Учебное пособие 2016

Here πk(m,n)(s), Пk(m,n)(s) are boundary functions (x = 1, 2) and s = τ/γ.

As the differential equation for the first component of the heat capacity vector in (1) does not contain the parameter γ, the equations should hold true

С1(m,n) ( ) 0 , (m 0) ;

1(m,n) (s) 0 , (любое m, n).

Using the ratios (4), (6), (1) by means of a standard procedure of the perturbation method we get the system of equations for the major and boundary functions in (4). For the above heat capacity of a disperse material, i.e. the first component of the heat capacity vector, we have

Restricting the second-order approximation with the parameters γ, λ using the equations (9)— (10) we get the following equations for the above heat capacities of the material and heat carrier:

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According to the expressions (11) and (12), the approximation to the equilibrium heat capacities and continuous subsystems of the layer is described by the following relaxation parameters:

The solution designed in the first approximation is characterized by only one relaxation time t(1)рел .

According to the expression for the above heat capacity (11), for the time of drying in the second period t >> tрел the moisture content of a disperse material is determined by the following approximated equation:

where w1н is the moisture content following a constant drying rate period.

Let us employ the above procedure to design an approximated solution of the equation describing the evolution of the temperatures of the material and heat carrier in the pseudoliquefied layer. Using the resolution (5), (7) and identical resolutions for the matrix elements and free members

aij ( ) aij(0) aij(1) ( ) ... , a12 a12(0) ,

ai ( ) ai(0) ai(1) ( ) ,

using the equations for the temperatures of the subsystems of the layer (2) we obtain a range of systems of differential equations for the functional coefficients in the resolutions (5). In the solutions of the temperature equations we will limit ourselves with the first approximations for the parameters λ and γ.

In the zero approximation using the parameters we get the following degenerated system

2

C1(0,0) 1(0,0) ( ) ( 1)n a1(0)n n(0,0) ( ) a1(0) ,

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The last condition that boundary functions reduce as s grows guarantees that they are determined correctly.

The solution of the system of the equations (14)—(16) is as follows:

used.

Let us move on to designing the equations and solutions of the following approximation. Using the system of the equations (2) and the resolutions (5) of the temperatures of the subsystems of the layer Θ1(τ) and Θ2(τ) and performing the standard procedures of separating the coefficients at λ and γ for the functions from τ and s individually, we get differential equations of first order approximation.

For the resolution members containing the parameter λ we get:

where the upper index «0» in the heat capacity symbols denotes the coefficient at γ0 in the resolutions C*n(0, k)(γ, s) using the degree γ, the second upper index in the coefficients a2n de-

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notes the corresponding resolution member of these functions at γk. The system of equations for the first-order approximation function using the parameter γ is as follows:

The solution of the system of the equations for the first approximations for the solutions of the temperature equations using the regular parameter (18) is as follows:

The solution of the system of the equations describing the first approximation to the temperatures of the material and heat carrier using the singular parameter γ can be the following:

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The rations (5) and (7) at N = 1 in combination with the expressions (17), (20) and (22) determine the temperatures of the material and heat carrier in the first approximation using the parameters λ and γ.

The above formulas show that the approximation of the temperatures of the disperse and continuous subsystems of the pseudoliquefied layer to the equilibrium values is characterized by a number of time scales. Transitions to the thermal equilibrium for these subsystems besides

Note that the main members of the approximated solutions (17) of the temperature equations

is characterized by two relaxation parameters t(3)рел and t(4)рел . The correction members of the solution contain the whole range of relaxation times from t(1)рел to t(5)рел .

With the drying taking considerably more than the relaxation time the main members of the expressions for the temperature of the material and heat carrier in the layer are approximated to the following specific values:

The formulas (23) for the relaxation times of the material and heat carrier show that the approximation of the temperatures to the equilibrium values is faster than that to the specific moisture contents of the phases of the layer, which might be significant for drying heatsensitive materials.

