Are you trying to figure out the differences between a reciprocating compressor and a centrifugal compressor? Don’t worry, we have got you covered! This article will provide a detailed comparison of these two types of compressors, focusing on their structure, operation, and applications. Not only will we delve into their individual characteristics, but we will also highlight their key differences. So, let’s dive into it.
What is a Reciprocating Compressor?
A reciprocating compressor is a positive-displacement compressor that uses a cylinder and piston mechanism to compress the gas. The gas in the inlet section is compressed by the reciprocating motion of the pistons. These compressors are widely used in refineries, gas pipelines, chemical and petrochemical plants, natural gas processing plants, and refrigeration plants.
What is a Centrifugal Compressor?
A centrifugal compressor, on the other hand, is a dynamic compressor with a radial design. The gaseous fluid enters the center of a rotating impeller with radial blades and is pushed toward the center by centrifugal force. This results in a pressure rise and increases in kinetic energy. Centrifugal compressors are popularly used in Process Industries, Oil and Gas, Refineries, Wastewater treatment plants, etc.
Difference between Centrifugal and Reciprocating Compressor
The differences between a centrifugal and reciprocating compressor can be studied based on various parameters like maximum and minimum flow, inlet and outlet pressure, efficiency, compression ratio, discharge temperature, flow range, materials of construction, cost, etc. Here is a tabular comparison:
|Can be sized for an inlet flow of 680,000 actual m3/h in a single body.
|The capacity is limited by cylinder size, the number of throws available, and the available driver speeds.
|Recommended for flow rates of actual 300 m3/h and above.
|Limited by the cylinder size, stroke, and speed.
|Typical polytropic efficiencies range from 70% to 85%.
|Has a very characteristic adiabatic efficiency curve.
|Cost – Capital and Operating
|Higher capital cost but lower operating costs.
|Lower capital cost but higher operating cost.
|Maximum Discharge (Outlet) Pressure
|For horizontally split compressors discharge pressures up to 100 barg are common. For radially split (barrel) compressors discharge pressures could go as high as 1000 barg.
|Typical reciprocating compressors in the process industry are used to generate discharge pressures as high as 800 barg. Special compressors known as hyper compressors used in low-density polyethylene manufacture will generate pressures as high as 3500 barg.
|Minimum Suction (Inlet) Pressure
|This can be atmospheric or sub-atmospheric (vacuum). For sub-atmospheric suction conditions, special seal and buffering designs are employed to prevent atmospheric air from being drawn into the compressor.
|Can be atmospheric or vacuum. Where suction conditions involve sub-atmospheric pressures, adequate measures must be taken to prevent atmospheric air from leaking into the cylinder through the piston rod packing.
|Flow Range (turndown)
|The flow range of a centrifugal compressor is determined by the surge and choke points. Typical turndown for a fixed-speed, multi-stage centrifugal pump is approximately 20-30%. With variable speed drive or adjustable inlet guide vanes, the turndown can be increased to 40-50%.
|Reciprocating Compressors have the ability to change flow through speed control, the addition of fixed clearance to a cylinder (fixed or variable volume clearance pockets), cylinder end deactivation, and gas recycling. The typical flow range might be from 100%, down to 20%, or even lower. The application will determine what type of capacity control method is required and used.
|Compressed Gas Molecular Weight
|The compression ratio is highly dependent on gas molecular weight. Centrifugal compressors are used for a broad range of molecular weights including low molecular weight applications such as hydrogen recycling and high molecular weight applications using refrigerant gases with molecular weights over 100.
|Reciprocating compressors are not limited by gas molecular weight. Both light and heavy gases are compressed very well. Over the range of molecular weight, different application configurations may be required.
|The reliability/availability of centrifugal compressors is typically 98 to 99%.
|The reliability/availability of reciprocating compressors is typically 95 to 98%. Since reciprocating compressors have many more parts and more rubbing seals (pressure packing, piston rings, and rider rings) that wear and require more frequent replacement, they are considered somewhat less reliable than centrifugal compressors.
Choosing between a reciprocating and a centrifugal compressor for an application depends on a host of operating conditions. These conditions range from maximum discharge pressure and temperature to efficiency and cost. The operator must carefully evaluate site conditions of the application before making a choice.
Both reciprocating and centrifugal compressors have their unique advantages and are suitable for different applications. The choice between the two largely depends on the specific requirements of the task at hand. It is essential to understand the characteristics of each type of compressor to make an informed decision. We hope this article has provided you with a clear understanding of the differences between these two types of compressors.