CALCULATION OF RELIEVING RATES, ACCORDING TO THE APPLICABLE EMERGENCY SCENARIO

The rate to be discharged from a PSV is normally to be calculated assuming all the applicable emergency scenario’s.

This is a time consuming task that requires expertise and often heavy hand calculations. PSV Plus provides a set of routines
to quickly guide the user towards the proper determination of this relieving rate, by suggesting typical parameters and
procedures to be considered, in addition to calculation methods:

  • Fire Load calculations
    PSV PlusTM eliminates the need to perform any fire load related calculation. The options available will allow to calculate
    fire loads for both Wetted and Unwetted vessel surface cases. The fire load will then depend on selected Vessel
    geometry, its dimensions and elevation and fluid latent heat. Up to three vessels can included as contributors to the
    total fire load calculation.
PSV
TM
Process Software for Pressure Relief Valves Calculation and Design
Plus
INLET AND OUTLET RIGOROUS LINES SIZING

Inlet and outlet lines sizing routines for single and two-phase flow patterns are also included in the software for proper sizing
after safety relief valve orifice has been calculated and selected. PSV PlusTM will automatically check that the specified back
pressure of the valve is consistent with the one calculated across the outlet line and will alert the designer in case of improper
valve selection, based on the back pressure to upstream pressure ratio criteria.

Inlet and outlet lines sizing is also checked against the pressure drop and velocity criteria commonly used by engineers. The
option of sizing the outlet line for sonic flow condition is also available.

A calculation form is provided for easy and quick calculation of inlet / outlet piping equivalent length, in case a detailed
calculation is required by the user.
ON-LINE GUIDE AND QUICK START TUTORIAL

PSVPlus is provided with an online help and a comprehensive quick start tutorial section that will guide the user through
main software capabilities.

One-hour self-training, using this tutorial, will be sufficient to an experienced professional to achieve a  satisfactory use of
the software.

Technical reference and background is also provided in the manual.
MAN-HOURS REDUCTION AND JOB QUALITY IMPROVEMENT

PSVPlus has proved to be effective in saving man-hours up to 70% for the pressure safety valves calculation and process
specification / reporting activities, when compared to a spreadsheet based activity.

Enhanced job quality is also provided by the standardization of calculation codes and full data consistency among the
generated reports.
INTEGRATION WITH SMART PLANT INSTRUMENTATION
PSVPlus generated database has been designed to be compatible with Smart Plant Instrumentation application. Setting the
link between the two databases is a 'one time' process and detailed instructions are provided in the Manual.

  • Fan Failure
    In case of failure of one or more fans
    the loss of cooling or condensing may
    lead to pressure increase in the
    system and subsequent opening of
    Pressure Safety Valve. Determination
    of the relief load is then achieved
    through typical parameters.

  • Reflux Failure
    Failure of a column top or side reflux
    causes pressure increase in the
    system as higher vapor rate than
    normal will be present into the
    column. Relieving rate determination is
    achieved through typical parameters.

  • Exchanger Tube Rupture (Single and
    Mixed Phases)
    When the differential pressure
    between the two sides of a S&T heat
    exchanger is high, the tube rupture
    contingency is a main concern since,
    should it occur, the low pressure side
    may be affected
    by pressure higher than design one.
    Determination of relieving load for this
    case is accomplished through complex
    calculation routines, that are available
    in PSV Plus.

  • Thermal Expansion
    Should a liquid filled portion of piping
    or equipment be blocked-in under
    solar radiation or any other heat
    source, this will cause pressurization
    due to specific volume change of the
    liquid. Calculation of relieving rate can
    be easily calculated through PSV Plus
    routines.

  • General Power Failure, Cooling
    Water Failure, Fire, Blocked Outlet,
    etc…
    The other emergency scenario’s can
    be selected from a comprehensive list.
    However no standard calculation
    method exists for them and the
    Process Engineer will have to calculate
    on his / her own. PSV Plus provide
    facilities to record all the
    considerations made to achieve the
    relieving rate figure, for later use or
    documenting purposes.
  • Control Valve Failure
    A detailed calculation form is
    available to rigorously calculate the
    consequences of the complete
    opening of a control valve.
    Calculation routines take into
    account control valve CV calculation,
    if not
    already available, and will cover also
    the gas break-through situation, that
    is one of the most frequent scenario
    encountered.