November 14: Daily Question: What is the principle of regeneration in the heat regenerator and stripping tower of low-temperature methanol washing?
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This post was last edited by 654262293 on 2010-11-14 16:51. What is the regeneration principle of the low-temperature methanol wash heat regeneration tower and the stripping tower? The answers will be announced tomorrow! Answer: The regeneration principle of the regeneration tower: Heating is used for regeneration within the tower. During thermal regeneration, the evaporation of methanol from the solution reduces the vapor pressures of H2S, COS, and CO2 at the solution interface, thereby increasing the mass transfer driving force. As a result, H2S, COS, and CO2 are desorbed from the solution to reach a new equilibrium. On the other hand, during thermal regeneration, the solubility of H2S, COS, and CO2 decreases, causing the dissolved gases to be released. The combined effect of these two factors enhances the regeneration of the solution in the regeneration tower. Principle of regeneration in the stripping tower: During stripping regeneration, the introduction of stripping nitrogen reduces the vapor pressure of CO2 at the solution interface, increasing the mass transfer driving force and thereby enhancing solution regeneration.
This post was last edited by 654262293 on 2011-1-8 23:19. Stripping is achieved primarily by reducing the partial pressure of carbon dioxide in the gas phase, while thermal regeneration is a process in which carbon dioxide and hydrogen sulfide dissolved in methanol are desorbed through heating.
This post was last edited by 654262293 on 2011-1-8 23:20. Principle of the thermal regeneration tower: Dissolution decreases at high temperatures, leading to separation. Principle of the stripping tower: Partial pressure is reduced through stripping gas, thereby enabling separation.
Using cold methanol as the absorption solvent, and taking advantage of methanol’s excellent property of having a very high solubility for acidic gases at low temperatures, the acidic gases in the feedstock are removed.
This post was last edited by 654262293 on January 8, 2011, at 23:20.
**Principle of low-temperature methanol washing for gas purification**
Low-temperature methanol washing is a process in which acidic gases such as CO₂, H₂S, COS, and mercaptans contained in shifted gas are removed under certain pressure and low temperature conditions. Since no chemical reactions occur during the absorption of acidic gases by methanol, this process falls under physical absorption. Its principle is as follows: Low-temperature methanol, an organic solvent, is used as the absorbent; due to the fact that CO₂, H₂S, and COS have higher solubility in methanol compared to H₂ and CO, they can be effectively removed. Regeneration of the absorbed solution involves simple flash desorption, allowing CO₂, H₂S, etc., to be released from the solution.
Physical absorption of acidic gases by methanol adheres to Henry’s Law initially (P = KX); the absorption capacity of methanol increases with rising partial pressures of acidic components. The volume of circulating solution depends on the amount of feed gas and operating conditions. Higher operating pressures and lower temperatures result in reduced circulation volumes.
**II. Basic Principles**
1. **Properties of methanol**: Molecular formula CH₃OH; relative molecular mass 32. It is a colorless, volatile, and flammable liquid with a freezing point of -97.8°C and boiling point of 64.7°C (at 0.1 MPa). Methanol is miscible with water in any proportion. It is a polar organic solvent, chemically stable, non-degradable, and non-corrosive to equipment.
2. **Absorption principle**: This is purely a physical absorption process. Acidic gases like CO₂, H₂S, and COS exhibit high solubility in methanol, whereas H₂, N₂, and CO exhibit very low solubility. Thus, methanol efficiently removes these acidic gases from feed gas while minimizing losses of valuable gases like H₂ and CO.
3. **Solubility differences**: The basis for regeneration of solutions containing absorbed acidic gases (e.g., H₂S, COS, CO₂) and recovery of less soluble gases (e.g., H₂, N₂, CO) lies in their differing solubilities in methanol. As shown in Figure 7-5 on page 159, at the same temperature, CO₂, H₂S, and H₂O exhibit far greater solubility than H₂ and CO. Lower temperatures further increase the solubility of CO₂ and H₂S in methanol, while minimal changes occur for H₂ and CO—making this process highly effective at low temperatures. Notably, since H₂S has even higher solubility than CO₂, simultaneous removal of both gases becomes possible. Many ammonia synthesis plants or coal-based methanol production facilities integrate sulfur removal into carbon removal processes, thereby reducing capital costs and operational expenses.
