2. Heat carried away by leaving gases. Determine the heat capacity flue gases when touch \u003d 8000s;
3. Heat loss through the thermal conductivity masonry.
Losses via arch
The thickness of the arch is 0.3 m, the material shape. We assume that the temperature of the inner surface of the arch is equal to the temperature of the gases.
The average temperature in the furnace:
At this temperature, we choose the coefficient of thermal conductivity of chamotte material:
Thus, losses through the arch are:
where α is the heat transfer coefficient from the outer surface of the walls to the surrounding air, equal to 71.2 kJ / (m2 * h * 0С)
Losses through the walls. The masonry of the walls is made of two-layer (shaft 345 mm, diatoms 115 mm)
Square wall, m2:
Methodical zone
Welding zone
Tomil zone
Torn
Full area of \u200b\u200bthe walls 162.73 m2
With a linear temperature distribution of the wall thickness, the average temperature of the chamot will be 5500C, and the diatomite 1500c.
Hence.
Full losses through the masonry
4. Heat losses with cooling water according to practical data we accept equal to 10% Qx arrival, that is, Qx + Q
5. Unaccounted losses take in the amount of 15% Q of heat arrival
Make an equation thermal Balance stove
The thermal balance of the furnace we cohere in Table 1; 2.
Table 1
table 2
| CD / H consumption | % |
| Heat spent on metal heating
| 53 |
| heat of outgoing gases | 26 |
| losses through the masonry
| 1,9 |
| cooling water losses | 6,7 |
| unrecorded losses | 10,6 |
| TOTAL: | 100 |
Specific heat consumption for heating 1 kg of metal will be
We accept that the ovens are installed burners of the type "pipe in the pipe".
In welding zones of 16 pieces, in the tomile 4pcs. The total number of burners 20pcs. Determine the calculated amount of air coming per burner.
Vv - hour air flow;
TV - 400 + 273 \u003d 673 K - air heating temperature;
N - the number of burners.
Air pressure in front of the burner accept 2.0 kPa. It follows that the required air consumption ensures DBV 225 burner.
We define the calculated amount of gas per burner;
Vg \u003d B \u003d 2667 hour fuel consumption;
TG \u003d 50 + 273 \u003d 323 K - gas temperature;
N - the number of burners.
8. Calculation of the recovery
For air heating, we design a metal loop heat recovery from pipes with a diameter of 57 / 49.5 mm with a corridious position
Initial data for calculation:
Hourly fuel consumption B \u003d 2667 kJ / h;
Air flow per 1 m3 of fuel Lα \u003d 13.08 m3 / m3;
The amount of combustion products from 1 m3 of combustible gas Vα \u003d 13.89 m3 / m3;
Heating temperature TB \u003d 4000С;
The temperature of the outgoing gases from the furnace Tow \u003d 8000s.
Hour air flow:
Smoke hour outlet:
An hourly amount of smoke passing through the recuperator, taking into account the loss of smoke on knocking out and through the bypass Sewber and air supply.
The M coefficient, taking into account the loss of smoke, take 0.7.
The coefficient, taking into account the air subcosition in the bills, we take 0.1.
The temperature of the smoke in front of the recuperator, taking into account the air supply;
where i - heat-containing gases at tuch \u003d 8000s
This heat generation corresponds to the temperature of the smoke TD \u003d 7500C. (see Fig.67 (3))
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 of the thermal balance of the furnace, the efficiency of the furnace 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 Pot - 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 of the outer surface of radiant pipes, the following values \u200b\u200bare:
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 the furnace device ideally, I want to have a design that automatically gave so much air as it is necessary for burning. At first glance, it can be done with chimney. Indeed, the more intense firewood burns, the more hot flue gases should be, the greater should be the thrust (model of the carburetor). But it is not. The thrust does not depend on the amount of hot flue gases formed. The thrust is the pressure drop in the pipe from the tube's tank before the fuel. It is determined by the height of the pipe and the temperature of the flue gases, or rather, their density.
The thrust is determined by the formula:
F \u003d A (P B - P D) H
where F is the traction, and the coefficient, P B is the density of the outer air, P d - the density of flue gases, H is the height of the pipe
The density of flue gases is calculated by the formula:
p d \u003d p in (273 + t c) / (273 + t)
where T B and T D is the temperature in degrees Celsius of external atmospheric air outside the pipe and flue gases in the pipe.
