An important thermotechnical characteristic of fuel is its specific heat of combustion.

Specific heat of combustion of fuel

Distinguish between specific higher and lower calorific value. Specific heat combustion of the working fuel, taking into account the additional heat that is released during the condensation of water vapor located in the combustion products, is called higher specific calorific value of working fuel. This additional amount of heat can be determined by multiplying the mass of water vapor generated from the evaporation of fuel moisture /100 and from the combustion of hydrogen 9 /100 , for the latent heat of condensation of water vapor, equal to approximately 2500 kJ / kg.

Specific lower heating value of fuel – the amount of heat that is released under normal practical conditions, i.e. when water vapor does not condense, but is released into the atmosphere.

Thus the relationship between higher and lower specific heat of combustion can be expressed by the equation - = =25(9 ).

64. Conditional fuel.

fuel is any substance that, during combustion (oxidation), releases a significant amount of heat per unit mass or volume and is available for mass use.

Natural and derivative organic compounds in solid, liquid and gaseous states are used as fuel.

Any organic fuel consists of carbon, hydrogen, oxygen, nitrogen, volatile sulfur, while solid and liquid fuels consist of ash (mineral residues) and moisture.

An important thermotechnical characteristic of fuel is its specific heat of combustion.

Specific heat of combustion of fuel is the amount of heat that is released during the complete combustion of a unit amount of fuel substance.

The lower the specific heat of combustion of the fuel, the more it is consumed in the boiler unit. For comparison various kinds fuel, according to their thermal effect, the concept of conventional fuel was introduced, the specific heat of combustion of which was taken = 29.3 MJ / kg.

The ratio of Q N R of this fuel to Q sp of standard fuel is called the equivalent of E. Then the conversion of the consumption of natural fuel V N into standard fuel V UT is carried out according to the formula:

Conditional fuel- the unit of accounting for fossil fuels, that is, oil and its derivatives, natural and specially obtained during the distillation of shale and coal, gas, peat, adopted in calculations, which is used to calculate the useful action of various types of fuel in their total accounting.

In the USSR and Russia per unit reference fuel(c.u.) was accepted calorific value 1 kg of coal = 29.3 MJ or 7000 kcal. International Energy Agency ( IEA) took the unit of oil equivalent, usually denoted by the abbreviation TOE(English . Tonne of oil equivalent). One tonne of oil equivalent equals 41.868 GJ or 11.63 MWh. The unit is also used - a barrel of oil equivalent ( BOE).

65. Excess air coefficient.

The number showing how many times the actual air flow is greater than the theoretically required amount of air is called excess air coefficient, i.e. actual air flow L (in kg/kg) or V (m 3 / m 3) is equal to its theoretically required amount L o or V o > multiplied by the coefficient of excess air a

V= aV 0 .

Calculations of the cost of 1 kWh:

• Diesel fuel. The specific heat of combustion of diesel fuel is 43 mJ/kg; or, taking into account the density of 35 mJ / liter; taking into account the efficiency of a diesel fuel boiler (89%), we get that when burning 1 liter, 31 mJ of energy is generated, or in more familiar units 8.6 kWh.
  • The cost of 1 liter of diesel fuel is 20 rubles.
  • The cost of 1 kWh of diesel fuel combustion energy is 2.33 rubles.

• Propane-butane mix SPBT(Liquefied hydrocarbon gas SUG). The specific calorific value of LPG is 45.2 mJ/kg or, taking into account the density, 27 mJ/liter, taking into account the efficiency gas boiler 95%, we get that when burning 1 liter, 25.65 mJ of energy is generated, or in more familiar units - 7.125 kWh.
  • The cost of 1 liter of LPG is 11.8 rubles.
  • The cost of 1 kWh of energy is 1.66 rubles.

The difference in the price of 1 kW of heat obtained from the combustion of diesel and LPG turned out to be 29%. The above figures show that liquefied gas is more economical of the listed heat sources. To get a more accurate calculation, you need to put the current energy prices.

