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Analysis of cooling and water-saving measures for laminated glass autoclave.

1. The introduction

The current manufacturing industry is facing various cost pressures. Enterprises are paying more and more attention to cost control and strengthening control from all aspects to reduce costs. The recycling economy is developing continuously, and environmental protection requirements are becoming more and more popular. Reducing resource waste and using limited resources to maximize efficiency are not only the needs of enterprise cost control but also the social responsibility of enterprises. Industrial water should adopt advanced technology, processes, and equipment to increase the reuse rate of high water in circulating pumps. Production enterprises using water as raw materials should adopt water-saving production processes and technologies to reduce losses. Cooling water should be recycled, and the recycling rate should meet the national water-saving city standards according to the requirements of urban water-saving professional planning. Laminated glass is widely used in the construction industry and security industry due to its special product performance. In the production process of laminated glass, high-temperature, and high-pressure cooling water is a process with a large amount of water in deep processing enterprises, and cooling water does not produce other pollution. It can be recycled multiple times to save water. Taking measures to increase the reuse rate of cooling water is an important measure to save water, which has significant economic and environmental significance.

2. Overview of the laminated glass production process

Laminated glass is made of two or more pieces of glass, bonded with PVB film as the intermediate material. PVB film has excellent adhesion and light transmittance so that laminated glass can still be completely bonded with the film without falling off after being broken, making it a glass product with better safety performance. There are two main production processes for laminated glass: dry interlayer and wet interlayer. Usually, laminated glass is mainly made by dry production process. The production process of dry laminated glass is glass-washing-combining-initial pressing-heating and pressure-insulating-cooling and pressure-finished product. Laminated glass made by dry process has good resistance and adhesion and can meet the product use requirements of various safety needs. It is the preferred glass product for buildings, automobiles, museums, banks, and security needs.

3. Analysis of water use for cooling autoclave

After the laminated glass is initially pressed by the root press, a large amount of air remains between the glass and the film. It needs to be removed by high temperature and high pressure to obtain a finished product with better light transmittance. During the high temperature and high-pressure process, the temperature in the autoclave rises to about 1353℃ and the pressure rises to about 1.2MPa. At this temperature and pressure, the temperature is kept at about 5 minutes, and then the temperature in the autoclave is reduced to below 45℃, the pressure is released, and the autoclave door is opened to complete the autoclave operation process and obtain the finished laminated glass. In this process, the closed autoclave is cooled down after the high temperature and high pressure are completed. Water cooling is currently the fastest and most effective way. The cooling of the autoclave needs to follow the corresponding process requirements to control the cooling speed. Generally, tap water at room temperature is used for cooling. According to the length and flow of the water pipes distributed in the autoclave, the cooling time is different. The entire autoclave high-pressure process is about 4 to 8 hours, of which about 50% of the time is used for cooling. The cooling process of about 3 hours uses a large amount of water. For example, for a 40m3 autoclave, the water flow rate for cooling a conventional autoclave is about 12 m3/h, that is, 12 m3 of water is needed per hour. If the cooling time is 3h, 36m3 of water is needed. Some autoclaves have a cooling time of more than 3 hours, and the water consumption is even greater. If the autoclave glass is calculated, it will consume about 1000 m3 of water per month. If one-time water cooling is adopted, the cooling water consumption is high, which not only increases the water cost of the enterprise but also forms a waste of water resources. Moreover, the cooling water used for cooling only increases the temperature and does not produce other pollution. Measures can be taken to cool it down and then recycle it. It is also feasible to use it for other purposes in glass production. Realizing the recycling of water and reducing water consumption can reduce the production cost of the enterprise on the one hand, and it is also conducive to reducing pollution emissions and meeting the requirements of energy conservation and environmental protection. Many enterprises have taken water-saving measures to control water consumption, but how to operate and which method is most economical and applicable varies according to actual conditions.

4. Introduction to water-saving measures for autoclaves

The cooling time of autoclaves is relatively long. During the cooling process, water needs to be continuously supplied to the cooling pipes in the autoclave. After circulating through the cooling pipes, the cooling is completed. The water temperature rises. At this time, the water with increased temperature is no longer suitable for entering the cooling pipes. Instead, it is necessary to supply normal-temperature water or circulating water after cooling to accelerate cooling by increasing the temperature difference until the temperature in the autoclave drops to about 45°C. The measures taken to save water are centered around how to collect and cool the water before entering the cooling pipe system in the autoclave, etc., to achieve recycling and reuse. In the actual production process, according to the characteristics and actual situation of interlayer production, the following different recycling methods can be adopted.

