Electric heater and method for providing process heat

Abstract

The present invention relates to an electric heater for providing process heat by electrically heating a gaseous fluid stream to a temperature of 1000 DEG C or higher. The electric heater includes a heating chamber having a gas inlet configured to provide a flow of gaseous fluid into an interior of the heating chamber and a gas outlet configured to provide a flow of gaseous fluid having a temperature exceeding 1000 DEG C to the exterior of the heating chamber. The electric heater also includes a first heating stage housed in the heating chamber. The first heating stage includes one or more first active ceramic resistive heating elements arranged and configured to generate heat having a first temperature of 1000 DEG C or higher upon application of an electrical current to the one or more first active ceramic resistive heating elements. Furthermore, the first heating stage comprises at least one passive thermal element arranged and configured to passively heat the gaseous fluid stream to a temperature of 1000 DEG C or higher, and / or for storing heat generated by the one or more first active ceramic resistive heating elements.

Description

TECHNICAL FIELD

[0001] The present invention relates to an electric heater configured in a modular way to provide process heat by electrically heating a gaseous fluid stream to a temperature of 1000°C or more, each unit providing between 200 kilo Watt (kW) and 3 Mega Watt (MW), in total up to 150 MW. Furthermore, the present invention relates to a heating system configured to generate and / or store process heat. The present invention also relates to a method of providing process heat with an electric heater and a method of maintenance of an electric heater. BACKGROUND

[0002] Various different industrial processes require MW-level process heat, sometimes also referred to as industrial heat, for the manufacturing of industrial products such as concrete, glass, steel or paper. Traditionally, the provision of process heat relies on the combustion of fuel, natural gas or coal. Obviously, the traditional way of providing process heat based on fossil energy sources leads to the emission of carbon dioxide (CO2), which in turn increases the natural greenhouse effect of the earth, resulting in a global temperature rise.

[0003] It is therefore desirable to provide a system and method that provides MW-level process heat for industrial processes that is carbon neutral or at least leads to a significant reduction of CO2emissions. SUMMARY

[0004] It is an object of the present invention to provide an improved electric heater and an improved method for providing process heat. Furthermore, it is an object of the present invention to provide an improved heating system for generating and / or storing process heat.

[0005] According to the present invention, an electric heater for providing process heat by electrically heating a gaseous fluid stream to a temperature of 1000°C or more is proposed. The electric heater comprises a heating chamber having a gas inlet configured to provide the gaseous fluid stream to an interior of the heating chamber and a gas outlet configured to provide the gaseous fluid stream having a temperature exceeding 1000°C to an exterior of the heating chamber. The electric heater further comprises a first heating stage accommodated in the heating chamber. The first heating stage comprises one or more first active ceramic resistance heating elements arranged and configured to generate heat having a first temperature of 1000°C or more upon application of an electric current to the one or more first active ceramic resistance heating elements. Furthermore, the first heating stage comprises at least one passive heat element, preferably comprising a ceramic material, arranged and configured to passively heat the gaseous fluid stream to a temperature of 1000°C or more and / or for storing heat generated by the one or more first active ceramic resistance heating elements.

[0006] The present invention comprises the insight that generating process heat above 1000°C with known solutions typically involves the combustion of natural gas. In order to avoid CO2emissions during the generation of process heat above 1000°C, a full decarbonization of high temperature process heat needs to be done by replacing the natural gas burners with the use of environmentally friendly solutions.

[0007] It is generally difficult to achieve process heat of 1000°C or higher without the combustion of fossil fuels. As a result, industries that are difficult to decarbonize, such as steel and cement, currently account for more than 6% of global CO2emissions. To date, there is no solution that is cost-competitive or easy to integrate compared to the combustion of fossil fuels. In fact, to date, the combustion of fossil fuels is the most economical way to generate high-temperature heat. Since research and optimization have both focused on manufacturing processes based on fossil fuels as energy carriers over the past few decades, there is generally no simple and quick way to directly “switch” to another technology. With the electric heater according to the present invention, an alternative solution is now available. In particular, the electric heater according to the present invention provides a clean solution that can be operated without emitting CO2into the atmosphere.

[0008] This is because, with the electric heater according to the present application, electrical power, preferably renewable electrical power, can be converted into process heat. By making use of the electric heater, this is achieved by employing a first heating stage comprising one or more first active ceramic resistance heating elements. By applying an electrical current to the one or more first active ceramic resistance heating elements, the one or more first active ceramic resistance heating elements generate heat which in turn is used to heat the gaseous fluid stream flowing from the gas inlet towards the gas outlet. Due to the employment of the one or more first active ceramic resistance heating elements, heat of 1000 °C or higher can be generated. In particular, the use of ceramic material in the one or more first active ceramic resistance heating elements enables heat of 1000 °C or higher to be generated. By also having one or more passive thermal elements, preferably made of ceramic material, in addition to the one or more first active ceramic resistance heating elements, the gaseous fluid stream passing through the heating chamber can be electrically heated to a temperature of 1000 °C or higher. In particular, the advantage of using one or more first passive thermal elements in addition to the one or more first active ceramic resistance heating elements is that the efficiency of the electric heater can be significantly increased and the operating costs are reduced. This is because active ceramic resistance heating elements, for example made of silicon carbide (SiC), can be subject to material oxidation and aging. Passive thermal elements, for example made of or comprising ceramic material such as SiC, are heated in operation by radiative heat transfer from the active ceramic heating elements. Passive thermal elements allow for aging while increasing the active convective heat transfer area to improve heating of the gaseous fluid stream to a temperature of 1000 °C or higher. Furthermore, passive thermal elements can beneficially aid operation of the electric heater as air flow guides by directing the gaseous fluid stream such that turbulence and mixing of the gaseous fluid stream is increased resulting in a more uniform air outlet temperature.

[0009] With the electric heater according to the present application, fossil fuels in energy-intensive industries can therefore be replaced by an environmentally friendly and cost-effective solution. For example, off-grid solar or wind power generation can be used to generate the electrical power used by the electric heater to generate process heat. The electric heater is relatively easy to integrate in common existing industrial plants by connecting the gas outlet to the process heat distribution system of the respective industrial plant.

[0010] Preferably, the gaseous fluid is ambient air. Preferably, the electric heater is configured to provide a total mass flow of the gaseous fluid stream of at least 2 kg / s (approximately 1.5 Nm3 / s) at a temperature of 1000 °C or more, for example 1250 °C or more. Preferably, the electric heater is configured to drive the gaseous fluid stream through the heating chamber from the gas inlet to the gas outlet at an average velocity of 10 m / s to 60 m / s. Preferably, the electric heater is configured to convert electrical power into process heat at a temperature of 1500 °C or more, for example 1800 °C or more, for example up to 2000 °C.

[0011] Preferably, the gas inlet comprises an inlet air blower for sucking in ambient air and pushing it through the heating chamber. Preferably, the gas inlet, in particular the blower, is configured to provide a gaseous fluid stream of at least 2 kg per second. For example, the gas inlet can comprise an inlet air blower and an upstream filter which directly conveys the sucked-in ambient air via a duct into the heating chamber. The temperature of the gaseous fluid stream can be measured directly after the gas inlet. To this end, the gas inlet can comprise a gas inlet temperature sensor.

[0012] The gas outlet can be configured as a duct which comprises a shut-off valve, such that if one or more electric heaters, for example arranged as electric heater modules in a vessel, are connected to a common hot air duct system, for example of an industrial plant, the individual outlets can be closed when the respective electric heater module is switched off. Preferably, the gas outlet comprises a gas outlet temperature sensor which is arranged and configured to measure the temperature of the gaseous fluid vapor at the gas outlet. The electric heater can comprise only the gas outlet temperature sensor and not the gas inlet temperature sensor, and vice versa.

[0013] Preferably, the heating chamber is configured as an insulated duct. The duct can be connected at the gas outlet to, for example, an industrial plant or a heat storage unit for storing process heat, i.e. thermal energy which can be provided as process heat to an industrial plant. For example, the insulation of the heating chamber, for example the heating chamber interior, can comprise ceramic fibers, firebricks or refractory concrete. Furthermore, the insulation of the heating chamber can comprise an alumina-based material, for example aluminum silicate or aluminum oxide. Preferably, the heating chamber comprises an outer shell which can be made of steel or can comprise steel.

[0014] Preferably, the electric heater comprises a control system. The control system is preferably configured to control the amount of electric current applied to the one or more first active ceramic resistive heating elements. Preferably, the control system is configured to control the electric current applied to one or more first active ceramic resistive heating elements of at least two groups of first active ceramic resistive heating elements. The control system can be configured to control the amount of electric current applied to each of the first active ceramic resistive heating elements, respectively. To control the electric current applied to the one or more first active ceramic resistive heating elements, the control system can take into account the gas inlet temperature measured by the gas inlet temperature sensor and the gas outlet temperature measured by the gas outlet temperature sensor. If the gas outlet temperature is lower or higher than a predetermined target gas outlet temperature, the control system can increase or decrease the amount of electric current applied to the one or more first active ceramic resistive heating elements in operation in order to provide a gaseous fluid flow at the gas outlet having the predetermined target gas outlet temperature.

[0015] The control system can also be configured to control the gas inlet (e.g. a blower fan) to increase or decrease the amount of ambient air drawn into the heating chamber in order to provide a gaseous fluid flow of at least 2 kg per second, for example. For example, one or more fluid flow sensors can be arranged at the gas inlet, within the heating chamber and / or within the gas outlet. A measured fluid flow of the gaseous fluid flow can be measured and the control system can be configured to adjust the operation of the gas inlet (e.g. the operation of the blower fan) in order to increase or decrease the amount of gaseous fluid flow through the heating chamber. For example, under full load, e.g. when considering a 3 MW electric heater and a process heat to be applied at 1500°C, the mass flow of ambient air can be approximately 2 kg / s and the volume flow can be 1.5 Nm3 / s.

[0016] Preferably, the electric heater comprises a housing having overall dimensions typical of a freight container, i.e. approximately 6m x 2.5m x 3m. In fact, the electric heater can be arranged in a retrofitted freight container so that the electric heater can be easily transported to an industrial plant and attached to the industrial plant to provide process heat.

[0017] Preferably, the first heating stage has a width of 0.3m to 1m, a height of 0.5m to 1.5m and a length of 2m to 3.5m.

