Off-gas temperature

A process has been developed to recover antimony and arsenic from speiss and other materials (11). The speiss is roasted along with a source of sohd sulfur and coal or coke at a temperature of 482—704 °C for a sufficient time to volatilise arsenic and antimony oxides. The arsenic can then be separated from the antimony through careful control of the off-gas temperature and oxygen potential (12). 

Semiwet. Water is added for conditioning furnace off-gas temperature and humidity prior to processing the gas in electrostatic precipitators or baghouses. 

Off-gas temperature, with detrimental effects on the refractories and gas handling systems (Fruehan et al., 1989)... 

How to maintain a fixed bed depth to insure a more uniform off -gas temperature thus allowing proper condenser operation ... 

The convertor stands 2.35 meters tall, has a base diameter of 0.84 meters and a top diameter of 0.70 meters. It is built of mild steel, typically two to three millimeters thick. Instrumentation includes a process air orifice, and dial thermometers for measuring bed, convertor off-gas and condenser off-gas temperature. 

Perhaps the two most important indices of system performance are the convertor and the condenser off-gas temperatures. If pro -per control of these two is maintained and correct interpretation of variations in these temperatures is made, the system operation can be relatively routine. To illustrate the average convertor off-gas temperature is not only important so far as oil production is concerned, but rapid increases in it may indicate the formation of cavities in the bed, while decreases may suggest that char is being removed too rapidly. Likewise the condenser off-gas temperature must be maintained above the dewpoint of the mixture to avoid water condensation, but not so high as to reduce the oil yields. 

FIGURE 5.2 Optimum firing time is determined by plotting off-gas temperature vs. time for several heats. 

Oxy/fuel burners are most efficient during cold scrap heating and meltdown. Typically, burner effectiveness decreases during the latter half of the meltdown period from an initial 60 to 80% to less than 20%, when firing on a flat molten bath. Excessive use of burners with low efficiency can result in yield loss and potential furnace damage due to higher off-gas temperatures. 

Disadvantages Reduced flame temperature Increased off-gas temperature... 

High Ambient and Off-Gas Temperatures Water cooling was employed for the launch and receiver modules, the pathlength control probes, and the break flange. A total of six thermocouples were used during the first several months of operation to monitor the thermal conditions of the optics modules and probes. Thermocouple data was recorded on a separate data logger located near the measurement location. Each module had an internal thermocouple, a thermocouple to measure enclosure water outlet temperature, and a thermocouple to monitor the water outlet temperature of each probe. 

We have already discussed under practical stoichiometry how the air requirements can be estimated based on the fuel composition (ultimate analysis). The primary and secondary air requirements for combustion of pulverized coal or coke are best estimated by mass and heat balance at the mill. In Appendix 6A we show a calculation taken from Musto (1997) for the primary and secondary air required for coal pulverizer with 4.5 metric ton per hour (10,0(X)lb/hr) coal feed rate at initial moisture of 15 percent which is required to be ground and dried to 2 percent with a 200 HP mill. In order to estimate the actual primary and secondary air, one has to make some estimation of the evaporation rate, the amount of gas entering the coal mill, and the bleed air required so that the quantity of air that should be vented from the hood off-take can be properly estimated. It shows that for a take-off gas temperature of 315°C (600° F) and vent gas temperature of 76°C (170°F) and allowing ambient air infiltration of 10 percent at 15°C (60°F) the primary air will be about 22 percent of stoichiometric air and 21 percent of total air. The remaining air (about 79 percent) will be the secondary air. With this information we can size a burner using a burner pipe diameter based on a Craya-Curtet parameter of choice bearing in mind the conditions that ensure the desired jet recirculation patterns described in Chapter 3. 

C or at least 20°C above the dewpoint, whichever is greater, in order to avoid moisture condensation within the filter. An auxiliary heater may be used to increase the off-gas temperature however, the maximum allowable filter temperature specified by the manufacturer for permanent operation must be taken into consideration if an auxiliary heater is used. 

The dry off-gas treatment systems are simpler and more economical to operate. These systems may preferably be used if there are no specific reasons for the incorporation of wet scrubbers. The dry systems keep the off-gas temperature well above the dewpoint so that corrosion by acid gas condensation can be minimized. A dry system may be selected when processing tritiated wastes (subject to regulatory conditions and to tritium concentrations) since it will release tritium, together with the dry-filtered off-gas, into the envirotunent. This practice may present a lesser radiological hazard when compared with the aqueous scrubbing of tritium and the consequent need for the handling and conditioning of the tritiated scrub solutions. 

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