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Date: 28/10/2020
Around 60 percent of
the energy demand is for aeration of any wastewater treatment facility. This
aeration is provided by blowers, holding bacteria suspended and allowing solids
to be isolated from liquids, which is very important for proper handling of wastewater.
In sewage and
wastewater treatment, Blowers is an often underrated, but important piece of
equipment. Usually used to provide aeration and facilitate aerobic digestion in
activated sludge plants, they also retain solids suspended in channels and aerated
grit chambers, which are essential to the proper environment of treatment.
Turndown is the
ability of a blower to decrease the flow rate of air to satisfy demand. It's
crucial to know if your blower would be able to accommodate potential shifts in
air demand while selecting a blower. Investing in the right blower for your
wastewater disposal effectively lets the plant optimize productivity and reduce
electricity costs.
So, let’s look upon the types of
blower:
For several years, positive displacement blower (rotary lobe blower) style blowers have become the workhorse of the industry. They are very easy to operate; the flow varies with the Variable Frequency Drive.
PD blowers have
a very wide turndown range, usually about 25 percent, which is the capacity of
a blower to go from the design point to the minimum point. So if the blower has
a rating of 1000m3 / hr, it will usually transform down to roughly 250m3 / hr.
Compared to other
technologies, maintenance specifications are deemed to be mild for this sort of
blower.
Screw blowers are also
known as hybrid blowers and positive displacement blowers are typically used
for small to medium flows (rotating lobe blowers). Since they use a
low-pressure screw rotor, hybrid blowers are known as screw blowers.
Hybrid blowers can
reach rates as low as 25 percent of the initial design point in applications
with wide differences in flow and strain. Hybrid blowers have lower initial and
maintenance costs than centrifugal blowers for special applications, though
their costs are comparable to that of standard turbo blowers.
As the turbo impeller is attached to the shaft, turbo blowers have high levels of power, which makes it easier to reduce transmission losses. When running at or close to the design stage, they are most efficient, performing cost-effectively in applications with narrow turndown swings.
They use less energy
than rotary lobe blowers for applications with low variance in operating
conditions, despite higher initial costs.
Centrifugal Blowers
are mostly used for modest to high flows. Typically, traditional vane-style
blowers operate at a constant speed, but by limiting the inlet valve, you can
adjust the airflow.
When working in the
design range, they achieve their maximum performance. Since they are sturdy
devices that do not take up a lot of space, controls are important to protect
against surges.
The high initial
investment is required for centrifugal blowers and can require expensive
repair. They will, however, last longer with careful care than most blowers.
All blower
technologies have their benefits and can offer both performance and reliability
under the right operational conditions and deployment. The best practice blends
the expertise of a customer of the application with the expertise of the blower
technologies from the equipment manufacturer.
You can first start
with the device when choosing a blower for your particular application.
Determine the flow criteria for your system. Then look at strain, whether the
variance is constant or unpredictable and just how big it is.
You then have to look
at the circumstances of the site. For eg, the height, which influences the air
density. The fact is, there is no simple rule of thumb when it comes to
selecting a blower. Making the right selection requires looking at the bigger
picture and taking all variables into careful consideration.
When the choices
depending on the framework have been narrowed down, you should perform a a cost-benefit study that covers both the capital investment and the operational
factors. Consider regular and seasonal swings in oxygen usage, fouling and
aging of diffusers, airflow control and turndown capability, overall blower
performance and energy usage over time, working mode, blower attachments, and
set-up of the plant when making your decision.