Fans, cost

This tower depends upon natural draft action the same as a chimney to draw cool air in at the bottom and expel it out the top as warm moist air (Figure 9-101). The action of the tower depends upon the atmospheric temperature therefore, on a hot day the action of the tower may be less than on a cool day. These towers are relatively large, and require power for pumping the water to a point in the tower which is usually lower than for an atmospheric tower. There are no fan costs. Units have been built 310 ft high, base diameter 210 ft and a throat of 120 ft, wdening to 134 ft in diameter at the top [30]. 

Initial Investment Can be built with less expensive materials like wood, asbestos-cement board and plastic imaterials. Fan cost is higher. Built with relatively expensive materials such as prestressed, precast and reinforced concrete and asbestos-cement for fill. 

A0 = Optimum Approach A0 = Optimum at Minimum Aq = Optimum Above Minimum Ml = Fan Cost Increase Small Ml" = Fan Cost Increase Large M2 = CT Pumping Cost M3 = Chiller Compressor Cost = Total Cost w/expensive CT... 

If the actual total operating cost of the CT is plotted against the approach (as in the right side of Figure 2.16), the fan cost (Ml) tends to drop and the compressor and pumping costs (M2 and M3) tend to rise with an increase in approach. Once a total operating cost curve is obtained, the optimum approach can be found as the minimum point on that curve and that becomes the set point of TIC-1 on Figure 2.11. 

Uses electrical forces to c ture the particles from the flue gas and collect them onto a grounded plate within an electrical field. The process has a somewhat lower performance for the particle sizes between 0.1 and 1 pm (90%-95%). Overall efficiency of these devices is over 99%. They work with low pressure drops which minimizes the fan costs. 

The wisest fan choice is frequently not the cheapest fan. A small fan operates well on its curve but may not have adequate capacity for maximum flow control, future needs, or process upset conditions. It may be so lightly constmcted that it is operating near its peak speed with no provision for speed increases in the future, if needed. As fan size is increased, efficiency generally improves and wheel speed is lower. These factors decrease operating cost and provide reserve capacity for the future. However, it is also possible to oversize a fan and impair its performance. 

The so-called hyperbar vacuum filtration is a combination of vacuum and pressure filtration in a pull—push arrangement, whereby a vacuum pump of a fan generates vacuum downstream of the filter medium, while a compressor maintains higher-than-atmospheric pressure upstream. If, for example, the vacuum produced is 80 kPa, ie, absolute pressure of 20 kPa, and the absolute pressure before the filter is 150 kPa, the total pressure drop of 130 kPa is created across the filter medium. This is a new idea in principle but in practice requires three primary movers a Hquid pump to pump in the suspension, a vacuum pump to produce the vacuum, and a compressor to supply the compressed air. The cost of having to provide, install, and maintain one additional primary mover has deterred the development of hyperbar vacuum filtration only Andrit2 in Austria offers a system commercially. 

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. 

In extremely cold environments, engines can quickly become difficult, sometimes nearly impossible, to start. If ordinary gasoline- or diesel-oil-fired heaters are used, the coolant circulation pump, air fan, etc, must be powered from the vehicle s batteries, thus curtailing the time the system can be used, especially at very low temperatures when it is needed the most. By adding PbTe thermoelectrics to such heater systems, about 2% of their thermal output can be turned into electricity to mn the heater s electronics, fuel pump, combustion fan, and coolant circulation pump, with stiH sufficient power left over to keep the vehicle s battery fliUy charged. The market for such units is in the hundreds of thousands if manufacturing costs can be reduced. 

The forced-draft design offers better accessibility to the fan for onstream maintenance and fan-blade adjustment. The design also provides a fan and V-belt assembly, which are not exposed to the hot-air stream that exits from the unit. Structural costs are less, and mechanical life is longer. 

Operating costs will include 5 to 10 percent of one worker s time, plus power and fuel required. Yearly maintenance costs will range From 50 to 10 percent of total installed costs. Total power for fans, dr er drive, and feed and prodirct conveyors will be in the range of 0.5 D to 1.0 D". Thermal efficiency of a high-temperature direc t-heat rotary dryer will range from 55 to 75 percent and, with steam-heated air, from 30 to 55 percent. 

Moderate to accurate, depending upon the accuracy of controls. Stepless up to 20% of V, at constant h.p. and up to 33% of N, at constant torque is possible. Pumps, ID fans etc., that call for speed variation during a process need may not necessarily be too accurate. Or variation in flow of fluid, gas or temperature etc. not calling for very accurate controls, that such drives find their extensive use. It may be made more accurate, but at higher cost of controls... 

For in-house correlations, the cost of electric motors should be correlated vs. horsepower with voltage, speed, and type of construction as correction factors or parameters. Correction factors for explosion proof or open drip-proof housings could he developed if most of the data is for TEFC (totally enclosed fan cooled) motors. Similarly, correction factors could be developed for 1,200 rpm and 3,600i pm with l.SOOrpm as the base. 

Flue gas recirculation (FGR) is the rerouting of some of the flue gases back to the furnace. By using the flue gas from the economizer outlet, both the furnace air temperature and the furnace oxygen concentration can be reduced. However, in retrofits FGR can be very expensive. Flue gas recirculation is typically applied to oil- and gas-fired boilers and reduces NO, emissions by 20 to 50%. Modifications to the boiler in the form of ducting and an energy efficiency loss due to the power requirements of the recirculation fans can make the cost of this option higher. 

A fan with a diameter of 60 cm and a speed of 100 RPM will have a heat transfer capacity of 100W/°C, needs a mechanical power of 4W, has a noise level of 40 dB(A) and costs 180 Euro. 

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