As the core component of the power transmission, the large ring gear of the rotary kiln is fixed on the cylinder of the rotary kiln through the spring plate, and drives the rotary kiln to drive stably and accurately under the driving of the pinion. After the core component is in operation for several years, the tooth profile will be worn and the running accuracy will be deteriorated, which will cause vibration and other undesirable phenomena, which will not only damage the foundation but also adversely affect the fire brick in the kiln. In order to ensure the good operation of the rotary kiln, the large ring gear must be used on the reverse side or directly replaced. For the convenience of replacement, the following method steps are listed for the replacement.

Rotary kiln big ring gear replacement steps

1. Prepare for the technology before replacement. Diligently digest the drawings and prepare the construction plan including the construction steps and technical requirements of the process.

2. Prepare for the substance. According to the construction plan, prepare various tools and required materials.

3. Be prepared for the staff. Refer to the plan and prepare all personnel including technology and labor.

4. After cleaning the new ring gear according to the plan, measure the item size, make a record, and repair and correct the detected discomfort.

5. After reviewing the dimensions of each part, the large ring gear should be pre-grouped and the dimensions of each part should be measured. The next process can be carried out without problems.

6. After the kiln is shut down for cooling, first remove the gear cover and place it in a safe place.

7. Properly clean the oil track, measure the radial and end face run of the large ring gear and the barrel of the slow drive, and record the data of the corresponding position.

8. Turn the two joint faces of the old large ring gear to the horizontal position, and then use the crane to hang the upper part of the large ring gear. After checking the problem, remove the spring plate and the ring gear pin and check the pin wear. Situation, prepare new sales. After that, the joint bolt and the positioning pin can be removed, and the upper half ring gear is slowly lifted off the scene.

9. Attach the new half-ring gear that has been prepared to the pair of old ring gears in the lower half, including the spring plate and ring gear, the joint bolts and pins of the new and old ring gears.

10. Slowly turn the kiln, turn the lower old ring gear to the upper part, remove it in the same way and place it in the right place.

11. Lift half of the new ring gear and connect to the new front ring gear.

12. After the new large ring gear is installed in place, replace the worn spring plate and the ring gear pin according to the preparation of the pin.

13. Start the slow drive and measure the radial runout and end face runout of the ring gear. And the maximum jump is transferred to the meshing gear and the tip clearance is measured. Ensure that the tip clearance is 1mm larger than the theoretical gap, the tooth width contact is not less than 70%, and the tooth height contact is not less than 40%. And the large ring gear is located in the middle of the pinion. (can be based on the specific location of the kiln)

14. If the radial runout, end face runout, gear contact, etc. of the large ring gear are checked within the control range, the gear cover is replaced and the replacement work is completed.

15. If during the inspection, the large ring gear is bouncing and the end face is out of tolerance, according to the specific situation, several jacks should be used between the cylinder and the ring gear to remove the spring pin, and the disk kiln is aligned and passed through the jack. Loosely adjust the beating condition until it is qualified, then cut off the spring plate and pin the pin head. After the pin and the ring gear and the spring plate spring plate are put on, they can be welded firmly. If the contact of the large and small gears does not meet the requirements, it can be solved by adjusting the kiln.

16. The 15th item in the article can be carried out simultaneously with the front installation and correction. It can be adjusted according to the actual situation on site, and other processes can also be interspersed.

In order to promote the development of active lime technology and provide good service, through long-term sampling experiments, a large number of practical production process control data were finally obtained, including the research of limestone calcination active lime preheating, calcination optimum time, calcination optimum temperature and other levels of diversification.

 

According to the experimental data, the preheating time, temperature, calcination time and temperature of limestone are closely related to the high activity of lime. Please check the results of the following experimental data sets.

 

(1) The range of calcination temperature and time corresponding to the highest activity of limestone becomes wider with the increase and extension of the preheating time of limestone from 600 to 700℃. When the calcination temperature is between 1100 and 1150℃, it is the calcination temperature zone of the highest activity of activated lime.

(2) When the preheating temperature is 700℃, the corresponding preheating temperature for the highest activity is 45 min, 5 min and 10 min, and the calcination temperature is 1150℃, the highest activity of lime appears; when the holding time is 15 min and 20 min, the final calcination temperature is 1000-1150℃, the highest activity of active lime is reached; but when the preheating time is increased to 60 min, the highest activity of active lime is reached. Regardless of the holding time during calcination, the final calcination temperature of the highest activity is 1100-1150℃. The highest activity of this group of lime experiment is 410ml, the corresponding preheating time is 45 minutes, the calcination temperature is 1150℃, and the calcination time is 15 minutes.

(3) When the preheating temperature is 800℃, the calcination condition of obtaining the highest activity is difficult to control. The preheating time is short, and the range of calcination temperature corresponding to the highest activity becomes smaller. When the preheating time is long, the highest activity is only 360ml, and the corresponding calcination temperature is 1150℃, and the calcination time is only 5 minutes.

(4) When the preheating temperature is 900℃, the whole calcination condition becomes more difficult to control in order to obtain high activity. This preheating temperature is recommended not to be used in the calcination process of limestone.

 

The above experimental results obtained from long-term sampling experiments are intended to provide effective data and technical support for the lime calcination process. Due to the complex and changeable thermal conditions in the lime production process, the experimental results and the final data may be biased and insufficient. It is hoped that professionals will come to our hospital to exchange guidance.

The global cement industry is pursuing the harmonious coexistence of environmental protection and cement production. Using cement rotary kiln to treat municipal solid waste synergistically has always been the common goal of the industry to achieve the ultimate reuse of waste resources. In the process of industrialization and urbanization in China, in order to meet the needs of all walks of life, a large number of materials have been consumed, but accompanied by a large number of domestic waste and garbage; especially the waste produced by industry and medical industry, not only caused a sharp damage to the environment, but also seriously threatened the health of all kinds of animals and plants, so such waste needs special treatment. This is also what people often call “dangerous waste”, also known as dangerous waste.

