A modern food or beverage plant is handling more and more powders either as a raw ingredient or a finished product in this era of global trade, as these powders are produced far away from where they are being consumed.
This may be dairy powder, infant formula powder, sugar, salt, dairy, flour, flavour or any of the myriad of dry bulk ingredients available today.
The equipment in these plants range from
- Powder Transport and Conveying Systems
- Powder Silos
- Powder Feeders
- Powder Blenders
- Powder De-Bagging
- Powder Filling Machines
The question is being raised more frequently about whether this equipment should be wet cleaned with a water base cleaning solution? Then once you make the decision that cleaning is required, it is asked whether this equipment can be effectively CIP cleaned.
The answer to whether the wet cleaning should be undertaken is purely up to the decision of the plant owner.
The answer to whether the equipment can be effectively cleaned is a resounding; yes.
What is CIP and what are the Alternatives?
For those unfamiliar with Cleaning-in-Place (CIP), this is when equipment is cleaned by an automatic system with little or no disassembly or operator intervention.
A system that is CIP cleanable includes a CIP Kitchen, with water tanks, cleaning solution tanks, pumps, heaters and valves ; as well as the necessary pipes and vales at the equipment to allow the cleaning solution to circulate to and from the equipment that is to be cleaned.
If it is a powder transport line to be cleaned, then the line is usually flooded so that a liquid velocity sufficient to achieve cleaning can be established.
If it is a vessel to be cleaned, then there are appropriately designed nozzles in the vessel to affect coverage within the vessel.
The two wet cleaning alternatives to CIP cleaning are either manual cleaning, where the equipment is opened up and cleaned by operators in its existing location or Cleaning-out-of-Place (COP), where the equipment is disassembled and loaded into circulating baths to be cleaned semi-automatically. Both of these options are labor intensive. The results of these two types of cleaning regimes are often inconsistent
Dry cleaning of equipment is also a valid alternative, and is often a procedure implemented to extend the operational cycle between wet cleanings.
The down-side to dry cleaning is that it is labor intensive and also carries safety concerns for the operators carrying out the work. Finally, it introduces an opportunity for contamination solely through the occasion of operator intervention.
Should a Food Powder System be wet cleaned?
There are several reasons that may drive the decision to wet clean a plant.
They may be:
- Product or Batch Segregation
- Allergen Class Segregation
- Bacteriological Contamination
- Contamination due to out-of-spec Product
- Product Build-up causing a Safety Hazard
There seems to be only one recurring reason not to wet clean, which certainly provides valid justification, and that is if the dry powder equipment is never wet cleaned, then bacteriological growth is almost impossible to initiate, unless outside factors cause contamination.
Never wet-cleaning your dry powder equipment is a very valid approach to maintaining hygiene within the dry areas of your plant. Many plants operate this way safely for very long periods of years, but if there is an episode of contamination, then the contingency must exist for the cleaning of the equipment by other means.
If the reasons for wet cleaning, as outlined above, outweigh the considerations for never wet cleaning, and appropriate cleaning regimes and operational and quality procedures can be implemented to wet clean the plant
Then the final decision to make is whether the capital cost of the CIP system outweighs the operational cost of longer downtime and labor required for manual wet-cleani ng or COP cleaning.
Can dry powder equipment be effectively CIP cleaned?
Yes. This has been proven time and time again that dry powder equipment can be CIP cleaned effectively when the correct equipment designs are implemented from the outset and the user has a clear set of goals they are trying to achieve during the CIP.
Some users only wish to CIP clean annually as part of a Quality Assurance Regime, in which case downtime and water usage may not be critical, but effectively cleaning the plant and doing so safely may be of value. A CIP regime like this may take 24-36 hours during an annual plant shut-down period.
At the other end of the cleaning frequency spectrum is a producer who changes batches and allergen classes several times per day in their production schedule. They need so clean the equipment, dry the equipment and get it back into operation quickly. A CIP cycle from off-product to on-product needs to be completed in an hour or less.
Process of CIP cleaning.
