IDEAL MODEL FOR NATURAL GAS PURIFICATION FROM ACIDIC COMPONENTS USING COMPOSITE ABSORBENT

ABSTRACT

The natural gas purification process involves the removals of sour gases such as hydrogen sulfide (H₂S) and carbon dioxide (CO₂) using absorbents. Mixed amine solvents such as methyldiethanolamine (MDEA), diethanolamine (DEA), and combinations of nitrogen-containing polyelectrolytes provide improved absorption efficiency, enhanced thermal stability, and cost- effectiveness. This study presents the results of modeling natural gas purification with mixed amine solvents using Aspen HYSYS, and it was observed that increasing the amount of polyelectrolyte enhances both H₂S and CO₂ sour gas removal efficiency, also reduces energy costs. The optimal polyelectrolyte content is 10% by weight, offering a good balance between removal efficiency and energy consumption.

АННОТАЦИЯ

Процесс очистки природного газа включает в себя удаления  кислых газов, таких как сероводород (H₂S) и диоксид углерода (CO₂), с использованием абсорбентов. Смешанные аминные растворители, такие как метилдиэтаноламин (МДЭА), диэтаноламин (ДЭА) и комбинации -азот содержащий полиэлектролитов обеспечивают улучшенную эффективность абсорбции, повышенную термическую стабильность и экономическую эффективность. В исследовании представлены результаты моделирования очистку  природного газа с помощью смешанных аминных растворителей с использованием Aspen HYSYS, и было отмечено, что увеличение количества полиэлектролита повышает эффективность удаления как кислого газа H₂S, так и CO₂, а также уменьшает затраты на энергию. Оптимальное содержание полиэлектролита составляет 10% по весу, что обеспечивает хороший баланс между эффективностью удаления и потреблением энергии.

Keywords: adsorption, absorption, absorption, monodiethanolamine, amine plant, viscosity, sulfur.

Ключевые слова: адсорбция, абсорбция, поглощение, монодиэтаноламин, аминовая установка, вязкость, сера.

Introduction

Natural gas is an important energy resource that must be refined to meet market standards and regulations. One of the main processes involved in the purification of natural gas involves is the removal of sour gases such as hydrogen sulfide (H₂S) and carbon dioxide (CO₂). In addition to being corrosive and toxic, these gases can reduce the calorific value of natural gas. The presence of H₂S and CO₂ in natural gas is not only poses technological challenges, but also significant environmental and health risks. Therefore, the separation of these gases is crucial for the safe and efficient use of natural gas [1].

Amines, particularly alkanolamines, have been found to be effective in treating sour gases and are widely used in this process. The most commonly used amines include monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA). Each of these amines has unique chemical properties that influence their absorption characteristics and overall. MEA is known for its high reactivity with H₂S and CO₂, while DEA and MDEA have advantages such as low vapor pressure and high selectivity for H₂S [2].

While the choice of amines and their concentration are important, the efficiency of the process also depends on the mixing conditions of the techno-economically effective amine mixture. Proper mixing ensures adequate interaction between the gas and liquid phases, thereby expanding the contact surface and enhancing the absorption of acidic gases [3]. However, optimal mixing conditions- including mixing speed, duration, and temperature- vary depending on the type of amine used. Improper mixing can result in insufficient gas-liquid contact, leading to low absorption, while excessive mixing increases energy consumption and operating costs without significantly affect improving efficiency [4].

Mixed amine solutions containing MDEA and DEA are formulated to combine the strengths of each component. As mentioned earlier, MDEA is characterized by high selectivity for H₂S, while DEA increases CO₂ absorption. Studies have shown that mixed amine solutions provide both absorption efficiency and operational flexibility [7]. Based on experiments conducted in this research, the optimal mixed amine solution had the following composition: MDEA (20-25 wt%), DEA (15-20 wt %), and nitrogen polyelectrolyte (5-15 wt %), with the remainder being water. In this mixture, nitrogenous polyelectrolyte acts as catalyst, improving the reaction kinetics and increasing the absorbency of the solution. Additionally,it has been shown that the addition of polyelectrolyte reduces the energy required for amine regeneration and enhances the solution  stability under operational conditions [4].

Methods

Experience Installation

1. Mixing Bowl:

• A 5 -liter cylindrical stirred tank reactor is used.
• The reactor is equipped with a mechanical stirrer with a variable speed control system.
• The vessel is fitted with a jacket heating system to control the temperature during mixing.

2. Composition of Amine Solution:

The amine mixture is prepared with the following composition:

• MDEA: 20-25 wt%
• DEA: 15-20 wt%
• Nitrogen polyelectrolyte: 5-15 wt%
• The remainder is water.

3. Temperature Control:

• The reactor is equipped with a jacket heating system to maintain the required temperature.
• The temperature varies from 25°C to 60°C.

Experimental Procedure

1. Preparation of Amine Solution:

• The required amounts of MDEA, DEA and nitrogen polyelectrolyte are measured and added to the reactor.
• Distilled water is added to the reactor to fill the remaining volume.

