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Production of polymer-bitumen binders. PMB production

DESCRIPTION OF THE CONTINUOUS PMB (PMB) MANUFACTURING PROCESS

Recently, the use of polymer has been growing significantly around the world - modified bitumen(PMB) or polymer-bitumen binder (PBV). Numerous tests confirm a significant increase in the life of roads with PMB pavement, especially in regions with large temperature differences and increased traffic on the roads.

ENH Engineering is one of the world's leading manufacturers of plants for the manufacture of PMB. We independently developed and produced a large number of continuous (flow) type plants, which have undeniable advantages compared to cyclic plants.

Here short description continuous production process of PMB.

Raw materials are introduced into the installation separately. The main element is bitumen, other materials interfere with it. The bitumen is heated to a temperature of 140-180°C in a constant flow through a heat exchanger, which is heated with thermal oil at a temperature of 240°C and has a power of 400kW. In some cases, one or more aromatic oils along with adhesive agents can be added to the bitumen to improve the properties of the final PMB. The dosage of all liquids is carried out by flowmeters. The actual value is registered by the control system and automatically adjusted according to the preset recipe.

Polymers, in this case SBS, are introduced by means of a weight dosing system. It consists of scales located on strain gauges. The strain gauges are connected to a computer that controls the dosage of polymers. The accuracy of the system is very high.

From the dosing system, the polymers are sent to a small container for pre-mixing with bitumen and other liquids. From this container, the mixture enters the mill. In the mill, the polymer granulate is crushed into small particles and effectively mixed into the bitumen.

For more than 10 years, there has been an inexorable trend towards an increase in state orders for the construction of roads using polymer bitumen binder (PMB). And from November 1, 2014, instead of the main standard for asphalt concrete - GOST 9128-2009, a new GOST 9128-2013 was introduced, with mixtures included in it on polymer-bitumen binders (PBB) based on block copolymers of the styrene-butadiene-styrene (SBS) type. Particularly frequent orders are on federal highways, toll highways and in two capitals - Moscow and St. Petersburg. The price of a modified binder produced at the plant can vary greatly from region to region, but on average it varies from 24 to 28 rubles with VAT per kg.

Description:

In fact, PMB- nothing more than a frayed thermoplastic styrene-butadiene-styrene (SBS) in bitumen. Thermoplastic elastomer has the property of stretching when hot and becoming elastic when cold. Roughly speaking, the vulcanization process in thermoplastic elastomers occurs due to a decrease in temperature and therefore, under normal conditions, it behaves like vulcanized rubber, and when hot, like primary rubber. In the process of grinding thermoplastic elastomer, it is important to crush it as finely as possible and disperse it throughout the volume of bitumen; for this, special attention should be paid to a colloid mill, the fineness of polymer grinding primarily depends on its operation.

Numbers:

Some major manufacturers PMBs replace SBS with cheaper polymers or crumb rubber, which, with the right approach, does not greatly affect the properties of the final product, but allows significant savings, compare for yourself:

The cost of SBS - from 180 rubles per kg,

The cost of crumb rubber up to 1 mm - 20 rubles per kg,

The cost of secondary plastics is from 15 rubles per kg.

If 40 kg of SBS is required for 1 ton of PBB, then even replacing 10 kg can save 1.5 thousand rubles.

Of course, none of the PMB manufacturers openly admits to replacing expensive material with secondary raw materials, however, if the properties of the final material comply with the requirements of GOST, why not?

It will not be possible to check the presence of crumb rubber and secondary plastics in a conventional laboratory.
This requires rare equipment - capable of dissolving bitumen, separating it from stone material and organic impurities (such as crumb rubber).

If you are interested in the production of PMB, but at the same time are actively looking for approaches to reduce the cost of production, here are a few recommendations:

Analyze the SBS market. In Russia, it is represented by major players such as Kroton, LG-Chem, Sibur, and little-known manufacturers from America, Korea, China, Japan, whose prices may compare favorably with well-known ones.

