US3043499A - Process and apparatus for circulating hot gases, especially under high pressures - Google Patents

Description

3 Sheets-Sheet 1 KNOBLOCH ETAL PROCESS AND APPARATUS FOR CIRCULATING HOT GASES. ESPECIALLY UNDER HIGH PRESSURES IIJJII 1 July 10, 1962 Filed Aug. 4, 1958 TOE v INVEJTORS ERICH KNOBLOCH KARL ADAM BERTRAM LINNARTZ BY ATT'YS July 10, 1962 E. KNOBLOCH ETAL 3,043,499

PROCESS AND APPARATUS FOR CIRCULATING HOT GASES. ESPECIAL-LY UNDER HIGH PRESSURES Filed Aug. 4, 1958 3 Sheets-Sheet 2 will I NH] j l 4 o E lNVENTORS ERICH KNOBLOCH KARL ADAM -BERTRAM LINNARTZ BY M W M ATT'YS July 10, 1962 E. KNOBLOCH ETAL 3,043,499

PROCESS AND APPARATUS FOR CIRCULATING HOT GASES. ESPECIALLY UNDER HIGH PRESSURES Filed Aug. 4, 1958 3 Sheets-Sheet 3 INVENTORSZ ERICH KNOBLOCH KARL ADAM BERTRAM ,LINNARTZ ATT'YS United States Patent 0.

3,043,49 PROCESS AND APPARATUS FOR CIRCULATENG gISRTEgASES, ESPECIALLY UNDER IHGH PRES- Erich Knobloch, Ludwigshafen (Rhine), Karl Adam,

Ludwigshafen (Rhine)-Gartenstadt, and Bertram Linnartz, Lndwigshafen (Rhine), Germany, assignors to Badische Anilin- & Soda-Fabrik Aktiengeseilschatt, Ludwigshafen (Rhine), Germany Filed Aug. 4, 1958, Ser. No. 753,066 Claims priority, application Germany Jan. 22, 1958 7 Ciaims. (Cl. 230-188) This invention relates to an improved method of conveying and circulating gases and apparatus therefor.

More specifically it relates to a new process for circulating gaseous media, such as hot gases or vapors or gasvapor mixtures under high pressure in chemical processes, and describes pumping plants for carrying out this process.

In many chemical processes carried out at high pressures and temperatures it is necessary to circulate the gas or gas-vapor mixture at operating pressure and operating temperature. It has heretofore already been known to convey hot liquids under high pressure by means of piston pumps (or plunger pumps), the hot working valves being located at a sufficiently great distance from the pump with its sensitive stuffing boxes and working parts. For this purpose pipes are provided in the pumping system as the connecting member between the cylinder and the hot valve block, but these pipes are not for the continuous conveyance of material but merely for the oscillatory movement of a certain amount of the medium. These pipes are therefore called oscillatory conduits. This method of hot circulation may be practiced without difiiculty in the case of incompressible media, such as liquids, with pumps of a relatively small number of strokes and great stroke volumes. It has however been known that in circulating gases by means of piston pumps the pumping capacity drops off considerably as the clearance increases. As a result, the clearance was hitherto kept as small as possible.

We have now made the discovery and this is the object of our invention that hot gases, gas-vapor mixtures and vapors can be conveyed by means of gas circulating pumps together with or without the admixture of liquid substances, especially at high pressures without any substantial drop of the pumping capacity by enlarging the pump clearance to a multiple of the stroke volume and subdividing it into a hot zone and a cold zone.

In the practice of our invention there are used simple or double acting gas circulating piston pumps in which the clearance is formed wholly or at least partly by oscillatory conduits. These oscillatory conduits connect the pump cylinder with the valves. Their capacity should amount to at least three times the stroke volume of the piston pump. At a stroke of the piston, only that part of the oscillatory conduit is filled with hot gas which lies nearest to the valve chest and of which the volume approximately corresponds to the stroke volume of the piston. The amount of gas sucked by the suction stroke is immediately forced out again from this part of the oscillatory conduit towards the hot side upon the pressure stroke. The pump end of the oscillatory conduit takes in the cold gas forced out by the piston, up to an amount which again corresponds to the stroke volume of the piston. The conduit containing the oscillating amount of the cycling medium is thus divided into a hot section and a cold section. In order to prevent the equalization of heat between the two parts of the gaseous medium by heat conduction or convection, it is good practice to provide a separation of the two sections, for example by an inbuilt cooler. An

