Abstract:
A pump system suitable for pumping a hot medium, such as hot mixtures of liquid and solid substances (slurries), includes at least one displacement pump, such as a membrane pump, at least one bidirectional flow pipe, and a second pipe connected to the pump chamber of the displacement pump. The bidirectional flow pipe is connected at a first end to a first and a second one-way valve. A supply pipe for drawing an amount of medium from the supply pipe is connected to the bidirectional flow pipe via the first one-way valve and a discharge pipe for discharging an identical amount of medium from the bidirectional flow pipe is connected to the bidirectional flow pipe via the second one-way valve. The second pipe is provided in a horizontal plane. The displacement pump is associated with an expansion accommodating feature to allow the displacement pump to move when the bidirectional flow pipe or second pipe expand. A partition element is provided in the bidirectional flow pipe to restrict flow through the pipe.

Description:
FIELD OF THE INVENTION 
     The invention relates to a pump system in particular suitable for pumping hot media, such as hot mixtures of liquid and solid substances (slurries). The system includes at least one displacement pump, preferably a membrane pump, and at least one bidirectional flow pipe. The bidirectional flow pipe is connected to a first and second one-way valve at the first end of the pipe. The bidirectional flow pipe is connected at a first end via the first one-way valve, to a supply pipe for drawing an amount of medium from said supply pipe and is also connected on the first end via the second one-way valve, to a discharge pipe for discharging an identical amount of medium from said bidirectional flow pipe. The bidirectional flow pipe is connected on its other side to a second pipe, which is circumferentially is provided with heat exchange means. The second pipe is connected at its other end to a pump chamber of the displacement pump. 
     BACKGROUND OF THE INVENTION 
     A pump system of the above kind is disclosed in published Dutch patent application No. 90 01 676 in the name of the present applicant. The known pump system is used for pumping a hot slurry from a supply pipe to a discharge pipe. An amount of a hot mass is drawn into the bidirectional flow pipe by means of the displacement pump with every stroke. The hot mass is forced from the bidirectional flow pipe into the discharge pipe with the subsequent delivery stroke. The displacement volume of the displacement pump and the volume of the bidirectional flow pipe are thereby geared to each other in such a manner that the amount of medium drawn in and forced out fills the bidirectional flow pipe entirely or only partially. The bidirectional flow pipe is connected to the pump chamber via a second pipe having a liquid column present therein. The movements of the pump casing are thereby transmitted to the liquid mass in the bidirectional flow pipe by the liquid column in the second pipe. The hot medium in the bidirectional flow pipe is kept separated from the pump casing by the liquid column present in the second pipe. In order to maintain the temperature at the location of the pump casing at an acceptable level, heat exchange elements are provided around the second pipe. These elements cool the medium column present in the pipe. With this known embodiment of such a pump system, the second pipe extends in a vertical direction. The advantage of this is that it enables a limited construction volume. A drawback of the vertical arrangement of said second cooled pipe is, however, that an enhanced heat transport will occur in the direction of the displacement pump as a result of conduction, and especially as a result of the occurrence of a convection current in the pipe. On the one hand, this leads to a higher temperature at the pump casing, which is no longer acceptable under certain circumstances. On the other hand, it also leads to greater heat losses, because a larger amount of heat must be removed by cooling. With slurry temperatures on the order of 150 C. these problems are still acceptable, but at higher medium temperatures, as will increasingly occur in the future, this leads to very large cooling capacities and a corresponding cooling water consumption in order to keep the temperature at the pump casing at an acceptable level. Furthermore this leads to large heat losses of the medium to be pumped, which is also disadvantageous from an energy point of view. 
     Another drawback of this known system is its very large construction height, which leads to very heavy concrete bases required for these systems. Furthermore, a high pressure of the medium in the supply pipe is necessary with these systems in order to overcome the pressure of the static liquid column in the vertical portion. 
     Another embodiment of a pump system as described above is known from EP-A-0048535. Also with this known pump system a vertical pipe is present between the bidirectional flow pipe and the pump device. The vertical pipe contains a medium column for transmitting the piston movements, whereby heat and mass transport in the direction of the pump device will again occur in this pipe as a result of conduction and convection. As a result of this, excessive temperatures will occur at the pump casing, especially with higher temperatures of the medium to be pumped, and a large amount of heat will have to be removed by cooling, which is disadvantageous from an energy point of view. 
     From PCT/US79/00697, a system is furthermore known wherein the inlet and outlet valves and the bidirectional flow pipe are positioned higher than the displacement pump. As a result, the direction of the convection current has a positive effect on heat transport, but the systems are only suitable for non-settling liquids, and certainly not for slurry suspensions, for which the present invention is particularly intended. 
