Determination of the estimated steam flow. Determination of the estimated steam consumption Calculation of steam consumption when steaming containers

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Heat supply

Sources of heat supply for enterprises of the confectionery industry can be their own boiler house or an external centralized heat source.

The consumption of thermal energy is the sum of the costs hot water and a couple for various needs:

technological;

household;

sanitary-technical (heating, ventilation, air conditioning).

As a heat carrier for technological needs, saturated steam is used (without the presence of hydrozine or other carcinogenic substances) with a pressure of 0.05-1.0 MPa (for specialized chocolate shops 0.8-1.0; for other shops 0.05-0.6 MPa).

The heat carrier for the ventilation and heating system is high-temperature water with parameters 150 - 70 0 С, 130 - 70 0 С; for hot water supply - high-temperature water of the same parameters or steam with a pressure of 0.3 MPa - for ventilation needs and 0.07 MPa - for heating.

It is recommended to install boilers of the E-35 / 40-11, E-50 / 40-11, E-75 / 40-11 types in boiler rooms of low-power confectionery factories, and vertical water-tube boilers of the DKVR type in factories of medium and high power. The boilers operate at a pressure of 0.9 MPa and without steam overheating. Steam with lower pressure for various needs is obtained by reduction.

The condensate returned to the boiler room for heating and ventilation systems is taken as 100%, for industrial steam supply - 80%, for hot water supply systems - 90%.

Steam consumption calculation

Steam consumption for technological needs can be determined by the consumption rates of individual devices and machines or by aggregated indicators.

The factory being designed or reconstructed may include various workshops in which 2-3 groups of confectionery products (sweets, caramels, cookies, etc.) are produced.

Steam consumption for technological needs D 1, kg / h is determined by the formula:

D 1 \u003d R 1 * q t

Where Р t - hourly productivity according to finished products, t/h;

q t - specific steam consumption, kg/t.

D 1 \u003d 2.88 * 1200 \u003d 3456 kg / h

Steam consumption for heating D 2, kg / h is calculated by the formula:

where Q OT is the maximum heat consumption for heating, W;

TO - efficiency of the heat exchanger (TO = 0.95).

When determining required flow heat should take into account the location of the confectionery factory, the duration heating season, calculated temperatures.

The heat consumption for heating the building Q from, W is determined by the formula:

Q FROM \u003d X 0 * V * q FROM * (t P - t H)

Where X 0 - specific thermal characteristic of the building, W / (m 3 * K);

q FROM - specific heat loss of 1 m 3 of the building, kJ / m 3;

V - the volume of the heated part, m 3 (V \u003d 11750 m 3);

t P - the average temperature of the heated room, 0 C (t P = 18-20 0 C);

t H - calculated winter temperature outdoor air for heating, 0 С;

Q FROM \u003d 0.5 * 11750 * 1.26 * (20-(-18)) \u003d 281295 W

Steam consumption for ventilation D 3, kg / h is determined by the formula:

where Q in is the hourly consumption of the amount of heat for ventilation (air heating), W;

i n - steam enthalpy, kJ/kg (at a steam pressure of 0.07 MPa, i n =2666.6 kJ/kg);

i k - enthalpy of condensate, kJ/kg (ik =375.6 kJ/kg);

TO - efficiency of the heat exchanger (TO = 0.95).

Heat consumption for ventilation Q in, W is determined by the formula:

where V in - the total amount of ventilated air, m 3 / h;

X in - specific characteristic of the building, W / (m 3 * K);

Air density, kg / m 3 (= 1.2 kg / m 3);

c - mass specific heat air, kJ/(kg*K) (s= 1.0 kJ/(kg*K);

t P - average temperature of ventilated premises, 0 C (t P = 18-20 0 C);

t H - estimated outdoor air temperature during the heating period, 0 C.

The total amount of ventilated air V in, m 3 / h is determined by the formula:

where P in - the percentage of ventilated premises (50-60);

V - building volume, m 3;

n is the average air exchange rate per hour (n=3-5).

Steam consumption for household needs, D 4 , kg / h is determined by the formula:

where Q x / b - the amount of heat for heating water for household needs, W

where W - water consumption for household needs, kg/h (W=800 kg/h);

c - specific heat capacity of water (c = 4.19 kJ / kg * K);

t H, t K - initial and final water temperature, (t H \u003d 10 0 С, t K \u003d 75 0 С).

