Application of plate heat exchanger in CARR

Application of Nuclear Power Engineering Plate Heat Exchanger in CARR Han Haifen, Zhang Jinshan, Jiang Baihua, Zhuang Yi (Reactor Engineering Research and Design Institute of B*Zi Energy Research Institute, Beijing, 102413) Abstract: Focus on heavy water exchange in CARR project Selection of heat exchangers and main heat exchangers and design process. Through comparisons between safety and economy, it can be seen that the plate heat exchanger is superior to the casing heat exchanger. The application of plate heat exchanger in the system has a classification for the future design: TL353+.丨3 1 The reactor coolant system of China Advanced Research Reactor (CARR), heavy water cooling system, emergency core cooling system is CARR Important system.

The reactor coolant system carries the core heat ft through the coolant, and transfers heat to the secondary cooling water system using the main heat exchanger. The extra-external portion of the system consists of four sets of main circulation pumps, main heat exchangers, and associated valves and lines in parallel.

The heavy water cooling system uses two heavy water chestnuts to transport the heavy water in the heavy water storage tank to the heavy water tank through the heavy water heat exchanger, and overflows into the heavy water storage tank through the outlet of the heavy water tank to form a heavy water circulation loop, and transmits the heat ft of the heavy water tank to the second Secondary cooling water system.

The function of the emergency core cooling system is to ensure that the core is adequately cooled during reactor accident conditions, keeping the core temperature within safe limits and preventing fuel element damage.

The above three important systems all require heat exchangers for heat transfer. Therefore, the heat exchanger is the key equipment of the system, and its quality plays an important role in performing system functions.

2 Heat exchanger design Because the medium in the heavy water heater is heavy water and secondary cooling water, the medium in the main heat exchanger and the water heat exchanger is deionized water and secondary cooling water, for different media, The requirements for sealing are also different. Therefore, the design of the heat exchanger will be described according to the design of the different weight water heat exchangers of the medium, the design of the main heat exchanger and the water heat exchanger.

2.1 Heavy water heat transfer design Because of the high price of heavy water, it is radioactive after being irradiated by neutrons. In order to avoid the leakage of heavy water and prevent radioactive pollution to the environment, the design of the heavy water heat exchanger must have the characteristics of sealable, radioactive protection and small volume.

2.1.1 Radioactive protection design has two main aspects: 1 to prevent internal leakage. It is necessary to ensure that the pressure on the light water side is greater than the pressure on the heavy water side, so that once the light water leaks, it leaks into the heavy water, and the environment is not polluted; 2 to prevent leakage. To be embodied in the structural design of the heat exchanger. 2.1.2 Material selection When determining the material, the water chemistry of the fluid, the electrochemical and thermal compatibility with the contact material, the erosion and corrosion resistance, the radiation resistance, and the processing properties (including weldability) are mainly considered. , malleability, etc. Based on the above requirements, the main material of the heat exchanger is 0Crl8Nil0Ti, and the material of the secondary water tank is 20 steel, which is consistent with the pipeline material of the loop system. 2.1.3 Structure and material of the heat exchanger 2.1.3. 结构 Structural design of the preliminary design stage The preliminary design of the heavy water heat exchanger uses a horizontal, countercurrent, single-pass casing-type heat exchanger. The heat exchanger has rich operation experience, and the secondary cooling water flows through the inner tube, and the heavy water flows backward through the annular gap between the inner tube and the outer tube, so that the heat transfer of the helium can be obtained with the minimum amount of heavy water filling. effectiveness.

2.1.3.2 Determination of plate heat exchangers During the construction design, it is known that AFLAF has a long history of manufacturing plate heat exchangers for heavy water, and has rich and reliable design, processing and manufacturing experience.

Compared with the casing heat exchanger, the plate heat exchanger is easy to assemble and disassemble, which is beneficial to cleaning and descaling, low cleaning frequency, low cleaning time, no need for regular inspection, and low failure rate. When the structural material of the plate is metal, the unit heat transfer surface is cheaper than the pipe. Due to the high degree of fluid turbulence in the flow channel, the possibility of fouling in the heat exchanger is greatly reduced and the heat transfer coefficient is relatively high. Its structure is shown in Figure 丨. The parameters of the two heat exchangers are compared as shown in Table 1.

Table 12 Comparison of various parameters of heat exchangers Table parameter casing heat exchanger for exchange of heavy water 1 secondary water heavy water side secondary water * heat work * / MW flow / m3 population / * c export waterfall / T resistance l*/m (water column) liquid material footprint (length X width y heat exchanger number / table from the table i can be found that the plate heat exchanger has the following advantages over the casing heat exchanger: (1) small size, The small footprint reduces the investment of funds.

