Rational Use of different fossil fuels

Whilst the Industrialised world continues to use fossil fuels for the majority of energy applications, it is important that the balance of fuels used is rationally based and the right fuel is used for the right application. The definitions of right fuel and right application may usually be based upon economic grounds, however their are other concerns if we hope to extend the time for which we can continue to exploit these reserves.

Reserves

The three main fossil fuels together with electricity may frequently be used for the same applications. However a number of factors affect their suitability for different roles. On a pure energy basis, given equal suitability, it would seem logical to make more use of the fuel which is the best combination of potential availability and least other potential uses, providing the technology exists to exploit it efficiently. Table 21 shows the proven reserves and the lifetime of those reserves, assuming that extraction continues at the current rate.

Primary Fuel Reserves (btoe) Extraction Rate Lifetime
    (mtoe/year) (years)
       
Oil 140 3300 42
Natural Gas 120 2000 62
Coal 620 2800 224

btoe: billion (109) tonnes oil equivalent

conversion rates assumed:

1tonne coal = 0.6tonne oil equivalent

1m3Natural Gas = 0.0024tonne oil equivalent

Table 21: World Fossil Fuel Reserves [45]

UK Use of Fossil Fuels

It may be derived from Table 21 that as reserves of coal are greater than those for other fossil fuels, a greater proportional use of coal would provide more time in which to find alternatives to fossil fuels. However, the trend in the UK is a decreasing use of coal.

Fuel %
   
natural gas 35
Petroleum 42
Electricity 16
Solid Fuels 6

Table 22: Energy Consumption by Fuel, 1996 [30]

International Trade

The UK is self sufficient in petroleum and at current extraction rates has a need to find an external

Million Tonnes          
Production Imports Exports UK Use Excess Total
        Production Traded
           
143 45 84 104 39 129

Table 23: UK Annual Trade in Crude Oil , 1996 [30]

market for nearly 40 million tonnes. As we import over 40 million tonnes, we need to export over 80 million tonnes, thus increasing external energies for transport energy three fold.

Oil

The delivery of fuels derived from crude oil represents the final stage in the oil industry. Each of the processes from feasibility through to delivery will involve energy use and efficiencies. The overall efficiency of any application using products from crude oil should consider the overall efficiencies derived from the product of these stages. Many of these stages will be duplicated in the delivery of other fossil (and renewable) fuels, though the methods and relative efficiencies will be different.

Pre feasibility studies (surveying of sites to decide if exploration is worthwhile).

Feasibility studies. Only 2% of drillings result in reservoirs which are considered commercially viable. As the most lucrative sites are exploited, this proportion is likely to decrease. 'Oil exploration is one of the costliest stages of the oil industry' [46].

Excavation. Losses of oil during excavation may occur due to failure to maintain adequate pressure within the well, resulting in pockets of oil left in the rock (either within the main reservoir or within cracks of upper layers) which may be impossible or very costly to remove. Initial excavations typically remove 20% to 30% of the oil. Secondary recovery may leave over 50% of the oil unexcavated, this remainder requiring high financial and energy implications in order to extract. The care and methods used to extract the oil will result in different achieved levels of extraction. This is heightened when natural gas is also present within the reservoir. Where a market does not exist locally for the natural gas it is frequently burnt at the well head even when the quantity is very significant.

Pre-transportation treatment removes major impurities (gas, salt, water, sand, hydrogen sulphide) and may result in losses [46].

Transportation to refineries (shipping tankers, pipeline) usually occurs over very long distances as markets for petroleum products are typically thousands of miles from crude oil sources. This incurs transportation energy expenses. Crude oil is the largest single internationally traded commodity.

Refining. Crude Oil is only of use when its hydrocarbon components are separated out. The mix of components will vary from one source to another, the actual mix not matching the real demand for products, in particular, the lighter products such as natural gas and gasoline. Further processing (cracking and reformation) is thus necessary to produce the products that the markets demand, creating more inefficiencies.

Natural Gas

Natural Gas may be sourced with (wet reservoir) or without (dry reservoir) crude oil. Natural Gas is a valuable source of the lighter hydrocarbons (methane, ethane, propane, butane, pentane). The efficiencies of the industry are associated with those of the crude oil industry. Its transportation is more difficult as it is a gas and has a much lower volumetric energy capacity. It is carried either in its natural form by pipeline or compressed and cooled as Liquified Petroleum Gas (LPG). Where no local market has been developed for it, the gas is frequently burned as a waste product.

One of the great virtues of both natural gas and petroleum is the wide variety of products that may be produced from it, including fertilisers, paints, plastics, fibres, synthetic rubbers, adhesives, pesticides. The rationality of burning a resource which has so many other potential applications may be questioned.

Electrical Energy

Of the main delivered fuels, electrical energy is special in that it can be derived from work done with other fuels. Electricity use has increased in all the main user sectors since 1960 (Table 24), the overall change being 9% from a 1960 base of 7%. As it is a fuel derived from other fuels (both Fossil and Renewable), its effective contribution to primary energy use is more significant than

  Industry   Transport   Domestic   Other  
  1960 1996 1960 1996 1960 1996 1960 1996
                 
Total 53843 37588 22197 52608 36329 48079 14905 22525
Electricity 3826 8869 194 639 2894 9246 1579 7533
Proportion (%) 7 24 1 1 8 19 11 93

Table 24: Growth in electricity use since 1960 [30]

statistics for delivered energy imply. Also, as electrical energy may be derived from a number of primary fuels, (including renewable) it is not only important to consider the applicability of electricity as an end use fuel but also the applicability of fuel choice in producing it. Historically, Coal has been used as the main fuel to produce electricity, however this role is expected to be overtaken by natural gas. In 1996, Natural Gas accounted for one fifth of fuel used in generation, this is expected to 'almost double' [47] by the end of 2000/1.

Method Electricity Proportion Thermal
  Generated   Efficiency
  GWh % %
       
Conventional Steam 177765 51 37
Nuclear 94671 27 37
CCGT 67112 19 44
       
Total 347369   39

Table 25: Main Electricity Generation Plant [47]

Natural Gas has been adopted for power generation as a relatively simple way of achieving reductions in greenhouse gas emissions and for the the improved efficiency of conversion over conventional coal fired stations. However, the potential efficiency of Combined Cycle Gas Turbine plant (CCGT) has not been achieved in practice (achieved: 44%, potential: 55%), and is at a lower level than that claimed for the current 'best' clean coal technology (Topping Cycle). The main argument for the use of Gas is concerned with emission levels. However, Natural Gas is also a very appropriate end-use fuel (for space heating, for example) compared with the alternative fossil

fuels. Its increased use in power generation reduces its long term availability for this application.

  Thermal Efficiency (%)
   
Conventional Coal Fired 39
'Clean Coal' 39 - 47
CCGT 55

Table 26: Thermal Efficiency of Coal and Gas Power Generation Plant [48]

Back.

Home