In the process of industrial production, steam boiler is a basic equipment and facility. The use of steam boilers corresponds to a large amount of energy consumption and waste discharge, including high salinity wastewater, high alkalinity water and high temperature condensate water. The secondary utilization of these waste resources is of great significance to energy conservation.
First, the steam boiler sewage utilization overview
(a) Use of steam boilers
As an extremely critical tool in the field of modern industrial production, such as steam boiler, it is necessary to rely on steam to ensure the temperature of materials in the kettle, and to solve the heating problem of the whole plant in winter with the help of heat exchanger units. The steam boiler will produce high salinity water, sewage and condensed water when it is used, and the amount of sewage is huge. In fact, there are problems of resource shortage, water shortage and energy shortage in China and even in the world. Therefore, it is an important choice to increase the application of energy-saving and environmental protection technologies, make full use of wastewater and sewage, and reduce the consumption of fresh water resources. In the domestic modern industrial system, how to classify and recycle the above three kinds of steam boiler wastewater has also become an important topic that researchers are very concerned about.
(B) the benefits of steam boiler sewage utilization
Relevant enterprises can achieve good economic benefits on the basis of recycling boiler wastewater. The company can save a lot of fresh water every year and control the sewage discharge at a low level. The recovery and utilization of condensed water in winter can raise the soft water from 20℃ to above 50℃, and also play a role in saving fuel to some extent, which is an important performance of saving capital cost. Generally speaking, the recycling of boiler wastewater is carried out according to the principle of "circular economy", which breaks through the limitations of traditional wastewater treatment methods in chemical enterprises, can effectively coordinate and control the relationship between enterprise operating costs and fulfilling social responsibilities, and achieve high social benefits.
Second, the boiler wastewater overview
(a) High salinity wastewater
The water used in the steam boiler is softened water. If the hardness of water is too high, after a long period of cooking, the calcium salt and magnesium salt components in water will gradually consolidate to form dirt. Once the scale is formed, the heat transfer performance of the metal pipes in the boiler will be obviously reduced, and the efficiency of boiling water will be reduced, which will not only waste materials, but also lead to the problem of overheating of the pipes. If the temperature exceeds the tolerance range of metal, the pipeline will be directly deformed, damaged or even exploded. According to the requirements of industrial boiler water quality standard, the hardness of boiler inlet water needs to be controlled within the normal range of 0.03mmol/L or below, but in fact, the index of municipal water supply is far below the standard of reasonable water use, which requires reducing the hardness of water quality through water softener to meet the requirements of boiler water use and ensure the safe use of boiler.
(2) High alkalinity water
There are many soluble or insoluble impurities in boiler water. During the normal start-up and use of the boiler, most of the above impurities remain in the water, and only a small part can be taken away by steam. In the whole stage of boiler water evaporation, the concentration of impurities will continue to rise. Once the impurity concentration of boiler water reaches a certain high value, the steam quality will obviously decrease, and the heating surface will scale or corrode, which will adversely affect the safe operation of boiler. In order to ensure the quality of boiler water, reasonable measures must be taken to discharge the boiler water polluted by salt and slag from the system and replace it with fresh water.
(3) High temperature condensate water
During the heating period in winter, the domestic heating circulating water is heated by steam in the intelligent heat exchange unit, and the steam condensate after heat exchange is directly discharged after being separated by the steam trap. Every year, enterprises discharge a large amount of wastewater into the sewage pipe network.
Third, comprehensive measures to reduce emissions from industrial steam boilers.
(A) the classification of boiler wastewater recycling
High salinity water, sewage and condensed water are common steam boiler wastewater, which are often concentrated in boiler rooms and other areas, and are easy to recycle. Among them, water and sewage with high salt content contain a lot of impurities. If recycled to the production process, it may cause some hidden dangers in product quality, so it is often recycled to the sanitary water system of the workshop, such as cleaning packaging barrels, floors and turnover tanks. On the other hand, the steam condensate has good water quality and high temperature. After testing, it was found that the hardness of water was below 0.0 1mmol/L, and the temperature was kept at about 90℃. Therefore, condensed water can be quickly introduced into the soft water tank for reuse, which has the dual effects of ensuring the utilization rate of water resources and raising the temperature of soft water. In the process of recovery, two stainless steel tanks are generally used to receive boiler wastewater, and high-temperature resistant float centrifugal pump is used to provide power. Condensed water is directly introduced into the boiler soft water tank, and high-salt water and high-alkalinity water are introduced into the workshop IBC tank, and high-pressure cleaning device is used to realize workshop hygiene.
(2) Install "waste heat recovery device"
In addition to the recovery of steam boiler wastewater, the high-temperature flue gas at the tail of organic heat carrier can be reused, which requires enterprises to install a "waste heat recovery device" to control the temperature of boiler flue gas in the range of 150℃ to 200℃.
(c) Promote dry ice cleaning technology.
During the long-term use of steam boilers, a large number of oil stains, coal stains and other stains will be formed, which requires enterprises to arrange professional and technical personnel for long-term follow-up treatment. Traditional stain cleaning methods rely on water, compressed air and other mechanical methods, and the cleaning effect is extremely general, and it is easy to damage the boiler wall. Under the new technical background, advanced dry ice cleaning technology can effectively solve this problem. Granular dry ice particles are sprayed on the surface of boiler heating surface by high-pressure air, and different substances are separated at different shrinkage rates by physical reaction of temperature difference. When the dry ice particles at -78℃ come into contact with the surface of oil dirt and ash dirt, a brittle explosion occurs, and the oil dirt and ash dirt can shrink and loosen rapidly, and the dry ice particles are vaporized and expanded hundreds of times.
(D) Promote low-power frequency conversion technology.
In the long-term use stage of boilers, it is often necessary to rely on the experience and subjective judgment of technicians for adjustment, which will bring serious waste of peak energy consumption. Popularizing the brand-new frequency conversion speed regulation technology can effectively control the motor speed decline, reduce the degree of mechanical wear, and avoid the problem of increased maintenance workload caused by the rapid increase of motor working temperature.
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