DE102011000655B4 - heat transport system - Google Patents

Abstract

A method for transporting heat, in which a storage material is transported in a transportable container from a heat source to a heat sink, the container having connections (A, B) for charging and removing gas, the storage of sensible heat at temperatures above 100 °C, a solid, porous, in particular mineral storage material (233) is used, which is introduced into the container as a bed, the bed being in fluid connection with the connections, with gas being used to store or remove high-temperature heat above 100 °C of the connections is passed through the bed, so that storage material is thermally charged or discharged in direct gas-solid contact, characterized in that the exhaust gas of an internal combustion engine (220) is passed through the bed for storage, the grain size distribution of the storage material (233 ) is chosen so that the differential pressure at the Du The flow through the completely heated bed and the installed exhaust system is in the range of 30 to 95 percent of the maximum permissible exhaust back pressure of the combustion engine (220).

Description

The invention relates to a heat transport system. In particular, the invention relates to a heat transport system that does not require any predefined, installed transport routes, e.g. lines, as well as the mobile heat storage tanks required for this and the methods for loading and unloading them.

Due to rising energy prices and the anthropogenic greenhouse effect caused by the burning of fossil fuels, it is necessary to use the available energy more efficiently and also to develop energy sources that have not been used up to now. With the help of the mobile heat storage devices described here, it is possible to transport previously unused waste heat from the point of origin (heat source) to heat consumers (heat sinks) in order to use it there. As a result, other energy sources can be substituted in the heat sinks and the burden on the environment can be reduced.

In principle, it is possible to transport this waste heat from the source via a local or district heating network to heat sinks. In many cases, however, the construction of such a pipe-bound heating network is difficult or uneconomical. This is particularly the case when there are difficult terrain situations such as crossing rivers or railway lines.

There are generally three physical processes available for storing thermal energy without a line connection: sensible, latent and thermochemical heat storage. The first systems that use the storage of latent heat in order to transport it without being tied to a line are already available on the market. With these latent heat accumulators based on sodium acetate, the temperature that can be extracted is limited to about 50 °C due to the process.

The document DD2 52 664 A1 describes a mobile heat storage system for transport by road, rail or water, in which both solid, liquid and gaseous heat storage materials can be used. The system is intended for use with decentralized heat consumers, with heating and hot water preparation systems.

The DE 31 15 988 A1 proposes a hot water storage tank in which both hot and cold water are present simultaneously and without mixing, with a separation between the hot and cold sides. The tank has cold water inlet and hot water outlet, there is a movable waterproof wall between inlet and outlet. It is intended to move the water from the inlet to the outlet side of the wall, at the same time displacing the wall

In the EP 2 158 432 B1 a heat accumulator is disclosed in which the energy is stored in heat accumulator blocks in which the evaporator tubes are embedded, into which a liquid condensate is dripped, after which vapor forms in the evaporator tubes and the heat content of the vapor is used for heating.

The EP 2 350 549 B1 describes a heat accumulator traversed by a pipe system. The system has a section in which a working medium flows to supply and remove thermal energy. A thermally chargeable storage material is arranged in a further section. A fluid flows through the sections when the storage material is being charged or discharged in order to transfer the heat energy between the piping system and the storage material, with the storage material containing flow channels for guiding the fluid.

The object of the invention is to make existing waste heat potential from other heat sources usable in a safe and efficient manner and thus to contribute to resource conservation and climate protection.

This object is achieved according to the invention by a method according to patent claim 1 and by a heat transport container according to patent claim 5.

The invention is based solely on sensible heat storage. The temperature of the heat carrier (the heat storage material) is therefore changed in order to absorb or release heat energy. The charged heat carriers are then taken from the location of a heat source to a heat sink, where the heat is discharged.

The invention is intended in particular for the mobile use of waste heat from industrial, commercial and agricultural sources.

In general, waste heat can occur as low-temperature heat (below 100 °C, e.g. cooling water from combined heat and power plants from biogas plants) and as high-temperature heat (above 100 °C, e.g. process steam or exhaust gas from combined heat and power plants). According to the invention, the storage of high-temperature heat is provided (T>100°C).

