Hydraulic pump system for handling a slurry medium

This disclosure relates to a hydraulic pump system for handling a slurry medium comprising at least two reciprocating positive displacement pumps, both pumps being arranged for alternating intake of slurry medium via a suction inlet and discharge of slurry medium via a discharge outlet, and piston/cylinder discharge valves for alternating closing and opening each discharge outlet. In a first aspect, a hydraulic pump system for handling a slurry medium, comprising at least two reciprocating positive displacement pumps, both pumps being arranged for alternating intake of slurry medium via a suction inlet and discharge of slurry medium via a discharge outlet, and piston/cylinder discharge valves for alternating closing and opening each discharge outlet, as well as control means for controlling the alternate closing and opening of both piston/cylinder discharge valves, such that during operation no volume difference occurs in the discharge of slurry medium is disclosed. In another aspect the control means comprise a lever assembly interconnecting the pistons of both piston/cylinder driven valves.

BACKGROUND ART

This disclosure relates to a hydraulic pump system for handling a slurry medium at least comprising at least two reciprocating positive displacement pumps, both pumps being arranged for alternating intake of slurry medium via a suction inlet and discharge of slurry medium via a discharge outlet, and piston/cylinder discharge valves for alternating closing and opening each discharge outlet.

In reciprocating positive displacement pumps, a displacement element, such as a piston or plunger, undergoes a reciprocating motion inside a cylinder housing enabling the positive displacement the slurry medium to be handled (displaced or pumped). In a particular embodiment of the reciprocating pump, the reciprocating motion of the displacement element is generated by a mechanism which transfers the rotating motion of the pump drive mechanism into a reciprocating motion of the displacement element. Particular embodiments of this mechanism may include crankshaft, excentric shaft, camshaft or cam disc mechanisms, for example as disclosed in FIG. 1 of WO2011/126367.

Such reciprocating positive displacement pumps are used for pumping slurry media against relatively high pressure, when compared to single stage centrifugal pumps, for example. Further characteristics of such positive displacement pumps include high efficiency and an accurate flow output, but a relatively low flow capacity when compared to centrifugal pumps. When the flow requirements of a typical application cannot be met with a single pump, multiple positive displacement pumps can be arranged in parallel in a manner so that their suction inlets and/or discharge outlets are connected and combined into a single suction and/or discharge line. This means that the sum flow of the individual pumps can meet the total flow requirements of the application. The combination of the individual displacement pumps and the interconnecting suction and discharge lines forms a pumping system.

In the aforementioned prior art publication WO2011/126367, a phase shift control system is disclosed for a pump system comprised of multiple reciprocating positive displacement pumps, wherein the speed of the individual pumps is controlled such that a desired phase shift between the pump cycles of the individual pumps is obtained and maintained. Each discharge outlet of the individual pumps is provided with a discharge valve, which is to be opened and closed at the right time during the individual pump cycles of the individual pumps. To create a nearly pulsation-free flow in the discharge outlet, apart from a proper phase shift control of the displacement pumps, the discharge valves also are closed and opened in a controlled manner, preferably such that the pressure across the discharge valve is zero.

To make sure that the pressure across the discharge valve is zero, a pre-compression stroke is performed prior to the opening of the respective discharge valve. Pressure fluctuations in the discharge flow of the displaced slurry medium results in variable consistency during further processing and hence adversely affects the product quality of the slurry medium.

Furthermore the displacement of the valve rods of the respective discharge valves, which are operated independently of each other, create a small change in the flow and therewith a fluctuation in the pressure in the outlet.

SUMMARY OF THE DISCLOSURE

In a first aspect, embodiments are disclosed of a hydraulic pump system for handling a slurry medium, comprising at least two reciprocating positive displacement pumps, both pumps being arranged for alternating intake of slurry medium via a suction inlet and discharge of slurry medium via a discharge outlet, and piston/cylinder discharge valves for alternating closing and opening each discharge outlet, as well as control means for controlling the alternate closing and opening of both piston/cylinder discharge valves, such that during operation no volume difference occurs in the discharge of slurry medium.

In another aspect of the hydraulic pump system said control means comprise a lever assembly interconnecting the pistons of both piston/cylinder driven valves.

In particular said lever assembly comprises a lever having two ends, each end being hingely connected with the piston of one of said piston/cylinder driven valves.

In another aspect said piston/cylinder discharge valves are hydraulic piston/cylinder driven discharge valves and wherein said control means comprise a hydraulic line interconnecting both cylinders of said hydraulic piston/cylinder driven discharge valves.