3,43,49 Patented July 10, 1962 interposed length of piping of smaller or somewhat increased diameter or a buffer container which function as a quiescent chamber may also be used in many cases to prevent temperature equalization. To prevent turbulence of flow in the oscillatory conduit the cross-section of the same may be so subdivided that a plurality of individual pipes are formed and a laminar total flow is ensured.

The miximum length of the oscillatory conduit is determined by the permissible size of the additionally provided clearance. Theoretically speaking, the capacity V of the whole of the oscillatory conduit including any additional chambers, such as buffer or separating flasks, should at the most be equal to the multiple of the stroke volume V Which is given by the ratio of the suction pressure p, to the pressure difference A achieved by the pump. Thus the equation:

should be fulfilled. Having regard to the economical size of the pum however, the clearance should not be too large. It is advantageous for the volumetric ratio of the pump volume with respect to the so-called clearance to amount to about one fifth of the ratio of the pres sures.

Depending on the viscosity or the density of the medium to be conveyed and on the speed of the pump, vibrations or beats may arise in the oscillatory conduits affecting the conveying efficiency considerably. The stroke volume, the oscillatory conduit and the valve chest form an oscillatory system in which, depending on the nature of the vibrations formed, vibration dampers, as for example throttle diaphragms, silencers or groups of parallel small tubes, or vibration promoters, such as resonators may be. provided. In the case of double-acting pumps there may also be provided as a special case a connection between two oscillatory conduits fitted with an adjustable throttle opening.

The apparatus according to this invention ofiers considerable advantages over the prior art circulating pumps for hot gases. Apart from the fact that-as described -abovethe sensitive pants of the pump do not come into contact with the hot medium, the apparatus can also be used to circulate gases which contain condensable compo nents or liquids. By the provisionof separators in the oscillatory conduits, such liquids, lubricants or condensable intermediate products can be withdrawn.

A further advantage lies in the fact that the valve cross-section is independent of the size and design of the pump and hence can be chosen according to requirement. The wrought steel cylinders of conventional gas circulating pumps provide little room for adequate valve cross-sections, especially those of high pressure gas circulating pumps as these are built as long-stroke machines with relatively small diameters by reason of the high surface loading. The result of an insufficient valve cross-section is an excessive expenditure of power. In the case of the valve block being arranged separately, the cross-sections of the valves can be of any desired size and consequently the losses can be kept low. Our invention furthermore provides locating the circulating pump far from the reaction apparatus, for example, in a powerhouse, While the valves are arranged directly at the apparatus. This is of special importance in chemical reactions which necessitate heightened safety precautions.

The invention will now be described with reference to the accompanying diagrammatic drawings.

FIGURE 1 is a diagrammatic showing of the invention.

FIGURE 2 is a diagrammatic showing of a modification of the invention. I

FIGURE 3 is a sectional view of the pump cylinder and stuffing box with the piston and rod shown in full.

clearance of the pump.

Referring to FIGURE 1, a piston 2 reciprocating in a cylinder 1 of a double-acting piston pump sucks gas from a high pressure reactor 3 through line 8 and suction valves 6 and 6a and feeds it back into the reactor 3 through line 9 and pressure valves 7 and 7a arranged between the cylinder l and the valve chests and 5a oscillatory conduits 4 and These are subdivided by coolers 10 and 10a into a hot section lying adjacent the valve chests 5 and 5a and a cold section lying adjacent the cylinder 1.

