In recent years, the increasing global carbon intensity has become a significant challenge, with maritime shipping accounting for nearly 3% of annual carbon-dioxide emissions. Liquefied Natural Gas (LNG) has emerged as a viable transitional marine fuel due to its economic and technological feasibility compared to other alternative fuels.
LNG is distinct from diesel fuel and other MGO because it is carried as a boiling liquid and is cryogenic at temperatures around -162°C (-259°F). This allows for easier transportation over long distances and enables a large storage capacity to be achieved in a relatively small space, as it occupies 600 times less volume in liquid form than in a gaseous state.
At HFM, we are dedicated to assisting shipping customers in achieving carbon-neutrality with the application of our LNG Heat Exchanger or Natural Gas Heat Exchanger.
In the separation step of the LNG process, raw natural gas is typically a mixture of various hydrocarbons and impurities, including water, CO2, and sulfur compounds. The separation process involves separating these components using a series of separation units, such as separators, scrubbers, and distillation columns. The process is based on the differences in boiling points and densities of the components, which allows for their separation.
The first step in the separation process is to remove any free liquids or solids from the natural gas stream. This is typically accomplished using a separator vessel, which uses gravity to separate the heavier liquids and solids from the lighter natural gas. The separated liquids and solids are then removed from the bottom of the vessel, while the natural gas is sent to the next separation unit.
The next step in the separation process is to remove any remaining liquids and condensates from the natural gas. This is typically accomplished using a scrubber or absorption column, which uses a liquid solvent, such as propane or ethylene glycol, to absorb the remaining liquids and condensates. The natural gas is then sent to the next separation unit, while the absorbed liquids and condensates are removed from the solvent using a regenerator.
The natural gas from a bore is often saturated with water vapor and must be dried to meet pipeline specifications and maximize its calorific content before being fed into a pipeline. There are various methods to accomplish this, but in the Low Temperature Separation(LTS) process, the dew point of natural gas is controlled by condensing the water vapor.
However, the natural gas industry has experienced issues with shell and tube condensers, where the mixture of the condensed water and heavy hydrocarbons at low temperatures (-5 to -15°C) can form hydrates. This can lead to a blockage of the condensate outlet of the heat exchanger. To prevent this, glycol or methanol is commonly injected into the LNG heat exchanger gas inlet.
The final step in the separation process is to remove any remaining impurities, such as CO2 and sulfur compounds, from the natural gas. This is typically accomplished using a distillation column, which uses differences in boiling points to separate the natural gas from the impurities. The natural gas is sent to the next stage of the LNG process, while the impurities are removed as a separate stream and sent for further treatment.
Natural gas often contains water vapor, which can lead to several issues during transportation and processing. The presence of water vapor in natural gas can cause corrosion in pipelines and other equipment, which can lead to damage and ultimately result in significant repair costs.
Moreover, if the gas is transported at high pressure, water vapor can combine with hydrocarbons to form hydrates, which can block pipelines and valves, causing production shutdowns and loss of revenue.
Therefore, to avoid these problems, the next step in natural gas treatment after removing contaminants is dehydration. Dehydration refers to the removal of water vapor from natural gas. There are several methods for achieving this, including adsorption, absorption, and refrigeration.
Adsorption involves the use of materials like activated alumina, silica gel, or molecular sieves that have a high affinity for water vapor. The gas is passed through a bed of these materials, which adsorb the water vapor, leaving dry gas. The adsorbent materials can be regenerated by heating or purging with a gas that does not contain water vapor, such as nitrogen or methane.
Absorption is another method of removing water vapor from natural gas. In this method, liquid desiccants, such as Tri ethylene glycol or methanol, are used to absorb water vapor from the gas.
The gas is passed through a column or vessel containing the liquid desiccant, which selectively removes the water vapor from the gas, leaving dry gas. The liquid desiccant can be regenerated by heating or by reducing the pressure, which causes the absorbed water vapor to evaporate.
Refrigeration is a third method of removing water vapor from natural gas. In this method, the gas is cooled to a temperature below the dew point of the water vapor using LNG heat exchanger, causing it to condense out of the gas. The water can then be removed by separating it from the gas using a separator or other equipment. Refrigeration is often used in combination with other methods of dehydration to achieve a higher degree of water vapor removal.
In conclusion, dehydration is an essential step in natural gas treatment to prevent corrosion and hydrate formation during downstream processing and transportation. The choice of method depends on various factors, such as the gas composition, the required degree of dehydration, and the availability of equipment and resources.
Natural gas sweetening is a crucial process that involves removing sulfur compounds, primarily hydrogen sulfide (H2S) and carbon dioxide (CO2), from natural gas. These compounds are highly corrosive and can damage equipment and pipelines, and also have negative environmental impacts.