Generally, for most gases, higher pressures and lower temperatures lead to greater solubility in solvents; at dew points, solubility becomes theoretically infinite (i.e., complete miscibility occurs). In real gases, intermolecular forces (van der Waals forces) reduce solubility and lower the dew point compared to single-component gases. When one easily soluble component dissolves, it acts as a solvent for other components. During desorption: Lower pressures and higher temperatures favor solute release; at the solvent’s boiling point, solubility drops to zero. Common desorption methods include:
- **Pressure reduction**: Reducing total system pressure (even to negative pressure) after solute absorption.
- **Gas stripping**: Introducing inert gases to lower partial pressures of solutes.
- **Thermal desorption**: Heating the solvent to its boiling point to eliminate solutes.
**Advantages of methanol over other solvents**: At low temperatures and high pressures, methanol absorbs significantly more acidic gases than N₂, CO, H₂, or CH₄—resulting in superior selectivity, reduced methanol circulation needs, and minimized losses of valuable gases like H₂ and CO. Its low equilibrium vapor pressure at low temperatures minimizes evaporation losses. Methanol also boasts excellent chemical stability, a low freezing point, low viscosity, and minimal corrosiveness. Its absorption capacity is roughly 100 times greater than water and 10 times that of Benfield chemical solvents; additionally, it is inexpensive and readily available.
**Disadvantages**: Operating at low temperatures necessitates high-grade materials for equipment. Energy conservation efforts require extensive heat exchangers, lengthening the process flow. Methanol is toxic, posing health risks; even 10 mL inhalation may cause blindness, while 30 mL can be fatal. Permissible airborne concentrations are limited to 50 mg/m³. Strict manufacturing standards and careful handling are essential to prevent leaks, with appropriate safety measures mandatory.
**III. Features of low-temperature methanol washing**
This method ensures H₂S and CO₂ levels in purified gas meet synthesis requirements while completely eliminating sulfides, extending catalyst lifespan. It simultaneously removes multiple components—including H₂S, COS, CS₂, RSH, C₄H₄S, CO₂, HCN, NH₃, NO, paraffins, aromatics, and crude gasoline—from gases at temperatures ranging from 30°C to -70°C. Dehydration also occurs during this process. Absorbed components can be recovered during methanol regeneration. High absorption capacity and low circulation volumes minimize piping/equipment sizes and energy consumption. Regenerated methanol undergoes flash desorption and thermal regeneration for reuse. Desorbed CO₂ meets emission standards, while sulfur byproducts are recoverable. Wastewater from thermal regeneration contains trace methanol, usable for coal slurry preparation, thus lowering water usage and wastewater treatment demands. Purified gas achieves ultra-low sulfur content (<0.1 cm³/m³) and CO₂ levels (<10 cm³/m³), making this technique ideal for industries with stringent sulfur limits. Selective removal and recovery of H₂S and CO₂ are feasible due to their high solubility at low temperatures; minimal losses of H₂ and CH₄ occur because their solubility remains low. Methanol’s thermal/chemical stability and affordability further enhance its utility.
**IV. Limitations**
Energy efficiency drives reliance on numerous heat exchangers, complicating the process—especially regeneration stages. Material requirements remain stringent due to low-temperature operations. Toxicity concerns demand rigorous safety protocols and leak prevention measures.
**V. Primary product streams**
Methanol synthesis gas: CO₂ concentration ≤3.42% (mol); total sulfur content..
