Thermophysical properties Gaseous combustion products needed to calculate the dependence of various parameters from the temperature of this gas environment can be set based on the values \u200b\u200bgiven in the table. In particular, the specified dependences for heat capacity were obtained in the form:
C PSM \u003d A -1/ D.,
where a. = 1,3615803; b. = 7,0065648; c. = 0,0053034712; d. = 20,761095;
C PSM \u003d A + bT SM. + ct. 2 SM.,
where a. = 0,94426057; b. = 0,00035133267; c. = -0,0000000539.
The first dependence is preferred by the accuracy of the approximation, the second dependence can be adopted for calculating less accuracy.
Physical parameters flue gases
(for P \u003d. 0.0981 MPa; r CO2 \u003d 0.13; p. H2O \u003d 0.11; r N2 \u003d 0.76)
| t., ° S. | γ, n · m -3 | with R., W (m 2 · ° С) -1 | λ · 10 2, W (M · K) -1 | but · 10 6, m 2 · s -1 | μ · 10 6, Pa · s | v. · 10 6, m 2 · s -1 | Pr. |
| 12,704 | 1,04 | 2,28 | 16,89 | 15,78 | 12,20 | 0,72 | |
| 9,320 | 1,07 | 3,13 | 30,83 | 20,39 | 21,54 | 0,69 | |
| 7,338 | 1,10 | 4,01 | 48,89 | 24,50 | 32,80 | 0,67 | |
| 6,053 | 1,12 | 4,84 | 69,89 | 28,23 | 45,81 | 0,65 | |
| 5,150 | 1,15 | 5,70 | 94,28 | 31,69 | 60,38 | 0,64 | |
| 4,483 | 1,18 | 6,56 | 121,14 | 34,85 | 76,30 | 0,63 | |
| 3,973 | 1,21 | 7,42 | 150,89 | 37,87 | 93,61 | 0,62 | |
| 3,561 | 1,24 | 8,27 | 183,81 | 40,69 | 112,10 | 0,61 | |
| 3,237 | 1,26 | 9,15 | 219,69 | 43,38 | 131,80 | 0,60 | |
| 2,953 | 1,29 | 10,01 | 257,97 | 45,91 | 152,50 | 0,59 | |
| 2,698 | 1,31 | 10,90 | 303,36 | 48,36 | 174,30 | 0,58 | |
| 2,521 | 1,32 | 11,75 | 345,47 | 40,90 | 197,10 | 0,57 | |
| 2,354 | 1,34 | 12,62 | 392,42 | 52,99 | 221,00 | 0,56 |
Appendix 3.
(reference)
Air and smoke permeability of air ducts and valves
1. To determine the leaks or drowshes of air, the following formulas obtained by approximation of tabular data can be used in relation to the ventilation channels of the scene systems:
for class H air ducts (in the pressure range of 0.2 - 1.4 kPa): ΔL. = but(R - b.) fromwhere ΔL. - Sumps (leaks) of air, m 3 / m 2 · h; R - pressure, kPa; but = 10,752331; b. = 0,0069397038; from = 0,66419906;
for air ducts class P (in the pressure range of 0.2 - 5.0 kPa): where a \u003d. 0,00913545; b \u003d. -3,1647682 · 10 8; c \u003d. -1.2724412 · 10 9; d \u003d 0,68424233.
2. For fire-fighting normally closed valves, the number values \u200b\u200bof the specific characteristic of the resistance to smoke-permeation depending on the temperature of the gas correspond to the data obtained during the standing firing tests of various products on the experimental base of VNIIPO:
| 1. General Provisions. 2 2. Source data. 3 3. Exhaust anti-ventilation. 4 3.1. Removing burning products directly from burning room. 4 3.2. Removal of combustion products from adjacent hot rooms. 7 4. Supply air ventilation. 9 4.1. Air supply to staircases. 9 4.2. Air supply to elevator shafts .. 14 4.3. Air supply to tambour gateways .. 16 4.4. Compensating air supply. 17 5. Specifications equipment. 17 5.1. Equipment of exhaust air ventilation systems. 17 5.2. Equipment of systems of the supply of aircraft ventilation. 21 6. Fire control modes. 21 References .. 22 Appendix 1. Determination of the basic parameters of the fire load of the premises. 22 Appendix 2. Thermophysical properties of flue gases. 24 Appendix 3. Air and smoke response of air ducts and valves. 25. |
State educational institution Higher vocational education
"Samara State Technical University»
Department "Chemical Technology and Industrial Ecology"
COURSE WORK
under the discipline "Technical thermodynamics and heat engineering"
Topic: Calculation of the installation of the heat of waste gases of the technological furnace
Completed: Student Ryabinin E.A.
ZF Course III Group 19
Checked: Consultant Churkina A.Yu.
Samara 2010
Introduction
Most chemical enterprises formed high and low-temperature thermal waste, which can be used as secondary energy resources (WEP). These include outgoing gases of various boilers and technological furnaces, cooled streams, cooling water and spent steam.
Thermal WER largely cover the need for the warmth of individual industries. Thus, in the nitrogen industry, at the expense of the WEP, the Bole is satisfied with a 26% heat need, in the soda industry - more than 11%.
The amount of WER used depends on three factors: WEP temperature, their thermal power and exit continuity.
Currently, heat disposal of exhaust production gases has been the greatest distribution, which almost all firefight processes have high temperature potential and in most industries can be used continuously. The heat of exhaust gases is the main substantive energy balance. It is used mainly for technological, and in some cases - both for energy purposes (in the boilers - utilizers).
However, the widespread use of high-temperature thermal WER is associated with the development of utilization methods, including heat hot slags, products, etc., new methods of heat disposal of exhaust gases, as well as with the improvement of the designs of existing utilization equipment.
