Steam Heated Calandrias

There are several alternatives for the solution of this problem. The best of those should be selected for any given application. No solution is best for all cases. These alternatives include  

This permits pressure controi of the steam the condensate tank wouid provide for adequate iiquid ievel control without requiring 

A similar problem sometimes occurs when heating with high pressure steam. In these cases there is not enough pressure differential between the steam supply header and the condensate return header to allow the steam condensate pressure to be properly controlled. This problem usually occurs when the process boiling temperature is lower than the saturated steam temperature at a pressure equal to that of the condensate return header. 

---

Steam-heated calandrias with process boiling temperature less than 100°C can present control problems, especially at reduced rates and during start-up. In most such cases, low-pressure steam is used for heating. Control is usually achieved by throttling the entering steam in order to reduce the pressure at which it is condensed. At reduced rates this often results in steam pressures less than atmospheric or less than the steam condensate return system pressure. The steam is usually removed through steam traps which require a positive pressure differential to fiinction. In order for the trap to function, steam condensate floods part of the steam chamber imtil the steam pressure is sufficient to operate the trap. This leads to poor control and all the problems associated with condensate flooding. 

A steam-heated natural-circulation calandria is to be designed to boil 5000 kg/h of chlorobenzene at atmospheric pressure, (a) Approximately how much heat-transfer surface will be required (h) How much area would be required if the average pressure in the calandria were 0.5 atm abs The normal boiling point of chlorobenzene is 132.0 C its critical temperature is 359,2°C. 

Most evaporation units are steam heated and a typical evaporator body used in evaporative crystallization is the short-tube vertical type in which steam condenses on the outside of the tubes Figure 8.41). A steam chest, or calandria, with a large central downcomer allows the magma to circulate through the tubes during operation the tops of the tubes are just covered with liquor. To increase the rate of heat transfer, especially in dealing with viscous liquors, a forced circulation of liquor may be effected by installing an impeller in the downcomer. 

Distilled water is produced from sea water by evaporation in a single-effect evaporator working on the vapour compression system. The vapour produced is compressed by a mechanical compressor of 50 per cent efficiency, and then returned to the calandria of the evaporator. Extra steam, dry and saturated at 650 kN/m2, is bled into the steam space through a throttling valve. The distilled water is withdrawn as condensate from the steam space. 50 per cent of the sea water is evaporated in the plant. The energy supplied in addition to that necessary to compress the vapour may be assumed to appear as superheat in the vapour. Calculate the quantity of extra steam required in kg/s. The production rate of distillate is 0.125 kg/s, the pressure in the vapour space is 101.3 kN/m2, the temperature difference from steam to liquor is 8 deg K, the boiling-point rise of sea water is 1.1 deg K and the specific heat capacity of sea water is 4.18 kJ/kgK. 

Considering the case where 0.25 kg/s is bled from the steam line to the calandria of the second effect, a heat balance across the first effect gives ... 

A single-effect evaporator is used to concentrate 0.075 kg/s of a 10 per cent caustic soda liquor to 30 per cent. The unit employs forced circulation in which the liquor is pumped through the vertical tubes of the calandria which are 32 mmo.d. by 28 mmi.d. and 1.2 m long. Steam is supplied at 394 K, dry and saturated, and the boiling-point rise of the 30 per cent solution is 15 degK. If the overall heat transfer coefficient is 1.75 kW/m2 K, how many tubes should be used, and what material of construction would be specified for the evaporator The latent heat of vaporisation under these conditions is 2270 kJ/kg. 

A triple-effect evaporator is fed with 5 kg/s of a liquor containing 15 per cent solids. The concentration in the last effect, which operates at 13.5 kN/m2, is 60 per cent solids. If the overall heat transfer coefficients in the three effects are 2.5, 2.0, and 1.1 kW/m2K, respectively, and the steam is fed at 388 K to the first effect, determine the temperature distribution and the area of heating surface required in each effect The calandrias are identical. What is the economy and what is the heat load on the condenser ... 

A salt solution at 293 K is fed at the rate of 6.3 kg/s to a forward-feed triple-effect evaporator and is concentrated from 2 per cent to 10 per cent of solids. Saturated steam at 170 kN/m2 is introduced into the calandria of the first effect and a pressure of 34 kN/m2 is maintained in the last effect. If the heat transfer coefficients in the three effects are 1.7, 1.4 and 1.1 kW/m2K respectively and the specific heat capacity of the liquid is approximately 4 kJ/kgK, what area is required if each effect is identical Condensate may be assumed to leave at the vapour temperature at each stage, and the effects of boiling point rise may be neglected. The latent heat of vaporisation may be taken as constant throughout. 