Conclusions

1.Asymptotic methods were for the first time used to obtain the solutions of a singularly and regularly perturbed system of equations describing the mass and heat equilibrium in the pseudoliquefied layer.

2.The dependences of the relaxation times of heat capacities and temperatures on kinetic and thermоphysical parameters of the solid and gaseous phases of the layer. There are also the expressions for the temperatures of the phases at times longer than those of relaxation.

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3. The results of the paper can be employed for developing the methods of engineering calcu-

lations of drying devices with a pseudoliquefied layer.

References

1.Agapov Yu. N., Byrdin A. P., Luk'yanenko V. I., Stogney V. G. Termokinetika dinamicheskogo sloya v nachal'nykh stadiyakh teplovoy relaksatsii [Thermokinetic dynamic layer in the initial stages of thermal relaxation]. Vestnik Voronezh. gos. tekhn. un-ta, 2007, vol. 3, no. 6, pp. 27—32.

2.Byrdin A. P., Sidorenko A. A., Stogney V. G. Kinetika teploobmena v kipyashchem sloe v stadii progreva materiala [The kinetics of heat exchange in a fluidized bed in the stage of heating the material]. Vestnik Voronezh. gos. tekhn. un-ta, 2011, vol. 7, no. 11.1, pp. 122—125.

3.Barakov A. V., Byrdin A. P., Nadeev A. A. Temperatury faz dinamicheskogo sloya vo vtorom periode sushki v zadannom diapazone reguliruemykh parametrov [Temperature of the phases of the dynamic layer in the second drying period in a specified range of adjustable parameters]. Vestnik Voronezh. gos. tekhn. un-ta, 2014, vol. 10, no. 6, pp. 97—100.

4.Vasil'eva A. V., Butuzov V. F. Asimptoticheskie razlozheniya resheniy singulyarno vozmushchennykh uravneniy [Asymptotic expansions of solutions of singularly perturbed equations]. Moscow, Nauka Publ., 1973.

272p.

5.Lykov A. V. Teoriya sushki [Theory drying]. Moscow, Energiya Publ., 1968. 472 p.

6.Baumshteyn I. P., Lykov A. B., Lyudmirskiy M. I., Mayzel' Yu. A. [Study of the drying units by means of mathematical modeling]. Teplo- i massoperenos v protsesse sushki i termoobrabotki [Heat and mass transfer in the drying process and heat treatment]. Minsk, Nauka i tekhnika Publ., 1970, pp. 53—79.

7.Barakov A. V., Kozhukhov N. N., Prutskikh D. A., Dubanin V. Yu. Modelirovanie teplomassoobmena v vozdukhookhladitele kosvenno-isparitel'nogo tipa [Modeling of the heat transfer in the air-cooler of indirect-

evaporation type]. Nauchnyy vestnik Voronezhskogo GASU. Stroitel'stvo i arkhitektura, 2014, no. № 4 (40),

pp. 28—33.

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WATER SUPPLY, SEWERAGE, BUILDING CONSTRUCTION

OF WATER RESOURCES PROTECTION

UDC 541.183

G. V. Slavinskaya1, O. V. Kurenkova2

LOW WASTE WATER NEKAL PURIFICATION

Voronezh State University of Architecture and Civil Engineering Russia, Voronezh, tel.: (473)249-89-70, e-mail: slavgv@mail.ru

1D. Sc. in Chemistry, Prof. of the Dept. of Chemistry

Cadet School (Engineering School) Military Educational Scientific Centre of Military Air Forces Russia, Voronezh, e-mail: vaiu@mil.ru

2PhD in Chemistry, Chemistry teacher

Statement of the problem. Surface active agents (surfactants) are contained in almost all reservoirs. Their presence in water has been long neglected. However, after negative effect of surfactants on human and aquatic life became clear, a method of removing the surfactant from water has been searched for. The disadvantage of the known processes — formation of a large volume of corrosive wastewater. The objective is to develop the process of sorption of water nekal purification with minimum waste water.

