Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Patent
1990-06-04
1991-05-28
Cintins, Ivars
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
210108, 210117, 210123, 210136, 210137, 210793, B01D 3704, C02F 900
Patent
active
050192760
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of purifying water in an open, solid filter bed in which, after the addition of chemicals, the water to be purified is passed through a filter bed, said filter bed being regenerated by counter-flow flushing. It also relates to plant for performing the method.
Conventional water purification using open sand filters comprises the steps of rough separation, mixing in chemicals, flocculation, sludge separation and then filtration through the sand bed. The bed is counter-flow flushed at certain intervals depending on the degree of pollution of the water entering. There are certain drawbacks to this process, one being that the water entering the sand bed must be relatively pure since the resistance caused by pollution build-up will otherwise quickly become too great for the pressure from the available water column to be able to force the water through the sand bed. Furthermore, the capacity is low, primarily because the net production, i.e. the quantity of pure water produced reduced by the quantity of flushing water, is low. The septic tanks also mean that the whole plant will require considerable space.
According to another technique pressure filters are utilized. In this case flocculation takes place after the rough separation, and the flocculated water is pumped into a pressure container in which the water is forced through the filter bed. The drawback here is that poor flocculation is obtained and that no control over the process is possible in the closed tank.
The use of continuous filters offers considerable advantages over the above methods. An example of such a filter is the CAREX filter (reg. trademark), where water is pumped into the bottom of a sand filter and forced up through the sand bed while clean sand is simultaneously added at the top and removed from the bottom of the filter. However, this type of filter is relatively complicated and is best suited to moderate volumes of water. It is far too expensive for small volumes of water, e.g. for individual households, greenhouses and the like.
The object of the present invention is to achieve a method of purifying water with the aid of an open, solid filter bed which offers high capacity and is also suitable for small quantities of water, and also to achieve a plant for performing the method, which is both reliable and economical.
This is achieved by the method according to the present invention which is characterised in that water to be purified in the filter bed is caused by force to flow through a bed at a constant rate by means of a partial vacuum created by a pump means arranged downstream of the bed, the flow being kept constant with the aid of a control valve arranged on the pressure side of the pump. The production of water is thus not dependent on a water column above the bed to force the water through the filter bed. The volume above the filter bed shall only ensure uniform distribution over the bed and that the surface of the filter bed never becomes dry.
According to a preferred embodiment of the method according to the invention, purified water is used to flush the filter bed, the supply of water being cut off when a certain predetermined partial vacuum is sensed on the suction side of the pump, and the bed is then flushed counter to the direction of flow of the water during the water purification phase.
According to another embodiment of the method according to the invention purified water is collected in separate flush and reservoir tanks or the like, control means being arranged to throttle the supply of untreated water when the tank is full, and initiate flushing of the filter bed, the flow of purified water to the flush-water tank is regulated depending on the degree of pollution of the untreated water so that when the tank is full it is time to flush the filter bed. The use of a less sophisticated control system increases operation reliability, giving a plant which is particularly suitable for projects in developing countries. Adjusting the filling rate in the flush tank to the degree of po
REFERENCES:
patent: 1248127 (1917-11-01), Jewell
patent: 3545619 (1970-12-01), Ettlich et al.
patent: 3627131 (1971-12-01), Goodman et al.
patent: 4187175 (1980-02-01), Roberts et al.
Holm Klas
Kock Bengt
BK Va-Leveranser AB
Cintins Ivars
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