Sliding pressure

In the simplest case, burnished molybdenum disulphide films are produced by applying a smooth sliding pressure to molybdenum disulphide powder against the hard surface which is to be coated. This can be done by means of a pad of soft material such as fabric or cotton waste under hand pressure, but a variety of mechanical devices has been used in order to produce more consistent films. Figure 6.1 shows an example of a device used to produce burnished films on rings or cylinders . 

The 10% secondary species serum incubation allows for protein to bind to charged sites on the specimen. The additional 10 min incubations are extra protection against unwanted antibody sticking nonspecifically. The concentration of the serum solution and the time of incubation may be increased if desired. In some cases, the use of charged slides, pressure cooking with Reveal (Biocare Medical, Concord, CA) (see Chapter 13), and special buffer systems such as the TBS plus buffer with Tween 20 added, may alleviate the need for extensive normal serum blocks. Incubations in buffer may be substituted for the 10% serum incubations. 

Polymer Melt Temperature Polymer melting was determined on dry, powdered polymer on a chrome-plated gradient temperature bar (14) and Is noted as the temperature at which the polymer under moderate sliding pressure leaves a molten or waxy trail adhering to the bar. 

The sliding-pressure Venturi scrubber developed by Siemens/KWU and described by Eckardt (1988) allows operation at the pressure level prevailing inside the containment down to an overpressure of about 0.1 MPa, without need of a throttle valve in the venting line the water droplets generated in the liquid phase of the scrubber during operation of the system are retained by a steel fiber filter located inside the scrubber tank. The scrubber can be designed in a manner to reduce water losses due to evaporation caused by the decay heat of the absorbed radionuclides to an insignificant level. 

A supercritical fossil-fired power plant with a once-through steam cycle is usually operated with a sliding pressure the turbine governor valve is kept open in the upper load range and the boiler outlet temperature is kept constant such that the boiler outlet pressure increases proportionally with the steam mass flow and thus with load. Consequently, the boiler is operated at subcritical pressure below approximately 80—90% load. However, such control is not permitted for the SCWR because dryout... 

The modified sliding pressure staitup as proposed by Yi et al. (2005) can be adapted to the proposed operating conditions in the Canadian SCWR concept. To provide a starting point for future analysis of critical performance characteristics (eg, fuel cladding temperatures and thermal-hydraulic and neutron stabilities), reference operating conditions (eg, flow rates, reactor power levels, and mechanical equipment configurations) have been selected. 

Yi, T.T., Ishiwatari, Y., Liu, J., Koshizuka, S., Oka, Y., 2005. Thermal and stability considerations of super LWR during sliding pressure startup. Journal of Nuclear Science Technology 42 (6), 537-548. 

In Japan, the first supercritical FPP, Anegasaki No.l started operation in 1967 with a rated power of 600 MWe. The supercritical FPP technologies have been improved constantly in Japan because of the high fossil fuel prices. Since fuel cost is the major part of the power generation cost in FPPs, improvement of the thermal efficiency would reduce the power cost. The sliding pressure plant Hirono No. 1 was deployed in 1980. It operates at subcritical pressure at partial load. Japanese... 

FPPs need to be operated in the daily load-follow mode. Frequent startups and shutdowns are necessary. Sliding pressure plants meet these needs. 

Since sliding pressure plants are operated at subcritical pressure at partial load, they achieve higher thermal efficiency than constant pressure operation at supercritical pressure. To improve the thermal efficiency at rated power, the high pressure plant, Kawagoe No. 2 started operation with conditions of 31 MPa and 566°C in 1989. This was followed by the high temperature plant, Tachibanawan No. 1, with conditions of 25 MPa and 610 C. 

There are two types of supercritical FPPs. One is the constant pressure FPP that starts heating and operates at partial load at the supercritical pressure. The other is the sliding pressure FPP that starts heating at a subcritical pressure, and operates at subcritical pressure at partial load. A steam-water separator and a drain tank are needed for the startup of the sliding pressure FPP. The sliding pressure FPP operates with better thermal efficiency at subcritical pressure at partial load than the constant pressure FPP. In Japan, nuclear power plants are used for base load, and the FPPs are used for daily load following. Minimum partial load is 30% for the constant pressure FPP and 25% for the sliding pressure one [41,42]. 

