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Compressor Q&A: Elliott Group

Published by , Senior Editor
Hydrocarbon Engineering,

In this special Q&A, Hydrocarbon Engineering sat down with Brian Pettinato, Manager of Aero and Structural Dynamics, Elliott Group, to talk about some key topics in the downstream compressor market.

Explain why compressor technology is so crucial to downstream operations.

Downstream operations such as oil refining, chemical, and petrochemical processes operate on a continuous basis often going anywhere from 3 to 10 years without ever shutting down. Each centrifugal compressor is an essential part of these processes constituting a major capital expense that is engineered to order and often the determining factor for plant or process throughput. Compressors require a considerable amount of energy and expense to operate. So, of course, compressor technology is quite crucial. Compressor technologies that address such typical concerns as efficiency, range, durability, and safety have been under continuous development from the beginning. More recent technologies include developments for reduced emissions, reduced noise, and improved operational flexibility.

How can compressor technology help to improve efficiency in gas processing and downstream operations?

Downstream operations are often looked at holistically. Simply stated, it is the overall efficiency that matters, and this is inclusive of the compressor, driver, and overall plant. The first step is to properly select and match the compressor to the requirements of the process, not just at a best efficiency point, but over the map of expected operation. Just as important is a good match between the compressor and the driver. Overall efficiency is essentially an exercise in multi-variable optimisation, and this is heavily dependent on available technology.

Centrifugal compressor technology has never stopped advancing. Stage efficiency has been improving via increasingly sophisticated 3D impeller and return system geometries and application of improved surface finishes. The efficiency of stacked stages has been improving via better stage-to-stage matching. Efficiency is better maintained over the long-term by wash systems and coatings that prevent compressor fouling and erosion. Compressor efficiency is further improved by management of secondary flows using advanced seal concepts. Finally, reduction of parasitic power losses at bearings and other locations provide further energy savings. Efficiency continues to improve as more advanced technology is put into play.

What steps do you take to improve equipment reliability and safety?

Quality, reliability and safety are very much inter-related. The starting point is people: their knowledge, training, communication, discipline to processes, ability to perform clean hand offs, their ability to ask ‘what could go wrong?’, and empowerment to apply foresight and make necessary changes. Of course, even with good people, there are always improvements to be found. Robust quality and corrective action systems are essential to ensure that necessary changes make it back to the people and vendors, and then into designs, procedures, and systems. The thought process for a good safety decision also applies to quality, and reliability. Technology development is only slightly different in that we intentionally go well beyond operational limits and actually confirm wear, breakage, instability, and other failure mechanisms for the purpose of establishing robust margins that improve the safety and reliability of our products.

How can compressor technology help to reduce emissions in downstream operations?

As previously stated, compressors require a considerable amount of energy to operate. They are often driven by very large motors, steam turbines, or gas turbines. Reducing the energy requirement through efficiency is a key to reducing emission in downstream operations.

Another form of emissions is that of the gas stream itself. Such emissions are of particular concern because they can have a greater impact on health, safety, and the environment. Gas stream emissions can be categorised as either captured or fugitive. Captured emissions occur along controlled leak paths, such as the oil or dry gas end seals of a compressor where the emissions are captured and then sent for processing or flaring. Fugitive emissions, if there are any, are uncontrolled and go directly to the atmosphere. These emissions typically occur at joints and other static seal locations throughout the plant, and this can include the horizontal or vertical joints of a centrifugal compressor as well as its nozzles and other connection points. More rarely, fugitive emissions will be the result of a material or weld rupture.

A new compressor when first installed will operate at its designed efficiency. Fugitive emissions are not a problem and captured emissions are as designed using acceptable amounts of available buffer gas. But it is not enough to have good efficiency and low emissions just at commissioning, these need to be maintained throughout the life of the equipment. Wash systems and coatings are applied to reduce fouling and keep compressors at peak efficiency between turnarounds. Specialty materials and cladding are used for resistance to wear from corrosion and erosion. Aerodynamics can be upgraded during planned outages to shift the compressor map for new operational requirements, new gas composition, or simply to improve the efficiency of older machines. Oil seal upgrades to better oil seals or to dry gas seals can reduce the amount of captured emissions that requires additional processing or flaring. Leak paths that develop along casing horizontal or vertical split-lines can be managed through repair, redesign, and in some cases, by advanced sealants.

Compressors are also an enabling technology for emission reduction through carbon capture and sequestration.

What has been your company’s biggest recent achievement or innovation in compressor technology?

Our most recent achievement has been the development of Very High Flow coefficient covered wheel compressor stages. The previous technology of High Flow Coefficient covered wheel compressor stages had been developed for flow coefficients above 0.10 and crossing just above 0.2. Our latest technology takes us above 0.25. This enables us to select a smaller and faster compressor that is a better match to a steam turbine or gas turbine driver.

What does the future hold for compressor technology?

There is no reason to think that the trends of the last several decades will change for the downstream sector. Compressors will continue to get more efficient. Power in a given compressor body will continue to go up. Speeds will continue to push even higher. Captured emissions will continue to be reduced. Noise and weight will continue to be concerns that are addressed. Controls and monitoring will continue to get smarter, more integrated, and more pervasive. I think it starts to get interesting when we consider what will be needed to achieve this future: from the technology standpoint, we need even more advanced manufacturing, materials, analysis, and instrumentation.

All questions answered by Brian Pettinato, Manager of Aero and Structural Dynamics, Elliott Group

Brian Pettinato is Manager of Aero and Structural Dynamics at Elliott Group in Jeannette, Pennsylvania, US. He has been with Elliott Group since 1995. His primary area of expertise is machinery dynamics. Brian is a fellow member of ASME, a member of STLE, and a registered Professional Engineer in the State of Pennsylvania. He serves on the Turbomachinery Advisory Committee of Texas A&M and on the API 684 rotordynamics task force.

This was a preview of the 'Compressor Q&A', which featured in the August issue of Hydrocarbon Engineering. To read the full Q&A, which includes answers from a number of leading experts in compressor technology, sign in here or register for a free trial subscription.

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