Burning cement for sludge building materials

In addition to organic matter, sludge usually contains 20% to 30% of inorganic matter, mainly calcium, silicon, iron, and aluminum. The construction of sludge is an effective method to make full use of inorganic matter in sludge.

In 1997, a company produced high-strength cement using sewage sludge and waste incineration fly ash as the main raw materials, and built the world’s first ecological cement plant. It also studied the use of dewatered sludge produced by urban sewage treatment plants as Raw material manufacturing cement technology. About 60% of its raw materials are waste materials, and the roasting temperature is 1000 ～ 1200 ℃, so the fuel consumption and CO2 emissions are also low, which is conducive to the reduction, harmlessness and resource utilization of municipal waste. Called “environment-friendly cement”. When burning cement with sludge, there is no need to pretreat the sludge, and at the same time, all organic matter can be decomposed and removed at high temperature without secondary pollution such as nitrogen oxides, soot and so on. Therefore, using sludge for burning cement is also an effective comprehensive utilization method.

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Sludge treatment definition, characteristics and main methods

1. Overview of sludge treatment and disposal

In the treatment of feed water and wastewater, various types of sediments and floating materials produced by different sludge treatment processes are collectively referred to as sludge. The composition and properties of the sludge mainly depend on the composition, properties and treatment process of the treated water. The composition of the sludge is complex, and there are various classification methods and different names.

1.1 sludge classification

According to the source, the sludge is roughly divided into three categories: feed water sludge, domestic sludge and industrial wastewater sludge.

According to the separation process of sludge from water, it can be divided into sediment sludge (including physical sedimentation sludge, coagulation sludge, chemical sludge) and biological treatment sludge (sludge produced by sewage in the secondary treatment process, including biological filtration). Humic sludge obtained by methods such as pool and biological turntable, and activated sludge obtained by activated sludge method). Most of the sewage from modern sewage treatment plants is a mixed pollution of sediment sludge and biological treatment sludge.

According to the sludge composition and quality, it can be divided into organic sludge and inorganic sludge.

More commonly used are classified according to the different treatment stages of sludge: biological sludge, concentrated sludge, digested sludge, dehydrated and dried sludge, dry sludge and sludge incineration ash.

1.2 Characteristics of sludge

(1) Moisture content and solid content The water content is the percentage of the water content in the sludge, and the solid content is the percentage of the solid or dry mud content in the sludge. When the water content is high and the sludge is in a fluid state, the volume of the sludge is inversely proportional to the solid content: V1V2=Ps1/Ps2=(100-Pw2y(100Pw1)
In the formula: V1 and V2 are the volume of wet sludge when the water content is Pw1 (solid content Ps1) and Pw2 (solid content Ps2).

Example: The original moisture content of the sludge is 99.5%, and the percentage of sludge volume reduction when the water content is reduced to 98.5% and 95% is obtained.

Solution: Let V1 be the volume of sludge when the water content is 99.5%, and the volume when V2 and V3 respectively have water content of 98.5% and 95%, and substitute each value into the above formula to obtain V1/V2=Ps1/Ps2= (100-98.5/(100-99.5)=3 V1/N3=Ps1/Ps2=(100-95/(100-99.5)=10 As can be seen from the above example, when the moisture content of the sludge is reduced from 99.5% to At 98.5%, the volume of the sludge is reduced to about one-third of the original sludge, and then reduced to 95% (when the solid content is 5%, the volume of the sludge is reduced to about one-tenth of the original sludge). .

(2) Volatile solids Volatile solids refer to the part of solids in the sludge that can be burned in a furnace at 600 ° C and escaped by gas, reflecting the degree of stabilization of the sludge.

(3) Toxic and harmful substances in sludge The sludge in urban sewage treatment plants contains a considerable amount of nitrogen, phosphorus and potassium, which has certain fertilizer effects and can be used to improve the soil, but it also contains germs.

Viruses, parasite eggs, etc., should be treated as necessary before application. The heavy metals in the sludge are the main harmful substances, and the sludge with a heavy metal content exceeding the prescribed amount cannot be used as the clothing fertilizer.

(4) Dewatering performance of sludge When the water content of the sludge is separated by filtration, the commonly used index is used to evaluate the sludge dewatering performance than the resistance value or capillary water absorption time.

