Figure 1. Fouling due to the rapid build up of deposits of gas and air causes compressor performance to suffer.
Figure 2. Software calculates compressor performance, providing insights for when maintenance should be scheduled. (click to enlarge)
Analysis based on thermodynamic modeling also enables the experts to predict with reasonable accuracy when a piece of equipment should be overhauled. A machine’s history of degradation offers insights on when the efficiency of that unit will drop below a certain level, signaling when it should be taken out of service. This knowledge allows maintenance planners to schedule downtime at the least disruptive time.
Because the raw data come from the regular documentation of ongoing operations, no special measurement equipment is needed on-site. Information can be taken from a data historian or even operators’ log sheets and communicated via the Internet; the actual monitoring and subsequent calculations are done remotely. In most cases, chemical makers create a special script so that performance data on selected machines are automatically communicated via periodic e-mail transmissions from anywhere in the world.
After the data are processed through the sophisticated model, analysts who are intimately familiar with each type of machinery evaluate the feedback and provide a full diagnostic report along with actionable recommendations via a secure web interface, so the end-user can access the information anywhere in the world. For example, a compressor in a plant in China might be monitored, the information processed and analyzed in the U.K., and the results sent to corporate engineers in Houston.
Plenty of possibilities
Chemical plants abound with opportunities for performance monitoring. For example, compressors, including air compressors and those that are integral to refrigeration systems where a process fluid must be maintained at a specific temperature, are frequently critical to production. However, multi-stage compressors are complex machines, making it hard for plant staff to spot degraded performance, let alone determine the source of the problem. A poorly performing multi-stage compressor can cost its operator hundreds of dollars per day in decreased production. Immediate action, possible only when the performance of the machine is being continuously monitored, may well be needed to prevent extended losses.
Temperature measurement plays a key role in the control of compression trains. Accurate readings directly impact the volume of gas compressed and flowing from the machine; that kind of information also can serve as a performance indicator. Using a thermodynamic model to characterize the performance of such a machine, the monitoring software can distinguish between performance deviations and instrumentation drift for all sections of the compressor train, allowing for a true evaluation of the performance of each section. Early identification of instrument error can also reduce production losses.
By using historical data to establish baseline performance for a given machine and checking that against a thermodynamic model of that type of equipment, it’s possible to get an accurate picture of lagging performance. For example, comparing production data on a centrifugal compressor train with manufacturer’s design data showed that a company was losing $800 per hour. Analysis not only revealed the bottleneck compressor but pinpointed the cause to be a faulty recycle valve, which was repaired with minimal downtime. Throughput was immediately boosted by 10%.
In another case, performance monitoring identified a rod drop on a reciprocating compressor. Such a fault could have gone unnoticed and might have caused a catastrophic failure of that equipment.
Likewise, the operational history developed via performance monitoring pinpointed when a stream turbine needed to be cleaned and led to an optimal washing plan. The approach also identified degraded performance of a boiler. It even showed the section of the boiler where the loss was occurring, the severity of the problem and what needed to be done to correct it.
These are areas where plant personnel, in all likelihood, wouldn’t recognize the existence of problems without assistance.
Take the challenge
Ask yourself four questions:
- Are your most critical pieces of equipment delivering optimal performance?
- If not, do you know how much the degraded performance (lost efficiency) is costing in excess energy demand or lower productivity?
- Can you calculate the losses?
- Do you know how to prevent them?
If most of your answers are “no,” performance monitoring may well be cost-effective for you.
One way to find out is to apply the thermodynamic-model-based technology to one critical asset in your plant for six-to-12 months via a straight service contract. This requires no capital expenditures and minimal staff involvement. (Typically, the cost of developing a thermodynamic model and monitoring is the same per piece of equipment, whether a steam boiler, heat exchanger, compressor or motor-pump train.)
You’ll undoubtedly get a clearer understanding of performance losses and the causes of degradation in that equipment. The resulting knowledge and actionable recommendations can be expected to yield improved performance, leading to gains in throughput, lower energy costs or both. Monitoring typically delivers a fast return on investment.
Todd Anderson is a business development manager for Emerson Process Management, based in Chicago. E-mail him at email@example.com.