US3056248A

US3056248A - Separating apparatus

Info

Publication number: US3056248A
Application number: US40076A
Authority: US
Inventors: Schmalfeld Paul
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1959-07-22
Filing date: 1960-06-30
Publication date: 1962-10-02
Anticipated expiration: 1979-10-02

Description

Oct- 2, 1962 P. SCHMALFELD SEPARATING APPARATUS Filed June 30, 1960 nite 3,056,248 Patented Oct. 2, 1962 fifice Frankfurt am Main, Germany Filed June 30, 1960, Ser. No. 40,076 Claims priority, application Germany July 22, 1959 2 Claims. (Cl. 55-435) This invention relates to a separating apparatus and, in particular, is directed to the separation and sorting of grains of solid material pneumatically conveyed by a gas.

In furnaces or reactors for the treatment of materials, especially in endothermic reactions, heat carriers composed of fine grains or granules are frequently used for the transfer of heat to the material being treated in the process, with such heat carriers being recycled in the process. As the partially heat-relieved heat carriers are removed from the reactor, they are advantageously pneumatically conveyed by hot gases through a vertical feed pipe wherein the heat carriers are re-heated by the hot gases in preparation for their return to the reactor.

Difiiculties are encountered in separating the grains of the heat carriers from the current of conveying gas. When a cyclone is used, the flow of gases must be turned from the vertical feed pipe into a horizontal pipe and the flow must then follow the coiled path of the cyclone. It has been found that the pipe bend from the vertical to the horizontal and the cyclone coil are subject to heavy Wear and that the grains of the heat carriers are rubbed and abraded against the pipe and the cyclone walls so as to be reduced to unusable fines and dust. Furthermore, the separating effect of a cyclone upon a dense stream of heat carriers is very great, and the mass of the heat carriers holds the finer grains and dust and removes the latter from the gas so that the unusable fines are not sorted out of the usable coarser grains and are recycled to the reactor. The use of a cyclone for separating heat carriers vertically lifted by a stream of gas has not been satisfactory.

Separation elforts have been tried by directing the flow of gas and entrained heat carriers emitted from the top of a vertical pipe into a widened space and against a bafile plate to disperse the gas flow and separate the heat car riers from the gas. This process also resulted in a considerable wear on the bafiie plate and disintegration of the heat carrier grains. Substantially similar results are obtained when the flow from the vertical feed pipe is discharged into a wide space in which the hot heat carrier grains fall down at a reduced velocity and in which the gases substantially freed from the coarser and heavier heat carrier grains then pass through one or more cyclones from which the heat carrier grains are recycled to the reactor.

It has also been tried to bend the outlet end of the vertical feed pipe at an angle of 90 or even up to near 180 causing a radial discharge of the gas and entrained heat carriers into a widened space in which the heat carrier grains drop and the gases flow upwardly at a low velocity. Again, considerable wear on the pipe bend and high grinding of the heat carrier grains occurs.

The object of this invention is to produce an apparatus in which the heat carrier grains are separated from the conveying gas without wear on the apparatus and without grinding of the heat carrier grains. Another object of the invention is to produce an apparatus in which, at the same time, the unusable fine particles and dust are sorted from the coarser heat carrier grains which are to be recycled to a reactor.

The means by which these and other objects of the invention are obtained are described more fully with reference to the accompanying drawings, in which:

FIGURE 1 is a vertical cross-sectional view through the separating apparatus of this invention; and

FIGURE 2 is a cross-sectional view taken on the line II-II of FIGURE 1.

The highly heated fine-grained heat carriers are entrained by and carried upwardly through vertical pipe 1 by hot gases. The upper end of pipe 1 discharges into a housing having a separating chamber 2 of considerably greater cross-sectional area than the cross-sectional area of pipe 1 so that the gas stream loses velocity and, by reason of the vertical, fiat surfaced partition 3, is reversed to a downwardly directed flow and then again reversed as it flows beneath the lower edge of partition 3 into an upward flow through exhaust chamber 4. Separating chamber 2 has a cross-sectional area of at least ten times, and preferably twenty times, that of the cross-sectional area of feed pipe 1. As the velocity of the gas drops in chamber 2, the entrained heat carriers also lose their upward velocity and the coarser and heavier heat carrier grains first separate out and drop downwardly into collecting chamber 5 from which they are removed through discharge pipe 6. The medium-sized heat carrier grains in chamber 2 are lifted a little higher before falling, and then the very fine heat carrier grains flow to a greater extent in dependence upon the velocity and movement of the current of gas. If, at a gas velocity of 15 to 20 meters per second in pipe 1 and a heat carrier grain size of from 0.1 to 1.4 mm., the distance between the outlet end of pipe 1 and the ceiling of chamber 2 is at least 5 meters and preferably 7 meters, only a few very fine grains will reach the ceiling, and therefore the abrasion of the ceiling and the grinding of the heat carrier grains is exceedingly slight. The partially slowed gas flowing downwardly from chamber 2 beneath the lower edge of partition 3 flows upwardly through exhaust chamber 4 and outwardly through exhaust pipe 7 located in the upper portion of the wall of chamber 4 or in the roof of the housing. By twice reversing the direction of gas flow, at least the heavier heat carrier grains fall out of the gas current and drop into collecting chamber 5 positioned beneath partition 3 and extending over a portion of both

chambers

2 and 4. The separated heat carriers having a temperature of from about 700 to 1000 C. are recycled through pipe 6 into the reactor or furnace being used. In view of the very high temperatures which exist in the entire apparatus, it is preferably lined with a highly refractory material. Even though the apparatus is structurally simple, it enables a substantially perfect separation of the heat carrier grains from the gas while preventing the disintegration of the grains and wear on the refractory lining.

