Drop-tube furnace

Biswas, S., Choudhury, N., Sarkar, P, Mukherjee, A., Sahu, S. G., Boral, P, and Choudhury, A. (2006). Studies on the combustion behaviour of blends of Indian coals by TGA and Drop Tube Furnace. Fuel Processing Technology 87,191-199. 

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). 

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. 

Slag Deposit Initiation Using a Drop-Tube Furnace... 

The purpose of the drop-tube furnace was to simulate utility boiler combustion and ash forming and deposit conditions, in a laboratory-scale device. In particular, the furnace was used to... 

Drop-tube furnace injector and preheater section. 

Figure 4. Drop-tube furnace pc fluid bed feeder.

Drop-tube furnace water-cooled ash deposit collector... 

Figure 6. Drop-tube furnace temperature profiles.

The principal questions posed by the results of this investigation were (1) can ash deposits be formed in the drop-tube furnace in the absence of iron-containing minerals or slag drops ... 

Schneider (9 ) with brown coals of different origin in a drop tube furnace similar to that used by Field clearly showed the influence of different mineral substances on ash deposition. Sand particles (Figure 2) maintained their former shape in combustion or showed changes only at their edges while other ash constituents fused together into dark brown or glassy-clear spheres. 

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. 

Experiments on the pyrolysis of cellulose were carried out in a controlled mixing history reactor (CMHR), which is a plasma-operated drop-tube furnace capable of operating at temperatures up to 2500 K. A schematic diagram of the CMHR is shown in Figure 15.1. The graphite core reactor tube is 2 inches in diameter and 60 inches long. The central test section of the reactor has two 24-inch long... 

Maximum volatile yield was measured by The Energy Institute of Pennsylvania State University [14-15] for a suite of fuels including an high volatile shot petroleum coke with 14.6 percent volatile matter (see Figure 2.1). Using a drop tube furnace at temperatures up to 1700°C (3092 F) and using air-dried fuel ground to 85 - 74 my m (140 x 200 mesh), maximum volatile yields were measured as shown below. The... 

The volatility determination was part of a program to determine devolatilization kinetics fen petroleum coke. Samples of the petroleum coke were reacted in the drop tube furnace at ten )eratuies fiom 1000"C to 1700 C, in an argon atmosphere, to determine the rate of devolatilization. The procedure for calculating the kinetics was as follows ... 

The fuel was weighed from the feeder before and after the test, to determine the total amount of fuel feed to the drop tube furnace. Likewise, the char was carefully collected and weighed from three sources the char deposited on top of the filter paper, the char trapped in the filt jK r, and the char deposited on the probe wall. The sum of these three yields the total char collected, for a given test time. From the weight of the fuel fed (Wf) and the weight of the char collected (Wc), the percent weight loss (V) was calculated using equation 2-2 ... 

The reactivity R, at a given drop tube furnace temperature, was calculated by equation 2-3 ... 

The centerline gas velocity was approximated by doubling the bulk gas velocity. The bulk gas velocity was calculated as the volumetric gas flow rate divided by the cross sectional area of the tube inside the drop tube furnace. Stokes law was used to calculate the terminal velocity. At a temperature of 1700 C (3092°F). the calculated residence time for the coal particles was 186ms. The resulting devolatilization kinetics for petroleum coke are shown in Hgure 2.2. The devolatilization reactivity equations among various petroleum cokes will be reasonably consistent rather, the significant variability will come fi om the maximum volatile yield. 

The computation of maximum volatile nitrogen yield was based upon the ultimate analysis of the chars generated at all drop tube furnace temperatures from 1000 C to 1700 C. Petroleum coke can have significant concentrations of fuel nitrogen measured in g/GJ (lb/10 Btu) as shown in Table 2.3. Further, this nitrogen can be concentrated more heavily in the char than the nitrogen in coal. 

Figure 2.6. Nitrogen/Carbon (N/C) Atomic Ratios for the Char Produced in Drop Tube Furnace Experiments as a Function of Temperature...

Kajitani, S., Hara, S., and Matsuda, H. (2002) Gasification rate analysis of coal char with a pressurized drop tube furnace. Fuel, 81 (5), 539-546. 

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