According to the invention, high-temperature heat is stored in a solid heat storage material stored, wherein a solid, porous, in particular mineral storage material (233) is used.

According to the invention, containers with the storage material are transported on the available transport routes between heat sources and heat sinks. The concepts are geared in particular to road transport, but other transport systems are also conceivable. Storage materials with a mass of 5 to 50 tons are used. For easier integration into existing logistics concepts, the storage tanks can be designed in a container-like design.

The high-temperature storage according to the invention is suitable for using the exhaust gas waste heat from generators to generate electricity or combined heat and power plants. There are currently around 5,000 biogas plants installed in Germany with a total electrical output of around 1.7 GW, which are operated with an average availability of 8,000 hours per year. The thermal output that can be used by biogas plants roughly corresponds to their electrical output. The proportion of usable high-temperature heat is almost half of the thermal output. The vast majority of biogas plants do not have sufficient heat utilization, which is mainly due to the installation sites in rural areas.

The high-temperature heat accumulator according to the invention is a variation of the functional principle of the hot blast stove of the blast furnace process (so-called Cowper), in which chamotte-based bricks are used as heat accumulator material and in which the heat transfer also takes place through direct gas-solid contact without additional heat exchangers. However, the use of fireclay bricks is ruled out for mobile heat storage because they have insufficient mechanical strength. In addition, their high thermal resilience is not required when storing engine exhaust gases. According to the invention, a solid, porous, preferably mineral storage material can be used. According to a preferred embodiment, a gravel pack represents a suitable combination of mechanical and thermal stability with low material costs at the same time.

With a storage density of around 100 kWh per tonne of storage material, the economically required transport radius for high-temperature heat is greater than that for low-temperature heat. In addition, the storage of high-temperature heat opens up further areas of application that hardly relate to the storage of low-temperature heat according to the invention or the first commercially available mobile latent heat storage devices based on sodium acetate (cf. www.latherm.de), in which the temperature that can be extracted is limited to around 50 °C due to the process to realize. These other areas of application include, for example, steam generation, the operation of adsorption chillers for low-temperature applications and the heating of process water to over 60 °C, which is required for reasons of drinking water hygiene to kill legionella. Even if a part of this area of application could theoretically be opened up by using other latent heat storage media, this would be done at the cost of overcoming corrosion problems and a possible classification in the Dangerous Goods Ordinance. To date, no processes have been able to establish themselves on the market for thermochemical mobile heat storage, e.g. with zeolites.

The loading and unloading of high-temperature heat takes place through direct gas-solid contact, as this allows the best heat transfer to be achieved. In addition, due to the process, there are no costs for heat exchangers. According to the invention, the heat storage material is transshipped by exchanging transport units, which can be designed as containers, for example.

Short transport and handling times are of particular economic importance for the realization of the invention. Depending on the technology used, the agreed prices for the waste heat and the storage material transported, the value of a storage charge ranges from 50 to over 100 euros. In the event of a future increase in the permissible total weight for truck transport, this value would increase accordingly.

With the current operating costs for trucks or larger tractors of around 60 to 80 euros per hour (including the driver), the economically justifiable transport radius is between 5 and 15 kilometers and is therefore significantly larger than the supply radius of most local heating networks.

The advantage of the mobile high-temperature heat storage according to the invention is the extremely simple and robust structure. If the heat accumulator is charged with the exhaust gases from internal combustion engines, the temperature of which is usually 400 - 500 °C, it can neither overheat nor be overcharged. In this temperature range, for example, gravel can be used as a heat storage material, since a thermal conversion of the material, the so-called quartz jump, would only take place at 573 °C and can thus be safely ruled out. With the purchase price of gravel, which in gravel works in the order of several thousand tons per day and is in the range of about 10 euros per ton, no other known heat storage material can compete. In addition, gravel is already commercially available in many particle size distributions, can be easily re-sieved and, compared to many other rocks, has a comparatively round structure, which has a positive effect on the flow of gas and on the loosening of the gravel bed, which is necessary for the process.