CIP Theory would say that when you are using water and cleaning chemicals to CIP clean stainless steel equipment, that there are five parameters which you should understand and can control
- Time – duration of the cleaning
- Temperature of the cleaning solution
- Pressure of the solution when spraying in an open vessel
- Velocity of the cleaning solution when cleaning a line
- Chemical Strength
Many more pages could be filled with discussion of CIP cleaning, so I’ll provide only a brief overview of these parameters and their trade-offs. The trade-offs generally are between time, energy cost and chemical costs.
In some instances, higher pressures are used to impinge upon product build-up to remove it more quickly, to the point where only a water solution is required at low temperature.
In other cases, product build-up is allowed to increase over months and becomes so severe that CIP solution is cycled to different areas to allow the chemicals to soak into a layer of build-up over time (minutes) before solution is sprayed again washing away the reacted layer of build-up an exposing a new layer. This continues until all product is removed.
CIP Time: It is self-explanatory that thick or aged build-up will take more time with the cleaning solution be sprayed onto the surfaces. If your objective is to reduce cleaning time, then you only have the other four parameters with which to work, or you would need to decrease the interval between CIP cleanings.
CIP Solution Temperature: Generally the hotter the cleaning solution, whether plain water or with cleaning chemicals the more effective the cleaning will be, but there are limits. Each cleaning chemical has an upper temperature limit above which it begins to lose effectiveness. Each product, especially proteinacious products, can be cooked when using high cleaning temperatures and potentially become insoluble or become more difficult to remove.
The rule of thumb is to use the lowest temperature solution possible to effect the cleaning based on the product being cleaned out and the chemicals chosen to perform the cleaning.
Pressure: When cleaning an open vessel like a silo or feeder, something that is not flooded during cleaning, the pressure at which the cleaning solution is being sprayed logically has an effect. Higher pressures will allow build-up to be removed by mechanical action of the sprayed solution. This holds true up to a limit where the spraying nozzle has such a high pressure drop that higher input pressures to the nozzle don’t create a higher output pressure from the nozzle.
Velocity: When a line, or possibly a small vessel, is completely flooded for cleaning, then adequate cleaning velocity is required... This is generally considered to be 5 feet per second (1.5 m/sec). Simple calculations allow the system to be designed to achieve this. Stubborn or denatured build-up may be able to be removed with higher cleaning velocity, but generally the other paramet e rs are adjusted to improve the cleaning.
Chemical Strength: Chemical strength can be increased or adjusted for particularly stubborn products. Chemicals are often expensive and it is the goal to reduce the amount required to the lowest level to effectively perform the cleaning.
Equipment for CIP Cleaning
As mentioned above, the CIP Equipment generally falls into two areas; 1) the CIP Kitchen of Tanks, Pumps, Heaters and Valves from which the cleaning solution is centrally prepared for the entire plant and 2) the field equipment of valves, return pumps and nozzles to effect the required cleaning.
The design of the CIP Kitchen is not within the scope of this article and could also fill many pages.
This article will focus on the nozzles and extra equipment needed to facilitate CIP cleaning of powder handling equipment.
First and foremost, because of the use of chemicals, high pressure and high temperature, safety of the personnel working on or around equipment to be CIP cleaned is paramount. Please review all of your plant procedures before proceeding with implementing anything discussed in this article, especially if CIP cleaning is new to you.
One of the most important aspects in the design of equipment, whether it is initially designed this way or retrofitted, is that equipment must be able to contain the liquid cleaning solution within the vessel. Don’t presume that because the system can contain powders that it will necessarily contain liquid properly.
Powder Conveying and transport lines generally will hold the pressure of liquid, especially when designed with fittings to hold under the pressure or vacuum of conveying, but most other vessels are atmospheric and would not necessarily be designed to hold the pressure of a head of water, particularly if they are designed to pressure vessel standards. For instance, the gasketing of powder blenders needs to be carefully considered before implementing then into a process where they are to be CIP cleaned.
