Prime Movers And Heat

For purposes of empirical estimation of other types of work, it is helpful to distinguish between two categories of fuel use. The first category is fuel used to do mechanical work, via so-called 'prime movers'. These include all kinds of internal and external combustion engines, from steam turbines to jet engines, as well as nuclear steam power plants. (Electric motors are not prime movers because a prime mover - such as a steam turbine - is needed to generate the electricity in the first place.) The second category is fuel used to generate heat as such, either at high temperatures for industry (process heat and chemical energy) and domestic or commercial cooking, or at low temperatures for space heat and hot water for washing for residential and/or commercial users.

The percentage consumption by prime movers for the three major fossil fuels (coal, petroleum and natural gas) was plotted in Figures 4.1a, 4.1b, 4.2a, 4.2b and 4.3a, 4.3b for the US and Japan. Fuelwood has never been used to a significant extent for driving prime movers, at least in the US, except in early 19th-century railroads or Mississippi River steamboats. In Japan, charcoal from biomass was used for buses and trucks briefly towards the end of World War II, but otherwise not (there are no published statistics).

Figures 4.1a and 4.1b show the fraction of coal consumption allocated to mechanical work since 1900. During the first half of the century steam locomotives for railroads were the major users, with stationary steam engines in mines and factories also significant contributors. These uses are not distinguished in published US statistics prior to 1917. Industrial uses for heat and work were estimated by assuming that fuel consumption for each category is proportional to total horsepower in that category of prime movers, for which data have been estimated separately.6

Figures 4.2a and 4.2b, for petroleum, are based on published data for liquid fuels, by type.7 At the beginning of the 20th century, the dominant product of the industry was 'illuminating oil' (kerosine) used for lamps in rural areas. Much of this was exported (in fact, the US was the major exporter of petroleum products until after World War II). Only 'natural' gasoline - a moderately volatile light fraction of the petroleum (15-18 percent) consisting of hydrocarbons with six to 12 or so carbon atoms -was used for early motor vehicles. The more volatile lighter fraction was mostly flared until after World War II. The fractions heavier than kerosine had little value except for fuel oil, lubricants, wax and asphalt.

Source: Data prior to 1958 from Ayres; data from 1958 on from Lakhani (p. 54).

Figure 4.5 Developments in petroleum 'cracking' fractions (USA, 1910-72)

Source: Data prior to 1958 from Ayres; data from 1958 on from Lakhani (p. 54).

Figure 4.5 Developments in petroleum 'cracking' fractions (USA, 1910-72)

The rapid increase in motor vehicle production and use after 1900 created a correspondingly rapid growth in demand for gasoline, which exceeded consumption of kerosine for the first time in 1911. This led to a series of technological developments in 'cracking' heavier petroleum fractions. Burton's batch-type thermal cracking (1913) was succeeded by continuous thermal cracking, followed by batch (Houdry) catalytic cracking and finally continuous catalytic cracking (Enos 1962) (Figure 4.5). Evidently the fraction of crude oil used to drive prime movers, rather than for heating, has been increasing for a long time. This is a crude measure of the increasing efficiency of petroleum use (Figure 4.6). In the US, roughly half of the mass of crude petroleum is converted into gasoline, with other liquid fuels (diesel oil, jet fuel, residual oil) accounting for much of the rest (Figure 4.7). In Japan, the split between gasoline and diesel or heating oils is somewhat tilted toward the heavier fractions.

Figures 4.3a and 4.3b, for natural gas, show the uses of gas. In the US, gas is mostly used for heating and chemical processes (such as ammonia synthesis). A small fraction is used to drive compressors in the gas pipelines and another small fraction is used by electric utilities to generate electric power. In Europe and Japan, a much larger fraction is used for electric power generation.

Figures 4.4a and 4.4b, combining Figures 4.1a, 4.1b, 4.2a, 4.2b, 4.3a and 4.3b, show the fraction of all fossil fuel exergy used to drive prime movers and perform mechanical work - for purposes of generating either electric power or mobile power. This share has been increasing more or less

—«—

• Gasoline

—0...

• Jet fuel

-

• Diesel fuel

— Electricity

— Subtotal of above

-

—«...

• 'Transport and electric'

Figure 4.6 Petroleum utilization efficiency: percent used as fuel for prime movers (USA, 1900-82)

1900

1920

1980

Figure 4.6 Petroleum utilization efficiency: percent used as fuel for prime movers (USA, 1900-82)

best fit best fit

1910 1920 1930

1940

1950

1960

1970

Figure 4.7 Percent of crude oil cracked to produce gasoline (USA, 1910-72)

1910 1920 1930

1940

1950

1960

1970

Figure 4.7 Percent of crude oil cracked to produce gasoline (USA, 1910-72)

1900

1920

1980

Economy 1900 1920
Figure 4.8 Farm mechanization: substitution of machinery for animals

continuously since the beginning of the 20th century, mostly because of the increasing fraction of the other fossil fuels, coal and gas that has been devoted to electric power generation. Transportation uses have remained roughly constant as a fraction of the total. The other major uses of fuel exergy are to do chemical or thermal work: they include industrial heating (direct or via steam), space heating, water heating and cooking. We classify the direct heat as 'quasi-work'.

Figures 4.4a and 4.4b, discussed above, reflect two different phenomena. One is structural change. For instance, the substitution of machines, especially tractors, for animals in agriculture (US) is shown in Figure 4.8. The other phenomenon is technical improvement in specific conversion processes, which we discuss next. Needless to say, efficiency gains, reflected in prices for exergy or power, drove some of the structural changes noted above.

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Responses

  • Haile Yonas
    Which motor used in prime movers?
    7 years ago

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