Why is fly ash added in the coal-to-hydrogen grinding process of SHELL?

It’s not to add fly ash, but because the ash contains some carbon, which increases the conversion rate of carbon.

Fly ash contains carbon, which is recovered through the coal grinding system.

If the ash content in the raw coal used is too low (e.g., ≤8%), its ash content should be increased through fly ash recycling to facilitate slag formation. There is a paradox: if the quality of the coal is truly so good, then choosing Shell gasification may not be appropriate. Fly ash circulation reduces its efficiency. It is generally believed that if Shell gasification is chosen, it is appropriate to use low-quality coal. If considering the use of the fluxing components present, an example can be given as follows: if it is necessary to lower the melting point, a certain component in coal ash should have a low value; however, recycling fly ash still cannot improve its physical properties, and additional components still need to be added. Therefore, most of the currently operating SCGP plants do not have fly ash recycling systems, including Nuon-SCGP. The ash content in the coal they use is generally around 20%; there are also so-called \"double-high\" coals with an ash content of over 30% (high ash content and high ash fusion point). If such high-quality coal is available in certain areas of Inner Mongolia for SCGP to use, it can only be considered a reckless waste of a valuable resource

SHELL has a design requirement stipulating that the ash content in coal should be less than 8%; fly ash recycling is recommended in such cases. If the ash content is below 6%, fly ash recycling is mandatory. The purpose of this is to prevent slag from accumulating on the unwater-cooled walls inside the gasifier, thus avoiding damage to those walls and the refractory layer on them and extending their service life. Generally, the carbon content in fly ash is above 5%, and in some cases it can even reach 20% (depending on the reactions taking place inside the furnace). Fly ash recycling can improve the carbon conversion rate; however, in practice, it is rare to see such recycling in operation. When the ash content is high, there is no need for recycling, while when the ash content is low, it is still necessary to consider whether the fly ash recycling process works smoothly. To avoid affecting the operation of the equipment, fly ash is generally not recycled.

Agree with the opinion on floor 4; since the coal quality is good at present, other gasification technologies can be chosen.

The carbon content in LS fly ash ranging from 5% to 20% may be incorrect. Under normal circumstances, the carbon content in fly ash is less than 1%, with a maximum value of 5%. When the carbon content in fly ash exceeds 1%, the solid content in the slag water will be above 5%, making it difficult to operate the slag removal and slurry treatment systems. If the carbon content in fly ash is high, the furnace temperature might be too low, or the ash melting point of the coal might be low (such coal could be replaced with Texaco)

Has LS used the data on the filter cake on a received basis? The carbon content on a basis of the filter cake is roughly the same, while the carbon content on a dried basis is even higher.

Moderator, does the “under normal circumstances” you mentioned in that post refer to shell technology, or does it apply to all types of gasification technologies? Thank you.

Of course, it’s shell technology!

What was said on the fourth floor is correct. The mention of fly ash recycling here probably refers to those two Shell gasification units owned by Shenhua. The Upper Bay coal used has excellent quality, with an ash content of less than 5%; fly ash recycling is necessary to meet the requirements related to slag formation.

Increasing the carbon conversion rate: as fly ash is added in a cyclic manner, the carbon conversion rate increases. In addition to fly ash, the filter cake from unit 1700 is also added before the coal grinder.

The coal used in the Datang Dalun project is lignite, with a moisture content of over 30%; its internal moisture level is also high, resulting in poor slurry-forming properties. As a result, coal slurry gasification could not be utilized. GSP technology for dry powder gasification was not yet mature at that time, so the Shell gasification method was the only option available. The enormous investment required for the SCGP process in the Dalun project left Datang in awe. For coal-to-natural gas projects, the Lurgi fixed-bed gasification method had to be chosen instead.

The person on the fourth floor is right; what I’m referring to are the two units in Shenhua Ordos’s gasification plant. They use Shangwan No. 3 coal, which is a high-quality coal with a carbon content of no more than 5%, which is why the Shell process involves the addition of fly ash. What was said on the fourth floor was a bit too technical and hard to understand. The references to the fifth and seventh floors are easy to understand at first hearing. My skills are not very good, and I have only been working with this process for a short time; thank you all for your guidance.

Another purpose of adding fly ash to the coal grinding section is likely to prevent spontaneous combustion from occurring during the coal grinding process.

I can assure you with certainty that the gasification process at Shenhua Ordos does not involve the use of fly ash recycling

Bro, you’re not gassed, are you? How dare you say no? Go and take a close look at the scene; it’s definitely there

It’s present on site, but has never been put into use.