The speed of movement of flue gases in the pipe (volume consumption, that is, the suction capacity of the pipe) G. It does not depend on the height of the pipe and is determined by the difference in temperature of flue gases and outdoor air, as well as area cross section chimney. Hence the number of practical conclusions.
FirstlyThe flue pipes are made high at all in order to increase the air flow through the fifthly, but only to increase the thrust (that is, the pressure drop in the pipe). It is very important to prevent overturning of the thrust (muffling of the furnace) with a winddrop (the magnitude of the thrust should always exceed the possible wind backup).
Secondly, adjust the air flow is conveniently using devices that change the area of \u200b\u200bthe live cross section of the pipe, that is, with the help of valves. With an increase in the cross-sectional area of \u200b\u200bthe chimney channel, for example, twice - you can expect a roughly twofold increase in the volumetric air flow through the fuel.
Explain it simple and visual example. We have two identical ovens. We combine them in one. We obtain a double furnace with a twin-lasting firewood, with two-time air consumption and cross-sectional pipe. Or (which is the same) if more than a firewood flare up in the fifuel, then you need to open the valves on the pipe more and more.
ThirdlyIf the stove burns normally in the steady mode, and we will add cold air stream by the burning firewood in the fifthly, the flue gases will come immediately, and air flow through the oven will be reduced. At the same time, burning firewood will begin to fade. That is, we seem to directly on firewood do not affect and send an additional flow by firewood, and it turns out that the pipe can skip less flue gases than before, when this additional air flow was absent. The pipe itself will reduce the flow of air on firewood, which was previously, and besides, it does not allow the additional flow of cold air. In other words, the smoke tube is running.
That is why it is so harmful to cold air superstar through the slots in the flue pipes, unnecessary air flows in the fuel cell and indeed any heat luminosity in the chimney, leading to a decrease in the temperature of the flue gases.
FourthThe greater the coefficient of gas-dynamic resistance of the chimney, the less air flow. That is, the walls of the chimney are preferably carried out as smooth, without twist and without turns.
FifthThe smaller the temperature of the flue gases, the more sharply changes the air flow during fluctuations in the temperature of the flue gases, which explains the situation of the stripping of the pipe under the ignition of the furnace.
At sixth, P. high temperatures flue gases Air flow does not depend on the temperature of the flue gases. That is, with a strong overest of the furnace, the air flow ceases to increase and begins to depend only on the cross section of the pipe.
Issues of instability arise not only when analyzing the thermal characteristics of the pipe, but also when considering the dynamics of gas flows in the pipe. Indeed, the chimney is a well filled with light chimneys. If this light flue gas rises not very fast, then the likelihood is not excluded that severe outer air It may simply be drowned in an easy gas and create a falling downward flow in the pipe. This is especially likely to such a situation with the cold walls of the chimney, that is, during the overseas oven.
Fig. 1. Gas movement scheme in a cold chimney: 1 - a fuel; 2 - air supply through pissed; 3-smoke trumpet; 4 - catch; 5 - Fireplace tooth; 6-smoke gases; 7-failing cold air; 8 - Air flow, causing tipping thrust.
a) smooth open vertical pipe
b) tube with a valve and tooth
c) pipe with top valve
Solid arrows - directions of movement of light hot flue gases. Dotted arrows - direction of movement of downward flows of cold heavy air from the atmosphere.
On the fig. 1A. The oven is schematically depicted in which the flue gases are supplied and removed through the flue tube. Even a fuel. This incident flow can replace the "regular" air flow through confused 2. Even if the furnace is locked to all the doors and all the flaps of the air intake holes will be closed, then the oven can burn due to the air from above. By the way, it is so often that happens when drovering coal with closed doors stoves. It may even happen complete tipping of thrust: the air will come on top through the pipe, and the flue gases - go out through the door.
In fact, on the inner wall of the chimney, there are always irregularities, thickening, roughness, with whose flue gases and counter-downward cold air flows are placed and mixed with each other. A cold downstream air flow is pushed out or, heating, begins to rise up a mixed-up with hot gases.
