SHELL dense-phase conveying
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The SHELL gasification process uses dense-phase transport to deliver coal powder from the coal powder feed bin to the gasifier. In processes for synthesizing methanol, CO2 is used as the carrier gas, while in other cases N2 is employed as the carrier gas. However, among those manufacturers that use nitrogen as a carrier gas, how many of them can achieve a dense-phase transport density of 400 kg/m3 as specified by SHELL? For those manufacturers that maintain a lower density level, what are the main considerations? Is it to ensure the stability of gasification transport, or is it related to the stability of the N2 gas supply? If the amount of N2 used for transporting coal powder per unit is reduced, it is clear that the N2 content in the syngas can be decreased.
Is density related to the load downstream?
Load is directly related to flow rate, but not directly related to density
Slurry transport is a relatively difficult process, as it tends to result in unstable fluids such as small clumps of pulverized coal; the key factors are the stability of the quality of the pulverized coal and the pressure applied.
It is clear at present that the nitrogen content in the syngas exported by shell is on the high side, but this is not necessarily due to a low transport density; it is also related to the amount of nitrogen used for purging. I wonder if anyone can provide approximate figures such as the flow rate and density of transportation, as well as the amount of purging, so that an approximate assessment can be made.
From my observations, the density is usually between 120 and 200, depending on the pressure; a higher transfer pressure results in a higher overall density for the coal dust and nitrogen mixture. In my opinion, this approach takes into account the stability of coal powder transportation. Dense-phase transportation involves fluid dynamics issues related to solid and gas mixtures; at a certain pressure, the more gas present, the better the fluidity, but the lower the efficiency ； As the solid content increases, fluidity decreases, and there is a balance point at which this occurs. The transport stability of pulverized coal, that is, the stability of the coal cycle, has a significant impact on the Shell gasification process. This post was last edited by China must strengthen itself on 2009-2-18 09:30]
In fact, the principle behind dense-phase pneumatic conveying is simple: it relies on gas as a carrier to transport powdered materials. The concentration of these materials (that is, the ratio of materials to gas) is crucial for the efficiency of transportation. I believe the main reasons why some manufacturers are unable to meet the requirements of Shell furnaces are as follows: 1. A high concentration of materials can lead to sedimentation in the upward sections and at corners of the conveying pipes, resulting in blockages or poor flow. 2. If the pressure on the carrier is increased in order to ensure smooth and efficient transportation, it can easily lead to rapid wear of the transportation pipes (or channels).
The density I have seen can be above 300 kg/m3, and it generally remains between 200 kg/m3 and 300 kg/m3.
Can it be understood that the dense-phase transport density of 400 kg/m3 specified by SHELL is merely a reference value; in actual operation, adjustments need to be made taking into account the type of coal used, the operating pressure, and pipeline wear. Originally, by increasing the density of the slurry transport and reducing the amount of nitrogen used per unit volume of coal powder transported, it was possible to partially reduce the N2 content in the syngas (although there are various factors that affect the nitrogen content). According to the syngas composition specified by SHELL, the N2 level can reach 6–8%, or even lower; however, I believe that few of the SHELL gasifiers in use in China manage to achieve this target value. This presents a challenge for manufacturers working in the syngas production sector – on one hand, they need to consider using CO2 as the carrier gas, and on the other hand, they need to find ways to reduce the amount of N2 entering the system.