Indirect heater

The Canadian Standards Association Standard Z343 (CSA 1998) presents test methods for in-line and firebox flame arresters. In this standard in-line flame arresters are limited to only detonation types and firebox flame arresters are defined as flame arresters installed in an enclosnre, or system of enclosnres, where the mn-np distance is less than 1.5 meters and open to the atmosphere. Firebox flame arresters are commonly nsed on eqnip-ment designed to heat flnids in prodnction operations snch as indirect heaters, emnlsion treaters, and glycol dehydrators. The development history of this standard is presented in Section 2.3.2. 

Figure 10.2 Continuous sterilizing systems, (a) Heat exchanger and continuous steam injection and (b) heat exchanger and indirect heater.

The solvent evaporated in the drying chamber has to be condensed and recovered. The off-gases from the condensation tower are then reheated in an indirect heater for being reused in the drying chamber. The process is shown in Figure 4.2. 

There are two types of air heaters which can be used in a spray-drying system, e.g., direct air heaters and indirect heaters. Direct air heaters, such as direct gas or oil fired furnace, can be used whenever the contact between combustion gas and spray is acceptable. When products of combustion of fossil fuels cannot contact with the spray, an indirect heater, such as indirect steam air heater, indirect gas, or oil-fired heater, is recommended. Interested readers can find more details about it in the literature (Matsers 1991). 

Vented closed cycle with indirect heater... 

FIGURE 9.38 Semiclosed-cycle layout (a) partial recycle cycle (b) vented closed cycle with indirect heater (c) vented closed cycle with direct heater. (From Masters, K., Spray drying. Advances in Drying, Vol. 1, A.S. Mujumdar, ed.. Hemisphere, New York, 1980, pp. 269—298.)... 

Check steam leakage or leaking tubes and fouled surfaces in indirect heaters... 

Figure 8 Typical layout of the closed-cycle spray dryer system c, coolant (diluent) f, feed 1, solvent recovery p, spray-dried product. 1, dried powder 2, cyclone 3, liquid-phase indirect heater 4, heat exchanger 5, scrubber-condenser. (Adapted from Ref. 11.)...

The mold can be directly heated by an integrated electric heater with heating elements of different shapes or by a heat transfer fluid that flows through the channels into the mold. The so-called indirect heaters are also used and are characterized by the required heat that is introduced to the mold through heating plates, which are integrated in the press by heat conduction. The molds are made out of heat-resistant steel to ensure that they can be operationally reliable under the required conditions of pressure and temperature. 

Heaters are vessels used to raise the temperature of the liquid before it enters a gunbarrel, wash tank, or horizontal flow treater. They are used to treat crude oil emulsions. The two types of heaters commonly used in upstream operations are indirect fired heaters and direct fired heaters. Both types have a shell and a fire tube. Indirect heaters have a third element, which is the process flow coil. Heaters have standard accessories such as burners, regulators, relief valves, thermometers, temperature controllers, etc. 

Figure 1.5 shows a typical indirect fired heater. Oil flows through tubes that are immersed in water, which in turn is heated by a fire tube. The heat may be supplied by a heating fluid medium, steam, or electric immersed heaters. Indirect heaters maintain a constant temperature over a long period of time and are safer than the direct heater. Hot spots are not as likely to occm if the calcium content of the heating water is controlled. The primary disadvantage is that these heaters require several hours to reach the desired temperature after they have been out of service. 

Indirect systems often require relatively larger equipment and much more costly instrumentation plus the maintenance and supervision that goes with that instrumentation. Direct heated vaporizers require simpler controls than indirect heaters plus avoid any danger of condensate fireezeup except if the steam trap gets blocked and traps condensate inside the shell. Desuperheaters can be added to give maximtun flexibility to exit vapor control temperature. 

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