Results. A type anion exchange resins was identified, which are able to absorb nekal. On the basis of kinetic and equilibrium sorption laws of nekal by anion exchangers the operation of an adsorber under dynamic conditions was optimized. A schematic diagram of sorption and desorption of nekal anion exchanger and a method for cleaning and regenerate from nekal alkali by electrodialysis were developed.

Conclusions. Anion exchangers with tertiary amine groups were found to be suitable. Desorption of nekal is carried out using a solution of 0.25 mol/l of alkali. The electrodialysis cell with two ca- tion-exchange membranes is separated from nekal alkali. Purified water is used for the preparation of the regenerating acid solutions and alkali.

Keywords: nekal, anion, adsorption, desorption, electrodialysis.

Introduction

It was around 1950 when household synthetic washing substances began being used [1]. Their major components, i.e. active compound, detergents with surface active properties.

© Slavinskaya G. V., Kurenkova О. V., 2016

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Their widespread use over the last years have led to them inevitably being part of natural waters not only surface but artesian ones. Surface artesian waters are currently considered the most common water toxicants.

It became obvious that surface active substances need to be prevented from getting into natural sources after their negative effects on human body and water ecosystems were known, i.e. they change blood composition, impair the immune system, cause atherosclerosis accumulate in brain and liver, facilitate the absorption of other toxic substances into tissues of fishes, reinforce the smell of water, worsen its taste and some are carcinogenic [2].

Pollution of water with surface active substances are due to the fact that they contain not only non-purified but also purified industrial and household waste water containing surface active substances.

The latter are divided into ionic, ion dissociation (cation and anion) and non-ionic (nondissociation) ones [3]. Surface active substances have no charge and can thus be absorbed by active coals. Surface active substances with a charge are hydrated by water molecules. The resulting water ―coat‖ keeps the particles of surface active substances from approaching the coal surface, which accounts for a low sorption capacity of such sorbents compared to surface active substances.

Low performance of water purification using surface active substances on modern purification equipment is a cause of their presence in drinking water of water pipes. Pollution of the country’s water by surface active substances caused a new guideline document (Health and Epidemiological Guideline (SanPiN) 2.1.4.559-96) being introduced in 1996 that included maximum permissible concentrations (MPCs) of some toxic impurities: phenols (0,25 mg/l), oil products (0,1 mg/l) and surface active substances (0,5 mg/l).

The same standards are provided in a new version of Health and Epidemiological Guideline [4] that came into force in 2001. In order to meet new health and safety standards, it is obvious that drinking water should be purified from surface active substances. This is a global issue as natural water around the globe is polluted with surface active substances.

Different methods are known to be employed for this purpose such as destruction, oxidation, thermal ones, etc. They are also chemical, electrochemical, thermal, radiation and biological oxidation. These methods assist in partial destruction of pollutants in water. The remainder generally has an adverse effect with the destruction products of a bi molecule of surface active substances being more toxic than the original ones. Therefore the methods that involve complete extraction of these substances from water are to be employed. This can be achieved only by means of sorption methods. They allow the removal of a variety of organic substances re-

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gardless of their chemical stability provided there is no secondary pollution. For that a lot of factors contributing to absorption have to be considered. Therefore it is becoming increasingly important to develop efficient technologies of extraction of surface active substances from water. It is promising to use sorption methods employing synthetic ion exchangers for anionic surface active substances.

1. Background. Voronezh is one of the few cities where water is supplied not from open reservoirs but artesian aquifers [5]. They are designed to pump water from a water-saturated sandy layer which is located along the Voronezh water reservoir. Artesian water is thought to be one of the cleanest as it is purified from a range of impurities primarily solids as it passes through the ground.