     The object of the invention is to provide a pump system of the kind indicated above, wherein the aforesaid drawbacks are obviated and by means of which high-temperature media can be pumped without this leading to excessively high temperatures at the displacement pump and without having to remove an excessive amount of heat in the second pipe by cooling. 
     SUMMARY OF THE INVENTION 
     In order to accomplish that objective the pump system according to the invention is characterized in that at least the second pipe is accommodated in a substantially horizontal plane in the system. The result of this surprisingly simple measure is that the heat and mass transport caused by convection currents in the second pipe have been reduced to a minimum. As a result of this, the temperature at the end of the second pipe remote from the bidirectional flow pipe can have a relatively low value. Also at high media temperatures cooling of the second pipe is not required. Another advantage is the fact that the amount of heat that has to be removed in the second pipe by cooling will be limited, which is attractive from an energy point of view. 
     An advantageous embodiment of the pump system includes a said second pipe that extends at an angle to the bidirectional flow pipe in the horizontal plane, whereby the two pipes are interconnected via a bent pipe. In this manner, the pipes may expand, which is caused by the fact that the temperature during assembly is much lower than during operation. Expansion is accommodated because the two pipes can bend slightly outwards, as a result of which the expansion can readily be accommodated in the device. In another embodiment of the pump system according to the invention, expansion differences can be accommodated by connecting the second pipe to the displacement pump at its end remote from the bidirectional flow pipe via a bend and another pipe. This further increases the flexibility of the system of pipes. 
     Another advantageous embodiment of the pump system according to the invention is characterized in that the second pipe and the bidirectional flow pipe, which likewise extends horizontally, are coaxially aligned, whereby the displacement pump is movably accommodated in the system in such a manner that the displacement pump can move under the influence of changes in length of the two pipes caused by changes in temperature. With this embodiment, the part of the system housing that contains the one-way valves, which can be connected to the supply pipe and the discharge pipe, can be fixedly disposed. Expansion of the two pipes causes them to exert such a force on the displacement pump that the pump will move as a result thereof. 
     According to another embodiment, it is also possible to use driving means, which move the pump device under the influence of temperature and/or expansion signals, rather than transmit the forces that occur during expansion of the two pipes to the displacement pump via the pipes. 
     In another embodiment of the pump system the bidirectional flow pipe and the second pipe are interconnected in coaxially aligned relationship, and their common axis exhibits a curved configuration. In this embodiment, any expansion differences caused by temperature changes will manifest themselves in the two pipes exhibiting a sharper or a wider bend. 
     According to another embodiment, in order to obtain a compact construction, the pump of the pump system is accommodated in the system in such a manner that the central axis of the pump extends substantially parallel to the central axis of the second pipe. 
     In another embodiment, the pump system includes a partition element that is disposed in the bidirectional flow pipe. The partition element at least partially shuts off the passage through the pipe. The partition element impedes the transport of the hot and frequently corrosive medium in the direction of the pump casing and the membrane pump to a considerable degree. In this manner the load on the device as a whole is reduced, demands on the individual components are reduced and a simpler and cheaper construction of the device is made possible. 
     The partition element may be capable of free reciprocating movement in the direction of the axis of the pipe, and in particular be slidably mounted on a guide bar disposed in line with the central axis of the bidirectional flow pipe. This prevents unnecessary influencing of the pumping action. 
     According to the invention the partition element may be provided with a number of through channels, which function to prevent any unnecessary negative influencing of the pumping action. The transport of the medium in the direction of the pump casing and the membrane pump can also be impeded by configuring the partition element as a disc-shaped element having a diameter which is smaller than the diameter of the bidirectional flow pipe, or as an elongated element. 
     In addition, the second pipe may be provided at the location of the heat exchange means with means which have a mixing effect on the medium present at that location, such that the medium will be placed into proper heat exchanging contact with the pipe wall. This leads to an enhanced cooling effect of the heat exchange means on the hot medium. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail hereafter with reference to the drawing, which shows a few embodiments of a pump system according to the invention. 
     FIG. 1 shows a diagrammatic view, not to scale, of a pump system for pumping hot media. 
     FIGS. 2 a  and  2   b  show a side view and a plan view respectively of a pump system, wherein the bidirectional flow pipe and the second pipe are horizontally in line. 
     FIGS. 3 a  and  3   b  and FIGS. 4 a  and  4   b  each show an embodiment, in side view and in plan view respectively, of the pump system according to the invention. 
