Discussion on the application of urban construction waste in cement production?

It is a systematic project to implement the recycling project of urban construction waste in cement plant, which includes four main steps: classification of urban construction waste, pretreatment before batching, batching and performance testing.

Classification of urban construction waste

1) classification purpose of urban construction waste. The urban construction waste transferred to the cement plant must be preliminarily classified. The main purposes are as follows: firstly, recycle effective resources, separate metal, glass, plastic, wood and other components in urban construction waste, and recycle recyclable resources as much as possible; Secondly, the amount of urban construction waste is reduced, the total weight of the remaining parts after sorting is reduced, and the chemical composition is relatively stable, which is conducive to the pretreatment, storage and transportation before the next batching. 2) Method and equipment. According to the specific situation in xinzheng city, the urban construction waste has been carefully sorted manually before being transported out of the construction site. Therefore, before entering the cement production line, it can be completed by simple manual sorting without adding equipment.

Pretreatment before batching

1) The purpose of pretreatment. The resource utilization of urban construction waste in cement plant means that the cement plant uses the existing crushing, transportation and storage facilities to pre-crush urban construction waste, and then uses it as a resource to replace some mixed materials. The rest of the sorted urban construction waste may have large particles or poor chemical composition uniformity, so it cannot directly enter the batching process, and must be crushed in large pieces to correct the chemical composition. Ensure its stability. 2) Method and equipment. The existing jaw crusher, belt conveyor, bucket elevator and raw material storage bin in cement production line are used to complete the crushing and homogenization of urban construction waste and achieve the effect of stable composition.

condiments

1) batching purpose: the sorted and pretreated urban construction waste is used to replace some mixed materials to prepare qualified cement. 2) Method and equipment. At the bottom of the cement production line of a cement plant in xinzheng city, the existing variable frequency speed regulating scale and microcomputer batching device are used for batching, and the storage batching equipment can fully meet the batching requirements of this project.

performance trial

1) test purpose. According to the requirements of conventional physical and chemical indexes of cement, the cement products mixed with urban construction waste were tested, and the changing laws of various physical and chemical data were summarized to determine the appropriate mix ratio. 2) Method and equipment. The cement factory has a laboratory that meets the requirements of national standards, and tests the physical and chemical indexes of cement, which fully meets the requirements of test and detection.

Composition, Properties and Utilization of Urban Construction Waste

The chemical composition of urban construction waste is similar to that of cement admixture (table 1). At the same time, limestone, hydrated portland cement and waste clay bricks in construction waste have certain potential activities. Therefore, it is feasible to use inorganic slag in construction waste as cement admixture after grinding. According to the experimental results of a cement factory in xinzheng city using 20 12 urban construction waste to produce cement, compared with the control group without adding urban construction waste, adding 10% and 20% construction waste reduced the corresponding amount of fly ash, and all cement inspection indexes were close to those of the control group (Table 2). The results show that when 20% inorganic slag is added as admixture, as long as the specific surface area reaches more than 350m2/kg, all the physical and chemical indexes of silicate series cement can meet the national standards.

Analysis and conclusion

The above test results show that the setting time of cement is shortened, other physical and chemical indexes have no obvious change, and the performance of cement is improved. As the raw material of cement production, urban construction waste is rich in resources and low in price, so it does not need to add any equipment in the process of treatment and utilization, and only needs to pay a small amount of transportation costs, and its cost is one quarter of that of fly ash. Moreover, most of the physical structure of urban construction waste has been destroyed in the process of demolition and pretreatment, so its grindability is greatly enhanced in the process of producing cement as cement admixture, which will increase the output per hour of cement mill by more than 10%. From this calculation, the production cost per ton of cement can be reduced by 5 ~ 8 yuan. According to the annual production capacity of a cement plant in xinzheng city, it can digest 200,000 tons for xinzheng city every year.

The one-time resource utilization of cement plant to treat urban construction waste conforms to the basic requirements of circular economy and sustainable development strategy advocated by China at present; Avoid the environmental pollution and occupation of precious land resources caused by the disposal methods of urban construction waste stacking and burying, improve the surrounding environment of the city, purify the air, reduce and avoid the pollution of urban underground water sources, and leave no environmental burden; Effectively reducing the health damage caused by environmental pollution, water pollution and air pollution to urban residents has very important environmental protection significance and environmental benefits. It can be seen that the recycling of urban construction waste to produce high-quality ecological cement can not only bring direct economic benefits to cement plants, but also solve the current problem of difficult disposal of urban construction waste, make a direct and great contribution to the development of national energy conservation and emission reduction and circular economy, and make cement enterprises transform from big polluters into living homes with clear water and blue sky.

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