The total steam consumption for production D s, kg / h is:

To determine the steam consumption for the auxiliary needs of the boiler house, it is necessary to determine the loss of condensate.

The return of condensate from the production steam supply system W k 1, kg / h of the confectionery factory is 80%, then

W k 1 \u003d 0.8 * D 1

W k 1 \u003d 0.8 * 3456 \u003d 2764.8 kg / h

Condensate return W k 4 , kg/h from the hot water supply system is 90%, then

W k 4 \u003d 0.9 * D 4

W k 4 \u003d 0.9 * 100.11 \u003d 90.1 kg / h

Condensate loss D n . k, kg/h are

D n . k \u003d D s - (W k 1 - W k 4)

D n . k \u003d 4562.99 - (2764.8 + 90.1) \u003d 1708.1 kg / h

Raw water consumption B, kg / h to cover the loss of condensate is taken 20% more, then

B \u003d 1.2 * D n. to

B \u003d 1.2 * 1708.1 \u003d 2049.72 kg / h

Steam consumption for water heating , kg/h is equal to:

where i 1 is the enthalpy of water at \u003d 40 0 С (168 kJ / kg);

i 2 - enthalpy of water at \u003d 5 0 C (21 kJ / kg);

i n - steam enthalpy at 0.6 MPa (2763 kJ/kg);

i k - condensate enthalpy, (669 kJ/kg);

Steam water heater efficiency (= 0.95).

Steam consumption for deaeration of water Dae, kg/h is equal to

where i cp is the average enthalpy of water entering the deaerator, kJ/kg (i cp = 433 kJ/kg);

W a.e. - condensate from the water heater before chemical water treatment, kg / h (W p.v = D p.v.).

The total need of the boiler room for steam D to, kg / h

D c \u003d D s + D pv + D ae

D c \u003d 4562.99 + 151.46 + 683.31 \u003d 5397.76 kg / h

Taking into account heat losses in steam pipelines, units, etc., which can be 8-10%, the estimated need for steam D total, kg / h (for the winter period) will be

D total \u003d D to * 1.1

D total \u003d 5397.76 * 1.1 \u003d 5937.54 kg / h

Choice of steam boilers

The choice of the type and number of boilers to meet all the needs of the enterprise is made in such a way that they ensure the maximum demand for steam in the winter period of operation, and in summer period there was a possibility of successive overhaul cats. Boilers are selected according to their steam and thermal conductivity. If the reference literature gives the heating surface area, then the total surface area F, m 2 of heating is determined by the formula:

where Dtot is the estimated need for steam for the winter period, kg / h;

h - safety factor equal to 1.1-1.2;

q k - specific vapor volume, kg / m 2 h, equal to 30-40, depending on the boiler and type of fuel;

Having determined the total heating surface, we select the E-35 / 40-11 boiler, and install 2 pcs.

coolant ventilation condensate

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3.2.2 Calculation of steam consumption for heating and ventilation

The calculation of heat costs for heating and ventilation is determined by the formula:

Q=q · V · (t pom – t calc ) · T year , kW/year, (3.11)

where q is the specific heat consumption for heating and ventilation of 1m 3 of the room at a temperature difference of 1 ° C, kW / (m 3 deg).

The average value of this value can be taken: for heating - 0.45 · 10 -3 kW / (m 3 .deg), for ventilation 0.9 · 10 -3 kW / (m 3 .deg).

V - the total volume of the premises of the site, excluding the volume of drying chambers, m 3;

t pom is the temperature in the room, assumed to be 20°С;

t calc - design temperature for heating and ventilation;

T year - the duration of the heating season is determined by the formula:

T year \u003d 24 * τ from, h,

where τ from is the duration of the heating season, days.

T year = 24 · 205 = 4920 hours

Q from = 0,45 · 10 -3 · 4456,872 · (20-(-26)) · 4920 = 453,9 · 10 3 kW/year.

Q vent = 0,09 · 10 -3 · 4456,872 · (20-(-12)) · 4920 = 63,15 · 10 3 kW/year.

