In recent years, any number of energy-from-waste (EfW) plants have been built in the UK but, inevitably, the scale of these facilities is dwarfed by those being established in the most heavily populated regions of the world.
Take, for example, the Luodai Town EfW plant which serves the Chinese city of Chengdu, the capital of Sichuan. Chengdu has more than 10.5 million inhabitants generating 3,600 tonnes of household refuse every day. The Luodai facility processes some 400,000 tonne of household waste a year, with the heat produced from the incineration operation used to generate electricity for 50,000 homes in Chengdu. The plant has an output capacity of 120 million kWh, and it is estimated that more than a million tonnes of CO2 emissions will be saved by 2015.
In an operation of this scale, continuous and uninterrupted incineration of waste material is of paramount importance to the efficiency of the plant. To meet the needs of the application and the volume of throughput, the operator specified an intermediate buffer store system, with two overhead travelling cranes, supplied by Demag Cranes and Components, for the materials handling operations. Both of the fully automatic cranes have a 28.5m span, 16-tonne SWL and are equipped with a 10cu m grabbing bucket.
Trucks from Chengdu deliver refuse to the plant, and deposit it into the 19.6 x 84sq m sunken intermediate buffer store from one of 12 tipping points. Once the trucks have left the operational area, the automatic grabbing cranes lift newly deposited material on to existing refuse within the store. By blending different types of waste, optimum calorific values are achieved for efficient incineration and maximum heat output.
The intelligent control system operates on a grid system, dividing the buffer store in to 156 zones, with the position and height of waste in each zone determined automatically. The grid system also provides reference points for the automated crane system, ensuring precise positioning.
The cranes are programmed to distribute waste evenly above the 45sq m chutes that feed the three furnaces, ensuring constant and uninterrupted incineration. In addition to feeding the furnaces with up to 50 tonnes of waste an hour, the grabbing cranes also perform a number of functions to blend and clear the waste.
To meet the required high cycle rate, the cranes have long travel speeds of 80m/min, with cross-travel and hoisting speeds of 60m/min. The cranes also feature a fully automatic load sway damping system, which not only provides accurate positioning of the grab but also eliminates the potential of damage caused by the grab colliding with the bunker walls.
The Demag automated crane system provides a low-maintenance solution for the particular materials handling requirements of the Chengdu operation, ensuring uninterrupted feeding of the furnaces for 24-hour operation. There are also positive health and safety implications of the automated system because there is no need for operators to access the potentially hazardous materials handling area.
The success of any EfW facility depends largely on the efficiency of its materials handling system. While it is unlikely that there will be many plants in the UK as large as the Chengu facility, the principle remains the same - it’s just a question of scale.
Paul Bartlett is sales director, industrial cranes, at Demag