Chemical reactions are accompanied by the release or absorption of energy. If energy is released or absorbed in the form of heat, then such reactions are written using the equations of chemical reactions indicating thermal effects, while it is necessary to indicate the phase composition of the reacting substances.
chemical reactions, flowing with the release of heat, are called exothermic, and with the absorption of heat - endothermic.
Thermochemistry is the study of the thermal effects of reactions. In thermochemistry, the thermal effect of a reaction is denoted by Q and is expressed in kJ.
Thermochemistry is one of the sections of chemical thermodynamics that studies the transitions of energy from one form to another and from one set of bodies to others, as well as the possibility, direction and depth of the implementation of chemical and phase processes under given conditions. Each individual substance or their combination is a thermodynamic system. If a thermodynamic system does not exchange matter or energy with the environment, it is called isolated. Such an idealized system is used as a physical abstraction when considering processes that exclude the influence of the external environment. A system that exchanges only energy with the environment is called a closed system. If energy and material exchange is possible, the system is open.
The state of the system is determined by the thermodynamic parameters of the state - temperature, pressure, concentration, volume, etc. The system is characterized, in addition, by such properties as internal energy U,enthalpy H, entropy S, Gibbs energy G. Of a change in progress chemical reactions characterize its energy system.
Internal energy of the system U consists of the energy of motion and interaction of molecules, the energy of binding in molecules, the energy of motion and interaction of electrons and nuclei, etc.
The absolute value of the internal energy cannot be determined, but its change during the transition of the system from the initial state to the final state as a result of the implementation of a chemical process can be calculated. If the system receives a certain amount of heat at a constant pressure Qp, the latter is spent on changing the internal energy of the system ΔU and doing work A = PΔV against external forces:
This equation expresses the law of conservation of energy or the first law of thermodynamics.
adiabatic process is a process of quasi-static expansion or compression of a gas in a vessel with heat-impermeable walls. The first law of thermodynamics for an adiabatic process takes the form:
Isothermal process is a process of quasi-static expansion or contraction of a substance in contact with a thermal reservoir (T = const).
Since the internal energy of an ideal gas depends only on temperature (Joule's law), the first law of thermodynamics for an isothermal process is written as: Q = A.
In an isochoric process (V = const), the absorption or release of heat (thermal effect) is associated only with a change in internal energy:
In chemistry, isobaric processes (P = const) are most often considered, and the thermal effect in this case is called the change in the enthalpy of the system or the enthalpy of the process:
∆H = ∆U + P∆V
Enthalpy has the dimension of energy (kJ). Its value is proportional to the amount of substance; the enthalpy of a unit amount of a substance (mol) is measured in kJ ∙ mol -1.
In a thermodynamic system, the released heat of a chemical process is considered to be negative (exothermic process, ΔH< 0), а поглощение системой теплоты соответствует эндотермическому процессу, ΔH > 0.
The equations of chemical reactions indicating the enthalpy of the process are called thermochemical. The numerical values of the enthalpy ΔH are indicated, separated by commas, in kJ and refer to the entire reaction, taking into account the stoichiometric coefficients of all reactants.
Since the reactants can be in different states of aggregation, it is indicated by the lower right index in brackets: (t) - solid, (j) - crystalline, (g) - liquid, (d) - gaseous, (p) - dissolved.
For example, when gaseous H 2 and Cl 2 react, two moles of gaseous HCl are formed. The thermochemical equation is written as follows:
When gaseous H 2 and O 2 interact, the resulting H 2 O can be in three states of aggregation, which will affect the change in enthalpy:
The given enthalpies of formation (reactions) are referred to standard conditions of temperature and pressure (T = 298 K, P = 101.325 kPa). The standard state of a thermodynamic function, such as enthalpy, is indicated by subscripts and superscripts: ΔΗ 0 298 The subscript is usually omitted: ΔΗ 0 .
The standard enthalpy of formation ΔΗ 0 arr is the thermal effect of the reaction of formation of one mole of a substance from simple substances, its components, which are in stable standard states. The enthalpy of formation of simple substances is assumed to be zero.
Using the tabular values ΔΗ 0 arr, ΔΗ 0 burnt, it is possible to calculate the enthalpies of various chemical processes and phase transformations.
The basis for such calculations is the Hess law, formulated by the St. Petersburg professor G. I. Hess (1841):
"The thermal effect (enthalpy) of the process depends only on the initial and final state and does not depend on the path of its transition from one state to another."
The following consequences follow from Hess's law:
1. The enthalpy of the reaction is equal to the difference between the sums of the enthalpies of formation of the final and initial participants in the reactions, taking into account their stoichiometric coefficients.
ΔH = ΣΔH return end – ΣΔH return start
2. The enthalpy of the reaction is equal to the difference between the sums of the enthalpies of combustion of the initial and final reactants, taking into account their stoichiometric coefficients.
ΔH = ΣΔH combustion start – ΣΔH combustion final
3. The enthalpy of the reaction is equal to the difference between the sums of the bond energies Eb of the initial and final reagents, taking into account their stoichiometric coefficients.
In the course of a chemical reaction, energy is expended on the destruction of bonds in the initial substances (ΣE ref) and is released during the formation of reaction products (–ΣE prod).
ΔH° = ΣE ref – ΣE cont
Hence, exothermic effect of the reaction indicates that compounds with stronger bonds than the original ones are formed. When endothermic reaction on the contrary, the starting materials are stronger.
4. The enthalpy of the formation reaction of a substance is equal to the enthalpy of the reaction of its decomposition to the starting substances with the opposite sign.
ΔH arr = –ΔH decom
5. The enthalpy of hydration is equal to the difference between the enthalpies of dissolution of an anhydrous salt ΔH sol b/s and crystalline hydrate ΔH sol crist.
Hess's law allows one to treat thermochemical equations as algebraic ones, i.e., to add and subtract them if the thermodynamic functions refer to the same conditions.
Ministry of Education of the Republic of Belarus
Ministry of Education of the Russian Federation
STATE INSTITUTION OF HIGHER
PROFESSIONAL EDUCATION
BELARUSIAN-RUSSIAN UNIVERSITY
Department of Metal Technology
Energy of chemical processes.
CHEMICAL AFFINITY
Guidelines for independent work of students and practical classes in chemistry
Mogilev 2003
UDC 54 Compiled by: dr. tech. sciences, prof. Lovshenko F.G.,
cand. tech. Sciences, Assoc. Lovshenko G.F.
Energy of chemical processes. chemical affinity. Guidelines for independent work of students and practical classes in chemistry. - Mogilev: Belarusian-Russian University, 2003. - 28 p.
The methodical instructions give the main provisions of thermodynamics. Examples of solving typical problems are presented. The conditions of tasks for independent work are given.
Approved by the Department of "Technology of Metals" of the Belarusian-Russian University (minutes of the meeting No. 1 dated September 1, 2003).
Reviewer Art. teacher Patsei V.F.
Responsible for the release of Lovshenko G.F.
© Compiled by F.G. Lovshenko, G.F. Lovshenko
ENERGY OF CHEMICAL PROCESSES. CHEMICAL AFFINITY
Signed for printing Format 60x84 1/16. Offset paper. Screen printing
Conv. oven l. Uch. from. L. Circulation 215 copies. Order No. _______
Publisher and printing design:
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"Belarusian-Russian University"
License LV No.
212005, Mogilev, Mira Ave., 43
Republic
Energy of chemical processes
Chemical thermodynamics studies the transitions of chemical energy into other forms - thermal, electrical, etc., establishes the quantitative laws of these transitions, as well as the direction and limits of the spontaneous occurrence of chemical reactions under given conditions.
The object of study in thermodynamics is a system.
system called the set of mutuallythe action of substances, mentally(oractually) separate fromenvironment.
Phase - Thispart of the system, homogeneous at all points in composition and propertiesand separated from other parts of the system by an interface.
Distinguish homogeneous And heterogeneous systems. Homogeneous systems consist of one phase, heterogeneous systems consist of two or more phases.