Advantages of Rotary Kiln in Disposal of Various Wastes

(1) Hazardous waste management in China started late, and the relevant system is not perfect. The common practice abroad is to pretreat the wastes that need to be incinerated first, which are operated by professional teams and equipment. After the wastes meet the conditions of rotary kiln incineration, they are sent to rotary kiln for incineration and disposal. However, the current situation in China is that hazardous wastes are collected directly and then sent directly to cement enterprises. Safe transportation and classified storage are the premises. Cement enterprises can not avoid the problem.

(2) Solid waste garbage usually contains a variety of components, and the calorific value of each component is deviated. In the process of rotary kiln contact operation, there are often “cold and hot” situations. There are many contradictions between safe disposal of hazardous waste and smooth operation of rotary kiln.

(3) Hazardous wastes can be divided into 47 categories. There are adverse reactions among a large number of wastes. Once improperly treated, there will be fever, explosion, fire, toxic gases, such as acidity and alkalinity, acidity and cyanide. Mastering physicochemistry is also a necessary skill to deal with hazardous wastes and avoid the occurrence of batching process in advance.

(4) In view of the different calorific value and stability of hazardous waste, not only should the waste be thoroughly incinerated, but also the different calorific value of waste be fully taken into account, and reasonable solutions such as the location and way of entering the kiln should be found.

(5) Cement kiln is sensitive to halogen elements and alkaline substances. If the amount is not appropriate, it will affect the quality of cement kiln and cement products. Therefore, it is necessary to constantly test and determine the incineration ratio of halogen-containing substances and alkaline substances.

Cooperative treatment of domestic waste by cement kiln can bring many conveniences to our life, help to protect the environment and save energy. Continuous improvement of relevant technology level can further provide energy utilization rate and solve the problem of hazardous waste discharge in urban life.

Oil sands are sedimentary sands rich in natural bitumen and are therefore also referred to as “asphalt sands”. China’s energy structure is rich in coal, lean in oil, and low in gas. Oil sands are unconventional oil and gas resources. The reserves are second only to coal. After oil sands are dry distillation, pyrolysis oil and combustible gas similar to crude oil can be obtained. As a supplement to conventional energy, Changing China’s energy structure has very important strategic significance.

The oil sand pyrolysis dry distillation product is divided into four parts: non-condensable gas, pyrolysis oil, pyrolysis semi-coke, water.

1. Non-condensable gas can be used as a heat source for pyrolysis retorting of gas;

2.The pyrolysis oil can be further fractionated as a crude oil into the fractionation column;

3.After oil extraction from Indonesian oil sands by pyrolysis and retorting system, about 80% of pyrolysis semi-coke is produced, the particle size is less than 1mm. If it is directly discharged, it will seriously pollute the environment, and the semi-coke still contains undecomposed organic matter and unburned. Fixed carbon, if not burned, will result in wasted energy. The main component of the semi-coke is CaO, which can be used as a raw material for the production of cement clinker.

1. Current status of urban domestic waste treatment in China

In 2008, China Statistical Yearbook, by the end of 2007, 655 cities across the country had 5.2 billion tons of domestic garbage and 453 kinds of domestic garbage dumps, with a processing capacity of 272,000 t/d and a centralized processing capacity of about 94 million tons. The rate is 62%; expected to be 2010:
The total output of domestic garbage above the county level is about 500 million tons. City: 180 million tons/year (average daily average is 493,000 tons) County: 0.7 billion tons/year (average daily average is about 194,000 tons)
Among them, there are 363 urban landfills, 17 composting plants and 68 incineration plants.

2. Comparison of various waste treatment investments

Processing method

Sanitary landfill

 

Compost

 

Incineration

Domestic technology

Foreign technology

Cement production process

Investment

(10,000 yuan/ton)

8-10 12-18 20-28 60-70

6-9

The amount of garbage disposal is 1000 tons/day, and the total investment in cement production is only about 70 million yuan.

3. Overview of municipal solid waste incineration plants

At the end of 2007, there were 68 garbage incineration plants that had been put into operation nationwide, and 25 sets of incinerators under construction. Recently, 82 statistics have been put into operation, 102 are under construction, and 38 will be built in the future. It is estimated that by 2010, the national urban waste disposal rate will increase from 40% in 2007 to 70%, and the disposal rate of waste incineration will be 6 in 2005. % rose to 18%. More than 1,000 PC cement kilns in China are able to make some contributions to this. The exit of the 1000-2000 tons / day production line?

The main problem in the operation of domestic waste incineration plants is?

1) High investment and operating costs;

2) It is waste incineration power generation that relies on higher on-grid tariffs;

3) The fly ash produced by incineration is not properly placed;

4) is a problem of dioxin pollution caused by waste incineration;

5) The heat generated by garbage is low, about one third of that in developed countries;

6) Garbage and coal incineration are helpless, and the heat utilization efficiency of coal is low.

Luoyang Building Material and Architectural Design and Reserach Institute cement kiln co-processing domestic garbage technology

The technical route adopted by our institute:

(1) In parallel with the dry clinker production line, the waste efficient incinerator is used;

(2) The high temperature residual air of the clinker cooler maintains the self-ignition of the garbage in the incinerator;

(3) The high-temperature flue gas is sent to the preheater system for utilization and purification.

