Almost every manufactured product uses water somewhere in the production process. According to the U.S. Geological Survey (USGS), industrial water is used for fabricating, processing, washing, diluting, cooling or transporting products.
Some industries such as food, beverage, paper, refineries and chemicals use a substantial amount of water. According to the U.S. Bureau of Reclamation, 59 percent of U.S. water use is part of an industrial manufacturing process. At the same time, sustainability practices have come a long way over the last decade. Companies are doing more to reduce carbon emissions, save natural resources and keep the environment as clean as possible for future generations.
In light of these market forces, and to be as resourceful as possible, companies today are getting more creative about where the water they need comes from.
In some areas, industrial manufacturing companies such as paper mills are using river water to cool products during the manufacturing process. Depending on the season, river water may vary from 33°F (0.5°C) to nearly 80°F (26°C). These process applications require a heat exchanger that can efficiently utilize the river water to take their product to its desired temperature.
Considerations for Using River Water in the Process
Depending on the location, runoff, climate and soil conditions, river water varies in quality. Many factors should be considered when evaluating whether river water could be used for a manufacturing process. The primary and most important consideration, however, is location. Is there a water source large enough and near the facility that can be used in the production process? What kinds of pollutants are in the water? (Does it matter in the specific application?) Does the river have run-off concerns? Are there large changes in weather, including flooding concerns? Will there be any dam requirements and alterations?
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Treating Industrial Water
The uses of water for industry are abundant. At intake, the raw river water brought into an industrial processing plant often requires treatment to ensure that it meets quality requirements. On the other end, requirements must be met to ensure the proper disposal or reuse of the water. State laws require a Department of Natural Resources (DNR) review of municipal and industrial treatment plant construction plans as well as related monitoring systems and groundwater monitoring wells.
For instance, in a paper mill manufacturing process, the raw water is run through a raw water treatment system to help improve efficiency and process performance. During treatment, contaminants are removed, including solid debris, iron and bacteria. The main purpose of the water treatment is to ensure the protection of the plant process equipment. Hard water can damage units in the form of scaling, fouling and corrosion.
How a Heat Exchanger Aids in Critical Industrial Cooling Applications
Heat exchangers are one of the most vital and widely used pieces of process equipment found in sanitary and industrial plants. Regardless of industry, its production will likely involve some type of temperature regulation requiring a heat exchanger. While exchangers can be used for both heating and cooling, industrial plants most commonly use heat exchangers for cooling applications.
Cooling systems, like heat exchangers, are used to remove heat from processes or process equipment. The heat removed from the water then is used in other parts of the process or flushed out as wastewater. In a paper mill manufacturing process, for example, a heat exchanger could be used as a vapor condenser/flash steam condenser, vapor cooler, water cooler or product cooler.
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Main Types of Thermal Equipment Used in Wastewater Applications
In addition to process heat transfer, industrial heat exchangers serve myriad roles. They are used for the safe temperature regulation of machinery, chemicals, water, gases and other substances. In addition, it should be noted that — though outside the focus of this article — they are used in comfort air-conditioning systems and heating systems. And, they are used to capture and transfer steam or heat exhaust that is released as a byproduct of a process, so the steam or heat can be reused elsewhere. This process improves production efficiency, saving the plant time, resources and money.
Some of the main types of equipment found in wastewater applications include vapor-to-vapor, vapor-to-liquid or liquid-to-vapor equipment.
Vapor Cooler. For optimal heat recovery, cool river water can help pull heat from process vapors. This heat then can be used on another part of the production process, increasing efficiency and sustainability. This heat could be used for demineralized or deionized water service, just to name a few.
Vapor Condenser or Flash Steam Condenser. Many applications require partial separation of a vapor stream. This means that the cooling water will lower the vapor to a temperature cold enough to condense the unwanted component. This could be something as simple as hot humid air, with a goal to cool the air enough so that water may condense out of the stream. Other processes may create unwanted flash steam, which simply may need to be condensed and subcooled to allow for safe and proper disposal or recycling.
Water or Product Cooler. A simple but extremely valuable resource, cold river water can be used to cool process water or any product in a mill manufacturing process. As long as cooling requirements or conditions stay safely above freezing temperatures, water is more effective at cooling versus a glycol mix, possibly up to 15 percent more effective.
In a paper mill manufacturing process, some products may need conditioning or treatment upon completion. Plants may use the river water to control various temperatures associated with treating or spraying the product. The river water is used as a medium for cooling the spray.
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Material Selection and Other Thermal Design Features to Consider
With so many factors to consider when choosing a shell-and-tube heat exchanger, here are a few items to get you started.
Material Selection. From carbon steel to stainless steel, corrosion is going to be the main factor. Over time, there will be more corrosion on carbon versus stainless steel. Most often recommended is 304 stainless steel, though some choose to upgrade to 316L stainless steel for added corrosion resistance. In addition, thermal efficiency, cost, availability, cleanability and durability will all be factors to consider when selecting a material for your heat exchanger.
Machined vs. Fabricated Channels. Like material selection, channel selection depends on budget and cleaning requirements yet also accessibility and viscosity. For many sanitary applications, the machined channel may be a better option. Fabricated channels may be better in some industrial applications and offer more customization.
Straight-Tube vs. U-Tube Designs. This decision often depends on space and production requirements. For many wastewater solutions, a straight-tube design is more appropriate due to the ease of cleaning. In a straight-tube design, there are no bends, and the channels often are removable for easy access to the tubes. Because U-tubes only have one channel, they often are the more cost-effective option. Cleaning can prove more difficult in the bends of the tubes, however.
Velocity. Units are sized to create an ideal flow. To achieve turbulent flow, a minimum of 3 to 3.5 feet per second flow rate must be achieved, with an ideal flow rate of 5 to 8 feet per second. Achieving this turbulent flow will provide better heat transfer and efficiency while also reducing the risk of fouling or plugging in the unit.
Finish. Most non-sanitary applications will come with a standard, all-mill finish. For sanitary applications in the food, dairy and pharmaceutical industries, polished finishes will be required.
Expansion Joints. To allow for thermal expansion, many applications will require an expansion joint. For many smaller applications, a bellows expansion joint is a cost-effective option. For units larger than 18" in diameter, a flanged and flued expansion is more robust and allows for a high point vent and a low point drain to be installed.
In conclusion, as you continue to look for ways to save your plant money while also saving our planet’s valuable resources, it may be time to look at reusing the natural resources found in our rivers. For many applications and solutions, a shell-and-tube heat exchanger can meet the thermal requirements for the products and manufacturing processes. If you have not looked at a shell-and-tube heat exchanger lately, it may be time.