Energy recovery: Smart management of waste
Waste to energy plants smart alternatives for managing waste, says David de Lara, Middle East country manager, ACCIONA Industrial
Managing the thousands of tonnes of waste that towns and cities produce every day is one of the most important challenges in order to preserve our environment.
In the case of solid waste, this is a triple challenge: firstly to reduce the quantity of this waste; secondly, to reuse the highest possible percentage of the waste produced; and lastly to recycle any waste that cannot be reused. It is known as the “3R” rule, an initiative that started in Japan in 2002 and advocated by the G8 Summit in June 2004, to globally promote a society that recycles and uses resources and materials efficiently.
Landfill has been the traditional method for treating waste that was technically impossible to recycle, or for which the cost of recycling outweighed the benefits. According to a recent study conducted by the Abu Dhabi Centre for Waste Management, the amount of waste in UAE averaged 4.892 million tonnes per year.
Landfill sites occupy large tracts of land with a significant impact on the environment and the landscape; while the biogas and the large amount of leachates they produce (liquids that filter into the subsoil and can enter surface or groundwater) pose an obvious risk of pollution. Consequently, new technologies have been developed to prevent these negative impacts, which focus on “energy recovery” plants, also known as “Waste to Energy” plants or W2E.
These plants thermally treat the waste, through complete oxidation, in order to release the energy contained in it, to produce electricity, heat or a combination of the two. There are even new technologies in development that aim to produce to commercially valuable chemicals from the waste.
W2E plants comprise a series of facilities with specific functions in order to convert waste into energy via a multi-stage process. The waste arrives at the reception and storage zone where it is weighed, unloaded and stored. Since the plants operate 24 hours a day throughout the year, sufficient waste must be stored to ensure uninterrupted operations at all times.
Another facility, which is typical within an energy recovery plant, is the mechanical waste classification zone, where waste is classified by size, density or type of material.
Plants that receive a significant amount of organic waste also have a biological treatment zone. Two types of processes are generally used: composting to produce compost (organic fertiliser) and anaerobic digestion, which produces a biogas that can be used for electricity or can be washed to produce natural gas.
The waste is burnt in combustion furnaces at temperatures in excess of 850º C in order to prevent dioxins forming. The by-product of this combustion is slag, which can be used as a construction material. The heat produced by the furnaces is converted into steam in the boilers, which are especially designed to collect the ash generated by the combustion. The steam drives the turbines to produce electricity or heat.
The unquestionable benefits of energy recovery processes based on urban waste have led to the regional expansion of this approach: The Abu Dhabi National Energy Company, TAQA, developed a facility near the sea port in Mussaffah that has an annual capacity of 1 million tonnes of solid waste which can be converted into 100 MW of energy, sufficient to power around 20,000 Abu Dhabi homes.
Also, the Abu Dhabi Fund for Development (ADFD) approved a concessionary loan to Emirates Waste to Energy Company (EWEC) for the development of the W2E facility in Sharjah, UAE. Once the first phase of operations begins by 2020, the plant will be able to convert 2,000 metric tonnes of municipal solid waste per day to produce 60MW of power. The UAE aims to be one of the leading countries in the GCC to achieve the highest rate of solid W2E management.
ACCIONA Industrial, one of the divisions of ACCIONA infrastructure with presence in the UAE since 2008 and in the region since 1993, is driving sustainable development in the industrial sector. We are focusing our strategy on increasing our portfolio of renewable energy projects and working towards clean and competitive technology all over the world and the GCC region.