1. Description of the technological scheme
In tubular furnaces that do not have convection chambers, or in a radiant-convection type furnaces, but having a relatively high initial temperature of the heated product, the temperature of the exhaust gases can be relatively high, which leads to increased heat loss, decrease in the Furnace efficiency and greater fuel consumption. Therefore, it is necessary to use the heat of exhaust gases. This can be achieved either by using an air heater, heating air entering the fuel combustion furnace, or the installation of waste-recyclars that allow you to obtain water vapor necessary for technological needs.
However, additional costs of the air heater, blower, and an additional electricity consumption consumed by the blower engine are required to carry out air heating.
To ensure normal operation of the air heater, it is important to prevent the possibility of corrosion of its surface from the flue side of the flue gases. This phenomenon is possible when the temperature of the heat exchange surface is below the temperature of the dew point; In this case, part of the flue gases, directly in contact with the surface of the air heater, is significantly cooled, the water vapor contained in them is partially condensed and, absorbing sulfur dioxide from gases, forms aggressive weak acid.
The dew point corresponds to the temperature at which the pressure of saturated vapor water turns out to be equal to partial pressure of water vapor contained in flue gases.
One of the most reliable corrosion protection methods is a pre-heating of air in any way (for example, in water or steam canal) to a temperature above the dew point. Such corrosion may occur on the surface of convection pipes, if the temperature of the raw material entering the furnace is lower than the dew point.
The heat source, to increase the temperature of a saturated steam, is the oxidation reaction (combustion) of the primary fuel. Smoke gases formed during combustion give their heat in radiation, and then convection chambers with raw flow (water pair). The superheated water vapor enters the consumer, and the combustion products leave the oven and enter the recycler boiler. At the outlet of the ku, the saturated water vapor arrives back to the supply of steam overheating in the oven, and the flue gases, which coolant the nutrient water is entered into the air heater. From the air-powered heater, the flue gases go to the tent, where the water coming on the coil is heated and goes to direct to the consumer, and the flue gases into the atmosphere.
2. Calculation of the furnace
2.1 Calculation of the process of burning
We define the low heat combustion of fuel Q. R N. . If the fuel is an individual hydrocarbon, then heat combustion Q. R N. It is equal to the standard heat of combustion minus the heat of evaporation of water in combustion products. It can also be calculated according to the standard thermal effects of the formation of source and final products based on the GESS law.
For fuel consisting of a mixture of hydrocarbons, the heat of combustion is determined, but the rule of additivity:
where Q PI N. - Heat of combustion i. -Ho fuel component;
y I. - Concentration i. -Go component of fuel in fractions from one, then:
Q. R N. cm = 35.84 ∙ 0.987 + 63.80 ∙ 0.00333+ 91.32 ∙ 0.0012+ 118.73 ∙ 0.0004 + 146.10 ∙ 0.0001 \u003d 35.75 MJ / m 3.
Molar mass of fuel:
M M. = Σ M I. ∙ y I. ,
where M I. - molar mass i. -Ho fuel component, from here:
M M \u003d. 16,042 ∙ 0,987 + 30.07 ∙ 0,0033 + 44.094 ∙ 0.0012 + 58,120 ∙ 0.0004 + 72.15 ∙ 0.0001 + 44.010 ∙ 0.001 + 28.01 ∙ 0.007 \u003d 16.25 kg / mol.
kg / m 3,
then Q. R N. cm , expressed in MJ / kg, is equal to:
MJ / kg.
The results of the calculation are reduced in Table. one:
Composition of fuel Table 1
We define the elementary composition of fuel,% (mass.):
,
where n i C. , n i H. , n i n. , n i O. - the number of carbon, hydrogen atoms, nitrogen and oxygen in the molecules of individual components included in the fuel;
The content of each component of fuel, masses. %;
x I. - The content of each fuel component, they say. %;
M I. - molar mass of individual components of fuel;
M M. - molar mass of fuel.
Checking the composition :
C + H + O + N \u003d 74.0 + 24,6 + 0.2 + 1.2 \u003d 100% (mass.).
We define the theoretical amount of air required for incineration of 1 kg of fuel, it is determined from the stoichiometric equation of the combustion reaction and oxygen content in atmospheric air. If the elementary composition of the fuel, theoretical amount of air is known L 0. , kg / kg, calculated by the formula:
In practice, an excessive amount of air is introduced to ensure completeness of the combustion of fuel in the furnace, we will find a valid air flow at α \u003d 1.25:
L. = αl 0 ,
where L. - valid air flow;
α - excess air coefficient,
L. = 1.25 ∙ 17.0 \u003d 21.25 kg / kg.
Specific air volume (n. Y.) For burning 1 kg of fuel:
where ρ B. \u003d 1,293 - air density under normal conditions,
m 3 / kg.
We find the number of combustion products formed when burning 1 kg of fuel:
if the elementary composition of the fuel is known, then the mass composition of flue gases per 1 kg of fuel in its full combustion can be determined on the basis of the following equations:
where m CO2. , m H2O. , m N2. , m O2. - Mass of appropriate gases, kg.
Total combustion products:
m. p. S. = m CO2 + M H2O + M N2 + M O2
m. p. S. \u003d 2.71 + 2.21 + 16.33 + 1.00 \u003d 22.25 kg / kg.
Check the value obtained:
where W F. - specific consumption Nozzle steam when burning liquid fuel, kg / kg (for gas fuel W F. = 0),
Since the fuel is gas, the content of moisture in the air is neglected, and the amount of water steam does not take into account.
