Energy from Waste

Key Situations:

Outline of the waste streams available that could be used for energy production - ideally bio-methane. However, plastics are today's "pollutants" to the viability of waste streams to energy. The plastic need a different method of treatment. Overall, we wish to avoid the less efficient {and problematic emissions} of incineration technologies.

WORK IN PROGRESS:

TYPES OF WASTE STREAMS

Homogeneous Organic Wastes, typically farming wastes These typically farm based bio-digesters, can create good volumes of bio-methane [with some CO2 and other contaminants - which can be removed] from a wide variety of soft organic wastes - from cattle slurry to oil-rich seeds. We have a database of the energy values of most farm wastes to be able to estimate economic viabilities in terms of exporting to the gas grid, generating electricity and exporting to the electric grid or even as transport fuels {compressed natural gas} CNG.

Palm Oil Wastes and other industrial processes In regions where Palm Oil production is prevalent, the waste lagoons associated with Palm Oil production, with the husks etc can be utilitise as rich source of bio-methane. The waste from these processes can be problematic in environmental terms - so bio-digestion is an ideal transformation into a commercial fuel or used in energy and heat production as a feed back into the industrial process itself.

Mixed Wastes and Rubbish Tips There are a great many pre-existing waste tips of varying sizes and "conditions" globally - [Some tips can be on-fire or explosive with the methane generation]. Comprehensive treatment and separation of the leachate and methane can produce vast quantities of bio-methane [again with CO2, H2S etc - all of which can be separated]. The Leachate is also rich in Ammonia and other compounds. Experience in the UK shows that a waste tip can produce methane [and other smaller impurities] for up to 30 years. The London Brick Works in Bedfordshire used bio-methane from the waste tip on their clay pits {as supplied from London}, to fire their brick kilns for decades.

Plastic Waste "Pollution" The vastly increased usage of plastics over the last decades, has changed the composition of waste globally. Plastic themselves are difficult {not impossible} to break down and thus make bio-digestion more difficult. In practice the separation of Plastic {and metals, builders rubble etc} needs to be carried out before digestion. Other technologies to deal with plastics {see below} like Cold Plasma Pyrolysis can yield methane and Hydrogen.

Anaerobic digestion can be used to generate energy from organic waste like food and animal products. In an oxygen-free tank, this material is broken down to biogas and fertiliser.

It’s an approach with big potential. If we treated 5.5 million tonnes of food waste this way, we’d generate enough energy to serve around 164,000 households while saving between 0.22 and 0.35 million tonnes of CO₂, in comparison to composting.

Extracting the biogas produced by biodegrading materials on landfill sites is another way of getting useful energy from waste. Although it’s an approach that’s in decline due to the reduction of the amount of organic matter going to landfill, it’s making a notable contribution to UK energy supply: the source 3.04TWh of green electricity in the last year, in fact.

Tackling the plastic problem

Plastic waste has risen to significant levels of public consciousness in recent years, for its negative impact on habitats and species. In response, the UK Government’s 25-year Environment Plan pledges to eliminate all ‘avoidable’ plastic waste by the end of 2042 – and it’s not alone in making such political commitments. Can waste-to-energy step in here?

Converting plastic waste to energy certain makes sense from a chemical perspective, given plastics come from the same origin as fossil fuels. We’ve already looked at the two main techniques involved: pyrolysis, where plastic is heated in the absence of oxygen, and gasification, where air or steam heats the waste, creating gases that either produce petrol or diesel, or are burned to generate electricity.

New techniques such as cold plasma pyrolysis, provide the potential to create fuels such as hydrogen and methane, as well as useful chemicals for industry.

But there are barriers in the way of wider uptake of plastic-to-energy techniques. Gasification of plastics requires significant investment, including advanced controls and pre-treatment facilities. Also, developing plastic-recycling plants presents a risk of limiting those facilities, when decision-makers may instinctively opt for waste strategies where general waste is processed together, rather than separating out different elements.

Novel approaches to waste management in the UK will surely rise in the coming years. Recycling rates seem to be plateauing, with minor increases only  seen. While generating energy from waste has a lot of promise, we need to focus on making products last longer, and when they really can’t be fixed, finding ways to recycle and reuse them. Only when those options are exhausted should we turn to waste-to-energy.

the prospect of using rubbish for fuel isn’t too far from reality. Plastics, in particular, contain mainly carbon and hydrogen, with similar energy content to conventional fuels such as diesel.

Plastics are among the most valuable waste materials – although with the way people discard them, you probably wouldn’t know it. It’s possible to convert all plastics directly into useful forms of energy and chemicals for industry, using a process called “cold plasma pyrolysis”.

Pyrolysis is a method of heating, which decomposes organic materials at temperatures between 400℃ and 650℃, in an environment with limited oxygen. Pyrolysis is normally used to generate energy in the form of heat, electricity or fuels, but it could be even more beneficial if cold plasma was incorporated into the process, to help recover other chemicals and materials.

The case for cold plasma pyrolysis

Cold plasma pyrolysis makes it possible to convert waste plastics into hydrogen, methane and ethylene. Both hydrogen and methane can be used as clean fuels, since they only produce minimal amounts of harmful compounds such as soot, un-burnt hydrocarbons and carbon dioxide (CO₂). And ethylene is the basic building block of most plastics used around the world today.

As it stands, 40% of waste plastic products in the US and 31% in the EU are sent to landfill. Plastic waste also makes up 10% to 13% of municipal solid waste. This wastage has huge detrimental impacts on oceans and other ecosystems.