How to Prepare an RFQ for a Centrifugal Compressor?
A centrifugal compressor RFQ is more than a request for a price. The supplier needs accurate operating and technical data to select the right compressor, define the configuration, and prepare a reliable quotation.
A professional RFQ should answer three basic questions:
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What gas will the compressor handle?
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What pressure does it need to achieve?
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What operating range must it cover?
The more complete the information, the more accurate the compressor selection and quotation will be.
I. Define the Basic Operating Conditions
Start with the basic operating conditions of the compressor.
| Parameter | Example |
|---|---|
| Gas | Natural Gas |
| Inlet Pressure | 0.5 MPa |
| Discharge Pressure | 2.0 MPa |
| Inlet Temperature | 30°C |
| Flow Rate | 50,000 Nm³/h |
These parameters provide the foundation for compressor selection and performance calculation.
II. Clearly Define the Flow Rate
Flow rate is one of the most important parameters in a centrifugal compressor RFQ.
Common units include:
Nm³/h
m³/h
kg/h
m³/min
It is important to specify whether the flow rate is standard volume flow, actual volume flow, or mass flow.
For example, 50,000 Nm³/h and 50,000 m³/h represent very different operating conditions. Confusing standard and actual flow can result in incorrect compressor selection.
III. Specify Whether Inlet and Discharge Pressure Are Absolute or Gauge Pressure
Pressure values must clearly state whether they are absolute pressure or gauge pressure.
For centrifugal compressors, pressure ratio is normally calculated using absolute pressure:
Pressure Ratio = Discharge Absolute Pressure ÷ Inlet Absolute Pressure
For example, if the inlet pressure is 0.5 MPa absolute and the discharge pressure is 2.0 MPa absolute:
Pressure Ratio = 2.0 ÷ 0.5 = 4.0
If the RFQ only provides gauge pressure without specifying the pressure basis, the supplier may need additional information before making an accurate selection.
IV. Do Not Omit Inlet Temperature
Inlet temperature directly affects gas density, flow characteristics, compressor power, and discharge temperature.
A typical RFQ should include the following:
| Condition | Inlet Temperature | Inlet Pressure | Flow Rate |
|---|---|---|---|
| Minimum | 20°C | 0.45 MPa | 40,000 Nm³/h |
| Normal | 30°C | 0.50 MPa | 50,000 Nm³/h |
| Maximum | 40°C | 0.55 MPa | 60,000 Nm³/h |
Providing only the normal temperature may not be enough for proper compressor selection, especially when the equipment operates under significant seasonal or process variations.
V. Provide Minimum, Normal, and Maximum Conditions
A centrifugal compressor rarely operates at only one fixed point.
A complete RFQ should provide at least:
Minimum operating condition
Normal operating condition
Maximum operating condition
Start-up or shutdown conditions, if relevant
Required turndown range
These conditions help the supplier evaluate the compressor’s stable operating range, surge margin, control strategy, and efficiency.
For variable-load applications, the minimum operating point is particularly important because the compressor must remain stable without excessive recirculation or surge risk.
VI. Gas Composition Is an Important Part of a Professional RFQ
For process-gas centrifugal compressors, gas composition is essential for compressor selection.
For example:
| Component | Content |
|---|---|
| Methane | 85% |
| Ethane | 8% |
| Propane | 4% |
| Nitrogen | 2% |
| CO₂ | 1% |
The RFQ should also provide important gas properties when available:
Molecular weight
Compressibility factor
Specific heat ratio
Gas density
Moisture content
Liquid content
Dust or solid particles
Oil content
Corrosive components
Changes in gas composition can affect density, required head, flow characteristics, power consumption, and compressor operating range.
VII. Define the Required Compressor Performance
he RFQ should clearly state the required performance parameters.
Typical requirements include:
Flow rate
Inlet pressure
Discharge pressure
Pressure ratio
Polytropic efficiency
Isentropic efficiency
Discharge temperature
Operating speed
Surge margin
Stable operating range
For industrial projects, efficiency should not be considered separately from operating conditions.
A lower purchase price may not mean a lower total cost if the compressor consumes significantly more energy during long-term operation.
A simple lifecycle cost concept is:
Total Cost = Equipment Cost + Energy Cost + Maintenance Cost
This is particularly important for compressors running continuously or at high load.
VIII. Define the Driver Type
The RFQ should specify the preferred driver type when the project has already defined it.
