Absolute combustion maximum achievable fuel

Figure 20.4 Point of absolute combustion in terms of maximum achievable combustion of fuel.

One definition of the point of absolute combustion is the point of maximum heater outlet temperature for a given amount of fuel (as illustrated in Fig. 29.3). Following this, we can say that the point of absolute combustion is also the point of best or maximum achievable combustion for a given amount of fuel (as illustrated by Fig. 29.4). 

A minimum export steam plant is defined as a plant that optimizes heat recovery in the plant to the maximum extent possible. This is often done when the value of steam is essentially zero or the price of the feedstock and fuel are exceptionally high. Minimum steam export is often achieved by first increasing the SMR process gas inlet temperature and then the combustion air preheat temperature, both of whieh reduce the fired duty of the SMR. Typical temperatures are 1150°F for the process gas and 900°F for the air preheat. These changes reduce the export steam to a low level, but typically not completely to zero. Additional modifications are required to reduce the export steam to an absolute minimum. 

---