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Typical controlled variables Plant Data analysis Approach to equilibrium Prediction of remaining catalyst life Tube wall temperature measurement
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Normal Operation of Steam Reformers on Hydrogen
PlantsBy:
Gerard B. HawkinsManaging Director, CEO
Contents
Typical controlled variables Plant data analysis Approach to equilibrium Prediction of remaining catalyst life Tube wall temperature measurement
Typical Controlled Variables
Process gas exit temperature Process gas and steam inlet temperature Steam/carbon ratio Process pressure Furnace parameters
• Air preheat temperature• Excess air
Exit
Met
hane
Slip
(mol
% D
ry)
CatalystActivity
40%
200 %
Plant Rate
130%
80%
ExitPressure
-1 bar+1 bar
ExitTemp(oC)
-10-20
+20+10
SteamRatio
-10%-8%
+8%+10%
5
4
3
2
1
0
Reformer Optimization : Hydrogen Reformer(Top-Fired) Exit Temperature 856oC (1573oF)
Note relatively small changes in exittemperature or steam to carbon ratio can have significant effect on exit Methane slipCatalyst activity has relatively less impact
CatalystActivity40%
60%
80%
150%200%
ExitTemp(oC)
+10-20
SteamRatio
+10%
-10%
ExitPressure
-1bar
+1bar
Plant Rate
120%
110%
90%80%
8
6
4
2
Met
hane
-Ste
am A
ppro
ach
Tem
pera
ture
(oC
)Reformer Optimization : Hydrogen Reformer(Top-Fired) Exit Temperature 856oC (1573oF)
Catalyst activity has relatively more impact on methane-steam approach to equilibrium temperature
Max
imum
Tub
e W
all
Tem
pera
ture
o C (o
F)
CatalystActivity40%
200%60%
Plant Rate
110%90%80%
120%
ExitTemp(oC)
-10
-20
+10
+20
SteamRatio
(Small effect)
890(1634)
880(1616)
870(1598)
860(1580)
850(1562)
ExitPressure
(Small effect)
Reformer Optimization : Hydrogen Reformer(Top-Fired) Exit Temperature 856oC (1573oF)
If exit temperature remains constant, then catalyst activity has relatively more impact on maximum tube wall temperatures
Monitoring Operations Furnace Inspection
• tube appearance• refractory condition
external hot-spots• burns
flame characteristics Steam reformer exit temperature measurement
• subheader/pigtail temp, measurements burner trimming
Feedstock purification performance sulfur/chlorides etc
Hot Band Hot Tube SettlingGiraffeNecking
TigerTailing
Reformer Tube Appearance
Contents
Typical controlled variables Plant data analysis Approach to equilibrium Prediction of remaining catalyst life Tube wall temperature measurement
Plant Data Analysis Important to cross-check measured data
• gas compositions inlet steam reformer exit steam reformer exit shift reactors(s)
• pressures/temperatures at these points• flowrates
recycle hydrogen hydrocarbon feedstocks steam (need also steam/BFW HTS feed
quench) fuel & air
Plant Data Analysis
Match measured plant data with heat/mass balance• if good match, then data accurate• if poor match, then errors in plant data
Total plant data computer fitting program• can use product rates and compositions etc for
cross-checking of data• can suggest likely sources of measurement error
Plant Data Analysis Total plant data fitting
• CO conversion across shift converter(s) temperature increase very accurate due to
multiple thermocouples cross-checks CO analysis AND steam rate
• Product rate/composition (methanator exit or PSA product and offgas) cross-checks feed rate, steam rate and
methane in reformer exit analysis• Methanator temperature rise
cross-checks CO slip from LTS and CO2 slip from CO2 removal system
Steam ReformerFeed flow (Nm3/hr)Steam flow (tonne/hr)Exit gas temperature (oC)Exit gas composition (mol % dry)
H2N2CH4COCO2
Exit gas flow (Nm3/hr)Steam : dry gas ratioEquilibrium temperature (oC)Approach to M/S equilb.(oC)Steam : carbon ratio
MeasuredValue1975
11.2750.0
65.27-
4.659.0221.05
7.009
Best FitValue2459
11.1765.0
71.370
3.238.6316.778634
1.1745755.59.5
5.575
PercentageError24.5
-1.11.4
-9.3-
30.54.320.3
Plant data Verification - Poor Fit
Plant Data Verification - Poor Fit
