Surge Analysis: FEED Condensate Line at Laffan Refinery, Qatar Gas

Surge Analysis For FEED Of Laffan Refinery Qatar Gas

Overview

iFluids Engineering & Consultancy W.L.L. conducted a surge analysis for the Feed Condensate Line at Laffan Refinery. The objective was to assess various transient scenarios and ensure that the maximum pressure levels remain below the system’s Maximum Allowable Surge Pressure (MASP).

The following scenarios were evaluated to analyze the transient behavior:

  • Pump startup, trip, and changeover
  • Emergency shutdowns

Surge analysis focuses on abrupt pressure fluctuations in pipeline systems caused by sudden changes in fluid velocity. For this study, maximum and minimum pressures were analyzed and confirmed to be within the system’s allowable limits.

Laffan Refinery Details

Qatar Gas operates two refineries: Laffan Refinery 1 (LR1) and Laffan Refinery 2 (LR2). Each has a design capacity of 146,000 BPSD of untreated field condensate sourced from QG(N) and QG(S) Inlet Receiving (IR) facilities.

  • LR1: Operates at 110% capacity (160,600 BPSD).
  • LR2: Operates at 100% design capacity (146,000 BPSD). Feasibility studies are ongoing for increasing operations to 110% capacity.

Process Units:

Both refineries feature advanced units, including:

  • Condensate Fractionation Unit
  • Naphtha Hydrotreating Unit (NHT)
  • Saturated Gas Plant
  • LPG Trim Treating and Splitting Unit
  • Kerosene Hydrotreating Unit
  • Amine Regeneration Unit
  • Hydrogen Production Unit
  • Sour Water Stripping Unit
  • Utilities and Effluent Treatment Plant
  • Shared Units: Diesel Hydrotreater and Zero Liquid Discharge system

Objective of the Study

The main goals of the surge analysis were:

  1. To determine the maximum and minimum pressures during transient conditions.
  2. To recommend preventive measures if surge pressures exceed MASP.
  3. To suggest mitigation measures for managing excessive surge/transient pressures.

Key Considerations

  1. Pipeline Configuration:
    • Modeled pipeline geometry, including diameter, length, bends, and fittings, based on piping isometrics and specifications provided by Qatar Gas.
    • Tie-in points were determined as per shared documents.
  2. Simulation Models:
    • Pressure drop: Modeled using the Coulson and Richardson approach.
    • Fluid Phase: Single-phase flow was considered.
  3. Boundary Conditions:
    • Simulated from the transfer pump suction to the condensate tower inlet.
  4. Valve and Pump Data:
    • Control valve Cv values and closure times were based on datasheets and P&ID notes.

Simulation Process

  1. Steady-State Analysis
    • Conducted for a baseline duration of 20 seconds.
  2. Transient Analysis
    • Simulated various scenarios such as pump trip/startup, pump changeover, and emergency shutdown valve (ESDV) closures.
    • Transient events were initiated post the 20-second steady-state period to observe pressure responses under dynamic conditions.

Following are the steps taken to perform Surge analysis:

Flowchart depicting the process for surge analysis in the Laffan Refinery feed line. The process includes stages such as Preliminary System Specification, Steady State Simulation, Estimation of Possible Transients, Transient Simulation, and identifying the worst loading case. It features decision points like evaluating transient analysis, modifying transients or the system, and using surge control devices, ending with a check for sufficient surge protection
Flowchart for Surge Analysis: A step-by-step process highlighting transient analysis, system modifications, and surge control measures to ensure adequate surge protection.

Findings and Recommendations

  • Pump Startup, Trip, and Changeover: All observed pressures were within MASP. No surge mitigation measures required.
  • Emergency Shutdown Valve (ESDV) Closures: Maximum observed pressures remained within MASP. No mitigation required.

The current pipeline design and operating parameters are sufficient to handle transient events without exceeding MASP.

Insights on LR2 Performance

Qatar Gas aims to optimize LR2 operations for a 110% feed rate.

  • The Naphtha Hydrotreating Unit (NHT) operates at full capacity, while the Condensate Fractionation Unit remains below capacity.
  • Modifications are under review to enhance operational efficiency and accommodate the increased feed rate.

Conclusion

The surge analysis confirmed that the Feed Condensate Line at Laffan Refinery is designed to manage transient scenarios effectively. All maximum and minimum pressures observed during the study were within allowable limits, eliminating the need for additional mitigation measures. Future optimization of LR2 will further enhance operational efficiency and align with Qatar Gas’s long-term goals.