January 2011 August2011

The CTBTO model E3 unit was installed in 2012 at VIP00 test station, Vienna - Austria

The E3 generator is microprocessor based and is capable of full integration into the IMS systems implemented at

CTBTO radionuclide stations. All system variables are accessible via a serial RS232 interface along with a built in

user interface (shown above). The station operator can view all system variables and error codes through the LCD

screen. A key switch controls the state of the system. Should any failure with the IMS integration occur, the station

operator can set the unit to manual operation as well as disabling the unit from dispensing any LN2 to the detector

storage dewar.

Bundled with the E3 generator is a software suite which displays operating variables and provides some control

over the unit. These variables are logged in monthly files that can be sent to the manufacturer for immediate

analysis. Should a system error occur, the software will alert the station operator immediately along with PTS,

through the IMS software. E3 generator software can be programmed to optimize alerts sent to PTS in case of

system failures (see below).

For autonomous control the E3 generator requires detector LN2 level feedback; a capacitance gauge type sensor

and controller is necessary for this. To prevent unnecessary detector warm-ups, PTS has mandated that real time

LN2 level information be present for all IMS stations running LN2 cooling on their detectors. At both RN26 and

RN47 the LN2 level logging is implemented. The E3 generator is designed to share this information and enable and

disable production when needed. Such measures ensure the detector dewar never overflows causing damage/injury

to the detector, building or station operators. Below is a schematic of an approved PTS configuration.

RN47 setup in July 2009

T3-P124

W. A. Little*, B. Nadalut**, M. Buckby*, M. Gledhill***, K. Khrustalev**, G. Beziat**, O.Kilgour**

*MMR Technologies, **CTBTO Preparatory Commission, ***Consultant MAASNZ Ltd

Disclaimer: The views expressed on this poster are those of the authors and do not necessarily reflect the view of the CTBTO Preparatory Commission. SnT 2013

With a mandate to reduce downtime related to use of electric coolers, the Engineering and Development Section of CTBTO started in 2009 a pilot project to evaluate implementation of liquid nitrogen (LN2) generators at IMS radionuclide stations. A commercially

available unit, produced by MMR Technologies, has been tested at IMS station NZP47 (Kaitaia) during the last 4 years and at FJP26 (Fiji) for 2 years. Close collaboration between PTS and MMR Technologies allowed the finalization, in 2012, of a new “CTBTO model

E3 Liquid Nitrogen Generator” fitting specific CTBTO needs for robustness, easy maintenance, long term reliability and full remote control. Features added to the E3 include full logging of key state of health information (which can be accessed on the station PC), the

ability for automatic control based on the detector LN2 level, and a complete redesign of the internal layout to allow for easy maintenance. The newly developed CTBTO E3 prototype has passed several stress tests at the factory, and since September 2012 has been in

testing and evaluation phase at the IMS test station in Vienna. Additional stress tests were done, by reproducing at VIP00 test station real cases of environmental control failures at IMS stations. No deterioration of performance has been recorded since installation.

The first ELAN2 unit was installed in 2009 at

RN47 station, Kaitaia – New Zealand.

Lessons learned in Kaitaia: - Real-time upgrades from the factory increased the

reliability of the ELAN2 during 2010 and 2011;

- Air compressor was identified as the most critical part;

- Spare parts on-site are necessary to ensure data availability

only in remote site.

Reasons for installing liquid nitrogen (LN2) generators

at IMS stations: - Increased data availability (DA) at IMS Radionuclide stations

in case of extended power outages, compared with electric

cooling systems;

- Reduced operating costs, compared with external provision of

nitrogen (savings estimated by RN47 Station Operator during

the first year of operations are about 70% for this station;

- Normal station operations (DA) assured for more than 10

days in case of cooling system failure;

- No station downtime in case of cooling system need for

troubleshooting and repairs.

The second upgraded ELAN2 unit was installed in 2011 at RN26 station, Nadi - Fiji.

