Project Background
The revamped oil platform originally operated with TEG and amine losses as well as constant condensate accumulation within some compressors, which forced frequent stops.
All original inlet devices were deflecting baffles. These baffles when operated under high gas velocity and momentum cause high condensate shear stress and increase fine droplets content – compromising mist eliminators global collection efficiency.
All vessels employed vane type mist eliminators. These mist eliminators are specifically recommended for low to moderate pressure operations with high fouling rate, but are equipment with lower collection efficiency when compared to other mist elimination devices, in special under high pressure conditions.
Therefore the original system inlet devices generated finer mist droplets which were inefficiently captured by the mist eliminators, justifying all observed operational problems.
This Revamp was developed with Clark Solutions design, manufacture and installation support in order to achieve better operational results, increasing uptime and production capacity.
Clark Solutions Revamp
Clark Solutions with its experience in mist eliminators and in capacity increase supplied all internals for the safety gas, the three compression stages for all compression trains A/BC, the TEG tower and all Amine towers A/B/C – a total of 14 oil platform vessels.
The adopted systems employed Evenflow® inlet devices, MaxiMesh® coalescer and HeliFlow® mist eliminators and were designed to operate under different loads and pressures for all 14 vessels, varying from 2.000.000 to 6.000.000 Nm³/d from 8 to 70 bar.
Not only were the internals customized to address each vessel particularities, but also were the support systems. Clark Solutions design weldless support systems which allow lower installation time and withdraw vessel recertification requirements.
Figure 1. Supplied Internals drawings for one of the 14 vessels debottlenecked during Revamp
Evenflow® Inlet Device
Inlet momentum can be evaluated with inlet velocity and mixture density. Clark Solutions select, design, manufacture and install inlet devices with recommended dimensions for each inlet momentum case.
High momentum cause droplets shear stress and compromise mist elimination global efficiency. Besides this, a high momentum hinders gas homogeneous distribution, creating preferential paths which may further reduce collection efficiency and increase collected droplet re-entrainment.
Evenflow® inlet devices of different sizes were designed in order to achieve a better gas-liquid separation within informed operational conditions to each vessel, replacing all original deflecting baffles.
For the purpose of equalizing flow (avoiding preferential paths) and perform a pre-separation (decreasing liquid load) we recommended Evenflow® inlet devices. The Evenflow® calms inlet flow, allows homogeneous distribution, separates larger droplets, minimizes droplets shear stress and lessens surge effects that may eventually occur. All these benefits have as main objectives a mist load decrease and a better gas flow distribution across all mist eliminator cross-section in order to improve droplet collection efficiency and reduce re-entrainment. Proposed internals are manufactured in order to pass through manholes.
The following image is a Computational Fluid Dynamics (CFD) simulation of one of the Revamp designed Evenflow®:
Figure 2. Evenflow® analysis with Computational Fluid Dynamics (CFD)
MaxiMesh® Coalescer
Figure 3. MaxiMesh® Coalescer with collection trough |
MaxiMesh® coalescer is a device that promotes liquid droplets diameter increase which are more easily collected and removed at the downstream mist eliminator. To achieve this coalescing effect the MaxiMesh coalescer is designed to operate in near-flooding regime.
Draining channels are positioned to remove excess liquid and admit eventual surges. All collected liquid is sent to vessel bottom through draining pipes. These coalescers also allow higher turndown, operating as pre-separators and conventional mist eliminators during reduced load. |
HeliFlow® Mist Eliminator
It was found that liquid carryover occurred mainly due to unfavorable conditions, notably very high pressures and gas densities, which compromise conventional mist eliminators efficiency. Moreover, it was verified high momentum in all vessels inlet, which do not had appropriate inlet devices.
In case of a Revamp, providing a greater operating capacity is the most appropriate way to solve liquid carryover. Heliflow® cyclones are mist eliminators that present greater capacity and, therefore, should be used in vessels that are applicable within pressure drop limits.
Cyclone type mist eliminators are recommended for compression systems as they handle high density gas and allow higher gas flow and liquid load than other conventional mist eliminators – with lower loss of efficiency due to re-entrainment.
Heliflow® operation with a MaxiMesh® coalescer offers significant flexibility and efficiency to higher gas velocities – lower diameters or higher capacities than conventional systems. The coalescer provides higher droplet diameters at the cyclone inlet, promoting higher global collection efficiency along all droplet diameter distribution.
| The gas flow after passing through both Evenflow® and MaxiMesh® is sent to a set of Heliflow® mist eliminators. The set is composed by a deck on which boxes with cyclones are positioned.
The operating principle of these cyclones is to force the gas to a rapid outwards radial flow and inertially de-entrain liquid droplets towards collection slots. Slots are positioned downstream from cyclone blades to drain collected liquid to vessel bottom through draining pipes inside each cyclone box. |
Figure 4. HeliFlow® 3D Schematic with CFD mesh |
While designing Heliflow® cyclones is important to evaluate drain pipe height with respect to pressure drop. All drain pipe heights must be higher than pressure drop equivalent height to ensure liquid will not siphon from vessel bottom through pipes during operation or surges.
All designed equipment take into account available vessel height to adequate cyclones system pressure drop to its draining and sealing pipes.
In a Revamp, cyclones offer a considerable increase in capacity and collection efficiency.
Figure 5. HeliFlow® CFD velocity profiles
Weldless Support
Figure 6. Internals 3D scheme with weldless support |
Weldless support systems were used in each vessel for the new internals installation. These weldless support systems bring several benefits:
For weldless support installation is necessary a qualified team of supervisors supplied by Clark Solutions. All support modules are manufactured in accordance to manhole sizes to guarantee easy access for all parts. |
CFD and Simulation Tools
Clark Solutions use CFD simulations and proprietary dimensioning tools to design and evaluate all manufactured and installed equipment.
Figure 7. Gas Streamlines
CFD simulations may support efficiency and pressure drop evaluation by means of pressure profile and particle tracing along streamlines. Velocity profiles enable homogeneous gas flow studies.
Figure 8. Pressure and velocity profiles
Efficiency curves assist in equipment comparison and when coupled with droplet size distributions and condensate rate may infer a global collected liquid rate.
Figure 9. HeliFlow® estimated efficiency and inlet-outlet droplet distribution curves
Results
The main Clark Solution Revamp results were the significant decreases in condensate accumulation inside compressors.
The Revamp also reduced TEG and Amine losses.
Installation time was reduced due to the Clark Solutions weldless support system.
Enhancements in the inlet devices to Evenflow® with an upgraded mist elimination system composed of MaxiMesh® coalescers and Heliflow® mist eliminators achieved all efficiency and capacity objectives.
The platform is operating longer than a year without the need to stops due to condensate accumulation inside compressors and with a higher available capacity.
HELIFLOW® is a registered trademark for Clark Solutions in Brazil.
MAXIMESH® is a registered trademark for Clark Solutions in Brazil.
EVENFLOW® is a registered trademark for Clark Solutions in Brazil.