Industrial Utility Efficiency    

System Assessment

One of the most satisfying parts of being a compressed air system auditor is resolving compressed air system reliability issues. This article exposes a seldom, if ever, mentioned problem that can occur when air dryers are dedicated to air compressors. It examines a real-world application and discusses the action taken to remedy the situation.

Compressor Controls

It was early summer, the air compressors were above the production floor on a mezzanine, and temperatures were heating up both outdoors and indoors. The compressed air system was comprised of three 500-horsepower centrifugal air compressors, and one 350-horsepower variable speed drive oil-free rotary screw air compressor.

Piping Storage

An air receiver tank (sometimes called an air compressor tank or compressed air storage tank) is a type of pressure vessel that receives air from the air compressor and holds it under pressure for future use. The tanks come in a range of sizes and in both vertical and horizontal configurations. An air receiver tank provides temporary storage for compressed air. It also helps your compressed air system run more efficiently.

End Uses

For Imerys S.A. there’s little question about the importance of managing dust collection systems it uses to control and reduce harmful particulates in its worldwide minerals processing facilities. And now there’s zero doubt about the tremendous energy savings it stands to save by reducing the amount of compressed air needed for these same dust collectors.

Pressure

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.

Air Treatment/N2

Dew point is simply the temperature to which air must be cooled for the water vapor within to condense into dew or frost. At any temperature, there is a maximum amount of water vapor that the air can hold. This maximum amount is called the water vapor saturation pressure. If more water vapor is added beyond this point, it will result in condensation.

Leaks

Awareness and interest in leak detection only continues to grow thanks to a number of factors. What we have seen over the last 20 years is a more sustainable way of thinking, established international energy efficiency standards, reliable leak detection technology, and best practices to implement leak detection.

Pneumatics

In manufacturing and packaging facilities that rely on pneumatics, there’s a four-letter word worse than virtually any other: leak. Unidentified air leakage and unexpected maintenance in pneumatic systems are significant sources of revenue and productivity loss but identifying the cause of leakages and preventing unforeseen downtime is typically a challenge.

Vacuum Blowers

Every municipality and utility is facing the reality of rising energy costs. In 2010, the Town of Billerica, MA, which is located 22 miles northwest of Boston with a population of just under 40,000 residents, engaged Process Energy Services and Woodard & Curran to conduct an energy evaluation of the Town’s Wastewater Treatment Facility (WWTF) and pump station systems sponsored by National Grid. The objective of the evaluation was to provide an overview of each facility system to determine how electrical energy and natural gas were being used at the facility and to identify and develop potential costsaving projects.
The project, which also involved the addition of a booster air compressor and receiver tank – along with the installation of an important pressure control valve – gives the automaker the ability to run fewer centrifugal air compressors during peak production. In so doing, the plant saves nearly 6.1 million kWh and more than $600,000 per year in energy costs. The project also qualified for a $369,374 rebate from the local utility, resulting in a six-month project payback – all while improving system reliability.
The compressed air system at the mail sorting facility has been in service since the 90’s. Two older 50-horsepower (hp) air-cooled fixed-speed lubricated air compressors are housed in the equipment room of the facility. The air compressors duty cycle alternates between one another on a set schedule. A 240-gallon wet storage receiver is used to help with air compressor control, with the air flowing through the receiver to a non-cycling refrigerated air dryer and system filters before finally being passed to the plant.
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.
With an eye toward strengthening its competitive edge, GKN opted for a new approach for the compressed air it uses to power metal molding machines in addition to a variety of other applications at its manufacturing facility. After careful analysis and planning with the Total Equipment Company located in Coraopolis, Pennsylvania, GKN opted to move beyond its aging compressed air system – and instead – outsource compressed air as a utility. Doing so allowed it to free up valuable floor space, while also achieving peace of mind since it can now count on a fixed cost for a reliable compressed air supply for years to come.
In terms of compressed air systems, it’s not unusual to see a plant with 10 to 15 air compressors, each of which is rated to provide 3,000 to 4,000 scfm of air. The air is used for everything from moving product, to powering pneumatic tools, pumps, and fans, to cleaning. There are easily 1,500 pneumatic control valves at a single plant.
Plant personnel had experienced ongoing problems with its process grinder performance due to unstable compressed air pressure. This created potential problems in terms of product quality. Grinders do not work properly without the proper pressure. Additionally, plant staff wanted to address these concerns, prior to a proposed 30% increase in production, and suggested raising the header pressure from the current operating pressure of 98 psig to 125 psig. The thought behind this was if the pressure from the header to the grinder process was dropping to 63 psig, then raising the pressure to the process would give the grinders enough pressure to work through higher peak production times.  
All industrial facilities use some form of compressed air, and in most, the air compressors consume a significant amount of the total energy bill. A facility with a good energy management system is likely to identify their compressed air system as a significant energy user (SEU). If the facility were using an energy management standard, such as ISO 50001, they would be required to assess and track the energy consumption of all their SEU’s. In the case of the metal processing facility, they were measuring the output of more than 250 devices within the plant, including building heaters, RTU’s, dust collectors, and also tracking the consumption of their electricity, natural gas and water. 
One observation I’ve made from 30 years of working with compressed air systems is to never underestimate the ingenuity of plant personnel when it comes to misapplying compressed air. We see something new in virtually every plant we visit, but one of the more common problems we encounter involves the use of expensive air for bearing cooling. 
By addressing inappropriate uses of compressed air and making changes to the compressed air production side of their compressed air system, a distiller of fine alcohol products reduced its energy consumption by 30%, saving $16,600 per year in energy costs - with more potential savings possible.
Experienced auditors become wary when they see desiccant dryers installed in customers’ plants. These dryers are required when a plant needs instrument-quality compressed air, or when compressed air piping is exposed to freezing temperatures. However, while desiccant dryers can gain this level of quality, the energy cost of stepping up from a dewpoint of 35 oF to a level of -40 oF increases quite considerably. To attempt to reduce the energy costs of drying to these low levels, heated blower desiccant styles may be used. This article describes three common desiccant dryer types, as well as some experiences, good and bad, with heated blower types.