Nov-2024

Advanced gasification for waste-to-energy products

Supportive policy needs to address development challenges.

Amna Bezanty
Kew Technology

Article Summary

We are at the heart of two major parallel market evolutions; the energy trilemma, in which the UK, along with many other parts of the world, grapples with the affordability, security and sustainability of energy and the creation of a circular economy (see Figure 1).

The issue with waste and problematic non-recyclable and single-use waste continues to be a major challenge. There is much talk of creating circular economies where waste is reused or regenerated as a material or product, but how do we deal with the vast quantities of different waste generated worldwide?

At the top of the circular waste hierarchy (see Figure 2) is reduction. We all know we have to create less waste. Then, there is reuse and recycle. Travel down the pyramid, and you hit the well-known solutions of how we traditionally deal with waste – incineration backed up by disposal in landfill. For many years, this has been the primary way local authorities have managed their waste, working with waste management companies to take as much waste as possible away from landfill and incinerate.

However, we are facing a huge problem – not just with the vast amounts of waste still generated but also with the pathway to net zero. The waste sector is a significant carbon emitter, with incineration accounting for around 4% of the UK’s total emissions, and this is set to rise.

Emissions Trading Scheme (ETS)
The government has also announced that, from 2028, domestic maritime transport, waste incineration, and energy from the waste sector will be added to its Emissions Trading Scheme (ETS) for the first time. Designed to tighten limits on emissions across key sectors such as industrial and aviation as the UK pushes for net zero, this change will have major implications.

In an effort to ensure a level playing field across different technologies, the scheme is targeting incineration, combustion, and energy recovery from waste, including emerging technology like Advanced Conversion Technology (ACT), such as advanced gasification, or Advanced Thermal Treatment (ATT), such as pyrolysis.

Waste management in the UK currently relies heavily on incineration and combustion, both of which produce significant fossil CO2 emissions. However, by including innovative technologies that can transform waste into valuable resources while reducing carbon emissions, some emerging technologies will be severely disadvantaged.

Given the lead times for changing waste management practices, many waste suppliers are looking for viable pathways to net-zero solutions and are currently trying to decarbonise via economically and technically challenging heat offtake or carbon capture, use and storage (CCUS).

The expansion of the scheme while solutions are still needed puts it at risk of becoming counterproductive. Taxing waste-to-energy, such as waste-to-syngas and similar products, without a policy support scheme in place acknowledging their lower carbon nature could undermine their potential to reduce greenhouse gas emissions by placing too great an economic burden on their innovation. These technologies could fundamentally change the waste management system by decarbonising waste before it hits incineration and landfill.

KEW’s advanced gasification technology
The use of ACT operating at elevated pressure gasification (8 bar rather than atmospheric) allows the higher-efficiency conversion of carbon-rich feedstocks such as waste and non-recyclable materials and biomass into valuable products such as syngas (a mixture of hydrogen and carbon dioxide, CO₂).

A feedstock can essentially be anything you put into the process, such as municipal solid waste (MSW) from households, commercial and industrial waste, medical waste, and biomass, including wood, crops, agricultural and forestry waste, and sewerage sludge.

Unlike incineration, which burns waste materials in the presence of excess air to produce heat and ash, gasification uses limited oxygen to partially oxidise the feedstock (see Figure 3). This process generates syngas and reduces the volume of residual ash, offering a cleaner and more controlled approach to waste conversion.

Being able to achieve a consistent hydrogen-rich, tar-free syngas composition regardless of the feedstock type and composition is a critical pathway to high-value energy molecules.

Ideally co-located on waste disposal sites, it means any feedstock can be used to produce the same consistent compressed fuel (syngas), halving the energy needed to compress captured CO2 and drastically reducing costs and greenhouse gas emissions (see Figures 4 and 5). This could allow waste suppliers to convert their ‘dirtiest’ waste, which costs them (and companies) the most to ‘deal with’, into a stable, clean gas that cuts carbon.

Put in a bag of waste or low-grade biomass, and it can be recycled into high-value molecules such as renewable and recycled carbon natural gas substitutes, hydrogen, methanol, and dimethyl ether, a low-carbon liquefied petroleum gas (LPG) and diesel substitute. The gas that comes out is a hydrogen-rich gas (syngas), which is the building block for everything that can then be converted into multiple fuels.

Feedstock challenges
However, while waste is all around us, sourcing and handling this waste ‘feedstock’ is not straightforward. The availability of waste is often grossly understated, dependent on type and where it is in relation to where it is needed.

The UK government recognises the importance of ACT technology in reaching net zero and has investigated and reported on the volumes and availability of different feedstocks, with biomass, household waste (MSW), and commercial and industrial waste generated in significant quantities.

Residual MSW and commercial and industrial waste contains almost 50% biogenic matter, with the rest coming from fossil fuels. Biogenic matter, a renewable feedstock input, generates significant CO₂ savings and must be prioritised for more efficient processes targeting the harder-to-abate sector.

The government’s review into advanced gasification technologies recognises the attractiveness of MSW and commercial and industrial waste as a fuel, given that it costs money to dispose of and the importance of diverting these waste streams away from landfill to avoid the release of carbon (90% methane) from landfill.

Despite the potential, many high-profile ACTs around the world, including recent examples in America, have struggled or failed. This is not only due to inherent flaws in some of the technologies, but because these projects pursued large-scale implementations. The absence of a smaller-scale validation phase led to unforeseen technology challenges and difficulties in managing the practicalities of waste feedstock logistics. Consequently, these projects often faced insurmountable issues related to feedstock specification and operational feasibility, highlighting the critical importance of phased validation and scale-up processes.