When replacing SBS with cheaper components, check how this will affect the final product. Most often, such a PBV either has a drop in extensibility, or a drop in temperature during CISH (ring and ball). To stabilize these indicators, we recommend using not only cheap substitutes,
but also chemical additives in bitumen, as well as to carry out preliminary preparation of raw materials before being fed to the installation.

If you work at an asphalt plant, then some of the components can be sent for dry batching, for example, the modifier can be introduced directly into the mixer, since it already contains chemical additives for pre-treatment of the supplied material.

In addition to the possibility of direct substitution of SBS for cheaper components, there is experience in the use of chemical additives to enhance the dispersion of polymer particles. One of these additives is polyphosphoric acid, which saves up to 20% of the input SBS. However, it is necessary to work with such additives very carefully, since some of them have side properties on the bitumen itself, which may not be manifested in the first year, but contribute to its accelerated aging (oxidation) in the future.

The BSA.PBV.01.5000 unit is intended for to obtain modified bitumen , including (PBV).

Multi-pass plant for short maturation times modified bitumen, with the possibility of using almost all known this moment polymer modifiers, both solid (in granules and powder) and liquid;
Massenza is used as part of the plant, which ensures high-quality grinding of the polymer during the preparation process. PMB, thereby increasing the specific contact surface of the mixed components, and, accordingly, the processes of swelling and dissolution of the polymer are accelerated, and, consequently, high performance installations;
The ability to control the process of polymer grinding and its dissolution in bitumen due to the ability to control the number of passes of the bitumen-polymer mixture through the colloid mill;
Tensometric weight dosing of bitumen and polymers.

Modern installations for modifying bitumen with polymeric materials

The pavement should provide maximum resistance to fatigue damage, be resistant to temperature changes in daily and seasonal cycles. One of promising directions, allowing to solve these problems, is the application, in particular (). Currently, there are many methods and materials for modifying road binders.

Most effective for PMB production should be considered equipment that contains(grinders), which ensure the grinding of the polymer during the preparation process PMB. When grinding the polymer, the specific contact surface of the mixed components increases, and, accordingly, the processes of swelling and dissolution of the polymer are accelerated. The use of this type of equipment makes it possible to obtain PMB with regulated technical requirements at a temperature not exceeding 160 degrees. C, the content of the modifier is not more than 3.5 wt. % and short duration of the process. In case of preparation PMB on equipment without high-speed grinders (colloidal mills), it is necessary to set a higher polymer concentration, a higher process temperature (this can lead to bitumen aging and oxidative degradation PMB, property level PMB this will significantly decrease), in addition, the duration of the cooking process increases by more than 2 times. At the moment, the best distribution (homogenization) rates are achieved only when using colloid mills with a high degree grinding.

Technological scheme of the process of obtaining PBB on bitumen modification plant type UNB-4 using colloid mill in the external circulation circuit is shown in fig. one.

Rice. 1. Technological scheme of the process of obtaining PBB at the installation for the modification of bitumen

Bitumen heated in a bitumen boiler to a temperature of 160 ... 180 ° C is supplied to the installation by the pump H1.1 through the three-way valve K1.2. The three-way valve K1.2 is installed in the middle position, which ensures mixing - circulation of bitumen in the boiler, in the case when the installation does not consume bitumen. When the K4 valve and the H2 pump are turned on, the bitumen from the boiler through the K3 valve enters the CM mixer, where it is mixed with the polymer, which is previously poured into the V tank. cranes K1, K2). After the production of the polymer from bitumen V until the sensor was triggered, the valve K3 was switched to the position of supplying bitumen to the reactor bypassing the mixer SM. Resin valve K7 and K6 are closed. The reactor vessel is filled with bitumen to the upper level (VU1 or VU2). Simultaneously with the filling of the reactor vessel with bitumen, it is mixed. Mixing is carried out during the time specified by the technological process (15...20 min). After the end of mixing, the corresponding tap (K1 or K2) is switched on, the pump H1 and the mill M3 are turned on. The K5 valve is installed in the position of bitumen supply after the mill to the corresponding reactor. After filling the first reactor vessel, the polymer is filled and introduced into the vessel of the second reactor P2. The technological cycle in the second reactor is similar to the first. The reactor block consists of two heated tanks made of a cylindrical shape with a conical bottom. TP-46 oil is used as a heat carrier. To reduce heat losses, the reactors are thermally insulated with thermal insulation jackets. On the top cover of the container are mounted: a paddle mixer drive; bitumen supply pipe; manhole; bitumen upper level float sensor. The agitator drive is made on the basis of worm gear motors.