In one embodiment, the hydraulic line can interconnect both cylinders at the piston side thereof, whereas in another embodiment said hydraulic line interconnects both cylinders at the cylinder side thereof. This means that no volume difference will occur during the closing and opening strokes of both discharge valves as the displaced hydraulic volume during opening of a discharge valve is added via the interconnecting hydraulic line to other discharge valve during closing. Since no volume fluctuations in the discharge flow of the displaced slurry medium will occur, this results in a product (the displaced slurry medium) with the same consistency and hence product quality.

In one embodiment, each hydraulic piston/cylinder driven discharge valve can comprise a first sensor for sensing the position of the piston in the closed position of the discharge valve as well as a second sensor for sensing the position of the piston in the open position of the discharge valve. Thus the opposite extreme positions of the pistons of both discharge valves are electronically monitored, as the assistance of these proximity switches guarantee a synchronized movement of both pistons. In addition, no change in combined volume on the discharge side will occur.

Due to this synchronization the opening of one discharge valve will automatically result in the closing of the other discharge valve and hence no undesired fluctuation in the flow through the discharge outlet will occur.

In one embodiment, the system may further comprise an hydraulic refill means for adding hydraulic medium to a hydraulic piston/cylinder driven discharge valve based on signals generated by the first sensor of a discharge valve and the second sensor of the other discharge valve such that the combined hydraulic volume of both pistons chambers and the interconnecting hydraulic line is always so that the pistons will reach their extreme position during operation of the pump system. In such an arrangement, the opening of one discharge valve will automatically result in the closing of the other discharge valve and unwanted fluctuation in the discharge flow is avoided.

In one embodiment, the pump system can further comprise one or more hydraulic piston/cylinder driven suction valves for alternating closing and opening each suction inlet.

In one embodiment, the pump system can further comprise a pump housing having a central inlet interconnecting both suction inlets as well as a central outlet interconnecting both discharge outlets.

In one embodiment, said pump housing can comprise two pump chambers, each pump chamber being interconnected with one of said reciprocating positive displacement pumps, and each pump chamber being provided with a suction inlet and a discharge outlet. This provides a simple but effective construction of the pump system with limited dimensions is obtained, which is beneficial in case of installation and maintenance.

Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of inventions disclosed.

DETAILED DESCRIPTION

FIG. 1andFIG. 2acombined disclose a non-limitative embodiment of an hydraulic pump system. The hydraulic pump system is denoted with reference numeral10and consists of at least two reciprocating positive displacement pumps100and200which are connected to a pump housing11. Each of the reciprocating positive displacement pumps100and200consist of a pump structure in which a displacement element101(201), shaped as a piston, is movable accommodated in a cylinder housing104(204). The displacement element101(201) is connected via a piston rod102(202), which is displaced in a reciprocating manner using a pump drive mechanism103(203), not shown.

Such a reciprocating positive displacement pump is capable of pumping or handling a slurry medium against relatively high pressure when compared to other types of pumps, such as centrifugal pumps. In particular, a positive displacement pump (as denoted with reference numeral100inFIG. 1) can operate at a high pressure level and generate an accurate flow output of the slurry medium to be displaced, albeit with a relatively low flow capacity. For increasing the flow capacity of the slurry medium to be displaced, multiple reciprocating positive displacement pumps (inFIG. 1two of such pumps100,200are shown) are used in a parallel manner as depicted inFIG. 1and their combined pump characteristic is used for obtaining the required and necessary increased discharge flow of the slurry medium.

The pump drive mechanism103(203) are driven in such a manner that the displacement elements101(201) are moving in a reciprocating manner, but also in an ‘out-of-phase’ manner. This means that one positive displacement pump performs its discharge stroke, whereas the other positive displacement pump performs its suction stroke. The alternating suction and discharge strokes of the two positive displacement pumps results in a combined discharge flow of the individual pumps, the sum of which can meet the total flow requirements of the industrial application in which the hydraulic pump system is to be implemented.

FIG. 2adiscloses in more detail another part of the pump system10in particular the pump housing11to which both reciprocating positive displacement pumps100and200are connected.

