Eva device hazop analysis essentials

HAZOP analysis is based on a simple principle: systematically examining the consequences when process parameters (such as flow, pressure, temperature, etc.) deviate from the design intent, and evaluating whether existing safety measures are sufficient.

Its core tools are the combination of "prompt words" and "process parameters."

Typical guiding words: none/blank, more, less, accompanied, part, on the contrary, unusual.

Typical process parameters: flow, pressure, temperature, level, composition, stirring, reaction.

For example, for a "traffic" parameter:

Application guidance word: "None"

Deviation: No traffic

Reasons: pump failure, valve misclosure, pipeline blockage, pump cavitation due to low liquid level, etc.

Consequences: Interruption of feed to downstream reactors may lead to reaction imbalance, catalyst deactivation, and even safety incidents; upstream equipment may overflow or experience overpressure.

Safety Measures: Is there a low flow alarm? Is there a low-low flow interlock to stop the pump or start the backup pump?

Recommendation: If existing measures are insufficient, propose adding a "low-low flow interlock switch."

The HAZOP analysis of EVA devices usually follows the standardized process, which is a team collaboration activity rather than an individual effort.

Phase 1: Preparation Stage

This is the foundation of analyzing success and is crucial.

1. Form a HAZOP team, which usually consists of 5-8 professionals, including:

Leader: An experienced and professionally trained HAZOP expert, responsible for guiding the meeting, keeping it on track, and ensuring the depth and consistency of the analysis.

Recorder: Responsible for recording the discussion content in real-time into the HAZOP software or forms, and generating the HAZOP report.

Process Engineer: Very familiar with the process design of EVA units, P&ID (Piping and Instrumentation Diagram), material balance, and thermodynamic data.

Equipment/Mechanical Engineer: Familiar with the specifications and limits of pressure vessels, pipelines, compressors, pumps, and other equipment.

Instrumentation and Control Engineer: Familiar with control systems (DCS/ESD/SIS), logic diagrams, alarm, and interlock settings.

Experienced operators: Provide practical experience and methods for handling exceptions in actual operations.

Other experts: If necessary, safety engineers, electrical engineers, etc., can be invited.
2. Define the scope and objectives of the analysis: Clearly specify the process units covered by this HAZOP analysis.

Units covered: (e.g., high-pressure polymerization reaction area, medium-pressure separation system, VA recovery unit, extrusion granulation system, etc.).

Identify the objectives of the analysis (e.g., identify hazards, assess existing protection layers, meet regulatory requirements, etc.).
3. Collect necessary information: This is the key to the HAZOP analysis of the EVA device. Required documents:

(1) Piping and Instrumentation Diagrams (P&IDs): The most important document, must be the latest version.

(2) Process Flow Diagrams (PFDs)

(3) Material Safety Data Sheet (MSDS): Especially for ethylene, vinyl acetate, solvents,

(4) The toxicity and flammability/explosiveness of various catalysts (such as organic peroxides and other initiators, which are extremely hazardous) and modifiers.

(5) Process Description and Operating Procedures.

(6) Equipment Data Sheet (Pump, Compressor, Reactor, High-Pressure Heat Exchanger).

(7) Control logic diagram, interlock diagram, alarm list.

(8) Floor plan and hazardous area classification diagram.

(9) Previous safety analysis reports (if any).

4. Make a plan

Determine the meeting time, location, and duration, and divide the P&ID into reasonable nodes for analysis one by one.

Phase Two: Analysis and Execution Stage

Team meeting, conduct a systematic analysis of each node.

1. Select Node: The team leader guides the team in selecting the first process node (e.g., high-pressure tubular reactor feed system).

2. Description of Design Intent: The process engineer provides a detailed introduction to the design purpose of the node, normal operating conditions (temperature, pressure, flow rate, composition, etc.).

3. Application of guide words to generate deviations: The team leader guides the team to apply guide words to key parameters one by one to propose meaningful deviations. Examples of deviations of particular concern for EVA devices:

(1) Flow: Excessive or insufficient feed of initiator (catalyst) leads to reaction runaway or inadequate reaction.