The same system can be in different states. Each state of the system is characterized by a certain set of values of thermodynamic parameters. The thermodynamic parameters are temperature, pressure, raftness, concentration, etc.. A change in at least one thermodynamic parameter leads to a change in the state of the system as a whole. Thermodynamic state of the nase systemvayutequilibrium , if it is characterized by the constancy of termodinamic parameters at all points of the system and does not changeetsya spontaneously (without the cost of work). In chemical thermodynamics, the properties of a system are considered in its equilibrium states.
Depending on the conditions for the transition of a system from one state to another, thermodynamics distinguishes between isothermal, isobaric, isochoric and adiabatic processes. The first - proceed at a constant temperature ( T= const), the second - at constant pressure (p = const), the third - at a constant volume (V= const), the fourth - in the absence of heat exchange between the system and the environment ( q = 0).
Chemical reactions often proceed under isobaric-isothermal conditions ( p= const, T= const). Such conditions are met when interactions between substances are carried out in open vessels without heating or at a higher but constant temperature.
Internal energy of the system.
During the transition of a system from one state to another, some of its properties change, in particular internal energy U.
Internal energy systems represents cofight her full energy, which is made up of kineticand potential energies of molecules, atoms, atomic nuclei, electronronov and others. Internal energy includes the energy of translational, rotational and oscillatory motions, as well as the potential energy due to the attractive and repulsive forces acting between molecules, atoms and intraatomic particles. It does not include the potential energy of the position of the system in space and the kinetic energy of the movement of the system as a whole.
The absolute internal energy of a system cannot be determined, but its change can be measured U when moving from one state to another. Value U considered positive ( U>0) if the internal energy of the system increases in any process.
Internal energy is thermodynamicfunctiontion states systems. This means that whenever the system is in a given state, its internal energy takes on a certain value inherent in this state. Consequently, the change in internal energy does not depend on the path and method of transition of the system from one state to another and is determined by the difference in the values of the internal energy of the system in these two states:
U = U 2 – U 1 , (1)
Where U 1 And U 2 – internal energy of the system in the final and initial states, respectively.
In any process, law of energy conservation , expressed by the equality
q = U+A (2)
which means that the heat q, brought to the system is spent on increasing its internal energy U and for the system to work A over the external environment. Equation (2) - mathematical expression first law of thermodynamics .
It follows from the first law of thermodynamics that the increment in the internal energy of the system U in any process is equal to the amount of heat communicated to the system q minus the amount of work done by the system A; since the quantities q And A are directly measurable, using equation (2) it is always possible to calculate the value U .
In the first law of thermodynamics, work A means the sum of all types of work against the forces acting on the system from the external environment. This amount may include work against the forces of an external electric field, and work against the forces of the gravitational field, and work of expansion against the forces of external pressure, and other types of work.
Due to the fact that the work of expansion is most characteristic of chemical interactions, it is usually distinguished from the total amount:
A = A' + p V, (p =const), (3)
Where A' - all types of work except extension work;
R - external pressure;
V– change in the volume of the system, equal to the difference V 2 – V 1 (V 2 – volume of reaction products, a V 1 – volume of starting materials).
If, during the course of a particular process, the expansion work is the only type of work, equation (3) takes the form
A = p V, (4)
Then the mathematical expression of the first law of thermodynamics (2) will be written as follows:
q p = U+R V, (5)
Where q p is the heat supplied to the system at constant pressure.
Taking into account the fact that U = U 2 – U 1 And V = V 2 – V 1 , equation (5) can be transformed by grouping the quantities U And V by indices related to the final and initial states of the system:
q p = (U 2 -U t ) + p(V 2 -V t ) = (U 2 +PV 2 )-(U 1 +PV 1 ). (6)
Sum (U + pV) are calledenthalpy (heat content) of the system and denoteletterH :
H=U +pv.(7)
Substituting the enthalpy H into equation (6), we obtain
q p = H 2 – H 1 = H, (8)
i.e. heat supplied to the system at constant pressure,is used to increase the enthalpy of the system.
As well as for the internal energy, the absolute value of the enthalpy of the system cannot be determined experimentally, but it can be done by measuring the value q p , find the enthalpy change H when the system changes from one state to another. the value H considered positive ( H>0) if the enthalpy of the system increases. Because the value H is determined by the difference ( H 2 – H 1 ) and does not depend on the way and method of carrying out the process, enthalpy, like internal energy, is referred to as thermodynamic functions of the state of the system.
Thermal effects of chemical reactions.
Algebraic summu of the heat absorbed during the reaction and the work done minus the work against the forces of external pressure (R V) namevayutthermal effect of a chemical reaction .
thermochemical laws. The independence of the heat of a chemical reaction from the path of the process at p= const and T= const was established in the first half of the 19th century. Russian scientist G.I. Hess: the thermal effect of a chemical reaction does not depend on the way it isflow, but depends only on the nature and physical statestarting materials and reaction products (Hess' law ).
The branch of chemical thermodynamics that studies thermaleffects of chemical reactions is calledthermochemistry . In thermochemistry, a simplified idea of the thermal effect of a chemical reaction is used, which meets the conditions for its independence from the process path. It's warmth q T , brought to the system during the reaction (or released as a result of the reaction) at a constant temperature.
If heat is supplied to the system ( q T> 0), the reaction is called endothermic, if heat is released in environment (q T < 0), реакцию называют экзотермической.
Thermochemistry, first of all, studies isobaric-isothermal reactions, as a result of which only the work of expansion is performed. V. The thermal effect of such reactions q p , T is equal to the change in the enthalpy of the system H.
Chemical reaction equations showing their heateffects are calledthermochemical equations . Since the state of the system as a whole depends on the states of aggregation of substances, in thermochemical equations the states of substances (crystalline, liquid, dissolved and gaseous) are denoted with the help of letter indices (k), (g), (p) or (d). The allotropic modification of the substance is also indicated if there are several such modifications. If the aggregate state of a substance or its modification under given conditions is obvious, the letter indices can be omitted. So, for example, when atmospheric pressure and room temperature, hydrogen and oxygen are gaseous (this is obvious), and the reaction product H 2 O formed during their interaction can be liquid and gaseous (water vapor). Therefore, in the thermochemical equation of the reaction, the state of aggregation of H 2 O should be indicated:
H 2 + ½O 2 \u003d H 2 O (g) or H 2 + ½O 2 \u003d H 2 O (g).
At present, it is customary to indicate the heat effect of a reaction in the form of a change in enthalpy
H, equal to the heat of the isobaric-isothermal process q p ,
T .
Often the enthalpy change is written as
H 
or
H 
.
Superscript 0
means the standard value of the thermal effect of the reaction, and lower - the temperature at which the interaction takes place. The following are examples of thermochemical equations for several reactions:
2C 6 H 6 (l) + 15O 2 \u003d 12CO 2 + 6H 2 O (l),
H 
= -6535.4 kJ, (а)
2C (graphite) + H 2 \u003d C 2 H 2,
H 
= 226.7 kJ, (b)
N 2 + 3H 2 \u003d 2NH 3 (g),
H 
= -92.4 kJ. (V)
In reactions (a) and (c), the enthalpy of the system decreases (
H 
<0).
Эти реакции экзотермические. В реакции
(б) энтальпия увеличивается
(
H 
>0); the reaction is endothermic. In all three examples, the value
H 
refers to the number of moles of substances that is defined by the reaction equation. In order for the thermal effect of the reaction to be expressed in kilo Joules per mol (kJ / mol) of one of the starting substances or reaction products, fractional coefficients are allowed in thermochemical equations:
C 6 H 6(g) + 7 
O 2 \u003d 6CO 2 + 3H 2 O (g),
H 
= -3267.7 kJ,
N2+ 
=NH 3 (g),
H 
= -46.2 kJ.
Enthalpy of formation of chemical compounds.
enthalpy (heat) education chemical compound H T calledenthalpy change in the process of obtaining one mole of this compoundfrom simple substances that are stable at a given temperature.
