Although various gases like oxygen,
nitrogen, carbon dioxide etc. are present in enormous quantities in the
atmosphere, a significant amount of money must be spent to separate and
purify them in their gaseous or liquid form. There are many factors to be
considered for the purchase of gas plants. It is a customer's individual
choice whether he wants the gas plant in his own site or in the
manufacturer's site. Whatever the case, the basic idea is to get a good
supply of purified gases in gaseous or solid form to be used in various
industrial and commercial applications. Gas plants and gas generating
systems range from small portable units to large tonnage plants suitable for
various applications.
Instantaneous demand for industrial gases is met from several sources:
- Gas withdrawn from the on-site production plant.
- Gas withdrawn from elevated gas storage vessels
- Gas withdrawn from distribution lines
- Additional gas generated by vaporizing stored liquid.
Why cryogenic plants?
Cryogenic process is used in gas plants to generate liquefied product. This
is used either for plant backup or for use in very low temperature
applications like food freezing. Cryogenic process is the most preferred
technique for the large sized plants. Cryogenic separations of air are most
cost effective at higher production rates. Cryogenic processes are used
exclusively by most manufacturers when gaseous product requirements are more
than 100 tons per day. Very good economics is achieved when a user's gas
demand is 50 tons per day or more and there is a potential local market for
merchant liquid products. Merchant plants co-producing gas products provide
economies of scale and a very good production backup to the on-site user due
to the huge quantities of liquid that will be stored on site to support
merchant liquid deliveries.
Why non-cryogenic plants?
Non-cryogenic processes are preferred for small sized plants. They are
economical processes when it is not necessary to produce very high purity
product. They are capable of producing relatively high purity gas(for
example, nitrogen) but then operating costs and capital go up with purity.
In some cases it is economical to make 99.9% or higher purity nitrogen by
first using a PSA to produce 99.5% purity nitrogen and then using a de-oxo
unit to remove the residual oxygen. Oxygen purity produced form
non-cryogenic process is generally less than 95%, with 90 - 93% the most
common purity target. That is why this technique is preferred at relatively
low production rates.
Required delivery pressure
The required delivery pressure affects the selection of the optimal plant.
It is advisable not to over-specify the required delivery pressure. Lower
pressure product is less expensive in almost all industrial gas plants.
Different process cycles will produce different gases at quite different
pressures. It is worth knowing the process simplicity, the trade-offs among
capital cost, and operating cost for various configurations. Oxygen
compression equipment is generally very expensive. Plants that produce
product at the required delivery pressure is always better than those that
require a product compressor.
Features
There are many types of industrial gas plants available like as follows:
- Cryogenic plant
- Non-cryogenic plant
- Single product plant
- Multi-product plant
- High-purity plant
- Lower-purity plant
Which type of plant is the best choice for a given application depends
on various factors, like as follows:
- Supply pressure requirement
- Product purity requirement
- The cost of power at the site
- Maximum flow rate needed
- Whether usage is steady or not, continuous or not.
- Low investment costs
- Low energy consumption
- High reliability
- Long lifetime
- Production rate
Buying
Tips
