Callide Oxyfuel Project Safety and Hazardous Areas Assessments

Dr Chris Spero(Project Director)

IEAGHG Oxy-Combustion Research Network28 & 29 October 2015 (Wuhan China)

Background

• Oxy-combustion and CO2 capture introduce additional health and safety hazard to traditional coal-fired power plant

• These new hazards are physical as well as chemical

• The Callide Oxyfuel Project was underpinned by a rigorous process of hazard identification and control from design through to operations – with good design, good systems and thorough training in elements important to safety

• This presentation gives an overview of how Health and Safety was managed at Callide A

• The Callide Oxyfuel Project has been delivered with an exemplary safety performance, despite the application of first-of-a-kind technology and elevated hazard potentials

Design Studies Plan• HAZOP Studies on Air Separation Units (ASU), Oxyfuel Boiler (OB), CO2 Capture Plant

(CPU), combined system.• Boiler Safety Integrity Level (SIL Studies) – for programmable safety systems on the

boiler and air separation units. Not required for the CPU which utilised a hard-wired system. Applicable Code IEC 61508.

• NFPA 85 Compliance study – to assess boiler hardware and logic against the requirements of NFPA 85 - Boiler and Combustion Systems Hazard Code

Hazardous Area Assessments• Subset of the HAZOP studies• Micro assessment of the risk and control of unintended releases of hazardous

substances from the ASU, OB and CPU plant

Original Equipment Manufacturer Guidelines• Joint sign-off on Elements Important to Safety check sheets

Designing for safety

Hazardous Area – Uncontrolled and controlled releases

ASU• N2 (asphyxiate) – displaces O2

• O2 from main ASU process• Hydrogen used as fuel for Hydrocarbon

analyzers

Boiler• Flue gas releases from pressurised duct

work and piping (Recycled flue gas downstream of Gas Recirculation Fan)

• Uncontrolled O2 release in O2 feedpipes to the O2 injection points

CPU• Flue gas within pressurised section of CPU• Pure CO2 or near pure recycled CO2

• Controlled release of flue gas and pure CO2 from registered release points such as Pressure Safety valves and main vent

• Ammonia from refrigeration plant

Hazardous area zoning

Non-hazardous area• An area in which a toxic gas atmosphere is not expected in quantities such as to

require special precautionsHazardous Area• The converse of a non-hazardous area• Zoning

• Zone 0 – an area where the toxic gas atmosphere is present continuously for long periods of time• Zone 1 – an area in which a toxic atmosphere is likely to occur in normal operation occasionally• Zone 2 – an area in which a toxic gas atmosphere is not likely to occur in normal operation, but if it

does occur, it will exist for a short period only

Risk Matrix

Oxyfuel boiler hazardous areas

Flue gas at positive pressure

Oxygen at positive pressure

CPU hazardous areas

① Low positive pressure CO2 rich flue gas② High pressure CO2 rich flue gas③ Moderate pressure anhydrous Ammonia④ High pressure pure CO2

Estimating a volume of impact of the uncontrolled release

• Assessments based on IEC 60079.10.1 (Standard), using the following process:

• Review plant design data and identify credible release points and classify areas (zones) according to the code

• For areas of concern, select a certain size of leak (hypothetical) and calculate the theoretical release rate considering chocked flow or not, T, P concentration of the gas component

• Using factors that relate to the ambient conditions and the extent to which the release area is ventilated, calculate the theoretical volume of the release envelope and concentration of component using the engineering calculations in the code

• Compare the concentration within the envelope with the STEL or LEL/UEL and rank the release as Safe or Unsafe

• Evaluate the likelihood and consequence of actual exposure using the Risk Matrix and establish protocols and additional controls for these high risk areas.

Actual: Gas leakage point (3 cm x 1 cm) in lower chamber of the Boiler Secondary Gas Heater(Leakage from Recycled flue gas side into the casing and eventually to atmosphere)

Case study – CPU, uncontrolled release of impure CO2

• Application of IEC 60079-10-1• Impure CO2 is recycled to the flue gas

compressor via a 100 mm pipe.• Assume there is a gas leak at a flange joint• Leakage point: equivalent to a 0.05 mm

clearance around the flange, A = 16 mm2

• Internal condition: P 1340 kPa(A), T 283 K• External conditions: P 101.3 kPa (A), T 313 K• Gas composition (ppmv): CO2 950,000, NO2 10,

Balance N2

• Type of flow: Choked (sonic) based on polytropic index of adiabatic expansion and internal/external pressure difference.

• Flow condition: Partially impeded in open air environment ( Impeded flow Factor, f = 3, (Ideal = 1, Impeded = 5)

• Safety Factor (k): 0.5 This means that the hypothetical volume will have a mean concentration equal to 0.5 x STEL (CO2)

• From Choked Flow calculations, release rate (dG/dt )CO2 = 0.0082 kg/s

• Minimum volumetric flow rate of fresh air (m3/s),

• STEL CO2, 5000 ppm = 0.00856 kg/m3 (at 313 K)• (dV/dt)min = 576 m3/s• Air replacement rate (C) – based on the

Standard C = 0.03 fresh air changes• Hypothetical volume of CO2 release • Vz = f x (dV/dt)/C = 57617 m3

• Assume a Control Volume (Vo) – 15 m x 15m x 15 m (3375 m3)

• Vz >> Vo, so the release condition is UNSAFE• Area classified as Hazardous, and requires

certain controls

( ) ( )293

max

min

TSTELkdt

dG

dtdV ×

×=

H&S Assurance

• Operators do plant walk-downs every shift• Two large ventilation fans and fixed CO2

detectors (2) installed in the CPU compressor house (3 measurement points)

• Personal CO2 monitors must be worn around boiler in oxy-mode

• Personal O2 monitors must be worn around the ASU plant

• Personal CO2 and NO2 monitors must be worn around CPU plant area

• Higher risk areas delineated with barrier tape, rails and signs as necessary

• Thorough training of personnel in the hazards associated with oxy-fuel and CO2 capture plants and how to respond

• All test work performed under a Minor Works Permit and Job Safety Analysis (JSA)

• All maintenance work performed under a Work Permit with isolations and JSA

• Oxy-combustion and CO2 capture technology has brought new challenges and risks given our background of traditional coal-fired power generation.

• With support from our OEMs a comprehensive Health and Safety program was undertaken from the design stage and implemented across all aspects of the COP operations.

• By any measure, the risks were clearly identified and properly managed, and the construction and operations of the project were undertaken over a 5 year period safely and effectively.

• During the operations phase, several leaks of flue gas occurred due to material failures on older parts of boiler which were detected early through careful observation and use of gas monitors.

• Our protocols and procedures for dealing with hazardous areas proved effective, and actual measurements and uncontrolled hazardous gas releases due to leaks, have correlated quite well with concentrations as predicted using the IEC 60079.10.1 Standard.

• The overwhelming conclusion is that oxy-combustion and CO2 capture (utilising cryogenic distillation) can be done safely, and can be effectively managed using the tools already well established in the industry.

Concluding comments

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