You can quickly, cheaply, and simply prepare the floor for laying the final decorative coating by following a simple dry leveling technology. Its principle is not new, but thanks to the improvement of materials it is extremely simple. Dry floor screed is attractive due to its versatility and low weight, which minimally increases the weight of structures. I am pleased with the relatively low price and the ability to do the work yourself, which undoubtedly has a convincing effect on thrifty owners.

Should I build a dry screed in a bathhouse?

To understand the issue, you need to read design features this leveling system. The list of main components of dry screed contains only two elements:

• insulation-leveling cushion, which is a backfill with expanded clay sand, river or quarry natural analogue or fine-grained slag;
• rigid flooring made of one or two layers of GVLV slabs, instead of which sheets of waterproof plywood, chipboard, OSB, asbestos-cement panels and similar materials can be used.

Since the materials used to form the top layer of dry leveling are extremely sensitive to moisture, for arranging a steam room and washing department The dry method, of course, will not work. But there is nothing better for laying the subfloor in the attic, in the dressing room, in the locker room and rest room, in the billiard room, if the owner of the bathhouse decided to acquire such an entertainment area.

True, one should not forget that all the rooms in the bathhouse will be more humidified than in a standard residential building. Just so that moisture does not reduce the insulating and technical qualities of the pillow, the dry screed will need to be insulated from water and steam not only from the side of the ceiling, but also from above.

Note. The upper waterproofing barrier is made by treating rigid flooring slabs bitumen mastic or by laying a double layer of other flexible insulation over a fully constructed dry screed.

If the base base does not need to be significantly leveled, slab polystyrene foam can be used instead of amorphous sands of organic and inorganic origin. They often supplement the backfill if the dry screed needs to be leveled and “increased” by more than 50 mm. In such cases, foamed polystyrene boards are laid over a layer of fine expanded clay or sand.

If a dry screed is performed by a home craftsman for the first time, experienced builders recommend not experimenting with plywood and other panels not intended directly for the production of dry screed. It is better to buy Knauf products. It offers flooring slabs glued together in a special way, resulting in a seam. Due to the presence of this ledge on the edge of the glued slabs, the flooring is monolithic. And the elements of the subfloor with unique guides are easier to connect.

As a backfill material, it is better to use different-grained expanded clay sand of a fine fraction of 0.3-0.5 cm supplied by the same manufacturer. It increases the weight to a minimum and compacts well due to the presence of particles in the amorphous mass different sizes.

Dry screed technology

The power of the planned dry screed is determined by differences in floor heights and the height of “underground” communications, if any in the room. The optimal thickness of a layered dry-leveling cake is considered to be 5 cm, of which 3 cm is the backfill layer. If the thickness of the expanded clay sand layer is reduced, the cushion will need to be diligently compacted; if it increases, it will need to be supplemented with the above-mentioned slab insulation or a layer of gypsum fiber board located between the layers of backfill. Options with additions associated with increased power are based on a general technological principle, the nuances of which we will get acquainted with.

Let's start with preparation and marking

The base surface, as usual, must be cleaned of construction and other debris and the cracks repaired polyurethane foam or cement mortar. Before installing a dry screed, you need to use a laser level gauge or spirit level to mark the height of the rough foundation being constructed. You need to subtract the thickness of the flooring from the height and note the level of backfill.

According to the last marks, beacons will be set - metal guides that help to form a perfectly flat surface of the insulating pad. Since it is precisely this that requires the most labor effort from performers, it is undesirable to make mistakes with the markings from the beginning.

We install insulating components

Waterproofing is necessary to protect expanded clay sand from capillary absorption of moisture from concrete, from the soil and from the humid air of the underground. Therefore, according to the technology for constructing a dry screed, in any type of premises, the first step is to lay waterproofing. Taking into account the specifics and differences in technical specifications basic basis:

• concrete floors are covered with a continuous layer of polyethylene film, at least 80 microns thick;
• the wood base is insulated using glassine, bitumen-impregnated paper or special waterproofing material for wooden floors.

Rolled materials must be laid with an overlap so that each subsequent strip of insulation overlaps the longitudinal edge of the previous one by 20-25 cm. The strips can additionally be secured with tape.

Important. Waterproofing should cover all walls around the perimeter to a height of approximately 15-20 cm. That is, the insulating material should be laid in the form of a kind of pallet.

The next step is to lay insulating tape around the perimeter, the width of which should be equal to or slightly greater than the thickness of the dry screed being installed. The edge tape performs several functions:

• fills the gap that is necessarily formed between the walls and the hard flooring, which is required to compensate for thermal movements of the subfloor;
• prevents the penetration of dust and moisture into the multi-layer floor structure;
• eliminates the transmission of sound waves from supporting structures;
• eliminates the possibility of the formation of cold bridges.

Tape thickness 7-10 mm. It is equal to the size of the gap between the rigid flooring and the walls. It can be purchased at finished form With the right sizes or cut it yourself from basalt wool or glass wool. Place the edge strip between the waterproofing and the dry screed.

Backfilling of the insulating leveling pad

This is the most labor-intensive work that determines the quality of the result. Since it is quite difficult to fill and distribute amorphous material evenly, beacons are installed to help the performers. There are two options:

• with rigid fastening to the base of U-shaped profiles turned upside down with “thin legs”, used as frame components for drywall;
• temporary installation of profiles on peculiar beds made of insulation with subsequent removal of metal guides from the leveled and compacted mass.

The profiles can be rigidly fixed using screws, which allow you to level the height by screwing and reverse actions. You can install guides for leveling sand on islands or beds made of alabaster. Note that the issue of removing profiles from an amorphous mass remains controversial. The developers of ready-made kits for installing dry screeds do not recommend leaving profiles, because in the process of spontaneous compaction of the cushion, the thin legs of the guides, not made of the strongest metal, may end up above the plane of the backfill. The consequence will be the curvature of first the profiles themselves, then the floor.

However, contrary to the opinion of engineers, craftsmen believe that beacon profiles will at the same time perform the work of joists under the slabs, and that in small rooms with little load on the floor they can be left. You just need to take into account that the space between the “legs” should be completely filled with backfill.

Masters who adhere to the opinion of the developers of dry leveling systems need to:

• form beds from expanded clay with a distance between them that allows the rule to rest firmly on two parallel “rails”;
• lay out the profiles on the beds and level them horizontally, focusing on the cushion level marks;
• fill the free space with expanded clay;
• using the rule, carefully level the surface, periodically tamping the pillow with a board and your own weight;
• remove the guides by filling the recesses with expanded clay.

“How to fall asleep on a pillow?” - Another one important question with numerous interpretations. After all, if you fill the entire space with amorphous insulation, moving along its surface in order to lay the flooring will entail a violation of the integrity and uniform compaction of the layer.

Again two options:

• experts advise cutting squares from plywood and laying them in the form of islands along the course of the planned actions, so as not to step directly on the backfill;
• thrifty craftsmen from among the people do not fill the entire area with expanded clay, but only an area for two or three slabs, then fill it up again, level it, lay the panels, and so on until they are finished.

