September 2019

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Reliability: Comparing and updating aeration blower technologies

As the main consumers of electricity in a wastewater treatment plant, aeration blowers can significantly affect the overall cost of plant operation.

Bloch, Heinz P., Hydrocarbon Processing Staff

As the main consumers of electricity in a wastewater treatment plant, aeration blowers can significantly affect the overall cost of plant operation. However, the most energy-efficient selection must be based on operating parameters, which are generally far from static.

FIG. 1. Rotary lobe blower stage. Image courtesy of Aerzen USA.
FIG. 1. Rotary lobe blower stage. Image courtesy of Aerzen USA.FIG. 1. Rotary lobe blower stage. Image courtesy of Aerzen USA.

 

Moreover, energy efficiency is rarely the governing factor in optimized blower selection, and comparisons made at a single hypothetical operating point are inaccurate. We asked Aerzen USA, one of the most experienced providers of aeration blower technology, about today’s selection criteria for air movers in this service category.

FIG. 2. Dry screw compressor rotors with timing. Image courtesy of Aerzen.
FIG. 2. Dry screw compressor rotors with timing. Image courtesy of Aerzen.

 

Aerzen USA directed us to www.aerzen.com/en-us/applications/water-and-waste-water-treatment.html for information to help engineers understand the importance of closely examining the many factors that separate different designs. Selection and thoughtful integration of subsystems are of paramount importance, as is the overall operating philosophy of the facility. The internet reference explains in more depth the extent to which subsystems and operating philosophy influence total cost of ownership.

FIG. 3. Section of a centrifugal blower with inlet guide vanes and diffuser vanes. Image courtesy of Dresser Industries.
FIG. 3. Section of a centrifugal blower with inlet guide vanes and diffuser vanes. Image courtesy of Dresser Industries.

 

Parameters to be compared. Experience shows that four parameters are important in blower selection:

  • Site condition
  • Type of aeration system
  • Instantaneous mass flow of air
  • Related system variables (upstream and downstream).

Available blower configurations are generally classified as either positive displacement [rotary lobe (see Fig. 1) and dry screw (see Fig. 2)], or the dynamic (centrifugal) machines shown in Fig. 3.

Dynamic blowers incorporate either a rotor with step-up gearing (Fig. 3) or a driver that can generate the requisite high (fixed or variable) speeds. Special-purpose, high-speed, single-stage centrifugal blowers (Fig. 3 and Fig. 4) incorporate inlet guide vanes and outlet diffuser vanes to achieve wide turndown at constant operating speed.

High-speed, single-stage centrifugal blowers can be operated with a variable frequency drive (VFD) to provide additional flexibility while maintaining the highest efficiency. They are also offered as self-contained packages (Fig. 4 and Fig. 5).

FIG. 4. Single-stage centrifugal blower package. Image courtesy of Siemens Turbo.
FIG. 4. Single-stage centrifugal blower package. Image courtesy of Siemens Turbo.

 

A standardized, high-speed, single-stage turbo blower is depicted in Fig. 5. These packaged assemblies incorporate a 3D radial-exit impeller, direct-driven by a high-speed permanent magnet synchronous motor (PMSM). Combined with an integrated VFD and control panel, the package enables a wide operating range for continuous operation. Non-contact magnetic or air foil bearings are utilized in high-speed turbo blowers to reduce friction, improve efficiency and reduce maintenance.

FIG. 5. High-speed, single-stage blower package assembly (left) and exploded view of its turbo blower core with permanent magnet motor and airfoil bearings (right). Image courtesy of Aerzen USA.
FIG. 5. High-speed, single-stage blower package assembly (left) and exploded view of its turbo blower core with permanent magnet motor and airfoil bearings (right). Image courtesy of Aerzen USA.

 

We found that aeration blower technology has advanced remarkably since the 1990s. The exemplary integration of control innovation and thoughtful component upgrading found in late-model packages avoids downtime and increases plant profitability.

Forethought and action are required for a plant to fully capture the benefits of control innovation and component upgrading. More specifically, reliability engineers must lead their organizations, be they engineering and procurement contractors or their in-house project leaders. Acquiring and acting on a “reliability mindset” is essential. Professionals with the proper mindset stay clear of simply opting to purchase from the lowest bidder. Experienced reliability engineers also guard against allowing piecemeal procurement of the various elements that make up wastewater treatment plants or any other “packaged” units. Cheap packaged units are often analogous to automobiles: “Your faulty tire was made by XYZ; go complain to them.”

The prudent course of action is to write and invoke a detailed specification that clearly avoids later disappointments. Follow up by making careful comparisons between the various bids or proposals received from seemingly capable providers. Pay attention to the exceptions some bidders take to several of the specified clauses. Ask these bidders if they know the intent of the request for compressor seal type “X” instead of their proposed type “Y.” After assigning full responsibility to the winning bidder, obtain their full concurrence. Remember: Small deviations combine to become major headaches. Ensuring reliability at the inception of the procurement cycle costs much less than being forced to make revisions a year after plant startup. HP

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