“Repair or Replace?”

A small town faces the common dilemma of “repair or replace?” and achieves notable operational and energy efficiency gains.  

By: Michael Camber

Traditionally, planning for blower system installations at wastewater treatment plants has been approached very differently than industrial compressed air system design. We have found, however, that applying techniques such as system energy audits and modern controls to blower systems yield similar benefits in terms of identifying energy reduction opportunities. That’s exactly what happened when one of our wastewater sales managers convinced management at a wastewater treatment plant to perform an Air Demand Analysis rather than simply replace aging equipment with newer versions of what they had.

Thinking outside the box and working with the local engineering company, we were able to show the town’s public utility department how they could save energy and then document the actual savings.

See the full case study published in the May 2019 issue of Water & Wastes Digest :

Fixed or Variable? Small town achieves efficiency gains with blower station options
Chapmanville Water Department in Logan County, W.Va., provides the water distribution and wastewater treatment services in the town of Chapmanville, which has a population of 1,200. It wastewater plant processes about 400,000 gal per day (gpd). The town planned a major upgrade for 2019 and 2020, including the replacement of three 40 hp multi-stage centrifugal blowers commissioned 25 years earlier.

At the beginning of 2018, one of these was no longer in service. Chapmanville planners hoped to limp along on the two remaining blowers, but in the spring of 2018, they lost another one. Down to one blower, the planners knew they could not wait for the planned upgrade, and the department had to do something.

Read the full story online here: https://www.wwdmag.com/blowers/fixed-or-variable

Applying Rotary Lobe and Rotary Screw Blower Technologies

By: Stephen Horne

Rotary lobe and rotary screw blowers utilize positive displacement. This means they pressurize air by trapping a fixed amount and forcing (or displacing) it into a discharge pipe. Industrial applications include fluid aeration (wastewater treatment, bioreactors, and flotation), process air, pneumatic conveying, as well as fluidization.

Although all of these applications generally work within a low pressure range (up to 14.5 psi), they have very different operating cycles and needs. Fluid aeration applications generally have variable flow rates, but at constant pressure.

Others, like pneumatic conveying, require a near constant flow rate with high pressure fluctuations. Sometimes the blowers are required to idle, running without back pressure from the process side. This happens when there are no bulk goods in the line to move.

Naturally it’s important to decide which blower technology is best suited to the application. Technical requirements must be taken into account, such as a broad flow rate curve during pressure fluctuations. Ultimately, the choice may hinge on the amount of energy savings achievable from different alternatives. In determining energy savings, the “power bill” is determined solely by output (kW) x time (h) x rate ($/kWh).

The big variable here is time, which significantly impacts energy costs. Unless the cost per kWh is very high, the more efficient blower may need to run a lot more hours to justify the higher investment.

External (isochoric) versus internal (isentropic) compression

To determine which of these blowers would be more cost effective for a given application, it is important to first understand in greater detail how each functions.

Rotary lobe blowers:
Image 1 shows a cross-section of the rotors and cylinders, running parallel in the longitudinal direction and illustrates how the volume enclosed between the housing and the rotor blade remains constant. In thermodynamics, this is referred to as isochoric compression. The pressure does not build until the air molecules are pushed beyond the blower into the connected process line. In this way, with rotary lobe blowers, pressurization occurs externally. Moreover, if the process line is free of resistance (e.g. no bulk goods in a pneumatic conveying line), there is virtually no back pressure. In this regard, the rotary lobe blower can also be seen as adaptive: it only produces the amount of pressure needed.

Lobe_Operation
Image 1

Screw blowers:
With screw blowers (image 2), the tried-and-true technology of the single-stage screw compressor has been optimized for low pressures.

The rotor geometry is based on the screw. The inlet air is initially captured within the cavity between the two rotors where its volume is gradually decreased along the length of the rotors and then pushed out through the discharge port. The geometry of the rotors and housing (i.e. contour of the discharge port) determine how much air is proportionally compressed within the screw blower and how much pressure is built up internally. This internal pressurization can also be called isentropic compression.

Screw_Operation
Image 2

Pushing an already compressed volume of gas against the system back pressure requires less energy than pushing the un-reduced volume created in isochoric compression (rotary lobe blower).  The result is significantly lower electrical demand, and in many cases the screw blower delivers great ROI over a lobe blower.  However, the better specific performance of the screw blower may not pay off if the running hours and/or cost per kWh don’t out-weigh the additional cost of the screw technology.  You must do the math.


This blog post is adapted from our white paper, “The Proper Application of Rotary Lobe and Rotary Screw Blower Technologies”. Download the complete whitepaper here.

How WWTPs Can Get Greener Grass on the Other Side of the IIoT

By: Stephen Horne

The next big thing is here and it’s the Industrial Internet of Things (IIoT). With pundits waxing philosophical on this big breakthrough, it’s hard to cut through the noise and understand what the IIoT actually is and how it applies to individual plants. I offer the following as a definition. The IIoT means collecting, interpreting, and applying data to actively improve processes or operations. To understand how the IIoT applies to a wastewater treatment plant, look no further than your front yard. Continue reading “How WWTPs Can Get Greener Grass on the Other Side of the IIoT”

It’s Alive…With Inefficiency

By: Stephen Horne

Have you got a Frankenstein blower package lurking in your system? Without a doubt, it comes alive when you flip the switch, but do you really know how efficient the package is? If you’ve got a monster of an electricity bill, you are not alone. Here’s how package integration can help keep that inefficiency monster at bay. Continue reading “It’s Alive…With Inefficiency”

Go with the Flow

By: Kaeser Compressors, Inc.

We recently published a blog entry on rotary blowers for vacuum applications and the benefits they can provide in providing better hold down, reduced footprint, and energy and maintenance savings. Here is a case study example from one of our customers who made the switch to blowers. Continue reading “Go with the Flow”