In the last few decades, the compressor industry has welcomed several innovative technologies that have reduced energy consumption and improved the operation and reliability of equipment. These recent advancements are derived from improvements throughout the compressor, machinery, component design, and the manufacturing process, which all contribute to an increase in energy efficiency, operation, performance, and reliability.
This article discusses how operator requests for technology improvements have influenced current compressor designs, and looks ahead at what the future holds for compressor fabrication, packaging, implementation, and operation.
Are your operator and vendor priorities competing?
Modern compressors are complicated pieces of equipment, and often it is only machinery specialists or manufacturer representatives that know them well. However, the typical operator’s knowledge of compressor related issues and machinery problems is relatively low. An operator-friendly integrated monitoring, control, and operation system is recommended to help ordinary operators with the day-to-day operation of compressors and machineries.
When the goals of the operator and the needs of the vendor are not in complete alignment, this can present challenges to smooth operation. Much of the focus of some manufacturers and vendors has been on contractual requirements, such as guaranteed performance, guaranteed efficiency, and trouble-free operation during the guarantee/warrantee period(s).
Also, some vendors are less concerned than operators with a trip (unscheduled shutdown), as long as the trip is not caused by component damage or it does not result in a serious event or a damage, or if the trip can be justified as a plant issue and not related to the vendor supplied package. On the other hand, a small component replacement during the guarantee period can often get the attention of vendors.
There also are cases where a condition monitoring system has been supplied by a sub-vendor or an independent vendor, sometimes with different views on operation than both the plant and the original compressor vendor, which can complicate the picture even more. For example, alarm and trip points may be set too conservatively in order to protect the vendor and sub-vendor, and less care is taken for optimum operation and operator’s concerns about unnecessary trips and alarm management.
List of requests from OperatoRS
Skilled operators have a good sense of what matters to them and to their facility, both at a strategic level and at a day-to-day level. At the level of daily operations, the following requests are usually raised by operation teams for machineries such as air compressors and gas compressors:
- Less trips (less unscheduled shutdowns) – scheduled shutdowns are unpopular, problematic, and risky. The trend is toward eliminating trips and introducing alarms for well-coordinated shutdowns. In this way, a special alarm will be issued with some suggestions for shutdown within a defined time period. Obviously, this cannot be implemented for some critical trip cases. For instance, it is not practical (or safe) for a low pressure lubrication oil supply because if an issue in a lubrication oil supply occurs, the compressor/machinery bearings could be damaged within a few seconds. However, this approach might be introduced for some trips related to seal systems and other similar low-risk cases.
- Better alarm management – too many alarms can be as bad as too little. Better alarm management is needed for many machineries and in general for many plants.
- Operation-oriented integrated condition monitoring and interface system – sometimes it is referred to as an operator’s friendly interface system.
At a strategic level, operator teams usually have two major requests. The first is for compressors to achieve higher reliability and availability. Modern compressor units are most often operated unmanned with minimal support from the operation and maintenance team during operation, whereas extensive involvement might be required at planned shutdowns or overhauls. The general expectation is that compressors should operate for some years without any unscheduled shutdown or major repairs.
For instance, a re-start of a compressor after a trip is a critical topic that has caused many problems, confusions, and even damage. The goal of minimizing the number of trips (unscheduled shutdowns) reinforces the request for a better interface system. This should be implemented so that the machinery does not trip for a minor (or tolerable) situation.
For better reliability and operation, only a substantial deviation (or a serious issue) should be allowed in a trip. In the case of a trip or shutdown, an integrated condition-monitoring and machinery interface system should suggest the proper on-site checks to let the operation team check and verify the situation on-site and safely start-up the compressor package (or generally the machinery).
The second strategic request heard from operators is for better flexibility, particularly operational flexibility. For instance, wider ranges of variable speed for turbo-compressors are often requested. A compressor should be flexible enough to let operation continue even if an operating parameter (related to the compressor package or upstream/downstream facilities) is changed or there is a problem with a device or equipment. Shutdown and repair should be delayed for some time to allow for a well-coordinated, scheduled shutdown. Even this might be delayed until the next major overhaul. Generally, an unscheduled shutdown is not popular and is hated by most parties involved.
The following three case studies help explain these concepts.
Case Study #1: 100% Bypass-line and Valve. For many small and medium sized compressors (such as screw compressors or reciprocating compressors) a 100% bypass valve is always recommended, whereas an internal capacity control (such as a slide-valve) is usually provided. Some compromised configurations have suggested a small bypass valve (say 20%, 40%, or 50%) just for steps or capacities that cannot be covered by the provided capacity control systems. However, a 100% bypass piping line and valve is still considered the best solution because in the case of any problems with the provided capacity control system, the compressor will continue operating for some time until a coordinated shutdown in near future. Even with this provision, the shutdown might be delayed until the next planned overhaul. The operation and capacity control using the bypass valve might not be very efficient, but it might be less costly than an unplanned shutdown.
Case Study #2: Operational Flexibility vs. Few Points of Reliability. As another example, on some small reciprocating compressors, the only available unloader option is a finger type unloader, which does not often have a good record of reliability. Fingers usually act on cylinder valve elements, and they might cause some wear or damage on the cylinder valve moving elements. Also, the overall mechanism and operation are not very reliable. It might be theoretically possible to eliminate unloaders for these small reciprocating compressors and rely on the bypass valve for the capacity control. However, this is just in theory, and the additional operational flexibility offered by the unloader is always considered more important than a 2 to 5% increase in reliability. Then, an unloader system and a 100% bypass valve are almost always the recommended option.
Case Study #3: Seal Issues and Lubrication Problems. The major causes of concern on turbo-compressors are usually seal issues, particularly dry gas seal problems. Because other seal options such as oil seals are out-of-date and impractical, the focus is on superior dry gas seal systems or the elimination of seals (seal-less compressors).\
Lubrication oil problems and bearing related issues are another area of concern. On this topic, there are two major ways for improvements: a superior bearing and well-designed lubrication oil skid; and alternative bearing systems, particularly magnetic bearings that could eliminate lubrication oil, wear, and physical contact altogether.
Modern magnetic bearings have many advantages. They can offer good energy efficiency because they eliminate friction and the associated energy losses and reliability issues. Also, they introduce far superior reliability and availability and built-in condition monitoring and control capabilities. Many experts believe the future of bearing technology and the compressor industry depends on new developments for magnetic bearings and their further usage in different machineries.
Other bearing options such as air bearing (foil bearings) and water bearings (which use water instead of lubrication oil) have been introduced for some small machineries. Using air or water instead of lubrication oil in specially-designed bearings has many advantages over conventional bearings. However, they need more research and developments for use on a wider scale.