Electric power generation advantages

The DMFC, based on a polymer electrolyte fuel cell (PEFC), uses methanol directly for electric power generation and promises technical advantages for power trains. The fuel can be delivered to the fuel cell in a gaseous or liquid form. The actual power densities of a DMFC are clearly lower than those of a conventional hydrogen-fed polymer electrolyte fuel cell. In addition, methanol permeates through the electrolyte and oxidizes at the cathode. This results in a mixed potential at the cathode (Hohlein et al., 2000). 

Finally, the low-sulfur char is used as a clean boiler fuel for electric power generation. The hot char can be used directly, at pressure, with obvious advantages in thermal efficiency by using a pressurized, fluidized-bed combustion system (PFBC). The size consist of the char should ensure good performance when fluidized in the PFBC. Because the char has been partially desulfurized, the flue gas can easily meet a S02 emission specification of less than 0.8 lb per 106 Btu without the need to add limestone. This is in contrast to burning the Wyodak feed coal in a... 

The cost-performance indicators of the electric power generation technology being offered, as compared to existing conventional and alternative technologies, have the following advantageous features ... 

Table 4-7 shows CO2 emissions for various coal- and natural gas-based electric power generation options. CO2 emissions from natural gas are lower than those from coal because natural gas has much lower carbon content per million Btu of fuel. However, more efficient designs and the avoidance of limestone-based sulfur recovery can significantly reduce CO2 emissions from coal. Coal gasification has clear advantages over direct coal combustion in both areas. 

Changes in electrical power generated can be accomplished simply by an alternation in the supply of CH3OH feed, which is the major advantage of this device. 

Methanol, a clean burning fuel relative to conventional industrial fuels other than natural gas, can be used advantageously in stationary turbines and boilers because of its low flame luminosity and combustion temperature. Low NO emissions and virtually no sulfur or particulate emissions have been observed (83). Methanol is also considered for dual fuel (methanol plus oil or natural gas) combustion power boilers (84) as well as to fuel gas turbines in combined methanol / electric power production plants using coal gasification (85) (see Power generation). 

If all these process and economic advantages are reahzed, the cost of electricity l be lowered, making circulating PFBC an extremely attractive coal-fired option for power generation. 

The emergence of electricity as a means of transmitting power late in the nineteenth century offered new life to devices that tapped the kinetic power of wind and water, since it offset one of the greatest advantages of steam power locational flexibility. With electricity, power could be generated far from the point at which it was used. 

Electrochemical power sources differ from others, such as thermal power plants, by the fact that the energy conversion occurs without any intermediate steps for example, in the case of thermal power plants fuel is first converted in thermal energy, and finally electric power is produced using generators. In the case of electrochemical power sources this otherwise multistep process is achieved directly in only one step. As a consequence, electrochemical systems show some advantages, such as energy efficiency. 

Fuel cells such as the one shown on Fig. 3.4a convert H2 to H20 and produce electrical power with no intermediate combustion cycle. Thus their thermodynamic efficiency compares favorably with thermal power generation which is limited by Carnot-type constraints. One important advantage of solid electrolyte fuel cells is that, due to their high operating temperature (typically 700° to 1100°C), they offer the possibility of "internal reforming" which permits the use of fuels such as methane without a separate external reformer.33 36... 

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