To remove these sulfur compounds, various methods can be used, including chemical absorption, physical adsorption, and catalytic conversion. Chemical absorption methods use liquid solvents like amine or caustic soda to absorb sulfur compounds, while physical adsorption methods use materials like activated carbon or zeolites. Catalytic conversion methods use chemical reactions to convert sulfur compounds into less harmful forms.
There are also other methods for sweetening natural gas, including adsorption and membrane separation. Adsorption involves the use of a solid adsorbent material, such as activated carbon or molecular sieve, to adsorb the sulfur compounds. Membrane separation uses a permeable membrane to separate the sulfur compounds from the natural gas.
Once the sulfur compounds are removed from the natural gas, the resulting gas is referred to as “sweet gas”. Sweet gas has a higher calorific value and is less corrosive, making it more valuable and easier to transport.
The sulfur compounds that are removed from the natural gas are typically further processed or treated to recover the sulfur or dispose of it safely. This is an important step in natural gas treatment to ensure the quality of the natural gas and prevent equipment corrosion and environmental pollution.
Absorption: Absorption is a widely used method for purifying natural gas. It is highly effective in removing impurities such as CO2, H2S, and other trace components. In this process, the natural gas is brought into contact with a solvent, such as amine, in a packed column. The solvent selectively absorbs the impurities from the gas stream, leaving behind pure natural gas. The solvent is then regenerated, typically by heating it to release the impurities, and recycled back to the column. This process can be repeated multiple times to achieve higher levels of purity.
Cryogenic process: Cryogenic processes are another highly effective method for purifying natural gas. In this process, the natural gas is cooled to extremely low temperatures using refrigerants like nitrogen or propane. The impurities in the gas, such as CO2 and H2S, are frozen out and removed as solids. The remaining gas is then warmed up and pressurized to return to its gaseous state. This process is highly efficient in removing impurities from natural gas and is often used in conjunction with absorption processes for maximum purity. However, it is also more energy-intensive and expensive than other purification methods.
Overall, the choice of purification method will depend on a number of factors, including the impurities present in the natural gas, the required level of purity, and economic considerations. Both absorption and cryogenic processes have their advantages and disadvantages, and the best method for a particular application will depend on the specific requirements and constraints of the project.
Compression: Compression is a crucial process in the production of liquefied natural gas (LNG), as it is necessary to increase the pressure of the natural gas to liquefy it. The two main types of compressors used in LNG facilities are reciprocating and centrifugal compressors.
Reciprocating compressors are typically used in smaller LNG facilities due to their high efficiency and compact design. These compressors use a piston and cylinder mechanism to compress the natural gas. The piston moves back and forth in the cylinder, compressing the gas in the process. Reciprocating compressors can be either single- or multi-stage, depending on the pressure required.
Centrifugal compressors, on the other hand, are used in larger LNG facilities due to their higher capacity and lower maintenance requirements. These compressors use a rotating impeller to compress the natural gas. As the impeller spins, the gas is drawn in and accelerated to high speeds, creating a high-pressure gas stream. Centrifugal compressors can be configured as single- or multi-stage units, depending on the pressure required.
Both types of compressors have their own advantages and disadvantages. Reciprocating compressors are more efficient at lower compression ratios and can handle a wider range of gas compositions. They are also more suitable for applications that require high pressure differentials. However, they are more expensive to maintain and can be noisy and vibration prone.
Centrifugal compressors, on the other hand, are more efficient at higher compression ratios and have a higher flow rate capacity. They are also quieter and require less maintenance than reciprocating compressors. However, they are less efficient at handling variable gas compositions and require more space and power to operate.
In summary, the choice between reciprocating and centrifugal compressors depends on the specific requirements of the LNG facility, including its size, capacity, and gas composition. Both types of compressors play a critical role in the compression process, which is essential for the production of LNG.
Pre-cooling is an essential step in the liquefaction process of natural gas. It involves cooling the natural gas to a temperature that is low enough to prepare it for liquefaction. This is accomplished using plate heat exchangers, which transfer heat between the natural gas and a refrigerant, typically nitrogen or propane. The refrigerant absorbs heat from the natural gas, causing its temperature to drop.
The cooled natural gas is then passed through a series of heat exchangers to further reduce its temperature and prepare it for liquefaction. This step is crucial in ensuring that the natural gas is at the right temperature for efficient liquefaction and helps to maximize the efficiency of the liquefaction process.
Liquefaction is a critical step in the LNG production process, during which natural gas is transformed into a liquid state. This process is accomplished using a series of heat exchangers, including plate heat exchangers, which transfer heat between the natural gas and the refrigerants used to cool it down to its liquefaction temperature of about -162°C.
The refrigerants, typically nitrogen or propane, are circulated through a closed loop refrigeration cycle that uses compressors to increase their pressure, causing them to release heat. This heat is then removed using heat exchangers, causing the refrigerants to cool down and become ready for another cycle.
