(s), over-the-fence supply, or catalytic naphtha reformer(s). Incoming hydrogen
may also be supplied by recovery unit(s).
One of the suppliers must be used as the swing unit to control the header
pressure. The other suppliers should then be base loaded or may have rates that
are set by other factors. For example, a naphtha reformer’s hydrogen production
will more often be set by the required naphtha octane and the catalyst age. You
would not normally set naphtha reformer rate just to supply hydrogen, although that
is an option.
The swing unit is usually an SMR unit that is large enough to control the fresh
hydrogen header pressure. The SMR is able to react more quickly than many other
units. An SMR does not like to be swung around too frequently, however; so, a
swing SMR may end up producing a small excess of hydrogen that is lost. One
objective is to minimize that loss.
Sour Hydrogen
Often, hydrogen is cascaded from high-pressure to low-pressure units for conservation and reuse. The hydrogen picks up H 2 S the first time it is used. Some
refineries scrub the H 2 S out of purged gases from the higher-pressure units, but
others purge sour gases.
The sour hydrogen is normally handled in a separate header. The gas from this
header can be used in lower-pressure or less severe units. It can also be used for
presulfiding or activation of hydrotreating catalysts.
Surplus hydrogen on the sour header may be cascaded to fuel gas.
Header Pressures
There are a number of strategies used to determine where to set hydrogen header
pressures during design. The philosophy described here is one of the more common
approaches.
The pressure for the fresh hydrogen header could be set at the maximum makeup
pressure required for the highest pressure user (hydrocracker or gas oil
hydrotreater), but this would mean compressing all the gas to the highest pressure
all the time. That would be wasteful.
It is similarly not optimum to just supply hydrogen at low pressure, like naphtha
reformer outlet pressure of 200–300 psig. That would mean installing compressors
at many different users or creating another header for higher pressures.
A compromise that works well is to compress and distribute the fresh hydrogen
supply at the makeup pressure required by the diesel hydrotreater (DHT). This
usually means the fresh header runs 700–1,000 psig. This eliminates the need to
compress within the DHT and most other units. It allows the DHT purge to be
cascaded to lower-pressure services. If a refinery has a hydrocracker or highpressure gas oil hydrotreater, the hydrogen for those services still requires additional compression.
Hydrogen Production and Management for Petroleum Processing
637
may also be supplied by recovery unit(s).
One of the suppliers must be used as the swing unit to control the header
pressure. The other suppliers should then be base loaded or may have rates that
are set by other factors. For example, a naphtha reformer’s hydrogen production
will more often be set by the required naphtha octane and the catalyst age. You
would not normally set naphtha reformer rate just to supply hydrogen, although that
is an option.
The swing unit is usually an SMR unit that is large enough to control the fresh
hydrogen header pressure. The SMR is able to react more quickly than many other
units. An SMR does not like to be swung around too frequently, however; so, a
swing SMR may end up producing a small excess of hydrogen that is lost. One
objective is to minimize that loss.
Sour Hydrogen
Often, hydrogen is cascaded from high-pressure to low-pressure units for conservation and reuse. The hydrogen picks up H 2 S the first time it is used. Some
refineries scrub the H 2 S out of purged gases from the higher-pressure units, but
others purge sour gases.
The sour hydrogen is normally handled in a separate header. The gas from this
header can be used in lower-pressure or less severe units. It can also be used for
presulfiding or activation of hydrotreating catalysts.
Surplus hydrogen on the sour header may be cascaded to fuel gas.
Header Pressures
There are a number of strategies used to determine where to set hydrogen header
pressures during design. The philosophy described here is one of the more common
approaches.
The pressure for the fresh hydrogen header could be set at the maximum makeup
pressure required for the highest pressure user (hydrocracker or gas oil
hydrotreater), but this would mean compressing all the gas to the highest pressure
all the time. That would be wasteful.
It is similarly not optimum to just supply hydrogen at low pressure, like naphtha
reformer outlet pressure of 200–300 psig. That would mean installing compressors
at many different users or creating another header for higher pressures.
A compromise that works well is to compress and distribute the fresh hydrogen
supply at the makeup pressure required by the diesel hydrotreater (DHT). This
usually means the fresh header runs 700–1,000 psig. This eliminates the need to
compress within the DHT and most other units. It allows the DHT purge to be
cascaded to lower-pressure services. If a refinery has a hydrocracker or highpressure gas oil hydrotreater, the hydrogen for those services still requires additional compression.
Hydrogen Production and Management for Petroleum Processing
637