## 3 Results and Discussions
### Influence of the Burners Turned on or off  
For the operation of a reformer, three basic requirements should be satisfied: safety, reliability and efficiency. When a steam reformer is operating, it is important to monitor the catalyst tube temperature because of the possible threats of thermal stress and creep damage. When the monitored temperature reaches a dangerous status, a prompt and feasible approach is to turn off some of the the burners. In this section, to explore the effect  
Figure 4: Outer surface temperatures and inner surface pressures of the catalyst tubes: (**a**) Temperatures; (**b**) Pressures. Figure 5: Lifetimes for the catalyst tubes of the prototype reformer. of the placement and numbers of burners turned on or off on the tube lifetime, the burners are divided into six groups, as shown in Figure 1d. The range of each group is as follows:  
1. the first group: \(x=0\sim 6.5\) m,
2. the second group: \(x=6.5\sim 12.67\) m,
3. the third group: \(x=12.67\sim 18.84\) m,
4. the fourth group: \(x=18.84\sim 25.01\) m,
5. the fifth group: \(x=25.01\sim 31.18\) m,
6. the sixth group: \(x=31.18\sim 37.68\) m.  
Each group contains 23 catalyst tubes and 36 burners. Further, each group can be controlled to be turned on or off. In the following discussion, we discuss twelve different burners on/off combinations, including fully opened, one group (group 1, 2, 3, 4, 5, or 6) turned off, two groups (group 1 & 2, 3 & 4, or 5 & 6) turned off, and three groups (group 1, 2 & 3 or 4, 5 & 6) turned off. Figure 6 compares the effect of the burners on/off combinations on the average outer surface temperatures of the catalyst tubes. Obviously, the burners on/off combinations have a significant influence on the temperature profiles, as shown in Figure 6. The catalyst tube temperatures have greater reductions in the areas of burners turned off. Further, the catalyst tube temperatures reduce to a higher extent when the upstream burners are turned off. On the other hand, the catalyst tube temperatures reduce to a lower extent when the central burners are turned off. The outer surface temperatures of the catalyst tubes decrease by about 106 \({}^{\circ}\)C, 163 \({}^{\circ}\)C or 215 \({}^{\circ}\)C, respectively, when one group, two groups, or three groups of burners are turned off. Figure 6: Outer surface average temperatures of the catalyst tubes using different burners on/off combinations. Figure 7 compares the effect of the burners on/off combinations on the outer surface temperature distributions of the catalyst tubes. It can be observed that the temperatures are higher at the lower portions of the catalyst tubes because of the weaker heat convection near the bottom wall. Further, the upstream portion of the reformer has higher temperatures. This is because the top portion (roof) of the reformer is divergent and the reformer outlet position is at the right-hand side reformer roof. Therefore, the upper portion and downstream portion of the reformer have larger heat dissipation space while the upstream portion has smaller heat dissipation space and hence higher temperatures. It is also observed that the thermal field is obviously influenced by the burners on/off combinations. For a reformer under normal operation, temperature is higher near the left-hand-side and right-hand-side walls because fluid motion is slow and heat dissipation is worse there. On the other hand, convection is better in the central area of the reformer. Therefore, turning off the burners near the left-hand-side and right-hand-side walls can mitigate the poor convection and hence yield a higher reduction in the catalyst tube temperatures. Further, heat transfer convected to the downstream area is reduced if the upstream burners are turned off; however, effect on the convection to the upstream area is minor if the downstream burners are turned off. Therefore, turning off the upstream burners can yield greater temperature reductions than turning off the downstream burners.