Common options include:
Electric motor
Steam turbine
Gas turbine
For electric motors, the supplier may need:
Rated voltage
Frequency
Motor speed
Motor power
Protection class
Explosion-proof requirements
Installation requirements
Starting method
IX. Define Materials and Corrosion Conditions
Material selection depends on the gas composition, temperature, pressure, and operating environment.
The RFQ should identify the required materials or service conditions for:
Casing
Impeller
Shaft
Seals
Bearings
Coolers and other pressure-containing components
Special attention should be given to corrosive gases or contaminants such as H₂S, CO₂, moisture, chlorides, and other aggressive components.
For example, an application involving wet H₂S may require different material and sealing considerations from a clean and dry air application.
X. Define Seal and Bearing Requirements
The RFQ should specify the preferred sealing and bearing arrangement when required by the project.
Common sealing solutions include:
Dry gas seal
Labyrinth seal
Mechanical seal
Typical bearing arrangements include:
Journal bearings
Thrust bearings
Oil-lubricated bearing systems
The selection depends on gas properties, pressure, speed, shaft arrangement, leakage requirements, and project standards.
XI. Specify Applicable Standards
The RFQ should identify the standards that the compressor must comply with.
For industrial centrifugal compressors, API 617 is one of the key international standards commonly specified for process applications.
Depending on the project, additional requirements may include:
Project specifications
National standards
Industry standards
Electrical standards
Safety and environmental requirements
Clearly defining applicable standards at the RFQ stage helps avoid technical differences between the buyer and supplier later in the project.
XII. Define Performance Testing and Acceptance Requirements
The RFQ should clearly state the required factory testing and acceptance criteria.
Typical requirements may include:
Factory performance test
Mechanical running test
Vibration test
Overspeed test
Noise test
Factory Acceptance Test (FAT)
The buyer should also define the required acceptance criteria, measurement conditions, allowable deviations, and performance guarantees.
Clear testing requirements make it easier to compare quotations from different suppliers on the same technical basis.
XIII. Require Complete Technical Information in the Quotation
A professional compressor quotation should include more than the equipment price.
The supplier should provide sufficient technical and commercial information, such as:
Technical Information
Compressor model
Performance curve
Flow and pressure range
Efficiency
Shaft power
Speed
Main dimensions
Materials
Seal and bearing configuration
Motor or driver information
Cooling system
Control system
Applicable standards
Commercial Information
Equipment price
Spare parts price
Delivery time
Warranty
Installation and commissioning support
Payment terms
Packing and shipping terms
This allows the buyer to conduct a more complete technical and commercial evaluation.
XIV. an RFQ for a Centrifugal CompressorParameter Checklist
Before sending an RFQ, the following checklist can be used:
| Parameter | Required Information |
|---|---|
| Gas | Gas name and composition |
| Flow Rate | Minimum / normal / maximum |
| Inlet Pressure | Absolute or gauge |
| Discharge Pressure | Absolute or gauge |
| Inlet Temperature | Minimum / normal / maximum |
| Molecular Weight | Value |
| Gas Density | Value or calculation basis |
| Compressibility Factor | Z value |
| Specific Heat Ratio | k value |
| Operating Range | Minimum / normal / maximum |
| Surge Requirement | Required margin |
| Driver | Motor / turbine |
| Materials | Required materials |
| Sealing | Seal type |
| Bearings | Bearing type |
| Standards | API / project standards |
| Testing | FAT and performance requirements |
| Installation | Indoor / outdoor / altitude / environment |
| Delivery | Required delivery date |
If some parameters are unavailable, provide the original equipment model, nameplate, process flow diagram, existing performance curve, or available operating data. The supplier can use these materials to identify missing information.
XV. Turbo Compre: Support from Compressor Selection to Manufacturing
Turbo Compre provides centrifugal compressor solutions for industrial applications, supporting customers from compressor selection and technical specification to manufacturing and delivery.
Our product scope includes:
Centrifugal compressors
Process gas centrifugal compressors
Containerized centrifugal compressors
Low-temperature nitrogen compressors
Centrifugal compressor spare parts
Replacement impellers, coolers, and other key components
For customers preparing an RFQ, Turbo Compre can support technical data review, compressor selection, performance evaluation, configuration, and manufacturing.
For replacement projects, even an incomplete RFQ can be a useful starting point. An original compressor model, nameplate, PFD, operating data, or performance curve can help establish the required technical basis.