Natural Gas- Fuel for the 21st Century

by Vaclav Smil

  As expected, high-volume industrial consumers get the cheapest gas, commercial establishments pay more, and residential consumers buy the most expensive gas. In 2013 in the United States, the three rates averaged, respectively, $4.66, $8.13, and $10.33/Mcf. The 2013 ratio of these prices 1:1.74:2.21 shows that natural gas has been getting relatively more expensive for commercial and residential consumers: in the year 2000, the ratio was 1:1.48:1.75 (USEIA [US Energy Information Administration], 2014c). The value of natural gas at the point of consumption (all totals are in current prices) rose from $837 million in 1945 to $8.5 billion in 1975, and with price deregulation, it increased to $30 billion by 1990 and $70 billion in the year 2000, and in 2013, it was roughly $113 billion with $51 billion from residential, $27 billion from commercial, and $35 billion from industrial sales (USEIA, 2014c).

  But American households still pay a much lower price than the Europeans or consumers in East Asia. In 2012, when the US price ($10.71/Mcf) prorated to $0.38/m3, the average residential price in EU-27 was $0.83/m3 (EC [European Commission], 2014). In 2013, when the US household price was $0.37/m3, the European residential prices in 22 of the continent’s capital cities averaged $0.95/m3, ranging from $2.66 in Stockholm (all gas imported) to $0.40 in Bucharest (still nearly 90% of total consumption from domestic sources), that is, 2.6 times higher than in the United States (Energy Price Index, 2013). Japanese households have to pay even more for their imported LNG, nearly $1.7/m3, roughly 4.6 times the US rate.

  4.1 INDUSTRIAL USES, HEATING, COOLING, AND COOKING

  The category of industrial gas uses is quite heterogeneous. Energy industries account for a large share in all countries with substantial hydrocarbon production: in the preceding chapter, I have already described how gas is used in field operations (including secondary recovery of crude oil), in gas processing plants, and in powering compressors to move the gas through the pipelines. A new and important use of natural gas in oil and gas industry is its critical role in producing liquid fuels from Canadian tar sands. Two major modes of extraction are excavation of tar sand in open mines and in situ recovery, either by cyclic steam stimulation or by steam-assisted gravity drainage: natural gas is burned to produce the needed steam and between 25 and 35 m3 of gas is required to produce a barrel of bitumen (NEB [National Energy Board], 2014a).

  As already noted, undoubtedly the earliest, and well-documented, use of natural gas was to evaporate brines in Sichuan, China’s most populous landlocked province (Adshead, 1992). That practice dates to the Han dynasty (200 BCE), and although it continued well into the early modern era, it has not been replicated anywhere else, and in the West, natural gas was used first (during the closing decades of the nineteenth century) for street lighting and as an excellent source of heat for many industrial processes. The first application was quickly eliminated by electric lights, but industry has remained the single largest user of natural gas ever since. The earliest reliable consumption breakdown for the US natural gas consumption shows that in 1906 industrial uses claimed roughly 72% of total sales, with the rest used by households and commercial enterprises (Schurr and Netschert, 1960). In Canada, Edmonton was the first city to switch to natural gas (delivered by 130 km long pipeline from Viking, Alberta) for heating and cooking in 1923.

  4.1.1 Industrial Uses of Natural Gas

  In 1950, the US industries used about 60% of all natural gas, and by 2013, the share declined to about 34%, but it was still slightly ahead of 31% used for electricity generation (USEIA, 2014e). Moreover, natural gas consumption by the industrial sector represents a larger fraction of the final energy use than for other sectors whose energy use is heavily dominated either by electricity (more than 75% in commercial sector, more than 66% by households) or by liquid fuels (more than 95% in transportation). Review of sectoral fuel inputs in American economy showed that natural gas accounted for about 55% of the total energy requirement in the fabrication of metal products, 52% in food industry, nearly 50% in metal casting and transportation equipment, and 45% in chemical industry, with the average of about 36% for all industrial sectors reported in the Manufacturing Energy Consumption Survey (ICF International, 2007).

