Requirements for nitrogen quality in dry coal powder fluidized bed gasification
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As we all know, dry coal powder gasification technologies such as shell and GSP require nitrogen for material transportation. Are there any specific requirements regarding the quality parameters of this nitrogen? Can a conventional air separation unit meet its requirements?
There are no special quality requirements for nitrogen used to transport coal powder in dry coal powder gasification. Texaco’s water gasification process also uses nitrogen for purging oxygen pipelines, and the nitrogen quality standards applicable to Texaco’s air separation processes can be used as well in dry coal powder gasification; the only difference lies in the required amounts of oxygen and nitrogen
For the power nitrogen used in the raw material conveying section, as long as its oxygen content is below 5% – that is, it is contaminated nitrogen – and it meets the safety requirements during coal powder preparation or conveying, a concentration of 50% of the lower explosion limit is sufficient. The nitrogen used for tasks such as purging and backwashing after the reaction section will enter the crude syngas, and this could have an impact on downstream chemical processing units; therefore, its purity is important, generally requiring levels in the PPm range, although this requirement can be relaxed in the case of IGCC. Generally, large air separation units can easily meet this requirement, unless there are design or modification errors that result in the ASU functioning as a nitrogen contaminator :(.
Dear experts, I have a layman’s question: in the SHELL process used in ammonia production plants, is it possible to use air to transport coal? Can some oxygen be saved?
It’s better not to; the oxygen level is too high!
The environment in which coal powder is located must be an inert one; for safety reasons, do not use air
In the coal or power industry, air is indeed often used as the conveying medium. But in the chemical industry, the requirements are much higher. This is especially true for new types of gasification. This is because the coal powder used in fluidized bed dry coal powder feeding has a fine particle size; on site, we can see that the coal powder produced by the coal grinder resembles black flour, with such a small particle size
Actually, there’s no difference; it just needs to be heated a little!
It seems that the requirements for purging nitrogen in nitrogen and oxygen pipelines are different; nitrogen used for purging oxygen pipelines must be free of oil, so liquid nitrogen or filters are generally used.
Air cannot be used for transporting coal powder for the following reasons: 1. There are requirements regarding the temperature of the medium used for transportation; at high temperatures, air and coal powder are more prone to explosion. 2. During coal powder circulation, it must return to the coal powder storage bin and be connected to the drying and pulverization system; using air would disrupt the entire inert environment and pose a danger. 3. The purging gas for the oxygen pipeline and the fluidization gas used for the vent cone must be oil-free, as oil can easily clog the micropores.
It can’t be transported using air, right? It seems that during the drying stage, the oxygen content must not exceed 8%, let alone using air. The reasons were explained very clearly by the guy above. Additionally, the purity of nitrogen seems to be different from what that guy said; I work in the IGCC field, haha. It seems that the design institute specifies a quite high purity level for nitrogen, around 99.99%. This is just for reference and learning purposes, so we can all improve together: handshake
Let me summarize. Firstly, for explosion prevention reasons, depending on the particle size of the coal powder and the conveying temperature, the oxygen content in the environment surrounding the coal powder in the coal chemical industry should
Although the oxygen content requirement for pneumatic conveying of coal powder is quite strict, the nitrogen produced by modern large-scale air separation plants has a purity of 99.999%, with an oxygen content of less than 10 ppm; therefore, it can be used with complete confidence.
Two additional points: 1, the temperature of N2 should be above 80 degrees; 2, N2 must not contain oil, or the oil content must be extremely low.
Transporting coal powder through pipes can generate static electricity, and it may cause dust explosions when exposed to oxygen