Heating system with heat storage

Abstract

Heating system (1) with a circuit (2) in which a boiler (3), a radiator (4) and a heat storage unit (5) are integrated, wherein the heat storage unit (5) comprises a heat distribution block (6) in which a heating element (8) is embedded, wherein the heat distribution block (5) is surrounded by a storage material (7), and wherein the storage material (7) is surrounded by an insulating layer (9) in which heat exchanger coils (10) run, which are fluidically integrated into the circuit (2).

Description

[0001] The invention relates to a heating system with LTHT heat storage (LTHT for "Long-Term High-Temperature Heat Storage"). Introduction and technological background of the invention:

[0002] Heat storage is crucial for harnessing solar energy. Thermochemical heat storage systems store heat through endothermic reactions and release it through exothermic reactions. The advantage of thermochemical heat storage systems over conventional water tanks lies in their higher storage density of 200 to 300 kWh per cubic meter compared to only about 60 kWh / m³. 3 in the case of water. The thermal energy used for regeneration can be retrieved at any time, even long afterward, by re-humidifying. This allows for long-term storage at ambient temperature, even without insulation.

[54] [Wikipedia - Thermochemical heat storage]

[0003] The reaction system based on the reversible hydration of CaO is promising for thermochemical energy storage because the material is a non-toxic, inexpensive industrial commodity with a comparatively high reaction enthalpy. The fine, cohesive powder has low thermal conductivity and poor flowability. This is advantageous when the reactor also serves as the storage unit (fixed-bed reactors).

[0004] The effective heat transfer coefficient of an electrically heated wall was determined to be 156 ± 16 W / m2 / K and 243 ± 52 W / m2 / K for the heating of CaO and the dehydration of Ca(OH)2, respectively

[16] .

[0005] Heating splits calcium hydroxide Ca(OH)2 into calcium oxide CaO and water: CaO(s) + H2O(g) ↔ Ca(OH)2(s) ΔH=104.4 kJ / mol 1 kg of CaO (burnt lime) reacts with 0.32 kg of water (steam) to form 1.32 kg of Ca(OH)2 (slaked lime). This reaction releases 1.86 kJ = 0.517 kWh of heat energy.

[0006] The decomposition temperature of calcium hydroxide depends on the partial pressure of water in the surrounding atmosphere. The higher the partial pressure of water, the higher the decomposition temperature.

[0007] Calcium hydroxide, Ca(OH)2; M = 74.10 g / mol; density 2.24 g / cm³ 3 Thermal decomposition up to 580°C.

[0008] Calcium oxide, CaO; M = 56.08 g / mol; density 3.37 g / cm³ 3 Melting point: 2580°C

[0009] The water released during burning is separated from the quicklime, thus preventing a reverse reaction when the temperature drops. The heat energy used for decomposition can therefore be stored indefinitely. When heat is needed later, the two separated components are recombined and the heat energy is recovered.

[0010] According to the German Aerospace Center (DLR), lime has enormous potential as a thermochemical heat storage medium. It should be possible for private households to use lime to store self-generated solar power decentrally and use it for heating buildings in winter. Efficiencies of up to 90% are said to be achievable. The storage medium is calcium oxide (calcium hydroxide, CaO). Energy is released when the lime is slaked with water to form calcium hydroxide. Regeneration occurs by driving off the water at temperatures above 450°C, producing calcium oxide and water again. Lime is inexpensive, available in large quantities, and environmentally friendly. (-> Wikipedia - Thermochemical heat storage) Source:

[0011] DLR - Climate-neutral heating with lime (https: / / www.dlr.de / aktuelles / nachrichten / 2021 / 03 / 20210806-klimaneutral_heizen_mit_kalk) Technical explanation of the invention for a heating system in the form of a building heating system with a combination of boiler and LTHT-WS (= long-term high-temperature heat storage):

[0012] The present invention is based on the following insight and concludes with the following: Excess solar power is used in summer to heat a large block (edge ​​length 2-6 m) with an electric heating element at its center. The block can contain a sensible heat storage medium (sandstone) or a thermochemical heat storage medium (constructed of limestone bricks). The thermal conductivity of the storage material must be as low as possible, and the block sufficiently large so that the heat takes months to travel from the center to the outer edge of the block, where it is transferred to the return line of the central heating system via a heat exchanger. Heating is achieved, in effect, using the unavoidable insulation losses of a large heat storage block. The long time delay in heat transfer from the center to the edge makes it possible to use heat stored in summer for building heating or domestic hot water production in winter.

[0013] In Fig. Figure 1 presents a principle for a central heating system for single-family homes, combining an LTHT heat storage tank and a boiler (condensing technology). The boiler can be replaced by a heat pump. The return flow is preheated in the heat storage tank using energy from the summer months, thereby reducing heating energy consumption in winter.

[0014] A basic diagram of the LTHT heat storage system with heat exchanger is shown. Fig. 2 can be seen.

[0015] The cast iron block in the center surrounding the heating element is necessary for heat distribution. It prevents local overheating and compensates for fluctuations in heating power throughout the day. This allows for short periods of several times the permissible average heating power (e.g., 3 kW for 8 hours and 0 kW for the remaining hours, instead of a constant 1 kW for 24 hours). If the maximum permissible heating power is exceeded for an extended period, the heating element will be destroyed.

[0016] If lime is used as a thermochemical storage material, it is advisable to make the inner insulation (calcium silicate) considerably thicker, the The storage block is essentially divided into an outer and an inner part, since the reaction temperature of 580°C is not reached in the outer part (inner insulation).

[0017] A cubic storage block with an edge length of 2m (volume 8 m³). 3A piece of sandstone can release 3250 kWh of heat when cooled from 800°C to 100°C.

[0018] In comparison, an equally sized storage block made of lime with a density of 1.2 g / cm³ develops 3 (in fired state) and a mass of 9.6×10 3 kg in the reaction with 3.1×10 3 Each kg of water vapor releases approximately 5000 kWh of thermochemical heat. The lime-based heat storage system can be constructed from individual lime briquettes. REFERENCE MARK 1 heating 2nd cycle 3 boilers (condensing technology) 4 radiators 5. Heat storage (especially long-term high-temperature heat storage) 6 blocks for heat distribution (e.g. 40×40×40cm) 3 ; e.g., made of cast iron) 7 Storage material (e.g. limestone or sandstone; with the lowest possible thermal conductivity) 8 Heating element (e.g. SiC high-temperature heating element) 9 Insulation layer (e.g. inner insulation with channels on the outside for heat exchanger tubes) 10 heat exchanger coils 11 Insulation covering (e.g. outer insulation) 12 Insulating sleeve 13 connection cables (e.g. for solar power) 14 Flow (boiler flow (e.g. 60 °C)) 15 Return (first part) (e.g. return from radiator (e.g. 45 °C)) 16 Return (second part) (boiler return (e.g. 55 °C)) QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] https: / / www.dlr.de / aktuelles / nachrichten / 2021 / 03 / 20210806-klimaneutr al_heizen_mit_kalk

[0011]

Claims

[1] Heating system (1) with a circuit (2) in which a boiler (3), a radiator (4) and a heat storage unit (5) are integrated, wherein the heat storage unit (5) comprises a heat distribution block (6) in which a heating element (8) is embedded, wherein the heat distribution block (5) is surrounded by a storage material (7), and wherein the storage material (7) is surrounded by an insulating layer (9) in which heat exchanger coils (10) run, which are fluid-mechanically integrated into the circuit (2).

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