Pizza sauce producer increases
product yield while enhancing process performance and filtration
reliability...
provided by: Spencer
Strainer Systems
A midwest producer
of RTU (ready to use) and concentrated pizza sauce has recently
increased productivity and is achieving consistently higher
product quality and yield through the use of self-cleaning
filtration in the process loop. The application and
implementation of self-cleaning filtration technology was
incorporated to remove undispersed spices and other unwanted
debris from the pizza sauce.
Preparation begins as tomato paste, water, spices and salts are combined in a tank utilizing a high shear mixer. Once blended the unsterilized sauce by means of a rotary lobe positive displacement pump is gently pushed through a "static" straining system to remove agglomerated spices and other foreign debris and into a large surge tank. The sauce, upon leaving the surge tank would be sterilized and directed into filler feed kettles where it would be placed into sealed pouches as a final product ready for shipment. The process is designed to operate 24 hours/day, seven days a week with little downtime, exception being system cleaning which occurs approximately every 50 hours.
Filtration problems
While the process was functional, on occasion
one to two bins (300 to 600 gallons) of product would be rejected
as it would not meet the established quality standards. Over time
undispersed spices would bridge at the static strainer screen and
back-up in the supply piping. By incorporating a rotary lobe
positive displacement pump in the process little decrease in flow
would be noticed and no indication of a problem would be evident
while the pump differential pressure would continue to rise due
to the loss of open screen area available at the static strainer.
This rise in pump differential pressure would result in collapsed
strainer screens and a continual increase in driver horsepower
eventually leading to driver overload.
A "static" filter represents vessels using filter bags, cartridges, screens and other media that allow unwanted solids to rest against their surface, or embed between weaves, fibers or sintered metals while the fluid continues to pass. The size of the media is generally expressed in terms of surface area, the volume of element area available to remove unwanted solids. As these solids are removed they decrease the volume of surface area available for the fluid to pass. Once the media has removed enough solids to effect the process performance, generally determined by a decrease in filter outlet flow or increase in filter differential pressure, the filter element(s) must be removed, disposed or cleaned depending on type, and reinstalled to obtain the designed process capacity. The type of pump supplying the fluid to the filter will have a dramatic effect on process capacity and pressure as solids loading occurs.
Identifying with supply pumps
Should a centrifugal pump be installed, as the
filter accumulates solids decreasing the volume of element
surface area available the resultant pressure drop will swing the
pump left on its performance curve and flow will decrease
accordingly. As solids continue to be removed the pressure will
continue to rise and flow will continue to fall. In some
instances blinding of the element will swing the centrifugal pump
to shut-off, a no flow condition, where driver horsepower is now
imparted into the fluid in the form of heat creating a dramatic
temperature rise within the pump possibly jeopardizing product
integrity and mechanically compromising pump components.
Rotary positive displacement pumps will reflect little decrease in flow due to inherent internal fluid slip as the pump senses an increase in pressure. As filter solids loading occurs and the differential pressure continues to rise a rotary positive displacement pump will continue to "push" the fluid through the filter element. Left unattended and permitted to rise this pressure can rapidly exceed element design pressure resulting in blown holes in bags, collapsed cartridges, and crushed perforated screens. Many rotary pumps incorporate internal relief valve arrangements to avoid over pressurizing the process system and pump driver. Should this relief valve remain open over heating of the fluid will occur and cavitation across the relief valve will induce premature pump failure.
Regardless which pump design, centrifugal or rotary positive displacement, both pumping technologies will require: appropriate stand-by filter(s) pending on the process demands, proper by-pass arrangements to protect the pump and other process components, and the instrumentation to indicate filter element change or cleaning prior to unscheduled interruptions.
While increasing screen surface area will provide longer run times between cleaning, and adding a second stand-by filter with the appropriate automation and instrumentation will provided process interuption solutions, both are shadowed by increased operator involvement, and a more complex filtration system.
Filtration solutions
To eliminate process interruptions the Spencer
Strainer Systems; Jeffersonville, Indiana discussed the
possibility of incorporating a mechanical self-cleaning filter.
After thoroughly investigating the technology and its practical
application within the process the tomato sauce manufacturer
agreed to the installation of the Spencer Strainer.
The Spencer
Strainer is a mechanical clean-in-place filter that continuously
removes unwanted debris from its screen keeping the filter at its
"clean" differential pressure throughout the process.
The Spencer Strainer was installed downstream of the rotary pump
in place of the static strainer and was mounted horizontally with
its in-line inlet and outlet connections accommodating ease of
installation.
As the sauce enters the inlet of the filter it is directed into the filter housing where it passes through a rotating screen leaving unwanted debris deposited on screen outside diameter. Two stationary scraper blades are applied to the surface of the screen to effectively remove the debris. These debris collect in the filter housing and are periodically purged from the bottom of the filter during the process. The now strained sauce exits the filter and proceeds to the surge tank.
By continuously removing the solids from the screen during the process the differential pressure across the filter remains constant and the pump pressure no longer increases as the process continues.
The simplicity of the Spencer Strainer installation has virtually eliminated any operator involvement without the addition of auxiliary process controls. Occasionally an operator will be required to open and close the flush valve to dispose of the removed solids, however, this represents a limited function and is accomplished in minutes.
Since the employment of the Spencer mechanical self-cleaning filter the process is no longer interrupted due to pump driver overloading and strainer cleaning due to plugging, now this portion of the process can produce consistently higher quality pizza products.
6205 Gheens Mill Road
Jeffersonville, Indiana USA 47130
Ph (812) 282-6300 / Fax (812) 282-7272
E-Mail for
additional information