Oil-filtration system with oil/air separation for automated food-fryers

A cooking-oil filtration system and method for automated food-fryers with a solids-removing filter for cleaning cooking oil from the food-fryer which includes and involves an oil/air separator for receiving air-containing oil from the filter and then returning air-separated oil to the food-fryer. In certain highly preferred embodiments the oil/air separator includes a cylindrical inner wall and an inlet conduit configured for tangential entry and spiral flow of oil. In another embodiment, the oil/air separator is a surge tank having upper and lower tank upper portions and conduits facilitating the in-flow of air-containing oil and the gravity out-flow of air-separated oil to the food-fryer. In-flow is preferably driven by a pump upstream of the filter media.

FIELD OF THE INVENTION

The invention relates generally to oil-filtration systems and methods for removing solids from cooking oil in industrial food-frying operations and, more particularly, to oil-filtration systems in automated, continuous industrial food-frying operations.

BACKGROUND OF THE INVENTION

During industrial food-frying operations, solids accumulate in the cooking oil. In high-quality food-frying operations, oil-filtration systems are employed as part of the equipment in order to remove solids from the frying oil and thus prolong the life of the cooking oil.

A variety of filtration systems are used in the food industry. One exemplary filtration system of the sort to which the present invention applies uses automatically replaced filter media and pump pressure to force solids-containing oil from the food-fryer through the filter media. Then, intermittently, i.e., after accumulation on the filter media of a filter cake of solids, the system applies air pressure in a “drying” step to remove as much oil as reasonably possible from the filter cake on the filter media (in order to reduce loss of oil), after which a new portion of filter media is moved into position and the “dried” cake of filtered-out solids from the cooking oil is discarded.

This and other generally similar types of oil-filtration systems for use in industrial food-frying have many advantages. However, certain shortcomings and problems exist related to air in the cooking oil, and it is to overcoming these and related problems that the present invention is addressed.

More specifically, systems such as described above have problems related to the presence of air entrained in the cooking oil. Air in the cooking oil is caused, or made more problematic, by the use of air pressure to drive filtered cooking oil out of the filter cake that has progressively accumulated on the filter media during filtration. During the “drying” phase of operation, in which air pressure is applied on and through the accumulated solids cake and filter media (on which the cake has accumulated) to drive cooking oil from the cake and filter for return to the food-frying vat itself, an air surge eventually occurs as the air breaks through the filter cake. This air surge into the return oil flow increases the quantity of air entrained in the filtered oil returning to the food-fryer and causes potentially hazardous turbulence, even splash risks. Turbulence can be a significant safety problem, considering that most food-fryers maintain cooking-oil temperatures of between about 275° F. and 415° F. Further, turbulence can stir up solids in the fryer which then may attached to the food and affect both taste and appearance. (Such solids are typically removed from the bottom of the fryer by settling to the bottom and being removed by a slow-moving conveyor.) Turbulence can also interfere with proper spacing of food objects being cooked, e.g., pieces of chicken, in the food-fryer.

Furthermore, air in cooking oil, however it might get there, can be deleterious to the food-frying operations. The oxygen content of the air naturally increases oxidation of the oil, and thus causes increased degradation of the oil. In other words, even beyond the turbulence problems referred to above, it is problematic to food-frying operations to have air entrained in the cooking oil, and it would be considered highly desirable to minimize the amount of air entrained in the cooking oil.

Moreover, returning filtered oil from cooking-oil filtration apparatus back to the food-fryer itself without in any way affecting the cooking operations can be problematic. Some possible ways of addressing such problems could involve complex equipment and multiple pumps, but this would increase service requirements and attendant operational costs.

There has been a continuing need for an efficient, safe and simple solution to all of the above-described problems in oil-filtration systems for industrial food-fryers.

OBJECTS OF THE INVENTION

It is an object of the invention to provide an improved oil-filtration system and method for use in continuous, industrial food-frying operations.

Another object of this invention is to provide an improved oil-filtration system overcoming some of the problems and shortcomings of the prior art, including those described above.

Another object of this invention is to improve and make more efficient and effective industrial food-frying equipment.