Table 3.3 - Calculation of heat consumption for heating and ventilation

Name of steam consumers	Specific consumption q, kW / (m 3 .deg).	Room volume	Temperature difference inside and outside the building (t room - t calculated), ° С	Length of the heating season	Annual consumption heat Q,
Heating of the drying area					453,9 · 10 3
Ventilation					63,15 · 10 3
					517,05 · 10 3

Calculation of the annual demand for steam for heating and ventilation is determined by the formula:

3.2.3 Calculation of heat (steam) consumption for domestic needs

The calculation of heat (steam) consumption for domestic needs is determined by the formula:

where q - steam consumption per 1 person per shift;

m is the number of people working on the busiest shift;

n is the number of shifts in the work of the section (it is advisable to take 2);

τ is the number of days of operation of the site per year.

3.2.4 Calculation of the total annual steam demand for technological and domestic needs, heating and ventilation

The calculation of the total annual steam demand for technological and domestic needs, heating and ventilation is determined by the formula:

D common = D academic year + D from + D life , t/year. (3.14)

D common \u003d 8.13 + 891.47 + 2.6 \u003d 902.2 tons / year.

The article contains a fragment of the table of saturated and superheated steam. With the help of this table, according to the value of steam pressure, the corresponding values of the parameters of its state are determined.

Steam pressure	Saturation temperature	Specific volume	Density		Steam enthalpy	Heat of vaporization (condensation)

Column 1: Steam pressure (p)

The table shows the absolute value of the steam pressure in bar. This fact must be kept in mind. When it comes to pressure, as a rule, they talk about the excess pressure that the pressure gauge shows. However, process engineers use absolute pressure in their calculations. In practice, this difference often leads to misunderstandings and usually backfires.

With the introduction of the SI system, it was accepted that only absolute pressure should be used in calculations. All pressure measuring instruments technological equipment(except barometers) basically show gauge pressure, we mean absolute pressure. Under normal atmospheric conditions (at sea level) is understood barometric pressure 1 bar. Gauge pressure is usually indicated in barg.

Column 2: Saturated steam temperature (ts)

In the table, along with the pressure, the corresponding saturated steam temperature is given. The temperature at the appropriate pressure determines the boiling point of water and thus the temperature of saturated steam. The temperature values in this column also determine the condensing temperature of the steam.

At a pressure of 8 bar, the saturated steam temperature is 170°C. The condensate formed from steam at a pressure of 5 bar has a corresponding temperature of 152°C.

Column 3: Specific volume (v”)

The specific volume is given in m3/kg. With increasing vapor pressure, the value of the specific volume decreases. At a pressure of 1 bar, the specific steam volume is 1.694 m3/kg. Or in other words, 1 dm3 (1 liter or 1 kg) of water during evaporation increases in volume by 1694 times compared to the original liquid state. At a pressure of 10 bar, the specific volume is 0.194 m3/kg, which is 194 times that of water. The specific volume value is used in calculating the diameters of steam and condensate pipelines.

Column 4: Specific Gravity (ρ=po)

Specific gravity (also called density) is given in kJ/kg. It shows how many kilograms of steam are contained in 1 m3 of volume. With increasing pressure specific gravity increases. At a pressure of 6 bar, steam with a volume of 1 m3 has a weight of 3.17 kg. At 10 bar - already 5.15 kg and at 25 bar - more than 12.5 kg.

Column 5: Enthalpy of saturation (h')

The enthalpy of boiling water is given in kJ/kg. The values in this column show how much heat energy is needed to bring 1 kg of water at a certain pressure to a boiling state, or how much heat energy is contained in the condensate, which condenses from 1 kg of steam at the same pressure. At a pressure of 1 bar, the specific enthalpy of boiling water is 417.5 kJ/kg, at 10 bar it is 762.6 kJ/kg, and at 40 bar it is 1087 kJ/kg. With increasing steam pressure, the enthalpy of water increases, and its share in the total enthalpy of steam is constantly growing. This means that the higher the vapor pressure, the more thermal energy remains in the condensate.

Column 6: Total enthalpy (h”)

Enthalpy is given in kJ/kg. This column of the table shows the steam enthalpy values. The table shows that the enthalpy increases up to a pressure of 31 bar and decreases with a further increase in pressure. At a pressure of 25 bar, the enthalpy value is 2801 kJ/kg. For comparison, the enthalpy value at 75 bar is 2767 kJ/kg.

Column 7: Thermal energy of vaporization (condensation) (r)

The enthalpy of vaporization (condensation) is given in kJ/kg. This column gives the amount of thermal energy required to completely evaporate 1 kg of boiling water at the appropriate pressure. And vice versa - the amount of thermal energy that is released in the process of complete condensation of (saturated) steam at a certain pressure.