The sliding pressure startup systems of the Super LWR and a supercritical FPP are shown in Fig. 1.17 [41]. A steam-water separator is installed on the bypass line for the Super LWR, while it is installed on the main steam line for the supercritical FPP. The Super LWR has an additional heater installed to recover heat from the drain of the steam-water separator. When the enthalpy is low, the drain is dumped into the condenser directly. A boiler circulation pump can be used instead of the additional heater the same as in the sliding pressure FPP. 

Boiling (and dryout) must be prevented in the water rods at subcritical pressures (in sliding pressure startup scheme). 

Fig. 1.17 Sliding pressure startup systems of the Super LWR and supercritical FPP. (a) Super LWR with additional heaters [41] (b) Super LWR with recirculation pumps [41]. (c) Supercritical FPP. (Taken from ref. [41] and used with permission from American Nuclear Society)...

The calculation model for sliding pressure startup of the Super LWR is shown in Fig. 1.18 [43]. Examples of the sliding pressure startup curves based on the thermal considerations are shown in Fig. 1.19 [43]. 

Fig. 1.18 Calculation model for sliding pressure startup scheme. (Taken from ref. [43] and used with permission from Atomic Energy Society of Japan)...

The sizes of the components required for the startup schemes are assessed. The sliding pressure startup with a steam separator in a bypass line is the best from the viewpoint of weight of the components. A study of the times needed for the startup schemes remains as future work. There is a limitation on the rate due to thermal stresses on thick-walled components such as the RPV. In BWRs, the temperature rise rate of the RPV wall is limited to below per hour. 

The present analysis is based on the heat transfer correlations for smooth tubes. When turbulence is promoted, the cladding temperature rise at dryout will be suppressed. The maximum allowable power between 20 and 22 MPa will increase. Ribbed or rifled tubes and spiral tapes are used in supercritical FPPs to suppress the boiling transition during the sliding pressure operation and the sliding pressure... 

Fig. 1.22 Revised sliding pressure startup system of the Super LWR and the Super FR...

Fig. 1.23 Redesigned curves of sliding pressure startup before the power raising phase...

Fig. 1.33 Sliding pressure startup curve with thermal and stability considerations...

Safety Transient and accident analysis at supercritical-and subcritrical pressure (SPRAT-F, SPRAT-DOWN), ATWS analysis (SPRAT-DOWN), LOCA analysis (SCRELA,SPRAT-DOWN-DP), Time-dependent subchannel analysis Start-up (sliding pressure and constant pressure)... 

Dryout or boiling transition may occur during the sliding-pressure startup of the once-through reactor as seen in Fig. 1.21 [43, 44]. Ribbed tubes and spiral tapes have been used for the supercritical boilers to improve the critical heat flux. The... 

There are two kinds of startup schemes currently used in FPPs [1]. One is the constant pressure startup scheme, in which the boiler operates at constant supercritical pressure after the coolant is pressurized to this point. The other is the sliding pressure startup scheme, in which the boiler operates with variable pressures and the pressure increases with the generation output. 

The plant system of the sliding pressure supercritical fossil-fired boiler is shown in Fig. 5.2. It requires a steam-water separator, a separator drain tank, drain valves, and recirculation pumps. A minimum flow rate is maintained through the furnace walls by using a recirculation pump to add a recirculating flow to that provided by a boiler feedwater pump. The water leaving the furnace is passed to the steam-water separators. The water from the separators is collected in the drain tank and routed back to the economizer inlet via the boiler recirculation pump. 

Faster ramp rates are possible in sliding pressure operation, as the thermal stress in the turbine during the load change is reduced. Plant thermal efficiency is much improved in partial load operations. Turbine life expenditure per cycle can also be reduced by ramping pressure with load. 

Fig. 5.7 Sliding pressure startup system of Super LWR with recirculation pumps (taken from ref. [2] and used with permission from American Nuclear Society)...

The sliding pressure startup system can be differentiated into six phases described below. 

During subcritical pressure operation in the sliding pressure startup of the Super LWR, a steam-water separator is required to separate the steam and water such that the water can be recirculated to the reactor inlet by recirculation pumps or by additional heaters, in order to maintain adequate core cooling. The size and weight of the steam-water separator are determined by referring to those of sliding pressure supercritical FFPs. The characteristics of the reference 700 MW supercritical boiler and the properties of its steam-water separators are given in Table 5.3. 

---