Allowable stack temperature

Gnu)cg is usually limited by the allowable stack temperature Ts. As a fraction of the heat supplied to the cogeneration plant it remains constant in this application. 

Reuse et al. [68] combined endothermic methanol steam reforming with exothermic methanol combustion. The reactor consisted of a stack of 40 foils, 20 dedicated to each reaction (see Figure 2.77). The total length of the foils was 78 mm and their thickness was 200 pm. The foils carried 34 S-shaped channels each with a length of 30 mm, a depth of 100 pm and a width of 310 pm. A special plate in the center of the stack allowed for temperature measurements. The plates were made of FeCrAlloy and an a-alumina film 5 pm thick was generated on their surface by temperature treatment at 1000 °C for 5 h to improve the adherence of the catalyst coatings (see Section 2.10.7). 

Assume a stack temperature 100°F lower than the flue gas leaving the convection section. Select a stack diameter to give a stack velocity of about 30 feet per second, and calculate the velocity head. Estimate the stack height and calculate the friction Loss through it, allowing 1.5 velocity heads for the inlet and exit losses, 1.5 velocity heads for the damper and 1 velocity head for each 50 diameters Df stack height. 

The National Energy Technology Laboratory (NETL) developed a 3-dimensional computational fluid dynamics (CFD) model to allow stack developers to reduce time-consuming build-and-test efforts. As opposed to systems models, 3-dimensional CFD models can address critical issues such as temperature profiles and fuel utilization important considerations in fuel cell development. 

The Shell Oil Sulfinol-M process removes sulfur (mostly as H2S) from the coal gas. This process uses a mixture of MDEA and a physical solvent. It has advantages over processes that use only physical solvents because it avoids refrigeration, flash gas recompression, and large electricity requirements (36). A Claus process then converts the H2S to by-product liquid elemental sulfur. A Shell Oil SCOT system processes the Claus tailgas for higher sulfur recovery efficiency. The overall sulfur recovery is about 99%, leaving less than 120 ppmv of total sulfur in the purified coal gas. The low sulfur levels in the coal gas allow low stack temperatures without acid dew point corrosion. 

Here, is the water-gas shift reaction s equilibrium constant dependent on Gibbs free energy and stack temperature, where and E2 are constants related to Gibbs free energy change. The assumption that this reaction is in equilibrium allows us to remove its reaction rate from the equation set. 

Panels then move into a cooling device, normally a wheel or rack, where they are held individually and air is circulated between them to remove the majority of heat remaining in the boards after pressing. It is desirable to reduce the average board surface temperature to about 55°C. This temperature is sufficient to complete the cure of adhesive in the core of the board. The heat also helps to redistribute moisture uniformly within the boards, because the board surfaces are drier than the core when the boards come out of the press. Warm boards are normally stacked for several hours to a day to allow for resin cure and moisture equalization. 

Alkali metal haHdes can be volatile at incineration temperatures. Rapid quenching of volatile salts results in the formation of a submicrometer aerosol which must be removed or else exhaust stack opacity is likely to exceed allowed limits. Sulfates have low volatiHty and should end up in the ash. Alkaline earths also form basic oxides. Calcium is the most common and sulfates are formed ahead of haHdes. Calcium carbonate is not stable at incineration temperatures (see Calcium compounds). Transition metals are more likely to form an oxide ash. Iron (qv), for example, forms ferric oxide in preference to haHdes, sulfates, or carbonates. SiHca and alumina form complexes with the basic oxides, eg, alkaH metals, alkaline earths, and some transition-metal oxidation states, in the ash. 

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