooling chlorine-containing high-temperature gas generated by high-sodium coal pyrolysis to 400-600 DEG C in a temperature control manner, and feeding the chlorine-containing high-temperature gas into a high-temperature dust remover for dust removal; feeding the dedusted chlorine-containing high-temperature coal gas into a multi-stage waste heat recovery device for temperature control condensation, wherein the temperature control range is 300-40 DEG C; in the temperature control condensation process, a continuous and compact tar liquid film layer is formed on the wall of a heat exchange pipe of the waste heat recovery device in an attached mode; through the formed tar liquid film layer, chlorine-containing high-temperature coal gas is isolated from being in direct contact with the wall of the heat exchange pipe, and corrosion of chlorine elements to the wall of the heat exchange pipe is avoided. The self-repairing tar liquid film is formed on the heat exchange surface through accurate temperature control, and the problem that metal equipment is corroded by a chlorine-containing medium is solved by combining sodium adsorption and chlorine blocking mechanisms.

Description

Technical Field

[0001] This invention relates to the field of coal pyrolysis and equipment corrosion protection technology, and in particular to a method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas. Background Technology

[0002] High-chlorine, high-sodium coal, such as Shaerhu coal, produces coal gas rich in chloride-based corrosive components (such as HCl gas, NaCl aerosol, etc.) during pyrolysis. These components condense and form an acidic liquid film in the temperature range below 350°C during the cooling process of the coal gas. This film is prone to chloride corrosion on the surface of equipment such as heat exchangers, resulting in problems such as thinner equipment walls, reduced heat exchange efficiency, and shortened equipment life.

[0003] Existing technologies typically rely on corrosion-resistant alloys or anti-corrosion coatings for protection. For example, Chinese patent document CN110579131A discloses a highly corrosion-resistant heat exchanger that uses a copper alloy with special anti-corrosion properties as the material and then coats the working surface of the heat exchanger with an anti-corrosion and anti-scaling coating to achieve a high degree of corrosion resistance.

[0004] Chinese patent document CN119931465A discloses an anti-corrosion coating for stainless steel tube heat exchanger plates and its preparation method; it includes a base coating, an intermediate coating, and a top coating; the base coating includes components A, B, and C; the intermediate coating includes components A, B, and C, and glass flakes; the top coating includes components A, B, and iron oxide red; wherein, component A includes bisphenol A type epoxy resin, xylene, and ethanol; component B includes m-phenylenediamine and ethanol; and component C includes dibutyl phthalate and xylene.

[0005] Chinese patent document CN119662106A discloses a special anti-corrosion and wear-resistant coating for heat exchangers and its preparation method. The coating comprises the following components by weight: 10-20 parts epoxy resin, 25-35 parts polyurethane resin, 10-25 parts zinc powder, 18-38 parts zinc phosphate, 8-18 parts silicon carbide, 15-37 parts alumina, and 10-22 parts additives. The coating is prepared through the following steps: Step 1: Pre-treatment of the raw materials; Step 2: Mixing and dispersing the pre-treated raw materials; Step 3: Grinding and refining the anti-corrosion pigments and wear-resistant fillers in the film-forming material; Step 4: Adjusting the viscosity by adding an appropriate amount of curing agent to the ground coating and stirring slowly until homogeneous; finally, adjusting the viscosity of the coating with a thinner according to the application requirements. By using epoxy resin and polyurethane resin as film-forming materials, a robust coating can be formed effectively.

[0006] However, current methods for protecting heat exchanger pipes have significant drawbacks and are not suitable for the pyrolysis of high-chlorine, high-sodium coal. Corrosion-resistant alloys cost several times more than carbon steel, resulting in high costs and susceptibility to failure. Under thermal cycling conditions, the coating is prone to cracking, forming galvanic corrosion cells at the cracks, causing a surge in localized corrosion rates and leading to high maintenance costs. Summary of the Invention

[0007] This invention provides a method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas. By precisely controlling the temperature, a self-healing tar film is formed on the heat exchange surface. Combined with sodium adsorption and chlorine blocking mechanisms, this method solves the corrosion problem of chlorine-containing media on metal equipment. It is applicable to the pyrolysis process of coal types such as Shar Lake coal with a chlorine content >0.3wt%.

