DE3637872C2 - - Google Patents

Description

The present invention relates to a device for off couple heat, e.g. B. in the combined gas turbine steam Turbine process according to the preamble of claim 1.

The combination of gas and steam turbine enables the thermal Efficiency of fossil power plants but also of a high temperature reactor can be increased significantly. To achieve it required heat at high temperature from 1000 to 1100 ° C coupling out of the boiler system or other heat generators and supply the compressed air to a hot air turbine. Furthermore, the decoupled heat in chemical is also conceivable Processes or use in gas production.

For heat extraction was already in GB-A 21 70 898 sodium as a heat carrier in High temperature sodium circuits suggested as they already do are known for low temperatures in the range up to about 600 ° C. However, the known sodium cycles are difficult or do not switch to high temperatures at all, as this Series of particularly difficult technical problems occurs for which are currently not seen as any solutions.

Some of these problems are the following:

• - High temperature materials with the required strength for piping and larger components of such circle runs are not yet known. The well-known Hochtem temperature materials can currently in the required high temperature range submit only up to approx. NW 50 with an acceptable wall thickness be set.
• - Na pumps of the required size are only for temperatures developed up to 600 ° C. The most developed principle is protected with a vertical shaft and slip ring seal provided space. Because at high temperatures a strong sodium vapor diffusion into the protective gas space and the shaft seal takes place, it is doubtful whether this principle of Ab seal can also be used at high temperatures.  
• - Impellers of such pumps are hydrostatic in sodium stored, with special material pairings required are. These must have good emergency operation to start the pumps have properties and are not allowed to stand on their own tend to weld. Such materials are also for high Temperatures not yet known. Electromagnetic pumps, that do not have the problems mentioned, there are in the necessary orders of magnitude not. Furthermore such pumps have the crucial disadvantage of a bad one Efficiency.
• - Similar material problems apply to sodium fittings for the pumps. The valve seat must be made of a material com combination exist, even under pressure not to self-confidence welding tends to apply to all moving, with each other parts in contact.

From DE-OS 27 25 670 heat pipes as recuperators be knows, but are not suitable for liquid metals.

JP 55-158 493 (abstract) shows heat exchanger tubes with a Heat source on the bottom and a heat sink on the top Side, these at different geodetic heights are ordered and the coolant evaporates or should condense.

From DE-AS 27 25 347 it is known to heat gas to what to transmit water using liquid metal. The liquid metal however, only forms a relatively thin layer between the heats exchange surfaces. There is no cycle in this zone instead of. The purpose of this device is to regulate the power of the Heat exchanger on influencing the level or Liquid metal mirror.

JP 52-116 950 (abstract) shows a single circuit evaporating coolant, in the upper part of which  there is a loop in which the coolant again should condense. However, this loop is not in within a tube carrying the secondary medium, but is attached to the outer wall.

Ultimately, DE-OS 19 10 378 is a heat exchanger or a recuperator known in which a pipe system with ge common main channel through the partition between two media is passed through.

Based on this prior art, the present one Invention for the task of a device described above level without creating pumps, which is particularly good for the use of boiling liquid metal is suitable and in the case of heat extraction dispense with large sodium circuits and their components can be.

The present Er proposes to solve this task Find the features that are in the characteristics of the patent Proverb 1 are listed. An advantageous embodiment results from the features in the characterizing part of claim 2.

In this way you can now use the excellent heat transfer and natural convection properties of boiling liquid metal in take advantage of compact natural convection loops that form modules be summarized. The temperature controllability is through Setting the boiling pressure very well, which, for. B. for Ma material stress in the high temperature range, however also for the use of heat in chemical processes  can be of great importance. The number of each Modules are not limited per se, i. H. it can be any desired amount of heat can be transferred without new components or having to develop systems.

The main advantages of the present invention are included:

High temperature materials are currently available, their Strength allows it to hold pipes up to approximately NW 50 in size use natural convection system according to the invention. By the compact structure, the required amount of expensive high temperature materials and liquid metal low compared to a nor paint circulatory system, e.g. B. Sodium per kW of heat output only 0.08 kg, 0.4 kg for the known sodium circuit. The development of new pumps, fittings and piping systems can ent fall. Sodium leaks in one of the modules pose no problems for the system, since the modules are separated or can be switched off separately.

Further details of the device according to the invention will be provided explained in more detail below with reference to the figure:

The figure shows the principle of a heat extraction device with boiling sodium as a heat carrier using one of the examples Pipe grinding.

The at least partially with a liquid metal such. B. sodium or a sodium-potassium alloy filled tube loop 1 transports the heat from a furnace 3, not shown, through the boiler wall 2 to the outside into a heater tube 4th The heater tube 4 guides the air to be heated and is between the manifold 5 z. B. a hot air turbine and the manifold 6 , the z. B. leads a compressor before compressed air, turned on. The pipe loop 1 is now - seen from the furnace 3 - divided into the following sections:

• The section assigned to the furnace 3 or the section 7 in which the heat is absorbed and the liquid metal is brought to the boil,
• the riser pipe 8 , which leads upwards over a certain geodetic height difference,
• the condensation loop 9 already located in the heater tube 4 , which practically forms the front part of the heat-absorbing tube section 10 ,
• - The other, assigned to the heater tube from vertical or section 10 and
• - The - viewed in the direction of flow - sloping down pipe 11 returning downward from section 10 to the beginning of section 7 .

In the area between these, an adjustable throttle point 12 is switched on, by means of which the coolant throughput can be varied.