Standard
enthalpy
(warmth)
image
calling
chemical compound
H 
,
arr call changeenthalpies in the process of formation of one mole of this compound,in the standard state (T = 298 K and
= 101.3 kPa), from simple substances,also in standard states and thermodynamically stable at a given temperature phases and modifications(table A.1).
The standard enthalpies of formation of simple substances taketoil equalzero , if their states of aggregation and modificationcations are stable under standard conditions. So, for example, the standard heat of formation of liquid bromine (rather than gaseous) and graphite (rather than diamond) are equal to zero.
Standard enthalpyformation of a compound is a measure of itsthermodynamic stability,strength, quantitative expressionenergy properties of the compoundopinion.
thermochemical calculations. Most thermochemical calculations are based on corollary of Hess' law : thermal effectThe effect of a chemical reaction is equal to the sum of the heats (enthalpies)reaction products minus the sum of heats (enthalpi) the formation of the starting substances, taking into account their stoichiometric coefficients in the reaction equation.
H x.r. = H arr. (prod. district) - H arr (out. in-in.) (9)
Equation (9) makes it possible to determine both the thermal effect of the reaction from the known enthalpies of formation of the substances participating in the reaction, and one of the enthalpies of formation, if the thermal effect of the reaction and all other enthalpies of formation are known.
The thermal effect of a chemical reaction is the energy effect of a process occurring at a constant temperature. Using the reference data, which refer to 298 K, it is possible to calculate the thermal effects of reactions occurring at this temperature. However, when performing thermochemical calculations, usually allowing a slight error, one can use the standard values of the heats of formation even when the process conditions differ from the standard ones.
Thermal effects of phase transformations. Phase transformations often accompany chemical reactions. However, the thermal effects of phase transformations, as a rule, are less than the thermal effects of chemical reactions. Below are examples of thermochemical equations for some phase transformations:
H 2 O (g) H 2 O (g),
H 
=
44.0 kJ/mol,
H 2 O (c) H 2 O (g),
H 
=
6.0 kJ/mol,
I 2 (k) I 2 (g),
H 
=
62.24 kJ/mol.
Based on the above data, it can be noted that a phase transition from a more to a less condensed state leads to an increase in the enthalpy of the system (heat is absorbed - the process is endothermic).
T 
AND 
G
The transfer of matter from amorphous state into a crystalline one is always accompanied by the release of heat ( H <0) – процесс экзотермический:
Sb (amorphous) Sb (c),
H 
=
-10.62 kJ/mol,
B 2 O 3 (amorphous) B 2 O 3 (c),
H 
=
-25.08 kJ/mol.
Spontaneous and non-spontaneous processes. Many processes are carried out spontaneously, that is, without the expenditure of work from outside. As a result, work can be obtained against external forces, which is proportional to the change in the energy of the system that has occurred. So, spontaneously, water flows down an inclined chute or heat is transferred from a more heated body to a less heated one. During a spontaneous process, the system loses the ability to produce useful work.
A spontaneous process cannot proceed in the reverse direction as spontaneously as in the forward direction.. Thus, water cannot by itself flow up an inclined chute, and heat cannot by itself pass from a cold body to a hot one. To pump water up or transfer heat from the cold part of the system to the hot part, work must be done on the system. For processes that are inverse to spontaneous, the term " non-spontaneous».
When studying chemical interactions, it is very important to assess the possibility or impossibility of their spontaneous occurrence under given conditions, to find out chemical naturesubstance. There must be a criterion by which it would be possible to establish the fundamental feasibility, direction and limits of the spontaneous course of the reaction at certain temperatures and pressures. The first law of thermodynamics does not provide such a criterion. The thermal effect of the reaction does not determine the direction of the process: both exothermic and endothermic reactions can occur spontaneously.
The criterion for the spontaneous flow of the process in isolationbathroom systemssecond law of thermodynamics . Before proceeding to the consideration of this law, we introduce the concept of the thermodynamic function of the state of the system, called entropy.
Entropy. To characterize the state of a certain amount of a substance, which is a collection of a very large number of molecules, one can either indicate the temperature, pressure and other thermodynamic parameters of the state of the system, or indicate the instantaneous coordinates of each molecule ( x i , y i , z i) and the speed of movement in all three directions (v xi , v yi , v zi ). In the first case, the macrostate of the system is characterized, in the second, the microstate. Each macrostate corresponds to a huge number of microstates. The number of microstates through which a given macrostate is realized is called terthe moddynamic probability of the state of the system and denote W.
The thermodynamic probability of the state of a system consisting of only 10 gas molecules is approximately 1000, and yet only 1 cm 3 of gas contains 2.710 19 molecules (n.a.). To move on to numbers that are more convenient for perception and calculations, thermodynamics does not use the quantity W, and its logarithm lnW. The latter can be given the dimension (J/K) by multiplying by the Boltzmann constant k:
klnW =S. (10)
the value S called entropy systems.
Entropy is a thermodynamic function of the state of the system and its value depends on the amount of the substance under consideration. Therefore, it is advisable to refer the entropy value to one mole of a substance (J / (molK)) and express it as
RlnW = S. (11)
Where R = kN A – molar gas constant;
N A is the Avogadro constant.
From equation (11) it follows that the entropy of the system increases in proportion to the logarithm of the thermodynamic probability of the state W. This relationship underlies modern statistical thermodynamics.
At p =const entropy is a function of temperature T, moreover, the freezing point and the boiling point are the points at which the entropy changes especially sharply, abruptly.
So, entropy Sis a measure of system disorder. "Carriers" of entropy are gases. If the number of moles of gaseous substances increases during the reaction, then the entropy also increases.. Those. Without making calculations, it is possible, if necessary, to determine the sign of the change in the entropy of the system:
C (k) + O 2 (g) \u003d CO 2 (g), S 0;
2C (c) + O 2 (g) \u003d 2CO (g), S\u003e 0;
N 2 (g) + 3H 2 (g) \u003d 2NH 3 (g), S< 0.
Table A.1 gives the values S
some substances (note that the absolute values of the entropy of substances are known, while the absolute values of the function U And H not known).
Because entropy is a function of the state of the system, then entropy change ( S) in a chemical reaction is equal to the sum of the entropies of the reaction products minus the sum of the entropies of the starting substancestaking into account their stoichiometric coefficients in the reaction equation.
S x.r. = S arr. (prod. district) - S arr (out. in-in.) (12)
Direction and limit of processes in isolatedsystems. The second law of thermodynamics. Isolated systems do not exchange heat or work with the environment. Based on equation (9), it can be argued that at q = 0 And A = 0 magnitude U is also equal to zero, i.e., the internal energy of an isolated system is constant (U= const); constant and its volume (V = const). In isolated systems,only those processes that are accompanied byan increase in the entropy of the system: S>0 ; in this case, the limit of the spontaneous flow of the process is the achievement of the maximum entropy S max for the given conditions.
The considered position is one of the formulations second law of thermodynamics (the law has a statistical character, i.e., it is applicable only to systems consisting of a very large number of particles). The requirement of constancy of the internal energy and volume of the system excludes the use of entropy as a criterion for the direction and limit of the course of chemical reactions, in which the internal energy of substances inevitably changes, and the work of expansion against external pressure is also performed.
Entropy and enthalpy factors of chemical reactions,flowing in isobaric-isothermal conditions. The driving force of a process occurring under isobaric-isothermal conditions can either be the desire of the system to go into a state with the lowest energy, i.e., to release heat into the environment, to reduce the enthalpy ( H<0), or the desire of the system to go into a state with the highest thermodynamic probability, i.e., to increase the entropy ( S>0). If the process proceeds in such a way that H=0 , then the growth of entropy becomes its only driving force. And vice versa, provided S = 0 the only driving force of the process is the loss of enthalpy. In this regard, we can talk about the enthalpy H and entropy T S process factors.
