Flue openings

Earthen pit kilns originally were used to produce charcoal. A circular mound-shaped pile of wood (15-45 cords) was built up with an open core 30-60 cm (1-2 ft) in diameter to serve as a flue. The entire surface of the pile, except for the top flue opening and several small openings around the bottom periphery, then was covered with dirt or sod sufficiently thick to exclude air. The mound was allowed to coal for 20-30 days to give the final product. 

An air reversal system is required in a regenerative air/fuel furnace. Oxy/fuel furnaces do not reverse, reducing capital requirements and eliminating a maintenance concern. With an 80% reduction in furnace exhaust, the flue opening and exhaust system can be greatly downsized, saving additional capital. 

Figure 15.5 Amino acid alignment of several key regions of representative Y-family DNA polymerases (DNAPs) in the (a) IV/k and (b) V/r class. The R-groups of the final three amino acids ( flue ) of the chimney s upper lip either do not plug (IV/K class) or plug (V/r class) the chimney, depending upon whether the first amino acid in the upper lip ( flue-handle ) is glycine (flue open, IV/K class) or is a bulky amino acid (often valine, flue closed, V/r class). The lowest line in each panel shows conserved residues, with...

Below some firing rate, for example, 10 kk Btu/hr, the burners should fire direct to increase mass flow to improve temperature uniformity, by firing direct, bypassing the regenerative beds. (The poc of these burners should exit through flue openings below the burners.)... 

Wilkinson Oven. A pottery bottle OVEN (q.V.) designed so that the hot gases rise through the bag-walls and the central well-hole, and descend between the saggars to leave the kiln through flue openings in the floor mid-way along radii. (A. J. Wilkinson, Brit. Pat. 4356, 20/3/1890.)... 

The construction site may contain features that could promote the rapid spread of fire, heat or smoke and affect escape routes. These features may include ducts or flues, openings in floors or walls, or combustible wall or ceiling linings. Where people are put at risk from these features, appropriate steps should be taken to reduce the potential for rapid fire spread by, for example, fitting non-combustible temporary partitions and/or providing an early warning of fire so that people can leave the workplace before their escape routes become unusable. 

Heavy fuel oil usually contains residuum that is mixed (cut back) to a specified viscosity with gas oils and fractionator bottoms. For some industrial purposes in which flames or flue gases contact the product (eg, ceramics, glass, heat treating, and open hearth furnaces), fuel oils must be blended to low sulfur specifications low sulfur residues are preferable for these fuels. 

Utihties that reduce emissions below the number of allowances they hold may trade emissions credits on the open market. Owners of plants affected by Phase I regulations can also petition the EPA for a two-year extension for meeting Phase I emissions if they have selected a control option capable of reducing SO2 emissions by 90% or more, such as is capable by flue-gas desulfurization. Owners of these units can receive bonus allowances for 1997—1999 if they have operated at SO2 emissions below 0.52 kg/10 kj (1.2 lb/10 Btu) of fuel heating value input. 

Constmction of new power plants in the coal region of the western United States presents serious problems in states whose laws dictate zero effluent. In these plants, cooling-tower water withdrawn from rivers cannot be returned to them. In these situations, cooling-tower effluent is purified by distillation (vapor-compression plants have predominated) and by a combination of distillation and membrane technology. The converted water then is used as boiler feedwater the plant blowdown (effluent) is evaporated from open-air lined pools, and pool sediment is periodically buried back in the coal mine with the flue ashes. 

As a result of the larger flues and the restric ted surface area per unit of gas passed, regenerators employed with this type of furnace exhibit much lower efficiency than would be reahzed with smaller flues. In view of the large amount of iron oxide contained in open-hearth exhaust gas and the alkah fume present in glass-tank stack gases, however, smaller checkerbrick dimensions are considered imprac tical. 

Temperature ehanges for the flue gas to the expander produee the effeets shown in Figure 4-63. The expander inlet temperature at design is 1,200°F. As the expander inlet temperature rises, the expander horsepower eurve moves to the left and upward while the ehange in the blower eurve is insignifieant. The results are that the lower horsepower balanee point moves to the left and down, the peak of the expander eurve moves to the left and up, the peak generator load inereases to G, and the expander bypass valve opens at a lower feed rate. 

At the rated duty point, the differential pressure eontroller is aetive. The inlet eontrol valve and trip valve are eompletely open. The main bypass valve is eompletely elosed and the small bypass valve eontrols the differential pressure. Approximately 96%-98% of the flue gas flows through the expander, with the rest passing through the small bypass valve, orifiee ehamber, and double slide valve to the expander outlet to rejoin the main flue gas flow. 

Fluetuations in the flue gas flowrate (typieally less than 3% of nominal) are deteeted by the differential pressure eontroller and eompensated for by adjusting the small bypass valve. The main bypass valve is eompletely elosed during normal operations, but ean open in the event of sharp inereases in the flue gas flowrate. Similarly, in the event the flue gas flowrate deereases, the small bypass valve eloses to a meehanieally preset minimal opening, and the inlet eontrol valve also partially eloses. The minimum opening is neeessary to keep the bypass lines to the minimum requisite operating temperature. 

Under normal operations, the existing differential pressure governor is switehed to manual and the double slide valve is wide open. This valve must be suffieiently opened so that, even in the event of an emergeney expander trip, the entire flue gas flow ean pass through the double slide valve without the regenerator diseharge pressure inereasing to nonpermissible levels. 

If, however, the FCC unit should be operated at a different duty point, whether this is due to a different flue gas flowrate or a different regenerator pressure, the bypass valves would either open too wide or not wide enough. The result is fluetuation in the regenerator outlet pressure. 

The characterization of PIC (products of incomplete combustion) from the combustion of wood treated with pentachlorophenol (penta) is more widely documented in the open literature than creosote alone. However, both products are similar in chemical composition and likely result in comparable forms and concentrations of PIC. Literature reported studies on the combustion of these chemicals and wood treated by them, and the PIC generated are based upon optimal conditions. Optimal conditions are defined as those in which the fuel burns at the designed heat release rate with nominally 160% excess air and a low level (< 100 ppm) of carbon monoxide (CO) emissions in combustion (flue) gases. 

The duct between the boiler outlet and the chimney connection should be designed to have a gas velocity no greater than the chimney flue, be complete with insulation, and cladding, access openings and expansion joints. It should have the least number of bends and changes of section possible and should preferably not fall between the boiler outlet and the chimney connection. 

Furnace temperatures (and in part, heat transfer rates) are controlled by the opening and closing of air and flue gas dampers and burner registers. 

Induced draft fans (ID fans) are located near the end of the flue-gas path and provide a negative static pressure below that of atmospheric pressure (creating a partial vacuum). This induces outside air to infiltrate any openings in the boiler. 

The back doors are opened, and all residuals from front-end cleaning are removed. Any additional rear-end cleaning is carried out. The deposit box at the base of the chimney flue is checked, and all flue soot is vacuumed away. 

Hot gases rise by thermal lift. Hence in the open air they will disperse. Within buildings this is a serious cause of fire escalation and toxic/asphyxiation hazards if smoke and hot gases are able to spread without restriction (or venting) to upper levels. A balanced flue can serve to effectively isolate a combustion process in a gas-fired appliance, but must be sound in construction and unrestricted to avoid leaks. 

---