How to address ash accumulation in shell gasification furnaces

By the way, it’s not just a matter of coal quality – who would want to use poor-quality coal when good coal is available? To solve the coal-related problems, an investment of around 100 to 200 million would be necessary. I mainly want to know if it’s possible to optimize operations and control parameters in order to avoid ash accumulation. Thank you.

Use ultrasound for dust removal. The common methods used for waste heat boilers are effective as long as they are installed in the right location, and their cost is not high. Driven by the energy of compressed air or steam, it activates the speaker to generate high-power ultrasonic waves. By controlling variable audio signals and sound pressure, it creates standing wave and reverberation effects, which cause vibration in the ash and slag with different mineral structures within the boiler. This vibration leads to oscillations of the dust particles; the particles in a suspended or fluidized state are carried away by gravity and the flue gases, preventing them from adhering to the surface of the heat exchanger. Thus, this approach solves the problem of preventing and removing ash accumulation in industrial boilers.

The problem of ash accumulation in the superheated steam section E1306 of the syngas cooler has been encountered by several operating plants, so this is not an isolated case; moreover, the quality of coal used by these plants varies as well. It is unclear what solution SHELL will propose. From what I’ve encountered, the dust accumulation problem can be alleviated from several aspects: 1. Increase the flow rate of the quenching air, as much as is possible without affecting the lifespan of the fly ash filter ； 2. Increase the amount of high-pressure nitrogen used for purging here ； 3. Regularly inspect the operation of the fly ash striker, and increase the striking frequency and amplitude as appropriate ； 4. Ensure that the temperature of the syngas coming out of the gasifier is below a certain value; this can be implemented simultaneously with point 1 ； 5. The last point is the issue of coal quality; by selecting appropriate coal blends, it is better to have lower viscosity of the fly ash produced under the same conditions ； The points mentioned above may only help alleviate the issue of dust accumulation, but they may not solve the problem fundamentally. Please share your own approaches, fellow users with more experience in operation. This post was last edited by jensse on 2009-3-31 13:34]

There are still quite a few dead zones for ultrasonic waves.

Yuntianan? As mentioned on the 4th floor, dust accumulation in the waste pot system of shell gasifiers is not an isolated case; it is very important to study the mechanisms behind this dust accumulation. All types of fly ash possess adhesive properties; they have a certain sticking force when in contact with other objects. The surface of small particles has a certain surface energy, and there is resistance between fly ash particles, with this phenomenon becoming more pronounced as the particle size of the fly ash becomes smaller. Studies have shown that the fly ash from waste boiler systems has an amorphous structure and is spherical in shape; numerous small particles adhere to the surface of larger particles, and trace analysis indicates that these small particles contain high levels of Ca ions. The mechanism is complex, and research on it is not yet thorough enough; no further explanation will be given. In addition to those mentioned on the 4th floor, other methods that can be employed in actual production to mitigate or improve the situation include: 1. Reducing the amount of CaO added, provided that this does not compromise the safe operation of the gasification furnace ； 2. Appropriately increase the particle size of pulverized coal, shifting it toward the upper limit within the original control range ； 3. Maintain a high vaporization load as much as possible ； 4. Slightly increase the quenching air volume ； 5. Keep the temperature at 19 points before the superheater from being too high ； 6. Adjust the frequency and duration of striking in accordance with the situation, appropriately increase the driving power of the striker in the waste pot system, and perform manual striking on-site if necessary ； ... but for raw coal that has a tendency to accumulate ash, these measures only provide temporary relief; some of them may even increase the erosion in the reverse chamber. The fundamental solution lies in improving the viscosity-temperature properties of the coal, such as by using blended coal or new, more efficient fluxes instead of limestone. Ignoring the coal itself, it is difficult to completely resolve the issue of ash accumulation, as raw coal is the key factor in the operation of gasifiers. Companies and relevant research institutions are already working to address such issues, in the hope of providing assistance to operating enterprises.