[0008] A method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas includes the following steps: The chlorine-containing high-temperature coal gas produced by the pyrolysis of high-sodium coal is cooled to 400-600℃ and then enters a high-temperature dust collector for dust removal. The chlorine-containing high-temperature coal gas after dust removal is sent to a multi-stage waste heat recovery device for temperature-controlled condensation, with a temperature control range of 300-40℃. During the temperature-controlled condensation process, a continuous and dense tar liquid film layer is formed on the heat exchange tube wall of the waste heat recovery device. The formed tar film layer isolates the chlorine-containing high-temperature coal gas from direct contact with the heat exchange tube wall, thus preventing chlorine from corroding the heat exchange tube wall.

[0009] The outlet temperature of pyrolysis gas is usually higher than 600℃. It needs to be cooled down to below 600℃ first through temperature control to prevent problems such as premature condensation of tar at the front end causing ash deposition and corrosion of high ash tar. At the same time, it enters the working temperature range of the electrostatic precipitator.

[0010] The temperature range for chlorine-induced low-temperature corrosion is typically below 300°C, where gaseous components such as Cl2 and HCl are more likely to condense and form a corrosive liquid film. The segmented condensation range of 300-40°C defined in this invention highly overlaps with the low-temperature corrosion initiation temperature range, ensuring that the tar liquid film forms at the critical temperature range where Cl-based corrosion is most intense, achieving a synergistic effect of on-site blocking and simultaneous protection.

[0011] Preferably, the chlorine-containing high-temperature coal gas generated from the pyrolysis of high-sodium coal is cooled to 400-550°C and then enters a high-temperature dust collector for dust removal.

[0012] Preferably, the multi-stage waste heat recovery device performs segmented temperature-controlled condensation of the chlorine-containing high-temperature gas, gradually reducing the temperature until the chlorine-containing high-temperature gas is cooled to 40°C at the outlet section of the multi-stage waste heat recovery device.

[0013] The coal gas produced by the pyrolysis of high-chlorine and high-sodium coal contains a small amount of sodium and chloride-related substances, which have a certain impact on the condensation of tar components. Segmented temperature-controlled condensation of tar components can better help film formation.

[0014] Furthermore, during the temperature-controlled condensation process, in the temperature range of 230-300℃, the heavy tar component in the tar liquid film layer is greater than the light tar component; in the temperature range of 40-230℃, the light tar component in the tar liquid film layer is greater than the heavy tar component.

[0015] Furthermore, the thickness of the tar film is 5–20 μm. It gradually thickens over time, forming a continuous and dense protective film, the final thickness of which depends on the sodium and chloride content in the gas.

[0016] Furthermore, the tar liquid film has a self-healing function. If the film is partially peeled off or has gaps, the tar continues to condense on the newly exposed surface and gradually forms a complete liquid film.

[0017] Furthermore, the tar film contains Cl, which does not disrupt the stability of the film. At the same time, Cl⁻ is coordinated and bonded to polycyclic aromatic hydrocarbons (anthracene, phenanthrene, etc.) to inhibit the ionization of HCl and slow down the diffusion rate of Cl, thereby further enhancing the synergistic protective performance.

[0018] This invention also provides the use of a tar liquid film layer to extend the service life of a waste heat recovery device, wherein a tar liquid film layer is formed on the heat exchange tube wall of the waste heat recovery device, and the specific process is as follows: After dust removal, the chlorine-containing high-temperature coal gas is sent to a multi-stage waste heat recovery device for temperature-controlled condensation, with a temperature control range of 300-40℃. During the temperature-controlled condensation process, a continuous and dense tar liquid film layer is formed on the heat exchange tube wall of the waste heat recovery device, thereby isolating the chlorine-containing high-temperature coal gas from direct contact with the heat exchange tube wall, preventing corrosion of the heat exchange tube wall by the chlorine-containing high-temperature coal gas, and extending the service life of the waste heat recovery device.

[0019] Compared with the prior art, the present invention has the following beneficial effects: Chlorine-induced metal corrosion is particularly severe below 300℃. At this temperature, the Cl component in the coal gas mainly exists as gaseous HCl or Cl2, which readily adsorbs and corrodes metal surfaces. This temperature range is also the main condensation zone for tar components. This invention proposes a novel technical solution: temperature-controlled condensation at the heat exchange surface within the 300-40℃ range. This controls the formation of a self-healing tar liquid film, achieving spatial isolation between gaseous Cl and solid metal, thereby significantly mitigating the corrosion rate. This technology offers the triple advantages of zero-cost materials, long-lasting protection, and improved energy efficiency. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of a method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas according to an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram illustrating the principle of tar film protection in an embodiment of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that, unless otherwise specified, the features in the following embodiments and implementation methods can be combined with each other.