Poor fit Areas to check
• feed flowrate• exit methane• exit CO/CO2
Feed flowrate originally quoted as 1.156 tonne/hr naphtha- Revised to be 1.59 te/hr naphtha
Plant Data Verification - Revised Fit
Steam ReformerFeed flow (Nm3/hr)Steam flow (tonne/hr)Exit gas temperature (oC)Exit gas composition (mol % dry)
H2N2CH4COCO2
Exit gas flow (Nm3/hr)Steam : dry gas ratioEquilibrium temperature (oC)Approach to M/S equilb.(oC)Steam : carbon ratio
MeasuredValue2644
11.2750.0
65.27-
4.659.0221.05
5.244
Best FitValue2554
11.2758.0
71.330
3.238.6816.768954
1.1384758.1
05.442
PercentageError-3.4
0.30.8
-9.3-
30.43.820.4
Plant Data Verification - Revised Fit Better fit for flowrate Significant error still on reformer exit gas
analysis CH4
CO/CO2
Methane slip originally quoted as 4.65 mol %(dry)- Revised to 3.56 mol % (dry)
Plant Data Verification - Final Fit
Steam ReformerFeed flow (Nm3/hr)Steam flow (tonne/hr)Exit gas temperature (oC)Exit gas composition (mol % dry)
H2N2CH4COCO2
Exit gas flow (Nm3/hr)Steam : dry gas ratioEquilibrium temperature (oC)Approach to M/S equilb.(oC)Steam : carbon ratio
MeasuredValue2644
11.2750.0
69.86-
3.568.2418.34
5.244
Best FitValue2554
11.2758.0
71.330
3.238.6816.768954
1.1384758.1
05.442
PercentageError-3.4
0.30.8
-2.1-
9.45.38.6
Plant Data Measurement - Problem Areas
Sampling/analysing exit gas compositions Exit temperature from reformer Flow measurement
Exit Gas Composition
CO shift reaction can occur if not quench cooled quickly
CO2 may dissolve in water• dry gas analysis!
Analysis of sample must be taken in the same time frame as the process data recording
Exit Reforming Catalyst
(mol % dry)
"Shifted" SampleAnalysis
(mol % dry)CH4 4.4 4.2CO 13.8 10.3CO2 8.6 11.4H2 71.9 72.8N2 1.3 1.3
CO>CO2 CO<CO2
“Shifting” in Gas Sample
Note also reduction in CH4
Exit Temperature
Heat/mass balance requires temperature exit catalyst
Plant temperature measurement often at inlet to waste heat boiler• large heat losses possible
outlet pigtails, headers, transfer mains
Top-fired : 10-20oC (18-36oF) heat loss
Side-fired : 25-35oC (45-63oF) heat loss (Air ingress at base of steam reformer can lead to further cooling)
Note that hydrocarbon composition variationsmay effect the metered accuracy and also the
steam/carbon ratio calculation
Flow Measurement
Hydrocarbon feedstock generally high accuracy• “costing” meter• multiple feed streams may be less accurate
Steam flow often less accurate• error in steam/carbon ratio can have a
significant effect on heat/mass balance
Plant Data Analysis Best to record trends
• relative changes partially remove measurement errors
Monitor monthly/quarterly• measures of catalyst activity
methane slip assuming constant operating conditions
• approach to equilibrium• tube wall temperature
Plant Data Analysis
00.5
11.5
22.5
33.5
44.5
5
0 10 20 30 40
Met
hane
Slip
(mol
%)
Months on line
Plant Data AnalysisN
atural Gas R
ate (x1000 N
m3/hr)8
6
4
2
Contents
Typical controlled variables Plant data analysis Approach to equilibrium Prediction of remaining catalyst life Tube wall temperature measurement
Approach Tms = Actual T gas - Equilibrium T gas (A.T.E.)
Measured Calculated
• Measure of catalyst activity• If ATE = O, system at equilibrium• As catalyst activity decreases, ATE increases
Approach to EquilibriumCH4 + H2O CO + 3H2⇔
Calculation of Approach to Equilibrium
1. Take gas samples and record steam reformer exit temperature
2. Calculate wet reformer exit composition- Hydrogen atom molar balance (inlet/exit)- Calculate steam in exit gas- Convert exit dry gas to wet gas composition
3. Calculate equilibrium temperaturecorresponding to this exit composition
- Use tables or equations4. Calculate approach to equilibrium
Contents
Typical controlled variables Plant data analysis Approach to equilibrium Prediction of remaining catalyst life Tube wall temperature measurement
Case Study
Terraced wall reformer How much longer will catalyst last (from
Jan’08) Change-out when?
