Abstract:
A filtration system utilizes a heater  40  and a heat exchange subsystem for elevating the temperature of a feed stream to a membrane filtration unit  12.  Upstream from the unit  12,  a solids-liquid stream is divided into two streams  32, 33  that pass through respective heat exchangers  22, 28  wherein heat from the concentrate stream  44  and the permeate stream  34  is transferred to the solids-liquid stream before entering the membrane filtration unit  12.  Flow regulators are provided to equalize the flow rates of the streams passing through the heat exchangers. The invention lowers the viscosity of the feed stream resulting in the benefits of increased filtration capacity and extended membrane life.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a novel and useful filtration system utilizing a heat exchanger. 
     Filtration systems such as those employing membranes have evolved into a preferred system of filtering solids from liquids. It has been found that membrane type filtration apparatuses may be scaled upwardly to fairly large capacities. Membrane filters also are capable of achieving a high degree of separation resulting in crystal-clear permeate. Particle size exclusion is also easily accomplished by selecting the requisite pore size of the membrane, generally from micron size to molecular dimensions. In addition, membranes may be obtained in various types of materials to match the characteristics of the products being separated. 
     A notable advance in the field of membrane separation may be found in U.S. Pat. Nos. 4,952,317 and 5,014,564 in which a membrane system using a vibratory motion to shear the face of the membrane is described, to successfully separate solids and liquids and prevent the membrane from being fouled. Although the vibratory shear system represents a notable advance in the field of membrane separation, limitations still exists due to the flow rate of the solids-liquid slurry being separated. 
     U.S. Pat. Nos. 4,834,874, 4,995,972, and 5,540,846 describe filtration processes in which heat is added directly to a filtration vessel, usually for the sake of vaporizing components therewithin. 
     U.S. Pat. No. 5,520,890 describes a solids-liquid slurry treatment apparatus which utilizes a multifaced catalytic reactor. The gaseous reactants are introduced into a slurry within the tubes of the reactor and a heat exchange medium is circulated around the outside of the tubes to effect a reaction within the reactor. 
     U.S. Pat. No. 5,556,539 describes an apparatus for separating a liquid by inducing shear in a membrane module. Heat is fed to a filtration device to boil the liquid mixture within the reactor to create a vapor drying apparatus. 
     A system for providing a heat exchange in a membrane filtration membrane for the purpose of regulating the viscosity on the liquid-solids mixture would be a notable advance in the field of separations. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention a novel and useful filtration system using a sub-system of heat exchange is herein provided. 
     The system of the present invention utilizes a membrane separator for accepting a solids-liquid inlet stream. The membrane filtration apparatus also includes a permeate and a concentrate outlet for permeate and concentrate streams. The source for the inlet solids-liquid inlet stream may be a holding tank, reservoir, or other similar component. Pump means delivers the solids-liquid inlet stream to the entry or inlet of the membrane filtration apparatus. 
     The inlet stream at the reservoir may lie at ambient temperature, but is heated by a heat exchanger which transfers heat from the permeate stream from the permeate outlet of the membrane filtration apparatus. In this regard, make-up heat may be selectively added to the solids-liquid inlet stream or to the exiting permeate stream from the membrane filtration apparatus. In any case, the heat exchanger reduces the viscosity of the solids-liquid stream entering the membrane filtration system. In many cases the heater used to elevate the permeate stream or the solids-liquid inlet stream may be a boiler of conventional configuration. In certain cases, a second heat exchanger may be employed to transfer heat between the solids-liquid inlet stream and the concentrate stream, also. In such an instance, the inlet stream would be split into first and second solids-liquid inlet streams, one passing through the first heat exchanger and the second passing through the second heat exchanger. Along these lines, a flow regulator may be also used to equalize the flow rates of the solids-liquid inlet stream and the exiting permeate stream from the membrane filtration apparatus. Likewise, another or second flow regulator may equalize the flow rates of the solids-liquid inlet stream to the flow rate of the concentrate stream. In any case, the membrane filtration system may comprise a vibration induced filtration system in which shear is applied across the membrane by an eccentric drive. 
     The concentrate stream exiting the concentrate outlet of the membrane filtration apparatus may be shunted to an evaporator. Thus, the concentrate stream may be further separated into solids and liquid which may be vaporized. The solids portion from the evaporator may be employed as a product or byproduct of the present process. 
     It may be apparent that a novel and useful filtration system has been described. 
     It is therefore an object of the present invention to provide a filtration system utilizing a membrane filtration apparatus which produces a decrease in viscosity of the inlet stream to the membrane filtration apparatus by the use of one or more heat exchangers. 
     A further object of the present invention is to provide a filtration system utilizing a membrane filtration apparatus in which the provision of heat to the inlet solids-liquid stream is able to decrease the size of a comparable non-heated membrane filtration apparatus by a large degree to produce an equal capacity. 
