Air coolers bundles

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. 

If one of the air coolers begins to experience tube-side fouling, the fluid flow will be reduced. But the tube-side pressure drop will remain the same. The pressure drop across all five air-cooler bundles, shown in Fig. 14.6, is 10 psig. 

Meanwhile, the air-cooler bundles nearest the inlet header tend to see a greater and greater percentage of the total flow, as the cooler bundles foul and plug. They tend to stay hot and clean, and those bundles farthest from the inlet header tend to run cool and dirty. 

A finned tube bundle acts as an air filter. Air is drawn up through the lower two rows of fins where much of the dust, dirt, bugs, and moths are filtered out, and thus restricts air flow. Water-washing is the most effective method of removing these deposits. However, many of my clients will not water-wash hot air cooler bundles while running for fear of pulling out the tubes from the tube sheets due to thermal contraction of the tubes. 

The air cooler bundle was then replaced with an ordinary finned tube bundle. The use of wire inserts in fouling service, where extra pressure drop is totally unacceptable, represents poor engineering design practice. This is especially so when the controlling resistance to heat transfer is going to be on the air side of the precondenser cooler. 

Figure 3-16. Plan views of air coolers with boys and bundles (From Gas Processors Suppliers Association, Engineering Data Book, 9th Edition.)...

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. 

In a forced-draft air cooler, cool air is blown through the underside of the fin tube bundle. In an induced-draft air cooler, cool air is drawn through the underside of the fin tubes. Either way, road dust, dead moths, catalyst fines, and greasy dirt accumulate along the lower row of tubes. As the tubes foul, they offer more resistance to the airflow. However, note that... 

Individual flows to parallel banks of air coolers are rarely—if ever-measured. Regardless, we can gauge the approximate relative flow to each bundle. This can be done by checking the outlet temperature of the bundles or banks. 

The best way to handle the nonsymmetrical flow problem described above is to make the pressure drops in both the inlet and outlet tube bundle headers very small, as compared to the bundle pressure drop itself. Many of my clients add additional tube bundles in parallel with existing air coolers. This helps at first, but they find that the long-term benefits are quite disappointing, because of high pressure drop in the new header lines. 

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.

Air coolers are usually 6 to 50 ft long. Tube bundle bays are normally 4 to 30 ft wide. Use of longer tubes tends to cost less as compared to using shorter, wider tubes. Tubes are stacked in horizontal rows. A two-pass tube bundle would have an equal number of tube rows dedicated to each pass, in which the top tube pass realizes a hotter air coming from the bottom section. Likewise, the tube bundle(s) can have multiple tube section passes, where each pass has the full count of tube rows in the air cooler. Here each tube bundle pass has a bottom-to-top tube row in the air cooler. (See Fig. 5.6.)... 

APSF, ratio of external tube OD bare surface area to bundle face area, ft2/ft2. (Figure 5.6 shows typical face areas of air coolers.)... 

Step 6. In this step, the number of tubes NT is calculated. First assume a tube length L in feet, which conforms to the area of the respective placement for the new air cooler. Next calculate the width of the tube bundle using your assumed tube length. 

Air cooled heat exchangers have rectangular bundles containing several rows of tubes, horizontally aligned and vertically offset. Air flows vertically upward across the tube bank. The flow can be induced by fans above the bundle or forced by fans below the bundle. The heat transfer is countercurrent, because the hot fluid enters at the top of the bundle and flows downward through successive passes. The cost of an air cooler depends on the length of the tubes and the number of the tube rows. 

The ratio of air cooler weight to the face area of bundle is ... 

The anodic protection technique now enables air coolers and tube bundles in sulfuric acid plants to be protected from corrosion reliably and economically. Anodic protection was provided for air coolers of sulfuric acid production plants for the first time in 1966. Since then, a combined cooler surface area exceeding 10,000 m in air-cooled and water-cooled sulfuric add plants has been protected in this way worldwide. The installed initial electrical direct current output of the potentiostats is >25 kW, corresponding to an energy requirement of 2.5 W/m for the surface needing protection (Kuron and Grafen 1988). 

Air cooler units are entirely different from the previously mentioned arrangements in that the cooling agent used is circulating air instead of a liquid As seen in Exhibit 6-9, an air cooler unit consists of fin-tube bundles with a header box attached to each end, supported horizontally by a steel frame or struaure. For the single-pass arrangement, the inlet nozzles are mounted on the top of the header box the outlet nozzles are at the opposite end and mounted on the bottom of the header box. For die double-pass arrangement, the outlet nozzles are located at the same end as the inlet nozzles. For additional surface area, more passes can be added or additional units can be... 

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