The undersized very fine heat carrier grains can be sorted from the heat carriers entrained in the gas stream by giving exhaust chamber 4 a predetermined size which is dependent upon the position of partition 3. If feed pipe 1 has a length of about 25 meters, gas velocities from about 15 to 20 meters per second are required for entraining and carrying heat carrier grains of a particular grain size through pipe 1. The gas current, after being slowed and reversed in chamber 2, again rises in exhaust chamber 4 at a velocity depending upon the cross-sectional area of the exhaust chamber.

The gas current in chamber 4 will entrain and carry only the very fine grains which have a suspension speed less than that of the gas velocity which will be suspended in a gas flow having a less velocity than that in chamber 4. If it is desired to remove from the recycled heat carriers all very fine grains having a size less than, for example, 0.25 mm. in diameter, and if grains of 0.25 mm. diameter have at the temperature, pressure and composition of the conveying gas a suspension velocity of 1.8

meters per second, the ascending gas current in chamber 4 must have a velocity of about 1.9 meters per second in order to entrain and pneumatically convey grains less than 0.25 mm. oil with the gas and through pipe 7.

The separation of the undersized grains from the heat carriers to be recycled is important in order that the gases and vapors formed in the thermal process being conducted in the reactor do not, by their velocity, entrain undersized grains in the reactor and carry them into a following apparatus wherein the undersized fines and dust can cause deposits and operating trouble. The recycling of undersized grains to the reactor can be largely prevented by keeping the gas velocity in chamber 4 greater than the gas velocity of the upper part of the reactor. The undersized grains and dust carried out through pipe 7 are then separated from the gas in the cyclone or other types of precipitators preferably before the gases are passed to a heat exchanger. In the reactor, the gas velocity is frequently predetermined by the conditions necessary for the thermal reaction of the material being treated, and therefore the gas velocity in exhaust chamber 4 must be in accordance therewith. However, the gas velocity of the conveying gas in feed pipe 11 is more or less fixed in advance and so the upward gas velocity in chamber 4 is governed by the cross-sectional area of this chamber or by the position of partition 3.

It is not always possible to fix in advance the gas velocity which will be used in the reactor because the most effective gas velocities become known only when performing the process. Consequently, the size for exhaust chamber 4 in the separating apparatus cannot be known in advance. Therefore, the partition 3 can be removably mounted within the housing so that the size of chamber 4 can be increased or decreased in order to control the velocity of the gases rising upwardly therethrough.

This is also of importance in that it is advantageous in certain thermal reaction processes for the gases and vapors leaving the reactor to carry off some very fine grains and dust. In such case, the gas velocity in chamber 4 is made equal to or less than the velocity of the gases and vapors in the upper part of the reactor. A diiference in velocity of 0.2 to 0.5 meter per second is generally sufiicient. By properly positioning partition 3 to divide the housing into separating chamber 2 and the smaller exhaust chamber 4, the undersized heat carrier grains and the very finely ground grains and dust can be sorted out of the heat carriers at the same time as the heat carriers of acceptable size are separated from the conveying gas for recycling the highly heated heat carriers to the reactor. This apparatus has been very successfully employed in the thermal cracking of hydrocarbons in the production of olefins with sand grains being used as the heat carriers.

Having now described the means by which the objects of the invention are obtained, I claim:

1. An apparatus for separating and sorting pneumatically conveyed highly heated and fine grain heat carriers comprising a pneumatic feed pipe, a housing lined with refractory material and communicating with an end of said feed pipe, and a flat partition extending downwardly to at least the level of the upper edge of said feed pipe and vertically dividing said housing into a grain separating chamber above said feed pipe and having a larger crosssectional area than said feed pipe for reducing the velocity of gas entering said housing from said feed pipe, and an exhaust gas chamber for first allowing the reversing of the direction of fiow of gas coming from said feed pipe in the separating chamber and then again reversing the direction of gas flow as it passes from the separating chamber into the exhaust chamber, said separating chamber and exhaust chamber having the same height, said separating chamber having a cross-sectional area ranging from about ten to twenty times greater than the cross-sectional area of said feed pipe, and said exhaust chamber having a crosssectional area such that the gas velocity therein entrains only undersized heat carrier grains.

2. An apparatus as in claim 1, said separating chamber having a ceiling spaced from the outlet end of said feed pipe a distance ranging from about 5 to 7 meters so that Substantially no fine heat carrier grains reach said ceiling.

References Cited in the file of this patent UNITED STATES PATENTS 1,185,274 Baker May 30, 1916 1,922,013 Brady Aug. 8, 1933 2,666,731 Bergstrom Jan, 19, 1954 2,954,843 Brzeski Oct. 4, 1960 FOREIGN PATENTS 198,602 Great Britain June 7, 1923 816,550 Great Britain July 15, 1959 A22,76l Germany Aug. 16, 1956