The most advanced chemical-free circulating water treatment systems abroad

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Chemical-free mechanical treatment of cooling water — General Mills Chahassen Plant. Project objective: To reduce and/or eliminate the chemical treatment of cooling tower water in the plant’s refrigeration system, to decrease the release of chemicals into the environment, and to improve work safety by reducing the handling of hazardous substances. Project results: After installing a chemical-free circulating water treatment system in the refrigeration cooling tower system, the following results were obtained: ● Avoiding the use of toxic and harmful chemical treatment agents (biocides, algaecides, and corrosion inhibitors) in the refrigeration cooling tower system. ● The water consumption of evaporative cooling towers has been reduced by 40% (3,674,000 gallons per year), which has had an impact on the plant’s process water and domestic wastewater. ● Reduce the amount of softened water used in cooling towers, thereby reducing the amount of softener needed. ● Improve the working conditions for workers. ● The factory saves approximately $108,000 per year, as well as $35,000 in terms of one-time SAC (short-term average cost). ● As a result of this project, General Mills installed another 18 chemical-free water recycling systems in its other factories, thereby improving the environmental conditions in those areas of the United States. The payback period for the Chahassen plant project is less than one year. Detailed explanation of the background and issue confirmation: The plant of General Mills Inc. (GMI) in Chanhassen, Minnesota, is equipped with two evaporative condenser cooling tower systems used to cool the ammonia refrigerant required for food processing and storage. Water is recycled from the collection tank to the heat exchanger to remove heat from the refrigerant. The water is then sent to the cooling tower to remove the heat absorbed during the heat exchange process. In a cooling tower, water is sprayed onto wet plates to achieve maximum evaporation and cooling; air is also blown through the cooling tower to facilitate the cooling process. The cooled water is recycled and pumped back to the collection tank, where it circulates again. Add water to the collection tank to compensate for the loss of water caused by evaporation and the dilution of concentrated water with wastewater. Wastewater discharge refers to the water discharged into the sewer system when the concentration of scaling components in the water is too high. The water supply needs to be treated chemically in order to prevent scaling, corrosion, and biological fouling, which can reduce cooling efficiency. The plant has two cooling tower systems, consisting of four and five condensers respectively, to support two engine rooms, namely ER-1 and ER-2. For about 245 days each year, water is sprayed on the condenser tubes to cool the refrigerant. In 1995, Randy Jacobson, a factory refrigeration operator, initiated the project by raising issues regarding the handling of hazardous chemicals in his workplace and the local environment. During the decision-making process, the Chahassen plant also utilized external resources to gain further insight into the impacts of handling hazardous chemicals. Nanette Geroux, a senior engineer at the City Council’s Department of Environmental Services, Industrial Waste, and Pollution Control, helped the plant workers understand that residues of commonly used chemicals such as molybdates can cause problems for wastewater treatment plants (POTWS) in terms of the effective use of sludge. Ruth Marston, the agricultural chemistry advisor from the Minnesota Department of Agriculture and Agronomy and the Department of Plant Protection, along with Secretary Greg Buzicky and department head Rick Hansen, provided further explanations regarding the use of bactericides and algaecides in cooling tower/evaporative condenser systems. The primary principle of implementing Integrated Pest Management (IPM) is that pesticides should not be used unless the pest to be eliminated has been identified (algaecides and fungicides are both considered pesticides). In other words, before using pesticides, you have already identified and determined the problem, as well as all possible solutions. When it comes to controlling pests that you cannot detect, the “target pest” principle remains applicable before using pesticides. For microbial and bacterial \"pests\", the standard for \"chemical usage\" or \"active concentration\" is based on the number of colonies per colony-forming unit (CFU). “\"Active concentration\" refers to 100,000 to 125,000 colonies per CFU. Colonies at these concentrations can cause scaling in cooling towers and reduce cooling efficiency, so they must be addressed. One of the reasons why MDA has become a type of antimicrobial treatment agent is to reduce the amount of pesticides released into the environment during the chemical treatment of cooling towers and condensers, and thus minimize their entry into water systems. In addition, chemicals, bacterial inhalation, and skin contact in the working environment (chiller tower maintenance) can also cause safety issues. Project solution: Since the mid-1990s, the Chahassen plant has been seeking alternative methods for treating cooling water without using chemicals. We found several non-chemical methods on the market, but none of them were effective. During the search process, all our suppliers and contacts hoped that we would reduce the use of these chemicals. The goal of eliminating chemical treatment at the Chahassen plant coincided with that of Power Process, a representative of industrial product manufacturers; in 1998, Power Process’s technicians assisted the plant in achieving