Liquid purification or separation – Flow – fluid pressure or material level – responsive – Fluid current controlled cyclic system
Reexamination Certificate
1999-05-20
2001-03-20
Walker, W. L. (Department: 1723)
Liquid purification or separation
Flow, fluid pressure or material level, responsive
Fluid current controlled cyclic system
C210S137000, C210S321660, C210S416100, C137S513300, C417S399000, C417S377000
Reexamination Certificate
active
06203696
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a fluid driven pump suitable for use in a reverse osmosis or filtration system for example a water purifying system, and to a system employing such a pump.
The preferred embodiment of the current invention provides a high pressure fluid output flow from two or more lower pressure fluid input flows. It is specifically but not exclusively intended to provide high pressure water for purification by reverse osmosis, where water contaminated by unwanted solutes is forced, at a pressure of typically 60 bar, through a semi-permeable membrane, effectively filtering out those solutes. This process is typically used for desalination of seawater.
It is a characteristic of reverse osmosis that the flow of contaminated water across the membrane needs to be typically ten times greater than the flow of purified water through the membrane, the excess flow acting to flush away contaminants accumulated at the membrane surface. In the simplest systems, this high pressure flushing flow is released to waste, taking with it, and wasting, typically 90% of the energy used to provide the high pressure input flow.
There are established methods to recover the energy contained in the high pressure flushing flow . . .
It may be used to drive a hydraulic motor mechanically coupled to the pressurising pump, with the balance of energy input provided by, for example, an electric motor. This method is complex and consequently expensive, with inevitable inefficiencies in the indirect mechanical transfer of energy. Standard, relatively inexpensive, hydraulic motors cannot be used since they are designed for use with hydraulic oils, relying on them for lubrication.
It may be used more directly to provide part of the energy used by the pressurising pump. U.S. Pat. No. Re.32,144 and U.S. Pat. No. Re.33,135 describe mechanically driven reciprocating-piston pumps where one side of the piston and cylinder act as a pump and the other side acts as a motor, driven by the flushing flow to provide most of the pumping power.
A further characteristic of reverse osmosis is that the contaminated water input flow needs to be thoroughly filtered, to prevent clogging of the membrane by particulates. It is often cost-effective to provide an additional low-pressure pump to drive the contaminated water input flow through the filter, since this allows a higher pressure drop across the filter, typically 1 bar, enabling a smaller and cheaper filter to be used. Without this additional pump, the pressure drop across the filter would limited to around 0.5 bar by the poor ability of the high pressure pump to suck against low pressures. The additional pump will also be required if, as is often the case, the high pressure pump is not self-priming.
The preferred embodiment of the invention is directed to avoiding or mitigating at least some of the disadvantages of these known devices.
SUMMARY OF THE INVENTION
In one aspect the invention provides a reverse osmosis or filtration system comprising a semi-permeable membrane or filter, a pump arranged to supply all high pressure fluid delivered to the membrane or filter, part of the said fluid passing through the membrane or filter as purified or filtered fluid, the remainder being a flow of return or flushing fluid which is returned to the pump, the pump being powered only by the return fluid and by an inlet flow of pressurised fluid to be purified or filtered.
The pump may comprise reciprocable means bounding a pair of first pressure chambers which alternately receive and exhaust return fluid to reciprocate the reciprocable means and a pair of second chambers also bounded by the reciprocable means and which alternately receive the pressured inlet fluid and deliver fluid at high pressure to the semi permeable membrane or filter.
The swept volume of the second chamber may be greater than that of the first chamber.
There may be valve means for controlling the admission and exhaust of pressure fluid to and from the first pressure chambers, the valve means comprising bistable elements elements movable between two positions and stable only in those positions, responsive to fluid pressure across them.
The valve means may comprise a plurality of primary poppet valves each having a secondary bleed valve to reduce a force necessary to operate the valve.
It will be appreciated that the pistons need not be part of a single reciprocable body (although this is preferred) nor need they reciprocate linearly. For example the invention can be realised using angular reciprocation.
However it is preferred that the reciprocable means comprises two double-acting pistons reciprocable in respective cylinders with co-linear axes, opposite faces of each piston respectively bounding a said first and a said second chamber defined by the cylinder, said pistons being joined by a common piston rod passing through a wall between the inner ends of the two cylinders, valve means to control fluid flow in and out of the enclosed volumes in each cylinder at either side of each piston, the pump having two alternating working strokes, a first working stroke supplying fluid to the membrane or filter from the outer face of the first piston and fluid to waste from the inner face of the second piston, the return or flushing flow being applied to the inner face of the first piston, the pressurised inlet flow being applied to the outer face of the second piston, a second working stroke being the reverse of the first working stroke.
In another aspect the invention provides a fluid operated pump comprising reciprocable means having a pair of first pressure surfaces and a pair of second pressure surfaces each bounding a respective first and second pressure chamber, control valve means to supply pressure fluid alternately to the chamber bounded by one of the first surfaces and to exhaust pressure fluid from the chamber bounded by the other of the first, surfaces thereby causing the reciprocable means to reciprocate, fluid inlet and outlet valve means communicating with the chambers bounded by the second surfaces whereby the second surfaces pump fluid through the second chambers upon reciprocation of the reciprocable means, the control valve means comprising a plurality of primary poppet valves each having a secondary bleed valve to reduce a force necessary to operate the valve.
The pistons may be coaxial and the first surfaces of the pistons may face in opposite directions.
The pressure chambers bounded by the first pressure surfaces may be arranged between those surfaces and separated by common wall structure.
The control valves may be operated by the pistons when the pistons reach the extremities of their stroke.
Preferably a said control valve is disposed in the common wall structure.
Two said control valves in the common wall structure may comprise a moveable element which is common to both valves.
A said control valve may comprise a moveable element stable only at the extremes of its travel.
The second surfaces may be of greater effective area than the first surfaces.
It is a feature of the preferred forms of the invention that single moving elements each act as both pump and motor, with the driving pressure applied to one part of each element while another part pressurises the pumped flow. In the preferred embodiment the pumps provide the high pressure input flow to the semi-permeable membrane, and are driven by the motors. One motor is powered by the high pressure flushing flow leaving the membrane, while the other is powered by the contaminated water input flow. This input flow is provided at moderate pressure, typically 5 to 10 bar, by a separate pump, which may be of a conventional type.
The benefits provided by the preferred embodiment of the current invention are . . .
It recovers the energy otherwise wasted in the high pressure flushing flow, increasing system efficiency typically by a factor of ten.
It has minimal mechanical losses, since the driving pressure is applied as directly as possible to provide pumping effort.
It offers great simplicity, and consequent low manufactur
Cecil Terry K.
Hodgson Russ Andrews Woods & Goodyear LLP
Walker W. L.
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