Customization of pressure-swing adsorbtion systems
An in-house industrial-scale PSA system can be precisely customized to meet the specific needs of an application. As an example,
systems provided by Parker Hannifin's Filtration and Separation Division (Baltimore, MD) include a number of features to ensure
that the optimum system is provided (see Figure 2). These features are described below.
Figure 2: An in-house industrial-scale pressure-swing-adsorption system. (FIGURES COURTESY OF INDUSTRIAL NITROGEN PRODUCTS,
FILTRATION AND SEPARATION DIVISION, PARKER HANNIFIN)
An energy-efficient control system.
If the demand for nitrogen decreases, the time for the production cycle increases. This leads to a longer period between desorption
steps, which reduces the amount of energy required to compress the feed stream. An additional benefit is that the seat life
of the process valves is extended as they are not cycling as frequently.
Differential pressure-bed monitoring.
High-bed differential pressure-bed monitoring protects the beds from excessive differential pressure during feed and equalization
Optimal bed-size ratio.
The length-to-diameter ratio of each bed is sized to provide superb performance. This prevents feed-gas channeling, which
leads to an inefficient separation.
Flanged bed covers.
The CMS bed is accessed via an ASMEflanged cover to allow for rapid reloading of the vessels (some systems use welded covers).
The use of a flanged cover for the chamber makes it easier to access the PSA bed as the cover can simply be lifted by an operator.
If, however, the cover is welded on, it is necessary to undo the weld and then reweld it in position.
Advanced valve design.
A valve leak-check system is incorporated in the valve to determine valve-seat health without having to remove the valves
from the system. The valve leak check can be performed in less than 10 min.
If nitrogen is no longer needed (e.g. the storage tank is full) the system will automatically shut down and turn off the compressor,
saving power and reducing wear and tear on the system. Once the system determines a need for the generation of additional
nitrogen, it will automatically start back up and seamlessly resume nitrogen production.
Routine operation of a dual-bed nitrogen-generation system
A dual-bed nitrogen-generation system can operate on a 24-hour, 7-day basis with a minimum of user interaction. Once the operational
parameters are established, the system automatically responds to changes in the nitrogen demand to minimize power consumption
and valve usage.
Required maintenance of an in-house nitrogen generation system
A significant benefit of an in-house PSA system is that an extremely low amount of maintenance is required. System maintenance
involves periodic checking and replacement of filter cartridges (if necessary), checking and repacking the valves, and changing
the oxygen analyzer fuel cell. In normal operation, the system's filter cartridges are checked every three months and replaced
every six months. The valves are checked every six months and rebuilt with new O rings annually. The oxygen analyzer fuel
cell should be replaced every year.
Economic benefits of nitrogen generation via PSA technology
Although the base cost of nitrogen generated via fractional distillation may be quite low, the overall cost of supplying the
requisite gas to a pharmaceutical manufacturing facility may be significantly higher due to transportation issues. As an example
of this point, the relative cost for bulk liquid nitrogen on an island such as Puerto Rico (which has a very limited local
supply of bulk liquid nitrogen) is significantly higher than in an industrialized, metropolitan area such as New Jersey. In
addition to the transportation costs, the end-user of nitrogen generated via fractional distillation must include a broad
range of additional costs such as the acquisition and maintenance of the storage facility, pipes to get the gas to the final
location from an external storage tank, loss of nitrogen due to venting of the storage tank, as well as the paperwork and
time required for purchasing activities. In contrast, the running cost of a PSA nitrogen generator is quite lower because
electricity for the compressor and replacement parts is all that is required.
The return on investment that can be expected from a PSA system for the generation of nitrogen is dependent on a variety of
factors and is typically less than two years; in some cases the system pays for itself in a year or less. In a typical facility,
the cost to generate nitrogen via a PSA generator is less than $0.15 per hundred cubic feet (CCF). This includes annual maintenance
costs, replacement parts and electricity. In comparison, the average cost of liquid nitrogen in areas where it is not readily
available, or if the facility is captive to a single supplier, can range up to $1 per CCF.
An additional economic benefit of the use of an on-site system for the generation of nitrogen is the fact that the user is
assured that the gas will be available when required. In contrast, obtaining nitrogen from an external source involves the
risk that it may not be received when required due to problems at the external source or transportation difficulties, which
could lead to a costly manufacturing delay.