The effect of deploying downstream cold air fluxes is enhanced in the presence of partially open valves, as well as the so-called tooth, widely used in the manufacture of fireplaces. fig. 1B). The tooth prevents the flow of cold air from the pipe into the fireplace space and thereby prevents the smelting of the fireplace.
The downstream air flows in the pipe are especially dangerous in foggy weather: the flue gases are not able to evaporate the smallest droplets of water, cooled, the thrust is reduced and can even tilt. The oven is very smoking, it does not flare up.
For the same reason, stoves with raw smoky pipes strongly smoke. To prevent the occurrence of downlinks, top valves are particularly effective ( fig. 1V.), regulated depending on the speed of flue gases in the chimney. However, the operation of such valves is inconvenient.
Fig. 2. The dependence of the excess air coefficient is from the time of the furnace protest (solid curve). The dotted curve is the required air flow rate G of the Potch for the complete oxidation of firewood products (including soot and volatile substances) in flue gases (in relative units). Barcode-dotted curve - the real air consumption of the pipe provided by the tube (in relative units). The excess air coefficient is a private compartment G pipe on G Potch
Stable and sufficiently strong thrust occurs only after heating the walls of the smoke tube, which requires considerable time, so that at the beginning of the air protesting is always missing. The coefficient of excess air at the same time less than one, and the smoke furnace ( fig. 2.). Conversely: At the end of the protood, the smoke tube remains hot, the thrust is preserved for a long time, although the firewood has already been almost burned (excess air coefficient is more than one). Metal furnaces with metal warmed flue pipes are faster to regime due to low heat capacity compared to brick trumpets.
Analysis of the processes in the chimney can be continued, but it is already so clear that no matter how good the furnace itself, all its advantages can be reduced to zero by a bad chimney. Of course, B. perfect version The smoke tube should be replaced modern system forced drawing flue gases using an electric fan with adjustable consumption and with pre-condensation of moisture from flue gases. Such a system, among other things, could clean the flue gases from soot, carbon monoxide and other harmful impurities, as well as cooling discharged flue gases and ensure heat recovery.
But all this is in a distant perspective. For a dacket and gardener, the smoke trumpet sometimes can become much more expensive than the oven itself, especially in the case of heating a multi-level house. Banned flue pipes are usually simpler and shorter, but the level of thermal power of the furnace can be very large. Such pipes, as a rule, are strongly launched along the entire length, they often fly out sparks and ashes, but condensate and soot falling insignificantly.
If you plan to use a bath building only as a bath, then the pipe can be made and tight. If the sauna is thinking by you and as a place of possible stay (temporary stay, overnight), especially in winter, then more expedient pipe Immediately do the insulated, and efficiently, "for life." The stoves can be changed at least every day, pick up the design of the dirty and in more detail, and the pipe will be the same.
At least if the stove works in mode long burning (Drying), then the insulation of the pipe is absolutely necessary, since at low facilities (1 - 5 kW), the tight metal pipe will become completely cold, the condensate will be abundantly flowing, which in the strongest frosts can even climb and overlap the pipe. This is especially dangerous in the presence of sparking mesh and umbrellas with small passing gaps. Incrochovers are suitable for intense proturtes in the summer and are extremely dangerous for weak burning modes of firewood in winter. Due to the possible clogging of ice pipes, the installation of deflectors and umbrellas on chimneys was banned in 1991 (and in chimneys gas furnaces even earlier).
According to the same reasons, it is not necessary to get involved in the height of the pipe - the level of thrust is not so important for unobormal bath Furnace. If it will simulate, you can always quickly ventilate the room. But the height above the ridge of the roof (not less than 0.5 m) should be observed to prevent tipping thrust during wind gusts. On the gentle roofs, the pipe should perform over the snow cover. In any case, it is better to have a pipe down, but warmer (what is higher, but colder). High pipes in winter are always cold and dangerous in operation.
Cold flue pipes have a lot of flaws. At the same time, tangled, but not very long pipes on metal furnaces during crossing heated quickly (much faster than brick pipes), remain hot with an energetic protostka and therefore in the baths (and not only in the baths) are used very widely, especially since they are relative to the cheap. Asbic cement pipes on metal furnaces are not used, as they have a lot of weight, and also destroy when overheating with the sprout of fragments.