:It seems that coal quality remains the most fundamental issue. Previously, we maintained a high gasification load, with an oxygen content of around 93%. There were no problems with the percussion devices, and their frequency was also high. When a high pressure difference occurred, the load was reduced. The amount of nitrogen used for backblowing didn’t increase, but the temperature was raised slightly. In my opinion, adding limestone mainly affects the slag; it seems to have little impact on the ash. Also, does the amount of quenching air have a significant effect on whether ash accumulates?

It is theorized that calcium oxide, in combination with aluminum oxide and silicon oxide present in coal ash, can form a eutectic system within a certain range of proportions when in a molten state; this system has the effect of reducing the melting point of the slag. However, calcium oxide does not change the shape of the viscosity-temperature curve of the slag, but rather shifts it in the direction of lower melting points – in other words, the operating temperature range remains unchanged. For the amorphous fly ash formed through high-temperature recooling, the calcium oxide present increases the adhesion or bonding strength between the fly ash particles as well as between the fly ash and the waste boiler, as confirmed by energy spectra during the research. There’s no need to discuss these dull details; a trial can be carried out during operation: Please keep track of the components of your raw coal that tend to accumulate ash more easily, as well as the flow temperature and the ratio of limestone added to the coal. Then, purchase an appropriate amount of raw coal whose ash fusion point is no higher than 1300 degrees (note: the calcium oxide content in this raw coal should not exceed 4.5%). Operate this coal separately for a while, after which mix it with your current raw coal in an appropriate ratio so that the ash fusion point is around 1350 degrees (without adding limestone), and use this mixed coal in the furnace for a period of time to compare their behavior regarding ash accumulation. You may find that the ash viscosity-temperature curve becomes flatter, the operating range of the gasifier widens, and the degree of ash accumulation is significantly reduced... As for whether the amount of quenching air has an impact on ash accumulation, it can be said that maintaining a certain airflow velocity in the waste heat recovery system helps to blow away the ash particles adhering to the pipe walls to some extent. Meanwhile, due to the high flow rate near the quenching ports, the ash particles that are carried upward may be larger, but the effect is limited and comes with its own costs. Generally, once the plant is running stably in the initial phase, the gas flow rate is kept at around the full-load level for oxygen loads below 80%, with little change made. Last edited by The purple bamboo is serene on 2009-3-31 15:36.]

The guys upstairs have spoken very well; all of that is valuable wealth. As long as it can be shared, the wide-scale adoption of shell is indeed an advantage

Everyone, I agree with the above approach as well, but it’s important to note that increasing the volume of the quenching air (with some excess capacity in the compressor) will create a negative pressure area in this region. The nitrogen present in the annular space will then flow rapidly into the furnace through the balance holes. If the sealing around the burners is not proper, it’s easy for furnace gas to enter the annular space from there, resulting in high temperatures that can damage the flexible connections. This is just my personal opinion

How is ash formed? At high temperatures, the molten droplets solidify to form fly ash. . . The higher the temperature, the greater the viscosity. . . Is it possible to add a substance that reduces its viscosity even at high temperatures? ? ? ? The viscosity of a substance is fixed and determined by its dynamic viscosity coefficient. So, could we consider adding some kind of additive during coal grinding in order to reduce the intermolecular forces between the fly ash particles in their molten state, thereby lowering its viscosity? ? Experts at Shell who are skilled in conducting research, please consider this issue. Thank you for your efforts; if you manage to solve it, we’ll treat you to a meal! ! :handshake

The possible reason for the high outlet temperature of the SGC due to ash accumulation on its surface is related to the quality of the coal, and this was discussed at length in the meeting. As for the high differential pressure in 13PDT0067 and 13PDT0077, the coal quality is likely not the main cause; dust accumulation here is what leads to the high differential pressure, with the dust mostly present in lump form above the lower coil of the cross-shaped structure. It is clearly related to water. In some units, this issue becomes more apparent after a short period of shutdown followed by restart, providing clear indications of the problem

The impact of quenching steam volume on ash accumulation is definite! If the quenching is insufficient, the temperature of the syngas and the fly ash entrained in it will be high! Fly ash tends to stick more easily to the gas transfer pipelines in the gasifier! It causes dust accumulation!

The best solution is to eliminate those useless things.