When an apparatus of this type is used, for example, for the catalytic hydrogenation of nitriles to amines at temperatures between 80 and 150 C. and pressures of about 300 atmospheres, by passing the nitrile over a catalyst together with hydrogen a side reaction occurs which reduces the yield of amine by an imine group being formed from two amine groups by the splitting off of ammonia. This undesired reaction is avoided if large amounts of ammonia are added to the cycling hydrogen current. If after leaving the reactor the hydrogen was cooled and again fed into the reactor in cooled condition by means of a circulating gas pump, the greater part of the ammonia would be separated and had to be supplied again to the reactor. It is considerably more economical to circulate the Whole of the circulating gas, i.e. hydrogen and ammonia, under pressure at high temerature; in this way large quantities of energy are saved and the operation is simplified because quite a number of apparatus can be dispensed with. In the present case the suction pressure p of the gas circulating pump is 300 atmospheres and the pressure needed to maintain the circulation of the gas is 12 atmospheres with the pump having a speed of 133 revolutions per minute. The amount of gas thus circulated amounts to 75,000 cubic meters per hour (N.T.P.).

The process according to this invention may be further improved so that it may be practiced under extremely high temperatures by introducing fresh gas or an inert gas into the oscillatory conduit or into the so-called In this way an additional selfregulating circulatory cooling is achieved in the cold section or sections of the oscillatory conduit, depending on whether single-acting or double-acting pumps are used, as well as in the cylinder of the pump. This embodiment of the invention is illustrated in FIGURE 2.

For the introduction of fresh gas into the cold sections of the oscillatory conduits 4 and 4a a connecting pipe 11 is provided between them, this pipe having a smaller cross-section than the oscillatory conduits 4 and 4a. A supply pipe 12 for the feed of fresh gas or inert gas opens into the connecting pipe 11. Feasibly, connecting pipe 11 is provided in the cold section of the oscillation conduits as near as possible to the pump cylinder 1.

The surprising fact is that the intercommunication of the oscillatory conduits 4 and 4:1 by connecting pipe 11 does not decrease the efiiciency of the pump in circulating the highly compressed gases. As experiments have shown there is no drop in the conveying capacity of the pump even if the internal width of connecting pipe 11 is 24 millimeters or more compared with about 120 millimeters internal Width of the oscillatory conduits 4 and 40. If the oscillatory conduit 4 functions as suction pipe, the fresh gas fed in at 12 flows through this conduit into the respective part of cylinder 1, whereas it flows through conduit 4a into the other part of cylinder 1 if conduit 4a is used as a suction pipe.

On the other hand the fresh gas or an inert gas may be introduced, with a similarly good effect, directly into the pump cylinder 1 and in the case of double-acting pumps into the stroke chambers on both sides of the piston 2. It is further possible to introduce the fresh gas or an inert gas through the stufling box chamber 13 in which the piston rod reciprocates, into the enlarged pump chamber. This arrangement is illustrated in FIGURE 3. The advantage obtained by this embodiment of our invention [l is that a more efiicient cooling is achieved at the critical point of the stuffing box and the piston rod.

Further advantages of this embodiment of our invention will hereinafter be set forth.

If the gas circulated by conventional type arrangements contains condensable vapors, there is the risk that small droplets of liquid will pass into the cylinder during the suction stroke, be thrown against the piston rod and cause the lubricating film to be interrupted or destroy it. By feeding the fresh gas into the stufifing box chamber according to this invention this shortcoming is remedied, especially if oscillatory conduits with sufiiciently large internal width are used. When a circulating pump with a conveying capacity of 70,000 cubic meters per hour (N.T.P.) is used, the free cross-section of the oscillatory conduit should be at least square centimeters. This allows of reducing the speed of flow in such a manner that a premature precipitation of condensed liquid droplets as well as oil droplets in the pipe is promoted. If each of the oscillatory conduits 4 and 4a is arranged with a sutlicient gradient toward their respective valve chests 5 and 5a, the whole of the liquid flows to either valve chest and is forced by the pressure stroke into the cycle of the hot gas. The condensed liquid then evaporates again, while the oil is collected in the hot cycle outside the oscillatory pipes and the valve chests. The conditions for this may be substantially improved by arranging the valves 6 and 7 and 6a and 7a in the valve chests laterally and joining the oscillatory conduits 4 and 4a at the top. The pipes 8 and 9 of the hot cycle are also joined at the sides. The tight closure of the valves is improved by this arrangement and the life of the valves considerably increased. With the above-specified arrangement of the valves in, and of the pipes at, each valve chest the provision of resonators and damping chambers in the cycle is not as a rule necessary.