     FIG. 5 shows another embodiment of the pump system according to the invention. 
     FIGS. 6 a  and  6   b  are detailed views of other embodiments for use in the pump system according to the invention. 
     FIG. 6 c  is a cross section taken along line A—A of FIG. 6 b.   
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a pump system comprising a supply pipe  2  and a discharge pipe  3 . The pump system furthermore comprises a displacement pump  4  (partially shown) for drawing in a medium  5 , for example a slurry, from supply pipe  2 , via a first one-way valve  6 , into a generally horizontally disposed bidirectional flow pipe  7 . The drawing in of medium  5  takes place in a suction phase, which is followed by a delivery phase, in which the medium  5 , which has collected in bidirectional flow pipe  7 , is forced into a discharge pipe  3  connected thereto via a second one-way valve  8 . The two one-way valves  6  and  8  used in the illustrated embodiment are ball valves and are positioned in valve casing  24 . It is also possible, however, to use other types of one-way valves, such as conical valves, ring valves or flat valves. Valve  6  is open and valve  8  is closed during the suction phase, whilst valve  6  is closed and valve  8  is open during the delivery phase. 
     Letter A indicates the point of reversal or the boundary layer in bidirectional flow pipe  7  that indicates the point to which the sucked-in medium  5  enters bidirectional flow pipe  7  before being removed therefrom again. 
     On its side remote from the valves bidirectional flow pipe  7  is connected to a horizontally extending pipe  10 , which is surrounded by a heat exchanger  11 , through which a cooling medium is passed from inlet  12  to outlet  12 ′. As shown in FIG. 1, the first  6  and second  8  one-way valves are attached to the bidirectional flow pipe  5  at a first end  30  of the pipe  5 . On the other end of pipe  5 , at second end of  32 , second pipe  10  is connected, via a bent pipe  13 , to the pump chamber  14  of a membrane pump  4 . Membrane pump  4  possesses a membrane  15  disposed in a pump casing  16  to which pipe  13  is connected. The membrane pump is provided with a piston rod  18 , which is reciprocated by driving means (not shown). Attached to piston rod  17  is a displacement member  18 , which is capable of movement within a cylinder  19 . Piston rod  17  may reciprocate membrane  15  directly, if desired, but the reciprocation may also be effected via an intermediate medium shown in the figure, which is reciprocated by displacement member  18  and which transmits said reciprocating movement to membrane  15 . The reciprocating movement of membrane  15  results in the suction phase and the delivery phase, as a result of which medium  5  is transported from supply pipe  2  to discharge pipe  3 . The hot medium  5  reciprocating through bidirectional flow pipe  7  is thereby separated from membrane by the column of medium present in second pipe  10 . As a result of the horizontal arrangement of both bidirectional flow pipe  7  and second pipe  10 , transport of heat from medium in the direction of membrane  15  is only possible to a very limited extent, namely via conduction and a small amount of admixing caused by turbulence. The small amount of heat is thereby removed from pipe  10  by cooling via heat exchange means  11 , so that membrane  15  will not be exposed to high temperatures. Due to the horizontal arrangement of the two pipes there will be hardly any heat transport, if at all, from the hot medium  5  present in bidirectional flow pipe  7  via convection current. In this manner a pump system has been obtained which is also capable of pumping media having very high temperatures, without exposing membrane  15  to excessively high temperatures thereby. Since the temperature of the two pipes  7  and  10  during assembly will be much lower than the temperatures that occur during operation of the pump system, the two pipes will exhibit expansion. Since it is generally desirable, for practical reasons, for the valve casing  24  comprising valves  6  and  8  to be fixedly disposed, because valve casing  24  is connected to supply and discharge pipes  2  and  3 , which form part of a larger, fixedly disposed installation, it will be necessary to accommodate the expansion of pipes  7  and  10  on the other side. In order to accommodate the expansions, displacement pump block  20  of the pump system according to the invention is disposed on foundation  21  with the interposition of a guide  22 , over which displacement pump block  20  can move. The guide may also be a friction guide, but it is also possible to place block  20  on a roller guide  22 , over which a slight movement of the block is possible in case of expansion of pipes  7  and  10 . The forces required for moving block  20  are thereby transmitted to the pump block by pipes  7  and  10  themselves. As will be explained hereafter, it is also possible to design the system of pipes  7  and  10  to have a certain flexibility. 
     In the embodiment shown in FIG. 1, the displacement pump is a membrane pump, which may either be a single-acting pump or a double-acting pump. In the case where the pump is a double-acting pump, an intermediate medium will be present to the right of displacement member  18 , which intermediate medium is capable of moving a membrane (not shown) and operating another pump system. Instead of using a membrane pump it is also possible to use ordinary displacement pumps, and the pump system may comprise several such displacement pumps. 