2. Reactor Setup:

• A mechanical stirrer is installed in the reactor.
• The reactor is sealed to prevent contamination and evaporation

3. Change Blending Parameters: Agitator Speed:

• The speed of a mechanical agitator varies from 100 to 1000 RPM.
• Mixing Duration: Mixing duration varies from 5 to 60 minutes.
• Temperature: Reactor temperature ranges from 25°C to 60°C.

4. Sampling and Analysis:

• During the mixing process, samples of the amine mixture are collected regularly.
• To ensure the homogeneity of the mixture, it is analyzed using spectroscopy or chromatography techniques.
• Viscosity and pH measurements are taken to assess the quality of the mixture.

5. Data Collection and Analysis:

• Data from experiments are recorded and analyzed to determine optimal mixing conditions for each parameter.
•  A statistical analysis is performed to evaluate the significance of the effect of mixing speed, duration and temperature on the homogeneity and quality of the mixture.

Mathematical Modeling and Equations

To model the relationship between the mixing parameters and the quality of the mixture, the following equations are considered [10]:

1. eynolds Number (Re):    

In this:

1. Power number (NP):

In this:

PPP = power input to mixer (W)

2. Mixing time (θ):

in this:

k and n are empirical constants

D = mixer diameter (m)

T = vessel diameter (m)

Results

1. Mixing Speed:

• At 100 RPM:The mixture shows poor uniformity with significant  variation in component distribution.
• At 500 RPM: The mixture achives optimal homogeneity, with uniform distribution of MDEA, DEA and polyelectrolyte.
• At 1000 RPM: The mixture remains the same as at RPM,but there is a risk of  the polyelectrolyte degradation

2. Mixing Duration:

• At 5 minutes: The mixture remains unmixed with visible layering.
• At 30 minutes: Optimal uniformity is achieved.
• At 60 minutes: No significant improvement compared to 30 minutes, indicating that 30 minutes is sufficient.

3. Temperature:

• At 25°C: Higher viscosity,requiring longer mixing time.
• At 40°C: Optimal temperature, providing good balance between viscosity and mixing efficiency.
• At 60°C: Longer viscosity, but the risk of component degradation increases.

Table 1.

Sample Data (approximate)

The methodology outlined above provides a systematic approach to studying the effects of mixing parameters on the homogeneity and quality of amine blends used in natural gas sweetening. By optimizing these parameters, the research aims to enhance the production process leading to more efficient and cost-effective preparation of the amine mixture - critical for effective preparation natural gas sweetening. The inclusion of equations and numerical results supports the development of a robust model to predict optimal mixing conditions.

Discussion

Modeling of natural gas purification from sour gases using mixed amine solvents the natural gas purification process involves the separation of sour gases, such as hydrogen sulfide (H₂S) and carbon dioxide (CO₂) using absorbents. Mixed amine solvents such as methyldiethanolamine (MDEA), diethanolamine (DEA), and combinations of nitrogen-containing polyelectrolytes, offer enhanced absorption efficiency, improved thermal stability, and cost effectiveness. This section presents the results of modeling the natural gas desouring process with mixed amine solvents using Aspen HYSYS. This process consists of an absorber, where the amines solution contacts the remove natural gas H₂S and CO₂ and a regenerator that removes the absorbed acid gases from the amine solution and recovers the solvent for reuse.

Figure 1. Computer model of natural gas purification from sour gases using amines [11]

Natural gas flow (in the case of Orta-bulok field):

The consumption of this gas flow is taken as 100 tons per hour, with the components distributed as follows:

Methane (CH₄): 86.32%

Ethane (C₂H₆): 1.80%

Propane (C₃H₈): 0.27%

 Butane (C₄H₁₀): 0.15% Carbon dioxide (CO₂): 4.70%

Hydrogen sulfide (H₂S): 5.00%

Nitrogen (N₂): 1.40%

Mixture of amine solutions:

The composition of the calculated amine solution is as follows:

• MDEA: 22.5 wt%
• DEA: 17.5 wt%
• Nitrogen storage polyelectrolyte: 10 wt%
• Water: 50 wt%

Sensitivity analysis results and analyses

During the modelling process, a sensitivity analysis was conducted based on change in the composition of solvents, and it was observed both the efficiency of sour gas separation and the required energy load increase proportionally with the amount of solvents in the mixture.

Table 2.

The effect of the change in the amount of MDEA in the mixture on the process

Increasing the MDEA content enhance CO₂ extraction efficiency but also increases energy consumption. In this case, the optimal MDEA content is around 22.5 wt%, providing a balance between efficiency and energy consumption.

Table 3.

The effect of the change in the amount of DEA in the mixture on the process

Higher DEA content improves higher H₂S removal efficiency while also providing moderate CO₂ removal efficiency. The optimal DEA content for efficient H₂S removal with moderate energy requirements is 17.5 wt%.

Table 4.

The effect of the change in the amount of polyelectrolyte in the mixture on the process Polyelectrolyte content (% by weight) H₂S extraction efficiency (%) CO₂ extraction efficiency (%) Energy load (MJ/h)

Conclusions

Enhance polyelectrolyte content was observed to increase both H₂S and CO₂ sour gas removal efficiency, and also reduces energy costs. Here, the optimal polyelectrolyte content is 10% by weight, offering a good balance between removal efficiency and energy consumption.

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