Seals retrofitting

Floating Roofs These must have a seal between the roof and the tank shell. If not protec ted by a fixed roof, they must have drains for the removal of water, and the tank shell must have a wind girder to avoid distortion. An industiy has developed to retrofit existing tanks with floating roofs. Much detail on the various types of tank roofs is given in manufacturers literature. Figure 10-182 shows types. These roofs cause less condensation buildup and are highly recommended. 

The first documented use of dry gas seals in turboexpanders was in 1989. At that time, an ethylene plant in Scotland worked with a dry gas seal manufacturer to retrofit a turboexpander-integral gear-generator package. The partial success of that project was sufficiently encouraging for both user plant and turboexpander manufacturer to undertake a redesign of all three expander stages. Dry face or gas seals were installed at that time. 

Commercial refrigeration - Alternatives to CFCs for new commercial refrigeration equipment include HCFCs (including HCFC mixtures) and HFCs and HFC mixtures. Retrofit of existing equipment is possible by using both HCFCs and HFCs, in conjunction with reduced charges and more efficient compressors. Hydrocarbons are, to a limited extent, applied in hermetically sealed systems. 

Figure 36 is an illustration of a CFBC boiler retrofitted from a stoker-fired boiler. Also, at the bottom is a bubbling bed operated at a higher velocity of 3.5 m/s. A tube bundle is installed at an inclination of 15° in the dense bed, which extends to a height of 1.5 m from the air nozzles. A channel separator is also used, and the separated solid particles are returned through an air seal to the combustor. 

For these reasons, high capacity trays using dynamic downcomer seals are best avoided on new columns. They should be reserved for use on retrofit tower expansion projects. 

The only way to seal off this gap is to use strips of plastic or Teflon attached to the inner wall of the shroud. When the fan is turned on it will cut through parts of the plastic strips and create its own seal. Field results have been positive, and the strips, called "tip seals," can be purchased as a retrofit kit from air cooler vendors. 

Retrofit assistance. Converting from an oil seal to a compressor gas seal can pay for itself in improved reliahilify and lower operating costs. The logistical complexity of a proposed changeover can t be underestimated, however. 

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