A method for heating and preventing carbon precipitation of gas to achieve CH4 pre-decomposition using low-order heat from a hot blast stove.

Abstract

The present application belongs to the technical field of blast furnace ironmaking, and specifically discloses a coal gas heating and carbon precipitation prevention method using low-grade heat of hot blast stove for CH4 pre-decomposition. First, the low-grade heat of the hot blast stove and the relevant parameters of the blast furnace decarburization coal gas are collected, a pre-decomposition section is added at the front end of the coal gas heating device, the low-grade heat of the hot blast stove is introduced to match the heat required for CH4 decomposition, and after the feasibility is verified by thermodynamics, CH4 in the coal gas is pre-decomposed, a carbon removal device is matched at the rear end to remove carbon, the pre-decomposed coal gas is heated in the 600-700 DEG C heating section, and the process parameters are monitored in real time. When slight carbon precipitation occurs, trace stepwise water addition is used for carbon control. In view of the problems of CH4 high-temperature cracking and carbon precipitation in the blast furnace decarburization coal gas, and the consumption of high-grade heat energy of the blast furnace, the present application realizes energy cascade utilization, saves high-grade heat energy of the blast furnace, improves the calorific value of the coal gas and the reduction efficiency of the blast furnace, reduces the coke ratio, and inhibits carbon precipitation from the root.

Description

Technical Field

[0001] This invention relates to the field of blast furnace ironmaking technology, specifically to a method for heating coal gas and preventing carbon precipitation by utilizing the low-order heat of a hot blast stove to achieve pre-decomposition of CH4. Background Technology

[0002] In the hydrogen-rich carbon-cycle oxygen blast furnace decarbonized gas heating and injection process, methane (CH4) in the gas composition is a key hidden danger affecting the blast furnace's thermal balance and smooth production. If decarbonized gas containing methane is injected directly into the blast furnace without pretreatment, the methane will undergo a cracking reaction in the high-temperature environment inside the blast furnace. This process consumes a large amount of scarce high-order thermal energy within the blast furnace, directly disrupting the original thermal balance system of the furnace body, leading to blast furnace temperature fluctuations, and consequently affecting smelting reaction efficiency and pig iron quality. At the same time, high-temperature methane cracking is a strongly endothermic reaction, accompanied by severe carbon precipitation side reactions. The precipitated solid carbon particles easily adhere to the gas conveying pipelines, the interior of heating heat exchangers, and even block the pores of the blast furnace burden, not only significantly reducing gas conveying and heating efficiency but also causing equipment failures.

[0003] To address the challenge of carbon release from methane cracking, current mainstream technologies often employ water-based carbon suppression, introducing steam into the gas to inhibit the carbon release reaction. However, this technology has significant limitations. It only alleviates the superficial problem of solid carbon release and cannot fundamentally block the methane cracking process, thus failing to address the issue of methane decomposition consuming high-order thermal energy from the blast furnace. Furthermore, improper control of the water addition during gas mixing can lead to excessive moisture, significantly increasing the gas's humidity and reducing its calorific value and the heat exchange efficiency of the heating device.

[0004] At present, methane cracking reactions in the industry can be triggered and completed by low-order thermal energy, but the problems of carbon release and thermal energy loss from methane cracking have not been fundamentally solved, becoming a technical challenge for the efficient utilization of blast furnace decarbonization gas. Summary of the Invention

[0005] The purpose of this invention is to provide a method for heating coal gas and preventing carbon precipitation by utilizing the low-order heat of a hot blast stove to achieve pre-decomposition of CH4, in order to solve the problem that the current methane cracking reaction in the industry can be triggered and completed by relying on low-order heat energy, but there are problems of carbon precipitation and heat energy loss during methane cracking.

