Organization of CCC production through the eyes of industrial equipment manufacturers

For a decade and a half of development of the production of dry building mixes, leading manufacturers have accumulated some experience in operating both domestic and European equipment for the production of CCC. A new trend is the emergence of Chinese suppliers of construction machinery and equipment for the production of SSS in the Far East. Some of them, such as the Zilin company, have also reached the western regions of Russia. The choice of industrial equipment is constantly growing, but the basic principles of effective organization of production of dry building mixes have not yet been seriously changed.

During the discussion held by the magazine " Dry Building Mixes "(No. 3, 2013), representatives of prominent machine-building enterprises offering equipment for the production of dry building mixes were listened to.: Russian company "Vsuh", Finnish "LAHTI PRECISION Oy" and German "M-TEC MATHIS TECHNIK GmbH". We invite you to read the report of A.V. Teleshov, head of MK "Vselug", who gave a detailed overview of the technical side of the organization of the production of SSS:

What is a modern plant for the production of CCC? This is a mixing tower with a height of 25-50 meters. Its upper part is formed by silos for storing initial components. Outside, the silos are covered with enclosing structures or left open. A finished goods warehouse adjoins the tower.

Product range. The CCC manufacturing plant is a universal tool. Virtually any type of dry mixes can be produced on one production line, if the line is equipped with modern equipment and has a vertical layout. The only limiting factor is the number of silos of the initial components. If the number of silos is, say, 8, and the recipes contain 12 initial components (not counting additives), it is obvious that some recipes will have to be abandoned. For ease of operation, two processing lines are sometimes placed under one group of silos. This is advisable in the case of simultaneous production of cement and gypsum mixtures. It is also more convenient to produce colored mixtures on a separate line.

Location. When choosing a location for a future plant, the main factor is often proximity to consumers. The sales area for simple mixtures is usually limited to a radius of 100 km. Factories focused on such mixtures are often located on the outskirts of large cities. The delivery distance for special purpose mixtures may exceed 1000 km, and there will be at least several large cities in the potential market. The factory can be located in one of them. There are also known cases of plants being located in sand pits, that is, near the main source of raw materials.

Number of silos. At foreign plants, the number of silos for storing basic components reaches 20 or more. In Russia, the number of types of binders available for use and, accordingly, the number of silos of initial components usually lies in the range from 8 to 12. In practice, many silo layout schemes are used, the simplest of them are:

• 4 components – a square of 4 silos.
• 8 components – two squares of 4 silos.
• 9 components – a square of 9 silos, one of which is in the center.
• 12 components – a square of 9 silos, 3 silos are divided by partitions into 2 parts.
• "camomile" – from 5 to 10 silos located around the circumference.

Providing production with sand. In Europe, along with cement and other mineral binders and aggregates, it is possible to buy dry fractionated sand and deliver it to the plant in pneumatically unloaded tanks. If there are no suppliers of dry sand within reach, the drying and classification of this component becomes the concern of the CCC manufacturer. In this case, a drying unit is placed next to the mixing tower, a vibrating classifier is installed above the silos, and a bucket elevator is used to supply sand from the drying unit to the classifier. The sand preparation line is a separate technological unit that operates independently.

Vertical diagram and its gap. When loading into silos, the original components are lifted up once. Further, when passing through all technological operations, the components move down. This is the principle of the so-called classical vertical scheme. The vertical diagram can be broken in two places: along the line "hopper scales-mixer" or "mixer-filling machine". To make a decision about breaking the vertical scheme, you need to have good reasons.

If a break in the vertical circuit is still necessary, it is important to choose the right type of transport device, which should not have dead zones and should have a closed design. If the gap is made along the line "hopper scales-mixer", it is also necessary to organize a batch feed without residues.

Mixing is the main technological operation. Since the vast majority of CCC plants in the world are equipped with Lodige mixers, the authors suggest that when assessing the capacity of plants, the terminology should be used that is tied to the volume of a mixer of this type. The capacity of the bagging plant must not be less than the mixing capacity, regardless of whether other types of shipment are provided or not. Modern filling machines have a modular design, the capacity of one module is about 300 bags/hour. The number of modules is determined based on the packing of 25 kg.

Stock of raw components. When designing a plant, the required inventory for each component is determined depending on the distance of suppliers and the organization of the transport scheme. To determine the total capacity of raw silos, you can use the following rule: the volume of the mixer in liters divided by 2 will give the volume of silos in cubic meters.