Fig. 3. The simplest designs of metal flue pipes: 1 - metal round chimney; 2 - sparkling; 3 - cap to protect the pipe from atmospheric precipitation; 4 - rafters; 5 - Roof lambers; 6. - Drainy Brucki between rafters (or beams) for registration of firefare (cutting) in the roof or overlap (if necessary); 7 - roof rustle; 8 - soft roofing (rubberoid, hydrohotelloisol, soft tile, corrugated cardboard-bitumen sheets, etc.); 9 - Metal sheet for roof flooring and overlaping the outlet (allowed to use flat sheet Aceida - an asbocate electrical insulating board); 10 - metal drainage lining; 11 - asbestos sealing of the gap (joint); 12 - metal cap-otter; 13 - ceiling beams (with the filling of space by insulation); 14 - ceiling cover; 15 - the sex of the attic (if necessary); 16 - metal sheet ceiling cutting; 17 - metal reinforcing corners; 18 - metal cover of the ceiling cutting (if necessary); 19 - insulation non-combustible heat-resistant (ceramzit, sand, perlite, minvat); 20 - protective pad (metal sheet on a layer of asbestos cardboard with a thickness of 8 mm); 21 - Metal screen pipe.
a) non-flagged tube;
b) the heat-insulated shielded pipe with heat transfer resistance of at least 0.3 m 2 -Grad / W (which is equivalent to the brick thickness of 130 mm or the thickness of the insulation of the MINVATA type 20 mm).
On the fig. 3. Presented typical mounting schemes Digged metal pipes. The pipe itself should be purchased from stainless steel with a thickness of at least 0.7 mm. The most undercarriage diameter of the Russian pipe is 120 mm, Finnish - 115 mm.
According to GOST 9817-95, the cross-sectional area of \u200b\u200bthe multi-turn chimney should be at least 8 cm 2 per 1 kW of the nominal thermal power released in the firebox when burning firewood. This power should not be confused with the heat power of the oven, released from the outer brick surface of the furnace to the room by SNiP 2.04.05-91. This is one of our numerous misunderstandings. regulatory documents. Since heat-drying furnaces are usually littered only 2-3 hours a day, then the power in the furnace is about ten times the power of heat release from the surface of the brick furnace.
Next time we will talk about the features of the flood pipe mounting.
Heat combustion. The lowest heat combustion of dry gaseous fuel QF varies widely from 4 to 47 mJ / m3 and depends on its composition - the ratio and quality of combustible and non-combustible
Components. The smallest value of QF in the domain gas, the average composition of which is about 30% composed of combustible gases (mainly carbon oxide CO) and approximately 60% of non-combustible nitrogen N2. Most
The value of QF in associated gases, which is characterized by an increased content of heavy hydrocarbons. The heat of the combustion of natural gases varies in the narrow range QF \u003d 35.5 ... 37.5 MJ / M3.
The lower heat of the combustion of individual gases included in the composition of gaseous fuels is given in Table. 3.2. On methods for determining the heat of combustion of gaseous fuel, see section 3.
Density. There are absolute and relative gas density.
The absolute density of the RG gas, kg / m3, is the mass of gas, which comes on 1 m3 of this gas in this gas. When calculating the density of a separate gas, the volume of its kilometer is taken equal to 22.41 m3 (as for the perfect gas).
The relative gas density Rott is the ratio of the absolute gas density under normal conditions and similar air density:
Rott \u003d Rg / PV \u003d RG / 1,293, (6.1)
Where Rg, re - respectively, the absolute density of gas and air under normal conditions, kg / m3. The relative density of gases is usually used to compare various gases among themselves.
Values \u200b\u200bof absolute and relative density simple gases Led in Table. 6.1.
The density of the PJM gas mixture, kg / m3 is determined on the basis of the additivity rule, according to which the properties of gases are summed up by their volume fraction in the mixture:
Where xj is the volumetric content of the 7th gas in the fuel,%; (RG); - the density of the j-th gas included in the fuel, kg / m3; The number of individual gases in the fuel.
