Environment Protection Authority v Orica Australia Pty Ltd
[2014] NSWLEC 104
At a glance
Source factsCourt
Land and Environment Court (NSW)
Decision date
2012-12-12
Before
Pepper J
Source
Original judgment source is linked above.
Judgment (42 paragraphs)
Background to the Evaporator Incident 22Orica manufactures 83% ammonium nitrate solution ("the Solution") at the Plant by combining gaseous ammonia and nitric acid in a vessel known as a 'neutraliser'. The Solution is then passed into a chamber, the Evaporator, where it is heated to reduce the water content of the Solution to approximately 5% by applying steam to the outside of the Evaporator. 23The amount of steam applied to the Evaporator is controlled by PV305, which can be opened or closed remotely via the Plant's computer system, which the defendant calls the 'Distributed Control System' ("DCS"). Electrical signals from the DCS are converted into pneumatic signals by a digital valve controller connected to PV305 ("the Positioner"), which enables PV305 to open or close via the pneumatic compression of air. 24The pneumatic operation described in the above paragraph requires the Positioner to expel excess air into the atmosphere via an exhaust vent, which is a long narrow pipe ("the Vent"). PV305 and the Positioner are partially enclosed by a box ("the Weatherhood"), which is open at the bottom where the Vent is located. 25In the event of an interruption to the air supply to PV305, a mechanical spring inside the valve will move it to a closed state. However, if the Positioner is not able to expel air through the Vent, PV305 will not be able to move. 26The temperature of the steam applied to the Evaporator's shell is directly related to the pressure of the steam at PV305. The relationship between steam pressure and steam temperature was set out in tabular form in the Agreed Facts and is not repeated here. 27Typically, the pressure of this steam is around 470kPag, which correlates to a steam temperature of 157C. The Solution passes through the Evaporator and reaches a concentration of approximately 95% as it passes out of the bottom of the Evaporator and into a tank. It is then pumped to a tower known to the defendant as the Prill Tower ("the Prill Tower"), where it is cooled to form solid ammonium nitrate in the form of a prilled product. Under the conditions at which the Plant is designed to operate, the temperature of the Solution as it exits the Evaporator is between 140C and 143C. The temperature of the Solution inside the Evaporator itself is not measured and the exact temperature is not known, but it is somewhere between the pressure of the steam applied to the shell and the temperature of the Solution at the exit of the Evaporator. 28Water evaporated from the Solution as it passes through the Evaporator is combined with air flow from a dry solids handling ventilation system and passes through a water scrubber, an apparatus designed to remove particles of ammonium nitrate from the dry solids handling ventilation system by passing it through a spray of water ("the Scrubber"), and is then emitted out of the adjacent Stack. The Scrubber is not able to remove submicron-sized particles of ammonium nitrate from the steam. Under normal operating conditions, steam and ammonium nitrate particulates are continuously emitted from the Stack and can extend for 10 to 20m from the Stack and to a height of approximately 50m before fully dissipating (depending on atmospheric conditions) while the Evaporator is in operation. 29As at 22 March 2011, Orica had in place the following mechanisms to monitor and control the temperature inside the Evaporator: (a)PIC305, a pressure-indicating control transmitter that measured the steam pressure at PV305 and sent a message via the DCS to close PV305 if the pressure became too great, thus reducing the flow of steam to the Evaporator and the temperature of the Solution inside the Evaporator; (b)TIC335, a temperature-indicating controller that measured the temperature of the Solution after the Evaporator and adjusted the set point of PIC305 to increase or reduce the steam pressure to the Evaporator. This in turn controlled the temperature of the Solution after the Evaporator. The controller triggered alarms when temperatures were outside of the operating range of 140C-142C; and (c)Valve PSV306, a pressure relief valve (safety device) that opened to release steam pressure if the pressure of the steam in the Evaporator exceeded 1250kPag (that is, 193C). 30Photographs showing the location of PV305, PSV306, the Scrubber, the Stack, the Evaporator and the Prill Tower were provided to the Court.