Understanding How HAZOP Helps Prevent and Mitigate Hydrofluoric Acid Hazards

Introduction

Hydrofluoric acid (HF) is one of the most hazardous substances used in industrial processes, particularly in petroleum refineries. Its unique properties and extreme toxicity make it both essential and dangerous. This article demonstrates how Saltegra Consulting LLC, a provider of PHA/HAZOP facilitators and safety consultants based in California, USA, manages risks in facilities handling HF, particularly in alkylation units within petroleum refineries.

What Is Hydrofluoric Acid (HF)?

HF, a solution of hydrogen fluoride in water, is a highly corrosive acid known for its ability to dissolve many materials, including glass. Its chemical formula is HF, and it is also referred to as hydrogen fluoride or fluoric acid. This colorless liquid has a pungent odor and poses significant hazards due to its corrosive nature.

Hydrofluoric acid can cause severe burns, systemic toxicity, and damage to bones and organs. The main routes of exposure are inhalation, skin contact, and ingestion, making it essential to handle this substance with extreme caution. This substance is among the highly hazardous chemicals listed by OSHA. Assistance from PHA experts and other professionals is necessary when implementing safeguards for handling this chemical.

HF has several critical industrial uses. In the petroleum industry, it serves as a catalyst in the alkylation process to produce high-octane gasoline. HF is also essential in glass etching, where it reacts with silica to create and manufacture glass products. In metal cleaning, HF removes oxides and other impurities from metal surfaces before further processing. The electronics industry relies on HF to clean and etch silicon wafers, which are vital in semiconductor production. Additionally, hydrofluoric acid is a precursor to many important fluorine-containing compounds, including refrigerants and pharmaceuticals.

Using HAZOP To Prevent and Mitigate Risks

Introduction to HAZOP

A Hazard and Operability (HAZOP) study is a systematic method for examining potential hazards and operability issues in a process or operation. The purpose of HAZOP is to identify deviations from the design intent by using guidewords, such as “No,” “More,” or “Less,” applied to different parameters like flow, temperature, and pressure.

This structured approach helps uncover potential safety and operational issues that might not be evident through routine analysis. The process involves a multidisciplinary team that systematically reviews the process in defined segments called nodes, identifying potential causes for deviations, assessing the consequences, and recommending measures to mitigate risks.

Conducting a HAZOP study involves several key steps. First, the project initiation phase includes confirming the scope and requirements, reviewing project information, and assembling the HAZOP team. This is followed by the preparation phase, where process safety information is assessed, nodes are defined, and worksheets are prepared. During the session phase, the team, led by an experienced HAZOP facilitator in the USA, reviews each node using guidewords to identify potential deviations and their consequences, as well as the safeguards and recommendations. 

Application of HAZOP to Alkylation Process

In the HF alkylation process, hydrofluoric acid is used as a catalyst to combine isobutane with olefins, such as propylene and butylene, to produce high-octane gasoline components. The process involves three key units: the reactor, the acid settler, and the product separation unit. Each unit has specific operating conditions and associated risks.

1. Reactor: The mixed feed of isobutane and olefins is introduced into the reactor, where HF is used as a catalyst. The reactor conditions are tightly controlled to optimize the reaction:
   • Temperature: 90°F – 120°F
   • Pressure: 150 – 200 psi
2. Acid Settler: The reactor effluent is directed to the acid settler, where hydrocarbons are separated from the HF acid. The HF is recycled back to the reactor, and the hydrocarbons proceed to the product separation unit:
   • Temperature: 80°F – 100°F
   • Pressure: 100 – 150 psi
3. Product Separation: The hydrocarbon mixture is sent to the product separation unit, where the alkylate (high-octane gasoline) is separated from lighter and heavier components:
   • Temperature: 100°F – 250°F
   • Pressure: 50 – 100 psi

Scenario 1: Reactor

In the reactor, maintaining optimal temperature and flow is crucial. One critical deviation is “More Flow,” where a control valve inadvertently opens, leading to increased reactant flow and a rise in temperature, potentially causing an acid runaway reaction. Safeguards include flow control systems and temperature sensors.