Find the volume of combustion products under normal conditions formed during combustion of 1 kg of fuel:
where m I. - the mass of the corresponding gas generated during combustion of 1 kg of fuel;
ρ I. - density of this gas under normal conditions, kg / m 3;
M I. - molar mass of this gas, kg / kmol;
22.4 - molar volume, m 3 / kmol,
m 3 / kg; 
m 3 / kg;
m 3 / kg; 
m 3 / kg.
The total volume of combustion products (n. Y.) In the actual flow of air:
V \u003d V CO2 + V H2O + V N2 + V O2 ,
V. = 1.38 + 2.75+ 13.06 + 0.70 \u003d 17.89 m 3 / kg.
The density of combustion products (n. Y.):
kg / m 3.
We will find the heat capacity and the enthalpy of combustion products 1 kg of fuel in the temperature range from 100 ° C (373 K) to 1500 ° C (1773 K) using data Table. 2.
Medium specific heat capacity of gases with P, KJ / (kg ∙ K) table 2
| t. , ° S. |
|||||
Enthalpy of flue gases formed during combustion of 1 kg of fuel:
where with CO2. , with H2O. , with N2. , with O2. - Middle specific heat capacity at constant pressure of the corresponding lawn at temperatures t. , KJ / (kg · k);
with T. - The average heat capacity of flue gases formed during combustion of 1 kg of fuel at temperatures t. , kj / (kg k);
at 100 ° C: KJ / (kg ∙ K);
at 200 ° C: KJ / (kg ∙ K);
at 300 ° C: KJ / (kg ∙ K);
at 400 ° C: KJ / (kg ∙ K);
at 500 ° C: KJ / (kg ∙ K);
at 600 ° C: KJ / (kg ∙ K);
at 700 ° C: KJ / (kg ∙ K);
at 800 ° C: KJ / (kg ∙ K);
at 1000 ° C: KJ / (kg ∙ K);
at 1500 ° C: KJ / (kg ∙ K);
The results of the calculations are reduced in Table. 3.
Enhaulpia products of combustion Table 3.
According to Table. 3 Build a Dependency Schedule H T. = f. ( t. ) (Fig. 1) see Attachment .
2.2 Calculation thermal Balance Furnaces, efficiency furnaces and fuel consumption
The heat flux, perceived by water steam in the furnace (useful thermal load):
where G. - the amount of overheated water vapor per unit of time, kg / s;
H V1. and N VP2.
Take the temperature of the flowing flue gases equal to 320 ° C (593 K). The heat loss by radiation to the environment will be 10%, and 9% of them are lost in the radiant chamber, and 1% in convection. The efficiency of the furnace η T \u003d 0.95.
Heat loss from chemical nosta, as well as the number of heat of incoming fuel and air neglect.
Determine the KPD furnace:
where How - enthalpy products of combustion at the temperature of flue gases leaving the oven, t Uk ; The temperature of the outgoing flue gases is usually taken 100 to 150 ° C above the initial temperature of the raw material at the entrance to the furnace; q sweat - heat loss by radiation to the environment,% or shares from Q floor ;
Fuel consumption, kg / s:
kg / s.
2.3 Calculation of the Radiant Camera and Convection Camera
We define the flue gas temperature on the pass: t. P \u003d 750 - 850 ° С, accept
t. P \u003d 800 ° С (1073 K). Enhaulpia combustion products at a temperature in the pass
H. P \u003d 21171.8 kJ / kg.
Thermal flow, perceived by water vapor in radiant pipes:
where N. P - enthalpy of combustion products at the temperature of flue gases Pa Perevali, KJ / kg;
η t - the efficiency of the furnace; It is recommended to take it equal to 0.95 - 0.98;
Thermal flow, perceived by water vapor in convection pipes:
The enthalpy of water vapor at the entrance to the radiant section will be:
KJ / kg.
We accept the magnitude of the pressure loss in the convection chamber ∆ P. to \u003d 0.1 MPa, then:
P. to = P. - P. to ,
P. to \u003d 1.2 - 0.1 \u003d 1.1 MPa.
Water vapor input temperature in the radiant section t. to \u003d 294 ° C, then the average temperature of the outer surface of radiant pipes will be:
where Δt. - the difference between the temperature of the outer surface of the radiant pipes and the temperature of the water vapor (raw materials) heated in the pipes; Δt. \u003d 20 - 60 ° C;
TO.
Maximum calculated combustion temperature:
where t O. - the reduced temperature of the initial mixture of fuel and air; It is accepted equal to the temperature of air supplied to burning;
tHX. - specific heat capacity of combustion products at temperatures t. P;
° С.
For t Max = 1772.8 ° C and t. P \u003d 800 ° C Heat-stance of absolutely black surface q S. for various temperatures The outer surface of radiant pipes has the following values:
Θ, ° C 200 400 600
q S. , W / m 2 1.50 ∙ 10 5 1.30 ∙ 10 5 0.70 ∙ 10 5
We build auxiliary chart (Fig. 2) see Attachment where we find heat-staring at θ \u003d 527 ° C: q S. \u003d 0.95 ∙ 10 5 W / m 2.
We calculate the full thermal stream introduced into the furnace:
Preliminary value of the area of \u200b\u200bequivalent absolutely black surface:
m 2.
We accept the degree of shielding of masonry ψ \u003d 0.45 and for α \u003d 1,25 we find that
H S. /H. L. = 0,73.
The value of the equivalent flat surface:
m 2.
We accept single-row pipe placement and step between them:
S. = 2d. N. \u003d 2 ∙ 0.152 \u003d 0.304 m. For these values \u200b\u200bForm factor TO = 0,87.
The magnitude of the covered masonry surface:
m 2.
The surface of heating radiant pipes:
m 2.
