Heat of combustion of sugar. Heat of combustion

I understand that polymers are a great variety of materials. I was confused by the dimension 18 kJ/kg, namely kiloJ/kg (taken from “Fire and explosion hazard of substances and materials and means of extinguishing them” Handbook ed. 2 edited by A.Ya. Korolchenko and D.A. Korolchenko, part I, p. 306, second from the top, if you don’t believe me, I can send it). That's actually why I was indignant.

All the fuss is due to the fact that on the doors of the warehouse, jam-packed with fuel, there is a big letter “D”. Well, when the internal audit saw it, it started cackling and flapping its wings (completely justified). I was burned - here is a guy who can count categories. Chief: "Count." OK. I came, tried them on, figured out the range of materials, looked at the ceiling, and there the amount of stored fuel was all indicated (well, sometimes you’re lucky), I did the math. They gave it to her - she (as I understand it, a former RTN inspector) said: how can you confirm the amount of stored materials. I told her: “What’s the difference in the world? The room is small - an AUPT is still not required. There is nothing explosive, and according to “B” the coolest is accepted. The fire barriers are all in place and satisfy even SP, even SNiP. And, most importantly, a warehouse consumables, full today, empty tomorrow." Well, she nodded her head, and then: “Where do you get the exact data on storage in kg?” I decided to change my mind. A fire inspector... Heh. I take a certificate from the warehouse manager: wood - 80 kg, rubber - 140 kg, felt 60 kg, cardboard 310 kg, etc. plus printing. I bring it to her: here is confirmation, try to refute it - the manager knows better what he has stored. She: “Oh! This is another thing - this is a document.” I'm crazy! Well, then I remembered about cartridges. And on Friday she needs to hand over this damn calculation and replace the letter on the gate. We have been spoiling paper for a week now, and at the same time, please note, we work in the same organization. That is, I am distracted from my direct responsibilities, we are doing some nonsense, getting paid, etc. for the sake of one letter on the gate. In short, everything is arranged very efficiently.

But this was a lyrical digression. My goal is to satisfy the auditor (a complete fraud). No one doubts that category B1, but she wants to see cartridges in the calculation. We both don’t know what they are made of. For every unconfirmed value of combustion heat, she snorts like a cat. Snaala didn’t even want to accept the railway VNTP as a certificate - like it doesn’t apply to us. Well, at least the arguments about universal submission to the laws of the universe in general and physics in particular had an effect. Therefore, I choose materials that are in reference literature or ND. Manufacturers claim (at least one, but as I talked to them - it’s a joke) that the toner contains graphite. I found it at Korolchenko’s, but it was written crookedly. Thank you, they told me the dimensions on the designers’ forum. I calmed down with this. Now I'm working on plastic. The cartridge body seems to be PVC, but for the same Korolchenko all PVC is white powder. It doesn't look like a cartridge at all. I found vinyl plastic, which is the result of various influences on PVC. HOORAY!!! But there 18 KILOJ/kg - well, it doesn’t fit into any gates. If it had been written there in human terms - MJ, then yesterday I would have calmed down.

The calorific value is understood as the heat of complete combustion of a unit mass of a substance. It takes into account heat losses associated with the dissociation of combustion products and the incompleteness of chemical combustion reactions. Calorific value is the maximum possible heat of combustion per unit mass of a substance.

Determine the calorific value of elements, their compounds and fuel mixtures. For elements, it is numerically equal to the heat of formation of the combustion product. The calorific value of mixtures is an additive quantity and can be found if the calorific value of the components of the mixture is known.

Combustion occurs not only due to the formation of oxides, therefore, in a broad sense, we can talk about the calorific value of elements and their compounds not only in oxygen, but also when interacting with fluorine, chlorine, nitrogen, boron, carbon, silicon, sulfur and phosphorus.

Calorific value is an important characteristic. It allows you to evaluate and compare with others the maximum possible heat release of a particular redox reaction and determine in relation to it the completeness of the actual combustion processes. Knowledge of the calorific value is necessary when selecting fuel components and mixtures for various purposes and when assessing their completeness of combustion.

There are higher H in and lower H n calorific value. Higher calorific value, in contrast to lower calorific value, includes the heat of phase transformations (condensation, solidification) of combustion products when cooled to room temperature. Thus, the highest calorific value is the heat of complete combustion of a substance when the physical state of the combustion products is considered at room temperature, and the lowest calorific value is at the combustion temperature. The higher calorific value is determined by burning the substance in a calorimetric bomb or by calculation. It includes, in particular, the heat released during the condensation of water vapor, which at 298 K is equal to 44 kJ/mol. The lower calorific value is calculated without taking into account the heat of condensation of water vapor, for example, using the formula

Where % H is the percentage of hydrogen in the fuel.

If calorific value values ​​indicate the physical state of the combustion products (solid, liquid or gaseous), then the “highest” and “lowest” subscripts are usually omitted.

