Nitrogen Generation on Ships: PSA or Membrane Technology?

January 19, 2018

GENERON IGS was awarded with the supply contract for Membrane based Nitrogen Generators, with a capacity 4500 m3/hr, at 95% purity, for 49,000 DWT   Stainless Steel IMO II, III Chemical and Oil Product Tankers 

GENERON is the world’s leading manufacturer of Nitrogen Generators. We manufacture both PSA nitrogen generators and Membrane nitrogen generators. GENERON® Membrane Systems make use of the superior performance of our proprietary GENERON® membrane fibers, manufactured in California, USA. GENERON® Membrane performance continues to lead the industry in terms of nitrogen flow capacity and air efficiency.  Our GENERON® PSA Systems are state-of-the-art with the highest air efficiency available, and can be operated in sequential configuration to allow minimum footprint requirement and weight.

We want to help you to decide on the right system type for your marine application. At GENERON you have the choice of a quality Membrane or PSA system made in USA (by GENERON-IGS) or a PSA made in China (by IGS-SMC).

In October 2017, GENERON was awarded a contract for the supply of (4) +(4)additional  Nitrogen Membrane Generator Shipsets; each with a design capacity of 4,500 m³/hr Nitrogen, at 95% purity, to the Chinese shipyard Hudong.

The 49,000 DWT Stainless Steel IMO II, III Chemical and Oil Product Tankers will be delivered to Norwegian owner Odfjell over a 3 year time frame.

During the bidding stage, both the ship owner and the ship constructors have gone through a detailed evaluation regarding the benefits of Membrane and PSA technologies for this nitrogen blanketing application.

Utilizing the newly developed GENERON® CP High Flow & High Efficiency Membrane Type, along with premium and innovative Tamrotor Marine Air Compressors and Dryer Solutions, it was determined that this Membrane Package offered substantial weight and footprint benefits, at the respective power consumption and overall cost.

Generally speaking, both PSA systems and Membrane systems are currently used to generate nitrogen on board ships.  The PSA technology was used before the membrane technology was invented and refined.  Now days, Membrane systems are, by far, the most widely used technology on ships, due to significant space improvements and maintenance advantages.  These membrane systems are also increasing in efficiency and allowing elevated operating temperatures, which provide a distinct advantage over comparable PSA systems.

The below summary and fact checks are valid for any Nitrogen flow (100 to 5000 m³/hr), at 95% design purity; and discharge pressure between 7-8 Barg to the deck tank.  For this table, 4500 m³/hr nitrogen flow is shown with a (2) x 50% split system configuration.

Advantages of a Membrane System over a PSA

Equipment Specs

PSA

Membrane System

Air Compressor

4 ea.
273 kW ea.

4 ea.
273 kW ea.

Air Dryer

2 ea.
9.4 kW ea.

2 ea.
9.4 kW ea.

Air Receiver

5 m³
(required by PSA for continuous flow)

5 m³
(Not required by membrane process)

System Valves
Control Valves
On/Off Valves
Solenoids

2
64
64

2
4
4

System Dimensions incl. Filtration
Length [m]
Width [m]
Height [m]

8.0
2.6
2.4

4.5
2.4
2.4

System Weight incl. Filtration
[kg]

39,250

16,250

 

  1. A) Simplicity of Equipment and Operation
    With identical or slightly lower air consumption over the PSA, the Membrane module system uses the same number of air compressors and membrane air dryers. The air receiver is an optional luxury for the membrane system, but a necessity for the PSA, to buffer the fluctuating air demand. The pre-filtration is identical between the two technologies and post-filtration is not required for the membrane system.  Due to the use of an air dryer, both technologies avoid the use of an electric process-heater, which can sometimes lead to ground fault alarms on board ships.  With only (4) on/off valves to realize the (2) x 50% split, the membrane system is, by far, much easier to control, operate, and maintain, if compared to the PSA system with (64) operational valves.
  2. B) Utility Consumption
    The total power and cooling water consumption is the same for both types of systems; at Nitrogen output purity of 95%.C) Installation Dimensions
    The Membrane Nitrogen system occupies about 40-60% of the footprint required by the PSA system. This is valuable space in a crowded machine room or utility room, that can be utilized for additional food or equipment storage.
  3. D) Weight Savings:
    A considerably large amount of weight can be saved when using a Membrane system over comparable PSA system. The new patented cabinet design from GENERON is reducing the weight and footprint of our current membrane systems even further. This can amount to a reduction of up to 23,000 kg between the two types of nitrogen generators.  This lower mass allows for either;  more cargo to be transported;  or considerable fuel-savings and reduced CO2 emissions over the life-time of the ship.
  4. E) Operating Purity
    Both technologies will produce Nitrogen ranging from 95% purity (for cargo filling/ unloading), up to 99.99% purity (for padding or purging applications at reduced flow).F) Lower Maintenance Cost
    The maintenance cost on membrane systems is lower, due to fewer moving parts (valves) and easier access to the main equipment, as well-known advantages in the industry. GENERON’s new patented cabinet design provides even further accessibility and maintainability. Both technologies require bi-annual filter changes, but the Membrane system does not require component overhauls, like the annual installation of valve seats and seals.

Better to use a GENERON® Membrane System and not a PSA!

GENERON IGS, 16250 Tomball Parkway, Houston, Texas 77086, USA

Phone: (713) 937-5200; Fax: (713) 937-5250, www.generon.com