November 2016 – Compressedairducation

I have a notification system that lets me know when the temperatures are expected to drop below freezing. Yes, it’s great to know ahead of time so I can plan an indoor day but the real reason for this is to notify my clients through twitter (www.twitter.com/fe_airsystems)

As most already know, compressed air systems can be devastated by freezing temps if your not ready.

When I received my first notice of the season last week I was shocked at far into the year we were. I guess it was the extended summer temperatures that caught me off guard and then but I noticed this weekend my area is predicted to see a low temp of 25 degrees.

I hope you’re keeping track better than me but if not, It’s time to get your compressed air system ready for the cold weather.

This is the first of several posts to help you be cold weather prepared.

Of course maintenance takes place all year long, whether by your own maintenance staff or bringing in your preferred compressed air service specialist but there are a list of additional checks and corrections that need to be made ahead of freezing temperatures.

Check all drains for proper operation

Check drains for obstructions or inefficiencies. If a drain is malfunctioning it can cause serious issues when the temperatures drop. In compressor rooms that are not heated, improperly drained condensate could freeze. If the drain trap is left open, it blows expensive compressed air to the atmosphere and let’s face it – efficiency means everything to companies today. If not already installed consider adding no air loss type auto drains. Be sure to inspect drains in the air system equipment, including dyers, receivers and filters.

Maintain air filters

Filters should be checked regularly for clogs or other problems indicated by a high differential pressure. This unnecessary pressure drop can decrease end-use pressure, causing the entire system to work harder and use more energy. Again, efficiency is king! Coalescing filter housings partially filled with water are at risk for freeze and rupture event and nobody wants to be around that time bomb. .

Locate and repair leaks

Leaks can account for up to 25 percent of compressed air use. Identifying and fixing leaks can lead to huge savings. Did I mention efficiency? Some larger leaks can be heard just walking through the area but smaller leaks will require monitoring equipment. You can purchase and utilize an ultrasonic acoustic leak detector or hire a “Quality” compressed air auditing firm. An auditing company can perform a leak audit only or you can go all out and have them perform a supply & demand side audit to determine additional potential savings for your entire system.

These are the first steps to take when winter is just around the corner. Follow the blog to learn more pre-cold weather tips.

In the segment we’ll discuss two critical characteristics of a centrifugal compressor prior to moving into our discussion of the main controller.

Surge

What is surge?

•Surge is the reversal of flow within a dynamic compression that takes place when the capacity being handled is reduced to a point where insufficient pressure is being generated to maintain flow.

In layman terms, this means that for the flow through the compressor at a given point, the pressure has reached the maximum limit the impeller of the compressor can push against. Therefore, since the compressor cannot overcome the pressure, the air flow slips backwards rather than being pushed into the system.

•This condition can potentially damage the compressor if it is severe and is allowed to remain in that state for a prolonged period; therefore, control and prevention is required.

The resulting problem with a surge condition is twofold:

The backward flow of air causes severe vibration within the compressor potentially resulting in damage to internal components.
As air is compressed, heat is generated. When a surge occurs, the air has been compressed (to a certain point) which has heated the air. The air then slips backwards on the impeller and will be grabbed at some point by the impeller to be compressed (moved forward in the compression sequence) at which point it is heated again. As we previously discussed, the temperature of the air moving from stage to stage plays a large part in the design of the entire compressor and at this point we are heating the air above it’s intended design point.

The term surge should also be clarified as the term can have multiple meanings.

Surge Terminology in Centrifugal Compressors:

•Throttle Surge – When flow across the compressor drops till the surge line while maintaining constant pressure.

• To prevent such occurrence, the bypass valve is open before reaching the surge point

• Natural Surge – When pressure reach the maximum the compressor can compress (exceed the physical limitation of the compressor).

•Typically 110% of compressor rated pressure

Stonewall

Stonewall is the effect at the opposite side of the curve from the surge point in the chart above. At some point, as the discharge pressure falls and the airflow through increases at full load, the physical limitations will not allow more air through the stages — this point is known as stonewall. Continued operation at or beyond this point can cause such high flow rates with greater pressure differential that the impellers will not totally fill the vane areas and a cavitation-like action will occur, creating another type of surge with damaging vibrations.

Month: November 2016

Winterization

Surge & Choke

Surge

Stonewall