Let us consider the calorific value of hydrocarbons and elements in oxygen per unit mass of the original fuel. The lower calorific value differs from the highest for paraffins by an average of 3220-3350 kJ/kg, for olefins and naphthenes - by 3140-3220 kJ/kg, for benzene - by 1590 kJ/kg. When experimentally determining the calorific value, it should be borne in mind that in a calorimetric bomb the substance burns at a constant volume, and in real conditions, often at a constant pressure. The correction for the difference in combustion conditions ranges from 2.1 to 12.6 for solid fuel, about 33.5 for fuel oil, 46.1 kJ/kg for gasoline, and reaches 210 kJ/m3 for gas. In practice, this correction is introduced only when determining the calorific value of the gas.

For paraffins, the calorific value decreases with increasing boiling point and increasing C/H ratio. For monocyclic alicyclic hydrocarbons this change is much less. In the benzene series, the calorific value increases when moving to higher homologues due to the side chain. Dinuclear aromatic hydrocarbons have a lower calorific value than the benzene series.

Only a few elements and their compounds have a calorific value that exceeds the calorific value of hydrocarbon fuels. These elements include hydrogen, boron, beryllium, lithium, their compounds and several organoelement compounds of boron and beryllium. The calorific value of elements such as sulfur, sodium, niobium, zirconium, calcium, vanadium, titanium, phosphorus, magnesium, silicon and aluminum lies in the range of 9210-32,240 kJ/kg. For the remaining elements of the periodic system, the calorific value does not exceed 8374 kJ/kg. Data on the gross calorific value of various classes of fuels are given in table. 1.18.

Table 1.18

Gross calorific value of various combustibles in oxygen (per unit mass of fuel)

Substance
Carbon monoxide
iso-butane
n-Dodecane
n-Hexadecane
Acetylene
Cyclopentane
Cyclohexane
Ethylbenzene
Beryllium
Aluminum
Zirconium
Beryllium hydride
Psntaboran
Metadiborane
Ethyldiborane

For liquid hydrocarbons, methanol and ethanol, heating values ​​are based on the liquid starting state.

The calorific value of some fuels was calculated on a computer. It is 24.75 kJ/kg for magnesium and 31.08 kJ/kg for aluminum (the state of the oxides is solid) and practically coincides with the data in Table. 1.18. The highest calorific value of paraffin C26H54, naphthalene C10H8, anthracene C14H10 and methenamine C6H12N4 are 47.00, 40.20, 39.80 and 29.80, respectively, and the lowest calorific value is 43.70, 39.00, 38.40 and 28.00 kJ/kg.

As an example, in relation to rocket fuels, we present the heats of combustion of various elements in oxygen and fluorine, per unit mass of combustion products. The heats of combustion are calculated for the state of combustion products at a temperature of 2700 K and are shown in Fig. 1.25 and in table. 1.19.

Puc. 1.25. Heat of combustion of elements in oxygen (1) and fluorine(2), calculated per kilogram of combustion products

As follows from the data presented, to obtain maximum combustion heat, the most preferred substances are those containing hydrogen, lithium and beryllium, and secondarily, boron, magnesium, aluminum and silicon. The advantage of hydrogen due to the low molecular weight of combustion products is obvious. It should be noted that beryllium has an advantage due to its high heat of combustion.

There is the possibility of the formation of mixed combustion products, in particular gaseous oxyfluorides of elements. Since oxyfluorides of trivalent elements are usually stable, most oxyfluorides are not effective as combustion products of rocket fuels due to their high molecular weight. The heat of combustion with the formation of COF2 (g) has an intermediate value between the heats of combustion of CO2 (g) and CF4 (g). The heat of combustion with the formation of SO2F2 (g) is greater than in the case of the formation of SO2 (g) or SF6; (G.). However, most rocket fuels contain highly reducing elements that prevent the formation of such substances.

The formation of aluminum oxyfluoride AlOF (g) releases less heat than the formation of oxide or fluoride, so it is not of interest. Boron oxyfluoride BOF (g) and its trimer (BOF)3 (g) are quite important components of the combustion products of rocket fuels. The heat of combustion to form BOF (g) is intermediate between the heats of combustion to form oxide and fluoride, but oxyfluoride is thermally more stable than either of these compounds.

Table 1.19

Heat of combustion of elements (in MJ/kg), per unit mass of combustion products ( T = 2700 K)

			oxyfluoride
Beryllium
Oxygen
Aluminum
Zirconium

When beryllium and boron nitrides are formed, a fairly large amount of heat is released, which allows them to be classified as important components of rocket fuel combustion products.

In table Table 1.20 shows the highest calorific value of elements when they interact with various reagents, referred to a unit mass of combustion products. The calorific value of elements when interacting with chlorine, nitrogen (except for the formation of Be3N2 and BN), boron, carbon, silicon, sulfur and phosphorus is significantly less than the calorific value of elements when interacting with oxygen and fluorine. The wide variety of requirements for combustion processes and reagents (in terms of temperature, composition, state of combustion products, etc.) makes it advisable to use the data in Table. 1.20 in the practical development of fuel mixtures for one purpose or another.

