Equations fired heaters

TABLE 8.16. Equations and Other Relations for Fired Heater Design... 

TABLE 8.17. Procedure for the Rating of a Fired Heater, Utilizing the Equations of Table 8.18... 

If we consider a source at 200°C and an object at 80°C, a change of 1°C in source temperature changes the quantity in parentheses by 0.4%. For most practical purposes in chlor-alkali production, the above approximation is justified. In fired heaters and similar equipment, where radiation is the principal mode of heat transfer, proper calculations based on the complete equation are necessary. 

Most processes are fundamentally nonlinear. If we examine some of the key equations governing process behaviour, this quickly becomes apparent. Heat transfer is fundamental to almost every process. Whichever way this is achieved involves nonlinearity. For example, in Chapter 10 we applied Stefan s Law to estimating benefits on a fired heater. 

Because it is known that the flowrate of naphthalene has been reduced by 50%, the new outiet pressure from P-201 can be calculated from Equation 119.71. The feed pressure remains at 80 kPa. At a naphthalene flow of 6.41 Mg h, Equation 119.71 gives a pressure increase of 455.73 kPa, so P3 = 535.73 kPa. Because the flowrate has decreased by a factor of 2, the pressure drop in the fired heater decreases by a factor of 4 (see Equation rE19.7a11. Therefore, P5 = 510.73 kPa. Therefore, the pressure of Stream 6 must be 510.73 kPa. The flowrate of air can now be calculated from the conpressor curve equatiom... 

Equation (4.15) should be considered the final oil-treatment stage, in which a 0.5 to 1% water cut in treated oil is produced. Here a heater-treater-type horizontal vessel is more commonly used. A direct-fired burner-heater is normally placed in a front section of the horizontal treater. Controlling the system temperature for viscosity is important and may be mandatory for successful water dehydration. 

The assumption that the gas sample obeys the ideal gas law is probably valid since the temperature of the gas (25.0 °C) is not particularly low and the gas pressure, about 1 atm, is not particularly high. However, the implicit assumption that all the heat of combustion could be transferred to the water was probably not valid. If the transfer were to occur in an ordinary gas-fired water heater, some of the heat would undoubtedly be lost through the exhaust vent. Thus, our calculation was of the highest temperature that could possibly be attained. Note that in using the ideal gas equation the simplest approach was to work with SI units because those were the units of the data that were given. 

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