At 1 bar r = 2258 kJ/kg, at 12 bar r = 1984 kJ/kg and at 80 bar r = only 1443 kJ/kg. With increasing pressure, the amount of thermal energy of vaporization or condensation decreases.

Rule:

With increasing steam pressure, the amount of thermal energy required to completely evaporate boiling water decreases. And in the process of condensing saturated steam at the appropriate pressure, less thermal energy is released.

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At enterprises, water vapor is used for technological, household and power purposes.

For technological purposes, deaf and live steam is used as a coolant. Live steam is used, for example, to boil raw materials in boilies or to heat and mix liquids by bubbling, to create excess pressure in autoclaves, and also to change the state of aggregation of a substance (evaporation or evaporation of a liquid, drying materials, etc.). Deaf steam is used in surface heat exchangers with steam heating. The steam pressure used in meat processing enterprises ranges from 0.15 to 1.2 MPa (1.5÷12 kg/cm2).

For each technological operation using water vapor, its consumption is determined according to the data heat balance everyone thermal process. In this case, the data of material balances of product calculations are used. For periodic processes, the heat treatment time for each cycle is taken into account.

In each particular case, the heat load of the apparatus (heat input) can be determined from the heat balance of the process. For example, the heat spent on heating the product from the initial ( t m) to the final ( t j) temperature for the apparatus continuous action, is determined by formula 72:

Q = Gc (t k – t n)φ, (72)

where Q- heat spent on heating, J / s (W), i.e. thermal load of the device;

from is the specific heat capacity of the product at its average temperature, J/kg K;

t to, t n – initial and final temperature, °C;

φ - coefficient taking into account heat loss to the environment
Wednesday ( φ = 1.03÷1.05).

The heat capacity of the product is chosen either from known directories, or calculated according to the principle of additivity for multicomponent systems.

To change the state of aggregation of a substance (solidification, melting, evaporation, condensation) is spent thermal energy, the amount of which is determined by formula 73:

where Q is the amount of heat, J/s (W);

G is the mass flow rate of the product, kg/s;

r is the heat of phase transition, J/kg.

Meaning r determined according to reference data, depending on the type of product and the type of phase transition of the substance. For example, the heat of fusion of ice is taken to be r 0 \u003d 335.2 10 3 J / kg, fat

r w = 134 10 3 J / kg. The heat of vaporization depends on the pressure in the working volume of the apparatus: r = f (P a). At atmospheric pressure r= 2259 10 3 J/kg.

For continuous devices, heat consumption is calculated per unit of time (J / s (W) - heat flow), and for batch devices - for a cycle of operation (J). To determine the heat consumption per shift (day), it is necessary to multiply the heat flow by the operating time of the device per shift, day or by the number of cycles of the device operation periodical action and the number of such devices.

The flow rate of saturated water vapor as a heat carrier, subject to its complete condensation, is determined by the equation:

where D- the amount of heating water vapor, kg (or flow rate, kg / s);

Q total - total heat consumption or heat load of a thermal device (kJ, kJ / s), determined from the equation of the heat balance of the device;

– enthalpy of dry saturated steam and condensate, J/kg;

r is the latent heat of vaporization, kJ/kg.

The consumption of live steam for mixing liquid products (bubbling) is taken at the rate of 0.25 kg / min per 1 m 2 of the cross section of the apparatus.

Steam consumption for economic and domestic needs under this heading, steam is used to heat water for showers, laundry, washing floors and equipment, and scalding equipment.

Steam consumption for scalding equipment and inventory is determined by its outflow from the pipe according to the flow equation:

(75)

where D w – steam consumption for scalding, kg/shift;

d– inner diameter of the hose (0.02÷0.03 m);

ω – speed of steam outflow from the pipe (25÷30 m/s);

ρ - vapor density, kg / m 3 (according to Vukalovich's tables ρ = f(ρ ));

τ – scalding time, h (0.3÷0.5 h).

If we take in the equation τ = 1 h, then the steam consumption is determined in kg/h.

The calculation of steam consumption for all items is summarized in table 8.3.

Table 8.3 - Steam consumption, kg

Expenditure	At one o'clock	On shift	Per day	In year

Total

Specific consumption steam is calculated using formula 76.

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