Feb-2018

Compressor improvements turn benchmarks into savings

How can refiners create real improvements at plant level? Reciprocating compressors are likely candidates.

CHRISTIAN PRINZ
Hoerbiger

Article Summary

For any major item of refinery capital equipment, a cut in the ratio of maintenance cost to replacement value from 2.5% to 1.5% is worth celebrating. With new ways available to benchmark and improve the performance of reciprocating compressors, such a result is perfectly achievable at most facilities.

It is achievable because many compressors across the world’s refineries operate well below their full potential in terms of reliability, efficiency, and environmental performance.

At first glance, this seems counter-intuitive. A dependable supply of hydrogen is essential to the hydrotreating and hydrocracking units on which refineries depend to remove sulphur and boost yields of valuable light products. Reciprocating compressors, in turn, are key to hydrogen supply. So it should be clear that efficient and reliable operation of recips is essential to the long-term prosperity of any refinery.

The basic design of reciprocating compressors has changed little in a century, however, and plenty of machines operating today are decades old. This longevity may make some operators unwilling to risk money on improvements; they may view these old machines as being beyond help, or perhaps they do not notice them at all. Engineering staff who are used to poorly performing ‘recips’ may think that is all they can expect.

As we will demonstrate, however, such views ignore valuable business opportunities to raise performance levels and cut costs. Big energy savings are possible, and savings in the cost of lost production can be even bigger.

The importance of benchmarking
The good news is that even old recips are far from obsolete. The parts that hinder the performance of old machines – mainly compressor valves, cylinder rings, packings, and control systems – can almost always be upgraded to modern standards. Even replacement pistons and cylinders can be custom-made at lower cost, and much more quickly, than it takes to order a new compressor.

This means there should be no reason not to benchmark any compressor against the best-in-class in a comparable duty, and upgrade it if necessary. Improvements often pay for themselves in just a few months through savings in energy and maintenance costs, and especially by reducing lost production.

Of course, this lesson is not limited to compressors. It is standard practice for refinery managers to benchmark their facilities against the industry as a whole using indices established by specialist consulting companies. Such a study from 2015, for example, showed that the effectiveness of a refinery’s operation and maintenance is more or less independent of its age (see Figure 1).

We can define an industry- leading refinery as one that combines high effectiveness (measured in terms of its mechanical availability) with high efficiency (measured in terms of the ratio of maintenance costs to replacement value, see Figure 2).

An average refinery spends more than necessary on maintenance without improving overall reliability. A sustainable approach to turning such a facility into an industry leader requires tackling both issues at the same time. Lower spending on maintenance is of little use unless it increases reliability. High reliability is questionable if it can only be achieved through high maintenance budgets.

We can apply exactly the same approach to assessing and improving compressors. Hoerbiger’s approach to compressor benchmarking builds on the familiarity and proven effectiveness of facility-scale benchmarking. Now, managers with a ‘helicopter view’ of their refineries have a clear path to follow if they want to make practical improvements at ground level. Hoerbiger benchmarks show which compressors it makes commercial sense to upgrade, exactly how this can be done, and what the resulting savings will be.
 
Understanding compressor ‘DNA’
For a compressor chosen at random, it is hard to predict the relationship between reliability and maintenance cost. This is a similar situation to that which we saw above for entire refineries.

The objective is a machine that operates sustainably, with high reliability, efficiency, and environmental soundness, and with low maintenance costs. In reality, many compressors achieve the reverse: low performance on many measures, yet with high maintenance costs.

Hoerbiger believes that the answer lies in understanding each compressor in detail – its ‘DNA’ – in terms of both the machine itself and its relationship to the process in which it operates. Best practice focuses on improving the fitness of a particular compressor for its intended purpose (see Figure 3). Too often, actual practice consists of simply recreating the status quo, even when this has been shown not to work in the long term. Troubleshooting tends to concentrate on symptoms rather than root causes.

Benchmarking is key to any effort to improve the performance of a compressor. Without knowing what best-in-class recips can achieve, it is hard to set targets.

To make the results of benchmarking easy to understand in a business context, Hoerbiger has developed a technique known as REE auditing. REE stands for reliability, efficiency, and environmental soundness, the three axes of a REE audit.

Our expert auditors assess the compressor’s DNA from a complex mixture of factors including its age, mechanical condition, components, maintenance routine, duty, and utilisation rate. They then distill this down to a numerical score for each of the three axes, on a scale from 0 to 10, and ultimately to a single score for the compressor as a whole. The lower the score, the greater the potential for improvement.

From audit scores to potential savings
The next step in the REE process is to predict the savings that can be achieved through upgrading compressors. Hoerbiger auditors work closely with the customer to suggest improvements that will increase reliability and save money, concentrating on those machines and those improvements that yield the best return on investment (ROI).

Key to the REE process is the principle that every suggested upgrade should yield a payback period that is acceptable to the customer. Whether the change is small (such as a new type of compressor valve), more extensive (a new control system, say), or fundamental (like a new custom-built piston and liner), it must make sense under the customer’s current business conditions.