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Principles of Reciprocating Compressor Sizing

By Joe Honeywell

Introduction

Selecting a reciprocating compressor can be a complex process. It involves many important considerations related to a compressor facility, including the design criteria, operating requirements and project economics. As an aid to the selection process, many users will solicit assistance from compressor manufacturers to help size and select the best machine. Their assistance is valuable, saving the user time and effort. The close working relationship of users and manufacturers will usually provide a compressor selection that brings the best offering to the project. However, how does the user know the project needs are fully considered in the sizing and selection of a compressor? How does the user know the machine selected is adequate without some knowledge of the sizing process? This article aims to answer these questions by providing engineers with basic insights into the sizing process and other considerations that contribute to a reciprocating compress selection. This article will also aid in the selection process by giving users an understanding of a compressor’s limitations.

Selecting a reciprocating compressor that meets only a given flow rate and pressure may not be the best solution for the project. Much more should be considered in the selection process. For example, does a compressor have adequate means of varying the flow rate if there is a turndown in the rate? Is the compressor arrangement the most economical or are there other less expensive arrangements that will meet the design criteria? Will the selected compressor perform well if the operating conditions change? Most compressors must adapt to changes in gas composition, suction and discharge pressures, temperatures, flow rate and ambient temperatures. These are only three important questions to consider. There are other aspects such as the manufacturer’s limitations in the compressor components, operating costs and much more to consider.

This article will examine the various aspects to consider in the sizing and selection of a reciprocating compressor. It will begin by briefly discussing the major compressor components, their purpose and design limitations. There are many major components and each is important to the selection process. Next, the basic criteria for sizing a reciprocating compressor will be discussed. This will include the various parameters that are affected by changes in operating conditions and controllability. Example problems are included for single-stage and two-stage applications, along with appendices of typical sizing data. Each of these problems will provide knowledge of the selection process to real world applications. Finally, a list that summarizes the selection and sizing recommendations is given. The list will help users verify that critical parameters have been considered in the selection process.

 

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