The fuel in cement production

The main technological fuels used in firing building materials (in particular, a cement clinker and lime) are coals and natural gas.

Fuel swap in the production of cement and lime

Coal

Preparation of the dust mixture is carried out on production lines, the main equipments which are vertical roller mill, equipped with bag filters, heat and weight.

Currently under research and development work on the use of cheaper high-sulfur coal.

Used tires

One of the most efficient methods of tire use as a fuel is its direct combustion in the rotary kiln calcination zone. High calcination temperatures promote efficient combustion of waste tires and a steel cord composed of cement clinker.

In the process of development of the technology of burning tires set an optimum quantity, which should not exceed 10-12% of the specific fuel consumption for clinker burning.

oil coke

Petcoke as fuel has several advantages, among them - high calorie (lower heating value in working QPH> 7500 kcal / kg) and low yield of ash. At the same time it is necessary to consider the presence of some negative characteristics that limit the use of petroleum coke volume: high sulfur content (S = 3-5%), heavy metals (RT <1800 ppm), lower grindability towards coals grades T and G.

Alternative fuel from municipal solid waste (AT from MSW, RDF)

In world practice, the production of cement clinker are widely used fuel waste. According to the classification adopted in the EU, waste fuels are divided into 14 groups, the list of which includes sorting combustible fraction of municipal solid waste (RDF). In the CIS countries, this group is classified as an alternative fuel from municipal solid waste (AT SDW).

According to the EU in cement kilns EU 5133 ths. Tons of waste fuels were used in 2004, of which the share RDFsostavila 734.3 thous. Tons, or about 14% of the total volume of waste. On a number of cement plants in Europe the share of incinerated waste fuel is 100% of the total heat consumption in the clinker burning, while the share of RDF 70-80% ("Helm", Poland).

RDF production from municipal solid waste abroad is carried out on garbage-processing plants (EMF) that are tailored to customer requirements due to hardware design of solid waste processing technology provides the fuel of different composition. Usually, the user sets the individual requirements:

- In aircraft fuel efficiency;

- Content of harmful impurities (CI-, S, heavy metals, etc.).

 

RDF differs from fossil fuels at lower cost, due to the presence in it of harmful impurities, which even under careful sorting waste affect product quality and stability of the furnace unit. In this connection there may be two options for using RDF:

- Limit the value of fuel swap (10-20% RDF);

- A high proportion of fuel swap (RDF> 50%) carried out the reconstruction of furnace units (the organization of the bypass gas furnace, installing pneumatic guns), which is associated with additional costs and an increase in specific fuel consumption for clinker burning.

Clinker cooler

In the cement industry for the final cooling of clinker after it leaves the cooling zone of the rotary kiln used refrigerators. clinker cooling mode affects the phase and mineralogical composition and it can therefore be regarded as an integral part of the process of clinker burning. The clinker is cooled by air entering the rotary kiln for burning fuel. Therefore, clinker coolers act as heat recovery boilers and improve the thermal efficiency of the furnace unit.

In Russia, 75% for cooling cement clinker and heat recovery in the furnace grate used refrigerators. This is, basically, two-chamber grate grate cooler type "Volga". Grate cooler unlike other heat recovery units, allow you to control the clinker cooling process or automate this process. In the United States, Japan and Western European countries used grate cooler with a number of chambers of three or more. The criteria for optimizing the following parameters can be selected: the maximum heat removal from grates or minimizing the output of clinker temperature.

The heat that is selected from the clinker cooler and partly returned to the furnace together with the secondary air, which is needed for combustion. According to different authors and producers of cement activities grate cooler automation can reduce fuel consumption needs for clinker firing by 2.5 - 5%. Automation of the cooling process can be one of the main and the first steps to improve production efficiency.

The most common clinker coolers are heat recovery (planetary), grates and drum (pipe). There are other types of refrigerators, but the extent of their application in industry are less significant.

Types of cooling drum depending on the cooling method of the processed material:

- Air cooled

- Water-cooled

- Tube refrigerators

-As Refrigerators, air-cooled material is cooled by air which is supplied in cocurrent or countercurrent fan.

-As Refrigerators with water cooling drum is irrigated outside water that has passed through the cooling bath. To increase the time of contact with a cooled wall of the material in the drum longitudinal shelves installed.

- Pipe refrigerator is an internal drum of the heat-resistant steel and an outer casing made of carbon steel. The inner drum mounted pipes. On the inner drum casing mounted guides, facilitating advancement of the product as the drum rotates. Upon rotation moves the product cooler the annulus and cooled in contact with the outer walls of the tubes. As a counter-tube space sucked air. The heated air is used in the lime burning kiln.

 

Storage of clinker

In order to have sufficient reserves (reserves) for grinding cement, clinker stocks are normalized. The stock is about a monthly productivity of the furnace. For this purpose, the closed space (capacity) to avoid dust emissions and a reduction in the quality of clinker due to weather conditions (rain, snow).

