Patent Description:
Screw and piston compressors for compressed air (but also other types of machinery such as marine engines) have the problem of producing large quantities of waste liquids in aqueous solution/ suspension that are very polluting and, if disposed, they are classified as special waste. The main pollutants present in these wastewaters are oily substances, for example lubricating oil used in compressors or other machinery. It is therefore necessary to treat this wastewater to separate oily substances from water.

The current common solution on the market, used to separate water from oily substances, is the use of coalescence filters, which however present several problems (soiling, reliability, degressive filtration, concentration limit, need for periodic maintenance, replacement costs, etc.).

<CIT> discloses an oil/water separator to separate the oil contained in the condensing water of a compressor. The separator uses an infrared lamp to heat and evaporate water selectively compared to oil. This apparatus, however, has a high energy consumption, since the evaporation of water uses electricity and consequently has a significant operating cost.

<CIT> discloses an apparatus to concentrate wastewater wherein wastewater is introduced into the jacket of a beam heat exchanger. Water evaporated is compressed and used in the tubes of the heat exchanger. The apparatus comprises an external tank wherein oil and water separate.

<CIT> discloses a compact array of vertical rising film evaporators in an evacuated multi-effect process for desalination of sea water using waste heat of thermal machines.

There is therefore a need for a new apparatus for the concentration of wastewater containing oily material that is efficient and presents low running costs.

The invention is directed to an apparatus for the concentration of wastewater containing oily substances, the apparatus comprising: a shell and tube heat exchanger, positioned vertically along the internal perimeter of the apparatus; a tank positioned inside the heat exchanger, wherein wastewater is stocked; an entrance pipe, for the entrance of wastewater, which pipe feeds a mechanic system which allows wastewater to percolate along an internal wall of tank; a pipe that connects the bottom of the tank to suction of a first pump; a pipe connecting the mandate of the first pump to a distribution plate of a heat exchanger; a pipe connecting a bottom of the heat exchanger where concentrated water percolating into the pipes collects, with a suction of a second pump; a pipe connecting a mandate of second pump with the bulk of the tank; an exit pipe connected to a ventilator, preferably centrifuge, that draws vapor into an exit from a head of the heat exchanger; a system for collecting and discharging the condensed vapor; a system that maintains a level in the tank, which system is connected to a collection pipe (<NUM>) that leads the withdrawn liquid to a collecting bin or to a disposal system.

The invention is also directed to a process for recovering oil from wastewater of at least one water cooled apparatus, which process comprises: collecting wastewater from the at least one water cooled apparatus; sending the collected wastewater to the above defined apparatus; recovering concentrated oil containing no more than <NUM>% water at the outlet pipe.

The invention is further directed to a system comprising: at least one water cooled apparatus; an apparatus for the concentration of wastewater as above defined; wherein an exit of cooling water of the at least one water cooled apparatus is connected with the entrance of heating water in the heat exchanger of the apparatus for the concentration of wastewater.

The invention is directed to an apparatus for the concentration of water containing oily substances, which apparatus uses the heat recovery of the machinery/apparatus from which the wastewater comes. Wastewater from a compressor has a lubricating oil content ranging from about <NUM> % by weight to about <NUM>% by weight, depending on the type of compressor and the operating conditions. The apparatus of the present invention allows recovery of highly concentrated oil from wastewater without energy consumption since evaporation of water is performed by recovering heat generated by a water cooled machinery, e.g. a water cooled compressor.

<FIG> shows a side view in section of an apparatus <NUM> according to the invention. Wastewater is sent to the central tank <NUM>, surrounded by the exchanger <NUM>, via the upper inlet tube <NUM>. The inlet flow (which can also be discontinuous) is percolated on the inner wall of the tank by a mechanical system <NUM>. In a preferred embodiment, the mechanical system <NUM> consists of an expansion chamber to expand the liquid that arrives under pressure, decreases the speed of liquid and prevents that the liquid already present in the tank undergoes perturbations that may compromise the stratification process. In a preferred embodiment, the mechanical system <NUM> consists of a small compensation tank to slow down the incoming flow, and a slit that allows the liquid to flow along the inner wall of the tank. The size of the slit depends on the flow of wastewater that is fed to the appliance. The higher the flow, the greater the area of the slit section that allows the liquid to reach the central tank. In a preferred embodiment, for an apparatus that receives from about <NUM> to about <NUM>/h of wastewater, inlet pipe <NUM> has preferably a diameter of from <NUM>" (<NUM>) to <NUM>" (<NUM>), and the slit will have a size from <NUM> to <NUM> times the diameter of the inlet pipe.

