96
4.6.1 NO conversion efficiency
In this section the NO conversion efficiency can be plotted against the calculated potential ammonia input from the spray, 4 gas and 5 gas with respect to the SCR brick length as shown in figure
4.6.1. NO conversion efficiency can be defined as below:
�� ���������� ���������� = �� �� − �� ���
�� �� × 100
From figure 4.6.1, the excessive urea spray setting only results in a NO conversion of approximately 30 for the 1 SCR brick shown in red and blue. The reason for this is due to the high space velocity
low residence time of around 182khour for the 1 SCR brick at a temperature in the region of 590K. As a result of the high space velocity, unconverted droplets can survive through the SCR brick
unreacted. The 1 SCR with spray and 4 gas shows a perfect match of NO conversion from around 400 to 1100 ppm ammonia input while the 5 gas shows NO conversion slightly higher for lower
range of ammonia input less than 500 ppm.
Figure 4.6.1 NO conversion with respect to SCR length.
20 40
60 80
100
200 400
600 800
1000 1200
1400
N O
c o
n v
e rs
io n
Ammonia input ppm
NO conversion efficiency
4SCR 5 gas 4SCR spray
1SCR 5 gas 1SCR spray
1SCR 4 gas
97 In contrast, the 4 SCR brick conversion efficiency was very high and close to 100 when ammonia
input was sufficient shown in green and purple. The space velocity for 4 SCR is reasonably low at around 45.5 khour, which gives higher residence time of the ammonia in the SCR bricks. The SCR
bricks space velocity at approximately 590 K is summarized in table 4.6.1
Table 4.6.1 Space velocity for SCR bricks used in the investigation. Number of SCR
brick Brick Length,
mm Space Velocity,
khour 1
91 182
2 182
91 3
273 61
4 364
45.5
4.6.2 NO
2
conversion efficiency
Similarly the NO
2
conversion efficiency was performed with the results from 1 and 4 SCR with urea spray, 1 and 4 SCR with 5 gas and 1 SCR with 4 gas. The NO
2
conversion efficiency is shown in figure 4.6.2
The NO
2
conversion efficiency is defined using the following equation:
��
2
���������� ���������� = ��
2
�� − ��
2
��� ��
2
�� × 100
The conversion efficiency for the 1 SCR spray case is too high based on the assumption that all droplets are converted within the bricks. The conversion efficiency for 4 SCR spray is over 100
based on the negative NO
2
out table 4.1.6 due to experimental error.
98 Figure 4.6.2 NO
2
conversion with respect to SCR brick length.
The NO
2
conversion was higher for the 4 SCR spray purple and 4 SCR 5 gas in green followed by the 1 SCR spray red. The 4 SCR 5 gas efficiency increased linearly from 0 to reach 100 at
ammonia input of 500 ppm. The NO
2
efficiency for 4 SCR spray ranged from 80 to 100 and reached the peak at ammonia input of 700 ppm. The 4 gas with 1 SCR NO
2
conversion shows slightly higher conversion as compared to the 5 with 1 SCR. The NO
2
conversion efficiency for 1 SCR spray is also higher from 70 to 90 as compared to 40 to 55 for 1 SCR 4 blue and below 45 for 1 SCR 5
yellow. Even with the high space velocity in the 1 SCR spray case, the NO
2
reaches up to 90 conversion. This will be discussed further in the following section.
4.6.3 Comparison of NO and NO
Kategori