More than 200 waste-to-energy (WtE) plants are operating in China. One of them in the city of Lianyungang in Shandong province, north of Shanghai, will be complemented by a pretreatment plant for municipal solid waste (MSW). The Austrian-German technology firm Redwave designed the process for the pretreatment plant. Tim van Heeswijk from the sales division of Redwave presented the concept and the design at Waste to Resources 2017, the Seventh International Symposium MBT, MRF & Recycling, in Hannover 16 to 18 May.
In China, household waste has a different composition than in Europe. It has a relatively high content of organics and moisture, so less energy efficiency is achieved when incinerated. Depending on regional conditions, the calorific value of MSW in China is in the range of 3 to 6.7 megajoules per kilogram, which is less than the 9 to 11 megajoules per kilogram in Europe.
China Jinjiang Environment Holding Co. Ltd. contracted with Redwave to supply, install and commission the Lianyungang MBT (mechanical biological treatment) plant. The MBT plant is designed for an annual throughput capacity of roughly 274,000 tons based and with a daily input of 750 tons. The client´s request was to increase the calorific value by drying the waste from an incoming moisture of 50% to a maximum moisture content of 30%.
Starting from a deep bunker, a fully automated delivery crane conveys the waste into the hopper of the preshedder. Via an overbelt magnet for ferrous separation, the preshredded material is fed to an intermediate bunker. A fully automated overhead gantry crane conveys the waste to one of the 18 biodrying units. When ambient or recirculated air ventilates the material in the box, it heats up by an aerobic microbiological process. The water is discharged of the drying box in the form of water vapour, and the dry material remains in the box. Because each box is individually controlled, it is possible to guarantee even and efficient drying, Redwave says. The relevant data, such as the flow rate of circulated and fresh air, heat output capacity and the temperature curves, are analysed in the process control.
Each biodrying unit has a removable lid on top and is designed as self-supporting insulated steel structure. The drying process inside the unit proceeds independently from the outside climatic conditions, the company says.
The dried waste then is processed in various steps, including screening, airstream sorting, shredding, overbelt magnets, eddy current separators (ECS) and Redwave sensor-based sorting systems and is turned into a homogenous solid recovered fuel (SRF), the system supplier says.
The biological drying and subsequent mechanical treatment increases the calorific value from 3 to 6.7 megajoules per kilogram to approximately 12 to 14 megajoules per kilogram, according to Redwave.
The MBT system in Lianyungang is under construction, with completion scheduled for the end of 2017.