(5) Sludge specific gravity refers to the ratio of the weight of the sludge to the weight of the same volume of water. The specific gravity of the sludge depends mainly on the water content and the specific gravity of the round body. The proportion of domestic sludge and similar industrial sludge is generally greater than one.

Sludge treatment is the process of filling, training, water, stability, incineration or incineration. With the development of the economy, the discharge of urban wastewater is increasing, and the amount of sludge generated is also increasing. Sludge treatment and disposal has gradually become the focus of attention at home and abroad.

(6) Existing treatment and disposal methods at home and abroad mainly include sanitary landfill, water body consumption, incineration, composting, and land use. In view of the existing technology, the main sludge disposal method is landfill. The most suitable sludge treatment method is land use. With the advancement of science and technology, it is bound to introduce more effective and reasonable treatment and disposal methods, and ultimately realize the reduction, harmlessness, stabilization and resource utilization of urban sludge treatment and disposal.

Sanitary landfill

The disposal method is simple, easy, and low in cost, and the sludge does not need to be highly dehydrated and has strong adaptability. However, there are also some problems with sludge landfill, especially the formation of landfill leachate and gas. Leachate is a heavily polluted liquid that can contaminate the underground water environment if the site is sited or not properly operated. The gas produced by landfills is mainly methane, which can cause explosions and combustion if appropriate measures are not taken.

Direct land use

Direct use of sludge land is considered to be the most promising disposal method due to the advantages of low investment, low energy consumption, low operating cost and organic component conversion into soil improver. Scientific and rational land use can be reduced. The negative effects of sludge. The use of forest land and municipal greening has become an effective way of sludge land use because it is not easy to cause pollution in the food chain. The use and use of sludge for the repair and reconstruction of heavily disturbed land (such as mine land, forest harvesting sites, landfills, and severely damaged areas) reduces the potential threat of sludge to human life. Both the sludge was disposed and the ecological environment was restored.

Incineration

The application of wet sludge to direct incineration is more common. It is not only difficult to directly incinerate without drying the sludge, but it is also extremely uneconomical in terms of energy consumption. The incineration-based sludge treatment method is the most thorough sludge treatment method, which can completely carbonize organic matter and kill pathogens, thereby minimizing sludge volume. However, the disadvantage is that the treatment facility has large investment and high treatment cost. .

Powdered organic and inorganic fertilizers Powdered organic and inorganic fertilizers refer to mechanically mixed fertilizers containing two or more nutrients; the ratio of nutrients is determined according to crop varieties, target yield, soil and climate, etc. Different crops have their own unique growth needs; and they can be blended with auxiliary additives (such as limestone, dolomite powder, etc.) and herbicides, insecticides, etc., which have improved soil physiological characteristics according to the specific needs of the crop in specific regions and seasons. Become a nutrient-rich, multi-purpose special organic and inorganic fertilizer.

2. Sludge treatment process

1. The treated sludge (living sludge, industrial sludge, etc.), inorganic raw materials (urea, monoammonium phosphate, etc.), trace elements (borax, ferrous sulfate, etc.) filler (shadow earth, vermiculite, etc.) ) and other raw materials are sent to the automatic lifting silo in proportion;

2. Transported to the organic fertilizer mixer (continuous), while the organic fertilizer mixer rotates, the material advances 2/3 forward, and the remaining 1/3 of the material reciprocates back and forth, and continues to mix with the newly delivered materials. After two to three times of circulating mixing; after the material has reached the purpose of uniform mixing, it is slowly pushed to the discharge port along the inclined direction of the organic fertilizer mixer;

3. Transported to the organic fertilizer special screening machine, special design can completely solve the problem of screen adhesion;

4. The large particles are pulverized by the pulverizer and returned to the horizontal mixer;

5. The finished product is transported to the finished silo, and the automatic packaging scale is weighed, packed and stored.

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Utilization technology of metallurgical solid waste

Metallurgical dust

The main components of metallurgical dust are gas dust, gas mud, steel-making dust and so on.

