Basic definition of thermal unit

Basic definition of thermal unit
Basic definition and calculation of thermal unit
⼀. Calorific value definition
The heat released by the complete combustion of 1kg of a certain solid,The calorific value reflects the fuel combustion characteristics, that is, the ability of different fuels to convert chemical energy into internal energy during combustion.
Standard coal is the abbreviation of standard coal. Due to the differences in the energy released during the combustion of various fuels, in order to facilitate the use of standard coal in the world, when comparing the quantity and quality of imported energy, coal, oil, natural coal, etc. are converted into standard coal according to the standard coal (the lower calorific value of one meter of standard coal is 29307.6 kilojoules, that is, per meter of standard coal). 12100 ℃ standard coal is 29307600 ℃.
"Standard coal" is the measurement unit of energy for short of "standard coal". Due to the different calorific values of various energy sources, the physical measurement unit of the collected energy is also different. Therefore, in order to facilitate the summary calculation and analysis of various energies, the physical units of various energies should be converted into the standard unit of energy measurement. In China, the standard coal mined before coal mining is the energy measurement unit, that is, 29271 kilojoules (7000 kcal) per kilogram of standard coal, that is, the standard coal is used to measure the energy.
The energy measurement unit is the standard coal mined before coal mining in China. The SI unit is the joule. The converted ⽅⽅⽅⽅⽅⽅⽅⽅⽅⽅ method is to measure various fuels and dynamic energy with 7000 kcal. Reference coefficient
⼆. ⽐ Heat capacity
Specific heat capacity is called specific heat, which is the heat capacity of substances with unit mass, i.e. the internal energy absorbed or released when the unit mass object changes the unit temperature. ⽐ heat capacity is a physical quantity that represents the thermal properties of ⽰ substances. Generally, the symbol c represents ⽰. The heat capacity is related to the state and type of matter.
When the temperature of a substance with constant mass rises, the product of the absorbed heat and the mass of the substance and the rising temperature is called the thermal capacity of the substance (⽐ heat). The ⽤ symbol c is ⽰. The unit in the International System of Units is joule per kilogram of Kel [J/(kg · K)] or joule per kilogram of photographic degree [J/(kg · C)]. J refers to the joule, and K refers to the thermal temperature scale, that is, the energy required to raise (or lower) the temperature of 1 kg of substance by 1 Kel. According to this theorem, the following formula can be obtained:
Q=cm Δ T
Q is the heat absorbed (or released); M is the mass of the object, Δ T is the rising (falling) value of temperature after heat absorption (release) Δ T written as Δ t. In fact, this is not standard (we often use ⽤ C as the unit of temperature, and rarely use ⽤ K, ⽽ and
Δ T= Δ t. Therefore, in the middle school stage Δ t. However, in international or more scientific fields Δ T)  。
In the International System of Units (SI), the main unit of energy, work and heat is the joule, and the main unit of temperature is the kelvin. Therefore, the international unit of heat capacity is J/(kg · K), which is read as "joule [[[[[]] per kilogram of kelvin]". (Words in [] can be omitted.)
Normal unit: J/(kg ·℃), J/(g ·℃), kJ/(kg ·℃), cal/(kg ·℃), kcal/(kg ·℃), etc. Note that the photographic degree and Kelvin are only different on the temperature scale,
It is equivalent in the magnitude meaning of the temperature difference in Table ⽰, so ℃ and K in these units can be replaced each other arbitrarily. For example, "Focal angle per kilogram" and "Focal angle per kilogram" are equivalent
。
The ⽐ heat capacity of ⽔ is 4.2 kJ/(kg · ℃)=1 kcal/(kg · ℃).
The ⽐ heat capacity of steam is 2.1 kJ/(kg · ℃)=0.5 kcal/(kg · ℃)
That is to say: 100 kcal of heat absorbed when 1Kg ⽔ rises from 0 ℃ to 100 ℃, 50 kcal of heat absorbed when 1Kg steam rises from 100 ℃ to 200 ℃
The heat of vaporization of ⽔ is 2260 kJ/kg=530 kcal/kg. Generally, the heat required to evaporate the water at its boiling point is five times as much as that required to heat the same amount of water from water to water.
⽯ Heat capacity of ⽐ paste 1.09kJ/(kg · ℃)=0.26kcal/(kg · ℃)
The heat capacity of air cooler is 0.31 kcal/(kg · ℃). Air cooler has different heat at different temperatures
3、 Formation and composition of chemical ointment
⽣⽯⽯⽔⽔⽔⽔⽔ calcium sulfate (Ca [SO4] · 2H2O), ⼜⽔⽔⽯ paste, ⽔⽯ paste or soft ⽯ paste, theoretical composition
CaO3 is 2.6%, SO346.5%, H2O+20.9%, and the content is 172. According to the grade calculation of the paste, if the crystal content of the raw material is 19%, the grade=100/20.9 * 19=90.9.
Desulfurization paste raw materials contain gypsum and free gypsum. The market raw materials generally contain 12% free gypsum, the grade is about 90 (crystal gypsum is 18.84%), and the crystal gypsum powder of cooked gypsum powder is generally controlled at 5%. Now calculate how many tons of cooked gypsum powder can be produced from 1 ton of desulfurization paste raw materials: 1T * (1-12%) * (1 - (18.84% - 5%))=0.758T. In turn, it can be calculated that 1/0.758=1.319T raw materials are required to produce 1 ton of cooked cream powder.
