Multicyclone

SNR s fluidized-bed cogeneiation system is an early example of the commercial development of AFBC technology. Foster Wheeler designed, fabricated, and erected the coal-fired AFBC/boHer, which generates 6.6 MWe and 37 MW thermal (also denoted as MWt) of heat energy. The thermal energy is transferred via medium-pressure hot water to satisfy the heat demand of the tank farm. The unit bums 6.4 t/h of coal and uses a calcium to sulfur mole ratio of 3 to set the limestone feed rate. The spent bed material may be reiajected iato the bed as needed to maintain or build bed iaventory. The fly ash, collected ia two multicyclone mechanical collectors, may also be transferred pneumatically back to the combustor to iacrease the carbon bumup efficiency from 93%, without fly ash reiajection, to 98%. 

Air pollution control systems using wet scrubbers will remove some water-soluble gases, but the removal of particulate matter is the primary concern for a control system. The air pollution control system, therefore, is usually a single device such as a wet scrubber, small-diameter multiple cyclones, fabric filters, or ESPs. The multicyclones are the least expensive system and the ESPs the most expensive. 

To obtain a high efficiency, the vessel diameter must be small, but in order to accommodate a required volumetric rate, many units in parallel may be needed. These units, called multicyclones, may be incorporated in a single shell at a cost that may be justifiable in view of greater efficiency and lower pressure drop. 

Tests were also performed on a Minnesota boiler equipped with a multicyclone and scrubber that normally burned a combination of coal, tree bark, and sludge (58). The measurements made by Pace Laboratories showed that with 15 percent tdf the particulate level rose to 0.09 pound per million Btu, compared to 0.05 pound per million Btu without tdf. The levels of S02 and NOx showed smaller increases, and polynuclear aromatic hydrocarbons were below detectable levels. 

Figure 5-1 is a schematic diagram of the process flow through Smurfit Newsprint s two hog-fuel boilers. Wood sludge, waste wood chips, and bark are fed into the two boilers. TDF is added as a supplemental fuel, and is currently limited by an air permit to 1 percent of the boiler fuel. Exhaust from the combustion chamber of the boilers exits through multicyclone systems and scrubbers, which collect ash from the exhaust streams.15... 

Field tests were conducted on a slip-stream connected downstream of the multicyclone, on a 5MW-bark fired boiler. The instrumentation of the set-up was as indicated in Fig. 2. Connections for isokinetic dust sampling (gravimetrical determination) were mounted on the upstream and downstream side of the filter unit. The following signals were connected to the data acquisition unit for continuous sampling of Pressure difference, between filter inlet and outlet (PTl) volume flow... 

Cyclones (Figure 4-3). These are robust and not susceptible to fouling or wax. Multicyclones are compact and are reasonably efficient for foam, but not for slugs. The efficiency of a cyclone decreases with increasing diameter, and cyclones are not applicable above 5 ft. diameter. They possess a good efficiency for smaller flow rates. However, cyclones are expensive to operate, especially under vacuum conditions, because they have a higher pressure drop than either a knockout drum or a demister separator. 

The Efficiency Coefficient of a Separator with Multicyclone Orifices... 

Let us now examine the dependence of the CE of a vertical separator equipped with centrifugal branch pipes (multicyclones) on various parameters. The dependence on thermobaric conditions (pressure and temperatures), geometrical parameters (diameter of supply pipeline, length of branch pipes), and also on the gas flow rate presents the greatest interest to us. 

If a fabric filter is used, several precautions need to be taken in order to protect the filter medium as discussed in Section 4.5.1.3. These include using a high temperature cyclone or multicyclone... 

In a spray drying process a simple cyclone system or a multicyclone system may be used. The choice between them depends upon the following factors ... 

Emission control systems for cement dryers must be designed for higher temperatures. Typical systems include multicyclones or other types of mechanical collectors, ESPs, or a combination of both. Where fabric filters are applied to drying operation, they must be fiber type suitable for tan-perature above 120°C (for more information on the selection of fabric filters see Table 53.8). 

For the design of the new electrocyclone cell, it was decided, in a first attempt, to adapt an existing cell of industrial multicyclone so that the increase of cost is minimized. Thus the new electrocyclone (cell n° 2) has an axial entry, and its nominal flow is about 750 m3/h. 

If this is confirmed by experience, it will be possible to reach low emission levels (100 mg/Nm3 or even 50 mg/Nm3) in one step (electromulticyclone) or two steps (multicyclone+electromulticyclone) depending on the initial dust loading and particle granulometry. 

We can give an idea of the scale where this becomes a consideration. In a cyclone with a tangential inlet of circular cross section working with ambient air at an inlet velocity of 15 m/s, = 2 x 10 would correspond to an inlet diameter of 2 cm. The reduced efficiency is therefore only a feature in small sampling cyclones or in very small multicyclone banks. Cyclones in small industrial units comprising multicyclone installations are seldom less than 15 cm in diameter. 

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