Features of use liquefied gas and diesel fuel

DIESEL FUEL. There are several varieties that differ in sulfur content. But for the boiler, this is not very important. But the division into winter and summer diesel fuel is important. The standard establishes three main grades of diesel fuel. The most common is summer (L), the range of its application is from O ° C and above. Winter diesel fuel(3) apply when negative temperatures air (up to -30°С). With more low temperatures arctic (A) diesel fuel should be used. hallmark diesel fuel is its cloud point. In fact, this is the temperature at which the paraffins contained in diesel fuel begin to crystallize. It really becomes cloudy, and with a further decrease in temperature, it becomes like jelly or frozen fatty soup. The smallest crystals of paraffin clog the pores of fuel filters and safety nets, settle in the pipeline channels and paralyze the work. For summer fuel, the cloud point is -5°C, and for winter fuel it is -25°C. An important indicator, which must be indicated in the passport for diesel fuel, is the maximum filterability temperature. Turbid diesel fuel can be used up to the filterability temperature, and then - a clogged filter and a fuel cutoff. Winter diesel fuel does not differ from summer diesel either in color or smell. So it turns out that only God (and the tanker) knows what is actually flooded. Some craftsmen mix summer diesel fuel with BGS (gasoline gas) and other vodka, achieving a lower filtering temperature, which is fraught with both pump failure and simply an explosion due to the fact that this infernal bodyagi has a reduced flash point. Also, instead of diesel, light heating oil can be supplied, outwardly it does not differ, but it contains more impurities, moreover, those that are not in diesel at all. Which is fraught with contamination of the fuel equipment and its not cheap cleaning. From the foregoing, we can conclude that if you purchase a diesel engine at a low price, from individuals or unverified organizations, you can get repaired or unfreeze the heating system. The price of diesel fuel, delivered to your home, fluctuates by a ruble from the prices at gas stations, both up and down depending on the remoteness of your cottage and the amount of fuel transported, everything that is cheaper should alert you if you are not extreme , and do not be afraid to spend the night in a cooling house in 30 degree frost.

LIQUEFIED GAS. As with diesel fuel, there are several grades of SPBT that differ in the composition of the mixture of propane and butane. Winter mix, summer and arctic. The winter mixture is 65% propane, 30% butane and 5% gas impurities. The summer mixture consists of 45% propane, 50% butane, 5% gas impurities. Arctic blend - 95% propane and 5% impurities. A mixture of 95% butane and 5% impurities can be supplied, such a mixture is called household. A very small amount of a sulfurous substance, an odorant, is added to each mixture in order to create a "gas smell". From the point of view of combustion and the effect on the equipment, the composition of the mixture has practically no effect. Butane, although much cheaper, is slightly better for heating than propane - it has more calories, but it has a very big drawback that makes it difficult to use it in Russian conditions - butane stops evaporating and remains liquid at zero degrees. If you have an imported tank with a low neck or a vertical one (the depth of the evaporation mirror is less than 1.5 meters) or is in a plastic sarcophagus that impairs heat transfer, then in prolonged frosts the tank may stop the evaporation of butane, not only due to frost, but also from - due to insufficient heat transfer (during evaporation, the gas cools itself). At temperatures below 3 degrees Celsius, imported containers made for the conditions of Germany, the Czech Republic, Italy, Poland, with intensive evaporation, stop producing gas after all the propane has evaporated, and only butane remains.

Now let's compare the consumer properties of LPG and diesel fuel

The use of LPG is 29% cheaper than diesel fuel. The quality of LPG does not affect its consumer properties when using AvtonomGas tanks, moreover than more content butane in the mixture, the better it works gas equipment. Low-quality diesel fuel can lead to serious damage heating equipment. The use of liquefied gas will relieve you of the presence of the smell of diesel fuel in the house. Liquefied gas contains less toxic sulfur compounds and, as a result, there is no air pollution on your personal plot. From liquefied gas, not only the boiler can work for you, but also gas stove, as well as a gas fireplace and a gas electric generator.

In addition to the main components, coal contains various non-combustible ash-forming additives, “rock”. Ash pollutes environment and sintered into slag on the grate, which makes it difficult to burn coal. In addition, the presence of rock reduces the specific heat of combustion of coal. Depending on the variety and conditions of extraction, the amount minerals varies greatly, the ash content of hard coal is about 15% (10–20%).
Another harmful component of coal is sulfur. During the combustion of sulfur, oxides are formed, which in the atmosphere turn into sulfuric acid. The sulfur content in the coal that we supply to customers through our network of representatives is about 0.5%, which is a very low value, which means that the ecology of your home will be saved.
The main indicator of any fuel - specific heat of combustion. For coal, this figure is:

These figures refer to coal concentrate. Actual numbers may differ significantly. So, for ordinary coal, which can be bought at coal depots, the value of 5000-5500 kcal / kg is indicated. We use 5300 kcal/kg in our calculations.
The density of coal is from 1 to 1.7 (hard coal - 1.3–1.4) g / cm 3, depending on the type and content of minerals. Also used in technology bulk density”, it is about 800-1,000 kg / m 3.

