Hydrogen Economy I Transportation


The Future of the Hydrogen Economy - Part 2
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January 7, 2003 View for printing

To Part One

Packaging of Hydrogen Energy Needed to Compress Hydrogen

Energy is needed to compress gases. The compression work depends on the thermodynamic compression process. The ideal isothermal compression cannot be realized.
The adiabatic compression equation [2] is more closely describing the thermodynamic process for ideal gases.

By Baldur Eliasson and Ulf Bossel EV World

W = [n/(n -1)] po Vo [(p1/po) (n-1)/n - 1] (1)

with W specific compression work J/kg po initial pressure Pa = N / m 2 p1 final pressure Pa = N / m 2 Vo initial specific volume m 3 /kg n adiabatic coefficient, ratio of specific

The compression work depends on the nature of the gas. This is illustrated by comparing hydrogen with helium and methane

H2 n = 1.41 Vo = 11.11 m 3 /kg He n = 1.66 Vo = 5.56 m 3 /kg CH4 n = 1.31 Vo = 1.39 m 3 /kg

Figure 2. Adiabatic compression work for hydrogen, helium and methane.

(Please visit http://evworld.com/databases/storybu ... subcookie=1 to view charts)

The energy invested in the adiabatic compression of ideal monatomic Helium, diatomic hydrogen and five-atomic methane from atmospheric conditions (1 bar = 100,000 Pa) to the final pressure is shown in Figure 2. Clearly, much more energy is required to compress hydrogen than methane.

Figure 3 Energy required for adiabatic and isothermal ideal-gas compression of hydrogen compared to its higher heating value HHV. The isothermal compression energy is determined by the simple equation: W = po Vo ln(p1/po)

Figure 3 illustrates the difference between adiabatic and isothermal ideal-gas compression of hydrogen. Multi-stage compressors with intercoolers operate between the two limits. Also, hydrogen readily passes compression heat to cooler walls, thereby approaching isothermal conditions. Numbers provided by a leading manufacturer [5a] of hydrogen compressors show that the energy invested in the compression of hydrogen is about 7.2% of its higher heating value (HHV). This number relates to a 5-stage compression of 1,000 kg of hydrogen per hour from 1 to 200 bar. For a final pressure of 800 bar 10% would perhaps be a realistic value. The analysis does not include
losses in the electric motor.

Energy Needed to Liquefy Hydrogen

Even more energy is needed to compact hydrogen by liquefaction. Theoretically only about 4MJ/kg have to be removed to cool hydrogen down to 20K (-253'C) and to condense the gas at atmospheric pressure. But the cooling process is extremely energy intensive with a Carnot efficiency of 7%. A theoretical analysis of the complicated, multi-stage liquefaction processes is difficult. We therefore use the actual energy requirements of existing hydrogen liquefaction plants as compiled by Linde Kryotechnik AG [5b]. The company is a well-known supplier of cryogenic equipment and cryogenic liquids.

The results of the compilation of the energy consumption of existing hydrogen liquefaction plants have been adapted to make them compatible with the current study. The liquefaction energy requirement depends on the process itself, the process optimization, the plant size, and on other parameters. Figure 4 shows the actual liquefaction energy consumption for plants having a capacity between 1 to 10,000 kg of liquid hydrogen per hour.

Figure 4 Typical energy requirements for the liquefaction of 1 kg hydrogen as a function of plant size and process optimization.

The energy requirement for liquefaction is substantial. For a plant capacity of 100 kg liquid hydrogen per hour about 60 MJ of electrical energy is consumed to liquefy 1 kg of hydrogen. The specific energy input decreases with plant size, but a theoretical minimum of about 40 MJ per kg H2 remains.

In Figure 5 the required energy input is compared to the higher heating value HHV of hydrogen.

Figure 5 Typical energy requirements for the liquefaction of 1 kg hydrogen compared to HHV of Hydrogen.

For small liquefaction plants the energy needed to liquefy hydrogen may exceed the HHV of the gas. But even with the largest plants (10,000 kg/h) about 30% of the HHV energy is needed for the liquefaction process.

Energy Needed to Store Hydrogen in Hydrides At this time only a generalized assessment can be presented for the physical (e.g. adsorption on metal hydrides) or chemical (e.g. formation of alkali metal hydrides) storage of hydrogen. There are many options for both types of hydrogen storage. This makes it difficult to present numbers. But a few cautious statements may be allowed.

The laws of nature certainly apply to this type of hydrogen storage as well. In the chemical case, a substantial amount of energy is needed to combine hydrogen with alkali metals. This energy is released when the hydrogen is liberated from the compound. The generated heat has to be removed by cooling and is normally lost.

For the physical hydride storage, the hydrogen gas must be pressurized. The energy required for compression has been assessed before. The compression energy is released as heat during the charging process. Also, external heating is needed to liberate the hydrogen from the hydride storage material. According to Ref. [11], p. 264 metal hydrides store only around 55-60 kg(H2)/m 3 compared to 71 kg(H2)/m 3 for liquid hydrogen. But 100 kg of hydrogen are contained in one cubic meter of methanol.

Hydride storage of hydrogen is by no means a low-energy process, but it may be compared to the compression of hydrogen. Generalized numbers cannot be presented today.


    California hydrogen  
Production of hydrogen off coast of California by using Motorwave technology

the object of this project is to use wave energy to produce very inexpensive hydrogen that can power power plants .

By burning Hydrogen Oxygen ,we eliminate 100% of any pollution .The combustion of hydrogen/oxygen releases only water .

What will it take to convince Power plants to switch to Hydrogen ?

Today Power plants are using natural gas (methane) .they pay approx 0.3 US$ per kg .

We Know that for the same weight hydrogen has 3 times more energetic power .

1kg of Hydrogen = 140 Mj 1 kg of methane = 40 Mj .

1 kg of hydrogen = 4 US$ (for the lowest) . hydrogen is then 450 % more expensive than natural gas .

The problematic is then simple .can we produce a kg of hydrogen for less than 1 US$ ?

How do we produce non polluted hydrogen ?

The only known method is by electrolysis of water .

It takes 50 kWh to produce 1 kg of hydrogen gas and about 70 kWh to produce 1 kg of liquid hydrogen .

We then need to find a way to produce a kWh for less than 0.015 US$ .

Wind energy can produce a kWh for 0.07-0.09 US$ . Pelamis technology for about 0.08- 0.10 US$

solar energy is even higher at approx 0.20-0.30 US$ and the production cost of these technologies is not going down .

The only technology so far that could do it is Motorwave .it's estimated production cost of a kWh is approx 0.005 US$ .

The problem is that Motorwave technology is still at the experimental stage and needs money to continue the development.

The owner of this technology ,being an environmentalist, is certainly willing to lower his profit in exchange for capital investment

to help speed up his development.

The plan will be to make use of a reformed oil platform ,anchor it at approx 10 kilometers of coast . Use Motorwave technology

to produce the needed electricity and use the oil platform as a facility to produce hydrogen and then either ship it out by ship or

install a flexible pipeline directly to the power plant .

The all process will be 100% pollution free . The production capacity can easily follow the needs of any power plants .

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