Turbo-machine

Non-contact seals with defined narrow clearances, such as labyrinth seals in turbo-machines (Fig. 4.1-47 A), are less problematic owing to the relatively low differential pressures however, the fluid should not have an erosive effect. Differential pressures up to several hundred bar occur at the axial-thrust compensation pistons of centrifugal pumps and compressors, but the fluid expansion is distributed over the many labyrinth stages. 

The load schedule specifies for normal at-power operation a unique plant steady state at each power level over the normal operating range, typically from 25 to 100% of full power. This includes the values of all plant forcing functions such as turbo-machine power inputs and reactor and cooler heat rates. For normal operating transients the load schedule gives conditions at which a transient begins and ends. If the transient is an upset event, then while it begins from a point on the load schedule it may terminate at some stable off-normal condition not found on the load schedule. 

The HTE hydrogen plant presents largely an electric load to the nuclear plant. Various scenarios can be envisioned under which the generator load might quickly disconnect from the turbo-machine shaft. These include an electrical distribution fault in the hydrogen plant, an electrical fault in the generator, or the need to stop hydrogen production for safety reasons. 

In the event of quick disconnect a torque imbalance occurs and the PCU shaft begins to over speed. If no control action is taken the terminal speed is a function of PCU loop friction losses and the turbo-machine performance curves. To prevent damage from the over speed condition, a bypass valve is opened to redirect flow from the high pressure compressor to the outlet of the turbine. 

Work to date has resulted in evolving designs for all three blowers, as shown in Figures 1, 2 and 3. All three designs utilized a typical turbo-machine design process that included tasks such as specific speed analysis, blade optimization, rotor-dynamic analysis, bearing analysis, thermal analysis, and motor optimization studies. Each machine has been... 

Because of their relatively low cost, duplicate full-capacity pumps are usually installed, but occasionally two pumps having different functions can be provided with a common backup. In the case of reciprocating machines, in addition to a complete backup (2x100% capacity), 2 x 66% capacity, or in exceptional cases 3 x 50% capacity, may also be considered. Turbo machines are usually installed at 1 x 100% capacity, but provision is made for rapid replaceability of parts which are subject to wear. Alternatively, two machines with 50% capacity are often installed. 

Flow distribution in various flow paths such as those among recuperator banks, at inlet and outlet of the turbo machines etc. will be measured. 

Methods and remote handling equipments (if necessary) for removal or installation of turbo-machines can be tested. 

Isomura K, Tanaka S, Togo SI, Esashi M (2005) Development of high-speed micro-gas bearings for three-dimensional micro-turbo machines. J Micromech Microeng 15 222-227... 

A summary of the Turbo-Machine/Generator design parameters are listed below Summary of plant conceptual design parameters... 

Turbo-machine Design Parameters Net Shaft Power Rotational Speed LP Compressor Stages HP Compressor Stages Turbme Tip Speed Bearings 298 MW 3600 RPM 14 19 322 m/sec Active magnetic, 3 radial, 1 thrust... 

Depressurization (Primary) Core Heat-up, air ingress, Over-speed/failure of turbo machine/compressor failure of magnetic bearings... 

Turbo machine Leakages, Ruptures (prunary) Very high level of quality (R) Magnetic beanngs (S) Very high quality level for pressure vessel (burst proof) (S) Limitation of connectmg pipe diameters (L) Provision of isolation valves to be closed automatically (L)... 

In order to simplify the system by reducing the number of turbo machines, the cathode off-gas is used for the combustion process. This measure leads to a high air ratio of 4.4 and a low adiabatic temperature of about 640 K. With regard to CH4 emissions, complete methane combustion requires a temperature of 723-773 K. 

As a result, 1.54 kW of electricity was supplied to the turbo machine and 10.47 kW to the fuel cell. Peripheral components, such as pumps and compressors, demanded... 

To reduce dose impacts on the personnel, aftercooling within the first month is performed without disconnecting the turbine plant cars from the reactor car. During this time, a reduced power operation of the gas turbine plant is used to remove heat, via heat exchangers, from the primary coolant. In this, turbo-machines could be used both jointly and separately, within a simple gas turbine cycle. Separate use of the turbo-machines makes it possible to organize two independent channels for aftercooling. 

To limit maximum temperature of the reactor module in the first period of aftercooling, forced circulation of the primary sodium is employed, using the sodium circulation pumps. In this, the power for the pumps is supplied either from the main generator or from small-power generators connected to the shafts of the turbo-machines, or from reserve power sources - on the total, there is a five-fold redundancy of power supply for the main circulating pumps. 

In addition to the turbo-machines, a gas-blower blowing the gas through gas heaters (heat exchangers) could be used at the first stage of an aftercooling. 

Compressors fall into one of two fundamental types - positive displacement and turbo-machines. Positive displacement machines can be either rotary or reciprocating. They both trap the gas in a cylinder and then force it into a smaller volume and so increase its pressure. Turbo-machines impart velocity to the gas and its momentum carries it into a narrowing space and so its pressure increases. Turbo-machines can be either axial (in which the flow is parallel to the shaft) or centrifugal (in which the flow is at right angles to the shaft). Multistage turbo-machines, with intercoohng, are common. 

Compressors are designed as turbo or positive displacement machines. The two types have different operahonal behaviour. With turbo machines the amount of compressed gas decreases with increasing pressure, while the machines of the second group deliver, owing to their displacement principle, nearly a constant mass flow independent from the discharge pressure. Piston and screw compressors are the most prominent displacement machines. 

Major power conversion system components require detailed design and validation. These components include the turbo machine (helium turbo compressor and generator), recuperator, and pre-cooler/intercooler. 

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