the coking properties of coal at elevated pressures. - Argonne ...

Two-Stage Combustion
Staged combustion has been proposed as a means of reducing NO from an AFBc
unit. Several investigators [2, 3, and 41 have conducted tests to'quantify the NO
reduction with staging. However, these tests were run in small units and only
overall effects were measured. To aid in evaluating the effect of staging on NO
reduction and performance variables, the 6' x 6' AFBC facility was modified to aylow
air injection at an elevation of 96 inches above the distributor plate. This
elevation was chosen based on data from previous tests [21. Two injection ports --
on opposite walls of the unit -- were installed with valves to control flow and an
orifice to measure flow.
Tests were conducted at the conditions listed in Table 3.
ConditionIVariable
Bed Temp, *F
Bed Height - inches
Table 3
Summary of Operating Conditions and Measured Performance Variables
Superficial Velocity - ftlsec
Coal Feed - lblhr
CaIS Ratio
Recycle - lblhr
In-Bed Air Flov - lblhr
Overbed Air Plov - lblhr
Flue Gas
o2 - x
SO2 - ppm
CO - ppm
NOx - ppm
Sulfur Capture - 2
Combustion Efficiency - I
- la
1564
51.8
7.3
1887
2.7
2560
19500
2.9
0
170
208
416
91.6
98.1
- Ib
1546
52.5
8.0
2042
2.7
2680
21500
0
2.9
265
185
372
86.1
97.4
Test
- 2a -
1544 1547
50.0 49.8
7.1 7.1
2070 2064
2.1 2.5
2800 2920
19400 19400
2300 2300
2.9
562
247
195
77.1
96.8
- 2b
3.1
527
203
175
75.1
96.7
- 3a
1512
47.7
6.5
2192
2.7
2280
18300
4850
2.9
46 1
248
88
74.9
96.0
- 3b
1553
47.8
7.0
2228
2.5
2280
18900
4670
At each test condition, gas traverses were made at six heights along the
centerline of the unit. The gas concentration profiles obtained in-bed (16 inches
above the distributor plate) are shown on Figure 17. Note the peak in O2 and the
drop in other gas concentrations near the 36-inch insertion depth. This is probably
due to the recycle stream which is being injected with transport air at the 36-inch
distance. Profiles above the bed (in the freeboard) were considerably more uniform.
An integrated average of the profile obtained at each elevation was calculated.
This average was then plotted versus distance above the distributor plate for CO,
SO2, and NO as shown on Figures 18, 19, and 20. There are several points that are
readily appzrent from these figures.
2.7
458
248
117
76. I
96.1
0 With zero overbed air, there is a significant reaction occurring in
the freeboard, e.g., reduction of CO and NO
X.
0 Two-stage combustion produces the expected trends in reducing NO
while increasing SO2 and CO in the bed.
232