Economizers design

Posttensioned Concrete This material is frequently used for tanks to about 57,000 m (15 X 10 gal), usually containing water. Their design is treated in detail by Creasy (Pre.stre.s.sed Concrete Cylindrical Tanks, Wiley, New York, 1961). For the most economical design of... 

Description These exchangers are typically a series of stacked helical-coiled tubes connected to manifolds, then inserted into a casing or shell. They have many advantages hke spiral-plate designs, such as avoiding differential expansion problems, acceleration effects of the helical flow increasing the heat transfer coefficient, and compactness of plot area. They are typically selected because of their economical design. 

As a general nile, the direct-heat units are the simplest and most economical in construction and are emploved when direct contact between the solids and flue gases or air can be tolerated. Because the total heat load must be introduced or removed in the gas stream, large gas volumes and high gas velocities are usually required. The latter will be rarely less than 0.5 m/s in an economical design. Therefore, employment of direct rotating equipment with solids containing extremely fine particles is likely to result in excessive entrainment losses in the exit-gas stream. 

An appropriate procedure for executing the design of an absorber-stripper system is to set up a carefully selected series of design cases and then evaluate the investment costs, the operating costs, and the operability of each case. Some of the economic factors that need to be considered in selec ting the optimum absorber-stripper design are discussed later in the subsec tion Economic Design of Absorption Systems. ... 

Usually, the geometry is determined by space limitations. Both horizontal or vertical cyhndrical vessels are designed as pressure vessels, and for pressures up to 50 psig, an L/D ratio of 2 to 3 results in an economic design. 

Honzontal-tube cabin heaters position the tubes of the radiant-section-coil horizontally along the walls and the slanting roof for the length of the cabin-shaped enclosure. The convection tube bank is placed horizontally above the combustion chamber. It may be fired From the floor, the side walls, or the end walls. As in the case of its vertical cylindrical counterpart, its economical design and high efficiency make it the most popular horizontal-tube heater. Duties are 11 to 105 GJ/h (10 to 100 10 Btu). 

The above exercise is only for a general guidance. In such cases, the manufacturer should be consulted who may offer a better and more economical design. 

A friction loss of 37.125 m In a total length of 1000 m is quite high and will require a larger motor. Therefore, a 150 mm main pipeline will offer a better and more economical design compared to a 125 mm pipeline such as the reduced cost of the prime mover and lower power consumption during the life of pumping system, in addition to a longer life span of a 150 mm pipe compared to a 125 mm pipe. 

A design engineer will be the best judge of the best and the most economical design and extruded sections. 

The above example is only for the outdoor part of the bus system. The indoor part, in any case, would be cooler than the outdoor one and will also provide a heat sink to the hotter enclosure and the conductor constructed outdoors. No separate exercise is therefore carried out for the indoor part of the bus system, for the sake of brevity. For a realistic design that would be essential. The above example provides a basic approach to the design of an IPB system. With some permutations and combinations, a more realistic and economical design can be achieved. A computer is necessary for this exercise. 

Economical design (capital and operating costs) H2S enrichment for sulfur recovery Special cases such as energy recovery... 

Although the total coil length is always smaller when there is no upstream coil (Lj = 0), the temperature could be so low at the outlet of the choke under these conditions that hydrates will form quickly and will partially plug the choke. In addition, the steel temperature in the choke body may become so cold that special steels are required. Therefore, some guidelines are necessary to choose Tj for an economical design. 

This is normally too large a value to be considered an economical design. However, in this case, future flow rates indicate that the 157 ft will be close to the needed area. Rather than handle and provide piping and special valves for two units, it is cheaper and easier from an operation viewpoint to install one large unit at this time. 

Mist type flow usually does not occur in an economic design, even though the recirculation rates may be high. 

The minimum number of the tube rows recommended to establish a proper air flow pattern is 4, although 3 rows can be used. The typical unit has 4-6 rows of tubes, but more can be used. Although more heat can be transferred by increasing the number of tubes, the required fan horsepower will be increased however, this balance must be optimized for an effective economical design. Tubes are laid out on transverse or longitudinal patterns however, the transverse is usually used due to the improved performance related to pressure drop and heat transfer. The tube pitch is quite important for best air-side performance. A typical representative tube arrangement for design optimization is for hare-tube O.D., tinned-tube O.D., and tube pitch ... 

In general, tube-side pressure drops less than one psi per pass should not be specified for economical designs. Drops as low as 15 mm Fig. have been specified, and designs obtained which were competitive with cooling tower installations. For viscous materials, pressure drop limitations can markedly influence a design and its economics. 

Because of the restrictions in the flow area of the ports on plate units it is usually difficult (unless a moderate pressure loss is available) to produce economic designs when it is necessary to handle large quantities of low-density fluids such as vapours and gases. 

Moldable holes and inserts can complicate molding and may require extra postmolding operations. Thus, the most economical designs are those that minimize the number of holes. With many plastics, both external and internal threads can be molded, but sharp V threads should be avoided because they can cause the plastic to bridge, resulting in incomplete thread fill. Rounded or modified buttress threads will allow improved thread fill. 

The modem FB boiler is a compact economical design (typically more compact than SM boilers) and provides minimum combustion efficiencies of 80% for gas-fired and 83% for oil-fired models. They usually are small units, seldom exceeding 150 hp, and operate on a variety of fuels at typically 4 to 5 sq ft of surface area per hp. 

There are various WT and FT boiler economizer designs, classified as either steaming economizer and nonsteaming economizer types according to thermal performance. These economizers are constructed in either bare tube or finned tube (extended surface) patterns. They may be positioned horizontally or vertically within the boiler system, in either cross-flow or counterflow arrangements. 

Stream flow-rates. Allocating the fluids with the lowest flow-rate to the shell-side will normally give the most economical design. 

The size, shape and materials of construction depend on the function of the facility, the net explosive weight (NEW) for the worst-case accidental explosion in the facility, and other factors. Both reinforced concrete and steel have been used as materials, and shapes range from box (room) shaped, through horizontal and vertical cylinders to spheres. Generally, the room-shaped structures are most economically designed and constructed of reinforced concrete, while cylindrical and spherical shapes are most efficiently designed when made of steel. 

Pre-enginecred concrete boxes can be used to provide smaller buildings. These buildings are manufactured in a factory, are pre-wired, come with HVAC installed and are truck delivered to the site ready to be secured to a foundation and connected to desired utilities. These buildings are economically designed to withstand 1 to 3 psi (0.9 to 21 kPa) side-on overpressures,... 

In less frequent situations a more comprehensive analysis approach is used to analyze the structure as a whole. For example, a finite element analysis of an entire building may be performed. Obviously, the load path need not be predetermined when such global analysis methods are used. However, the load path is influenced by the type and level of detail of the modeling so that engineering judgment and experience are also necessary to achieve a safe and economical design,... 

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