Batch furnaces types

Batch Furnaces, Other Furnace Types, and Kilns. 12-45... 

Batch Furnaces This type of furnace is employed mainly for the heat treatment of metals and for the drying and calcination or ceramic articles. In the chemical process industry, batch furnaces may be used for the same purposes as batch-tray and truck dryers when the drying or process temperature exceeds 600 K (620°F). They are employed also for small-batch calcinations, thermal decompositions, and other chemical reactions which, on a larger scale, are performed in rotary Idlns, hearth furnaces, and shaft furnaces. 

Batch Furnaces This type of furnace is employed mainly for the... 

This furnace type is only used for non-ferrous metal melting. Due to the indirect heating (through the crucible wall) no bum-off or gas take-up can take place. These furnaces are used for the production of small amounts of molten metal (less than 500 kg per batch) and for low production capacities. Example furnaces are displayed in Figure 2.20. 

The relative rates of heat conduction and temperature leveling when burners are intermittently off, as in batch furnaces, can change the justification for added insulation. This depends on the thicknesses of heavy refractory and insulation, on the types of each, and on the continuity of furnace operation. The way in which the %heat saving changes with three of these variables can be seen in table 5.4, an extension of table 5.3, which was for steady operation only. Both tables refer to wall losses only and not to the total heat consumption of the furnace. One-week cycle means continuous operation for 6 days, 24 hr per day. For 5-day, 24 hr per day operation, the savings would be reduced by about 10%. One-day cycle means 8 to 10 hr per day. The tabular values must be reduced somewhat if the wall is thick relative to the interior dimensions of the furnace. The tabular values apply only to those furnaces entirely covered with insulation. 

With the previous type control system and burners, the temperature control above the loads can be excellent, provided sufficient zones are installed. For batch furnaces, the minimum number of zones should be three—one for each end wall and one for the main body of the furnace. If there are two side-by-side doors, five zones are desirable—one for each side wall, two for furnace body, and one behind the center doorjambs. 

If the contaminant sorbates are relatively, i.e., with boiling points less than 200°C, quite effective regeneration can be achieved using steam. This process can be carried out either in situ, using the fixed bed column system, or by removing the spent adsorbent (for example, after batch adsorber filtration) to a furnace-type regeneration system. The contaminant-laden steam can then be condensed at a suitable temperature to condense and recover the volatiles from the chemical spill. Further separation can be appUed if necessary, such as distillation. 

Batching, melting and fining operations are common to all glass manufacturing processes with some variations according to the furnace type. The forming and post-process depend on the end product. 

The most widely used and best known resistance furnaces are iadirect-heat resistance furnaces or electric resistor furnaces. They are categorized by a combination of four factors batch or continuous protective atmosphere or air atmosphere method of heat transfer and operating temperature. The primary method of heat transfer ia an electric furnace is usually a function of the operating temperature range. The three methods of heat transfer are radiation, convection, and conduction. Radiation and convection apply to all of the furnaces described. Conductive heat transfer is limited to special types of furnaces. 

These furnaces may operate batchwise or continuous. In the batch, intermittent, or periodic types, the content is heated at the desired temperature for the stipulated time and then removed. In the continuous type, the charge moves at a predeterrnined rate through one or more heating 2ones to emerge in most cases at the end opposite the point of entry. Figures 9 and 10 are representative examples of typical, industrial refractory-wall furnaces. 

Control Devices. Control devices have advanced from manual control to sophisticated computet-assisted operation. Radiation pyrometers in conjunction with thermocouples monitor furnace temperatures at several locations (see Temperature measurement). Batch tilting is usually automatically controlled. Combustion air and fuel are metered and controlled for optimum efficiency. For regeneration-type units, furnace reversal also operates on a timed program. Data acquisition and digital display of operating parameters are part of a supervisory control system. The grouping of display information at the control center is typical of modem furnaces. 

The carbon slurry has to be received and dewatered before feeding it to the furnace. There are two basic carbon column operating systems the batch and the intermittent or slug type. Depending on which system is used, the receiving, dewatering, and feed operations are performed differently. 

Batch-type production processes, particularly those with small batch sizes, have less energy efficiency as compared to continuous processes. A typical example of a batch operation on a relatively small scale is the production of titanium in 1-ton batches of the metal. The energy efficiency of the process is much less than that of continuous methods such as iron being produced in a blast furnace, or even of large-scale batch methods such as basic oxygen steel-making. The heat losses per unit of production are much less in continuous and large-batch processes, and this also enables the waste heat from process streams to be used. 

They used a vertical cylindrical pot furnace of batch type, like Rogers. Two conversion concepts were simulated (a) overfired, updraft, fixed horizontal grate, and batch reactor and (b) underfired, updraft, fixed horizontal grate, and batch reactor. The diameter was 178 mm and primary air was supplied under the grate (Figure 7). A mirror was placed above the overbed section to be able to observe the combustion behaviour. 

The objectives of Aho s study [8] were to investigate the effects of peat type, particle density, diameter and moisture content, and oxygen concentration on the flue gas emissions of nitrogen oxides and sulphur dioxide from a homogenous countercurrent batch bed combustion using a pot furnace. His aim was to simulate the interaction of chemistry between the fuel bed system and the combustion chamber of a overfired batch bed. However, he also presented some results on the combustion heat rate. 

The nonfertilizer calcium phosphates are manufactured by the neutralization of phosphoric acid with lime. The processes for different calcium phosphates differ substantially in the amount and type of lime and amount of process water used. Relatively pure, food-grade monocalcium phosphate (MCP), dicalcium phosphate (DCP), and tricalcium phosphate (TCP) are manufactured in a stirred batch reactor from furnace-grade acid and lime slurry, as shown in the process flow diagram of Figure 3. Dicalcium phosphate is also manufacmred for livestock feed supplement use, with much lower specifications on product purity. 

---