Bringing cleaner electricity generation to Hong Kong - overview of D1 unit at CLP Power’s Black Point Power Station

Bringing cleaner electricity generation to Hong Kong – overview of D1 unit at CLP Power’s Black Point Power Station.

The project to construct one additional gas-fired generation unit at Black Point Power Station (D1 Project) is a strategic project and evidence of the effort by CLP Power Hong Kong Limited (CLP Power) towards reducing carbon intensity and combating climate change.  The D1 Project supports the government’s target to increase the share of natural gas in the fuel mix of electricity generation, helping Hong Kong’s transformation into a smarter and greener city.  The D1 Project provides a strategic infrastructure to serve the city with a lower carbon energy supply.

Development and preparation for construction of the D1 Project began in 2015 in order that advanced civil works on the project could commence as soon as project approval was granted by the Executive Council in December 2016.

The D1 Project consists of construction of a new Combined Cycle Gas Turbine (CCGT) with an installed capacity of 550 MW.  It is built within CLP Power’s Black Point Power Station next to the existing eight running CCGT units adopting the latest CCGT technology, at an efficiency exceeding 60%, higher than any of the current units in use in Hong Kong and amongst the highest in the world. The new D1 unit will also be more effective in reducing emissions, as well as saving fuel and cost, thereby further improving Hong Kong’s air quality and reducing the effects of climate change. After completon, the annual carbon emission will be reduced approximately by one million tonnes, which is equivalent to planting 42 million trees every year.

The challenge and solution

During the engineering design stage, engineering experts had to overcome two major challenges. The first challenge was to minimise impact during construction to the operation of the existing eight CCGT units that supply up to 60% of electricity needs for CLP Power’s customers. As one can imagine, there is a complex network of above and underground cables and pipework for gas, oil, water, hydrogen, chemicals and fire-fighting pipes connecting between utility rooms and the generating units, all of which must remain operational during construction. 

The second challenge was to avoid any marine construction to minimise environmental impact and maintain the very tight project schedule. Cooling water is required for the D1 unit and direct seawater cooling is the most efficient generating configuration. Considering the locations for intake and discharge of cooling water and the large amount of existing utilities across the site, the adopted engineering scheme was to construct deep shafts and tunneling with pipe-jacking for the construction of the underground cooling water system for the D1 Project. In the original plan, four vertical shafts to depths of 24-34 m were excavated and connected with three straight underground pipe sections with outside diameter of 3.3 m and total lengths of 500 m. These underground pipes were driven by tunnel boring machines (TBMs) to accommodate the compact Black Point site which was reclaimed when the site was first formed in the early 1990s.

While preparing for the vertical shaft excavation new challenges began to show up.  Two of the four shafts were located close to existing sea wall and even though the site was formed some three decades ago it proved to be challenging to minimise disturbance to nearby areas. The team reviewed the site data, carried out additional monitoring, geotechnical investigations, and confirmed with both the pipe supplier Bonna and the TBM manufacturer Herrenknecht the original contracting arrangements.  During the construction phase, based upon key reviews, additional improvements were identified through the introduction of civil construction expertise. This resulted in two straight tunnelling sections being revised to one curved tunnelling alignment scheme with one shaft deleted. Additional preventive grouting, online monitoring and inter-jacks were just some of the measures employed to ensure safety. 

Safety is never compromised at CLP Power. This is particularly so for construction of mega projects where safety risk is inherently high. In the D1 Project, safety leadership from top management, contractor senior management and project management team meant everyone working onsite from managers to supervisors to frontline workers understood and valued the importance of safety to ensure that everyone went home safely every night and day.  For the tunnelling and pipe jacking work, joint risk assessment workshop, reviews, training and supervision all ensured that the work was completed without any incidents.  Online monitoring system was employed at all times to check conditions of the excavation rock face.

The two TBMs used were named after ladies, in line with tradition and after a site competition. Fernanda, a bold voyager, drives from shaft “F” to end in shaft “A” while Sarah, named after Ms Sarah Lee - Hong Kong’s professional track cyclist and Olympic medal winner, tunnelled through the curved route safely and with fortitude.

Preparing TBM Sarah to start tunnelling and pipe jacking

The D1 Project is a multi-discipline mega-project combining engineering and construction expertise in civil, electrical and mechanical installation to overall plant commissioning.  With the small site footprint and the need to reserve space for a second gas turbine facility, limited area remained for laydown, site storage or pre-assembly onsite.  By mid-2018 more than 1,200 packages of major components had been delivered to the site. The advanced 8000H-class gas turbine, weighing more than 450 tonnes, was delivered from the Siemens Energy’s Berlin factory in Germany. To reduce impact on the environment and road traffic in the vicinity, the project’s component delivery – a total cargo weight of more than 10,000 tonnes – was conducted by sea. 

The D1 Project is a truly multi-national project with equipment and materials supplied from countries around the globe including Europe, America and Asia. Safety messages were delivered in Chinese, English and Nepalese to ensure clear understanding by everyone on the project team. On site, the workforce came from more than 20 nationalities bringing experience and cultural diversity to deliver a high quality project.

