System and method for producing ammonia

Abstract

The invention relates to a system and a method for generating ammonia, wherein, in an ammonia reactor, ammonia (NH3) is generated from a synthesis gas, wherein the synthesis gas contains hydrogen (H2) and nitrogen (N2), wherein a nitrogren supply flow and a first heat exchanger are used, which are designed in such a way that the hot ammonia (NH3) flowing out of the ammonia reactor heats the nitrogen used as synthesis gas in the nitrogen supply flow.

Description

[0001] Description

[0002] Plant and process for the production of ammonia

[0003] The invention relates to a plant and a method for producing ammonia, wherein ammonia (NH3) is produced from a synthesis gas in an ammonia reactor, wherein the synthesis gas comprises hydrogen (H2) and nitrogen (N2).

[0004] Ammonia production is based on a well-known process that typically requires a great deal of energy. According to initial estimates, around 1% of the world's energy is currently used for ammonia production.

[0005] Ammonia produced from renewable energy sources is referred to as green ammonia. Green ammonia is considered a rapidly growing energy carrier for hydrogen. It is also used in many industrial processes, especially fertilizers. It is estimated that approximately 50% of the green hydrogen produced in the coming years will be processed directly into liquid ammonia for long-distance hydrogen transport, as the liquefaction of pure hydrogen is highly energy-intensive.

[0006] The greatest energy and compression expenditure, in addition to hydrogen production through electrolysis and nitrogen production through air separation plants, is the synthesis gas compression, which compresses the nitrogen-hydrogen mixture to the pressure of 150-200 bar required for the synthesis process, and the cold box, which provides the cooling energy for the liquefaction and cooling of the ammonia to approximately -33°C at atmospheric pressure.

[0007] Typically, a preheating unit is required to heat the synthesis gas to the reaction temperature. Currently, the nitrogen and hydrogen required for ammonia production are typically compressed to the required synthesis pressure in a synthesis gas compressor. The intake pressure for this compressor is typically determined by the hydrogen pressure, which, in green ammonia applications where electrolysis is operated on-site, is limited to the maximum outlet pressure of an electrolysis system (max. 30-40 bar).

[0008] The shaft power for the compressor is supplied by a steam turbine, while the required steam is generated from the heat released during ammonia synthesis. Preheating of the synthesis gas must be achieved either by a fuel- or electricity-fired heater or by utilizing waste heat from the ammonia process, which reduces the amount of steam that can be generated for the steam turbine.

[0009] Condensation occurs through a refrigerant circuit.

[0010] The invention has for its object to provide an improved plant and an improved process for the production of ammonia, in particular with regard to the use of the energy required for the production of the ammonia.

[0011] This object is achieved by a system according to claim 1 and a method according to claim 7.

[0012] The invention proposes an innovative concept for an environmentally friendly ammonia plant by integrating an electrolyzer using renewable energy and an air separation plant using cold to reduce the overall energy demand and improve the overall economic efficiency.

[0013] Advantageous further developments are specified in the subclaims. The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings.

[0014] Identical components or components with the same function are marked with the same reference symbols.

[0015] Embodiments of the invention are described below with reference to the drawings. These are not intended to represent the embodiments to scale; rather, where useful for explanation, the drawings are presented in a schematic and / or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art.

[0016] The figure shows a schematic representation of a plant for the production of ammonia.

[0017] The figure shows a plant 1 for producing ammonia. A key component of plant 1 is the ammonia reactor (2), which is designed according to the state of the art. A detailed description of the ammonia reactor 2 is therefore omitted here.

[0018] In ammonia reactor 2, a synthesis gas is fed. The synthesis gas comprises hydrogen (H2) and nitrogen (N2). The hydrogen (H2) and nitrogen (N2) react in the ammonia reactor according to the chemical reaction

[0019] N2+ 3 H2-> 2 NH3+ 92 kJ / mol

[0020] This chemical reaction is a strongly exothermic reaction, ie the ammonia NH3 produced in the ammonia reactor has a comparatively high temperature, and this high temperature is used according to the invention to preheat the nitrogen N2.

[0021] The system 1 has a nitrogen supply 3 for supplying nitrogen as synthesis gas. The nitrogen is fed to a first pump 4 and from there to a heat exchanger 5. The nitrogen heated in the heat exchanger 5 is fed to another heat exchanger 6 and is further heated there. The nitrogen heated in the heat exchanger 6 is fed to another heat exchanger 7 and is further heated there.

[0022] Plant 1 includes a feed line 8 for hot ammonia produced in the ammonia reactor. The hot ammonia flows successively through heat exchangers 7, 6, and 5, cooling down while simultaneously increasing the temperature of the nitrogen.

[0023] Before the heated nitrogen flows into the ammonia reactor, the nitrogen is heated via another heat exchanger 9.

[0024] System 1 has an air supply 10 for supplying air. The air is fed to a first compressor 11 and from there to the heat exchanger 9. The compressor 11 is part of an air separation plant and is therefore also referred to as the main air compressor (MAC). The air flows through the heat exchanger 9, cooling it down, and simultaneously increasing the temperature of the nitrogen.

[0025] The nitrogen heated in the heat exchanger 9 reaches the ammonia reactor 2.

