Air cooler fans

Most rotating equipment includes electric motors or steam dryers that generate noise at a constant frequency. Air cooler fans are a source of noise that can be reduced by lowering the fan speed and increasing the number of blades. Pump motor noise can be reduced by including a shroud or fan cover that is accurately lined. Centrifugal compressor noise reduction can be achieved by blade design and the use of compressor pulsation noise reduction, silencers, and vibration isolation. 

Noise can cause a serious nuisance in the neighbourhood of a process plant. Care needs to be taken when selecting and specifying equipment such as compressors, air-cooler fans, induced and forced draught fans for furnaces, and other noisy plant. Excessive noise can also be generated when venting through steam and other relief valves, and from flare stacks. Such equipment should be fitted with silencers. Vendors specifications should be checked to ensure that equipment complies with statutory noise levels both for the protection of employees (see Chapter 9), as well as for noise pollution considerations. Noisy equipment should, as far as practicable, be sited well away from the site boundary. Earth banks and screens of trees can be used to reduce the noise level perceived outside the site. 

Air-cooled acid plants, 18 822 Air-cooled condensers, 23 218 in refrigeration systems, 21 537 Air cooler fans, as a source of noise, 19 522 Air core, in hydrocyclones, 22 285, 286 Aircraft... 

Air cooler fans are normally 14 to 16 ft in diameter. Fan motors are almost always electric, although a few hydraulic and gasoline engines have been used. Fan tip speeds are normally 12,000 ft/min or less. In order to produce this speed, U.S. practice is to use V-belt drives or reduction gearboxes. V-belt drives up to about 30 hp are used, and gear drives at a higher motor horsepower. Single fan motors are usually limited to 50 hp. 

All values in Table 5.5 are calculated using this procedure. Table 5.5 also matches up accurately with GPSA [15] Fig. 10-16. As a general rule, I have found that DR is in the 0.85 to 0.90 range in almost every air-cooler fan case. Of course, this assumes elevation is sea level or less than 1000 ft. Using a DR value of 0.87 is a conservative approach and is advised if you want a quick but reasonable answer. 

If the column is cooled by two or more unrelated coolants, failm e of each coolant can often be considered independently. For instance, if air-cooled and water-cooled condensers share the column-cooling duty, credit for the air cooling can often be taken when cooling water fails. The above credit, however, may not apply when site power or steam failure is considered here both the cooling water pump and the air cooler fan may simultaneously fail due to loss of power or steam. Failure of the reflux pump during a power failure may also back liquid into the condenser and stop condensation. 

Targe updraft air cooler fans create induced air currents to provide cooling for process requirements. These air coolers create a considerable updraft current that ingests the surrounding atmosphere and disperses it upwards. 

Other energy considerations for cooling towers include the use of two-speed or variable-speed drives on cooling-tower fans, and proper cooling-water chemistry to prevent fouling in users (see Water, industrial water treatment). Air coolers can be a cost-effective alternative to cooling towers at 50—90°C, just below the level where heat recovery is economical. 

Large Fans These could be used to dilute a vapor cloud below its LFL with ambient air (see, for example, Whiting and Shaffer, Feasi-bihty Study of Hazardous Vapor Amelioration Techniques, Proc. 1978 Nat. Conf. on Control of Hazardous Material Spills, USEPA, Miami Beach, April 1978). But caution must be exercised because the turbulence produced by fans will likely promote rapid combustion and a resulting UVCE unless vapors are diluted below the LFL. Nevertheless, in new plants, strategic placement of air coolers may provide enough air flow to reduce the risk of a UVCE. 

Oil coolers either dissipate the heat into a vv ater stream or the air. Water coolers (Fig, 29-85) are significantly more compact, but a supply of vv ater is required. Air coolers (Fig, 29-86) are large and require a fan that increases the air flow ov er the cooling fins,... 

Another hazard with air coolers is that even though the motor is isolated, air currents have caused the fans to rotate while they were being maintained. Fans should therefore be prevented from moving before any maintenance work is carried out on or near them. 

A hot-water heating system forces water into pipes, or arrangements of pipes called registers that warm from contact with warm water. Air in the room warms from contact with the pipes. Usually, the pipes are on the floor of a room so that warmer, less dense air around the pipes rises somewhat like a helium-filled balloon rises in air. The warmer air cools as it mixes with cooler air near the ceiling and falls as its density increases. This process is called convection and the moving air is referred to as convection current. The process of convection described here is pipe-to-air and usually does a better job of heating evenly than in an air-to-air convection system—the circulation of air by fans as in a forced-air heating system. 

Air coolers Tubes are 0.75-1.OOin. 00, total finned surface 15-20 sqft/sqft bare surface, U = 80-100 Btu/(hr)(sqft bare surface)(°F), fan power input 2-5 PIP/(MBtu/hr), approach 50°F or more. 