The values \u200b\u200bof the density of gaseous fuels are shown in Table. P.5.
The density of gases p, kg / m3, depending on temperature and pressure, can be calculated by the formula
Where P0 is the gas density under normal conditions (T0 \u003d 273 K and P0 \u003d 101.3 kPa), kg / m3; P and T-, respectively, valid pressure, kPa, and absolute gas temperature, K.
Almost all kinds of gaseous fuel are lighter than air, so when leakage, the gas accumulates under the floors. For security reasons before starting the boiler, the absence of gas is checked in the most likely places of its cluster.
Gas viscosity increases with increasing temperature. The values \u200b\u200bof the dynamic viscosity of the r, PA-C, can be calculated by the Siezer Empirical Equation - Lend
Table 6.1
Characteristics of gas fuel components (at T - O ° C CHR \u003d 101.3 kPa)
|
Chemical |
Molar mass m, |
Density |
Volume concentrate |
||
|
Name Gaza |
Absolute |
Relative |
Gas flammability limits in a mixture with air,% |
||
|
Combustible gases |
|||||
|
Propylene |
|||||
|
Carbon oxide |
|||||
|
Hydrogen sulfide |
|||||
|
Non-combustible gases |
|||||
|
Carbon dioxide |
|||||
|
sulphur dioxide |
|||||
|
Oxygen |
|||||
|
Air atmosphere. |
|||||
|
Water par |
Where P0 is the coefficient of the dynamic viscosity of the gas under normal conditions (g0 \u003d 273 K and P0 - 101.3 kPa), PA-C; T - absolute gas temperature, K; C is a coefficient depending on the type of gas, K, is accepted in Table. 6.2.
For a mixture of gases, the dynamic viscosity coefficient can be approximately determined by the viscosity values \u200b\u200bof individual components:
Where the GJ is a mass fraction of the j-th gas in fuel,%; The dynamic viscosity of the j-th component, PA-C; P is the number of individual gases in the fuel.
In practice, the coefficient of kinematic viscosity V, M2 / C, which
ry associated with dynamic viscosity p through the density p dependence
V \u003d p / p. (6.6)
Taking into account (6.4) and (6.6), the coefficient of kinematic viscosity V, m2 / s, depending on pressure and temperature, can be calculated by the formula
Where V0 is the coefficient of the kinematic viscosity of the gas under normal conditions (th \u003d 273 K and P0 \u003d 101.3 kPa), m2 / s; p and g-respectively valid pressure, kPa, and absolute gas temperature, k; C is a coefficient depending on the type of gas, K, is accepted in Table. 6.2.
The values \u200b\u200bof kinematic viscosity coefficients for gaseous fuels are shown in Table. P.9.
Table 6.2.
The viscosity and thermal conductivity coefficients of gas fuel components
(at t \u003d 0 ° С Ir \u003d 101.3 kPa)
|
Name Gaza |
Viscosity coefficient |
The coefficient of thermal conductivity of YO3, W / (M-K) |
Ceff seserld with, to |
|
|
Dynamic R-106, PA-C |
Kinematic V-106, m2 / s |
|||
|
Combustible gases |
||||
|
Propylene |
||||
|
Carbon oxide |
||||
|
Hydrogen sulfide |
||||
|
Non-combustible gases Carbon dioxide |
||||
|
Oxygen |
||||
|
Air atmospheric air |
||||
|
Water steam at 100 ° C |
Thermal conductivity. Molecular power transfer in gases is characterized by the thermal conductivity coefficient 'K, W / (M-K). The thermal conductivity coefficient is inversely proportional to the pressure and increases with increasing temperature. The values \u200b\u200bof the X coefficient can be calculated by the Formula of the Seorerand
Where X, 0 is the coefficient of thermal conductivity of the gas under normal conditions (g0 \u003d 273 K and PO \u003d 101.3 kPa), W / (M-K); P and T-, respectively, the valid pressure, kPa, and the absolute temperature of the gas, K; C is a coefficient depending on the type of gas, K, is accepted in Table. 6.2.
The values \u200b\u200bof thermal conductivity coefficients for gaseous fuels are shown in Table. P.9.