Wide application in the field produced by PMB according to a similar technological scheme also received MASSENZA installation, specially designed for the production of modified bitumen. The MASSENZA mill has a special rotor/stator configuration that allows 100% of the power to be used solely for the grinding action. In fact, the increase in gap that occurs in mills from other manufacturers, when material with a high polymer content is supplied, means a decrease in the grinding effect, while, on the contrary, it is required to sufficiently grind (split) the polymer. MASSENZA has developed a completely different system that allows the most efficient 100% polymer grinding work, regardless of the polymer content of the material. In fact, the MASSENZA mill has a special system equipped with an external gear pump for feeding into the mill.

In many countries, in particular in Russia, ultra-modern installations are used, which are manufactured in Germany, implementing the same scheme with. Benninghoven has been developing and perfecting for ten years the lineup installations in mobile or transportable execution. The main equipment can be additionally completed with special components in accordance with the individual specification, depending on the purpose of the equipment and the recipe. Complexes for the production of modified bitumen include: capacitive storage park of initial bitumen; unit for preparation and mixing of several grades of bitumen; block bitumen modifications with reactor and ; system for introducing plasticizers and additives; heating system; dosing system; concentrate mixing system with initial bitumen; capacitive park for product ripening with agitators, unloading device: loading rack with vapor removal, high-temperature polymer in the open state. The mill is heated either electrically or with thermal oil. Due to the adjustable gap between the cutting surfaces of the mill, a homogeneous PMB in just one work pass.

Technology is mastered bitumen modifications cavitation currents. A prominent representative of this direction is OJSC Military Engineering Corporation (VIKor). circuit diagram production plants PMB shown in fig. 2.

Rice. Fig. 2. Schematic diagram of the PMB installation based on the standard equipment of the bitumen reception and storage area of a typical ABZ

Rice. 3. Cavitation disperser KEM-20

The bitumen charged into the boiler is heated to a temperature of 170 ° C and pre-mixed with paddle mixers for 5 minutes, without turning off the mixers, 4% by weight of Kraton D1101 is gradually introduced through the loading hatch and subjected to mixing with mixers for 30 minutes to pre-dissolve (swell) the polymer, then, for 60 min, the bitumen-polymer mixture is circulated through the KEM-20 disperser along the circulating bitumen pipeline. Dispersion in this case proceeds in a cavitation disperser (Fig. 3). The device works as follows: the polymer modifier is pre-dissolved in kerosene and fed to the input. Bitumen is also supplied there and cavitation provides an intense mixing effect.

Disperser KEM-20 in a special design with a capacity of up to 30 cubic meters. m/h, installed in the circulating bitumen pipeline after the bitumen station and allows to achieve high homogenization of the modifier in bitumen. To work on this technological scheme, an experimental PMB production plant in JSC DST No. 2, Gomel.

known plant for the production of PMB according to the technological scheme in-line, which is shown in Fig. 4.

