Heat recovery from furnace gases

Heat recovery from furnace off-gas (LCV gas) normally used to preheat coke and blast air LCV gas has also been burned to heat melting baths and generate steam and power. 

One way to improve carbon emissions and overall efficiency is to ensure that all furnace operations employ efficient heat recovery from the flue gas. Ideally the flue gas should be cooled in order to recover the heat of condensation of the water produced in the combustion process. 

Cold air can be sucked into the furnace convective section through holes in the furnace skin. This reduces the efficiency of heat recovery from the hot flue gas. At lower crude rates, flue gas flow drops, but cold air in-leakage remains constant. Thus, at lower crude rates, holes in the furnace exterior will hurt efficiency more than at higher throughputs. A roll of aluminum tape can go a long way toward correcting this problem. 

Reducing products of combustion from furnaces, steam boilers, and gas turbines by making the process more energy efficient through improved heat recovery. 

The waste heat recovery system is associated with flue gas from the reformer furnace and process gas from the secondary reformer. It generates high-pressure steam in specially... 

In a methanol plant (Figure 4.3), the synthesis gas passes from the reformer furnace to a heat recovery section where it is cooled to room temperature. The synthesis gas is then compressed to 750 to 1,500 psia (5,170 to 10,345 kPa) and fed to the converter vessel through preheat exchangers. Methanol is formed as the gas passes over catalyst beds in the converter vessel at 400 to 600° F (205 to 315 C). The methanol product is then cooled and fed to separators and then to fractionators to complete the purification. 

The earlier plants operated at deficit, and needed an auxiliary boiler, which was integrated in the flue gas duct. Auxiliary burners in tunnels or flue gas duet were additionally used in some instances. This situation was partially caused by inadequate waste heat recovery and low efficiency in some energy consumers. Typically, the furnace flue gas was discharged in the stack at rather high temperature because there was no air preheating and too much of the reaction heat in the synthesis loop was rejected to the cooling media (water or air). In addition, efficiency of the mechanical drivers was low and the heat demand for regenerating the solvent from the C02 removal unit (at... 

The requirements for water pollution control have been forcing a shift to concentrating spent sulfite pulping liquor by evaporation, followed by incineration with heat recovery (102). When calcium-base liquor is burned, the sulfur emerges as calcium sulfate and is not available for recycle to the pulping process. The flue gas from such furnaces in Sweden is reported to contain 0.2—0.3% sulfur dioxide, and in one Swedish mill a Bahco wet limestone scrubber is used to treat the gases (115). 

From geological studies to aerospace engineering, physical modeling has been widely used in the industry to study complex fluid dynamics where engineering calculations or computational fluid dynamics are deemed either unreliable (the former) or uneconomical (the latter). In the field of combustion, physical modeling is employed in studying flow distribution involving combustion air, over-fire air (OFA), and flue gas recirculation (FGR) as well as isothermal flows in combustion chambers of furnaces, boilers, heat recovery and steam... 

---