Retrofitting advanced Flue Gas Desulfurization (FGD) into the very cramped quarters on Hong Kong Electric’s Lamma Island coal plant was a major engineering challenge. But while the project has been a tremendous success, further reductions in emissions and carbon intensity must surely come from increasing nuclear supply, the company tells Blue Skies China.
Space is in short supply in Hong Kong. Families crowd into 400sq ft apartments in 60 storey towers while malls such as Langham Place squeeze into unusual vertical spaces, with hundreds of shops sprouting from the tiniest ground level footprint. The situation is no different in heavy industry, with Hong Kong Electric’s Lamma Power Station perched on the edge of a land reclamation project between a mountain of coal and the South China Sea. Within the eight coal-fired and combined cycle units, every square foot of the power station land is accounted for – which made retrofitting flue gas desulfurization (FGD) to meet government emission limits a major challenge.
The typical wet limestone-gypsum FGD plant for a 350MW generating unit would normally require an area of at least 1,500m2, according to engineers Frank Lau, General Manager, Projects; and YL Kwan, Chief Mechanical Engineer with Hong Kong Electric.
But in the case of Lamma Island Units 4 and 5 (350MW each), the plant areas were fully occupied by flue gas ducts, oil tanks, oil separators, high voltage cables, pipes and trenches. Even clearing all available space left only 600m2 for any new plant, around a quarter of the space needed for the FGD equipment for Units 6, 7 and 8.
The options available to the engineers were limited. The first was to change the technology, using a steam gas exchanger instead of a gas-gas heater (GGH) for reheating the treated flue gas. The second was to stack up the FGD components, to make the most of a small footprint, placing the GGH on top of the absorber tower, unlike the conventional FGD design where they are laid side by side.
Engineers chose the second option, since using a steam gas exchanger would increase boiler load.
Stacking the components led to its own challenges, with substantial increase in the length of gas ductworks required and much stronger steel structures required to support the GGH 55 metres above the ground. Not taking any chances, and using three different structural analysis software packages (Staff, Sap and Satwe) for cross checking, engineers found the column load was around 40,000kN, requiring careful design of a safe and optimized steel supporting structure.
To meet government deadlines and 2010 emission targets, Hong Kong Electric had a window of only 42 months for design approval, engineering, fabrication, equipment delivery, site installation, testing and commissioning of the three FGD plants. Further complicating the site installation was that the plant is a heavy workhorse in Hong Kong Electric’s fleet – the installation was required to tie in with each annual unit outage to ensure reliable power supply to meet system demand.
Steel fabrication was assigned to more than three manufacturers in China, in order to speed up fabrication works – manufacturing of the major steel structures was completed within 4.5 months.
Despite the site constraints and difficulties encountered during shop fabrication and site erection works, Unit 5 FGD plant was successfully commissioned in July 2009, whilst the Units 4 & 2 FGD plants were put into commercial operation in April 2010 in accordance with the planned schedule.
Performance tests of the three FGDs for Units 2, 4&5 reveal that the actual SO2 removal efficiency is about 95%, exceeding the guaranteed figure of 92%. The results for Unit 5 are given in the table.
The future is nuclear
While such work on the coal-fired units has enabled HK Electric to meet its 2010 emissions targets, coal is not the future in Hong Kong. The government has proposed that the ratio of power generation supplied by natural has be increased to 50% by 2020, and the ratio of nuclear power increased to 40% by the same date.
According to TY Ip, Environmental Affairs manager with Hong Kong Electric, the power company fully supports these targets in terms of achieving a reduction in the Hong Kong’s carbon intensity.
“However, given the significant impact of the proposed fuel mix on the electricity market in the coming decades, more detailed study and closer collaboration with local and Mainland stakeholders should be carried out,” he says.
A major issue with increasing the use of natural gas is the supply problem. “Hong Kong Electric anticipates power companies in Hong Kong will face challenges in securing natural gas supplies of sufficient flexibility to adapt to the changing pattern of local electricity consumption,” says Ip.
Considering that meeting the reduced emission allowances in future is very challenging, Hong Kong Electric stresses the need for a long-term policy on increase of the use of natural gas for electricity generation as gas suppliers have no flexibility for any ad hoc natural gas supply.
“We urge and welcome the government to continue playing the role of a proactive facilitator to assist local power companies in overcoming possible hurdles in securing new and additional natural gas supplies. With the support of the government, Hong Kong Electric is hopeful that it can resolve additional natural gas supply problems to achieve the increased electricity generation by natural gas,” he says.
But Ip says nuclear power is a far more viable option. “The introduction of more nuclear power to Hong Kong can help alleviate the potential risks of over-reliance on natural gas, the demand and market prices of which are ever rising. Overall, Hong Kong Electric considers it feasible for Hong Kong to import a large quantity of nuclear power from Guangdong,” he says.
Additional reporting: Cadence Poon