Types and grades of coal

Coal is classified according to many parameters (geography of production, chemical composition), but from a “household” point of view, when buying coal for use in furnaces, it is enough to understand the labeling and the possibility of using it in Thermorobot.

According to the degree of coalification, there are three types of coal: brown, stone And anthracite. The following coal designation system is used: Variety = (brand) + (size).

In addition to the main grades listed in the table, intermediate grades of hard coal are also distinguished: DG (long-flame gas), GZh (fat gas), KZh (coke fat), PA (semi-anthracite), brown coals are also divided into groups.
Coking grades of coal (G, coke, Zh, K, OS) are practically not used in thermal power engineering, since they are a scarce raw material for the coking industry.
According to the size class (size of pieces, fraction), high-quality coal is divided into:

In addition to sized coal, combined fractions and screenings are on sale (PC, KO, OM, MS, SSH, MSSh, OMSSH). The size of the coal is determined based on the smaller value of the smallest fraction and the larger value of the largest fraction indicated in the name of the coal grade.
For example, the OM fraction (M - 13–25, O - 25-50) is 13–50 mm.

In addition to these types of coal, coal briquettes can be found on sale, which are pressed from low-enriched coal sludge.

How coal burns

Coal consists of two combustible components: volatiles And solid (coke) residue.

At the first stage of combustion, volatile substances are released; with an excess of oxygen, they quickly burn out, giving a long flame, but a small amount of heat.

After that, the coke residue burns out; the intensity of its combustion and the ignition temperature depend on the degree of coalification, that is, on the type of coal (brown, stone, anthracite).
The higher the degree of coalification (anthracite has the highest), the higher the ignition temperature and calorific value, but the lower the combustion intensity.

Coal grades D, G

Due to the high content of volatile substances, such coal quickly flares up and burns quickly. Coal of these grades is available and suitable for almost all types of boilers, however, for complete combustion, this coal must be supplied in small portions so that the released volatile substances have time to fully combine with atmospheric oxygen. Complete combustion of coal is characterized by a yellow flame and clear flue gases; incomplete combustion of volatile substances gives a crimson flame and black smoke.
For efficient combustion of such coal, the process must be constantly monitored; this mode of operation is implemented in the Thermorobot automatic boiler house.

Grade A coal

It is more difficult to kindle it, but it burns for a long time and releases much more heat. Coal can be loaded in large batches, since they burn mainly coke residue, there is no mass release of volatile substances. The blowing mode is very important, since with a lack of air, combustion occurs slowly, it may stop, or, conversely, an excessive increase in temperature, leading to heat loss and burnout of the boiler.

5. THERMAL BALANCE OF COMBUSTION

Consider calculation methods heat balance combustion process of gaseous, liquid and solid fuels. The calculation is reduced to solving the following problems.

· Determination of heat of combustion (calorific value) of fuel.

· Determination of the theoretical combustion temperature.

5.1. HEAT OF BURNING

Chemical reactions are accompanied by the release or absorption of heat. When heat is released, the reaction is called exothermic, and when it is absorbed, it is called endothermic. All combustion reactions are exothermic, and combustion products are exothermic compounds.

Released (or absorbed) during the course chemical reaction heat is called the heat of reaction. In exothermic reactions it is positive, in endothermic reactions it is negative. The combustion reaction is always accompanied by the release of heat. Heat of combustion Q g(J / mol) is the amount of heat that is released during the complete combustion of one mole of a substance and the transformation of a combustible substance into products of complete combustion. The mole is the basic SI unit for the amount of a substance. One mole is such an amount of a substance that contains as many particles (atoms, molecules, etc.) as there are atoms in 12 g of the carbon-12 isotope. The mass of an amount of a substance equal to 1 mole (molecular or molar mass) numerically coincides with the relative molecular weight of the given substance.

