US 3161139 A
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Dec. 15, 1964 T. BORELL! 3,161,139
METHOD AND MEANS FOR PUMPING CORROSIVE LIQUIDS Filed July 30, 1962 INVENTOR.
United States Patent F 3,161,139 ME'ii-lt'lfi AND MEAN FUR PUMPHJG C(ERRUSKVE LIIQUKDS lito lsorelli, Milan, ltaly, assignor to Mohteeatirit Soeieta Generate per llndustria Mineraria e Qhimica, li iiian, Etaiy, a corporation of Itaiy Filed July 30, 1962, Ser. No. 213,345 Claims priority, application Italy 3, 1961 4 Claims. (til. 163-44) 7 carbarnate solution back into the synthesis column or autoclave at high pressures, which difiiculties are caused by the concurrent action of high pressure and the highly corrosive aggressiveness of the aqueous solution of ammonium carbamate containing also ammonia and carbon dioxide. Suitable pumps of the prior art, generally of the reciprocating type, are therefore customarily made entirely of special alloy steels, such as A181 316, which have good corrosion resistance but are poorly suited for severe mechanical service because of their low surface hardness. The 'plungers especially, and other working parts of the pump become scratched easily, with resulting damage to the piston gaskets, which must then be replaced at relatively short intervals; this involves shut-down, production losses and considerable expense in material and labor.
All of these inconveniences and disadvantages of mechanical and chemical nature can be avoided with the present invention, which in its industrial application has.
proven capable of eliminating them completely.
It is therefore anobject of my invention to provide a method and apparatus for pumping corrosive liquids wherein the main pump itself does not come in contact with the corrosive liquid and thus can be made of ordinary materials such as straight carbon steel.
Another object of the invention is to provide means for adding a certain predetermined minimum amount of auxiliary liquid, such as water, to the corrosive liquid being pumped and simultaneously to increase the pressure of the corrosive liquid in the pumping direction.
. It is a further object of the invention to provide a method and means for pumping liquids difficult to handle, either corrosive or. containing solid substances in' suspension, such as, for example, but not exclusively, aqueous solutions of ammonium carbamate, aqueous's'olutions of formic acid, and cupro us ammoniacal solutions.
Still another object of the invention is to provide a liquid piston between a reciprocating pump and a valve box for transmitting reciprocating motion to the latter.
To these ends and inaccordance with the present invention, a reciprocating pump, made of an ordinary material such as straight carbon steel, is arranged to'pump only water or other non-corrosive auxiliaryliquid. A separate valve box, connected to the pumpby a connecting pipe, has intake and outlet valv'eswhich open and close by movement and-pressure cycles of the auxiliary liquid pumped by the-main pump. lfhe movement of the auxiliary liquid in the connecting pipe 'thus'serves as a 3,161,139 Patented Dec. 15, 1964 ice tion of the connecting pipe which brings the water from the main pump to the valve box. An auxiliary reciprocating pump introduces a certain amount of water or other auxiliary liquid continuously into the pipe line between the main pump and the valve box in order to replenish losses and maintain constant and controlled the concentration level. The amount of auxiliary liquid added at each cycle of the main pump is synchronized with the quantity of corrosive solution being pumped by a linkage between the main pump and the auxiliary pump.
Other objects, advantages and features of the invention will hereinafter become more fully apparent from the following description of the drawing annexed hereto, which illustrates schematically the apparatus according to the invention.
As shown in the drawing, a reciprocating pump 1 which may be made of plain carbon steel, is provided with v a reciprocating piston 10. The pump 1 is connected by means of a pipeline 2 of any desired length, which may be considerable, to a valve box 3 provided with an inlet suction valve 3a and an outlet pressure valve 3b. The valve box 3, the valves 3a and 3b, as well as the adjoining sections of the piping are made of corrosion-resistant material such as AlSI 316 steel, inox steel or other materials resistant to chemical corrosion by the material to be pumped. An inlet line 3 introduces the corrosive liquid into the valve box 3 through valve 3a, and an outlet conduit 9 carries the corrosive liquid in the direction of the arrow out of the valve box 3 through valve 3b. Inserted into the pipeline 2 between the main pump 1 and the valve box 3 is a cylindricalpipe portion 4,, preferably but not necessarily, vertically disposed. The pipe 4 contains a free floating piston 6 slidable axially within the cylinder 4 between two baffle or orifice plates '7. The open plates can limit the longitudinal or upward and downward motion of piston d mechanically,but will not seal oif the flow of liquid, which can pass through the orifice openings in battle plates 7 and around the piston 6. v An auxiliary pump 5 is provided for introducing auxiliary liquid, such as water, into the pipeline 2 at a point 2a near the main pump 1. The main reciprocating pump 1 is driven through connecting rod 1b from a crank w eel 1a bymeans of a motor M. The wheella is mechanically connected, as indicated by the dash-dot line It to an auxiliary crank wheel 5a, which drives the auxiliary pump 5 through a connecting rod 5b. The main crank wheel 1a drives the main pump 1 through connecting rod lb.
