Preheating fuel saved

Oxy/fuel combustion has been used in many applications in the steel industry including both continuous and batch reheat furnaces, soaking pits, and ladle preheaters. Fuel savings of up to 60% have been reported.27 Typical fuel savings achieved by converting from air/fuel to oxy/fuel combustion are given in Table 1.4.28... 

Figure 19.3 Fuel saving versus air preheat temperature (stoichiometric conditions)...

As a fuel-saving and more productive design, the continuous multi-chamber kiln was developed it comprised a series of periodic kilns (chambers) joined side by side and fired in succession. This allowed the exhaust gases from the chamber being fired to be drawn through the adjacent chambers, thus preheating the charge. The combustion... 

The fuel-saving rate, S, that represents the energy-saving effects, is obtained by preheating the combustion air. The fuel energy savings can be calculated as follows. 

Percent fuel saving with air preheat temperature. (From The Japan Industrial Furnace Manufacturer Association, "Promotion of Energy-Saving Industrial Furnace," 3-16,1978.)... 

From the foregoing relations, the fuel-saving rate, S, caused by preheating of the combustion air becomes ... 

Therefore by using the temperature of the exhaust gas as a parameter, the relationship between the preheated air temperature and the fuel-saving rate can be predicted. The results are shown in Figure 21.6. This calculation assumes that combustion occurs at 20% excess air with JIS Class 1 No.l heavy oil. 

TABLE 5.1. Fuel saved by use of various degrees of air preheat with 6 fuel oil with 10% excess air. For other fuels, send higher heating value and fuel analysis (volumetric for gas, gravimetric with liquid or solid fuel) to North American Mfg. Co. (Cleveland, OH 44105). Reproduced with permission from Ref. 49. 

At the site of a thirteenth century cathedral, a bronze bell foundry loaded their melting furnace by putting raw pig metal down the stack for preheating to save time and fuel each morning while the women of the town carried wood from diminishing surrounding forests. 

To determine how much fuel can be saved by preheating air, read %available heat from figure 5.1 with and without preheated air, and use equation 5.7. In rare cases, fuel also can be preheated, but not if the fuel contains hydrocarbons that may crack when heated and deposit on the heat transfer surfaces. Preheating fuel usually is not justifiable if the fuel has a heating value greater than about 350 Btu/ft (13 MJ/m ). 

Find The %fuel saved by preheating the air to 900 F (427 C) (using an air temperature compensator in the air/fuel ratio controller to continue to hold only 10% excess air at all firing rates). 

The temperature of preheated air that can be obtained-/reat recovery (calculated as fuel saved due to preheated air) should be weighed against initial investment and maintenance. 

Air Preheating. The majority of the gas burners installed in cracking furnaces are natural draft burners. As combustion air is introduced at ambient conditions, a part of the heat released from the fuel has to be used to heat up the combustion air to the fire box temperature. Therefore, preheated air reduces the fired duty. Figure 6 shows the fuel consumption as a function of combustion air temperature. For example, preheating combustion air from 0° to 100 °C reduces the fired duty from 100 to 95.5%, which means savings of 4.5% fuel. 

Typical Cost Savings with Oxy-Fuel Ladle Preheating... 

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