Why are large ammonia synthesis compressors powered by steam instead of electricity?
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Currently, centrifugal compressors used for producing 300,000 tons of synthetic ammonia per year are all driven by steam turbines. I think using steam is not cost-effective, as it requires the installation of steam boilers as well. With such strict environmental regulations nowadays, modifying the exhaust gases from these boilers also incurs significant costs. So why not use electric motors to drive the compressors? The electric motors used in China’s high-speed trains are extremely advanced; modifying them to power compressors should not be a major issue. Moreover, these electric motors generate much less vibration and noise, and they make operation more convenient compared to steam turbines. Speed control is also more flexible, accurate, and timely, and there is no need to build steam pipelines, which would result in heat losses. . . There are so many advantages – why isn’t an electric version used?
The synthetic ammonia system itself has a waste heat boiler
Synthetic ammonia inherently generates a large amount of steam as a by-product; this is taken into account from the perspective of energy savings and reduced consumption.
From a safety perspective, steam is safer than electricity; in terms of cost, steam is also cheaper than electricity； However, some factories take overall factors into consideration; for example, if there is insufficient electricity or an inadequate steam balance, they can use electric power to drive the compressor. However, for 300,000 tons of synthetic ammonia, the electric drive power is likely to be high; my preliminary estimate is 15,000 KW. The motors required for this purpose take up a lot of space, and high-power motors need corresponding cooling systems
The most important thing is that steam turbines are stable; with electricity, the plant has to stop operating due to fluctuations in the power grid, whereas steam pipelines are easier to control
It can save energy, right? Some manufacturers use electric compressors, and there are quite a few such manufacturers
It is generally cost-effective and stable, with steam that can be recycled. Typically, ammonia plants have their own generators.
Large ammonia synthesis plants all have power plants, and power plants produce steam
In fact, each has its advantages and disadvantages. The main advantages of steam-driven systems are as follows: 1. Considering the issue of steam balance, large-scale ammonia synthesis plants equipped with urea production units generally use boilers and their own power plants; high-quality steam is used for power generation, while lower-quality steam can be utilized to drive large-scale machinery. Without steam drive, a large amount of low-quality steam that cannot be utilized leads to the boiler operating at reduced capacity and results in waste, which is very uneconomical. Using steam driven throughout the plant makes it easier to achieve balanced economic operation. 2. Using steam drive for load regulation is simple, and the design is relatively mature. It is convenient to make adjustments in the face of large load fluctuations. 3. When paired with a combustible gas compression unit, the safety factor of steam drive is higher. Disadvantages: 1. High initial investment. 2. Startup and shutdown are complex. 3. The maintenance workload is large. 4. Spare parts are expensive. The main advantages of electric drive are: 1. Low investment, as there is no need for steam generators or delivery pipelines and valves; only motors are required as a replacement. 2. It is simple to operate, with few restrictions on starting and stopping; unlike steam turbines, whose operation is complex and subject to large fluctuations in temperature. It can be started quickly, and recovery from a short pause is also very fast. 3. Lower operating costs: without a steam system, there is no need to consider things such as steam piping, heat losses, condensate recovery, or condensate purification; or the size of the equipment can be reduced. 4. It eliminates the need for an investment in boilers, reducing environmental pressure; there are already factories in China that use entirely electric drives without any accompanying boilers. The entire plant covers a much smaller area. Disadvantages: 1. Large-scale explosion-proof motors are already quite mature in China, but the technology related to large-scale frequency converters has not kept up. Given the high degree of operational flexibility required in ammonia synthesis plants, there is a need for frequent frequency adjustments of the equipment; therefore, it may be necessary to consider importing such products. 2. Operational economics: Without on-site power plants, costs are highly influenced by electricity prices. The elimination of preferential electricity rates for urea has further increased operating costs. However, **direct power supply is being promoted in an effort to reduce companies’ electricity costs; it remains to be seen whether this will lead to positive changes.