**Principle of low-temperature methanol washing for gas purification**
Low-temperature methanol washing is a process in which acidic gases such as CO₂, H₂S, COS, and mercaptans contained in shifted gas are removed under certain pressure and low temperature conditions. Since no chemical reactions occur during the absorption of acidic gases by methanol, this process falls under physical absorption. Its principle is as follows: Low-temperature methanol, an organic solvent, is used as the absorbent; due to the fact that CO₂, H₂S, and COS have higher solubility in methanol compared to H₂ and CO, they can be effectively removed. Regeneration of the absorbed solution involves simple flash desorption, allowing CO₂, H₂S, etc., to be released from the solution.
Physical absorption of acidic gases by methanol adheres to Henry’s Law initially (P = KX); the absorption capacity of methanol increases with rising partial pressures of acidic components. The volume of circulating solution depends on the amount of feed gas and operating conditions. Higher operating pressures and lower temperatures result in reduced circulation volumes.
**II. Basic Principles**
1. **Properties of methanol**: Molecular formula CH₃OH; relative molecular mass 32. It is a colorless, volatile, and flammable liquid with a freezing point of -97.8°C and boiling point of 64.7°C (at 0.1 MPa). Methanol is miscible with water in any proportion. It is a polar organic solvent, chemically stable, non-degradable, and non-corrosive to equipment.
2. **Absorption principle**: This is purely a physical absorption process. Acidic gases like CO₂, H₂S, and COS exhibit high solubility in methanol, whereas H₂, N₂, and CO exhibit very low solubility. Thus, methanol efficiently removes these acidic gases from feed gas while minimizing losses of valuable gases like H₂ and CO.
3. **Solubility differences**: The basis for regeneration of solutions containing absorbed acidic gases (e.g., H₂S, COS, CO₂) and recovery of less soluble gases (e.g., H₂, N₂, CO) lies in their differing solubilities in methanol. As shown in Figure 7-5 on page 159, at the same temperature, CO₂, H₂S, and H₂O exhibit far greater solubility than H₂ and CO. Lower temperatures further increase the solubility of CO₂ and H₂S in methanol, while minimal changes occur for H₂ and CO—making this process highly effective at low temperatures. Notably, since H₂S has even higher solubility than CO₂, simultaneous removal of both gases becomes possible. Many ammonia synthesis plants or coal-based methanol production facilities integrate sulfur removal into carbon removal processes, thereby reducing capital costs and operational expenses.
Generally, for most gases, higher pressures and lower temperatures lead to greater solubility in solvents; at dew points, solubility becomes theoretically infinite (i.e., complete miscibility occurs). In real gases, intermolecular forces (van der Waals forces) reduce solubility and lower the dew point compared to single-component gases. When one easily soluble component dissolves, it acts as a solvent for other components. During desorption: Lower pressures and higher temperatures favor solute release; at the solvent’s boiling point, solubility drops to zero. Common desorption methods include:
- **Pressure reduction**: Reducing total system pressure (even to negative pressure) after solute absorption.
- **Gas stripping**: Introducing inert gases to lower partial pressures of solutes.
- **Thermal desorption**: Heating the solvent to its boiling point to eliminate solutes.
**Advantages of methanol over other solvents**: At low temperatures and high pressures, methanol absorbs significantly more acidic gases than N₂, CO, H₂, or CH₄—resulting in superior selectivity, reduced methanol circulation needs, and minimized losses of valuable gases like H₂ and CO. Its low equilibrium vapor pressure at low temperatures minimizes evaporation losses. Methanol also boasts excellent chemical stability, a low freezing point, low viscosity, and minimal corrosiveness. Its absorption capacity is roughly 100 times greater than water and 10 times that of Benfield chemical solvents; additionally, it is inexpensive and readily available.
**Disadvantages**: Operating at low temperatures necessitates high-grade materials for equipment. Energy conservation efforts require extensive heat exchangers, lengthening the process flow. Methanol is toxic, posing health risks; even 10 mL inhalation may cause blindness, while 30 mL can be fatal. Permissible airborne concentrations are limited to 50 mg/m³. Strict manufacturing standards and careful handling are essential to prevent leaks, with appropriate safety measures mandatory.
