Drop tube furnace system

The primary research tools used in this program were C-E s Drop Tube Furnace System (DTFS), a bench scale entrained laminar flow furnace and the Controlled Mixing History Furnace (CMHF), a pilot scale entrained plug flow furnace. Both the DTFS and CMHF by virtue of their ability to resolve combustion time into distance along their respective furnace lengths were used to examine carbon burnout phenomena associated with the SRC and reference coals. In addition, the CMHF by virtue of its staged combustion capabilities was used extensively to evaluate N0X emissions and to establish conditions conducive to low N0X ... 

A number of standard and special bench scale tests along with the Drop Tube Furnace System (DTFS) and pilot scale Controlled Mixing History Furnace (CMHF) were employed in this program. 

The Drop Tube Furnace System (DTFS) consists essentially of an electrically heated 2 inch I.D. x 18 inch long furnace where fuel (1 gm/min) and preheated secondary gas (air or inerts) are introduced. The history of combustion is monitored by solids/gas sampling at various points along the length of the furnace. 

In order to obtain detailed information on the evolution of fuel nitrogen, a laminar flow drop tube furnace, able to simulate conditions found in actual combustion systems, was adopted for this study. 

The experimental furnace is a vertically oriented laminar flow drop tube furnace having a 30 cm long uniformly hot test section with optical access. The fuel droplet array is introduced on the logitudinal axis concurrently with the ambient gas. The droplet stream is interrupted at several points in its trajectory by a sampling probe inserted axially from the base of the furnace. The probe quenches and transports the entire flow to a sampling train which recovers the fuel droplet residue for analysis. The above process is repeated at several furnace temperatures for each fuel. A detailed description of the system is to be found in references (3) and (4). 

Finally, the FT-IR system operates by coding the infrared source with an amplitude modulation which is unique to each infrared frequency. The detector is sensitive to the modulated radiation so that unmodulated stray radiation is eliminated from the experiment, permitting the use of the FT-IR as an in-situ detector in many experiments. For example, an FT-IR has been used to monitor the evolution of coal pyrolysis products within a drop tube furnace (24) and within an entrained flow reactor (25). The latter has been operated up to 1200 C. 

Most often, forced circulation is used with fired reboilers. If flow is lost to such a reboiler, furnace tube damage is likely to result. Hopefully, this is less likely to occur with a forced-circulation reboiler. Also, the higher pressure drop of a furnace may force the designer to use a pump. Sometimes, we also see a forced-circulation reboiler system, if the reboiler heat is to be recovered from a number of dispersed heat sources that are far away from the tower, and hence a lot of pressure drop has to be overcome. 

Forced draft systems use a fan or blower to provide air to the burner by way of a plenum or air duct. The air being supplied to the burner can be either at ambient temperature or preheated to as high as 900°F depending on the system being simulated. Pitot tubes are used to measure the static pressure just before the inlet to the burner. The difference in static pressure between the duct and the floor of the furnace provide the pressure drop across the burner. 

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