Engineering controls to mitigate this risk involve implementing redundant flow control systems to ensure backup in case of primary control failure. Additionally, installing high-temperature alarms that trigger automated emergency shutdown procedures can provide immediate containment, preventing the reaction from reaching dangerous levels.

Scenario 2: Acid Settler

In the acid settler, ensuring the proper separation of hydrocarbons from HF is crucial. A potential deviation, such as a “High Level” in the separator due to blocked liquid outlet, can lead to HF carryover into the product stream, resulting in product contamination and liquid overfill overpressure. To safeguard against these risks, level sensors, basic control systems, and regular maintenance of the separator are essential.

Additionally, PSVs and ESDs should be in place to manage overpressure scenarios. Recommended actions include conducting regular inspections, implementing redundant level monitoring systems, and enhancing real-time level monitoring to detect and address any issues promptly. These measures help maintain the integrity of the separation process, prevent contamination, and avoid overpressure incidents.

Scenario 3: Product Separator

In the product separation unit, a high temperature deviation due to inadvertently opening the steam supply in the heat exchanger can cause overheating and pressure build-up, posing risks of equipment damage and safety hazards identified during the HAZOP study.

To mitigate these risks, safeguards such as temperature sensors, high-temperature alarms, pressure relief valves, and ESDs are essential. Recommended actions include regular maintenance of heat exchangers, conducting emergency shutdown drills, training operators on steam supply controls, and implementing procedural checks for steam supply operations. These measures help ensure safe and reliable operation by preventing and effectively responding to high temperature and pressure conditions.

Preventing Hydrofluoric Acid Release

Based on the recommendations from HAZOP worksheets provided by PHA experts, several measures can be implemented to prevent and mitigate the risks associated with hydrofluoric acid in the alkylation process:

Proper Design and Construction

Ensuring that HF alkylation units are designed and constructed to minimize the risk of HF releases is crucial. This includes using materials that resist HF corrosion, such as Teflon or certain plastics, and implementing robust containment systems to prevent leaks and spills. Storage tanks should be equipped with reliable level sensors and high-level alarms to prevent overfilling. Regular calibration and testing of these sensors are necessary to maintain their accuracy and functionality.

Operations, Inspection, and Maintenance Programs

Establishing procedures for the safe operation and maintenance of HF alkylation units is vital. Routine maintenance schedules and standardized operational protocols help maintain safe working conditions. Conducting frequent inspections and maintenance of equipment can prevent leaks and accidental releases.

Enhancing the frequency of inspections and installing additional sensors can help detect potential issues early. A robust maintenance schedule should include checking the integrity of pipelines, valves, and reactors to ensure all components function correctly under operating conditions.

Training and Emergency Response

Providing comprehensive training for personnel and developing effective emergency response plans are essential. Training programs should cover HF handling, emergency procedures, and the use of personal protective equipment (PPE). Workers should wear appropriate PPE, including acid-resistant clothing, gloves, and face shields, to protect them from HF exposure.

PPE should be regularly inspected for damage and replaced as needed to ensure optimal protection. Having clear emergency procedures and readily available calcium gluconate gel to treat HF burns is critical. Regular emergency drills should be conducted to ensure preparedness, and establishing quick-response teams trained specifically for HF incidents can enhance emergency response effectiveness. 

Conclusion

Hydrofluoric acid, while indispensable in many industrial applications, poses significant health and safety risks. Understanding its properties, uses, and the necessary precautions can help mitigate these risks and ensure safe handling in industrial environments. Applying HAZOP in processes involving HF, such as the alkylation process, allows for the identification and mitigation of potential hazards, enhancing overall safety and reliability.

By implementing the recommended actions from HAZOP studies led by an experienced facilitator in the USA and adhering to industry best practices like API RP 751,  industries can prevent HF-related incidents and protect both workers and the environment.