Select BB2 furnace, its parameters:
radiation chamber surface, m 2 180
convection chamber surface, m 2 180
working length oven, M 9
radiation chamber width, M 1,2
b. Execution
fuel combustion method Flame
diameter of pipe diameter radiation, mm 152 × 6
diameter of tubes of convection chamber, mm 114 × 6
The number of pipes in the radiation chamber:
where d. H is the outer diameter of pipes in the radiation chamber, m;
l. Paul - useful length of radiant pipes, washed by flue gases, m,
l. gender \u003d 9 - 0.42 \u003d 8.2 m,
.
The heat change of the surface of radiant pipes:
W / m 2.
We determine the number of pipes of the convection chamber:
We have them in a checker order 3 in one horizontal row. Step between pipes S \u003d 1.7 d. H \u003d 0.19 m.
The average temperature difference is determined by the formula:
° С.
Coefficient of heat transfer in the convection chamber:
W / (m 2 ∙ k).
The heat change of the surface of convection pipes is determined by the formula:
W / m 2.
2.4 Hydraulic calculation of the stove coil
The hydraulic calculation of the furnace coil is to determine the loss of water vapor pressure in radiant and convection pipes.
where G.
ρ to V.P. - the density of water vapor at an average temperature and pressure in the Concents chamber, kg / m 3;
d. k - the inner diameter of convection pipes, m;
z. K - the number of streams in the convection chamber,
m / s.
ν K \u003d 3.311 ∙ 10 -6 m 2 / s.
The value of the Reynolds criterion:
m.
Pressure loss for friction:
Pa \u003d 14.4 kPa.
Pa \u003d 20.2 kPa.
where σ. ζ K.
- The number of turns.
Total pressure loss:
2.5 Calculation of water vapor pressure loss in the radiation chamber
Average water vapor speed:
where G. - consumption of overheated in the furnace of water vapor, kg / s;
ρ R.P. - the density of water vapor at an average temperature and pressure in the Concents chamber, kg / m 3;
d. P - Intrunny diameter of convection pipes, m;
z. P is the number of streams in the cell chamber,
m / s.
The kinematic viscosity of the water vapor at an average temperature and pressure in the convection chamber ν P \u003d 8.59 ∙ 10 -6 m 2 / s.
The value of the Reynolds criterion:
The total length of pipes on the straight area:
m.
Hydraulic friction coefficient:
Pressure loss for friction:
Pa \u003d 15.1 kPa.
Pressure Loss Overcoming local resistances:
Pa \u003d 11.3 kPa,
where σ. ζ R. \u003d 0.35 - the resistance coefficient when rotating 180 ºС,
- The number of turns.
Total pressure loss:
Calculations showed that the selected furnace will provide the process of overheating the water vapor in a given mode.
3. Calculation of the boiler-utilizer
We find the average temperature of flue gases:
where t. 1 - Temperature of flue gases at the entrance,
t. 2 - the temperature of the flue gases at the outlet, ° C;
° С (538 K).
Mass flow of flue gases:
where in - fuel consumption, kg / s;
For flue gases, specific enthalpy determines based on the data table. 3 and fig. 1 by formula:
Entalpy heat carriers Table 4.
Heat flow transmitted by smoke gases:
where N. 1 I. H. 2 - the enthalpy of flue gases at the temperature of the entrance and exit from ku, respectively, formed during combustion of 1 kg of fuel, KJ / kg;
B - fuel consumption, kg / s;
h. 1 I. h. 2 - Specific enthalpies of flue gases, KJ / kg,
Heat flow, perceived by water, W:
where η ku - the coefficient of use of heat in ku; η ku \u003d 0.97;
G. n - steam output, kg / s;
h. to VP - enthalpy of saturated water vapor at the exit temperature, kJ / kg;
h. N in - Entalugaya nutrient water, kj / kg,
The amount of water vapor obtained in ku, we define the formula:
kg / s.
The heat flow, perceived by water in the heating zone:
where h. to - specific enthalpy of water at evaporation temperature, KJ / kg;
Thermal flow made by flue gases of water in the heating zone (useful heat):
where h. X - Specific enthalpy of flue gases at temperatures t. X, Hence:
kJ / kg.
The value of the combustion of 1 kg of fuel:
In fig. 1 smoke temperature corresponding to value H. x \u003d 5700.45 kJ / kg:
t. X \u003d 270 ° C.
The average temperature difference in the heating zone:
° С.
270 flue gases 210, taking into account the index of countercurrent:
where TO F - heat transfer coefficient;
m 2.
The average temperature difference in the evaporation zone:
° С.
320 flue gases 270, taking into account the index of countercurrent:
187 water vapor 187
The surface area of \u200b\u200bheat exchange in the heating zone:
where TO F - T6 coefficient;
m 2.
The total area of \u200b\u200bthe heat exchange surface:
F. = F. N +. F. u,
F. \u003d 22,6 + 80 \u003d 102.6 m 2.
In accordance with GOST 14248-79, we choose a standard evaporator with steam space with the following characteristics:
casing diameter, mm 1600
the number of pipe beams 1
the number of pipes in one bundle 362
surface heat exchange, m 2 170
singing Singing Single
by pipes, m 2 0,055
4. Heat Balance Air Heater
Atmospheric air with temperature t ° in x Enters the device where heats up to temperature t x in x Due to the heat of flue gases.
Air flow, kg / s is determined based on their required quantity of fuel:
where IN - fuel consumption, kg / s;
L. - valid air flow for burning 1 kg of fuel, kg / kg,
Flue gases, giving out their warmth, cooled from t DHG = t DG2. before t DG4. .
=
where H 3. and H 4. - The enthalpy of flue gases at temperatures t dg3 and t DG4. Accordingly, KJ / kg,
Thermal flow, perceived by air, W:
where with in-x - the average specific heat capacity, KJ / (kg to);
0.97 - efficiency of the air heater,
Ultimate air temperature ( t x in x) Determined from the heat balance equation:
TO.
