Decarbonisation Technology - May 2023 Issue

of carbon and other elements, can be seasonal and dependent on the source of the waste, whether it be municipal solid waste (MSW), commercial and industrial, or construction waste. Solid feedstock preparation is a standard requirement for gasification processes to ensure the feedstock size, distribution, moisture content, and metal levels are controlled within the design limits for optimal operation of the gasifier. This is performed in the feedstock processing stage. RDF is shredded, screened, subjected to removal of ferrous and other metals, and then dried before it is routed to the gasification step. Some of the physical variability of the RDF, as mentioned above, is controlled RDF composition data sources focus mainly on the characteristics that are relevant to describe it as a fuel source, such as its calorific value, water, and ash content. Other critical parameters for use in a conversion process include concentration levels of specific metals and components, which can vary depending on the RDF source. These components can affect sensitive catalytic processes by reducing catalyst life. The criticality of selecting the right feedstock processing and gasification steps is visible in the fact that the RDF composition variation needs to be attenuated to a more narrowly controlled syngas quality range to produce syncrude (and eventually SAF) from the process and mixed in the feedstock processing. However, there are other compositional challenges, as described below.

with a stringent specification. It requires thorough assessment of the RDF compositional variability, the key influencing factors, and the required process operating conditions via close collaboration between the end users, RDF suppliers, technology providers, and the engineering contractor to develop a design to accommodate a variable feedstock and produce a consistent grade product. A lifecycle assessment for sourcing RDF feedstock from any supplier should be performed to ensure the emissions from collecting, processing, and transporting to the consumption site are optimised and fall within the sustainability criteria for SAF as defined by the International Civil Aviation Organisation (ICAO). It may happen that the facilities would need to be located close to RDF sources, making modularised design more amenable. This may limit efficiencies and economies of scale, therefore, targeting design to work at lower rates by maximising performance within the constraints for equipment such as reactors, heat exchangers, columns, compressors, and others. ABSL’s RadGas gasification ABSL’s gasification technology uses a two- stage approach to address the tar formed in gasification and produces a relatively clean syngas. The first stage, operating above 700°C, is like conventional gasifiers as it breaks down the complex lignocellulosic materials, in the presence

Gasication (R ad G as )

Refuse derived fuel (RDF) processing

CO capture

GTL

Fischer - Tropsch

Feedstock preparation

Gasication + tar conversion

Water gas shift

Acid gas removal

CO compression & dehydration

Bio syncrude stabilisation

Waste heat boiler

Syngas polishing

Syngas compression

Gas cleaning

CO export

Syncrude export

Euent treatment

Figure 2 Block flow diagram of Protos Biofuels process