Table 1.20

Higher calorific value of elements (in MJ/kg) when interacting with oxygen, fluorine, chlorine, nitrogen, per unit mass of combustion products

• See also: Joulin S., Clavin R. Op. cit.

Chemical reactions are accompanied by the absorption or release of energy, in particular heat. reactions accompanied by the absorption of heat, as well as the compounds formed during this process, are called endothermic . In endothermic reactions, heating of the reacting substances is necessary not only for the occurrence of the reaction, but also during the entire time of their occurrence. Without external heating, the endothermic reaction stops.

reactions accompanied by the release of heat, as well as the compounds formed during this process, are called exothermic . All combustion reactions are exothermic. Due to the release of heat, they, having arisen at one point, are able to spread to the entire mass of reacting substances.

The amount of heat released during complete combustion of a substance and related to one mole, unit of mass (kg, g) or volume (m 3) of a combustible substance is called heat of combustion. The heat of combustion can be calculated from tabular data using Hess's law. Russian chemist G.G. Hess in 1840 discovered a law that is a special case of the law of conservation of energy. Hess's law is as follows: the thermal effect of a chemical transformation does not depend on the path along which the reaction occurs, but depends only on the initial and final states of the system, provided that the temperature and pressure (or volume) at the beginning and end of the reaction are the same.

Let's consider this using the example of calculating the heat of combustion of methane. Methane can be produced from 1 mole of carbon and 2 moles of hydrogen. When methane is burned, it produces 2 moles of water and 1 mole of carbon dioxide.

C + 2H 2 = CH 4 + 74.8 kJ (Q 1).

CH 4 + 2O 2 = CO 2 + 2H 2 O + Q horizon.

The same products are formed by the combustion of hydrogen and carbon. During these reactions, the total amount of heat released is 963.5 kJ.

2H 2 + O 2 = 2H 2 O + 570.6 kJ

C + O 2 = CO 2 + 392.9 kJ.

Since the initial and final products are the same in both cases, their total thermal effects must be equal according to Hess's law, i.e.

Q 1 + Q mountains = Q,

Q mountains = Q - Q 1. (1.11)

Therefore, the heat of combustion of methane will be equal to

Q mountains = 963.5 - 74.8 = 888.7 kJ/mol.

Thus, the heat of combustion of a chemical compound (or their mixture) is equal to the difference between the sum of the heats of formation of combustion products and the heat of formation of the burned chemical compound (or substances that make up the combustible mixture). Therefore, to determine the heat of combustion of chemical compounds, it is necessary to know the heat of their formation and the heat of formation of the products obtained after combustion.

Below are the heats of formation of some chemical compounds:

Aluminum oxide Al 2 O 3 ………		Methane CH 4 …………………………
Iron oxide Fe 2 O 3 …………		Ethane C 2 H 6 ……………………
Carbon monoxide CO………….		Acetylene C 2 H 2 ………………
Carbon dioxide CO2………		Benzene C 6 H 6 …………………
Water H 2 O ………………………….		Ethylene C 2 H 4 …………………
Water vapor H 2 O ……………		Toluene C 6 H 5 CH 3 …………….

Example 1.5 .Determine the combustion temperature of ethane if the heat of its formationQ 1 = 88.4 kJ. Let's write the combustion equation for ethane.

C 2 H 6 + 3.5O 2 = 2 CO 2 + 3 H 2 O + Qmountains.

For determiningQmountainsit is necessary to know the heat of formation of combustion products. the heat of formation of carbon dioxide is 396.9 kJ, and that of water is 286.6 kJ. Hence,Qwill be equal

Q = 2 × 396,9 + 3 × 286.6 = 1653.6 kJ,

and the heat of combustion of ethane

Qmountains= Q - Q 1 = 1653.6 - 88.4 = 1565.2 kJ.

The heat of combustion is experimentally determined in a bomb calorimeter and a gas calorimeter. There are higher and lower calorific values. Higher calorific value Q in is the amount of heat released during the complete combustion of 1 kg or 1 m 3 of a combustible substance, provided that the hydrogen contained in it burns to form liquid water. Lower calorific value Qn is the amount of heat released during the complete combustion of 1 kg or 1 m 3 of a combustible substance, provided that hydrogen is burned until water vapor is formed and the moisture of the combustible substance is evaporated.

The higher and lower heats of combustion of solid and liquid combustible substances can be determined using the formulas of D.I. Mendeleev:

where Q in, Q n - higher and lower calorific values, kJ/kg; W – content of carbon, hydrogen, oxygen, combustible sulfur and moisture in the combustible substance, %.

