last reactor. Practical operating constraints have led to a historical range of operating pressures from 345 to 3,450 kPa (50–500 psig). As a feed passes through the
heaters, reactors, and catalyst beds, the overall pressure drop can be as large as
50–60 psig. It is best to minimize the pressure drops in the unit as much as possible
so as to operate all the reactors at a lower pressure.
The main benefit of lower pressure is increased aromatic, hydrogen, and reformate yields and decreased temperature requirement to achieve a target product
quality (utility savings). However, lower pressure shortens the catalyst cycle
because of the increased catalyst coking rate. The higher catalyst deactivation
rate associated with operating in the 50–150 psig pressure range requires continuous catalyst regeneration.
Temperature and Space Velocity
The primary control for product quality in catalytic reforming is the temperature of
the catalyst beds. Reforming catalysts are capable of operating over a wide range of
temperatures. By adjusting the heater outlet temperatures, a refiner can change the
octane of the reformate and the quantity of aromatics produced.
The reactor temperature is usually expressed as the weighted average inlet
temperature (WAIT). The WAIT is the summation of the product of the fraction
of catalyst in each reactor multiplied by the inlet temperature of the reactor.
Typically, SR units operate over a WAIT range of 490–525
C (914–977
F),
while continuous units operate over a WAIT range of about 525–540
C
(977–1,004
F). CCR Platforming units can operate at even higher temperatures
to produce a more aromatic-rich product.
Because the main reforming reactions are endothermic, there is a significant
drop in temperature along the catalyst beds. The temperature drop is largest in the
first reactor position due to the dehydrogenation of the naphthenes contained in the
naphtha feed. The temperature drop is still substantial in the second reactor position
but smaller for each successive reactor. It is convenient to also define a weighted
average bed temperature (WABT) which accounts for the temperature drops.
The WABT is the summation of the weight fraction of catalyst in a bed multiplied
by the average of the inlet and outlet bed temperatures.
The amount of naphtha processed over a given amount of catalyst over a set length
of time is referred to as space velocity. Space velocity corresponds to the reciprocal of
the residence time or time of contact between reactants and catalyst. Since most
refiners define their charge rate by volume such as barrels, it is most common to
define a liquid hourly space velocity (LHSV, h
À1
) which is calculated by dividing the
volumetric charge rate per hour by the total volume of reforming catalyst in the
reactors. The typical commercial LHSVs range from about 1 to 3. Alternatively, a
weight hourly space velocity (WHSV, h
À1
) can be defined by dividing the weight of
naphtha feed per hour by the total weight of catalyst in the reactors.
The combination of space velocity and reactor temperature is used to adjust the
conversion of the naphtha feed in order to achieve the target product octane or
252
M.P. Lapinski et al.
heaters, reactors, and catalyst beds, the overall pressure drop can be as large as
50–60 psig. It is best to minimize the pressure drops in the unit as much as possible
so as to operate all the reactors at a lower pressure.
The main benefit of lower pressure is increased aromatic, hydrogen, and reformate yields and decreased temperature requirement to achieve a target product
quality (utility savings). However, lower pressure shortens the catalyst cycle
because of the increased catalyst coking rate. The higher catalyst deactivation
rate associated with operating in the 50–150 psig pressure range requires continuous catalyst regeneration.
Temperature and Space Velocity
The primary control for product quality in catalytic reforming is the temperature of
the catalyst beds. Reforming catalysts are capable of operating over a wide range of
temperatures. By adjusting the heater outlet temperatures, a refiner can change the
octane of the reformate and the quantity of aromatics produced.
The reactor temperature is usually expressed as the weighted average inlet
temperature (WAIT). The WAIT is the summation of the product of the fraction
of catalyst in each reactor multiplied by the inlet temperature of the reactor.
Typically, SR units operate over a WAIT range of 490–525
C (914–977
F),
while continuous units operate over a WAIT range of about 525–540
C
(977–1,004
F). CCR Platforming units can operate at even higher temperatures
to produce a more aromatic-rich product.
Because the main reforming reactions are endothermic, there is a significant
drop in temperature along the catalyst beds. The temperature drop is largest in the
first reactor position due to the dehydrogenation of the naphthenes contained in the
naphtha feed. The temperature drop is still substantial in the second reactor position
but smaller for each successive reactor. It is convenient to also define a weighted
average bed temperature (WABT) which accounts for the temperature drops.
The WABT is the summation of the weight fraction of catalyst in a bed multiplied
by the average of the inlet and outlet bed temperatures.
The amount of naphtha processed over a given amount of catalyst over a set length
of time is referred to as space velocity. Space velocity corresponds to the reciprocal of
the residence time or time of contact between reactants and catalyst. Since most
refiners define their charge rate by volume such as barrels, it is most common to
define a liquid hourly space velocity (LHSV, h
À1
) which is calculated by dividing the
volumetric charge rate per hour by the total volume of reforming catalyst in the
reactors. The typical commercial LHSVs range from about 1 to 3. Alternatively, a
weight hourly space velocity (WHSV, h
À1
) can be defined by dividing the weight of
naphtha feed per hour by the total weight of catalyst in the reactors.
The combination of space velocity and reactor temperature is used to adjust the
conversion of the naphtha feed in order to achieve the target product octane or
252
M.P. Lapinski et al.