Maximum work. The Dutch physical chemist Van't Hoff proposed a new theory of chemical affinity, which, without explaining the nature of chemical affinity, is limited to indicating the method of its measurement, i.e., gives a quantitative estimate of chemical affinity.
van't Hoff uses maximum work as a measure of chemical affinity A 
or A 
for reactions taking place at V,
T= const or p, T = const respectively.
The maximum work is equal to the energy that must be applied to the system in order to stop the reaction, that is, to overcome the forces of chemical affinity. Since the reaction proceeds in the direction of doing positive maximum work, the sign A 
or A 
determines the direction of the spontaneous flow of chemical interaction.
The maximum work done at constant volume is
A 
=
-
U+T
S(13)
A 
= -(U 2
– U 1
) + T(S 2
– S 1
) = -[(U 2
– TS 2
) – (U 1
– TS 1
)]
(14)
where U 1 , S 1 and U 2 , S 2 are the internal energy and entropy of the system in the initial and final states, respectively.
Difference (U - TS) called Helmholtz energy systems and are denoted by the letter F. Thus,
A 
=
-
F.
(15)
Purpose of the work Familiarization with the technology of water treatment for nuclear power plants by the ion exchange method and comparison of water quality: for technological needs of nuclear power plants, drinking and lake water. Familiarization with the technology of water treatment for nuclear power plants by the ion exchange method and comparison of water quality: for technological needs of nuclear power plants, drinking and lake water.
Tasks of the work Tasks of the work to study the requirements for water used for technological needs at a modern nuclear power plant on the example of the Kalinin nuclear power plant. study the requirements for water used for technological needs at a modern nuclear power plant using the example of the Kalinin nuclear power plant. get acquainted with the theory of the ion exchange method, get acquainted with the theory of the ion exchange method, visit the water intake station of Udomlya and get acquainted with chemical composition drinking water and lake water. visit the water intake station of Udomlya and get acquainted with the chemical composition of drinking water and lake water. compare indicators of chemical analysis of drinking water and water of the NPP II circuit. compare indicators of chemical analysis of drinking water and water of the NPP II circuit.
Tasks of the work Tasks of the work to visit the chemical shop of the Kalinin NPP and get acquainted: visit the chemical shop of the Kalinin NPP and get acquainted: with the process of water preparation at the chemical water treatment; with the process of water purification at a block desalination plant; visit the express laboratory of the second circuit; visit the express laboratory of the second circuit; get acquainted theoretically with the work of special water treatment. get acquainted theoretically with the work of special water treatment. draw conclusions about the importance of ion exchange in the preparation of water. draw conclusions about the importance of ion exchange in the preparation of water.
NPP equipment is subject to strict safety, reliability and cost-effectiveness requirements. NPP equipment is subject to strict safety, reliability and cost-effectiveness requirements. The water-chemical regime of the NPP must be organized so that corrosion and other effects on the equipment and pipelines of the NPP systems do not lead to violation of the limits and conditions of its safe operation. The water-chemical regime of the NPP must be organized so that corrosion and other effects on the equipment and pipelines of the NPP systems do not lead to violation of the limits and conditions of its safe operation. Relevance
Comparative characteristics drinking water and water of the second circuit of the NPP Indicator Unit of measurement Drinking water MPC Water of the second circuit Reference values Femg/l0.0945.00.005 
Schematic diagram of the desalination part of chemical water treatment (ionization) For make-up BSN FSD 14 OH II BCHOV OH I 10 H I H II 78 Pretreated (clarified) water
100% of condensate is passed through electromagnetic filters; through mixed action filters it is possible to pass both 100% of water and part of it. Thus, with one operating mixed-action filter (cleaning 20% of the condensate), the specific electrical conductivity decreased: χ=0.23 µS/cm - before the block desalination plant and χ=0.21 µS/cm - after the block desalination plant.
The power unit with VVER-1000 reactors has four closed loops for wastewater collection and processing: organized leakages and primary circuit blowdown water; boric concentrate; blowdown water of steam generators; drain waters and special laundry waters. These installations include: mechanical filters, H-cation and OH-anion filters.
Conclusion All drains from the pre-treatment and chemical water treatment equipment are collected in an underground drainage water tank. After neutralization, the water is fed to the filter block of the deep burial ground. The settled water is injected into the wells to a depth of about 1.5 km. Thus, the commissioning of a deep disposal site excludes the possibility of discharging industrial non-radioactive effluents into the environment.
Conclusion Water treatment by ion exchange method allows reaching the required values necessary for safe, reliable and economical operation of the equipment. However, this is a rather expensive process: the cost of 1 m 3 of drinking water is 6.19 rubles, and the cost of 1 m 3 of chemically desalted water is 20.4 rubles. (data from 2007) - for which closed cycles of water circulation are used.
The whole history of the development of civilization is the search for energy sources. This is very relevant even today. After all, energy is opportunity. further development industries, obtaining sustainable crops, beautifying cities and helping nature heal the wounds inflicted by civilization. Therefore, the solution of the energy problem requires global efforts. Chemistry makes its considerable contribution as a link between modern natural science and modern technology.
Energy supply is essential condition socio-economic development of any country, its industry, transport, Agriculture, spheres of culture and life.
But in the next decade, neither wood, nor coal, nor oil, nor gas will be discounted in the energy sector. At the same time, they must work hard to develop new ways of generating energy.
The chemical industry is characterized by close links with all sectors National economy thanks to its wide range of products. This area of production is characterized by high material consumption. Material and energy costs in the production of products can range from 2/3 to 4/5 of the cost of the final product.
The development of chemical technology follows the path of the integrated use of raw materials and energy, the use of continuous and waste-free processes, taking into account the environmental safety of the environment, the use of high pressures and temperatures, the achievements of automation and cybernetization.
The chemical industry in particular consumes a lot of energy. Energy is spent on the implementation of endothermic processes, on the transportation of materials, crushing and grinding of solids, filtering, compressing gases, etc. Significant energy costs are needed in the production of calcium carbide, phosphorus, ammonia, polyethylene, isoprene, styrene, etc. Chemical industries, together with petrochemical industries, are energy-intensive industries. Producing almost 7% of industrial output, they consume within 13-20% of the energy used by the entire industry.
Energy sources are most often traditional non-renewable Natural resources- coal, oil, natural gas, peat, shale. IN Lately they deplete very quickly. Oil reserves are declining at a particularly accelerated pace and natural gas, but they are limited and irreparable. Not surprisingly, this creates an energy problem.
For 80 years, one main source of energy was replaced by another: wood was replaced by coal, coal - by oil, oil - by gas, hydrocarbon fuel - by nuclear. By the beginning of the 1980s, about 70% of the world's energy demand was met by oil and natural gas, 25% by hard and brown coal, and only about 5% by other energy sources.
IN different countries The energy problem is solved in different ways, nevertheless, chemistry makes a significant contribution to its solution everywhere. Thus, chemists believe that in the future (approximately another 25-30 years) oil will retain its leadership position. But its contribution to energy resources will noticeably decrease and will be compensated by the increased use of coal, gas, hydrogen energy, nuclear fuel, solar energy, energy of the earth's depths and other types of restorative energy, including bioenergy.
Even today, chemists are worried about the maximum and comprehensive energy-technological use of fuel resources - reducing heat loss to the environment, secondary use heat, maximum use of local fuel resources, etc..
Since liquid fuel is the most scarce among fuels, large funds have been allocated in many countries to create a cost-effective technology for converting coal into liquid (as well as gaseous) fuel. Scientists from Russia and Germany are cooperating in this area. essence modern process processing of coal into synthesis gas is as follows. A mixture of water vapor and oxygen is supplied to the plasma generator, which is heated up to 3000°C. And then coal dust enters the hot gas torch, and as a result of a chemical reaction, a mixture of carbon monoxide (II) and hydrogen is formed, i.e. synthesis gas. Methanol is obtained from it: CO + 2H2CH3OH. Methanol can replace gasoline in internal combustion engines. In terms of solution environmental problem it compares favorably with oil, gas, coal, but, unfortunately, its heat of compression is 2 times lower than that of gasoline, and, in addition, it is aggressive towards certain metals and plastics.
