The heat capacity of complete combustion products in the stoichiometric volume of air. Coursework: Calculation of the Recycling Recycling Recycling Gas Technological Furnaces The Physical Properties of flue gases Table
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 intensively burning firewood, the more hot flue gasesThe 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.
Let us explain it a 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 up not very fast, then the likelihood is not excluded that heavy outer air can simply drown in the light gas and create a falling downstream 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 are displayed through the flue tube 6. If the cross section of the pipe is large (or the flux of flue gas movement), then as a result of any fluctuations in the pipe begins to penetrate the cold atmospheric air 7, achieving even the 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, in the perfect version, the smoke pipe would have to replace modern system Forced flushing exhaust with 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 bath is thinking by you and as a place of possible stay (temporary residence, overnight), especially in winter, then it is more expedient to immediately do the insulated, and qualitatively, "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 pipes Ice, the installation of deflectors and umbrellas on chimney pipes was banned in 1991 (and in chimneys gas furnaces even earlier).
According to the same considerations, it is not necessary to get involved in the pipe height - the level of thrust is not so important for a non-free bath oven. 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 extractors heated quickly (much faster than brick pipes), remain hot with an energetic protest and therefore in the baths (and not only in the baths) are used very widely, especially since They are relatively 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; eight - soft roof (rubberoid, hydrokhotloizol, soft tile, corrugated cardboard-bitumen sheets, etc.); 9 - Metal sheet for roof flooring and overlap of the outlet (it is allowed to use a flat sheet of an aceida - an asbo-cement 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 of tangled 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.
2. Heat carried away by leaving gases. We define the heat capacity of the flue gases at Tukh \u003d 8000s;
3. Heat loss through the thermal conductivity masonry.
Losses via arch
The thickness of the arch is 0.3 m, the material shaft. We accept that temperature internal surface 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 * 0c)
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 average temperature Chamot will be equal to 5500C, and diatomitia 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
The choice and calculation of the burner
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 calculated number 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))
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 is formed a large number of Water vapor, sometimes exceeding the volume C02. The presence of moisture in the top
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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.
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.
The values \u200b\u200bof the absolute and relative density of simple gases are shown 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 |
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|
Name Gaza |
Absolute |
Relative |
Gas flammability limits in a mixture with air,% |
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Combustible gases |
|||||
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Propylene |
|||||
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Carbon oxide |
|||||
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Hydrogen sulfide |
|||||
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Non-combustible gases |
|||||
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Carbon dioxide |
|||||
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sulphur dioxide |
|||||
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Oxygen |
|||||
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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 |
|
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Dynamic R-106, PA-C |
Kinematic V-106, m2 / s |
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Combustible gases |
||||
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Propylene |
||||
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Carbon oxide |
||||
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Hydrogen sulfide |
||||
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Non-combustible gases Carbon dioxide |
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Oxygen |
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Air atmospheric air |
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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:
