Industrial Utility Efficiency    

Technology

Among the many “systems” plant personnel are concerned with, the compressed air system often provides the biggest opportunity for improvement and overall savings. There are many manufacturers and several air compressor technologies to choose from. Reciprocating or rotary? Fixed speed or variable speed? Oil flooded or oil free? Single-stage or two-stage technology? It’s enough to make anyone want to run and hide!

Air Compressors

Properly sizing a compressed air system can help determine if your facility has enough air to adequately supply your production equipment. Designing a cost effective system that minimizes any interruptions to productivity requires thoughtful planning and design. Typically, the desired outcomes of such a system focus on stable pressure and efficient operation, though it is important to note that each of these elements requires a unique solution. This article will provide guidance in proper selection considerations and suggest when a centrifugal air compressor may be ideal for your needs.

Air Treatment

Air compressors can produce a lot of water. Humidity in ambient air, once compressed, results in much of this water falling out, which we know as condensate. On a warm and humid summer day with inlet air temperatures of 80 oF, a 75-horsepower (hp) air compressor running fully loaded can produce over 25 gallons of condensate in just one eight-hour shift, with another five gallons being produced once the compressed air is sent through a dryer. The compression process allows for the air, water vapor, and lubricating fluids to mix. Once the condensate leaves the system, trace amounts of lubricant travel with it. This condensate should be processed through an oil-water separator before being discharged to groundwater or wastewater treatment plants.

Blowers

The plant upgrades, in combination with a progressive management strategy, allows the plant to consume less energy and reduce its reliance on outside contractors for biosolids removal, resulting in total operational savings of approximately $60,000 per year.  The plant is also positioned to efficiently manage the area’s wastewater for decades to come.

Compressor Controls

Companies will experience periods of increased production, as well as periods of slower or stopped production. It’s the nature of being in business. Understanding the implications of these business shifts for compressed-air installations (the powerhouse behind a facility’s production) is key for ensuring that air compressors remain functional and efficient. Here are guidelines to ensure your facility’s compressed-air system operates at top performance, no matter the speed of production.

Instrumentation

Like any system, to properly manage compressed air equipment some measurements have to be taken. Typically, some sort of data logging equipment is installed to measure various pressures, amps or power, flow, and sometimes temperatures and dewpoints. Placing this equipment on a system is like putting an electrocardiograph machine on a human heart, the heartbeat of the compressed air system in a plant can be analyzed to determine if everything is normal or if there is a problem, all without interrupting the system. 

Pneumatics

In this article, we discuss problems associated with static electricity in industrial manufacturing operations and how to effectively address them. At the atomic level, materials have a balance of positively charged protons in the nucleus and negatively charged electrons in the shell. Balance requires the same number of each.  A static charge occurs when that balance shifts due to the loss or gain of one or more electrons from the atom or molecule. The primary mechanism for this loss or gain, among several possibilities, is friction.

Vacuum

It’s one thing to move materials during the production process, but when it’s a finished product on the packaging line, choosing the right material handling system is essential. Getting it wrong results in squandered production time when product loss occurs, and wasted raw materials.

Cooling Systems

As a result of compressed air awareness training and a focus on energy management, two facilities in different parts of the world have reduced their compressed air demand substantially by removing vortex style cabinet coolers from some of their electrical panels and reworking the cooling systems.  These facilities were previously unaware of the high cost of compressed air and how much could be saved if other methods of cooling were used. This article describes some of their efforts in demand reduction.
There are three essential ways to transmit power in heavy industry today: Mechanical, Electrical and Fluid Power. Under the umbrella of fluid power, you have hydraulics and pneumatics as the two fundamental technologies. Both use a form of fluid – hydraulics as a liquid and pneumatics as a gas, to transmit power from one location to another.
Compressed air dryers need to get the ball handed to them on the 25 yard-line by a compressor providing low enough temperature, and high enough pressure for the dryer to take it to the design dew point. If not, the dryer is not able to work properly. Once the dryer gets the right moisture level, it needs to operate properly. Heat exchangers, drains, switching valves, etc., all have to work with the proper control sequence to provide reliable dew point to the plant.
ANSI /ISA–7.0.0–1996 is the globally-recognized quality standard for instrument air as defined by the Instrument Society of America. In this article, we’ll go through the Standard’s four elements of instrument air quality for use in pneumatic instruments.
The air we breathe and the air compressors ingest is a mixture of gases, aerosols, biological material, and particulates. It’s a real mess! Particulate, for instance, is very harmful to humans, because lungs are complex oxygen separators, not filters. They tend to load up with particulate, this is harmful over time. There isn’t a sufficient “pre-filter” to prevent all harmful particulate from entering the lungs. However, humans prefer water in the air, gas, aerosol, and to a certain level, liquid form. A de-humidifier would not typically be a healthy addition to our built environments.
Load-sharing is an important part of a multiple centrifugal-compressor master control system. It minimizes blow-off based on the available turn-down. In addition, remote start-stop saves more energy if load floats between different ranges. Finally, adding a screw compressor and implementing a hybrid control system might save the most energy and provide the best back-up. In any case, a well-instrumented system allows engineers and operators to assess, optimize and tune the system.
There are many choices of compressor technology and types of controls that can be used for variable demands. Some examples are rotary screw compressors with inlet valve control: variable speed drives: load/unload control; or centrifugal compressors with variable inlet guide vanes. However, in many cases, the efficiency of the overall compression process can be reduced significantly during lower flow demands, leading to more power per unit of air flow being delivered. It is very important to evaluate different available options and see how a plant can run most efficiently.
Larger air compressors, typically over 500 hp, in refineries, pulp and paper plants, chemical and other processing plants often have high-speed, multi-stage air compressors called “centrifugal” air compressors. As seen from a total system perspective, they are not much different than screw air compressors. They compress air to plant pressure from atmospheric conditions, and deliver it to the dryer. These types of air compressors have no internal wearing parts, besides bearings and seals, and are very reliable and efficient, at their best efficiency point. 
Knowing when to overhaul a unit is important, and there are certain signs indicating a unit needs attention. Performing routine fluid checks, taking oil samples and routinely checking for bearing vibration can unveil indicators suggesting an upcoming failure. Oil contamination with metal fragments usually indicates parts are wearing. It’s also important to take notice of airend temperature increases. If internal air compressor temperatures go up, it’s a good indicator the cooler may be failing.
When a system has the right combination of VFD and base-load air compressors, how do you coordinate their control? What tells the air compressors to run and load, to have just enough (or no) base-load air compressors and a VFD running, all the time air is needed? Appropriate master controls are needed. These controls are often called “sequencers” or “master control systems”.
It is becoming a “best practice” to install a variable frequency drive (VFD) air compressor whenever one is replacing an old air compressor.  As a result, real systems have fixed-speed and VFD air compressors, mixed.  I have observed several VFD compressor sizing methods.  In my last article, I referred to a common method: size one VFD compressor for the whole system.  This can work.  However, if it doesn’t meet a higher peak demand, one or more of the old compressors will be started, and a mixed system results.   Another method is to replace a compressor with the same size, but with a VFD.  If the compressor that was replaced is large, a big VFD is installed.  If small, a small one.