Flexible connectors on items like vibrating bin bottom, drop ducts, etc. need to be considered. Manway as well, especially those on the lower sidewalls of hoppers and vessels. Instruments and their connections fall into this category as well.
Design standards exist for all of these situations so that a system can be designed properly to process powders during normal operation, but also to be CIP cleaned.
The spraying of Liquid Cleaning Solutions into the vessels is the next consideration. Usually this is done with nozzles of some type, and the nozzles can either be permanently mounted, thereby reducing set-up time or removable allowing maintenance of the device during production, but extra set-up time during the switch-over from production to CIP.
Generally nozzles fall into three categories;
- Static Nozzles
- Rotating Nozzles
- Orbital Cleaners
Static Nozzles for the cleaning of vessels, tanks and containers, such as storage tank and clean-in-place (CIP) tanks, are designed to work with low pressure. A fixed spray head sprays the cleaning medium onto the surface to be cleaned. Cleaning is achieved by rinsing or impingement of the tank walls. By adding appropriate cleaning agents, the cleaning effect can be enhanced while cleaning times are reduced. The flow rate ranges between 2.4-42 m3/h, at a pressure difference of 1 bar. The cleaning diameter is 0.8-8.0 m.
These are generally the lowest cost and easiest to retrofit into a vessel. There are wide variety of sizes and spray patterns to choose from, so that each location within a vessel or system can have a uniquely selected nozzle best suited to the application. These are often called spray balls, and look like a ball on a stalk with holes drilled into it.
With Static Nozzles, it’s difficult to clean the largest vessels, like silos. The other downside is that they protrude into the vessel and are generally not left in place during production, requiring the additiona l set-up time to begin a CIP cleaning.
These are not the best choice when time is a consideration.
Rotating cleaners are used for the cleaning of tanks, vessels and containers with heavy product encrustations (e.g. larger storage tanks, fermentation tanks, tanks with internal agitators). These cleaners are designed to work with low pressure; a flow gear unit generates a fan-shaped jet, which slowly rotates in one plane, thereby wetting the entire surface. The flow rate ranges between 7.1 and 28 m3/h, at a supply pressure of 2.3-4.3 bar. The cleaning diameter is 2 to 10 m. Depending on the material, operating temperatures in the range between 80°C and 100°C are possible.
Rotating cleaners can either be inserted and removed with each cleaning or left in place, proving the same trade-offs as static nozzles.
Flush mounted automatically retractable rotating CIP nozzle
Some modern rotating nozzles are automatically retractable and flush mounted, allowing them to remain in place without interfering with the product flow.
Rotating spray nozzle
Orbital cleaners, for the cleaning of tanks, vessels and containers that require special mechanical treatment of the inner surfaces by a concentrated jet (e.g. road tankers, product tanks and kegs), are designed to work with low, medium or high pressure. A flow gear unit generates a highly concentrated cleaning jet that rotates in two planes. The ideal jet geometry is produced by specially shaped round-jet nozzles and bevel gears that produce a dense orbital cleaning pattern which covers the entire surface to be cleaned. The flow rate ranges between 1.8 and 27 m3/h, at a supply pressure of 4.5-80 bar. The cleaning diameter is 2 to 14 m.
Drying out after CIP Cleaning
In the case of powder transport line with blowers, the means to dry out the line is readily available. Turn on the blower for 10-15 minutes prior to the introduction of powder and the system will be fine.
Most vessels and powder silos don’t have a facility to create the heat and airflow needed to effect the drying in a reasonable amount of time.
If your entire powder handling facility needs to be dried at once and in a short time, then a dedicated arrangement of fans and heaters may be required to facilitate the drying.
If only one area of your powder handling system gets cleaned at a time, then a portable fan and heater may provide a solution to dry out each area consecutively or as needed.
Either way, drying out of the process equipment needs to be considered when designing the operation of a CIP cleaned powder handling system in you plant.