Example 1.6. Determine the lowest combustion temperature of sulfur fuel oil consisting of 82.5% C, 10.65% H, 3.1%Sand 0.5% O; A (ash) = 0.25%,W = 3%. Using the equation of D.I. Mendeleev (1.13), we obtain

=38622.7 kJ/kg

The lower calorific value of 1 m3 of dry gases can be determined by the equation

The lower calorific value of some flammable gases and liquids, obtained experimentally, is given below:

Hydrocarbons: methane………………………..
ethane …………………………
propane………………………
methyl………………….
ethyl…………………………
propyl………………………

The lower calorific value of some combustible materials, calculated from their elemental composition, has the following values:

Gasoline……………………		Synthetic rubber
Paper ……………………		Kerosene………………
Wood		Organic glass..
air-dry………..		Rubber ………………..
in building structures...		Peat ( W = 20 %) …….

There is a lower limit of calorific value, below which substances become incapable of combustion in the air atmosphere.

Experiments show that substances are non-flammable if they are not explosive and if their lower calorific value in air does not exceed 2100 kJ/kg. Consequently, the heat of combustion can serve as an approximate estimate of the flammability of substances. However, it should be noted that the flammability of solids and materials largely depends on their condition. Thus, a sheet of paper, easily ignited by the flame of a match, when applied to the smooth surface of a metal plate or concrete wall, becomes difficult to combust. Consequently, the flammability of substances also depends on the rate of heat removal from the combustion zone.

In practice, during the combustion process, especially in fires, the heat of combustion indicated in the tables is not completely released, since combustion is accompanied by underburning. It is known that petroleum products, as well as benzene, toluene, acetylene, i.e. substances rich

carbon, burn in fires with the formation of a significant amount of soot. Soot (carbon) can burn and produce heat. If it is formed during combustion, then, consequently, the combustible substance emits less heat than the amount indicated in the tables. For substances rich in carbon, the underburning coefficient h is 0.8 - 0.9. Consequently, in fires when burning 1 kg of rubber, not 33520 kJ can be released, but only 33520´0.8 = 26816 kJ.

Fire size is usually characterized by the area of ​​the fire. The amount of heat released per unit area of ​​fire per unit time is called heat of fire Q p

QP= Qnυ mh ,

Where υ m– mass burnout rate, kg/(m 2 ×s).

The specific heat of fire during internal fires characterizes the thermal load on the structures of buildings and structures and is used to calculate the fire temperature.

1.6. Combustion temperature

The heat released in the combustion zone is perceived by the combustion products, so they heat up to a high temperature. The temperature to which combustion products are heated during combustion is called combustion temperature . There are calorimetric, theoretical and actual combustion temperatures. The actual combustion temperature for fire conditions is called fire temperature.

The calorimetric combustion temperature is understood as the temperature to which the products of complete combustion are heated under the following conditions:

1) all the heat released during combustion is spent on heating the combustion products (heat loss is zero);

2) the initial temperatures of air and flammable substances are 0 0 C;

3) the amount of air is equal to the theoretically required (a = 1);

4) complete combustion occurs.

The calorimetric combustion temperature depends only on the composition of the combustible substance and does not depend on its quantity.

Theoretical temperature, in contrast to calorimetric temperature, characterizes combustion taking into account the endothermic process of dissociation of combustion products at high temperature

2СО 2 2СО + О 2 - 566.5 kJ.

2H 2 O2H 2 + O 2 - 478.5 kJ.

In practice, the dissociation of combustion products must be taken into account only at temperatures above 1700 0 C. During diffusion combustion of substances in fire conditions, the actual combustion temperatures do not reach such values, therefore, to assess fire conditions, only the calorimetric combustion temperature and the fire temperature are used. There is a distinction between internal and external fire temperatures. The internal fire temperature is the average temperature of the smoke in the room where the fire occurs. External fire temperature – flame temperature.

When calculating the calorimetric combustion temperature and the internal fire temperature, it is assumed that the lower heat of combustion Qn of a combustible substance is equal to the energy qg required to heat the combustion products from 0 0 C to the calorimetric combustion temperature

, - heat capacity of the components of combustion products (heat capacity of CO 2 is taken for a mixture of CO 2 and SO 2), kJ/(m 3 ? K).

In fact, not all the heat released during combustion under fire conditions is spent on heating the combustion products. Most of it is spent on heating structures, preparing flammable substances for combustion, heating excess air, etc. Therefore, the temperature of an internal fire is significantly lower than the calorimetric temperature. The combustion temperature calculation method assumes that the entire volume of combustion products is heated to the same temperature. In reality, the temperature at different points of the combustion center is not the same. The highest temperature is in the region of space where the combustion reaction occurs, i.e. in the combustion (flame) zone. The temperature is significantly lower in places where there are flammable vapors and gases released from the burning substance and combustion products mixed with excess air.

