Associated gas refers to natural gas that coexists with oil, and its recovery methods mainly include the following:
Compression method
Principle: Use a compressor to compress the associated gas, increase the pressure of the gas, thereby reducing its volume and facilitating storage and transportation. During this process, the pressure of the gas can be gradually increased through multi-stage compression.
Applicable scenario: It is more suitable for associated gas with small gas volume and low pressure. For example, in the recovery of associated gas from some small oil wells, it can be effectively collected through a small compressor.
Advantages: The equipment is relatively simple, the operation is convenient, and the initial investment cost is low.
Disadvantages: The compression process requires a certain amount of energy consumption, and if the gas contains a large amount of impurities, it may cause damage to the compressor.
Absorption method
Principle: Use absorbents to absorb natural gas components in associated gas. Absorbents are usually liquids that have good solubility in natural gas, such as certain organic solvents. The associated gas and absorbent come into full contact in the absorption tower, and the natural gas components are absorbed by the absorbent, while other impurities that are not absorbed (such as some solid particles) are separated. Afterwards, natural gas is desorbed from the absorbent through heating or depressurization, thereby achieving recovery.
Applicable scenarios: Suitable for processing associated gas containing multiple impurity components, especially for situations that require initial purification of natural gas. For example, in the recovery of associated gas containing a high amount of heavy hydrocarbons, absorption method can effectively separate natural gas and heavy hydrocarbons.
Advantages: It can effectively remove impurities from associated gas and recover natural gas with high purity.
Disadvantage: The selection of absorbent is crucial, and factors such as its absorption performance, desorption performance, and cost for natural gas need to be considered. Moreover, the absorption and desorption processes involve complex technological processes, with relatively high equipment investment and operating costs.
Adsorption method
Principle: Use solid adsorbents (such as activated carbon, molecular sieves, etc.) to adsorb natural gas components in associated gas. During the adsorption process, the associated gas passes through an adsorption bed equipped with an adsorbent, and natural gas molecules are adsorbed on the surface of the adsorbent, while other components (such as water vapor, impurity gases, etc.) flow out through the adsorption bed. After the adsorbent reaches saturation, regeneration is carried out by changing conditions such as temperature and pressure to desorb the adsorbed natural gas.
Applicable scenario: It is more effective for handling associated gas with low flow and high purity requirements. For example, in some fine chemical production processes that require extremely high purity of natural gas, adsorption methods can be used to recover high-purity natural gas.
Advantages: It can obtain high-purity natural gas and has strong selective adsorption ability for different gas components.
Disadvantages: The adsorption capacity of the adsorbent is limited, requiring regular regeneration, and the cost of the adsorbent is relatively high. In addition, the operating conditions of the adsorption process (such as temperature, pressure, etc.) need to be strictly controlled.
Low temperature separation method
Principle: Based on the different boiling points of each component in the associated gas, the gas is liquefied by lowering the temperature, and then gas-liquid separation is carried out at low temperature. In this process, refrigeration equipment is used to cool the associated gas to a very low temperature, causing heavy hydrocarbons and other components to liquefy first, while light hydrocarbons such as methane liquefy or remain in a gaseous state at lower temperatures, thereby achieving separation and recovery of different components.
Applicable scenarios: Suitable for processing associated gas containing a high amount of heavy hydrocarbon components, especially in situations where heavy hydrocarbon products need to be recovered. For example, in some oil regions with high production of natural gas condensate (NGL), low-temperature separation methods can effectively separate natural gas and condensate.
Advantages: It can simultaneously recover valuable products such as natural gas and heavy hydrocarbons, with good separation efficiency.
Disadvantages: Requires complex refrigeration equipment, high investment costs, and high energy consumption during low-temperature operation. At the same time, there are also high requirements for insulation and sealing of the equipment.
Comparison between them:
1. In terms of energy consumption
Compression method: The main energy consumption lies in the compression process of gas by the compressor. Its energy consumption is related to factors such as compression ratio and gas flow rate. Generally speaking, when the compression ratio is high and the gas flow rate is large, energy consumption will significantly increase. For example, when compressing low-pressure associated gas from 0.1MPa to 1MPa, the required power of the compressor will increase accordingly with the increase of gas flow rate.
Absorption method: Energy consumption mainly occurs in the circulation process of the absorbent, including the pumping of the absorbent and the heating required during the desorption process. Relatively speaking, its energy consumption may be lower than that of compression methods, especially when dealing with large-scale, low-pressure associated gas, as it does not require high-pressure compression of the gas like compression methods.
