Hong Kong WENT Landfill ranks among the world's top 20 largest landfills. China Light and Power's Castle Peak Power Station can burn up to 1,450 tonnes of coal per hour. And Green Island Cement will incinerate municipal solid waste at 1,450¢XC to create fly ash to mix in its cement.

These are just a few of the intriguing facts that 34 members learned during the Chamber's environmental fieldtrip, led by General Committee member Manohar Chugh on April 11, to see how Green Island Cement, Castle Peak and Black Point power stations, and WENT Landfill manage waste.

Starting at Green Island Cement plant, members learned that the facility runs a waste reduction plan under that philosophy that any waste is wasted money. Its environmental awareness programme works on an inverted pyramid principle of: avoid, minimise, recycle, treat and dispose.

Cement production is a very energy intensive process. Basically, a mixture of limestone, iron oxide, silica and fly ash are first crushed in a raw mill, which is then heated from 50¢XC to 950¢XC within 40 seconds in a preheater tower and kiln. This is then heated up to 1,450¢XC. Once cooled, the mixture -- clinker -- is then finely ground in a finishing mill.

Coal is the primary fuel used in the burning process, but the plant has developed a process for burning municipal solid waste, and plans to build an incinerator onsite. This will help with Hong Kong's garbage problem as well as reduce some of its energy costs and provide more fly ash for use in the cement, said Michael Wong, senior environmental process engineer, for Green Island Cement Co., Ltd.

By incinerating rubbish at temperatures between 1,450¢XC and 2,000¢XC, many chemical pollutants released during the burning process will be broken down into harmless elements. Emissions will then be further scrubbed using lime, which will absorb many of the remaining pollutants. The fly ash which remains after burning the garbage will then used in the its cement production, along with the lime.

Mr Wong said rubbish will be sorted on site to remove any undesirable products, such as batteries, before burning.

Located directly next to Green Island Cement is CLP's Castle Peak Power Station. The eight generating units have a capacity of 4,110 megawatts (MW) and are fuelled primarily by coal.

Low nitrogen oxide burners have been installed at the plant to reduce the emission of nitrogen oxide by over 50 per cent compared to the originally installed equipment, Joseph Chow, plant manager for Castle Peak Power Station told members.

Before entering the chimney, the flue gases pass through electrostatic precipitators to remove the fine fly ash which is entrained in the gas flow. Each precipitator is capable of collecting tens of tonnes of dust per hour with a collection efficiency of over 99.3 per cent.

The fly ash is used as a cement substitute in concrete, as a raw material for making cement and building blocks, and for landfill purposes. Any surplus ash is mixed with water and pumped through buried pipelines to Tsang Tsui Lagoon, some 5.5 kilometres north of the station. The coarser furnace bottom ash collected from the boilers is conditioned with water before road transportation for use as an aggregate or as landfill.

Leaving Castle Peak Power Station behind, members travelled to Black Point Power Station four miles away. The station is the first natural gas-fired plant and the latest power project, and is owned by CAPCO.

When fully functional by 2004, the station will have a total capacity of 2,500 MW, consisting of eight units of 312.5 MW each, and will be one of the largest natural gas-fired combined-cycle power stations in the world.

The plant produces electricity using turbines. The surplus heat from this process is harnessed and used to make steam, which in turn drives a steam turbine to generate additional electricity. For a similar fuel consumption, gas turbines produce approximately 30 percent more electricity than conventional fossil-fired power stations.

Natural gas is piped from the Yacheng 13-1 gas field to the south of Hainan Island in the South China Sea along a 780-kilometre pipeline.

After touring the generator plants and having lunch at the station's canteen, members were shown Tsang Tsui Lagoon, where CLP stores its fly ash. Then it was on to the nearby West New Territories (WENT) Landfill.

The humongous size of the landfill has to be seen to be believed. An entire hillside measuring 110 hectares is basically being levelled to create a gentle slopping hillside.

Two thirds of the rubbish arrives by sea from various points around Hong Kong, the rest is by road. Rubbish is compressed into sealed containers and shipped to a dock at the foot of the landfill. Containers are loaded onto convoys of lorries which then trundle up the landfill to designated dumping zones. About 200 containers disgorge their contents into the landfill daily.

The maximum depth of the waste at the landfill is expected to be 120 metres, and its capacity is about 61 million tonnes.

All manner of waste is dumped into the landfill, from tyres to hospital waste. About 320 tonnes of restaurant grease is also dumped into the landfill every day. Mike Campbell, chief operating officer for Swire SITA Waste Services Ltd, which oversees the operations of the landfill, said work to collect this grease and convert it into fuel is underway and he hopes to get approval from the government soon.

To ensure that no residue from the landfill seeps into the surrounding environment, a system of filter layers of rocks, matting, and polyethylene liner contains any residue. A complex of pipes running along the bottom of the landfill carries away leachate which is treated at onsite tanks. Gases are also sucked out of the landfill and burnt off onsite.

The landfill is expected to be full in 10 to 15 years, but Mr Campbell said it is difficult to say exactly when this will be because of so many outside influences. By that time, Hong Kong is expected to have an additional 2 million more people who will be producing rubbish. Interestingly, the state of the economy also affects the amount of rubbish that citizens produce. If Hong Kong's GDP grows 1 per cent, then there is an average increase of 0.5 per cent in the amount of rubbish that the territory produces, he said.

Once full, the landfill will be covered with soil and landscaped to become a recreation area. The contractor, Swire SITA Waste Services Ltd, will be responsible for maintenance and environmental control, and monitoring of the landfill site for 30 years after its closure.