Hot gas duct

The hot gas duct is represented by coaxial pipes between core and reformer. The iimer hot gas pipe is insulated on the inside and cooled by counterflow on the outside. Since the steam generator has to be on the alert in case of a decay heat removal action, the pipe system has to be safely constructed. In particular, fast pressure transients which could be destructive should be avoided by means of flow limitation. 

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The reactor core and the steam generator are housed in two steel pressure vessels, which are connected by a connecting vessel. Inside the connecting vessel, the hot gas duct is mounted. All pressure-retaining components, which comprise the primary pressure boundary, are in touch with the cold helium of the reactor inlet temperature. 

Fig. 2-14 Schematic of a hot gas duct between the reactor core and the steam reformer, from [36]...

Protective coatings for the hot gas duct tested were a NiCrAlY basis layer followed by a Y2O3 stabilized Zr02 layer. Other components which need to be especially designed are the isolation valves. Two different kinds have been investigated, axial-type and ball-type valves. Further tests before application are still necessary [41]. 

Two concepts of a He - He intermediate heat exchanger for a heat rating of 125 - 170 MW have been selected. For both, a 10 MW test plant has been operated in the KVK loop verifying the operation of reformers with convective helium. A 10 MW decay heat removal system cooler, hot gas ducts including insulation and liner, hot gas valves, and a steam generator were other components of the KVK loop. Furthermore, a helium purification system was operated in a bypass of the main system. Starting in 1982, the KVK facility was operated for 18,400 h with approx. 7000 h above 900 C [28]. Hot gas duct with internal insulation was operated at temperatures up to 950 °C. The KVK experimental loop has demonstrated reliability and availability even of newly developed components. 

The construction of a follow-up reformer test stand, EVA-II, was started in 1980. EVA-n consisted of a bundle of 30 reforming tubes based on the baffle plate design with an irmer/outer diameter of 100/120 mm and a length of 11.4 m. Helium throughput was 4 kg/s. The other components of this helium loop besides the 10 MW electric heater were a hot gas duct, steam generator, and helium circulator. Methane input was 0.6 kg/s. The product gas was generated at a rate of 4400 kg/h. 

Developments for the application of continuous fiber reinforced SiC matrix composites (CMCs) have started with and are concentrating on hot components in military and space technology hot gas ducts and thermal heat shields for space... 

The reactor and the steam generator are arranged side by side. The pressure boundary of the primary circuit is consisted by the reactor vessel, the steam generator vessel and the connected vessel (hot gas duct vessel)... 

The test components of the fuel handling system and the small absorber ball system, the prototype of the control rod driving apparatus and the test section of the hot gas duct are designed in 1 1 scale. It is planed to perform the experiments at the operation temperature and helium atmosphere conditions. The experiments of the fuel handling system and small absorber ball simulating system at ambient temperature had been carried out. 

The HCIHX for the HTTP is a vertical helically-coiled counter flow type heat exchanger in which the primary helium gas flows on the shell side and the secondary in the tube side as shown in Fig.2. The major specification is shown in Table 1. The primary helium gas of the maximum 950°C enters the HCIHX through the inner tube In the primary concentric hot gas duct. It is deflected under a hot header and discharged around the heat transfer tubes to transfer primary heat to the secondary cooling system. It flows to the primary circulator via an upper outlet nozzle and returns between the inner and outer shell in order to cool the outer shell. 

On the other hand, the secondary helium gas flows downwards inside the heat transfer tubes and is heated up to 905°C. It flows upwards inside the central hot gas duct. The inner insulation is installed inside the inner shell to maintain the temperature of the inner shell under the allowable one. The thermal insulator outside and inside the central hot gas duct prevents the heat transfer between the primary and secondary coolant except the heat transfer area on the heat transfer tubes so that high heat transfer efficiency can be obtained, and the temperature of the central hot gas duct is maintained under the allowable one. The pressure of the secondary helium gas is controlied higher than that of primary helium gas for prevention of fission product release even if the heat transfer tube should be broken. 

A tube support assemblies hold the heat tubes. Both central hot gas duct and heat tube support assemblies are hanged with a vessel top so that thermal expansion cannot be constrained. 

Behaviour of hot gas ducts, bellows, valves and insulation under thermal loads, pressure gradients, acoustic emissions and helium impurities... 

Helium turbine with gas seals, oil seals, bearings, cooling systems, insulation Helium compressor with gas seals, oil seals, bearings Helium/helium heat exchangers/recuperators, coolers Hot gas ducts with valves, butter fly valves, bellows, bends Helium purification Coatings in helium atmosphere... 

The highest helium-temperatures were achieved at the HP compressor outlet. Hot helium could be conducted completely or partially through the test section or directly bypassed back to the turbine for expansion by means of hot gas ducts provided with regulation valves. 

Helium flowed through the inlet nozzle into the turbine section. Behind the compressor outlet helium flowed through the outlet diffiisor into the outlet nozzle and from there into the hot gas duct. Inside the turbomachinery only the inlet and outlet nozzles, the diffusors and the blading channel were exposed to high temperatures. All other sections of the machine (blade feet, rotor and housing) were cooled by means of the cooling gas system or the sealing gas system (see Fig. 8). 

After performing the above described modifications the seal of the horizontal turboset flange as well as the front seal of the shaft seal carrier proved their reliability. The measured leak tightness of these flange joints was better than 10 Torr 1 per second. The weld lip seals of the hot gas duct were tight. Thus the helium losses against the ambient environment amounted to 10 - 20 NmVd at 51 bar (out of total helium inventory of about 8000 Nm ). 

The modal composition of the acoustic emissions released into the hot gas duct was determined also. Fig. 29 shows the modal compositions measured at different pressures and temperatures during the trial run. 

Fig. 29 Modal composition of the acoustic emmissions into the hot gas duct...

A coaxial design was selected for the hot gas ducts of the EVO plant. The hot helium (750 °C) flows in an inner liner tube, with a fibre-type insulation provided on the exterior, enclosed by a inner pressure bearing tube. The colder helium flows in a surround annulus, with the outer tube designed for full system pressure. 

Hot Gas Ducts with Insulation. Regulation Valves. Bellows Hot eas Ducts... 

For development purposes three different types of hot gas duct sections were used and evaluated ... 

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