     Another object of the present invention is to provide a filtration system utilizing a membrane filtration apparatus which is far cheaper to manufacture and operate, due to a decrease in viscosity of the inlet solids-liquid stream. 
     A further object of the present invention is to provide a filtration system utilizing a membrane filtration apparatus in which the solids-liquid inlet stream may be optionally heated through the use of heat exchangers for use during all seasons, where the source of the inlet stream varies in temperature between winter and summer. 
     A further object of the present invention is to provide a filtration system utilizing a membrane filtration apparatus in which the use of heat exchangers to elevate the temperature of the solids-liquid inlet stream to decrease viscosity of the system prevents overdesigning of the system and result in the savings of capital. 
     A further object of the present invention is to provide a filtration system utilizing a membrane filtration apparatus in which the capacity of the system may be optionally boosted at certain times to coincide with peak and slack periods of demand, permitting shutting down of the system during slack times without substantial waste. 
     Another object of the present invention is to provide a filtration system utilizing a membrane filtration apparatus which obviates the need for an inventory of membranes since the life of the membranes may be extended by the use of heat exchangers to elevate the solids-liquid inlet stream to the membrane filtration apparatus. 
     Another object of the present invention is to provide a filtration system utilizing a membrane filtration apparatus which has wide application in water purification, waste treatment, separation of colloidal suspensions, and the like. 
     The invention possesses other objects and advantages especially as concerns particular characteristics and features thereof which will become apparent as the specification continues. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view showing the system of the present invention with a pair of heat exchangers in conjunction with a shear induction membrane filtration apparatus. 
     FIG. 2 is a partial schematic view showing another embodiment of the present invention in which an evaporator and condenser are employed. 
    
    
     For a better understanding of the invention reference is made to the following detailed description of the preferred embodiments thereof which should be referenced to the prior described drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention as a whole is shown in the drawings by reference characters  10  or  10 A. 
     Filtration system  10  of the present invention is utilized in conjunction with a membrane filtration apparatus  12 . Membrane filtration apparatus  12  may be of many types, such as those using membranes that are spiral wound, tubular cross flow membranes, spinning disc membranes, hollow fiber membranes and the like. Of notable importance is a shear enhanced membrane system which employs a vibratory mechanism. Such a system is less susceptible to fouling than other systems of the prior art. This system may be found in U.S. Pat. No. 4,952,317. Although the latter system was a notable advance in the field of membrane filtration, the present invention further improves membrane filtration systems in order to reduce the overall cost of the same. 
     The filtration apparatus  12  shown in FIGS. 1 and 2 is intended to be an exemplary system having an eccentric drive unit  52 . As prior noted, any membrane filtration system would suffice for use with the present system  10 . 
     The present system employs a source  14  of the liquids-solids mixture, which is to be separated by filtration apparatus  12 . Source  14  may be a reservoir containing the solids-liquid mixture which may be in the form of a slurry colloidal suspension, and the like. Reservoir or source  14  could contain salt water intended for desalinization, biologically contaminated drinking water, sewage, colloidal mixtures such as clay and water, calcium carbonate and water, coal fines in water, paints and pigments in solvents and the like. solids-liquid stream  16  passes to pump  18  which discharges exit stream  20 . In certain cases exit stream  20  is passed to heat exchanger  22  via flow regulator  24 . In other cases, stream  20  is split into a second stream  26  and passed to a second heat exchanger  28  via flow regulator  30 . 
     Heat exchangers  22  and  28  may be of the plate and frame type of the shell and tube type, and are preferably a countercurrent flow type exchangers. As may be observed in FIG. 1, heat exchanger  22  accepts the solids-liquid stream  32  which is a portion of stream inlet  20 . In other embodiments, solids-liquid streams  20  and  32  may be identical when solids-liquid stream  26  is not employed in the present system  10 . Exchanger  22  obtains heat from permeate stream  34  leaving membrane filtration apparatus  12 . The heated solids-liquid stream  36  exiting exchanger  22  forms all, or a portion of, inlet stream  38  to membrane filtration apparatus  12 . An auxiliary heater  40 , typically in the form of a boiler, may be employed to elevate solids-liquid inlet stream  38  prior to entering apparatus  12 . 
     Likewise, with respect to heat exchanger  28 , inlet solids-liquid stream  42  is heated by the exchange of heat from concentrate stream  44  exiting apparatus  12 . Solids-liquid exit stream  46  from heat exchanger  28  combines with exit stream  36  from heat exchanger  22  to form the solids-liquid inlet to apparatus  12 , in certain cases. It should be noted that in many instances, the flow of concentrate from apparatus  10  is at too low a level to warrant the inclusion of heat exchanger  28  in the present system. 