[0006] To achieve the above objectives, the basic solution provided by this invention is: a method for heating coal gas and preventing carbon precipitation by utilizing the low-order heat of a hot blast stove to achieve CH4 pre-decomposition, comprising the following steps: S1. Collect the temperature range and heat flow of the low-order heat of the hot blast stove, the composition, flow rate, CH4 mole fraction of the blast furnace decarbonization gas, and the design heating temperature and total system pressure of the gas heating device; S2. Set up a pre-decomposition section at the front end of the gas heating device, introduce the low-order heat of the hot blast stove into the pre-decomposition section, control the temperature of the pre-decomposition section to 800-900℃, and calculate the usable heat of the low-order heat of the hot blast stove based on the principle of heat balance, and match the theoretical heat required for the complete decomposition of CH4 in the gas. S3. Based on the HCO equilibrium theory, predict the carbon evolution risk level of the coal gas before decomposition. At the same time, obtain the equilibrium constant of the CH4 decomposition reaction at 800-900℃ through thermodynamic calculations to verify the thermodynamic feasibility of CH4 decomposition at this temperature and ensure that the CH4 molar fraction in the coal gas after pre-decomposition is ≤0.5%. S4. The decarbonized gas from the blast furnace is introduced into the pre-decomposition section, and the CH4 is pre-decomposed using the low-order heat of the hot blast stove. The decomposition products are H2 and a small amount of solid carbon. The pre-decomposed gas enters the gas heating device. S5. The heating temperature of the gas heating device is controlled at 600-700℃, and the composition change of the gas in the heating section is monitored in real time to ensure that the gas is in the non-carbon precipitation zone. S6. Monitor the heat exchange efficiency and CH4 decomposition rate of the CH4 pre-decomposition section, as well as the gas temperature and carbon precipitation rate of the heating section in real time. If the CH4 decomposition rate is <95%, appropriately increase the gas residence time or temperature of the pre-decomposition section. If slight carbon precipitation occurs in the heating section, use a micro-step water addition method to assist in carbon suppression.

[0007] The beneficial effects of this invention are as follows: ① By combining the low-order heat of the hot blast stove with CH4 pre-decomposition, the previously underutilized low-order heat of the hot blast stove is used to complete CH4 decomposition, replacing the high-order heat energy in the blast furnace, saving 15%-20% of the high-order heat energy in the blast furnace, realizing the cascade utilization of energy, and reducing the energy consumption and carbon emissions of blast furnace smelting; ② The pre-decomposition section reduces the molar fraction of CH4 in the gas to ≤0.5%, fundamentally solving the carbon precipitation problem caused by CH4 decomposition; ③ The H2 produced by CH4 pre-decomposition can improve the reducibility and calorific value of the gas. The value ensures that the heated gas injected into the blast furnace can improve the reduction efficiency of the blast furnace, reduce the coke ratio by 5%-8%, and reduce the heat consumption of the reduction reaction in the blast furnace; ④ The process can be modified by adding a pre-decomposition section at the front end of the existing gas heating device without large-scale adjustment of the existing system, and the process parameters can be dynamically adapted according to the blast furnace production load, making operation easy; ⑤ The heating section adopts medium and low temperature heating, combined with micro-step water addition to assist in carbon suppression, which avoids high temperature heating from aggravating carbon precipitation and prevents excessive water addition from reducing the gas heating efficiency.

[0008] Option 2, which is the preferred option of the basic option, in S1, the pre-decomposition section is a shell and tube heat exchange structure. The heat medium side is introduced with low-order heat from the hot blast stove, and the gas side is introduced with decarbonized gas from the blast furnace. Turbulence-inducing components are installed inside the tubes to improve heat exchange efficiency and gas mixing effect, ensuring uniform decomposition of CH4.

[0009] Option 3, which is the preferred option of the basic option, involves setting a carbon removal device at the rear end of the pre-decomposition section in S4, and removing solid carbon through the carbon removal device in the pre-decomposition section.

[0010] Option 4, which is the preferred option of Option 3, uses a combination of cyclone separation and electrostatic decarbonization for the carbon removal device. Cyclone separation removes large solid carbon particles, while electrostatic decarbonization removes small carbon particles. The carbon removal efficiency is ≥99%, preventing solid carbon from entering subsequent heating devices and the blast furnace.