Blast furnace dust

The blast furnace dust mainly refers to the metal vapor captured by the dust collector in the metallurgical operation, such as the raw material dust generated along with the blast furnace gas movement, the fuel dust in the blast furnace, etc. There are two ways for dust collector to collect blast furnace dust and mud, namely dry and wet. Dry dust collector is used to collect powdery solid. It is called blast furnace gas ash. Wet collection is to collect the dust and mud in slurry state by using wet dust collector, which is called blast furnace gas mud. Blast furnace dust is rich in zinc, iron and other elements. At present, most enterprises in our country use weak magnetic iron separation technology for classification and selection, to recover the iron concentrate contained in the dust, and to recover the carbon concentrate contained in the dust by flotation technology.

Steelmaking dust

The steelmaking dust refers to the phenomenon that some metal impurities with lower melting point will burst or even splash the boiling molten iron due to the change of high temperature environment when the molten iron is heated and smelted in the metallurgical converter. When the molten iron is discharged from the high temperature furnace, a large number of fine metal liquids will exchange with the cold air outside the furnace rapidly, and will form when the air continues to cool Metal dust. The main component of steelmaking dust is metal dust, which contains calcium, iron and other elements, usually in the form of oxide. At present, there are three ways to deal with steel-making dust and mud in China. The first is to mix and shake the steel-making dust and other dry powder according to a certain proportion, and then add some sintering raw materials for de coagulation and reuse. Second, because there are a lot of iron elements in the steel-making dust, the metal in the dust can be turned into pellets, which can be put into the converter again for roasting and utilization. Third, because the steel-making dust contains calcium element, the steel-making dust can play the role of replacing quicklime.

Fly ash

Fly ash refers to the fine ash collected in the smoke generated after coal combustion. Because of its strong adsorption activity and water absorption performance, most of the coal dust is used as admixture of concrete to realize resource reuse. In the process of making concrete, adding a proper amount of coal dust can save cement and fine aggregate, reduce water consumption and workability of concrete, and improve the impermeability of concrete. Nowadays, fly ash has been widely used in building materials, municipal construction and other industries in China.

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Development trend of heavy metal detection in soil

In recent years, soil heavy metal detection technology has been developed rapidly, but there is still a big gap with the actual demand, and there is a huge room for improvement in some key technologies. The spectral method can be used to analyze and determine the heavy metal content in various complex environmental samples with high sensitivity and accuracy. However, considering that most of them need large-scale expensive instruments, high cost of analysis, need to be digested, analysis time is long and safety factors, its application in the determination of heavy metal content in soil has not been popularized yet. The electrochemical method is used in the determination of heavy metal content in soil Trace element detection has good research and application, but there are still some problems in the current detection process, such as ion interference, wave peak overlapping, etc. in addition, soil sample digestion is needed in the pretreatment process of soil samples, and the use of strong acid may bring secondary pollution to the soil. How to overcome these problems has become the key to its popularization and application; new detection technologies show good response But considering that these technologies are relatively new, the preparation of specific antibodies is difficult, terahertz and other equipment are relatively expensive at present, these all urgently need interdisciplinary support of biology, optics and other disciplines and carry out more collaborative innovation research. These problems indicate the direction for the further research and development of soil heavy metal detection technology.

Pretreatment technology of heavy metal detection samples in soil is a very important link, which can have a great impact on the accuracy of the analysis results. In order to achieve a unified pretreatment technology for heavy metal samples, a large number of analysts need to further explore and study, synthesize the advantages of several methods, and effectively avoid the disadvantages, so as to propose an efficient, simple and non polluting treatment method.

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Sludge brick building materials

In addition to organic matter, sludge usually contains 20% to 30% of inorganic substances, mainly calcium, silicon, iron and aluminum. Sludge building materials are an effective method for making full use of inorganic substances in sludge.

The research team incorporated 10% to 30% of the sewage sludge into clay bricks and burned it into an ordinary “ecological brick” for construction at 900 °C. This method not only treats the sludge, but also seals the toxic heavy metals in the sludge during the firing process, kills all harmful bacteria, decomposes toxic organic matter, and the brick does not have any odor. Professor Weng Huanxin of Zhejiang University, when presiding over the provincial key project “Study on the development and utilization of sludge resources in wastewater treatment”, based on a large number of experimental studies to obtain various technical parameters, the use of sludge has the characteristics of high calorific value and light texture. Successfully developed a lightweight brick. The main index of this kind of lightweight brick reaches the national standard of ordinary sintered brick, and has the advantages of high compressive strength, energy saving of 10%, light weight of ordinary bricks of the same volume, and saving 10% to 15% of clay resources. . Therefore, the use of sludge for burning bricks not only achieves waste utilization, but also relieves the pressure of sludge treatment, opening up a new path for the comprehensive utilization of sludge.