Air coolers often consist of two tube bundles in one frame with one set of fans. In this case one tube bundle may be adequate for the initial capacity, and the space where the other tube bundle would reside can be blocked off by sheet metal to prevent the air from bypassing the cooling section. The other tube bundle can then be purchased when more cooling capacity is needed. 

Ambient air is compressed in a turbocharger, powered by the expansion of the hot pressurized exhaust gases. Following this first compression stage, the air is intercooled by a fm fan air cooler and fed into a second turbocharger. The high-pressure air is fed directly to the PEFC... 

Most air coolers are either induced-draft or forced-draft, as shown in Fig. 14.1. The more common arrangement being forced draft. The air is moved by rather large fans. The tubes are surrounded with foil-type... 

Loss of airflow through a finned tube air cooler bundle is a universal problem. The effect is to reduce the exchanger s cooling efficiency. To restore cooling, you might wish to try the Norm Lieberman method, which consists of reversing the polarity of the fan motor electric leads. The fan will now spin backward. Depending on the nature of the deposits, a portion of the accumulated dirt will be blown off the tubes— but all over the unit. Personnel observe this procedure from a safe distance. 

Belt slipping used to be a major problem on air coolers. The resulting low RPM routinely reduced airflow. Modern air coolers have notched belts, which are far less subject to belt slippage. Regardless, a slipping belt will result in a reduced amp load on the fan s motor driver. 

Spraying water on fin-fan air coolers is generally not a good idea. It is really effective only in dry climates with low humidity. The evaporation of water by the dry air cools the surface of the fins that is, the latent heat of vaporization of the water, robs sensible heat from the tubes. 

Induction motors are the most frequent in use because of their simple and rugged construction, and simple installation and control. They are constant speed devices available as 3600 (two-pole), 1800, 1200, and 900 rpm (eight-pole). Two speed models with special windings with 2 1 speed ratios are sometimes used with agitators, centrifugal pumps and compressors and fans for air coolers and cooling towers. Capacities up to 20,000 HP are made. With speed... 

Figure 8.4. Example of tubular heat exchangers (see also Fig. 8.14). (a) Double-pipe exchanger, (b) Scraped inner surface of a double-pipe exchanger, (c) Shell-and-tube exchanger with fixed tube sheets, (d) Kettle-type reboiler, (e) Horizontal shell side thermosiphon reboiler, (f) Vertical tube side thermosiphon reboiler, (g) Internal reboiler in a tower, (h) Air cooler with induced draft fan above the tube bank, (i) Air cooler with forced draft fan below the tube bank.

In such equipment the process fluid flows through finned tubes and cooling air is blown across them with fans. Figures 8.4(g) and (h) show the two possible arrangements. The economics of application of air coolers favors services that allow 25-40°F temperature difference between ambient air and process outlet. In the range above 10MBtu/(hr), air coolers can be economically competitive with water coolers when water of adequate quality is available in sufficient amount. 

Fig. 3. Rough layout sketch (/) the two fined heaters F-l and F-2 are located together but are separated from the other equipment with a subpipeway connecting the process area to the heater area (2) the reboiler E-2 is located adjacent to its column, T-l. The preheat exchanger E-4 is located adjacent to tower T-3 (3) the elevated overhead condenser E-3 is located next to the overhead accumulator V-l. Also, the air condenser FF-3 is located adjacent to its overhead accumulator V-2 (4) the rest of the air coolers (FF-1—3, -5) are grouped together in a common fan structure (3) all equipment and related piping is routed to and from the existing piperack saving the addition of a new piperack (6) all pumps (P-1—P-6) are located in a row under the piperack, and each...

Air-cooled exchangers are classified as forced-draft when the tube section is located on the discharge side of the fan (see Fig. 5.4). Air coolers are classed as induced-draft when the tube section is located on the suction side of the fan. 

Figure 5.5 Typical plan views of air coolers (a) two fan bays with three tube bundles, and (6) one fan bay with three tube bundles.

A second note about Table 5.3 is the number of tube rows to be used. Almost every air cooler of any significant heat-transfer value—say, 0.5 MBtu/h or greater—must have three or more tube rows. If there are fewer than three rows, uneconomical fan equipment and structural support will be required, so use three or more rows in your new designs. 

Equation (5.52) is Bernoulli s theorem [16], an energy equation that is well known to be equal to the sum of the elevation head, the pressure head, and the velocity head. Here the elevation head has been left out because the fan suction air pressure and the exiting air pressure from the air cooler are both equal. 

The DPAT variable is found by applying Eq. (5.48), the static pressure loss per tube row, a key equation that is to be experimentally determined. The last term, u2/2g, is the velocity head energy of the fan required to move the required airflow through the air cooler. As the air is heated while passing through the fin tubes, it expands, causing an increase in velocity. The air velocity difference, (v2 - iq)2, is the velocity head in the Bernoulli equation. 

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