4.1 Process Layout Considerations

The main processes involving water use in glass processing enterprises are glass edge grinding and washing, interlayer and insulated. Low-E glass and some special glass have high requirements for water quality. Deionized water must be used for production, and it is not suitable for circulating water. However, it is feasible to use circulating water for conventional glass products in the edge grinding process. The use of cooling water for interlayer autoclaves in these processes can meet the production process requirements. When planning the equipment process layout, the recycling of water in the above three water-using processes is considered, and a comprehensive and reasonable layout is made, so that the water that is no longer suitable for high-pressure cooling after high-pressure cooling or after multiple cycles can be used for other production processes, achieving the best recycling purpose and improving water utilization.

4.2 Water tower cooling

Usually, the cooling water of the sandwich autoclave can be collected by building a pool or using a water tank with a large enough capacity. There is no fixed requirement for the size of the pool or water tank, but the volume should generally be greater than 30m3 to achieve water collection, sufficient cooling, and recycling. As for the pool, a pool can be set up, or the pool can be segmented, and a cooling tower can be installed above or on the side of the pool. The hot water from the autoclave cooling pipe enters the pool after cooling and then enters the autoclave cooling pipe to cool the autoclave, ensuring that the water temperature entering the autoclave reaches or is close to normal temperature as much as possible. Water tower cooling can well ensure that the water temperature is reduced, and it is the most suitable cooling method. The cooling water tower has a low capital investment and can achieve water cooling in a relatively economical way to achieve the temperature requirements of circulating into the cooling pipe.

The location of the pool can be built indoors or outdoors according to the site conditions and climatic factors. Some companies even build the pool directly under the autoclave, without any site occupation and waste.

4.4 Timely cooling and cooling system scale

The cooling water pipe in the autoclave is of fixed length and diameter. During the long-term production process, because the water contains a certain amount of calcium ions, it constantly enters the pipe to dissipate heat, and the heated water will accelerate the scaling of the pipe. We know that scaling of the pipeline will cause pipeline blockage, resulting in a decrease in the amount of water entering the kettle, increasing the cooling time and affecting the cooling effect; on the other hand, the accumulation of a large amount of scale is equivalent to increasing the wall thickness of the water pipe. The heat absorbed by the cold water entering the pipeline system in the kettle is reduced, and the cooling effect will be greatly reduced. LIJIANG Glass laminated glass autoclave has had such a situation. When the autoclave was first put into production, the cooling time was about 3 hours, but as the scale in the pipe continued to thicken, the cooling time was delayed to more than 5 hours, which seriously affected the production efficiency of the autoclave. Therefore, effectively avoiding scaling the cooling pipeline and cleaning the scale in time can reduce the production time-consuming problem caused by scaling the equipment pipeline, which is also a disguised measure to save water. To prevent scaling, softened water can be used to cool the autoclave to reduce the scaling caused by calcium ions entering the cooling pipe, but the cost of water treatment is high; it can also be used for some time to ask professional cleaning personnel to clean the pipeline. The main method used for cleaning the pipeline is a chemical method with dilute hydrochloric acid as the main medium. This cleaning method will cause certain damage to the wall of the cooling system, but it can effectively dredge the pipeline, eliminate scaling, and meet the cooling water flow requirements.

4.5 Use cooling water from the autoclave for other production processes

During the cooling process, the cooling water of the autoclave only increases in water temperature, and no other pollution is generated. In addition to taking measures to cool down and recycle the water, the water in the Tai-end shield ring and the water that stays in the collection pool for a long time will inevitably reduce the cleanliness of the water due to factors such as dust and is no longer suitable for cooling the autoclave. Such water can be used in other processes through pre-set water pipes to achieve full recycling of water.

5. Conclusion

Through some simple technical transformations, the economic investment is not large, but the water-saving measures adopted can realize the recycling of autoclave cooling water, which can be used in the grinding and washing process with low production water requirements, and realize the repeated use of water resources, which greatly improves the reuse rate of production water and reduces water consumption. Some measures also play a role in reducing production time. From the perspective of reducing production costs, this is an effective and reasonable measure, and it also has significant energy-saving and environmental protection significance from the perspective of energy saving and emission reduction. Fortunately, some laminated glass equipment manufacturers have also paid attention to the problem of water consumption in autoclave cooling. From the perspective of glass production enterprises, when enterprises order laminated production equipment, they will recommend and provide cooling towers for enterprises to achieve cooling water recycling. From the beginning, they have assisted enterprises in solving the problem of water waste, which is relatively convenient and beneficial for glass production enterprises.

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