its goal of stopping the use of chlorinated organic compounds by the year 2000. At the end of 1999, A.W. Chesterton introduced a new, non-traditional cooling water treatment technology to the market through Power Process Company – a chemical-free circulating water treatment system. The manufacturer of this system believes that this technology can control scale, corrosion, and microbial activity in cooling water without the use of chemicals. Furthermore, the cooling water can operate at a higher concentration ratio, thereby reducing the need for make-up water and wastewater discharge. Other factory projects that utilize external assistance, including those under Minnesota’s technical assistance program, are already working toward the goal of reducing water usage in factories. Between 1999 and 2000, due to new strict measures taken to prevent allergen contamination from spreading from one product to another, the concentration factor of wastewater from line cleaning increased by about 6–7 times. Due to the addition of production line cleaning procedures that reduced allergen contamination, the factory’s new (SAC) service access fee for the period from April to June 2000 was $135,300. Therefore, any plan to reduce water consumption benefits this device, thereby further increasing interest in Power Process technology. A team composed of internal companies, external companies, and state resources evaluated this new technology. Project partners come from the following groups. Minnesota Office of Technical Assistance, Massachusetts OTA, Urban Environment Committee, Minnesota Public Utilities Commission, Industrial Waste Services Department, University of Minnesota Power, ERPI, Food Technology Center, Power Process, Exel Energy Company, Kriss Water Treatment Products Company, General Mills (GMI) and its plant staff, Service Environment and Engineering Company. By participating in Exel Energy Company’s customized efficiency and engineering assistance programs, Exel Energy Company became a partner in this collaborative effort. General Mills’ (GMI) projects include energy-efficient refrigeration upgrades and the installation of chemical-free closed-loop water treatment systems. The funding provided by Exil Energy enabled an external comparative study to demonstrate the capabilities of this technology. The commissioned research conducted comparative tests between a chemical-free circulating water treatment system and chemical-based treatment methods; it started on July 14, 2000, and ended on October 17, 2000. Test design: Chahassen Plant purchased a chemical-free circulating water treatment system with a processing capacity of 60 gpm (system units and separators), and installed this system on the sump of ER-1. A filtration system with a separate pump is connected to the other side of the collection tank to separate and remove sediments from the wastewater flow. The ER-1 system operates under the strictest testing conditions, including: 1. The make-up water is changed from softened water to tap water with higher hardness. 2. This test is conducted in the summer, when the load on the condenser is at its highest and the consumption of water and chemicals is greatest. 3. A large amount of scale had accumulated in the tube bundle of the condenser, and it was not cleaned at the start of the test. The components of the ER-1 chemical treatment system remain in their original positions (unused) to ensure continued cooling in the event that this technology fails to deliver its promised functions. The ER-2 system still uses softened water, primarily treated through a chemical treatment system, for comparison with the ER-1 system in the test design. At the beginning of the study, 30 cold-rolled steel plates and 30 galvanized plates were installed in each ER system respectively for corrosion and microbial analysis. Flow meters are installed on both the water supply pipes and the sewage pipes, with readings recorded weekly. Water samples are collected weekly and submitted to Shibichun Company for analysis. Additionally, it is necessary to regularly inspect the scale buildup on the collection tanks of the cooling tower system and on the condenser tubes. Summary of test results: Overall, these two treatment methods (chemical treatment and chemical-free recirculating water treatment system) demonstrated similar performance during the 92-day study, with the following results: Environmental impact: Scaling – No scaling was observed in either treatment system. It should be noted that the calcium content in the make-up water of ER-1 treated by the chemical-free water recycling system exceeds 200 ppm, existing in the form of CaCO3 (73 mg/L of calcium). In the chemically treated ER-2, the calcium content in the softening make-up water is below 20 ppm (1.0 mg/L of calcium). A chemical-free circulating water treatment system is used to make the water in the cooling system harder, eliminating the need for softened water. Weekly measurements of the wastewater show an average calcium content of 28 mg/L. This shows that calcium is continuously removed during the testing process. During the first month of this study, the chemical-free recirculating water treatment system not only prevented scaling but also effectively cleaned the existing system, removing an additional 350 pounds of sludge from the ER-1 system. The system also makes it easier to remove the remaining scale without using acid, which is usually required for scale removal. Algal/bacterial growth was observed visually, and no significant bacterial slime was found on the tube bundles. In October 2000, some bacterial discoloration was observed in ER-2 (chemical treatment). At the end of the study, due to a failure in the chemical feed pump in ER-2, the colony count on its slugs was extremely high, reaching 