Recuperative furnaces

Continuous recuperative furnaces employing metallic recuperators (heat exchangers) have been in use since the 1940s. Operation of these furnaces is simplified and the combustion process is more precisely controlled no reversal of air flow causes temperature variations. The recuperator metal must be caretiiUy selected because of chemical attack at high temperature. Recuperative furnaces are often used in the production of textile fiber glass because they maintain a constant temperature. 

These furnaces are good candidates for full oxy/fuel. Recuperative heat exchanger efficiencies are much lower than with regenerative furnaces, and therefore fuel savings can help to drive the conversion. Also, recuperative furnaces operate in a continuous and steady firing mode of operation similar to oxy/fuel furnaces. 

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. 

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. 

Combustion/ Solid fuel-fired furnaces Fuel in direct contact Recuperative Manual and Batch, periodic Natural/self, Crucible, shaft Melting roasting Shaft, muffle... 

Reactions (1) - (4) pass on the catalyst in a warmed pipe in a recuperative mode. The main disadvantage of considered process is the necessity to use the surplus of H20 [1], The surplus is defined with molar ratio (mol H20)/C = N. Depending on operation conditions, tubular furnaces designs and the used catalyst 2 power consumption of hydrocarbons conversion process as a whole. Necessity of increase N is connected with allocation of carbon on the catalyst (the mechanism of carbon allocation is... 

A recuperative tank furnace of lower output for container glass production is... 

Boneberg, J. H., Oxygen enrichment test on a non-recuperative reverberatory remelt furnace, paper presented at Aluminum Industry Energy Conservation Workshop IX Papers, Aluminum Association, Washington, D.C., 1986. 

Conversion to full oxy/fuel also provides an opportunity for production increase. The change in pull rate achieved with an oxy/fuel furnace, in comparison with an air/fuel furnace, varies depending on furnace type. Pull rate increases of up to 60% have been observed for unit melters. Cross-fired regenerative furnaces have seen increases as little as 10%. End-fired regenerative furnaces converted to oxy/fuel increase pull capacity by 20%. Recuperative melters typically achieve a 30% pull rate increase. 

Three types of furnace are in use regenerative, recuperative and unit melters. The last, while cheaper to install and easier to maintain, with shorter downtime on colour changes, is more expensive on fuel. Regenerative furnaces are in the majority. Several types of container glass are generally recognised ... 

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. 

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... 

These data show that the temperature difference is larger if the furnace temperature decreases. In the recuperative case the average temperature difference in all measured data is 112°C (standard deviation 24.5°C). In the regenerative case it is 71°C (standard deviation 31.7), so that the value is lower by 41°C but the standard deviation is better by 7°C than the recuperative case. 

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.)... 

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... 

Recuperative heating This involves the transfer of the residual ( latent ) heat of the fluegases to the combustion air. The flue-gases are collected at the top of the furnace, mixed with sufficient air and then burned in a post combustion unit. This provokes the exothermic oxidation of CO. The burnt gases are led through a heat-exchanger (recuperator) where the heat is transferred to the combustion air. Typically the blast air is heated at temperatures of 500 to 600 °C. Above these temperatures, problems arise with the sintering of fiimace dust on the surface of the recuperator... 

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