Bo Weidema’s example shows how to assess a refinery with several useful outputs without dividing shared environmental burdens between products using a fixed allocation factor. Instead, it models how changes in supply or demand affect connected processes. This consequential approach asks which production or treatment activities change when the system changes.
The hypothetical refinery uses crude oil and waste hydrocarbons from garages, wood preservation and the food industry. Its variable outputs are fuel oil, naphtha and kerosene. Residues are dependent outputs: their quantities depend on the inputs and product mix. The example assumes a small change that does not encounter the technical limits of the refinery industry.
Waste lubricants and other waste hydrocarbons are independently variable because their supply comes from upstream activities, not from demand for refinery products. The model assumes that the wastes are fully used and that their market supply does not exceed refinery demand. The refinery therefore acts as a waste-treatment process, with a cut-off at its gate for the other refinery products.
Using the wastes displaces crude oil production, and the avoided production is credited to the main products of the waste-generating activities. The model also accounts for changes in refinery and downstream emissions caused by the alternative inputs, including different processing needs and contaminants. For example, it considers how heavy metals may pass into fuel fractions, plastics or residue-derived products, while some organic contaminants may decompose during processing.
In the illustrative calculation, one kilotonne of waste hydrocarbons yields 0.91 kilotonnes of selected products and upgrading residues. One kilotonne of crude oil yields 0.66 kilotonnes of those outputs. The example therefore assumes that one kilotonne of waste hydrocarbons displaces 1.38 kilotonnes of crude oil. These values depend on the assumed process losses and material composition; they are not universal refinery factors.
When demand changes for fuel oil, naphtha or kerosene, the model includes the related crude oil production, refinery processing, residue upgrading and the products displaced by using the residues. Environmental exchanges are attributed to the output that caused the change, rather than allocated by mass, energy content or economic value.
The calculation needs information on refinery outputs, crude oil displacement, processing emissions, residue treatment and contaminant fate. Weidema uses simplifying assumptions and selected literature data to demonstrate the procedure, and notes that better information about the waste hydrocarbons could refine the assumptions and results. The example is methodological: a real assessment must define the relevant market, technical constraints, displaced processes and data for its decision context.
