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Industrial compressors

by Matteo Cicciotti

Compressors general

A compressor is a machine that increases the pressure of a gas. Compressors are important components of industrial plants. They account for a large portion of the energy consumption of the whole factory. They are typically tailored to a particular application, have high capital costs and are highly integrated with other plant components A compressor stage realizes the increase of pressure in two consecutive steps. At first, the gas flow is accelerated by a rotating component (i.e. impeller). Secondly, the gas flow is slowed down by a stationary component (i.e. diffuser: divergent duct) that converts the kinetic energy of the gas into pressure increase. The performance of the compressor stage depends on the aerodynamic profile of the rotating and stationary components. For high ratios of compression, several stages can be arranged together over the same rotating shaft so as to form a so-called multistage compressor, at the extremities of the shaft are attached bearings, gears and prime movers Typically electric motors are employed for driving the shaft; and the resulting electricity consumption is the major part of the operating costs of the system. Often, multistage compressors are also equipped with heat exchangers (intercoolers) which have the purpose of improving the thermodynamic efficiency of the compression.

Faults affecting mechanical parts

Generally speaking, faults can be of two types: leading to equipment failure and not leading to equipment failure. The first type of faults affects the reliability and availability of the machine. These faults are caused by continued mechanical stress, inappropriate lubrication or insufficient cooling of the rotating parts. Specific examples of these are: rotor misalignment, degraded gears or bearings and blade fractures. The second type of faults do not affect reliability but degrade operative margins and energy efficiency, specific examples are changes in aerofoil geometry or increase in surface roughness. These faults are caused by the continued degrading action of external agents, which corrode, erode and foul the flow path surface.

The focus of my research

Current practice in condition monitoring of turbomachinery in chemical industry is aimed to detect and isolate (mainly) faults that could lead to equipment failure, for the sake of guaranteeing availability and reliability. However, due to the ever growing concern for energy efficiency and environmental impact, it is possible to observe an increasing demand for performance monitoring solutions. My research focus is on performance monitoring for industrial compressors. My goal is that of developing a method for monitoring and then modelling the effects of mechanical degradation of the components on the gas path. This is to be achieved by using first-principle modelling and a limited number of information and measurements. The methods are tested on the BASF SE facilities. The findings are integrated within optimization frameworks for optimal operation and maintenance of compressor networks.