Sorbents calcium oxide

The carbon dioxide sorbent, calcium oxide, serves three functions in the process. First, the adsorption of carbon dioxide by calcium oxide to produce calcium carbonate is an exothermic chemical reaction that also delivers energy to the reforming reactions in the form of chemical potential energy. During the air regeneration step, the process of decomposing the calcium carbonate to calcium oxide largely absorbs heat released by oxidation of nickel, and... 

Dry sorbents are also used to remove sulfur dioxide. Lime (calcium oxide) and slaked lime (calcium hydroxide) combine with sulfur dioxide to form calcium... 

Figure 17.6 illustrates a gasification process integrated with the calcium looping process. Once the water gas mixture is formed at the exit of the gasifier, calcium oxide fines are injected into the fuel gas stream. As the fuel gas flows past the WGS catalyst, the WGS reaction takes place and forms additional C02. The injected CaO sorbent particles react with C02 and H2S in the gas stream, thereby allowing further catalytic WGS reaction to occur. The reactions involved in the calcium looping scheme are... 

Ding and Alpay also studied sorption-enhanced reforming with K-HTC as sorbent [28], using a commercial Ni-based catalyst. They found that the SER process benefits from higher pressures and that lower steam to methane ratios can be used than in ordinary reforming. Reijers et al. [25] have shown that K-HTC is an effective sorbent between 400 and 500 °C, with an C02 uptake of approx. 0.2 mmol g 1. This capacity is low compared with calcium oxides and lithium zirconates. Above 500 °C, the C02 sorption capacity of K-HTC decreases rapidly to zero [36]. 

The UMR process can be improved by introducing calcium oxide, a carbon dioxide sorbent, into the packed bed. The potential advantages of using calcium oxide as a carbon dioxide sorbent have been previously recognized. The use of calcium oxide to enhance the steam reforming process has been patented by Gluud et al.( 1931). More recently Harrison and coworkers (Han and Harrison, 1994) have reported laboratory-scale data for the steam reforming of methane in the presence of calcium oxide. 

Oiled debris, beach material, and sorbents are sometimes disposed of at landfill sites. Legislation requires that this material not contain free oil that could migrate from the site and contaminate groundwater. Some governments have standard leach-ability test procedures that determine whether the material will release oil. Several stabilization processes have been developed to ensure that free oil does not contaminate soil or groundwater. One process uses quick lime (calcium oxide) to form a cement-like material, which can be used on roads as a dust-inhibitor. Another form of disposal is to process liquid oil in a bioreactor and thus attempt to break it down. This is usually not successful because of the many slowly degraded components in some oils. 

The sulfur dioxide penetrates the pores and reacts with the calcium oxide to form solid calcuim sulfate that can be removed with the ash. Dolomite (CaCOs MgC03) and hydrated lime [Ca(OH)2] are also used as sorbents. Sulfur scrabbers based on a variety of chemical reactions have become more common since 1990. Such systems produce by-products with some commercial value, such as elemental sulfur, sulfuric acid, and gypsum. Scrubbers have added benefits of removing some NOx, mercury, arsenic, and other pollutarrts that either crrrrerrtly or in the futrrre may fall rrrrder formal regulation. However, scrubbers add about 25% to the capital and operating costs of a power statiorr, leading most power stations to switch to low-sulfirr coals rather than build scrubbers. 

FGD is a chemical process to remove sulfur oxides from the flue gas at coal-burning power plants. Many methods have been developed to varying stages of applicability and the goal of these processes is to chemically combine the sulfur gases released in coal combustion by reacting them with a sorbent, such as limestone (calcium carbonate, CaC03), hme (calcium oxide, CaO), or ammonia (NHj) (Chapters 15 and 23). 

A central draft tube is used primarily for recirculating solids, and the dense, dry char collects in the fluidized bed at the top of the draft tube and is withdrawn at this point. Dolomite or calcium oxide (sorbent) is added to the fluidized bed to absorb the sulfur present as hydrogen sulfide in the fuel gas and spent sorbent is withdrawn from the bottom of the reactor and regenerated. The heat for devolatilization is supplied primarily by the high-temperature fuel gas produced in the gasifier combustor. After separation of fines and ash, product gas is cooled and scrubbed with water for final purification. 

