NZSC

DUST EXPLOSION PROTECTION EQUIPMENT

CASE STUDIES

October 2016

NZ SUGAR CO LTD

New Zealand Sugar Co Ltd operates a Refinery at its site in

Birkenhead, Auckland, New Zealand.

The Refinery is used for processing raw sugar into refined

white sugar and other products. Approximately 210,000

tonnes of raw sugar are processed every year on a nominal

24hr 5 day/week shift pattern.

Between 2002 and 2010 NZSC rolled out a number of dust

explosion risk reduction (DERR) measures

NZSC DERR PROTECTION SYSTEMS

Containment systems for 2 sugar mills

Improved belt tracking and suppression systems for 6

elevators. Silo (3), Refinery (1) and Packing (2) elevators.

Venting, and chemical barrier systems for 3 dry product dust

collectors. Silo dust collector, Blends plant and PH2 (Torit)

dust collectors

Venting for sugar storage bins. IBC (8), Bulk (3), Packing (1)

Ignition source detection and FSGV isolation systems for

protection of storage bins. 800T Silo, Dry sugar bins (8) and

20T Hesser bin

Antistatic bonding throughout – key is ongoing

implementation and consistent standards

EVENTS AT OTHER SUGAR PLANTS

An event at the Sydney sugar storage and packing plant in

2004 prompted an increased focus on suppression and

venting systems throughout the dry sugar handling systems

at NZSC

The ongoing progress on DERR improvements was

reinforced by the devastating accident at the Imperial Sugar

in 2008

MAINTENANCE OF DERR SYSTEMS

Three examples of accidental protection equipment

activations, all determined to be false - to date

1) Elevator run back systems – PC09 run back event.

Mechanical anti runback failed

2) Torit Dust Collector suppression activation

3) Blends plant vacuum receiver hopper explosion vent

failure. Due to excess process pressure fluctuations

1) ELEVATOR PCO9

This twin leg elevator has close fitting casings around the

buckets and belt, in addition to a build up of sugar inside

The mechanical anti runback failed, causing the elevator to

run backwards at increasing speed. This caused an air

pressure build-up in the elevator boot. In addition to sugar

flow pressures, this was sufficient to trigger the PDS

PDS sensor activates the explosion suppression system

zones both top and bottom of the elevator.

1) ELEVATOR PCO9

Refinery Elevator PC09

Note: Grecon ISD

1) PC09 BUCKET ELEVATOR BOOT

1) ELEVATOR PCO9 – PDS SENSOR

PC09 bucket elevator PDS (static pressure switch)

Potential blocking of the static pressure trigger sensor.

STUVEX

2) DUST COLLECTOR SUPPRESSION ACTIVATION

Torit Dust Collector activation – this dust collector (DC) is protected by

suppression, as its location is a long distance from the nearest outer

wall, precluding venting to the outside. Hence the body of the DC is

protected by suppression.

The trigger sensor is the PDP type - pressure rise curve type. The PDP

enables to sensor to distinguish between reverse pulse cleaning and an

explosion. In hindsight perhaps an over complex solution to the

problem.

Torit activation cause not fully understood, but explosion ruled out, due

to lack of burn marks. Filters seriously blocked at the time. This DC

services a bag dump with an air tight lid.

2) TORIT DUST COLLECTOR

Theory is that, the bag

dump lid slammed shut

causing a pulse of air back

up the line. This was

sufficient to trigger the PDP

sensor.

As the filters were seriously

blocked, this created

sufficient back pressure to

register on the PDP as an

explosion.

2) DUST COLLECTOR SUPPRESSION ACTIVATION

Torit dust collector

Stuvex PDP02 sensor

Pressure rate rise dp/dt

Static pressure also

One of kind on NZSC site

3) EXPLOSION VENT VRH

Below : Vent leaking sugar dust

Right : VRH installation and vent duct

3) VRH EXPLOSION VENT INSTALLATION

Vacuum receiver hopper = VRH

Vents are required on dust collectors and vacuum receiver

hoppers for protection against various dust explosion

hazards

However there are some difficulties operating a vent in an

environment of fluctuating pressures, e.g., reverse pulse.

However the pulse pressure was within vent design criteria

The vent may rupture due to process conditions – or

process blockages or unusual events.

Explosion vents are not cheap to replace

Flatness of the mounting flange is important

Vacuum rated to 1000mbar, rupture + 0.1barg, tol. +/-

0.1barg

NZSC DRY DUST COLLECTORS

Blends plant – Fresco bag filter. Performs well in a

conditioned dry environment

Packing Hall 2 - Torit pleated filter – a poor performer in

terms of filter changes

Silo and Grader DC – Filtair bag house – reliable and well

sized

Dry dust collector information. Refinery has part wet

scrubbers and part bag house type dry duct collectors and

the later has better emissions performance. Wet scrubbers

have lower risks of dust explosion.