Centrifugal Compressor Controls Tuning

March 21, 2017Ken Bean

A simple concept of air density is cool air is more dense than warm air. In a centrifugal compressor application where the flows and pressure are created dynamically the inlet conditions play a major role in the performance of the compressor.

Several factors play a contributing role in the performance including inlet pressure which should remain constant at your physical location. However, the variable factors include inlet air temperature, humidity and cooling water temperature.

Lower intake air temperatures as well as cooling water temperatures usually go hand in hand. The lower temperature air will be more dense and will result in higher free air delivery (ACFM) and also higher power consumption of the compressor.

Another factor in air density changes is the available turndown of the compressor. Meaning the effective flow range through the use of a throttle valve or inlet guide vanes is possible. A lower temperature inlet air will allow for a wider range of operation in the compressor thus offering a larger amount of turndown.

The lower inlet temperature air also increase the surge pressure!

During the heat of summer the alternate is true where less volume is produced by the compressor and subsequently, less horsepower is used but there may exist an circumstance that the unit will not be able to produce the required plant volume if the unit was not sized appropriately at the onset.

All of this information is critical in initially sizing a dynamic compressors but the point we’re looking to make is the ambient conditions do change the performance of the machine.

Modern controls are designed to keep the compressor out of surge or choke conditions by moving the surge line to an acceptable position. However, by moving the surge line the performance of the unit is also altered.

This is the primary reason we suggest re-tuning each centrifugal compressor based on the season. At least twice per year (as the ambient temperatures increase for summer and decrease for winter) is an ideal time to tune the compressor to achieve peak performance and maximize energy savings.

If your plant has a maintenance contract with a service provider, make sure that tuning the compressor is included twice per year as recommended. If you perform you own service I would advise contacting a local service company to perform these tuning parameters for your as a one off service. Typically, tuning controls is outside the expertise of plant maintenance personnel.

Do You Have a Matched System

April 12, 2016Ken Bean

Simply put, does the drawing left of the red line (Supply) match the right side (Demand) in terms of air flow and pressure? Does it continually match? Likely it does not as demand is in constant fluctuation whether from changes in use, shift change or downtime.

Within a compressed air system, the system dynamics (changes in demand over time) are especially important. Using controls, storage, and demand management to effectively design a system that meets peak requirements but also operates efficiently at part-load is key to a high performance compressed air system.

In many systems, compressor controls are not coordinated to meet the demand requirements, which can result in compressors operating in conflict with each other, short-cycling, or blowing off are all signs of inefficient system operation.

As in most relationships, the key is communication. Communication between the compressors so that each (or a central controller) knows the status of all the other units. Communication is also key between the compressors (or central controller) and the demand side of the system. The compressors perform based on information from a pressure sensor located downstream of the compressor discharge. But where is this sensor located?

A common mistake is the pressure sensor is located close to the compressor discharge. Perhaps even before the dryer. If this is the case in our system drawing above, you can see that the compressor is performing based on pressure data before the air enters the dryer or the subsequent filter, both of which have pressure drop as air passes through. This drop can range from 5 PSIG up to 12 PSIG or higher depending on how well the system was designed as well as the condition of the filter element. A dirty element near the end of it’s life will have substantially more pressure differential than a clean filter element.

If the compressors are discharging at 100 PSIG and there is a 10 pound drop through the dryer and filter, then the plant is only receiving 90 PSIG and this doesn’t include the pressure drop throughout the plant piping system. When a cyclical event occurs, such as several blow guns operating at the same time, the pressure drop has to travel back through the entire system before the compressors see the event and can respond to correct the drop in pressure by increasing their output.

All factors must be considered when designing or updating a compressed air system. Your best course of action is to consult with a compressed air professional to assist in your design or upgrades prior to writing any equipment specifications.

Compressor 1, Compressor 2, Compressor 3…You Get The Idea

April 5, 2016Ken Bean

With a room full of compressors, how do you keep them all playing together nicely? Central controls is the key to an energy efficient system with multiple compressor. Even with various types and brands a central control system can form a chain of command that keeps the plant satisfied while reducing energy costs.

The simplest central control is utilizing the existing compressor controllers for communication between the compressors allowing one or two units to focus as the lead machine and calling on the remaining compressors to assist in high load conditions. This could be by automatically loading or modulating one or several of the remaining units.

System master controls have many functional capabilities, including the ability to monitor and control all components in the system as well as trending data to enhance maintenance functions and minimize costs of operation.

What if your compressors are from multiple manufacturers and the controllers will not communicate with each other? Time to call on an outside source such as IZ Systems. The IZ Systems central control system can communicate with all compressor manufacturers controls and allow many enhanced functions not usually associated with normal compressor controls such as web based control, real time energy consumption and even contracts allowing our specialist to monitor your compressed air components for you remotely, giving you piece of mind 24/7/365.

Does the C-Suite Have Room For One More?

March 29, 2016Ken Bean

For over a decade I’ve been focusing on client education related to the true cost of compressed air. We’re all making progress but there are still those that fight the price tag on energy efficient systems. Instead, choosing the low initial investment route when the overall cost of ownership is primarily dictated by energy cost.