Attention. If the insulation-leveling pad has been filled and leveled completely throughout the room, laying the rigid flooring begins at the door.

For those who decide to fill and level the expanded clay gradually, it is better to start from the far corner, moving towards the exit.

Installation of hard flooring

When using rebated slabs, the work is quite simple. Laying the first sheet can cause difficulty. It will be too difficult for one to handle a rather heavy and wide panel. An assistant is needed to lay the first sheet flat without burying it in the expanded clay.

Important. From the side adjacent to the walls, or more precisely to the insulating edge tape, the fold of the slab must be cut off, otherwise expanded clay will be redistributed into the void of the recess. The density characteristics and surface level of the backfill will change.

The slabs are laid so that the “step” of the fold is turned upward. Before installing the next element of the dry screed, a zigzag strip of glue is applied to it, then the next panel of rigid flooring is laid. The joining points are additionally reinforced with self-tapping screws with a self-tapping design, recessing the head by min. 1 mm. The fastener installation step is from 15 to 30 cm, it is selected depending on the degree of load on the floor.

The slabs are laid in strips in a direction convenient for the performers. When finishing the installation of the first strip, we should not forget that there must be a gap between the wall and the flooring. It must be remembered that in plan the arrangement of the slabs should resemble brickwork, that is, there should be no cross joints. To achieve a masonry-like offset, the piece of slab on which the first strip ended is used as a starting element for laying the second strip. This scheme, in addition to convenience, also saves material.

Attention. When installing rigid flooring panels in two layers, the connecting seams of the lower and upper rows should not coincide. It is more convenient to start laying the strips from the back side of the room, then the run-up will happen spontaneously.

The dry screed device does not require independent masters special skills in construction. You don't need any special wisdom either. You only need to strictly follow the manufacturer’s recommendations when using factory-made products and take into account the technical features of the premises being equipped.

Powdered milk is obtained from cow's milk as a result of difficult technological process, consisting of several stages. The peculiarity of this product and its difference from its whole counterpart is its longer shelf life, without loss of quality and nutritional properties. Production of the product requires special equipment and adherence to certain technologies.

The milk powder production technology consists of several successive stages:

• Normalization (reducing the percentage of fat),
• Pasteurization (carried out at temperature conditions of +81 +86 C),
• Pre-thickening (the process is aimed at increasing the percentage of dry components),
• Drying,
• Receipt and packaging of finished powdered milk.

During the cooking process, water from whole milk is evaporated in two stages. Thickening the product is the first step, and the second is drying.

The already condensed milk mixture undergoes a drying process until a powder with a given moisture content is formed. Humidity level is determined finished product quality of connection of powdered components with water. And the permissible humidity is up to 15% of the mass fraction of milk protein.

The moisture level of milk powder is determined by the quality of the connection between the dry components of the powder and water. The permissible moisture content of the product is up to 15% of the mass fraction of milk protein.

The production of milk powder involves the gradual supply of concentrated milk raw materials to a special dryer, after which the product acquires a moisture content of three percent. Using this technology allows you to get powdered milk High Quality.

When the condensed product comes into contact with the hot drum of the drying unit, the caramelization process begins. Skimmed milk powder, which is produced using a roller dryer, has a higher fat content. The only disadvantage of this method is rather low productivity.

Once drying is complete, the skim milk powder is cooled, filtered and packaged.

Necessary equipment

The production of milk powder is impossible without special and rather bulky equipment, as well as without a reliable source of electricity and water supply. The premises where the equipment is installed must have good ventilation and be in accordance with sanitary requirements.

Necessary equipment for the production of milk powder:

• Vacuum evaporation equipment,
• Crystallization equipment,
• Spray drying equipment.

Vacuum evaporation unit

This equipment allows you to obtain concentrated whey and milk itself. The peculiarity of the installation is that it is equipped with special devices that resemble the shape of a pipe. They separate milk fractions from condensate. Standard units also have blocks for larger milk capacity, and parts that cool the finished product. So the finished product does not require additional cooling, which is very convenient for manufacturers. The vacuum evaporation unit is quite easy to use because it has a built-in automatic control panel.

Crystallization equipment

The main function of this equipment is the crystallization of whey and condensate, preparing them for the drying apparatus. Crystallization is possible thanks to the work of inert gases that fill the chamber. The body of the device is made of durable steel. The installation also has complex system pneumatic valves and pumps that simplify the recycling of dairy raw materials.

Spray Drying Plant

This device undergoes the final stage of production. In the chamber of the drying unit, the remaining liquid evaporates, which has a positive effect on the shelf life of the finished product. The result of the dryer is well-flowing and quickly soluble granules of white or light beige color.

The drying technology is very simple: with the help of an internal pump, crystallized milk raw materials are delivered to spray nozzles inside the fluid bottom chamber. It mixes cold and hot air flow, which ensure the evaporation of residual moisture from the raw material.

Types of milk powder

Regular or whole milk powder is more nutritious because it contains more fat.

It cannot be stored for as long as its low-fat counterpart, and the energy value per hundred grams of powder is 550 kcal. Skim milk powder contains very little milk fat and can be stored for eight months. One hundred grams of low-fat product contains no more than 370 kcal. There is also instant milk powder. It is a mixture of skim milk powder and whole milk powder. Usually this type used in the preparation of baby food and many fast food products. The manufacturing process and manufacturing technology do not depend in any way on the type of product.

Compound

If the types of milk powder differ in the ratio of fats, proteins and carbohydrates, then what they have in common is their vitamin composition, which also includes minerals and beneficial amino acids. By state standard the composition must contain vitamins B, PP, A, D, E and C, choline, calcium (at least 1000 mg per hundred grams of product), potassium (at least 1200 mg per hundred grams of product), phosphorus (at least 780 mg per hundred grams of product), sodium (not less than 400 mg per hundred grams of product). It also contains quite a lot of selenium, cobalt, molybdenum and iron. Of the essential amino acids, it contains lysine, methionine, tryptophan, leucine and isoleucine.

Benefits and harms

Not everyone knows about the beneficial qualities of milk powder. Many people claim that powdered milk has nothing beneficial, and all the vitamins are killed in the process of preparing the powder. This statement is not true. This product plays an important role in the life of northern regions and peoples, since it can be stored for a longer time. During the preparation process, raw materials undergo complex stages of thermal and physical processing, which means they contain much less dangerous pathogenic bacteria.

If you use the product regularly, the risk of anemia and rickets is reduced, bones and tendons are strengthened, and the normal functioning of the nervous system is restored.

Powdered milk may also have Negative influence to your health. The product is especially dangerous for people with congenital lactose intolerance or an allergy to milk protein. Consequences - slight redness skin to swelling and anaphylactic shock. Another risk is related to the quality of the product and the rules for its storage. Unscrupulous manufacturers add vegetable fats, including palm oil, to reduce the cost of the finished product. This reduces not only the quality and nutritional value, but also makes the product hazardous to health. Violation of storage conditions and sealed packaging can provoke the growth of harmful bacteria and mold, which will cause serious poisoning.

Producers of powdered milk in Russia actively cooperate with many food industry enterprises, since it is much more profitable to use powdered milk in the preparation of many products. Whole milk spoils quickly, is quite expensive to transport and takes up quite a lot of space during storage.

