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Since historical times mankind is dependent on the use of fossil fuels. The exploitation and use of fossil fuel grew exponentially in the last two centuries when world experienced the industrial development. This period was characterized by extensive combustion of petroleum, natural gas, coal and as a consequence there are produced visible unbalances in the natural environment, especially due to the associated CO2 emissions.

Residential

Transportation ^---17%

Commercial 17%

Agriculture Industry 8%

Fig. 5.1 Distribution of CO2 emissions from various sectors in North America (data from PEW Center, 2008)

In the march toward a non-polluting economy that relates mostly on renewable resources, there is a need of transitional solutions, like finding alternative synthetic fuels for clean (zero-emission) vehicles. The transportation sector is responsible for 28% of the total CO2 emission in North America and this situation is about the same for other industrialized countries. The distribution of CO2 emissions from various sectors is illustrated in Fig. 5.1.

Commercial 17%

I. Dincer et al. (eds.), Global Warming, Green Energy and Technology,

DOI 10.1007/978-1-4419-1017-2_5, © Springer Science+Business Media, LLC 2010

For reducing the CO2 emissions from transportation sector and the associated global warming impact, a broadly accepted solution suggests using fossil fuels and renewable energy sources to produce hydrogen as an ideal synthetic and clean fuel (see Veziroglu, 2007 and Dincer, 2007). However, in order to make the hydrogen-based economy a reality, there is a need of major investments for the development of competitive production, distribution, and especially hydrogen storage technologies, which in the present are not satisfactory enough. The barrier to be overcome is represented by the development of the hydrogen distribution infrastructure that implies complicated safety issues because hydrogen is volatile and has a low flash point, presents high explosion danger, and its flame is invisible.

Ammonia, NH3, known mainly as nitrogen source for agriculture and refrigerant has high content of hydrogen atoms per unit of volume. Because of this reason, as reviewed by Bomelburg (1982), ammonia has been used occasionally in the past as a hydrogen source for internal combustion engines and fuel cells. There are 108 kg H2/m3 embedded in liquid ammonia at 20oC and 8.6 bar. The most advanced storage methods in metal hydrides reach about 25 kg H2/m3; this storage density is ~3 times lower than that in NH3.

The toxicity of NH3 is a challenge in its serious consideration for use as hydrogen source on a global scale. However, this issue has largely been addressed for ammonia handling, storage, and use in various forms (i.e., gaseous, liquid, and solid), especially in agriculture, chemical, and refrigeration.

As suggested by Christensen et al. (2006) a way to cope with the ammonia toxicity is by adsorbing it in porous metal ammine complexes, e.g., hexaam-minemagnesium chloride, Mg(NH3)6Cl2. To do this NH3 is passed over an anhydrous magnesium chloride (MgCl2) powder at room temperature. The absorption and desorption of ammonia in and from MgCl2 are reversible. The ammine can store 0.09 kg H2/kg and 100 kg H2/m3.

Despite its toxicity, NH3 is still one of the most attractive ways to store and distribute H2 due to the following facts:

• It can be thermally cracked into hydrogen and nitrogen using low energy, i.e., ~12% from the higher heating value (HHV) to produce hydrogen for fuel cells and internal combustion engines.

• The distribution infrastructure already exists for ammonia (see Christensen et al., 2006) to deliver it in amounts larger than 100 million tons yearly or more.

• It is also an excellent working fluid for thermodynamic cycles. Such cycles, operating for cooling, heating, power, or any combination of those can be coupled with internal combustion engines. Recently, Zamfirescu and Dincer (2008a-c) and Zamfirescu and Dincer (2009) have analyzed the possibility to use the onboard ammonia as refrigerant while it is consumed as fuel for vehicle propulsion.

• It is still safer than pure hydrogen and various other hydrogen sources like methanol, ethanol, methane, gasoline due to the following properties:

- If escapes into the atmosphere it dissipates rapidly because its density is lighter than that of air.

- It is self-alarming: any leakage can be detected by nose in concentrations as low as 5 ppm.

- It has a narrow flammability range and therefore, it is generally considered non-flammable and presenting no explosion danger when properly transported; this fact is evident from the data listed in Table 5.1 which were compiled from various sources (indicated below the table).

Table 5.1 Some features of ammonia as compared to other conventional fuels.

Property

Gasoline

Diesel

Natural gas

H2

NH3

Flammability limit, volumes % in air

1.4-7.6

0.6-5.5

5-15

4-75

16-25

Auto-ignition temperature, oC

300

230

450

571

651

Peak flame temperature, oC

1,977

2,053

1,884

2,000

1,850

Source: From Brandhorst et al. (2007), McFarlan (2007), Olson (2007), Lide (1991)

Source: From Brandhorst et al. (2007), McFarlan (2007), Olson (2007), Lide (1991)

Hydrogen can easily be obtained from ammonia via thermal cracking, which is a kind of well-known technology, even though there is still room for further development. The main challenge is to device the reforming unit sufficiently compact and yet capable of decomposing the ammonia at a rate in accordance with the consumption. Such units are currently in development and there are several promising results published in the open literature (Ganley et al., 2004, Soren-sen et al., 2005).

Ammonia can be produced either from fossil fuels of all kinds (coal, natural gas, petroleum, naphtha, etc.), from any renewable energy source (e.g., solar, wind, hydro, geothermal, ocean thermal energy conversion) or from heat waste or electricity (e.g., nuclear) using water, biomass, or organic/city waste and air as primary.

Using ammonia as a hydrogen source is a fully recyclable solution because, at production place, ammonia is synthesized basically from water and nitrogen, substances available everywhere in the environment, and at the consumption point (on vehicles), after decomposition followed by hydrogen combustion, the same amounts of water and nitrogen are returned back into the environment. It may be argued that due to its qualities ammonia provides both a short- and long-term solution to the hydrogen economy. There are former studies and occasional implementations regarding the use of ammonia as hydrogen source either for internal combustion engines (e.g., Starkman et al., 1967, Kroch 1945, Holbroock, 2007, Stockes, 2007) or for fuel cells (e.g., Cairns, 1968, Kordesh et al., 2007, Maffei et al., 2007 Xie et al., 2007).

In the first part of this chapter the use of ammonia as hydrogen source is analyzed and the advantages of such a alternative to hydrogen economy are discussed. Hydrogen stored in the form of ammonia is compared with other conventional fuels as well as with pure hydrogen from the point of energy storage density per unit of volume and of mass, and the cost per unit of storage tank volume. In the subsequent section the possibility of using ammonia on vehicles simultaneously as hydrogen source, as working fluid (for engine heat recovery and work conversion), and refrigerant (for engine/fuel cell system cooling or air conditioning) is proposed. The cooling effect is quantified in terms of refrigeration power vs. generated power. We further study some more technical parameters, namely driving range, tank compactness, and cost associated with 100 km driving range for the hydrogen from ammonia alternative.

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Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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