Secondary circulation loop

Secondary Circulation Loop Temperature Control Systems... 

This is the simplest system for temperature control of a reactor only the jacket temperature is controlled and maintained constant, leaving the reaction medium following its temperature course as a result of the heat balance between the heat flow across the wall and the heat release rate due to the reaction (Figure 9.9). This simplicity has a price in terms of reaction control, as analysed in Sections 6.7 and 7.6. Isoperibolic temperature control can be achieved with a single heat carrier circuit, as well as with the more sophisticated secondary circulation loop. 

Figure 9.8 Heating cooling system with secondary circulation loop.

Figure 9.9 Isoperibolic temperature control with a secondary circulation loop.

In the Messo turbulence crystallizer, a secondary circulation loop (see vortex) -driven by the primary circulation loop - is created in the outer suspension section. This secondary circulation loop serves the purpose of sorting out the coarser crystals from the inner draft tube recirculation process, concentrating them in an outer... 

Performing a reaction under isothermal conditions is somewhat more complex. It requires two temperature probes, one for the measurement of the reaction mass temperature and a second for the jacket temperature. Depending on the internal reactor temperature, the jacket temperature is adjustable. The simplest method is to use a single heat carrier circuit to act either on the flow rate of cooling water or on the steam valve. With a secondary heat carrier circulation loop, the temperature controller acts directly on the heating and cooling valves by using a conventional... 

Figure 9.10 Isothermal control with a secondary heat carrier circulation loop.

Nuclear heat transfer to desalination plant The nuclear power plant supplies steam to three turbogenerators and to a desalination plant (80 000 tonnes of desalinated water per day). To transfer the heat from the reactor to the intermediate heat exchangers six primary parallel sodium loops and six independent secondary sodium loops are provided. The turbine exhaust steam under the pressure of 0.6 MPa (6 bar) is supplied to the desalination plant, and the condensate produced with the temperature of about 100°C flows to a heater and a deaerator and is pumped by feedwater pumps to the natural circulation steam generators (Fig. 4). 

There are no pumps or valves in the primary and secondary coolant loops. The coolants flow by natural circulation ... 

Decay heat removal. Several types of passive decay heat removal systems have been used in liquid-metal reactors. The AHTR, like S-PRISM, uses RVACs. There are other options such as DRACs, a secondary natural circulation loop to remove heat from the reactor vessel to the environment. This provides multiple longer-term cooling options including the options that may ultimately allow larger power outputs. 

The primary, secondary and tertiary (steam-water) circuits each have three loops. Each secondary circuit loop includes two intermediate heat exchangers (enclosed in the reactor vessel), steam generator, sodium expansion tank, main circulating pump and pipes. The once-through steam generator consists of eight sections, each comprising three modules evaporator, superheater and reheater. Every section can be isolated (if necessary) by valves. 

Sodium filling into the systems and start of circulation operation - Primary system - Reactor tank and loop 1 (i.e. constructicHi completed) - loop 2/loop 3 -Secondary system loop 1/loop 2/loop 3 -Emergency core cooling system -Na-cooled fuel store and cooling system 28.04.85 02.05.85/09.05.85 24.11.84/07.02.85/ 28.02.85 15./19.06.85 30.03.85-05.05.85... 

The FC crystallizer contains an external circulation loop through a heat exchanger and may also contain an evaporation zone within the main vessel with crystals removed at its base, as shown in Figure 3.3 (ii). Since both crystals and liquor circulate through the pump, secondary nucleation rates and crystal breakage are high. The product crystals are typically in the size range 200-500 pm. 

The MBIR reactor configuration is typical for SFR with three loops with a secondary sodium loop (Tretiyakov and Dragunov 2012). MBIR safety features include a passive removal of decay heat in the primary loop by natural circulation, physical separation of the primary and secondary systems to cancel out the possibility of radioactive sodium leakage, and a fuel core catcher inside the reactor vessel. The operations and controls of MBIR also have safety features built in, such as automated process control systems to decrease the chances of operator error. CDF and LRF are estimated at 9.8 X 10 per reactor year and 6.1 x 10 per reactor year, respectively (Tretiyakov et al., 2014). The main design characteristics of the MBIR reactor are given in Table 12.4. 

Develop conceptual designs of primary and secondary coolant loops. The feasibility of natural circulation for both should be investigated in more detail. 

