Temperatures, industrial boiler

For industrial boilers the mean gas temperature at the furnace exit, or at the entrance to the convection section of the boiler, may be calculated using the relationship ... 

The radiant section of an industrial boiler may typically contain only 10 per cent of the total heating surface, yet, because of the large temperature difference, it can absorb 30-50 per cent of the total heat exchange. The mean temperature difference available for heat transfer in the convective section is much smaller. To achieve a thermally efficient yet commercially viable design it is necessary to make full use of forced convection within the constraint of acceptable pressure drop. 

Typically, industrial WT boilers operate at pressures within the 100 to 650 psig range (sometimes up to 900-950 psig) and are rated for steam capacities within the range 40,000 to 200,000 lb/hr (5-21 kg/s) and steam temperatures of up to, say, 900 °F (482 °C). Industrial boiler designs tend to rely on natural, internal steam-water circulation. 

At medium temperatures of 400 °F/205 °C (equivalent to 250 psig, 17 bar, and typical of slightly larger industrial boilers), CHZ decomposes without the production of IDS to form nitrogen, ammonia, and water (see equation 2). 

Limits on flue-gas velocities for gas- or oil-fired industrial boilers are usually determined by the need to limit draft loss. For coal firing, design gas velocities are established to minimize fouling and pluKing of tube banks in high-temperature zones and erosion in low-temperature zones. 

The removal of NO from the exhaust gases of vehicle engines and industrial boilers is an important environmental problem. Many researchers have focused on finding better catalysts than the present Pt-Rh or Pt-Pd-Rh three-way catalysts for efficient NO, abatement. For the Pt-Rh three-way catalysts, it was reported that Pt is the most active component for the oxidation of CO and hydrocarbons at low temperatures, whereas Rh is most active for NO reduction (335). A recent study with PtRh/NaY catalysts shows that alloy particles of PtRh2 in NaY are superior to either monometallic component in CO oxidation and NO-CO reaction (336). Besides the high cost of the extremely scarce element Rh for these catalysts, a major problem... 

The EPA method is appropriate for a lower-temperature, nonreactive gas sample obtained, for example, from a utility boiler. However, this method should not be used to obtain samples from higher-temperature industrial furnaces used in glass or metal production. Flue gas temperatures from such furnaces, as well as from some incinerators, can be greater than 2400°F (1600 K). This would cause the probe to overheat and affect the measurements because of high temperature surface reactions. 

Blevins, L. G., Shaddix, C. R., Sickafoose, S. M., and Walsh, P. M. "Laser-Induced Breakdown Spectroscopy at High Temperatures in Industrial Boilers and Furnaces." Applied Optics 42 (2003) 6107-18. 

Selective non catalytic reduction (SNCR) with NH3 is limited to industrial boilers in consequence of the relatively narrow temperature range for the reaction. Selective catalytic reduction (SCR) by ammonia has high efficiency and it can be used for many stationary sources, especially for nitric acid plants [1], and it is based on the catalytic pairing of nitrogen atoms, one fi-om nitric oxide, one fi om ammonia. This method, however, is imsuitable for small sources and vehicles. As far as automotive emission is concerned nonselective catalytic reduction (NSCR) by hydrocarbons, CO and H2 from the exhaust stream has been reported over various catalysts recently [1,3,4]. 

Metals and ceramics come into contact with molten salts, either by design or by accident, in many high-temperature industrial processes, as in oil-fired boilers used for generating electricity, for example. The mechanisms of corrosion at elevated temperatures have received far less attention than those pertaining to aqueous solutions. The important differences between corrosion by molten salts and by aqueous media therefore need to be considered, together with the special features which distinguish the former phenomena. ... 

Most boilers operate at 800 to 900°C, but few experimental investigations have been carried out at elevated temperatures. Industrial CFB combustion systems have risers that are usually rectangular in cross section, manufactured from membrane water walls. Surfaces may be rough, especially where refractory is present. The lower section is commonly tapered or constricted. In addition to primary gas from the base, secondary gas may be injected through nozzles at higher levels. Given these factors, data obtained in laboratory CFBs are not always representative of industrial-scale CFB reactors. 

The reaction rate of hydrazine with oxygen increases rapidly with temperature to the extent that oxygen can be substantially removed at 200 °C (400 °F) with reasonable values of reaction time and N2H4 concentration. At feed-water temperatures normally encountered in most industrial boiler systems, 105 to 115 °C (220 to 235 °F), the reaction rate of hydrazine is considerably slower than the sulfite-dissolved oxygen reaction rate. 

Methanol, a clean burning fuel relative to conventional industrial fuels other than natural gas, can be used advantageously in stationary turbines and boilers because of its low flame luminosity and combustion temperature. Low NO emissions and virtually no sulfur or particulate emissions have been observed (83). Methanol is also considered for dual fuel (methanol plus oil or natural gas) combustion power boilers (84) as well as to fuel gas turbines in combined methanol / electric power production plants using coal gasification (85) (see Power generation). 

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