In order to increase the heat transfer from the hot exhaust gas to the colder gravel, the greatest possible turbulence in the gas flow is required, which leads to an increased differential pressure on the gas side or pressure loss across the gravel bed. This pressure loss has an upper limit on the engine side due to the increasing exhaust gas temperatures. Different engine types allow different maximum exhaust back pressures. However, a maximum exhaust back pressure of 10 mbar can be regarded as a generally applicable upper limit. The high-temperature storage tank must therefore be dimensioned in such a way that a maximum back pressure of around 7 mbar cannot be exceeded.

The calculation of the pressure loss when flowing through beds can be calculated using the Ergun equation, which includes the superficial flow rate of the gas, its temperature, density and viscosity as well as the sphere diameter of the bed and its degree of voids.

With increasing temperature and a constant gas flow, the pressure drop across the bed increases due to the increase in the viscosity of the gas. The high-temperature accumulators must therefore be designed in such a way that the pressure loss when the accumulator is fully heated and with a given exhaust gas volume flow remains safely below 7 mbar, for example.

The control of increased edge currents, which occur when flowing through bulk materials in fixed geometries, is comparatively easy to achieve by attaching a temperature-resistant, soft layer, such as glass wool, to the container walls. Glass wool also offers the advantage that it is chemically resistant if the water and acid dew point is not reached due to the process (e.g. in biogas plants from the combustion of hydrogen sulfide). For this reason, the parts of the high-temperature heat accumulator that come into contact with the gas should be made of high-quality stainless steel, such as 1.4571. Steels that are particularly resistant to sulfuric acid, such as 1.4539, can also be used for parts that are also subjected to high mechanical loads, such as the lower support grid and possibly also the gas-permeable support system below the support grid.

The main challenge is to control the thermal stresses that arise when the fill is heated and cooled. The linear expansion of individual pebbles is around one percent for a temperature change of 400 Kelvin. When the fill cools, it contracts and there is a risk that individual stones will slide down to a lower level, causing the fill to collapse and become compacted in the lower part. When it heats up again, ever stronger forces occur in the lower part due to the thermal expansion of the storage material. After a larger number of exchange cycles, this can lead to mechanical destruction of the containers surrounding the storage material in stationary heat accumulators.

In the case of mobile heat storage tanks, which are filled with rather round gravel, for example, the storage material is continuously loosened up simply by vibrations caused by transport. The conical container walls, which optionally widen upwards, allow the thermal stresses during the heating process to be dissipated upwards, which promotes loosening due to vibrations during transport.

The following example illustrates an embodiment of the high-temperature heat accumulator according to the invention: three conical containers made of stainless steel (e.g. 1.4571) with a height of 2,300 mm, an upper diameter of 2,000 mm and a lower diameter of 1,500 mm are installed in a container that is thermally insulated on the inside and with a total of 23 filled with tons of gravel. With charging up to an average temperature of 450 °C and discharging down to 50 °C, around 2,300 kWh of heat can be stored. In the event that truck transports of up to 60 tons (so-called gigaliners) are permitted in the future, the scope of all mobile heat storage processes will increase considerably.

The metal construction of the mobile high-temperature heat storage according to the above example is the same for all sizes of biogas plants and engine types used. Depending on the respective exhaust gas volume flow and the maximum permissible exhaust gas back pressure, different gravel packings are used.

The storage density of the high-temperature heat storage according to the invention per container load is about 100 kWh per ton of storage material, regardless of the legally permissible Limitation of the transport tonnage, about 50 percent higher than that of the low-temperature heat storage according to the invention, and thus in the range of commercially available latent heat storage devices based on sodium acetate.

• 1 bis 4 zeigen die Be- und Entladung eines Mobilspeichers mit festem mineralischen Speichermaterial gemäß der Erfindung;
• 5 und 6 zeigen eine Ausführungsform des Mobilspeichers mit festem mineralischen Speichermaterial gemäß der Erfindung;
• 7 bis 11 zeigen alternative Ausführungsformen des Mobilspeichers mit festem mineralischen Speichermaterial gemäß der Erfindung;

The principle of mobile sensible heat storage according to the invention is explained in more detail on the basis of the drawings:

• 1 until 4 show the loading and unloading of a mobile storage with solid mineral storage material according to the invention;
• 5 and 6 Figure 12 shows an embodiment of the mobile memory with solid mineral storage material according to the invention;
• 7 until 11 Figure 12 shows alternative embodiments of mobile storage with solid mineral storage material according to the invention;

In 1 until 4 the loading and unloading of a mobile storage tank with solid mineral storage material is shown as an example.

