Research Article |
Corresponding author: Sergey V. Yaurov ( yaurovsv@nvnpp1.rosenergoatom.ru ) Academic editor: Georgy Tikhomirov
© 2022 Sergey V. Yaurov, Andrey V. Borovoy, Andrey V. Yudin, Mikhail V. Bolgov, Aleksandr D. Danilov.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Yaurov SV, Borovoy AV, Yudin AV, Bolgov MV, Danilov AD (2022) Computational and experimental justification for increasing the performance of the regenerative heat exchanger in the steam generator blowdown system of the AES-2006 project (RU V-392M). Nuclear Energy and Technology 8(4): 297-302. https://doi.org/10.3897/nucet.8.97652
|
The article discusses the design and operation modes of the regenerative heat exchanger (RHE) in the steam generator (SG) blowdown and drainage system (LCQ) at Novovoronezh NPP-II 1 and 2 (Project AES-2006).
The results of mathematical modeling of the RHE operating modes are presented in order to identify the causes of its low efficiency.
Based on the results of the commissioning of the SG blowdown and drainage system at NvNPP-II 1, as well as the thermohydraulic calculations of the RHE operating modes, the authors put forward assumptions regarding changes in the rerouting of the piping (
The upgrading in the RHE piping was implemented first at NvNPP-II 2 at the stage of installing the systems and, after the expected result was confirmed, it was applied in April 2020 at NvNPP-II 1.
In addition, the authors carried out a comparative analysis of the results of testing the thermohydraulic characteristics of RHEs of the blowdown and drainage system for NvNPP-II 1 (before upgrading, after upgrading in scheduled maintenance 2020) and NvNPP-II 2.
These improvements made it possible to achieve more efficient operation of the RHE in the SG blowdown and drainage system and the system as a whole.
AES-2006, blowdown, steam generator, upgrading, regenerative heat exchanger, piping, rerouting, RU V-392M, operation
The regenerative heat exchanger (RHE) is part of the blowdown and drainage system of the steam generators (SGs) at Novovoronezh NPP-II 1 and 2 and is designed to cool the blowdown (boiler) water from the SGs, before it undergoes special water treatment (SVO-5), and to subsequently heat the purified blowdown water returning to the SGs in different operating modes of the unit (
The heat exchanger is a vertical type apparatus, consisting of two removable covers, a body, nozzles, supports, sling devices, cylindrical multi-pass coils (located inside the body between two tube sheets). A general view of the heat exchanger is shown in Fig.
Design of the regenerative heat exchanger in the SG blowdown and drainage system: 1 – supply of the cooled medium from the SG; 2 – supply of the cooled medium from the RHE to the blowdown aftercooler; 3 – supply of the purified coolant from SVO-5 for heating; 4 – return of the purified and heated coolant to the SG
The medium being cooled from the SGs (for purification) is supplied “from the bottom up” through the tubular space, and the heated purified medium (from SVO-5) is supplied “from the top down”.
The main characteristics of the heat exchanger are presented in Table
Parameter | Value |
---|---|
Outer diameter of the heat exchange pipes and their thickness, mm | 15×1.5 |
Total number of the heat exchange pipes, pcs. | 488 |
Heat exchange surface area (according to the outer diameter of the pipes), m2 | 310 |
Outer diameter and thickness of the body in the central part, mm | 1200×65 |
The main parameters of the heat exchanger are presented in Table
Parameter | Value |
---|---|
Temperature of the cooled medium at the RHE inlet, from special water treatment in the SG (intertubular space), °С | 50 |
Temperature of the cooled medium at the RHE outlet, from special water treatment in the SG (intertubular space), °С | 237–251 |
Medium pressure, MPa | 6.9 |
Temperature of the cooled medium at the RHE inlet, from the SG (tubular space), °С | 285 |
Temperature of the cooled medium at the RHE outlet, from the SG for special water treatment (tubular space), °С | ≥ 100 |
Medium flow rate, t/h | 140 |
The commissioning work of the SG blowdown system showed the low performance of the RHE system at NvNPP-II 1 (
Table
Results of Commissioning of the RHE in the SG Blowdown System (Before Upgrading)
Parameter | Test results | Design data | |
---|---|---|---|
Blowdown flow rate at the RHE inlet (from the SG), t/h | 148.2 | 60.0 | 140 |
Temperature of the cooled medium at the RHE inlet, from the SG (tubular space), °С | 281.2 | 280.0 | 285.0 |
Temperature of the cooled medium at the RHE outlet, from the SG for special water treatment (tubular space), °С | 144.4 | 205.0 | ≤ 100 |
Temperature of the cooling medium at the RHE inlet, from special water treatment in the SG (intertubular space), °С | 62.08 | 60.0 | 50 |
Temperature of the cooling medium at the RHE outlet, from special water treatment in the SG (intertubular space), °С | 212.12 | 156.0 | 237–251 |
The measured temperature changes in the tubular and intertubular space of the RHE at NvNPP-II 1 for a flow rate of 60 t/h and 148.2 t/h are shown in Fig.
