White Papers

Steam purity can have a major impact on steam turbine performance and reliability.  Online steam purity monitoring is considered standard practice in thermal and nuclear power plants with steam turbines to enable the rapid identification of out of specification steam purity that could lead to turbine damage.  Steam purity is not routinely monitored in real time in geothermal power plants for a variety of reasons including the difficulty of conditioning samples for analysis with online instrumentation. This is as a result of high levels of non-condensable gases that interfere with analysis techniques, as well as concerns as to whether a steam sample is representative of the bulk steam flow due to the two-phase nature of many geothermal steam supplies.  Operators may also have concerns about what actions they have available to them to improve steam purity should it be found to be insufficient.

This paper describes the considerations to be taken into account when developing online steam purity monitoring systems for geothermal power plants.  A case study demonstrating some of the benefits of geothermal steam purity monitoring is also discussed.

 This paper outlines the challenges of an ion exchange water treatment plant used to produce high quality make-up water for heat recovery steam generators (HRSGs).  These HRSGs produce steam for use in both dairy food production and electricity production via a steam turbine, at a large dairy products processing factory in New Zealand.  The site produces from raw milk, the largest volume of dairy ingredients in a single factory, anywhere in the world.  It also has a cogeneration plant comprising of multiple gas turbines, HRSGs and a steam turbine, which produces all of the sites process steam and electricity demand, with the surplus electricity supplied to the national grid.  

The failure to accurately sample and analyse saturated, superheated and reheated steam from boilers or heat recovery steam generators (HRSGs) can lead to significant deposition and corrosion related failures of the steam path in boilers, HRSGs, steam turbines and any process equipment that comes into contact with the steam. Minimum acceptable equipment standards for sampling and online analysis of steam from boilers and HRSGs are discussed along with the need for routine carryover testing. Multiple real world case studies of steam sampling, analysis and purity issues are presented with key lessons identified. 

Enhanced geothermal systems (EGS) are a new technology that involves the hydraulic enhancement of the permeability of deep (3–5 kilometers) hot rock underground systems to allow the extraction of thermal energy to the surface. High pressure cold water is injected under pressure via an injection well into the fractured hot rock, whereby the water increases in temperature as it travels through the rock. This water returns to the surface via a production well where the thermal energy of the water is then extracted with a non-contact heat exchanger into another working fluid, in this case demineralized water, which is heated and converted into saturated steam. This secondary loop is then used to power a conventional steam turbine. The condensed steam is returned to the heat exchanger loop and the cooled EGS water is then returned to the injection well as both systems operate as essentially closed loops.

The paper provides a brief background to EGS systems and then focuses on the potential cycle chemistry issues associated with an EGS surface power plant, with the Geodynamics Limited, Habanero 1 MW EGS proof of concept plant at Innamincka in the Cooper Basin in South Australia described in detail. 

Mighty River Power (MRP) operates a diverse fleet of geothermal power plants, including two geothermal power plants with condensing steam turbines. The cooling water used to condense the exhausted steam is condensed geothermal steam, recirculated through a mechanical draft evaporative cooling tower. The use of condensed geothermal steam as cooling water presents both opportunities and challenges when compared to the use of surface water or groundwater for cooling. The condensed steam has low levels of dissolved solids, and very low levels of suspended solids, reducing the likelihood of mineral scale formation and erosion within the cooling water system. The presence of hydrogen sulphide in the geothermal steam (and the condensed steam) presents several challenges to the management of the cooling water system, including the build-up of sulphur deposits, the management of sulphur metabolizing bacteria and the limited choice of sulphide compatible biocides. This paper discusses the implications of these challenges to the management of cooling water systems using condensed geothermal steam including discussion of significant cooling water events resulting from these challenges.

The importance of a chemist/chemical engineer for the reliable and efficient operation of combined cycle gas turbine (CCGT) plants is discussed along with the key differences between routine and strategic chemistry and how these potentially impact on CCGT plant operation. Potential risks and issues with the full outsourcing of cycle chemistry services for a CCGT plant to chemical service providers are outlined. Also discussed are the interactions between a chemist/chemical engineer and plant management, operations, engineering and maintenance personnel. Proposed chemist/chemical engineer staffing levels for a number of hypothetical CCGT plants are also discussed. 

Water treatment plants need to reliably produce water with the correct quality and required quantity for boiler and heat recovery steam generator feedwater, gas turbine water injection, or co-generation plant feedwater. Without the quality guarantees, the process that utilises the water will suffer from corrosion and/or deposition issues, and if the quantity is not produced reliably, then the process which uses the final water product cannot operate correctly. This paper discusses the practical tools to ensure "Reliability", "Quality" and "Quantity" – the "R & Q's" of a water treatment plant, in the form of a performance management plan and two water treatment plant case studies.