[0018] Preferably, the passive thermal elements of the one or more first passive thermal elements are arranged to at least partially surround one of the first active ceramic resistive heating elements, such that when an electrical current is applied to the first active ceramic resistive heating elements, the respective passive thermal element is heated by radiative heat transfer from the surrounded first active ceramic resistive heating element. The free outer surface of the first active ceramic resistive heating elements can be substantially completely covered or surrounded by the passive thermal elements. For example, the passive thermal elements can have the shape of a hollow tube and the respective one of the first active ceramic resistive heating elements can be at least partially arranged within the hollow interior of the passive thermal element. The cross section of the passive thermal elements can be circular, i.e. the passive thermal elements can have the shape of a hollow cylinder. However, different non-circular cross sections are also possible. The passive thermal elements at least partially surrounding one of the first active ceramic resistive heating elements can act as convection heating elements. The first active ceramic resistive heating elements surrounded by the passive thermal elements can each act as a radiative heating element. Those first active ceramic resistive heating elements not surrounded by a passive thermal element can act as convection heating elements.

[0019] For example, the passive thermal elements at least partially surrounding one of the first active ceramic resistive heating elements are configured as a heating jacket completely surrounding the respective first active ceramic resistive heating element. Thus, the heating jacket can be placed over the first active ceramic resistive heating element and, in operation, then heated by radiation. In turn, the gaseous fluid flow can be heated by forced convection by passing through the jacketed area. A further advantage of the heating jacket is that it also protects the first active ceramic resistive heating element from loads caused by high flow rates, thereby reducing or preventing the risk of breakage of the first active ceramic resistive heating element.

[0020] An advantage of using passive thermal elements at least partially surrounding one of the first active ceramic resistive heating elements is that the total number of first active ceramic resistive heating elements can be reduced and, thereby, the costs and maintenance associated with the first active ceramic resistive heating elements can be reduced.

[0021] Preferably, the surface area of the passive thermal element at least partially surrounding one of the first active ceramic resistive heating elements is greater than the surface area of the respective surrounded first active ceramic resistive heating element. Preferably, the surface area of the passive thermal element is at least twice the surface area of the surrounded first active ceramic resistive heating element.

[0022] Preferably, the one or more first passive thermal elements are made of or comprise a ceramic material, such as SiC, AI2O3, or Si3N4, or the like. Preferably, the passive thermal elements of the one or more first passive thermal elements have a circular, elliptical, or a blade or wing shaped cross section. The advantage of a wing shaped passive thermal element is that a gaseous fluid flow flowing around the wing shaped passive thermal element is in contact with the passive thermal element for a relatively longer time due to a larger surface contact in the flow direction. Thereby, the heat transfer from the wing shaped passive thermal element to the gaseous fluid flow can be improved. Furthermore, a more uniform temperature distribution of the gaseous fluid flow can be achieved.

[0023] Preferably, the one or more first active ceramic resistance heating elements are made of or comprise a ceramic material, such as SiC, SiSiC, Molybdenum disilicide (MoSi2), or ZrO2. Preferably, the one or more first active ceramic resistance heating elements have a diameter of 25 mm to 50 mm, for example 30 mm to 40 mm, such as 32 mm or 35 mm. Preferably, the one or more first active ceramic resistance heating elements have a length of 400 mm to 600 mm, for example 450 mm to 550 mm, such as 475 mm. Preferably, the one or more first active ceramic resistance heating elements have a rod shape.

[0024] Preferably, the passive thermal elements of the one or more first passive thermal elements are distributed with a plurality of bumps and / or ribs on their outer surface. Thereby, the surface area of the passive thermal elements can be increased and the convective heating of the gaseous fluid flow can be improved.

[0025] The electric heater can comprise a baffle arranged and configured to deflect at least a portion of the gaseous fluid flow away from the gas outlet. For example, the baffle can be arranged in the vicinity of the gas outlet to deflect at least a portion of the gaseous fluid flow away from the gas outlet and back into the heating chamber. The advantage of using a baffle is that the circulation of the gaseous fluid flow inside the heating chamber can be increased. Furthermore, the residence time of the gaseous fluid inside the heating chamber can be increased, which can improve the efficiency of the electric heater. The baffle can have a flat shape or a curved shape, for example curved towards the gas inlet, or can be curved only in some regions of the baffle. Multiple baffles can be provided at different locations inside the heating chamber separated from each other. The baffle can also have multiple holes such that only a portion of the gaseous fluid flow can pass through the baffle towards the gas outlet, while the remaining portion of the gaseous fluid flow is reflected from the baffle and remains inside the heating chamber. For example, the baffle can be made of or comprise a ceramic material, such as SiC, AI2O3, or Si3N4, or the like.

[0026] Preferably, the passive thermal elements of the one or more first passive thermal elements have a hollow interior and the first active ceramic resistance heating elements of the one or more first active ceramic resistance heating elements are arranged within the hollow interior of the passive thermal elements.

[0027] Preferably, the passive thermal element of the one or more first passive thermal elements comprises a bulk material or bulk goods, preferably in the form of granules. The bulk material preferably comprises or is made of a ceramic material. If the electric heater comprises a passive thermal element in the form of a bulk material, the electric heater preferably additionally comprises at least two further first passive thermal elements of the one or more first passive thermal elements having a plate-like shape. Preferably, the at least two further passive thermal elements are arranged opposite to each other inside the heating chamber. Preferably, the bulk material is arranged between the at least two plate-like first passive thermal elements. Preferably, the at least two plate-like further first passive thermal elements and the passive thermal element in the form of a bulk material are arranged within the heating chamber such that the passive thermal element in the form of a bulk material is not in direct contact with the one or more first active ceramic resistance heating elements. Thereby, the one or more first active ceramic resistance heating elements can be protected from being damaged by the passive thermal element in the form of a bulk material by the at least two plate-like further first passive thermal elements.

[0028] The passive thermal element in the form of a bulk material can be used as a ceramic thermal storage material. Thus, the storage material is preferably configured as a bulk material. Preferably, the passive thermal element in the form of a bulk material has a bulk density of up to 2500 kg / m3and / or a particle size of 2.5 mm to 8 mm, e.g. 3 mm to 6 mm, e.g. 5 mm.

[0029] Preferably, the at least two further first passive thermal elements having a plate-like shape between which the bulk material is arranged are made of or comprise a fine-pored ceramic foam, e.g. having a number of pores per inch (ppi) equal to 70 or more and a porosity φ of φ < 80%. Preferably, the at least two further first passive thermal elements having a plate-like shape are made of or comprise a ceramic material, such as SiC, SiSiC or Zr02. Preferably, the at least two further first passive thermal elements having a plate-like shape have a minimum width of 25 mm. Preferably, the minimum distance of the heating elements to the at least two further first passive thermal elements having a plate-like shape corresponds to the diameter of a first active ceramic resistance heating element of the one or more first active ceramic resistance heating elements.

[0030] Additionally or alternatively, a plurality of the first active ceramic resistive heating elements of the one or more first active ceramic resistive heating elements can each be surrounded by a passive thermal element of the one or more first passive thermal elements. Preferably, the electric heater comprises a further passive thermal element of the one or more first passive thermal elements configured as a bulk material and arranged between the passive thermal elements surrounding the plurality of first active ceramic resistive heating elements, respectively. Thus, the further passive thermal element of the one or more first passive thermal elements configured as a bulk material fills the space between the passive thermal elements surrounding the plurality of first active ceramic resistive heating elements, respectively. Thereby, direct contact between the further passive thermal element of the one or more first passive thermal elements configured as a bulk material and the plurality of first active ceramic resistive heating elements is prevented to protect the plurality of first active ceramic resistive heating elements from damage caused by the bulk material.

[0031] It is thus possible to use passive thermal elements in the form of a bulk material as a ceramic thermal storage material within the first heating stage having one or more first active ceramic resistive heating elements. The space between the one or more first active ceramic resistive heating elements surrounded by passive thermal elements in the first heating stage is filled with the further passive thermal element of the one or more first passive thermal elements configured as a bulk material. For example, a bulk material having a bulk density of up to 2500 kg / m3and a particle size of 2.5 mm to 8 mm, for example 3 mm to 6 mm, for example 5 mm, can be used. Thereby, the one or more first active ceramic resistive heating elements, which can be made of or can comprise SiC or MoSi2, are completely surrounded by the heating jacket as described above, for example, such that there is no physical contact between the one or more first active ceramic resistive heating elements and the bulk material.

[0032] Additionally or alternatively, the passive thermal elements of the one or more first passive thermal elements can be configured in a block form, the block extending between two opposite heating chamber walls and having one or more feed-throughs, and the one or more first active ceramic resistance heating elements of the one or more first active ceramic resistance heating elements are arranged within the one or more feed-throughs, respectively. Thereby, in the first heating stage, an additional passive heat exchanger is provided, which is heated in operation by the thermal radiation of the one or more first active ceramic resistance heating elements arranged in the feed-throughs of the passive thermal element in block form. The passive thermal element in block form can be made of or can comprise a ceramic foam. In operation of the electric heater, the passive thermal element in block form transfers heat via convection to the gaseous fluid flow inside the heating chamber. If the passive thermal element in block form is made of or comprises a ceramic foam, preferably, the ceramic foam is fine-pored, having a ppi of 70 or more, resulting in a high porosity φ of φ > 80%. The ceramic foam can be made of a ceramic material, such as SiC, SiSiC or Zr02. Preferably, the minimum distance between the one or more first active ceramic resistance heating elements placed inside the feed-throughs of the ceramic foam and the ceramic foam corresponds to one diameter of the first active ceramic resistance heating elements of the one or more first active ceramic resistance heating elements.

[0033] Additionally or alternatively, in the electric heater, at least one of the one or more first passive thermal elements can be configured in the form of a plate having a wave shape, arranged such that it is wrapped around a respective one of the one or more first active ceramic resistive heating elements. Within the first heating stage comprising the one or more first active ceramic resistive heating elements, an additional passive thermal exchanger can thus also be included, implemented by the at least one passive thermal element in the form of a plate having a wave shape. In operation, the at least one passive thermal element in the form of a plate having a wave shape can be heated by thermal radiation of the one or more first active ceramic resistive heating elements and can transfer heat to the gaseous fluid stream via convection. The at least one passive thermal element in the form of a plate having a wave shape can be made of or can comprise a ceramic foam plate having a wave shape. Preferably, the shape of the ceramic foam plate is such that the surface area towards the respective one of the one or more first active ceramic resistive heating elements is maximized while maintaining a minimum distance between the one or more first active ceramic resistive heating elements and the ceramic foam plate as the diameter of the first active ceramic resistive heating elements. The ceramic foam plate can be fine-pored, have a ppi of 70 or more, and have a high porosity φ of φ > 80%. Preferably, the at least one of the one or more first passive thermal elements can be configured in the form of a plate having a wave shape with a minimum thickness of 20 mm. Preferably, the ceramic foam plate is made of or comprises a ceramic material, such as SiC, SiSiC, or Zr02.