In tank <NUM>, water tends to settle at the bottom of the tank, while oil, having a lower density, tends to separate and form a layer above water. The first pump <NUM> draws water having a low oil content from the bottom of the tank and sends it to the distribution plate <NUM> of the heat exchanger <NUM>. In pipes <NUM> water is partly evaporated and the residual mixture water/oil is collected in reservoir 115frmed in the lower part of the heat exchanger. In this reservoir <NUM> is preferably present a conductimetric level probe. The second pump <NUM> is activated and deactivated by the level of the reservoir <NUM>. When the level reaches a set maximum, pump <NUM> is turned on, and when reaching a set minimum the pomp turned off.

<FIG> is a top view in section along plane C of the apparatus of <FIG>. The figure shows the first pump <NUM>, the second pump <NUM>, the heat exchanger <NUM>, pipe <NUM>, and collection pipe <NUM>.

<FIG> is a detail of <FIG>, in which the upper profile of the tubes of the heat exchanger is shown. From this figure it is possible to better see the distribution plate <NUM> and the tubes <NUM> protruding from the plate, and the groove <NUM>, preferably V shaped.

<FIG> is a cross-section view along the plane J of the upper right part of the apparatus. The figure shows the "cap" device <NUM> mounted at the outlet of the heat exchanger supply pipe <NUM>.

<FIG> is a side view in section along the plane E of the apparatus. The figures shows the weir <NUM> and outlet pipe <NUM>, connected to the weir by collection pipe <NUM> (not shown).

<FIG> is a side view in section of an apparatus according to the invention, having circular section. A circular section is advantageous because it allows a better flow in the jacket of the heat exchanger, it is easier and cheaper to realize and allows the use of helical flow conveyors. This conveyor allows an optimal heating of all pipes in the heat exchanger and is particularly useful when water temperature is moderate. The helical flow can be derived by the position of sets <NUM> which are at a different level on the left and on the right of the heat exchanger. Furthermore, in <FIG> it is present an optional feature of the apparatus according to the invention, i.e. a three-way valve <NUM>.

<FIG> is a scheme of the system according to invention comprising three compressors and one apparatus for the concentration of wastewater. The apparatus <NUM> receives wastewaters from compressors <NUM>, <NUM> and <NUM> through pipes <NUM>, <NUM> and <NUM> which joins into pipe <NUM> on which, before entry into the tank, is present an optional three-way valve <NUM>. The heat exchanger of the apparatus <NUM> is fed by water exiting compressor <NUM> and returns to the cooling circuit of compressor <NUM> through pipe <NUM>.

In the apparatus according to the invention, the central position of the tank allows wastewater to be kept warm, avoiding heat dispersions. The heat exchanger <NUM> placed around central tank <NUM> is preferably a thin film shell and tube heat exchanger. A pump <NUM>, fed by a suction pipe <NUM> placed at the bottom of the central tank <NUM>, sends the cleanest water present at the bottom of tank <NUM> via pipe <NUM> to the distribution plate <NUM> at the head to the shell and tube exchanger <NUM> vertically mounted.

Preferably, tank <NUM> comprises a conductimetric level probe and a regulation system connected to it. Since oil has a low conductivity, the probe measures the level of water within central tank <NUM>. If the level is too low, the regulation system stops the first pump <NUM>, avoiding that, by evaporation in the heat exchanger, the amount of water in the tank further decreases. If the level is too high, the regulation system reacts, for example by closing valve <NUM> shown in <FIG>, placed on the pipe <NUM> that feeds wastewater to the tank <NUM>. This valve avoids the entrance of wastewater to the tank when water level within tank <NUM> is above a maximum level. The presence of the three-way valve is however optional. Alternatively, in case of a too high level of water in tank <NUM>, it is possible to heat up water coming entering the heat exchanger. In this way, it is possible to increase heat exchange and lower the level of water in the tank.

The level of water in the tank <NUM> is preferably maintained in a correct range, e.g. between <NUM>% and <NUM> %, preferably between <NUM> and <NUM> % of the maximum level of the tank, e.g. the level defined by the level regulation system e.g. weir <NUM>. If the level is too low, there is the risk that water pumped from first pump <NUM> contains a too high amount of oil, if the amount is too high, the oil recovered from outlet pipe <NUM> contains a too high amount of water.

In a preferred embodiment, it is used a "cap" system <NUM>, purposely studied and mounted to the exit of pipe <NUM> feeding the distribution plate of the heat exchanger, that allows the fluid to spread evenly along the entire upper surface of the plate <NUM> feeding in the same way every single tube <NUM>.