The amount of heat Q _k is thus absorbed in the radiation part of the furnace by the section 7 , supplied in the boiling phase of the coolant through the upper riser 8 and the heat-releasing sections 9 and 10 and then as heat Q _L in the heater tube 4 , which flows in the direction 13 of the hot-air turbine Hot air supplied. The temperature in the condensation loop 9 remains constant as a result of the back condensation, the loop area with two-phase flow 14 of the liquid metal is shown by the dashed accompanying line on the outer edge of the loop.

The air heater in the form of the tube 4 is thus practically arranged on the outer wall 2 of the boiler, since the geodetic height arrangement and distance from the boiler are inherently prescribed by the convection principle in the tube loop 1 . Since the pipe length of the loop 1 can only be varied within narrow limits, large air heater units are not possible individually, but a modular construction must be used, of which a single loop is shown in the figure. The modular air heaters or loops 1 all open with their respective heater tube 4 in the manifold 5 to the hot air turbine. On the liquid metal side, there is no need for the collectors that are otherwise customary with pipe registers with a pipe connecting the heat-absorbing and heat-emitting exchanger surface.

For a natural convection system that transmits 300,000 kW _th , the following key data are given as an example:

Number of natural convection pipe loops 12,000
Air heater modules with 18 loops 666 each
Sodium content of the system 30 tons
required amount of high temperature material 204 tons
Material number 4967 (C 0.1%, Co 52%, Cr 20%, Ni 10%, W 15%, Fe 3%)

Compared to a heat transfer circuit with liquid Sodium in forced convection is exceptional low values.

The functionality of a natural convection loop is largely determined by the ratio of the pressure loss of the two-phase flow to the lift gain, which results from the weight difference between the hot two-phase column and the cold single-phase column of the loop. This ratio was calculated assuming a vertically arranged pipe loop with an inner diameter of 20 mm and a power of 20 or 50 kW to be transported. Only the vapor phase (1100 ° C at 5.6 bar) was taken into account for heat transport. The result shows that at 25 kW the buoyancy over the range of the steam content (x = 0.05 to 0.7) is several times greater than the pressure loss due to the two-phase flow, a prerequisite for the safe operation of the natural circulation system. At 50 kW, the two-phase pressure drop increases sharply due to the doubling of the steam speed. Only for steam contents above X = 0.15 will the two-phase pressure drop be less than the buoyancy. There is no longer a safety factor for safe operation due to a higher lift. The limit of the transferable power for a pipe loop NW 20 is in the range between 25 and 50 kW. Since an additional throttle point 12 is provided in the phase region of the loop or section 10 for reasons of stabilization of the natural con vection loop, a throttled, lower power of 25 kW is assumed in the following considerations. When the boiling temperature is reduced, the power that can be dissipated also decreases because the two-phase pressure loss - assuming the same power - increases sharply as a result of the lower vapor density and thus higher vapor velocity. An optimal function of the natural convection loop is therefore only possible at boiling temperatures of 950 ° C (1.77 bar steam pressure). In the example shown in the figure and described above, the temperatures are 1000 ° C at the beginning and 1100 ° C at the end of Pipe section 7 .

Such a pipe loop must meet the following two criteria can be optimized:

The overall piping of the loop should be as short as possible, while maximizing the height difference between heat-absorbing and heat-emitting loop sections 7 and 10 .

For a suitable arrangement according to the figure, the total pipe length is 16 meters. The required amount of liquid metal in two-phase operation is approximately 2.5 liters per loop, ie approximately so much that the heating surface on the furnace 3 is fully covered. With a wall thickness of 2 mm, 17 kg of a heat-resistant material are required for the loop. The following specific data result from this estimate, based on 1 kW of heat output to be transferred:

Required flow cross section 0.125 cm³ / kW
Liquid metal quantity 0.08 kg / kW
Highly heat-resistant material 0.68 kg / kW

Reference symbol list

1 pipe loop
2 boiler wall
3 firing
4 heater tube
5 manifold to the turbine
6 manifold from the compressor
7 section for heat absorption
8 riser pipe
9 condensation loop
10 section for heat emission
11 downpipe
12 throttling point
13 flow direction
14 Loop area with two-phase flow

Claims (2)

1. Device for decoupling heat from a heat generator through the wall thereof by means of a circuit with liquid metal as a heat carrier for the heat transfer from the heat generator to a heat consumer, characterized in that the heat carrier circuit is divided into a plurality of modularly combined individual circuits, in which the Circulation of the heat transfer medium by natural convection and heat absorption when the heat transfer medium is boiling in the range of approximately 1000 to 1100 ° C means that the individual circuits each consist of a tube loop ( 1 ), in which the heat is transferred to a heater tube ( 4 ) and parallel in the heater tube ( 4 ) extending section ( 10 ) is arranged at a greater geodetic height than the heat-absorbing section ( 7 ) and these two essentially vertical sections ( 10, 7 ) at their respective ends through an inclined upward riser pipe ( 8 ) and an oblique downward-running downpipe ( 11 ) are connected to one another, the heat-emitting section ( 10 ) being designed in its upper region as a pipe loop ( 9 ) likewise located inside the heating pipe ( 4 ), in which the heat transfer medium, flowing in two phases, condensed, and which, with its end facing the heat-absorbing section ( 7 ), is connected to the riser pipe ( 8 ) guiding the boiling heat transfer medium. 2. Device according to claim 1, characterized in that as liquid metal Na or a NaK alloy is used.