Operating costs are low. Since the heavy water heat exchanger adopts a countercurrent type, in order to reduce the radioactive leakage, it is necessary to ensure that the light water side pressure is greater than the heavy water side pressure, that is, the secondary water outlet pressure is greater than the heavy water inlet pressure. It is not difficult to see from Table 1 that the use of the plate heat exchanger reduces the lift of the heavy water pump and the secondary water pump by 25.7 m and 19.86 m, respectively, and reduces the flow rate of the secondary cooling water by 674 m3/h, respectively. Operating expenses.

The heavy water heat exchanger was changed from casing type to plate type, and it was changed from the original 2 sets to 1 set, which saved 21 valves and dozens of pipelines of large and small, and changed the specifications of some pipes from the original <>219x8. It is 4>159x6, which simplifies the pipeline layout. It is easier and more convenient to overhaul. It reduces the hidden danger of heavy water leakage and saves 1.8m3 of heavy water (worth RMB 3.96 million).

Maintenance and cleaning are easier and more convenient.

The price is low. The total cost of manufacturing, processing and design of plate heat exchangers is about 75,000 euros (750,000 yuan), while the processing price of casing heat exchangers is about 1.5 million yuan per unit. The total cost of the machine will reach 3 million yuan.

Through the above analysis, the original casing heat exchanger design was replaced by a plate heat exchanger in the construction design stage.

2.1.3.3 Plate heat exchanger material selection The choice of plate material and gasket material is also very important. According to the fluid water quality index, it is determined that the plate still selects 0Crl8Nil0Ti, and the gasket selects NBR (acrylonitrile butadiene rubber). Codex AFLAF experts believe that in the application of heavy water systems, the conventional plate heat exchanger is sufficient to ensure that it does not bleed, because heavy water does not cause any corrosion to the gasket. Usually, the gasket used in heavy water 5 It needs to be replaced only once in a year or so. Considering the impact of heavy water leakage on the environment and certain economic losses, a semi-welded plate heat exchanger was selected, that is, two plates for circulating heavy water were sealed by laser sealing, and two of the secondary cooling water were circulated. The plates are connected by conventional gaskets, making the design safer, more economical, more reasonable and more advanced. The structure of the seal weld is as shown.

2.2 Design of main heat exchanger and pool water heat exchanger Since the fluid medium in the main heat exchanger and the pool water heat exchanger are both deionized water and secondary cooling water, the main heat exchanger is a safe secondary, the pool water heat exchanger For safety-related grades, the design description here is only for the main heat exchanger.

The model selected for the main heat exchanger is M30*FD. This heat exchanger is the same type of the same heat exchanger used by HANARO in Korea. The heat exchanger has been used for several years, and its experience is worth learning. During the 10-year period, the gasket was replaced twice.

Zhang Zhanli (1976-), male, assistant engineer. In 1997, he graduated from Beijing Nuclear Industry School with a major in nuclear reactor engineering and testing. Now working on reactor engineering.

Fan Yuerong (1970-), female, engineer.丨 Graduated from the mechanical manufacturing process and equipment of Jimei University in Xiamen in 996. Now from the reactor engineering design... Dai Shoutong (1974-), male, sulphur. In 2006, he graduated from China Academy of Atomic Energy with a major in reactor science and engineering. Now from the mechanical analysis of reactor piping.

(Editor: Liu Jun) (Continued from page 85) In fact, the replacement cycle of the gasket depends on the operation of the heat exchanger, because the gasket is fixed in the groove of the heat exchanger by pressing, and is pressurized. After the deformation occurs, it will not return to the original state, so if there is no leakage during the operation or the heat exchanger can not meet the heat transfer efficiency, do not disassemble the heat transfer plate 3. The application of the plate heat exchanger in the domestic research reactor For the first time, the device is currently in the installation phase. Due to the small footprint, low operating cost, long maintenance period and easy maintenance, and low investment, it is reasonable to believe that the plate heat exchanger is further applied in the research reactor field.

Han Haifen (1972-), female, engineer. In 1997, he graduated from Zhongnan Institute of Technology majoring in chemical machinery.

Zhang Jinshan (1974-), male, engineer. In 1998, he graduated from Harbin Engineering University with a major in thermal engineering.

Jiang Baihua (1977-), female, engineer. In 2000, he graduated from Harbin Engineering University with a major in nuclear engineering.

(Editor: Liu Jun)

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