Circulating fluidized bed boilers burn anthracite coal

I don’t know whether the boiler used by the original poster is a fluidized bed boiler with a medium-temperature cycle or a high-temperature cycle I’d like to share my views on medium-temperature separation: First of all, I suggest that the original poster check whether the quality of the coal has deteriorated. If the quality of the coal deteriorates and its calorific value decreases compared to the original or designed value, then the oxygen content in the boiler exhaust gases will increase. In such a case, it is necessary to increase the coal supply in order to raise the bed temperature. Secondly, it is recommended that the poster check whether the particle size of the coal fed into the furnace is too small. If the ash content of the fuel coal is higher than designed, or if the particle size distribution of the coal fed into the furnace is more concentrated on smaller particles than intended, then the finer coal particles will stay in the dense phase region for a shorter time. This leads to a decrease in the proportion of combustion that takes place in the dense phase region, as well as a drop in the bed temperature. In such cases, it is necessary to reduce the amount of primary air and increase the amount of secondary air. Once again, if the oxygen level in the flue gas remains constant, the bed temperature decreases slowly, and the temperature of the entire combustion system drops as well, while the boiler load stays unchanged. This could be due to an increased amount of ash returning to the furnace, which causes the furnace temperature to drop; therefore, some of this ash should be discharged from beneath the cyclone separator in order to raise the furnace temperature again.

Friend, there’s only one reason: the amount of ash returning is too high. Ash circulation in a circulating fluidized bed is very important; just control the amount of ash that is returned.

I personally think the particle size of the coal you feed into the furnace is too small.

5000-calorie coal should burn quite well. Yet the bed temperature of the owner’s furnace is maintained by adding ash, probably because the coal particles used are too fine. What is the pressure at the upper part of the furnace in the boiler used by the poster? Our 220T boiler also experienced high pressure at the upper part of the furnace due to the use of coal particles that were too fine; the bed temperature was maintained by relying on the ash from the return feeder. It will be fine after modifying the crusher later.

Is the temperature at the upper part of your boiler high? If it is, it indicates that too much combustion occurs in the dilute-phase zone and too little in the dense-phase zone. The main reason for this is an excessive amount of return material; the cause of this excessive return material is that the coal is too fine (obviously, the ash content of your coal is not high), as well as an excessive amount of primary air. Additionally, the calorific value of your coal is too high. It is only economical to use coal with a calorific value of 5,000 kcal per kilogram in pulverized coal boilers, while circulating fluidized bed boilers can demonstrate their advantages when using coal with a calorific value of 3,000–4,000 kcal per kilogram. Therefore, the solution is to increase the particle size of the coal. As mentioned on the second floor, it is also necessary to adjust the air flow by reducing the amount of primary air and increasing the amount of secondary air. If this does not yield results, then mixing coal is the only option – that is, burning some coal gangue along with the regular coal. Discharging the return ash alone would result in excessive heat loss, which is not feasible.

When burning difficult-to-burn anthracite, it is necessary to appropriately increase the bed temperature, raise the amount of primary air, increase the proportion of combustion in the dense-phase zone, and thus raise the bed temperature.

What was said on the sixth floor is correct – the coal we used this time had a calorific value of just over 5,000 kcal; during combustion, the slag layer couldn’t be stabilized. Only by adding some slag from previous burns to the coal was it possible to maintain stability. In fact, the circulating fluidized bed boiler was invented precisely for burning low-quality coal; using high-quality coal would be a waste.

Have you noticed the differential pressure across the material layer? If the differential pressure across the material layer becomes lower, it means there is less return ash; conversely, if the differential pressure increases, it indicates more return ash. The best approach is to change the type of coal and switch to using lower-quality coal.

It’s likely that the design efficiency of the separator system is too high, resulting in excessive ash accumulation, which leads to: 1. Issues with the separator design. Construction causes 2, coal particle size causes it

Hello, our boiler uses high-temperature separation