Question 5.21: Because the greenhouse effect of carbon dioxide gas is well ...
Because the greenhouse effect of carbon dioxide gas is well established and human activities are the largest source of CO_{2} entering the atmosphere, the burden rests upon humanity to solve the economic conundrum currently limiting efforts to bring CO_{2} emission under control. The wet scrubber system introduced in Example 20 or a similar wet scrubber system is quite capable of removal of CO_{2} from an air emission stream. However, the economic and political considerations currently are such that even in developed nations, such as the United States and the European Union, governments are not willing to force their domestic industries to institute such well-proven methods of CO_{2} emission control. Discuss the following:
1. Technical limitations to removal of carbon dioxide from an air emission stream.
2. The economic and political solutions and driving forces for carbon dioxide control.
3. The possible combined technical and economic solutions to carbon dioxide emission reduction.
1. The technical limitations for removal of carbon dioxide from an air emission stream are presented in the following discussion. From a strictly engineering viewpoint, CO_{2} could be easily removed from the air emission of any industrial facility (such as a coal-fired power plant or other single-source site of CO_{2}) using an alkali (such as sodium carbonate/caustic) and a wet scrubber packed with highly efficient mass transfer media (such as Q-PAC or similar).
There is no technical limitation to removing CO_{2} from an air emission stream. The only limitation to such a scrubber would be that absorption of CO_{2} beyond 360 ppmv, the ambient level of CO_{2} in the atmosphere, would obviously not be an effective use of resources.
2. Following is a discussion on the economic and political solutions and driving forces for carbon dioxide control: Economic solutions for CO_{2} emission reduction and control are very difficult to find. The wet scrubbing technology for CO_{2} emission control (shown in Example 20) is widely rejected as being too costly for industry and society, in general, to accept. Although the societal benefits of CO_{2} emission reduction and control are no longer widely debated, the realities of the marketplace, global competition, and the parochial individual interests of various nations have all combined to prevent forward movement and application of proven methods of keeping CO_{2} from entering the atmosphere. When products are sold in the world marketplace that are of equal or similar quality, the lowest-cost product will eventually dominate the marketplace. Higher-cost competition will be driven to extinction as a result.
As an example, the US government will not force CO_{2} emission limitations on its coal-burning electrical generating facilities because this would force its industries, such as steel, automotives, and chemicals, to accept much higher electrical power costs. Such costs would need to be recovered by the various industries affected through higher pricing, and as just mentioned, this will not be allowed by the global forces driving the current world economy. Only if all industries in all nations are required to implement CO_{2} reduction technologies will the competitive disadvantage of single nations or groups of nations placing CO_{2} emission requirements on their respective industries be negated.
At present the international community is attempting to educate world leaders in the hope that a political solution, even if temporary, may be found for this problem (63). Also, as awareness of the harmful effects of CO_{2} emissions grows, governments will become more likely to commit resources to development of alternative technologies to limit CO_{2} emission.
3. The possible combined technical and economic solutions to carbon dioxide emission reduction are presented as follows. A plausible alternative technology is collection of CO_{2} emission streams for reuse. Research for utilization and reduction of CO_{2} emissions has been conducted by Wang and colleagues (48,49). Wang and Lee (49) have reported that collection of carbon dioxide emissions at tanneries, dairies, watertreatment plants, and municipal wastewater-treatment plants for in-plant reuse as chemicals will be technically and economically feasible.
About 20\% of organic pollutants in a tannery’s wastewater are dissolved proteins, which can be recovered using the tannery’s own stack gas (containing mainly carbon dioxide). Similarly, 78\% of dissolved proteins in a dairy factory can be recovered by bubbling its stack gas (containing mainly carbon dioxide) through its waste stream using a new type of wet scrubber (see Example 25). The recovered proteins from both tanneries and dairies can be reused as animal feeds. In water-softening plants for treating hard-water removal using a chemical precipitation process, the stack gas can be reused as a precipitation agent for hardness removal. In municipal wastewater-treatment plants, the stack gas containing carbon dioxide can be reused as both a neutralization agent and a warming agent. Because a large volume of carbon dioxide gases can be immediately reused as chemicals in various in-plant applications, the plants producing carbon dioxide gas actually may save chemical costs, produce valuable byproducts, conserve heat energy, and reduce the global warming problem (48,49).