[0034] Additionally or alternatively, the passive thermal element of the one or more first passive thermal elements can be configured in the form of a plate having a plurality of feedthroughs arranged to allow the gaseous fluid stream to flow from the gas inlet to the gas outlet. The passive thermal element in the form of a plate having a plurality of feedthroughs implements a ceramic thermal storage material, which can be a SiC plate. The passive thermal element in the form of a plate has holes in the flow direction. Preferably, the minimum distance between the one or more first active ceramic resistive heating elements and the plate corresponds to the diameter of a first active ceramic resistive heating element of the one or more first active ceramic resistive heating elements.

[0035] Additionally or alternatively, at least one of the one or more first passive thermal elements can be configured in the form of a rod having a plurality of bumps and / or ribs distributed over its outer surface and arranged between the one or more first active ceramic resistance heating elements. The at least one passive thermal element in the form of a rod implements a passive heat exchanger which is heated by thermal radiation of the one or more first active ceramic resistance heating elements during operation of the heater and transfers heat to the gaseous fluid stream via convection. Preferably, a plurality of first passive thermal elements in the form of rods are arranged offset from each other within the heating chamber. In operation of the electric heater, the rods can also serve as short-term heat accumulators and thereby introduce inertia into the electric heater, making it easier to regulate the flow of the gaseous fluid stream. Preferably, the at least one passive thermal element in the form of a rod is made of or comprises a ceramic material, such as SiC, SiSiC or Zr02. Preferably, the maximum diameter of the rod is half the diameter of the one or more first active ceramic resistance heating elements. Preferably, the surface area of the rod is increased by indentations or ridges, so that the heat exchange with the gaseous fluid stream is improved.

[0036] In the electric heater, it is generally preferred that at least one of the one or more first passive thermal elements is or comprises a porous ceramic material (preferably, a ceramic foam).

[0037] In a preferred embodiment, both the one or more first active ceramic resistance heating elements and / or the one or more first passive thermal elements comprise or are made of SiC and / or MoSi2. Preferably, both the one or more first active ceramic resistance heating elements and / or the one or more first passive thermal elements have a porosity of 5% or less.

[0038] In particular, if a plurality of the one or more first active ceramic resistance heating elements have a rod shape or the form of a plate, for example a wavy line shaped plate, it is preferred that the minimum distance between adjacent first active ceramic heating elements of the plurality of first active ceramic resistance heating elements is twice the diameter or width of the first active ceramic heating elements of the plurality of first active ceramic resistance heating elements. For example, the electric heater can comprise 450 to 720 first active ceramic heating elements in the first heating stage. Preferably, the one or more first active ceramic heating elements are arranged in a regular pattern. Preferably, in the case of rod-shaped elements, at least some of the one or more first active ceramic heating elements have six directly adjacent first active ceramic heating elements.

[0039] Preferably, the electric heater comprises a second heating stage with one or more active metal resistance heating elements arranged closer to the gas inlet than the first heating stage. Preferably, the second heating stage is configured to heat the gaseous fluid stream to a second temperature when providing electrical current to the one or more active metal resistance heating elements. Preferably, the second temperature is lower than the first temperature of 1000 °C or more.

[0040] If the electric heater comprises a first heating stage and a second heating stage, a cascading heating of the gaseous fluid stream within the heating chamber is possible. With the second heating stage closer to the gas inlet, the gaseous fluid stream can be heated to a second temperature which is less than the first temperature of 1000 °C or more. Specifically, with the second heating stage comprising one or more active metal resistance heating elements, a low-cost preheating technology based on metal resistance heating elements can be employed to preheat the gaseous fluid stream to the second temperature. The first heating stage comprises higher-cost ceramic heating elements, i.e. one or more first active ceramic resistance heating elements. For example, with SiC first active ceramic resistance heating elements, the gaseous fluid stream can be heated to the first temperature of 1000 °C or more, e.g. up to 1500 °C. It is therefore preferred that, in the heating chamber, the one or more active metal resistance heating elements are arranged closer to the inlet port than the one or more first active ceramic resistance heating elements. In operation of the heater, the second heating stage can be used to preheat to the second temperature with the one or more metal resistance heating elements, and the first heating stage can be used to heat to the first temperature with the one or more active first ceramic resistance heating elements. Possible materials of the one or more active metal resistance heating elements are, for example, ferrochrome-aluminum alloy, nickel-chromium alloy, nickel-iron alloy, or copper-nickel alloy.

[0041] Optionally, the electric heater can comprise a high-temperature blower fan, e.g. arranged between the second heating stage and the first heating stage, e.g. at a fluid stream temperature of about 600 °C, to maintain a flow rate of the gaseous fluid stream and / or to overcome a pressure loss of the gaseous fluid stream.

[0042] Preferably, the electric heater can comprise a third heating stage comprising one or more second active ceramic resistance heating elements made of a different ceramic material than the one or more first active ceramic resistance heating elements. The third heating stage is preferably configured to heat the gaseous fluid to a third temperature higher than the first temperature when providing electrical current to the one or more second active ceramic resistance heating elements. Thus, if a higher gas outlet temperature than the first temperature is required, the third heating stage can be employed. Preferably, the one or more second active ceramic resistance heating elements are made of and / or can comprise MoSi2, and thus are suitable for achieving a third temperature of up to 1800 °C.

[0043] The electric heater can comprise only the first heating stage and optionally a second heating stage, or a third heating stage, or a second and third heating stage.

[0044] Thus, a cascaded electric heater with up to three heating stages can be implemented. First, the gaseous fluid stream can be heated to 1000°C using the second heating stage by a low-cost preheating technology based on metallic resistance heating elements. Second, the air temperature can be raised to 1500°C by a higher-cost ceramic resistance first heating stage, e.g. comprising SiC-based first active ceramic resistance heating elements. Third, if higher temperatures are required, MoSi2-based second active ceramic resistance heating elements can be employed to achieve gas outlet temperatures of up to 1800°C or more. Preferably, the one or more second active ceramic resistance heating elements comprise or are made of MoSi2. Preferably, the one or more second active ceramic heating elements are arranged closer to the gas outlet than the one or more first active ceramic heating elements. If required, further heating stages can be added in a modular fashion.

[0045] If the electric heater comprises a third heating stage, at least one of the one or more second active ceramic heating elements is preferably at least partially surrounded by a second passive thermal element, such that when an electric current is applied to the second active ceramic resistance heating element, the second passive thermal element is heated by radiative heat transfer from the surrounded second active ceramic resistance heating element. Preferably, the second passive thermal element is shaped to extend further towards the outlet port than towards the inlet port relative to the first active ceramic resistance heating element surrounded by the second passive thermal element. Preferably, the second passive thermal element is shaped such that it is adjacent to the gas stream, which leads to a larger heat transfer area, more uniform heat transfer and temperature distribution. An advantage of employing a second passive thermal element is that the risk of ceramic heating element breakage due to high flow rates can be reduced. Furthermore, the operating costs of the electric heater can be improved by reducing the load and thermal stress on the active ceramic heating elements. Moreover, the lifetime and durability of the electric heater can be improved.

[0046] Generally, the one or more second passive thermal elements can be configured in the same way as the one or more first passive thermal elements described herein. Thus, a second passive thermal element of the one or more second passive thermal elements can be a block of material, can be a plate (e.g. a plate made of ceramic foam), can be a plate with a wave shape, can be a block with a feedthrough, etc. The details described herein with respect to the one or more first passive thermal elements can also apply to the one or more second passive thermal elements. The main difference between the one or more first passive thermal elements and the one or more second passive thermal elements is that the one or more first passive thermal elements are arranged in the first heating stage and the one or more second passive thermal elements are arranged in the third heating stage.

[0047] Optionally, the electric heater comprises one or more passive flow resistance elements arranged at the heating chamber wall and configured to direct the fluid flow away from the heating chamber wall.

[0048] The passive flow resistance elements on the wall preferably act as flow resistors to prevent the occurrence of runaway cold zones on the heating chamber wall. Preferably, the active ceramic resistance heating elements are kept at a minimum distance from the heating chamber wall. A larger space near the heating chamber wall can ensure that the gaseous fluid flow can flow faster at this point and correspondingly heat less (so-called "runaway cold zones"). To achieve a more uniform heating of the air, preferably, the passive flow resistance elements are integrated on the heating chamber wall in the same form as the active ceramic resistance heating elements in order to achieve a constant distance between the components arranged within the heating chamber.

[0049] In a preferred embodiment, the one or more first active ceramic resistance heating elements are arranged offset from each other and the passive flow resistance elements are arranged on the heating chamber wall to achieve a uniform temperature distribution of the gaseous fluid flow over the cross section of the heating chamber. Preferably, the one or more first active ceramic resistance heating elements have a small distance from each other, for example, the spacing distance corresponds to the diameter or width of the one or more first active ceramic resistance heating elements, to improve heat transfer and achieve a high energy transfer density. Thereby, the pressure loss inside the heating chamber can be reduced. Thus, the electric heater has the advantage that the parasitic losses associated with the gas flow through the electric heater are relatively low while achieving a uniform heating performance and avoiding runaway cold zones.

[0050] The electric heater can comprise a connecting line arranged and configured to feed at least a portion of the heated gaseous fluid flow from the gas outlet back to the gas inlet such that the heated gaseous fluid flow can enter the heating chamber again at the gas inlet. Thus, the connecting line fluidically connects the gas outlet with the gas inlet. This can include further components connected to the connecting line. For example, there can be a heat storage unit within the fluidic connection between the gas outlet and the gas inlet. The gaseous fluid flow circulating back into the heating chamber can be heated again to reach a higher temperature.

[0051] At least one of the one or more first and / or second active ceramic resistance heating elements can have an electrically heated zone, a non-electrically heated zone, and an electrical connection. In this case, it is preferred that the electrically heated zone is arranged within the heating chamber and can be electrically heated upon application of an electrical current to the at least one first active ceramic resistance heating element. Preferably, the non-electrically heated zone is arranged between the electrically heated zone and the electrical connection. The electrical connection is preferably arranged outside of the heating chamber. The electrical connection can be arranged within an optional gas-tight chamber, which is preferably arranged outside of the heating chamber to enclose the electrical connection and comprises a gas-tight chamber gas inlet configured to provide ambient gas into the gas-tight chamber. To this end, the gas-tight chamber gas inlet can be connected to a gas-tight chamber air blower, which is arranged and configured to draw ambient air into the gas-tight chamber.

