Method by way of which process heat is provided for thermo-metallurgical or thermo-physical applications, using at least one ammonia burner

Abstract

The method according to the invention provides process heat for thermo-metallurgical or thermo-physical applications, using at least one burner, the at least one burner being operated at least to some extent with ammonia and oxygen or with an oxygen-containing gas mixture.

Description

[0001] METHOD BY WHICH PROCESS HEAT IS PROVIDED FOR THERMO-METALLURGICAL OR THERMO-PHYSICAL APPLICATIONS WITH AT LEAST ONE AMMONIA BURNER The invention relates to a method by which process heat is provided for thermometallurgical or thermo-physical applications with at least one burner.

[0002] The present invention refers to the current and future technical requirements for industrial process technology, which are associated with the

[0003] Climate Protection Plan 2050 in the Federal Republic of Germany. The aim is to reduce greenhouse gas emissions by at least 80% compared to 1990. For many thermoprocessing manufacturing processes,

[0004] Furnaces are used in which the process heat is provided by gas burners (natural gas or liquefied petroleum gas). Gas-fired crucible, hearth, and shaft furnaces for melting and holding metal alloys; gas-fired heat treatment furnaces for metallurgical processes, particularly for metal parts made of iron, steel, and non-ferrous alloys; and gas- and oil-fired kilns in the glass, ceramics, and refractory industries, as well as in cement production, are of great economic importance.

[0005] The problem, however, is that the combustion of natural gas (or liquefied petroleum gas) as an energy source to generate the necessary process heat generates significant CCH emissions. In particular, the batch operation of furnaces over the required duration of several hours results in a product-specific, very high CCH footprint, with correspondingly negative impacts on the environment and the competitiveness of the companies.

[0006] To achieve the desired transformation toward low-carbon dioxide (CO2) industrial processes within the framework of the required energy transition, various technological developments are available. Developments in recent years to improve thermal process technology relate in particular to increasing the efficiency of natural gas burner technology, reducing waste heat losses through more efficient refractory materials in furnace lining, optimizing furnace charging, shortening process times, or using hydrogen as a fuel gas. Most measures merely reduce the amount of emissions emitted, which, however, falls far short of the technical requirements. It can therefore be stated that the core problem has not yet been solved. A CO2-free process is only possible through the combustion of hydrogen, but sufficient quantities of "green" hydrogen are not available.

[0007] The measures implemented to date to reduce CO2 emissions are not effective enough and therefore insufficient to meet the technical requirements for CO2-free production. Green hydrogen has the disadvantage of requiring pipeline-based transport and limited availability. While the electrification of technical processes leads to a reduction or elimination of CO2 emissions (when electricity generated without CO2 is used), it also leads to massive technical and economic limitations and a reduction in product quality, resulting in disadvantages in terms of economic viability and international competitiveness.

[0008] Melting aluminum alloys with electrically heated furnaces leads to massive disadvantages due to the different process requirements in the various steps, which make this technology unsuitable for industrial scale. Electrically resistance-heated furnaces are only used for holding heat and not for melting, as the energy input is too low and thus the melting times are too long and uneconomical. Electrically resistance-heated furnaces have not been able to establish themselves on a large scale for melting aluminum alloys due to insurmountable disadvantages. Charging entire ingot batches or large-volume return from the foundry is not feasible with the required melting capacity and melt quality. Metallurgical disadvantages arise because harmful deposits, such as moisture or residues from machining processes, are not eliminated, thus contaminating the melt.While inductively heated melting furnaces meet emission-free requirements (when using CO2-free electricity), their characteristic strong bath movement leads to oxide inclusions in the melt that impair quality and, under poor coupling conditions, to low melting performance. Shaft and hearth furnaces with gas or oil burners have therefore proven to be highly effective melting units in industry. Typical applications include melting entire stacks of ingots, large-volume return material, or bulky metal scrap, while maintaining high melt quality and high melting performance. Metallurgical advantages are achieved by countercurrent melting.

[0009] The heat treatment of metal parts, especially those made of iron and steel alloys, is primarily carried out in gas-fired heat treatment furnaces. For energy and economic reasons, electric heating methods are only suitable for comparatively small furnace volumes. The present invention is based on the object of providing process heat for thermo-metallurgical and thermo-physical processes, preferably in a furnace, using the flame or torch of at least one burner, without generating direct CO2 emissions. This allows the advantages of a free torch or flame to be utilized while allowing existing process systems to continue to be used.

[0010] According to the invention, this object is achieved by a method that utilizes the features of claim 1. Advantageous embodiments and further developments can be realized with features defined in dependent claims.

[0011] In the process, at least one burner is operated, at least temporarily, with ammonia and oxygen or an oxygen-containing gas mixture, in particular air. "At least temporarily" is understood to mean, in particular, an operating interval during which a chemical reaction of the hydrogen, chemically bound in the ammonia, with the oxygen is possible. This can particularly be the time period following any necessary preheating, which is achieved by the combustion reaction of a fuel other than ammonia.

