Speaking of wastewater cooling, many people may not pay much attention to it, but it is a crucial task in factories. Think about it, a lot of wastewater discharged during the production process has a high temperature. Directly discharging it not only wastes energy, but may also affect the environment and even burden subsequent treatment equipment. So reducing the temperature of wastewater is not just a matter of pouring some cold water casually, there are quite a few tricks involved.
First, let's talk about the most down-to-earth method - natural cooling. This method, as the name suggests, relies entirely on the help of nature. Usually, it is to build a large pond, pour hot water in, and let it slowly stay inside. The sun shines and the wind blows, and the water itself dissipates heat into the air. In some places, some partitions are added to the pool to allow the water to flow in a circular pattern. Staying longer can have a better cooling effect. The advantage of this method is that it saves money, requires minimal equipment, and has simple maintenance in the later stages. But the drawbacks are also quite obvious, it's too much up to the heavens. If it's a hot and humid cloudy day with no wind or sun, the water temperature drops very slowly; Moreover, the water pool takes up a considerable amount of space, and sometimes it's really difficult to arrange in the factory area where every inch of land is valuable.
Let's talk about forced ventilation cooling, which is much more proactive than natural cooling. The most common one is the cooling tower, which can be seen on many factory rooftops or open spaces. Its principle is to spray hot water from above and use a fan to blow it upwards. When the water and air collide, the heat is carried away by the air. Cooling towers are usually filled with fillers, such as plastic grids or corrugated sheets, to evenly distribute water and increase the area in contact with air, resulting in faster cooling. This method is not affected by weather, has high cooling efficiency, and occupies a much smaller area than a pool. However, it requires electricity to drive the fan, and over time, electricity bills will also be an expense. Additionally, the fan will make some noise when running, and if there are residential areas around, sound insulation must also be considered.
There is also a type called water water heat exchange, which simply means using cold water to cool hot water. For example, if there is low-temperature water for other purposes in the factory, it can be "brushed" by the wastewater through a heat exchanger. The two types of water are not directly mixed together, but heat can be transferred through the metal wall. When the wastewater becomes cold, the cold water becomes hot, and maybe it can be reused. This method has a stable cooling effect, especially suitable for situations where the wastewater temperature is not too high but requires precise control of the temperature after cooling. However, it needs to have a readily available low-temperature water source, and if not, it will require a specialized set of refrigeration equipment, which will increase the cost. Moreover, if the heat exchanger is used for a long time, it may form scale on the surface, which affects the heat transfer efficiency and requires regular cleaning and maintenance.
Some places still use the idea of evaporative cooling, but instead of relying on fans like cooling towers, it allows wastewater to boil in a low-pressure environment. The boiling point of water will decrease under low pressure, and it will evaporate without boiling to 100 degrees. When evaporating, a large amount of heat will be taken away, and the temperature of the remaining water will drop. This method can achieve a large cooling range and is particularly suitable for treating high-temperature wastewater. But it requires a set of equipment that can vacuum, with high energy consumption, and the evaporated water vapor may contain pollutants, which need to be treated, otherwise it will pollute the air.
In addition, some factories will implement combined cooling according to their own situation. For example, first passing the wastewater through a heat exchanger, pre cooling it with cold water, and then sending it to a cooling tower for further cooling can improve efficiency and save energy. In some places, spray devices are added to the natural cooling pool. When it's hot, the spray is turned on, which is equivalent to adding a "buff" to the natural cooling, making the cooling rate faster.
Overall, there is no absolute best method for cooling wastewater, it depends on the actual situation of the factory. For example, the temperature of the wastewater, the daily processing capacity, whether the site is sufficient, whether there are existing resources to utilize, and the budget, etc. Choosing the right method can not only meet the treatment standards for wastewater, but also save a lot of costs, and even reuse wasted heat, which can be considered as contributing to environmental protection.