For storage of clinker in modern cement plants installed clinker stocks of various designs.

International AUMUND group developed a clinker storage depots of the following types:

- Round, without central support capacity of 3500... 156 000 tonnes;

- Cylindrical silos with a capacity of 5,000... 60,000 m;

- Round, with central support capacity 51000... 190000 tonnes;

- In-depth warehouses with a capacity of 45000... 201 000 tonnes;

(Bulk density clinker γ = 1500 kg / m3).

Round without central support clinker warehouse made of reinforced concrete, a cylindrical shape with a diameter of 40... 80 m, a height of 10... 25 m, the top cone

Cooler SF (Smidth-Fuller).

The basic principle of all types of cooling is that cooling air passes through the clinker layer on the grate and the cross-flow heated air completely or partially fed to an incinerator nozzle fuel supplied to the furnace. It is important clinker cooling mode selection, since the cooling mode and the quality depends on the microstructure of clinker. By optimizing the clinker cooling process created a good opportunity to improve clinker production at the lowest possible capital and operating zatratami.V JSC "Kokshe Cement" for the clinker cooling a refrigerator SF (Smidth-Fuller) cross output of 5500 tons / day. Grate area is 139 m2. Design feature of the refrigerator is mixed with the clinker via crossbars moving over the fixed grate, and the flow is controlled by motor controllers available in each reshetke.Kolosnikovye lattice modules in the refrigerator as well as in the inlet modules are mounted in the foundation. clinker is transported by a reciprocating compressor with crossbars, located on the line 50 mm above the grate. Each unit has a refrigerator 12 crossbars, 6 fixed and 6 mobile. Moving cross connected to two longitudinal profiles, which are actuated by a hydraulic cylinder, located under the grate, one for each module. a drive system connected to the unit drive system in the previous and next module. Settings "to the right" modules "in the middle" and "left" then can be moved independently of each other for optimum distribution and transport of clinker. Since reserved grates fixed bed of clinker, they, unlike the other contemporary refrigerators and will not wear out and degrade air distribution with a large amount of sealing air. Grate is made with labyrinth air path to avoid loss of clinker. Therefore, transportation equipment under the grate is missing. Grate has a low pressure drop. To ensure optimum air distribution grate, each equipped with a mechanical flow regulator (MPP). MPP maintains a constant flow of air through the grate and independent of the layer height clinker the clinker bed, the particle size distribution, temperature, etc.: a separate flow control for each of the grate. RAM allows one fan for relatively large areas and completely eliminates the use arranged under the grate tubes and louvers that are present in other modern refrigerators. SF modular principle allows the refrigerator factory assembly of large parts of the refrigerator and quick installation on the construction site.

Storage of clinker

In order to have sufficient reserves (reserves) for grinding cement, clinker stocks are normalized. The stock is about a monthly productivity of the furnace. For this purpose, the closed space (capacity) to avoid dust emissions and a reduction in the quality of clinker due to weather conditions (rain, snow). For storage of clinker in modern cement plants, clinker stocks set different konstruktsii.Mezhdunarodnaya AUMUND group for clinker storage warehouses has developed the following types:

- Round, without central support capacity of 3500... 156 000 tonnes;

- Cylindrical silos with a capacity of 5,000... 60,000 m;

- Round, with central support capacity 51000... 190000 tonnes;

- In-depth warehouses with a capacity of 45000... 201 000 tonnes;

(Bulk density clinker γ = 1500 kg / m3).

Round without central support clinker warehouse made of reinforced concrete, a cylindrical shape with a diameter of 40... 80 m, a height of 10... 25 m, the top cone. The top of the conveyor and mounted precipitators. Discharging clinker is carried out by 2... 4 channels.

Cement Grinding

clinker crushing

While the raw material mixture for the preparation requires two steps of cleavage - primary and secondary, clinker crushing is performed in a single operation and, moreover, not everywhere. Typically, the clinker discharged from the rotary kiln, is small, so that optionally crush it. In addition, when a two-stage grinding clinker pre-grinding it is produced.

Recently, however, are increasingly practiced by the special grinding clinker, which da'et opportunity to feed the mill for more uniform material size, improve its efficiency and to minimize fluctuations in the grind and mill performance. They do not need to be pre-split only such clinkers, which are highly uniform particle size.

But if clinker crushing is not always necessary, pre-grinding it plays an important role in grinding technologies. As in the raw material grinding, in this case, the mills of two types: centrifugal ball and which have different structures depending on the purpose. Some types of mills for the pre-crushing are characterized by low energy consumption, but expensive to operate; others have high performance at minimal cost to install and take up little space; others have good mechanical and performance characteristics, but do not provide the necessary grain composition of ground clinker, which may affect the quality of the final product - cement.