In China, there are still many difficulties and problems in using cement kiln to treat waste. In addition to the use of hazardous wastes by a few manufacturers such as Beijing Cement Plant, the technical application of replacing raw materials and fuel is almost blank. China’s urban landfill has reached 8 billion tons, covering an area of ​​more than 800 million square meters, and garbage has become a major public hazard. There are more than 1,000 large-scale new dry-process cement kiln in the country, which is the best substitute for waste incinerator. If all sorting treatments and as AFR are used in the cement industry, it can replace 1/4 of the existing standard coal consumption in the national cement industry. If the standard coal consumption of clinker in each cement plant is reduced by an average of 25%, the extent of energy saving and cost reduction is considerable.

Ⅰ.Market Demand Situation

As an energy-saving, green and environmentally friendly mineral filler, heavy calcium is mainly consumed in paper making, plastics, rubber, paint and coatings. Paper and plastics industry is the main industry for large-scale demand and fine application of heavy calcium. The consumption of heavy calcium in the world paper industry has increased from 9% of its total output in 1981 to 50% in 2005. Especially in Asia, new papermaking enterprises mostly use high-brightness wood-free pulp to make paper, requiring heavy calcium to make high-brightness coatings. According to statistics, in the next few years, the paper industry will still be the main market of heavy calcium, and its market share will increase slightly. It is expected that by 2012, the annual average growth will be about 5.5%, of which Asia will grow by more than 8.5%. Especially in the paper industry, the new technology of using light calcium and heavy calcium mixed fine powder has developed rapidly, and the demand for coated heavy calcium has increased. The amount of heavy calcium in synthetic materials (plastics and rubber) increased by about 5% annually. The amount of heavy calcium used in paints and coatings increased by about 4% annually. According to the statistics of the Calcium Carbonate Professional Committee of China Nonmetallic Mineral Association, there are more than 400 heavy calcium carbonate enterprises with an annual output of about 4 million tons in China. From the product structure, 200-325 meshes account for 50%, 325-1250 meshes account for 35%, 1250 meshes account for 15%, and surface treatment accounts for 12%. Large-scale heavy calcium enterprises in the world basically adopt large-scale equipment and advanced production technology, such as vertical mill or ball mill and other large-scale dry grinding equipment technology combined with super-fine classifier or large-scale wet equipment technology, to achieve industrial scale and fine production of products. However, the energy consumption per ton of products with high ball mill technology is still an urgent problem to be solved in the industry. Vertical mill equipment and its supporting technology have attracted wide attention in the industry because of its advantages of high efficiency and energy saving.

Ⅱ.Production Technology and Equipment of Heavy Calcium

At present, the mainstream demand in China’s heavy calcium market is 600-1500 purpose heavy calcium products; the value-added rate of heavy calcium products is low (compared with talc, barite, kaolin, etc.), and scale is one of the main factors affecting the benefits. In order to meet the requirements of the market and the profit of enterprises, we should achieve in principle the following two conditions when choosing heavy calcium processing technology and equipment: mature technology, reliable operation of equipment, stable product quality, less investment per ton of products and low energy consumption of products.

The dry superfine processing equipment of heavy calcium mainly consists of grinding and grading equipment. Mature grinding equipment mainly includes Raymond mill, vibration mill, ring mill, dry stirring mill, vertical roller mill and ball mill. The classifier is an impeller type Superfine Classifier Based on forced eddy current principle. The following is mainly from the technical characteristics of our design, analysis and evaluation.

Ultrafine powder grinding system

Ultrafine powder grinding system

Technology of Ball Mill+Classifier

The crushing principle of ball mill is that materials and grinding media impact and grind each other in the rotating process of ball mill. The output of fine grinding is lower than that of dry stirring mill and vibration mill, but higher than that of other crushing equipment. After modification in grinding, the grinding ability has been greatly improved, the content of fine powder is close to that of vibration grinding, and the phenomenon of over grinding is much lower than that of vibration grinding. At present, it is one of the main equipments for large-scale production of heavy calcium.

The technology of high-fine ball mill with classifier is strongly recommended by advanced powder technology companies in the world and widely adopted by famous Powder Companies in Europe and America. It is widely used in the processing of non-metallic ores such as calcite, barite, talc and kaolin. Taking the production of heavy calcium powder as an example, 600-6000 items can be produced, which is especially suitable for 800-2500 items. The production scale of single machine is 1-100,000 t/a. This production process fully conforms to the principle of producing low added value products of heavy calcium, requiring less investment, mature technology, simple process equipment, low energy consumption and higher output. The advantages of this scheme have been tested in practice.

What is oil sludge?

Oil sludge refers to oily solid waste generated during oil extraction, transportation, refining and oily wastewater treatment. The oil sludge generally has an oil content of 10-50% and a water content of 40-90%. In China’s petrochemical industry, an average of 800,000 tons of tank bottom mud and pool bottom mud are produced each year.

What is the hazard of oil sludge?

The oil sludge contains a large amount of odorous substances such as benzene, phenols, strontium and barium. If it is not treated directly, it will not only occupy a large amount of cultivated land, but also pollute the surrounding soil, water and air. The mud also contains a large number of pathogenic bacteria, parasites (eggs), heavy metals such as copper, zinc, chromium, mercury, salts and toxic and harmful substances that are difficult to degrade such as polychlorinated biphenyls, dioxins and radionuclides. At present, oil sand has been classified as hazardous waste by the state. The comprehensive treatment of oil-free sludge in a harmless, clean and recycling of resources has become one of the key points of environmental protection and petroleum industry at home and abroad.

How to deal with oil sludge with different oil content?

Oil sludge

1.Oil sludge with less than 5% oil content

The oil sludge containing less than 5% oil is biologically treated. The biological method refers to the process in which microorganisms use petroleum hydrocarbons as carbon sources for assimilation and degradation, and finally they are completely mineralized and converted into harmless inorganic substances. The biological treatment method has the characteristics of not forming secondary pollution or causing pollutant transfer and low cost.