Tubes <NUM> protrude from the plate of a height that can vary from about <NUM> to about <NUM>, preferably from about <NUM> to about <NUM>. Thus, during operation, a layer of liquid is formed on plate <NUM> approximately equal to the height of the hinge of tubes <NUM> on the plate. Preferably, each individual tube <NUM> also presents "V" grooves <NUM> at the top end; these grooves allow the liquid to enter gradually and in a distributed way into the tube, creating a liquid film on the inner surface of the tube. The liquid flows along the inner wall of the tubes allowing the formed vapour to rise upwards. The hot liquid accumulates in the lower part of the exchanger. A second pump <NUM> sends the concentrated liquid into the central tank through tube <NUM> to a height where the concentration of oil in the liquid in the tank is similar to the concentration of oil in the liquid in tube <NUM>. In a preferred embodiment, the tube <NUM> enters the tank at a height between ½ and ¾ of the total height of the liquid in the tank. The functioning of pump <NUM>, in a preferred embodiment, is discontinuous and the pump is activated when the level of liquid in the bottom of the exchanger reaches a predetermined value. This operation is also calibrated so as not to disturb and mix the surface of the liquid. Both (low power) pumps are therefore controlled by a level logic and therefore have a discontinuous operation and absorption over time.

In a preferred embodiment, the heating water enters the jacket of the heat exchanger <NUM> from the bottom and comes out from the top, thus it has an inverse path compared to the wastewater that enters from the top and descends by gravity downwards. Thus, in a preferred embodiment, the heat exchanger works counter current. To increase efficiency (especially at low temperatures), a series of intermediate septa between inlet and outlet may preferably be fitted, making the water path compulsory and layered to lap and heat all pipes equally. The large heat exchange surface allows the equipment to work well even with recovery water at low temperatures (<NUM>-<NUM>) that derive, for example, from the return of steam condensation, engine and compressor cooling, process heat recovery, etc..

Water evaporated in tubes <NUM> is then discharged either as vapour or as condensed liquid. Vapour rises upwards and partly condenses in the dome of the apparatus, whose outside surface is in contact with external air, at ambient temperature. Water condensed in the dome or in exit pipe <NUM> is collected on surface <NUM>. A fan, preferably centrifugal, on the outlet pipe <NUM> of the apparatus removes wet steam present in the overhead of the apparatus creating a slight depression. The apparatus according to the invention also provides a system to collect and discharge condensate. In a preferred embodiment, water that condenses in the upper part of the apparatus is collected through a funnel <NUM> that conveys the condensate into tube <NUM>. The water thus collected can be discharged into sewage or surface water having a degree of purity in line with the ARPA parameters established by law.

The level of the tank is kept constant by means of a tank level adjustment system. A simple and effective way to adjust the tank level is through a weir <NUM> placed on the wall at the top of the tank. In order to minimise possible disturbances in the composition of the liquid leaving the tank, the level regulation system shall preferably be placed in a distal position relative to inlet <NUM> of wastewater. Weir <NUM> is connected to a collection tube <NUM> that brings the collected liquid to a collection bin or to a storage and disposal system via outlet pipe <NUM>. The collected liquid shall preferably include at least <NUM> % by weight of lubricating oil, preferably at least <NUM> % by weight of lubricating oil.

Claim 1:
An apparatus (<NUM>) for the concentration of wastewater containing oily substances, the apparatus comprising:
a. a shell and tube heat exchanger (<NUM>), positioned vertically along the internal perimeter of the apparatus;
b. a tank (<NUM>) positioned inside the shell and tube heat exchanger (<NUM>), wherein wastewater is stocked;
c. an entrance pipe (<NUM>), for the entrance of wastewater, which pipe feeds a mechanic system (<NUM>), which allows wastewater to percolate along an internal wall of tank (<NUM>);
d. a pump (<NUM>) and a second pump (<NUM>);
e. a pipe (<NUM>) that connects the bottom of tank (<NUM>) to suction of a pump (<NUM>);
f. a pipe (<NUM>) connecting the mandate of pump (<NUM>) to a distribution plate (<NUM>) of heat exchanger (<NUM>);
g. a pipe (<NUM>) connecting a bottom (<NUM>) of the heat exchanger (<NUM>) where concentrated water percolating into the pipes (<NUM>) of the shell and tube heat exchanger collects, with suction of a second pump (<NUM>);
h. a pipe (<NUM>) connecting a mandate of pump (<NUM>) with the bulk of tank (<NUM>);
i. a ventilator, preferably a centrifuge ventilator;
j. an exit pipe (<NUM>) connected to the ventilator, that draws vapors into exit (<NUM>) from a head of the heat exchanger (<NUM>);
k. a system for collecting and discharging the condensed vapors which condenses in the dome of the apparatus, whose outside surface is configured to be in contact with external air, at ambient temperature;
l. a system that maintains a level in the tank, which system is connected to an outlet pipe (<NUM>) by a collection pipe (<NUM>).