The design temperature changes in the tubular and intertubular space of the RHE are shown in Fig.
The authors of this article have previously put forward an assumption about the reasons for low temperatures before and after the RHE, namely, the low flow rate of the coolant in the intertubular and tubular space of the heat exchanger (0.34 m/s and 0.63 m/s) for the design flow rates of the medium in the system (
The calculations were carried out using the Ansys program (CFX thermohydraulic module) (
To estimate the rate in the heat exchange tubes of the regenerative heat exchanger, a 3D model was built (Fig.
The calculation results showed that the average rate in the RHE tubes was no more than 0.47 m/s.
The calculation, in which hot water from the SG to the RHE tubes is supplied “from the top down” (that is, the scheme for connecting the RHE piping proposed by the authors, opposite to the design scheme) showed that the average rate in the RHE tubes would be 0.7 m/s.
Thus, the assumption about the influence of the piping connection scheme on the RHE performance was confirmed.
The proposed option for rerouting the RHE piping was initially accepted for implementation at NvNPP-II 2 during the installation of the blowdown system, and after the expected result was confirmed during the commissioning of the system, it was applied in April 2020 at NvNPP-II 1 (Fig.
RHE piping of the SG blowdown system: a. before upgrading at NvNPP-II 1; b. after upgrading in 2020 at NvNPP-II 1 and 2 (1 – supply of the medium being cooled from the SG into the RHE; 2 – supply of the cooled medium from the RHE to the blowdown aftercooler and further to SVO-5; 3 – supply of the purified coolant from SVO-5 to the RHE for heating; 4 – return of the purified and heated coolant from the RHE to the SG)
Changing the direction of the flow of the cooled and heated medium increases the heat exchanger performance (Figs
Figs
Based on Figs
The results of testing the new RHE connection configuration at NvNPP-II 1 showed that the RHE of this power unit provides the temperature difference in the tubular and intertubular space as close as possible to the design (calculated) data.
The commissioning of the SG blowdown system at NvNPP-II 1 revealed insufficient RHE performance in terms of ensuring temperature differences in the tubular and intertubular space.
Based on the results of the commissioning of the RHE in the SG blowdown system at NvNPP-II 1, according to the proposals made by the authors of this article (with a confirmed thermohydraulic calculation of the heat exchanger), with the recommendations of the developers of the system and the RHE manufacturer taken into account, the RHE piping at NvNPP-II 2 was rerouted so that the medium being cooled from the SG in the tubular space is supplied “from the top down” and the heated medium in the tubular space is supplied “from the bottom up” (forced and convective movement of the medium coincide).
The results of testing this RHE connection configuration at NvNPP-II 2 showed that the RHE of this power unit provides the temperature difference in the tubular and intertubular space as close as possible to the design (calculated) data.
The test results of the new RHE connection configuration at NvNPP-II 1 showed as follows:
The RHE also provides temperature differences in the tubular and intertubular space as close as possible to the design (calculated) data; and
The expected (calculated) result from the RHE upgrading was confirmed.
Changing the RHE connection scheme made it possible as follows:
To reduce the temperature difference between the feed water pipelines and the blowdown water return pipes to the SG;
To reduce the heat load on the blowdown aftercooler and, as a result, reduce the heat load on the intermediate circuit system of normal operation consumers; and
To ensure the design modes of operation of the SG blowdown system and the intermediate circuit system of normal operation consumers.
According to the test results, it was decided to modernize the RHE piping at NvNPP-II 1 as well.