Florida Wildfires "Fan" Demand for New Water Production Facilities
An article by Mark Mullin, Markair, Inc.

Voluntary water rationing is almost a way of life in Florida. During hot summer months, watering lawns and washing cars are restricted to minimize peak demands on municipal water plants.
When last years drought conditions spawned several large forest fires, water rationing became mandatory. At one point, almost every county in Florida was on fire and thousands of residents were evacuated from their homes. These devastating wildfires magnified the need for newer and larger water production facilities.

The gases and chemicals present in water and wastewater treatment facilities cause corrosion, equipment failures, plant shutdowns, and increased maintenance and operation costs. In some applications, these corrosive gases cause odor complaints, unsafe working conditions, and can even be explosive. Chlorine, methane and hydrogen sulfide are lethal gases typical to these industrial facilities. The air handling systems and equipment used in these installations must be designed for each specific application. Standard commercial grade HVAC equipment is not suitable for these types of corrosive environments.

Aerovent equipment has been the basis of design for the City of Jacksonville's water and wastewater treatment facilities for over ten years. Each fan is custom built to a set of specifications designed for a specific application. For instance, Aerovent's fiberglass axial "TF" fans (shown right) are used for forced draft aeration and dilution ventilation for Jacksonville's ground water reservoirs. A two million gallon reservoir has six 43" TF fans exhausting a total of 120,000 CFM. The TF fans are sized to exhaust one air change per minute, based on the average high and low water levels inside the tanks. Fresh air is drawn through the screened aerators and overflow vents. The large volumes of fresh air mix with the aeration process to dilute and substantially reduce overall levels of corrosive gases. The fans are staggered to distribute the air and eliminate condensation and corrosion on the interior tank surfaces.

The Brierwood WTP currently under construction has five reservoirs utilizing 20 Aerovent 43" TF fans. Other completed projects include the Mayo Clinic WTP (6 fans), the Community Hall WTP (6 fans), and the Julington Creek WTP (6 fans).

These municipal water production facilities are required to pass a variety of tests and inspections prior to receiving an operating permit. Insects carry disease and are considered a health hazard. The tank vent fans are inspected by the Department of Health for "insect-proof construction". Fan curb bases and exhaust dampers are specified with "continuous, insect-proof neoprene gaskets mechanically fastened with 316 stainless steel hardware." Adhesives are not acceptable because the gaskets of some manufacturers have come off and fallen into the tanks. Improper gaskets will delay the plant operating permit until approved by the Department of health and accepted by the owner. Aerovent has designed and furnished a special gasket arrangement to meet these requirements. (See picture above)

Rust is also a health hazard on a water production facility. The specifications call for all-fiberglass construction with 316 stainless steel shaft, motor pedestal, motor slide base, lube lines and hardware, inside and out. Coated or encapsulated steel is not acceptable.

Aerovent's fiberglass fans are molded, and the structural integrity is achieved through extra thickness. (See photo above.) The one-piece, Solid FRP propeller is straight bored and keyed to a stepped 316 stainless steel shaft. (See photo below.)

Figure 2 (below) shows two Type 316 stainless steel collar washers (A) and a 316 stainless steel bolt threaded into the end of the shaft to secure the propeller (B). The construction facilitates easy propeller removal for access to shaft seals and fan bearings. The shaft seals shown in figure 3 isolate the bearings from the corrosive exhaust air and maintain "insect-proof" construction.

Commercial grade products coat carbon steel with fiberglass to build strength and lower manufacturing costs. Propellers typically have carbon steel hubs coated with fiberglass and are secured to carbon steel fan shafts with taper-lock carbon steel bushings. The top of the bushing is resin and gel coated prior to shipping. To access the shaft seal and bearings, the resin coating must be cut off. Many times a wheel puller is required to pull the hub away from the shaft. The fiberglass becomes cracked, the fan balance is affected, and the corrosion resistant integrity is lost.

316 stainless steel motor bases are mounted between two integral FRP fan flanges to form a rigid structure. The fan motors are positioned and mounted for alignment of sheaves and belts. Belts are tensioned by loosening four bolts in the slotted stainless steel bases. On larger horsepower motors (or where specified by the owner) 316 stainless steel NEMA motor slide bases are furnished to facilitate easy belt tensioning and replacement. FRP weather enclosures are furnished to cover the motors. (See photo above.)

Commercial manufacturers encapsulate a carbon steel plate and cantilever a painted carbon steel motor base on four jack bolts. Belt tensioning and alignment problems occur frequently with this arrangement. Over a period of time, the weight of the motor, the lever-type force applied from tensioning the belts, and the vibration from the rotating motor and propeller cause the fiberglass and steel plate to separate. The painted steel motor bases and standard painted steel motor covers rust quickly. The rust streaks the tanks and can be seen easily from a distance.

Bearing lubrication lines and grease fittings typically furnished in copper, brass and bronze are attacked by chlorine. Lube lines and fittings on the specified Aerovent fans are all 316 stainless steel.
The color of the fans is matched to the building color. This is done by pigmenting the fiberglass resin and has an advantage over a painted surface: the coloration can not chip or loosen from the surface, discoloring the fan.

FRP curb bases must be anchored to poured-in-place concrete curbs through the side to eliminate leaking. A minimum 4" overlap is specified to keep anchors from cracking the edges of the concrete surfaces. Fan bases are curved to reduce pressure losses and corrosion due to fan inlet velocities. Flanges are turned out so that bolted fan connections are weatherproof and out of the airstream. (See photo below.)

These fans run 24 hours per day, 365 days per year. One 20,000 CFM fan handles 1080 tons of corrosive air each day. Fan shafts are 316 stainless steel, and bearings are oversized to provide extended operating life. The large 34' pitched, seven-bladed FRP propellers provide quiet and stable performance as water levels change and inlet screens become dirty. The vertical upblast design discharges air at high velocities into the wind to become further diluted.

Markair's engineering and industrial quality product selection abilities have made them the best solution in solving the most difficult and demanding ventilation problems presented by water and wastewater facilities.

If you require similar information for your specific industry or application, please contact us!