water is preferred.
liquid piston to pump the corrosive liquid through the fvalve box. A free floating'-- piston is inserted in a por- The term liquid piston as used herein is intended to describe the liquid located in the conduit between the piston member 10 of pump 1 and the valves 3a and 3b of the valve box 3, which liquid acts as a fluid piston in an enclosed space, reciprocating back and forth in synchronisrn with the reciprocating motion of the member 10 of pump 1 in order to transmit such reciprocating motion to the valves 3:; and 31b.
The auxiliary liquid introduced by auxiliary pump 5 at point 2:: into the pipeline 2 can be a liquid which is not miscible with the liquid being pumped. 1 When pumping ammonium carbarnate from inlet conduit 8 into outlet conduit 9, a parailinic oil mixture may be used as the auxiliary liquid introduced by pump 5, but generally In order toprev'ent' the carbamate, which is water miscible, fronrditlusing backward through line 2 toward the main pump due to the turbulent motion occurring in the liquid piston line, and thus providing the danger that the corrosive liquid would corrode the plain steel of which the main pump is made, the auxiliary pipe 5 continuously injects at 2n under pressure a certain amount of the auxiliary liquid, such as. water.
in the vicinity of the main pump l. The purpose of adding waterorother auxiliary liquid is to make up tor l'osses;
3 and maintain constant the concentration level of the liquid in the pipe 2 between the pump 1 and the valve box 3, so that the main pump 1 as well as the auxiliary pump both pump only the non-corrosive auxiliary liquid, and consequently may be made of mechanically most suitable materials, with the necessary surface hardness for long wear and abrasion resistance. At the same time, the addition of the auxiliary liquid makes up for possible losses through the glands of the main pump 1.
A certain amount of auxiliary liquid will fiow past the floating separating body 6 into the valve box 3 and become mixed with the solution being pumped. In order to reduce to a minimum, this loss and thus the amount of auxiliary solution or water which must be introduced, the floating separating body 6, which is positioned in vertical conduit 4 located near the terminal end of the pipe 2 close to the valve box, is made to fit within pipe 4 with a little clearance which, ho, ever, need not be liquidtight. Although pipe 4 is shown as vertical, this conduit may be horizontal or inclined, since the member 6 moves back and forth axially with the movement of the liquid piston produced by the pumping action of pump 1. As mentioned, the separating body 6 is positioned between suitable bathe plates or orifice plates 7 which can stop the piston 6 mechanically but not seal off the flow tightly. With the clearance between the separating body 6 and the pipe walls of conduit 4 reduced to a minimum, the mixing of the auxiliary fluid such as water with the fluid to be pumped may thus be reduced considerably, so that the water added from auxiliary pump 5 may be maintained within the range of 1% of the capacity of the main pump 1.
Operation of the apparatus is as follows:
In its reciprocating movement, the pump piston 10 transmits its motion through the liquid in pipes 2 and 4 to the floating piston 6 which in turn act'uates' the valves 3a and 3b to perform the pumping of the carbamate or other corrosive solution, which thus passes from inlet conduit 8 through valve box 3 and out under pressure through outlet conduit 9.
The separating body 6 may assume a variety of shapes, for example it may be a solid or hollow ball, or a cylinder as illustrated. The separating body 6 may be provided with high-pressure valves if desired (not shown), or it may be water-tight or porous. The body 6 may be made of metal or other material of lighter specific gravity. Best results were obtained by using a small clearance between the outer circumference of body 6 and the inner wall of conduit 4, the clearance being preferably in the range of tenths of a millimeter. .The material of body 4 should preferably have a density as close as possible to that of the carbamate or other corrosive solution being pumped. Plastic materials having such density areparticularly suitable.
The introduction of wash-water as the auxiliary liquid by means of pump 5, properly synchronized with the stroke cycle of main pump ll, through crank wheels la, 5a and the mechanical connection it maintains the motion of separating body 6 in phase with the pump cycle movement and forces applied to the liquid piston in pipe 2 by the main pump 1.
