Power plants alkali metals

Many electrochemical devices and plants (chemical power sources, electrolyzers, and others) contain electrolytes which are melts of various metal halides (particularly chlorides), also nitrates, carbonates, and certain other salts with melting points between 150 and 1500°C. The salt melts can be single- (neat) or multicomponent (i.e., consist of mixtures of several salts, for their lower melting points in the eutectic region). Melts are highly valuable as electrolytes, since processes can be realized in them at high temperatures that would be too slow at ordinary temperatures or which yield products that are unstable in aqueous solutions (e.g., electrolytic production of the alkali metals). 

Projected economics were also highly promising [41] capital and operating costs would be a fraction of those required by standard methods, e.g. scrubbing. Furthermore, no chemical reagents would be required and no waste stream produced. However, the high melting points of the alkali-metal sulfates (T > 512 °C) offered severe limitations to application, especially for use in power plants, where the flue gas typically is unavailable for treatment at temperatures below 400 °C. 

There are two principal synthetic routes to dicarboxylate complexes. One of these uses an aqueous solution of the alkali metal dicarboxylate and the corresponding metal halide,93 while the other depends upon the dicarboxylic acid reduction of higher oxidation state metals. This reductive property of oxalic acid results in its ready dissolution of iron oxides and hence a cleaning utility in nuclear power plants.94 Mention must also be made of the successful ligand exchange synthesis of molybdenum dicarboxylates, Mo(dicarboxylate)2 H2 O, from the corresponding acetate complex. Unfortunately the polymeric, amorphous and insoluble nature of these complexes has restricted the study of these systems, which may well provide examples of multiple M—M bonding in dicarboxylate coordination chemistry.95... 

The commercial importance of this metal was first recognized in 1950s when its high strength/density ratios were found attractive in aerospace applications. The corrosion resistance in a variety of conditions led to its use in wet chlorine gas coolers for chlor-alkali cells, chlorine and chlorine dioxide bleaching equipment in pulp/paper mills, and reactor interiors for pressure acid leaching of metallic ores. The metal and its alloys were used in seawater power plant condensers, with over 400 million feet installed in application.65,66 The most commonly used alloys and their composition are given in Table 4.48. 

Radioactive waste from certain nuclear power plants and from weapons testing can lead to health problems. For example, ions of the radioactive isotope strontium-90, an alkali metal, exhibit chemical behaviour similar to calcium ions. This leads to incorporation of the ions in bone tissue, sending ionizing radiation into bone marrow, and possibly causing leukemia. Given the following equation for the decay of strontium-90, how would you complete it ... 

Ash deposition in biomass combustion systems has been the focus of numerous research efforts.559,659 The basic mechanism for deposit formation in biomass combustion systems starts with the vaporization of alkali metals, usually chlorides, in the combustor. Fly ash particles, which are predominantly silica, impact and stick to boiler tube surfaces. As the flue cools the alkali metal vapors and aerosols quench on the tube surfaces. When the ash chemistry approaches equilibrium on the surface and the deposit becomes molten, the likelihood increases that additional fly ash particles will stick, and deposits grow rapidly. Ash deposits can also accelerate the corrosion or erosion of the heat transfer surfaces. This greatly increases the maintenance requirements of the power plant often causing unscheduled plant interruptions and shutdown. 

When biomass is co-fired with coal (even in small percentages), the alkali metals in biomass ash can alter the properties of the resulting mixed ash. This could have a significant impact on the coal plant s operating and maintenance costs or even operability. The addition of biomass to a coal-fired power plant can also nullify ash sales contracts for coal flyash. Biomass ash components in feedstocks may also reduce the long-term efficiency and effectiveness of certain (selective catalytic reduction, SCR) systems for the selective catalytic reduction ofNOx. 

Empirical experience with conventional coal-fired power plants has indicated minerals containing alkali metal (Na, K), sulfur- and chlorine-bearing species to be the most aggressive fuel components leading to fire-side or hot corrosion (5). 

As alluded to in Chapter 8, the ideal biomass feedstock for thermal conversion, whether it be combustion, gasification, or a combination of both, is one that contains low or zero levels of elements such as nitrogen, sulfur, or chlorine, which can form undesirable pollutants and acids that cause corrosion, and no mineral elements that can form inorganic ash and particulates. Ash formation, especially from alkali metals such as potassium and sodium, can lead to fouling of heat exchange surfaces and erosion of turbine blades, in the case of power production systems that use gas turbines, and cause efficiency losses and plant upsets. In addition to undesirable emissions that form acids (SOx), sulfur can... 