Three conical gas-tight containers (230), inside which the porous heat storage material is located, are, as exemplified in 1 shown mounted in a container (231). To reduce heat loss, the three tanks and the interior of the container are insulated with mineral wool (232). The hot exhaust gas from a generator with an internal combustion engine (220) is fed into the left of the three tanks via port A, flows through the porous heat storage material (233) from bottom to top and exits again in the upper part of the left tank. The heat transfer from the hot exhaust gas to the heat storage material is unimpeded by direct gas-solid contact. As an additional option, a drain connector (236) for condensate falling out of the gas during cooling is attached to the bottom of each of the three containers. To protect the combustion engine, an additional maximum exhaust back pressure must not be exceeded. As a general guide value, 10 mbar can be assumed for the entire exhaust system after the silencer. As a design basis and to take pipe losses into account, the maximum pressure loss across the entire storage material when heated, including the flow losses within the mobile storage tank, should be 7 mbar. For additional safety, a safety valve (221) is installed between the combustion engine and the mobile accumulator, which opens in the event of an impermissibly high pressure loss across the mobile accumulator, diverts the hot exhaust gas to the environment via an emergency chimney (222), thus protecting the engine from damage. 1 shows the mobile memory during the advanced loading process. Exhaust gas at a temperature of 450 °C from the combustion engine is fed into the accumulator via connection A. The storage material in the container on the left has an average temperature of 400 °C, that in the middle container is 200 °C, while the storage material in the container on the left still has an average temperature of around 50 °C. The exhaust gas is discharged to the environment via a chimney (223).

In 1 until 3 the three containers (230) are connected in series, for example. Likewise, the containers can be connected in parallel, as in 4 shown. The parallel connection reduces the flow velocity of the exhaust gas onto the storage material, so that the pressure loss across the storage material decreases significantly with the same bed. This reduction in pressure loss when the three tanks are connected in parallel can be counteracted by choosing a smaller grain diameter for the storage material.

As an example, for a power generator with an electrical output of 500 kW, in which the pressure loss across the storage material should be around 7 mbar, with the three containers connected in series, a gravel bed with a grain diameter of 32 to 38 mm and with a parallel connection a gravel bed with a grain diameter of 3 up to 7 mm can be used.

2 shows the same arrangement as 1 , but at the end of the charging process. The storage material on the left has almost reached the inlet temperature of the exhaust gas. The temperature of the storage material on the right is only slightly below the inlet temperature at socket A, so that exhaust gas with a temperature of 400 °C is released into the environment via the chimney (223). As the three storage materials continue to heat up, the exhaust gas loss causes the ratio of exhaust gas heat from the combustion engine to stored heat to deteriorate. In order to achieve a high level of storage efficiency, the charging of the entire storage material should therefore not be carried out up to the exhaust gas temperature. As a guideline for the end of charging, the gas temperature measured in degrees Celsius at port B is around 85 to 90 percent of the temperature measured in degrees Celsius at port A.

Should it be necessary to comply with a prescribed minimum flue gas temperature in the chimney, for example 60 K above the water dew point, from the point of view of licensing law, this may make it necessary to reheat the cold flue gas exiting the storage tank. The exit temperatures of the exhaust gas (e.g 1 , connector B) are typically in the range of around 40 to 65 °C and increase during the loading process to almost the exhaust gas temperature at the inlet port (A). If the exhaust gas were to be reheated to at least 120 °C, for example, the exhaust gas exiting the accumulator at port B would have to be heated until the accumulator is charged to such an extent that the outlet temperature at port B exceeds this minimum value of 120 °C.