(2) Temperature: Reactor cooling failure leading to the formation of "hot spots," which may trigger ethylene decomposition explosion (extremely dangerous!).

(3) Pressure: Leakage in the high-pressure system leads to air ingress forming an explosive mixture, or material ejection.

(4) Composition: Excessive impurities in the raw materials (such as acetylene, hydrogen, sulfur) affect the catalyst activity or lead to side reactions.

(5) Reaction: Reaction out of control, pressure and temperature rise sharply.

(6) No stirring: The mixture in the polymerization kettle is stratified, locally overheated, or blocked.

4. Analyze the reasons for deviation: The team brainstorms and lists all possible causes of the deviation.

5. Consequence Evaluation: Analyze the final consequences of the deviation on safety, environment, equipment, and production.

6. Identification of existing protective measures: List all existing safety measures (alarms, interlocks, pressure relief valves, operating procedures, fire protection facilities, etc.).

7. Risk Assessment: Evaluate the severity and likelihood of an accident caused by the deviation under existing protective measures. Sometimes a risk matrix is used for qualitative or semi-quantitative assessment.

8. Propose Recommendations: If the team believes that the existing protective measures are insufficient (risk is unacceptable), they will propose improvement suggestions. For example:

(1) "Add a high-high temperature interlock."

(2) "Add a low-low flow alarm at the initiator pump outlet."

"(3) Modify the operating procedures to specify that a strict leak test and nitrogen purging of the high-pressure system must be conducted before startup."

9. Documentation: The recorder shall document all the above discussion content (deviations, causes, consequences, measures, recommendations) in detail into the HAZOP analysis sheet.

10. Repeat the cycle: Repeat steps 3-9 for all important parameters of this node. After completion, proceed to the next node until all nodes have been analyzed.

Phase Three: Reporting and Follow-up Tracking

1. Generate Report: After the meeting ends, the recorder compiles the meeting notes to generate a draft of the formal HAZOP analysis report, which is then submitted to team members for review and confirmation.

2. Propose Recommendations: The core output of the report is a clear list of actionable recommendations, specifying the responsible person, department, and required completion date for each suggestion.

3. Implementation and Tracking of Measures: Management needs to allocate resources to ensure that each recommendation is implemented (design modifications, program updates, adding equipment, etc.). An "action tracking table" is usually used to monitor progress until all recommendations are closed.

4. Management Review: The final report and action completion status need to be submitted to the management for review and record.

Due to the characteristics of the EVA (especially high-pressure method) process, special attention should be paid in the HAZOP analysis.

1. High-pressure process: The operating pressure is extremely high (up to over 300 MPa), and any leakage could lead to catastrophic consequences. It is necessary to focus on analyzing overpressure, leakage, fatigue failure, etc.

2. Decomposition explosion of ethylene: Ethylene can undergo an uncontrollable decomposition reaction at high temperature and high pressure, releasing a huge amount of energy, which is the most significant potential hazard. It is essential to thoroughly analyze all scenarios that could lead to excessive temperatures.

The hazards of the initiator (catalyst) system: The organic peroxides and other initiators used are usually extremely unstable, very sensitive to temperature and impurities, and pose risks of self-decomposition and explosion. The transportation, storage, and injection systems are key points of analysis.

4. Self-polymerization and blockage: Vinyl acetate and EVA melt are prone to self-polymerization, leading to blockages in heat exchangers, valves, and pipelines, which can cause localized overpressure. It is necessary to analyze deviations such as "reverse flow" and "reduced flow."

5. Phase change: Under high pressure and temperature variations, materials undergo complex phase changes (supercritical fluid), which poses high demands on the design of the pressure relief system.

6. Reaction termination system: The ability to quickly and reliably inject termination agents in emergency situations is crucial for safety. It is necessary to analyze the reliability of the termination agent system itself ("no flow", "excessive flow").

The HAZOP analysis of the EVA device is a rigorous, meticulous process that highly relies on the professional knowledge and collaboration of the team. It is not only a necessary step to meet regulatory requirements but also a crucial engineering practice to deeply uncover potential process hazards, prevent major accidents, and ensure personnel safety and stable operation of the device.