Fly ash treatment in fluidized bed gasifiers
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Regarding the fly ash treatment method for the atmospheric-pressure circulating fluidized bed gasifier used by Al Electrochemical Company, since the carbon content in the fly ash is as high as 60%, is it feasible to send this fly ash to boilers used for power generation for combustion?
Of course it’s possible, as long as you find a way to collect the fly ash and transport it to the boiler. In circulating fluidized bed gasification, the fly ash carried away by the gas exiting the fluidized bed gasifier is separated using a cyclone separator. The separated fly ash is then sent back into the gasifier via gas transport for combustion, thus creating a cycle. This is why this type of furnace is called a circulating fluidized bed gasification furnace. If this portion of fly ash is not recycled but instead sent to the boiler. As a result, both the gas production volume of the gasifier and the composition of the gas undergo significant changes, with a decrease in gas production volume occurring as well.
What I mean is the utilization of fly ash after the two-stage separator. Since fly ash is very fine, has a high carbon content, poor combustibility, and is difficult to handle, I’m not sure whether it can be sent directly to another coal-fired boiler used for power generation in the company for burning
If delivered directly, the cost is likely to be higher; transporting fly ash probably requires gas transportation. It’s more convenient to simply deliver it to the raw coal yard and burn it together with thermal coal
One of the problems with circulating fluidized bed boilers is the high residual carbon content in the fly ash. Moreover, the particles of gasification fly ash are small, and their carbon structure is altered, resulting in low activity; therefore, the combustion efficiency in such boilers is likely to be poor. I wonder if what I’m saying makes sense?
It makes sense, but dealing with this fly ash poses a major challenge for the company; it also causes significant pollution. The company uses conventional coal-fired boilers for power generation, and the temperature in these boilers is much higher than that in fluidized bed boilers, resulting in a much faster combustion rate. It’s unclear whether it’s possible to completely burn up the carbon contained in the fly ash~
If the temperature is not high, a bag filter can be used for dust collection
Once the cyclone is created, its efficiency is fixed; in other words, the efficiency of the cyclone cannot be adjusted. If the dust is not captured by the first-stage cyclone, it will inevitably escape even if multiple stages of cyclones are used afterward. Therefore, the key issue here is not where to send the dust, but rather how to remove it
Isn’t there a dust collector behind the separator? The economics of pneumatic conveying and reburning of fly ash are considered. . .
According to traditional understanding, of course a boiler is used for combustion (that’s what is generally said and done when using fluidized beds)! But as everyone has said above, it becomes more and more complicated, the costs keep rising, and expenses exceed income. In fact, by using carbon molecular gasification technology to transform the fuel gas in the aluminum industry, the carbon content can be reduced by over 90% (to below 5%), the amount of fly ash can be lowered to below 200 mg/m3, and the gasification system can save more than 60% in energy consumption.
Which company’s circulating fluidized bed gasification technology are you using? The conventional method for handling fly ash involves mixing it with pulverized coal and using it as fuel in circulating fluidized bed boilers. However, given the low volatility, high ignition point, and difficulty in complete combustion of fly ash, our organization has developed two new combustion technologies that can achieve a combustion efficiency of over 95%.