| Abstract |
Geothermal surface facilities are exposed to a number of unique hazards that present risk to the safety of people and the environment. Hot geothermal fluid, at pressure, is utilised for direct heat applications or for generating electricity, and is discharged to atmosphere under certain situations. Non-condensable gases can be present in the geothermal fluid. Chemicals such as caustic soda, biocide treatment, or acid may be required depending on the energy conversion technology employed. Furthermore if an Organic Rankine Cycle (ORC) plant is considered then flammable hydrocarbons may be present. More generic hazards, typical of non-geothermal industrial plant, including high voltage electrical systems, rotating equipment, elevated working areas, and elevated noise levels will also be present. An increased level of construction hazard may be present, particularly for the gathering system which may be spread out over a wide area of often challenging terrain. Safety considerations and treatment of these hazards start in the engineering design phase. In a general sense ‘safety by design’ is a concept that encourages product designers to ‘design out’ health and safety risks during design development. This concept is not unique to geothermal design, and covers a range of industry sectors. The concept is supported by legal regulations in many jurisdictions that require designers to specifically identify and treat hazards. A safety by design framework tailored for the engineering of geothermal facilities is presented. All aspects of the facility life-cycle (i.e. construction, operations and maintenance, decommissioning) are considered. A collaborative approach between the designer and project stakeholders is recognised as essential for sharing knowledge and lessons learned to inform the design process. Specific processes within this framework, including hazard identification, hazard and operability study (HAZOP), and constructability reviews are discussed. Documentation of the treatment of hazards through the design process is essential as any residual risks are either mitigated by the design, or treated through plans later on in the facility life-cycle. The application of this framework is illustrated with design features from specific geothermal case studies. An engineering design must consider different criteria including safety, operational performance, usability, environmental impact, capital cost, operational cost, constructability, redundancy, and future proofing. The project location, with respect to local safety culture towards construction and operation, can also be a consideration. Project stakeholders will have different, and sometimes competing, views of the important criteria and a good design will need to achieve an appropriate balance of factors. Considering safety by design processes in the engineering of geothermal facilities ensures that safety thinking is considered early and in parallel with other design criteria prior to construction. |