Reduce Cooling Tower Water Consumption by 20
Percent
By Sam R. Owens
Water conservation and environmentally friendly technologies are becoming more important,
especially in areas where access to water is expensive or restricted. This is especially important
in the water-intensive ethanol industry, where 3.63 gallons of water are used to create each
gallon of ethanol.
Of an ethanol plant's total utility water, approximately 90 percent is used as cooling water, and a
plant's discharge effluent primarily consists of cooling water blowdown. New water conservation
technologies can reduce the amount of water required to produce ethanol to 2.9 gallons per
gallon of ethanol—a 20 percent savings in water usage.
Table 1. A cost comparison for cooling tower system using HiCycler in 2004 compared with a
conventional treatment used in 2003. Source: Customer utility bills for the calendar years 2003
to 2004.
A typical cooling tower using hard make-up water commonly operates at five cycles of
concentration. Approximately 750,000 gallons of water are evaporated for every 1 million
gallons of make up water. Blowdown is responsible for 250,000 gallons of evaporation.
Cooling tower evaporation results in leftover solids, which are typically removed by releasing
the concentrated hard water commonly called blowdown. This wastewater creates a cost when
purchased as make up water, including and the typical treatment fee for discharge. Therefore,
conserving the wastewater provides a significant monetary savings to the ethanol producer.
A 20 percent reduction in the consumption of cooling water is possible through a patented water
conservation technology. HiCycler is a side-stream hardness and silica removal process that
reduces blowdown by 95 percent in an environmentally friendly way. The process gets its name
from the higher cycles of concentration achieved using the method of water treatment.
The system's operation is significantly different than traditional systems. The process works
especially well in high-hardness, open-circulation water systems. Hardness is dissolved in an
organic solvent where the solubility is higher than conventional treatments.
The main components of the system are a reactor and two solutions. The first solution uses
chemicals necessary to form organic compounds with calcium, magnesium and some forms of
phosphorous. The solution reacts with existing scale deposits and hardness within the make up
water. It also contains corrosion inhibitors for multi-metal systems. The solution is added at the
reactor outlet, which provides ample time for the product to be thoroughly mixed with the water
prior to entering the cooling water system.
A second solution consisting of another blend of chemicals is then applied to precipitate the
hardness. The solution initiates cross-linking and makes the precipitate heavy enough to settle at
the bottom of the reactor. The second solution is added inside the reactor to cause the hardness to
be absorbed on a fluid bed. The contact time in the reactor determines the density and viscosity
of the material to be released as blowdown.
The fluid bed is an organic, semi-viscous liquid blown down from the reaction chamber. It can
be used in wastewater treatment facilities to improve operating stability and productivity. It
forms from hardness and airborne and is collected at the bottom of the reactor.
The reactor itself is typically sized to process 0.3 percent of the water recirculated through the
cooling system. A portion of the solids collected in the bottom of the reactor are blown down as
a part of the fluid bed. However, a quantity of the fluid bed is maintained in the reactor to help
drive the reactions. Partially softened water from the reactor is returned to the cooling tower for
reuse.
The solubility of hardness in the system water is greater at higher temperatures. Solubility of the
organic hardness compound is approximately 45 percent at 25 degrees Celsius (77 degrees
Fahrenheit) and 47 percent at 30 degrees Celsius (86 degrees Fahrenheit). Deposits from drift
loss are more water soluble than from conventional treatments, which is beneficial when
equipment or buildings are located downwind of the cooling tower. In fact, zero blowdown can
be achieved by using one or more flocculants and a bag-type filter to remove water from the
reactor solids. The filtered water would then be returned to the cooling system and the solids
disposed.
Controlling the new treatment method is also fundamentally different than conventional cooling
water systems. Figure 1 illustrates a typical equipment set up. The system is controlled with two
pH sensors, two hardness sensors and a flow meter. Conductivity is not normally used.
Figure 1. The typical Hicycler process
This unique control package is monitored by a technician from a remote location, where sensors
are adjusted or calibrated as required. Conventional cooling water systems rely on chemical tests,
typically titration, to monitor and control the water systems. Chemical testing also requires an
on-site technician.
This system relies mainly on remote monitoring and some visual on-site inspections, allowing
pumps and controllers to be adjusted as needed. Remote monitoring systems can be used to
quickly recalibrate sensors, adjust equipment and display alarms when on-site attention is
needed.
The two-part conservation chemistry offers a unique method to treat open circulation cooling
water. It's a green technology providing significant water conservation. It also results in cleaner
heat transfer surfaces. Finally, the process reduces water system corrosiveness along with the
scaling potential of calcium, magnesium and silica. The economics are justified by the
significant reduction in the quantity and costs of the make up and wastewater.
Sam R. Owens is president and founder of Chemico International Inc. Chemico is a sales and
service company specializing in safe, effective industrial water treatment products for cooling
towers, boilers and closed-loop systems. He is a member of AWT, NACE and the Association of
Water Technologies, the National Association of Corrosion Engineers and the American Institute
of Chemists. He can be reached at [email protected] or (800) 272-4997.
The claims and statements made in this article belong exclusively to the author(s) and do not
necessarily reflect the views of Ethanol Producer Magazine or its advertisers. All questions
pertaining to this article should be directed to the author(s).