For example, the relative molecular weight of oxygen (O 2 ) is 32, carbon dioxide (CO 2 ) is 44, and the corresponding molecular weights would be M=32 g/mol and M=44 g/mol. Thus, one mole of oxygen contains 32 grams of this substance, and one mole of CO 2 contains 44 grams of carbon dioxide.

In technical calculations, not the heat of combustion is often used Q g, and the calorific value of the fuel Q(J / kg or J / m 3). The calorific value of a substance is the amount of heat that is released during the complete combustion of 1 kg or 1 m 3 of a substance. For liquid and solid substances, the calculation is carried out per 1 kg, and for gaseous substances, per 1 m 3.

Knowledge of the heat of combustion and the calorific value of the fuel is necessary to calculate the combustion or explosion temperature, explosion pressure, flame propagation speed, and other characteristics. The calorific value of the fuel is determined either experimentally or by calculation. In the experimental determination of the calorific value, a given mass of solid or liquid fuel is burned in a calorimetric bomb, and in the case of gaseous fuel, in a gas calorimeter. These devices measure the total heat Q 0 , released during the combustion of a sample of fuel weighing m. Calorific value Q g is found according to the formula

Relationship between heat of combustion and
fuel calorific value

To establish a relationship between the heat of combustion and the calorific value of a substance, it is necessary to write down the equation for the chemical reaction of combustion.

Product complete burning carbon is carbon dioxide:

C + O 2 → CO 2.

The product of complete combustion of hydrogen is water:

2H 2 + O 2 → 2H 2 O.

The product of complete combustion of sulfur is sulfur dioxide:

S + O 2 → SO 2.

At the same time, nitrogen, halides and other non-combustible elements are released in a free form.

combustible gas

As an example, we will calculate the calorific value of methane CH 4, for which the heat of combustion is equal to Q g=882.6 .

Determine the molecular weight of methane in accordance with its chemical formula(CH 4):

М=1∙12+4∙1=16 g/mol.

Determine the calorific value of 1 kg of methane:

Let's find the volume of 1 kg of methane, knowing its density ρ=0.717 kg/m 3 under normal conditions:

.

Determine the calorific value of 1 m 3 of methane:

The calorific value of any combustible gases is determined similarly. For many common substances, the calorific values ​​and calorific values ​​have been measured with high accuracy and are given in the relevant reference literature. Here is a table of calorific values ​​of some gaseous substances(Table 5.1). Value Q in this table it is given in MJ / m 3 and in kcal / m 3, since 1 kcal = 4.1868 kJ is often used as a unit of heat.

Table 5.1

Calorific value of gaseous fuels

Substance			Acetylene
Q

combustible liquid or solid

As an example, we will calculate the calorific value of ethyl alcohol C 2 H 5 OH, for which the heat of combustion Q g= 1373.3 kJ/mol.

Determine the molecular weight of ethyl alcohol in accordance with its chemical formula (C 2 H 5 OH):

М = 2∙12 + 5∙1 + 1∙16 + 1∙1 = 46 g/mol.

Determine the calorific value of 1 kg of ethyl alcohol:

The calorific value of any liquid and solid combustibles is determined similarly. In table. 5.2 and 5.3 show the calorific values Q(MJ/kg and kcal/kg) for some liquid and solid substances.

Table 5.2

Calorific value of liquid fuels

Substance		Methyl alcohol	Ethanol			Fuel oil, oil
Q

Table 5.3

Calorific value of solid fuels

Substance		wood fresh	wood dry	Brown coal	Peat dry	Anthracite, coke
Q

Mendeleev's formula

If the calorific value of the fuel is unknown, then it can be calculated using the empirical formula proposed by D.I. Mendeleev. To do this, you need to know the elemental composition of the fuel (the equivalent formula of the fuel), that is, the percentage of the following elements in it:

Oxygen (O);

Hydrogen (H);

Carbon (C);

Sulfur (S);

Ashes (A);

Water (W).

The combustion products of fuels always contain water vapor, which is formed both due to the presence of moisture in the fuel and during the combustion of hydrogen. Waste products of combustion leave the industrial plant at a temperature above the dew point temperature. Therefore, the heat that is released during the condensation of water vapor cannot be usefully used and should not be taken into account in thermal calculations.

