RU2724135C2 - Method for determination of residual life of thermal enclosures of high-temperature units - Google Patents

Abstract

FIELD: heat power engineering.SUBSTANCE: invention relates to determination of residual life of thermal enclosures of high-temperature units. Summary: residual resource of thermal enclosures of high-temperature units is determined, using as reliability indexes reliability criteria of strength for compression and for expansion, defined by the formula: k=Σ/Σ, wherein ΣN—the sum totals values of compression defined by formula: N=σ·(z+1), where z is a coefficient which takes into account lengths of compression and expansion zones, in which temperature stresses exceed allowable ones, σ—occurring stresses in compression zone, ΣN—the sum values of the total compression rates at the same point at the same time is similarly ΣN, but at a value of σequal to the limit of the material strength, and nresidual resource determined by the formula: n=Σ/Σ− n, where ΣNis the arithmetic mean value of the total compression ratios per one cycle; n is number of high-temperature unit cycles, which have passed at the moment after replacement of lining, wherein calculation of strength reliability criterion and residual life for expansion are determined by similar formulas.EFFECT: obtaining data on residual life of thermal enclosures of high-temperature units during operation and use of said values during their operation.1 cl

Description

The invention relates to a power system, and in particular to determining the residual life of thermal fencing of high-temperature units.

A known method for assessing the residual life of tube furnaces of oil refining, petrochemical and chemical industries [DiOR-05 "Methodology for assessing the residual life of tube furnaces of oil refining, petrochemical and chemical industries" OJSC "VNIKTIneftekhimoborudovaniya", Volgograd, 2006, 87 pp.] In which forecasting The resource of residual performance of parts and assemblies of the furnace is based on the results of an examination of its technical condition, investigation of mechanical properties, chemical composition, metal structure, causes of corrosion, erosion, and strength calculations.

The disadvantage of this method is the need to stop the furnace to assess the residual life: its inspection, thickness gauge, evaluation of the geometric shape of the main load-bearing elements of the furnace, hardness measurements, etc.

The closest technical solution, selected as a prototype, is a method for determining the residual life of the thermomechanical equipment of nuclear power plants, in which wear and aging of pressure vessels are determined based on the mathematical model "load - bearing capacity", where the internal pressure is taken as the load, and as the bearing capacity is the wall thickness of the pressure vessels [Patent 2126955 RF, IPC G01D 21/00. A method for determining the residual life of thermomechanical equipment of nuclear power plants].

The disadvantage of this method is the absence in the used mathematical model of the influence of temperature stresses arising in the walls.

The technical result of the invention is to obtain data on the residual life of thermal fencing of high-temperature units during operation and the use of these values during their operation.

This is achieved by the fact that in the method for determining the residual life of thermal fencing of high-temperature units, reliability criteria are used as reliability indicators - reliability criteria for strength both for compression and expansion, determined by the formula:

where ΣN _SJ - the amount of value totals compression, defined by the formula:

N _cr = σ _cr ⋅ (z + 1),

where z is a coefficient that takes into account the lengths of the compression and tension zones, in which the temperature stresses exceed the permissible ones, σ _squ are the stresses arising in the compression zone,

ΣN ^additional _{compression channel} - the sum values of the total compression rates at the same point at the same time, is similarly ΣN _{compression channel,} but at a value equal to the limit σ _{compression channel} material strength, and the remaining service life _ost n is given by:

where ΣN _compression - the arithmetic mean of the total compression indicators for one cycle; n is the number of cycles of the high-temperature unit that have passed at the moment after the lining has been replaced, and the calculation of the reliability criterion for strength and the residual life for expansion are determined by similar formulas.

In this case, the determination of the residual resource is carried out continuously during the operation of the energy unit.

The residual life of thermal fencing of high-temperature units, during operation of which the thickness of the thermal fencing does not change, depends on a number of factors, including the value of temperature stresses that exceed the allowable ones and their numbers from the moment the power unit began to operate. The action of other factors - the aggressive action of the environment, the quality of the materials used and the work performed, the vibration level, etc. can be assumed constant for this unit under unchanged working conditions.

The work of the method is as follows.

The temperature distribution is found by any known method (for example, Innovative patent No. 30372 Republic of Kazakhstan, IPC G01K 13/00 publ. September 15, 2015, bull. No. 9).

Then, the emerging stresses are found in the tensile zone σ _p and compression σ _s according to the formula:

where α is the coefficient of thermal expansion, (1 / ° C);

T _cf - the average temperature of the refractory layer, ° C;

T _i is the temperature of the point at which the temperature stress is calculated, ° C;

E - modulus of elasticity of the material, MPa

ν is the Poisson's ratio.

Find two indicators: the total compression ratio (N _cr ) and the total tensile index (N _pac ) as follows. To calculate these parameters using only the values of thermal stress σ _races (stretching) or a _{compression channel} σ (compression) that exceed the ultimate strength value for this type of refractory material.

To take into account the lengths of the compression and tension zones, in which the temperature stresses exceed the permissible ones, we introduce a coefficient taking these lengths into account. By the length of the compression zone we mean the distance between two neighboring points at which stresses are determined, provided that at these two points the compression stresses exceed the permissible ones. That is, if the compression stresses at this time step exceed the permissible values at three points, then z = 2. The formula for calculating the total compression criterion (N _sr ) at this time step (for example, for a time of 1:40) will look like this:

where z is the number of compression zones in which temperature stresses exceed permissible.

