Boilers dust removed

Boiler exit gas is passed through electrostatic precipitators for further dust removal, Figs. 4.3 and 4.4. 

St. Joe Minerals Corporation uses a fluid-bed roaster to finish the roasting at 950°C of material that has been deleaded in a modified multiple-hearth furnace operated with insufficient oxidation (34). First, sulfur is reduced from 31 to 22% and lead from 0.5 to 0.013%. Somewhat aggregated, the product is hammer-milled before final roasting. Half of the calcined product is bed overflow and special hot cyclones before the boiler remove the other half total sulfur is ca 1.5%. Boiler and precipitator dusts are higher in sulfur, lead, etc, and are separated. 

A device used to remove fly-ash from boiler exit-gases in order to reduce the atmospheric pollution load. It places an electric charge on the dust particle and removes the particle onto a collecting plate. 

The majority of these units have a Third Stage Separator (TSS) or electrostatic precipitator (ESP) located before the SCR catalyst bed to protect against upsets in the FCC regenerator. The catalyst can easily be designed to handle the normal dust loading (60 mg-700 mg/Nm ), which is much lower than the typical coal fired boiler (5 g-9 g/Nm ). To handle a FCC upset (>15 g/Nm ) without a PM removal device, the catalyst volume would need to increase. 

Because most of the ash is removed as molten slag, addition of a bottom grate is not necessary.7 However, small TDF is required, because much of the combustion must occur in suspension.7 TDF that is too large to combust completely can get carried over into the boiler or dust collection system, and cause blockage problems.9 Therefore, particle size may inversely determine the amount of TDF that can be used in a cyclone boiler.11 Three cyclone-fired boilers at utilities have burned 1M x 1" TDF in test operation, one at the 2 percent, one at the 5 percent, and one at up to a 10 percent level.3,9,12 One pulp and paper mill plans the use of TDF in a cyclone-fired hog-fuel boiler.13... 

About 70% of the dust-in-offgas is removed in the waste heat boiler and about 30% in electrostatic precipitators. The small remainder ( 1%) is removed by water scrubbing, next section. 

Figure 1 shows the three possible locations of the SCR unit inunediately after the boiler (high-dust arrangement, HD), after the particulate removal (low-dust arrangement, LD), and after the sulfur dioxide removal (tail-end arrangement, TE) [20]. 

Pressurized fluidized-bed combustion (PFBC) of coal This is probably the most promising application field for inorganic filters, despite the fact that only a few large-scale examples of application have been successfully tested in very recent years [14]. Dust is removed just at the outlet of the boiler, allowing heat recovery from cleaned gases. 

Firing the raw gas in boilers or heat applications such as kilns after removal of dust and particulates is the simplest application since the gas is kept hot and the tar problem is avoided. However, surprising enough, there are very few known successful applications, which have been operating in a commercial environment. This market is one where all types of gasifiers can compete and more concerted efforts have to be undertaken by the gasification industry to increase the number of successful cases. 

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