Operational Risks Involved on Integrating Flare Gas to Fuel System

Flaring is a safe industrial process to dispose waste or excess gas from a plant. But, it has limitations in energy conservation and environmental loss. Flare gas integration to cogeneration plant benefits from utilizing high calorific value waste gases as supplemental fuel to cogeneration plant or gas turbines. Earlier studies on flare gas integration have shown environmental incentive and economic viability. However, the impact of flare gas quality on the operation of cogeneration plants are yet to be identified.

This study delves into the operational hazards and risks arising from the variability of flare gas stream. A novel framework is proposed which can be applied to new or integrated processes which has inadequate information on its operational performance and associated hazards. The study identifies the technical hazards through design data collection, process simulation and sensitivity analysis. Followed by a systematic approach to evaluate the critical operational event occurrences and their impacts through scenario development and quantitative risk assessment.

An important outcome from this study is the identification of critical flare-fuel gas parameters affecting the cogeneration operation through process simulation. High hydrogen content and rich fuel-air ratio in the boiler can affect the boiler operating conditions. Increase in the hydrogen content in fuel system can increase the boiler gas temperature, combustion mixture and flame stability inside the firebox. Risk analysis through Bayesian Network showed a significant risk escalation. With a presumed frequency of 12 hrs/year of high and medium hydrogen gas flaring, there is a substantial rise in the occurrence of boiler gas temperature exceeding design limit and rich fuel mixture formation in the firebox. These top events has major influence on the operational time as well as loss control events - flame impingement and tube rupture.