     Generally, the displacement volume of the displacement pump will be smaller than the interior volume of bidirectional flow pipe  7 , so that the boundary layer A will remain within bidirectional flow pipe  7 . The extent to which the displacement volume will be smaller thereby depends on a factor which is determined empirically and, given the temperature of the slurry, on the basis of the Reynolds number. Generally, the factor will range between 1.05 and 5, in practice. 
     As is shown in FIG. 1, the displacement pump is disposed in the illustrated pump system in such a manner that the central axes of the rods extend parallel to second pipe  10 . This has resulted in a highly compact construction of the pump system. 
     The figures to be discussed hereafter show a number of possible arrangements of pump systems according to the invention. All these arrangements comprise as common elements, which are consequently indicated by the same numerals in the various figures, a pump unit  20 , which in this embodiment comprises four displacement pumps, which are each provided with a pump chamber  14 . The pump unit is thereby disposed on a foundation  21 . Furthermore each of these embodiments comprises four valve casings  24  housing valves  6  and  8 , which are connected to a supply pipe  2  and a discharge pipe  3 , respectively. 
     In the embodiment shown in FIGS. 2 a  and  2   b , bidirectional flow pipe  7  and second pipe  10  are disposed in coaxially aligned relationship between valve casings  24  on the one hand and pump unit  20  on the other hand. Valve housings  24  are fixedly disposed thereby, and pump unit  20  is disposed on foundation  21  via roller guides  23  so as to accommodate expansion differences between pipes  7  and  10  caused by temperature differences. If expansion differences occur in pipes  7  and  10 , the pipes will move the pump unit a small distance, thus accommodating the expansion differences. 
     FIGS. 3 a  and  3   b  show another possible embodiment, which in principle corresponds with the embodiment which is diagrammatically shown in FIG.  1 . In FIGS. 3 a  and  3   b , pipes  7  and  10  extend between valve casings  24  and pump chambers  14  in such a manner that pipe  10  extends parallel to pump unit  20 . This leads to a compact construction of the pump system. Pipe is connected to pump chamber  14  via a pipe  25 , which extends at an angle to pipe  10 . This arrangement has resulted in a certain amount of flexibility in the pipe system, as a result of which expansion differences occurring in pipes  7  and  10  can at least partially be compensated. Although pipe  25  is a straight pipe in this embodiment, it may also be configured as a large bend connected to pump chamber  14  on one side and to pipe  10  on the other side, whilst still retaining its advantages. 
     Another possibility of accommodating expansion differences in pipes  7  and  10  is shown in FIGS. 4 a  and  4   b , wherein pipes  7  and  10  connect to one another in coaxially aligned relationship, but wherein said pipes are substantially arcuate or bent between valve casings  24  and pump chambers  14 . As a result of this bent configuration, expansion differences in pipes  7  and  10  will cause the bend or curve in the pipes to become sharper or wider, thus accommodating expansion differences in the pipes. 
     The possibilities of accommodating expansion differences in the system of pipes are by no means limited to the possibilities that have been discussed above, of course, with several other configurations being possible. Thus it is, for example, possible to have pipes  7  and  10  extend at an angle to each other in the horizontal plane as well. 
     In the above, a possibility of slidably mounting pump block  20  on its foundation in order to accommodate expansions in pipes  7  and  10  has been discussed, whereby pipes  7  and  10  transmit the expansion forces to pump block  20  themselves, as a result of which the block is slightly moved. On the other hand, it is also possible to activate driving means by means of a temperature signal or an expansion signal. The driving means will move pump block  20  over a certain distance, which is determined on the basis of the signal being delivered. 
     FIG. 5 shows another embodiment of a pump system according to the invention. The parts shown in this figure are numbered the same as in FIG.  1 . Bidirectional flow pipe  7  of this pump system is provided with an intermediate pipe  50 , which is connected to pipe  10  by means of a flange  51   b , and which is connected to supply and discharge pipes  2  and  3  by means of a flange  51   a . Analogously to what is shown in FIG. 1, intermediate pipe  50  normally forms part of bidirectional flow pipe  7 , in which medium  5  collects. The embodiment of the pump system as shown includes a partition element  52  in the intermediate pipe  50  (also called bidirectional flow pipe  1 ). The partition element  52  can freely reciprocate in the direction of the axis of intermediate pipe  50 . To this end, partition element  52  is provided with guides  54 , and it is slidably mounted on a guide bar  53  extending along the central axis of intermediate pipe  50 . The guide bar  53  is connected to intermediate pipe  50  near flanges  51   a  and  51   b , in a manner which is known, but which is not shown. 