5. Thermal Balance of Ktana
After the air heater, the flue gases enter the contact apparatus with an active nozzle (tant), where their temperature decreases from t DG5 = t DG4. to temperature t dg6 \u003d 60 ° C.
The warmth of flue gases is removed by two separate water flows. One stream comes into direct contact with the flue gases, and the other is alternating with them heat through the wall of the coil.
Heat flow given by smoke gases, W:
where H 5. and H 6. - The enthalpy of flue gases at temperatures t DG5 and t dg6 Accordingly, KJ / kg,
The amount of cooling water (total), kg / s is determined from the heat balance equation:
where η - KPD KTAN, η \u003d 0.9,
kg / s.
Thermal flow, perceived by cooling water, W:
where G water - cooling water consumption, kg / s:
with water - specific water heat capacity, 4.19 kJ / (kg to);
t n water and t to water - water temperature at the entrance and outlet of Ktana, respectively,
6. Calculation of the efficiency of the heat removal installation
When determining the efficiency of the synthesized system ( η TU) The traditional approach is used.
The calculation of the electricity installation efficiency is carried out by the formula:
7. EXERGETICAL EVALUATION OF THE SYSTEM OF THE SYSTEM - COILE-UTILISTOR SYSTEM
The extracetic method for analyzing energy technological systems allows the most objectively and qualitatively evaluate energy losses, which are not detected in any way with the usual estimate using the first law of thermodynamics. As a criterion for estimates in the case under consideration, an extracetic efficiency is used, which is defined as the relation of the reserved exergy to the exergy of the listed in the system:
where E Dutch - exsertigation of fuel, MJ / kg;
E Any - exsertigation, perceived by the flow of water vapor in the furnace and the boiler-utilization.
In the case of gaseous fuel, the external exterioric is consigned from the exserving fuel ( E DT1) and the exserving air ( E PLAY2.):
where N N. and N O. - air enthalpy at the input temperature in the furnace furnace and the ambulsion temperature, respectively, KJ / kg;
T O. - 298 K (25 ° C);
Δs. - change of air entropy, KJ / (kg k).
In most cases, the amount of exserving air can be neglected, that is:
The reserved exsertigation for the system under consideration is made of exsertiga, perceived by water ferry in the furnace ( E Ans1), and the exxiga, perceived by water ferry in ku ( E Avd2.).
For the flow of water vapor heated in the furnace:
where G. - steam consumption in the furnace, kg / s;
N VP1. and N VP2. - enthalpy of water vapor at the entrance and outlet of the furnace, respectively, KJ / kg;
ΔS VP - change of entropy of water vapor, KJ / (kg k).
For the flow of water vapor obtained in Ku:
where G N. - steam consumption in ku, kg / s;
h to VP - enthalpy of saturated water vapor at the exit of ku, kj / kg;
h N B. - Enthalpy of nutritious water at the entrance in Ku, KJ / kg.
E Any = E DV1 + E Ans2 ,
E Any \u003d 1965.8 + 296.3 \u003d 2262.1 J / kg.
Conclusion
Conducting the calculation on the proposed installation (utilization of the heat of the exhaust gases of the technological furnace), it can be concluded that with this composition of the fuel, the performance of the furnace on a water pair, other indicators - the magnitude of the efficiency of the synthesized system is high, so the installation is effective; This also showed the extracetic assessment of the "furnace-boiler-boiler" system, but at energy costs the installation leaves much to be desired and requires refinement.
List of used literature
1. Kharaz D. . AND . Ways to use secondary energy resources in chemical industries / D. I. Kharaz, B. I. Psakhis. - M.: Chemistry, 1984. - 224 p.
2. Skoblo A. . AND . Processes and devices of the oil refining and petrochemical industry / A. I. Skoblo, I. A. Tregubova, Yu. K., Molokanov. - 2nd ed., Pererab. and add. - M.: Chemistry, 1982. - 584 p.
3. Pavlov K. . F. . Examples and tasks at the rate of processes and devices of chemical technology: studies. Allowance for universities / K. F. Pavlov, P. G. Romankov, A. A. Soskov; Ed. P. G. Romakova. - 10th ed., Pererab. and add. - L.: Chemistry, 1987. - 576 p.
application
When combustion of fuel carbon in the air, the equation (21c + 2102 + 79n2 \u003d 21c02 + 79n2) on each volume C02 in combustion products accounts for 79: 21 \u003d 3.76 volume N2.
When combustion of anthracite, skinny coals and other types of fuel with a high carbon content, combustion products are formed close to the composition of carbon combustion products. When combustion of hydrogen by equation
42h2 + 2102 + 79n2 \u003d 42h20 + 79n2
On each volume H20 accounts for 79:42 \u003d 1.88 volume of nitrogen.
In the combustion products of natural, liquefied and coke gases, liquid fuel, firewood, peat, brown coal, long-flame and gas coal and other types of fuel with a significant content of hydrogen in a combustible mass, a large amount of water vapor is formed, sometimes exceeding the volume C02. The presence of moisture in the top
|
Table 36. Heat capacity, kcal / (MW. ° C) |
Live, naturally, increases the content of water vapor in combustion products.
The composition of the full combustion products of the main fuels in the steam chiometric volume is given in Table. 34. From these this table, it can be seen that in products of combustion of all types of fuel, the N2 content significantly exceeds the total content of C02-F-H20, and in carbon combustion products it is 79%.
The combustion products of hydrogen contains 65% N2, in the combustion products of natural and liquefied gases, gasoline, fuel oil and other types of hydrocarbon fuel, its content is 70-74%.