  In absolute terms, the largest consumer of natural gas is chemical industry followed by petroleum refining, food manufacturing, and pulp and paper. The three most common categories of use include the production of hot water and steam required for many kinds of industrial processing; the combustion of natural gas for space heating, centralized air conditioning, waste treatment, and incineration; and the production of direct heat for preheating and melting of materials (particularly metals), for drying, and for dehumidification. Gas-fired desiccant systems assure that moisture in materials and products is lowered below the levels that could cause defects. Many industries also use natural gas to supplement combustion of other fuels: this cofiring with wood and other biomass or coal increases overall efficiency and reduces emissions. General quest for cleaner production—virtually no particulates and no SOx emissions, effective control of NOx, and reduced greenhouse gas generation—means that with greater gas availability, the dependence of the industrial sector on natural gas is likely to increase.

  Particularly, efficient uses of natural gas include infrared heating units and direct-contact water heaters. Standard industrial water heaters and boilers raise the temperature of water indirectly, by using heat exchangers with the liquid enclosed in vessels or tubes, and they operate with efficiencies of no more than 70%. In direct-contact water heaters, cold water is introduced at the top of a unit, and as it flows down through packing (stainless steel nodules, rings), it is heated by combustion gases rising from a burner at the bottom of the unit, and the overall efficiency can be as high as 99.7%. Direct-contact water heaters are used for space heating, in textile and food manufacturing, and also in large laundries (Quik Water, 2014).

  Food production needs large volumes of heated water, steam and dry heat for cooking, baking, fermenting and sterilizing, and virtually all canned and conserved items, as well as dairy products, juices, wines and vinegar must undergo pasteurization, that is heating to 72°C to eliminate harmful pathogens. Depending on the requirements, this may be done during the processing or as the last production step before releasing a product. By far the highest demand for heat in paper manufacturing is for drying wet paper: it requires removing 1.1–1.3 kg of water for every kg of paper, and it is done by contact with steam-heated cylinders (Ghosh, 2011).

  Kilns used to fire bricks, stoneware, and ceramics as well as fine china are commonly heated by natural gas. In the United States, 80% of bricks are made in gas-fired kilns where the temperature reaches up to 1,360°C during the last (vitrification) stage of the firing (BIA [Brick Industry Association], 2014). But natural gas has been usually too expensive for much more massive production of Portland cement: even in the United States, the sector has relied mostly on coal, petroleum coke, and combustible waste, with natural gas supplying only about 5% of all energy. Production of primary iron in blast furnaces also remains highly dependent on coal, specifically on coke produced by carbonization (high-temperature destructive distillation) of coal in oxygen-poor atmosphere, but during the twentieth century, the metal’s smelting has seen more than a 60% decrease in coke-charging rates due to supplementary injection of pulverized coal, oil, or natural gas (de Beer, Worrell, and Blok, 1998).

  Fabrication of steel parts uses natural gas for a variety of heat treatments including hardening (heating to a prescribed temperature followed by rapid cooling by quenching into oil, water, or brine, most commonly done for steels), tempering (to reduce brittleness by heating to a specified temperature and then letting the metal to cool), annealing (to make metal more ductile and to refine their grain structure by heating to a specified temperature, holding it for a desired time, and then cooling it slowly), and case hardening deposition of more carbon into steel surfaces by heating in the presence of a specific material. Nonferrous metals undergo annealing and solution heat treatment (
heating followed by rapid quenching).

  4.1.2 Natural Gas for Space Heating and Cooling

  Before WWII, the North American wood stoves were still common in many rural areas, and urban houses were heated mostly by coal stoves in individual rooms or centrally by basement coal-fired boilers that heated water circulating through cast iron radiators or (after 1885) by warm air rising through ducts by natural convection from riveted-steel coal furnace introduced by Dave Lennox. Furnaces heated by fuel oil were the next option before the introduction of the first forced air coal-fired furnace in 1935. After WWII, the forced air heating became dominant, but the fuel changed rapidly from coal to natural gas.