2.Oil sludge with 5-10% oil content

The sludge with a oil content of 5-10% is incinerated. The oil sludge is pretreated and dehydrated, and the concentrated sludge is dehydrated and dried by the equipment. The mud cake is sent to the incinerator for incineration. The ash is used for road construction or embedding in the designated ash landfill, and is incinerated. The heat is used for heat generation. The incineration temperature is generally controlled at 800-1000°C, the incineration time is controlled at 0.5-1.5h, and 50-100% excess air is used. After the oil sludge is incinerated, almost all kinds of harmful substances are removed, and the effect is good. However, its investment is large, the cost is high, it is often necessary to add combustion-supporting fuel, the incineration process is accompanied by severe air pollution, and the crude oil cannot be recovered, so the actual utilization rate of the incinerator in China is low.

3.Oil sludge with 10-20% oil content

Solvent extraction is used for sludges containing 10-20% oil. The process uses an extractant to dissolve the oily sludge. After stirring and centrifuging, most of the organic matter and oil are extracted from the mud by the extractant; then the extract is recovered for distillation, and the solvent is separated from the mixture for recycling and recycling. The oil is used for refining. Solvent extraction is generally carried out at room temperature. The larger the solvent ratio, the better the extraction effect, but the solvent becomes larger than the large extraction equipment and the energy consumption is relatively large. After the extracted oil sludge is subjected to distillation treatment, the heavy oil in the oil sludge can be effectively removed, and the oil removal rate can reach more than 90%. Due to the high cost, the extraction method has not been applied in practice with refinery oil sludge treatment.

4.Oil sludge with oil content greater than 30%

The oil sludge with oil content greater than 30% adopts thermal desorption method (Luoyang Building Material and Architectural Design and Research Institute) adopts this separation method and has obtained national patent). The specific process is as follows: Firstly add hot alkaline water with a temperature of 70-90°C to the oil-containing mud sand, the amount of which is added so that the ratio of the oil-containing mud to the hot water is between 1:6 and 1:1; after stirring, the oil sludge is mixed with. The water is fully mixed until the oil reaches equilibrium in the solid phase and the liquid phase, and then the water is circulated to separate the oil from the mixed phase; when the oil in the mixed phase is separated by the oil separator, the oil sludge is completed. The cleaning in the reactor, and then the slurry is subjected to a jet separation and centrifugation. The agitation (generally by mechanical means), prior to high-speed agitation in the reactor, the speed is from 250r/rain to 300r/rain, so that the water and the oil sludge are thoroughly mixed to accelerate the separation and desorption rate. Wherein the volume of the mixed phase of the oil-containing sludge and the hot water accounts for 70% to 90% of the volume of the reactor; when the oil-containing sludge completes the cleaning in the reactor. After the oil in the mixed phase is separated by the oil separation, the slurry can be separated by a jet flow and centrifuged. The oil content after solid-liquid separation treatment is three thousandths, and the treated solid phase can be used for paving, well site, brick making and other comprehensive utilization. This method not only improves the utilization rate of refined oil, but also produces good economic benefits and solves the problem of oil sludge pollution.

The water demand of cement has already attracted the attention of cement users. Especially in the areas where commercial concrete is developed, more and more users are placing higher and higher requirements on the water demand of cement. Concrete producers are hoping to choose cements that require less water, which affects the competitiveness and price of cement companies’ products, and affects the costs and benefits of cement producers.

There are many factors affecting the water demand of cement, and the restriction of the grinding process is one of them. In other words, the cement produced by different grinding processes has different water requirements. This is understood by everyone. However, precisely because everyone understands this, if we want to improve the efficiency of the grinding system, no matter what more advanced grinding process we use, we must consider whether the water demand of the cement is appropriate. Otherwise, we must strike a balance between grinding efficiency, grinding costs and water demand.

Cement water demand

Cement standard consistency water demand (hereinafter referred to as cement water demand), the accurate characteristic parameter should be the standard consistency water consumption of concrete, which refers to the amount of mixing water required to make the cement slurry reach a certain degree of plasticity and fluidity. It is used for cement. An important indicator of performance.
The water demand of cement directly affects the water-cement ratio of concrete, which in turn affects the strength, corrosion resistance, frost resistance and durability of concrete, affects the amount of cement used in concrete production and the amount of admixture, which affects the cost and benefit of users.

The greater the standard consistency of cement, the greater the amount of water used to reach the standard consistency of the cement paste, the amount of water used to reach the specified degree of fluidity of the cement mortar, and the greater the amount of water used to achieve a certain slump in the cement concrete. The greater the water-cement ratio of mortar and concrete, the more intergranular voids and the smaller the compactness, which deteriorates the construction performance, mechanical properties and durability of cement and concrete.

Intuitively, the formulation of concrete has three basic parameters: water-cement ratio, water consumption, and sanding rate.

Two of the three parameters relate to water, which shows the importance of the water consumption problem of cement standard consistency in concrete. The strength of concrete is inversely proportional to the amount of water used. In order to increase the strength of concrete, it is necessary to reduce its water consumption.

In theory, to maintain the strength of the concrete, when the water consumption of the concrete changes, the water-cement ratio should be kept constant, and the amount of cement should be adjusted accordingly, but this is difficult to achieve in actual production operations.

Due to the limitations of experimental conditions and process equipment, it is difficult for ready-mixed concrete plants to adjust the amount of cement according to the change in water demand of each batch of cement. In most cases, the amount of cement and the amount of sand and other materials are kept constant, and the amount of water is adjusted according to the slump value. Thus, the actual water-cement ratio of the concrete will vary with the change in the water demand of the cement, which in turn affects the strength of the concrete. Therefore, in order to stabilize the strength of the concrete, it is necessary to stabilize the standard consistency water consumption of the cement.