[0052] Preferably, the gas-tight chamber is fluidly connected to the heating chamber, such that ambient gas entering the gas-tight chamber through the gas-tight chamber gas inlet can enter the heating chamber. The use of the optional gas-tight chamber with the gas-tight chamber gas inlet for providing a flow of ambient air from the gas-tight chamber gas inlet into the heating chamber has the advantage that an improved sealing of the heating chamber can be achieved. The flow of ambient air from the gas-tight chamber gas inlet into the heating chamber can act as sealing air, which prevents gaseous fluid flow from escaping the heating chamber at the location of the one or more first and / or second active ceramic resistance heating elements. Another advantage of having the gas-tight chamber is that ambient air can act as cooling air for the non-electrically heated zone of the active ceramic resistance heating elements. When the heated ambient / cooling air re-enters the heating chamber, overall efficiency can be improved. That is, since the one or more first and / or second active ceramic resistance heating elements typically have electrical connections located outside of the heating chamber, at the location of the one or more first and / or second active ceramic resistance heating elements, the heating chamber needs to have feedthroughs, which accommodate the one or more first active ceramic resistance heating elements and, in particular, the non-electrically heated zone of the one or more first and / or second active ceramic resistance heating elements, respectively. At these locations, the gas-tight chamber, which encloses the respective electrical connection of the one or more first and / or second active ceramic resistance heating elements, can provide an improved sealing by providing sealing air through the gas-tight chamber gas inlet.

[0053] If an airtight chamber is used to improve the sealing of the heating chamber, such an airtight chamber can be arranged and configured to surround only one of the one or more first active ceramic resistance heating elements and / or the second active ceramic resistance heating element. It is therefore preferred that several or even all of the one or more first active ceramic resistance heating elements and / or the second active ceramic resistance heating element have an airtight chamber surrounding their respective electrical connection. Thus, a plurality of airtight chambers can be provided, each surrounding an electrical connection of one of the one or more first active ceramic resistance heating elements and / or the second active ceramic resistance heating element. However, one airtight chamber is arranged and configured to surround at least two electrical connections of at least two different ones of the one or more first active ceramic resistance heating elements or the second active ceramic resistance heating element. For example, a plurality of airtight chambers can be employed, each surrounding the electrical connections of a group of a plurality of first active ceramic resistance heating elements or the second active ceramic resistance heating element.

[0054] The present application also relates to a heating system configured to generate and store process heat (in particular, heat energy that can be provided as process heat to an industrial plant). The heating system comprises the electric heater described herein and additionally comprises a heat storage unit operably connected to the electric heater to receive the heated gaseous fluid stream from the electric heater and for storing heat energy that can be provided as process heat to an industrial plant. The heat storage unit is configured to store the heat energy provided by the electric heater. For example, the heat storage unit can comprise a solid material in the form of particles, such as sand, gravel, bricks or stones.

[0055] Preferably, the heat storage unit is fluidly connected to the gas inlet of the electric heater to provide at least a portion of the stored heat energy together with the gaseous fluid stream to the interior of the heating chamber. For example, the fluid connection can be implemented with a fluid connection line.

[0056] An advantage of fluidly connecting the heat storage unit with the gas inlet of the electric heater to each other is that the thermal energy stored in the heat storage unit and thus the temperature level of the heat storage material can be increased in a stepwise manner. In other words, the heat storage unit can thereby be charged in a stepwise manner by circulating the thermal energy through the electric heating system. For example, it can be the case that when the heated gaseous fluid stream enters the heat storage unit to store the delivered thermal energy, only a part of the delivered thermal energy is transferred to the heat storage material, while the remaining thermal energy is delivered outside the heat storage unit. The gaseous fluid at the storage outlet now has a lower temperature level than at the inlet of the heat storage unit. Without fluidly connecting the heat storage unit to the gas inlet of the electric heater, such remaining thermal energy can be lost, for example, it can be released into the ambient atmosphere. However, when fluidly connecting the heat storage unit to the gas inlet of the electric heater, the heated gaseous fluid stream delivering the remaining thermal energy can be circulated back to the gas inlet and into the heating chamber to again increase the temperature level and again enter the heat storage unit. Thereby, the thermal energy delivered by the gaseous fluid stream can be stored in the heat storage unit in a stepwise (or closed loop) manner and, thereby, thermal losses can be reduced. Furthermore, fluidly connecting the heat storage unit to the gas inlet of the electric heater can contribute to achieving a more efficient electric heating system with improved thermal energy usage.

[0057] Preferably, the fluid connection between the heat storage unit and the gas inlet of the electric heater (e.g. realized via a connection line) comprises a cooling valve connected to a cooling air blower fan, such that when the cooling valve is opened, ambient air can be provided into the fluid connection to mix with the gaseous fluid stream flowing in the fluid connection towards the gas inlet of the electric heater. Thereby, the gaseous fluid stream can be cooled to a temperature below the initial temperature of the gaseous fluid stream, e.g. not to exceed a maximum inlet temperature. For example, the maximum inlet temperature can be 800 °C, and by mixing the gaseous fluid stream fed back from the heat storage unit to the gas inlet of the electric heater with ambient air via the cooling valve, the temperature of the gaseous fluid stream can be reduced below 800 °C.

[0058] Advantageously, the heat storage unit comprises a high-temperature heat storage unit connected to the electric heater to receive and store thermal energy provided by the electric heater and a low-temperature heat storage unit connected to the high-temperature heat storage unit to receive and store residual heat (e.g. at a lower temperature) from the high-temperature heat storage unit. For example, in the high-temperature heat storage unit, thermal energy exceeding 1000 °C (e.g. up to 1600 °C) can be stored. The residual heat from the high-temperature heat storage unit can be stored as thermal energy in the low-temperature heat storage unit, e.g. at a temperature below 1600 °C. Thereby, the overall efficiency of the heating system can be increased and thermal losses can be reduced.

[0059] Preferably, the heating system comprises an outlet valve, which can be part of the gas outlet and arranged between the electric heater and the heat storage unit, and which can be closed to prevent heat energy stored in the heat storage unit from being transported back into the heating chamber by the gaseous fluid stream. Preferably, the outlet valve is configured as a high-temperature valve for temperatures of 1000 °C or more. Preferably, the outlet valve is arranged and configured such that, when closed, heat energy cannot be transported from the heat storage unit back into the electric heater. For example, if process heat is to be extracted from the heat storage unit, the outlet valve can be closed to transport the process heat from the heat storage unit into the industrial process that needs it, and thereby to prevent heat energy from being transported into the heating chamber of the electric heater.

[0060] In the heating system, the gas inlet can be fluidly connected to or comprise an inlet air blower fan to provide the gaseous fluid stream to the inside of the heating chamber. Additionally or alternatively, the gas outlet of the heat storage unit can be fluidly connected to an outlet air blower fan, which is arranged and configured to mix the heated gaseous fluid stream having a temperature exceeding 1000 °C, which is provided to the outside of the heat storage unit via the gas outlet, with ambient air. With the outlet air blower fan, the heated gaseous fluid stream can be mixed with ambient air in order to provide process heat at a desired temperature as needed in the industrial process.

[0061] Optionally, the heating system comprises a battery storage device, which is operably connected to the electric heater and configured to provide electric current to the heating elements of the first heating stage, and if present, to the heating elements of the second heating stage and / or the third heating stage. The first heating stage and / or the third heating stage in combination with the battery storage device can act as a high-temperature supercharger.

[0062] The present invention also relates to a method of providing process heat with an electric heater as described herein. The method comprises the following steps: - providing a gaseous fluid stream to the inside of the heating chamber; - applying electric current to one or more first active ceramic resistance heating elements to generate heat having a first temperature of 1000 °C or more; - passively heating the gaseous fluid stream to a temperature of 1000 °C or more, and / or storing heat generated by the one or more first active ceramic resistance heating elements; and - providing the gaseous fluid stream having a temperature exceeding 1000 °C to the outside of the heating chamber.

[0063] The present invention also relates to a method of maintenance for the electric heater described herein. The method of maintenance comprises servicing or replacing at least one of the one or more first active ceramic resistance heating elements and / or at least one of the one or more first passive heat elements.

[0064] It is to be understood that the aspects described above, and in particular the electric heater according to claim 1, the system according to claim 15 and the method according to claim 22 have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0065] It is to be understood that preferred embodiments of the present application can also be any combination of the above embodiments with the respective independent claim.

[0066] These and other aspects of the present application will become apparent from and will be elucidated with respect to the embodiments described hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0067] Figure 1 An electric heater with a first heating stage and a second heating stage arranged in a freight container is schematically and exemplarily shown; Figure 2 An electric heater with a first heating stage, a second heating stage and a third heating stage connected to an industrial plant is schematically and exemplarily shown; Figure 3 A first heating stage comprising a plurality of ceramic foam plates as passive thermal elements and ceramic bulk material arranged between two adjacent ceramic foam plates as further passive thermal elements is schematically and exemplarily shown; Figure 4 A first heating stage with a plurality of first active ceramic resistive heating elements surrounded by respective passive thermal elements, wherein further passive thermal elements are configured as bulk material and arranged in spaces between the passive thermal elements surrounding the plurality of first active ceramic resistive heating elements is schematically and exemplarily shown; Figure 5 A first passive thermal element with a corrugated outer surface is schematically and exemplarily shown in a cross-sectional view; Figure 6 A first passive thermal element with ribs arranged on an outer surface is schematically and exemplarily shown in a cross-sectional view; Figure 7 A first passive thermal element with protrusions arranged on an outer surface is schematically and exemplarily shown in a cross-sectional view; Figure 8 A first passive thermal element with protrusions arranged on an outer surface is schematically and exemplarily shown in a cross-sectional view, the first passive thermal element having a wing profile; Figure 9 The transfer of heat from a first active ceramic resistive heating element to a first passive thermal element and further to a gaseous fluid flow is schematically and exemplarily shown; Figure 10The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 11 The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 12 The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 13 The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 14 The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 15 The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 16 The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 17 The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 18 The first heating stage is schematically and exemplarily shown to comprise first passive thermal elements configured in the form of blocks having feed-throughs, with the first active ceramic resistive heating elements arranged within the feed-throughs; Figure 19Three different first heating stages are schematically and exemplarily shown, wherein the first heating stage on the left side comprises only a first active ceramic resistance heating element, the first heating stage in the middle comprises a first active ceramic resistance heating element and a first passive thermal element in the shape of a rod, and the first heating stage on the right side comprises a first active ceramic resistance heating element and a first passive thermal element in the shape of a bend; Figure 20 A heating system operating in a standard mode of operation is schematically and exemplarily shown; Figure 21 A heating system operating in a P AC mode of operation is schematically and exemplarily shown; Figure 22 A heating system operating in a charging mode of operation is schematically and exemplarily shown; Figure 23 A heating system is schematically and exemplarily shown, which comprises a connecting line between the thermal storage unit and the gas inlet of the electric heater to circulate the gaseous fluid stream from the thermal storage unit through the gas inlet back into the heating chamber of the electric heater; Figure 24 A heating system operating in a charging mode of operation is schematically and exemplarily shown; Figure 23 of the heating system; Figure 25 A heating system operating in a discharge mode of operation is schematically and exemplarily shown; Figure 23 of the heating system; Figure 26 An active ceramic resistance heating element is schematically and exemplarily shown, whose electric heating zone is arranged within a heating chamber, wherein the electric connection of the active ceramic resistance heating element is arranged within a gas-tight chamber; and Figure 27 A first or third heating stage of an electric heater is schematically and exemplarily shown, wherein the heating chamber accommodates a baffle. DETAILED DESCRIPTION

[0068] Figure 1An electric heater 100 with a first heating stage 102 and a second heating stage 104 arranged in a freight container 106 is shown schematically and exemplarily. The electric heater comprises a gas inlet 107 with a blower fan 110 and an ambient air filter 108 connected to a heating chamber 112 which houses the first heating stage 102 and the second heating stage 104. The first heating stage 102 comprises a first active ceramic resistance heating element (not shown) arranged and configured to generate heat with a first temperature of 1000 °C or more. The second heating stage 104 is arranged closer to the gas inlet 107 and comprises active metal resistance heating elements for heating a gaseous fluid to a second temperature when electric current is provided to the one or more active metal resistance heating elements. The second temperature is lower than the first temperature such that the gaseous fluid is heated in two steps in a cascading manner. The fluid flow is then provided as process heat via a gas outlet 114 which can be connected to a piping system (not shown) of an industrial plant for using the process heat in an industrial process.

