Energy recovery includes any technique or method for minimising energy input to an overall system by exchanging energy from one subsystem of the overall system to another. Energy can be in any form in either subsystem, but most energy recovery systems exchange thermal energy in either sensible or latent form.
In some circumstances, it is necessary to use a supporting technology, either daily thermal energy storage or seasonal thermal energy storage (STES, which allows storage of heat or cold between opposing seasons), to make energy recovery feasible. An example is waste heat from air-conditioning machinery that is stored in a buffer tank to assist night-time heating.
Processes such as incineration and anaerobic digestion not only provide energy sources, but also reduce the volume of waste.
The term “energy recovery” is often applied to only a small number of methods for converting waste to energy, when in fact it applies to a wide range of technologies used to create heat, electricity or fuel.
Energy recovery offers governments and businesses another way to reduce their waste streams. Once the recyclable materials have been removed, the remaining waste can be treated to release energy.
There are two types of technologies generally used to convert waste streams into energy: thermal and biological. Thermal waste-to-energy is done by burning the waste, while biological processes usually focus on anaerobic digestion.
Advantages of energy recycling
Waste-to-energy can reduce landfilled waste by up to 90% and is considered a renewable, low-emission energy source that provides well-paying domestic energy jobs (waste collection cannot be diverted). And the US Environmental Protection Agency has found that waste-to-energy recovery produces electricity “with less environmental impact than almost any other source of electricity”. The EPA estimates that the energy recovery technology currently in use helps avoid the emission of 33 million metric tons of carbon dioxide per year.
This type of waste-to-energy technology is just one way to recover the energy inherent in non-recycled plastics. Today, there are innovative and promising technologies that can convert used plastics into fuels and other valuable materials. The Plastics Division of the American Chemistry Council (ACC) has helped sponsor numerous demonstration projects and is working with related industries across the country to help bring three emerging technologies to market.
Examples of energy recycling
Emerging energy recovery technologies:
Just as it sounds, this technology converts unrecycled plastics into oil that can be refined and used as fuel for automobiles and other purposes. The process varies, but usually involves these steps:
First, plastics are collected and sorted for recycling (since plastics recycling is preferred over energy recovery); then the unrecycled plastics are sent to a plastics-to-fuel facility.
These non-recycled plastics are heated in an oxygen-free environment, where they melt into a liquid and then vaporise into gases.
The gases are cooled and condensed into a wide variety of useful products, such as synthetic crude oil, synthetic diesel, paraffin, etc.
The conversion of plastics into fuel is very promising: one company claims that its system can convert 50 tonnes of plastic waste into 26,000 gallons of oil per day. If all non-recycled plastics could be converted in this way, we could create enough oil to power nine million cars for an entire year.
Emerging energy recovery technologies:
Engineered solid fuel.
This technology converts non-recycled plastics (and other materials) into solid fuel pellets that could one day be used like traditional solid fuels, such as coal, in facilities that make steel and cement and other products.
Research on this technology generally focuses on the non-recyclable “waste” left over from recycling facilities. A recent test has shown that solid fuel made from this waste (a mixture of plastics and waste fibres) can be used as an alternative fuel in a cement kiln. The BTU content of the solid fuel is similar to that of bituminous coal used in cement kilns, and significantly higher than that of sub-bituminous coals and lignite.
An analysis of the test data showed that replacing coal with this solid fuel could reduce fossil energy use by approximately 6% per year in the cement kiln, which is equivalent to the amount of coal needed to power 1,500 homes for a year. To put this in a broader perspective, if we were able to convert just five per cent of the waste passing through US recycling facilities into solid fuel, that could displace enough coal to power 700,000 homes, as well as resulting in CO2 reductions equivalent to removing more than a million cars from the road… all with materials that are now being buried in landfills.
Emerging energy recovery technologies:
Plastics can also be converted into a gaseous fuel that can be used to produce electricity or converted into liquid fuels and even feedstocks (chemicals) for manufacturing.
Gasification is nothing new: it has been used around the world for almost 200 years to convert carbon-based materials into energy, heat, fuels and chemicals. Gasification of wood waste and agricultural biomass, for example, is commonly used for electricity and heat production.
But waste gasification is not yet widespread. While Japan and South Korea have been using rubbish and industrial waste gasification for a couple of decades, commercial installations in the US and Europe have not yet taken off.
However, interest in gasification has grown over the last decade. In 2013, there were 21 companies with pilot and demonstration facilities, in addition to 17 commercial-scale facilities under development or construction.
The main output of gasification is synthesis fuel gas (syngas), which is valuable as a fuel or intermediate product. Syngas can be used to produce energy, converted into liquid fuels (ethanol) and transformed into hydrogen and methanol, which in turn can be transformed into countless fuels and chemicals.
The relationship between recycling and energy savings
Recycling and energy saving are closely related. When we recycle, not only is there less waste in the environment, but also CO2, oil, electricity and water emissions are reduced, allowing us to put raw materials and energy to other uses. Making a product from recycled materials almost always requires less energy than making the product from new materials. For example, using recycled aluminium cans to make new aluminium cans uses 95% less energy than using bauxite ore, the raw material from which aluminium is made. In the case of recycled paper, the energy consumed in the manufacturing process is reduced by up to 65%. On the other hand, recycled glass maintains its properties in perfect condition and allows energy savings of up to 38%.
Benefits of recycling in energy savings:
Lower energy consumption: By reusing materials, we manage to reduce the cost of extraction, transformation and raw materials. We reduce energy consumption.
Less CO2 in the environment: We reduce CO2 emissions, thus reducing air pollution and the greenhouse effect.
Thanks to recycling and a circular economy based on reuse, we will significantly reduce the need for raw materials and minimise energy consumption, increasing efficiency and achieving economic savings at the same time.
Beneficios del reciclaje en el ahorro de energía:
Menor consumo de energía: Al reutilizar materiales conseguimos reducir el gasto de extracción, transformación y materias primas. Disminuimos los consumos de energía.
Menor CO2 en el ambiente: Disminuimos las emisiones de Co2 por lo que disminuye la contaminación del aire y con ello el efecto invernadero.
Gracias al reciclaje y a una economía circular basada en la reutilización, reduciremos notablemente la necesidad de materia primas y minimizaremos el consumo energético, aumentando la eficiencia y logrando, al mismo tiempo, un ahorro económico.