Landfill vs Skyfill

How landfill might be the better option for disposal of low-grade plastics

WITH levels of waste plastics rising in the UK as a result of China’s National Sword scrap import policies, the debate is picking up over what to do with it. Could landfilling, rather than incineration, be the better option?

China’s crackdown on imports of contaminated recyclables is leading to an ever-increasing stockpile of waste plastics materials worldwide. Tackling this problem waste stream will probably lead to increased incineration of waste to produce energy as the ‘best’ solution. An attractive option perhaps, but when the carbon produced by that process is taken into account, is it really the best environmental solution?

Doing the math

Creating energy from waste plastics also produces between 25–30% residual incinerator bottom ash (IBA), which still requires waste disposal or long-term storage. Although generating heat and power from waste sounds appealing, it is inefficient when compared to burning gas in a modern generator system. Burning natural gas also produces fewer emissions and there is zero solid ash waste to dispose of.

The carbon release from waste incineration needs to be considered and compared to the alternative methods of generating an equivalent amount of electrical power.

Typical energy-from-waste (EfW) plants have efficiencies of up to 30% for converting feed material into electricity. In contrast, a modern combined cycle gas turbine (CCGT) efficiency is typically about 50%. As shown in Figure 1, this disparity in efficiencies means that producing 1 MWh of electricity from a CCGT produces just 40% of the CO₂ emissions for the same amount of energy made from plastic incinerated at an EfW plant.

It is true that a best-in-class EfW plant with integrated heat recovery (ie combined heat and power, CHP, plant) can recover a further 35% of the available energy from the waste fuel. However, this heat could instead be generated by a natural gas boiler that has an efficiency of at least 90%. Even taking this additional heat efficiency into account, a combination of CCGT and boiler still only emits about 65% of the CO₂ of the leading EfW plants.

Using the CO₂ metric alone suggests that it makes more sense to bury large amounts of plastic in a long-term carbon sink in the ground and efficiently combust natural gas to satisfy our immediate power needs. However, until world leaders are prepared to transform the taxation on fossil-based fuels in a way that truly reflects the high environmental cost of “free carbon release”, then this numeric analysis remains an esoteric academic study.