As the natural gas flows through the heat exchangers, it is cooled down to its boiling point, causing it to condense into a liquid. The heat exchangers are arranged in a cascade, with the coldest heat exchangers at the bottom and the warmest at the top. The natural gas flows downward through the heat exchangers, and the refrigerants flow upward, countercurrent to the gas flow.
The heat exchangers are designed to optimize the transfer of heat between the natural gas and the refrigerants, ensuring that the natural gas is cooled down to its liquefaction temperature with maximum efficiency.
After liquefaction, the LNG is typically stored in insulated tanks until it is ready to be loaded onto LNG carriers for transport to markets around the world. The LNG is kept at a temperature of around -162°C to maintain its liquid state and ensure that it remains stable during storage and transport.
LNG production is a complex and energy-intensive process that requires careful engineering and specialized equipment. The liquefied natural gas produced through this process is transported by ships or pipelines to markets where it can be used as a fuel or as a feedstock for various industrial processes. There are three basic liquefaction techniques that are commonly used in natural gas processing: Cascade refrigeration, MRC, and Expander based liquefaction.
Natural gas liquefaction technology is continually evolving, with the aim of improving production capacity, reducing energy consumption, enhancing thermodynamic efficiency, and increasing reliability. The most advanced liquefaction technology combines the three basic liquefaction processes with the actual conditions of raw natural gas to generate a mixed refrigerant-based composite process technology that is optimized for performance.
In the early days of natural gas liquefaction, plants were relatively simple and relied on either cascaded refrigeration or single mixed refrigerant (SMR) processes with train capacities under one million tonnes per annum (MTPA). However, these processes were quickly replaced by the two-cycle propane precooled mixed refrigerant (C3MR) process developed by Air Products and Chemicals Inc. (APCI). This process became the dominant liquefaction process technology by the late 1970s and remains competitive in many cases today.
Overall, natural gas liquefaction plays a vital role in the production, transportation, and use of natural gas around the world. As the technology continues to evolve and improve, it is likely to become even more important in meeting the growing demand for energy in the years to come.
Once the LNG is liquefied and stored, it can be transported to its final destination. LNG is typically transported by ship or truck, depending on the distance and location of the destination. During transportation, the LNG is stored in specialized cryogenic tanks, which are designed to maintain the LNG at a temperature of -162°C. These tanks are heavily insulated and may be double-walled to prevent any leaks or spills.
Transportation of LNG by ship requires specialized vessels that are designed to withstand the extreme temperatures and pressures associated with LNG. These vessels are typically large and may be powered by steam or diesel engines. They are also equipped with advanced safety systems to prevent any leaks or spills during transport.
Transportation of LNG by truck is typically used for shorter distances or in areas where pipeline infrastructure is not available. LNG trucks are equipped with specialized cryogenic tanks and may also be double-walled for safety. The tanks are usually mounted on trailers and may be designed for either highway or off-road use.
Once the LNG reaches its destination, it is regasified to convert it back into a gaseous state. Regasification is typically accomplished using either heat exchangers or vaporizers. Heat exchangers transfer heat from a warm fluid, such as water or air, to the LNG, causing it to vaporize.
Vaporizers use a heat source, such as natural gas, to vaporize the LNG. The regasified natural gas can then be distributed through pipelines to customers or used as fuel for power generation or other industrial processes.
A scrubber or absorption column is used to remove any remaining liquids and condensates from the natural gas. The process uses a liquid solvent, such as propane or ethylene glycol, to absorb the remaining liquids and condensates, and the natural gas is sent to the next separation unit. This step may require a LNG heat exchanger or natural gas heat exchanger for the solvent regeneration process.
Various methods can be used. For example, in absorption dehydration, the natural gas is usually heated before it enters the absorber column to increase its water vapor carrying capacity. After the gas has passed through the absorber column, it is cooled to condense and remove the absorbed water vapor. A LNG heat exchanger or natural gas heat exchanger can be used to transfer heat from the warm, dehydrated gas leaving the absorber to the incoming gas that needs to be dehydrated. This heat exchange can improve the energy efficiency of the process.
Similarly, in refrigeration dehydration, a LNG heat exchanger can be used to cool the natural gas to the required temperature for water vapor condensation. The LNG heat exchanger can use a refrigerant, such as propane or ethylene, to cool the natural gas before it enters the condenser. The refrigerant is then cooled by a cooling medium, such as water or air, in another heat exchanger.
In adsorption dehydration, heat can be used to regenerate the adsorbent material after it has become saturated with water vapor. This can be done by passing a hot gas, such as steam or nitrogen, through the bed of adsorbent material. The LNG heat exchanger can be used to transfer heat from the regeneration gas to the adsorbent bed.
Catalytic conversion methods use chemical reactions to convert sulfur compounds into less harmful forms. The reaction may require a LNG heat exchanger to maintain the required temperature.
The cryogenic process involves cooling the natural gas to extremely low temperatures using refrigerants like nitrogen or propane. The process may require a LNG heat exchanger to cool the gas before it enters the cryogenic process.