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Tradition method of disposal municipal sewage sludge

At present, the main disposal methods commonly used for sludge are sanitary landfill, incineration treatment, direct land use, etc. These disposal methods have played a certain role in practical applications, but as environmental standards become more stringent, their problems Exposed.

1. Sanitary landfill

The sanitary landfill of sludge began in the 1960s and has developed into a relatively mature sludge disposal method. Its advantages are low investment, simple method, quick effect and large processing capacity; the disadvantage is that it requires high soil mechanical properties of landfill sludge, and requires a large area of ​​space and a large amount of transportation costs, and at the same time, to prevent it from polluting groundwater. The foundation also needs to be treated with anti-seepage treatment.

However, there are many problems with sanitary landfills. The various toxic and harmful substances contained in the sludge will cause secondary pollution of groundwater and the atmosphere through the erosion and leakage of rainwater. In addition, due to the large output of municipal sewage sludge, there are fewer and fewer places that can be used for sludge landfill. The US Environmental Protection Agency predicts that 5,000 of the 6,500 landfills will be shut down in the next few decades.

2. Incineration treatment

The most important feature of sludge incineration treatment is that it can realize the harmlessness, reduction and resource utilization of sludge, and it is the most “complete” treatment. At present, developed countries such as the United States, Japan, France, Switzerland, and Germany mainly use incineration to treat sludge. In recent years, sludge incineration technology has gradually become the mainstream of sludge treatment, and it is increasingly favored by countries all over the world. However, sludge must be dehydrated before incineration. As far as the current technical level is concerned, the cost of mechanical dewatering is relatively high. Although natural dehydration is low in cost, it takes a long time, covers a large area, is affected by the climate, and pollutes the surrounding air during drying. In addition, the incineration treatment generally requires a heating value of 1000 kJ/kg or more. When incinerated, harmful gases such as sulfur dioxide and dioxins are generated, and heavy metals in the sludge also pollute the air with the diffusion of soot; the incineration cost is other treatment process 2 ~4 times.

3. Direct land use

The sludge contains a large amount of organic matter and nutrients required by plants, and is a very valuable resource for using sludge as a resource for land use. Direct use of sludge land has the advantages of low investment, low energy consumption, low operating cost, and organic components can be converted into soil improver components. It is mainly used in farmland, vegetable fields, orchards, grasslands, municipal greening, seedling substrates and severe disturbances. Land restoration and reconstruction. However, the composition and source of sludge are quite complicated. Including nutrients, it also inevitably contains harmful components such as a large number of pathogenic bacteria, parasites (eggs), and heavy metals such as copper, arsenic, lead, zinc, aluminum and mercury. And refractory organic compounds such as polychlorinated biphenyls and dioxins, and radionuclides, which are used without treatment, will cause soil or water pollution.

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Status of urban sewage sludge

Municipal sewage sludge is solid, semi-solid and liquid waste generated in the sewage treatment process. The sludge composition is complex, including solid particles such as fibers, sediments and animal and plant residues mixed into domestic sewage or industrial wastewater. A solid substance of coagulated flocs, various colloids, organic matter, and adsorbed metal elements, germs, microorganisms, and eggs. If these sludges are discharged or disposed of improperly, they will cause serious pollution to the surrounding environment. Therefore, it is of great significance to seek economical and effective reduction, harmless and resource sludge treatment technologies.

With the acceleration of urbanization in China, the number of urban sewage treatment plants has increased year by year, and the sewage treatment capacity has gradually increased, and the production of sludge has also increased dramatically. According to the survey, as of the end of September 2010, a total of 2,631 sewage treatment plants have been built in cities, counties and some key towns, and the daily sewage treatment capacity has reached 1.22×108 m3. The urban sewage treatment project under construction in the country has reached 1849. The total design capacity is about 0.466×108m3/day. According to the sludge yield of 3.8%, the daily sludge discharge is about 6.4×106m3. The sludge disposal method of most sewage treatment plants is to transport the sludge to the landfill or form it directly by proper concentration. On the one hand, it is easy to cause secondary pollution, on the other hand, the useful resources in the sludge are lost, resulting in waste of resources.