Reducing the standard consistency of cement requires water. It is of great significance to the concrete industry to reduce the single cubic water consumption of concrete, thereby increasing its strength, reducing the amount of cement, and saving concrete production costs.

Main factors affecting cement water demand

The first is the influence of cement specific surface area, particle gradation, and particle shape.
The second is the influence of the type and amount of cement mixed materials.
The third is the effect of gypsum on the water demand of cement.
The fourth is the effect of clinker on the water demand of cement.
The fifth is the impact of the grinding process on water demand.

1. The influence of specific surface area, particle gradation and particle shape of cement

Relevant research shows that if the cement specific surface area is 300~400m2/kg, if the particle size distribution slope n of the cement and the clinker reactivity are unchanged, the water content of the standard consistency will increase by 100m2/kg. 6%. The German Cement Research Institute has carried out tests on the influence of specific surface area, particle gradation and particle shape on the water demand of cement for cements of different strength grades. The correlation between cement water demand and specific surface area is strong, with the increase of specific surface area. The water demand has increased significantly.

Tests have shown that cement particle size has a large impact on the water demand of cement. Good cement particle grading reduces the inter-particle gap, which can reduce the filling water, thereby reducing the water demand of the cement. Therefore, in our improvement of the grinding system in recent years, it is felt that both the powder separator and the entire grinding system, as long as the efficiency of the powder selection is increased, the water demand is increased.

The narrower the distribution of cement particles, the larger the porosity of the stack, the greater the water demand

For the strength of cement, the particles with 3μm~32μm play a leading role, especially the particles of 16μm~24μm are very important for cement performance, the more the content is better; the fine particles of <3μm are easy to agglomerate, especially <1μm (mainly refers to Clinker) granules hydrate quickly after adding water, which has a great influence on the water demand of cement, but has little effect on concrete strength, and it is easy to cause concrete cracking, affecting the durability of concrete and affecting the adaptability of cement and admixture. ;>65μm particles hydrated very slowly, contributing little to the 28d strength.

Tests have shown that the shape of the cement particles also has a large impact on the water demand of the cement. The effect of the sphericity of cement particles on their water demand is shown in the table below. The higher the sphericity of the cement particles, the:

(1) The smaller the surface area of ​​the particles, the smaller the surface area required for lubrication → the smaller the water demand of the cement;

(2) The smaller the internal friction between the particles, the smaller the surface water film thickness required for the flow → the smaller the cement water requirement;

(3) The smaller the voids in which the particles are deposited, the smaller the required filling water is. The smaller the cement water requirement is.

Effect of sphericity of cement particles on its water demand

project Specific surface area Particle sphericity Cement water demand
unit M2/kg % %
Sample A 345 47 30.40
Sample B 348 73 27.30

When the specific surface area is basically the same, when the sphericity of the cement particles is increased from 47% to 73%, the cement water demand drops from 30.4% to 27.3%.

2. Effect of grinding process on water demand

Although there are more than one factor affecting the water demand of cement, the grinding process factor is optional during construction and is not easily changed once selected. Because of its subsequent production and the impact of water demand on the balance of other factors, it is a price. Therefore, when initially selecting the grinding process, the factor of water demand should be considered.

In the case of the same raw materials, the cement produced by different grinding processes differs in water demand due to the difference in particle gradation and particle shape. In terms of the existing common grinding process, the order of the cement water demand is roughly as follows: semi-finished grinding of the roller press>double closed circuit combined grinding>single closed circuit combined grinding>closed grinding>opening grinding.

Compared with the ordinary circle flow grinding cement, the open flow grinding cement particles have a wide distribution, the roundness coefficient is large, and the cement requires less water; and the cement produced by the roller press and the vertical mill includes the final grinding and the semi-final grinding. Combined grinding, due to the narrow distribution of cement particles and the low spherical shape of the particles, the cement requires relatively large water.

At present, the cement grinding of most cement enterprises adopts the double closed circuit combined grinding system of “roller press + ball mill”. The grinding efficiency is indeed high, and the power consumption is indeed reduced. However, due to the excessive concentration of cement particles, the water demand is still high. This is necessary to increase the amount of concrete water reducing agent used and increase the cost of the concrete mixing plant. In the case of oversupply in the cement market, the mixing station does not buy much, and ultimately it will affect the sales volume and selling price of the company.

In addition to the influence of the roller press on the shape of the cement particles, in general, the closed-circuit grinding system, especially the closed-circuit system using the high-efficiency classifier, has a narrow particle size distribution, the particle size uniformity coefficient is 1.0~1.2, and the water demand is required. Up to 26.0% to 28.0%. The cement of the open grinding system has a wide particle size distribution range, the uniformity coefficient is 0.9~1.0, and the water demand of cement is about 24%.

Semi-final grinding and cement water demand

The so-called semi-final grinding, precisely in the pre-grinding stage of the grinding system, select a part of the semi-finished products that have passed the fineness in advance, and directly add them to the finished product, so that the products with fineness have passed, leave early. The grinding system no longer accepts subsequent grinding, which improves the powder selection efficiency of the entire grinding system (not only the classifier), reduces the phenomenon of over-grinding, reduces the waste of grinding energy, and improves the grinding efficiency of the system. The semi-finish grinding process is actually an optimization of the original grinding process by using the closed circuit process of the powder selecting equipment. Depending on the pre-grinding equipment selected, there are many specific forms, but due to the improved efficiency of the system, the grinding efficiency is certain. At present, the pre-grinding equipment used in the semi-finishing grinding process is mainly a roller press, and other vertical grinding, wind-selecting grinding, ball grinding and the like.

