Hydrogen utilisation

Catalytic hydrogen combustion, hydrogen combustion, hydrogen utilisation in PEM fuel cells, hydrogen production from fossil fuels (TUBITAK-MRC). 

The amount of hydrogen utilised in specific processes of energy conversion and application will increase. For example, such occasions will increase as the case of stationary fuel cell, in which hydrogen is produced by the steam reforming of natural gas, kerosene or petroleum gas, and immediately consumed in a fuel cell for power generation. 

By measuring the volumes of hydrogen utilised in this way in unit time per unit volume of metallic hydrosol, a measure of the relative efficiencies of the colloidal metals is obtained. The results obtained by Paal and his co-workcrs arc as follow ... 

Amphlett et al. calculated that for a methanol steam reformer the hydrogen utilisation needs to be maintained around 80% to avoid methanol combustion in the burner of the fuel processor. The maximum overall system efficiency had a weak maximum at the lowest possible hydrogen utilisation 407]. 

Schmid et al. [16] compared steam reforming and autothermal reforming of methane. They assumed that the anode off-gas was burnt in an external burner. The heat was utilised for heating purposes of a combined heat and power system. The analysis revealed much lower practical efficiency for autothermal reforming compared with steam reforming at 73% hydrogen utilisation in the fuel cell anode, as shown in Figure 5.44. 

Figure 5.44 Fuel processor efficiency versus anode fuel utilisation for different fuel processor configurations steam reforming with 100, 90 and 80% efficiency (SR 1.0, 0.9, 0.8) and autothermal reforming with 80% efficiency the arrow compares steam reforming and autothermal reforming at 80% efficiency for a hydrogen utilisation of 73% [16].

Other factors affecting the water balance are the hydrogen utilisation in the fuel cell anode and the oxygen stoichiometry on the cathode side. Increasing hydrogen utilisation requires a surplus of cathode air and consequently cathode stoichiometry needs to be increased. This dilutes the burner off-gas, which has a detrimental effect on the water balance of the fuel cell/fuel processor system [435]. 

An 85% hydrogen utilisation was assumed for the fuel cell anode of the conventional system, while 95% utilisation was assumed for the membrane devices [405]. 

Cifre PG, Badr O (2007) Renewable hydrogen utilisation for the production of methanol. Energ Convers Manage 48 519-527... 

As mentioned in Section 7.2, fuel and oxidant utilisations are important operating parameters for fuel cells such as the PAFC. In a fuel gas that is obtained, for example, by steam reforming of natural gas (see next chapter) the carbon dioxide and umeacted hydrocarbons (e.g. methane) are electrochemically inert and act as diluents. Because the anode reaction is nearly reversible, the fuel composition and hydrogen utilisation generally do not strongly influence cell performance. The RT term in equation 7.4 is clearly lower than for the MCFC and SOFC. Further discussion is given in Hirschenhofer et al. (1998). 

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