Guangzhou Salvage Bureau’s Nan Tian Long, a special floating crane with lifting capacity of 900 tonnes, was used to  oist the gas turbine of over 450-tonne into place

The generator for D1 unit, weighing approximately 450 tonnes, was unloaded at Black Point Power Station

One of the 15 Heat Recovery Steam Generator heat surface modules was being unloaded. Each module is more than 30 m long - equivalent to the length of three double decker buses

One of 15 HRSG modules weighing over 100 tonnes being installed

Green construction

The D1 Turbine Hall houses the heart of the D1 unit which is comprised of the gas turbine, steam turbine and generator. The building was designed with sustainability in mind from day one, equipped with an extensive rainwater harvesting system and a roof top solar panel system.  In recognition of the environmental-friendly measures implemented, the project was  awarded a Provisional Platinum Certificateby HKGBC BEAM Plus Society. Part of the project consideration was sustainability to ensure that Hong Kong’s volatile typhoon conditions and other climatic conditions were addressed as we have seen over past few years in Hong Kong and the proximity of the plant to the sea, the D1 Project is also engineered to meet “super-typhoon” and “extreme flooding” requirements.

The D1 unit Turbine Hall with extensive glazing reduces lighting and ventilation requirements

Technology and Innovation

New technologies have been applied throughout the D1 Project.  The project designers used BIM (Building Information Models) from project inception to avoid clashes between building structures and plant pipework and equipment, which enhanced safety and reduced potential re-work.  BIM was also used in the construction sequencing to ensure safety and for planning visualisation. Pre-cast concrete structures were used where possible.  Another feature was the extensive use of pre-fabricated pipe rack modules where pipe sections completed with insulation and cables installed were delivered to site to minimise site fabrication and installation. Large tanks were also fabricated off-site, then shipped to the site ready for installation to minimise laydown area use and take advantage of marine transportation.

The D1 unit state-of-the-art advanced CCGT technology was employed to achieve an efficiency of more than 60%. The world class efficiency was achieved primarily by employing an ultra-high combustion temperature in the gas turbine with the ability to recover as much heat energy as possible from the exhaust gas in the triple-pressure Heat Recovery Steam Generator (HRSG) with an inlet temperature of 620°C.  These ultra-high temperatures require advanced gas turbine blade materials supplemented with special thermal barrier coatings.  The HRSG piping and steam drum components are exposed to temperatures as high as 620°C and pressure as high as 166 bar over the design life of 25 years. High alloy steel P91 and P92, with cost roughly 10 times more than carbon steel, are selected for their enhanced creep strength, reatly reduce thermal fatigue of thick-walled components including main and reheat steam piping and superheater headers. P91/P92 materials also require pre-heating and specific welding technique using backing argon gas to avoid oxidation at back side of welds, then cool down to about 90°C to form martensite microstructure and finally followed by post weld heat treatment to 750°C to form 100% tempered martensite.  This calls for qualified and experienced welders and suitable heat treatment machines during peak period of onsite pipe fabrication.

Specialist welders prepare to weld P91/P92 steam pipe headers

The D1 unit design was predicated on a low NOx combustion system and a Selective Catalytic Reduction (SCR) system was also installed to further reduce the NOx emissions to single digits.

Fuel efficiency and flexibility play a key role in the D1 unit configuration. Natural gas-fired CCGTs are normally fueled by a specific gas source with the combustion system customised to a narrow range of Wobbe Index. The D1 unit was engineered with a wide range of natural gas supply in mind to enable the future utilisation of imported liquified natural gas (LNG).  This opens up the opportunity for a wider choice of gas supply from around the world.

The D1 unit is a single-shaft configuration meaning the gas turbine, generator and steam turbines are all connected together as “one shaft”.  During operation the whole shaft weighing more than 1,200 tonnes is controlled to rotate at 3,000 rpm to maintain electricity supply at 50Hz frequency. A “clutch” is installed between the generator and steam turbines in the D1 unit. With this clutch the D1 unit can achieve faster start times with gas turbine and generator only from firing the unit to synchronisation to the electricity grid. This provides flexibility during operation and allows for the high and low pressure steam turbines to slowly warm up to the required metal temperatures at which the clutch will “engage” them with the gas turbine-generator.

The D1 single-shaft CCGT unit, from left to right are steam turbines, generator and gas turbine

As the world digitalises, cyber threat is a critical concern. The D1 Project team worked closely with Siemens Energy and additional CLP independent cyber experts to review and enhance the system design.  Key additional features to secure the control system from cyber threat include a strong cybersecurity perimeter using waterfall data diode on external connection to entirely prevent attacks launched from outside. Also, the application whitelisting feature only allows approved programmes to run on the system and continuous threat detection monitors and reports any adverse activities. A  comprehensive backup and recovery plan is in place as well. The cyber security defense profile was not only tested in the factory but also on site.   External cyber experts were engaged to perform assessment with thorough inspection on the network and system configurations. Test virus was used to verify that the system is properly protected with warning alarm correctly initiated to alert the operator.

Conclusion

Despite the impact of COVID-19, the D1 unit was commissioned in 2020 and CLP was able to achieve the target of approximately 50% of electricity generated from gas.  The project was a memorable journey for everyone involved from advanced civil works to plant commissioning. At the peak and critical construction period in 2019 when work continued 24x7 on site for a couple of months to meet the project schedule, more than 1,500 workers were on site.  At one point a ferry was used to transport people to and from the D1 site as road transport was affected by emerging social events. In 2020, when the unit commissioning was underway, overseas experts could not travel to Hong Kong due to the COVID-19 pandemic. The project team quickly applied various advanced technologies to connect the experts and site team despite significant differences in time zones.  These are just some of the memorable moments as everyone involved was determined to deliver the highly efficient, low emissions generating plant to reduce carbon emissions in Hong Kong.