For a small community, Greenfield, Mo., was plagued with what appeared to be major inflow and infiltration (I&I) problems. The sewer pipes...
As you have read in previous articles, ozone is a gas made
from oxygen. One of the processes used to produce ozone is called corona
discharge (CD). The CD method is a combination of high voltage electricity and
air, dry air or oxygen in a given space.
The efficiency of the ozone generator (ozonator) is based on
the quality of the incoming feed gas.
Why Use Dry Air?
The feed gas can be air, dry air or oxygen. Air is the least
costly method. It produces the lowest concentration of ozone and could lead to
increased servicing. This is due to the combination of ozone and
moisture/humidity. When you combine a certain concentration of ozone with a
certain concentration of moisture, you can create a byproduct called nitric
acid. All parts from the ozonator out to the injection location should be resistant
to ozone and nitric acid.
Dry air can increase ozone production and reduce maintenance
compared to atmospheric/moist air. Air dryers typically remove all of the
humidity and moisture from the air prior to the ozonator. The measurement of
dryness is called the dew point. The proper range for it is -40° to
How Will I Know If I Need a Dryer?
If your manufacturer does not require you to use a dryer,
then here is the rule of thumb as to whether you should.
humidity in the area where the ozone unit is located is 30 percent or greater.
walls and/or floor where the equipment is located is damp/wet.
pipes and/or tanks sweat/drip from condensation.
ozone unit is located in a damp, dusty, dirty environment such as a well pit, pump
house, crawl space or anywhere there is "an enclosed dirt floor.
The formula to use to determine whether a dryer should be
Environmental Conditions + %Relative Humidity + Operational
Time = Dryer Use and Type
Here's another rule of thumb: If you can go two years
without service relating to moisture, then a dryer is not necessary. A dryer
always can be installed at a later date, providing the customer is made aware
of the option, choice and related service. Never put yourself in the position after
the sale and installation of "Oh, by the way, it looks like you need a
dryer." Being up front, honest and well-informed is far more important and
will reap the greatest reward.
Types of Air Dryers
The most common air dryer you will encounter is the desiccant
type. Desiccant dryers consist of a material that absorbs a certain amount of
moisture. Desiccant dryer material can be disposed of once saturated or
regenerated by heating the material to a set temperature. This heating process
causes the release of the accumulated moisture.
Automatically regenerative air dryers automatically
regenerate themselves. As with any filter, dryers have a set capacity, and your
supplier can recommend the correct device for your application. Dryer
capacities are indicated in terms of hours of operation between regeneration.
Oxygen concentrators are sophisticated air dryers that
separate the oxygen from the other gases in air. They then concentrate or
pressurize the oxygen in a storage tank from which oxygen may be drawn when
percent oxygen as the feed gas theoretically can increase the ozone production
by two to four times, though typical field results show an increase of less
than two times. Good for small-scale laboratory-type use.
cost is extremely high given the gas flow rate needed to properly oxidize a
given gpm water flow rate. They are complex in operation and could require a
high degree of maintenance (depending on the manufacturer).
Application--If a higher concentration of ozone is needed, use a larger
ozonator and air dryer rather than an oxygen concentrator. The ultimate costs
(initial purchase and maintenance) will be much lower.
Anhydrous dryer material. A very poor type of dryer is a
container filled with a material that turns to liquid when saturated with
moisture. This is very maintenance intensive and can be quite dangerous to your
ozone equipment if not changed often. This should never be used, even
How Do I Know the Air Dryer is Working?
All dryers should have an indicator (color beads or paper)
that will indicate whether the air from the dryer to the ozonator is indeed
dry. Blue indicates dry air (less than 10 percent relative humidity) and
pink/amber indicates moist. (A dryer without an indicator is like a car without
a gas gauge.) Humidity monitors (hygrometers) can be used, but they can be very
expensive and color beads or paper are less expensive alternatives.
Dryers Are Not Always Mandatory
Again, not all ozonators and moisture levels produce nitric
acid in concentrations that will cause damage. Not all ozonators suffer greatly
reduced ozone production when using atmospheric air rather than dry air.
There are some ozone generators on the market that are only
slightly affected by moisture. They are able to withstand moisture in the feed
air/gas for years without any detrimental affects. Others, however, can require constant cleaning, suffer
severe damage in a short time and produce insufficient amounts of ozone, which
will cause poor water treatment results. Talk to your supplier about the
"hows and whys" of dryer use related to their specific ozonators.