[0069] Figure 2 A 3 to 5 MW electric heater 200 configured in a modular manner is shown schematically and exemplarily connected to an industrial plant 208 and having a first heating stage 202, a second heating stage 204 and a third heating stage 206. The electric heater 200 is part of a heating system 209. The electric heater 200 comprises a gas inlet 208 with an air filter 210 and a blower fan 212. The second heating stage 204 comprises active metal resistance heating elements 214 for preheating a gaseous fluid. Between the second heating stage 204 and the first heating stage 202, an optional high-temperature blower fan 216 is arranged. The first heating stage 202 comprises a first active ceramic resistance heating element 218, e.g. made of SiC and configured to heat the gaseous fluid to a temperature of up to 1500 °C. The third heating stage 206 comprises a second active ceramic resistance heating element 220, e.g. made of MoSi2 for heating the gaseous fluid to a temperature of up to 1800 °C. The heated gaseous fluid flow is provided as process heat at an outlet 222 of the electric heater. The electric heater 200 is arranged in a freight container 238 with dimensions of 2.4 m x 2.6 m x 6 m.

[0070] To control the heating of the gaseous fluid stream inside the heating chamber 224, the electric heater 200 comprises a control system 226, for example comprising power electronics. With the control system 226, the air blower fan 212 is controlled to adjust the amount of ambient air drawn into the heating chamber 224. Furthermore, with the control system 226, the amount of current applied to the active metal resistance heating element 214, the first active ceramic resistance heating element 218, and the second active ceramic resistance heating element 220 can be controlled. The current applied to the active metal resistance heating element 214, the first active ceramic resistance heating element 218, and the second active ceramic resistance heating element 220 can be generated as renewable electric power 228 by converting wind energy or solar energy into electric power. The heating system 209 comprises a battery storage device 236 operably connected to the electric heater 200. With the battery storage device 236, current can be provided to the heating elements 218 of the first heating stage 202 and the heating elements 214 of the second heating stage 204, as well as the heating elements 220 of the third heating stage 206. The first heating stage 202 and the third heating stage 206 in combination with the battery storage device 236 act as a high-temperature supercharger.

[0071] The gas outlet 222 can optionally be connected to a thermal storage device 230 to store the generated process heat, i.e. the thermal energy that can be provided as process heat to the industrial plant. From the thermal storage device 230, the process heat can be transported to a gas flow management system 232 and further to a collection pipe 234. The collection pipe 234 can be connected to a further electric heater (not shown) to collect process heat 240 from a plurality of electric heaters. The process heat is then provided from the collection pipe 234 to the industrial plant 208.

[0072] Figure 3 The first heating stage 300 is schematically and exemplarily shown in a top view, comprising a plurality of ceramic foam plates 302 as passive thermal elements and ceramic bulk material 304 arranged between two adjacent ceramic foam plates 302 as further passive thermal elements; a gaseous fluid stream 306 enters a heating chamber 308 and is heated by first active ceramic resistance heating elements 310 arranged in rows. The rows of first active ceramic resistance heating elements 310 are separated by ceramic foam plates 302 and ceramic bulk material 304 arranged between two adjacent ceramic foam plates 302, respectively. Thus, the gaseous fluid stream 306 passes in an alternating manner through the rows of first active ceramic resistance heating elements 310 and ceramic foam plates 302 with ceramic bulk material 304 arranged between two adjacent ceramic foam plates 302. The ceramic bulk material 304 can have a thermal conductivity of up to 2500 kg / m 3The ceramic bulk material 304 can have a density of up to 2500 kg / m3. In addition, the particles of the ceramic bulk material 304 can have a size of about 5 mm. The ceramic foam plate 302 has a porosity of less than 80% and can be made of SiC, SiSiC or Zr02, for example. In addition, the ceramic foam plate 302 has a minimum width of 25 mm. The minimum distance between the first active ceramic resistance heating elements 310 and the adjacent ceramic foam plate 302 corresponds at least to the diameter of the first active ceramic resistance heating elements 310. After passing through the first heating stage 300, the heated gaseous fluid stream 312 is provided to the third heating stage, if present, or directly to the gas outlet.

[0073] Figure 4 The first heating stage 400 is shown schematically and exemplarily in a top view with a plurality of first active ceramic resistance heating elements 402, for example made of SiC or MoSi2, surrounded by a respective passive thermal element 404. The passive thermal elements 404 surrounding the plurality of first active ceramic resistance heating elements 402 have a sleeve shape with protrusions arranged on their outer surface to increase the surface area and thereby improve convective heating of the gaseous fluid stream 408 entering the first heating stage 400.

[0074] The further passive thermal elements 406 are bulk material and arranged in the spaces between the passive thermal elements 404 surrounding the plurality of first active ceramic resistance heating elements 402. For example, the empty spaces between the passive thermal elements 404 surrounding the plurality of first active ceramic resistance heating elements 402 in the first heating stage 400 can be filled with further passive thermal elements 406 in bulk form. The ceramic bulk material 406 can have a density of up to 2500 kg / m3and can comprise particles having a size of about 5 mm. As the passive thermal elements 404 surround the plurality of first active ceramic resistance heating elements 402 as a heating sleeve, there is no direct contact between the ceramic bulk material 406 and the first active ceramic resistance heating elements 402 to avoid damage of the first active ceramic resistance heating elements 402 by the ceramic bulk material 406. In operation, the ceramic bulk material 406 can act as a ceramic thermal storage material for storing the heat provided by the sleeve-shaped passive thermal elements 404, which are heated by radiative heating of the first active ceramic resistance heating elements 402. After passing through the first heating stage 400, the heated fluid stream 410 is provided to the third heating stage, if present, or directly to the gas outlet. 3

[0075] Figure 5 ​A first passive thermal element 500 with a corrugated outer surface 504 is shown schematically and exemplarily in a cross-sectional view. In order to increase the outer surface area, the corrugated outer surface 504 can comprise fins, pinch-offs, protrusions 502, etc. The first passive thermal element 500 is hollow, such that a first active ceramic resistance heating element can be arranged inside the first passive thermal element 500.

[0076] Figure 6 A first passive thermal element 600 with ribs 602 arranged on an outer surface 604 is shown schematically and exemplarily in a cross-sectional view. Figure 7 Another first passive thermal element 700 with protrusions 702 arranged on an outer surface 704 is shown schematically and exemplarily in a cross-sectional view. Figure 8 A first passive thermal element 800 with protrusions 802 arranged on an outer surface 804 is shown schematically and exemplarily in a cross-sectional view, the first passive thermal element having an airfoil profile. The first passive thermal elements 600, 700, 800 all have an increased surface area to improve heat transfer to the gaseous fluid stream. In particular, if the first passive thermal element 800 has an airfoil profile, the heat transfer to the gaseous fluid stream can be further improved since the gaseous fluid stream is in contact with the first passive thermal element 800 over a longer distance. The first passive thermal elements 600, 700, 800 all have a hollow interior, such that the first passive thermal elements 600, 700, 800 can be fitted over a respective first active ceramic resistance heating element.

[0077] Figure 9 The heat transfer from a first active ceramic resistance heating element 900 to a first passive thermal element 902 and further to a gaseous fluid stream 904 is shown schematically and exemplarily. Figure 9 The working principle of convective heating of a gaseous fluid stream by means of a first passive thermal element 902, which at least partially surrounds or even fits over the first active ceramic resistance heating element 900, is thus shown. The first active ceramic resistance heating element 900 generates heat upon application of an electric current to the first active ceramic resistance heating element 900. For example, the first active ceramic resistance heating element 900 can be made of SiC. The generated heat is transferred as radiative heat 906 to the first passive thermal element 902. The outer surface of the first passive thermal element 902 is increased by providing ribs 908, such that the first passive thermal element 902 has a corrugated surface. The first passive thermal element 902 can be made of SiC, SiSiC, MoSi2 or ZrO2. Within the ceramic material of the first passive thermal element 902, a conductive heat transfer 910 takes place. The heat of the first passive thermal element 902 is then provided to the gaseous fluid stream 904 passing through the first passive thermal element 902 via a convective heat transfer 912.

[0078] Figure 10A first heating stage 1000 is schematically and exemplarily shown, which comprises a first passive thermal element 1002 configured in the form of a block with a feedthrough 1004, wherein a first active ceramic resistive heating element 1006 is arranged within the feedthrough 1004. The first passive thermal element 1002 in the form of a block with a feedthrough 1004 is made of ceramic foam. The block ceramic foam 1002 implements a passive heat exchanger which is heated in operation by thermal radiation of the first active ceramic resistive heating element 1006 arranged within the feedthrough 1004. Subsequently, the block ceramic foam 1002 transfers heat to a fluid flow 1008 via convection. After passing through the block ceramic foam 1002, a heated fluid flow 1010 is provided to a third heating stage, if present, or directly to a gas outlet.

[0079] Figure 11 A first heating stage 1100 is schematically and exemplarily shown in a top view, which comprises a first passive thermal element 1102 configured in the form of a plate with a wave shape, which is wrapped around a respective one of first active ceramic resistive heating elements 1104. The wave shape plate 1102 is made of a ceramic material, such as SiC, SiSiC or Zr02, with a porosity of 95%. Alternatively, the wave shape plate 1102 can have a porosity of 80% or more. Generally, a high porosity is preferred. Furthermore, the wave shape plate 1102 has a thickness of 30 mm. Generally, a minimum thickness of 20 mm is preferred.