Chemical methods have been developed to remove binder oil (contains high molecular weight hydrocarbons), a significant part of which remains in underground pits. To increase the yield of oil into the water that is pumped into the reservoirs, surfactants are added, their molecules are located at the oil-water interface, which increases the mobility of the oil.
The future replenishment of fuel resources is combined with the rational processing of coal. For example, crushed coal is mixed with oil, and the extracted paste is treated with pressurized hydrogen. In this case, a mixture of hydrocarbons is formed. About 1 ton of coal and 1500 m of hydrogen are spent on the extraction of 1 ton of artificial gasoline. So far, artificial gasoline is more expensive than that produced from oil, however, the fundamental possibility of obtaining it is important.
Hydrogen energy is seen as very promising, which is based on the combustion of hydrogen, during which harmful emissions do not arise. Nevertheless, for its development it is necessary to solve a number of problems related to reducing the cost of hydrogen, creating reliable means of its storage and transportation, etc. If these problems are solved, hydrogen will be widely used in aviation, water and land transport, industrial and agricultural productions.
Nuclear energy contains inexhaustible possibilities, its development for the production of electricity and heat makes it possible to release a significant amount of organic fuel. Here, chemists are faced with the task of creating complex technological systems covering the energy costs that occur during the implementation of endothermic reactions with the help of nuclear energy. Now nuclear power is developing along the path of widespread introduction of fast neutron reactors. Such reactors use uranium enriched in the 235U isotope (at least 20%), and a neutron moderator is not required.
Currently, nuclear power and reactor building is a powerful industry with a large amount of capital investment. For many countries, it is an important export item. Reactors and auxiliary equipment require special materials, including those of high frequency. The task of chemists, metallurgists and other specialists is the creation of such materials. Chemists and representatives of other related professions are also working on uranium enrichment.
Now the nuclear power industry is faced with the task of displacing fossil fuels not only from the production of electricity, but also from heat supply and, to some extent, from the metallurgical and chemical industries by creating reactors of energy-technological significance.
Nuclear power plants in the future will find another application - for the production of hydrogen. Part of the resulting hydrogen will be consumed by the chemical industry, the other part will be used to power gas turbine plants that are switched on at peak loads.
Great hopes are placed on the use solar radiation(solar energy). Solar panels operate in Crimea, photovoltaic cells of which turn sunlight into electricity. For water desalination and home heating, solar thermal installations are widely used, which convert solar energy into heat. Solar panels have long been used in navigation facilities and on spaceships. Unlike nuclear, the cost of energy produced by solar panels is constantly decreasing.
For the manufacture of solar cells, the main semiconductor material is silicon and silicon compounds. Chemists are currently working on the development of new energy converter materials. It can be different systems salts as energy storage. Further success in solar energy depends on the materials that chemists will offer for energy conversion.
In the new millennium, the increase in electricity production will occur due to the development of solar energy, as well as methane fermentation of household waste and other non-traditional sources of energy production.
Along with giant power plants, there are also autonomous chemical current sources that convert the energy of chemical reactions directly into electrical energy. Chemistry plays a major role in solving this problem. In 1780 italian doctor L. Galvani, observing the contraction of the cut off leg of a frog after touching it with wires of different metals, decided that there was electricity in the muscles, and called it "animal electricity". A. Volta, continuing the experience of his compatriot, suggested that the source of electricity is not the body of an animal: an electric current arises from the contact of different metal wires. The "ancestor" of modern galvanic cells can be considered the "electric pole" created by A. Volta in 1800. This invention is similar to a layer cake of several pairs of metal plates: one plate is made of zinc, the second is made of copper, stacked on top of each other, and between they placed a felt pad soaked in dilute sulfuric acid. Before the invention in Germany by W. Siemens in 1867. dynamo galvanic cells were the only source electric current. Nowadays, when autonomous energy sources are needed for aviation, submarine fleet, rocket technology, electronics, the attention of scientists is again drawn to them.
VI international competition scientific and educational projects
"Energy of the Future"
Competitive work
The role of chemistry in the energy sector: preparation of chemically demineralized water
ion exchange method for nuclear power plants
MOU gymnasium No. 3 named after.
, 10 "a" class
Leaders:
KNPP chemical shop laboratory assistant
- physics teacher, gymnasium No. 3
Contact phone numbers:
annotation
Kalinin NPP is the largest water consumer in the Udomelsky district.
This paper provides information on the requirements for the quality of drinking and circuit water. Comparative tables and histograms of chemical indicators of drinking, lake and water of the II circuit are given. given short description about the results of the visit to the water intake station and the chemical shop of the Kalinin NPP. A brief description of the theory of ion exchange and a description of the principal schemes of chemical water treatment and a block desalination plant are also given; a brief theoretical description of the principle of water purification from radioactive contamination - special water purification is also given.
This work helps to increase the motivation to study chemistry, physics, introduces the chemical technologies used in the energy sector on the example of the Kalinin NPP.
1.Introduction 3
2. Literature review on water treatment by method 4
ion exchange
2.1.Principle of NPP operation with VVER-1000 type reactors 4
2.2. Requirements for water used for
technological needs at NPP 5
2.3. Chemical indicators of the quality of natural and contour waters. 5
2.4 Theory of ion exchange 6
2.5 Working cycle of ion exchange resin 9
2.6.Features of the use of ion-exchange materials 10
3. Practical study 11
3.1.Visit to the water intake station 11
3.2.Visit to the Kalinin NPP 13
3.3 Description circuit diagram chemical water treatment 15
3.4 Description of the circuit diagram
block demineralization plant 18
3.5. Theoretical description of the principle of operation
special water treatment 20
4.Conclusion 20
5. References 22
1. Introduction
1.1. Goal of the work:
familiarization with the technology of water treatment for nuclear power plants by the ion exchange method and comparison of water quality: for technological needs of nuclear power plants, drinking and lake water.
1.2. Work tasks:
1. to study the requirements for water used for technological needs at a modern nuclear power plant using the example of the Kalinin nuclear power plant.
2. get acquainted with the theory of the ion exchange method,
3. visit the water intake station of Udomlya and get acquainted with the chemical composition of drinking water and lake water.
4. compare the indicators of chemical analysis of drinking water and water of the second circuit of the NPP.
5. visit the chemical shop of the Kalinin NPP and get acquainted with:
¾ with the process of water treatment at chemical water treatment;
¾ with the process of water purification at a block desalination plant;
¾ visit the express laboratory of the II circuit;
¾ get acquainted theoretically with the work of special water treatment.
6. draw conclusions about the importance of ion exchange in water treatment.
1.3. Relevance
Russia's energy strategy envisages nearly doubling electricity generation from 2000 to 2020. With predominant growth in nuclear energy: the relative share of electricity generation at nuclear power plants over this period should increase from 16% to 22%.
NPP equipment, like no other, is subject to safety, reliability and cost-effectiveness requirements.
One of the most important factors affecting the reliable and safe operation of nuclear power plants is compliance with the water chemistry regime and maintaining water quality indicators at the level of established standards.
The NPP water chemistry regime must be organized in such a way as to ensure the integrity of the barriers (fuel cladding, coolant circuit boundary, hermetic barriers, localizing safety systems) on the path of possible spread of radioactive substances into the environment. The corrosive effect of the coolant and other working media on the equipment and pipelines of NPP systems should not lead to violation of the limits and conditions of its safe operation. The water-chemical regime should provide minimal amount deposits on the heat transfer surfaces of equipment and pipelines, as this leads to a deterioration in the heat transfer properties of the equipment and, as a result, to a reduction in the service life of the equipment.
2. Literature review on water treatment by ion exchange
2.1. The principle of operation of NPPs with VVER-1000 reactors
The principle of operation of most existing nuclear power plants is based on the use of heat released during the fission of the 235U nucleus under the action of neutrons. In the reactor core, under the action of neutrons, the 235U nucleus is split, releasing energy and heating the coolant - water.