  These furnaces heat incoming fresh air and distribute warm air through ducts underneath floors and inside walls. They are equipped with a pilot light and an electric motor to force the heated air, they became common after 1950, and their evolution has been marked by a shrinking size and an improving performance. North American natural gas furnaces are rated by their annual fuel utilization efficiency (AFUE). Pre-1975 furnaces had AFUE of just 55–60%, wasting 40–45% of all purchased natural gas in hot exhaust gas escaping through a lined chimney. Improved versions of so-called mid-efficiency furnaces had eventually converted as much as 78–82% of energy in gas into household heat.

  In Canada, sales of mid-efficiency furnaces ended on December 31, 2009, and only high-efficiency (condensing) furnaces (AFUE of at least 90%) and furnaces with Energy Star label (AFUE of at least 95%) are available (Figure 4.2). They are microprocessor controlled; have electronic ignition (hence no pilot light), secondary heat exchanger, and high-efficiency fan motor; and can be turned on and off by a programmed thermostat placed in a living area. Their heat loss is so small that there is no need for a chimney as warm CO2-laden exhaust gas is led out through a polyvinyl chloride (PVC) or ABS plastic pipe on a side of a house and water generated by combustion is disposed into a floor drain. Many homes also use natural gas for heating water, and again, the latest heater designs have efficiencies superior to the previous models.

  Figure 4.2 High-efficiency natural gas furnace.

  Post-WWII expansion of commercial (offices, stores, shopping malls) and institutional (schools, universities, hospital, museums) space created a large new category of heating preferably served by natural gas. In 2013, the US commercial sector consumed more than eight times the volume of the gas than it did in 1950, an equivalent of two-thirds of household consumption (in 1950, it was equal to less than a third). And commercial and institutional users have been also the pioneers of natural gas-powered cooling, an option that is particularly attractive for large facilities with high daytime (schools, offices) or often nearly constant cooling loads for hospitals, hotels, and supermarkets in hot climates (ESC [Energy Solutions Center], 2005; Uniongas, 2013). The choices of natural gas-powered cooling equipment include quiet and efficient absorption chillers (they can also use waste from other on-site burning of natural gas), engine-driven and steam turbine-driven chillers, and desiccant dehumidification (making high temperatures more bearable, reducing frost coating in supermarket chillers, keeping ice rinks fog-free).

  4.1.3 Cooking with Natural Gas

  Cooking (and water heating) with town gas began to make the first inroads in large Western cities during the last two decades of the nineteenth century as the town gas producers looked for replacing sales lost to electric lighting. In the United Kingdom, one out of four urban households used cooking gas by 1898 and one out of three in 1901 (Fouquet, 2008). Gas ranges became common in all major cities of the industrializing world during the first two decades of the twentieth century, and by 1930 in the United States, they outnumbered (burning town gas as well as natural gas) wood and coal stoves by nearly two to one. Cheaper electricity limited their post-WWII adoption in North America, but, even so, at the beginning of the twenty-first century, about one-third of US households cooked with gas.

  Advantages of cooking with gas include more even heat distribution (flame heating also the sides of cooking vessels) and hence faster completion of a task; more precise, instant control of heat intensity (always preferred by professional chefs, particularly for rapid Chinese-style cooking); and the ability to change temperature rapidly and to cut off heat instantly (hence being able to leave pots and pans resting on the stove). But gas ranges are more expensive than the electric ones, less easy to clean (particularly when compared to new electric flat tops), not as good for baking (combustion releases water), and potentially more dangerous (risks associated with open flame, leaks, gas escaping after accidentally quenching the flame), and they can be, especially when used without an exhaust hood, a nontrivial source of indoor air pollution.

