Recuperative burners

The recuperator can be positioned in the flue of the furnace or be integral with the burner (i.e. a recuperative burner). The separate recuperator is usually less costly. 

Cross section of recuperative burner. (From Hosoi, K., "Development of Recuperative Burner," Periodical of Japan Burner Research Association, no. 53,1986,16. With permission.)... 

For single-ended, P-shaped, and double P-shaped radiant tubes recuperative burners can be used. Figure 24.5 shows the application of a recuperative burner in a SER tube. There are also regenerative burners on... 

Application of a recuperative burner in a single-ended radiant tube. 

Tube skin temperature profile along the tube length in the recuperative burner. (Sudo, and Mochida, S., Internal paper on Radiant Tube Burner Testing, Yokohama, Japan Nippon Furnace Co., Ltd., 2009. With permission.)... 

The results are shown in Table 24.6 where the maximum stress on the tube between the regenerative and the recuperative burner is almost the same for both tube inside pressures of 0-0.6 MPa. These values are thought to be low enough than the creep rupture strength at 900°C with a long working time—about... 

High-thermal stability and thermal conductivity High-temperature heat exchangers, recuperative burners SiC... 

The recuperative melter is amenable to supplemental oxy/fuel technique or the premixed oxygen enrichment technique (see Chapter 1). Oxygen lancing is typically not used. In the supplemental oxy/fuel technique, an air/fuel burner is simply replaced by an oxy/fuel burner. When premix is applied, oxygen injection into the air main typically occurs downstream of the recuperator to avoid problems associated with air leaks in the recuperator. Care should be taken in locating the oxygen diffuser as discussed in Chapter 10. 

Several thousand high velocity FLOX burners (especially recuperative natural gas burners with efficient, built-in air preheating) are in fact satisfactorily firing in free flame or in radiant tubes in heat treatment and or heating furnaces [14,18,19]. In other circumstances, however, air and fuel jets from the burner nozzles cannot follow the basic formulae of the free jet and recirculation of flue gases is not unconditional. 

Comparative Performance Data Between Regenerative and Recuperative Radiant Tube Burners.494... 

Within this chapter, measurements at a radiant tube with recuperative and regenerative burner technologies will be shown as an example of how measurements should be carried out. The measurements have been accomplished at the lab-scale furnace of KTH, Stockholm [6-8], which has been shown (Figure 24.7). A W-shape radiant tube, shown in Figure 24.9, was used in the experiments. The outer diameter of the tube was... 

The measurement and calculation results (Table 24.4) clearly reveal that efficiency of the whole system is higher in the case of a HRS. The difference is significantly big, up to 25%. It becomes bigger in higher temperatures of the reference point. Higher efficiency for HRS is mainly due to a lower temperature of flue gases. The surface losses are also lower, because of a smaller surface area of burner units and pipes in comparison with a recuperative system. 

Radiant tubes are used in industry for heat treatment application in which products are treated under a protective gas atmosphere within the heat treatment furnaces. There are different radiant tubes with different geometries, burners, air preheating technologies, and materials on the market. In order to increase the efficiency of radiant tubes, plug in recuperators, and recuperative or regenerative burners will be used at radiant tubes to... 

Point 3 of the previous paragraph is confirmed by the following data comparing a W-tube fired by a recuperative one-way burner versus a pair of regenerative burners alternatively firing both ways. 

Regenerative burners and oxy-fuel firing lack mass flow to load bottoms in pits, therefore increasing top-to-bottom temperature differentials from 40°F to 100°F (22°F to 56°C). (See sec. 7.4.6.) B = batch. C = continuous. He = hot charge. Hr = heat recovery. Rec = recuperative. Reg = regenerative, longs = billets, blooms, pipe, rails, and structurals (but not rounds or short pieces). 

Ambient air (stream 200) is compressed in a two-stage compressor with intercooling to conditions of approximately 193 °C (380 °F) and 8.33 atmospheres (122.4 psia). The majority of the compressed air (stream 203) is utilized in the fuel cell cathode however, a small amount of air is split off (stream 210) for use in the reformer burner. The spent oxidant (stream 205) enters a recuperative heat exchange before entering a cathode exhaust contact cooler, which removes moisture to be reused in the cycle. The dehumidified stream (stream 207) is again heated, mixed with the small reformer air stream, and sent to the reformer burner (stream 211). The reformer burner exhaust (stream 300) preheats the incoming oxidant and is sent to the auxiliary burner, where a small amount of natural gas (stream 118) is introduced. The amount of natural gas required in the auxiliary burner is set so the turbine shaft work balances the work required at the compressor shaft. The cycle exhaust (stream 304) is at approximately 177 °C (350 F). 

A conventional recuperative (closed-loop) system s illustrated in Exhibit 7-13. Oil is circulated through fie convection section tubes, heated, and sent through Sie inlet air duct, where it releases its heat. The hot air len enters the burner for combustion, and the hot oil 5 recirculated to a storage tank for recycling. From a lyout standpoint, the hot oil system with a storage... 

In a recuperative furnace, the burners are fired continuously and heat is exchanged continuously in the exhaust system, where the exhaust gases flow outward through a central tube or tubes with the incoming air channeled along the outside of the tubes. 

---