Nuclear fuel transfers thermal energy to the primary coolant, which is water under high pressure (16 MPa), at the outlet of the reactor, the water temperature is 3200. Further, thermal energy is transferred to the secondary water. There is no direct contact between the coolant and the secondary circuit water. The coolant circulates in a closed loop: reactor - steam generator - main circulation pump - reactor. There are four such circuits. In the steam generator, the primary circuit coolant heats the secondary circuit water to vaporization. The steam enters the turbine, which rotates due to this steam. This steam is called the working fluid. The turbine is directly connected to an electric generator that generates electrical energy. Further, the exhaust steam with low pressure enters the condenser, where it is condensed due to cooling by lake water. Then additional cleaning and return to the steam generator. And so the cycle repeats: evaporation, condensation, evaporation.
https://pandia.ru/text/77/500/images/image002_125.gif" width="408" height="336">
rice. 1. Technological scheme of a double-circuit NPP:
1 - reactor; 2 – turbogenerator; 3 - capacitor; 4 - feed pump; 5 – steam generator; 6 - main circulation pump.
2.2. Requirements for water used for technological needs at nuclear power plants
With the growth of steam and water parameters, the impact of water chemistry regimes increased. This led to an increase in the specific heat loads of the heating surfaces. Under these conditions, even slight deposits on the inner surfaces of the pipes cause overheating and destruction of the metal. High steam parameters (pressure and temperature) increase its dissolving power in relation to impurities contained in the feed water. As a result, the intensity of the drift of the flow part of the turbines increases, which can lead to a decrease in the efficiency of the units and, in some cases, to limit their power, and reduce the life of the equipment.
Elimination of shortcomings of water-chemical regimes is necessary not only in case of violations that create an emergency, but also in case of seemingly insignificant deviations from the norms. So, for example, from experience it follows that:
§ deposits of salts and corrosion products on the blades of the high-pressure cylinder of turbines of 300 MW units in the amount of 1 kg cause an increase in pressure in the turbine control stage by 0.5 - 1 MPa (5 - 10 kgf / cm2) and lead to a decrease in turbine power by 5 - 10 MW;
§ deposition of corrosion products on the inner and outer surfaces of the high-pressure heater pipes in the amount of 300–500 g/m2 reduces the feed water heating temperature by 2–30 °C and worsens the efficiency of the unit;
§ deposits in the steam-water path of blocks increase its hydraulic resistance and energy losses for pumping water and steam. An increase in the block path resistance of 300 MW per 1 MW (10 kgf/cm2) leads to an overexpenditure of 3 million kWh of electricity per year.
The following systems serve to meet the requirements for ensuring the water chemistry regime at nuclear power plants:
§ chemical water treatment;
§ system of condensation and degassing;
§ block desalination plant;
§ Installation of corrective treatment of the working environment of the primary and secondary circuits;
§ deaerators;
§ steam generator purge system;
§ steam generator blowdown water treatment unit (special water treatment);
§ system of purge-make-up of the primary circuit.
2.3. Chemical indicators of the quality of natural and contour waters
The water coolant for filling the energy circuits and feeding them is prepared from natural waters at water treatment plants of various types and usually contains the same impurities that characterize natural water, but in significantly lower (by several orders of magnitude) concentrations.
The main indicators of water quality include the following.
The content of coarse (suspended) substances , present in the loop waters - in the form of sludge, consisting of sparingly soluble compounds such as CaCO3 , CaSO4, Mg(OH)2, particles of corrosion products of structural materials (Fe3O4, Fe2O3, etc.), the content of which is determined by filtration through a paper filter with drying at C or by an indirect method by water transparency.
Salinity - the total concentration of cations and anions in water, calculated from the total ionic composition and expressed in milligrams per kilogram. To characterize and control waters and condensates with low salinity in the absence of dissolved CO2 and NH3 gases, the indicator is often used electrical conductivity . The condensate with a salt content of about 0.5 mg/kg has a specific electrical conductivity of 1 µS/cm.
Water hardness total - total calcium concentration ( calcium hardness) and magnesium ( magnesium rigidity), expressed in equivalent units of milligram equivalent per kilogram or microgram equivalent per kilogram:
ZHO \u003d ZhSa + ZhMg
Water oxidizability is expressed by the consumption of a strong oxidant (usually KMnO4) required for the oxidation of organic water impurities under standard conditions, and is measured in milligrams per kilogram of KMnO4 or O2, equivalent to the consumption of potassium permanganate.
Hydrogen concentration indicator ions (pH) of water characterizes the reaction of water (acidic, alkaline, neutral) and is taken into account in all types of water treatment and use.
Specific electrical conductivity (χ) is determined by the mobility of ions in a solution placed in an electric field; for pure water its value is 0.04 μS/cm, for demineralized turbine condensates χ = 0.1 μS/cm (microsiemens per centimeter).
2.4. Ion exchange theory
Preparation of water for filling the circuits of nuclear power plants and replenishing losses in them is carried out at the expense of demineralized water prepared by chemical desalination in two or three stages of the initial low-mineralized water (Nitrogen "href="/text/category/azot/" rel="bookmark">nitrogen N and many other elements.Coal is practically insoluble in water, but upon contact with oxygen dissolved in water, slow oxidation occurs, leading to the formation of various oxidized groups.On the surface of the coal, hydroxyl or carboxyl groups are formed, firmly bound to the base of the coal.If conditionally designate this unchanged base with the letter R, then the structure of such a material can be described by the formula ROH or RCOOH, depending on which oxidized group of the hydroxyl OH or carboxyl COOH formed on its surface during oxidation.These groups are capable of dissociation, i.e. in water processes occur in the environment:
RCOOH = RCOO - + H+.
If cations, for example, calcium, are present in water, then cation exchange processes become possible:
2RCOOH+Ca2+ = (RCOO)2Ca +2H+.
In this case, calcium ions are fixed on carbon, and an equivalent amount of hydrogen ions enters the solution. The exchange can also take place for other ions, such as sodium, iron, copper, etc.
2.4.2. Cation and anion exchangers.
All materials capable of cation exchange are called cation exchangers. Materials capable of anion exchange are called anion exchangers. They have other ion exchange groups, usually NH2 or NH, which form NH2OH with water.
Cation exchangers are able to exchange positively charged ions (cations) with the solution. The process of exchange of cations between the cation exchanger immersed in the water to be purified and this water is called cationization. Anion exchangers are capable of exchanging negatively charged ions with the electrolyte. The process of anion exchange between the anion resin and the treated water is called anionization.
On fig. 2 schematically shows the structure of ion exchanger grains. The grain practically insoluble in water is surrounded by dissociated grains - positively charged for the cation exchanger (Fig. 2a) and negatively charged for the anion exchanger (Fig. 2b). In the very grain of the ion exchanger, due to the separation of ions, a negative charge arises for the cation exchanger and a positive charge for the anion exchanger.
rice. 2. Scheme of the structure of ion exchanger grains.
a) – cation exchanger; b) - anion exchanger; 1- solid polyatomic framework of the ion exchanger; 2 – immobile ions of active groups bound to the framework (potential-forming ions); 3 - limitedly mobile ions of active groups capable of exchange (counterions).
Most of the currently used ion-exchange materials belong to the category of synthetic resins. Their molecules consist of thousands, and sometimes tens of thousands of interconnected atoms. Ion-exchange materials are a kind of solid electrolytes. Depending on the nature of the active groups of the ion exchanger, its mobile, exchangeable ions can have a positive or negative charge. When the positive, mobile cation is the hydrogen ion H+, then such a cation exchanger is essentially a polyvalent acid, just as an anion exchanger with an exchangeable hydroxyl ion OH - is a polyvalent base.
The mobility of ions capable of exchange is limited by distances at which their reciprocity with immobile ions of opposite charge on the surface of the ion exchanger is not lost. This space, bounded around the molecules of the ionite, in which there are mobile and exchangeable ions, is called the ionic atmosphere of the ionite.
