Discussion on the issue of air recovery during plant startup and shutdown
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As the title suggests, many experts these days are suggesting that the air released during the start-up and shutdown of coal chemical plants should be captured and used as fuel. I’ve also heard that some areas have already required new projects to adopt this approach. What are everyone’s thoughts on the feasibility of implementing this?
This post was last edited by sinoeng on 2022-6-12 at 16:58. This is both a technological trend and an environmental requirement. It cannot be recycled now; perhaps a cluster of facilities has not been established and there are insufficient conditions for disposal in cross-border areas ； It could also be due to limitations in the technical capabilities of the internal system. One of the significances of technological progress is to make the impossible possible. Modern oil refining and chemical complexes have already achieved the recovery of vent gas. The smaller and more independent it is, the harder it is to recycle.
This post was last edited by The wise are enlightened on 2022-6-12 at 16:17. Some experts can only be considered “common-sense experts” in fields outside their area of specialization. Common sense tells us: When air is released, it goes to the torch for burning – so why can’t it be recycled as fuel? It’s a shame to burn it as it also pollutes the environment, especially with such large amounts released during starting and stopping the vehicle. What is not realized is that the vent gases generated during the start-up and shutdown of chemical processing units (and not just coal-based chemical units) cannot be recovered. Why? For safety reasons! Chemical processing units experience unstable operation during startup and shutdown; large amounts of air often escape suddenly, requiring rapid venting on a second-by-second basis. Attempting to recover this air would have an impact on the entire system, creating significant risks of instability.
Flare gas recovery is one of the common auxiliary facilities in large-scale petrochemical projects. However, for safety reasons, only the flare gas emitted during normal operation is recovered; flare gas released during startup/shutdown or in emergency situations is not recovered.
We often see black smoke coming from the flare stack during start-up, shutdown, and accident conditions; this is due to the immediate release of emissions before the flare stack has time to handle them. If you consider shutting down the torch and using the gas holder for recovery, think about how great the impact on that recovery gas holder will be
That’s the general trend. Perhaps by appropriately limiting the speed of starting and stopping to reduce impacts, partial recovery can be achieved
In unstable start-up and shutdown conditions, the safest measure is to release quickly, rather than considering recovery.
In some special cases, taking an example I was in charge of, ammonia synthesis catalysts need to be reduced using hydrogen during the initial startup process over a period of about a week. Of the gas flow of over 10,000 cubic meters per hour, only around 10% is utilized; the rest is usually vented as fuel. I applied this approach to another production system, which manages to produce nearly 100 tons of liquid ammonia per day, generating benefits of almost 2 million yuan for the company over the course of a week