Case Study 1 : CIP Cleaning of a Powder Handling System for Formulated Nutritional Powder
A brief was received from a producer of Infant Formula Powder. There specification included building a dry powder handling facility that included 6 powder silos, 3 powder blenders with integral bag dump stations, the associated interconnecting gravity drop ductwork and 4 dense phase powder conveying systems. These all needed to be CIP cleaned at an interval of every 3 months to separate allergen classes and to meet kosher production requirements. A KPI was set to complete all the CIP cleaning and have the system back in production 24 hours after the final powder left the system.
A CIP kitchen with the required tanks, pumps, heaters and valving already existed in the plant and would be used to supply the powder handling equipment. Only the new programming needed to be developed to automate the new CIP sub-circuits. The 24 hour timeline allowed us to be each sub-circuit consecutively, with none of them being washed concurrently.
Has the client required a shorter downtime than 24 hours, the existing CIP kitchen would not have been adequately sized because multiple sub-circuits would have had to have been washed concurrently, thereby driving up the cost of the entire project
The following scheme was devised and successfully implemented.
It was identified that the 6 powder silos would be easiest to clean and more importantly, the easiest equipment to set up to start the CIP cleaning , allowing the 24 hour time allowance to be used effectively. Furthermore, it was identified that the silos would also require the longest drying out time, so it was important to get them cleaned first.
The silos also each included a Bin Vent from which the filter socks would need to be removed for cleaning. The Bin Vents were designed for quick opening and easy top bag removal. The Bin Vet Fan could be isolated with a simple vapour tight damper.
A large diameter item like a powder silos is most effectively cleaned with an orbital cleaner. A port was designed into the top of each silo such that an orbital type cleaner could be installed on a fixed stalk about 10 ft. long.
The Bin Vents were designed to be CIP cleaned on the same circuit as their associated silo. When the Bin Vent was opened for filter sock removal, two static nozzles were installed manually, one above the filter tubesheet and one below.
This design allowed the first silo with bin vent to be ready for CIP within 20 minutes of the end of production. Then the automatic washing program was started which cycled through a water rinse, followed by a caustic wash, followed by a final rinse and then a sanitizer. The automatic wash program was completed in about 45 minutes.
While the first silo was washing, each subsequent silo was set of for CIP cleaning by the operators.
As each silo was finished washing, a dedicated fan and heater was manually connected to a port on the silos to create airflow to dry the silos. Because the time required to assure complete drying out was 2-3 hours, the fan and heater was sized to dry our 3-4 units operation at once.
The six silos were able to be cleaned about 5 hours, with the first 3 dried out within that time also.
The powder blenders provided the next challenge. It would have been desirable based on the size of the blender to permanently install nozzles on them to reduce operator set up time. But with the moving internals of a blender, this was not able to be done, Furthermore, the blender agitator, even when stationary during CIP, created a lot of shadows within the blender, so more nozzles than normal would have to be installed.
Each blender also had an associated ingredient bag dump station and it was decided that these would be cleaned with the blender. The Bag Dump station was handled very much like the Bin Vent. The operators would remove the integral filter socks. In this case, permanently mounted retractable nozzles were used. The key piece of design of the bag dump station was that the lid gasketing had to be designed so that the seal could be assured during CIP cleaning so that no liquid leaked into the room.
The blender Infeed and outfeed gravity ductwork was also cleaned with each blender. The ductwork has permanently mounted retractable nozzles installed to minimize the operator set-up time.
The blenders and associated bag dumps and ductwork were cleaned using the same regime as the silos. The set-up of each of the 3 unit operators took approximately 20 minutes by 3 experienced operators. The first blender was set-up while the last silos was washing.
The same dry-out system as was used for the silos was used for the blender systems.
Finally the four dense phase powder conveying systems had to be washed. The lines themselves would prove easy to wash and to dry out, but the unique challenge for these sub-systems was the manual set-up. Every 10 feet (3M) along the conveying line was a compressed air injection assembly. To meet sanitary requirements, these assemblies needed to be individually disconnected and capped off along the conveying line. The horizontal portions of the line would be fairly straightforward, but the line extended 120 feet (40m) vertically through the building. N array of platforms needed to be built to access the air injection points along the vertical legs of the conveying lines.