[0011] Option 5, which is the preferred option of the basic option, involves setting the residence time of the blast furnace decarbonized gas in the pre-decomposition section according to the gas flow rate in S4 to ensure that CH4 is fully decomposed.

[0012] Option 6, which is the preferred option of the basic option, in S5, if coke oven gas or natural gas needs to be added due to production scheduling, the addition ratio is controlled at ≤20% for coke oven gas and ≤10% for natural gas, and carbon suppression is assisted by adding water. The H2O / CH4 ratio is controlled at 1.0-1.2 to avoid excessive water addition.

[0013] Option 7, which is the preferred option of the basic option, involves a micro-step water addition method in S6: increasing the water addition in the middle section by 5%-10% until the carbon precipitation rate drops below 0.01 kg-C / min. Detailed Implementation

[0014] The present invention will be further described in detail below through specific embodiments: A method for heating and preventing carbon precipitation of gas using low-order heat from a hot blast stove to achieve CH4 pre-decomposition includes the following steps: S1. Collect the temperature range and heat flow of the low-order heat of the hot blast stove, the composition, flow rate, CH4 mole fraction of the blast furnace decarbonized gas, the design heating temperature of the gas heating device, and the total pressure of the system. The pre-decomposition section is a shell-and-tube heat exchange structure. The low-order heat of the hot blast stove is introduced on the heat medium side, and the blast furnace decarbonized gas is introduced on the gas side. Turbulence-inducing components are installed inside the tubes. S2. Set up a pre-decomposition section at the front end of the gas heating device, introduce the low-order heat of the hot blast stove into the pre-decomposition section, control the temperature of the pre-decomposition section to 800-900℃, and calculate the usable heat of the low-order heat of the hot blast stove based on the principle of heat balance, and match the theoretical heat required for the complete decomposition of CH4 in the gas. S3. Based on the HCO equilibrium theory, predict the carbon evolution risk level of the coal gas before decomposition. At the same time, obtain the equilibrium constant of the CH4 decomposition reaction at 800-900℃ through thermodynamic calculations to verify the thermodynamic feasibility of CH4 decomposition at this temperature and ensure that the CH4 molar fraction in the coal gas after pre-decomposition is ≤0.5%. S4. The blast furnace decarburized gas is introduced into the pre-decomposition section, and the CH4 is pre-decomposed using the low-order heat of the hot blast stove. The residence time of the blast furnace decarburized gas in the pre-decomposition section is set according to the gas flow rate to ensure that the CH4 is fully decomposed. The decomposition products are H2 and a small amount of solid carbon. A decarbonization device is set at the rear end of the pre-decomposition section to remove solid carbon. The decarbonization device adopts a combination of cyclone separation and electrostatic decarbonization. Cyclone separation removes large solid carbon particles, and electrostatic decarbonization removes small carbon particles. The pre-decomposed gas enters the gas heating device. S5. The heating temperature of the gas heating device is controlled at 600-700℃. The composition change of the gas in the heating section is monitored in real time to ensure that the gas is in the non-carbon precipitation zone. If coke oven gas or natural gas needs to be added due to production scheduling, the addition ratio is controlled at ≤20% for coke oven gas and ≤10% for natural gas. Carbon suppression is assisted by adding water. The H2O / CH4 ratio is controlled at 1.0-1.2 to avoid excessive water addition. S6. Monitor the heat exchange efficiency and CH4 decomposition rate of the CH4 pre-decomposition section, as well as the gas temperature and carbon precipitation rate of the heating section in real time. If the CH4 decomposition rate is <95%, appropriately increase the gas residence time or temperature of the pre-decomposition section. If slight carbon precipitation occurs in the heating section, use a micro-step water addition method to assist in carbon suppression. The micro-step water addition method is to increase the water addition in the middle section by 5%-10% until the carbon precipitation rate drops below 0.01 kg-C / min.

[0015] Based on changes in blast furnace production load, dynamically adjust the gas flow rate and the input of low-order heat from the hot blast stove to maintain thermal balance in the CH4 pre-decomposition section; at the same time, periodically collect operating data from the pre-decomposition and heating sections, correct the critical carbon deposition curve of HCO theory, optimize the pre-decomposition temperature, residence time, and heating section process parameters to adapt to on-site conditions.

