Determination of indicators of reliability of thermal power equipment. On the assessment of the reliability of urban heat supply systems. Equipment limit state

The article was prepared on the basis of materials from the collection of reports of the VI International Scientific and Technical Conference "Theoretical Foundations of Heat and Gas Supply and Ventilation" NRU MGSU.

The analysis of the heat supply systems, carried out by the employees of the research laboratory “Heat power systems and installations” (NIL TESU) of UlSTU in a number of Russian cities, showed that due to the high degree of physical and moral deterioration of heating networks and the main equipment of heat sources, the reliability of the systems is constantly decreasing. This is confirmed by statistical data, for example, the number of damages during hydraulic tests in the heating networks of the city of Ulyanovsk has grown 3.5 times over eight years. In some cities (St. Petersburg, Samara, etc.) major accidents occurred in the main heat pipelines while maintaining high temperatures and pressures in heating networks, therefore, even in severe frosts, the temperature of the coolant at the outlet from the heat source does not rise above 90-110 ° C, then there are heat sources forced to work with systematic underheating of the network water to the standard temperature ("underheating").

Insufficient costs of heat supply organizations for renovation and overhaul of heating networks and equipment of heat sources lead to a significant increase in the number of damages and to an increase in the number of failures of centralized heat supply systems. Meanwhile, urban heat supply systems are life support systems, and their failure leads to changes in the microclimate of buildings that are unacceptable for humans. In such conditions, designers and builders in a number of cities refuse to supply heating in new residential areas and envisage the construction of local heat sources there: roof, block boiler houses or individual boilers for apartment heating.

At the same time, Federal Law No. 190-FZ "On Heat Supply" provides for the priority use of district heating, that is, the combined generation of electricity and heat for organizing heat supply in cities. Despite the fact that decentralized heat supply systems do not have the thermodynamic advantages of heating systems, their economic attractiveness today is higher than that of centralized heat and power plants.

At the same time, ensuring a given level of reliability and energy efficiency of heat supply to consumers is one of the main requirements that are imposed on the selection and design of heating systems in accordance with Federal Law No. 190-FZ "On Heat Supply" and SNiP 41-02-2003 "Heating Networks". The standard level of reliability is determined by the following three criteria: the probability of failure-free operation, the availability (quality) of heat supply, and survivability.

The reliability of heat supply systems can be increased either by improving the quality of the elements of which they are composed, or by redundancy. The main distinguishing feature of a non-redundant system is that the failure of any of its elements leads to the failure of the entire system, while in a redundant system the probability of such a phenomenon is significantly reduced. In heat supply systems, one of the methods of functional redundancy is the joint operation of various heat sources.

In order to improve the reliability and energy efficiency of heat supply systems, R&D Laboratory of TESU UlSTU has developed technologies for the operation of combined heating systems with centralized main and local peak heat sources, which combine the structural elements of centralized and decentralized heat supply systems.

In fig. 1 shows a block diagram of a combined heating system with a series connection of centralized main and local peak heat sources. In such a heat supply system, the CHPP will operate with maximum efficiency with a district heating coefficient equal to 1.0, since the entire heat load is provided due to the heat extraction of steam from the turbines to the network heaters. However, this system provides only redundancy of the heat source and an improvement in the quality of heat supply due to local regulation of the heat load. The possibilities of increasing the reliability and energy efficiency of the district heating system are not fully used in this solution.

To eliminate the shortcomings of the previous system and further improve the technologies of combined heat supply, combined heating systems have been proposed, with the parallel inclusion of centralized and local peak heat sources, which, when the pressure or temperature drops below the set level, make it possible to hydraulically isolate the local heat supply systems from the centralized one. The change in the peak heat load in such systems is carried out by local quantitative regulation for each of the subscribers by changing the flow of network water circulating through autonomous peak heat sources and local systems of the subscribers. In an emergency, the local peak heat source can be used as the base one, and the circulation of heating water through it and the local heat supply system is carried out using a circulation pump. The analysis of the reliability of heat supply systems is carried out from the standpoint of their ability to perform specified functions. The ability of a district heating system to perform specified functions is determined by its states with the corresponding levels of power, productivity, etc. In this regard, it is necessary to distinguish between an operable state, a partial failure and a complete failure of the system as a whole.

Technologies for operation of combined heating systems with centralized main and local peak heat sources have been created at the Research Laboratory of TESU UlSTU

The concept of failure is central to assessing the reliability of a heat supply system. Considering the fact that heat and power plants and systems are recoverable objects, failures of elements, assemblies and systems should be divided into failures of operability and failures of functioning. The first category of failures is associated with the transition of an element or system at time t from an operable state to an inoperative (or partially inoperative) state. Failures of functioning are associated with the fact that the system at a given time t does not provide (or partially does not provide) the level of heat supply specified by the consumer. It is obvious that a failure of an element or a system does not mean a failure of functioning. Conversely, a functional failure can occur even when no functional failure has occurred. Taking this into account, the choice of indicators of the reliability of the systems is made.

The known indicators can be used as single indicators of the reliability of elements or heat supply systems as a whole: λ (τ) is the intensity (parameter of the flow of failures) of failures; μ (τ) —recovery rate; P(τ) is the probability of no-failure operation during the time period τ; F(τ) is the probability of recovery over a period of time τ.

Let us compare the reliability of traditional and combined heating systems with the same heat load of 418.7 MW, of which the base load of 203.1 MW is provided at a CHPP with a T-100-130 turbine (network water consumption 1250 kg / s), and the peak load is the size of 215.6 MW peak heat sources. The CHPP and the consumer are connected by a two-pipe heating network 10 km long. In a traditional district heating system, the entire heat load is supplied to the CHP. In one combined system, the peak heat source is installed in series centralized (Fig. 1), in the other - in parallel (Fig. 2).

The consumer has three hot water boilers installed in the boiler room, one of which is reserve.

As seen from Fig. 1 and 2, any district heating system is a complex structure. Calculating the reliability indicators of such multifunctional systems is a rather time-consuming task. Therefore, to calculate the reliability indicators of such systems, the decomposition method is used, according to which the mathematical model for calculating the reliability indicators of the system is divided into a number of submodels. This division is carried out according to technological and functional characteristics. In accordance with this, a main heat source (CHP), a heat transport system from CHP to consumers, a decentralized peak heat source and a distribution network system to cover heating loads are allocated in the district heating system. This approach allows the calculation of reliability indicators for individual subsystems independently. The calculation of the reliability indicators of the entire district heating system is carried out as for a parallel-serial structure.

From the point of view of reliability, the heating unit of a CHPP is a complex structure of series-connected elements: a boiler unit, a turbine, a cogeneration plant. For such a structural diagram, the failure of one of the units leads to the failure of the entire installation. Therefore, the availability factor of the heating unit is determined by the formula:

where k g CHP, k r to, k r t and k r tu - the availability factors of the entire CHPP, boiler unit, turbine and cogeneration plant, respectively.

Stationary values ​​of the availability factor k r for the corresponding elements of the circuit are determined depending on the intensity of the restorations }