【Weekly Topic】Discussion on the process flow of synthetic ammonia
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In response to the call for an upgraded format, weekly topic-based activities are proposed; starting with a simple topic to get things off the ground. Everyone please talk about the ammonia synthesis processes they are familiar with, whether they are those in use, those they have heard of, or those that have been phased out; try to provide as detailed an explanation as possible. Each post is required to introduce one manufacturing process; copying others’ posts is strictly prohibited. For processes that are identical, different aspects can be highlighted. Posts that meet the requirements will receive bonus points: +5 points. Those that include illustrations will get an additional +5 points, while more detailed descriptions will earn additional points ranging from +5 to +20, depending on the level of detail
We use Topso ammonia synthesis. Medium-pressure synthesis results in lower compression power consumption; heat is recovered in the form of by-product medium-pressure superheated steam, and ammonia is condensed and separated using two-stage liquid ammonia.
Brief description of the ammonia synthesis process: (1) Hydrogen production by pressure swing adsorption – The feed gas (off-gas) passes through a gas-liquid separator at 3.2–3.5 MPa and 40°C to remove liquid substances, after which it enters the PSA system for hydrogen purification. In the product hydrogen purification process, it is mixed with nitrogen and dried to obtain qualified synthetic ammonia feed gas. The desorbed gas is sent for use after pressure stabilization in the desorbed gas buffer tank and mixing tank. (2) Raw gas purification process: Crude nitrogen enters the pressure swing adsorption raw gas purification process at a pressure of 3.0 MPa. A small amount of hydrogen is used, in the presence of a catalyst, to react with the trace amounts of oxygen present in nitrogen to produce water, thereby removing the oxygen from it. It is then mixed with the hydrogen from the PSA hydrogen production unit and fed into a drying system to remove the moisture contained therein. (3) Ammonia synthesis process: The highly purified gas (fresh gas) from the raw gas purification process is compressed by a fresh gas compressor, and then it enters the ammonia synthesis tower together with the recycled gas (at 38°C) coming from the outlet of the recycle compressor. The ammonia synthesis reaction takes place in a synthesis tower. The temperature of the reaction gas leaving the synthesis tower is approximately 300–330°C, and it enters the waste heat boiler. Steam at 1.3–2.5 MPa is generated in the waste heat boiler, and after its temperature is reduced to around 200°C, it enters the heat exchanger (inside the tubes); there the temperature drops to about 80°C. It then proceeds to the water cooler, where its temperature is brought down to room temperature. After that, it goes through the cold exchanger, primary ammonia cooling, and secondary ammonia cooling before reaching the ammonia separator. The circulating gas exiting the separator is used in the cold exchanger to cool the gas coming out of the synthesis tower, and then it returns to the inlet of the syngas compressor’s circulation section. The synthetic ammonia, which is the product obtained by the separator, is depressurized to approximately 3.6 MPa in a pressure reduction tank, and then further depressurized before being sent to the synthetic ammonia storage tank at 0.6 MPa. (4) Freezing process: Two ice makers are installed in the freezing process. The gaseous ammonia exiting the ice makers is condensed and then flows naturally to the ammonia storage tank of the ice maker system; from there, the liquid ammonia in the storage tank is sent to the ammonia condenser in the synthesis process to provide cooling for that system.
Synthetic ammonia process flow: Desulfurization. Transformation, synthesis, copper washing, carbonization, compression. . .
The Topso plant in Denmark produces 1,500 tons of liquid ammonia per day; it features a side-fired furnace, high and low shift furnaces, two-stage MDEA absorption for decarburization, a methanation furnace, a vertical synthesis tower, and two-stage ammonia cooling for freezing. The current overall energy consumption is 30.5 GJ
We employ a hydroformylation production process, which includes oxygen-enriched oxidation for gas generation, desulfurization, pressure swing adsorption for carbon removal, low-pressure methanol production, alcohol-to-hydrocarbon conversion, and a synthesis tower. Currently, the power consumption for ammonia synthesis is relatively high, mainly due to the high pressure in the fresh gas system, around 30 MPa. Do anyone have any effective measures to reduce power consumption?
Vague understanding 1. How much does electricity cost per year? 1. How many days are there for production in a year? 1. Should combined methanol production absorb both CO and CO2 from the feedstock? No CO conversion? Hydrogenation to methanol. 1. Is ammonia synthesis sales measured in tons or cubic meters? Price.
There is a transformation; I missed mentioning it, my apologies! Liquid ammonia is sold by ton, at around 2,800 yuan per ton, and the annual electricity consumption is approximately 1.2 billion kWh.