SU731912A3 - Heat-exchanger - Google Patents

Abstract

1483666 Preheating feed material ALUMINIUM PECHINEY 1 Aug 1974 [6 Aug 1973] 33923/74 Headings F4B and F4S A powder, for example alumina, is indirectly heated by gas, for example issuing from a rotary kiln 1, in a heat exchanger compartment 6, thereby generating gas which fluidizes the powder, the powder falling from an upper fluidization chamber 24 under the action of gravity in a substantially vertical tube 22, which may be disposed within the compartment 6, Fig. 2 (not shown), into a lower fluidization chamber 25 from which the powder passes upwardly under the action of the generated gas in a series of tubes 23, each of smaller diameter than the tube 22, to the upper chamber 24, the powder then partly leaving the chamber 24 and the remainder circulating within the compartment. As shown in Fig. 1 the gas from the kiln 1 passes through the compartment 6 into an electrostatic filter 13, purified gas being discharged into the atmosphere through a chimney 14. The powder is fed into the chamber 6 by means of a feeder 12, the heated powder leaving the chamber at outlet 11 to be fed into the kiln 1 for discharge at 5. The compartment 6 may house a series of stages of the pipes 22 and 23, Fig. 2 (not shown).

Description

(54) HEAT EXCHANGER

one

This invention relates to a heat exchange technique and can be used in the chemical, metallurgical and other industries of the industry.

A heat exchanger is known that contains a heated casing and at least one heat exchange section with vertical circulation pipes of a downward and upward flow of dispersed material, the latter of which are located in the housing 10, 1. Downstream pipes are also located in the housing.

A disadvantage of the known heat exchanger is low efficiency.

The purpose of the invention is to increase the econot 15 of miichnost.

This goal is achieved by the fact that the tubes of the downward flow of the dispersed material are made with a diameter greater than the diameter of the upflow tubes, and 20 have a total heat transfer surface not exceeding the total heat exchange surface of the upflow tubes.

In addition, downcomer flow tubes 25 of particulate material may be located outside the casing.

FIG. 1 is a schematic diagram of the installation, including the described heat exchanger; in fig. 2 - heat exchanger in vertical section; in fig. 3 - version of the heat exchanger.

The plant mainly for producing dry anhydrous alumina (Fig. 1) contains a rotary kiln 1 with inlet 2 of incoming air and outlet 3 of flue gases, inlet 4 and outlet 5 of dispersed material (aluminum hydroxide). In front of the furnace 1, in the course of the movement of the dispersed material, there is a heat exchanger 6 with a casing 7 having a supply pipe 8 and a discharge pipe 9 for flue gases, as well as a feed pipe 10 and a discharge pipe 11 for the material being processed. The charging nozzle 10 is connected to the feeder 12. The flue gases from the casing 7 through the nozzle 9 are discharged into the electrostatic precipitator 13 and further into the exhaust pipe 14.

The heat exchanger 6 is an apparatus (Fig. 2), in which spontaneous fluidization of the dispersed material is carried out due to the vapors or gases evolved from it during processing. It contains vertical downward circulation tubes placed in the housing 7.

15 and i bcxoAaiMero 16 dispersed material streams, which in each of the heat exchange sections are connected at the top through the mixing chamber 17 and below through the fluidization chamber 18. Chambers 17 are connected to each other in series with the help of flows 19.

The diameter of pipes 15 exceeds the diameter of pipes 16, but the total heat exchange surface of pipes 15 does not exceed the total heat exchange surface of pipes 16.

In the embodiment of the heat exchanger (Fig. 3), the pipe 15 is located outside the casing 7.

The heat exchanger works in the following way.

The wet aluminum hydroxide is fed through the nozzle 10 directly into the mixing chamber 17 of the first section, where, thanks to the vortices created by the boiling, it is intimately mixed with the already dry alumina, which is a temperature of 130-160 ° C. temperature of this section. Aluminum oxide, the outlet of the shaft through the pipe I from the heat exchanger 6, contains es, about 11% of chemically bound water at a temperature of the order of the average temperature of the outlet section. Indeed, the alumina trihydrate loses about two water molecules, and the latter molecule splits off only at about 700 ° C in rotary kiln 1.

The main resistance to heat transfer has a film of flue gases. The design in which the heat-transfer gas (flue gases), coming from the furnace 1, moves outside the pipes 15 and 16 and perpendicular to them, is most appropriate. The resulting heat transfer coefficients are in the order of 50 kcal / m-h for pipes with a diameter of 50 mm and a temperature of the heat transfer gas of 500 ° C at a gas velocity of the order of 6-8 m / s. The heat exchange surface required to produce 1000 tons of baked alumina per day is about 1500 m in the conversion of aluminum hydroxide containing 15% hygroscopic water and having a temperature of 60 ° C to alumina containing 11% chemically bound water and having a temperature of 300 ° C. Such a heat exchanger adapted to operate with a rotary kiln saves 15-20 kg of liquid fuel per ton.

baked alumina without saMeTHopj increase in power consumption compared to known heat exchangers.

An experimental installation similar to that shown in FIG. 2, but having only one section, contains a pipe 15 with a diameter of 222 mm, a length of 5 meters, i.e. with a surface area of 3.5 m and sixteen pipes 16

with a diameter of 54 mm and a length of 5 meters, i.e., with a total surface area of 13.6 m, the heat exchange surface of the pipes 16 is four times the heat exchange surface of the pipes 15. The heat exchange coefficient for

pipes with a diameter of 54 mm are 50 kcal / m -h-hail, and for pipes with a diameter of 222 mm - 25 kcal / m -h-hail.

The temperature difference between pipes 15 and 16 reaches 5–20 ° C, depending on the flow rate and recirculation. Consequently, the release of water vapor in the pipes 16 is much more intense than in the pipe 15, especially since at some temperatures the dehydration reaction is very sensitive to

temperature The corresponding speed of the downward flow in the pipe 15 reaches 1.5-3 m / min. The circulating mass is 4–8 times the mass delivered by the heat exchanger per unit time.

Claims (2)

1. A heat exchanger containing a heated jacket and at least one heat exchange section with vertical circulation pipes of a downward and upward flow of dispersed material, the latter of which are located in the housing, characterized in that, in order to increase efficiency, the downward flow of a dispersed material The material is made with a diameter greater than the diameter of the upflow pipes and have a total heat exchange surface not exceeding the total heat exchange surface of the upflow pipes. 2. Heat exchanger according to claim 1, characterized in that the downward pipes of the dispersed material are located outside the casing. Information sources, taken into account during the examination 1. USSR Copyright Certificate No. 251133, cl. F 28D 19/04, 1966. 17 ISIB 7