The above-described pumping apparatus has been successfully used for pumping ammonium carbamate at pressures up to 450 atm. It was also successfully tried with other liquids which are difficult to pump, such as, for example, but not limited to, cuprous ammoniacal solutions, formic acid solutions, and solutions containing finely divided solids.
The method of the invention may be further understood from the following example.
Example About 18 cubic meters per hour of an ammonium carbamate solution having a composition of 45% ammonia, 33% carbon dioxide and 22% water, and at a temperature of about and a pressure of about 18 atmospheres, were sucked through a valve box 3 and sent back to an urea synthesis autoclave at a pressure of 200 atmospheres by means of several liquid pistons moved by a Triplex main pump 1 rotating at about 72 r.p.m. The Triplex pump had a stroke of 220 millimeters and a bore of millimeters inner diameter.
The pump 1 was made of common straight carbon steel, as was also the connecting pipe 2, the latter being 30 millimeters in diameter.
The valve slides 3a, 3b, and the valve box 3, were made of A181 316 steel, and were located directly under the synthesis autoclave apparatus, at about 25 meters from the pump 1.
In the end of each of the connecting pipes 2 toward the Valve slide that widens over a length of about 500 millimeters to a diameter of 70 millimeters, was contained a separator body 6 made of plastic material, with a clearance around it resulting from it having an outer diameter about one-tenth of a millimeter less than the inner diameter of the pipe 4 which contains this body 6.
With a delivery of washing water, as the auxiliary liquid, of about 260 liters per hour over all, pumped in by a Triplex pump 5 synchronized with the main pump 1, the ammonia content in the connecting pipe immediately following the separator body 6 becomes stabilized at about 5 g./l. This washing water was added in practice at point 2c at about 1 meter distance from the main pump.
Under these conditions, no chemical attack whatsoever was observed on the piping or on the pump bodies during operation over long periods.
It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.
1. A method for pumping into a urea synthesis plant at superatmospheric pressures a corrosive liquid consisting essentially of a solution of aqueous ammonium carbamaate containing ammonia, water and carbon dioxide, comprising the steps of sucking in the corrosive liquid into the intake side of a valve box made of material chemically resistant to said corrosive liquid, cyclically forcing, from an auxiliary supply means of material chemically corrodible by said corrosive liquid, water under pressure into said valve box and into intimate contact with said corrosive liquid therein so that said water mixes with and diffuses into said corrosive liquid, and forcing the resulting diffused mixture of water and corrosive liquid out of an outlet side of said valve box to said urea synthesis plant while obstructing fluid flow of said corrosive'liquid into said auxiliary supply means so that said auxiliary supply means is protected from said corrosive liquid.
2. Apparatus for pumping liquids difiicult to handle and liquids containing solids in suspension, comprising a reciprocating main pump adapted to pump a noncorrosive auxiliary liquid only, a valve box having an 'inlet side'and an outlet side for how therethrough of a first liquid and provided with intake and outlet valve means, conduit means connecting said main pump with said valve box and adapted to contain said auxiliary liquid, whereby said auxiliary liquid forms a liquid piston within said conduit means reciprocable therein by said main pump to activate said valve means within the valve box, an auxiliary reciprocating pump in synchronizing connection with said main pump and connected to said conduit means for replenishing auxiliary liquid into said conduit means so as to maintain constant the concentration level of the liquid in said conduit means, a separating body axially movable within. said conduit means and having a slight clearance between said body and body comprising a piston having an outer diameter smaller than the inner diameter of said conduit means by an amount at least one tenth of a millimeter, the portions of said main pump'coming in contact with said auxiliary liquid being of plain carbon steel, and the portion of said valve box and conduit coming in contact with the solution being pumped being essentially of corrosionresistant material chemically unreaetive with the liquid being pumped. r
4. Apparatus according to claim 3, said conduit means having a portion located in the end thereof near said valve box, baffle means located ahead and behind said separating body for mechanically limiting the axial movement of the latter Witiiin said conduit means but permitting liquid flow past said baiile means in either direction, said separating body being of a material having a specific gravity close to that of the corrosiveliquid being pumped.
References (Cited in the file of this patent UNITED STATES PATENTS 862,867 Eggleston Aug. 6, 1907 2,196,959 Crothers Apr. 9, 1940 2,591,441 Kollsman Apr. 1, 1952 2,644,401 Ragland July 7, 1953 2,753,865 Boivinet July 10, 1956 2,971,465 Caillaud Feb. 14, 1961