Numerical Modeling and Optimization of a Natural Gas and Coke Oven Gas Mixing Flow Field

Abstract

Coke oven gas (COG) is a by-product of the coke making process. In the steelmaking industry, COG is often injected along with natural gas as fuel into blast furnace to replace coke for cost reduction. For an integrated steel plant, NG is always more expensive than COG. Especially, NG is purchased externally, and COG is generated internally. To lower the total fuel cost, the operators always try to maximize COG usage and only use NG as supplement for thermal control. However, it is found that such simple concept could not be implemented successfully. Every time, as NG flow rate increases, the COG flow rate decreases automatically. As a result, total fuel supply is short than expected, and the blast furnace finally loses thermal stability. A comprehensive investigation was conducted. Computational fluid dynamics (CFD) was used to model the COG and NG pipeline system. It is identified that mixing of COG and NG has a critical impact. In the existing pipeline system, COG and NG is simply mixed at a joint where COG and NG meet. CFD simulation identified that the current mixing of COG and NG is not adequate, causing COG flow out of control as NG flow varies. A new design of COG and NG joint is developed by adding baffles to ensure the COG flow can be adjusted as needed.