Upgrades implemented in Nadi: - Joule-Thompson valve reconfigured for

removal, cleaning and replacement in the field;

- Intermediary dewar removed;

- Copper after-cooler units turned into stainless

steel, for better life of the air-compressor

- All plastic seals replaced with brass seals;

- Dewar lids replaced with aluminium versions;

- Set of instructions provided to local operators.

Lessons learned in Nadi: - Set of instructions and detailed training on ELAN2 are

not preventing problems due to erroneous actions by

local operators;

- Remote monitoring and control of ELAN2 parameters

is necessary to ensure proper station operations;

Production more than 5 liters per day;

Ruggedized design, with user entry;

Low and easy maintenance;

Small Real estate (max 2.5m x 2.5m);

Automatic operation;

Error reporting for improved diagnostics;

Remote monitoring and control;

Low noise, 75-78 db;

Direct connection to spectrometer dewar, with

built in safety shutdown to prevent overfilling.

CTBTO model E3 units will be installed at selected IMS radionuclide stations;

Long term performance of the CTBT-model E3 generator will be assessed;

Backup use of E3 in the context of the OSI RN laboratory is being explored. Future plans:

Below is a plot of the recorded LN2

production over time, E3 internal LN2 level

and detector LN2 level; data were recorded

from VIP00 test station in October 2012.

The CTBTO model E3 liquid nitrogen generator allows liquid

nitrogen to be produced easily in a laboratory or office. (~5Lt/Day)

The system consists of two main components:

•The Compressor/PSA unit.

•The E3 Generator (Liquefier) unit.

Air Compressor / PSA Air from the surrounding environment is taken in through a non serviceable filter and compressed to 100Psi.

Moisture is then removed by means of an automated water wrap which disposes of collected moisture

periodically. The semi dry air is then passed to a pressure swing absorber (PSA), using multiple columns

each containing zeolite sieves which lower the dew point to approx -55C.

This level of humidity is necessary to ensure proper operation of the liquefier and prevent freezing of

residual/excess moisture. Because of the “limited” life of the air pump (2 to 3 years full duty) the unit is

housed in a separate enclosure for easy replacement in the field. This avoids station downtime should the air

compressor fail. (The liquefier contains numerous sensors to detect when an air-compressor is failing and

will alert IMS and station operators.)

E3 Generator (Liquefier) Consisting of nitrogen separation and cryo-liquefaction technology, this unit makes up the main component

of the liquid nitrogen generation system. The liquefier can be broken into four individual systems.

•Nitrogen Separation and Handling The nitrogen separation is performed via a membrane filter, resulting dry nitrogen approx. with a purity of

>99% (residual gases are Oxygen and Argon). The dry nitrogen gas is then handled via a series of valves to

direct the nitrogen flow where needed in the system. (The nitrogen gas is used primarily for liquefaction but

also for maintenance to purge the system of any built up ice).

•Refrigeration System The internal refrigeration system is comprised of a single-stream multi-component Klimenko cooler. This

system is similar in part to a household refrigeration system; special mixtures and separation/expansion

techniques are employed to achieve temperatures of around 100K; however, this alone is not sufficient for

nitrogen liquefaction.

•Joule-Thomson Expansion Device Within the refrigeration evaporator is a heat exchanger cooling the compressed dry nitrogen stream to 100K;

at the end of the heat exchanger the nitrogen gas is throttled by a small capillary also known as a ‘JT

Capillary’. The resulting low pressure side expansion of this metering capillary causes the temperature to

drop to ~77K (JT Effect). At this point liquefaction is possible and the resulting liquid nitrogen (LN2) is

collected and stored in an internal dewar.

•LN2 Handling System. When approx 500g of LN2 has accumulated, the system carries out a “Transfer”. This happens when the

nitrogen gas handling system pressurizes the internal dewar to 8 psi above atmospheric pressure. The LN2 is

displaced (aerosol effect) out of the internal dewar directly into the CTBTO detector storage dewar. This

process is automated and controlled by IMS input when the detector dewar becomes full.

To the left is a view of the CTBTO

software interface and data logger.

Control CTBTO Model E3 Liquid Nitrogen Generator Theory of Operation