In order to judge the nature of temperature changes during a fire depending on various combustion conditions, the concept of average volumetric fire temperature was introduced, which is understood as the average value of the temperatures measured by thermometers at various points of the internal fire. This temperature is determined from experience.

The tables present the mass specific heat of combustion of fuel (liquid, solid and gaseous) and some other combustible materials. The following fuels were considered: coal, firewood, coke, peat, kerosene, oil, alcohol, gasoline, natural gas, etc.

List of tables:

During the exothermic reaction of fuel oxidation, its chemical energy is converted into thermal energy with the release of a certain amount of heat. The resulting thermal energy is usually called the heat of combustion of the fuel. It depends on its chemical composition, humidity and is the main one. The heat of combustion of fuel per 1 kg of mass or 1 m 3 of volume forms the mass or volumetric specific heat of combustion.

The specific heat of combustion of a fuel is the amount of heat released during the complete combustion of a unit mass or volume of solid, liquid or gaseous fuel. In the International System of Units, this value is measured in J/kg or J/m 3.

The specific heat of combustion of a fuel can be determined experimentally or calculated analytically. Experimental methods for determining calorific value are based on practical measurement of the amount of heat released when a fuel burns, for example in a calorimeter with a thermostat and a combustion bomb. For fuel with a known chemical composition, the specific heat of combustion can be determined using the periodic formula.

There are higher and lower specific heats of combustion. The higher calorific value is equal to the maximum amount of heat released during complete combustion of the fuel, taking into account the heat expended on the evaporation of moisture contained in the fuel. The lowest heat of combustion is less than the highest value by the amount of heat of condensation, which is formed from the moisture of the fuel and hydrogen of the organic mass, which turns into water during combustion.

To determine fuel quality indicators, as well as in thermal calculations usually use the lowest specific heat of combustion, which is the most important thermal and operational characteristic of the fuel and is shown in the tables below.

Specific heat of combustion of solid fuels (coal, firewood, peat, coke)

The table presents the values ​​of the specific heat of combustion of dry solid fuel in the dimension MJ/kg. Fuel in the table is arranged by name in alphabetical order.

Of the solid fuels considered, coking coal has the highest calorific value - its specific heat of combustion is 36.3 MJ/kg (or in SI units 36.3·10 6 J/kg). In addition, high calorific value is characteristic of hard coal, anthracite, charcoal and brown coal.

Fuels with low energy efficiency include wood, firewood, gunpowder, milling peat, and oil shale. For example, the specific heat of combustion of firewood is 8.4...12.5, and that of gunpowder is only 3.8 MJ/kg.

Specific heat of combustion of solid fuels (coal, firewood, peat, coke)

Fuel
Anthracite	26,8…34,8
Wood pellets (pellets)	18,5
Dry firewood	8,4…11
Dry birch firewood	12,5
Gas coke	26,9
Blast coke	30,4
Semi-coke	27,3
Powder	3,8
Slate	4,6…9
Oil shale	5,9…15
Solid rocket fuel	4,2…10,5
Peat	16,3
Fibrous peat	21,8
Milled peat	8,1…10,5
Peat crumb	10,8
Brown coal	13…25
Brown coal (briquettes)	20,2
Brown coal (dust)	25
Donetsk coal	19,7…24
Charcoal	31,5…34,4
Coal	27
Coking coal	36,3
Kuznetsk coal	22,8…25,1
Chelyabinsk coal	12,8
Ekibastuz coal	16,7
Freztorf	8,1
Slag	27,5

Specific heat of combustion of liquid fuels (alcohol, gasoline, kerosene, oil)

A table is given of the specific heat of combustion of liquid fuel and some other organic liquids. It should be noted that fuels such as gasoline, diesel fuel and oil have high heat release during combustion.

The specific heat of combustion of alcohol and acetone is significantly lower than traditional motor fuels. In addition, liquid rocket fuel has a relatively low calorific value and, with complete combustion of 1 kg of these hydrocarbons, an amount of heat will be released equal to 9.2 and 13.3 MJ, respectively.

Specific heat of combustion of liquid fuels (alcohol, gasoline, kerosene, oil)

Fuel	Specific heat of combustion, MJ/kg
Acetone	31,4
Gasoline A-72 (GOST 2084-67)	44,2
Aviation gasoline B-70 (GOST 1012-72)	44,1
Gasoline AI-93 (GOST 2084-67)	43,6
Benzene	40,6
Winter diesel fuel (GOST 305-73)	43,6
Summer diesel fuel (GOST 305-73)	43,4
Liquid rocket fuel (kerosene + liquid oxygen)	9,2
Aviation kerosene	42,9
Kerosene for lighting (GOST 4753-68)	43,7
Xylene	43,2
High sulfur fuel oil	39
Low sulfur fuel oil	40,5
Low-sulfur fuel oil	41,7
Sulphurous fuel oil	39,6
Methyl alcohol (methanol)	21,1
n-Butyl alcohol	36,8
Oil	43,5…46
Methane oil	21,5
Toluene	40,9
White spirit (GOST 313452)	44
Ethylene glycol	13,3
Ethyl alcohol (ethanol)	30,6

Specific heat of combustion of gaseous fuels and combustible gases

A table is presented of the specific heat of combustion of gaseous fuel and some other combustible gases in the dimension MJ/kg. Of the gases considered, it has the highest mass specific heat of combustion. The complete combustion of one kilogram of this gas will release 119.83 MJ of heat. Also, fuel such as natural gas has a high calorific value - the specific heat of combustion of natural gas is 41...49 MJ/kg (for pure gas it is 50 MJ/kg).