[0080] In operation, the wave shape plate 1102 acts as a passive heat exchanger, which is heated by the radiated heat provided by the first active ceramic resistive heating elements 1104 by applying an electric current. For this purpose, preferably, the minimum distance of the wave shape plate 1102 to the next first active ceramic resistive heating element 1104 corresponds to the diameter of a first active ceramic resistive heating element of the first active ceramic resistive heating elements 1104. Ambient air 1106 entering the first heating stage 1100 passes one after the other through the wave shape plate 1102 and is thereby heated by the convection heating by the wave shape plate 1102 and the first active ceramic resistive heating elements 1104. Finally, after passing through the first heating stage 1100, a heated fluid flow 1108 is provided to a third heating stage, if present, or directly to a gas outlet.

[0081] Figure 12A first heating stage 1200 is shown schematically and exemplarily in a top view, which comprises only first active ceramic resistance heating elements 1204 and no first passive thermal elements in a first section 1202. In a second section 1206, the first heating stage 1200 comprises first active ceramic resistance heating elements 1208 as well as first passive thermal elements 1210 in the form of a plate with a wavy shape. Furthermore, in a third section 1212, the first heating stage 1200 comprises further first passive thermal elements 1214 configured in the form of a block extending between opposite walls 1220, 1222 of the heating chamber and having a feedthrough 1216, wherein the first active ceramic resistance heating elements 1216 are arranged within the feedthrough 1216.

[0082] In operation, a gaseous fluid 1218 entering the first heating stage 1200 is first heated by convective heating via the first active ceramic resistance heating elements 1204. The first active ceramic resistance heating elements 1204 are arranged in a regular pattern such that the first active ceramic resistance heating elements 1204 in the central region have six directly neighboring first active ceramic resistance heating elements 1204. The distance al to the directly neighboring first active ceramic resistance heating elements 1204 is constant. Furthermore, the directly neighboring first active ceramic resistance heating elements 1204 have a constant diameter dl.

[0083] After passing the first section 1202, the gaseous fluid flow 1218 enters the second section 1206, wherein the gaseous fluid flow 1218 is heated by the first active ceramic resistance heating elements 1208, which are configured in the same way as the first active ceramic resistance heating elements 1204 of the first section 1202. For example, these first active ceramic resistance heating elements 1204, 1208 can be made of SiC. In the second section 1206, the wavy shaped plate is arranged as the first passive thermal elements 1210. In particular, the second section 1206 can be configured in the same way as the first heating stage 1100 described with reference to Figure 11 The wavy shaped plate 1210 has a thickness t2 of 20 mm, but can also have a larger thickness. The minimum distance a2 between the wavy shaped plate 1210 and the first active ceramic resistance heating elements 1208 in the second section 1206 corresponds at least to the diameter dl, but can also be larger.

[0084] The third section 1212 can be configured in the same way as the first heating stage 1000 described with reference to Figure 10 The first passive thermal elements 1214 are configured in the form of a block of ceramic foam material having a feedthrough 1216. As in the first heating stage 1000 described with reference to Figure 12As can be seen in the third section 1212, the first active ceramic resistive heating elements 1216 are arranged in a regular pattern and have a larger diameter d3 than the diameter dl of the first active ceramic resistive heating elements 1204, 1208 in the first section 1202 and the second section 1206, respectively. The ceramic foam block 1214 has a width w3. In the feedthroughs 1216, the first active ceramic resistive heating elements 1204 are arranged for radiative heating of the ceramic foam block 1214. For example, the first active ceramic resistive heating elements 1216 of the third section 1212 can be made of a different material than the first active ceramic resistive heating elements 1204, 1208 of the first section 1202 and the second section 1206. For example, the first active ceramic resistive heating elements 1216 of the third section 1212 can be made of MoSi2. After passing through the third section 1212, the heated fluid stream 1224 is provided to a third heating stage, if present, or directly to the gas outlet.

[0085] Figure 13 A first heating stage 1300 is schematically and exemplarily shown in a top view, comprising first passive thermal elements 1302 in the form of plates, each plate having a plurality of feedthroughs 1304 to allow a gaseous fluid stream 1306 to flow from a gas inlet to a gas outlet. The plate-shaped first passive thermal elements 1302 can be made of SiC. Between the plate-shaped first passive thermal elements 1302, a plurality of rows of first active ceramic resistive heating elements 1308 are arranged such that the fluid stream is convectively heated in an alternating fashion by the first active ceramic resistive heating elements 1308 and the plate-shaped first passive thermal elements 1302. The plate-shaped first passive thermal elements 1302 can also serve to store heat radiated by the first active ceramic resistive heating elements 1308. The heated fluid stream 1310 is then provided to a third heating stage, if present, or directly to the gas outlet.

[0086] Figure 14 A first heating stage 1400 is schematically and exemplarily shown, comprising a plurality of first passive thermal elements 1402 in the form of rods, as Figure 15 As schematically and exemplarily shown in the third section 1212, the rods 1402 thus have a plurality of bumps and / or ribs 1404 distributed over their respective outer surfaces 1406. The rods 1402 are arranged between the first active ceramic resistive heating elements 1408. In operation, the rods 1402 are thus heated by radiative heat transfer from the first active ceramic resistive heating elements 1408. The gaseous fluid stream 1410 through the rods 1402 and the first active ceramic resistive heating elements 1408 is then heated via convective heating, such that a heated gaseous fluid stream 1410 is provided after passing through the first heating stage 1400.

[0087] Figure 16 A first heating stage 1600 is schematically and exemplarily shown, comprising first active ceramic resistance heating elements 1602 and passive flow resistance elements 1604 arranged at a wall 1606 of a heating chamber 1608. The passive flow resistance elements 1604 have a semi-circular shape, but can also have other shapes in other embodiments, such as a triangular shape or a rectangular shape. The passive flow resistance elements 1604 act as flow resistors to prevent the occurrence of runaway cold zones on the heating chamber wall 1606. Such passive flow resistance elements 1604 can also be used in the first heating stage described with reference to Figures 1 to 15 The passive flow resistance elements 1604 can also be present and can be used to avoid the occurrence of runaway cold zones in the second heating stage and / or the third heating stage, if present.

[0088] Figure 17 A first heating stage 1700 is schematically and exemplarily shown in 3D, comprising first active ceramic resistance heating elements 1702 and passive flow resistance elements 1704 arranged at a wall 1706 of a heating chamber 1708. The first heating stage 1700 can be configured in the same way as the first heating stage 1600 described with reference to Figure 16 The total number of first active ceramic resistance heating elements 1702 can be greater than the number of first active ceramic resistance heating elements 1702 as shown in Figure 17 and can range from 450 to 720 first active ceramic resistance heating elements. Preferably, the first active ceramic resistance heating elements 1702 are made of SiC. The gaseous fluid flow 1710 can pass through the first heating stage 1700 with a flow rate of 2 to 3.3 kg / s or 1.5 to 2.5 Nm 3 / s. The heated fluid flow 1712 can be provided, for example, to a third heating stage or directly to a gas outlet. The first heating stage 1700 has a length 1714 of 2 m to 4 m, a width 1716 of 0.45 m to 0.55 m and a height 1718 of 0.45 m to 1.65 m.

[0089] Figure 18 A first heating stage 1800 is schematically and exemplarily shown, comprising first active ceramic resistance heating elements 1802 made of SiC, and a control scheme for controlling the first active ceramic resistance heating elements 1802 in groups of 30 to 36 first active ceramic resistance heating elements. As indicated by the straight lines 1804, the surface load 1805 is varied by changing the voltage or current input of the respective group of first active ceramic resistance heating elements 1802 in the range of 11 W / cm 3 to 3 W / cm 3linearly applied between, for example, using a control system of electric heaters. In particular, the surface load 1805 varies along the length 1806 of the first heating stage 1800.

[0090] Figure 19 Three different first heating stages 1900, 1910, 1920 are schematically and exemplarily shown. The first heating stage 1900 shown on the left comprises only first active ceramic resistance heating elements 1902. The first heating stage 1910 shown in the middle comprises first active ceramic resistance heating elements 1912 and first passive thermal elements 1914 in the shape of rods. In particular, in the first heating stage 1910 shown in the middle, the plurality of first active ceramic resistance heating elements has been replaced by first passive thermal elements 1914 in the shape of rods compared to the first heating stage 1900 shown on the left, such that there is a sequence of alternating rows of first active ceramic resistance heating elements 1912 and first passive thermal elements 1914 in the shape of rods.

[0091] The first heating stage 1920 shown on the right comprises first active ceramic resistance heating elements 1922 and first passive thermal elements 1924 in the shape of bends. In the first heating stage 1920 shown on the right, the first passive thermal elements in the shape of rods have been replaced by first passive thermal elements 1924 in the shape of bends compared to the first heating stage 1910 shown in the middle, which first passive thermal elements in the shape of bends can locally change the direction of the fluid flow, such that the turbulence and mixing of the gaseous fluid flow is increased, resulting in a more uniform fluid flow outlet temperature.

[0092] Figure 20 A heating system 2000 operating in a standard operating mode is schematically and exemplarily shown. The heating system comprises a blower fan 2002 for providing ambient air 2003 to one or more electric heaters 2004. In order to heat the ambient air 2003, a power input P h is provided to the one or more electric heaters 2004. The power input P h is provided, for example, by a wind turbine or a solar panel 2007 as part of the power input P AC . The power input P AC also includes surplus power P s stored in a thermal storage device 2006. The volumetric flow rate dV h / dt of the heated fluid flow is set by a control system to match the power input P h . The heated fluid flow is then provided as process power P r to an industrial plant 2008, which process power is converted into process heat T proc .

[0093] Figure 21 A heating system 2100 operating in a power deficit mode is schematically and exemplarily shown. The heating system comprises a blower fan 2102 for providing ambient air 2103 to one or more electric heaters 2104. In order to heat the ambient air 2103, a power input P ACHeating system 2100 operating in insufficient mode. (In P) AC In the insufficient mode, the power P fed into one or more electric heaters 2104 h Insufficient to meet the required process heat T proc Provide the necessary process power P r Then, the volumetric flow rate dV h / dt can be reduced accordingly to match a lower power input P h Thus still providing T proc Additional power, i.e., additional volumetric flow rate, is drawn from the thermal storage device 2106 and combined with the power (i.e., volumetric flow rate) from one or more electric heaters 2104 to deliver the required process power P. r .

[0094] Figure 22 A heating system 2200 operating in charging mode is illustrated schematically and exemplary. In charging mode, power is not supplied from the renewable energy power plant 2207. Only stored power can be used and drawn from the thermal storage device 2206 to provide the required process power P. r .

