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Equi Flow Hydro
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A DECADE OF DEVELOPMENT Ten years of R&D in one of the most difficult regimes of all, mixed-phase flow through catalyst beds, has enabled nearly-ideal fluid distribution to be obtained in hydrogenation reactor catalyst beds. If distribution is less than ideal, the following can be expected: • High radial temperature differentials (Radial ΔTs). These cause unsatisfactory catalyst activity in low temperature zones preventing even the most active catalysts from achieving maximum long-term effectiveness. • Low selectivity due to improper hydrogen distribution/diffusion between vapor and liquid phases. Low hydrogen concentrations lead to oligomer formation while high hydrogen concentrations lead to over-hydrogenation of desired olefins. • Low stability associated with high temperature zones. Premature catalyst fouling can occur. Under these conditions, economic performance drops: this means lower yields, shorter cycle lengths, higher recycle flows, more off-specification product, higher feed and utility expense, CO 2 emissions increase. Some sophisticated techniques were employed to understand and avoid the causes of poor distribution and to find optimum solutions. These include: • Glass mock-ups for simple systems evaluation • Modeling • Computational Fluid Dynamics • X-Ray Tomography In the latter technique, X-rays traverse reactor bed cross-sections to detectors for observation of gas and liquid phase distributions. X-Ray tomography equipment used in flow studies The development effort culminated in EquiFlow Hydro distributor trays, a series of application-specific high-efficiency trays designed for specific flow regimes encountered in selective hydrogenation reactors: up flow, downflow in separate phases, downflow in mixed phases and liquid quench trays. THE RESULT: EQUIFLOW HY TRAYS Upflow Hy-Up Hy-Up H 2 (G) HC (L) Hy-Sep Hy-Sep H 2 (G) HC (L) Downflow Mixed Phases Hy-Mix Hy-Mix H 2 (G) + HC (L) Hy-Quench Hy- Quench H 2 +HC (G/L) HC (L) Upflow Hy-Up Catalytic Bed Hy-Up H 2 (G) HC (L) Hy-Sep Catalytic Bed Hy-Sep H 2 (G) HC (L) Downflow Mixed Phases Hy-Mix Catalytic Bed Hy-Mix H 2 (G) + HC (L) Hy-Quench Catalytic Bed Hy- Quench H 2 +HC (G/L) Catalytic Bed HC (L) Flow distribution using the conventional distribution tray illustrated below is clearly not uniform, unlike that of the EquiFlow installation where flow distribution is nearly homogeneous. Red coloration in the tomographs EquiFlow ® Hydro Trays NEAR-IDEAL FLOW DISTRIBUTION IN HYDROGENATION REACTORS
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Equi Flow Hydro
Transcript of Equi Flow Hydro
A DECADE OF DEVELOPMENT
Ten years of R&D in one of the most difficult regimes of all, mixed-phase flow through catalyst beds, has enabled nearly-ideal fluid distribution to be obtained in hydrogenation reactor catalyst beds. If distribution is less than ideal, the following can be expected: • High radial temperature differentials (Radial ΔTs). These cause unsatisfactory catalyst activity in low temperature zones preventing even the most active catalysts from achieving maximum long-term effectiveness. • Low selectivity due to improper hydrogen distribution/diffusion between vapor and liquid phases. Low hydrogen concentrations lead to oligomer formation while high hydrogen concentrations lead to over-hydrogenation of desired olefins. • Low stability associated with high temperature zones. Premature catalyst fouling can occur. Under these conditions, economic performance drops: this means lower yields, shorter cycle lengths, higher recycle flows, more off-specification product, higher feed and utility expense, CO2 emissions increase. Some sophisticated techniques were employed to understand and avoid the causes of poor distribution and to find optimum solutions. These include: • Glass mock-ups for simple systems evaluation • Modeling • Computational Fluid Dynamics • X-Ray Tomography
In the latter technique, X-rays traverse reactor bed cross-sections to detectors for observation of gas and liquid phase distributions.
X-Ray tomography equipment used in flow studies
The development effort culminated in EquiFlow Hydro distributor trays, a series of application-specific high-efficiency trays designed for specific flow regimes encountered in selective hydrogenation reactors: up flow, downflow in separate phases, downflow in mixed phases and liquid quench trays.
THE RESULT: EQUIFLOW HY TRAYS
Upflow
Hy-Up
Catalytic
Bed
Hy-UpH2 (G)
HC (L)
Hy-Sep
Catalytic
Bed
Hy-Sep
H2 (G)HC (L)
DownflowMixed Phases
Hy-Mix
Catalytic
Bed
Hy-Mix
H2 (G) + HC (L)
Hy-Quench
Catalytic
Bed
Hy-Quench
H2+HC (G/L)
Catalytic
Bed
HC (L)
Upflow
Hy-Up
Catalytic
Bed
Hy-UpH2 (G)
HC (L)
Hy-Sep
Catalytic
Bed
Hy-Sep
H2 (G)HC (L)
DownflowMixed Phases
Hy-Mix
Catalytic
Bed
Hy-Mix
H2 (G) + HC (L)
Hy-Quench
Catalytic
Bed
Hy-Quench
H2+HC (G/L)
Catalytic
Bed
HC (L)
Flow distribution using the conventional distribution tray illustrated below is clearly not uniform, unlike that of the EquiFlow installation where flow distribution is nearly homogeneous. Red coloration in the tomographs
EquiFlow® Hydro Trays NEAR-IDEAL FLOW DISTRIBUTION IN HYDROGENATION REACTORS
indicates excessive flow zones while dark blue indicates insufficient flows in the tomographs.