Specific heat of combustion of gaseous fuel and combustible gases (hydrogen, natural gas, methane)

Fuel	Specific heat of combustion, MJ/kg
1-Butene	45,3
Ammonia	18,6
Acetylene	48,3
Hydrogen	119,83
Hydrogen, mixture with methane (50% H 2 and 50% CH 4 by weight)	85
Hydrogen, mixture with methane and carbon monoxide (33-33-33% by weight)	60
Hydrogen, mixture with carbon monoxide (50% H 2 50% CO 2 by weight)	65
Blast furnace gas	3
Coke Oven Gas	38,5
Liquefied hydrocarbon gas LPG (propane-butane)	43,8
Isobutane	45,6
Methane	50
n-Butane	45,7
n-Hexane	45,1
n-Pentane	45,4
Associated gas	40,6…43
Natural gas	41…49
Propadiene	46,3
Propane	46,3
Propylene	45,8
Propylene, mixture with hydrogen and carbon monoxide (90%-9%-1% by weight)	52
Ethane	47,5
Ethylene	47,2

Specific heat of combustion of some combustible materials

A table is provided of the specific heat of combustion of some combustible materials (wood, paper, plastic, straw, rubber, etc.). Materials with high heat release during combustion should be noted. Such materials include: rubber of various types, expanded polystyrene (foam), polypropylene and polyethylene.

Specific heat of combustion of some combustible materials

Fuel	Specific heat of combustion, MJ/kg
Paper	17,6
Leatherette	21,5
Wood (bars with 14% moisture content)	13,8
Wood in stacks	16,6
Oak wood	19,9
Spruce wood	20,3
Wood green	6,3
Pine wood	20,9
Capron	31,1
Carbolite products	26,9
Cardboard	16,5
Styrene butadiene rubber SKS-30AR	43,9
Natural rubber	44,8
Synthetic rubber	40,2
Rubber SKS	43,9
Chloroprene rubber	28
Polyvinyl chloride linoleum	14,3
Double-layer polyvinyl chloride linoleum	17,9
Polyvinyl chloride linoleum on a felt basis	16,6
Warm-based polyvinyl chloride linoleum	17,6
Fabric-based polyvinyl chloride linoleum	20,3
Rubber linoleum (Relin)	27,2
Paraffin paraffin	11,2
Foam plastic PVC-1	19,5
Foam plastic FS-7	24,4
Foam plastic FF	31,4
Expanded polystyrene PSB-S	41,6
Polyurethane foam	24,3
Fiberboard	20,9
Polyvinyl chloride (PVC)	20,7
Polycarbonate	31
Polypropylene	45,7
Polystyrene	39
High pressure polyethylene	47
Low-pressure polyethylene	46,7
Rubber	33,5
Ruberoid	29,5
Channel soot	28,3
Hay	16,7
Straw	17
Organic glass (plexiglass)	27,7
Textolite	20,9
Tol	16
TNT	15
Cotton	17,5
Cellulose	16,4
Wool and wool fibers	23,1

Sources:

1. GOST 147-2013 Solid mineral fuel. Determination of the higher calorific value and calculation of the lower calorific value.
2. GOST 21261-91 Petroleum products. Method for determining the higher calorific value and calculating the lower calorific value.
3. GOST 22667-82 Natural flammable gases. Calculation method for determining the calorific value, relative density and Wobbe number.
4. GOST 31369-2008 Natural gas. Calculation of calorific value, density, relative density and Wobbe number based on component composition.
5. Zemsky G. T. Flammable properties of inorganic and organic materials: reference book M.: VNIIPO, 2016 - 970 p.

First of all, let’s define the terms, since the question is not posed quite correctly.

, and you won’t find a list “cable type - value in MJ/m2”, it doesn’t exist and cannot exist. Specific fire load is calculated for indoors, in which different types and quantities of cable are laid, taking into account how much area they occupy. That is why the specific fire load dimension is Joules (Megajoules) per square meter.

The calculation of the specific fire load includes the quantities of different materials that create this fire load - in fact, everything that can burn. You write about the weight of one linear meter of cable, but in fact you need to take into account the mass flammable components in the cable, not the entire cable. It is the combustible mass that forms the fire load - mainly cable insulation.

