Towards a zero (net) carbon refinery
Review of options for refiners to reduce the carbon emissions from their refineries. The technologies already exist to develop a refinery that has zero net emissions
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The well-to-wheel emissions for petrol and diesel can be split into three main parts: oil production and transportation, oil processing and transportation, and emissions from the consuming engines. In order to reduce emissions and meet targets for carbon reduction, it is likely that all three parts of the chain will need to make some contribution.
While the processing of oil in the refinery contributes around only 5-10% of the total well-to-wheel emissions, the opportunities for reducing these are significant due to the nature of the processes used, the fuels available and the fact that these are large-scale fixed location processes making applications such as carbon capture and storage (CCS) more practical than they would be on individual vehicles.
This article will look at the main sources of carbon emissions from a refinery and consider a range of options for reducing the carbon impact of the refinery, starting with fuel substitution and energy efficiency, then moving on to how technologies such as CCS and renewable power generation could be integrated into the refinery.
The article will look at the impact of making these changes on refinery economics and show one possible solution that, at a sufficiently high carbon price, could see a zero net carbon refinery (that is, one where no fossil fuel-derived carbon is emitted).
Sources of CO2 in the refinery
Sources of carbon dioxide (CO2) in the refinery can be categorised into four main groups:
• Fuel to process units
• Steam and power production
• Hydrogen production
• FCC coke (where applicable).
The emissions of an individual refinery depend on a number of factors. The configuration of the refinery is a key factor, as complex upgrading refineries produce more CO2 than simple hydroskimming configurations, but they tend to produce more of the fuels society demands (gasoline and diesel) per barrel of oil processed. The fuels used in the refinery also have an impact, as do the crudes processed. Heavy, sour crudes require more energy to process than do light, sweet crudes.
In order to quantify the relative sizes of the emissions, we can look at a typical refinery configuration and the CO2 emitted from it. In this article, we have considered an FCC-based European refinery processing 150 000 b/d of Ekofisk Crude that generates all power and steam on-site from refinery fuel gas and fuel oil. Figure 1 shows the main configuration of this refinery. The emissions from this refinery are shown in Figure 2.
Options for reducing refinery carbon emissions
There are a number of ways of reducing the carbon emissions of a refinery, ranging from relatively simple, low-cost options to complex, capital-cost-intensive options. These options can be grouped into a number of areas and we will consider each area in turn.
The first area of focus is energy efficiency. The other options we pursue will tend to be more expensive than the current energy sources in the refinery (if they were cheaper, they would already be used) and so making the most of the energy we do use will become even more important.
Even refineries that consider themselves good performers in terms of energy efficiency can do more, and this is illustrated by a recent study Foster Wheeler completed for a top-quartile refinery in northern Europe. This study resulted in operational improvement and investments being identified that could save around 10% of the fuel used in the refinery, and the potential projects had an estimated payback of less than 18 months. In our example, we will assume our base case 150 000 b/d refinery has already achieved a high level of efficiency and will focus on other options to reduce the emissions from the refinery.
Hydrocarbon fuels contain very different levels of carbon and result in significant carbon emissions for the same level of energy requirement. Table 1 compares the impact of different fuel sources on carbon emissions.
Figure 3 shows the total refinery CO2 emissions from our 150 000 b/d refinery, assuming all heat and power is generated on-site, compared with likely emissions if natural gas was imported into the refinery for power generation.
We can see that moving from fuel oil firing to natural gas firing reduces emissions from the refinery by about 13%. Of course, the economics of this option are highly dependent on the relative prices of natural gas and fuel oil. In the US, where the differential between natural gas and crude price is wide, natural gas firing will be increasingly attractive. In Europe, the incentive will be lower, but will still generally favour natural gas firing where available. Figure 4 shows the natural gas price required to break even on energy cost versus fuel oil at varying carbon prices.
Green heat and power
In our example 150 000 b/d refinery, we have assumed that all of the refinery's power requirements are generated on-site. One way to reduce the refinery's emissions would be to generate this power from low-carbon sources, either on-site or by purchasing green power over the fence.
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