93 The differences between the one SCR spray and 4 gas can be utilised to deduce how much NH
3
exits from one SCR brick in droplet i.e. non-gaseous ammonia form. This is considered as one of the most significant finding in the investigation and will be discussed later.
4.5 Analysis of droplet behaviour.
In this section the analysis of ammonia released from the urea spray is discussed. Section 4.5.1 discusses ammonia release from urea spray upstream of the SCR for both 1 SCR and 4 SCR cases.
Section 4.5.2 discusses ammonia released within the 4 SCR bricks. Finally section 4.5.3 discusses ammonia passing through the 1 SCR brick in droplet form.
4.5.1 Ammonia released from urea spray upstream of the SCR bricks.
In order to analyse the droplet behaviour upstream of the SCR, the information from potential ammonia from the spray see appendix 4.1.5 and the deduced ammonia from the upstream
measurements of 1 SCR and 4 SCR bricks are used see table 4.1.5 and 4.1.6. This information is plotted against the potential ammonia input from the spray in figure 4.5.1.
Figure 4.5.1 Ammonia released from spray upstream of the SCR bricks From figure 4.5.1, it is observed that from half to three quarters of the droplets from the urea spray
remained in droplet form, or possibly as HNCO at the inlet of the first SCR bricks. This is obtained from deduction of the potential ammonia upstream to the deduced ammonia upstream of the brick.
The 1 SCR and 4 SCR results vary due to experimental variation. The SUM values represent a series of experiments performed at various times using the same method.
200 400
600 800
1000 1200
500 600
700 800
900 1000
1100
p p
m
Potential NH
3
input from spray, ppm Ammonia in spray experiments - Release of NH
3
upstream of SCR bricks
Potential ups 1SCR Pot NH3
Potential ups 4SCR Pot NH3
Deduced ammonia ups 1SCR SUM-
NOx Deduced ammonia
ups 4SCR SUM- NOx
Ammonia ups 1SCR retained as
drops Ammonia ups
4SCR retained as drops
94
4.5.2 Ammonia released from urea spray within the 4 SCR bricks
In order to analyse this, the measurements of ammonia gas entering and consumed in the 4 SCR brick are needed. Figure 4.5.2 shows the ammonia released from the spray within the 4 SCR bricks.
Figure 4.5.2 Ammonia released from urea spray within 4 SCR bricks.
From figure 4.5.2, the differences between the ammonia consumed by the 4 SCR and the ammonia released upstream of the 4 SCR gives the ammonia released within the 4 SCR bricks. It is observed
that approximately 200 ppm or less ammonia is being released within the bricks to be consumed by the SCR reactions. It also shows that, as the spray injection flow rates increases, the ammonia
released within the bricks reduced possibly as a result of lower brick temperatures. This is probably due to the excess spray cooling the SCR bricks.
4.5.3 Ammonia passing through 1 SCR brick in droplets form.