6,600,000 colonies per slug. Table 1 summarizes the data from the tests on other bacteria. In this study, ER-2 used two types of fungicides: one containing sodium hypochlorite, and the other a mixture of carbonates. During the study of these two systems, no significant algae growth was observed on the plates; however, in October 2000, green algae were found on the demister of the chemically treated ER-2. Table 1: Test results for bacterial slurry tests. Note: EC-1 (evaporative condenser) and EC-2 represent ER-1 and ER-2, respectively. Since the use of chemical-free circulating water treatment systems, microbial growth has been reduced, **improving the efficiency of the coil plates, as shown in the figure below. Figure 1 — Demister cover, with microbial fouling and scaling prior to the installation of a chemical-free water treatment system. Figure 2 — Demister plate, with no microbial fouling after being treated by a chemical circulating water treatment system for one and a half years. The test results for the corrosion coupons in the corrosion tests are shown in Table 2. No pits were found on the test specimens. For galvanized steel, the corrosion rate of ER-1 treated with chemical-free circulating water treatment is only about one-third that of ER-2 treated with chemicals. Overall, both treatment methods exhibit excellent corrosion inhibition properties, while the chemical-free water treatment system demonstrates the ability to suppress corrosion in water cooling systems and avoid the use of corrosion inhibitors. Table 2: Test results of corrosion coupons – Environmental impact. Table 3 summarizes the water replenishment amounts recorded for the two systems after standardization based on cooling tons. The data shows that after treatment with a chemical-free recirculating water treatment system, water replenishment was reduced by nearly 30%, resulting in approximately 1 million gallons less water usage over the 90-day study period. Thanks to the use of chemical-free water recycling technology, the number of water circulation cycles in the collection system has increased from 2 to 6, reducing wastewater discharge and thus minimizing the amount of water that needs to be replenished. Since the chemical-free circulating water treatment system was installed in the two cooling systems, the annual water consumption has been reduced by approximately 3,674,000 gallons. Table 3: Water replenishment volume after normalization by tonnage. Note: EC-1 (evaporative condenser) and EC-2 represent ER-1 and ER-2, respectively. The power consumption evaporation rate is calculated based on water replenishment and wastewater discharge data, indicating that ER-1 has a slightly higher evaporation rate. A higher evaporation rate is the result of faster heat transfer between the condenser tubes, which improves the performance of the cooling system and reduces energy consumption. The energy efficiency of ER-1 increased by 10%, resulting in a reduction of 1.8 million kWh in annual electricity consumption. According to Exil Energy’s calculations, the corresponding emissions are as follows: ● Sulfur dioxide: 6,200 pounds ● Nitrous oxide: 5,900 pounds ● Particulates: 400 pounds ● Carbon dioxide: 2,445,000 pounds The table below summarizes the chemicals used by the two treatment systems during the 90-day testing period. Table 1 — Total gallons of chemicals used in refrigeration systems. Chemicals: None. Chemicals for water treatment in circulation systems (gallons): Conventional system (gallons); Conventional system (pounds). Scale and corrosion inhibitors containing sodium hydroxide: 0, 720, 6155. Biocides containing ethylene diamine carbamate and sodium diethyldithiocarbamate: 0, 21, 207. Biocides containing sodium hypochlorite: 0, 174, 31. Avoiding the use of these chemicals **reduces regulatory requirements. Due to the installation of a chemical-free circulating water treatment system in the cooling tower systems of the two refrigeration chambers, the actual reduction in chemical usage at the Chahassen plant each year is as follows: ● 620 gallons of chlorine solution ● 1,900 gallons of sulfuric acid and sodium molybdate solution ● 3,694 gallons of sodium hydroxide and sodium molybdate solution ● 330 gallons of biological and microbial disinfectants. Economic benefits: Studies have shown that a chemical-free circulating water treatment system can effectively control problems related to cooling water without the need for chemicals. During the study period, despite the use of hard water as make-up water, no scaling or biofouling was found in the condenser tubes of the ER-1 system treated by the chemical-free water recycling system. The corrosion rate for carbon steel and galvanized steel also remains at a very low level. Since switching to a chemical-free recirculating water treatment system, the Chahassen plant has saved the following amount each year: reduced chemical usage of $68,000, lower costs for water/wastewater treatment of $13,500, estimated savings on electricity usage of $12,000, and savings on water softeners of $7,300. The total annual savings amount to $108,000. There is also a one-time cost saving of $35,000 related to wastewater treatment. The system brings the following intangible economic benefits: ● Maintaining positive employee relations, enabling employees to identify and help resolve issues in the work environment. ● Significantly reduce chemicals released into the environment. ● Improve the working environment for employees by reducing the handling of hazardous chemicals. ● Reduce the risk of chemical leaks. Note: Another 18 units have been installed in the chemical-free circulating water treatment systems at other GMI plants, allowing the above test results to be applied to other areas and working environments of **. The company’s commitment