Liquid heaters

Viscous-liquid heaters lower the viscosity of very heavy oils to pumpable levels. 

Condensing vapor to liquid 50-200 [283.9-1136] 150-800 [851.7-1542.4] Steam to water Liquid heaters and condensers... 

Alternatives to straight-line horizontal continuous furnaces are rotary hearth (disc or donut) furnaces (fig. 1.8 and secs. 4.6 and 6.4), inclined rotary drum furnaces (fig. 1.10), tower furnaces, shaft furnaces (fig. 1.11), and fluidized bed furnaces (fig. 1.12), and liquid heaters and boilers (sec. 4.7.1 and 4.7.2). 

Liquid heaters. See Liquid Baths and Heaters, sec. 4.7.1, and Boilers and Liquid Flow Heaters, sec. 4.7.2. 

Continuous liquid flow furnaces include boiler furnaces, fluid heaters (such as Dow-therm heaters), evaporators, cookers, and many liquid heaters used in the chemical process industries. (See figs. 1.12 and 4.25.) The tubing through which the liquid fluids flow is often built as an integral part of the furnace, for which many textbooks are readily available therefore, they will not be discussed at length here. 

This alloy also resists intergranular corrosion and is approved for use in contact with foods. Applications include heat exchanger tubing, overhead condensers, reboilers, and feed heaters (petroleum refining), pulp and paper liquid heaters, organic acid heaters and condensers, and nitric acid cooler condensers. 

Figure 10.6 shows a liquid heater with an electrical heating element. The outflow depends on the hquid level in the vessel as described in the previous example. 

Either mechanical or electronic methods can be used to terminate the charge at the desired temperature. A mechanical snap-action or bimetallic thermostat such as those used commercially in gas heaters, liquid heaters, percolators, fire alarm detectors, clothes dryers and the like has been used to terminate charge. 

All calorimeters consist of the calorimeter proper and its surround. This surround, which may be a jacket or a batii, is used to control tlie temperature of the calorimeter and the rate of heat leak to the environment. For temperatures not too far removed from room temperature, the jacket or bath usually contains a stirred liquid at a controlled temperature. For measurements at extreme temperatures, the jacket usually consists of a metal block containing a heater to control the temperature. With non-isothemial calorimeters (calorimeters where the temperature either increases or decreases as the reaction proceeds), if the jacket is kept at a constant temperature there will be some heat leak to the jacket when the temperature of the calorimeter changes. 

Figure Bl.27.8. Schematic view of Picker s flow microcalorimeter. A, reference liquid B, liquid under study P, constant flow circulating pump and 2, Zener diodes acting as heaters T and T2, thennistors acting as temperature sensing devices F, feedback control N, null detector R, recorder Q, themiostat. In the above A is the reference liquid and C2is the reference cell. When B circulates in cell C this cell is the working cell. (Reproduced by pemiission from Picker P, Leduc P-A, Philip P R and Desnoyers J E 1971 J. Chem. Thermo. B41.)...

A typical arrangement for producing a particle beam from a stream of liquid, showing (1) the nebulizer, (2) the desolvation chamber, (3) the wall heater, (4) the exit nozzle, (5, 6) skimmers 1, 2, (7) the end of the ion source, (8) the ion source, and (9) the mass analyzer. An optional GC inlet into the ion source is shown. 

This ammonia is recycled to the reactor via a compressor and a heater. Liquid ammonia is used as reflux on the top of the absorber. The net amount of carbon dioxide formed in the reactor is removed as bottom product from the absorber in the form of a weak ammonium carbamate solution, which is concentrated in a desorber-washing column system. The bottom product of this washing column is a concentrated ammonium carbamate solution which is reprocessed in a urea plant. The top product, pure ammonia, is Hquefted and used as reflux together with Hquid makeup ammonia. The desorber bottom product, practically pure water, is used in the quench system in addition to the recycled mother Hquor. 

On/Off Control An on/off controller is used for manipulated variables having only two states. They commonly control temperatures in homes, electric water-heaters and refrigerators, and pressure and liquid level in pumped storage systems. On7off control is satisfac-toiy where slow cychng is acceptable because it always leads to cycling when the load hes between the two states of the manipulated variable. The cycle will be positioned symmetrically about the set point only if the normal value of the load is equidistant between the two states of the manipulated variable. The period of the symmetrical cycle will be approximately 40, where 0 is the deadtime in the loop. If the load is not centered between the states of the manipulated variable, the period will tend to increase, and the cycle follows a sawtooth pattern. 

Heater Imparts sensible heat to a liquid or a gas by means of condensing steam or Dowtherm. 

Vaporizer A heater which vaporizes part of the liquid. 

Applications Most PHE applications are liquid-liquid seiwices but there are numerous steam heater and evaporator uses from their heritage in the food industry. Industrial users typically have chevron style channel plates while some food apphcations are washboard style. 

In a submerged-tube FC evaporator, all heat is imparted as sensible heat, resulting in a temperature rise of the circulating hquor that reduces the overall temperature difference available for heat transfer. Temperature rise, tube proportions, tube velocity, and head requirements on the circulating pump all influence the selec tion of circulation rate. Head requirements are frequently difficult to estimate since they consist not only of the usual friction, entrance and contraction, and elevation losses when the return to the flash chamber is above the liquid level but also of increased friction losses due to flashing in the return line and vortex losses in the flash chamber. Circulation is sometimes limited by vapor in the pump suction hne. This may be drawn in as a result of inadequate vapor-liquid separation or may come from vortices near the pump suction connection to the body or may be formed in the line itself by short circuiting from heater outlet to pump inlet of liquor that has not flashed completely to equilibrium at the pressure in the vapor head. 

FIG. 22-80 Simplified flow schematic for a pervaporation system. Heated feed enters from left through a feed pump. Heaters in a recirculating feed loop may he required (not shown). Stripped liquid exits at the top of the pervaporation membrane. Vapor exits at the bottom to a condenser. Liquid and noncondensibles are removed under vac-imm. Cowiesif Hoechst Celanese. )... 

Fractionator-feed preheaters partially vaporize charge stock from an upstream unfired preheater en route to a fractionating column. A typical refinery application a crude feed to an atmospheric column enters the fired heater as a liquid at 505 K (450°F) and leaves at 644 K (700°F), having become 60 percent vaporized. 

Heat-transfer-fluid heaters maintain the temperature of a circulating liquid heating medium (e.g., a paraffinic hydrocarbon mixture, a Dowtherm, or a molten salt) at a level that may exceed 673 K (750°F). 

Storage of heat is a temporary operation since perfect thermal insulators are unknown thus, heat is absorbed in solids or liquids as sensible or latent heat to be released later at designated times and conditions. The collection and release of heat can be achieved in two modes on a batch basis, as in the checkerbrick regenerator for blast furnaces, or on a continuous basis, as in the Ljungstrom air heater. 

Figure 4.6 is interesting because it shows that for the best refining performance we need both a long zone and an impurity that is relatively insoluble in the solid (low k). Unfortunately long liquid zones can be destabilised by convection, and impurities with a low k do not come to order Commercial zone refining processes may therefore involve a large number of passes done one after the other (Fig. 4.7). This obviously adds a lot to the cost of the pure material, but the process can be speeded up considerably by using the multi-heater arrangement shown in Fig. 4.8.

---