The system is the union of two old ideas enhanced by new technology. The old ideas are singlepipe distribution and primarysecondary pumping. The new technology consists of the use of maintenance-free wet rotor circulators. The primary distribution system is a single-pipe loop the secondary distribution system is a decoupled secondary piping loop for each terminal unit in the system. 

Natural circulation flow rate is 4% rated flowrate for each primary coolant loop and 3% rated flowrate for each secondary side loop of SG respectively. Air flowrate is about 290Kg/s for each air cooler. 

FIG. 17. Natural circulation flowrate for secondary side loop of each SG... 

Consider a simple nonuniform diameter natural circulation loop as shown in Fig. 1 with a horizontal heat source at the bottom and a horizontal heat sink at the top. The heat sink is maintained by providing cooling water to the secondary side of the cooler at a specified inlet temperature of Tj. In this analysis, the secondary side temperature is assumed to remain constant. The heat flux at the heat source is maintained constant. Assuming the loop to be filled with an incompressible fluid of constant properties except density (Boussinesq approximation where density is assumed to vary as p=pr[l-P(T-Tr)]) with negligible heat losses, axial conduction and viscous heating effects, the governing differential equations can be written as... 

The term channel induction furnace is appHed to those in which the energy for the process is produced in a channel of molten metal that forms the secondary circuit of an iron core transformer. The primary circuit consists of a copper cod which also encircles the core. This arrangement is quite similar to that used in a utdity transformer. Metal is heated within the loop by the passage of electric current and circulates to the hearth above to overcome the thermal losses of the furnace and provide power to melt additional metal as it is added. Figure 9 illustrates the simplest configuration of a single-channel induction melting furnace. Multiple inductors are also used for appHcations where additional power is required or increased rehabdity is necessary for continuous operation (11). 

In the other design, PWRs have two closed loops of water circulating in the plant plus a third, external loop to remove the waste heat. Water is pumped through the reactor core in the primary coolant loop to moderate the neutrons and to remove the heat from the core as in the BWR. However, the reactor vessel is pressurized so that the water does not boil. Steam is necessary to run the turbines, so the primary loop transfers the heat to a secondary loop. The water in the secondary loop is allowed to boil, producing steam that is isolated from both the core and the outside. The water in the primary loop usually contains boron (as boric acid H3BO3 0.025 M) to control the reactivity of the reactor. The steam in the secondary loop is allowed to expand and cool through a set of turbines as in the BWR the cold steam condenses and is returned to the primary heat exchanger. A third loop of water is used to maintain the low-temperature end of the expansion near room temperature and remove the waste heat. 

Secondary Cooler The secondary cooler takes the exit gases from the oxidation unit at 140°C and cools them down to 65°C, a suitable temperature for entry into the absorption column. It is a shell and tube-type heat exchanger constructed of SS304L. The cooling medium is circulating warm water from the warm-water loop. The inlet temperature is 50°C and the exit temperature is about 80°C. The design pressure for this unit is about 1200 kPa. 

The ammonia vaporizer receives liquid ammonia from the adjacent plant at - 15°C and 1240 kPa and vaporizes it at 35°C using warm water. The warm-water loop circulates water from the ammonia vaporizer to the secondary cooler. Water enters the ammonia vaporizer at 80°C and exits at about 50°C. 

In the secondary loop, a feed water pump circulates water through a heat exchanger where the primary and secondary loops exchange heat. The water in the secondary loop is turned to steam here and feeds a turbine, where electricity is generated. In the boiling-water reactor, there is only one loop, and as a result, the overall efficiencies are higher at the added expense... 

The product gas leaves the secondary reformer at a temperature of 885°C and is heat-exchanged in the primary membrane reformer. After that, the product gas leaving the gas-heated reformer is utilised for preheating of the natural gas feed, heating of circulating water in the saturator loop and generation of LP steam at 3 bar. Finally, after a temperature decrease to 265°C the gas is fed to a shift converter, after which again methanation takes place and removal of CO2 and traces of water. 

Energy produced in the reactor is carried away by means of a coolant such as pressurized water, liquid sodium, or carbon dioxide gas. The circulating coolant absorbs heat in the reactor once outside the reactor, it is allowed to boil or the heat it contains is used to boil water in a secondary loop. Steam produced in either of these ways is then piped into the electrical generating unit, where it turns the blades of a turbine. The turbine, in turn, turns a generator that produces electrical energy. 

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