SU1611855A1 - Method of controlling thermal duty of electric vacuum furnaces in making of carbon articles - Google Patents

Abstract

The invention relates to the control of the thermal mode of vacuum furnaces in the production of carbon products, can be used in the chemical industry and reduces the loss of electricity. Measured temperature in the furnace to enter the initial capacity and the end of each interval equal to the time constant of the transient, and a predetermined amount of electricity for each subsequent interval? E _{I + 1} is determined by the formula? E _{I + 1} = 1 / ε @ C _{T ( I + 1)} ΔE ₁ / C _T1 (T ₁ -T ₀ ) ^. T _{I + 1} + C _ex ^{. A.} ϕ [(T _{I +} 1/100) ⁴ - (T _I / 100) ⁴ ] @, where ε is the coefficient of blackness of the heater material

C _{T (I + 1)} is the specific heat capacity of the material of the system of heating bodies in each (I + 1) -th interval. C _{T (I + 1)} = A ₀ + A ₁ (T _{I + 1} -T _I / 2 + A ₂ ) (T _{I + 1} -T _I / 2) ^-2 , where A ₀ , A ₁ , A ₂ - constant for a certain type of material of the heated bodies system

C _T1 , ΔЕ ₁ - specific heat and increment of electricity in the first interval

ΔT _{I + 1} = T _{I + 1} -T _I -0.158T _I-2 -0.37T _I-1 is the predicted temperature increment for each subsequent interval

Τ - post-transition time

T _{I + 1} - the temperature specified in the schedule for the I + 1st interval

T _, T ₁ , T _I - measured temperature in the furnace before entering the initial power, at the end of the first and I-th interval, respectively, K

C _pr = 1/1 / C ₁ + A ₁ / A ₂ ) 1 / C ₂ -1 / C @) is the reduced emissivity of the system of bodies, W / m ^. K, A, A ₁ , A ₂ - the surface area of the charge, heaters and the inner surface of the lining, respectively, m ²

C @ = 5.67 ^. 10 W / m C @ - constant Stefan-Boltzmann

C ₁ and C ₂ are the radiation coefficients of the heaters and the inner surface of the lining, W / m, respectively ^. K. 1 tab., 3 Il.

Description

The invention relates to the control of thermal objects and can be applied in the chemical industry to control thermal conditions on a complex temperature-time schedule in vacuum furnaces in the production of carbon and semiconductor materials, annealing transformer steel.

The purpose of the invention is to reduce the loss of electricity.

FIG. 1 shows a schematic diagram of the implementation of the proposed method; in fig. 2 and 3 are graphs of heating an electrovacuum furnace with the known and proposed methods.

The control system (Fig. 1) contains a furnace 1, a pyrometer 2, a control computing complex 3, an ammeter, a voltmeter 5, and an electric furnace transformer 6.

The method is carried out as follows.

The temperature is measured in the working space of the furnace 1 using a pyrometer 2. The measured temperature data is fed to the input of the control computer complex (UHF) 3. The same current data on current I and voltage U of furnace heaters measured by an ammeter 4 and a voltmeter 3 installed in the secondary circuit of an electric furnace transformer 6.

In UVK 3, the measured current values of I and determine the amount of energy consumed per each time interval, the specified amount of electricity is calculated for each subsequent time interval, depending on which the power change signal is generated. The power is changed by switching the steps of the electric furnace transformer 6 (roughly) and changing the saturation magnetization of the reactor (smoothly).

The algorithm for calculating the control actions and control is as follows.

1. The temperature graph of heating T f (t) is set.

2. The initial power of the power supply R is introduced.

3. The temperature in the furnace is measured at the time of power supply to the heaters T.

. The time delay i) is carried out, equal to the constant transition time in the furnace.

5. The temperature T is measured in the furnace at the time the c time is reached.

6. Measure the amount of energy expended on heating during the exposure period.

7. The average specific heat of the graphite-graphite system is determined over a specified temperature range:

t with, - and. + (-Ij ±:: Ii)

15

+ al (

(one)

where ao, a and a are coefficients.

8. The maximum temperature value in the furnace is predicted from the initial power input.

T - I 1 max: 07§32

9. The average specific heat of the system is predicted for each subsequent time interval (i-fl).

10. The task for temperature increment is predicted for the subsequent time interval T fl, according to the formula (1) T -t .. -0.1 t:, t-H

- 0,233 T, H

11. The increment of energy is predicted for the subsequent time interval AE l according to the formula

AE

1 G / R .AE;

  with,; yG- T

.ATjl, .c „p, A.. (-. IjtM (-Ь, -) |,

where - the coefficient of blackness of the material of the heater;

Cfjp is the reduced radiation coefficient of a system of bodies, determined by the formula

R

1, A4 / 1 t X

C, Ai 02.

where C, j are the radiation coefficients of the heaters and the inner surface of the lining;

CU is the Stefan-Boltzmann constant;

AA. A;), Aj - surface areas of the set, heaters and the inner surface of the lining.

5161

12. Introduces additional power.

LR

4E-, 41

H-1

13. Next, repeat steps 8-12 until the temperature reaches a predetermined temperature.

The table shows an example of the calculation of the choice of the power supplied to the furnace for heating at a given speed and at a specified time.

FIG. Figures 2 and 3 show the samples of the heating of an electrovacuum furnace obtained for the initial conditions indicated in the table with the known control method (a, b, c) and proposed (d).

Claims (1)

The lack of dosing of the input power, taking into account the specific for each process mass of the charge, the condition of the lining and heaters, as well as the absence of the optimal frequency of the adjustments of the input power leads to uneven heating of the products or lengthening the furnace heating time, i.e. additional power loss. All of these factors, combined with a product defect due to noncompliance with the regime, cause significant losses. Invention Formula The method of controlling thermal conditions of electrovacuum furnaces in the production of carbon products, including setting the amount of electricity per heating interval, entering the initial heating power, measuring the amount of electricity consumed by the furnace and periodically changing the power depending on the amount of electricity specified for each heating interval that, in order to reduce electricity losses, the temperature in the furnace is measured additionally before entering the initial power and at the end of each interval, is equal to on the time constant of the transient, and a predetermined amount of electricity for each subsequent interval DE q., determined by the formula X. 1 Gg. E; , .it 1855 pr iTil ,, + sr A - (- 1Y5 - - where 6 is the coefficient of blackness of the heater; WITH,. , - specific heat capacity of the material of heated bodies in each (1 + 1) -th interval, defined by the formula + a, (t, + 0 1 2 . gr tg Ijii-.:-iib ) -2, where a, a, constant coefficients. Cycles for a certain type of material of heated arbors; LT is the predicted temperature increment for each subsequent interval, determined by the formula t. t: ;, -t o, 158 t .; ·, - 0.37 t ;. , where T, T- is the measured temperature in the furnace before the input of the initial power and at the end of the i-ro interval, respectively; T / is the boundary value of the temperature per (i + l) interval; С п, is the reduced emissivity of a system of bodies, defined by the formula 1 45  g: Ar :: g: t  c, A / C e A, A, A are the surface areas of the set, heaters and the inner surface of the lining, respectively; C, C are the radiation coefficients of the heaters and the inner surface of the lining;  f constant Stefan Boltzmann. Gj j program input / / / / 1 2 3 5 6 t S S 10 1 2 3 Л S 6 Т 8 S Ю (K / tZ P, Ktm Tit (, mc 123 5678910 Fig.Z  S, h as