Obviously, with the construction of urban sewage treatment plants, how to properly treat and dispose of sludge will become more and more important. At present, China’s traditional sludge disposal methods include landfill, incineration, and direct land use. These treatment methods do not effectively utilize the sludge, and there are many social and environmental problems, not sludge disposal. The best way. Therefore, the search for appropriate resource utilization methods is the most important research in sludge treatment and disposal.

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Sludge carbonization treatment technology

The resource utilization after the sludge has been paid more and more attention as people pay more attention to sustainable economic development. In recent years, with the development of China’s economy and the continuous advancement of urbanization, urban sludge production has gradually increased. The traditional methods are sludge landfill, sludge farming and sludge incineration. After the sludge is landfilled, it will cause certain environmental problems. In order to meet the three principles of “harmlessness”, “reduction”, “resources” and “reduction” of sludge treatment, sludge carbonization treatment technology is adopted to fully realize the resource utilization of sludge.

The key to the research on sludge resource utilization is to be harmless and stabilized.

The sludge carbonization process can recover about 80% of the organic energy in the sludge, and produce biochar with ordinary use. Compared with other technologies on the market, it realizes the resource utilization of sludge, which is a veritable waste turning into treasure. The main use value of the final product is mainly reflected in: 1 floor tiles, trays and other general construction raw materials; 2 can be used as green fuel, which can be used for heating of the system itself, coal-fired thermal power plants, waste incineration plants, etc.; The land compaction problem helps the salt-alkali land to quickly recover into a good field; 4 new adsorption material – activated carbon, fast adsorption speed, outstanding adsorption balance; 5 parts of sludge production can be used for snow melting agent, auxiliary road cleaning; 6 straw can be used as paper pulp ; 7 kitchen waste can be used as high-value biomass charcoal.

The sludge low-temperature treatment technology can not only solve the adverse effects of sludge on the environment, but also solve the problem of sludge land occupation, and turn waste into treasure, which is more in line with the ecological sustainable development strategy!

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What are the main forms of industrial waste heat utilization?

At present, there are three main forms of industrial waste heat utilization. The first one is waste heat boiler to recover waste heat steam for process use of saturated steam or for power generation; the second is to use heat pump or lithium bromide absorption unit to recover waste heat and make hot water or Steam, used in process, air conditioning and domestic heating; the third is to use the screw expander to recover waste heat, directly drive the generator to generate electricity or drive pumps, fans and compressors. In addition to recovering waste heat, the screw expander is also used in the recovery of residual pressure.

1. Middle and high temperature waste heat utilization

The waste heat boiler produces steam steam heat boiler to recover steam by recovering waste heat from the production process.

At present, waste heat boilers are mainly used to recover gaseous residual heat such as high temperature flue gas and combustible exhaust gas. The steam produced has two directions of use, one can be directly used for production and domestic steam, and the other is steam can be used for steam turbine generators to generate electricity.

2. Low-temperature waste heat utilization

The heat pump unit and the lithium bromide absorption refrigeration unit comprise two types of units. First, the lithium bromide absorption refrigeration unit utilizes industrial waste heat to provide cold water or air conditioning refrigeration for the industry. Second, heat pump units (such as lithium bromide absorption heat pumps) use hot water or steam to absorb heat from low-grade heat sources for industrial or urban heating. The driving heat source of the lithium bromide absorption heat pump is steam, high temperature flue gas, heat generated by direct combustion fuel (gas, fuel), waste hot water, waste heat steam, and the like.

Compared with waste heat boilers, lithium bromide absorption heat pump units are commonly used for low temperature waste heat recovery, while waste heat boilers are more used for medium and high temperature waste heat recovery. Secondly, the application fields are different. The hot water and steam supplied by the lithium bromide absorption heat pump are used for process and air conditioning refrigeration, and the steam provided by the waste heat boiler can be used for steam turbine power generation. Third, in the current waste heat recovery project, the waste heat boiler is mostly used to recover gaseous waste heat, and the lithium bromide heat pump unit can recover waste heat (such as waste hot water and fuel) after recovering gaseous residual heat.

3. The use of residual pressure

Screw expander screw expander can use steam, high temperature hot water, vapor-liquid two-phase fluid and other media as the power, convert thermal energy into mechanical energy to drive generators to generate electricity or directly drive pumps, fans, compressors, etc. . At present, there are two main methods for the application of the screw expander: one is to recover the residual pressure of the steam, and the other is to use the organic refrigerant Langken cycle system to recover the waste heat.