[0016] Below is 400m 3 Taking the blast furnace decarburization gas heating system of a hydrogen-rich carbon-circulating oxygen blast furnace as an example, a more detailed explanation will be given: The temperature of the low-level hot flue gas collected from the hot blast furnace is 850-900℃, and the heat flow rate is 20000 Nm³. 3 / h, blast furnace decarbonization gas composition: CO2 5%, CO2 4%, H2 65%, H2O 3%, CH4 3%, gas flow rate is 15000 Nm³ / h. 3 / h; The total pressure of the gas heating system is 0.5MPa, and the designed heating temperature is 700℃.

[0017] Based on heat balance calculations, the usable low-order heat of the hot blast stove is 1.2 × 10⁻⁶. 6 The theoretical heat required for the complete decomposition of CH4 is 8.0 × 10 kJ / h. 5 kJ / h, determining the heat exchange area of ​​the CH4 pre-decomposition section to be 80m².2 The gas residence time is 12s; the temperature of the pre-decomposition section is controlled at 850℃, the total system pressure is 0.5MPa, and the gas residence time is 12s.

[0018] Based on the verification of the pre-decomposition process using the HCO system, the calculated O / C ratio of the gas before pre-decomposition was 0.32 and the H / C ratio was 4.15, indicating that the gas was in the carbon precipitation zone with a high risk level. Thermodynamic calculations showed that the equilibrium constant K for the CH4 decomposition reaction at 850℃ was 1.2 × 10⁻⁶. 3 The thermodynamic feasibility of CH4 decomposition at this temperature was verified, and the theoretical decomposition rate can reach over 98%.

[0019] The decarbonized blast furnace gas was introduced into the pre-decomposition section, and CH4 pre-decomposition was completed using the low-order heat of the hot blast stove. After testing, the CH4 molar fraction in the gas after pre-decomposition was 0.4%, and the decomposition rate reached 93.3%. The solid carbon produced by decomposition was removed by a carbon removal device with a carbon removal efficiency of 99.5%. The H2 molar fraction in the gas after pre-decomposition increased to 68.8%, and the calorific value of the gas increased by 12%.

[0020] The pre-decomposed coal gas enters the heating device, and the heating temperature is controlled at 650℃. The O / C ratio of the coal gas is calculated in real time to be 0.33 and H / C ratio to be 4.32. This point is in the non-carbon precipitation zone. Due to production needs, 15% coke oven gas is added. After the addition, a stepped water addition is used to assist in carbon suppression. The heating device is divided into 3 sections, with the water addition amount distributed as follows: 25% in the front section, 50% in the middle section, and 25% in the rear section. The H2O / CH4 ratio is controlled at 1.1.

[0021] Thermal efficiency and carbon deposition status monitoring showed that the heat exchange efficiency of the CH4 pre-decomposition section was 92%, and the CH4 decomposition rate was stable at 93%-95%; the gas heating efficiency of the heating section was 91%, and the carbon deposition rate was 0.005 kg-C / min, indicating a state with no risk of carbon deposition.

[0022] Dynamic adaptation and optimization of process parameters: When the blast furnace production load increases by 10%, the gas flow rate increases to 16500 Nm³. 3 When the gas flow rate is / h, the flue gas input of the hot blast stove is appropriately increased, and the residence time of the gas in the pre-decomposition section is extended to 13s to maintain the CH4 decomposition rate ≥93%. The operation data is collected regularly, and the critical carbon precipitation curve of the HCO theoretical system is corrected. After optimization, the temperature of the pre-decomposition section can be lowered to 830℃, while still ensuring that the CH4 decomposition rate ≥93%, further saving thermal energy.