**III. Features of low-temperature methanol washing**
This method ensures H₂S and CO₂ levels in purified gas meet synthesis requirements while completely eliminating sulfides, extending catalyst lifespan. It simultaneously removes multiple components—including H₂S, COS, CS₂, RSH, C₄H₄S, CO₂, HCN, NH₃, NO, paraffins, aromatics, and crude gasoline—from gases at temperatures ranging from 30°C to -70°C. Dehydration also occurs during this process. Absorbed components can be recovered during methanol regeneration. High absorption capacity and low circulation volumes minimize piping/equipment sizes and energy consumption. Regenerated methanol undergoes flash desorption and thermal regeneration for reuse. Desorbed CO₂ meets emission standards, while sulfur byproducts are recoverable. Wastewater from thermal regeneration contains trace methanol, usable for coal slurry preparation, thus lowering water usage and wastewater treatment demands. Purified gas achieves ultra-low sulfur content (<0.1 cm³/m³) and CO₂ levels (<10 cm³/m³), making this technique ideal for industries with stringent sulfur limits. Selective removal and recovery of H₂S and CO₂ are feasible due to their high solubility at low temperatures; minimal losses of H₂ and CH₄ occur because their solubility remains low. Methanol’s thermal/chemical stability and affordability further enhance its utility.
**IV. Limitations**
Energy efficiency drives reliance on numerous heat exchangers, complicating the process—especially regeneration stages. Material requirements remain stringent due to low-temperature operations. Toxicity concerns demand rigorous safety protocols and leak prevention measures.
**V. Primary product streams**
Methanol synthesis gas: CO₂ concentration ≤3.42% (mol); total sulfur content..
This post was last edited by 654262293 on 2011-1-8 23:22. Rectifier tower, with a heating medium at the bottom to provide the driving force for upward movement; stripping tower, absorption tower. The gas-liquid two phases come into countercurrent contact in the tower to absorb and release substances from each other.
Answer to this question: The regeneration principle of the regeneration tower: Heating is used for regeneration within the tower. During thermal regeneration, the evaporation of methanol from the solution reduces the vapor pressures of H2S, COS, and CO2 at the solution interface, thereby increasing the driving force for mass transfer. As a result, H2S, COS, and CO2 are desorbed from the solution to reach a new equilibrium. On the other hand, during thermal regeneration, the solubility of H2S, COS, and CO2 decreases, causing the dissolved gases to be released. The combined effect of these two factors enhances the regeneration of the solution in the regeneration tower. Principle of regeneration in the stripping tower: During stripping regeneration, the introduction of stripping nitrogen reduces the vapor pressure of CO2 at the solution interface, increasing the mass transfer driving force and thereby enhancing solution regeneration.
I don’t know that yet; looking forward to the answer
This post was last edited by 654262293 on 2011-1-8 at 23:23. Personally, I think the view expressed in post 7 is correct; let’s take a look at the opinions of other forum users as well.
I’m here to learn more. I’m a sales engineer for Sulzer tower internals, packing, trays, distributors, and separators in Shanghai. Please feel free to contact me if you need anything
This post was last edited by 654262293 on 2011-1-8 23:23. Water hammer phenomenon: When a valve in a pressurized pipeline is suddenly opened or closed, or when a water pump stops working suddenly for some reason, the flow velocity of the water changes rapidly, resulting in significant fluctuations in the pressure inside the pipeline. This change propagates upstream or downstream at a certain speed and is reflected at the boundaries; this water flow phenomenon is known as water hammer. Measures to prevent damage caused by direct water hammer: 1) Shorten the length of the pressure pipeline ； 2) Extend the time the valve remains closed ； 3) Due to the constraints imposed by the layout of hydraulic structures, when the length of the pressure pipeline cannot be changed, a surge tank can be constructed near the valve in order to reduce the range of influence of the surge pressure and lower its magnitude