Booster compressors are essential in the oil and gas industry, serving as specialized units designed to increase the pressure of gases beyond what primary compressors achieve. They boost gas pressure for efficient transportation through pipelines, enable further processing, and support storage operations. When purchasing a booster compressor, pressure and flow requirements should guide selection of the compressor technology, and fuel availability should guide selection of the drive type. Control systems for booster compressors are responsible for regulating pressure/ flow, protecting equipment, and providing monitoring options.
What Is a Booster Compressor?
A booster compressor is a secondary compression unit that receives gas already compressed by a primary compressor and elevates its pressure to even higher levels. These compressors supply high-pressure gas to downstream equipment. Where equipment and processes don’t require high pressure, booster compressors can be used to overcome friction, elevation changes, as well as long distances.
Common Applications of Booster Compressors
Booster compressors are common in several applications, including the following:
- Natural gas pipelines: To maintain or increase pressure for long-distance transmission and distribution.
- Gas processing plants: To meet the pressure requirements for separation, treatment, or liquefaction processes.
- Petrochemical facilities: To support high-pressure reactions and feedstock delivery.
- Underground gas storage: To inject gas into storage reservoirs by overcoming reservoir pressure.
- Industrial gas supply (nitrogen, hydrogen, CO₂): To deliver high pressure gas for manufacturing, metalworking, and laboratory use.
Working Principle of Booster Compressors
Fundamental Compression Mechanism
Booster compressors increase the pressure of gas by mechanically reducing its volume. They can be described by their pressure ratio, which is defined as the ratio of absolute discharge pressure to absolute inlet pressure. For example, a booster compressor with a pressure ratio of 2:1 will double the pressure of the gas it receives from the primary compressor.
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Thermodynamic Process
The compression process can be idealized as either isentropic or polytropic.
- Isentropic compression: Assumes the process is reversible, meaning no energy enters or leaves the system. This neglects heat transfer, friction, and other energy losses during compression. This results in the highest theoretical efficiency, but rarely occurs in practice.
Isentropic compression obeys the following relation between pressure (P) and volume (V). Gamma (γ) represents the ratio of specific heat at constant pressure (Cp) to specific heat at constant volume (Cv).
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- Polytropic compression: A polytropic process is one that obeys the following relation:
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Here, n is the polytropic index. If n = γ, then the process is also isentropic. However, when modeling compressor work, the value of n is typically between 1 and γ. This models real-world conditions where some heat exchange occurs between the gas and surroundings during compression. The polytropic process better represents actual compressor operation, accounting for temperature changes and heat losses.
Reducing the volume of a gas creates heat and mechanical stress, which limit the amount of pressure that a compressor can generate. Booster compressors manage heat using intercooling and aftercooling.
- Intercooling: Gases cool between compression stages, reducing the volume of the gas while maintaining pressure. Because compression is a polytropic process, reducing the volume lowers the amount of work required to achieve a desired pressure. Intercooling makes multistage compression more efficient than single stage compression.
- Aftercooling: Cools the gas after the final compression stage. Moreover, this removes residual heat, protects downstream equipment, and helps condense moisture and contaminants.
Stages of Operation
Booster compressors operate through a series of stages.
Inlet Phase
The booster compressor receives gas that has already been compressed to a moderate pressure level by a primary compressor.
Compression Phase
The gas is further compressed using mechanical means such as rotary, reciprocating piston, or centrifugal mechanisms. This reduces the gas volume and increases its pressure to the desired high level.
Discharge Phase
The high-pressure gas is then pushed out of the booster compressor. It either moves to the next compression stage for further pressure increase or flows directly into the pipeline or storage system.
Types of Booster Compressors
Based on Technology
- Reciprocating Booster Compressors: Use a crankshaft to drive pistons, which compress gasses. They are suitable for high-pressure, low-flow applications such as pipeline injection and wellhead boosting.
- Rotary Screw Booster Compressors: Use a pair of asymmetric screws to squeeze a gas through their threads, called “lobes”. The volume between the lobes gets progressively smaller, thus compressing the gas. These compressors provide continuous operation with moderate pressure and steady flow rates, hence they are common in industrial gas processing.
- Centrifugal Booster Compressors: Use a rotor, called an impeller, to increase the velocity of a gas before passing it through a diffuser to convert that kinetic energy to potential energy. These are designed for high-flow, low-to-medium pressure applications, so they are often used in large gas transmission lines.
Based on Drive Type
- Electric Motor-Driven: Common in stationary installations where reliable electrical power is available. They offer precise speed control and low emissions.
- Gas Turbine-Driven: Used in remote or high-power applications where electricity is limited.
