Clean Gas Vent Line: Eliminating Blast Furnace Blow–Down Dust emissions

Emissions during Blow–Down

During the process of stopping the blast furnace process, the top gas calorific value reduces given the lower CO content and higher CO₂ content. In addition, oxygen is produced.

While the oxygen imposes a risk of explosions, feeding gas with lower calorific value towards the power plant the combustion properties. Therefore, top gas is traditionally isolated at some point during a blow–down, causing raw gas emissions to the atmosphere. This raw gas contains particulate dust, cyanides, ammonia, hydrogen and substantial amounts of carbon monoxide – all of which are unwanted emissions.

Objectives and Requirements

The clean gas vent line was developed with the objective of being able to redirect the lower calorific value top gas from downstream of the gas cleaning system and prevent it from being fed to the power plant.

Not only does such a system need to be clean and safe to operate, best practices also dictate that existing blow–down methodologies can remain in place since it is important for operational staff to be able to rely on the established set of operating guidelines during such special operational situations.

Clean Gas Vent Line

A large–diameter duct, including several valves and an electrical control system, is used
to redirect the clean gas from a pick–up point after the gas cleaning system and before
the isolation valve towards the bleeder platform. Routing is optimized to ensure
constructability while maximizing draft effects.

Installation

The clean gas vent line was first installed in 2020 at Blast Furnace No. 2 owned and operated by Hyundai Steel in Dangjin, Korea. To meet the tight project schedule, fabrication took place partly in parallel to engineering activities. HAZOP and SIL analyses were completed to minimize risk during project execution.

Application

Hyundai Steel has used the clean gas vent lines installed on all their Dangjin furnaces since its first implementation in 2020. Blow–down methodologies as they were used before the installation remain in place and are can be followed without having to open the bleeder valves. Operation of the clean gas vent line has proven clean and safe, with zero incidents of explosive gas mixtures having been detected during any of the blow–downs and shutdowns since 2020.

Added Value

Through the implementation of a clean gas vent line, the blast furnace can be blown down without having to use the bleeder valves when the top gas is isolated from the power plant. Emissions of particulate matter as well as pollutants such as cyanides and ammonia are strongly reduced or eliminated.

The clean gas vent line arrangement greatly contributes to sustaining a plant’s license to operate during times of increasingly stringent environmental requirements and regulations.