[0012] During and with preheating, at least one heating element arranged on at least one burner at a distance from the outlets for ammonia and oxygen or the oxygen-containing gas mixture should be heated to a temperature of at least 750 °C before a chemical reaction, in which the hydrogen contained in the ammonia is chemically converted, can be initiated by ignition of a flame or the operation of the at least one burner can be carried out with ammonia as fuel. A burner known per se, as is already used in conventional operation, in particular with natural gas as fuel, in which nozzle-shaped outlets for fuel and oxidant, such as oxygen or an oxygen-containing gas mixture, in particular air, are present, can be used and a heating element can be integrated. In addition, at least one additional outlet for a fuel other than ammonia can be provided on the burner.By operating the burner with a liquid or gaseous hydrocarbon compound (preferably natural gas), at least one heating element can be heated to a temperature of at least 750 °C and, once this minimum temperature has been reached, a switch to ammonia as fuel can be made, whereby CO2 is released only during the relatively short preheating phase.

[0013] Outlets for fuel and oxidizer can be designed as in conventional burners.

[0014] However, the preheating of at least one heating element can also be achieved by means of electrical resistance heating, either alone or in addition to preheating by combustion of another fuel. In this case, an electrical current can be passed through a heating element made of or with an electrically conductive material. For example, a heating element made of an electrically non-conductive material can utilize electrical heating conductors, which can be arranged in the form of electrically conductive wires or layers on or in the respective heating element and connected to an electrical voltage source.

[0015] The preheating and in particular the electrical resistance heating can be stopped or switched off when the desired minimum temperature of 750 °C, preferably at least 800 °C and most preferably at least 1000 °C is reached and the chemical reaction in which the hydrogen of the ammonia is chemically converted can be carried out in a stable manner.

[0016] A heating element fulfils the function of a heat energy storing element.

[0017] During the combustion reaction, oxygen or an oxygen-containing gas mixture should be supplied in such a way that a proportion of oxygen is present that ensures stoichiometric oxidation or a slight excess of oxygen. This prevents the release of non-chemically reacted ammonia, allowing the ammonia to burn completely. A heating element made of a metallic or ceramic material, a tubular element, and / or a heating element with raised and recessed surfaces can be used. The fuel, ammonia, and oxygen or air, as the preferred gas mixture, can flow past the surface of the heating element, and the mixture can be heated to break down the chemical bond of ammonia, allowing the chemical conversion of the hydrogen it contains to take place.The porosity, surface profiling and / or tubular design increase the surface area of ​​the heating element that can be used for heat exchange.

[0018] One or more heating elements with a heat capacity of at least 600 J / (kg*K) should be used to ensure effective preheating and to maintain a sufficiently high temperature at which the NH3 oxidation reaction can take place.

[0019] The at least one heating element can be positioned at a distance of between 10 mm and 50 mm from the outlets for ammonia and oxygen or the oxygen-containing gas mixture. This allows flame formation around the entire heating element. The chemical reaction / combustion begins when the fuel, ammonia, and the oxygen or gas mixture impact the heating element. The heating element can then be maintained at the required temperature by the chemical reaction.

[0020] A temperature sensor, which can preferably measure the temperature of the heating element without contact, can be advantageously used for control. This allows for controlled opening and closing of the respective outlet openings for the oxidizer and fuel, and should also allow for control of the respective flow rates.

[0021] The flame or flare emerging from the burner can then provide the desired process heat for the applications already mentioned, as is the case with conventional burners powered by natural gas, for example. An effective way to decarbonize industrial thermal processing technology in metal production / metal processing, as well as the glass, ceramics, and refractory industries, therefore lies in the invention of replacing conventional gas burners in furnaces with burners that can be operated with ammonia as fuel. Ammonia burns to form N2 and H2O. Consequently, no CO2 is produced during combustion. The calorific value of ammonia is 14,319 kJ / m3 3 For comparison, the calorific values ​​for hydrogen are 10,760 kJ / m 3 and for methane at 35,898 kJ / m 3With comparable burner performance, while maintaining the required furnace chamber temperatures and process times, emission-neutral thermal processing technology is enabled by eliminating gas as an energy source and hydrocarbon compound. The intended extensive use of existing, proven, and well-known furnace types for melting, holding, heat treatment, and firing will thus allow the characteristic advantages of conventional furnace designs to continue to be utilized.

[0022] The essential innovation of this invention lies in the use of burners that can be operated with ammonia as fuel to provide process heat for effectively melting metals, conducting heat treatments, or producing non-metallic materials without directly generating CO2 emissions. This is a new technology that is not yet established on the market. The core of the invention lies in the use of a hot gas flare, which is technically necessary / advantageous for CO2-free heat generation.

[0023] The current state of the art involves melting using natural gas and oil burners, which emit considerable amounts of CO2. The invention solves the problem of (h) emissions. At the same time, however, the advantageous and proven torch or flame can also be used.

[0024] Ammonia is one of the most widely produced and used chemicals. With its low boiling point of -33.34°C, ammonia is technically very easy and safe to handle, unlike hydrogen, which has a boiling point of -252.9°C. As an energy carrier, ammonia can be transported to the respective point of use not only via pipelines but also in tanks (ships, trucks).