The heat capacity of the gaseous fuel classified by 1 m3 of dry gas depends on its composition and is generally defined as
4l \u003d 0. , 01 (CH2N2 + SS0 +
SSN4SH4 + CSO2Cog + - + Cx. X;), (6.9) where CH2, CRs0, schsch, ss02, ..., cx. - heat capacity of components of fuel components, respectively hydrogen, carbon monoxide, methane, carbon dioxide and / th component, KJ / (M3-K); H2, CO, CH4, C02, ..., xG--
The heat capacity of the combustible components of gaseous fuels is shown in Table. P.6, non-combustible - in table. P.7.
The heat capacity of wet gaseous fuel
SGGTL, KJ / (M3-K) is defined as
<тл = ctrn + 0,00124cHzq йтля, (6.10) где drTn- влагосодержание газообразного топлива,
Explosion. A mixture of combustible gas with air in certain proportions in the presence of fire or even sparks can explode, i.e., the process of its ignition and combustion at a speed close to the speed of sound propagation occurs. Explosive combustible gas concentrations in air depend on the chemical composition and gas properties. Volumetric concentration limits of ignition for individual combustible gases in the mixture with air are previously shown in Table. 6.1. Hydrogen has the widest limits of ignition (4 .. .74% by volume) and carbon oxide (12.5 ... 74%). For natural gas, the averaged lower and upper limits of ignition are 4.5 and 17%, respectively; for coke - 5.6 and 31%; For domain - 35 and 74%.
Toxicity. Under toxicity, the ability of gas to cause poisoning of living organisms. The degree of toxicity depends on the type of gas and its concentration. Most dangerous gas components in this respect are carbon monoxide and hydrogen sulfide H2S.
The toxicity of gas mixtures is mainly determined by the concentration of the most toxic component present in the mixture, with its harmful effect, as a rule, is noticeably enhanced in the presence of other harmful gases.
The presence and concentration in the air of harmful gases can be determined by a special instrument - a gas analyzer.
Almost all natural gases do not smell. To detect gas leakage and safety measures, natural gas before admission to the highway is odds, that is, is saturated with a substance having a sharp smell (for example, mercaptans).
The heat of combustion of various fuels fluctuates widely. For fuel oil, for example, it is over 40 mJ / kg, and for domain gas and some fuel flask brands - about 4 MJ / kg. The composition of energy fuels also varies widely. Thus, the same qualitative characteristics depending on the type and fuel brand can be sharply different between themselves quantitatively.
Specified fuel characteristics. For comparative analysis in the role of characteristics, generalizing the quality of fuel, the given fuel characteristics,% -KG / MJ, are used, which are generally calculated by the formula
Where hg is an indicator of the quality of work fuel,%; Q [- Specific heat combustion (lower), MJ / kg.
So, for example, to calculate the above
Humidity of sulfur sulfur s "p and
Nitrogen N ^ p (for the working condition of the fuel)
Formula (7.1) acquires the following form,% -KG / MJ:
Toc O "1-3" h z kp \u003d kl gt; (7.2)
4F \u003d l7e [; (7.3)
SNP. \u003d S '/ ї; (7.4)
^ p \u003d n7 q [. (7.5)
As a visual example, the following comparison is indicative of the incineration of various fuels in the boilers of the same thermal power. So, a comparison of the reduced humidity of the coal
Brands 2B (WјP \u003d 3.72% -KG / MJ) and Nazarov
2b coal (W ^ p \u003d 3.04% -KG / MJ) shows that in the first case the amount of moisture entered into the fuel boiler firebox will be about 1.2 times more than in the second, despite the fact that the working humidity in the coal near Moscow (W [\u003d 31%) is less than that
Nazarovsky coal (WF \u003d 39%).
Conditional fuel. In the energy sector to compare the efficiency of fuel use in various boiler installations, the concept of conditional fuel is introduced to plan the production and consumption of fuel in economic calculations. This fuel is accepted as a conditional fuel, the specific heat of the combustion (lower) of which in the operating state is equal to qy t \u003d 29300 kJ / kg (or
7000 kcal / kg).
For each natural fuel, there is a so-called dimensionless thermal equivalent E, which may be greater or less than one:
