Patent Application
20180251204
Exemplary embodiments of the invention relate to a method for filtering seawater, in particular onboard a ship.
Seawater taken onto ships as ballast water from a body of water contains numerous impurities and living organisms such as bacteria, seaweed, plants etc. Current environmental regulations therefore require that ballast water, which has been taken onboard, be purified, for example filtered, and then optionally additionally be subjected to UV irradiation and/or ultrasonication before it can be transferred as purified ballast water into ballast water tanks provided for this purpose.
Such a filter apparatus is known, for example, from German patent document DE102009054387 A1 or WO 2011 064 260 A1. This apparatus has the disadvantage that a relatively large quantity of water is flushed out together with the concentrate and does not reach the ballast water tank.
In view this background, exemplary embodiments of the invention provide an efficient method for filtering seawater, which may then be subjected to a post-treatment such as UV irradiation and is then usable as ballast water.
Exemplary embodiments of the invention implement an adaptive filter control measure that always adapts filter cleaning to actually prevailing requirements. Filtration reliability is greatly improved as a result and at the same time the flow of filtrate to the ballast water tanks is maximized.
Monitoring the state of contamination of a filter by establishing the differential pressure (pressure in the filter inlet minus pressure in the filter outlet) is indeed already known per se, for example from German patent document DE10 2006 045 558 A1 or PCT International patent document WO 2007 130 029 A1. These documents disclose that exceeding a differential pressure limit value is used to flush the filter clean again by reversing the flow direction of the medium to be filtered. This procedure has the disadvantage that the filtration process or filtering method has to be interrupted while the backflushing is to be carried out for example with the assistance of appropriate valves and pipework. In contrast, exemplary embodiments of the invention take a more advantageous approach.
The invention is described below by way of exemplary embodiments with reference to the drawings, in which:
The installation of
The filtration apparatus comprises a tank 5 in which a cylindrical filter element 6 is arranged. The inlet 3 opens into the tank 5 at one end of the tank 5 in such a manner that the seawater which is pumped with the pump 4 into the tank 5 from the body of water (not shown) is passed into the interior of the cylindrical filter element 6. In the filtration device 2, the seawater flows through the filter element 6, wherein a “contaminant phase” of contaminant particles and living organisms together with a fraction of seawater is separated as a concentrate. The purified seawater flows through the filter element from the inside outwards and forms the filtrate. Optionally after having passed through further purification stages, the water is usable onboard the ship as ballast water.
An outlet 7 from the tank 5 for the filtered ballast water is located radially outside the filter element 6. An outlet line 8 is provided at the outlet 7, with which line the filtered ballast water can be passed directly or via further purification stages (for example one or more filtration stages and/or an irradiation stage or the like) into at least one ballast water tank 9 for filtered ballast water. The outlet line 8 includes a preferably actuatable control valve 10 that can be used to vary the cross-section of the outlet line 8.
A cleaning device 11 is preferably arranged within the cylindrical filter element 6. The cleaning apparatus 11 is designed to detach contaminants from the filter element 6 and to discharge, in particular aspirate, a contaminant concentrate phase consisting of water and the contaminants from the filter element 6. To this end, the cleaning apparatus comprises a means 12 for cleaning the filter element 6, a drive 18 (preferably a motor) for moving the means 12 on the filter element 6 and a discharge line 13 for discharging the contaminant concentrate phase.
According to
A drive 18 serves to rotate the shaft 16. When the shaft 16 is rotated, the aspiration elements 14 move along on the inside surface of the filter element 6 and clean the latter of contaminant particles which they detach and aspirate there. In addition, displacement of the aspiration elements 14 and/or the shaft 16 may be provided, in particular in the axial direction, in the tank, to allow the filter element 6 to clean the entire inner surface. Alternatively, the aspiration elements 14 can overlap axially if they are arranged at an angular offset (viewed in the circumferential direction of the shaft 16). An aspiration pump 25 (
Contaminants are detached onto/with the aspiration elements 14 and, together with a seawater fraction, passed as a concentrate or contaminant phase out of the tank 5 through the arms 15 or lines on the arms and through the shaft 16 or a line on the shaft 16. A line portion 19, which is downstream of the shaft 16, of the discharge line 13 here disposes of the contaminant phase, for example in a disposal area (not shown). It is desirable for the smallest possible fraction of seawater to be present in the contaminant phase.
An actuatable control valve 20 and/or the previously mentioned speed-controlled aspiration pump 25 (
The sensors 22, 23, 24 in particular sense the following pressures:
sensor 22: an inlet/input pressure P_in within the filter element 6,
sensor 23: a filtrate outlet pressure/output pressure of the filtrate or ballast water P_out outside the filter element 6; and
sensor 24: a concentrate pressure P_conc. (concentrate) in the discharge line 13.
The sensors 22, 23, 24 or corresponding pressure transmitters for P_in, P_out and P_conc. may be mounted in the filter tank 5 within and outside the filter element 6 or in adjoining (pipe)lines (inflow lines or outflow lines 1, 8, 13).
Advantageous methods for filtering seawater taken from a body of water in order to obtain ballast water can be implemented using the installation shown.
The following parameters are here established with the control apparatus:
contamination pressure difference ΔPF:=P_in−P_out; and
aspiration pressure difference ΔPK:=P_out−P_conc.
In particular, a method for filtering seawater onboard a ship for obtaining ballast water is thus implemented with the filtration device 2, which comprises the, in particular, cylindrical filter element 6 arranged in the tank 5 and the cleaning apparatus 11 for detaching contaminants from the filter element 6 and for discharging the concentrate phase consisting of water and the contaminants from the filter element and from the filtration device 2; with the following steps:
A change in filter efficiency is here simply identified in that a change in contamination pressure difference ΔPF is established.
The contaminant particles or contaminant phase and some of the seawater are preferably and structurally simply aspirated on the inner side of the filter element 6 in the tank 5 by means of the aspiration elements 14 which, during operation, are constantly or in any event from time to time in rotation with the shaft 16.
The aspiration elements 14 roll in motor-driven manner on the inner side of the filter element 6. As the contaminant loading of the seawater increases, the load on the filter element 6 also increases and the contamination pressure difference (P_in−P_out) rises. The seawater aspirated by means of the aspiration pressure difference ΔPK is disposed of, for example is passed directly back into the sea, is in this manner lost from the ballast water and thus does not reach the ballast water tanks. This effect should be minimized as far as possible.
One condition for increasing filter efficiency of the filter element 6 consists by definition in a rise in the contamination pressure difference ΔPF.
According to one advantageous variant of the invention, in the event of an increasing contamination pressure difference ΔPF, the aspiration pressure difference ΔPK, and thus the aspirated quantity of water, is raised. This control measure also operates in the reverse direction: in the event of a falling contamination pressure difference ΔPF, the aspiration pressure difference ΔPK and thus the quantity of water aspirated or lost or discharged with the contaminant phase is reduced. In this case, the loss of water due to the aspirated water is reduced and the efficiency of the method or installation increases. As a consequence, the time required for ballasting is shortened.
The aspiration pressure difference ΔPK is preferably adjusted as a function of the contamination pressure difference ΔPF, in particular in a range from 0 to 5 bar, preferably 1.2-2.2 bar, since these values have proved particularly advantageous for efficient operation of the installation.
It is furthermore advantageous if, according to a further variant of the invention, the frequency of aspiration (f motor) per m2 filter area is raised in order to reduce the contamination pressure difference ΔPF. This means that the motor speed of the drive 18 or the shaft 16 is modified or adapted. In this method variant, an increasing contamination pressure difference ΔPF accordingly leads to an increase in rotational speed of the shaft 16 and vice versa. The mechanical load on the aspiration elements 14 is adapted to the actual requirement. Unnecessary wear is avoided. In addition, or alternatively, the volumetric flow rate [m3/h] aspirated with the aspiration pump 25, if present, may be raised and/or the control valve 20 opened wider.
The rotational speed of the shaft 16 or thus of the aspiration elements 14 is set at a rotational speed of between 0 and 100 rpm, preferably between 12 and 50 rpm.
According to a further advantageous variant of the invention, the volumetric flow rate (filtrate flow) of seawater through the filter element 6 of the filtration device 2 is reduced if the contamination pressure difference ΔPF exceeds an upper limit value (of for example 1.1 bar). The described control measures on the valves 10, 20 and/or an aspiration pump 25 and/or a rotational speed of the shaft 16 are then already running at the maximum values. The volumetric flow rate [m3/h] is reduced until the contamination pressure difference ΔPF falls below a lower limit value (for example 0.9 bar). The volumetric flow rate [m3/h] and thus the filter load are consequently adapted to the maximum possible filter cleaning and clogging of the filter element 6 is prevented. It is ensured that intake of ballast water need not be interrupted if the water has a very high contaminant loading.
The maximum or possible volumetric flow rate [m3/h] may optionally be raised, in particular in steps, by parallel connection of further filtration devices 1 or filter inserts 6 in the tank 5.
The aspiration pressure difference ΔPK is preferably increased by means of modifying the cross-section in the discharge line 13 by opening the control valve 20. Should this prove insufficient, the pressure P_conc. is optionally additionally further reduced, in particular in the discharge portion 19 for the concentrate, with the preferably speed-controlled aspiration pump 25, see
In
By way of example, the method according to the invention is here implemented with regard to steps e) and f) as illustrated in
According thereto, the contamination pressure difference is again denoted ΔPF=P_in−P_out and the aspiration pressure difference is denoted ΔPK=P_out−P_conc.
The state ΔPF<=0.8 bar is denoted “filter clean” or “filter element clean”. Control valve V1 is open, valve V2 is throttled to reduce concentrate discharge and a low rotational speed is set for the drive M1 for the shaft 16.
The state 0.8 bar <ΔPF<=1.1 bar is denoted “filter contaminated” or “filter element contaminated”. Control valve V1 is open, valve V2 is opened wider to increase concentrate discharge and a higher rotational speed is set for the drive M1 for the shaft 16.
The state ΔPF>1.1 bar is denoted “filter severely contaminated” or “filter element severely contaminated”. In order to avoid overloading the filter element, control valve V1 is throttled, valve V2 is opened to increase concentrate discharge and a higher rotational speed is set for the drive M1 for the shaft 16. If necessary, aspiration pump P2 may additionally be started in order to raise concentrate discharge further.
The actual increase or reduction may be achieved by pre-stored functions or functional interrelationships which have been established by testing. In this manner, interrelationships ΔPK=function_1 (ΔPF) and rotational speed M1=function_2 (ΔPF) may be established which are then used for adjustment/control in the stated ΔPF states.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 114 473.5 | Aug 2015 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/069529 | 8/17/2016 | WO | 00 |