The product is widely used:

• In the confectionery business,
• In the production of bread, pastries,
• In the production of dairy products: cheeses, condensed milk, curd products, yoghurts and milk drinks,
• At meat processing plants,
• In the production of alcoholic beverages,
• In the cosmetology industry,
• In the production of various semi-finished products,
• In the preparation of dry animal feed.

Enterprises producing milk powder

There are about seventy dairy plants operating in Russia. Some of them are also engaged in the production of dry products. This:

• Lyubinsky Dairy Plant, Omsk Region,
• Blagoveshchensk Dairy Plant, Amur Region,
• Bryansk Dairy Plant, Bryansk Region,
• Ulyanovsk Dairy Plant, Ulyanovsk region,
• Meleuzovsky milk canning plant, Bashkortostan
• Sukhonsky Dairy Plant, Vologda Region.

In any room, achieving the smoothest surface possible is very important point at construction work. A flat, durable floor is the key to durability and proper installation of the finishing coating.

Dry floor screed, the price of which compares favorably with other methods of leveling the base, is of interest to an increasing number of people who want to carry out an extensive range of repair and construction work in a short time.

Are there any renovations coming up? Which screed should I choose?

To level the base, use different technologies. For this, a concrete mixture or leveling surface is used, filling the entire space to the specified level. But as an alternative, there is another alignment option that has advantages and disadvantages. This is a dry screed. You need to know when it is more profitable to use it, and what are its features, what are the pros and cons of dry floor screed?

Before you begin the important work of leveling the surface, you need to consider several factors:

• features of the base;
• time of year in which repair work is carried out;
• deadlines that must be met;
• financial capabilities of the premises owner.

To create a high-quality floor, you need to know all the nuances of the screed and choose best option, ideal for a specific surface. Taking into account all of the above, the technology of creating a “dry floor” is increasingly being used as an alternative.

Dry floor screed - what is it?

For the coating to last a long time, it is not at all necessary to level it with a concrete mixture and wait about 28 days to dry. A worthy alternative to the “wet” process is leveling using dry mixtures. If a dry screed is required, it will be completed in record time, not inferior in quality and strength to a coating made using a different technology.

Emergence this method surface leveling came from the 70s of the last century. Then, for the first time, prefabricated dry floors were used in mass construction. Today the principle remains the same, but the materials have changed. performed using this method have virtually no disadvantages. New types of prefabricated coverings are widely used in construction.

Why is it important to follow technology?

To obtain a coating that has all the advantages of a set of measures that compares favorably in terms of completion time and installation, the technology of dry floor screed must be followed exactly. If you ignore the requirements for its installation, there is a risk of getting an uneven coating, which threatens to negatively affect the appearance and the quality of the finished floor even with an ideal finishing coating. There is also a high probability that deviation from the requirements will lead to deformation and destruction of the building or its foundation. When purchasing a mixture, you should pay attention to the instructions. Carefully studying the rules and strictly following them will eliminate common mistakes.

Stages of work execution

Features of dry screed in an apartment

When carrying out work to level the surface, you should take into account the characteristics of the room, because different bases require and different training. So, the dry screed should be at the same level. The bathroom and toilet are not taken into account. You should take care in advance finishing materials for the floor in every room. To avoid mistakes, you need to accurately calculate the height of the finished floor covering to correctly mark the thickness of the screed.

Plates placed in the same plane guarantee a perfect fit of the finished floor. To ensure that the work is done correctly, you need to use a bubble building level. If the slabs provide for overlap during installation, then they are fastened to each other.

How to correctly calculate material consumption

If dry floor screed is being done, the consumption of materials should be based on certain parameters:

• dimensions of the room being repaired, its area;
• the thickness of the layer that is poured onto the base;
• variability of materials used.

When answering the question “Dry floor screed - what is it?” It is important to list the list of materials that make up a solid foundation.

1. The number of gypsum fiber board, fiberboard or chipboard sheets, or thick plywood is calculated based on the floor area. The length of the room is multiplied by its width, the resulting result is divided by the area of ​​the sheet. If the surface is complex, then it is necessary to divide it into simple squares, after which it is easy to calculate the total area to be covered with slabs.
2. The waterproofing film is calculated taking into account an overlap of 15 cm and a bend on each wall of 10 cm. The sleeve of the film is 150 cm, if cut, it turns out to be 300 cm. It is important to know how the film spreads - along or across. After this, the exact material consumption is calculated.
3. Expanded clay is needed in granules of different sizes; slag is also used, less often sand. Material consumption depends on the thickness of the backfill. Due to differences in the base of the coating, an average value is taken, which is calculated from the minimum and maximum thickness measurements. A small supply will not hurt, since it is difficult to take accurate measurements.

Variety of materials. How not to make a mistake in choosing?

The technology that was relevant several decades ago, when surfaces were leveled with P-71g-2, is a thing of the past. Prefabricated floors based on dry screed are now successfully used everywhere. Dry floor screed "Knauf" compares favorably on the building materials market with German manufacturer, famous for its unsurpassed quality.

Application of the technology of this company, which uses special gypsum fiber boards "Knauf Superpol" and waterproofing film with leveling mixture, very popular. This method saves time, does not require huge labor costs, and the load on the floors is minimal.

The materials used (gypsum fiber board and expanded clay) are the key to successful work and long-term operation coverings. When assessing the pros and cons of dry floor screed, craftsmen note only its advantages.

Is dry screed expensive?

When carrying out work, an important factor is its cost. When compared with concrete pouring, the advantages of bulk technology are undeniable. How much does dry floor screed cost? The price of the issue depends on the quality of the materials used. On average for square meter masters charge from 400 rubles for surfaces.

But in any case, it will cost several times cheaper alternative work to level the surface. And this is an important argument in favor of this technique in construction.

Advantages of dry screed

The undeniable advantages of “dry” work also include:

• accuracy of work, eliminating splashes, drips and dust (this cannot be avoided in the case of concrete-sand screed);
• there is no need to wait for the surface to dry, but you can use it immediately by covering it with the finishing coat;
• work is carried out regardless of the time of year;
• minimal loads on the floors of the building, which is especially important in old buildings;
• the use of a bulk layer for laying communications when organizing a heated floor;
• providing sound and heat insulation;
• minimal involvement of labor, because if necessary, the screed is carried out without assistants.

Flaws

Considering the pros and cons of dry floor screed, it turns out that its main disadvantage is the fear of moisture. Therefore, during installation work Special attention is given to the waterproofing layer.

The film must protect against leaks, which have a detrimental effect on the bulk mixture and the material laid on it. After all, a swollen floor will lead to deformation of the laminate or linoleum finish. For prevention, wooden floors are coated with a special protective compound.

But with only one drawback, dry screed has advantages that make it popular and relevant when carrying out repair and construction work.

The simple technology of dry screed when leveling the floor allows you to cheaply and quickly prepare it for laying the final decorative coating. Its principle has long been known, and improved materials make it even easier to implement.