[0026] System 1 has a hydrogen supply 12 for supplying hydrogen. The hydrogen is fed to a compressor unit 13 and from there to the heat exchanger 14. The heat exchanger 9 is supplied with air from the air supply 10. The air cools, and the temperature of the nitrogen is simultaneously increased.

[0027] System 1 has an oxygen supply 15 for supplying oxygen. The oxygen flows through two heat exchangers 16 and 17, where it is heated. The ammonia cooled in heat exchangers 2, 3, and 4 is further cooled in heat exchangers 16 and 17, so that the ammonia is ultimately in the liquid phase and can therefore be easily transported.

[0028] This invention therefore proposes a concept to improve energy efficiency through three main considerations:

[0029] 1. Pumping liquid N2 from the air separation plant instead of compressing it in the gas phase to reactor pressure.

[0030] 2. Use of the cooling energy from the air separation plant for partial liquefaction and cooling of NH3.

[0031] 3. Preheating of N2 and H2 using waste heat generated during air compression in the air separation plant.

[0032] The essential features of Appendix 1 are explained again below. The reference symbols used below refer to the reference symbols enclosed within the components. These reference symbols are therefore marked with either rectangular boxes or round boxes.

[0033] - Liquid N2 (stream 1) is produced in the air separation plant at atmospheric pressure and approximately -195°C, pumped to reactor pressure (150-210 bar) by a pump (pump 1) and then heated to up to 250°C (heat exchanger 2) with ammonia (stream 7) and hot air (stream 13), which is generated in the main air compressor of the air separation plant (compressor 13), evaporated (heat exchanger 3) and superheated (heat exchangers 4 and 5). - Hydrogen is either produced on-site by electrolysis or supplied via a pipeline at a pressure between 1 and 60 bar (stream 28) and then compressed to the reactor pressure (150-210 bar) in an H2 compressor (compressors 17 and 19 with heat exchanger 18 as intercooler), which can be either a turbo or a piston compressor, and then preheated to 168°C by hot air (stream 17) produced in the booster air compressor of the air separation plant (compressors 14 and 16 with heat exchanger 15 as intercooler).

[0034] - The actual ammonia reaction process remains unchanged, ie the exothermic reaction heat is used to generate steam, which can be used to generate electricity and / or drive compression plants, and the unconverted synthesis gas is recycled.

[0035] - The NH3 leaving the boiler at 40-50°C (stream 7) is cooled in heat exchangers 12, 11, 4, 3, and 2 by cold nitrogen and oxygen from the ASU and partially liquefied (11%). The remaining 89% (stream 9) is fed to a refrigerant system (heat exchanger 9) and liquefied there. The three liquid NH3 streams (stream 11, stream 23, and stream 27) can then be collected in a storage tank for later transport.

Claims

Patent claims 1. Plant for the production of ammonia, comprising an ammonia reactor designed to produce ammonia (NH3) from a synthesis gas, wherein the synthesis gas comprises hydrogen (H2) and nitrogen (N2), with a nitrogen inlet and a first heat exchanger designed such that the hot ammonia (NH3) flowing out of the ammonia reactor heats the nitrogen used as synthesis gas in the nitrogen inlet.

2. Plant according to claim 1, comprising a further heat exchanger designed such that air heated in an air separation plant further heats the nitrogen heated from the first heat exchanger.

3. Plant according to claim 1 or 2, comprising an electrolizer designed to produce hydrogen (H2) used as synthesis gas, wherein the hydrogen (H2) is heated by a compressor unit.

4. Plant according to claim 3, comprising a heat exchanger designed such that the air heated in the air separation plant further heats the hydrogen heated from the heat exchanger.

5. Plant according to one of the preceding claims, comprising a heat exchanger designed such that oxygen produced in an air separation plant cools the ammonia produced in the ammonia reactor.

6. Plant according to one of the preceding claims, wherein the ammonia from the ammonia reactor is cooled via the heat exchangers such that the ammonia comprises a liquid phase. A process for producing ammonia, wherein ammonia (NH3) is produced in an ammonia reactor from a synthesis gas comprising hydrogen (H2) and nitrogen (N2), wherein a nitrogen inlet and a first heat exchanger are employed, the latter being configured such that the hot ammonia (NH3) flowing out of the ammonia reactor heats the nitrogen used as synthesis gas in the nitrogen inlet. A process according to claim 7, wherein a further heat exchanger is employed, the latter being configured such that air heated in an air separation plant further heats the nitrogen heated from the first heat exchanger. A process according to claim 7 or 8, wherein an electrolizer is employed, the electrolizer being configured to produce hydrogen (H2) used as synthesis gas, the hydrogen (H2) being heated by a compressor unit.A method according to claim 9, wherein a heat exchanger is used which is designed such that the air heated in the air separation plant further heats the hydrogen heated from the heat exchanger. A method according to any one of claims 7 to 10, wherein a heat exchanger is used which is designed such that oxygen produced in an air separation plant cools the ammonia produced in the ammonia reactor. A method according to any one of claims 7 to 11, wherein the ammonia from the ammonia reactor is transferred via the heat exchanger. The exchange process cools down to such an extent that the ammonia comprises a liquid phase.

Images