Heat balance calculation furnaces

The mean specific heat of coal ash and slag, which is used for calculating heat balances on furnaces, gasifiers, and other coal-consuming systems, follows. 

Mass and energy balances are used to evaluate blast furnace performance. Many companies now use sophisticated computeri2ed data acquisition and analysis systems to automatically gather the required data for daily calculation of the mass and heat balances. Typical mass and heat balances are shown in Figure 4 and Table 5, respectively. 

Calculation of the heat balance results in the stated heat transfer efficiencies. The cold blast cupola shows an efficiency of <30 %. The application of oxygen or secondary air increases the efficiency to 37 - 40 %. The hot blast cupola shows a further increased efficiency, providing the furnace wall is refractory lined. In liningless operation, the efficiency drops below 40 %, which may be somewhat compensated for by adding oxygen. The cokeless cupola with inductive superheating results in a very high efficiency, close to 60 %. 

CALCULATIONS/MAINTENANCE/QUALITY/SPECIFYING A FURNACE TABLE 8.15 Heat balance. Refractory loss worksheet2 for sample problem 8.1... 

The calculations involve three levels of interaction. Each increment of reactor must be in heat flux and temperature balance each furnace zone must satisfy outlet temperature or overall heat flux specifications and the overall reactor must satisfy... 

Heat balance terms such as furnace stack heat loss as a fiiaction of fired fuel heating value and furnace efficiency are not calculated, mainly since these indices of performanee are not required in an optimization system that has the plant-wide operating profit as an objective function. These indices are remnants of local equipment or design optimization approaches. T5q)ically a plant s operation should not be constrained nor its performanee judged by these indices. Models can of course be easily used to ealculate these indices, and plant built to the furnace models to perform these calculations on-line. 

The calculation of the location of the freezing point in the lining is a part of the thermal balance calculation (which is a very complicated problem) and the calculation of the heat flow through the multi-layer lining (side wall or bottom). The heat flow in different parts of the furnace will differ (heat transfer from the area above the metal and from the area with metal) [34]. 

The calculations necessary to define the heat balance around the base section of the tower are shown on Figure 3,8. This illustration is self-explanatory as to the calculation of the total feed heat input and the furnace duty. 

Note the role played by the condensed overflash liquid. If this stream is returned to the system, either as overflow from the draw tray to the flash zone or as recycle from the draw tray to the furnace, it must be taken into account in the heat balance. If it leaves the system as a product stream, it will not be seen as a heat input to the flash zone. This is the reason for the cjiuestion mark in the equation for calculating the feed heat input. 

A different approach has been taken by TA Instruments, in using two horizontal balances. The balance arms, each with a thermocouple attached to a pan carrier, hold the sample and reference adjacent to each other in the furnace. Unusually, in this instrument there is no heat flow path between the sample and reference, other than through the surrounding atmosphere, which limits the quality of the DTA data. Mettler-Toledo now offer a technique in which a form of DTA is obtained by comparing the sample temperature with a calculated reference temperature profile. Modern TG-DTA instruments are capable in general of a TG resolution around 1 g, use samples typically from 5 to 100 mg, and can give sensitive and quantitative DTA performance when the head is of... 

The startup trials also demonstrated that furnace pressure can be controlled to a very precise level under all three firing conditions, namely, oxy fuel burner only, TCR syngas burner only, and TCR-oxy fuel burner mixed firing. First temperature and flow data were collected and analyzed. In addition, detailed mapping of regenerator and port neck surface and ambient temperatures were concluded. These temperature data will be used to calculate convective wall heat losses appropriately for total energy balances later. 

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