The fundamental division of the oscillatory conduit into a cold section and a hot section, such as is shown in FIGURE 1, is again considerably improved quantitatively by the introduction of the cold fresh gas or an inert gas into the connecting pipe. In the case of a gas consisting of 71% of hydrogen, 22% of ammonia, 6% of nitrogen and 1% of residual gases and vapors, which is to be led, at a temperature of C., in a cycle through a reactor, a temperature of only 28 C. is measured in the cylinder of the gas circulating pump when the process described above is adopted. Even with the circulating gas having high temperatures there is only a very slight rise of the temperature in the pump. The effect achieved by the introduction of cold fresh gas or an inert gas into the clearance of the pump, provided the quantity fed in is large enough, is so great that the provision of the coolers 10 and 10a in the oscillatory conduits can be dispensed with, without the subdivision of these conduits into cold and hot zones being interfered with.

The clearance in the pumping chamber is understood to be the remaining volume in the pumping chamber between the piston and the walls of the piston head when the pump crank is at top dead center. In this reference, the clearance in the pumping chamber includes only the clearance volume in the pump housing. The portion of the total clearance of the pump external of the pump housing is defined as an extension of the pumping chamher. The total clearance of the pump is the sum of the clearance in the pumping chamber plus the volume of the extension of the pumping chamber.

We claim:

1. A pumping system for the circulation of hot gases comprising a piston pump with a clearance in the pumping chamber, an elongated, gas-conveying extension of said clearance in said pumping chamber terminating in a valved chamber having an entrance and exit adapted to be connected in a hot gas circulatory system, said valved chamber having an inlet valve and an outlet valve, said clearance and said elongated extension of said pumping chamber having a total volume which is at least three times the stroke volume of said piston pump, and heat exchange means in said extension at a point between said pumping chamber clearance and valved chamber for cooling the gas passing through said heat exchange means and thereby adapted to divide said extension into a cool gas section on the pump side of said heat exchange means and a hot gas section on the Opposite side of said heat exchange means.

2. The pumping system of claim 1 wherein means are provided for feeding additional gas to said pumping system into the cool gas side thereof.

3. A pumping system for the circulation of hot gases comprising a double-acting piston pump with a clearance in each pumping chamber, an elongated gas-conveying extension on each clearance of said pumping chambers terminating in a valved chamber having an entrance and exit adapted to be connected in a hot gas circulatory system, said valved chamber having an inlet valve and an outlet valve, each pumping chamber clearance and its respective elongated extension havinga total volume which is at least three times the stroke volume of each pumping chamber of said double acting piston pump, and heat exchange means on each of said extensions at a point between said pumping chamber clearance and said valved chamber for cooling the gas passing through said heat exchange means and thereby adapted to divide each extension into a cool gas section on the pump side of said heat exchange means and a hot gas section on the opposite side of said heat exchange means.

4. The pumping system of claim 3 wherein said extensions are intercommunicated by a connecting pipe having means for supplying additional gas to said connecting pipe.

5. The pumping system of claim 4 wherein said connecting pipe intercommunicates the cool gas sections of said extensions.

'6. The pumping system of claim 3wherein said extensions are intercornmunicated by a pipe of smaller internal cross-sectional area than the internal cross-sectional areas of said extensions.

7. A pumping system .for the circulation of hot gases comprising a piston pump with a clearance in the pumping chamber, an elongated gas-conveying extension of said clearance terminating in a valve chamber having a valved entrance and a valved exit connected in a hot gas circulatory system, .said clearance and said extension of said pumping chamber having a total volume which is at least three times the stroke volume of said piston pump, and means for maintaining during the operation of said piston pump an oscillating volume of gas in said pumping chamber and in a part of said extension contiguous to said pumping chamber at a temperature substantially below the gas temperature in the hot gas circulatory system.

References Cited in the file of this patent UNITED STATES PATENTS Shapiro Dec. 2, 1958

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