Rice. 4. Technological scheme of the PMB preparation process using the PMB Inline Mixer 10-15 t/h

essence technological process according to the scheme in accordance with Fig. 4 is reduced to the transfer of the polymer from a dry state to a liquid state by extrusion and the subsequent mixing of a viscous-fluid polymer with bitumen heated to the operating temperature. At the same time, several processes are simultaneously carried out along the movement of materials: polymer extrusion, which combines the mixing and dissolution of the resulting melt with a certain amount of bitumen or plasticizer; mixing the resulting abnormally viscous fluid with some bitumen and resulting in a high or super high polymer content; subsequent mixing of the polymer-bitumen concentrate with the main bitumen flow in proportions that provide the required polymer content in the finished PMB.

The process is carried out in-line, in a clean in-line mode, that is, at the entrance to the installation we have bitumen and dry polymer, at the exit - PMB immediately ready for use. In the same in-line mode, any other liquid component can be added to the binder in accordance with the recipe, as well as, for example, an additional amount of plasticizer or thinner. The bitumen temperature at the outlet of the plant is determined by the bitumen temperature at the inlet. If there is a need for the preparation of thinned bitumen, bitumen with an adhesive additive, etc., the energetically powerful extrusion process does not need to be involved, the usual operation of the dosing lines and the mixer is sufficient.

Speaking about the process of polymer dissolution, it should be noted that its solubility is closely related not only to the corresponding ability of bitumen, the temperature of the bitumen itself, as is usually noted in studies on PMB, but also with the temperature of the polymer itself, as well as with the area of the phase boundary. The higher the temperature of the polymer, the higher the area of its contact with bitumen, the higher the dissolution rate.

The next process according to the technological scheme is also the process of mixing, but already liquids with not so different viscosities - polymer-bitumen concentrate and pure bitumen. In addition, adhesive additive and other liquid components can be added at this stage, if the formulation requires it. Mixing is carried out by an efficient dynamic mixer.

as a container finished products a heat-insulated vertical container with stirring and heating is provided.

At the moment, the market for equipment for the production of PMB a wide range of installations and mixer options are available, with mixers of various configurations to go with them. The problem of retrofitting existing asphalt plants to technological schemes produced by ABS, based on a modified PMB can be decided according to the type of modifying materials.

In road construction common materials provided satisfactory quality for many years. Today, ever-increasing traffic loads, the need for reliable and durable roads, and the demands for economy have made the disadvantages of conventional bitumen obvious. Unmodified bitumens show the following disadvantages in practice:

high thermal sensitivity (softening at high temperatures ah and brittleness at low);
bad mechanical characteristics and low elasticity;
prone to aging.

In view of these shortcomings, as well as many practical and economic factors, a number of studies have been carried out over the past 40 years. They demonstrated that polymeric materials are the best modifiers to improve the processing properties of bitumen. PBV (polymer-bitumen binder) is a qualitatively new material that allows to increase the service life of the road surface.

Modified bitumen, formed by combining conventional bitumen and polymer, provides a higher level of quality:

improved performance at high and low temperatures;
improvement of elastoplastic characteristics;
increased material fatigue resistance;
improvement of cohesion and adhesion with fillers;
increased resistance to aging.

MASSENZA produces plants for the production of polymer-modified bitumen using only colloid mills, which ensure the grinding of the polymer during the preparation of PMB. When grinding the polymer, the specific contact surface of the mixed components increases, and, accordingly, the processes of swelling and dissolution of the polymer are accelerated. The use of equipment of this type makes it possible to obtain WSP with regulated technical requirements.

High performance is only achieved with precise control of the dosage of the crushed polymer and its distribution in the bituminous mass. And as a result, at the moment, the best distribution (homogenization) rates are only achieved when using colloid mills with a high degree of grinding.