Voronezh is faced with the problem regarding surface active substances in drinking water. Besides surface active substances that come into natural water with household wasters (washing powder), there is a constant threat of extra pollution of drinking water with anionic nekal surfactant – dibutyl naphthalene sulfonate of natrium (C18H23SO3Na). Nekal is a sodium salt of an organic aromatic sulfonic acid where an organic radical is a singly charged anion.

In 1935 in Voronezh a plant for manufacturing synthetic rubber was opened. Nekal had been part of the technology over many decades. Waste water was damped onto filtration fields – ponds with a permeable bottom. Water was leaked out through the ground and purified from nekal. It usually happens till the dirt capacity of a reservoir has run out. If it has run out, polluted water gets into an underground water-bearing layer with pure artesian water, which happened in the city.

Leaking out of waste water of the synthesis rubber plant into a water-bearing horizon and pollution of underground water with nekal took place as early as in 1956 [6]. In 1959 an article by V. A. Ivanov was published [7] where nekal was said to not only be able to easily filtrate through the layers of ground but it also involves other organic compounds. There were fears that there might be water exchange between them if underground horizons are not sufficiently isolated. There were reasons to think so as a sandy sublayer does not stop pollution unlike water-resistant clay which can also be penetrable for nekal. The analysis of samples of underground water selected in 1958 at different distances from the filtration fields of the synthesis rubber plant found the content of nekal of 330 mg/l 400 m away to the South-West to the Voronezh River [7].

In 2007 the Environment Protection Ministry came up with ―Report on the Environmental Situation and Nature Conservation in the City of Voronezh in 2006‖ [5]. It states that there is

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some underground water that was forming from 1949 to 1969 which is not polluted with nekal. In [8] it is said to be 7,5 km2. The concentration of neka is up to 1660 MPC. There is some nekal found in some water samples.

One of the ways to combat surfactant pollution is to destroy the molecules electronically. From 1984 to 2000 there was destructive purification of underground water by treating it with a flow of electrons onto two electron-beam devices. The purification technology was developed in All-Russian Scientific Research Institute of Technical Physics and Automatization (Moscow) and electronic-beam devices were developed and manufactured by the G.I. Budker Institute of Nuclear Physics (Novosibirsk). It is not known what fragments nekal molecules fall into as they are exposed to an electron beam. There is no guarantee that the resulting substances are less toxic than nekal. There are two benzene nuclei in a nekal molecule. They are hard to destroy, thus only individual benzene nuclei, which will stay in water this way, can be obtained. Therefore nekal should not be destroyed but removed. In this case we are meeting the major requirement for drinking water – it should be safe to drink.

In [7] there is a statement of a real threat of the pollution of water-bearing layers as a result of water coming from some area of nekal water. Therefore the performance of some water supply points is restricted and some wells are not used at all. Hydrogeologists in [9] point out that ―some wells can be used for protection and pump about 2500 m3 of water per day‖. But where is this off-grade water supposed to go? Should it be purified or dumped into a water reservoir? If it is, the content of nekal in water is to increase but MPC will be 0,5 mg/l compared to the overall content of nekal. Therefore the only way forward is to purify water using the sorption method.

2. Experiment. It is not to say that there have been no attempts to use ion-exchangers for that. But there are few descriptions of them in the literature. In Voronezh this has been addressed for over 50 years in the context of nekal. The technology of using anionite for purifying waste water of the synthesis rubber plant was proposed [10]. For a sorbent to work, its sorption capacity has to be restored, i.e. it has to be regenerated. In [10] desorption of nekal with a salt solution in a methyl or ethyl alcohol. In [11] it is a sulphuric acid solution in a methyl alcohol or acetone followed by distillation of a light solvent.

Our task was to develop a technology for nekal water purification that would rule out the use of organic toxic solvents by starting with searching for an effective anion-exchanger. There are currently different ion-exchange materials manufactured on a wide scale, which makes it possible to choose an effective sorbent to be used for water purification.

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