A recent article in the Harvard Business Review shared information about how much utility waste actually occurs in manufacturing. I felt the article had such impact that I’m choosing to take this weeks #TipTuesday post and simply direct you to read their article.

Considering that compressed air consumes a major portion of the utility budget there will always be savings opportunities related to the compressed air system. I’m always available to assist you in your search for a more energy efficient system.

I hope this article arms you with valuable information in your efforts to become a more energy conscience consumer while boosting your profit margin at the same time.

The full article can be viewed at http://bit.ly/1RFY1Z8

Contact me to discuss a compressed air energy audit.

Should I Use Compressed Air?

March 15, 2016March 15, 2016Ken Bean

Decisions, Decisions!

Last month I posted an article discussing the options of using compressed air vs. electric. There were several questions regarding cost calculations.

As a follow up, Todays post will discuss compressed air cost calculations to determine if compressed air should be used for specific applications.

This allows you to determine if compressed air should be used in specific applications (ie. as fans or blowers), or if other electric-motor operated equipment would be more efficient.

First calculate the volume of air produced annually for a specific operation by multiplying:

horsepower (hp)

cubic feet per minute per horsepower (cfm/hp)

total operating hours per year (hr/yr)

60 minutes per hour (60 min/hr)

% time fully loaded

% full-load horsepower

Volume of air produced annually

Then calculate the cost per 1,000 cubic feet (cf) by dividing the total energy cost to operate the air compressor by the volume of air produced annually, then multiply by 1,000. Cost per year / Volume of air products * 1000 cf

Example Calculations

The following example represents a typical small job-shop manufacturer.

A facility operates a 100 hp air compressor 4,160 hours annually. It runs fully loaded, at 94.5 percent efficiency, 85 percent of the time. It runs unloaded at 25 percent of full load at 90 percent efficiency, 15 percent of the time. The electric rate is $0.06 per kWh, including energy and demand costs. The cost per year to power the air compressor will be as follows.

Fully Loaded

Unloaded

The total annual energy cost to operate the air compressor is $17,524. The following calculation shows how much it will cost to use compressed air to operate a specific end use. Assume 3.6 cfm per horsepower and that this rate applies when the compressor is fully loaded.

Volume of air produced annually Cost per 1,000cf ($17,524 / 76,377,600) * 1000 = $0.23

Over the life of a compressor, energy costs will be five to 10 times the compressor’s purchase cost. Energy savings can rapidly recover the extra capital required to purchase an energy-efficient air compressor .

A 1.17 rated horsepower air operated mixer uses 45 cfm at 80 pounds-per-square-inch (psi) and operates 40 hours per week. The cost of the compressed air to operate this motor over a year is $1,292. A comparably sized electric motor of Energy Policy Act (EPACT) efficiency, rated for hazardous locations, is around $350. The cost to operate the EPACT motor under the same conditions is less than $100 per year. Including installation, payback is under one year.

Can Your Air Compressor Make Phone Calls

March 1, 2016August 3, 2016Ken Bean

I read an article (link below) Sunday night from “Plant Services” discussing how the IIoT is coming to compressed air. If you’re not familiar with IIoT, it’s the industrial version of the IoT. In case you’ve not heard of IoT, let me give you a quick explanation. IoT stands for the “Internet of Things” and subsequently, IIoT stands for the “Industrial Internet of Things”.

The premise of IoT is that you and your entire home can be connected with all the components and subsystems being able to communicate and interact with each other. Basically, a Smart Home. What drives me crazy is that the authors of these articles promote this is new. This is NOT NEW! My house has been automated for over 20 years. The lighting, HVAC, security system, garage doors, home theater, whole house sound system along with others all respond to the central computer that controls it all and can be activated by buttons on my iPhone, keypads in the house or timed based controls. It doesn’t need access to the internet, nor do I want it connected to the internet. One less thing I have to be concerned with related to viruses and hacking. Sure a connection to the internet could add a few features to my system but it’s not worth the worry at this point.

Now on the article in “Plant Services” discussing IIoT and how its coming to compressed air equipment. It states how compressed air equipment utilizing IIoT and connecting to the internet will be “a game changer based on the energy-saving impact”. It further states “it will bring smarter control for better efficiency and easier compliance reporting”. My question is: compliance to what and reporting to who?

The goal of any compressed air system in today’s world is better efficiency but you certainly do not need an internet connection for that to happen. My vendor for central compressed air system control (IZ Systems) has been providing this capability for years. Maybe not as long as my house has been automated but for a lot of years. The current system doesn’t require changes to the local controls and can be tied into nearly any type or brand of compressed air equipment. Thus making the system reliable as any failure in the central system will revert control back to the local controller.

The key to energy efficiency has nothing to do with the internet but rather with the central processor that controls the compressed air equipment while monitoring the entire compressed air system and more importantly, the proprietary algorithm that resides in the central processor. Yes, they can use an internet connection to remotely monitor the system but this plays no part in the efficiency and in fact, many of my existing clients will not allow their equipment to access an internet connection due to the same concerns I have over my house. Additional security concerns. The benefits just don’t outweigh the potential headaches.