Dry concrete screed is attractive due to its low weight and versatility. It increases the mass of the structure being built to a minimum, is relatively inexpensive, and the fact that you can work with it yourself without spending money on hired labor will help you save money.

• Why "dry"?
• Pros and cons of dry screed
• Materials and tools for dry floor screed
  • Material consumption for dry screed
• Surface preparation
• Dry screed laying technology
  • Display of beacons
  • Expanded clay backfill
  • Laying sheet material
• Screed cost and material consumption

Why "dry"?

They have been successfully used in practice for many decades traditional types cement screeds. The classic components for such screeds were necessarily:

• cement;
• sand;
• water.

Only their ratio and the quality of individual components changed. But specialists from the German company Knauf took up the implementation of a new project suitable for leveling the floor - it was they who came up with the joint use of materials such as dry screed and gypsum fiber sheets (gypsum fiber sheets). The technology turned out to be so simple that it became accessible to everyone. Here, in addition to GVL, expanded clay sand will be required as the basis of the screed.

First, bulk material is poured onto the subfloor - expanded clay, which is sprinkled with sand or perlite, and then tile materials are laid on top: gypsum fiber board, fiberboard, chipboard or plywood. The modules of the upper fastening layer are fastened with self-tapping screws and glued.

Pros and cons of dry screed

Dry floor screeding is quick and easy. But besides these two advantages, it has a number of others:

• Materials for dry floor screed cost several times less than for concrete, which is always a significant advantage.
• Greater cleanliness of work - since the cement-sand mixture does not mix with water, dirty streaks and puddles do not appear.
• The cushion under the dry screed is most often bulk insulation, which guarantees good thermal insulation of the floor.
• The design is much lighter than with a traditional cement screed, because the leveling material and expanded clay weigh much less, in addition, their use reduces the consumption of dry mixture on the screed, which means the load on the floor is reduced. Therefore, this system is preferable when renovating floors in old wooden houses.
• The bulk layer can also be used for laying various communications or, for example, a warm electric floor in the form of mats or cables. After installing a dry screed, you can immediately begin laying the finishing coating, while after laying a “raw” cement screed, you will have to wait a very long time until the concrete is completely dry.

As you can see, there are many advantages here, and if you list the disadvantages of dry screed, then perhaps one will come to mind, but it is very significant and unusual - the fear of water getting in. As soon as a small amount of water gets on the surface of plywood, gypsum fiber board or chipboard, they swell with bubbles and warp.

Materials and tools for dry floor screed

In order to perform a dry screed, a knowledgeable master will probably invite an assistant. No matter how light the materials are, you will have to drag them around a lot, and it’s easier for two people to stack large sheets.

So, here are the materials you will need:

• GVL with dimensions 60x120 cm. This sheet format is specially reduced so that even one worker can handle them when laying them. These are two sheets glued together with some displacement, which are also called “dry floor elements.”
• Expanded clay of fine fraction. The dry mixture for floor screed can be not only expanded clay, but also a fine-grained fraction of slag, perlite, and even crumbs from polystyrene foam boards.
• Polyethylene film as waterproofing, which is laid on the base before filling with expanded clay sand.
• Self-tapping screws for fastening GVL.
• PVA glue.
• Edge tape.

And also tools for work:

• roulette;
• pencil;
• a jigsaw or knife that can be used to cut gypsum plasterboard;
• screwdriver;
• narrow spatula;
• rule;
• metal profile PN-27/28 (it will serve as beacons).

As an additional tool, you may need a paint brush, which will be useful when, before applying glue at the joints of the slabs, you need to sweep away expanded clay crumbs from them.

Material consumption for dry screed

First of all, you need to take care of the required amount of materials, because when dry screed is produced, their consumption can be significant, so it is important to correctly calculate their quantity:

• The volume of expanded clay is determined by the thickness of the layer and the total area of ​​the backfill. The minimum you can fill is 3 centimeters of expanded clay, however, the thicker the layer, the better the floor will be thermally insulated. On the other hand, we must not forget that the higher the floor rises, the closer the ceiling will be to it, that is, the room will become lower.
• For waterproofing, it is cheapest to use ordinary polyethylene film, the thickness of which is at least 0.2 mm. Its quantity should exceed the area of ​​the room, since part of it will be used for overlaps and allowances on the walls.
• The number of guide metal profiles will also depend on the size of the floor.
• The length of the damper tape, which is laid along the perimeter of the walls, is determined by this perimeter.
• Slab leveling materials should also collectively have an area equal to the area of ​​the room, but with some margin.

Surface preparation

1. If the renovation is taking place in an apartment, then before making a dry screed, you need to remove the old flooring and all the layers underneath until the reinforced concrete floor appears.

1. The surface of the slab must be inspected and all defects found on it must be repaired (grooves, cracks, chips), using a ready-made plaster mixture or cement-sand mortar for this purpose.

1. The repaired areas should be allowed to dry, after which the corrected subfloor should be thoroughly swept away from dust and dirt, and then waterproofing material – polyethylene – should be placed on it. The film should completely cover the floor surface and “climb” onto the walls along the entire perimeter to a height determined by the thickness of the dry screed.

1. The film is usually laid in the form of several parallel strips, which should overlap each other by 10-15 cm. To make the waterproofing airtight, the edges of the strips must be glued together with construction tape.

The question may arise: if the screed technology is completely dry, then why is waterproofing needed? The thing is that the floor slabs are not monolithic; they have gaps that allow moisture to pass through, albeit slowly, from the lower floor or from the subfloor (if we are talking about the first floor). Therefore, only high-quality waterproofing can stop the flow of moisture. These precautions are also justified by the fact that dry screed does not like the ingress of water.

1. Then you need to place a damper tape around the perimeter of the walls. This tape is made of foamed PVC, one of the sides of which is self-adhesive, protected by plastic film. The protective film must be removed and the tape must be immediately glued to the wall surface. The purpose of the damper tape is to compensate for the thermal expansion of the dry screed. In addition, it will prevent contact of the leveling sheets with the walls, which will protect them from deformation, and residents from unpleasant squeaking.

1. After installing the edge strip along the perimeter of the walls, the entire vapor barrier structure at the base of the floor is considered complete.

Dry screed laying technology

If a dry floor screed is chosen, its technology consists of several successive stages. These stages will be listed below with reference to the fact that expanded clay will serve as backfill.

The process of installing a dry screed begins with attaching beacons as guide elements. It is with their help that the dry screed - expanded clay - is leveled in height, they determine the thickness of the bulk layer. Some seasoned craftsmen manage to do without beacons, but beginners are strongly recommended to use them.

Display of beacons

Most often, for dry screeds, special T-shaped beacon profiles are used, which are attached with self-tapping screws to the base of the floor, but before that they need to be set using certain tools, which include:

• rule;
• laser level;
• pencil.