and leadership in environmental protection projects: This project is just one aspect of General Mills’ and its Chahassen plant’s overall commitment to preventing pollution and reducing waste. The company’s commitments include formulating strategies, values, motivation goals, and performance evaluations. General Mills has established the following strategies for safety and environmental protection: “General Mills’ strategy is to manage its business in a way that promotes workplace safety and protects the environment.” The Chahassen plant has developed a hierarchy for waste minimization as well as strategies to prevent transfer across media (preventing problems from arising vs. transferring problems from one waste area to another). General Mills has established the following values: ● Pollution and leaks are preventable. ● Nothing we do should damage the environment. ● Everyone has a responsibility to protect the environment. To implement this policy and uphold its established values, General Mills has set environmental standards that include requirements for continuous improvement, in order to minimize waste and emissions from its facilities and reduce transfers across different media as much as possible. Based on these standards, each factory sets goals to meet them. Since its establishment, the projects and goals achieved by Hasen Factory are as follows: ● By using a bulk transportation system, 620 tons of packaging waste are reduced each year. ● 90-95% is recovered from total solid waste each year. ● Remove liquid chlorinated organic compounds weighing over 20 pounds, CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbons), asbestos-containing materials, hazardous fluorescent lamps and bulbs, as well as light ballasts containing PCBs (polychlorinated biphenyls). Employees handle pesticides. Track performance and goals, and establish environmental protection incentives for hourly workers at all levels within the organization. General Mills provides planning, training sessions, and support to implement these policies. This project originated from these regular meetings. In terms of innovation: This project is innovative for the following reasons: 1. It addresses employees’ desire to reduce exposure to harmful chemicals and pesticides. 2. This project is aimed at an operational area (factory refrigeration and cooling towers), rather than a demonstration area for improving the environment or saving costs. 3. The project utilized a team composed of professionals from the business, **, utility, and academic sectors to conduct comprehensive testing without disrupting the operation of the power plant. The team took advantage of the diverse perspectives from chemical suppliers, environmental organizations, infrastructure providers, and academia to identify the advantages and disadvantages of this test, which will help to develop a more comprehensive test design. 4. This project identified and validated a new chemical-free mechanical treatment technique for cooling tower water, thereby improving the operational efficiency of the cooling tower system, reducing the need for factory workers to handle hazardous substances, decreasing the amount of water used in the factory (both intake water and wastewater), lowering energy consumption, and minimizing the environmental impact of chemical waste. Model role: This project has become a new Best Available Technology (BAT) for General Mills. When a system is defined as BAT, it becomes the standard for all General Mills plants. To date, General Mills has installed 18 chemical-free mechanical processing systems in its plants, which are in operation there. Purchase orders for another 4 systems are also being processed. General Mills (Dotti Shay) and Service Environment and Engineering Company (Hubert Huls) used Minnesota’s technical assistance program to present the results of this research at a seminar on test results held by the Minnesota Pollution Control Agency. This sparked discussions within the state, leading the Massachusetts Office of Technical Assistance to publish a \"Technical Summary Report on Strategic Environmental Cooperation\" as part of the U.S. Department of Energy’s Green Book. This has resulted in General Mills receiving inquiries almost daily, from within and outside the company, asking for detailed information about this system. According to economic analysis, all cooling towers with a capacity of over 500 tons can benefit from this chemical-free technology, whether they are used in manufacturing plants, office buildings, or other applications. According to data from the Cooling Tower Institute, there are 750,000 cooling towers on the U.S. mainland, of which about 250,000 have a capacity of over 1,000 tons. Based on the data from these states, alone Minnesota has 20,000 to 30,000 cooling towers weighing over 500 tons. Based on the research and calculations conducted by GMI (General Mills), the average chemical cost is $12 per ton of refrigeration per year. With 25,000 units capable of handling 500 tons each, Minnesota can achieve the following positive environmental benefits: ● A reduction of $30 million in costs related to the purchase, use, and emission of chemicals each year. ●3.5 billion gallons of water are saved each year. ●1.7 billion kWh of energy is saved each year, along with a reduction in related toxic and greenhouse gas emissions. General Mills found that this technology is cost-effective in various regions with different costs for wastewater, water, and energy. Another 18 chemical-free water recycling systems installed across the country prove this point. Furthermore, in factories located in states that have fewer water resources than Minnesota, these scarce resources can be conserved for other uses, while maintaining and improving their production efficiency.