Regarding the problem of cement water demand in the semi-finishing grinding process, several semi-finish grinding processes are not the same. It depends on what equipment is used in the pre-grinding stage, and the semi-finished products that have been qualified in advance are selected in advance. What is the difference between some finished products, resulting in changes in the content of fine powder, particle gradation and particle shape in the final product.

The increase in the content of the fine powder, the narrowing of the particle gradation, and the non-spherication of the particle shape all lead to an increase in the water demand of the cement. For example, the early two-ball mill grinding process (the first one is closed) is the earliest semi-finish grinding, which not only improves the grinding efficiency, but also reduces the phenomenon of over-grinding and reduces the micro-powder content of cement. Reduce the water demand of cement; for example, in recent years, cement mills that have been modified from unloading and drying mills in raw materials should be compact semi-finished grinding, although the grinding efficiency is not reduced, but due to the particle size of the cement. With a narrower distribution, the water demand of cement has increased, so it has not been promoted. Nowadays, most of them say that the semi-final grinding actually refers to the semi-final grinding of the roller press, which is to add part of the unshaped fine powder collected by the closed circuit system of the roller press to the finished cement product.

The water requirement for the semi-finished cement of the roller press depends on the fine powder content (hydration speed) of the cement, the particle grading (bulk density), and the particle shape of the cement (flow internal friction). The reduction of the content of the micropowder and the widening of the gradation can reduce the water demand of the cement; however, the dissimilation of the particle shape (non-spherical) can increase the water demand of the cement. It has been proved that the water demand of the cement of the semi-finish grinding system of the roller press is generally increased. As for the increase in water demand, it is related to the characteristics and fineness of the raw material entering the roller press, that is, the degree of dissimilation of the particle shape of the roller press.

Because of the addition of a classifier between the V-selector and the cyclone, it ensures that the materials collected by the cyclone dust collector all meet the requirements of the finished cement product. This improvement can increase the capacity of the grinding system and reduce the power consumption of the grinding, but at the same time reduce the expansion capability of the finished cement particle grading. Moreover, it is certain that this part of the material is mainly a fine powder of a roller press which is not shaped by a ball mill, and the sphericity of the particles is inferior.

The bulk density and fluidity that affect the water demand of the cement are related to the particle size of the cement, and also related to the particle shape of the cement. The roundness coefficient (the circumference of the circle equal to the projected area of ​​the particle and the actual circumference of the projected area of ​​the particle) The higher the ratio, the smaller the internal friction of the cement particles, the smaller the surface area of ​​contact with water, and the smaller the standard consistency water requirement.

The roller press is crushed once by the material bed, and the efficiency is high, but the sphericity is not good. The ball mill is a multi-impact grinding machine with low efficiency and high sphericity, which is the main reason why the roller press can not drop the ball mill. But this does not mean that the roller press semi-final grinding system is useless, but it can be said to be a result of refined management. Although the semi-finish grinding of the roller press has the disadvantage of high water demand of cement, it is indeed effective for improving the output of the grinding system and reducing the power consumption. Any improvement in performance is accompanied by a targeted improvement and a decline in adaptability. As long as we can use it to avoid it, the semi-finishing of the roller press can still make a difference.

The conditions for the semi-final grinding of the roller press are: the materials with small particle shape of the roller press (such as fine fly ash), the market and users who are not sensitive to the water demand of the cement, and most of the low-grade cement. For the cement open-circuit grinding system, the cement with relatively low surface area control, the clinker with low water demand, and the cement with fine slag powder.

The factors that are not suitable for the semi-final grinding of roller presses are: for the market and users with demanding water requirements for cement, for most high-grade cements, for cement closed-circuit grinding systems, for cements with relatively high specific surface area control, Clinker with high water content, for relatively poor limestone mines, for raw materials with relatively high alkali content.

In fact, the above conditions are not static, and sometimes they are not adapted. We can design or transform the process of “half-finish grinding” and “combined grinding” to switch on demand. When the conditions are met, the capacity will be maximized, the power consumption will be minimized, and the joint grinding will be switched when the conditions are not met. If there is some potential, the adjustment of the semi-finished powder separator can be appropriately reduced. The final amount.

Vertical mill grinding and cement water demand

Although the vertical grinding final grinding system has many advantages such as high grinding and drying efficiency, good adaptability to the grinding materials, simple process flow, compact space arrangement and low maintenance cost, cement grinding is the guarantee of the quality of cement products. At the last level, everyone is still worried about the performance of vertical mill cement, especially for the high water demand of cement. The process technology of this cement grinding is still limited in China.

In fact, the cement vertical grinding final grinding products can be compared with the ball mill, which can meet various engineering needs. The selection rate of the cement vertical grinding final grinding process has shown an increasing trend year by year.

The selection rate of cement vertical grinding final grinding process is increasing year by year.

area 2000 2005 2010
World (excluding China) 15% 45% 70%
China Mainland 0.0% 0.2% 0.8%

According to relevant information, from 2005 to 2008, about 360 new cement production lines in the world (except mainland China), the annual cement production capacity reached 440 million tons, and more than 600 sets of cement grinding equipment were used. The selection rate of vertical mill increased from 45% in 2005 to 61% in 2008, while the selection rate of cement ball mill decreased from 50% to 27%.

With the gradual increase of the final grinding process, the technology is further improved and matured. The problem of cement particle shape and gradation, fineness control and water demand, which are worried about the cement performance, is now also It is not a problem.