4、 ⽔ Calculation of evaporation energy consumption
The heat required for 1Kg ⽔ steam from 20 ℃ to 150 ℃ is calculated in three parts
Part ⼀, the heat absorbed by 1Kg ⽔ heated from 20 ℃ to 100 ℃ 1Kg * (100-20) ℃ * 1 kcal/(kg · ℃)=80 kcal
The third part is 530 kcal of heat absorbed by 1Kg of steam from 100 ℃ to 100 ℃. The third part is 1Kg * (150-100) ℃ * 0.5kcal/(kg · ℃)=25 kcal of heat absorbed by 1Kg of steam from 100 ℃ to 150 ℃
So the heat required when 1Kg ⽔ changes from 20 ℃ to 150 ℃ steam is 80+530+25=635 kcal
5、 Calculation of Heat Demand for Calcination of ⽯ Paste Powder
1 ton of cooked paste requires 1.319 tons of raw materials, all of which are evaporated, and the heat demand is composed of the following parts:
Part ⼀ 0.319t ⽔ heat absorbed by heating from 20 ℃ to 100 ℃, 0.319T=319Kg, 319 Kg * (100-20) ℃=25520kcal Part ⼆ continues to heat up, and 100 ℃ ⽔ becomes 100 ℃ steam absorbed heat
319 Kg *530530 kcal/kg =169070kcal
In the third part, the heat absorbed by 100 ℃ steam continues to rise to 170 ℃, 319 kg * (170-100) ℃ * 0.5 kcal/(kg · ℃)=11165 kcal In the fourth part, the heat absorbed by ⽯ paste heated from 20 ℃ to 170 ℃, 1000 kg * (170-20) ℃ * 0.26 kcal/(kg · ℃)=39000 kcal
Therefore, theoretically, the heat required to produce 1 ton of cooked gypsum powder is 25520+169070+11165+39000=244755 kcal. If 5000 kcal/kg coal is burned, it needs=244755 kcal/5000 kcal/kg=48.951 kg. Equivalent to standard coal (7000 kcal/kg) 34.965 kg
In the actual production, in addition to evaporation and material heating, the air heater also carries about 14-20% of the heat, the mechanical equipment surface has about 5% of the heat, the chemical and mechanical incomplete combustion has about 2% of the heat, and the slag has about 1% of the heat. It is impossible to achieve 75% of the efficiency in the actual production. When the efficiency reaches 75%, 5000 kcal/kg of coal is required to reach 48. 951 kg/75%=65.268kg. The energy consumption index of Thai paste in the national paste board industry is the lowest, and the comprehensive thermal efficiency in the 30 million mature paste area only reaches 61.62%, which also makes a lot of energy saving measures.
6、 Calculation of heat demand for baking paste plate
The amount of raw material ⽤ for each flat ⽶⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⽯⼭⽯⽯⽯⽯⼭⽯⽯⽯⽯⽯⽯⽯ paste as an example) ⽯⽯ paste powder 5.6kg, protective paper 360g, starch 16g, reducing agent 26g, latex 2g, foaming agent 6g, citric acid 0.5g, ⽔⽔⽔%). The weight of the paste plate is 6.7 kg.
If the standard thickness of paste powder is 64%, and the evaporation capacity of each flat paste plate is 2.6kg, then
The required heat is 635 * 2.6=1651 kcal.
When baking, the temperature of the board core of the paste board must not exceed 90 ℃. The heat of the paste is 0.26 kcal/(kg · ℃). The temperature of the paste rises from 20 ℃ to 85 ℃
by
6.7 kg*  (85-20)  ℃*0.26 kcal/(kg·℃)=113 kcal
Then, the theoretical heat required for baking a flat paste plate is 1651 kcal+113 kcal=1764 kcal.
The output of the 20 million yuan paste plate production line is 2880 square meters per hour, the evaporation volume is 7488 kg, the heat demand is 5080320 kcal=5.08 million kcal, and the comprehensive thermal efficiency in the actual production is 65% (the thermal efficiency for the plate is 61%). Then the heat demand of the hot air furnace supporting the production line is 7.79 million kcal. If the standard thickness is too high or the weight of the plate reaches about 7 kg, The installed capacity of hot blast stove must reach 10 million kcal.
According to different heat sources, the thermal efficiency is not nearly the same. If coal is burned (5000 kcal/kg), then 1764 kcal/65%/5000 kcal/kg=0.542 kg * 2880 kcal=1560 kg is required for the flat paste plate.
7、 Various heat sources
Since then, the thermal efficiency of heat sources has been the basis for the survival and development of enterprises. Many enterprises and research departments at home and abroad have invested in a large amount of energy to improve the thermal efficiency. Thermoelectric energy is also a coal consumer and a more solid enterprise, but the thermal efficiency of electricity has been hovering between 35% and 43%.
1Kw · h=3.6 for 1 kilowatt hour ×  10 ^ 6J=860 kcal, 300g standard coal is required to generate 1 kilowatt hour power, that is, 7000 * 0.3=2100 kcal, and the thermal efficiency is 41%. This is mainly because the coal is first heated into steam, and then the steam drives the turbine generator, which is a secondary energy source,
Two level thermal efficiency. If we use electricity to heat, it belongs to the third heat source, and the thermal efficiency will be lower. Therefore, multiple heat sources shall be avoided in the production process.
The market price of 1000 kcal coal (5000 kcal/kg, 500 yuan per ton) is 0.1 yuan; The market price of 1000 kcal electricity (860 kcal/kWh, 1 yuan per kWh) is 1.16 yuan; The market price of 1000 kcal of natural ⽓ (8500 kcal/⽴ ⽅ RMB 3.6 per ⽴) is
0.42 yuan