Tube heat exchanger

Explosion-bonded metals are produced by several manufacturers in the United States, Europe, and Japan. The chemical industry is the principal consumer of explosion-bonded metals which are used in the constmction of clad reaction vessels and heat-exchanger tube sheets for corrosion-resistant service. The primary market segments for explosion-bonded metals are for corrosion-resistant pressure vessels, tube sheets for heat exchangers, electrical transition joints, and stmctural transition joints. Total world markets for explosion-clad metals are estimated to fluctuate between 30 x 10 to 60 x 10 annually. 

The commercial production equipment consists of a furnace, heat-exchanger tubes, a fractionating column packed with Rachig rings, a KCl feed, a waste removal system, and a vapor condensing system (Fig. 1). 

If severe heat-transfer requirements are imposed, heating or cooling zones can be incorporated within or external to the CSTR. For example, impellers or centrally mounted draft tubes circulate Hquid upward, then downward through vertical heat-exchanger tubes. In a similar fashion, reactor contents can be recycled through external heat exchangers. 

In the chemical industry, titanium is used in heat-exchanger tubing for salt production, in the production of ethylene glycol, ethylene oxide, propylene oxide, and terephthaHc acid, and in industrial wastewater treatment. Titanium is used in environments of aqueous chloride salts, eg, ZnCl2, NH4CI, CaCl2, and MgCl2 chlorine gas chlorinated hydrocarbons and nitric acid. 

Fluidized combustion of coal entails the burning of coal particles in a hot fluidized bed of noncombustible particles, usually a mixture of ash and limestone. Once the coal is fed into the bed it is rapidly dispersed throughout the bed as it bums. The bed temperature is controUed by means of heat exchanger tubes. Elutriation is responsible for the removal of the smallest soHd particles and the larger soHd particles are removed through bed drain pipes. To increase combustion efficiency the particles elutriated from the bed are coUected in a cyclone and are either re-injected into the main bed or burned in a separate bed operated at lower fluidizing velocity and higher temperature. 

The modeling of fluidized beds remains a difficult problem since the usual assumptions made for the heat and mass transfer processes in coal combustion in stagnant air are no longer vaUd. Furthermore, the prediction of bubble behavior, generation, growth, coalescence, stabiUty, and interaction with heat exchange tubes, as well as attrition and elutriation of particles, are not well understood and much more research needs to be done. Good reviews on various aspects of fluidized-bed combustion appear in References 121 and 122 (Table 2). 

Copper and its alloys also have relatively good thermal conductivity, which accounts for thek appHcation where heat removal is important, such as for heat sinks, condensers, and heat exchanger tubes (see Heatexchangetechnology). Thermal conductivity and electrical conductivity depend similarly on composition primarily because the conduction electrons carry some of the thermal energy. 

Tubes Standard heat-exchanger tubing is V4, Yh, V2., Yh, %, 1, IV4, and IV2. in in outside diameter (in X 25.4 = mm). Wall thickness is measured in Birmingham wire gauge (BWG) units. (A comprehensive list of tubing characteristics and sizes is given in section 9, table D-7 of TEMA.) The most commonly used tubes in chemical plants and petroleum refineries are 19- and 25-mm (%- and 1-in) outside diameter. Standard tube lengths are 8, 10, 12, 16, and 20 ft, with 20 ft now the most common (ft x 0.3048 = m). 

The variables in tube-end welding were discussed in two unpublished papers (Emhardt, Heat Exchanger Tube-to-Tubesheet Joints, ASME Pap. 69-WA/HT-47 and Reynolds, Tube Welding for Conventional and Nuclear Power Plant Heat Exchangers, ASME Pap. 69-WA/HT-24), which were presented at the November 1969 meeting of the American Society of Mechanical Engineers. 

Cupronickels (10 to 30 percent Ni) have become very important as copper alloys. They have the highest corrosion resistance of all copper alloys and find apphcation as heat-exchanger tubing. Resistance to seawater is particularly outstanding. 

Carbon steel, low-alloy steels Transfer lines, beat exchanger shells, baffles, pump components, heat exchanger tubing, fan blades and shrouds, valves, screens, fasteners... 

Bronzes Bearings, pump impellers, special-purpose tubing, heat exchanger tubing, screens... 

Copper and brasses Heat exchanger tubing, bearings, valve components, gaskets, brewing equipment... 

Aluminum Heat exchanger tubing, transfer piping... 

Figure 2.9 Severely attacked crevice between rolled brass heat exchanger tube and mild steel tube sheet.

An ethylene heat exchanger tube failed in service. The tube was severely thinned beneath a baffle and tore in half (Fig. 2.27). 

Figure 2.27 Close-up of severely thinned heat exchanger tube in a baffle.

Figure 4.2 Severe localized wastage on a 316 stainless steel heat exchanger tube. Attack occurred beneath deposits, which were removed to show wastage.

Figure 4.4 Corrosion product mounds covering localized areas of metal loss on an aluminum heat exchanger tube. Attack initiated beneath a thin deposit layer.

Figure AAOA Deposits on a 316 stainless steel heat exchanger tube.

Figure 4.20 Sulfide deposits (dark patches) on longitudinally split brass heat exchanger tube. Note the perforation where wastsige penetrated the tube wall. Sulfide was spalled after perforation by escaping fluids.

Figure 4.26 Internal surface of steel heat exchanger tube after removal of deposits. Note the mutually intersecting areas of metal loss.

A duplex heat exchanger tube containing a single small perforation was examined. Perforation occurred due to internal surface wastage beneath a deposit layer containing large concentrations of sulfur compounds (Fig. 4.28). 

Heat exchanger tubing from a cooling tower Vertical... 

A 1-ft. (30-cm)-long section of steel heat exchanger tubing containing no failure was received. The section was submitted for evaluation of the internal surface, which was lined with a phenolic epoxy resin. 

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