Through the combination of the grinding disc and the grinding roller grinding curve, the improvement of the performance of the grinding machine, the height of the retaining ring, the adjustment of the rotating speed and pressure of the grinding disc, the optimization of the shape and grading of the cement particles is realized. In terms of system operation, it is also possible to optimize the performance of the cement by increasing the temperature inside the vertical mill and exerting an influence on the dehydration of the gypsum. By comprehensively using these control methods, the performance of vertical mill cement can be controlled in a wide range, so that the particle ratio ratio is even more reasonable than ball mill cement.
Studies on different grinding systems have shown that the highest water requirement is the cement of the closed-circuit combined grinding system, not the cement of the vertical grinding system.

Grinding and water demand separately

The separate grinding of cement is a grinding technology that saves electricity (reduced electricity consumption) and reduces carbon consumption (reduced carbon emissions). In addition, it optimizes the performance of the cement and meets the different requirements of the user for cement performance (such as the water demand of cement). How to achieve the optimal particle distribution of various components such as clinker in cement under the condition that the wearability of each component is very different, it should be said that grinding is the best choice at present.

Grinding separately can set and realize the optimal particle size distribution of each component of cement to achieve the maximum utilization of clinker activity and full digging of the active potential of the mixture. At present, cement mills in advanced countries have rarely used mixed grinding processes.

One of the advantages of separate grinding is that it can easily adjust the particle gradation. The fine powder in the cement not only reduces the water demand due to its ability to increase the fluidity of the cement, but also increases the water demand by speeding up the hydration speed. The grinding has created the conditions for the balance of our balance. Further analysis will reveal that the main factors affecting the hydration rate of cement are clinker components. As long as we reduce the fine powder of clinker and increase the fine powder of other inert mixed materials (such as limestone), we can satisfy the contradiction between the two parties to reduce the water demand of cement. Claim.

Germany’s research shows that in the mixed slag cement, the characteristic particle size of the clinker is smaller than that of cement. The characteristic particle size of the slag is larger than that of cement. The characteristic particle size of gypsum is much smaller than that of cement. In the separately ground cement, When the material composition and the specific surface area are the same, the characteristic particle size of the clinker is reduced by 2.0 μm on average, and the characteristic particle size of the slag is reduced by 7.5 μm on average.

The so-called “characteristic particle size” is actually an approximate embodiment of “volume average particle size”. That is to say, in the case of the same specific surface area, the separate grinding can make the clinker and slag finer, and the fine powder is not too much, which is exactly what we expect. The operation of grinding in foreign countries has not stopped. There is a company that supplies cement for the concrete mixing station. In order to meet the various requirements of the mixing station for cement, and to reduce the production cost, nearly 20 targeted ones have been developed. The variety of cement.

The benefits of separate grinding:

1. The particle size distribution of clinker powder is close to the optimal performance RRSB equation, the clinker fine particles affecting the performance of cement and concrete are few, and the clinker coarse particles affecting the hydration rate are also rare;

2. The fineness of the mixed material is significantly thinner than the clinker. After mixing with the clinker powder, the particle size distribution of the cement is close to the Fuller curve, which ensures that the cement has a lower porosity;

3. The clinker powder with different particle size distribution and the mixed material with different particle size distribution can be combined in a certain ratio to realize the particle gradation design of cement and produce the cement with the expected performance;

4. Not only the early strength of the cement is high, but also the late and long-term strength develops well;
5. Hydration heat, especially early hydration heat is low, compatibility with water reducing agent is good, concrete has good workability;

6. It is possible to mix a variety of mixed materials to produce a multi-component combination of cement, thereby exerting performance complementation and superposition effects of different types and different particle distributions to optimize cement performance;

7. It can flexibly organize the production of multi-variety cement, and the process of changing production is quick and convenient, meeting the different needs of customers;

8. Even with the hard-grinding high-fine slag powder, the cement with a specific surface area of ​​350~420m2/kg has a combined power consumption of only 31~35kWh/t.

The layout of the cement production line is to build a cement clinker production line in the mining area and establish a cement grinding station near the cement sales market to reduce transportation costs. If the clinker production line is built near the city, for every 1t of clinker produced, about 1.6t of cement raw material is needed, and the transportation cost should be increased by 60%.

If the cement grinding station and the clinker production line are built together in the mine, since most of the mixed materials are waste generated by the city, these mixed materials are transported to the cement factory built near the mine, ground into cement and then transported to the city. Increased transportation costs. Therefore, the clinker production line should be built near the mine, and the cement grinding station should be built near the market.

First, the design of the raw material grinding and batching station should meet the following requirements:

(1) The capacity of the batching bin should meet the needs of raw material grinding production. When using the storage batching ingredients, the storage capacity should be determined according to the storage requirements;

(2) The batching bin should prevent the material from arching, wall hanging, and blocking the warehouse in the warehouse, and flow smoothly from top to bottom; the wet storage material warehouse should adopt anti-blocking measures;

(3) Feeding equipment should use a quantitative feeder, the measurement accuracy level should not be lower than O.5, the feeding amount adjustment range should be 1: 10; the wetted material should be added before the quantitative feeder. Low pre-feeding plate feeding machine, or chain plate scale, and the length-to-width ratio of the discharge port of the silo should be appropriately increased;

(4) When the batching bin is set in the joint storage, the upper port size of the bin should meet the requirements for the unloading of the grab crane;

(5) When using the car-type grinding machine and the car-pressing machine as the grinding equipment, an iron and metal detection and alarm device should be provided.

Second, the selection of the raw material grinding system should meet the following requirements:

(1) The drying heat source should utilize the waste heat of the preheater and the cooler;

(2) A kiln should be equipped with a set of raw material grinding system;

(3) The selection of the main machine should be determined according to the wearability and abrasiveness of the raw materials, the output requirements of the system and the characteristics of various grinding systems. The final grinding system or the series grinding system of the radiation machine with good energy-saving effect should be selected.