• September ‘08• April ‘09• September ‘09
11/Apr/06 03/Oct/06 27/Mar/07 18/Sep/07 12/Mar/08
1,320
1,340
1,360
1,380
1,400
1,420
6
7
8
9
10
Date
Met
hane
Slip
(m
Outlet Temperature Methane Slip
Steam Reformer Performance
GBH Enterprises Ltd.
10/Feb/04 22/Dec/05 02/Nov/05 12/Sep/06 24/Jul/07 04/Jun/080
Design EOR
Design SORCatalyst On- line: Oct ‘02
01/Apr/03
10
20
30
40
Date
App
roac
h to
Equ
ilibr
ium
(oF)
Catalyst Performance Monitoring
GBH Enterprises Ltd.
1,300
1,400
1,500
1,600
1,700
Date
01/Apr/05 26/May/06 20/Jul/07 12/Sep/08 06/Nov/09
Design temperature
Tube wall temperatures (Top)
Tube wall temperatures (Bottom)
Tube Wall TemperaturesTu
be W
all T
empe
ratu
re (o
F)
GBH Enterprises Ltd.
0 0.2 0.4 0.6 0.8
1260
1360
1460
1560
Fraction down Tube (%)
Tube Wall Temperature Process Gas
Delta T
1
Tube Wall Temperatures
GBH Enterprises Ltd.
Bottom minus Top
01/Apr/06 26/May/07 20/Jul/08 12/Sep/08 06/Nov/090
20
40
60
80100
120
140-9oF/year
Tube wall Temperatures
Date
GBH Enterprises Ltd.
June 06 June 07 June 08 Sep 08 Sep 09
Exit CH4 (mol% dry) 7 7 7 7 7
Exit Temp oC(oF)
787(1432)
789(1452)
795(1463)
795(1463)
795(1463)
Max Tube Temp oC(oF)
829(1524)
831(1528)
838(1540)
838(1540)
838(1540)
M/S Equilib. Approach oC(oF)
10(18)
12(22)
13(23)
14(25)
15(27)
Steam Reformer Data
Looks OK to September ‘09 BUT……..….
0 0.2 0.4 0.6 0.8 1500
600
700
800
900
Fraction from inlet of tube
Carbon Formation Catalyst ageing
New catalyst
Carbon Formation
GBH Enterprises Ltd.
Activity Decay Factor Need to consider carbon formation
• Accurate model of catalyst activities needed to correctly simulate catalyst ageing
Take data at different times and calculate relative activity• for terraced wall reformer
(i) top 30% slowly poisoned (ii) middle 30% very slowly poisoned (iii) bottom 40% sinters very slowly
(i) and (ii) account for delta T(iii) accounts for increased approach
GBH Enterprises Ltd.
Jan 02
May Sep Jan 03
May Sep Jan 04
May Sep Jan 05
May Sep0
50
100
150
200
250
Today September‘04
September‘05
Carbon margin
Date
Car
bon
Mar
gin
(oF)
Carbon Margin with Time
GBH Enterprises Ltd.
Activity(arbitrary)
Time (years)
Carbon forming region
Initial sintering
"Stable" activity
Margin
Period where carbon can be formed at anytime due to variation in process conditions
Catalyst Deactivation (Schematic)
GBH Enterprises Ltd.
Conclusions #1
In terms of M/S Approach and Tube Wall Temperatures, can run till September ‘05
Concern about carbon margin from April ‘05 onwards• options
change April ‘05 - CHOSEN OPTIONOR run with spare on site and change
September ‘05
GBH Enterprises Ltd.
Conclusions #2
• Sometimes difficult for operator to predict change-out requirement– Couldn’t rely on M/S Equilibrium Approach
and Tube Wall Temperature trending– Needed complex reformer simulation
• HOWEVER, recording of historic data from start-of-run conditions allowed accurate assessment by the catalyst vendor– Take data from SOR!
GBH Enterprises Ltd.
Contents
Typical controlled variables Plant data analysis Approach to equilibrium Prediction of remaining catalyst life Tube wall temperature measurement
GBH Enterprises Ltd.
Importance of Tube Wall Temperature Measurement
Need accurate information• Tube life !• Artificial limitation on plant rate
GBH Enterprises Ltd.
