Fuels sources, decarbonization

The second long-term trend in energy has been the decarbonization of our fuel sources. The world has moved from energy sources... 

If hydrogen is made from decarbonized fossil fuels, fuel-cycle emissions can be cut by up to 80 percent. With renewable energy sources such as biomass, solar, or wind, the fuel cycle greenhouse gas emissions are virtually eliminated. It is possible to envision a future energy system based on hydrogen and fuel cells with little or no emissions of pollutants or greenhouse gases in fuel production, distribution, or use. 

As mentioned earlier, separation of C02 at concentrated sources is easier than from the environment, and carbon capture at upstream decarbonizes many subsequent economic sectors. However, it does require significant changes in the existing infrastructure of power and chemical plants. Furthermore, approximately half of all emissions arise from small, distributed sources. Many of these emitters are vehicles for which onboard capture is not practical. Thus, unless all the existing automobiles are replaced by either hydrogen-powered fuel cell cars or electric cars, the capture of C02 from the air provides another alternative for small mobile emitters. 

There are several possible ways to mitigate C02 emission problems. Among them are traditional approaches including (i) more efficient use of fossil fuel energy resources, (ii) increased use of clean fossil fuels, such as NG, and (iii) increased use of non-fossil fuels (nuclear power and renewable sources). The novel and most radical approach to effectively manage carbon emissions is the decarbonization of fossil fuels. Three main scenarios of fossil fuels decarbonization are currently discussed in the literature ... 

In the case of the cement rotary kiln, the fluid flow through the kiln freeboard comes from several sources such as secondary hot combustion air, combustion and decarbonation products and inleakage air. In direct firing kilns, the pulverized solid fuel is injected through the burner pipe nozzle with the external diameter in the range of 250 to 600 mm into the kiln with an internal diameter of 2.4 to 6.2 m. 

Sources of CO2 associated with Portland cement manufacture include (i) the decarbonization of limestone (ii) the exhausts of kiln fuel combustion and (iii) the exhausts of the vehicles used in cement plants and distribution. Of these sources, the first produces a minimum of about 0.47 kg CO2 kg cement, whilst production via the second source varies with the plant efficiency. For example, an efficient precalciner plant will produce 0.24kg CO2 kg cement, while a low-efficiency wet process may produce up to 0.65 kg CO2 kg . The production of CO2 via the third source is almost insignificant (0.002-0.005 kg CO2 kg cement). Hence, the typical total CO2 footprint is around 0.80 kg CO2 kg finished cement This leaves aside the CO2 associated with electric power consumption, which varies according to the local generation type and efficiency. Typical electrical energy consumption is of the order of 90-150 kWh per metric ton of cement this is equivalent to 0.09-0.15 kg CO2 kg finished cement if the electricity is coalgenerated. All of this amounts to about 7% of the total CO2 generated worldwide (Malhotra, 1999). 

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