Fig. 5. Volumetric heat capacity
Products combustion
4 - carbon combustion products
5 - hydrogen combustion products
The average heat capacity of complete combustion products that do not contain oxygen can be calculated by the formula
C \u003d 0.01 (CC02C02 + CSO2S02 + C "20H20 + CN2N2) kcal / (m3- ° C), (vi. 1)
Where CC0G, CSO2, SINA0, CNA is the volumetric heat capacity of carbon dioxide, sulfur gas, water vapor and nitrogen, and C02, S02, H20 and N2 is the content of the corresponding components in combustion products,% (volume).
In accordance with this, the formula (VI. 1) acquires the following form:
C \u003d 0.01. (CC02 /? 02 + CHJ0H20-BCNI! N2) kcal / (m3 "° С). (VI.2)
The average volumetric heat capacity C02, H20 and N2 in the temperature range from 0 to 2500 ° C is given in Table. 36. Curves characterizing the change in the average volumetric heat capacity of these gases with an increase in temperature are shown in Fig. five.
From those shown in table. 16 data and curves depicted in fig. 5, you can see the following:
1. The bulk heat capacity of C02 significantly exceeds the heat capacity H20, which, in turn, exceeds the heat capacity N2 throughout the temperature range from 0 to 2000 ° C.
2. The heat capacity of C02 increases with increasing temperature faster than the heat capacity H20, and the heat capacity H20 is faster than the heat capacity N2. However, despite this, the weighted average volumetric heat capacity of the combustion of carbon and hydrogen combustion in the stoichiometric volume of air differ little.
The specified position, somewhat unexpected at first glance, is due to the fact that in the products of complete combustion of carbon in the air for each cubic meter of C02, which has the highest volumetric heat capacity, accounts for 3.76 m3 n2 with minimal volumetric
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Average volumetric heat capacity of carbon and hydrogen combustion products in theoretically necessary amount of air, kcal / (M3- ° C)
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Heat capacity, and in hydrogen combustion products for each cubic meter of water vapor, the volumetric heat capacity of which is less than that of the SHO, but more than in N2, there is half a smaller amount of nitrogen (1.88 m3).
As a result, the average volumetric heat capacity of carbon and hydrogen combustion products in the air is aligned, as can be seen from the data table. 37 and comparison of curves 4 and 5 in Fig. 5. The difference in the weighted average heat supply products of the combustion of carbon and hydrogen in the air does not exceed 2%. Naturally, the heat capacity of the fuel combustion products consisting mainly of carbon and hydrogen, in the stoichiometric volume of air, lie in a narrow area between curves 4 and 5 (shaded in Fig. 5) ..
Full combustion products of various types; Fuel in stoichiometric air in temperature range from 0 to 2100 ° C have the following heat capacity, kcal / (m3\u003e ° C):
Wipers in heat capacity in combustion products different species Fuel is relatively small. W. solid fuel with high moisture content (firewood, peat, brown coals, etc.) The heat capacity of combustion products in the same temperature range is higher than that of fuel with low moisture content (anthracite, stone coals, fuel oil, natural gas, etc.) . This is due to the fact that when combustion of fuel with a high moisture content in combustion products, the content of water vapor has a higher heat capacity compared to dioxide gas - nitrogen.
In tab. 38 shows the average volumetric heat capacity of full combustion products that are not diluted with air for different temperature ranges.
Table 38.
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The value of the average heatabases not diluted with air combustion and air combustion in temperature range from 0 to T ° C
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The increase in moisture content in fuel increases the heat capacity of combustion products due to the increase in the content of water vapor in the same temperature range compared with the heat capacity of fuel combustion products with a lower moisture content, and at the same time lowers the combustion temperature of the fuel due to the increase in the volume of combustion products due to water couple.
With an increase in the content of moisture in the fuel, the bulk heat capacity of combustion products in a given temperature range increases and, at the same time, the temperature range from 0 to £ takh is reduced due to a decrease in the value<тах. ПОСКОЛЬКУ ТЄПЛОЄМКОСТЬ ГЭЗОВ уМвНЬ — шается с понижением температуры, теплоемкость продуктов сгорания топлива с различной влажностью в интервале температур от нуля до <тах для данного топлива претерпевает незначительные колебания (табл. 39). В соответствии с этим можно принять теплоемкость продуктов сгорания всех видов твердого топлива от 0 до tmax равной 0,405, жидкого топлива 0,401, природного, доменного и генераторного газов 0,400 ккал/(м3-°С).
This makes it possible to significantly simplify the determination of the calorimetric and calculated combustion temperatures (according to the procedure set out in ch. VII). The accuracy of the error usually does not exceed 1%, or 20 °.
From consideration of curves 4 and 5 in Fig. 5 It can be seen that the ratio of heat - containers of complete combustion of carbon in the stoichiometric volume of air in the temperature range from 0 to T ° C, for example from 0 to
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The heat capacity of combustion products from 0 to T'mayl of various types of solid fuels with a content from 0 to 40% moisture, in stoichiometric air volume
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200 and from 0 to 2100 ° C are virtually equal to the ratio of the heat of the products of the combustion of hydrogen in the same temperature intervals. The specified ratio of heat-capacity C 'remains almost constant and for the products of complete combustion of various types of fuel in the stoichiometon volume of air.
In tab. 40 shows the relations of heat-capacity products of the full combustion of fuel with a small content of ballast, moving into gaseous combustion products (anthracite, coke, stone coals, liquid fuel, natural, oil, coke gases, etc.) in temperature range from 0 to T ° C and in the temperature range from 0 to 2100 ° C. Since the heat-producing of these fuels is close to 2100 ° C, the specified ratio of heat-capacity with 'is equal to the ratio of heat-capacity in the temperature range from 0 to T and from 0 to TM & X-
In tab. 40 are also given values \u200b\u200bof the value C ', counted for the products of combustion of fuel with a high content of ballast, moving when burning fuel into gaseous combustion products, i.e., moisture in solid fuel, nitrogen and carbon dioxide in gaseous. Heat productivity of specified fuels (firewood, peat, brown coals, mixed generator, air and domain gases) is equal to 1600-1700 ° C.