A similar formula is used for tensile stresses. Next, we summarize all the obtained values of the total indicators (separately for compression and stretching) for all time steps. This amount in the calculation for the entire working unit of the campaign is the ultimate measure of the total compression (ΣN _SJ) and the ultimate tensile summary measure (ΣN _pac). These total indicators take into account only stresses exceeding the tensile strength and leading to the destruction of building envelopes.

To introduce criteria for the residual life, we introduce the concept of total allowable indicators that will take into account stresses that occur at a time and at points where, in reality, the stresses exceed the permissible ones. Only when calculating the total allowable indicators, instead of the real stress values, we substitute the values of the tensile strength of the material. For example, at a time of 0:40, a temperature stress of 113 MPa occurs at a point (with a tensile strength of 40 MPa), which we take into account to calculate the total indicator. To calculate the total allowable indicators, it is necessary to take into account the voltage value at the same point at the same time, but at a value of 40 MPa.

If we divide the resulting total indicators by the total allowable, then we obtain a reliability criterion for strength (for example, for compression):

In this case, the time and coordinate step in determining the stresses will determine the accuracy of the calculation of reliability criteria. To estimate the residual life, it is also necessary to calculate two arithmetic mean values of the total indicators for one cycle (for compression - ΣN _{sr cf} ; for stretching - ΣN _{sr sr} ).

The obtained criteria of the residual resource will determine the residual resource for subsequent work campaigns of this unit under the same operating conditions of the unit and the use of the same materials, layer thicknesses, etc. That is, after the next major overhaul, temperature measurements are taken, temperature stresses are calculated (σ _races and σ _cr ) , total indicators and reliability criteria for strength. A prerequisite is the use of the same time step for these calculations that was chosen to calculate the criteria for the residual resource.

After the first cycle of the unit, we have two values: N _sr1 and N _ras1 . After the second and subsequent cycles adds the totals available with the newly obtained for the cycle n and obtain the totals after a cycle n (ΣN _{compression channel} n and ΣN _{pac n).} Moreover, for each next cycle n, we evaluate the possibility of its trouble-free operation by adding to the sum ΣN cr _n and ΣN _{pac n the} values of ΣN cr _cf and ΣN _{pac cf,} respectively. If the obtained values are greater than the limiting totals compression (ΣN _SJ) or exemplary totals stretching (ΣN _p), then use the machine in the next cycle irrationally.

Show the following criteria: if a high temperature operation test unit to compress _{compression channels} k and k criterion for expanding _races exceed the values obtained, it is necessary to output high-temperature unit to be repaired. If during the working campaign k> 1, then the operation of the high-temperature unit is carried out with voltages exceeding the allowable limit, if k <1, then the resulting stresses do not exceed the tensile strength of the materials used.

The _remaining resource n _ost (in the number of cycles) can be estimated by the following formula:

EXAMPLE

During the heating of the steel pouring ladle, the values of temperature stresses were obtained, while during the heating process two periods of time are distinguished, the temperature tensile stresses in which exceed the permissible ones: (0 h 20 m - 2 h 10 m; 5 h 10 m - 7 h 30 m) ; compression stress: (0 h 30 m - 0 h 50 m; 5 h 20 m - 8 h 10 m).

Now, having the values of the real temperature stresses arising during the heating of the lining of the steel pouring ladle taking into account the step in coordinate and time, it is possible to calculate the criteria for the residual life. Here are the following data: when determining temperature stresses in time steps of 10 minutes and dividing the thickness of the refractory layer of the lining into six sections, with the above heating schedule, we obtain the values of the ultimate summary indicators for one cycle for compression - ΣN _{sr cf} = 6951.215; for tension ΣN _{pac cf} = 8516.46. Removing the temperature readings for the maintenance period ladle in general (overhaul) for 40 cycles, and calculating totals, we get the following: compression ΣN _SJ = 279,883.314; for tension, ΣN _pac = 342826.321. The calculated reliability criteria for strength are: for compression k _sr = 2.17; for expansion k _races = 1.91.

Technical and economic efficiency of the implementation of the proposed technical solution is to obtain data on the residual resource of thermal fencing of high-temperature units during operation and the use of these values during their operation.

Claims (9)

1. A method for determining the residual life of thermal fencing of high-temperature units, characterized in that reliability criteria are used as reliability indicators for reliability both for compression and expansion, determined by the formula:

where ΣN _SJ - the amount of value totals compression, defined by the formula: N _cr = σ _cr ⋅ (z + 1), where z is a coefficient taking into account the lengths of the compression and tension zones, in which the temperature stresses exceed the permissible ones, σ _squ are the stresses arising in the compression zone, ΣN ^additional _{compression channel} - the sum values of the total compression rates at the same point at the same time is similarly ΣN _{compression channel,} but at a value of σ _{compression channel} equal to the limit of the material strength, and the remaining service life _ost n is given by:

where ΣN _compression - the arithmetic mean of the total compression indicators for one cycle; n is the number of cycles of the high-temperature unit that have passed at the moment after the lining has been replaced, and the calculation of the reliability criterion for strength and the residual life for expansion are determined by similar formulas. 2. The method for determining the residual resource of thermal fencing of high-temperature units according to claim 1, characterized in that the determination of the residual resource is carried out continuously during operation of the energy unit.