The net calorific value is usually used for the calculation. Q n fuel, which takes into account heat losses with water vapor. For solid and liquid fuels, the value Q n(MJ / kg) is approximately determined by the Mendeleev formula:

Q n=0.339+1.025+0.1085 – 0.1085 – 0.025, (5.1)

where the percentage (mass %) content of the corresponding elements in the fuel composition is indicated in parentheses.

This formula takes into account the heat of exothermic combustion reactions of carbon, hydrogen and sulfur (with a plus sign). Oxygen, which is part of the fuel, partially replaces the oxygen in the air, so the corresponding term in formula (5.1) is taken with a minus sign. When moisture evaporates, heat is consumed, so the corresponding term containing W is also taken with a minus sign.

Comparison of calculated and experimental data on the calorific value of different fuels (wood, peat, coal, oil) showed that the calculation according to the Mendeleev formula (5.1) gives an error not exceeding 10%.

Net calorific value Q n(MJ / m 3) of dry combustible gases can be calculated with sufficient accuracy as the sum of the products of the calorific value of individual components and their percentage in 1 m 3 of gaseous fuel.

Q n= 0.108[Н 2 ] + 0.126[СО] + 0.358[CH 4 ] + 0.5[С 2 Н 2 ] + 0.234[Н 2 S ]…, (5.2)

where the percentage (vol.%) content of the corresponding gases in the mixture is indicated in parentheses.

Average calorific value natural gas is approximately 53.6 MJ/m 3 . In artificially produced combustible gases, the content of CH 4 methane is negligible. The main combustible components are hydrogen H 2 and carbon monoxide CO. In coke oven gas, for example, the content of H 2 reaches (55 ÷ 60)%, and the net calorific value of such gas reaches 17.6 MJ/m 3 . In the generator gas, the content of CO ~ 30% and H 2 ~ 15%, while the net calorific value of the generator gas Q n= (5.2÷6.5) MJ/m 3 . In blast-furnace gas, the content of CO and H 2 is less; magnitude Q n= (4.0÷4.2) MJ/m 3 .

Consider examples of calculating the calorific value of substances using the Mendeleev formula.

Let us determine the calorific value of coal, the elemental composition of which is given in Table. 5.4.

Table 5.4

Elemental composition of coal

Let's substitute given in tab. 5.4 data in the Mendeleev formula (5.1) (nitrogen N and ash A are not included in this formula, since they are inert substances and do not participate in the combustion reaction):

Q n=0.339∙37.2+1.025∙2.6+0.1085∙0.6–0.1085∙12–0.025∙40=13.04 MJ/kg.

Let us determine the amount of firewood required to heat 50 liters of water from 10 ° C to 100 ° C, if 5% of the heat released during combustion is spent on heating, and the heat capacity of water from\u003d 1 kcal / (kg ∙ deg) or 4.1868 kJ / (kg ∙ deg). The elemental composition of firewood is given in Table. 5.5:

Table 5.5

Elemental composition of firewood

	Let's find the calorific value of firewood according to Mendeleev's formula (5.1): Q n=0.339∙43+1.025∙7–0.1085∙41–0.025∙7= 17.12 MJ/kg. Determine the amount of heat spent on heating water when burning 1 kg of firewood (taking into account the fact that 5% of the heat (a = 0.05) released during combustion is spent on heating it): Q 2=a Q n=0.05 17.12=0.86 MJ/kg. Determine the amount of firewood needed to heat 50 liters of water from 10° C to 100° C: kg. Thus, about 22 kg of firewood is required to heat water.

Today, people are extremely dependent on fuel. Without it, heating of dwellings, cooking, operation of equipment and Vehicle. Most of the fuels used are hydrocarbons. To evaluate their effectiveness, the values ​​of the specific heat of combustion are used. Kerosene has a relatively impressive indicator. Due to this quality, it is used in rocket and aircraft engines.

Due to its properties, kerosene is used in rocket engines.

Properties, obtaining and application

The history of kerosene goes back more than 2 thousand years and begins when Arab scientists came up with a method for distilling oil into individual components. It was officially opened in 1853, when Canadian physician Abraham Gesner developed and patented a method for extracting a clear flammable liquid from bitumen and oil shale.