The exchange capacity of ion exchangers depends on the number of active groups on the surface of the ion exchanger grains. The surface of the ion exchanger is also the surface of recesses, pores, channels, etc. Therefore, it is preferable to have ion exchangers with a porous structure. The grain size of domestic and foreign ion exchangers is characterized by fractions ranging from 0.3 to 1.5 mm with an average grain diameter of 0.5-0.7 mm and a heterogeneity coefficient of about 2.0-2.5.
There are ion exchangers in which almost all the functional groups contained in their composition or only a small percentage of them undergo dissociation, in accordance with which strong acid cation exchangers are distinguished - they are capable of absorbing cations (sodium Na +, magnesium Mg2 +, etc.); and weakly acidic - capable of absorbing hardness cations (magnesium Mg2+, calcium Ca2+). Similarly, the division into two groups of anion exchangers: strongly basic - capable of absorbing both strong and weak acids (for example, carbonic, silicic, etc.). and weakly basic - are capable of absorbing predominantly anion exchangers of strong acids (, etc.).
2.5. Working cycle of ion exchange resin
The layer of ion exchanger (ion exchange resin) in the course of movement of the treated water in the process of ion exchange can be divided into three zones.
The first zone is the zone of depleted ion exchanger, since all the counterions in it are used for exchange for ions of the treated water. In this zone, the selective exchange between the ions of the treated water itself continues, i.e., the most mobile ions contained in the water displace the less mobile ones from the ion exchanger (Fig. 3).
The second zone is called the useful exchange zone. Here begins and ends the useful exchange of ion exchanger counterions for treated water ions. In this zone, the frequency of exchange of ions of the treated water for counterions of the ion exchanger prevails over the frequency of the reverse exchange of ions of the treated water and ions absorbed by the ion exchanger.
The third zone is the zone of idle, or fresh, ion exchanger. The water passing through this layer of the ion exchanger contains only the counterions of the ion exchanger and therefore does not change either its composition or the composition of the ion exchanger.
As the filter operates, the first zone - the zone of depleted ion exchanger - increases, forcing the working zone 2 to fall due to the reduction of the zone of fresh ion exchanger 3, and, finally, goes beyond the lower limit of the filter load. Here the height of the third zone is zero. The concentration of the least sorbed ions appears in the filtrate and begins to increase, and useful work ion exchanger ends.
Technology of the regeneration process.
The process of regeneration of ion exchange filters consists of three main operations:
Loosening of the ion exchanger layer (loose washing);
Passing through it the working solution of the reagent at a given speed;
Washing the ion exchanger from regeneration products.
Loose wash.
During the operation of filters, products of gradual destruction and grinding of ion exchangers always occur, which must be periodically removed. This is achieved by loosening washes, this operation is mandatory before each regeneration.
It is very important to comply with the conditions for washing, which should ensure a more complete removal of fine dust-like parts of ion-exchange materials from the filter. In addition, the loosening washing eliminates the compaction of the material, which makes it difficult for the regeneration solution to contact with the grains of the ion exchanger.
Loosening is carried out by a flow of water from the bottom up at a speed that brings the entire mass of the ion-exchange material into suspension. When the water at the outlet of the filter becomes transparent, loosening is stopped.
Passing the regeneration solution.
Regeneration and washing of the ion exchanger from the products of regeneration are usually carried out at the same speed. In this case, the passage of reagents is possible both along the treated water - forward flow, and in the opposite direction to the movement of the treated water - countercurrent, depending on the technology adopted.
When regeneration solutions are skipped, the ions absorbed by the ion exchanger are replaced by ions of the regeneration solution (containing H + or OH - ion). At the same time, ionites are transferred to their original ionic form.
There are two types of regeneration: internal and external. Remote regeneration is used in mixed-bed filters on a block desalination plant in order to avoid regeneration water from entering the secondary circuit.
Washing out the remnants of regeneration products.
The last operation of the regeneration cycle - washing - is intended to remove the remnants of regeneration products from it.
The washing of the filter layer is stopped when certain indicators of the quality of the washing water are reached. The filter is ready for use.
These processes allow the ion exchanger to be used repeatedly.
2.6. Features of the use of ion-exchange materials at nuclear power plants
The removal of radionuclides from water by the ion exchange method is based on the fact that many radionuclides are in water in the form of ions or colloids, which, when in contact with the ion exchanger, are also absorbed by the filter material, but absorption is of a physical nature. The volumetric capacity of resins in relation to colloids is much lower than in relation to ions.
The completeness of absorption of radionuclides by ion exchangers is influenced by the content in water a large number inactive elements that are chemical analogues of radionuclides.
Under conditions of ionizing radiation, only highly pure ion exchangers in hydrogen and hydroxyl form (strong base anion exchangers and strong acid cation exchangers) are used. This is due to the insufficient resistance of ion-exchange materials to the action of ionizing radiation and more stringent requirements for the water regime of the NPP primary circuit.
3. Practical research
3.1. Visit to the water intake station
In 1980, the first stage of the Udomlya water intake station was put into operation. The main task, which is the extraction and preparation of water for consumer needs. Water from artesian wells is pumped for purification, which includes: aeration and filtration. Then the water is chlorinated and served to consumers.
On December 14, 2007, an excursion to the water intake station took place in order to get acquainted with the processes: water preparation, determination of the main indicators of the quality of drinking and lake water.
Determination of pH solutions on a pH meter at a water intake station.
Preparation of samples for the determination of iron on the KFK-3 photocolorimeter.
https://pandia.ru/text/77/500/images/image018_6.jpg" width="275" height="214 src=">
Determination of chlorides by back titration.
Determination of hardness salts.
The data obtained in the course of joint research with the employees of the water intake are given in the tables.
Table 1. Comparison of quality indicators of lake water (using the example of Lake Kubycha) and drinking water.
Index | Unit | lake water | Drinking water | |
lake Kubycha |
||||
Chroma | ||||
Turbidity | ||||
Rigidity | ||||
Mineralization | ||||
MPC* - maximum permissible concentration - is regulated by GOST of water quality.
Histogram 1. pH value of Kubycha Lake, drinking water and maximum allowable concentration.
https://pandia.ru/text/77/500/images/image024_26.gif" width="336" height="167 src=">
Histogram 3. The content of hardness salts in Lake Kubycha, drinking water and the maximum allowable concentration.
December 25" href="/text/category/25_dekabrya/" rel="bookmark"> December 25, 2007 nuclear power plant in order to get acquainted with the work of the departments of the chemical shop. During the tour, we visited a chemical water treatment plant and got acquainted with the technology for the production of chemically desalted water. During the visit to the engine room, they got acquainted with the technology of purification of the main condensate of the secondary circuit, with the work of the express laboratory of the secondary circuit, and received data on the quality of the secondary water.
It is interesting to compare some chemical indicators of the quality of water in the secondary circuit of the Kalinin NPP and drinking water obtained at the water intake.
Table 2. Comparative characteristics of drinking water and water of the second circuit of the NPP.
* - data are not indicated, since the concentration of hardness is less than the sensitivity of the method for determining this indicator.
Conclusion: 1. As follows from Table 2, the maximum permissible concentration drinking water and control values of secondary water have significant differences. This is due to the higher requirements for water used for process needs, necessary for the safe and reliable operation of the equipment.
2. Drinking water received at the water intake has high quality, chemical indicators are much lower than the maximum permissible concentration impurities in drinking water.
3. Water of the second circuit corresponds to the control values. This is achieved by purifying water by ion exchange during its preparation and post-treatment of condensate at block desalination plants.
Histogram 4. The content of chlorides in drinking water and water of the secondary circuit of the Kalinin NPP.
https://pandia.ru/text/77/500/images/image027_24.gif" width="362" height="205 src=">
High requirements for the content of hardness salts in the water of the secondary circuit are caused by the fact that scale-forming salt deposits appear on the walls of the heat exchangers. This leads to: worsening of heat transfer, reduction of hydraulic resistance, reduction of equipment service life.
Histogram 6. Iron content in drinking water and secondary water.
