– Steam systems
Adjust blowdown rates to target conductivities. This may be automatic.
Adjust BFW preheat conditions. This must be coordinated with other
conditions.
The steam system controls will normally handle changes in the plant.
Stripping conditions in the shift condensate degassing system need some
attention to ensure the CO 2 is removed. Use the system design as a
guideline to what conditions to expect.
• Shutdown
Shutdown of a hydrogen plant generally follows the same sequence, regardless
of the type of unit. The primary steps are:
– Cool reforming furnace to 1,200–1,300
F process outlet temperature.
– Stop feed, but continue steam. Stop the PSA, if present.
– Steam the catalysts for 2–6 h at 1,200
F in the reformer.
The LTS converter may be bypassed and shut down separately.
– Cool the reforming furnace with steam flow at no more than 100
F per hour
to about 800
F at the flue gas outlet from the radiant box.
During this time, inert gas flow can be reintroduced to the process, if desired.
Inert flow will help cool the HTS converter and other equipment.
If the unit has a methanator, it should be removed from the flowing system
and separately purged at least five times with nitrogen before cooling
below 400–450
F to prevent nickel carbonyl formation.
– Stop steam flow. If using inert flow, continue cooling with the inert gas. The
SMR furnace can be shut down when firing reaches minimum.
– Purge the entire system with nitrogen to eliminate hydrogen and hydrocarbons. Test for CO in the gas. The concern is that nickel carbonyl may form at
low temperatures (<$450
F). CO must be less than 10 vppm in the system if
you are below this temperature. The methanator is especially susceptible to
nickel carbonyl and should be managed separately as noted above.
Monitoring
Table 6 provides a list of the key variables to monitor in an SMR hydrogen plant,
along with the frequency. The following discussion describes calculation of some
of these key variables. Issues around tube wall temperature monitoring in reforming
furnaces are also discussed.
Most catalyst suppliers for hydrogen plants will provide a detailed material
balance and analysis of your unit’s performance if you provide them with operating
data. Table 7 indicates the information needed to obtain a detailed performance
analysis from a supplier. You should be continually monitoring the unit yourself;
but, it is still a good idea to have a third party evaluation periodically (say
quarterly). This service is usually provided at no cost.
• Material balance
Successful monitoring of an SMR hydrogen plant process starts with a
good material balance for the plant at a point in time. The flow, composition,
604
S.A. Treese
Adjust blowdown rates to target conductivities. This may be automatic.
Adjust BFW preheat conditions. This must be coordinated with other
conditions.
The steam system controls will normally handle changes in the plant.
Stripping conditions in the shift condensate degassing system need some
attention to ensure the CO 2 is removed. Use the system design as a
guideline to what conditions to expect.
• Shutdown
Shutdown of a hydrogen plant generally follows the same sequence, regardless
of the type of unit. The primary steps are:
– Cool reforming furnace to 1,200–1,300
F process outlet temperature.
– Stop feed, but continue steam. Stop the PSA, if present.
– Steam the catalysts for 2–6 h at 1,200
F in the reformer.
The LTS converter may be bypassed and shut down separately.
– Cool the reforming furnace with steam flow at no more than 100
F per hour
to about 800
F at the flue gas outlet from the radiant box.
During this time, inert gas flow can be reintroduced to the process, if desired.
Inert flow will help cool the HTS converter and other equipment.
If the unit has a methanator, it should be removed from the flowing system
and separately purged at least five times with nitrogen before cooling
below 400–450
F to prevent nickel carbonyl formation.
– Stop steam flow. If using inert flow, continue cooling with the inert gas. The
SMR furnace can be shut down when firing reaches minimum.
– Purge the entire system with nitrogen to eliminate hydrogen and hydrocarbons. Test for CO in the gas. The concern is that nickel carbonyl may form at
low temperatures (<$450
F). CO must be less than 10 vppm in the system if
you are below this temperature. The methanator is especially susceptible to
nickel carbonyl and should be managed separately as noted above.
Monitoring
Table 6 provides a list of the key variables to monitor in an SMR hydrogen plant,
along with the frequency. The following discussion describes calculation of some
of these key variables. Issues around tube wall temperature monitoring in reforming
furnaces are also discussed.
Most catalyst suppliers for hydrogen plants will provide a detailed material
balance and analysis of your unit’s performance if you provide them with operating
data. Table 7 indicates the information needed to obtain a detailed performance
analysis from a supplier. You should be continually monitoring the unit yourself;
but, it is still a good idea to have a third party evaluation periodically (say
quarterly). This service is usually provided at no cost.
• Material balance
Successful monitoring of an SMR hydrogen plant process starts with a
good material balance for the plant at a point in time. The flow, composition,
604
S.A. Treese