Air blowers

Do not allow rain/wash water to enter the blower. 

Switch off motor and remove fuses when carrying out maintenance. 

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The basic fluid-bed unit consists of a refractory-lined vessel, a perforated plate that supports a bed of granular material and distributes air, a section above the fluid bed referred to as freeboard, an air blower to move air through the unit, a cyclone to remove all but the smallest particulates and return them to the fluid bed, an air preheater for thermal economy, an auxiUary heater for start-up, and a system to move and distribute the feed in the bed. Air is distributed across the cross section of the bed by a distributor to fluidize the granular soflds. Over a proper range of airflow velocities, usually 0.8-3.0 m/s, the sohds become suspended in the air and move freely through the bed. 

P r ho. The Paraho retorting technology is similar to the PETROSIX technology except that it can be operated in the direct heat (DH) mode. The unique feature of the Paraho technology is the two levels of heat input (Fig. 4). In the IH mode, the air blower shown in Figure 4 is replaced by a recycle gas heater. The Paraho DH operation has been carried out neat Rifle, Colorado since the 1970s operations to produce asphalt (qv) from shale oil are continuing. 

The overall benefits of this high efficiency combustor over a conventional bubbling- or turbulent-bed regenerator are enhanced and controlled carbon-bum kinetics (carbon on regenerated catalyst at less than 0.05 wt %) ease of start-up and routiae operabiUty uniform radial carbon and temperature profiles limited afterbum ia the upper regenerator section and uniform cyclone temperatures and reduced catalyst iaventory and air-blower horsepower. By 1990, this design was well estabUshed. More than 30 units are ia commercial operation. 

The expansion turbine converts the dynamic energy of the flue gas into mechanical energy. The recoverable energy is determined by the pressure drop through the expander, the expander inlet temperature, and the mass flow of gas (66). This power is then typically used to drive the regenerator air blower. 

A power recovery train—occasionally called a string—(Figure 4-53) employing a turboexpander usually consists of four main elements or casings the expander, a motor-generator, an air blower, and a steam turbine. The steam turbine is used primarily for startup and often to supplement the expander for generation of energy. This topic will be discussed in more detail later in this chapter. 

The motor-generator ean either produee or absorb power. In some FCC units, the expander horsepower exeeeds the power needed to drive the air blower. In this ease, the exeess power is transmitted to the refinery power grid. If the expander generates less power than required by the blower, the motor-generator provides the power to hold the entire train at the desired speed. 

A seeond type of design allows the regenerator to operate at a pressure high enough so that the expander has a horsepower reeovery potential exeeeding the requirements of the air blower. Most new FCC units are likely designed for higher pressure. 

It is most likely that in designing a new FCC unit the expander will drive the air blower and produee enough horsepower in the end-of-bladelife eondition to supply the horsepower required by the air blower at the expander s end-of-run effieieney. There would also be an allowanee for deviations from expeeted expander performanee and air blower performanee. Thus, the expander ean be expeeted to have available, at start of run, a eonsiderable amount of exeess horsepower. This exeess horsepower must be used in some eeonomie manner without jeopardizing the eontinued safe operation of the FCC unit over its normal on-stream run time. 

An inerease in ambient air temperature will deerease the available energy for the generator. This assumes that the fresh feed and eoke burn remains eonstant. The expander horsepower does not ehange, but the air blower horsepower inereases with inereased air temperature, eausing the exeess energy to deerease. Steam and water may need to be added to the flue gas flow at various points in the system to eontrol afterburning. In Figure 4-64, the solid eurves are for a normal flow of steam. The dotted eurves are for inereases in the steam rate by 3.05 times, 4.85 times, and 6.05 times the normal flowrate. 

Step 1. Selection of normal operating conditions for the regenerator system. This sets normal air blower flow and head, and expander flow and head. If the proposed installation is being designed for an existing FCC unit, only a... 

Step 2. System calculations over the entire range of possible operating conditions are required. The range must cover from the air blower minimum flow point to the expander bypass point for all reasonable variations in the applicable parameters of COj/CO ratio, fresh feed rate, flue gas temperature, ambient air temperature, and so forth. 

Step 3. The final selection of a specific air blower and turboexpander must be made after fully considerating the results of Steps 1 and 2. The normal operating point must be located on the system operating map (similar to Figure 4-66) so that reasonable latitude is available in operating variables between normal operating point and air blower minimum flow, and between operating point and expander bypass point. 

The second step in developing the process air train is selecting the air blower main driver. This step includes many alternatives such as power recovery expanders, steam turbines, and electric motors. The following example illustrates these alternatives. 

Direct Material Costs — Major Equipment Motor — Induction Type Steam Turbine Driven Air Blower Motor Driven Air Blower One Stage Expander Driven Air Blower Two Stage Expander Driven Air Blower... 

POWER RECOVERY EXPANDERS FOR FCC UNITS IN MAIN AIR BLOWER OR GENERATOR DRIVE SERVICE ... 

For Main Air Blower serviee without a steam turbine in the string, the unit shall be started by first applying windage steam and then aeeelerating the train to rated speed using the eleetrie motor. After aehieving stable rated speed, the expander inlet valve will be... 

For Main Air Blower Serviee, rated speed (in revolutions per minute) is the speed at whieh the expander operates without... 

The expander train supplier shall assist with the selection of the expander inlet and bypass valve configurations and closure rates by performing an open loop dynamic simulation study. For a main air blower train dais could be closed loop. 

Full Main Air Blower Train Valve Arrangements... 

Several main air blower train valve arrangements are possible. 

The foregoing comparison of different valve arrangements for both full main air blower trains and TPG trains emphasizes its importance. The range of desired regenerator control, expected modes of operation, and system constraints all influence the choice of valve aiTangements. The selected arrangement depends on safety consciousness, cost considerations, and desired process flexibility. 

Items Expander Air blower Steam turbine Motor/ generator... 

The pressure in the regenerator depends on several factors. As the actual inlet pressure is adjusted to 0.22-0.24 MPa, the expander matches the system, but power loss is considerable. The power consumption on the air blower may be reduced at the same time as the pressure in the regenerator is lowered. However, the overall efficiency of the power recovery system is not significantly affected. 

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