This process will produce biogas that will be burned to generate electricity, providing a new source of renewable power. The sludge left after treatment will be used as compost. But the Hong Kong government had to be sure the proposal could meet waste management requirements and represented a sound investment of public money. Income from electricity sales will be topped-up with a subsidy to make the plant economically attractive enough for companies to bid for the design and build contract, so it was important to prevent the project becoming too expensive for the government.
Accurate predictions for power generation levels were critical. If these predictions were too high, an inflated income for the treatment facility would be forecast. This would reduce the subsidy paid, making it an unattractive prospect for potential contractors. If the predictions were too low, the subsidy provided to contractors would be excessive, leaving the government out of pocket.
We modelled different options for electricity production under various scenarios, which required meticulous analysis as there were no comparable local facilities and no operational data available. The restricted size of the site meant we also designed different plant layouts based on whether there would be a composting facility and the effect this would have on generating equipment and energy output levels.
The contracting tenders submitted used our analyses, modelling and design work to conclude that the facility would be able to export about 24,000m3 of gas per day or generate 7.3MW of renewable electricity and heat. We provided technical evaluation of the tenders, with two standing out – one would deliver a facility generating electricity from biogas onsite, the other would see the biogas being exported to a separate power generation plant. Both options include a sludge composting facility. Our work will be key to the final decision on the facility to be built. The client already intends to develop another organic waste treatment facility, which will build on the knowledge and experience gained through this project.