But, the article states, with the IIoT, my compressor can call the service technician if there is a potential problem. I’m sure this would save all my clients some time however most of my clients already tie equipment monitoring into their DCS and trend various data points such as temperature, pressure and vibration. If there is an escalating problem the DCS notifies them and they determine who needs to be called for further inspection or repair. So in my opinion, having your air compressor make phone calls is not going to add a lot of hours to your day.

Rather than waiting and hoping the IIoT progresses to a usable point, in my opinion, your money would be better spent investing today in a solid service contract with a company that can provide true vibration analysis. I’m not talking about trending but rather vibration analysis by professionals that know what the frequency’s should be on your equipment and can spot problems from one initial vibration analysis.

I think you can determine that I’m no luddite. In fact, quite the opposite. I love technology and the great things it can provide us. I just don’t want my clients getting caught up in the wave of hype surrounding a supposed new technology and spending money on features that are either easily available today or worse, for something they don’t really need.

Perhaps as the IIoT progresses I’ll be proven wrong and this technology can truly provide value to my clients. But for today, I see it as a half baked cookie that nobody really needs to bite into.

Here is a link to the original article if you’re interested.

Desiccant Dryer Control

February 21, 2016Ken Bean

Desiccant air dryers utilize a tremendous amount of energy through the consumption of compressed air and/or heat to regenerate the desiccant bed.

The use of hygrometers or dew point meters is commonly applied to reduce the amount of energy usage.

A recent article by “Compressed Air Best Practices” informs end users that this type of control is not the panacea that manufacturers would have you believe.

Seeing is not always believing

However, the use of an in (desiccant) bed capacitance probe can assure a lifetime of proper operation with no calibration required. The AMLOC capacitance probe used exclusively on dryers manufactured by Pneumatic Products Corporation (PPC)

AMLOC®

The AMLOC Energy Management Systems maintain accuracy, dew point stability and never need recalibration. Patented one quarter century ago, AMLOC® generates tens-of-thousands of dollars in energy saving annuities for industry leaders. The model of durability, THE PTFE or ceramic coated, stainless steel capacitance probes sense the changes to the dielectric constant imparted upon the desiccant by the extracted water vapor. Capable of identifying an aging or fouled bed, desiccant regeneration cycles are managed with precision.

Air or Electric

February 16, 2016Ken Bean

Air Audits can discover a multitude of energy saving ideas in your plant.

Point Of Use Compressed Air Storage

February 9, 2016Ken Bean

There are frequent articles on the site touting the benefits of compressed air storage. We usually refer to large receiver tanks as the ones pictured above. This article will focus on the benefits of local storage or receivers located at or near the point of use where there are one of just a few intermittent high flow demands. I have found this technique to be extremely beneficial in bag house pulsing applications.

A correctly-sized storage receiver close to the point of the intermittent demand with a check valve and a metering valve can be an effective and lower cost alternative. For this type of storage strategy, a check valve and a tapered plug or needle valve are installed upstream of the receiver. The check valve will maintain receiver pressure at the maximum system pressure and only allow air to be consumed from the receiver when the system line pressure falls below the pressure of the receiver. The plug or needle valve will meter the flow of compressed air to “slow fill” the receiver during the interval between demand events. This will have the effect of reducing the large intermittent requirement into a much smaller average demand.

Understand Your System

February 2, 2016Ken Bean

Compressed air system’s are complex. Each components carries it’s own difficulties in understanding but once multiples of these components are installed in an industrial plant, a simple area drawing gets complicated really quick.

Before implementing energy reduction strategies, be familiar with all aspects of your compressed air system.

System Supply

Analyze the supply side of your compressed air system for the types of compressors and dryers used, suitability and settings of capacity controls and other operating conditions. Understand the basic capabilities of the system and its various modes of operation. Verify that air compressors are not too big for end uses. For example, an air compressor is oversized if the end use only requires air pressure that is 50 % of the pressure that the compressor is capable of producing. Once the big picture is in view, supply side operating conditions can be modified, within the constraints of the compressed air unit, to better match the demand side uses of compressed air.

System demand

Identify all the uses of compressed air in the plant. Quantify the volume of air used in each application and generate a demand profile, quantity of air used as a function of time, for the compressor. Equipment specifications for operations that use air are good resources for obtaining data on air volume use rates. The profile highlights peak and low demand. A general assessment of compressed air use will help identify inappropriate uses of air.

System diagram

Develop a sketch of your compressed air system including compressors, dryers, receivers, filtration, drain traps, air supply lines with dimensions, and compressed air end uses to provide an overall view of the entire compressed air process.

Distribution system

Investigate the distribution system for any problems related to line size, pressure loss, air storage capacity, air leaks and condensation drains. Verify that all condensation drains are operating properly because inadequate drainage can increase pressure drop across the distribution system.

Maintenance

Evaluate maintenance procedures, records and training. Ensure that procedures are in place for operating and maintaining the compressed air system, and that employees are trained in these procedures.

Qualified audit engineers can give you a complete understanding of your system.