• a) Mit Abwärme des Verbrennungsmotors
  • - Einstufig über Erwärmung des Abgases über einen Ölkühler (Abgas-Motoröl-Wärmetauscher) mit Motoröltemperaturen deutlich über 150 °C
  • - Zweistufig: Vorwärmung des Abgases mit Kühlwasser auf etwa 80 °C. Zur weiteren Aufheizung kann ein Teilvolumenstrom des heißen Abgases gemäß b) erfolgen
• b) Durch Beimischung eines Teilvolumenstroms des heißen Abgases vom Stutzen A, der im Bypass um den Wärmespeicher herumgeführt wird und dem kalten Abgas vor dem Eintritt in den Kamin (223) beigemischt wird.

In principle, reheating can take place in different ways:

• a) With waste heat from the internal combustion engine
  • - Single-stage heating of the exhaust gas via an oil cooler (exhaust gas engine oil heat exchanger) with engine oil temperatures well above 150 °C
  • - Two-stage: preheating of the exhaust gas with cooling water to around 80 °C. For further heating, a partial volume flow of the hot exhaust gas can take place according to b).
• b) By adding a partial volume flow of the hot exhaust gas from nozzle A, which bypasses the heat accumulator and is added to the cold exhaust gas before it enters the chimney (223).

In general, reheating the exhaust gases before they enter the chimney considerably increases the amount of equipment required for operation. In particular, reheating the cold exhaust gas with a partial volume flow of the hot exhaust gas counteracts the idea of the invention, since the charging process of the memory takes longer and therefore less of the exhaust gas waste heat can be used for delivery to the heat customer. From the point of view of emission and immission protection, no reduction is achieved as a result of the reheating, the condensation is spatially shifted from the chimney into the atmosphere, where it takes place again when the exhaust gases cool down.

If a reheating of the exhaust gases is not mandatory by an approval authority, this should be avoided in any case from an ecological and economic point of view.

In general, to discharge the mobile storage tank, regardless of whether the tanks are connected in parallel or in series, the cooler air should be introduced into the storage tank via port B (gas outlet port during charging). As a result, the air first hits the cooler part of the storage material and can continue to heat up as it flows through. The outlet temperature of the hot air is thus maximized and the heat transfer in the heat exchanger (234) is improved, so that it can be dimensioned smaller.

In 3 the discharging of the mobile memory at a heat sink (108) is shown. Similar to charging, discharging also takes place in direct gas-solid contact. As an example, the unloading takes place here on containers connected in series, but, as already mentioned, it can also take place on containers connected in parallel (using finer bulk material to maintain the pressure loss). A fan (235) supplies air, for example at a temperature of 50 to 100 °C, via connection B to the heated mobile accumulator. The fan is mounted on the cold side to protect the material. When flowing through the heated storage material, it heats up to almost the maximum temperature of the storage. 4 shows an example of the discharging of the mobile storage tank with gas-tight inner containers connected in parallel. As well in 3 as well as in 4 the air leaves the storage tank at 420 °C and gives off its heat in a gas-liquid heat exchanger (234), from which the heat sink (108) is supplied.

5 : Representation of the storage device according to the invention for charging and discharging a solid storage material with thermal energy through direct gas contact. The accumulator has a solid storage material (233) with an internal pore or lane system through which the heat carrier gas flows via inlet A to outlet B, a gas-tight casing (inner container, 230) with soft material (240) on the inside, such as glass wool to reduce the edge movement of the gas flow, as well as load-bearing thermal decoupling (241) attached on all sides, shown here as an example. The gas-tight casing (230) ensures that the heat transfer gas introduced via socket A is directed through the solid heat storage material (233) and exits at socket B without leakage into the insulation (232) or the environment. The inflow and outflow surfaces (242, 243) can be designed, for example, as grates, perforated plates or grids. The weight of the heat storage material is transferred to the outer container shell (231) via the lower inflow grate (242), the lower gas-permeable support structure (244), the load-bearing thermal decoupling (241). On the underside of the gas-tight casing (230) there is a drain connector (236) for condensate that occurs when the gas is cooled.

The reversal of the flow direction of the gas from connection piece B to connection piece A is part of the invention even without an explicit graphic representation.