Sequence of work:

1. The laser level must be installed in the center of the room and turned on.
2. After this, half a meter from one of the corners of the room, you should screw a self-tapping screw into the floor, install a rule on it vertically and mark the trace of the laser beam on it with a pencil.
3. After this, diagonally across the room, closer to the other corner, also screw another screw into the floor, put a rule on it and check that the line drawn on it coincides with the laser beam.
4. If they diverge, then the screw should either be screwed in even deeper or unscrewed a little, ensuring that the mark exactly matches the laser marker.
5. Carry out similar actions with all intermediate screws, or do it easier: stretch a fairly thin and strong thread between the outer fasteners, and, focusing on its level, screw the screws through 20 cm into the floor.
6. Then you can check the work - put a level strip on the screws, and a regular water level on it. If everything is done correctly, the level will confirm that the slats are horizontal.

1. After this, the lighthouse must be secured with cement or gypsum mortar.
2. The guide element on both sides of the screws should be covered with a solution and allowed to dry.
3. Do the same with all other beacons.

Expanded clay backfill

If the screed is not made with dry sand, but with expanded clay granules, then they should be as small as possible. After all, sheets of leveling material will rest on them, which in the case of large granules will have a point, chaotically located support and this will cause deformation, and failures will appear.

1. Expanded clay for dry floor screed should not be poured onto the entire floor at once, but only a section of it.

1. Having reached the level of the beacons in this place, you should immediately put a tiled leveling material on top, for example, gypsum fiber board.
2. The feet of a working person should be on a clean, expanded clay-free floor.
3. After this, you can proceed to backfilling the next section and laying the next slab on it.

But a number of craftsmen also have an alternative approach - they first cover the entire floor with expanded clay, level it according to the level of the beacons, and then move along the floor, placing pieces of gypsum fiber board or plywood under themselves.

Laying sheet material

There are a number of points that require special attention:

1. If gypsum fiber sheets are used for leveling, then it is advisable to lay them in two layers, which must be fastened with self-tapping screws, and then coat the joints with glue. Taking this feature into account, Knauf began to produce ready-made double sheets with a seam connection - “Knauf superfloor”. With its help it is easy to create a beautiful floor covering that meets all modern requirements.
2. If plywood or chipboard is used, they can be laid in one layer, but only if their thickness is at least 12 mm. These materials also need to be treated with protective agents - bitumen mastic or hot drying oil.
3. When laying, the sheets must be pressed tightly against each other. If gaps do appear, they should be filled with putty solution.

If expanded clay is backfilled in sections, then installation should begin from the furthest from front door corner premises. If the floor is first completely covered with expanded clay, then installation, on the contrary, should begin from the front door so that you can move along the previously laid slabs without any problems.

1. In the case of using “Knauf superfloor”, the folds of the slabs must be coated with glue and connected with special self-tapping screws having a length of 19 mm. These self-tapping screws have countersinking heads, thanks to which the fasteners are deeply recessed into the gypsum plasterboard. This helps in the installation process to get rid of unnecessary height differences.

1. When all installation work are completed, then all protruding edges of the damper tape and polyethylene film you need to cut it off and fill the resulting gap between the walls and the dry screed with sealant.

Screed cost and material consumption

Calculating a dry screed is quite easy to do. So, for a room of 100 m2 you will need approximately 150 m2 of waterproofing, 100 m of profile, 5 kg of glue and 1200 screws.

The consumption of the dry mixture for the screed here will depend on the thickness of the screed: if the average thickness of the backfill is about 3 centimeters, then 4 m3 of bulk material will be required to accommodate such an area.

Well, the answer to the question, how much does a dry screed cost, consists of the cost of all the materials necessary for the work.

Would you dry-screed the floor in your apartment or house? Or do you already have experience working with it? Why did you like it, and what shortcomings did you note? Tell us about it in the comments.

Spray drying has proven to be the most suitable technology removing residual water from the evaporated product, as it allows you to turn milk concentrate into powder, preserving the valuable properties of milk.

The principle of all spray dryers is to turn the concentrate into fine droplets, which are fed into a rapid stream of hot air. Due to the very large surface area of ​​the droplets (1 liter of concentrate is sprayed onto 1.5×10 10 droplets with a diameter of 50 µm with a total surface of 120 m 2 ) evaporation of water occurs almost instantly, and
the drops turn into powder particles.

Single stage drying

Single-stage drying is a spray drying process in which the product is dried to a final residual moisture content in a spray dryer chamber, see Figure 1. The theory of droplet formation and evaporation in the first drying period is the same for both single-stage and two-stage drying and is outlined here.

The initial speed of droplets falling from the rotary atomizer is approximately 150 m/s. The main drying process occurs while the drop is slowed down by friction with the air. Drops with a diameter of 100 microns have a braking path of 1 m, and drops with a diameter of 10 microns have only a few centimeters. The main decrease in the temperature of the drying air, caused by the evaporation of water from the concentrate, occurs during this period.

Enormous heat and mass transfer occurs between particles and the surrounding airin a very short time, so the quality of the product may suffer greatly if those factors that contribute to the deterioration of the product are left unattended.

When water is removed from the droplets, a significant decrease in the mass, volume and diameter of the particle occurs. Under ideal drying conditions, droplet mass from a rotary atomizer
decreases by approximately 50%, volume by 40%, and diameter by 75%. (see Figure 2).

However, the ideal technique for creating droplets and drying has not yet been developed. Some amount of air is always included in the concentrate when it is pumped from the evaporator and especially when the concentrate is supplied to the feed tank due to splashing.

But even when spraying the concentrate with a rotary atomizer, a lot of air is included in the product, since the atomizer disk acts as a fan and sucks in air. The inclusion of air in the concentrate can be counteracted by using discs special design. On a disk with curved blades (the so-called disk of high bulk density), see Figure 3, the air, under the influence of the same centrifugal force, is partially separated from the concentrate, and in a disk washed by steam, see Figure 4, the problem is partially solved by the fact that Instead of liquid-air contact, there is liquid-vapor contact. It is believed that when spraying with nozzles, air is not included in the concentrate or is included to a very small extent. However, it turns out that some air is included in the concentrate early in the atomization process, outside and inside the spray pattern due to friction between the liquid and the air before droplets are formed. The higher the nozzle output (kg/h), the more air enters the concentrate.

The ability of a concentrate to incorporate air (i.e. foaming ability) depends on its composition, temperature and dry matter content. It turned out that the concentrate with a low solids content has significant foaming ability, which increases with temperature. Concentrate with a high solids content foams significantly less, which is especially noticeable as the temperature increases, see Figure 5. Generally speaking, whole milk concentrate foams less than skim milk concentrate.

Thus, the air content in droplets (in the form of microscopic bubbles) largely determines the decrease in droplet volume during drying. Another, even more important factor is the ambient temperature. As already noted, intense exchange of heat and water vapor occurs between the drying air and the drop.

Therefore, a temperature and concentration gradient is created around the particle, so that the whole process becomes complex and not entirely clear. Drops of pure water (100% water activity) evaporate when in contact with high-temperature air, maintaining the wet-bulb temperature until the very end of evaporation. On the other hand, products containing dry matter at extreme drying (i.e. when water activity approaches zero) are heated at the end of drying to the ambient air temperature, which in relation to a spray dryer means the outlet air temperature. (see Figure 6).

Therefore, a concentration gradient exists not only from the center to the surface, but also between points on the surface, as a result, different parts of the surface have different temperatures. The larger the particle diameter, the greater the overall gradient, since this means a smaller relative surface area. Therefore, small particles dry more quickly
evenly.

