*4.2. Conceptual Methods for Achieving NG Pre-Heating*

Several potential methods could be used to achieve an increase in NG temperature from ambient (~300 K or 25 ◦C) temperature to the range of pre-heating explored in this study (~600 K or 325 ◦C). From a practical standpoint, it would likely be best to apply a pre-heating method that does not require any additional heat sources or fuel use in order to maximize the operating expense reduction benefits highlighted in the previous section. It is clear that a single capital investment to develop and implement an NG pre-heating system with minimal ongoing costs would certainly be more attractive to BF operators than the alternative. The previously reported exploration of NG pre-heating at two Russian BFs [4,5] approached the concept from this angle, electing to route the incoming ambient NG through cooling flanges around the exterior of the blowpipe and elbow in an effort to capture heat that would otherwise be lost to the environment from the hot blast and direct it back into the BF.

Some preliminary CFD modeling of similar concepts was undertaken for the industry BF studied in this research. Some sample designs of a blowpipe-based heat exchanger or heat recovery system were explored, including in-refractory channels and an exterior piping wrap similar to the concepts shared in previous publications. A visualization of these potential designs is shown in Figure 10.

**Figure 10.** Conceptual designs for (**a**) the blowpipe channel NG pre-heater; and (**b**) the exterior wrap NG pre-heater.

Preliminary CFD simulations of convection heat transfer using the blowpipe channel NG pre-heater were conducted using baseline operating conditions (hot blast temperature, wind rate, and natural gas injection rate). These simple trials predicted a NG pre-heat of 170 K (NG temperature of 470 K) by the end of the channel, though the exact impact of this heat exchanger design on the hot blast temperature flowing through the blowpipe has yet to be determined. A potential loss in hot blast temperature would certainly be a significant detractor from such a design implementation and might serve to encourage the exploration of alternative approaches.

In addition, these designs present significant complexity in a region of the BF that can already have a great deal of design constraints, so it may be beneficial to explore methods for pre-heating elsewhere. A heat recovery system based around the exhaust or ambient heat losses from the BF hot stoves may present an acceptable solution, and future work may focus on determining the viability of such a system in terms of achievable NG pre-heat and specific impacts on BF coke rate, top gas temperature, and FTA.