[0025] The possible applications therefore extend to the replacement of previously used fossil gas burner technologies with the burner technology according to the invention using ammonia as a fuel. A key advantage of the invention is the extensive continued use of investment-intensive existing plants. No new furnace technology is required. Industrial conversions can be achieved by largely utilizing existing units simply by substituting the burner technology. Furthermore, the provision of ammonia as a fuel for generating process heat can be grid-independent, meaning that the technology change eliminates the need for large investments in grid infrastructure. The chemical properties of ammonia make it relatively easy to store large quantities (loss-free in tanks without cooling) for any length of time. Tanks with 20,000 liters of ammonia are state of the art.

[0026] Ammonia is a climate-neutral energy source if the required hydrogen is produced through electrolysis during extraction and the required electricity is generated from renewable energy sources, such as photovoltaic or wind power plants. The potential basic prerequisites for possible applications are met, in particular, by the fact that hydrogen is stored in the chemical compound ammonia, thus already technically resolving issues regarding storage and transport, including imports from sources such as North Africa or Australia. In the solid-state ammonia synthesis process (SSAS process), ammonia can be produced electrolytically directly from water, air, and electricity.

[0027] Based on the invention, a wide range of applications is possible. Innovative applications are feasible for various melting furnace designs (e.g., shaft furnaces, hearth furnaces, crucible furnaces), preheating stations for ladle heating, heat treatment furnaces, and furnaces in the ceramics and basic materials industries. A significant substitution potential arises from the 1,500–2,000 gas-fired furnaces currently in use in the German non-ferrous foundry industry alone. Many times more are installed in Asia and America.

[0028] The invention will be explained in more detail below by way of example.

[0029] Using an otherwise conventional burner from whose outlets ammonia, air as a gas mixture and natural gas are supplied, the chemical reaction initially takes place in such a way that with the outlet opening for ammonia closed and the outlet opening(s) for natural gas and oxygen open, a flare is formed in the conventional way. At a distance of 30 mm, a tubular heating element with an outer diameter of 3 mm, an inner diameter of 1 mm and a length of 90 mm made of a ceramic material, in particular aluminum oxide, is arranged. This tubular heating element is heated by the torch / flame to a temperature of 1000 °C ± 50 K. Natural gas flows at a volume flow of 5 l / min and oxygen at a volume flow of 10 l / min from the respective outlet openings, which are equipped with controllable valves, towards the heating element during the combustion process, allowing the heating element to be heated accordingly.

[0030] The above-mentioned burner can thus be operated with an output of approximately 3 kW. The heating element is thus preheated to a temperature of approximately 1000 °C. Once this temperature has been reached at the heating element, the volume flow of natural gas can be gradually reduced to zero, and the volume flow of supplied ammonia can be increased by opening the respective outlet openings until an ammonia volume flow of 3.5 l / min is reached. At this point at the latest, the supply of natural gas is stopped. The flare / flame is then formed by the combustion of the hydrogen contained in the ammonia, and its thermal energy can be used as process heat. Released nitrogen can be released into the environment.

[0031] The example described here can be scaled up for larger systems and applications, for example, to heat larger quantities using ammonia combustion for melting. The preheating of the heating element can also be supplemented by electrical resistance heating. For this purpose, electrical resistance heating elements can be integrated into the heating element or arranged on it.

Claims

Patent claims 1. A method by which process heat is provided for thermo-metallurgical or thermo-physical applications with at least one burner, wherein the at least one burner is operated at least temporarily with ammonia and oxygen or an oxygen-containing gas mixture.

2. Method according to claim 1, characterized in that at least one heating element arranged on the at least one burner at a distance from the outlets for ammonia and oxygen or the oxygen-containing gas mixture is heated to a temperature of at least 750 °C before a chemical reaction in which hydrogen contained in the ammonia reacts chemically with oxygen is initiated by ignition of a flame and the operation of the at least one burner is carried out with ammonia as fuel.

3. Method according to one of the preceding claims, characterized in that the heating element is heated to a temperature of at least 750 °C by electrical resistance heating and / or by operating the burner with a liquid or gaseous hydrocarbon compound as fuel.

4. Method according to one of the preceding claims, characterized in that a heating element made of a metallic or ceramic material, a tubular element and / or a heating element having raised areas and depressions on its surface is used. A method according to any one of the preceding claims, characterized in that a heating element formed with a porous material is used. A method according to any one of the preceding claims, characterized in that one or more heating elements with a heat capacity of at least 600 J / (kg*K) are used. A method according to any one of the preceding claims, characterized in that the at least one heating element is heated to a temperature of at least 750 °C, preferably at least 1000 °C, before the chemical reaction in which hydrogen contained in the ammonia reacts chemically with oxygen is initiated by ignition of a flame and the operation of the at least one burner with ammonia as fuel is carried out.Method according to one of the preceding claims, characterized in that the at least one heating element is arranged at a distance of between 10 mm and 50 mm from the outlets for ammonia and oxygen or the oxygen-containing gas mixture.