6 shows the structure of the lower support grid in more detail. The lower support grid (242) consists, for example, of angle profiles made of stainless steel, which are attached to one another with a sufficient distance for the passage of gas. The support grid is firmly connected to the gas-permeable support structure (244). On the support grid there is a multi-layered layer of large stones (246) which are so large that they cannot fall through the support grid and which are held firmly on the support grid by a stainless steel net (245). Fixing the large stones in this way prevents them from floating up in the fine-grained layer of the storage material as a result of transport-related vibrations, which would ultimately cause the fine-grained layer to trickle through the support grid.

The proportions of the stones should be selected in such a way that the fine-grain storage material cannot trickle through the pore spaces of the large stones. In the case of particularly fine-grained storage material, a second layer with medium-sized stones (not shown here) can also be added.

In 7 is a variant of discharging the store with solid storage material represented by a fan (247) sucking in cold air, in which the hot air is used directly, ie without a heat exchanger and circulation.

In 8th until 11 1 shows variations of the memory according to the invention with solid storage material.

In 8th a central partition (250) is installed so that the gas is deflected within a gas tight container (230). The longer path of the gas through the storage material can be used to increase the pressure loss.

In 9 there is a horizontal flow through the solid storage material. The gas-tight container can be round or square. The lateral boundary gratings (251, 252) keep the heat storage materials in shape and can be designed as in the vertical variants or as lamellar or louvered gratings open at the side or by slanting flat bars, through which thermal stresses in the heat storage material can be reduced by lateral movement of the fill .

In 10 shows the flow through several parallel chambers (253) of storage material.

11 shows a radially symmetrical structure with concentric inflow and outflow grates (254, 255) which keep the bed of heat storage material in shape.

A reversal of the direction of flow (between the inlet and outlet connectors A and B) is part of the invention in all of the drawings shown, even without an explicit graphic representation.

Claims (6)

A method for transporting heat, in which a storage material is transported in a transportable container from a heat source to a heat sink, the container having connections (A, B) for gas charging and gas extraction, for the storage of sensible heat at temperatures above of 100 °C, a solid, porous, in particular mineral storage material (233) is used, which is introduced into the container as a bed, the bed being in fluid connection with the connections, with gas for storing or removing high-temperature heat above 100 °C is passed through the bed by means of the connections, so that storage material is thermally charged or discharged in direct gas-solid contact, characterized in that the exhaust gas of an internal combustion engine (220) is passed through the bed for storage, with the grain size distribution of the storage material (233) is chosen so that the differential pressure at the flow through the completely heated bed and the installed exhaust gas system is in the range of 30 to 95 percent of the maximum permissible exhaust gas back pressure of the internal combustion engine (220). Heat transfer method claim 1 , characterized in that for the storage of heat at temperatures up to 550 ° C gravel is used as a storage material. Heat transfer method claim 1 or 2 , characterized in that the cold exhaust gas (connector B) exiting the storage tank is heated with the waste heat from the internal combustion engine or with a partial volume flow of the hot exhaust gas (connector A) until a specified minimum gas temperature for entry into a chimney (223) is reached. Process for heat transport according to one of Claims 1 or 2 , characterized in that the grain size distribution of the storage material is selected so that the differential pressure when flowing through the fully heated bed and the installed exhaust system is in the range of 50 to 80 percent of the maximum permissible exhaust back pressure of the combustion engine. Transportable container for transporting heat from a heat source to a heat sink according to a method according to any one of Claims 1 until 4 , wherein the container has connection pieces (A, B) for loading and emptying, characterized in that the container has at least one gas-tight chamber (230) containing a bed of solid, porous storage material (233), the chamber being in fluid communication with the connecting pieces (A, B) so that the gas that is introduced can flow through the bed, with the grain size distribution of the storage material (233) being selected in such a way that the differential pressure when flowing through the completely heated bed and the installed exhaust gas system is in the range of 30 up to 95 percent of the maximum permissible exhaust back pressure of a combustion engine to be connected. Transportable container according to Claim 5 , wherein the chamber (230) has at least one downwardly tapering conical section through which a flow can take place and which allows gas-solid contact, so that the thermal stresses occurring during heating and cooling are reduced upwards by the conical container geometry.

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