If an evaporator, fed with steam at 399 K with a total heat of 2714 kJ/kg, is evaporating water at 373 K, then each kilogram of water vapour produced will have a total heat content of 2675 kJ. If this heat is allowed to go to waste, by condensing it in a tubular condenser or by direct contact in a jet condenser for example, such a system makes very poor use of steam. The vapour produced is, however, suitable for passing to the calandria of a similar unit, provided the boiling temperature in the second unit is reduced so that an adequate temperature difference is maintained. This, as discussed in Section 14.2.4, can be effected by applying a vacuum to the second effect in order to reduce the boiling point of the liquor. This is the principle reached in the multiple effect systems which were introduced by Rillieux in about 1830. 

An evaporator, working at atmospheric pressure, is to concentrate a solution from 5 per cent to 20 per cent solids at the rate of 1.25 kg/s. The solution, which has a specific heat capacity of 4.18 kJ/kg K, is fed to the evaporator at 295 K and boils at 380 K. Dry saturated steam at 240 kN/m2 is fed to the calandria, and the condensate leaves at the temperature of the condensing stream. If the heat transfer coefficient is 2.3 kW/m2 K, what is the required area of heat transfer surface and how much steam is required The latent heat of vaporisation of the solution may be taken as being equal to that of water. 

Fractionation columns in tar-acid refineries are generally operated under vacuum and heated by high pressure steam or circulating hot oil. Calandria in the reboilers, condensers, rundown lines, and receiving tanks are constructed of stainless steel, or, in the case of the condensers, of tin or nickel. 

Steam is introduced at the base of the whiskey column through a sparger. Where economy is an important factor, as in a fuel alcohol plant, a calandria is employed as the source of indirect heat. The diameter of the still, number of perforated and bubble cap plates, capacity of the doubler, and proof of distillation are the critical factors that largely determine the characteristics of a whiskey. 

Saturated steam is available at 50 psig. Neglect any sensible heat transfer from steam condensate to boiling liquid. The temperature-difference driving force At in the calandria may be assumed to be 90°F. 

A vapor-recompression evaporator is to concentrate a very dilute aqueous solution. The feed rate is to be 30,000 Ib/h the evaporation rate will be 20,000 Ib/h. The evaporator will operate at atmospheric pressure, with the vapor mechanically compressed as shown in Fig. 16.12 except that a natural-circulation calandria will be used. If steam costs 8 per 1000 lb, electricity costs 3 cents per kilowatthour, and heat-transfer surface in the heater costs 70 per square foot, calculate the optimum pressure to which the vapor should be compressed. The overall compressor efficiency is 72 percent. Assume all other costs are independent of the pressure of the compressed vapor. To how many effects will this evaporator be equivalent ... 

Used solvent is liable to foul heat exchanger surfaces and so will almost always be on the tube side of a shell and tube heat exchanger with steam on the shell side. While it is possible to use a natural circulation external calandria if the solvent to be evaporated is clean, forced circulation is more reliable if the solvent contains residue (Fig. 4.1) despite the fact that it may be a diliicult duty as regards both cavitation and seal maintenance. 

In an inclined tube evaporator the tubes are inclined, usually 30 to 45 degrees from horizontal. (See Figure 11-9.) In early designs the inclined calandria was mounted directly to the bottom head of a vapor body and the downcomer recirculating the product from the separator back to the bottom of the calandria was incorporated within the steam chest. Circulation in this configuration was sometimes impaired because of heat transfer across the downcomer. A first Improvement was to insulate the downcomer. Circulation was further improved by providing a downcomer external to the evaporator. 

Both pumping traps and liquid movers use steam as a motive force to pump condensate to the desired location. The steam must be vented between each cycle. For vacuum operation, a vacuum vent is required and usually represents an energy inefficiency unless the vent can be condensed in the process to recover the heat. The steam can be vented back to the calandria steam chest and condensed directly against the process, however, this may represent an operational Instability unless properly designed. The vent rate must be controlled at a rate which does not create problems in the calandria or evaporation system. The receiver must be adequately sized to permit stable operation. Generally, it is better to vent to a separate condensing location. 

Decay Heat Removal Steam Generator cooling/shutdown cooling/ECCS Cooling by fire water through steam generator/cold moderator, calandria vault water... 

The CANDU 300 utilizes the standard CANDU lattice design and fuel channel arrangement, with 208 fuel channels. The fuel channels are contained within an atmospheric pressure tank (known as the calandria), which is filled with low-temperature heavy-water moderator. Each channel contains 12 standard CANDU 37 element natural uranium fuel bundles. The heat transport system is a pressurized high temperature system which circulates heavy water through the fuel channels and transports the heat of fission from the fuel to the steam generators, to produce steam. 

---