  Logue et al. (2013) found that in southern California typical gas range-generated indoor exposures to CO exceed the standards for ambient air and that hoodless cooking also causes excessive NO2 levels. Data collected as a part of the European Community Respiratory Health Survey showed no significant association between respiratory symptoms and gas cooking in males, but for females there, compared to electric cooking, symptoms suggestive of some airway obstruction (Jarvis et al., 1998). A more recent Norwegian study found that gas cooking produces higher levels of cancer-causing fumes than does electric cooking, but all recorded levels were below permissible occupational thresholds (Sjaastad, Jørgensen, and Svendsen, 2010).

  4.1.4 Liquefied Petroleum Gas

  Finally, a couple of paragraphs are presented on liquefied petroleum gas (LPG, mixture of propane and butane) as fuel. Many of its industrial uses are identical to the uses of natural gas as a fuel for ovens, furnaces, and kilns, in process and water heating, and high-temperature treatment of metals, but the mixture is also used in oxy–propane cutting and welding and as an aerosol propellant for a variety of household products ranging from cosmetics to insecticides. On construction sites, this portable fuel is used to heat buildings and bitumen during road repair. LPG’s many agricultural applications include space heating of animal barns, grain and fruit drying, and also powering of agricultural machinery (for more on this mobile use, see Chapter 7).

  LPG is also used for a range of leisure activities. The best known use is portable fuel for cooking—be it for occasional camping or as the fuel for ranges in recreational vehicles—available in a variety of refillable metallic cylinders, but there are also LPG-fueled boats (because of its minimal impact on the water if spilled, it is a better choice than gasoline), and the modern ballooning industry depends on powerful LPG-fueled burners to lift and to maneuver large balloons used for aerial sightseeing. And while there are no LPG-fueled cars in North America, there are now 4.5 million LPG vehicles in Europe (AEGPL, 2014). Again, I will look in some detail at this mobile application in Chapter 7.

  4.2 ELECTRICITY GENERATION

  Once natural gas became available at affordable prices and in larger volumes, electricity generation was its next obvious market, but long-established coal- and oil-fired generation (and, starting in the 1960s, expansion of nuclear generation) has made it a slow process. In 1950, even in the United States, after more than half a century of expanding natural gas extraction, twice as much natural gas was destined for households than for electricity generation, the residential use was still 55% higher in 1975, and combustion of natural gas for electricity generation surpassed the domestic uses for heating and cooking only during the last year of the twentieth century. Until the late 1950s, virtually all gas-fired electricity-generating capacity was in medium- and large-sized central power plants where gas was burned in boilers to produce steam for turbogenerators.

  Between 1950 and 2000, consumption of natural gas for electricity generation rose more than eight times, and between 2000 and 2012, it rose by 75%. In 1950, natural gas contributed almost exactly 20% of all primary fossil fuel energies used to generate American electricity (coal dominated with 66%). By 1975, its share rose only to 21%, but the total gas consumption had quintupled. Subsequent rise of gas turbines made them the preferred choice for g
as combustion in electricity generation, and these highly efficient and reliable machines now dominate the market in all major economies. By the year 2000, the share dropped once again below 20%, but (starting in 2007) the increased availability of cheaper gas pushed the share to 33% in 2013. In terms of actual generation, the share originating from natural gas is lower, about 27% in 2013. And the global share is not that much lower: in 2010, 21% of the world’s electricity was produced by burning natural gas, either in large boilers or in gas turbines.

  The difference between the shares of installed capacity and actual gas-fired generation is mainly due to the rising importance of gas turbines. As I will show in the following pages, turbines burning natural gas have unequaled efficiencies (when working in a combined cycle with steam turbines up to 50% higher than steam turbogenerators in large coal-fired stations)—but their capacity (load) factor is relatively low because they cover mostly peak and emergency demand unlike the steam turbines in large central power plants steam turbines that cover the base load. Calculations based on the US data for 2012 show average load factor of 55% for coal-fired but only 33% for natural gas-fired electricity generation (USEIA, 2013a).