The pump housing11is provided with a central suction inlet12and a central discharge outlet18for the intake and discharge of slurry medium to be pumped by the pump system10. For each individual positive displacement pump100(200) the central suction inlet12is in fluid communication with suction inlet chambers14a(14b) via suction inlets13a(13b). Each individual suction inlet13a(13b) can be opened and closed by so-called hydraulic piston/cylinder driven suction valves30a(30b). Each suction valve30a(30b) comprises a valve body31a(31b) which cooperates with the seat of the individual suction inlet13a(13b) when said suction valve30a(30b) is in his closed position. Each valve body31a(31b) is mounted to a piston rod32a′ (32b′), which rod32a′ (32b′) is provided with a piston element32a(32b) which is movable accommodated in a valve housing30a′ (30b′). The piston element32a(32b) and the valve housing30a′ (30b′) define a cylinder chamber33a(33b) which is filled with a hydraulic medium.

The hydraulic medium can be introduced in an alternating manner on either side of the piston element32a(32b) via hydraulic lines34a-35a(34b-35b) and by means of a manifold valve36a(36b) which connects to supply lines P2and T2. Supply line P2contains a reservoir40for hydraulic medium. Supply of hydraulic medium to either side of the piston element32a(32b) causes the hydraulic valve30a(30b) to open or close the respective suction inlet13a(13b) by means of the valve body31a(31b).

Each suction chamber14a(14b) is in fluid communication with the cylinder chamber104(204) in which the displacement element101(201) is displaced in a reciprocating manner during operation.

Each individual suction chamber14a(14b) is furthermore provided with a discharge outlet15a(15b). Both discharge outlets15a(15b) communicates in a combined discharge chamber16and further with the central discharge outlet18.

Both individual discharge outlets15a(15b) are arranged to be opened and closed by discharge valves20a(20b). Each discharge valve20a(20b) comprises a valve body21a(21b) which cooperates with the seat of the individual discharge outlet15a(15b) when said discharge valve20a(20b) is in his closed position.

InFIG. 2a, the discharge valve20bis depicted in its closed position where valve body21bfits in the seat of the discharge outlet15bthereby closing the suction chamber14bfrom the combined discharge chamber16. Likewise the discharge valve20ais in its open position allowing fluid communication between the suction chamber14aand the central discharge chamber16(and hence the central discharge outlet18).

Also depicted inFIG. 2ain this operational situation the suction valve30ais in its closed position having a valve body31awhich closes the seat of the suction inlet13a. Similarly the other suction valve30bis in its open condition allowing the suction inlet13bto be in fluid communication with the central inlet12and the suction chamber14b.

In this operational situation, the positive displacement pump100performs its discharge stroke wherein the discharge element101is displaced in the cylinder104discharging any slurry medium contained in the suction chamber14via the discharge outlet15a, the central discharge chamber16towards the central discharge outlet18, and hence out of the pump system. Likewise the positive displacement pump200performs its suction stroke wherein the displacement element201performs a movement which is contrary to the movement of the displacement element101of the positive displacement pump100during the discharge stroke. During the suction stroke of the displacement element201slurry medium is taken from the central suction inlet12through the suction inlet13binto the suction chamber14b.

In general the intake amount of slurry via the suction inlet is defined by the amount of slurry medium being displaced by the previous discharge stroke of said positive displacement pump.

After completion of the suction stroke of the positive displacement pump200and the simultaneous completion of the discharge stroke of the other positive displacement pump100, the suction valve30bis closed under simultaneous opening of the suction valve30a. Likewise the discharge valve20ais closed whereas the discharge valve20bis opened.

The subsequent suction stroke of the positive displacement pump100causes slurry medium to be taken in the now discharged pump chamber14avia the suction inlet13aand the slurry medium contained in the other suction chamber14bis now being discharged by the positive displacement pump200during its discharge stroke. Said discharged slurry medium is forced through the now open discharge outlet15binto the combined discharge chamber16and towards the central discharge outlet18.

As already described in the preamble of this patent application, an accurate control of the reciprocating pump cycles of the individual pumps is desired to create a nearly pulsating free flow in the central discharge outlet. However in the presently known prior art pump systems, pressure pulsations in the discharge flow still occur for several operational and hydraulic causes.

In the known pump systems, the discharge valves are operated independently. When looking toFIG. 2a, and in particularly to the closed discharge valve20b, it is evident that the valve body21btogether with the part of the piston rod22bextending in the discharge chamber16represents a certain volume, which is not occupied by slurry medium present in the discharge chamber16. At the time of opening of the discharge valve20b, this volume previously occupied by the extended piston rod and valve body becomes available to the overall slurry medium volume in the discharge chamber16. This extra volume becoming available causes a volume drop and hence a temporary pressure drop occurs.

