Water screens made from a variety of metals and alloys play an important function in stopping trash and debris from damaging pumps and different sensitive parts used in industrial cooling tower systems. Many kinds of industrial process plants depend on cooling towers to remove waste heat, including oil and gas refineries; chemical, fertilizer and plastics manufacturers; power plants and even paper mills.
Their cooling system pumps draw cool water at a consistent temperature and movement from a close by waterway or retention pond and direct it over a heat sink in the tower. As the water runs over the heat sink, the waste heat is siphoned off into the water, which evaporates into steam. Giant followers at the highest of the cooling tower pull the steam out into the air in order that the cooling process can continue. Any water that isn’t evaporated falls to the bottom of the cooling tower; then, it is returned to its source.
If system pumps turn out to be obstructed with debris and water flow is impeded, cooling tower temperatures rise and efficiency suffers. The system must eat even more energy to realize proper cooling levels, and premature equipment failure can result. Even worse, debris may damage a pump or plug a heat exchanger, resulting in a pricey shutdown while equipment is serviced.
Filters usually used in cooling tower systems include static water screens, trash racks and touring water screens. Three elements assist decide filter choice:
This article will take a closer look at each type.
Static Water Screens
The most commonly used filters in cooling towers are static water screens. They’re the best choice when debris accrues infrequently.
Ranging in dimension from two-by-three toes to 10-by-15 ft and even bigger, static screens are supplied by some manufacturers. The display specifications and steel mesh openings are determined by how a lot water is required to stream by way of to the cooling tower.
Utilizing two screens per water-circulation opening with the screens set about three feet apart is beneficial. Each display has a debris catch-basket at its base. Using two screens is necessary because when one display is pulled for upkeep, some trash will fall off its face and be reintroduced to the water system. The second display screen then catches that debris. Having screens installed in a series also permits plant personnel to wash the screens without shutting down any gear.
Though the frequency varies depending upon location and season, for best upkeep, static screens must be lifted from the water month-to-month. A crane raises the screens, and a hose or rake is used to scrub the metal floor.
Static screens usually are made from T304 stainless steel. For extra corrosive environments, T316SS usually is used. Stainless screens are durable and will final 20 to forty years if they’re mostly catching leaves and litter from a retention pond. When water is pumped from waterways where bigger debris is an element, the screens are topic to more extreme put on and may need to be refurbished each 4 to five years.
Different metallic options embody epoxy-coated or galvanized mild steel, which could be cheaper, but they will rust and deteriorate more shortly. It additionally is feasible to passivate T316SS screens in a citric acid bath. This course of makes use of the citric acid to dissolve the free iron on the floor of the stainless steel, leaving a floor layer rich in chromium, nickel and molybdenum. Passivation helps T316SS screens additional resist corrosion.
Many screens are made for alternative in present purposes. In producing static screens for each new and existing prospects, fabrication engineers first take a look at cooling system drawings and make hydrodynamic calculations to determine water stream. Typically, they then design for “full dam,the highest water pressure the system may presumably encounter. This situation represents the forces a display screen would see if it were to turn into totally plugged with debris so that no water is allowed by way of.
This worst-case state of affairs tells engineers how huge the static display screen structural members need to be and how far apart they should be spaced. To account for water stress, the members are positioned nearer together at the bottom and then moved farther apart as you advance up the screen. Variable spacing permits the display screen manufacturer to use the minimal quantity of material crucial, which lowers costs and improves water circulation. Lowering materials in the water stream lessens the drag force from the screens.
The engineer then produces a rough design that gauges the quantity of fabric wanted and estimates a venture value for the customer. Once an order is acquired, engineers create a model using CAD design software program. The drawing is distributed to the customer for final approval.
At some fabricators, production on the structural members begins by taking a flat sheet of steel, chopping it on a laser after which bending it on a press break. The members then are welded to kind the body. Customized-constructed members are really helpful over frames made with customary structural angles, eye beams and channels by some manufacturers. Also, customized-constructed members might provide financial savings that can be passed on to the customer.
Usually, customers will specify the opening size that’s desired in the mesh. Skilled screen design engineers can also have a look at pump manuals to find out the biggest-sized particle the sump can take in with out getting damaged. As soon as the opening dimension has been selected, the mesh is sheared to size and welded to the face of the frame. Some manufacturers have the ability to weave metal mesh in home. The opening sizes available are infinitely customizable, and the only option for the customer could be chosen.
Screens are transported by flatbeds and put in in existing methods. For new methods, anchor guides may must be mounted. If the guides have rusted out or been broken at a facility that is replacing current screens, new hardware may be required.
Trash racks are a variation of static screens and are designed for heavy-duty use. They are constructed with coarser filtration that is meant to catch bigger debris corresponding to logs and plenty of aquatic grass often discovered floating in energetic waterways.
Trash racks normally are constructed from welded zero.25thick flat bars relatively than woven wire mesh. This durable construction permits them to withstand the impression of a log coming down a river at high velocity throughout flood circumstances or different high stress conditions.
Traveling Water Screens
For plants trying to reduce manpower related to regular upkeep and cleaning, touring water screens present a low maintenance choice. The rotating screens function by motors with timing mechanisms for periodic cleaning.
As a result of they’re automated and self-cleaning, far less attention from plant personnel is required. Entry to energy and water strains, however, is required for his or her operation. While they’re extra efficient, the upfront material and manufacturing prices for touring screens are larger.