In the molten carbonate process a molten eutectic mixture of lithium, sodium, and potassium carbonates removes sulfur oxides from power plant stack gases. The resulting molten solution of alkali metal sulfites, sulfates, and unreacted car bonate is regenerated in a two-step process to the alkali carbonate for recycling. Hydrogen sulfide, which is evolved in the regeneration step, is converted to sulfur in a conventional Claus plant. A 10 MW pilot plant of the process has been constructed at the Consolidated Edison Arthur KiU Station on Staten Island, and startup is underway. 

Some radioactive nuclides are especially damaging because they tend to concentrate in particular parts of the body. For example, because both strontium and calcium are alkaline earth metals in group 2 on the periodic table, they combine with other elements in similar ways. Therefore, if radioactive strontium-90 is ingested, it concentrates in the bones in substances that would normally contain calcium. This can lead to bone cancer or leukemia. For similar reasons, radioactive cesium-137 can enter the cells of the body in place of its fellow alkali metal potassium, leading to tissue damage. Non-radioactive iodine and radioactive iodine-131 are both absorbed by thyroid glands. Because iodine-131 is one of the radioactive nuclides produced in nuclear power plants, the... 

Preparation of uranium metal. As discussed previously, some nuclear power plant reactors such as the UNGG type have required in the past a nonenriched uranium metal as nuclear fuel. Hence, such reactors were the major consumer of pure uranium metal. Uranium metal can be prepared using several reduction processes. First, it can be obtained by direct reduction of uranium halides (e.g., uranium tetrafluoride) by molten alkali metals (e.g., Na, K) or alkali-earth metals (e.g.. Mg, Ca). For instance, in the Ames process, uranium tetrafluoride, UF, is directly reduced by molten calcium or magnesium at yoO C in a steel bomb. Another process consists in reducing uranium oxides with calcium, aluminum (i.e., thermite or aluminothermic process), or carbon. Third, the pure metal can also be recovered by molten-salt electrolysis of a fused bath made of a molten mixture of CaCl and NaCl, with a solute of KUFj or UF. However, like hafnium or zirconium, high-purity uranium can be prepared according to the Van Arkel-deBoer process, i.e., by the hot-wire process, which consists of thermal decomposition of uranium halides on a hot tungsten filament (similar in that way to chemical vapor deposition, CVD). 

Coal ash corrosion is a widespread problem for superheater and reheater tubes in coal fired power plants that bum high-sulfur coals. The accelerated corrosion is caused by liquid sulfates on the surface of the metal beneath an over-lying ash deposit. Coal ash corrosion is very severe between 540 and 740°C (1000°F and 1364°F) because of the formation of molten alkali iron-trisulfate. Considerable work has been done to predict corrosion rates based on the nature of the coal (its sulfur and ash content). This was accomplished by the exposure of various alloys to synthetic ash mixtures and synthetic flue gases. The corrosion rates of various alloys were repotted in the form of iso-corrosion curves for various sulfur dioxide, alkali sulfiite, and temperature combinations. An equation was developed to predict corrosion rates for selected alloys from details of the nature of ash by analyzing deposits removed from steam generator tubes and from test probes installed in a boiler [33]. Then laboratory tests were conducted using coupons of various tdloys coated with synthetic coal ash that was exposed to simulated combustion gas atmospheres. 

Ash from a wood-fired power plant (as in Exercise 44) comprises mainly oxides of alkali (Na, K) and alkaline earth (Mg, Ca) metals and creates an average particle concentration of 27 pg/m in the air over a small watershed covered by a fir forest. To determine whether ash deposition could offset to some degree the effects of acid... 

Based on the bioisosterism, the salts of alkylphosphonates lA or IC were assumed to have a more powerful inhibitory effect against plant PDHc El and better h iddal activity than the corresponding alkylphosphonates, because sodium D-methyl acety-Iphosphonate 1-1 has been reported as a powerful PDHc El inhibitor [1]. Five series of novel alkali metal salts of D-alkyl 1-(substituted phenoxyacetoxy)alkylphosphonates IIA-IIE were first designed as potential plant PDHC El inhibitors. IIA-IIE could be easily synthesized from corresponding D,D-dialkyl 1-(substituted phenoxyacetoxy) alkylphosphonates lA or IC in one step. It was also expected that 1-(substituted phenoxyacetoxy)alkylphosphonic acids (Scheme 3.2) could have better herbicidal activity, because they were more analogous to pymvic acid which acted as the substrate of PDHc. However, 1-(substituted phenoxyacetoxy)alkylphosphonic acids were not stable for long-time storage. 

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