[0025] like Figure 1 As shown, a method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas includes the following steps: A method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas includes the following steps: S1, the chlorine-containing high-temperature coal gas produced by the pyrolysis of high-sodium coal is cooled to 400-600℃ and then enters the high-temperature dust collector for dust removal.

[0026] In this embodiment of the invention, Shar Lake coal is used as the pyrolysis raw material. Through a high-sodium low-rank coal pyrolysis combustion graded conversion and multi-product device, Shar Lake coal particles with a particle size of 0-10mm are fed into the pyrolysis furnace. In the fluidized bed pyrolysis furnace, they are rapidly mixed with high-temperature ash particles from the combustion furnace and heated to thermally desorb volatiles.

[0027] The outlet temperature of the pyrolysis gas produced in the pyrolysis furnace exceeds 600°C. In this embodiment, the temperature is first reduced to 400°C by temperature control and cooling to prevent premature condensation of the front-end tar, which would cause ash deposition and corrosion by high-ash tar, and to meet the working temperature requirements of the dust collector.

[0028] S2 sends the dust-removed, chlorine-containing high-temperature coal gas into a multi-stage waste heat recovery device for temperature-controlled condensation, with a temperature control range of 300-40℃.

[0029] The multi-stage waste heat recovery device performs segmented temperature-controlled condensation of chlorine-containing high-temperature gas, gradually reducing the temperature until the chlorine-containing high-temperature gas is cooled to 40°C at the outlet of the multi-stage waste heat recovery device.

[0030] The coal gas produced by the pyrolysis of high-chlorine and high-sodium coal contains a small amount of sodium and chloride-related substances, which have a certain impact on the condensation of tar components. Segmented temperature-controlled condensation of tar components can better help film formation.

[0031] S3, during the temperature-controlled condensation process, a continuous and dense tar liquid film layer is formed on the heat exchange tube wall of the waste heat recovery device.

[0032] During the temperature-controlled condensation process, in the temperature range of 230-300℃, the heavy tar component in the tar liquid film layer is greater than the light tar component, and it is mainly heavy tar component; in the temperature range of 40-230℃, the light tar component in the tar liquid film layer is greater than the heavy tar component, and it is mainly light tar component.

[0033] S4, through the formation of a tar film layer, isolates the chlorine-containing high-temperature coal gas from direct contact with the heat exchange tube wall, thus avoiding corrosion of the heat exchange tube wall by chlorine.

[0034] The tar liquid film has a self-healing function. If the film is partially peeled off or has gaps, the tar continues to condense on the newly exposed surface and gradually forms a complete liquid film.

[0035] Because the pyrolysis gas system is constantly transporting and operating, the tar liquid film is dynamically maintained, exhibiting self-healing capabilities. In the actual pyrolysis gas cooling zone, tar components continuously flow and condense in the temperature drop range. If local peeling or voids occur in the film layer, the tar can continue to condense on the newly exposed surface, gradually forming a complete liquid film. The thickness of the tar liquid film layer is 5~20μm, gradually thickening with the extension of operating time to form a continuous and dense protective film layer. The specific formation rate and thickness are related to the operating conditions.

[0036] like Figure 2 As shown, a tar film layer 2 is formed on the metal substrate 1, and it gradually thickens over time.

[0037] Further testing and research have shown that the tar obtained from the pyrolysis of high-chlorine coal has a low Cl content, which not only has the ability to inhibit the ionization of HCl, but also prevents chlorine-containing coal gas from directly contacting the heat exchange tube wall, effectively preventing the corrosion of metal pipes by chlorine elements, and exhibiting good protective performance.

[0038] The method of this invention forms a self-healing tar film on the heat exchange surface through precise temperature control, and combines sodium adsorption and chlorine blocking mechanisms to solve the corrosion problem of chlorine-containing media on metal equipment. It is applicable to the pyrolysis process of coal types such as Shar Lake coal with a chlorine content >0.3wt%.