Likewise when closing a discharge valve by displacing the valve body and the piston rod into the seat of their respective discharge outlet, this additional volume is added to the discharge chamber16, causing an additional slurry medium volume change to the slurry medium volume being displaced via the central discharge outlet18and hence a temporary pressure increase. The independent control of the discharge valves in the prior art pump systems creates undesired volume changes during opening and closing which adds to the small pressure fluctuations in the slurry medium being discharged via the central discharge outlet18.

In addition to the above drawback, to make sure that the pressure across the discharge valve bodies21aand21bduring the switching over between the suction and discharge strokes is as minimal as possible, each positive displacement pump performs a pre-compression stroke on the slurry medium to be discharged in their respective pumping chamber14a(or14b) prior to the opening of the respective valve body21a(or21b) of the discharge valves20a(or20b). Such pre-compression stroke is depicted inFIG. 3, which discloses to the pump characteristic and sequence control of one displacement element101(201) of each positive displacement pump. Each pump performs three stages in a sequential manner:

a. First the discharge stroke in which starting from t=0 the velocity is ramped up from the pre-compression velocity to the required discharge velocity V1at tacc.

b. After completing the discharge stroke the pump switches to the suction stroke. The actual required velocity V2of the suction stroke is determined by controlling the time on which the discharge valve of the pre-compressed pump is opened.

c. Finally, the pre-compression stroke, in which the pressure in the cylinder of the pump is pre-compressed to the same pressure as the pressure in the second pump, which performs at that moment the discharge stroke.

However, due to the mass and inertia of the heavy components of such pumps, pre-compression of the slurry medium requires extra drive time and therefore the speed of the respective cylinder is increased during its suction stroke. Unfortunately pressure fluctuations still occur because, in the known systems, the pre-compression of the cylinder is not 100% completed at the moment that the ramp up—ramp down step starts (the switching over between the suction and discharge stroke of positive displacement pumps100and200), which can occur if the filling is lower than expected.

The above drawbacks together with mass and inertia constraints of the pump components still create small pressure fluctuations over the valve body21b(or21b) during the switching over from the discharge towards the suction stroke of each positive displacement pump100(200). Such small pressure fluctuations are undesirable when the slurry medium to be pumped by said pump system has a biomass nature.

Pump systems as described above when used in biomass applications, for example where the slurry medium to be pumped consists of wood pulp, requires no pressure pulsations in the central discharge outlet. No pressure fluctuations in the central discharge outlet18leads to a better biomass product produced in the biomass installation connected to the central discharge outlet18. In practice, it is evidenced that a small pressure fluctuation in the discharge flow leads to a biomass product having a different consistency and therefore an inferior quality.

The pump system10as disclosed inFIGS. 1 and 2ais capable of generating a discharge flow of the displaced slurry medium through the central discharge outlet18with no pressure fluctuations resulting in a constant consistency of the biomass slurry medium. This leads to an improved and constant product quality of the biomass slurry medium for further processing in a biomass installation.

According to the present disclosure, the pump system is now capable in providing a pulsation free flow in the discharge outlet18. This is accomplished by means of control means, which control the alternate closing and opening of both piston/cylinder discharge valves20a-20b, such that during operation no volume difference occurs in the discharge18of slurry medium. InFIG. 2asaid control means comprise a hydraulic line24which interconnects both cylinder chambers23aand23bof the discharge valves20aand20b.

As outlined, each discharge valve20acomprises a valve body21a(21b) which fits in the seat of the discharge outlet15a(15b). The valve body is mounted on a piston rod22a′ (22b′) which ends with a piston element22a(22b), which is movable accommodated in a valve housing20a′ (20b′). The piston element22a(22b) and the valve housing20a′ (20b′) define a cylinder chamber23a(23b) which is filled with a hydraulic medium. Due to the hydraulic interconnection between both cylinder chambers23aand23bvia the interconnecting hydraulic line24, no volume difference between both discharge valves will occur during the simultaneous switching of both discharge valves20aand20bfrom their open and closed position.

This means that once the valve21bof the discharge valve20bis displaced from its closed position towards its open position (as shown inFIG. 2a), the hydraulic medium contained in the cylinder chamber23bis displaced by means of the piston element22bvia the interconnecting hydraulic line24towards the cylinder chamber23acausing the piston element22a, the piston rod22a′ and the valve body21ato be displaced towards the closed position until the valve body21arests in the seat of the discharge outlet15a.

No volume differences will occur inside the discharge chamber16as the slurry medium volume increases, due to the withdrawal of the (volume of) piston rod22b′ into valve housing20b′ (and partly of valve body21b), which will be simultaneously compensated by the slurry medium volume decrease, due to the expansion of the (volume of) piston rod22a′ out of valve housing20a(and partly of valve body21a).

