Intermediate heat exchangers

Most fast reactors that use Na or NaK as coolant utilize an intermediate heat exchanger (IHX) that transfers heat from the radioactive core coolant to a nonradio active Hquid-metal coolant loop, which has the reactor s steam generator. This helps minimize the spread of contamination in the event of a leak or fire. 

FIG. 13-2 Complex distillation operations with single columns, a) Use of intermediate heat exchangers, (h) Coupling of intermediate heat exchangers with heat pump, (c) Heat pump with external refrigerant, (d) Heat pump with vapor compression, (e) Heat pump with hottoms flashing. 

Identify cases where feed or intermediate heat exchangers would be helpful, when only one of the operating lines is too far from the equilibrium curve. A large gap for the bottom section could indicate potential for feed preheat or an interreboiler. A large gap for the top section could portend precooler or intercondenser need. 

As of 1990, seven industrial-scale plants were operating in Russia (Bunimovich et al., 1990). The first plant started up in 1982. The design of these plants generally follows the schematic given in Fig. 7. Some employ an intermediate heat exchanger, but details have not been published. Designs are marketed around the world by several organizations. 

Intermediate frequency (IF), 23 142 Intermediate heat exchanger (IHX), in fast reactors, 17 586... 

The most effective method of SNG production with an HTGR is the stcam-carbon reforming process in which superheated steam reacts with pulverized coal to form methane-rich SNG. A system for accomplishing this process is shown in Fig. 24. In this system, an intermediate heat exchanger (1HX) has been used to isolate the nuclear heat source from the process steam, thus allowing the use of conventional equipment for... 

Both gas turbine and process heat versions of the HTGR are based on the demonstrated high-temperature capability of the fuel and core structure. However, some development in the metallic components, such as the turbine, hot duels and intermediate heat exchanger is necessary, Present commercial alloys would have limited lifetime under service conditions at 1650°F (899°C) and above. However, currently envisioned advancements in ceramics and carbon-carbon composites indicate that high-temperature nonmctallic substitutes for metallic alloys will soon be available. These materials advances are the key to making future application of the IITGR a reality. 

Takeda T, Kunitomi K, Horie T, Iwata K. Feasibility of the applicability of a diffusion-welded compact intermediate heat exchanger to next-generation high-temperature gas-cooled reactors. Nucl Eng Design, 1997 168 11-21. 

Takeda, T., Kunitomi, K., Horie, T., Iwata, K., Feasibility study on the applicability of a diffusion-welded compact intermediate heat exchanger to next-generation high temperature gas-cooled reactor, Nucl. Eng. Des. 1997, 168,11-21. Bier W., Keller W., Linder G., Seidel, D., Schubert, K., Martin, H., Gas-to-gas heat transfer in micro heat exchangers, Chem. Eng. Process. 1993, 32, 33-43. Schubert, K., Brandner J., Fichtner M., Linder G., Schygulla, U., Wenka, A., Microstructure devices for applications in thermal and chemical process engineering, Microscale Therm. Eng. 2001, 5,17-39. www.fzk.de, Forschungszentrum Karlsruhe, 17 July 2004. 

Equation (6.14) is used for the temperature of gas in the tubes of the intermediate heat exchanger used in the multistage adiabatic reactor system. Heat is transferred from the hot gas to saturated water on the shell side generating steam at temperature Tst. The overall heat transfer coefficient Uux is constant and is equal to 0.227 kJ s-1 m-2 K-1. The heat transfer area per volume Ahx/Vhx is 157 m2/m3 ... 

H. Sato (JAEA) presented a paper discussing detection methods and system behaviour assessments for a tube rupture of the intermediate heat exchanger (IHX) for a sulphur-iodine based nuclear hydrogen plant. A rupture could be detected by monitoring the secondary helium gas supply using a control system that monitors the differential pressure between the primary and secondary helium gas supply. Isolation valves would be used to reduce the helium flow between the primary and secondary cooling systems. The study showed that the maximum temperature of the reactor core does not exceed its initial value and that system behaviour did not exceed acceptance criteria. 

Figure 3 briefly shows the structure, major specification and the history of the HTTR R D by JAEA. The reactor core is composed of graphite prismatic blocks. Fuels are inserted in the blocks as a shape of cylindrical graphite compacts in which tri-isotropic (TRISO)-coated fuel particles with U02 kernel are dispersed. The coolant helium gas of the HTTR is circulated at 4 MPa to an intermediate heat exchanger where high temperature heat is transferred to hydrogen production process. 

In general, there are two alternatives for coupling the S-I process to a VHTR. In the first, secondary helium is initially used to supply heat to the MT/HT1 sulphuric acid decomposition steps. LT helium heat is then consumed by the HI decomposition section before the helium return to the intermediate heat exchanger. In the second alternative, heat integration between the chemical process steps allows for helium heat supply solely to the MT/HT sulphuric acid decomposition steps. Residual process LT heat recovered there is utilised in the HI decomposition section. 

VT Voltage transformer (from 15 kV to 400 V), SG Steam generator (or the intermediate heat exchanger), SH Superheater (steam heated from 770°C up to 800°C), HR Heat recuperators (at low and high temperature), WT Water treatment. 

Intermediate heat exchanger failure Damage of SSC Blow-down effects Large mass transfer Pressurisation of either secondary or primary side... 

The reaction chamber energy balance is written in terms of the total internal energy, U. In each reaction chamber, reactant with a given energy is added, reactant with a given energy leaves, and heat is added via the intermediate heat exchanger. Thus ... 

The heat transfer through the intermediate heat exchanger is the crux of the coupled system. The heat transfer through the intermediate heat exchanger is given via the following simple expression ... 

In a coupled nuclear hydrogen generation system, the reactor loop will be coupled to the chemical loop via an intermediate heat exchanger (IHX). This coupling is illustrated in Figure 1. 

Conceptual design of the HTTR-IS nuclear hydrogen production system Detection of the heat transfer tube rupture in intermediate heat exchanger... 

Figure 1 Primary system and intermediate heat exchanger...

In ammonia synthesis, high temperatures correspond to small reactor volumes. For exothermic reactions, the equilibrium conversion Xe decreases as the temperature increases. Therefore, these reactions are often carried out in a series of adiabatic beds with either intermediate heat exchangers to cool the gases or bypass the cold feed to decrease the temperatures between the beds. Some compromise can be achieved between high temperatures involving small reactor volumes and high equilibrium conversions. 

If a gradual addition of reactant has kinetic advantages compared to the total addition to the feed (here a suitably designed intermediate heat exchanger ensures a uniform distribution and mixing within the reaction gas stream). 

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