After drilling the first oil well in 1859, oil became the main raw material for kerosene. Due to its ubiquitous use in lamps, it was considered a staple of the petroleum refining industry for decades. Only the advent of electricity reduced its importance for lighting. Kerosene production has also fallen as the popularity of automobiles has risen.- this circumstance significantly increased the importance of gasoline as a petroleum product. However, today in many parts of the world, kerosene is used for heating and lighting, and modern jet fuel is the same product, but of a higher quality.

With the increase in the use of cars, the popularity of kerosene has fallen

Kerosene is a light transparent liquid, chemically a mixture of organic compounds. Its composition largely depends on the raw material, but, as a rule, it consists of a dozen different hydrocarbons, each of which contains from 10 to 16 carbon atoms. Kerosene is less volatile than gasoline. The comparative ignition temperature of kerosene and gasoline, at which they emit flammable vapors near the surface, is 38 and -40°C, respectively.

This property makes it possible to consider kerosene as a relatively safe fuel in terms of storage, use and transportation. Based on its boiling point (150 to 350°C), it is classified as one of the so-called middle distillates of crude oil.

Kerosene can be obtained straight-run, that is, physically separated from oil, by distillation, or by chemical decomposition of heavier fractions as a result of a cracking process.

Characteristics of kerosene as a fuel

Combustion is the process of rapid oxidation of substances with the release of heat. As a rule, oxygen contained in the air participates in the reaction. During the combustion of hydrocarbons, the following main combustion products are formed:

• carbon dioxide;
• water vapor;
• soot.

The amount of energy generated during the combustion of a fuel depends on its type, combustion conditions, mass or volume. Energy is measured in joules or calories. Specific (per unit of measurement of the amount of substance) calorific value is the energy obtained by burning a unit of fuel:

• molar (for example, J / mol);
• mass (for example, J / kg);
• volumetric (for example, kcal / l).

In most cases, for the evaluation of gaseous, liquid and solid fuels operate with an indicator of mass heat of combustion, expressed in J / kg.

During the combustion of carbohydrate, several elements are formed, for example, soot

The value of the calorific value will depend on whether the processes occurring with water during combustion were taken into account. Evaporation of moisture is an energy-intensive process, and taking into account heat transfer during the condensation of these vapors can also affect the result.

The result of measurements made before the condensed steam returns energy to the system is called the lower calorific value, and the figure obtained after the vapors condense is called the higher calorific value. Hydrocarbon engines cannot use the additional energy of water vapor in the exhaust, so the net figure is relevant for engine manufacturers and is found more often in reference books.

Often, when specifying the calorific value, they do not specify which of the quantities is meant, which can lead to confusion. Knowing that in the Russian Federation it is traditionally customary to indicate the lowest helps to navigate.

Lower calorific value is an important indicator

It should be noted that for some types of fuel, the division into net and gross energy does not make sense, since they do not form water during combustion. With regard to kerosene, this is irrelevant, since the content of hydrocarbons in it is high. With relatively low density (between 780 kg/m³ and 810 kg/m³) its calorific value is similar to that of diesel fuel and is:

• the lowest - 43.1 MJ / kg;
• the highest - 46.2 MJ / kg.

Comparison with other types of fuel

This indicator is very convenient for estimating the potential amount of heat contained in the fuel. For example, the calorific value of gasoline per unit mass is comparable to that of kerosene, but the former is much denser. As a consequence, in the same comparison, a liter of gasoline contains less energy.

The specific heat of combustion of oil as a mixture of hydrocarbons depends on its density, which is not constant for different fields (43-46 MJ/kg). Calculation methods make it possible to determine this value with high accuracy, if there are initial data on its composition.

The average indicators for some types of combustible liquids that make up oil look like this (in MJ / kg):

• diesel fuel - 42-44;
• gasoline - 43-45;
• kerosene - 43-44.

The calorie content of solid fuels, such as peat and coal, has a greater range. This is due to the fact that their composition can vary greatly both in terms of the content of non-combustible substances and the calorific value of hydrocarbons. For example, the calorific value of peat various types can fluctuate within 8-24 MJ/kg, and coal - 13-36 MJ/kg. Among common gases, hydrogen has a high calorific value - 120 MJ / kg. Next in terms of specific heat of combustion is methane (50 MJ/kg).

We can say that kerosene is a fuel that has stood the test of time precisely because of its relatively high energy intensity at a low price. Its use is not only economically justified, but in some cases there is no alternative.