Finished product warehouse. Bags with finished products are stored on pallets in two tiers without racks and up to 5-6 tiers on racks. The capacity of the warehouse should correspond to approximately two weeks ' production volume: the volume of the mixer in liters multiplied by a thousand will give an idea of the required warehouse capacity.

Silage equipment. Pneumatically filled silos are equipped with pressure filters, which serve to purify the air released into the atmosphere. All silos are equipped with different types of upper and lower level alarms. Sand silos, if sand comes from a drying line, must also be equipped with level meters.

Dosage of the main components. From the silos, the components are delivered to the scales sequentially, one after the other. The dosing cycle of each component includes 3 stages: high-speed feed, low-speed feed, pause to calm down and check the actual mass. During one mixing cycle, up to 10 components are weighed sequentially on a single hopper scale. Binders and fine aggregates are fed to the scale using two-speed augers. To interrupt the supply of the product to the scale at the end of the dosing cycle, pneumatic butterfly valves are used. To ensure reliable unloading of fine components from the silo, the conical part of the silo is equipped with an aeration system. Sand feed augers must meet a number of requirements related to abrasiveness. The speed of rotation is limited, metal of greater thickness and hard alloy surfacing are used, intermediate supports are excluded.

Hopper scales, as well as all component supply paths, are made in a completely closed version. They are equipped with self-contained filters or connected to an aspiration system. A stand-alone filter is preferable, since the trapped dust is returned back to the process. Dosage of additives. They are dosed by weight. When designing a plant, you can choose one of three options: automatic system of weight dosing of additives, weight dosing of premixes, manual input of additives. The automatic dosing system is similar to the main component dosing system. It includes bins for storing additives, metering screws and hopper scales. Many additives have poor flowability, which must be taken into account when designing equipment. In the case of using premixes, equipment costs are significantly lower. The scheme of working with premixes makes sense when organizing the production of identical formulations at different plants, as well as to reduce their own costs for functional additives due to their forced activation.

Manual introduction of additives is used to save money. Additives are weighed on conventional commercial scales, packaged in plastic bags or cans, and at the right time introduced directly into the mixer or funnel located on the floor above.

Mixing. The status of a generally recognized standard in the production of CCC belongs to single-shaft horizontal mixers operating in a centrifuge mode. Their main features are: simple design, high intensity, no dead zones and the ability to unload without residues. The intensity of mixing is evaluated using the dimensionless Froude criterion Fr, which characterizes the ratio of centrifugal force and gravity acting on the particles of the mixed components. For Fr< For the preparation of CCC, the most intensive mixing mode is recommended at Fr=6-8. In addition, to distribute additives that are prone to agglomeration, centrifuge mixers are equipped with additional high-speed agitators-deagglomerators.

Packaging. Various systems are used to load bulk products into the valve bag. In the case of CVS, use a pneumatic chamber and a turbine. Machines with aeration feed are not used because of the danger of stratification of the mixture. The screw feed is designed for powdery products and is characterized by a very low speed. Belt propellant blowers are used for sugar and grain, but they are not suitable for powdered products.

The pneumatic chamber feed is characterized by high speed and versatility of application. On machines with this system, it is equally easy to pack both coarse and fine mixtures. The disadvantage of pneumatic chamber machines is a large amount of dusty air, which leads to more stringent requirements for the aspiration system.

Turbine feed is also characterized by high speed, but the scope of its application is narrower. It is intended for finely dispersed aerated products, that is, for products that acquire liquid properties in the aerated state. These are cement, lime, gypsum, tile adhesives with a high cement content.

A computer-based plant management system usually has a two-level structure. The upper level, implemented on the basis of a PC, is intended for creating databases on recipes and components, generating reports on product development and consumption of components, displaying a mnemonic diagram on the monitor showing the status of all sensors and drives, displaying messages about failures in operation and acknowledging them, and configuring process parameters. The lower level, implemented on the basis of programmable controllers, is intended for polling all sensors and issuing control signals to actuators. The most important function of the control system – dosing-can be implemented both at the controller level and at the computer level.

Up to 8 people are most often employed directly in the production process: 1-process management, 1-unpacking of initial components from bags and soft containers, 1 - loading of additives, 1 - packaging of products, 3 – stacking bags on pallets (or installing automatic lines for stacking products on pallets), 1-transportation of products, raw materials, packaging materials in the warehouse.

Source: Dry Building Mixes Magazine