Limestone, absorption calcined

CO2 is also recovered economically from the flue gases resulting from combustion of carbonaceous fuels, from fermentation of sugars and from the calcination of limestone recovery is by reversible absorption either in aqueous Na2COi or aqueous ethanolamine (Girbotol process). 

Option 2. Calcining to Nonacidk State. Capital costs for kilns, absorption towers, and baghouses were estimated at 3 H 200 000, 13 600 000, and 14 400 000 for plants A(H), B(H), and C(H), respectively, with the remainder of the cost being that of the lime and limestone required for neutralization of the SO2 and maintaining an alkaline environment in the kilns. No operating costs are included. Costs for Plants A(A), B(A), and (i(A) were determined by ratioing. 

Examples of eq. (6.14) include the roasting of metal sulfides the absorption of sulfur dioxide by calcium oxide that is formed by simultaneous calcination of limestone the formation of silicon nitride from silica, carbon and nitrogen. Examples of eq. (6.15) the baking of clay the burning of limestone the pyrolysis of coal, lignite, wood, peat, or other organic materials the calcination of sodium bicarbonate and similar salts. 

An important gas-solid reaction for wHich porosity decreases with time of exposure to the reactant gas is the absorption of SO2 by calcined limestone (CaO) or dolomite (CaO/MgO) to produce calcium sulfate (CaSO or CaSO./MgO), which has a larger molar volume than the reactant solid. If diffusional limitations in the pores are important, the porosity decrease will be greater near the surface of the solid particle and pores will plug, limiting access to part of the reactant solid. 

Prepared calcium carbonates are purified forms of native material. Conversion of calcium oxide and hydroxide produced from the calcination of material such as limestone and the subsequent absorption of atmospheric carbon dioxide furttier accounts for the occurrence of pigments such as those sometimes called lime. 

The process requires a large amount of fuel to calcine both the limestone and sodium bicarbonate and to generate steam for ammonia recovery. For the reaction proper, no fuel is required. In fact, large volumes of cooling water are required to remove the heat generated by the absorption and reaction of ammonia and carbon dioxide. The process has an imperfection in that an undesirable solution of calcium chloride also is produced. 

The thermodynamics of SO2 absorption by limestone has been described by Reid [78]. On the assumption that conversion of limestone into lime is necessary first step, a temperature somewhat greater than 1400" F (750°C) was calculated as being necessary to bring about a calcination of calcium carbonate in a furnace atmosphere of 14% CO2 (a typical value for a power plant). Figure 8.16 shows the SO2 concentration in a gas containing 2.7% oxygen in equilibrium with magnesia and with calcia at various temperatures. It is ob-... 

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