Direct-fired heater

FIG. 12-104 Open spray-drying system with direct-fired heater. (NIRO, Inc. )... 

Direct-fired heater A heat generator that allows the combustion products to be mixed with the air to be heated. 

The BSD can either shut down the entire facility, or it can be designed for two levels of shutdown. The first level shuts down equipment such as compressors, lean oil pumps, and direct fired heaters, and either shuts in the process or diverts flow around the process by closing inlet/outlet block valves and opening bypass valves. The second level shuts down the remaining utilities and support facilities, including generators and electrical feeds. 

Another method of increasing the overall cycle efficiency is to use the waste heat energy in the exhaust air to heat process fluids as depicted in Figure 16-10. This is a direct savings in fuel gas that would otherwise be consumed in direct-fired heaters. Overall thermal efficiencies can be as high as 50 to 60% in this type of installation. 

The most logical place to begin is to size the furnaces and direct-fired heaters. Often the chemistry of the process has dictated the conditions, but frequently they can be modified in order to conserve energy usage. The burning of waste materials should also be considered as a means of both disposing of unwanted by-products and reducing fuel requirements. For each of these units, the amount of fuel needed per pound of product should be determined. 

Gallagher, J.T., Cost of Direct-Fired Heaters, July 17,1967, p. 232. 

Process furnace or direct-fired heater Design type, absorbed heat duty, pressure, tube material, capacity... 

Figure 8.2 is based on shop fabrication up to 15 mmBtu/h heat absorption units and field-erected 20 mmBtu/h heat absorption units and larger. Direct-fired heaters generally are 30 mmBtu/h duty or less, although field erections have been much greater, 50 mmBtu/h or greater. 

Figure 8.2 is based on direct-fired heaters, both shop and field-erected, with carbon steel tubes, and includes all direct materials, shop and field labor, and subcontractor overhead and profit. 

Figure 8.2 Direct-fired heater base cost.

TABLE 8.6 Direct-Fired Heater Cost Factors... 

The total modular factor, 227.5% for the direct-fired heater, multiplied by the base cost, is equal to this particular equipment module field-erected and ready to commission. 

TABLE 8.7 Direct-Fired Heater Module Associated Cost Factor Additions, in Percent... 

Indirect or direct fired heaters are widely used in the process industries. Heat loss is kept to a minimum by refractory coatings on the furnace wall. Any material in the fuel that is corrosive or forms excess soot has to be avoided. Usually 20-25% excess air is required for fuel oil vs. 5-10% for gaseous fuel, hence the latter is more economic. Energy in the exit flue gas not used to heat water or a product can be recovered by heat exchangers that generate additional steam or preheat the entering air. 

Costs for forced circulation evaporators, long tube evaporators, and agitated falling-film evaporators are presented in Figs. 15-26 and 15-27. Information on purchased cost of specialized heaters is given in Figs. 15-28 and 15-29, while Figs. 15-30 and 15-31 present costs for process furnaces and direct-fired heaters. 

Cost of direct-fired heaters, cylindrical type with vertical tubes. 

An isothermal reactor concept incorporating a ceramic membrane is more attractive compared to an adiabatic reactor concept from a thermodynamic point of view. In this concept we assumed a reactor with reactor tubes located in a direct-fired heater and operated in a cyclic way to remove coke formed on the catalyst. Parallel bed and heaters have been assumed [35-37]. 

FIGURE 23.22 Self-inertizing spray drying system (1) drying chamber with rotary atomizer (2) cyclone (3) scrubber condenser (4) direct-fired heater (5) heat exchanger for waste-heat recovery (6) exhaust to atmosphere (7) fuel (8) combustion air (9) cooler (10) condensate F, feed P product. 

Direct-fired heaters Isolate or use other type of heater ... 

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