In many cases, manufacturing facilities provide a great opportunity for water efficiency and conservation. Depending on the industrial process, this sector usually contains the water utilities’ largest customers. The most common uses for water in manufacturing are cooling, process uses, cleaning, employee sanitation, and steam generation. All five of these water uses can be fraught with waste and inefficiencies. There is great water conservation potential for those who invest the time and effort to implement programs and efficiencies in this sector.
Most every manufacturing processes involves the use of energy, lots of it. There are four ways to handle this "waste heat." By far, the two best ways are (1) to modify existing processes so that energy is conserved and less waste heat is generated and (2) to find ways to capture the "waste heat" for uses in the manufacturing processes. An example of this is co-generation. Even with the best energy efficiency practices, cooling may still be needed. This cooling can be performed either with air or with water. Air cooling has been used for centuries, but it has its economic limits. Where water must be used, there are three ways to dissipate this waste heat, single-pass cooling, a recirculating cooling pond, or a cooling tower.
Water is often the most acceptable medium to transfer heat away from the machinery. It was once common to use single-pass cooling water, and simply dispose of the hot water into the sewer after a single pass through the machinery or equipment. This method is rarely used today because of rising water costs, regulations prohibiting single-pass cooling, and other options available for the reuse of cooling water. The other two are the use of a recirculating cooling pond or cooling tower. In these latter two cases, cooling water is pumped to a cooling pond or tower where evaporative techniques are employed to rid the waste heat and cool the water. The cooled water is then reused in the equipment cooling system or for some other beneficial use in the building or project. This is not to say there is no water loss and water waste because of this process; in fact, most cooling towers are notoriously inefficient in the use of water.
More detailed information on cooling tower efficiency can be found at the following link: Cooling Tower Introduction
There are many uses of water within any give manufacturing process. Each process is different, but many diverse manufacturing operations use water for either:
(1) cleaning and rinsing products, parts and vessels,
(2) transporting parts or ingredients,
(3) as a lubricant,
(4) as a solvent or reactant in a chemical reaction,
(5) forming a water seal to block out contact with air,
(6) pollution control, or
(7) inclusion in the product such as in beverage manufacturing.
When examining a manufacturing operation, it is important to take all water saving opportunities into consideration, including the use of water-efficient equipment as well as the use of water conserving practices.
There is a ranking of five water saving possibilities to look at in any manufacturing operation. This order starts at the simplest to that requiring larger changes. These include:
- Adjusting the flow of water;
- Modifying the equipment or installing water saving devices;
- Replacing existing equipment with more water-efficient equipment;
- Water treatment, recycling, and reuse and
- Changing to a waterless process.
Reuse and recycling of water produced within the facility is a promising option. Here the quantity and quality of discharge from each operation is examined to see if it would be possible to reuse that water in another process with or without additional treatment. The following simplified table illustrates this process. The use of reclaimed municipal water or water from another facility are other possibilities.
Steam Generation and Boilers
While some manufacturing processes use water to remove heat (as described above), other processes use water to generate steam needed in the manufacturing process. Steam boilers lose water as the steam escapes the system. This water loss can be minimized with heat exchangers to collect the condensate and return it to the boiler.
Boilers suffer the same water quality problems as cooling towers. As the water vapor (steam) escapes the system, the minerals in the water are left behind. These minerals are referred to as Total Dissolved Solids (TDS). If the TDS is not removed from the boiler water, a build-up of the minerals will collect on the inside of the boiler and pipes. This build-up is called “scale”. The accumulation of scale can greatly hamper the efficiency of the system and eventually cause catastrophic failure. To prevent scale, some of the boiler water must be periodically removed and replaced with fresh water; referred to as “blow-down”.
Blow-down water losses can be reduced by similar means as those used in the efficient operation of cooling towers; acidification of the water, side-stream filtration, magnetic pulse technology, and scale inhibitors. For more information on these treatments, use the following link: Cooling Tower Introduction
Sanitation, Irrigation, food Service and Housekeeping
As with any place where people gather, the processes of life continue. Manufacturing facilities all have restrooms, general areas must be cleaned, landscape watered, and in many cases food service is offered and even laundry facilities are required for uniforms and special clothing. Water efficiency in these areas is also important. This site contains water efficiency information on all of these operations.
Each manufacturing process is unique in its water use. A thorough audit of the water use is usually needed to assess: where the water is used; the water quality needs of each end use; and where the savings opportunities exist. Industrial processes are often complicated and sensitive to water quality. The facility engineers and management must be intimately familiar with and involved in the audit process to achieve a satisfactory plan for water use reduction.
The strategies of reduce, reuse, and recycle should be applied to all water uses. Water use reductions are often found in the ability to reuse the water several times before discharging it into the sewer system. Many manufacturing facilities are surrounded with irrigated landscape; much of the water used in manufacturing is suitable for irrigating the landscape, sometimes requiring only minimal treatment. Caution should be used if the water collects solvents or toxic chemicals during the manufacturing process; these pollutants can percolate into the groundwater when applied as part of irrigation water.
Water utilities have discovered the best water-related actions i for the manufacturing sector are working with the facility managers and engineers to provide a comprehensive survey of water use and water efficiency strategies. This cannot be accomplished in only a two hour site visit nor can it be performed by someone unfamiliar with manufacturing processes and techniquies of engineering analysis. Comprehensive audits within process industries require highly skilled, technically experienced individuals (preferably engineers) to perform the required water balance calculations, technical analyses of processes, and development of cost-effective strategies and plans for reducing water consumption. Anything less than that will only yield superficial results and less-than-optimum water savings. Furthermore, the utility must be dedicated to a long process of repeated site visits and meetings with engineers and management to prepare and implement a suitable water efficiency action plan for each participating facility.
Links to more information:
GE Water (2007) Solutions for Sustainable Water Savings - A Guide to Water Efficiency