- Diesel Engine-Driven: Ideal for portable or off-grid operations. Diesel engines provide robust power and are favored in field applications where fuel availability is better than electricity.
Single-Stage vs Multi-Stage Booster Compressors
| Feature | Single-Stage Booster | Multi-Stage Booster |
| Pressure Ratio | Lower, suitable for moderate pressure. | Higher, achieves high overall pressure. |
| Number of Compression Steps | One compression step. | Multiple compression steps in series. |
| Cooling | Usually no intercooling. | Intercooling between stages improves efficiency and reduces heat. |
| Application | Simple, lower pressure requirements. | Complex, high-pressure industrial needs. |
Key Components and System
- Inlet Filter System: Removes debris and particulates from the incoming gas, ensuring clean operation and preventing damage.
- Compressor Core: Consists of reciprocating pistons, rotary screws, or centrifugal impellers that mechanically compress the gas.
- Cooling Systems: Include intercoolers and aftercoolers to manage heat generated during compression.
- Lubrication System: Reduces friction and wear on moving parts, ensuring smooth operation and longevity.
- Pressure Relief Valves and Safety Controls: Prevent overpressure conditions by safely releasing excess pressure.
- Control Panel and Instrumentation: Provides real-time monitoring of critical parameters such as pressure and flow to ensure safe and efficient operation.
Role of Booster Compressors in Pipeline Operations
Pressure Drop Compensation
Gas pressure naturally drops over long pipeline distances due to friction and elevation changes. Booster stations restore this lost pressure, thus ensuring consistent flow and delivery.
Pipeline Throughput Maximization
By increasing gas pressure, booster compressors enable higher flow rates and larger delivery volumes, therefore optimizing pipeline capacity.
Gas Injection and Withdrawal in Storage Facilities
Boosters facilitate efficient gas injection during low demand and withdrawal during peak demand periods, maintaining supply balance.
Midstream Applications
Booster compressors are integrated with gas metering, odorization, and dehydration units to support safe and efficient gas transmission.
Role of Booster Compressors in Gas Processing Facilities
Feeding Gas to Processing Units
Booster compressors maintain the optimal pressure required for processes like amine treating, cryogenic separation, and dehydration.
Recompression of Flash Gas
They recover and recompress flash or vented gases, reducing waste and improving overall plant efficiency.
Support for LNG Preprocessing
Boosters deliver high-pressure feed gas essential for liquefaction in LNG plants.
Control and Automation in Booster Compressor Systems
Pressure and Flow Regulation
PID control loops continuously adjust compressor operation to maintain desired pressure and flow setpoints, resulting in stable and efficient performance.
Surge and Anti-Surge Protection
Critical for centrifugal booster compressors, these systems detect and prevent surge conditions that can damage equipment by modulating flow or speed.
Remote Monitoring and Diagnostics
Integration with SCADA and Distributed Control Systems (DCS) enables real-time monitoring, predictive maintenance, as well as automated alerts. This enhances operational reliability and reduces downtime through early fault detection.
Installation Considerations
Successful booster compressor installation depends on several key factors:
- Location and Environmental Conditions: Indoor installations offer better temperature control and noise reduction, while outdoor setups require weather protection.
- Foundation and Vibration Management: Foundations should be flat, level, and strong enough to support the compressor. Skid-mounted or base-mounted systems use vibration pads or platforms to reduce noise and mechanical stress.
- Piping Design: Proper piping minimizes pressure drops and pulsations. Secure connections prevent leaks and maintain efficiency.
- Accessibility for Maintenance: Adequate clearance around valves, filters, and cylinder heads ensures easy inspection and servicing.
Maintenance and Reliability Best Practices
Routine inspections and preventive maintenance keep compressors reliable:
- Routine Inspections: Monitor vibration, temperature, and lubrication to detect early issues.
- Preventive Maintenance: Follow schedules for filter changes, oil replacements, and valve recalibrations.
- Spare Parts: Maintain an inventory of critical parts to minimize downtime.
How Petrotech Supports Booster Compressor Performance
At Petrotech, we are committed to enhancing booster compressor performance through tailored solutions and dedicated support, ensuring your operations run safely and efficiently:
- Custom Control Solutions: Open architecture systems tailored for booster compressors, ensuring flexibility and seamless integration.
- Anti-Surge and Load-Sharing Controls: Protect your assets while optimizing throughput and efficiency.
- Retrofit Services: Upgrade legacy systems to meet compliance and improve performance without full replacements.
- 24/7 Support: Around-the-clock technical services, spare parts availability, and expert field engineering to maximize uptime.
Ready to reduce risk and improve efficiency?
Contact us today to schedule a consultation with our specialists and see how Petrotech can transform your operations.