Pressure

Do the questions in the title seem like simple questions? There are many things that confuse the issue including air compressor condition, controls as applied, interconnecting pipe size and configuration and effective storage. All of these have been covered in many technical compressed air papers and articles. The topic many don’t use or understand is how to calculate the actual value of these initial questions at the operating sites and conditions. 
 

When the design capabilities of an installed compressed air system didn’t align with real-world production needs at its ore processing mill in northern Michigan, Eagle Mine decided to move beyond theoretical compressed air concepts and deal in reality. After thorough analyses of its compressed air challenges and implementing a variety of solutions, the team at the mill bolstered the operation’s ability to efficiently mill approximately 2,200 metric tons of ore per day. 
 

Analysis of the pressure data logging showed that, while the variable speed drive compressor maintained a constant discharge pressure near 120 psi, the pressure at various critical points fell to as low as 85 psi during peak production operations. General pressure in the plants, especially Plant 2, fluctuated between 102 and 112 psi, showing that the pressure/flow control valve was not regulating properly, and that Plant 2 lacked enough general storage volume to support transient flows.  

The information contained in this article, will help the operator to assess his/her systems, and identify where these systems fall within a three-level category. There are many ways, and opportunities to make a compressed air system produce reliable and good quality air. The three levels discussed here could also be characterized as a “continuous improvement plan” which can be achieved over the course of time, and with the occasional investment of money.

Most industrial systems like compressed air have essentially random demand if you look at the long-term life cycle of the system. Hundreds, even thousands of independent small and large subsystems require constant or varying flow. These demands are typically not timed or synchronized with each other, so they aggregate to a fairly random flow profile, within a range. That range changes significantly when production processes change. Certainly a 2-week audit might show some patterns that appear predictable for demand A (“production”) and demand B (“non-production”) or day type, but they change over time as the plant adapts to new production systems and removes old ones. If demand was that profile forever, a lesser experienced auditor might be tempted to size one set of compressors that work perfectly for that profile but not for alternates.

There are some fundamentals when it comes to compressed air system improvements. One strategy that is overlooked is just drawing the details of whatever aspect of a system you are looking at. It is fairly common to see a misdiagnosis of some particular technical issue that would have been obvious should someone have created the drawing to describe the problem.

A food processor was having compressed air problems, so they invited a compressed air auditor into their plant for an assessment and to help them size future permanent air compressors. The plant was experiencing low air pressure and detecting water in the compressed air lines despite having a desiccant air dryer. The auditor thoroughly analyzed the compressed air system production equipment and did end-use assessment and leakage detection. This article discusses the findings leading to a potential cost savings of 52% of the current level.

This article reviews the benefits and design considerations of controlling system pressure from the air compressor room to the production headers and selected production processes and areas. Over the last several decades, the phrase “demand-side control” has become the generic term to describe establishing a “flat line” header pressure using proper storage and an appropriate pressure regulator, or “pressure flow controller.” Use of a demand-side controller to control pressure and flow can be implemented at the entry to the production area header(s) and at selected production areas or processes.

Baseline measurements include flow, power, pressure, production output, and other relevant variables impacting compressed air use. These data evaluate trending averages to develop Key Performance Indicator (KPI) and Energy Performance Indicator (EnPI) parameters and establish base‑year performance. The focus of this article is the application, evaluation, and analysis of baseline measurements to provide information necessary to improve Compressed Air Supply Efficiency.

A chemical packaging facility had done everything right when they last upgraded their compressed air system a few years ago. They installed a Variable Speed Drive (VSD) air compressor and implemented other energy efficiency measures, but plant expansions caused increased system demand, which exceeded the capacity of the system. The packaging lines were now seeing low pressure, causing shut downs in production. And projections showed plant demand would increase even further.