How to increase the circulating ash amount in a circulating fluidized bed boiler when it is very low

Based on my experience, the reasons for a low circulation rate are as follows: 1. The efficiency of the separator is too low, which is the main reason； 2. Low coal feeding rate ； 3. The drum and induced air flow are too low.

Come and learn a bit~~~ We have this here as well, but we haven’t dealt with it yet; let’s first get some basics down here~~~ Hehe~

What was said on the 2nd floor is correct; it’s also possible that there isn’t enough coal ash, or that balance hasn’t been established in the material circuit (is there a fault with the return conveyor?) Is the return air flow too high? ）

1. The separator has poor separation efficiency. 2. The coal has a low ash content. 3. The fuel is too coarse. It should contain a certain amount of fine coal. 4. The boiler load is too low.

1. The particle size distribution in the fuel is unreasonable, with too many small particles (contrary to what was said above). It is recommended to verify the designed coal type, add particle size screening criteria, and strengthen the management of raw coal. 2. The quality of the raw coal is higher than that of the designed coal type, and it burns out in the furnace (this possibility is very high if there isn’t much fine coal dust in the flue gas purification system as well). It mainly refers to ash (lower than designed) and volatile matter (higher than designed). It is recommended to compare the purchase prices of raw materials; if this can improve cost efficiency, the requirements regarding raw coal can be appropriately reduced. If the current economic efficiency is high and the temperature at the tail of the flue is normal, a small amount of large-grained slag can be added to the feed to prevent the material layer from becoming too thin and difficult to handle. 3. The separation efficiency of the separator is insufficient, and the recycling ratio is inadequate. Design problems are rather difficult to solve. It is recommended to find a specialized book, calculate your current separation efficiency, and then make a decision. 4. Failure of the return feeder, resulting in blockage (usually low-temperature coking forms inside the ash return pipe). Suggestion: Check whether there are any errors in the installation angle of the ash return pipe, and whether the inlet for the return air is properly installed. (Refer to relevant articles in the Proceedings on Circulating Fluidized Bed (CFB) Units.)

Look at the ash-to-slag ratio; too little ash indicates that there is no circulation, it’s still a boiling furnace

With a constant cycle ratio and a constant load, the amount of ash in each cycle is related to many parameters such as the boiler’s negative pressure, the output of the return air fan, the pressure in the air chamber, the particles and thickness of the material layer, and the air intake volume of the boiler. 1. To simply and quickly increase the circulating ash in the boiler, one can only change the type of coal or add more ash (limestone works as well); this is the direct and most effective method. 2. Attempting to increase the amount of circulating ash through adjustments takes time and does not necessarily yield the best results; this mainly depends on the type of coal used in the furnace. If the ash content in the coal is not sufficient or is even very low, no amount of adjustment can ensure that the boiler has a large amount of circulating ash. The simple adjustments are as follows: 1) Increase the positive pressure in the boiler, but not too much; a slight positive pressure is sufficient to help the separator separate more fine ash. 2) As long as the bed temperature permits, slightly reduce the amount of primary air to decrease the resistance to the flow of fine ash back into the furnace. 3) Increase the bed pressure so that the bed material can absorb the bed temperature, thereby making the temperature in the furnace more stable. 4) Ensure even slag discharge by the slag extractor, and maintain a high bed pressure during operation. 5) Try to increase the coal supply as long as the bed temperature does not rise excessively; coal is the main source of circulating ash. 6) Add limestone to lower the bed temperature, which in turn can indirectly increase the amount of circulating ash. 7) As the fine ash rises, the bed temperature in the boiler will drop; in such cases, we can gradually increase the coal supply. This adjustment method is effective only with sulfur-type returners, and I have applied it multiple times with this type of returner – it works without any problems. Generally, it takes more than 6 hours for ash to accumulate; of course, this depends mainly on the ash content of the coal type. Keep in mind that the amount of ash accumulated is closely related to the boiler’s return conveyor, following a parabolic pattern. When the amount of circulating ash reaches a certain limit, adding more coal will theoretically lead to an increase in ash production. However, due to the properties of the return conveyor and the cyclone, the amount of circulating ash no longer increases. Once this point is reached, the added coal will not increase the amount of circulating ash but rather raise the bed temperature. Additionally, other dust accumulation methods need to be figured out on your own depending on the return feeder. I need to make adjustments to the furnace based on different situations in order to find the best solution; there’s no need to always strive for the highest level – sometimes it’s sufficient to stop at an appropriate point. It’s difficult for everyone to pinpoint the highest point of a parabola, and I’m no exception; but we can get close to that point, and that is the greatest success of adjustment.