During drying, the solids content naturally increases due to the removal of water, and both viscosity and surface tension increase. This means that the diffusion coefficient, i.e. the time and zone of diffusion transfer of water and steam becomes smaller, and due to the slowdown in the evaporation rate, overheating occurs. In extreme cases, so-called surface hardening occurs, i.e. formation of a hard crust on the surface through which water and steam or absorbed air diffuse
So slow. In the case of surface hardening, the residual moisture of the particle is 10-30%; at this stage, proteins, especially casein, are very sensitive to heat and easily denature, resulting in a poorly soluble powder. In addition, amorphous lactose becomes solid and almost impermeable to water vapor, so that the temperature of the particle increases even more when the rate of evaporation, i.e. the diffusion coefficient approaches zero.

Because water vapor and air bubbles remain inside the particles, they become overheated, and if the ambient air temperature is high enough, the vapor and air expand. The pressure in the particle increases, and it swells into a ball with a smooth surface, see Figure 7. Such a particle contains many vacuoles, see Figure 8. If the ambient temperature is high enough, the particle may even explode, but if this does not happen, the particle still has a very thin crust, about 1 micron, and will not withstand machining in a cyclone or transport system so that it leaves the dryer with exhaust air. (see Figure 9).

If there are few air bubbles in the particle, then the expansion, even with overheating, will not be too strong. However, overheating as a result of surface hardening degrades the quality of casein, which reduces the solubility of the powder.

If the ambient temperature, i.e. If the temperature at the outlet of the dryer is maintained low, the particle temperature will also be low.

The outlet temperature is determined by many factors, the main of which are:

• moisture content of the finished powder
• temperature and humidity of drying air
• dry matter content in concentrate
• spraying
• concentrate viscosity

Moisture content of the finished powder

The first and most important factor is the moisture content of the finished powder. The lower the residual humidity must be, the lower the required outlet relative humidity, which means higher air and particle temperatures.

Temperature and humidity of drying air

The moisture content of the powder is directly related to the humidity of the outlet air, and increasing the air supply to the chamber will lead to a slightly larger increase in the output air flow rate, since due to increased evaporation there will be more moisture in the air. The moisture content of the drying air also plays an important role, and if it is high, it is necessary to increase the outlet air temperature to compensate for the additional moisture.

Dry matter content in concentrate

Increasing the dry matter content will require more high temperature at the exit, because evaporation is slower (the average diffusion coefficient is lower) and requires a larger temperature difference ( driving force) between the particle and the surrounding air.

Spraying

Improving atomization and creating a more finely dispersed aerosol allows you to reduce the outlet temperature, because the relative surface area of ​​the particles increases. Because of this, evaporation occurs more easily and the driving force can be reduced.

Concentrate viscosity

Atomization depends on viscosity. Viscosity increases with increasing protein content, crystalline lactose and total solids content. Heating the concentrate (be aware of thickening as it ages) and increasing the spray disc speed or nozzle pressure can solve this problem.

The overall drying efficiency is expressed by the following approximate formula:

where: T i - inlet air temperature; T o - outlet air temperature; T a - ambient temperature

Obviously, to increase the efficiency of spray drying, it is necessary to either increase the ambient temperature, i.e. preheat the extracted air, for example, with condensate from an evaporator, or increase the inlet air temperature, or lower the outlet temperature.

Dependence ζ on temperature is a good indicator of the dryer's operating efficiency, since the outlet temperature is determined by the residual moisture content of the product, which must meet a certain standard. A high outlet temperature means that the drying air is not being used optimally, for example due to poor atomization, poor air distribution, high viscosity, etc.

For a normal spray dryer processing skim milk (T i = 200°C, T o = 95°C),ζ ≈ 0.56.

The drying technology discussed so far refers to a plant with a pneumatic conveying and cooling system, in which the product discharged from the bottom of the chamber is dried to the required moisture content. At this stage, the powder is warm and consists of cohesive particles, very loosely bound into large loose agglomerates formed during primary agglomeration in the spray plume, where particles of different diameters have at different speeds and therefore they collide. However, when passing through the pneumatic transport system, the agglomerates are subjected to mechanical stress and crumble into individual particles. This type of powder, (see Figure 10), can be characterized as follows:

• individual particles
• high bulk density
• dusting if it is skimmed milk powder
• not instant

Two-stage drying

The particle temperature is determined by the ambient air temperature (outlet temperature). Since bound moisture is difficult to remove by traditional drying, the outlet temperature must be high enough to provide driving force (Δ t, i.e. temperature difference between the particle and the air) capable of removing residual moisture. Very often this degrades the quality of the particles, as discussed above.

It is therefore not surprising that a completely different drying technology was developed, designed to evaporate the last 2-10% of moisture from such particles.

Since evaporation at this stage is very slow due to the low diffusion coefficient, the equipment for post-drying must be such that the powder remains in it for a long time. This drying can be carried out in a pneumatic conveying system, using hot conveying air to increase the driving force of the process.

However, since the speed in the transport channel must be≈ 20 m/s, for effective drying a channel of considerable length will be required. Another system is the so-called “hot chamber” with a tangential entrance to increase the holding time. Once drying is complete, the powder is separated in a cyclone and sent to another pneumatic conveying system with cold or dried air, where the powder is cooled. After separation in the cyclone, the powder is ready for packaging in bags.

Another additional drying system is the VIBRO-FLUIDIZER device, i.e. a large horizontal chamber divided by a perforated plate welded to the body into upper and lower sections. (Figure 11). For drying and subsequent cooling, warm and cold air and is evenly distributed over the working area with a special perforated plate, BUBBLE PLATE.

This provides the following benefits:

• The air is directed downward towards the surface of the plate, so particles move along the plate, which has sparse but large holes and can therefore operate for a long time without cleaning. In addition, it releases powder very well.
• The unique manufacturing method prevents the formation of cracks. Therefore, BUBBLE PLATE meets strict sanitary requirements and USDA approved.

The size and shape of the holes and the air flow rate are determined by the air velocity required to fluidize the powder, which in turn is determined by the properties of the powder, such as moisture content and thermoplasticity.

The temperature is determined by the required evaporation. The size of the holes is chosen so that the air speed ensures fluidization of the powder on the plate. The air speed should not be too high so that the agglomerates are not destroyed by abrasion. However, it is not possible (and sometimes not desirable) to avoid the entrainment of some (especially small) particles from the fluidized bed with the air. Therefore, the air must pass through a cyclone or bag filter, where the particles are separated and returned to the process.

This new equipment allows you to carefully evaporate the last percent of moisture from the powder. But this means that the spray dryer can be operated in a manner different from that described above, in which the powder leaving the chamber has the moisture content of the finished product.

The advantages of two-stage drying can be summarized as follows:

• higher output per kg of drying air
• increased efficiency
• best product quality:

1. good solubility
2. high bulk density
3. low free fat content
4. low absorbed air content

• Less powder emissions

The fluidized bed can be either a piston-type vibrating fluidized bed (VibroFluidizer) or a fixed back-mix fluidized bed.

