EMERGENCY VESSELS BLOWDOWN SIMULATIONS

Transcription

1 EMERGENCY VESSELS BLOWDOWN SIMULATIONS

2 AGENDA INTRODUCTION TYPICAL FIRST STUDIES IN TOTAL UPSTREAM INTERNAL RULES BASED ON API METHODOLOGY STUDY RESULTS DEVELOPMENT WORK - COLLABORATION BETWEEN SIMSCI & TOTAL PROPOSED ENHANCEMENTS TO BE DONE CONCLUSION Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 2

3 INTRODUCTION Why to depressurize? Loss of control (fire, power failure, leak ) Pressurized hydrocarbons Hazard for installation and people (explosion, oil spill ) Solution: Emergency depressurization Pressure decrease leads to temperature drop because of the Joule-Thomson effect and of the liquid vaporization Hydrocarbons sent to the flare Main concerns Wall vessel temperature Vessel material to be chosen to resist low temperatures Maximum flowrate to be flared Reliable predictive simulation tools needed Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 3

4 TYPICAL DEVELOPMENT STUDIES IN TOTAL UPSTREAM Screening Conceptual studies Pre-project Project A few weeks 3 months 6 months Short time periods + Fluctuating data Calculations done internally with process simulators Longer periods + detailed studies External tools Depressurization calculations are done at early stage of the studies: The flare size or safety zones have a significant impact on the facilities layout or on a platform size. It can be of major importance in the choice of a concept. RADIATIONS Calculations are done through flaresim (softbits) software It models thermal radiation and noise footprints generated by flare systems and predicts the temperature of exposed surfaces DISPERSION Calculations are done through PHAST (DNV) software It models atmospherics dispersion to determine the safety zones. Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 4

5 INTERNAL RULES DERIVED FROM API 521 Initial conditions - Initial pressure =system design pressure - Initial temperature = MinOT (or ambiant T if lower) - Initial liquid level in the drum, the calculations shall be conducted for both LAL and LAH. The worst case shall be retained. Final conditions - P down to 8 bara or 50% of design pressure (whichever is the most stringent) in 15 minutes. For cold cases, P down to atmospheric pressure to get the right minimum temperature. Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 5

6 METHODOLOGY Two Reference tools considered in Total: Blowdown (from Imperial College of London) and LNGDYN (From Technip) not available for Total initial development studies (have to be subcontracted to ICL or Technip, which is not compatible with the initial studies planning) 4 commercial software Un m Pro/II Hy..s Dynsim Very few experimental data Comparisons to the results of reference software LNGDYN and BLOWDOWN Why do we use pro/ii for dynamic simulations? PRO/II used for performing all the process simulations in conceptual and pre-projects studies more comfortable to use the same tool. Dynsim too onerous at these early stages of a project More efficient to use pro/ii features such as controller to adjust the orifice size Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 6

7 OBJECTIVES AND RESULTS OF THE STUDY Objectives of the study Decide if PRO/II can be used in our studies by comparison of the results to those of the reference tools Determine margins to be applied on simulation results during conceptual and project studies Focuss on vessel depressurization (no multi-units were checked and no pipes) with no water phase Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 7

8 Project progress RESULTS AND WORK AHEAD Conclusions of the validation study This study exhibited relatively good predictions for pro/ii for flowrate and temperature Recommended margins: 10% on flowrate predictions and 10 C on Minimum temperature Drawbacks: Only one wall temperature, poor flexibility on vessels geometry (head types, wall thickness ), no orifice models Total and SimSci worked together to address the weaknesses of pro/ii depressurization tool. This work led to significant enhancements into pro/ii software 1. Definition of the required improvement by Total 2. Prioritization from Total 3. Reviewing of the detailed specifications issued by SimSci 4. Tests of issued versions Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 8

9 DEVELOPMENT WORK - COLLABORATION BETWEEN SIMSCI & TOTAL USABILITY Report temperature downstream the relief valve Add Depressuring Time vs. Pressure Summary to Depressuring report Indicate whether flow through valve is critical or subcritical Re-order product streams Create pseudo-streams corresponding to instantaneous vent rates at specific times Supply wall and liquid temperature profiles Documentation on depressurization unit VESSEL CONFIGURATION New Valve Mode Orifice: It will automatically detect if the flow is sonic or subsonic and use the appropriate equations. Different head type (hemispherical, flat ) Valve Policy & user control of flow rate and depressuring time Rigorous Dynamic Wetted Area calculation Support Density and thickness in Vessel Geometry Require final pressure in depressuring unit to be exactly the specified PFINAL Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 9

10 FURTHER ENHANCEMENTS PROPOSED TO BE DONE Two main concerns for Total Solid CO2 predictions: The aim is to predict accurately amounts and conditions of formation of Solid CO2 during cold Blowdown for gas with a high CO2 content Two wall temperatures: T wliq for the liquid side and T wgas for gas side T wgas T wliq We do not expect a multi equipment depressurization (Dynsim to be used in such cases) Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 10

11 CONCLUSIONS Pro/II Software is able to perform vessel depressurizations at early stages of upstream development projects Comparison were done with reference tools in Total Pro/II leads to satisfying results compared to these reference tools (appropriate margins have been defined) Software development project permitted to successfully improve Pro/II depressurization tools Further enhancements are currently studied to have a more powerful tool Emergency vessels blowdown simulations - Orlando Schneider-Electric Global Customer Conference 11