Operat or s were set to this task early, while the other sub-systems were washing and drying, but the system was designed to allow 120 minutes for the set-up of the four lines for CP cleaning after the blender washes were complete and then another 120 minutes was allowed for the set-up for production after the line washes were complete.
At the end of the conveying lie CIP, the downstream the compressed air that was the motive force for the system was used to dry out the lines. The lines were dry within minutes due to the dryness of the compressed air and the velocity of the air in the conveying line.
During the commissioning phase of the project all the operation and cleaning was validated and the time objectives were met to the satisfaction of the client.
Case Study 2: Flour Silos – A Cleaning Challenge
In this practical example, the development of an effective cleaning technology for a flour silo involved applying the different available cleaners and cleaning methods to ensure optimised hygiene.
This work was analysed by Wolfgang Haucke (Wolfgang.email@example.com) of GEA Tuchenhagen GmbH. In this example, GEA Tuchenhagen engineers worked closely with a well-known manufacturer of bakery products to find effective solutions to the challenges of cleaning the operation’s flour silos.
Component to be cleaned: an aluminium flour silo, 3.5 m in diameter, 33 m in height.
The bakery manufacturer’s products are made to the highest quality standards and are in compliance with extensive ecological and economic requirements. The hygiene requirements placed on the process plant make it necessary to clean all systems and machine components used for this type of production to a level at which no residues remain. For these cyclically repeated production processes, the customer’s quality assurance staff was looking for an advanced cleaning system for the interior cleaning of their flour storage silos (Figure 1).
The cylindrical flour silos, approximately 3.5 m in diameter and 33 m in height, which were presented to engineers for examination and advice on cleaning, do not have any internal structures. The silo walls are made of uninsulated aluminium and each has a conical outlet and a flat silo top with an eccentric manhole.
Located outside near the production building, the storage towers are arranged in a silo farm.
The flour is discharged from the silo by gravity onto a conveyor worm, and compressed air is used for further conveyance downstream. Production runs 24 hours a day all year long, and as such, each silo is periodically completely filled with flour and is then emptied continuously or intermittently, depending on process requirements.
As a result, the inside of the tank is irregularly contaminated with product residue deposits (Figure 4). These contaminants build up at various points and various levels; in particular, lumps of flour form at all heights of the silo wall, which, after the level has risen to a certain point, tend to drop down uncontrollably and cause recurring blockages with subsequent standstill of the downstream flour conveying and production plants.
This results in cost-intensive production downtimes for remedying the damage. The type and thickness as well as the adhesion behaviour of the contamination is largely determined by the quality of the flour; the flowing and emptying properties of the flour, depending on the discharge rate; the air humidity in the suppliers’ transport silos and in the storage silo itself; and the seasonal fluctuations in temperature and other parameters.
The previous cleaning process was such that hired cleaning workers/industrial climbers, equipped with manual lifting gear and watched by a safety supervisor, and entered the silos in order to clean them. Flour residues, which vary from light dust to heavily encrusted or sticky residues, were then removed either using brushes or brooms for light contamination or with spatulas and scrapers, in miner's fashion, for stubborn residues. The main drawback of this solution not only was that the mental and phy sic al strain for the workers, who had to be provided with breathable air, was extremely high, but cleaning also took several hours or even an entire day.
Additionally, the cleaning efficiency and results varied from cleaner to cleaner and the result was not repeatable. Due to the eccentric manhole, positioning of the personal safety and lifting gear for the cleaning workers was complicated and time-consuming. In order to minimise the time and effort described above as much as possible and to remedy existing problems, the company sought an improved cleaning process based on water with reliably repeatable results. An essential prerequisite was unreserved compliance with all customer requirements with regard to food hygiene regulations.
Cost-effectiveness, minimisation of cleaning times, cleaning media, utilities and auxiliary materials, and system sustainability also were of foremost importance to the bakery product manufacturer. An inventory of requirements, technical details and on-site conditions were recorded during a personal visit to the site. These initial engineering considerations were subsequently translated into a cleaning concept, which was then put to a practical test (i.e., basic engineering).
