Renewable fuels and biofuels in a petroleum refinery
Sound judgement of process environment, logistics and product properties is needed to process fossil and bio-derived raw materials on a single site
Jukka Keyriläinen and Matti Koskinen
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Bio-based raw materials and associated process technologies form an entirely new engineering challenge for integrated petroleum refineries. The composition variation of raw materials, including trace components, various logistical problems and the difficulty of coming up with the right integration approach compared to conventional engineering of fuel refineries using petroleum feedstocks, needs new types of skills and experience. The fundamental engineering challenge is to combine existing advanced petroleum process technologies with various aspects of the problems faced in renewable fuels process engineering and to come up with the optimal design approach that enables the implementation of biomaterial streams to the highly integrated process environment of a petroleum refinery.
Renewable fuels have been one of the hottest topics so far in this millennium’s energy debate. The reason for the growing interest is obvious: the ever-increasing concern about CO2 release to the atmosphere and its impact on global warming. Another significant factor is political instability in the areas where crude oil is produced. And thirdly, local agricultural economics and trade deficits, partly due to historically high crude oil prices, provide an additional driver to get more energy from domestic sources among quite a few of the leading consumers of petroleum.
During past centuries, flora has been the source of fuel as well as many valuable and vital substances and constituents. In the oil era, many of those products became cheaper and performed better when derived from fossil feedstocks. For renewable fuels, the sustainable way would be to encourage benefiting first from the value chain of the biomass constituents and to produce fuel only from the residues, or from an entirely different feedstock such as algae — not part of the food chain or the traditional green industry. This method of switching from pollution to solution is already on the research agenda of many enterprises.
Petroleum refinery as a platform for renewable fuels production
Petroleum refineries are natural locations for renewable fuels production. They are, after all, built for the production of advanced fuels by the most cost-effective means to deliver appropriate products for surrounding societies.Refiners are very experienced with their raw materials and equipment, which is mainly due to the fact that they have been utilising them for a long enough time to gain thorough knowledge on all relevant issues. Typically, the refineries also have an extensive knowledge of product and fuel markets, albeit for petroleum-based fuels only. The processing of biofeedstocks means entering an unknown territory. One could say, from a traditional viewpoint, that anything “bio” means additional problems by way of fouling, decreased efficiencies or an additional work burden. Biomaterials are living organisms containing and producing a multitude of compounds. In traditional applications, the smaller scale impurities might not be relevant or even recognised due to relaxed requirements, but they can be of paramount importance in petroleum refineries with regard to catalyst activity or when accumulating within equipment.
Another important issue is that the simplest and cheapest way to process renewable feeds in an existing refinery, as co-feeds, is not necessarily the most economical one. Also, the available trading specifications for renewable feed materials resemble merely the key factors for present applications, while a complete description of biomaterial properties is lacking. Only experience will reveal the significant factors and surprises.
However, in current circumstances, “bio” also means a premium in product value, which changes the picture, not least in the current economical climate, wherein refinery margins are low or non-existent. The engineering challenge is to do the integration correctly, when bioproducts are manufactured in a petroleum refinery. Moreover, the key is to create molecules as similar as possible to existing fuel molecules in their structures.
Conventional petroleum refineries can be modified to process bio-basestocks into renewable fuels.
Routes to renewable fuels
A biorefinery concept could be built on three main initial platforms to promote different product slates (see Figure 1). The sugar platform is based on biochemical conversion processes and focuses on the fermentation of sugars extracted from biomass, including lignocellulosic material. This platform requires strong know-how of bio- and genetic engineering and chemical engineering, because the conversion is done by micro-organisms.
The syngas platform is based on thermochemical conversion processes and focuses on the gasification of variable biomass feedstocks. It can use almost any organic feed and produces synthesis gas that can be converted to components other than fuels. Although the syngas platform seems to consist of known technology blocks that are proven in other applications, there are many challenges that are not simple to overcome. Some of the technology blocks were designed originally for other purposes and applications and, often, quite a few must be redesigned and adapted for this specific application. Also, bio-based feedstocks contain small quantities of components that are different to those of fossil origin, which, of course, requires experimental demonstration.
The constituent platform, based on fractionation processes, focuses on the separation of valuable biomass constituents for further processing. The residues may be utilised by bioconversion or thermochemical means.
Perhaps the best example of a biorefinery is a traditional pulp mill, a constituent platform, where a primary product, fibres, is separated from chemical constituents using chemical or thermomechanical processes. From the chemical fraction, multiple products may be produced, including commodities, fine chemicals, functional food and pharmaceuticals. Volume-wise, the main by-products so far are different biofuels in liquid or solid form. However, other routes do exist (see Figure 2).
The fats and oils route is currently widely practised in FAME production. It generates a commercial product, which, however, has significantly compromised properties, resulting in blending limitations in normal diesel use or dedicated automotive equipment. The emerging hydroprocessing route provides far superior products and is currently practised in the NExBTL process, with two operating references in Neste Oil’s Porvoo refinery and the third unit was started up in Singapore during November 2010. The biomass route depicted in Figure 2 is yet to be fully commercialised.
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