The easy and fast way to a Combined Cycle Gas Turbine (CCGT) project is to just forget about good chemistry. The easy and fast path will get your project built and commissioned quickly but it will then suffer from Heat Recovery Steam Generator (HRSG) and Steam Turbine related chemistry issues for the rest of its operational life. For an operator of a CCGT unit this is not a position that one would wish to be in.

Chemistry is an integral part of the success of CCGT projects. The power plant chemist plays a vital part in the long-term future reliability of any power plant and has a significant role in all phases of a CCGT project from specification to commissioning. 

New Zealand is an island country in the south-western Pacific Ocean comprising two main land masses and has a total population of approximately 4.2 million people. The fossil power industry in New Zealand comprises of a combination of 1970s and 1980s vintage gas and coal fired conventional units, three large F Class single shaft Combined Cycle stations from different manufacturers commissioned from 1998 to 2007 all with horizontal, triple pressure heat Recovery Steam Generators (HRSGs), and a number of small aero-derivative gas turbine/HRSG co-generation plants. Flow-accelerated Corrosion (FAC) issues, in varying degrees, have occurred at all sites with a number of different monitoring and resolution strategies employed to ensure plant reliability, and safe operation. These strategies have included operating and cycle chemistry changes, improved monitoring, increased non-destructive testing (NDT), and improved specification of later units. This paper provides a clear and concise summary of the New Zealand fossil power industry experiences with FAC in Combined Cycle Gas Turbine (CCGT) plants and future activities in relation to FAC.

With the technical justification for the inclusion of a condensate polisher for a Combined Cycle Gas Turbine (CCGT) new generation project is simple and straightforward with the benefits of condensate polishing clearly understood, very few projects worldwide are specified and constructed with a condensate polisher. This situation often arises because the robust financial justification and cost benefit analysis required for the inclusion of a condensate polisher into a project is often unable to be completed with the required level of detail to withstand the intense financial scrutiny of new CCGT projects. Available condensate polishing technologies are reviewed with budget estimates provided for each key technology type. Technical and financial justification methodologies for the inclusion of condensate polishers on CCGT projects are outlined and discussed. The cost of condensate polishing on a new CCGT project is shown to be approximately 1% of the cost of a standardised, new CCGT unit.

The use of condensate polishing on modern Combined Cycle Gas Turbine (CCGT) power plants is often neglected due to incorrect cost benefit assumptions and short term project objectives. This has resulted in very few CCGT plants worldwide having condensate polishing plants so the short term and long term benefits of condensate polishing have not been fully realised. The application of separate bed condensate polishing on CCGT plants has, until now, been unheard of. This situation has now changed with the construction and commissioning of Huntly Power Station Unit 5, a 400 MW CCGT plant that utilises a cost effective, high performance, easy to operate, separate bed condensate polishing system (TRIPOL®) that delivers clear short term and long term benefits over the entire life of the CCGT plant.

Modern Engineer, Procure and Construct (EPC) contracts can, at times, lack suitable thermal power station chemistry expertise, resulting in less than best practice design choices being made. It is the responsibility of thermal power station chemists with organisations that are the clients of EPC contracts to ensure that thermal power station chemistry knowledge and good practice is utilised for new projects. This approach has been followed with Genesis Energy’s new “Energy, Efficiency, Enhancement (e3p) 385MW combined cycle gas turbine (CCGT) plant, located at its Huntly Power Station site in New Zealand. This project has also shown that the inclusion of condensate polishing for CCGT units is economically viable with significant long term benefits of lower plant operating costs and improved plant reliability.

Due to concerns over Flow Accelerated Corrosion (FAC) damage at Huntly Power Station, a cycle chemistry change from All Volatile Treatment [oxidising] (AVTo) to Oxygenated Treatment (OT) was trialled on Huntly Power Station unit 2. This has led to significant decreases in iron corrosion product transport rates to the boiler with corresponding observable physical changes in oxide layer morphology. Magnetite (Fe₃0₄) dominated FAC damaged areas showing significant material loss have changed to haematite (Fe₂0₃) dominated areas that are resistant to FAC damage and can be considered fully protected.

This paper describes comparisons made between corrosion product transport rates for AVTo and OT operation for both base load and 2-shifting operation along with comparisons between return to service iron corrosion product transport rates for AVTo and OT units. Also covered are oxygen injection and control system issues in relation to Economiser/Boiler dissolved oxygen (dO2) rations at varying boiler pressures and the assessment of any copper migration from boiler water and steam touched surfaces to the high pressure (HP) turbine.