Third, the output of the raw material mill should be determined according to factors such as the daily output of the kiln, the material consumption, the working hours of the mill, and the number of units.

Fourth, the arrangement of the raw material grinding system should meet the following requirements:

(1) When the raw material grinding system uses the preheater exhaust gas to dry the raw materials, it should be arranged near the preheater tower and the exhaust gas treatment system;

(2) The grinding machine with drying should be equipped with a wind lock device at the inlet and outlet;

(3) A spare hot blast stove can be installed by using a raw material grinding system for waste heat of exhaust gas;

(4) The spoke mill should be arranged in the open air;

(5) Mill lubrication system The arrangement of the oil pump station should ensure that the return pipe is unblocked.

Fifth, the product quality of the raw material grinding system should meet the following requirements:

(1) The raw material moisture should be controlled below 0.5%, and the maximum should not exceed 1.0%;

(2) The raw material fineness should be determined according to the raw material flammability test and clinker quality requirements, and the fineness fluctuation range should be +2%.

Sixth, the dust collection design of the raw material grinding system should meet the following requirements:

(1) The top of the batching warehouse and the bottom of the warehouse and the transfer point of the conveying equipment shall be set up according to the characteristics of the materials;

(2) When the preheater exhaust gas of the mill is used as the drying heat source, a dust collector should be used together with the preheater exhaust gas. When the raw material moisture is large and the waste heat of the preheater or the cooler is required, a dust collector should be shared, and the dust collection system should be kept warm.

Seventh, the batching control of the raw material grinding system should ensure that the raw material reaches the specified chemical composition, and the production control system should comply with the automation requirements of the production process.

At present, the use of slag powder is becoming more and more common, and fly ash will also be utilized in its fine form. Therefore, all new grinding stations should consider the slag (or fly ash) micro-powder and slag (or fly ash) weighing scales in front of the cement grinding and cement storage, so as to match the grinding cement after “homogenization” Into the cement store. This will not only improve the quality of the cement, but also increase the cement production of the grinding station.

The pre-homogenization technology used in the design of cement plants is to use the scientific stacking and reclaiming technology to realize the initial homogenization of raw materials in the process of depositing and taking raw materials, so that the raw material storage yard has the functions of storage and homogenization.

The basic principle of raw material pre-homogenization is that when the materials are stacked, the incoming raw materials are continuously stacked in a certain manner into as many parallel layers, upper and lower overlaps and the same thickness. When taking the material, in the direction perpendicular to the layer of the material, all the layers are cut as much as possible, and cut in order, until the end is taken, that is, “tiling straight”.

The storage period of various materials should be determined according to the scale of the plant, material source, material properties, transportation mode, storage type, factory control level, market factors, etc., and should meet the requirements of the following table.

Various material storage period (d)

Serial number Material name Material storage period
Wet material Dry material
1 Calcareous raw material 3~7
2 Silicon-aluminum raw material 5~30
3 Iron raw material 10~30
4 Coal 7~30
5 Raw material 1~3
6 Clinker 5~20
7 Plaster 7~30
8 Mixed material 7~30
9 cement 3~14

Note:

1. The material storage period is calculated based on the kiln mouth output as the basis;

2. If the calcareous raw materials and the silico-alumina raw materials are purchased, the upper limit may be taken; the storage period of the materials;

3. The clinker storage period of clinker shipment and cement powder grinding may be appropriately relaxed;

4. The mixed materials shall be determined according to their source, distance and variety;

5. The storage period of cement should be considered in conjunction with the storage period of clinker. Combined with market demand, transportation conditions are determined;

6. Material storage period refers to the total storage period in each storage mode such as stacking shed, combined storage, pre-homogenized storage yard, and round storage.

First. In any of the following cases, the raw material should be pre-homogenized:

1. The deposit conditions are complex, and the fluctuation of ore grade or major harmful elements is relatively large;

2. There are low-grade raw materials such as interlayers, coverings and crackers that can be used together in the deposit.

Second. In any of the following cases, the pre-homogenization yard should be set for the raw coal:

1. The quality of raw coal varies greatly, or the quality of pulverized coal into the kiln cannot guarantee the fluctuation range of two adjacent tests;

2. The original coal comes from many places, or the coal types are also various;

3. Poor coal quality, does not meet the requirements of this specification, or the coal blending method is required for adjusting the ratio of sulfur to alkali.

Third, the pre-homogenization yard should be designed according to the nature of raw materials and fuels, and should meet the requirements of factory scale, storage mode, automation level, environmental protection and technical requirements.

Fourth, the design of raw materials and fuel pre-homogenization yards should meet the following requirements:

1. The number of layers should be 400 ~ 500 layers, the homogenization coefficient can be 3 ~ 7, should be determined according to the fluctuation of the raw materials and fuel components entering the yard;

2. The choice of yard form should be determined according to the overall layout of the plant, plant topography, expansion prospects, material performance, quality fluctuations and economic factors;

3. The stacking method can adopt the stacking method such as herringbone and conical, and the type of stacker should be selected according to the yard type;

4. The method of reclaiming can adopt end-face reclaiming or side reclaiming;

5. Mixing pre-homogenization yards, pre-dosing should be carried out before pre-mixing;

6. When two or more types of coal are used, they should be combined into the pre-homogenization yard;

7. The material discharge detector shall be provided at the discharge end of the stacker, and the height of the discharge point shall be automatically adjusted according to the height of the pile;

8. Ventilation facilities should be provided in the trench of the reclaimer.

Fifth. The pre-homogenization yard should be equipped with a closed factory.