There are no amendments to the wording of the third paragraph; it is correct.

All these terms, indicators and values ​​are used in the “Method for determining the categories of premises B1 - B4”, as described by the documents of the Ministry of Emergency Situations “On approval of the set of rules “Determination of categories of premises, buildings and external installations for explosion and fire hazards”, mandatory Appendix B. That The same approach is used in other regulatory documents, including departmental instructions. Below are excerpts from the document relevant to your question and our comments.

According to explosion and fire hazard, premises are divided into categories A, B, B1 - B4, D and D, and buildings - into categories A, B, C, D and D.

[Comment from the consultation section]: your question is about premises, we give a classification for them.

Room category	Characteristics of substances and materials located (circulating) in the premises
A increased explosion and fire hazard	Combustible gases, flammable liquids with a flash point of not more than 28°C in such quantities that they can form explosive vapor-gas-air mixtures, upon ignition of which a calculated excess explosion pressure in the room develops exceeding 5 kPa, and (or) substances and materials capable of exploding and burn when interacting with water, atmospheric oxygen or with each other, in such quantities that the calculated excess pressure of the explosion in the room exceeds 5 kPa.
B explosion and fire hazard	Combustible dusts or fibers, flammable liquids with a flash point of more than 28°C, flammable liquids in such quantities that they can form explosive dust-air or steam-air mixtures, the ignition of which develops a calculated excess explosion pressure in the room exceeding 5 kPa.
B1 – B4 fire hazard	Flammable and low-flammable liquids, solid flammable and low-flammable substances and materials (including dust and fibers), substances and materials that can only burn when interacting with water, air oxygen or with each other, provided that the rooms in which they are located (apply) do not belong to category A or B.
G moderate fire hazard	Non-combustible substances and materials in a hot, incandescent or molten state, the processing of which is accompanied by the release of radiant heat, sparks and flames, and (or) flammable gases, liquids and solids that are burned or disposed of as fuel.
D reduced fire hazard	Non-flammable substances and materials in a cold state.

Classification of a room into category B1, B2, B3 or B4 is carried out depending on the quantity and method of placing the fire load in the specified room and its space-planning characteristics, as well as on the fire hazardous properties of the substances and materials that make up the fire load.

[Comment from the consultation section]: your case includes categories B1 – B4, fire hazard. Moreover, there is a high probability that your premises will be classified as category B4, but this must be supported by calculations.

Methods for determining categories of premises B1 - B4

Determination of categories of premises B1 - B4 is carried out by comparing the maximum value of the specific temporary fire load (hereinafter referred to as the fire load) in any of the areas with the value of the specific fire load given in the table:

Specific fire load and placement methods for categories B1 – B4

For a fire load that includes various combinations (mixtures) of flammable, combustible, low-flammable liquids, solid flammable and low-flammable substances and materials within a fire-hazardous area, the fire load Q (in MJ) is determined by the formula:

- quantity i th material fire load, kg;

- net calorific value i th material fire load, MJ/kg.

(in MJ/m2) is defined as the ratio of the calculated fire load to the occupied area:

Where S– fire load placement area, m2, not less than 10 m2.

Part 2. Application practice

To perform calculations, it is necessary to determine the mass in kg for each combustible material that will be located in the room. Strictly speaking, for this you need to know how much insulation and other combustible components are in each meter of cable of the corresponding type, and take the footage from your project. But conventional product specifications, at best, contain a linear weight in g/m or kg/km for the cable as a whole; it is formed by all elements, including non-flammable ones. Only packaging – reel or box – is excluded from the net value.

In optical cables that do not have armor or built-in supporting metal cables, one can agree with this and use the linear weight in the calculations as is, deliberately neglecting the mass of the quartz fiber, since it is small. Here, for example, are the linear weights for universal XGLO™ and LightSystem cables with a tight buffer, intended for indoor/external use (the article begins with the symbols 9GD(X)H......, such cables are in your list):

Number of fibers	Linear weight, kg/km
4	23
6	25
8	30
12	35
16	49
24	61
48	255
72	384

And this is a table for XGLO™ and LightSystem cables with a free buffer, also intended for indoor/external use (the article begins with the symbols 9GG(X)H......):

Number of fibers	Linear weight, kg/km
2	67
4	67
6	67
8	67
12	67
16	103
24	103
36	103
48	115
72	115
96	139
144	139

So, if a 25 m long section of ten cables of 24 fibers each is laid in a room, their total weight will be 15.25 kg for a cable with a tight buffer and 25.75 kg for a cable with a loose buffer. As you can see, the numbers may vary, and for large quantities of cable the difference can be quite significant.

