Compressor Insights from Detechtion – May 2016

By May 16, 2016 Blog post No Comments


Thought of the Day


Finding Hidden Revenue In Your Existing Compressor Fleet

The current downturn in commodity pricing has had a massive effect on the capital and operational expenditures of Oil and Gas Producers in North America. With these companies cutting their capital spending and investment, they are no longer able to increase revenues by drilling new wells and must look elsewhere to create business value. While many of these companies are focused on decreasing operating expenses to weather the current downturn, there are other alternatives that can be used to unlock hidden potential in their existing assets.

The three main KPIs to measure the success of a fleet of compressors are utilization, availability and reliability. Most companies employing compression fleets have programs to address availability and reliability, but few address utilization. Common problems in utilization include lost revenue opportunities caused by damaged valves, piston rings or suboptimal configurations. Without a tool to measure these missed business opportunities, the companies are blind to the business intelligence that could highlight them.

If you are responsible for the profit and loss of a group of compression assets and you have not equipped your Reliability, Engineering, and Operations groups with a tool that measures utilization, you will never know if your compression assets are running as close as possible to their true potential. Equally, if you are a member of one of those groups and are given the responsibility to optimize your company’s compression assets, a tool that measures utilization and gives actionable information on how to achieve optimal performance is vital to your success.

At Detechtion, we offer Enalysis™ as that tool. We routinely find 1 ½% to 2% revenue increases by finding opportunities such as:

  1. Unseen production potential
  2. Unseen maintenance issues
  3. Fuel and power overconsumption
  4. Risk of catastrophic equipment failure

If you’ve been limited in investing in the health and potential of your compression fleet due to the current downturn in commodity pricing, now is the time to invest in a tool that will give you visibility into both.

Next Issue’s Topic: The pros and cons of the different operating philosophies in managing compression assets


Representative Win


Total Fleet Performance – Increased Utilization

Proposed:

Continuous optimization of the client’s compressor fleet for maximum throughput and equipment utilization.

Outcome:

Compressor performance is tracked within Detechtion Technologies’ Enalysis™ system every time a compressor’s operating data is entered to generate an Enalysis™ performance report. Clients, therefore, have the ability to track and report compressor fleet performance and various other parameters via Fleet Management Reports and Tools within Enalysis™.

The Performance Graph in Enalysis™ graphs the average performance (compressor flow divided by the total potential flow) of the compressor in a certain region over a period of time. This graph is, therefore, a direct indication of the utilization of the compressor, as determined by the greater of the power utilization and the cylinder capacity utilization, and allows the client to identify the regions where production is not optimized.

The graph shown below represents the performance for the entire compressor fleet of a long term Detechtion client over a period of 5 years. The graph shows a continuous improvement in compressor fleet performance over the last four years and a total, fleet-wide performance improvement of more than 7.5%.

What is the value of 7.5% increase in total fleet performance?

In the case of this client, with a compressor fleet of well over 100 operating units and more than 200,000HP, 7.5% could represent 15,000HP of power used more effectively.

Alternatively, with a reported daily throughput of more than 1,000mmscfd, 7.5% could represent 75mmscfd of increased potential production.

Input your average daily gas price ($/mscfd) to see what this could be worth to your company:

Gas price: $
Throughput: mmscfd

Result: $54,750,000.00/Year

Background:

Maximizing the throughput of a compressor simply means maximizing the capacity of the compressor. In a competitive natural gas gathering application, maintaining the lowest suction pressure can provide a significant production advantage to any gas producer.

To maximize the throughput of a reciprocating compressor there are two concepts in play. The first concept being, the gas has to go through the first stage of a compressor to go through the rest of the unit; hence the importance of maximizing the capacity of the first stage cylinder(s). The capacity can be impacted by clearance devices such as Variable Volume Clearance Pockets (VVCP) or Fixed Volume Clearance Pockets (FVCP) that add clearance to the head end of a cylinder. Clearance can be added to the crank end of a cylinder by adding valve spacers under the valves. The running speed of the compressor and single acting the crank end or head end of a cylinder will also influence the capacity of the machine. The second concept is to increase the capacity of a compressor by increasing the suction pressure; which means that the suction pressure is dictated by the flow of the compressor or vice versa.

The loading curve shown in the figure below shows the optimized performance of a two stage unit at a discharge pressure of 870 psig. The curve can be divided into three segments: the cylinder capacity, the knee and the power section.

  • The cylinder capacity portion of the curve implies a cylinder capacity utilization of 100%, which means no clearance is added to the first stage cylinder(s) and the driver is running at maximum speed. This can be translated on to having the first stage cylinders double acted with no spacers, the VVCP or FVP fully closed and the driver speed set to the maximum.
  • The power section of the curve indicates a horsepower utilization of 100%. In this portion of the curve, clearance devices are generally used to unload the driver and this is translated as an increased capacity while maintaining the horsepower usage to the maximum.
  • The knee of the curve is the only point on an optimized loading curve where the cylinder capacity utilization and horsepower used is at 100%.

For a reciprocating compressor to be fully optimized for maximum throughput, either or both the cylinder capacity utilization and the horsepower utilization should be at 100%.
Through the use of individual compressor performance curves, such as the one above, and a Detechtion Technologies Start-up Package of high and low pressure trip-points, shown below, compressor units can be evaluated for opportunities to:

  • Increase running speed
  • Reduce added cylinder clearance
  • Optimize suction pressure
  • Decrease recycle set point

Thus resulting in increased utilisation and maximising throughput.


Tech Tip


Over/Under Compression in a Rotary Screw Compressor

Screw compressors are a crucial part to the natural gas industry, and typically operate under wide variants of operating conditions in both gathering and process applications. Whether the compressor is experiencing pressure and volume fluctuations, temperature swings or changing gas composition, the screw compressor is a reliable piece of equipment that powers through operational swings without issue. However, this doesn’t mean that the compressor is operating as efficiently as it could be!

Optimization can result in significant power savings and/or reduce the potential for catastrophic failure. It is beneficial to analyse the performance at frequent intervals to ensure your screw compressors continues to operate without issue, at low cost. The most common method to optimize a screw compressor is by adjusting the Internal Volumetric Ratio (Vi). Adjustments to the Vi are recommended when the unit is experiencing over or under compression, or the internal discharge pressure exceeds the max allowable.

The following graphic allows you to visualize the relationship between pressures, Vi and gas composition to better understand the compression process, and the effects those variables have on power requirement. Note that the process highlighted in the graph is as follows:

  1. A volume of gas is captured in the rotors: (At Suction Pressure)
  2. The volume of gas is compressed in the rotors: (Increasing Pressure)
  3. The volume of gas is exposed to the discharge line and expelled: (At Discharge Pressure)


*Note that the graphic is conceptual, and does not account for partial loading due to the slide valve.

For questions regarding the performance of your screw compressors, please contact your Detechtion representative.