Adsorption method: The adsorption process itself has relatively low energy consumption, but the adsorbent regeneration process may require a certain amount of energy consumption, such as heat supply during heating or pressure reduction regeneration or energy consumption of vacuum pumps. Overall, under appropriate operating conditions, the energy consumption of adsorption methods can be controlled at a lower level, especially when dealing with low flow associated gas.
Low temperature separation method: Due to the need for refrigeration equipment to cool the associated gas to a very low temperature, the energy consumption is very high. The refrigeration process requires a large amount of electrical energy to maintain a low-temperature environment, which is the main energy consumption of the low-temperature separation method, usually the highest among several methods.
2. In terms of recycling efficiency
Compression method: The recovery efficiency mainly depends on the performance and operating conditions of the compressor. For relatively pure associated gas, a high recovery efficiency can be achieved, but if the gas contains impurities, it may affect the working efficiency of the compressor, thereby reducing the recovery efficiency. Generally, the recovery efficiency can reach around 70% to 90%, with specific values depending on the gas composition and equipment conditions.
Absorption method: It can effectively remove impurities and has a high recovery efficiency for natural gas. By selecting absorbents reasonably and optimizing the operating conditions of the absorption tower, a recovery efficiency of over 90% can be achieved, especially for some high value-added natural gas components.
Adsorption method: It has strong adsorption selectivity for natural gas and can recover high-purity natural gas. The recovery efficiency can usually reach a high level, reaching about 80% to 95%. However, the adsorption capacity of the adsorbent is limited and requires timely regeneration to ensure sustained and efficient recovery.
Low temperature separation method: Due to the separation based on the different boiling points of each component, the separation and recovery efficiency of different components in associated gas is very high, especially for the separation of heavy hydrocarbons and natural gas, which can achieve a recovery efficiency of over 95% and effectively recover various valuable products.
3. Equipment complexity and investment cost
Compression method: The equipment is relatively simple, mainly consisting of a compressor and supporting buffer tanks. The investment cost is relatively low, and small compression equipment may only cost tens of thousands to hundreds of thousands of yuan, making it suitable for small oil wells or situations with limited funds.
Absorption method: The equipment includes absorption tower, desorption tower, pump, heat exchanger, etc., and the process flow is relatively complex. The investment cost is relatively high, and it is necessary to consider the storage and circulation system of the absorbent. A medium-sized absorption method recovery device may require millions to tens of millions of yuan in investment.
Adsorption method: requires adsorption bed, vacuum pump (for vacuuming during regeneration), heating or cooling equipment (for adsorbent regeneration), etc. The complexity of the equipment is moderate, and the investment cost is also at a moderate level. The investment for a set of adsorption devices may range from tens of thousands to millions, and regular replacement of adsorbents will also increase costs.
Low temperature separation method: The equipment is the most complex, requiring a series of low-temperature equipment such as refrigeration units, low-temperature separators, and heat exchangers. The investment cost is very high because the manufacturing and maintenance requirements of low-temperature equipment are high, and a set of low-temperature separation devices may require tens of millions of yuan in investment.
4. Applicable associated gas components and scenarios
Compression method: suitable for associated gas with small gas volume, low pressure, and relatively simple composition. For example, in some small oil wells in remote areas, the associated gas production is not high, and the gas is mainly composed of conventional natural gas components. The purity requirements for the recovered gas are not particularly high.
Absorption method: Suitable for processing associated gas containing multiple impurity components, especially in scenarios where initial purification or recovery of specific components (such as heavy hydrocarbons) is required for natural gas. In refineries or natural gas processing plants, it is commonly used for centralized processing of associated gas from different oil wells with complex compositions.
Adsorption method: It has advantages for the treatment of associated gas with low flow rate and high purity requirements. For example, in some chemical production processes that require extremely high purity of natural gas, such as the preparation of raw gas for producing electronic grade chemicals, adsorption method can effectively remove trace impurities in associated gas and provide high-purity natural gas.
Low temperature separation method: suitable for processing associated gas containing a large amount of heavy hydrocarbon components, especially in situations where both natural gas and heavy hydrocarbon products need to be recovered simultaneously. In large natural gas condensate production bases or offshore oil and gas platforms with high associated gas production and heavy hydrocarbon content, low-temperature separation methods can fully leverage their advantages.
