Operator access towers

A sufficient number of access doors, ladders and walkways shall be provided for safe and easy accessibility to internals and mechanical equipment of the tower for inspection and maintenance. Access doors shall be tight, resistant and easy to operate. Access ladders from the ground should be located in such a position to permit future cell addition. 

Similar to towers, drum elevations are diaated by the NPSH, as illustrated in Exhibit 5-7, minimum clearance, common platforming, and maintenance and operator access. Within structures, especially chemical facilities, drums could be elevated above the minimum requirements of accommodate floor space avail-... 

If process requirements permit, shell and tube exchangers can also be mounted in a vertical position, supported by lugs and tower nozzles in a tower-sup-ported installation (as shown in Exhibit 6-17), within concrete or steel structures (as shown in Exhibit 6-18), and by concrete piers (as shown in Exhibit 6-19). The same considerations for maintenance, control, and operator access should be given for vertical installations as are for horizontal installations. 

Although the minimum NPSH requirement was a key factor in elevating the tower in this example, the height was finally dictated by operator access clearance, which was the greater of the two dimensions. If the configuration shown in Exhibit 10-12 (NPSH) had been used, the tangent line elevation would be 108.5 ft (102,600 mm). 

Level, pressure, and temperature instruments control the operation of the tower and must be placed in a position that enhances operation and maintenance without obstructing operator access. Instrument requirements for towers are usually highlighted on an instrument vessel sketch furnished by the instrument engineer. Exhibit 10-58 is a typical instrument vessel sketch. 

Freestanding process towers should be located adjacent to the structure to facilitate operator access from the tower platforms to the struaure. 

Large towers often have the motor mounted horizontally connected to a right angle gear drive. The motor can be closely coupled- in the air stream- or connected with a drive shaft with the motor outside the air stream. Maintenance personnel typically prefer the external TEFC motor- when available- for its easier access. Cooling tower fans- like all fans- operate in accordance with the fan laws one of which states that the horsepower required to drive a fan increases to the cube of fan speed. 

Leading characteristics of five main kinds of reactors are described following. Stirred tanks, fixed beds, slurries, and three-phase fluidized beds are used. Catalyst particle sizes are a compromise between pressure drop, ease of separation from the fluids, and ease of fluidization. For particles above about 0.04 mm dia, diffusion of liquid into the pores and, consequently, accessibility of the internal surface of the catalyst have a minor effect on the overall conversion rate, so that catalysts with small specific surfaces, of the order of 1 m2/g, are adequate with liquid systems. Except in trickle beds the gas phase is the discontinuous one. Except in some operations of bubble towers, the catalyst remains in the vessel, although minor amounts of catalyst entrainment may occur. 

If the operation involves liquids that contain dispersed solids, use of a plat -tower is preferred because the plates are more accessible for cleaning. 

Ease of operation—Control valves shall be easily accessible work platforms shall be available at field instruments, near inspection windows and cleaning manholes for reactors, heat exchangers, and absorption towers. 

Traditionally mining headframes are constructed over the mine shaft to facilitate hoisting, provide head cover, facilitate safe access to the shaft and in some cases, to house a tower mounted friction hoist. In an effort to increase production and minimize down time, schedule, capital and construction costs, an approach was conceived to convert an existing service shaft into a production shaft. To better streamline the conversion process, a two phased approach was developed for the surface conversion. First, a penthouse would be constructed over the existing operational headframe and outfitted with a pre-commissioned hoisting plant. Second, the existing service headframe would be demoHshed and replaced with a new modular production headframe complex. 

Designing the 107 m tall penthouse over the operating service headframe allowed continued access to the mine while providing the permanent infrastructure to install the hoist, one of the largest tower mounted friction hoists in the world. 

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