[0039] This invention also provides the use of a tar liquid film layer to extend the service life of a waste heat recovery device. The tar liquid film layer is formed on the heat exchange tube wall of the waste heat recovery device, and the specific process is as follows: After dust removal, the chlorine-containing high-temperature coal gas is sent to a multi-stage waste heat recovery device for temperature-controlled condensation, with a temperature control range of 300-40℃. During the temperature-controlled condensation process, a continuous and dense tar liquid film layer is formed on the heat exchange tube wall of the waste heat recovery device, thereby isolating the chlorine-containing high-temperature coal gas from direct contact with the heat exchange tube wall, preventing corrosion of the heat exchange tube wall by the chlorine-containing high-temperature coal gas, and extending the service life of the waste heat recovery device.

[0040] Based on existing literature and experimental data, the corrosion rate of ordinary carbon steel in a high-chlorine coal pyrolysis atmosphere with a Cl content higher than 0.3 wt.% is generally much higher than 0.3 mm / a, and the designed service life is far less than the general requirement of 10 years. For existing ceramic anti-corrosion coatings, the typical service life is about 10 years, which can be extended to 15 years if a composite coating system is used. Therefore, most engineering designs set the anti-corrosion coating to a maintenance-free period of 10–15 years. However, in actual operation, thermal stress cycles can easily induce microcracks, leading to local pitting corrosion or premature failure, resulting in high maintenance costs.

[0041] In contrast, this invention controls the condensation of tar components within the critical corrosion temperature range of 300–40°C, forming a continuous liquid tar film in situ on the heat exchanger surface, thus constructing a dynamic barrier structure. This film effectively isolates chlorine-based corrosive components from contact with the metal wall, reducing their diffusion rate. Preliminary experiments show that under typical operating conditions, the tar film formed by this invention can remain stable and maintain its protective effectiveness, with a significantly reduced corrosion rate. Its estimated service life exceeds 15 years, demonstrating high engineering application value and economic benefits.

[0042] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas, characterized in that, Includes the following steps: The chlorine-containing high-temperature coal gas produced by the pyrolysis of high-sodium coal is cooled to 400-600℃ and then enters a high-temperature dust collector for dust removal. The chlorine-containing high-temperature coal gas after dust removal is sent to a multi-stage waste heat recovery device for temperature-controlled condensation, with a temperature control range of 300-40℃. During the temperature-controlled condensation process, a continuous and dense tar liquid film layer is formed on the heat exchange tube wall of the waste heat recovery device. The formed tar film layer isolates the chlorine-containing high-temperature coal gas from direct contact with the heat exchange tube wall, thus preventing chlorine from corroding the heat exchange tube wall.

2. The method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas according to claim 1, characterized in that, The chlorine-containing high-temperature coal gas produced by the pyrolysis of high-sodium coal is cooled to 400-550℃ and then enters a high-temperature dust collector for dust removal.

3. The method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas according to claim 1, characterized in that, The multi-stage waste heat recovery device performs segmented temperature-controlled condensation of chlorine-containing high-temperature gas, gradually reducing the temperature until the chlorine-containing high-temperature gas is cooled to 40°C at the outlet of the multi-stage waste heat recovery device.

4. The method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas according to claim 1, characterized in that, During the temperature-controlled condensation process, in the temperature range of 230-300℃, the heavy tar component in the tar liquid film layer is greater than the light tar component; in the temperature range of 40-230℃, the light tar component in the tar liquid film layer is greater than the heavy tar component.

5. The method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas according to claim 1, characterized in that, The thickness of the tar film is 5–20 μm.

6. The method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas according to claim 1, characterized in that, The tar liquid film has a self-healing function. If the film is partially peeled off or has gaps, the tar continues to condense on the newly exposed surface and gradually forms a complete liquid film.

7. The method for protecting against low-temperature corrosion of high-sodium coal pyrolysis gas according to claim 1, characterized in that, The tar film contains chlorine (Cl), which does not disrupt the stability of the film and inhibits the ionization of HCl.

8. The use of a tar liquid film layer to extend the service life of a waste heat recovery device, characterized in that, The formation of a tar liquid film layer on the heat exchanger tube wall of the waste heat recovery device is specifically as follows: After dust removal, the chlorine-containing high-temperature coal gas is sent to a multi-stage waste heat recovery device for temperature-controlled condensation, with a temperature control range of 300-40℃. During the temperature-controlled condensation process, a continuous and dense tar liquid film layer is formed on the heat exchange tube wall of the waste heat recovery device, thereby isolating the chlorine-containing high-temperature coal gas from direct contact with the heat exchange tube wall, preventing corrosion of the heat exchange tube wall by the chlorine-containing high-temperature coal gas, and extending the service life of the waste heat recovery device.

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