     The freely movable partition element  52  forms a more or less physical partition in bidirectional flow pipe  7 , and impedes to a considerable extent transport of the hot and frequently corrosive medium  5  in the direction of pump casing  16 . It has become apparent that the hot medium  5  moves slowly in the direction of pump casing  15  as a result of the periodic suction and delivery phases of membrane  15 . Thus, the placing of partition element  52  provides additional protection of the pump casing and membrane  15 , whilst it furthermore prevents unnecessary loading of heat exchanger  11 . 
     This arrangement makes it possible to lower the requirements that are made of heat exchanger  11 , thus enabling a simpler and cheaper construction thereof. Furthermore, pump casing  16  and in particular membrane will be loaded to a much smaller extent by the hot medium  5 , as a result of which the life of these components is considerably prolonged. Consequently, the requirements made of the construction may be lowered as well, which enables a cheaper overall installation. 
     Another aspect of the invention is indicated at  55 . Numeral  55  indicates mixing means, which are placed in pipe at the location of heat exchanger  11 . In this embodiment the mixing means  55  consist of a large number of blades  56 , which are mounted on a shaft  57  extending along the central axis of pipe  10 . Alternatively, the blades  56  may be mounted on the inner wall of pipe  10 . The mixing means have a mixing effect on medium  5 , such that medium  5  is placed into proper heat-exchanging contact with the wall of pipe  10  of heat exchanger  11 . The mixing action of the mixing means consists primarily of increasing the flow turbulence of medium  5  in pipe  10 , which functions to increase the contact between heat exchanger  11  and the hot medium and thus obtain a greater cooling effect on hot medium  5 . In particular, if medium  5  exhibits a flow behavior with predominantly low flow velocities, the static mixing means  55  will increase the turbulence of the hot medium considerably, thus increasing the cooling effect which heat exchanger  11  has on the medium. 
     FIGS. 6 a  and  6   b  show two embodiments of the partition element according to the invention. The two figures show intermediate pipe  50 , which can be fitted into bidirectional flow pipe  7  of FIG. 5 by means of flanges  51   a  and  51   b . Analogously to FIG. 5, FIG. 6A shows a guide bar  53 , which is disposed along the central axis of intermediate pipe  50 , and which is fixedly connected at its ends  60   a  and  60   b  to flanges  51   a  and  51   b  respectively in a manner which is known per se. A partition element  52  provided with suitable guide means bar  54  is mounted over the guide bar  53  in a manner which allows free reciprocating movement. Partition element  52  at least partially shuts off the passage through intermediate pipe  50 . In the embodiment shown in FIG. 6 a , partition element  52  is configured as a disc-shaped element having a diameter which is smaller than the diameter of pipe  50 . The disc-shaped element is preferably made of a flexible, heat and corrosion resistant rubber material, so as not to affect the pumping action of the membrane pump, in particular when the pump system is being started. FIG. 6 b  shows another embodiment of the partition element according to the invention. Analogously to FIG. 6 a , a guide bar  53  is mounted along the central axis of intermediate pipe  50 , which guide bar is fixedly connected at its ends  60   a  and  60   b  to flanges  51   a  and  51   b  respectively in a manner which is known per se. Partition element  61  of this embodiment is elongated, however, and is built up of a number of through channels  62 , which are arranged in a row around guide bar  53 . This is shown in section A—A of FIG. 6 b . Unlike the embodiment shown in FIG. 6 a , the partition element  61  of this embodiment is not capable of free reciprocating movement, but it is fixedly mounted on guide bar  53 . 
     The presence of channels  62  allows hot medium to pass in the direction of heat exchanger  11  and pump casing  16 . During the suction phase of the membrane pump, the medium flowing in will exhibit a turbulent flow behavior, which turbulence is converted into a laminar flow by channels  62 . As a result of this, the convection of heat in the direction of heat exchanger  11  and pump casing  16  (and membrane  15 ) will decrease considerably, and the constructional demands to be made of heat exchanger  11  and pump casing  16  may be lowered. 
     This makes it possible to achieve a simpler and cheaper construction. 
     It will be apparent that also the disc-shaped element  52  shown in FIG. 6 a  may be provided with a number of through channels. The partition element may be configured in the form of a sphere, which is provided in pipe  50  in a manner which allows free reciprocating movement. Also a brush-shaped element provided with a large number of protrusions will be satisfactory.