Lime or calcium oxide is usually employed as sorbent in this process in which the flue gas is given into a reactor vessel and the lime slurry is atomized into the same vessel. The water in the slurry is completely evaporated in the spray dry absorber. It is possible to remove 85%-90% of the sulfur dioxide for moderately high-suUur fuels. A solid by-product needing disposal op tion is produced. 

Despite the favourable CO2 capture performances of some of the sorbents derived from synthetic calcium oxide precursors when compared with limestone, the characteristic drop in the cychc CO2 capture capacity could still be observed [75]. 

Lu H, Reddy EP, Smimiotis PG (2(X)6) Calcium oxide based sorbents for capture of carbon dioxide at high temperatures. J Ind Eng Chem 45 3944-3949... 

Sorbents that are considered in the literature for sorption-enhanced reforming process are potassium promoted hydrotalcite (K-HTC), lithium orthosilicate (LiSi04), lithium zir-conate (LiZr03), sodium zirconate (Na2Zr03) and calcium oxide (CaO). The affinity of a sorbent to a molecule can be expressed by the equilibrium partial pressure at different temperatures. For example, the equilibrium partial pressure of carbon dioxide for different sorbents is shown in Figure 6.2. 

A promising sorbent for SER applications is calcium oxide (as pure CaO or dolomite), which can react with CO2 generating CaC03 according to the following carbonation reaction (6.3) ... 

The results of H2 S sorption experiments conducted at between 700 and 900 C and using a variety of sorbents are reported in Figure 11.29. These show Ca- and Cu-based sorbents to be unsuitable for reducing H2S concentrations below 1 ppmv at these temperatures. The sorbent composition is important - slag lime, which contains several oxides beside calcium oxide, achieving the best H2S reduction (down to 50 ppmv) of all the Ca-based sorbents. 

The CLP process uses calcium oxide (CaO) as a sorbent in the water gas shift reaction to simultaneously remove CO2, sulfur, and chloride impurities at a high temperature as ... 

Regenerative sulfur dioxide sorbents based on calcium oxide and on titanium oxide—to be applied during AFBC—were synthesized by agglomeration. This technique as well as the starting materials were selected considering technical and economical feasibilities. The sorbents were tested by TG methods and by measurements using a laboratory-scale AFB reactor. 

CALCIUM OXIDE BASED SORBENTS 2.1. Sulfation behaviour... 

Figure 1 Conversion to calcium oxide during calcium sulfate regeneration (sorbent C.C1.2/S in 5% H2)...

Figure 5 Sulfation/regeneration weight changes in TG during 8 cycles of a calcium oxide based sorbent (sorbent C.C1.2/s in 5% H2). 

Calcium oxide can absorb CO2 from pre-combustion systems. Natural sources of CaO, such as limestone, CaCOg, produce sorbents that lose reactivity relatively fast. Good CO2 sorbents were prepared with CaO precursors templated on three natural polysaccharides chitosan, agar and carrageenan, or three synthetic polymers poly(acrylic acid), poly(ethylene glycol) and poly(ethylene oxide-b-propylene oxide-b-ethylene oxide), respectively. Calcium oxide confined onto S5mthetic polymers exhibited better CO2 uptake activity and stability than CaO derived from commercial... 

Today s major emissions control methods are sorbent injection and flue gas desulfurization. Sorbent injection involves adding an alkali compound to the coal combustion gases for reaction with the sulfur dioxide. Typical calcium sorbents include lime and variants of lime. Sodium-based compounds are also used. Sorbent injection processes remove 30 to 60% of sulfur oxide emissions. 

Among the metal oxides, calcium-based sorbents have been extensively investigated. The CCR process, which uses the reengineered limestone sorbent has efficiently and economically shown to capture C02 at 600-700°C. Although limestone sorbent is inexpensive, its effective sorption capacity is generally low due to its small surface area and pore sizes (-30% conversion). Hence, the modification of limestone sorbent to form calcium-based sorbents possessing mesopores has been the main focus of the development of CCR process. The conversion of the engineered calcium-based sorbents in carbonation reaction is >90%. 

Since wet purification methods are insufficiently effective, solid sorbents are used. The systems based on calcium and aluminium oxides and hydroxides are promising as such sorbents. A sorbent should provide a minimum gas dynamic resistance, therefore, it is produced as the granules of complicated shape. Sorbents based on lime and aluminium hydroxide are good fluorine absorbers. However, lime sorbents do not possess sufficient mechanical strength, while the use of aluminium hydroxide alone as a sorbent is limited by its high cost. 

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