Polymer-bitumen binder (hereinafter referred to as PBB) is one of the main components of the top layer of asphalt concrete pavement of modern roads, significantly extending their service life from 3–4 years (when using traditional road bitumen) to 7–10 years. PMB significantly increases the strength, crack resistance, heat resistance, shear resistance, water and frost resistance of the road surface. The most indicative characteristic of asphalt pavement produced using PMB, which makes it possible to identify the difference between polymer asphalt concrete and traditional asphalt concrete, is the coefficient of temperature sensitivity. Asphalt on PMB is much less sensitive to temperature changes. Rise in the total cost of construction highway with the use of PBB is no more than 1%. At the same time, the costs are fully paid off in several years of operation of the road.

The practice of using PMB is widespread in the USA, Europe and China. Last years In Russia, this technology is becoming more and more in demand. So, for example, in May 2013, the industry road methodological document ODM 218.3.026-2012 “Recommendations for the use of high-density asphalt concrete based on polymer-bitumen binders for road pavements in various climatic conditions” was adopted and put into effect. Russian Federation". In accordance with these documents, it is recommended to use PMB in accordance with GOST R 52056 in the composition of high-density asphalt concrete instead of bitumen in accordance with GOST 22245, which can significantly improve the quality of the road surface, take into account the actual climatic conditions and traffic conditions of vehicles under which road surfaces are operated in any region of Russia. The performance of the coating, its evenness, the absence or presence of defects on it is the most important, and in some cases even main characteristic consumer quality road, as it is determined quickly and visually.

As you know, Russia is distinguished by a harsh and sharply continental climate, on the one hand, with low negative temperatures and high positive temperatures, on the other hand. So, for example, the air temperature of the coldest regions in winter can reach minus 63°C, and on hot summer days the surface of the coating can heat up to high temperatures, from 55°C to 62°C. Thus, the temperature range in which the coating operates reaches 125°C. In addition, in the flow of cars, a significant part is made up of trucks, which determine the increased dynamic effects on the coatings, increasing the deflection amplitude, provoking fatigue processes and accelerating the accumulation of plastic deformations and microcracks.

In order to take into account the climatic conditions of operation of coatings, to ensure their required crack resistance and shear resistance, PBB must satisfy all high requirements. Thermal sensitivity does not allow conventional bitumen to behave well at both high and low temperatures, forcing it to "modify" the properties of the bitumen in some way. The presence of asphaltenes determines the specific properties of bitumen, namely, viscosity (plasticity) and elasticity, resistance to certain types of deformations, cohesive and binding properties. Elasticity and plasticity are due to the presence of resins and maltenes. By analyzing the group composition of bitumen and the properties of the components, it is possible to assess which parameters are the most important when modifying bitumen with polymers. The determining factor is the compatibility of bitumen with polymers. Solubility polymer materials in bitumen depends on many parameters, of which the most important are: the difference in the solubility parameters of the polymer and the maltenic phase of the polymer, as well as the amount and types of asphaltenes contained in bitumen.

The technological process of PMB production can be divided into two parts: direct production, when bitumen is mixed with polymer at a specialized plant, and ripening in finished PMB storage tanks, where, when in contact with bitumen, the elastomeric polymer blocks swell, absorbing a significant proportion of the maltenic bitumen fraction. Thus, after mixing with bitumen, the polymer swells and the volume of the enriched phase is 5-10 times higher than the volume of the polymer added to the mixture. High performance is only achieved with precise control of the polymer dosage and its distribution in the bituminous mass. As studies by European experts have shown, the best distribution (homogenization) rates are achieved when using a mill with a high degree of grinding. The mill (homogenizer) is the main part of the plant for the production of PMB. There are several types of mills on the market, and most of them are designed for other industries (food, chemical, woodworking), but are used for the production of polymer-modified bitumen. MASSENZA has developed its own mill model, specially designed for the production of modified bitumen, which is the best in the industry. In addition, MASSENZA has developed special system with a variable speed pump feeding the mill. Such a system allows the mill itself not to waste energy on pumping (as happens with most other manufacturers), directing all of it to grinding, and also constantly ensures maximum product yield by regulating the flow of raw materials. It should be noted that MASSENZA specialists constantly continue research in the field of interaction between polymer and bitumen, the impact of the grinding process in the mill on the quality of the final product, and in 2014 the factory produced new model mill - PMB 490-S, the structural elements of which are designed so that the final product has the highest characteristics. The new mill provides a finer dispersion, which in turn helps to reduce the time for the chemical ripening phase and increase productivity. This model, compared to the previous ones, includes the following improvements:

large rotor and stator;
more wear-resistant materials;
improved system for supplying bitumen and polymer to the mill;
new design of the grinding elements of the rotor and stator.