Table 40.
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The treatment of heat-capacity of combustion products with 'and air K in a temperature range from 0 to T ° C to the heat capacity of combustion products from 0 to (sch
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As can be seen from the table. 40, values \u200b\u200bwith 'and to little differ even for fuel combustion products with different content of ballast and heat - performance.
Wet air is a mixture of dry air and water vapor. In the unsaturated air, the moisture is in a state of overheated steam, and therefore the properties of wet air can approximately be described by the laws of ideal gases.
The main characteristics of wet air are:
1. Absolute humidity g.determining the amount of water vapor contained in 1 m 3 wet air. Water steam occupies the entire volume of the mixture, so the absolute humidity of the air is equal to mass 1 m 3 of water vapor or density of steam, kg / m 3
2. The relative humidity of the air j is expressed by the ratio of absolute humidity of the air to the maximum possible moisture content at the same pressure and temperature or the ratio of the mass of the water vapor concluded in 1 m 3 of wet air, to the mass of the water vapor required for the total saturation of 1 m 3 wet air Under the same pressure and temperature.
Relative humidity determines the degree of air saturation in moisture:
, (1.2)
where - the partial pressure of the water vapor, corresponding to its density of PA; - the pressure of a saturated pair at the same temperature, PA; - the maximum possible amount of steam in 1 m 3 saturated wet air, kg / m 3; - pair density during its partial pressure and humid air temperature, kg / m 3.
The ratio (1.2) is valid only when it can be assumed that the pairs of liquid is the perfect gas up to saturation state.
The density of wet air R is the amount of densities of water vapor and dry air in partial pressures in 1 m 3 of wet air at a humid air temperature T.To:
(1.3)
where is the density of dry air during its partial pressure in 1 m 3 of wet air, kg / m 3; - partial pressure of dry air, PA; - Gas constant of dry air, J / (kg × k).
Expressing both the equation for the condition for air and water vapor, we get
, (1.5)
where is the mass flow of air and water vapor, kg / s.
These equalities are valid for the same volume V. Wet air and the same temperature. Sharing the second equality on the first, we get another expression for moisture content
. (1.6)
Substituting the values \u200b\u200bof gas constant for air J / (kg × K) and for water vapor J / (kg × K), we obtain the value of moisture content, expressed in water vapor kilograms per 1 kg of dry air
. (1.7)
Replacing the partial air pressure of the magnitude, where from the previous one and IN - barometric air pressure in the same units as r, I get for wet air under barometric pressure
. (1.8)
Thus, at a given barometric pressure, the moisture content of air depends only on the partial pressure of the water vapor. Maximum possible moisture content in the air, from where
. (1.9)
Since saturation pressure grows with a temperature, then the maximum possible amount of moisture, which may be contained in the air depends on its temperature, the greater the higher the temperature. If equations (1.7) and (1.8) solve relatively and, then we get
(1.10)
. (1.11)
The volume of wet air in cubic meters per 1 kg of dry air is calculated by the formula
(1.12)
Specific volume of wet air v., m 3 / kg is determined by dividing the volume of wet air on a mass of a mixture per 1 kg of dry air:
Wet air as a coolant is characterized by enthalpy (in kilodzhoules per 1 kg of dry air), equal to the amount of dry air enthalpy and water vapor
(1.14)
where is the specific heat capacity of dry air, KJ / (kg × K); t. - air temperature, ° C; i. - Enthalpy of superheated steam, KJ / kg.
Enthalpy 1 kg of dry saturated water vapor at low pressures is determined by the empirical formula, KJ / kg:
where - a permanent coefficient, approximately equal to the enthalpy of the pair at 0 ° C; \u003d 1.97 kJ / (kg × K) - specific steam heat capacity.
Substituting meanings i. In the expression (1.14) and taking the specific heat capacity of dry air permanent and equal to 1.0036 kJ / (kg × K), we will find the enthalpy of wet air in kilodzhoules per 1 kg of dry air:
To determine the parameters of wet gas, similar to the equation discussed above are used.
, (1.17)
where is the gas constant for the gas under study; R - Gas pressure.
Entalpy Gas, KJ / kg,
where is the specific heat capacity of the gas, KJ / (kg × K).
Absolute moisture content of gas:
. (1.19)
When calculating contact heat exchangers for coolants of air-water, you can use the data Table. 1.1-1.2 or calculated dependencies to determine the physicochemical parameters of air (1.24-1.34) and water (1.35). For flue gases, data Table can be used. 1.3.
Waste gas density, kg / m 3:
, (1.20)
where - the density of dry gas at 0 ° C, kg / m 3; MG, M P is molecular weights of gas and steam.
The dynamic viscosity coefficient of wet gas, PA × C:
, (1.21)
where is the dynamic viscosity coefficient of water vapor, PA × C; - coefficient of dynamic viscosity of dry gas, PA × C; 
- mass concentration of steam, kg / kg.
Specific heat capacity of wet gas, KJ / (kg × K):
The coefficient of thermal conductivity of wet gas, W / (M × K):
, (1.23)
where k. - Indicator adiabat; IN - coefficient (for monatomic gases IN \u003d 2.5; For diatomic gases IN \u003d 1.9; For trochatomic gases IN = 1,72).
