How to address the issue of excessive emissions during the shutdown of sulfur recovery units?
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This post was last edited by liaifeng on 2018-9-1 at 10:42. July 1st of this year is approaching soon; have everyone prepared to meet the new environmental standards that will come into effect? Especially during periods when the plant is shut down, how can emissions be kept within acceptable limits?
The recycling system should continue to be improved; there is no need to pursue rapid replacement, but rather to do so within the limits permitted by the recycling conditions.
Nowadays, environmental regulations are becoming increasingly strict, and various organizations are considering introducing further measures to reduce sulfur dioxide emissions. The most commonly considered approach is to carry out alkaline washing of exhaust gases, but this in turn creates new environmental problems (such as the generation of waste alkaline solutions). What are your thoughts on this matter?
Submit an application for that – there’s no problem with that. Additionally, if conditions permit, the exhaust gases can also be directed to the boiler’s desulfurization and denitration systems
A reasonable plant design is very important, which is inevitable in the SCOT process; it is recommended to adopt a two-stage Claus process combined with ion liquid recovery to save energy and protect the environment
Given the suddenness of the requirements imposed by the new national standards, most providers of retrofitting technologies lack the necessary technical expertise. The time pressure has forced these providers to focus their efforts on market development, which has resulted in a lack of effective cleaning and emission control technologies for the devices that have been retrofitted. Currently, the available shutdown technical solutions are those proposed by Zhenhai and Sanwei; each of these two solutions has its own advantages and disadvantages, which are mainly reflected in aspects such as operational complexity, further technical modifications, and nitrogen consumption. These are just my personal opinions, and there are undoubtedly other factors to consider.
To put it simply, the risk of excessive levels during the shutdown of sulfur treatment units mainly arises during the sulfur purging phase, as the oxygen supply in this stage results in a much higher sulfur dioxide content in the gases from the Claus process than under normal conditions； During sulfur injection, the excess sulfur dioxide and elemental sulfur pose a strain on the hydrogenation and absorption systems, easily leading to excessive emissions. We have identified the reasons for the excess emissions during shutdown; now let’s discuss the solutions. These solutions can be categorized as follows: 1. If there are subsequent facilities such as post-combustion alkaline washing, then when sulfur is being blown out, the load on these subsequent alkaline washing facilities should be increased. A bypass system for exhaust gas purification should be used, taking advantage of the chemical reaction between acids and bases to remove the excess sulfur dioxide ； 2. Without post-alkaline washing equipment, excessive acid gas is used in conjunction with air for sulfur removal, or natural gas is utilized for this purpose; this approach allows for good control of the air-fuel ratio while preventing carbon deposition in the bed, keeping the flow rate of process gas at a low level and ensuring the plant operates normally. In short, it comes down to maintaining an appropriate air-to-sulfur ratio and using the lowest possible flow rate for sulfur injection; during the sulfur injection process, the process gas is sent to the exhaust gas purification system for recovery. In other words, time is used to achieve effective desulfurization and to ensure that the exhaust gas meets regulatory standards. 3. Other innovative methods for shutting down operations: 1) Using hot nitrogen for sulfur injection – instead of using process gas during shutdown, hot nitrogen is employed; the process gas is then sent to the exhaust gas purification system for recovery, thereby preventing temperature spikes and increased hydrogenation load (an advanced practice from Qilu Petrochemical). 2) Using an alkaline injection tower in the quench tower or an alkaline scrubber before the incinerator to address issues related to excessive emissions during shutdown. 3) The purified exhaust gas is pressurized by a fan and then circulated back to the inlet of the primary reactor heater for repeated sulfur injection
It’s really hard to understand what’s so good about pre-alkaline washing compared to post-alkaline washing
This post was last edited by Sideback on 2017-9-9 08:50. From the perspective of technological innovation alone, I believe that ionic liquids truly deserve to be promoted; in the long run, sulfur recovery should not remain stuck at the current level of the Claus + alkali process. Ionic liquids are not considered high-tech; domestic technologies should be given priority support first. However, when ionic liquids are used with sulfur, there are issues regarding ownership of the related technology – the Claus process and ionic liquids are under the control of different companies, so it is necessary to coordinate the interests of all parties involved.