In armored optical cables and twisted pair copper cables, a significant proportion of the linear weight is formed by the mass of metal, and then the spread of numbers and the difference between the linear weight and the content of flammable substances can be even greater. For example, the net weight of 1 km of twisted pair cable can vary from 21 kg to 76 kg depending on the category, manufacturer and the presence/absence of a screen and other structural elements. At the same time, a simple calculation shows that for category 5e with a core diameter of 0.511 mm, the minimum weight of copper in 1 km (8 conductors, copper density 8920 kg/m3) will be 14.6 kg, and for category 7A with a core diameter of 0.643 mm - not less than 23.2 kg. And this does not take into account the laying, which leads to the fact that in fact the length of the copper conductors will obviously be more than 1 km.

On the same section of 25 m of, say, 120 twisted pair cables, the total mass of the cables can be from 63 kg to 228 kg depending on their type, while the copper in them can be from 43.8 kg and higher for category 5e and from 69.6 kg and above for category 7A.

The difference is large even for the quantities that we took, meaning not the largest telecommunications room, into which the cable is routed through a suspended tray or route under the raised floor. For armored and other specific cables with metal structural elements, the difference will be much greater, but at the same time they can be found mainly on the street, and not indoors.

If you take the calculation strictly, then for each type of cable you need to have a complete breakdown of the flammable and non-flammable components included in it and their weight content per unit length. In addition, the lower heating value in MJ/kg must be known for each combustible component. For polymers widely used in telecommunications, various sources give the following net calorific value values:

• Polyethylene – from 46 to 48 MJ/kg
• Polyvinyl chloride (PVC) – from 14 to 21 MJ/kg
• Polytetrafluoroethylene (fluoroplastic) – from 4 to 8 MJ/kg

Depending on what input data you use, the output may vary. Here are 2 examples of calculations for the already mentioned room with 120 twisted pair cables:

Example 1.

• 120 cables twisted pair category 5e
• Linear cable weight 23 kg/km

Total cable weight (excluding non-combustible components)

G i= 120 · 25 m · 23 · 10 -3 kg/m = 69 kg

Q= 69 kg · 18 MJ/kg = 1242 MJ

S tray= 25 m · 0.3 m = 7.5 m 2

g= 1242 / 10 = 124.2 MJ/m 2

The specific fire load refers to the range from 1 to 180 MJ/m 2, despite the fact that we have not subtracted the weight content of copper in the cable. If it had been subtracted, then the premises would have been classified as category B4.

Example 2.

• 120 twisted pair cables category 6/6A
• Wire gauge 23 AWG
• PVC sheath, lower calorific value 18 MJ/kg
• Linear cable weight 45 kg/km
• Tray length 25 m, width 300 mm

Total cable weight excluding non-combustible components

G i= 120 · 25 m · 45 · 10 -3 kg/m = 135 kg

Q= 135 kg · 18 MJ/kg = 2430 MJ

S tray= 25 m · 0.3 m = 7.5 m 2

In accordance with the calculation methodology, it is necessary to use an area of ​​at least 10 m 2 in the calculations.

g= 2430 / 10 = 243 MJ/m2

The specific fire load exceeded 180 MJ/m2 and fell into the range corresponding to the higher room category B3. But if we subtracted the weight of the copper, the calculation would be different.

23 AWG conductor gauge corresponds to a diameter of 0.574 mm. The cable has 8 copper conductors, therefore, each kilometer of cable contains at least 18.46 kg of copper.

G i= 120 · 25 m · (45 – 18.46) · 10 -3 kg/m = 79.62 kg of combustible components

Q= 79.62 kg 18 MJ/kg = 1433.16 MJ

g= 1433.16 / 10 = 143.3 MJ/m2

In this case, we get room category B4. As you can see, the component component can influence the calculations quite significantly.

Accurate data on weight content and lower calorific value can only be obtained from the manufacturer of a specific product. Otherwise, you will have to personally “gut” each specific type of cable, measure the mass of each element on high-precision scales, and establish all the chemical compositions (which in itself can be a very non-trivial task, even if you have a well-equipped chemical laboratory). And after all this, make an accurate calculation. For category 6/6A cable, in our calculation, for example, the weight and material of the separator partition were not taken into account. If it is made of polyethylene, you need to take into account that its lower calorific value is higher than that of PVC.

Chemical and physical reference books provide values ​​for the lower calorific value for pure substances and indicative values ​​for the most popular building materials. But manufacturers can use mixtures of substances, additives, and vary the weight content of components. For accurate calculations, data from a specific manufacturer is needed for each type of product. They are usually not publicly available, but they should be provided upon request; this is not classified information.

However, if you have to wait a long time for such information, and you need to do the calculation now, you can perform approximate calculations, setting the maximum values ​​- i.e. take the worst case scenario. The designer chooses the maximum possible value of the lower calorific value, the maximum weight content of combustible substances, deliberately making a big mistake, not in his favor. In some cases, because of this, the premises will fall into a more dangerous category, as we first did in Example 2. It is absolutely impossible to “err” in the other direction, deliberately making the calculations more optimistic. In case of any doubt, the interpretation should always be in the direction of additional security measures.