Two-stage drying in the Vibro-Fluidizer(piston flow)

In the Vibro-Fluidizer, the entire fluidized bed vibrates. The perforations in the plate are made so that the drying air is directed along with the flow of powder. ForTo ensure that the perforated plate does not vibrate at its own frequency, it is mounted on special supports. (see Figure 12).

Figure 12 - Spray dryer with Vibro-Fluidizer for two-stage drying

The spray dryer operates at a lower outlet temperature, resulting in higher moisture content and lower particle temperature. The wet powder is discharged by gravity from the drying chamber into the Vibro-Fluidizer.

There is, however, a limit to lowering the temperature, since due to the increased humidity the powder becomes sticky even at lower temperatures and forms lumps and deposits in the chamber.

Typically, the use of a Vibro-Fluidizer can reduce the outlet temperature by 10-15 °C. This results in much gentler drying, especially at the critical stage of the process (30 to 10% humidity), the drying of the particles (see Figure 13) is not interrupted by surface hardening, so that the drying conditions are close to optimal. The lower particle temperature is partly due to the lower ambient temperature, but also to the higher moisture content, so that the particle temperature is close to the wet bulb temperature. This naturally has a positive effect on the solubility of the finished powder.

A decrease in outlet temperature means a higher efficiency of the drying chamber due to an increaseΔ t. Very often, drying is carried out at a higher temperature and at a higher solids content in the raw material, which further increases the efficiency of the dryer. In this case, of course, the outlet temperature also increases, but the increased moisture content reduces the temperature of the particles, so that overheating and surface hardening of the particles do not occur.

Experience shows that drying temperatures can reach 250 °C or even 275 °C when drying skim milk, which raises the drying efficiency to 0.75.

Particles reaching the bottom of the chamber have higher humidity and more low temperature than with traditional drying. From the bottom of the chamber, the powder flows directly into the drying section of the Vibro-Fluidizer and is immediately liquefied. Any holding or transportation will cause the warm, moist thermoplastic particles to stick together and form hard-to-break clumps. This would reduce the drying efficiency of the Vibro-Fluidizer and some of the finished powder would have too high a moisture content, i.e. the quality of the product would suffer.

Only the powder from the drying chamber flows into the Vibro-Fluidizer by gravity. Fines from the main cyclone and from the cyclone serving the Vibro-Fluidizer (or from a washable bag filter) are fed into the Vibro-Fluidizer by a transport system.

Since this fraction is a smaller particle size than the powder from the drying chamber, the moisture content of the particles is lower and they do not require the same degree of secondary drying. Very often they are quite dry, however, they are usually fed into the last third of the drying section of the Vibro-Fluidizer to ensure the required moisture content of the product.

The cyclone powder discharge point cannot always be located directly above the Vibro-Fluidizer so that the powder flows into the drying section by gravity. Therefore, a pressure pneumatic conveying system is often used to move powder. The pressure pneumatic conveying system makes it easy to deliver powder to any part of the installation, since the transport line is usually represented by a 3 or 4 inch milk pipe. The system consists of a low-flow, high-pressure blower and a blow-off valve, and collects and transports the powder, see Figure 14. The amount of air is small relative to the amount of powder conveyed (only 1/5).

A small portion of this powder is again airborne from the Vibro-Fluidizer and then transported from the cyclone back to the Vibro-Fluidizer. Therefore, if you do not provide special devices, when the dryer is stopped, it takes a certain time to stop this circulation.

For example, a distribution valve can be installed in the transfer line that will direct the powder to the very last part of the Vibro-Fluidizer, where it will be discharged in a few minutes.

On final stage the powder is sifted and packed into bags. Since the powder may contain primary agglomerates, it is recommended that it be conveyed to the hopper via another pressure pneumatic conveying system to increase the bulk density.

It is well known that when water evaporates from milk, energy consumption per kg of evaporated water increases as the residual moisture approaches zero. (Figure 15).

Drying efficiency depends on the air inlet and outlet temperatures.

If the steam consumption in the evaporator is 0.10-0.20 kg per kg of evaporated water, then in a traditional single-stage spray dryer it is 2.0-2.5 kg per kg of evaporated water, i.e. 20 times higher than in an evaporator. Therefore, attempts have always been made to increase the dry matter content of the evaporated product. This means that the evaporator will remove a higher proportion of water and energy consumption will be reduced.

Of course, this will slightly increase the energy consumption per kg of water evaporated in the spray dryer, but the overall energy consumption will be reduced.

The above steam consumption per kg of evaporated water is an average figure, since the steam consumption at the beginning of the process is much lower than at the end of drying. Calculations show that to obtain a powder with a moisture content of 3.5%, 1595 kcal/kg of powder is required, and to obtain a powder with a moisture content of 6%, only 1250 kcal/kg of powder is required. In other words, final stage evaporation requires approximately 23 kg of steam per kg of water evaporated.

The table illustrates these calculations. The first column reflects the operating conditions in a traditional plant, where the powder from the drying chamber is conveyed to the cyclones by a pneumatic conveying and cooling system. The next column reflects the operating conditions in a two-stage dryer in which drying from 6 to 3.5% moisture is carried out in a Vibro-Fluidizer. The third column represents two-stage drying at high inlet temperature.

From the indicators marked *), we find: 1595 – 1250 = 345 kcal/kg of powder

Evaporation per kg of powder is: 0.025 kg (6% - 3.5% + 2.5%)

This means that the energy consumption per kg of evaporated water is: 345/0.025 = 13.800 kcal/kg, which corresponds to 23 kg of heating steam per kg of evaporated water.

In the Vibro-Fluidizer, the average steam consumption is 4 kg per kg of evaporated water; naturally, it depends on the temperature and flow of drying air. Even if the steam consumption of a Vibro-Fluidizer is twice as high as a spray dryer, the energy consumption to evaporate the same amount of water is still much lower (since the product processing time is 8-10 minutes, and not 0-25 seconds, as in spray dryer). And at the same time, the productivity of such an installation is greater, the quality of the product is higher, powder emissions are lower, and the functionality is wider.

Two-stage fixed fluid bed drying (back-mix)

To improve drying efficiency, the air temperature at the outlet To during two-stage drying is reduced to the level at which the powder with a moisture content of 5-7% becomes sticky and begins to settle on the walls of the chamber.

However, the creation of a fluidized bed in the conical part of the chamber provides further improvement in the process. Air for secondary drying is supplied to a chamber under a perforated plate, through which it is distributed over the powder layer. This type of dryer can operate in a mode in which the primary particles dry to a humidity of 8-12%, which corresponds to an outlet air temperature of 65-70 °C. Such utilization of drying air makes it possible to significantly reduce the size of the installation with the same dryer performance.

Powdered milk has always been considered difficult to fluidize. However, a special patented plate design, see Figure 17, ensures that the air and powder move in the same direction as the primary drying air. This plate, provided the bed height and fluidization start speed are correctly selected, allows you to create a static fluidized bed for any product made from milk.