     Permeate stream  34  from membrane filtration apparatus  12  may optionally include a pump  48 , although this is not necessary in most cases. Also, heater  50  may be employed to elevate the temperature of the permeate stream prior to entering heat exchanger  22 , in addition to or as an alternate to the use of heater  40 , prior described. It should be noted that permeate stream  34  may be delivered to heat exchanger  22  at a higher pressure than solids-liquid inlet stream  32 . In this manner, the purity of permeate stream  34  is assured, should a leak develop in heat exchanger  22 . Pressurization of permeate stream  34  may be accomplished using a pressure regulator, a valve, or the like. 
     FIG. 2 shows an alternative system to that depicted in FIG. 1, although many of the components depicted therein are the same. System  10 A includes a single heat exchanger  22  in which the solids-liquid inlet stream is heated by the exiting permeate stream  34 . The exit solids-liquid stream  36  is passed to a condenser  54  prior to serving as the inlet stream  56  to filtration apparatus  12 . concentrate stream  44  coming from filtration apparatus  12  is passed to an evaporator  58 . Exit heated vapor stream  60  from evaporator  58  passes to condenser  54  and leaves as a liquid stream  62 , which may be used or may be considered to be waste. Solids stream  64  from evaporator  58  may also be employed as desired. 
     The following is a working example illustrative of a typical application of the systems  10  and  10 A of the present invention, but is not deemed to limit the scope of the invention as defined by the claims hereinafter. 
     WORKING EXAMPLE 
     A filtration apparatus  12  known as a V♦SEP, manufactured by New Logic International, Emeryville, Calif., was employed in the system  10  of the present invention. The filtration apparatus included a membrane area of 930 square feet using a 0.1 millimicron teflon membrane. The filtration apparatus  12  closely follows that disclosed in U.S. Pat. No. 4,952,317 heretofore noted. Elastomeric seals were composed of EPDM, while the steel trays were formed of 304 stainless steel. The filter pack housing consisted of a vinyl ester 8084 DEREKANE fiberglass structure having feed channels formed of 304 stainless steel grommets. The feed and permeate connections to the filtration apparatus were composed of 2 inch material manufactured by Victaulic. The motor aiding in the eccentric drive  52  consisted of a custom unit of  20  horsepower rating manufactured by Baldor. The motor speed controller was manufactured by AC Tech. The overall size of the filtration unit  12  was 6 ½ feet long, by 4 feet wide, and 17 feet in height. The unit weighed approximately 5,300 pounds. 
     A heat exchanger  22  was also employed in system  10 . The heat exchanger  22  was manufactured by Alfa Laval Thermal, having a 120 gallons per minute flow rate of countercurrent construction. Plate area measured 379.8 square feet and included 147 plates. The plates were constructed of AISI 304 stainless steel while the gasket material was nitrile. The inlet and outlet connection sizes were 4 inches and the overall dimension of the heat exchanger measured 6 feet in length, 2 feet in width, and 3.5 feet in height. The exchanger weighed 1,120 pounds. 
     To make up the heat entering the permeate stream  34 , a boiler of 500,000 BTU/HR was employed. The boiler was manufactured by Ray Pack. A booster pump was placed in front of the exchanger  22  of the type manufactured by Gould, 1.5 horsepower, 3,500 RPM, model number GL885. Another high pressure pump, a Gould 304 stainless steel centrifugal type, 3,500 RPM, series SST-C was also placed in front of the V♦SEP unit. 
     The components above described were connected and tested at New Logic International facility in Emeryville, Calif. A small booster pump (1.5 HP) was placed in front of the heat exchanger  22  to overcome the pressure drop in the system. The solids-liquid stream passed through the warm side of the exchanger and entered the high pressure pump (series SST-C), which is normally used to drive the separation inside the membrane module of the V♦SEP device. Waste energy from the high pressure pump and the vibration via eccentric drive  52  caused the temperature of the fluid in filtration apparatus  12  to increase by 1.5 degrees centigrade. Since the heat exchanger  22  was designed to operate on a 5 degrees centigrade driving temperature, the boiler was used to heat the permeate exiting the V♦SEP unit to make up the heat necessary to allow the exchanger  22  to operate at capacity. The permeate was recirculated through the exchanger. 
     It was determined that the viscosity of the solids-liquid stream entering the filtration apparatus  12  (V♦SEP) increased the capacity of the system by a factor of 2, by raising the temperature of the inlet stream 25 degrees centigrade. At 65 degrees centigrade a four fold increase was realized, while at 90 degrees centigrade a 6 fold gain came forth from the present system. 
     While in the foregoing, embodiments of the present invention have been set forth in considerable detail for the purposes of making a complete disclosure of the invention, it may be apparent to those of skill in the art that numerous changes may be made in such details without departing from the spirit and principles of the invention.