In the pre-grinding and final grinding of clinker should always bear in mind the construction properties of cement. This differs from the grinding of clinker grinding raw materials. In this case it is necessary not only to grind the clinker to a certain size, such as to obtain a product of the mineralogical and grain composition to the required chemical and physical characteristics of the 'cement were provided. In this regard, some plants are more willing to remodel the old, proven mill for pre-grinding clinker than establish new, although the costs are about the same. At one plant manufacturing high-early portland cement, it was found that when installing a new mill for pre-grinding of cement quality has deteriorated, although grinding is produced to the same surface area as before.

The final grinding

For final grinding of cement used is basically the same equipment as for the secondary grinding of raw materials, namely, tube mill and combined in different sizes. The two-stage in the grinding tube mills discussed above, is still the most common system for cement grinding. This system is very flexible and provides good grain structure of the finished product. With proper separation chamber otgtrtntr mill to corresponding selection double grinding bodies and grinding (if necessary) an optimal match between the preliminary and final grinding even in cases where the cements produced with different specific surface area. At two hundred-diynom grinding mill temperature is usually below ceteris paribus.

In order to provide greater flexibility of the grinding system, the application of multi-mills are increasingly used air separation. Fig. 24 shows a typical separator commonly used in cement plants.

Air separation makes it possible to produce cement with different fineness or specific surface at a constant load and the size of the grinding bodies. Also, when grinding from cage relatively hot material moves in a system with a large radiating surface, whereby its temperature is reduced significantly and improving the working conditions of the mill. In some plants to further reduce the temperature in the system is used water or air cooling mills and separators.

When grinding a clinker are added a few percent unfired gypsum to control the setting (such that the total content of SO3 in the cement was not more than 3%), and 15% granulated blast slag or active siliceous drbavok or up to 10% inert additives which, while not lowering practically cement quality, increase its amount, In the manufacture of blended cements

with more aktivnyx or inert additives can grind clinker and additive separately and as thin as possible, and then mix them.

Ready Portland - very fine powder is greenish-gray color. After exiting the mill it is still high Temperature (up to 120-130 °) and directed by conveyor or pneumatic pump to storage in silos. Soaking in the cement silos is necessary for cooling and quenching of free calcium oxide residues, which occurs under the influence of air vglagi. Cement silos maintained as long as the test it will not detect a uniform change in volume and have a normal setting time.

From silos cement is supplied to weigh out and pack

Milling equipment

Currently used for grinding cement and vertical tubular ball mill roll which can reduce power consumption compared with ball mills 25 to 40% [4, 100].

In order to improve grinding efficiency by about 50% using the press roller (roller presses) - High-pressure rollers (Figure 1.22). In cement plants Roller - press mainly used for pre-grinding clinker to cement grinding in a ball mill pulverizing [99].

Grinding the material in the press roller is made between two rolls rotating towards each other, which are compressed high pressure of about 150 bar. Material flows into the expansion box, the amount of material is regulated by the metering slide valve

Clinker is ground in a mill together with 4-10% gypsum (anhydrite). and other additives are introduced if necessary. Dosage is carried out by means of weight feeders or feeders.

Figure 1.23 shows a two-compartment mill construction company UMS FL SMIDTH to support housing and driven by the ring gear.

When the mill, especially in dry grinding, the bearing can be very warm by passing through a pin of hot material. The temperature coming out of the cement mill is 100... 150 ° C. There is also heated by friction bearings, especially in the case of dust. To cool the bearings provides their water cooling.

On the performance of tube mill the following factors:

- Grindability of the material (hardness);

- Size of food material;

- Fineness of the finished product;

- The range and weight of grinding bodies;

- Design and dimensions of the mill;

- Grinding technology used (open or closed loop, grinding aids, press rolls, etc.).

Clinker Grinding can be carried out in the open and closed tsikle. When grinding in an open loop whole material received by the mill exits therefrom as a finished product and can not achieve high udelnoy surface, increasing energy consumption for grinding, since a significant amount of fines accumulated in the mill.

Ready cement has a particle size range that impairs its properties. In open loop cements ordinarily is milled to udelnoy surface not more than 300 m2 / kg. To achieve a higher specific surface area is necessary in the process of grinding to separate fine particles, ie. E. Closed tsiklpomola apply. This izmelchaemy material passes through the separator, which separates the fine fraction, which is a finished product, and cereals Thanks to the timely removal of the fine fraction of mill finished product more uniform in composition granulometricheskomu contains significantly less major fraktsy that remain in the cement stone ballast, and have almost no influence on the strength. Grinding clinker in a closed loop can osuschestvlyat two schemes. Cement grinding process in a closed loop circuit is shown in Figure 1.24.

For this skhemeizmelchenny in the pipe mill clinker fed by bucket elevator and chanels in cages, where grit is returned to regrinding mill in the first chamber, and the finished product is supplied in silos. This scheme is simple and easy to use, it can be quickly translated into an open loop. High dispersion Material directed into the separator promotes effektivnosti last work as fine fractions increases yield and increased plant productivity. Lack of installation - increased power consumption due to some