Interior surface of a storage silo heavily contaminated with flour.
As a next step, a suitable nozzle and cleaning pattern for the selected pressure cleaning method was chosen from the following nozzle systems, in accordance with the type of contamination, in this case an Orbital Cleaner was chosen.
When the engineering considerations for the method to be selected were finally aligned with the customer’s requirements, the relatively low-priced spray balls were excluded right from the start due to the degree of contamination, which can be very high at times. The rotating jet cleaner would have worked in the upper section of the silo, but it would not have been possible to implement the optimum cleaning line near the bottom of a 33-m high silo. To avoid an additional investment on the customer’s part for the necessary pumps, considerations with regard to medium- and high-pressure cleaning were not pursued.
Due to on-site conditions, the type of contamination and the silo geometry, a low-pressure method was selected for optimised water-based cleaning, which typically works with a pump capacity of 8-9 bar, cold water. As no external utilities were available on the silo dome, a turbine-powered cleaner was selected for testing.
For cost reasons, cleaning chemicals and thermal support for the cleaning process were not to be used. Considering an installation height of more than 33 m, an orbital cleaner with four nozzles of 7 mm each was selected, which discharges approximately 12 m3/h cleaning water at a working pressure at the cleaner of approximately 5 bar (Figure 5). The engineers expected short cycle times for cleaning when the cleaning result was first assessed, so it was decided to discharge the cleaning water into the onsite wastewater system.
To test the selected orbital cleaner under the given conditions, the cleaner was connected via a pressure hose to a centrifugal pump placed on the bottom of the silo and then introduced eccentrically into the silo and positioned at an immersion depth of 2500 mm and at a lateral distance from the wall of 500 mm (Figure 6). After positioning the cleaner, the cleaning process was started and monitored.
When the process was stopped after three minutes, a large part of the adhering, even critical, contamination had already been removed from those silo surfaces that were covered by the strong cleaning jets. This cleaning result, achieved just after a few minutes, confirmed that the selected path was correct. After an overall cleaning duration of just 15 minutes, all contamination, especially stubborn flour encrustations, were removed (Figure 7).
Despite the cleaner’s eccentric position, it worked without any oscillating movement in the silo, while generating a jet pattern that covered the entire surface of the silo, even in the deeper zones.
After completion of a water-based cleaning of the silo another point to consider was drying, as this is an indispensable step from a process engineering point of view.
Due to the seasonally ideal conditions for the cleaning process described and as the silos are installed outdoors, it was decided to remove residual moisture by convection. Direct sunlight on the surface of the silo ensured sufficient drying from a technical and economical viewpoint. To allow any residual water to evaporate easily, the upper manhole and the connection in the bottom section of the silo outlet cone were opened to enable optimum venting and discharging of moisture.
In similar applications where it is not possible to dry the silos by solar radiation, using hot water as a cleaning medium lends itself as a supplementary solution. The hot water heats up the silo walls during cleaning and afterwards dries off the inside surface of the silo by convection.
If hot water is not available for cleaning, another feasible solution for the reliable drying of the silo contact surfaces is blowing filtrated hot air into the tank via the openings at the top and bottom. Attention must be paid here that sufficient air flow rates are selected.
The silo after the cleaning operation with an orbital cleaner.
Approximately 3,000 litres of cold water were consumed to achieve the cleaning result, which were discharged into the factory wastewater system together with the removed flour.
The final laboratory analysis of the silo surface samples confirmed that the desired and expected results had been achieved. The water-based cleaning process selected and described in this article is repeatable under the conditions determined and achieves the desired result efficiently and effectively. In addition, the process defined allows for intermediate cleaning at any time in the event that contamination increases. Expensive external cleaning specialists are no longer required as water-based cleaning can easily be carried out by the customer's own staff and without any expensive production downtimes.
By Jim Kent and Wolfgang Haucke
Business Development Manager
GEA Nu-Con Ltd
GEA Colby Ltd
GEA Tuchenhagen GmbH