Static fluidized bed (SFB) devices are available in three configurations:

• with annular fluidized bed (Compact dryers)
• with circulating fluidized bed (MSD dryers)
• with a combination of such layers (IFD dryers)

Annular fluidized bed (Compact dryers)

An annular reverse-mix fluidized bed is located at the bottom of the cone of a traditional drying chamber around central pipe exhaust air removal. Thus, there are no parts in the conical part of the chamber that interfere with the air flow, and this, together with the jets emerging from the fluidized bed, prevents the formation of deposits on the walls of the cone, even when processing sticky powders with a high moisture content. The cylindrical part of the chamber is protected from deposits by a wall blowing system: a small amount of air is tangentially supplied at high speed through specially designed nozzles in the same direction in which the primary drying air is swirled.

Due to the rotation of the air-dust mixture and the cyclone effect that occurs in the chamber, only a small amount of powder is carried away by the exhaust air. Therefore, the proportion of powder entering the cyclone or washable bag filter, as well as powder emissions into the atmosphere, is reduced for this type of dryer.

Powder is continuously discharged from the fluidized bed by flowing through an adjustable height baffle, thereby maintaining a certain level of the fluidized bed.

Due to the low outlet air temperature, the drying efficiency is significantly increased compared to traditional two-stage drying, see table.

After leaving the drying chamber, the powder can be cooled in a pneumatic conveying system, see Figure 20. The resulting powder consists of individual particles and has the same or better bulk density than that obtained by two-stage drying.

P Products containing fat should be cooled in a vibrating fluidized bed, in which the powder is simultaneously agglomerated. In this case, the fines fraction is returned from the cyclone to the atomizer for agglomeration. (see Figure 21).

Circulating fluidized bed (MSD dryers)

To further improve drying efficiency without creating problems with deposit build-up, a completely new spray dryer concept has been developed - the MultiStage Dryer, MSD.

In this apparatus, drying is performed in three stages, each of which is adapted to the characteristic moisture content of the product. At the pre-drying stage, the concentrate is sprayed with direct-flow nozzles located in the hot air channel.

Air is supplied vertically into the dryer at high speed through an air distributor, which ensures optimal mixing of the droplets with the drying air. As already noted, in this case evaporation occurs instantly while the droplets move vertically down through a specially designed drying chamber. The moisture content of the particles is reduced to 6-15%, depending on the type of product. At such high humidity, the powder has high thermoplasticity and stickiness. The air entering at high speed creates the Venturi effect, i.e. sucks in the surrounding air and carries small particles into a moist cloud near the sprayer. This leads to “spontaneous secondary agglomeration”. The air coming from below has sufficient speed to fluidize the layer of settled particles, and its temperature provides the second stage of drying. The air leaving this fluidized back-mixing bed, together with the exhaust air of the first drying stage, exits the chamber from above and is fed into the primary cyclone. From this cyclone, the powder is returned to the backmix fluidized bed and air is supplied to the secondary cyclone for final cleaning.

When the moisture content of the powder is reduced to a certain level, it is discharged through the rotary valve into the Vibro-Fluidizer for final drying and subsequent cooling.

Drying and cooling air from the Vibro-Fluidizer passes through a cyclone where the powder is separated. This fine powder is returned to the atomizer, chamber cone (static fluidized bed) or Vibro-Fluidizer. IN modern dryers cyclones are replaced by bag filters with SIP.

The installation produces a coarse powder, which is due to “spontaneous secondary agglomeration” in the atomizer cloud, where dry fine particles constantly rising from below stick to semi-dry particles, forming agglomerates. The agglomeration process continues when the atomized particles come into contact with the fluidized bed particles. (see Figure 22).

Such a plant can be operated at very high air inlet temperatures (220-275 °C) and extremely short contact times, nevertheless achieving good powder solubility. This installation is very compact, which reduces the requirements for room size. This, as well as the reduced operating cost due to the higher inlet temperature (10-15% less compared to traditional two-stage drying), makes this solution very attractive, especially for agglomerated products.

Figure 22 - Multi-stage spray dryer (MSD)

Spray drying with integrated filters and fluidized beds (IFD)

The patented dryer design with built-in filter, (Figure 23), uses proven spray drying systems such as:

• Feeding system with heating, filtration and concentrate homogenization, equipped with high-pressure pumps. The equipment is the same as in traditional spray dryers.
• Spraying is done either by jet nozzles or by an atomizer. Jet nozzles are used mainly for fatty or high protein products, while rotary atomizers are used for any product, especially those containing crystals.
• The drying air is filtered, heated and distributed by a device that creates a rotating or vertical flow.
• The drying chamber is designed to ensure maximum hygiene and minimize heat loss, for example through the use of removable
  hollow panels.
• The integrated fluidized bed is a combination of a back-mix bed for drying and a piston-type bed for cooling. The fluidized bed apparatus is completely welded and has no cavities. There is an air gap between the backmix layer and the surrounding piston-type layer to prevent heat transfer. It uses the new patented Niro BUBBLE PLATE.

The air removal system, while revolutionary, is based on the same principles as the Niro SANICIP bag filter. The fines are collected on filters built into the drying chamber. The filter sleeves are supported by mesh made of of stainless steel, attached to the ceiling around the circumference of the drying chamber. These filter elements are backflushed clean, just like the SANICIP™ filter.

The hoses are blown out one or four at a time with a stream of compressed air, which is fed into the hose through a nozzle. This ensures regular and frequent removal of the powder that falls into the fluidized bed.

It uses the same filter material as the SANICIP™ bag filter and provides the same air flow per unit area of ​​material.

The backflush nozzles serve two functions. During operation, the nozzle serves for purging, and during CIP, liquid is supplied through it, washing the hoses from the inside out to the dirty surface. Clean water is injected through the backflow nozzle, sprayed with compressed air on the inner surface of the hose and squeezed out. This patented design is very important because it is very difficult or impossible to clean the filter media by external washing.

To clean the underside of the chamber ceiling around the sleeves, specially designed nozzles are used, which also play a dual role. During drying, air is supplied through the nozzle, which prevents powder deposits on the ceiling, and when washing, it is used like a regular CIP nozzle. Camera clean air cleaned with a standard CIP nozzle.

Benefits of installing IFD™

Product

• Higher yield of premium powder. In traditional dryers with cyclones and bag filters, the second grade product is collected from the filters, the share of which is approximately 1%.
• The product is not subjected to mechanical stress in channels, cyclones and bag filters, eliminating the need to return fines from external separators, since the distribution of flows within the dryer ensures optimal primary and secondary agglomeration.
• Product quality is improved because the IFD™ can operate at a lower exit air temperature than a traditional spray dryer. This means that higher drying performance per kg of air can be achieved.

Safety

• The protection system is simpler, since the entire drying process takes place in one apparatus.
• Fewer components require protection.
• Lower maintenance costs

Design

• Easier installation
• Smaller building sizes
• Simpler support structure

Environment protection

• Less possibility of powder leakage into the working area
• More easy cleaning, since the contact area of ​​the equipment with the product is reduced.
• Less waste volume with CIP
• Less powder emission, up to 10-20 mg/nm3.
• Energy savings up to 15%
• Lower noise level due to lower pressure drop in the exhaust system