Tube erosion

Morpholine is still the standard by which other amines are compared for pH control, and AMP has commonly been employed to control carbon steel boiler tube erosion-corrosion problems in European gas-cooled reactor stations. 

Designing a model fluidized bed which simulates the hydrodynamics of a commercial bed requires accounting for all of the mechanical forces in the system. In some instances, convective heat transfer can also be scaled but, at present, proper scaling relationships for chemical reactions or hydromechanical effects, such as particle attrition or the rate of tube erosion, have not been established. 

Tube erosion has been observed in both atmospheric and pressurized bed combustors. The scaling analysis presented earlier can be used to construct an accurate hydrodynamic simulation of the commercial bed. This can be used to qualitatively investigate factors related to tube wear such as the location of highest wear around the circumference of an individual tube and the location within the bed of the tube experiencing the highest wear. Quantitative wear rates cannot be obtained from model tests... 

Excessive us of high-pressure steam soot blowers is a common source of tube erosion-corrosion. Other boiler cleaning methods less threating to boiler tubes are available such as mechanical rapping, shot cleaning, and compressed air soot blowing. 

E. K. Levy and F. Bayat, The Bubble Coalescence Mechanism of Tube Erosion in Fluidized Beds, in Fluidization VI, p. 605, Engineering Foundation, Banff, Canada, 1989. 

The advantages of using a mechanical system include a relatively low investment cost with low space requirements. The system is relatively simple to operate in comparison to a chemical dosing system that requires constant surveillance. The disadvantages are represented by the high cost of ball (or brush) replacement, the possibility of tube erosion by the abrasive surfaces of balls (or brushes). The effectiveness of the system may be impaired by the presence of hard scales and inadequate filtering of the feed water. 

Tubeside velocities should be sufficient to provide reasonable distribution and to reduce fouling. When a minimum velocity has not been established, tubeside velocities should be as high as pressure drop will permit but should not be so high as to result in tube erosion. In general, increased velocities decrease the rate of fouling. 

Tube erosion decreases at high pressures. Bed-to-tube heat transfer coefficient increases significantly with increasing pressure. 

Tube erosion in a sparse tube bank higher than in densely packed bank. Larger sand more erosive than smaller strong coupling between tube erosion and bubble rise velocity. 

Tube bundles design with the consideration of tube erosion Bubble size, tube erosion, tube bundle design Bubble eruption, particle elutriation process Prediction of the bubble size distribution... 

Similar to bubbling beds, fast fluidized beds often require cooling or heating in order to maintain a steady thermal state. Unlike bubbling beds, the use of submerged heat exchanger tubes is not common practice in FFBs, because of concern about tube erosion by the faster gas/particle flows. The usual practice is to use walls of the FFB as the heat exchange sur-... 

A fixed soot blower, shown in Exhibit 7-26, is mounted directly on the convection section wall and is hard-piped as shown. A retractable soot blower, illustrated in Exhibit 7-27, allows the lance to be removed from the convection. seaion during operation. Some of the principal components are the support channel, the gear-driven carriage, the poppet valve (used to control the flow of the cleaning medium), and the lance with nozzles. Exhibit 7-28 depicts a soot blower in operation. As the lance enters the heater, the blowing medium cuts a path through the deposits until the lance reaches its apex. The lance then reverses rotation and is indexed so that on the retraction path it cleans surfaces not covered on insertion. The reversed rotation and indexing allow the soot blower to peel and strip all deposits efficiently and with less chance of heater tube erosion. 

One of the most interesting aspects of the flow shown in Fig. 12.1.3b, and another potiential cause of vortex tube erosion, is the very abrupt change in flow direction at the location where gas that has already entered the cyclone circles around and encounters the incoming gas stream. In the detailed plan view shown in Fig. 12.1.4, this is seen to occur at about the 2 30 clock position. It is here that the gas that is abont to complete its first revolntion within the... 

Fig. 12.1.6. Gas outlet tube erosion caused by high velocity particles entering...

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