The new configuration of the homogenizer makes it possible to increase its efficiency by 40% compared to previous models, which in turn increased the productivity of the PMB plants themselves.

In addition to the grinding process, the quality of PMB is highly dependent on the exact adherence to the recipe, and, accordingly, on the accuracy of the dosage of the components at the plant. Often, plants for the production of PMB do not have a system for measuring the dosage of the polymer and the dosage is regulated by the operator, measuring the amount in bags, or a system for volumetric measurement of the dosage of the polymer into the container is implemented, which also has large errors. MASSENZA PMB production plants are equipped with a 600 liter feed hopper, which has an automatic weighing polymer dosing system. The hopper is located on strain gauges, which allows for precise control of the polymer dosage. No less important is the accuracy of bitumen dosing. Plant manufacturers solve this problem in two ways: either they equip the mixing tanks with strain gauges, and with their help they control the dosage of both bitumen and polymer. What is wrong technological solution as the container, where the polymer is dispensed, is pressed by the mass of the dosing polymer auger and all connected pipelines, and the vibration from the operation of the units (pumps, mill, mixers) is also transmitted. All this leads to the fact that this system produces a very large error in readings. Or at the installations, volumetric dosing of bitumen is implemented, depending on the accuracy of pump delivery, opening - closing of valves. The dosage of bitumen during injection into the MASSENZA unit is more than in an innovative way through a special device according to the Coriolis principle (measuring system in the casing, measures the flow rate regardless of other liquid parameters, such as: density, temperature, pressure, viscosity, electrical conductivity, etc.). Moreover, this system is equipped with temperature control of the incoming bitumen, since for the correct modification of bitumen by polymers great importance have temperature regimes and the accuracy of their observance. That is, if the original bitumen does not meet the required temperature (for any possible reason), the process stops and the system signals this to the operator.

As is known, road bitumen produced in Russia do not meet the requirements for PMB production. Bitumens are insufficiently crack-resistant, not heat-resistant, not elastic and oxidized (poor in aromatics). To improve the compatibility of the polymer with bitumen and create a spatial structural network, special additives or aromatic oils are used as one of the PMB components (in order to enrich bitumen that is poor in oils, i.e. to make a kind of initial modification of bitumen with oils). MASSENZA units have a plasticizer (aromatic oils) injection line, and this system with a heating jacket is specially designed for the most popular plasticizers in Russia, dosed at temperatures up to 120 degrees Celsius.
In addition to the accuracy of dosage of all components and effective homogenization of bitumen with polymer, an important criterion on which the quality of the final product strongly depends is the temperature regime of production. In MASSENZA plants, all pumps, tanks, valves and mills are heated with thermal oil. This system"indirect heating" provides a number of advantages over steam, flame and electric heating. First of all, due to oil heating, it is possible to provide heating of all the required equipment with one oil circulation circuit: internal pipelines and units of the PMB production plant, as well as all auxiliary infrastructure (pipelines, bitumen pumps, tanks, valves, gate valves). With oil "soft heating" there is no oxidation and coking of bitumen, and, accordingly, deterioration of the bituminous binder, which is not ideal in terms of its performance characteristics. Also, oil heating systems, as a rule, are the most efficient in terms of operating costs for heat energy, and it is very important that such a heating system allows you to accurately maintain all temperature conditions at all technological stages of PMB production, which qualitatively affects the characteristics of the final product.