Click here to load reader
Upload
gerard-b-hawkins
View
2.617
Download
27
Tags:
Embed Size (px)
DESCRIPTION
OBJECTIVES Best practices Sock Loading Unidense Pressure Drop Measurement Common Problems
Citation preview
Gerard B. Hawkins Managing Director
The aim of this presentation is to • Give an understanding of ◦ Best practices ◦ Sock Loading ◦ Unidense ◦ Pressure Drop Measurement ◦ Common Problems
Use approved drum handling techniques Do not roll drums Do not lift on forks of fork lift truck Do not stack more than 4 high - even on
pallets Protect from rain and standing water Keep lids on Do not expose to temperature extremes
Before loading • Inspect vessel for stress damage • Check conditions of thermocouples
– Document their location with respect to inlet flange or tangent line
• Check support balls for breakage or extraneous materials
• Check support grids for condition (e.g., damaged clips; grid binding)
• During charging – Use appropriate personnel protection Dust masks Gloves Full body coverage Fresh air in vessels
• Support workers in reactors with boards • Snow shoes
During charging – Use hopper or supersack with attached sock
– Ensure uniform distribution by moving sock
– Maximum catalyst freefall 3ft (1m)
– Minimum catalyst freefall 1ft (.3m)
– Helps ensure dense loading
Aim is to achieve • Same flow through each tube ◦ No hot tubes
• No bridging ◦ No hot spots
• Ultimately ◦ Minimize methane slip ◦ Extends tube life
Inspection • Check tubes for defects using LOTISTM or eddy
current etc
• Internal surfaces - Look smooth
• Catalyst support grids are in place
• Inlet and exit pigtails are not blocked
• Procedure is ◦ Only have one type of catalyst on
the steam reformer at any one time ◦ Ensure sock “rope” is longer than
catalyst tube ◦ Anchor free and of rope, or fit object
• to prevent rope falling into tube ◦ One end sealed for attachment of
lowering rope ◦ Other end folded over - 10cm (4”)
flap ◦ Calculate weight per sock to give
whole number of socks per tube
• Sock OD should be 20mm (3/4”) smaller than tube ID
• Filled sock length should be around 150cm (5’)
• Socks material is canvas, polythene or similar
• Fill socks with same known weight
• Label socks for different types of catalyst
Filling Tubes Folding Over Attaching Rope
Jerking Rope Topping Up Checking Outage
Compressed air
Inletpressure
Handvalve
Orificeplate
Catalystpressuredrop
Cam and leverto expand bung
Cam and leverto expand bung
Guidering
Catalysttube
Developed by Hydro Agri of Norway Proprietary technique available through a select number of
licensees Widely practiced - more than 260 steam reformer charges
have been loaded using this technique Leads to “denser” packing
– less pd variation more uniform gas flows
– easier procedure shorter loading time (70%)
– slightly higher pd effect on throughput - marginal
Outlet pigtail
Brushes
Catalyst tube
Catalyst drum
Charging hopper
Inlet pigtail
Move rope upwards
Aim to pack catalyst to uniform voidage Measure pd
– Not outage in tube at any one time – Not weight per tube – Not catalyst density – After 50% – After full loading
Use defined and consistent procedure throughout
Fixed flow of air (choked flow through orifice)
Mass flowrate through orifice function of ◦ upstream pressure ◦ orifice diameter (known) ◦ temperature (known)
Downstream pressure is measure of pd
• For air, the critical value of P2 is around 50% of P1
• If flow is sonic, then mass flow is constant • Resistance to flow downstream (pd) can be
read now as P2 value
P1 P2
Orifice
Flow must be sonic to obtain meaningful results ◦ requires a minimum upstream/downstream
pressure ratio ◦ check upstream pressure adequate
If using a shared air supply, monitor pressure carefully - other users can lead to a drop in supply pressure.
PD rig
Inlet pigtail
Exit pigtail
4a. Exit pigtail
Empty tube
PD rig
4b. Catalyst
catalyst
PD rig
4c. Inlet pigtail
catalyst
If too high then – suck out catalyst and recharge
If too low then – Vibrate tube – Use a soft faced hammer – Top up if outage too great
Voids Stacking
Voids
Broken Pellet
Voids Voids
-20 -15 -10 -5 0 5 10 15 20-15
-10
-5
0
5
10
15
-40-30-20-10010203040
Pressure Drop Variation (%)
Flow
Var
iatio
n (%
)
Tube
Tem
pera
ture
Var
iatio
n (°
C)
• If loading is poor • variety of flows in tubes
• Each tube has different exit temperature ◦ Each tube has a close approach ◦ Mixture of all tubes far from equilibrium ◦ Methane slip not linear with temperature ◦ Methane slip higher than it should be ◦ Tube temperature distribution ◦ Some tubes will be hot
• Therefore fail sooner ◦ Operational costs - High Slip ◦ Maintenance costs - Failed tubes
Mixed Gas Exit
Reformer
872 1602
9 16
3.9
Process Gas Exit (°C) Temp (°F)
Methane/Steam (°C) Approach (°F)
Methane Slip (% dry) Max twt (°C) (°F)
Well Balance
870 1598
2 3
3.6
891 1636
Poorly Balance
834 - 992 1533 - 1692
1 - 3 1 - 5
1.6 - 6.5
860 - 930 1580 - 1706
Charging tube
high pressure drop
Support Grid Catalyst Support
More larger particles low pressure drop
• This means that there is ◦ A high voidage at the walls ◦ A low voidage in the center
• This will cause flow mal-distribution ◦ More flow at walls ◦ Less in the centre
• Will cause a shortened life
Giraffe Necking
Tiger Tailing
“Bridging”
Settling
Not enough catalyst, or overcompaction and breakage
Outage (Pressure Drop)
Amount of vibration or hammering
Overcompacted
Correctly Settled
Two methods: – Vacuum from top Most desirable form informational standpoint Costly Difficult if catalyst pyrophoric
– Bottom dump Faster Cheaper
Nickel containing catalyst – Potential for nickel carbonyl – Formed by CO reacting with Ni – Stable below 200oC (390oF)
Use a device as illustrated below
15cms Clip
Mesh
Hose
Vacuum System