Sodium gas heat exchanger

Figure 3.3 Concept of sodium gas heat exchanger for ASTRID.

In the ASTRID project, different power conversion systems (PCSs) are investigated based on the classical steam/water Rankine cycle and on an innovative gas (pure nitrogen) Brayton cycle. It is mainly motivated by enhanced safety and public acceptance with the practical elimination of the sodium/water reaction risk [22]. In this gas PCS, the main innovative component is the compact sodium gas heat exchanger (SGHE),... 

Figure 17.4 Photographs of machined plates for compact a sodium gas heat exchanger [22],...

O. Gastaldi, G. Laffont, Stams of the sodium gas heat exchanger (SGHE) development for the nitrogen power conversion system planned for the ASTRID SFR prototype, in Proceedings of ICAPP 2015, Paper 15362, Nice, France, 2015. 

After purification in dry boxes, the gas was pressurized slightly (lo 20-30 in. water) preheated in a gas-to-gas heat exchanger to about 430°-570°F and passed through the bed of catalyst. Oxidation of the sulfur compounds, and some of the hydrogen, caused an increase in gas temperature to about 700°F at the catalyst bed exit. The hot gas was partially cooled in the heat exchanger then further cooled by washing with a dilute solution of. sodium carbonate, which also served to remove the SO2. 

The purpose of the liquid metal test was to provide NRPCT experience with a lithium liquid metal system and to understand the nature of liquid lithium, freeze/thaw issues, and operational issues. The NRPCT directed MSFC to modify an existing stainless steel sodium/potassium (NaK) circuit to allow it to be operated with lithium. Basic circuit components included a simulated reactor segment (a 37 pin core block, outer pressure shell, inlet plenum, outlet plenum), lithium to gas heat exchanger, electromagnetic (EM) liquid metal pump, load/drain reservoir, expansion reservoir, instrumentation, and trace heaters, as shown in Figure 13-21. Testing was to occur in the Early Flight Fission Test Facility (EFF-TF) vacuum chamber described in Section 13.3.2. 

Titanium is the only one of the more common structural metals which is not attacked by wet chlorine gas and it is thus widely used as a heat exchange material for cooling the gas after the electrolysis stage. Preheating of sodium chloride brine is carried out in titanium plate heat exchangers, while titanium butterfly valves, demisters, and precipitators handle the chlorine gas produced in the cell. The most important use of titanium in chlorine production is as anodes in place of graphite in the electrolytic process. This is covered in more detail later. 

The manufacture of sponge rubber products such as gaskets for heat exchangers is based on the inclusion in the compound of chemicals which cause gas formation during vulcanization and thereby produce the desired porosity. Sodium bicarbonate and ammonium bicarbonate are examples of popular blowing agents. 

Carbonate Process. In this process the ores are leached with hot sodium carbonate for 24 hours, with sparging with air to provide oxidation. The leachate is cooled in counter-current heat exchangers, heating the carbonate solution for the next batch. The carbonate leachate is filtered on rotary drums, and the uranium is precipitated with sodium hydroxide and filtered. The filtrate is converted back to carbonate by sparging with carbon dioxide, usually from a boiler flue gas, and... 

As alluded to in Chapter 8, the ideal biomass feedstock for thermal conversion, whether it be combustion, gasification, or a combination of both, is one that contains low or zero levels of elements such as nitrogen, sulfur, or chlorine, which can form undesirable pollutants and acids that cause corrosion, and no mineral elements that can form inorganic ash and particulates. Ash formation, especially from alkali metals such as potassium and sodium, can lead to fouling of heat exchange surfaces and erosion of turbine blades, in the case of power production systems that use gas turbines, and cause efficiency losses and plant upsets. In addition to undesirable emissions that form acids (SOx), sulfur can... 

In the recleaning of the heat exchanger, several of the parallel, return-bend U-tubes (1 inch in diameter) were purposely pitched to assure a long section (approximately 10 feet) of trapped sodium. As would be expected from the previous estimate of the diffusion coefficient for water through concentrated caustic, the humid gas was not effective in removing these sodium pockets. The humid gas did successfully reclean the balance of the heat-exchanger circuits. In this phase of the operation, the maximum temperature rise did not exceed 130 °F. 

---