[0023] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for heating and preventing carbon precipitation of coal gas using low-order heat from a hot blast stove to achieve pre-decomposition of CH4, characterized in that, Includes the following steps: S1. Collect the temperature range and heat flow of the low-order heat of the hot blast stove, the composition, flow rate, CH4 mole fraction of the blast furnace decarbonization gas, and the design heating temperature and total system pressure of the gas heating device; S2. Set up a pre-decomposition section at the front end of the gas heating device, introduce the low-order heat of the hot blast stove into the pre-decomposition section, control the temperature of the pre-decomposition section to 800-900℃, and calculate the usable heat of the low-order heat of the hot blast stove based on the principle of heat balance, and match the theoretical heat required for the complete decomposition of CH4 in the gas. S3. Based on the HCO equilibrium theory, predict the carbon evolution risk level of the coal gas before decomposition. At the same time, obtain the equilibrium constant of the CH4 decomposition reaction at 800-900℃ through thermodynamic calculations to verify the thermodynamic feasibility of CH4 decomposition at this temperature and ensure that the CH4 molar fraction in the coal gas after pre-decomposition is ≤0.5%. S4. The decarbonized gas from the blast furnace is introduced into the pre-decomposition section, and the CH4 is pre-decomposed using the low-order heat of the hot blast stove. The decomposition products are H2 and a small amount of solid carbon. The pre-decomposed gas enters the gas heating device. S5. The heating temperature of the gas heating device is controlled at 600-700℃, and the composition change of the gas in the heating section is monitored in real time to ensure that the gas is in the non-carbon precipitation zone. S6. Monitor the heat exchange efficiency and CH4 decomposition rate of the CH4 pre-decomposition section, as well as the gas temperature and carbon precipitation rate of the heating section in real time. If the CH4 decomposition rate is <95%, appropriately increase the gas residence time or temperature of the pre-decomposition section. If slight carbon precipitation occurs in the heating section, use a micro-step water addition method to assist in carbon suppression.

2. The method for heating and preventing carbon precipitation of coal gas by utilizing the low-order heat of a hot blast stove to achieve CH4 pre-decomposition according to claim 1, characterized in that, In S1, the pre-decomposition section is a tubular heat exchange structure. The heat medium side is supplied with low-order heat from the hot blast stove, and the gas side is supplied with decarbonized gas from the blast furnace. Turbulence-inducing components are installed inside the tubes.

3. The method for heating and preventing carbon precipitation of coal gas by utilizing the low-order heat of a hot blast stove to achieve CH4 pre-decomposition according to claim 1, characterized in that, In S4, a carbon removal device is installed at the rear end of the pre-decomposition section, and solid carbon is removed through the carbon removal device of the pre-decomposition section.

4. The method for heating and preventing carbon precipitation of coal gas by utilizing the low-order heat of a hot blast stove to achieve CH4 pre-decomposition according to claim 3, characterized in that, The carbon removal device uses a combination of cyclone separation and electrostatic carbon removal. Cyclone separation removes large solid carbon particles, while electrostatic carbon removal removes small carbon particles.

5. A method for heating and preventing carbon precipitation of coal gas by utilizing the low-order heat of a hot blast stove to achieve CH4 pre-decomposition, as described in claim 1, is characterized in that... In S4, the residence time of the blast furnace decarbonized gas in the pre-decomposition section is set according to the gas flow rate to ensure that CH4 is fully decomposed.

6. The method for heating and preventing carbon precipitation of coal gas by utilizing the low-order heat of a hot blast stove to achieve CH4 pre-decomposition according to claim 1, characterized in that, In S5, if coke oven gas or natural gas needs to be added due to production scheduling, the addition ratio should be controlled at ≤20% for coke oven gas and ≤10% for natural gas. Carbon suppression should be assisted by adding water, and the H2O / CH4 ratio should be controlled at 1.0-1.2 to avoid excessive water addition.

7. A method for heating and preventing carbon precipitation of coal gas by utilizing the low-order heat of a hot blast stove to achieve CH4 pre-decomposition, as described in claim 1, is characterized in that... In S6, the micro-step water addition method is to increase the water addition in the middle section by 5%-10% until the carbon precipitation rate drops below 0.01 kg-C / min.