Tomographic Cross-Sectional Images 0.5 m from Top of Bed
Conventional Chimney Tray
EquiflowTM
EquiFlow, Latest Generationof Commercial Distributors
-100 1000
Δ% of ideal flowrate
100-100 0
Δ% of ideal flowrate
Tomographic Cross-Sectional Images 0.5 m from Top of Bed
Conventional Chimney Tray
EquiflowTM
EquiFlow, Latest Generationof Commercial Distributors
-100 1000
Δ% of ideal flowrate
100-100 0
Δ% of ideal flowrate
100-100 0
Δ% of ideal flowrate
EQUIFLOW HY-UP
This tray is used in upflow reactors where hydrogen is injected into liquid hydrocarbons within the reactor. Typical applications are: • Steam cracker C3 or C4 hydrogenation finishing reactors • C4 alkyfining reactors, etc. First installed as part of a C4 hydrogenation unit revamp project in Asia, the EquiFlow Hy-Up tray enabled effluent quality to be maintained even though butadiene content in the feed was doubled from its original 0.4 wt% specification.
EQUIFLOW HY-SEP
This tray is used in downflow reactors where hydrogen is injected separately from liquid hydrocarbons into the reactor. The Hy-Sep tray is ideal for applications such as: • Main reactors in steam cracker C3 or C4 hydrogenation units • First stage hydrogenation (diolefins and alkenyl aromatics hydrogenation) reactors in pyrolysis gasoline units. The first commercial application of an EquiFlow Hy-Sep Tray reduced radial temperature excursions along the length of an existing pygas reactor by a factor of three and extended the cycle length of the first-stage hydrogenation reactor as shown below.
-15.0
-10.0
-5.0
0.0
5.0
10.0
15.0
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radial DT (before new tray) radial DT (new tray)
Radial ΔT, °C
-15.0
-10.0
-5.0
0.0
5.0
10.0
15.0
02/03/03 01/11/03 02/07/04 03/03
radial DT (before new tray) radial DT (new tray)
Radial ΔT, °C
EQUIFLOW HY-MIX
This tray is for use in downflow reactors where hydrogen is injected mixed with liquid hydrocarbons into the reactor. Typical applications are: • Main reactors in steam cracker C3 or C4 hydrogenation units • First stage hydrogenation (diolefins and alkenyl aromatics hydrogenation) reactors in pyrolysis gasoline units. • Aromatics hydrogenation units. The first EquiFlow Hy-Mix application enabled a benzene hydrogenation reactor to reduce benzene concentration in a light reformate stream to continuously less than 0.1 wt. %. This replacement tray surpassed by far the best performance (0.5 wt. %) ever achieved by the original system operating under the same operating conditions
EQUIFLOW HY-QUENCH
This tray is designed for reactors where liquid quenches are injected into liquid, mixed or vapor phases upstream of catalytic beds to control the temperature profile. Typical EquiFlow Hy-Quench applications are: - First stage hydrogenation (diolefins and alkenyl aromatics hydrogenation) reactors in pyrolysis gasoline units - Second stage pyrolysis gasoline
hydrogenation units for desulfurization and olefins removal - Vapor phase hydrotreating reactors.
The first Hy-Quench, installed in a mixed-phase reactor (cracked naphtha hydrotreating), produced a significant reduction in the reactor radial ΔTs. As illustrated below, very high initial radial ΔTs, actually increasing with quench rate, were reduced considerably by the new tray operating at high quench rate. This enabled the reactor to finally achieve target product specifications.
0
20
40
60
80
100
0 100 200 300 400 500 600 700Quench flow
Radial Delta T, °COld quench New quench
0
20
40
60
80
100
0 100 200 300 400 500 600 700Quench flow
Radial Delta T, °COld quench New quench
When a Hy-Quench tray was installed in a mixed phase reactor in a first stage pygas hydrogenation unit, the operator could then increase activity by 100% as compared to the previous distribution device. Styrene content in the product was decreased and cycle length extended.
OTHER TECHNOLOGY MUST-HAVES
EquiFlow Hydro trays are now an integral parts of the Hydrogenation technology package. All trays developed over the last years have demonstrated their efficiency in improving activity, selectivity and stability. Implementation of high efficiency trays is coupled in most cases to the Catapac™ dense loading system which maximizes the catalyst surface in a reactor (up to 25% more compared to sock loading) while ensuring homogeneous catalyst distribution throughout the bed.
Other items, associated with EquiFlow trays, are essential for top performance, such as guard beds to remove debris and chemically convert troublesome reactants upstream of the catalyst bed. For this, Axens recommends its ACT grading materials for which size and bed configurations are optimized to ensure proper distribution.
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