As a result, undesirable pressure differences across the discharge outlet will be avoided, and a fully pressure pulsation free discharge flow in the central discharge outlet18is obtained.

Furthermore, the pre-compression stroke is fully completed at the moment the ramp up—ramp down action is initiated and the sum of the hydraulic medium flows of both cylinders is always 100%.

InFIG. 2athe hydraulic line24interconnects both valve housings20a′ and20b′ (cylinder chambers23aand23b) of the discharge valves20aand20bon the piston side thereof at the side of the piston elements22a(22b). InFIG. 2banother embodiment of a pump system is shown. The embodiment ofFIG. 2bis largely identical to the embodiment of the pump system disclosed inFIG. 2aand described above and also its operation is identical. However inFIG. 2breference numeral24′ depicts a hydraulic line, similar to the hydraulic line24ofFIG. 2a, which interconnects both valve housings20a′ and20b′ of the discharge valves20aand20bon the cylinder side thereof at the side of the piston rods22a′-22b′ opposite to the side of the piston elements22a(22b).

By interconnecting both valve housings20a′ and20b′ via the interconnecting hydraulic line24-24′, these small volume and pressure pulsations are no longer present as the displaced volume of one discharge valve is compensated by the same volume change created by the other discharge valve.

In order to guarantee the simultaneous closing and opening of both discharge valves such that no volume differences between both cylinder chambers23aand23boccurs, in both embodiments shown inFIGS. 2a, 2band 2ceach discharge valve20a(20b) is provided with sensors25a-26a(25b-26b) which detect the extreme positions of the piston elements22a(22b) within the cylinder chamber23a(23b) when in fully closed or fully open position.

In particular, the sensor25a(25b) will generate a signal when the valve body21a(21b) is completely closing their respective discharge outlet15a(15b) as the sensor25a(25b) will properly detect the position of the piston element22a(22b) in that extreme closing position. Likewise sensor26a(26b) will detect the piston element22a(22b) in its other extreme position, meaning that the discharge valve20a(20b) is fully open. In particular the control mechanisms of both of the discharge valves20a-20bare interconnected.

Sensor25a(which detects the fully closed position of the discharge valve20a) is interconnected with the sensor26b(which detects the fully open position of the discharge valve20b) and likewise sensor25b(which detects the fully closed position of the discharge valve20b) is interconnected with the sensor26a(which detects the fully open position of the discharge valve20a). By interconnecting the sensors of both discharge valves20a-20bon opposite sides of the piston element22a-22b, a proper control is obtained as their simultaneous actuation by their respective closing or opening valve guarantees a fully synchronization of the opening and closing of both discharge valves.

This also guarantees that no change will occur in the hydraulic medium volume in both cylinder chambers23a-23band the interconnecting hydraulic line24(24′).

The opening of say the hydraulic valve20b(starting from the situation inFIG. 2) will be detected by the sensor25band will simultaneously also be detected by sensor26aas the discharge valve20ais being moved towards its closed position. The simultaneous actuation of the sensor26band25awill trigger the fully open position of the discharge valve20band the fully closed position of the discharge valve20a. Any deviation of the simultaneous actuation of both sensor pairs25a-26band25b-26awill be a signal that a change in the volume occupied by the hydraulic medium in the cylinder chambers23aand23band the hydraulic line24-24′ has occurred.

Any shortage of hydraulic medium can be supplied via the valve29and interconnecting line24(24′). Likewise any surplus of hydraulic medium can be removed interconnecting line24(24′) and valve29.

InFIG. 2cyet another embodiment of a pump system is disclosed, wherein the control means for controlling the alternate closing and opening of both piston/cylinder discharge valves, such that during operation no volume difference occurs in the discharge of slurry medium comprise a lever assembly240interconnecting the piston elements22a-22bof both piston/cylinder valves20a-20b.

As shown said lever assembly240comprises a lever241having two ends, each end being hingely connected with either piston element22a(22b) of one of said piston/cylinder driven valves20a-20b. In addition and as shown inFIG. 2cthe lever assembly240comprises two sub-lever elements230a-230b, each connected to their respective piston element22a-22bas well as with either end of the lever241.

Preferably each connection is a hinge connection.

The lever241is hingely connected at its midpoint241awith the solid wall.

In the foregoing description of preferred embodiments, specific terminology has been resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as “front” and “rear”, “inner” and “outer”, “above”, “below”, “upper” and “lower” and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.