Firing bottom

Institute Shanghai SMS 5 60 coal-fired bottoming cycle test facihty... 

Other problems that limit production rates in either longitudinally fired or side-fired bottom zones are restricted gas passages in the bottom zones, and low-velocity luminous flame burners. Low-velocity luminous flames with their variable temperature profiles (hot at the burner wall at low firing rates, and hotter beyond the T-sensor at high firing rates) cause the melting of scale into the bottom zones. To counter this scale build-up problem, operators are prone to lower the bottom zone temperature by 100 F (56 C) or more. 

Side view of a batch car-hearth furnace with top-firing, bottom-fiuing. 

Additional methodological difficulties accompany self-ignition measurements in complicated geometry systems however, such systems are of most practical interest. In shaped combustion chambers (curvilinear walls, non-planar fire bottom, wall perforation or special gadgets for the mixture components supply [7, 76]) a thorough control of spatial location of blast generation centers is required. 

N. R. Johanson and J. W. Muehlhauser, "MHD Bottoming Cycle Operations and Test Results at the CFFF," paper presented at Second International Workshop on Fossil Fuel Fired MHD, Bologna, Italy, 1989. 

Reboilers need to be located next to the tower they serve, except for the pump-through types, which can be located elsewhere. Fired heater reboilers are always located away from the associated tower and use a pump to circulate the bottoms. Ketde-type reboders are preferred from an operational and hydraulic standpoint because they can be designed without the worry of having to ensure sufficient head for circulation required by thermosyphon reboders. However, ketde reboders require a larger-diameter shed that is more cosdy, and the reboder must be supported at a sufficient elevation to get the product to the bottoms pump with adequate NPSH. 

Similar to oil-fired plants, either low NO burners, SCR, or SNCR can be appHed for NO control at PC-fired plants. Likewise, fabric filter baghouses or electrostatic precipitators can be used to capture flyash (see Airpollution controlmethods). The collection and removal of significant levels of bottom ash, unbumed matter that drops to the bottom of the furnace, is a unique challenge associated with coal-fired faciUties. Once removed, significant levels of both bottom ash and flyash may require transport for landfilling. Some beneficial reuses of this ash have been identified, such as in the manufacture of Pordand cement. 

NOj Control. NO control limitations are described in both Tide 1 and Tide 4 of the CAAA of 1990. Tide 4 requirements affect only coal-fired boilers and take effect at the same time that the boilers are impacted by CAAA SO2 requirements. As of 1996, EPA had estabHshed Tide 4 NO limits only for tangentially fired and waH-fired, dry-bottom boilers that would be impacted by Phase I of the CAAA SO2 regulations (Tide 4). Limits of 0.22 kg/10 kJ (0.5 lb/10 Btu) and 0.19 kg/10 kJ (0.45 lb/10 Btu) have been set for wall-fired and tangentially fired units, respectively. The EPA based these levels on what was achievable using low NO burners. However, plants can employ a number of different front- or back-end emissions controls, including a combination of options, to achieve these levels. EPA plans to announce Tide 4 NO requirements for 300 additional boilers by late 1996 or eady 1997. 

Bottom drop Smoke and particulates precipitator, wetting to extinguish fire... 

Started to rise from the reaction, causing the vessel bottom head to fail at the weld seam. The force from the escaping gases propelled the tank into the ceiling and overhead structural steel. A small fire erupted which was quickly brought under control by the automatic sprinkler system. Even though the chemists had reviewed the chemistry and did not anticipate any problems, use testing could have identified this problem in the laboratory rather than the plant. 

Install fire safe bottom valves Install fire safe valves on major solvent lines Install remote shut off of fuel sources Eliminate points of leakage (flanges, hoses). Replace with fixed/welded pipes Move flammable material storage away from vessel (e.g., pallets, etc.)... 

An electron microscope picture of dislocation lines in stainless steel. The picture was taken by firing electrons through a very thin slice of steel about lOOnm thick. The dislocation lines here ore only about 1000 atom diameters long because they have been chopped off where they meet the top and bottom surfaces of the thin slice. But a sugar-cube-sized piece of ony engineering alloy contains about 10 km of dislocation line. (Courtesy of Dr. Peter Southwick.)... 

The failure took place in a large water-tube boiler used for generating steam in a chemical plant. The layout of the boiler is shown in Fig. 13.1. At the bottom of the boiler is a cylindrical pressure vessel - the mud drum - which contains water and sediments. At the top of the boiler is the steam drum, which contains water and steam. The two drums are connected by 200 tubes through which the water circulates. The tubes are heated from the outside by the flue gases from a coal-fired furnace. The water in the "hot" tubes moves upwards from the mud drum to the steam drum, and the water in the "cool" tubes moves downwards from the steam drum to the mud drum. A convection circuit is therefore set up where water circulates around the boiler and picks up heat in the process. The water tubes are 10 m long, have an outside diameter of 100 mm and are 5 mm thick in the wall. They are made from a steel of composition Fe-0.18% C, 0.45% Mn, 0.20% Si. The boiler operates with a working pressure of 50 bar and a water temperature of 264°C. 

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