More specifically, a major object of this invention is to address the problems associated with air entrained in cooking-oil in automatic food-fryer operations.

Still more specifically, an object of this invention is to solve problems associated with air surges in the stream of oil after oil-filtration in automatic food-frying equipment.

In particular, one object of this invention is to eliminate potentially hazardous turbulence and oil splashing in food-frying equipment.

Another object of this invention is to avoid the problem of spacing of food objects being cooked in automatic, industrial food-fryers.

Still another object of this invention is to provide equipment minimizing degradation of the quality of cooking oil used in industrial, high-volume food-fryers.

Yet another object of this invention is to accomplish the above objectives in a system that avoids complex equipment with moving parts and/or multiple pumps, and thus provide improved oil-filtration systems which minimize service and the costs of operation.

How these and other objects are accomplished will become apparent from the following descriptions and the figures.

BRIEF SUMMARY OF THE INVENTION

The invention is an improved cooking-oil filtration system for automated food-fryers of the type that include a solids-removing filter for cleaning cooking oil from the food-fryer. The improvement in such filtration systems involves an oil/air separator that receives air-containing oil from the filter, and after oil/air separation returns the air-separated oil (oil after air removal) to the food-fryer.

In highly preferred embodiments, the oil/air separator includes a housing having a cylindrical inner wall that extends from a wall upper portion thereof to a wall lower portion thereof, and an inlet conduit configured to direct the air-containing oil tangentially onto the wall upper portion to create a spiraling flow of the air-containing oil which drives the air in the air-containing oil radially inward and from there out of the oil to produce the air-separated oil.

Such embodiments preferably include a pump which drives air-containing oil from the filter to the separator and into the separator through the inlet conduit. Such pump is preferably upstream of the filter. The oil/air separator preferably includes an oil-outlet conduit at the lower end of the housing configured to return the air-separated oil to the food-fryer by gravity. An air-outlet conduit is preferably included at the upper end of the housing of such oil/air separator. And such air-outlet conduit preferably extends to the hood above the food-fryer.

The cooking-oil filtration system of this invention preferably includes a pressure filter which has replaceable filter media from which oil is substantially removed (prior to filter media replacement) by air pressure from a compressed air source.

Another embodiment of this invention has a pump, preferably upstream of the filter, which drives air-containing oil from the filter and to the oil/air separator, and the oil/air separator includes a surge tank. The surge tank has a tank upper portion and a tank lower portion, an inlet conduit at the tank upper portion configured to direct air-containing oil into the surge tank, and an oil-outlet conduit at the lower end of the tank configured to return the air-separated oil to the food-fryer by gravity. In preferred embodiments, the oil/air separator includes an air-outlet conduit at the upper end of the tank, which preferably extends to the hood above the food-fryer.

This embodiment of the invention, like the embodiment with spiral flow first described above, provides in effect a flow “buffer” to isolate the food-fryer from the turbulence caused by a surge of air breaking through the filter cake.

While key embodiments of the invention are improved cooking-oil filtration systems, the invention is also cooking-oil oil/air separation apparatus for cooking-oil filtration systems. The invention is also a method of separating air from air-containing cooking oil downstream of a cooking-oil filter of a food-fryer cooking system that includes a cooking-oil flow path for circulating cooking oil through the filter. The inventive method includes directing pump-driven air-containing cooking oil from downstream of the filter into a separator vessel, the separator vessel providing an expanded portion to the cooking-oil flow path apart from the fryer, the filter and connecting conduits thereof, and returning air-separated oil by gravity from the separator vessel to the food-fryer. In preferred embodiments, the separator vessel has a cylindrical inner wall extending from a wall upper portion thereof to a wall lower portion thereof and the directing step includes directing the air-containing oil tangentially onto the wall upper portion, thereby creating spiraling flow of the air-containing oil, driving the air therein radially inward and out of the oil to produce the air-separated oil for return to the food-fryer.

All of the objects of the invention are provided by the present invention.

