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1 Transport
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| Biomass (digestible sludge) | District cooling | Comfortable indoor climate |
| Biomass (fermentable sludge) | District heating | Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| Water | Fuel: Solid | Process heat (> 1000 °C) |
| Wind | Local cooling (ind. house) | 1 Transport |
| Residual oils/fats etc | Local heating (ind. house) |
Though electricity is the ultimate energy carrier for transport – mechanical work requires high-exergy energy carriers – todays batteries are not sufficient for 100% electrical cars to be competitive. The best means for transport today, from a thermodynamic standpoint, is electric trains running on hydroelectricity or wind power. Third best will be trains running on electricity contracted from biomass-fired CHP or tri-generation plants.
This is so obvious that there is nothing more to say about it so for the rest, transportation in this material will only deal with such means for transport that are based on fuels.
The transport sector includes three segments putting different demands on the fuels supplied:
- Airborne transport. For aeroplanes, the crucial things about the fuel are two. First it must not be too voluminous as compared to its energy content. Second it must not be too heavy with respect to its energy content. Therefore, the heating values per volume as well as per weight unit are crucial. Then comes a third aspect: For gaseous fuels, the weight of the pressurised container has to be included in the weight of the fuel, so the heating value per weight unit for gaseous fuels must be reduced by the additional weight for the container. This effectively excludes gaseous fuels for air-borne transports.
- Land-borne transport. For land-borne transport purposes the condition about heating value expressed per weight unit still remains but the restriction is eased so that at least some gaseous fuels may be accepted. The demand on high heating value per volume unit remains strict for land-borne transport but not really as strict as for air-borne.
- Sea-borne transport. For sea-borne transports both restrictions are eased to a great extent.
There are a number of other restrictions, criteria and demands on fuel such as the cleanness (most important for gas turbines and hence for aviation fuels and marine gas turbines), the octane number (the capacity to stand compression without igniting, most important for aviation fuels and for Otto engines), the cetane number (the ignition delay, most important for Diesel engines at land or at sea), but going into these would lead to far for the present material.
The engine types used are mainly gas turbines (turbo-jet and turbo-prop for airliners, power-station-like for marine applications), spark-ignited Otto engines for cars and for small private aircraft and compression-ignited Diesel engines for cars, lorries and also for marine applications. Steam turbines may be used in marine applications. Hence the demands on the fuel quality reflect not only the application but also the types of engines used.
In this material, focus is on land transport and on Otto and Diesel engine fuel.
Ethanol was used as a car fuel already more than 100 years ago, was successively replaced by fossil gasoline until the second world war and has again returned to the car fuel market since the 1970's/-80's. Today's global use exceeds 85 million m3 per year, less than 5 million m3 in Europe.
Methane gas, sng-quality biogas, is an alternative first for Otto engines. The energy efficiency is generally equal to that of gasoline engines, but lower compared with modern diesel engines. Gasoline/petrol vehicles converted to run on natural gas tend to suffer because of the low compression ratio, resulting in a reduction about 10-15% of delivered power while running on gas. The total, raw, biogas production worldwide amounts to some 30 000 million m3, 10% of which occurs in Europe.
The Diesel engine was first constructed to run on coal powder but was later modified to run or raw vegetable oils. Diesel oil is a less refined product than gasoline and was hence used for engines earlier than gasoline replaced ethanol. For biodiesel, the current world production amounts to some 20 million m3 of FAME per annum, the main part of which is produced from palm oil, soy, rapeseed oil and waste oil/fat, where the latter resources is so far only minor. About half this production occurs in the European federation.
Thermochemical conversion of solid biomass include low-temperature pyrolysis, high-temperature pyrolysis, thermal liquefaction and thermal gasification. Thermal liquefaction is generally not considered a favourable route since the oil produced tends to have inferior quality. Thermal gasification is one of the most complicated conversion processes but it is also one of those that open up the most possibilities for subsequent processing.
Gasifier gas ("product gas" or "gasifier gas", in special cases "syngas", not to be mistaken for biogas) quality can be set within wide limits, from the simplest gasifiers that produce wet, nitrogen- and tar laden gas mainly suitable for direct combustion to highly advanced gasification processes producing synthesis gas well aimed for subsequent chemical upgrading to a number of products including bio-DME which would be a suitable fuel for Diesel engines.
For Otto engines, if solid biomass was selected as the energy source, liquefaction followed by upgrading would be the main route. Another possible route is enzymatic pre-treatment of solid biomass to transform cellulose and hemicellulose to fermentable sugars followed by a fermentation process to produce ethanol.
Bio-DME, liquefaction and lingo-cellulosic alcohol are generally termed "second generation biofuel" and are not yet commercial. Therefore, they will be left out from this material.