(1) Recover steam pressure difference

Case: If the steam generated from the boiler is supplied to the industrial steam after being depressurized, the screw expander can be used to recover the residual pressure for power generation.

Unit composition: screw expansion power machine + generator (circulation pump, compressor, fan, etc.) + condensing unit (optional)

Supplement: It is especially suitable for saturated steam differential power generation system with steam pressure ≥0.3MPa, temperature ≤300°C, and inlet and outlet pressure difference between 0.2~1.0MPa. When the pressure difference is greater than 1.0 Mp, multiple screw expanders can be stepped down in series. In the waste heat recovery, the steam pressure generated by the waste heat boiler is usually larger than that of the industrial steam, and the screw expander can be combined with the screw expander to realize the pressure reduction and power generation.

(2) Organic working fluid circulation system to recover industrial waste heat

Case: If there is industrial hot water (above 60 °C), organic working fluid can be exchanged with hot water for heat exchange. The organic working fluid becomes vapor-liquid two-phase and then enters the screw expander. The screw expander drives the generator through work. The power is generated, and the steam-liquid mixture after the work enters the condenser to be condensed, and then returned to the heater through the working fluid pump, so that the work is cycled.

Unit composition: heat exchanger + screw expansion power machine + generator + high efficiency condensing unit + auxiliary equipment
Supplement: screw expander recovery The main difference between waste heat power generation and waste heat boiler combined with steam turbine power generation is that the screw expander replaces the steam turbine. Compared with the steam turbine, the advantage is that the working fluid entering the screw expander can be hot water (above 60 ° C), steam, gas and liquid, and the steam turbine can only be steam; secondly, the screw expander can drive the generator. Power generation, can also directly drive fans, pumps, compressors; third, steam in the screw expander flow rate is low, low noise, internal wear and tear.

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Treatment status of Landfill Leachate

At present, there are two current situations of filtrate treatment in China:
1. Serious shortage of investment funds

At present, the total investment in the leachate treatment system of more than 70 waste treatment plants is about 400-500 million yuan, which can not be compared with the investment in urban sewage treatment of hundreds of billion yuan every year in China. Due to the withdrawal of pepper noodle investment, some systems can barely run up to the standard, some can not even run and then abandon. In recent years, although some new processes have begun to enter the market, most of them are exploratory tests, which have not yet withstood the test of actual project operation, mainly manifested in unstable treatment effect and low rate of reaching the standard.

2. Treatment technology to be improved

At present, there are three kinds of leachate treatment technologies in China: one is to use the traditional domestic sewage treatment technology, mainly simple biochemistry, which is basically not up to the standard. This kind of project accounts for more than 60% of the total leachate project. Second, in recent years, considering the characteristics of landfill leachate, many scientific research institutes have continuously explored some new technologies, improved some old methods, integrated some new processes, and applied them to practical projects, but the effect is not ideal. Such projects account for about 10%. Third, some landfills suffer from the lack of good treatment technology and are simply dealt with. Such projects account for more than 20%.

In the 1950s, the western developed countries paid attention to and carried out large-scale leachate treatment, which was basically explored in frustration and failure. Until the 1980s, with the application of membrane treatment technology in leachate treatment, they came out of the technical route of mainly reverse osmosis technology, high-efficiency bioreactor combined with reverse osmosis. From the development of leachate treatment technology in foreign countries in recent ten years, the technology of simple biochemical treatment of leachate has been gradually eliminated, replaced by the membrane treatment technology mainly based on reverse osmosis and the advanced technology of high-efficiency biochemical treatment combined with membrane method. Since 2003, with the increase of environmental protection, garbage and leachate treatment, the project of introducing advanced reverse osmosis technology from foreign countries has been completed successively, which has raised the level of leachate treatment in China to a higher level and ushered in a new era of leachate treatment
Due to its unique open channel, short process and turbulent technology, the equipment has strong adaptability to leachate, its treatment efficiency does not change with the change of leachate quality, and the effluent quality is stable. The superior effluent quality has proved that the dish tube reverse osmosis is highly adaptable to the complex water quality with high concentration and great change of leachate.

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