[0095] Figure 23 A heating system 2300 is schematically and exemplaryly shown, including a connecting line 2302 extending between a heat storage unit 2304 and a gas inlet 2306 of an electric heater 2308. The electric heater 2308 can be connected to a reference... Figure 1 , Figure 2 , Figure 20 , Figure 21 and Figure 22 The electric heater described is configured in the same manner. The electric heater includes three heating stages: a first heating stage 2314 having one or more first active ceramic resistance heating elements and one or more first passive heating elements; an optional second heating stage 2312 having one or more active metal resistance heating elements and arranged closer to the gas inlet than the first heating stage; and an optional third heating stage 2316 including one or more second active ceramic resistance heating elements. The first heating stage 2314 can be configured in the same manner as the referenced... Figures 3 to 19 The first heating stage is configured in the same way as described.

[0096] The heating system 2300 further comprises a high temperature (HT) air filter 2318 having a maximum inlet temperature of 800 °C. The high temperature air filter 2318 is fluidly connected to a high temperature inlet air blower 2320 also having a maximum inlet temperature of 800 °C. In operation, using the high temperature inlet air blower 2320, ambient air 2322 can be sucked into the heating system 2300, thereby passing through the high temperature air filter 2318. In order to introduce the sucked ambient air into the heating chamber 2310, the high temperature inlet air blower 2320 is fluidly connected to an inlet valve 2307, which is further fluidly connected to a gas inlet 2306. The inlet valve 2307 can also be part of the gas inlet 2306. A gas outlet 2324 of the heating chamber 2310 is fluidly connected to the thermal storage unit 2304. Between the gas outlet 2324 and the thermal storage unit 2304, an outlet valve 2326 is arranged. Preferably, the outlet valve 2326 is configured as a high temperature valve for temperatures of 1000 °C or more. The outlet valve 2326 can be closed to prevent the delivery of thermal energy from the thermal storage unit 2304 back into the heating chamber 2310.

[0097] The thermal storage unit 2304 comprises a high temperature thermal storage unit 2328 fluidly connected to the gas outlet 2324 and a low temperature thermal storage unit 2330 fluidly connected to the high temperature thermal storage unit 2328. The high temperature thermal storage unit 2328 is exemplarily configured to store thermal energy at temperatures of, for example, up to 1600 °C; the low temperature thermal storage unit 2330 is configured to store residual heat from the high temperature thermal storage unit 2328 to increase the efficiency of the heating system 2300. The low temperature thermal storage unit 2330 is exemplarily configured to store thermal energy at temperatures lower than 1600 °C.

[0098] The low temperature thermal storage unit 2330 is fluidly connected to the connection line 2302. The connection line 2302 comprises an optional cooling valve 2332 connecting the connection line 2302 to a cooling air blower 2334. Upon opening the cooling valve 2332, ambient air 2338 can be sucked in using the cooling air blower 2334 and mixed with the gaseous fluid stream delivered in the connection line 2302.

[0099] The connection line 2302 comprises a charging line 2303 connecting the thermal storage unit 2304 with the high temperature air filter 2318 to circulate the gaseous fluid stream from the thermal storage unit 2304 back to the high temperature air filter 2318 in a charging mode, as described in more detail with respect to Figure 24 The charging line 2303 comprises a charging valve 2309. Furthermore, the connection line 2302 comprises a discharge line 2305 connecting the thermal storage unit 2304 with the inlet valve 2307 to direct ambient air to the thermal storage unit 2304 in a discharge mode, as described in more detail with respect to Figure 25The described. The discharge line 2305 comprises a discharge valve 2311. This can be an alternative to the connection line 2302 comprising the charge line 2303 and the discharge line 2305, which can be completely separate from each other, wherein the charge line 2303 connects the heat storage unit 2304 with the high-temperature air filter 2318 and the discharge line 2305 connects the heat storage unit 2304 with the inlet valve 2307.

[0100] In the heating system 2300, the heat storage unit 2304 is connected via an outlet connection line 2346 to an industrial plant 2342 to provide process heat for an industrial process. The outlet connection line 2346 comprises an optional temperature adjustment valve 2354, which is connected to an optional temperature adjustment air blower 2348. With the temperature adjustment air blower 2348, ambient air can be sucked in and mixed with the gaseous fluid stream leaving the heat storage unit 2304 and, in particular, passing through the high-temperature heat storage unit 2328. By mixing the gaseous fluid stream leaving the heat storage unit 2304 with ambient air, the temperature of the process heat can be reduced to a desired temperature required in the industrial process. Thus, the temperature of the process heat can be tailored to fit the respective industrial process. When providing the process heat to the industrial plant 2342, the outlet valve 2326 can be closed to prevent backflow of thermal energy from the heat storage unit 2304 to the heating chamber 2310 of the electric heater 2308. For controlling the release of process heat to the industrial plant, the outlet connection line 2346 comprises a process heat control valve 2347.

[0101] Figure 24 The heating system 2300 is schematically and exemplarily shown operating in a discharge operation mode. Figure 23 In the discharge mode, thermal energy is delivered into the heat storage unit 2304 and stored therein. To this end, in the discharge mode, the charge valve 2309 is closed and the discharge valve 2311 is open.

[0102] Since only a fraction of the thermal energy transported by the gaseous fluid stream leaving the heating chamber can be stored in the thermal storage unit 2304, it can be beneficial to circulate the exhaust gaseous fluid stream 2436 from the thermal storage unit 2304 back into the heating chamber 2310 of the electric heater 2308 through the gas inlet 2306. Thereby, the residual heat is not wasted but retained and circulated within the heating system 2300. It can be necessary to circulate the gaseous fluid stream several times until a desired amount of thermal energy is actually stored in the thermal storage unit 2304. For example, it is desired to store thermal energy at a temperature of 1600 °C in the thermal storage unit 2304. However, with each circulation of the gaseous fluid stream within the heating system 2300, the temperature in the thermal storage unit 2304 can only decrease by, for example, 100 °C. Therefore, it is necessary to perform several circulations of the gaseous fluid stream in the heating system 2300 until the desired temperature in the thermal storage unit 2304 is reached. Since the gaseous fluid stream is circulated within the heating system 2300, no thermal energy is intentionally released into the ambient atmosphere, such that thermal losses can be reduced. Residual heat from the high-temperature thermal storage unit 2328 can also be stored in the low-temperature thermal storage unit 2330.

[0103] When circulating back the gaseous fluid stream 2346, the gaseous fluid stream 2346 can have a relatively high temperature, for example, above 1000 °C. However, the high-temperature air filter 2318 and the high-temperature inlet air blower 2320 can have a maximum inlet temperature of 800 °C. Therefore, it can be beneficial to reduce the temperature of the circulating back gaseous fluid stream 2436. Cooling its temperature can be achieved by mixing the gaseous fluid stream 2436 with ambient air 2438. To this end, the heating system 2300 comprises an optional cooling valve 2332 and an optional cooling air blower 2334. By opening the cooling valve 2332, using the cooling air blower 2334, ambient air 2438 can be sucked into the connection line 2302 to mix with the gaseous fluid stream 2436, thereby cooling the gaseous fluid stream 2436. For example, the mixed gaseous fluid stream 2440 can have a temperature below 800 °C, so as not to exceed the maximum temperature of the high-temperature air filter 2318 and the high-temperature inlet air blower 2320.

[0104] Figure 25 The heating system 2300 of Fig. 23 is schematically and exemplarily shown operating in a discharge operation mode. Figure 23 In the discharge mode, process heat 2544 is provided from the thermal storage unit 2304 to the industrial plant 2342. To this end, in the discharge mode, the discharge valve 2311 is open and the charging valve 2309 is closed.

[0105] In the discharge mode, ambient air 2522 is provided to the thermal storage unit 2304 at a volumetric flow rate of Ambient air 2522 is drawn in by the high-temperature inlet air blower 2320 and passes through the high-temperature air filter 2318. The inlet valve 2307 is closed, allowing the electric heater 2308 to be bypassed and the ambient air 2522 to flow through the exhaust valve 2311 and the exhaust line 2305. The ambient air 2522 enters the low-temperature heat storage unit 2330 and subsequently the high-temperature heat storage unit 2328. Thus, the ambient air 2522 is heated by the thermal energy stored in the heat storage unit 2304. Since the outlet valve 2326 is also closed, the heated gaseous fluid flow 2524 flows toward the industrial plant 2342 into the outlet connection line 2346. If the industrial plant 2342 requires process heat, the process heat control valve 2347 is opened. If the temperature of the process heat supplied to the industrial plant 2342 should be adjusted to the desired temperature required in the industrial process, the heated gaseous fluid flow 2524 can be mixed with the ambient air 2550. For this purpose, the temperature regulating valve 2354 can be opened and the temperature regulating air blower 2348 can be used to mix at a volumetric flow rate. Ambient air 2550 is drawn in and mixed with a heated gaseous fluid stream 2524. Thus, by mixing the ambient air 2550 with the heated gaseous fluid stream 2524 from the high-temperature heat storage unit 2328, the heat output supplied to the industrial plant 2342 can be controlled to achieve the desired temperature and flow rate. The following provides process heat 2544 for industrial processes. Preferably, the volumetric flow rate of ambient air 2522 drawn in by the high-temperature inlet air blower 2320 is... and the volumetric flow rate of ambient air 2550 drawn in by the temperature-regulating air blower fan 2348 Coupling, for example, can be achieved using a control unit that controls both the high-temperature inlet air blower 2320 and the temperature-regulating air blower 2348. Therefore, coupling means that the high-temperature inlet air blower 2320 and the temperature-regulating air blower 2348 are controlled in a coupled manner.

[0106] Figure 26 An active ceramic resistance heating element 2600 is schematically and exemplaryly shown. This active ceramic resistance heating element may be, for example, a first active ceramic resistance heating element or a second active ceramic resistance heating element, preferably made of or including SiC. The active ceramic resistance heating element 2600 is arranged such that its electric heating zone 2602 is located within a heating chamber 2604. The electrical connection portion 2606 of the active ceramic resistance heating element 2600 is arranged within an airtight chamber 2608.

[0107] The active ceramic resistance heating element 2600 comprises an electrically heated zone 2602, a non-electrically heated zone 2610, and an electrical connection 2606. With the electrical connection 2606, the active ceramic resistance heating element 2600 can be connected to a voltage source to apply an electrical current to the active ceramic resistance heating element 2600 for electrical heating in the electrically heated zone 2602. Herein, for example, reference is made to the active ceramic resistance heating element 2600 as a first heating stage or as a third heating stage. Figures 1 to 24 One or more of the active ceramic resistance heating elements of the described first heating stage and / or third heating stage can be configured in the same way as the active ceramic resistance heating element 2600 with its electrical connection 2606 being surrounded by the gas-tight chamber 2608.

