(41an) What Went Right in Preventing Solvent Storage Tank over-Pressurization and Explosion during External Fire Incident

Incident Background: On 29th November 2023, due to a leakage from the bottom valve of the THF storage tank, solvent accumulated in the dyke surrounding the THF tank caught fire, resulting in an external fire outside the tank, igniting externally and causing a fire with flames reaching 5.0 meters height. The fire's intensity created a significant risk of tank over-pressurization and potential explosion, highlighting the critical need for effective safety measures.

Introduction: Emergency Relief Vents (ERV) are installed to storage tanks to allow emergency flow due to the excessive venting requirement from a fire burning around a storage tank. This eliminates a costly tank rupture, providing emergency venting from abnormal internal pressure beyond the capability of the pressure relief vent. In the event of a fire, the pallet will lift at a pre-determined pressure, thus creating a large venting area. This study looks at how ERV, combined with nitrogen blanketing and pressure vacuum relief valves (PVRV), helped prevent a tank explosion during a severe fire incident. The installations were aligned with API 2000 7th edition standards, highlighting the need for proactive design.

Objectives: The main goal is to show how ERV stop tank pressurization and bursting solvent storage tank during fires. It also emphasizes the importance of designing these safety measures according to API 2000 7th edition during the project stage.

Methods: We equipped our flat-bottom, low-pressure storage tanks with PVRV set to 250 mmWC pressure, nitrogen blanketing using a nitrogen PRV set to 70 mmWC pressure, and ERV set to 500 mmWC pressure. Despite the external fire outside the THF storage tank, filled THF (Tetrahydrofuran) tank did not over-pressurize due to continuous venting through the ERV. We collected and analyzed DCS trend data on tank pressure.

Results: The ERV activated at 500 mmWC set pressure inside the solvent tank during the fire, venting solvent vapors and preventing over-pressurization. The tank maintained its integrity and did not explode, proving the ERV's effectiveness. The nitrogen blanketing also prevented internal fires by maintaining a non-flammable atmosphere inside the tank. This incident shows that ERV, combined with nitrogen blanketing and PVRVs, can protect storage tanks during severe fires.

Discussion: The ERV's performance during the incident highlights its importance in tank safety. This case aligns with API standards, proving their effectiveness. Key factors include ERV design for external fire scenarios, pressure settings, and continuous operation during the fire.

Philosophy for Tank Over-Pressurization Design: This case study shows the need for a proactive design approach during the project stage, focusing on over-pressurization prevention in low-pressure storage tanks. As per API 2000 7th edition, designing over-pressurization devices with external fire scenarios in mind is essential. Implementing safety systems like ERV can significantly reduce risks.

Lessons Learned from Incident: The THF tank incident highlights the critical role of ERV in plant safety. Adhering to API 2000 7th edition for designing over-pressurization devices is crucial for preventing failures. This study supports a proactive design philosophy to ensure the safety and integrity of low-pressure storage tanks during external fires.