Calciner heat balance

Flow Measurements Measurement of flow rates of clean gases presents no problem. Flow measurement of gas streams containing solids is almost always avoided. The flow of solids is usually controlled but not measured except solids flows added to or taken from the system. Solids flows in the system are usually adjusted on an inferential basis (temperature, pressure level, catalyst activity, gas analysis, heat balance, etc.). In many roasting operations, the color of the calcine discharge material indicates whether the solids feed rate is too high or too low. 

Particular attention, in the design of this model calciner, was given to the utilization of combustion heat of volatile matter emitted from the coke feed and to obtaining an accurate heat balance data for the two-stage calcining system. 

Table VI summarizes a typical heat balance in second stage of the above calcining system (Case A) in comparison with that of an alternative system (Case B) in which the exhaust gas from first stage kiln is not utilized for second stage calcination. The amount, composition and temperature of the exhaust gas from first stage kiln determine the auxiliary fuel requirements for second stage kiln.

Table VI, Heat Balance of Model Calciner (Second Stage)...

Table 9.16 covers the sensible heat of the components of the output gas. Table 9.17 covers the lime product output sensible heat. Table 9.18 covers the sensible heat from the dust. Table 9.19 covers the heat releases from the combustion reaction. Table 9.20 covers the heat consumed by calcinations. Table 9.21 covers the material and energy balance for the dolomitic lime process. Table 9.22 gives a summary and analysis, including the material balance and the heat balance. 

SO2 removal experiments with CEB were performed in a thermogravimetric analysis (TGA) set-up to simulate the process during its combustion. The sample was first heated in a mixture of 70% CO2 in N2 to produce CaCOj, followed by the decomposition of CaCOj to CaO under N2 and O2. This calcined material was sulfated using a mixture containing 3000 ppm SO2, 12% O2, and the balance N2. 

Calcining magnesium hydroxide, such as that produced in either a brine or seawater process, involves heating a filter cake that contains between 50 and 72% magnesium hydroxide solids, the balance being water. The thermal decomposition involves the following reaction ... 

The sample thickness was chosen to give an absorbance (A/tx) of about 1.0 in the Pt edge region, corresponding to approximately 100 mg of catalyst. The sample was centered in a continuous-flow in-situ EXAFS reactor tube (18 in. long, 0.75-in. dia) fitted at both ends with polyimide windows. The calcined catalysts were first measured in air at room temperature. The catalysts were then reduced in 5% H2 (balance He) at 300 C for 1 h and cooled to room temperature. The second series of EXAFS data were collected at room temperature in H2. Thereafter, the pre-reduced catalysts were purged with He at room temperature, then heated to 300°C in 5% O2 (balance He) for 1 h. After the oxidizing pretreatment, the EXAFS data were collected at room temperature in O2. 

A calcination step at 573-773 K in air converts the Al- and Zr-polyoxycation precursors into rigid alumina and zirconia oxide pillars. This heating process is necessary to obtain a stable PILC with a permanent microporosity, not subject to swelling or hydrolysis phenomena. During calcination, dehydration and dehydroxylation reactions of the charged pillar precursors occur to give neutral oxide particles. The equilibrium in electrical balance is maintained by the release of protons during the conversion at elevated temperature ... 

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