[0108] With the active ceramic resistance heating element 2600 as part of the first heating stage or the third heating stage, a gaseous fluid stream 2612 can be heated to a temperature of 1000 °C or more. The heating chamber 2604 is surrounded by a thermal insulation 2614. The thermal insulation 2614 is surrounded by a metal frame 2618. In the thermal insulation 2614 and the metal frame 2618, there are feedthroughs 2616 connecting the heating chamber 2604 and the outside of the heating chamber 2604. The feedthroughs 2616 have side walls formed by a ceramic muffle 2620, for example, made of or including SiC, AI2O3, or Si3N4, etc. With its non-electrically heated zone 2610, the active ceramic resistance heating element 2600 is arranged within the feedthroughs 2616 such that there is still space between the ceramic muffle 2620 and the active ceramic resistance heating element 2600.

[0109] The ceramic muffle 2620 extends into the gas-tight chamber 2608 and comprises one or more ceramic sleeve inlets 2622 fluidically connecting the gas-tight chamber 2608 with the feedthroughs 2616 such that ambient air 2626 can flow from the gas-tight chamber 2608 through the ceramic sleeve inlets 2622 into the feedthroughs 2616 and further into the heating chamber 2604. The gas-tight chamber 2608 comprises a gas-tight chamber blowing fan 2624 for sucking ambient air 2626 into the gas-tight chamber 2608 and for delivering the ambient air 2626 into the heating chamber 2604.

[0110] Thereby, leakage of the heated gaseous fluid stream from the heating chamber 2604 of the electric heater can be prevented. This is possible because ambient air 2626 can be inserted into the air-tight chamber 2608 above the electrical connection 2606 of the active ceramic resistance heating element 2600 by the air-tight chamber air blower 2624. The air-tight chamber 2608 is arranged around the electrical connection 2606 of the active ceramic resistance heating element 2600. The ambient air 2626 can enter the heating chamber 2604 via the ceramic sleeve, i.e. the ceramic muffle 2620, which has an inlet 2622 below the electrical connection 2606 of the active ceramic resistance heating element 2600. Thus, the ambient air 2626 can act as a barrier or sealing air. The ambient air 2626 can also act as cooling air for the electrical connection 2606 as well as for the non-electrically heated zone 2610 of the active ceramic resistance heating element 2600. Cooling can be necessary because both the electrical connection 2606 and the non-electrically heated zone 2610 can be heated via heat conduction from the electrically heated zone 2602 of the active ceramic resistance heating element 2600.

[0111] Figure 27 A heating chamber 2700 of a first heating stage or an optional third heating stage of an electric heater is schematically and exemplarily shown in a top view, wherein the heating chamber accommodates a baffle 2702 and a plurality of first or second active ceramic resistance heating elements 2704 as well as one or more first or second passive thermal elements (not shown). The baffle can be present in any of the electric heaters described herein.

[0112] In operation, a gaseous fluid stream 2706 flows from an inlet side 2712 to an opposite outlet side 2714 and is heated by the first or second active ceramic resistance heating elements 2704 as well as the one or more first or second passive thermal elements. Due to the baffle 2702 being arranged in the vicinity of the outlet side 2714, the impinging gaseous fluid stream 2706 is deflected and circulates back into the heating chamber 2700 as a deflected gaseous fluid stream 2708, e.g. towards the inlet side 2712. Only the portions of the gaseous fluid stream 2706 and the deflected gaseous fluid 2708 that are able to pass the baffle 2702 can exit the heating chamber 2700 as a heated gaseous fluid stream 2710. Thus, the installation of the baffle 2702, e.g. at the outlet side 2714 of the heating chamber 2700, can force the heated gaseous fluid stream inside the heating chamber 2700 to circulate in order to increase the retention time of the gaseous fluid stream inside the heating chamber 2700 and thus to increase the efficiency of the electric heater.

[0113] In the claims, the word "comprising" does not exclude other elements or steps, and the

[0114] A single unit or device can implement the functionality of several items recited in the claims. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0115] The reference signs in the claims should not be construed as limiting the scope.

Claims

1. An electric heater configured to provide megawatt scale process heat by electrically heating a gaseous fluid stream to a temperature of 1000 °C or more, wherein, The electric heater comprises: - a heating chamber having a gas inlet configured to provide a gaseous fluid stream to the inside of the heating chamber and a gas outlet configured to provide the gaseous fluid stream having a temperature exceeding 1000°C to the outside of the heating chamber, wherein the heating chamber houses: - a first heating stage comprising: - one or more first active ceramic resistive heating elements arranged and configured to generate heat having a first temperature of 1000°C or more upon application of an electric current to the one or more first active ceramic resistive heating elements; and - one or more first passive thermal elements, preferably comprising a ceramic material, arranged and configured to passively heat the gaseous fluid stream to a temperature of 1000°C or more and / or to store heat generated by the one or more first active ceramic resistive heating elements.

2. The electric heater according to claim 1, wherein, At least one passive thermal element of the one or more first passive thermal elements is arranged to at least partially surround one of the one or more first active ceramic resistive heating elements, such that the at least one passive thermal element is heated by radiative heat transfer from the respective at least partially surrounded first active ceramic resistive heating element upon application of an electric current to the at least one first active ceramic resistive heating element.

3. The electric heater according to claim 1 or 2, wherein The passive thermal element has a plurality of bumps and / or ribs distributed on its outer surface.

4. The electric heater according to at least one of the preceding claims, wherein, At least one of the first passive thermal elements comprises a block-shaped material.

5. The electric heater according to at least one of the preceding claims, wherein, The one or more first active ceramic resistive heating elements are surrounded by a plurality of first passive thermal elements, and there is a further passive thermal element configured as a block-shaped material arranged between the plurality of first passive thermal elements surrounding the one or more first active ceramic resistive heating elements.

6. The electric heater according to at least one of the preceding claims, wherein, At least one of the one or more first passive thermal elements is configured in the form of a block having one or more feed-throughs, and wherein one or more of the one or more first active ceramic resistive heating elements are respectively arranged within the one or more feed-throughs.

7. The electric heater according to at least one of the preceding claims, wherein, At least one of the one or more first passive thermal elements is configured in the form of a plate having a wave-like shape arranged such that it winds around a respective one of the one or more first active ceramic resistive heating elements.

8. The electric heater according to at least one of the preceding claims, wherein, At least one of the one or more first passive thermal elements is configured in the form of a plate having a plurality of feed-throughs arranged to allow the gaseous fluid stream to flow from the gas inlet to the gas outlet.

9. The electric heater according to at least one of the preceding claims, wherein, At least one of the one or more first passive thermal elements is configured in the form of a rod having a plurality of bumps and / or ribs distributed on its outer surface and arranged between the one or more first active ceramic resistive heating elements.

10. The electric heater according to at least one of the preceding claims, comprising a baffle arranged and configured to deflect at least a portion of the gaseous fluid stream away from the gas outlet.

11. The electric heater according to at least one of the preceding claims, comprising a second heating stage having one or more active metallic resistance heating elements, the second heating stage being arranged closer to the gas inlet than the first heating stage and being configured to heat the gaseous fluid to a second temperature, which is lower than the first temperature, when providing an electric current to the one or more active metallic resistance heating elements.

12. The electric heater according to at least one of the preceding claims, comprising a third heating stage comprising one or more second active ceramic resistance heating elements made of a different ceramic material than the one or more first active ceramic resistance heating elements and being configured to heat the gaseous fluid to a third temperature, which is higher than the second temperature, when providing an electric current to the one or more second active ceramic resistance heating elements.

13. The electric heater according to at least one of the preceding claims, comprising a connection line arranged and configured to guide at least a portion of the heated gaseous fluid stream from the gas outlet back to the gas inlet, such that the heated gaseous fluid stream can re-enter the heating chamber at the gas inlet.

14. The electric heater according to at least one of the preceding claims, wherein, At least one of the one or more first active ceramic resistance heating elements has an electric heating zone arranged within the heating chamber and being electrically heated when an electric current is applied to the at least one first active ceramic resistance heating element, a non-electric heating zone arranged between the electric heating zone and an electric connection, and the electric connection arranged outside the heating chamber, wherein the electric connection is arranged within a gas-tight chamber arranged outside the heating chamber to enclose the electric connection, and the gas-tight chamber is arranged comprising a gas-tight chamber gas inlet configured to provide ambient gas into the gas-tight chamber, wherein the gas-tight chamber is fluidly connected to the heating chamber such that ambient gas entering the gas-tight chamber through the gas-tight chamber gas inlet can enter the heating chamber.

15. A heating system configured to generate and store process heat, the heating system comprising an electric heater according to at least one of the preceding claims and a heat storage unit fluidly connected to the electric heater to receive process heat from the electric heater and configured to store the process heat provided by the electric heater.

16. The heating system of claim 15, wherein, The heat storage unit is fluidly connected to the gas inlet of the electric heater.

17. The heating system of claim 16, wherein, The fluid connection between the heat storage unit and the gas inlet of the electric heater comprises a cooling valve connected to a cooling air blower fan such that ambient air can mix with the gaseous fluid stream flowing through the fluid connection towards the gas inlet of the electric heater when the cooling valve is open.

18. The heating system of at least one of claims 15 to 17, wherein, The thermal storage unit comprises a high temperature thermal storage unit connected to the electric heater to receive and store thermal energy from the electric heater, and a low temperature thermal storage unit connected to the high temperature thermal storage unit to receive and store residual heat from the high temperature thermal storage unit.

19. The heating system according to at least one of claims 15 to 18, comprising: An outlet valve arranged between the electric heater and the thermal storage unit and being closable to prevent thermal energy stored in the thermal storage unit from being delivered back into the heating chamber.

20. The heating system of at least one of claims 15 to 19, wherein, The gas inlet is fluidly connected to or comprises an inlet air blower to provide a gaseous fluid flow to the heating chamber interior, and / or the thermal storage unit is fluidly connected to an outlet air blower arranged and configured to mix heated gaseous fluid flow provided by the thermal storage unit with ambient air.

21. The heating system of at least one of claims 15 to 20, comprising: A battery storage device operably connected to the electric heater and configured to provide electric current to the heating elements of the first heating stage, and if present, to the heating elements of the second heating stage and / or the third heating stage.

22. A method of providing process heat with an electric heater according to at least one of claims 1 to 14, the method comprising the steps of: - providing a gaseous fluid flow to the heating chamber interior; - applying electric current to the one or more first active ceramic resistance heating elements to generate heat having a first temperature of 1000 °C or more; - passively heating the gaseous fluid flow to a temperature of 1000 °C or more, and / or storing heat generated by the one or more first active ceramic resistance heating elements; and - providing the gaseous fluid flow having a temperature exceeding 1000 °C to the heating chamber exterior.

23. A method of maintenance for an electric heater according to at least one of claims 1 to 14, the method comprising: repairing or replacing at least one of the one or more first active ceramic resistance heating elements and / or at least one of the one or more first passive thermal elements.

Images