Tube
Life
(Yea
rs)
850(1560)
900(1650)
950(1740)
1000(1830)
0.10.2
0.5
1
2
5
1020
Design
Effect of Tube Wall Temperature on Tube Life
Temperature oC (oF)
+ 20oC+ 36oF
GBH Enterprises Ltd.
Tube Wall Temperature Measurement
Contact• surface Thermocouple
“Pseudo-contact”• Gold Cup Pyrometer
Non-contact• disappearing filament• infra-red optical pyrometer• laser pyrometer
GBH Enterprises Ltd.
Surface Thermocouples
Continuous measurement, by condution “Slotting” can weaken tube wall Spray-welding leads to high readings Short, unpredictable lives (6-12 months)
Not commonly used for steam reformer tubes
GBH Enterprises Ltd.
Disappearing Filament Hand held instrument Tungsten filament superimposed on
image of target Current through filament altered until it
“disappears” Current calibrated to temperature Range 800-3000oC (1470 - 5430oF)
Very operator sensitiveLargely displaced by IR
GBH Enterprises Ltd.
Infra-red Pyrometer
Easy to use Need to correct for
emissivity and reflected radiation
Inexpensive
GBH Enterprises Ltd.
Radiation Methods
Measure emitted energy at given wavelength Use Planck’s Law to give temperature Correction factors needed
• target emissivity real versus black body
• reflected radiation
GBH Enterprises Ltd.
Tw
"e" is the emissivity of the tube
Target TubeTt
Refractory Wall
MeasuredTemperature
Tm
Flame Tf
e
The Effect of Reflected Radiation from Target Surroundings
Measured True Averagedtarget target background
temperature temperature temperature
e = emissivityr = reflectance
= (1-e)
Temperature Correction
E (Tm) = e E (Tt) + r E (T’w)
GBH Enterprises Ltd.
0.7 0.75 0.8 0.85 0.9 0.95 1
Difference in wall and target temperature oC (oF)
300
200
100
Deg C Deg F(540 F)
(360 F)
(180 F)
200
150
100
50
0
392
302
212
122
0
Target Emissivity
Error in measured tube temperature
Theoretical Effect of Wall Temperature(0.9 micron pyrometer)
GBH Enterprises Ltd.
Laser Pyrometers
Laser pulse fired at target and return signal detected
Can determine target emissivity Must correct for background radiation High speed selectivity Very accurate for flat surfaces
GBH Enterprises Ltd.
TUBE
Laser Pyrometer
Laser Pyrometer - Angle of IncidenceScattered laser pulse
GBH Enterprises Ltd.
Gold Cup Pyrometer
Excludes all reflected radiation Approximates to black body conditions High accuracy/reproducibility But…..
• limited access• awkward to use
GBH Enterprises Ltd.
TubeFurnace Wall
WaterCooling
ToRecorder
Gold CupLance
*
Gold Cup Pyrometer
GBH Enterprises Ltd.
Accurate Temperature Measurement
Combination of IR pyrometer and Gold Cup• Gold Cup allows us to calculate “e”• Full accurate survey of reformer
possible with IR
GBH Enterprises Ltd.
• Measure Tt using Gold Cup• Measure Tm and Tw using Infra Red Pyrometer• Calculate e
Calculate "e"Use IR to give Tt with measured T’w and Tm and calculated e
Accurate Temperature Measurement
E (Tm) = e E (Tt) + (1-e) E (T’w)
GBH Enterprises Ltd.
A
a (Nearby tubes)2
Background Temperature Measurement
Background Measurement for Tube A
a1
RefractoryWall
GBH Enterprises Ltd.
950
900
850
800
750
1742
1652
1562
1472
1382
Tem
pera
ture
(oC
)
Tem
pera
ture
(oF)
0 0.2 0.4 0.6 0.8 1
UncorrectedPyrometer
Corrected Pyrometer
Calculated = Gold Cup Measurements
Fraction down tube
Comparison of IR pyrometer and Calculated Tube Wall Temperature
Measurements
GBH Enterprises Ltd.
Tube Wall TemperatureMeasurement - Conclusions
IR typically reads high• top-fired reformer 32oC (58oF)• side-fired reformer 50oC (90oF)
IR with Gold Cup “calibration”• top-fired reformer 2oC (4oF)• side-fired reformer 16oC (29oF)
GBH Enterprises Ltd.
Summary Effect of operating variables on performance Plant data analysis
• fitting plant data• problem areas
reformer exit temperature flow errors sample analysis shifting
Approach to equilibrium Prediction of remaining catalyst life Tube wall temperature measurement
GBH Enterprises Ltd.