A large Midwest pharmaceutical plant for animal vaccines and medications caters to cattle, swine, equine and companion animals such as cats and dogs. Highly sophisticated processes are utilized to produce pharmaceuticals, and cooling is a very important component of these processes. In-plant cooling means cooling towers, and the twin-cell cooling tower at this site acts as a wet air scrubber trying to clean the atmosphere of the entire agricultural community.
Plant engineers soon discovered that the small 400-gpm side-stream four-bag filtration system on their 5,300-gpm cooling tower system did not provide the protection they needed for heat exchangers, condensers and vessel cooling jackets scattered throughout their facility in addition to an 800-ton chiller. Plus, changing the bags based on a differential pressure alarm was labor-intensive and not always attended to in a timely manner.
Their Capital Projects Engineering Department began looking for a full-stream filtration system to filter the entire 5,300-gpm flow with 40- to 50-psi operating pressure down to 100 microns. Space on the outdoor concrete pad was very limited. To make matters worse, the concrete pad’s surface was partially flat and partially inclined. Two pumps moved water from the cooling tower basin up to an 18-inch header located about 7 feet above the concrete pad. A third pump was to be added when the filtration system was installed to provide a backup.
Designing a Solution
When designing mechanical filtration equipment, one must provide adequate hydraulic capacity. However, a bigger design criterion is sufficient screen area to handle water-quality conditions. As at most Midwest settings, insects, sand, leaves, dust, pollen, cottonwood seeds and algae – as well as man-made debris such as paper, cups and grass clippings – influence the water quality greatly. The filter flux, defined as the flow rate per unit area of screen media (gpm/square inch of usable screen surface), must be of appropriate value to meet the specific conditions of filtration degree, TSS loading and type of solids. A filter model with small footprint and large screen area was chosen to meet the specific demands of this application. Five ORIVAL Model ORG-080-LS automatic self-cleaning filters were mounted on a 16-inch manifold that included a blind flange so that a sixth filter could be added at a later date should it become necessary (Figure 1).
A 16-inch pneumatically actuated bypass valve was incorporated into the manifold system to be opened automatically should the filtration system controller sense a fault in the filtration process. The controller also has a set of dry contacts for connecting an alarm system for fault situations. An 8-inch manual butterfly valve was located at each filter inlet and outlet to allow the isolation of any individual filter for maintenance or repairs.
Normally, the hydraulic piston used to move the self-cleaning mechanism (dirt collector) linearly inside each filter and the rinse valve are operated by the water and pressure in the system. However, these filters would possibly operate during the winter months when freezing would be a problem. Therefore, available industrial pressurized air is used to pneumatically operate the pistons and rinse valves. Cleaning cycles automatically occur when a 7-psi pressure differential develops across the inlet and outlet manifolds or when a preset timer lapses. Filter No. 1 goes through its 15-second cleaning cycle and then Filter No. 2 and so on sequentially until all five filters have cleaned themselves. Each filter remains online at all times with no disruption of the filtration process.
A design/build firm installed the filtration system about 12 feet above ground level on a mezzanine built on-site (Figure 2). This overcame the uneven concrete pad problem and put the filters in line with the piping entrance to the building. Each filter is equipped with a liquid-filled pressure gauge and a three-way selector valve. This allows the inlet pressure, outlet pressure and rinse chamber pressure to be conveniently observed with one gauge on each filter unit, eliminating variations between gauges. Using these pressures allows one to run a number of diagnostics on each filter.
After three years of operation, the cooling tower was expanded and flow rate increased. A sixth ORIVAL filter unit was added to the system to increase filtration capacity. Prudent use of appropriate chemical additives, routine blow-down and proper filtration has resulted in exemplary performance with no maintenance issues or process interruptions for over six years.
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