DETAILED DESCRIPTIONS OF PREFERRED EMBODIMENTS

The present invention is an improvement of a cooking-oil filtration system for automated food-fryers which have a solids-removing filter for cleaning cooking oil from the food-fryer. An embodiment of one such system is described in U.S. Pat. No. 7,566,468 (Oberlin et al.) entitled “Oil Filtration Process” which issued on Jul. 28, 2009 and is incorporated herein in its entirety. The embodiments of the present invention now to be described in detail will be described as improvements of systems employing a flatbed pressure filter type that is commercially available from Oberlin Filter Company of Waukesha, Wis.

FIG. 1is a schematic diagram of an embodiment of the improved cooking-oil filtration system10for an automated food-fryer14. Improved cooking-oil filtration system10ofFIG. 1incorporates an oil/air separator50for separating air from the cooking oil16which is being circulated within filtration system10.

In this embodiment, filtration system10includes cooking-oil filter12which is an automated solids-removing filter. A cooking-oil pump20circulates cooking oil16from a food fryer14, through a fryer outlet conduit22and a filter inlet conduit24to filter12. Pump20further moves cooking oil16through filter12and on to separator50through a filter outlet conduit26. Cooking oil16may become mixed with air in filter12, and cooking oil16leaving filter12through conduit26is also referred to as air-containing oil16ac. The air in air-containing oil16acis separated from cooking oil16in separator50, and the resulting air-separated oil16as is returned by gravity to fryer14through oil-outlet conduit30.

Pump20may be one of a number types of pumps including, for example, a centrifugal pump or an air-operated diaphragm pump. Whatever type of pump is employed, pump20must be able to withstand the high operating temperature of cooking oil16.

Referring toFIGS. 2A and 2Bfor more detail of the configuration and operation of filter12, filter12is a flatbed pressure filter. Filter12utilizes a filter aid12aand a replaceable filter medium12mwhich during filtering operation is sealed in a horizontally-oriented upper filter chamber12ucover a lower filter chamber121c. Filter aid12ais a material added to oil16in filter12to create a filter cake (also referred to by reference number12a) on filter medium12m. Filter medium12mand filter cake12atogether provide the filtering properties of filter12.

Filter media12mcan be a filter cloth, a filter paper or any other media capable of retaining filter aid12aand the impurities in cooking oil16. Most preferably, a highly-efficient non-woven filter fabric is used so that only one pass through filter12is necessary to remove all of the solids in oil16and to enable the added filter aid12ato be removed from oil16and to easily form a filtering layer (filter cake12a) on filter medium12m. Typically, filter medium12mis capable of retaining particles of size down to one micron.

Filter aid12amay be a passive filter aid material such as diatomaceous earth or an active filter aid such as an adsorbing, purifying agent like magnesium silicate. Other additives may be included to enhance the quality of oil16and food product being processed, including, for example, activated carbons, alumina, bleaching materials, silicates, silicas, and silica gels. The horizontal nature of flatbed pressure filter12facilitates easy formation and maintenance of filter cake12a. Oil16containing solids from fryer14is pumped into upper filter chamber12uc, and filter aid12acollects onto filter medium12mon a filter substrate12fs. Filter substrate12fssupports filter medium12mand filter cake12aover lower filter chamber121c. Filtered air-containing oil16acflows through filter cake12aand filter medium12minto lower filter chamber121cand out of filter12through filter outlet conduit26to separator50.

The operation of filter12is cyclical. During operation, a section of filter medium12mand filter cake12aformed on it is discharged from filter12when the pressure drop across the filter chamber indicates that the section has become fully loaded with removed solids. A portion of this discharge cycle is illustrated inFIG. 2B. Filter upper chamber12ucis raised by a filter chamber lift12c1. During this portion of the cycle, a new section of filter medium is placed into position in filter12while spent filter medium12mand filter cake12aare removed from filter12. Filter medium12mis supplied from a roll of new filter media12mnand is taken up onto a roll of used filter media12mu.