Cooling systems" href="/text/category/sistemi_ohlazhdeniya/" rel="bookmark">cooling systems for generator stator windings, electrolysis tanks, special laundry. Productivity of chemical water treatment for demineralized water = 150m3.
Description of the main technological scheme of the desalination part of chemical water treatment.
The clarified water after the mechanical pre-filter enters the chain of H-cation exchange filters. In the H-cationite filter of the 1st stage, loaded with a weakly acidic cation exchanger, water is purified from cruelty ions (Сa2+ and Mg2+). In the H-cationite filter of the 2nd stage, loaded with a strongly acidic cation exchanger, water is additionally purified from the hardness ions and Na + ions remaining after the 1st stage.
H-cation exchange water after the 2nd stage is collected in tanks of partially demineralized water of the cation exchange filter.
From the tank of partially demineralized water, pumps direct the water to a chain of OH-anion-exchange filters. In the OH-anion filter of the 1st stage, loaded with a low-basic anion exchanger, water is purified from anions of strong acids (https://pandia.ru/text/77/500/images/image010_45.gif" width="37" height=" 24 src=">). In the OH-anion filter of the 2nd stage, loaded with a highly basic anion exchanger, water is additionally purified from the anions of strong acids and anions of weak acids remaining after the 1st stage (; ).
OH-anioned water after the 2nd stage anion exchange filter is collected in the auxiliary tank.
The desalinated water from the auxiliary tank is pumped to the 3rd stage of desalination - a mixed-bed filter. The mixed bed filter is loaded with a 1:1 mixture of strong acid cation and strong base anion. At the 3rd stage of desalination, the demineralized water is additionally purified from cations and anions to the concentrations required by the standard of the STP-EO enterprise. On the common pipeline, chemically desalinated water after the mixed-action filter is equipped with 2 parallel-connected traps of filtering materials (1 - in operation; 1 - in reserve in case of repair of the first one) of chemically desalinated water from the auxiliary tank and after the mixed-action filter is given to consumers: for make-up 2 -th circuit to the turbine hall; for feeding the 1st circuit into a special building; to the pre-treatment scheme of chemical water treatment, to the chemical reagent warehouse, to the special laundry, to the electrolysis, to the start-up and reserve boiler house, to the storage tanks of chemically desalted water (V = 3000 m3).
To increase the reliability of the chemical water treatment and create a supply of chemically desalted water, chemically desalinated water storage tanks (3000 m3 each) are included in the scheme of the desalination part of the chemical water treatment.
To prevent corrosion of metal pipelines in concentrated and dilute acid solutions, the piping of the concentrated acid unit and the route for supplying the regenerating acid solution from the mixer to the H-cation exchange filters are made of pipelines lined with fluoroplastic.
Commissioning" href="/text/category/vvod_v_dejstvie/" rel="bookmark"> was put into operation in August 2007, the service life is about 20 years, the effluent distribution radius is about 3 km.
Thus, it can be concluded that the commissioning of a deep disposal site excludes the possibility of discharging industrial non-radioactive effluents into the environment.
3.4. Description of the block diagram of a block desalination plant (condensate treatment)
Condensate treatment at the block desalination plant is carried out in two stages:
The first step is cleaning from undissolved corrosion products of structural materials on electromagnetic filters loaded with steel soft magnetic balls;
The second step is cleaning from dissolved ionic impurities and colloidal-dispersed substances on mixed-action ion-exchange filters.
Turbine condensate is supplied by condensate pumps of the first stage to an electromagnetic filter, where it is cleaned from mechanical impurities, mainly undissolved corrosion products of structural materials.
After the electromagnetic filter, the condensate enters the suction manifold of the condensate pumps of the second stage (with the ion-exchange part of the block desalination plant turned off), or is sent to a mixed-action filter for purification from dissolved and colloidal-dispersed impurities.
The removal of ferromagnetic and non-magnetic iron oxides retained on the ball load is carried out by washing the electromagnetic filter with demineralized water from the bottom - up with the voltage removed on the coils and the demagnetized state of the balls.
In case of unsatisfactory quality of the condensate downstream of the operating mixed-bed filter, the filter is taken out for regeneration, and the reserve mixed-bed filter is put into operation.
The mixed resin brought out for regeneration is reloaded into the filter-regenerator, where it is hydraulically divided into cation exchanger and anion exchanger. To transfer the cation exchanger and anion exchanger into a working form, they are regenerated.
Fig.5. Scheme of a block desalination plant.
EMF - electromagnetic filter; FSD - mixed action filter; LFM is a trap of filter materials.
All regenerative waters are supplied to radiation control tanks and, after radiation control, if the established levels are not exceeded, they are pumped out to chemical water treatment neutralizer tanks.
After each mixed-action filter, filters are installed - traps of ion exchangers.
During a visit to the Kalinin NPP, the following data on the operation of the block desalination plant were obtained:
100% of condensate is passed through electromagnetic filters, it is possible to pass through a mixed-action filter both 100% of water and part of it. Thus, with one operating mixed-action filter (cleaning 20% of the condensate), the specific electrical conductivity decreased: χ=0.23 µS/cm - before the block desalination plant and χ=0.21 µS/cm - after the block desalination plant.
3.5. Theoretical description of the principle of operation of a special water treatment
Ion-exchange filters of the primary circuit, as a rule, operate continuously, and approximately 0.2 - 0.5% of the main water flow in the circuit is branched off to them.
Primary circuit water is purified at a special water treatment plant, consisting of a mixed-bed filter. It serves both to remove corrosion products from reactor water and to regulate the physicochemical composition of water (normalized indicators are maintained). The special water treatment plant improves the radiation situation by reducing the radioactivity of the coolant by one or two orders of magnitude.
The circulation water of the primary circuit is supplied to the special water treatment plant from the main circulation pump and is returned to the circuit after cleaning.
In the mixed bed for the treatment of radioactive water, ion exchangers are used at a ratio of cation exchanger and anion exchanger equal to 1:1 or 1:2.
A homogeneous mixture of ion exchangers (charge) makes it possible to remove contaminants from the loop water that accidentally enter during poor-quality washing from the reagents of the filters of the installations associated with feeding the loop, as well as from the decomposition products of ion-exchange materials under the action of ionizing radiation and high temperature.
When depleted, the ion exchangers of special water treatment plants are regenerated: cation exchanger - nitric acid(at the same time it is converted into the H-form), anion exchanger - with caustic soda or caustic potash (translated again into the OH-form).
Conclusion
Having studied the materials on the technology of energy production at NPPs with VVER-1000 reactors, we came to the conclusion that one of the most important factors for the reliable operation of NPPs is high-quality treated water. This is achieved through the use of various physical and chemical methods water purification, namely through the use of pre-treatment - clarification and deep desalination by ion exchange.
The visit to the water intake station made a special impression, namely, the performance of chemical analyzes using instruments and equipment that are not used at school. This increased confidence in the quality of drinking water supplied by the water intake station for the needs of the city. But the quality parameters of the water used at the Kalinin NPP made a greater impression. Big interest caused the technological processes of water treatment in the chemical workshop, which they got acquainted with during a visit to the Kalinin NPP.
Water treatment by ion exchange allows reaching the required values necessary for the safe, reliable and economical operation of the equipment. However, this is a rather expensive process: the cost of 1 m3 of chemically desalted water is 20.4 rubles, and the cost of 1 m3 of drinking water is 6.19 rubles. (data from 2007).
In this regard, there is a need for a more economical use of chemically demineralized water, for which closed water circulation cycles are used. To maintain the required water parameters (removal of incoming impurities), condensate cleaning (on the second circuit) and special water treatment (on the first circuit) are used. The presence of closed cycles prevents the discharge of water from the primary and secondary circuits into the environment, and for industrial effluents there is a system of neutralization and disposal, which reduces the technogenic load.
Despite the fact that the material presented in the project goes beyond school curriculum, acquaintance with him motivates high school students to study chemistry more deeply, as well as make an informed choice future profession associated with nuclear energy.
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