Program to Prevent Scaling Within Centrifugal Gas Compressors
Authors: Swearingen S.D. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

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Centrifugal gas compressors normally can provide greater availability than reciprocating provide greater availability than reciprocating types, can deliver more horsepower per weight of installation and will very likely be used widely on offshore platforms where loading and space requirements are critical. However, scale deposition within the centrifugal compressor has prevented the continuous operation of these machines due to shutdowns for rotor disassembly and scale removal.

The following case study of scaling within the impellers of Solar centrifugal gas compressors led to a step-wise program to prevent this deposition. Scale analyses of materials deposited within these machines showed primarily FeS and FeCO3 with lesser amounts of Fe(OH)2.H2O and Fe2O3 as well as varying amounts of hydrocarbons and carbonaceous acid insoluble residue. Each step of the program was designed to reduce or eliminate one or more of the scale components to provide increased compressor availability. This program involved gas well inhibition, the use of various types of bactericides, and vapor phase inhibition of the compressors. Should this technique not be successful, additional equipment such as filters may necessarily be required. This could mean sufficient increases in capital costs and space requirements to make reciprocating compressors more economical and practical.

Introduction

Centrifugal compressors provide certain advantages over reciprocating type machines for offshore gas compression service. In particular, they deliver more horsepower per weight of installation and per square foot of space occupied. Should per square foot of space occupied. Should satisfactory equipment availability be realized with this type of machine, its widespread utilization in offshore gas compression applications would be attractive. However, Shell has encountered a major deterrent to the availability of this equipment. Scale deposits formed within the impellers of our compressors have reduced their output capacity and have caused eventual shutdown due to vibration. Complete disassembly and a physical cleaning of the impeller wheels were required before these parts could be reinstalled and the compressor returned to service. This 3–4 day procedure has had a definite effect on availability.