A pressure sensor13measures the pressure drop across filter cake12aand filter medium12mduring normal filter operation. An increase in pressure drop to a predetermined level triggers the start of a “drying cycle” which removes excess oil16from filter medium12mand filter cake12aprior to discharge of filter cake12aand the introduction of a new section of filter media12mn. Such new section of filter medium12mis automatically and quickly positioned in filter12, and a fresh batch of filter aid12ais introduced to form then a new filter cake12aas normal filtering operation resumes.

In cooking-oil filtration system10, it is this “drying cycle” which is the primary source of the air in air-containing oil16ac. Air may be introduced into cooking oil16in several ways such as turbulence in fryer14or other such incidental mechanism. However, during such drying cycle, compressed air from a compressed air source42is used to drive a substantial portion of cooking oil16which is in filter medium12mand filter cake12aat the time the drying cycle is triggered due to the pressure drop reaching its predetermined level. During drying, a filter valve12vcloses off the flow of cooking oil16into filter12. This drying cycle therefore creates significant opportunity for air being introduced into oil16. After the drying portion of the cyclical operation of filter12is complete, the cycle continues on to the discharge portion of the cycle. Further details of an embodiment of filter12are shown in U.S. Pat. No. 7,566,468 which has been incorporated herein by reference.

Another significant opportunity for air to be introduced into air-containing oil16acoccurs at the end of the drying cycle when most of oil16in filter medium12mand filter cake12ahas been driven out by the compressed air. At this point, a surge of air can occur in the flow from filter12to separator50.

Referring particularly toFIGS. 3 and 4which illustrate an embodiment of separator50in more detail, separator50includes a separator housing52supported by three housing supports52s. Separator50is installed on supports52sin order to elevate separator50appropriately above fryer14to facilitate gravity-driven flow of air-separated oil16as from separator50to fryer14. Housing52is a cylindrical tank having a cylindrical inner wall54. Cylindrical housing is also a surge tank60. Reference numbers52,54and60are all shown on the same component of separator50since housing52is also surge tank60and since housing52is cylindrical and includes cylindrical inner wall54with no internal structure. Inner wall54and portions of inner wall54are indicated externally in the figures.

Cylindrical inner wall54of housing52extends from a wall upper portion56of inner wall54to a wall lower portion58of inner wall54. Air-containing oil16ac, driven by pump20through filter12, enters separator50through filter outlet conduit26and inlet conduit28. Inlet conduit28is located and oriented to direct flow tangentially onto an upper wall portion56of inner wall54. Air-containing oil16acflows in a spiral path down and along inner wall54from upper wall portion56to lower wall portion58, driving the air in air-containing oil16acradially inward and out of air-containing oil16acto produce air-separated oil16as. The spiral flow of air-containing oil16acalong inner wall54creates a pressure gradient in air-containing oil16acwhich, because air is much less dense than oil16, drives the air radially inward and oil16radially outward, thus separating air from air-containing oil16ac. The flow along inner wall54also creates flow with significant surface area providing opportunity for the air to find its way to this surface and to escape from air-containing oil16ac.

During operation of cooking-oil filtration system10, some air-separated oil16as may rise in surge tank60(housing52) to an equilibrium level at lower end68of surge tank60. This equilibrium level serves to smooth out the flow of air-separated oil16as from separator50to fryer14if flow of air-containing oil16acinto separator50is somewhat uneven. Further, during a surge of air into separator50from filter12which can occur at the end of a drying cycle, the volume of surge tank60facilitates separation of such large amounts of air from air-containing oil16ac. The surge of air is prevented from reaching fryer14. This effect is assisted by the equilibrium level of air-separated oil16as at lower end68of surge tank60.

Cooking-oil filtration system10also includes a bleed-off conduit32with a bleed-off valve38. Bleed-off valve38is closed during most of the normal cycle12except at the end of the drying cycle, at which point bleed-off valve38is opened temporarily to release any residual pressure in filter12prior to the removal and replacement of the filter media section and filter aid replenishment.

Separator50also includes an access port40at upper end66of surge tank60(housing52). Access port40is not used during normal operation of separator50.

Separator50and generally all components in cooking-oil filtration system10are fabricated of stainless steel.

While the principles of the invention have been shown and described in connection with specific embodiments, it is to be understood that such embodiments are by way of example and are not limiting.