Table 1.1. Physical properties of dry air ( r \u003d 0,101 MPa)
| t., ° C. | , kg / m 3 | , kj / (kg × k) | , W / (m × k) | , PA × C | , m 2 / s | Pr. |
| -20 | 1,395 | 1,009 | 2,28 | 16,2 | 12,79 | 0,716 |
| -10 | 1,342 | 1,009 | 2,36 | 16,7 | 12,43 | 0,712 |
| 1,293 | 1,005 | 2,44 | 17,2 | 13,28 | 0,707 | |
| 1,247 | 1,005 | 2,51 | 17,6 | 14,16 | 0,705 | |
| 1,205 | 1,005 | 2,59 | 18,1 | 15,06 | 0,703 | |
| 1,165 | 1,005 | 2,67 | 18,6 | 16,00 | 0,701 | |
| 1,128 | 1,005 | 2,76 | 19,1 | 16,96 | 0,699 | |
| 1,093 | 1,005 | 2,83 | 19,6 | 17,95 | 0,698 | |
| 1,060 | 1,005 | 2,90 | 20,1 | 18,97 | 0,696 | |
| 1,029 | 1,009 | 2,96 | 20,6 | 20,02 | 0,694 | |
| 1,000 | 1,009 | 3,05 | 21,1 | 21,09 | 0,692 | |
| 0,972 | 1,009 | 3,13 | 21,5 | 22,10 | 0,690 | |
| 0,946 | 1,009 | 3,21 | 21,9 | 23,13 | 0,688 | |
| 0,898 | 1,009 | 3,34 | 22,8 | 25,45 | 0,686 | |
| 0,854 | 1,013 | 3,49 | 23,7 | 27,80 | 0,684 | |
| 0,815 | 1,017 | 3,64 | 24,5 | 30,09 | 0,682 | |
| 0,779 | 1,022 | 3,78 | 25,3 | 32,49 | 0,681 | |
| 0,746 | 1,026 | 3,93 | 26,0 | 34,85 | 0,680 | |
| 0,674 | 1,038 | 4,27 | 27,4 | 40,61 | 0,677 | |
| 0,615 | 1,047 | 4,60 | 29,7 | 48,33 | 0,674 | |
| 0,566 | 1,059 | 4,91 | 31,4 | 55,46 | 0,676 | |
| 0,524 | 1,068 | 5,21 | 33,6 | 63,09 | 0,678 | |
| 0,456 | 1,093 | 5,74 | 36,2 | 79,38 | 0,687 | |
| 0,404 | 1,114 | 6,22 | 39,1 | 96,89 | 0,699 | |
| 0,362 | 1,135 | 6,71 | 41,8 | 115,4 | 0,706 | |
| 0,329 | 1,156 | 7,18 | 44,3 | 134,8 | 0,713 | |
| 0,301 | 1,172 | 7,63 | 46,7 | 155,1 | 0,717 | |
| 0,277 | 1,185 | 8,07 | 49,0 | 177,1 | 0,719 | |
| 0,257 | 1,197 | 8,50 | 51,2 | 199,3 | 0,722 | |
| 0,239 | 1,210 | 9,15 | 53,5 | 233,7 | 0,724 |
The thermophysical properties of dry air can be approximated by the following equations.
Kinematic viscosity of dry air at a temperature from -20 to +140 ° C, m 2 / s:
PA; (1.24)
and from 140 to 400 ° C, m 2 / s:
. (1.25)
Table 1.2. Physical properties of water in saturation state
| t., ° C. | , kg / m 3 | , kj / (kg × k) | , W / (m × k) | , m 2 / s | , N / m | Pr. | |
| 999,9 | 4,212 | 55,1 | 1,789 | -0,63 | 756,4 | 13,67 | |
| 999,7 | 4,191 | 57,4 | 1,306 | 0,7 | 741,6 | 9,52 | |
| 998,2 | 4,183 | 59,9 | 1,006 | 1,82 | 726,9 | 7,02 | |
| 995,7 | 4,174 | 61,8 | 0,805 | 3,21 | 712,2 | 5,42 | |
| 992,2 | 4,174 | 63,5 | 0,659 | 3,87 | 696,5 | 4,31 | |
| 988,1 | 4,174 | 64,8 | 0,556 | 4,49 | 676,9 | 3,54 | |
| 983,2 | 4,179 | 65,9 | 0,478 | 5,11 | 662,2 | 2,98 | |
| 977,8 | 4,187 | 66,8 | 0,415 | 5,70 | 643,5 | 2,55 | |
| 971,8 | 4,195 | 67,4 | 0,365 | 6,32 | 625,9 | 2,21 | |
| 965,3 | 4,208 | 68,0 | 0,326 | 6,95 | 607,2 | 1,95 | |
| 958,4 | 4,220 | 68,3 | 0,295 | 7,52 | 588,6 | 1,75 | |
| 951,0 | 4,233 | 68,5 | 0,272 | 8,08 | 569,0 | 1,60 | |
| 943,1 | 4,250 | 68,6 | 0,252 | 8,64 | 548,4 | 1,47 | |
| 934,8 | 4,266 | 68,6 | 0,233 | 9,19 | 528,8 | 1,36 | |
| 926,1 | 4,287 | 68,5 | 0,217 | 9,72 | 507,2 | 1,26 | |
| 917,0 | 4,313 | 68,4 | 0,203 | 10,3 | 486,6 | 1,17 | |
| 907,4 | 4,346 | 68,3 | 0,191 | 10,7 | 466,0 | 1,10 | |
| 897,3 | 4,380 | 67,9 | 0,181 | 11,3 | 443,4 | 1,05 | |
| 886,9 | 4,417 | 67,4 | 0,173 | 11,9 | 422,8 | 1,00 | |
| 876,0 | 4,459 | 67,0 | 0,165 | 12,6 | 400,2 | 0,96 | |
| 863,0 | 4,505 | 66,3 | 0,158 | 13,3 | 376,7 | 0,93 |
Density of wet gas, kg / m 3.
