N.Y. Comp. Codes R. & Regs. tit. 1, Appendices, app 11
EVAPORATING, DRYING AND DRY PRODUCT
EQUIPMENT CLEANING
(cf. Part 3)
I. Cleaning of Evaporators and Condensers
Some evaporators are designed to that the product is exposed to large surface areas for a long period of time at temperatures conducive to the growth of micro-organisms.
Pipelines and/or equipment designed for automated mechanical cleaning of evaporators should meet the following requirements:
1. A pH recording device should be installed in the return solution line to record the pH and time which the line or equipment is exposed during the cleaning and sanitizing operation.
2. These pH recording charts should be identified, dated, and retained for 3 months.
3. During each official inspection the regulatory agency should examine and initial the pH recording charts to verify the time of exposure to the cleaning solutions and their pH.
The following are suggested procedures for cleaning and sanitizing evaporators and condensers:
The surface area inside an evaporator is extremely large. Not only is there a large separator chamber and vapor lines but steam chests may also have as many as 500 heating tubes from 8 to 10 feet long. The total surface area may be 3000 to 4000 square feet which may require large volumes for recirculation. This surface area must be cleaned and sanitized carefully or it will contaminate the product. The operating temperatures in an evaporator are very close to the growing temperatures of thermoduric and certain mesophyllic types of bacteria. The first effect may operate at 140°F to 170°F (60°C to 77°C) the second effect at 125°F to 145°F (52°C to 63°C), and the third effect at 100°F to 120°F (38°C to 49°C). The product being evaporated is often recirculated in the last effect several times until the right concentration is reached which may give bacteria ample time to grow. A clean evaporator operates more efficiently. It is necessary to clean the evaporators after long periods of operations because burned-on material reduces heat transfer and efficiency. A point is reached where it will be more economical to stop and clean up than to continue to operate. Evaporators need cleaning for sanitary reasons as well as for efficient operation. Tube chests and heating plates must be cleaned to get good heat transfer. If vapor lines are not cleaned, it is possible to get a back surge of vapor when the vacuum is released. This can carry soil back into the product thus lowering the quality. This soil may drop into the thermo-compression unit, block passage of vapors and actually prevent good operation. Compounds for cleaning are usually divided into two main groups:
1. The alkaline cleaners usually contain caustic with water conditioners, synthetic detergents and foam depressants added to enchance cleaning action. The purpose of the alkaline cleaner is to digest the bulk of the soil. The alkaline solutions are usually run first at concentrations ranging from 1 percent to 3 percent at temperatures of 180°F to 190°F (83°C to 88°C) for 30 to 60 minutes.
2. Acid cleaners are usually food grade with synthetic detergents and inhibitors to prevent attack on metal surfaces. The purpose of acid cleaners is to remove mineral films, alkali cleaner residues, and shine the inside surfaces. Acid solutions are usually used last at concentrations of 0.2 percent to 0.5 percent at 140°F to 160°F (60°C to 71°C) In all cases cleaners and cleaning instructions should be followed as recommended by the manufacturer of cleaning compounds. It is also necessary to follow the recommendations and instructions of evaporator manufacturers. The evaporators operating with compressed ammonia require special cleaning precautions.
Cleaning Methods.-There are three basic methods of cleaning evaporators: boil-out; circulation; spray cleaning; or a combination of the three methods. The boil-out method is the oldest but it is still very effective. It is accomplished by rolling or boiling the cleaning solution under partial vacuum. Heat is applied by the evaporator and just enough vacuum is used to roll the solution. Cleaning solutions are elevated to the dome and upper parts by opening and closing the vacuum breaker. Hand brushing of some areas is often necessary following boil-out because it is difficult to thoroughly clean the upper surfaces with this method.
Circulation cleaning is a newer method of cleaning. The cleaning solution actually follows the product path. The solution is circulated by returning it back to the starting point. Heat is applied by a pre-heater, tube chest, or steam jet, sometimes called a boil-out nozzle. This method is not adaptable to all types of evaporators and it is usually necessary to add spray cleaning devices to thoroughly clean separators and the bottom tube sheet in steam chests.
Spray cleaning is the newest method of cleaning evaporators. Cleaning solutions are pumped through spray devices and distributed over the surfaces which are contacted by the product. Heat is applied by pre-heater, a surge tank, or on the run with live steam. When properly designed and operated spray cleaning systems are used, cleaning problems are at a minimum. Spray cleaning offers many advantages over boil-out or circulation methods of cleaning. Less water and less cleaning solution is required. This not only results in a saving of water, heat and cleaners, but more concentrated cleaning solutions can be used giving faster, more effective cleaning. Heat for the rinse water and cleaning solutions is applied externally, preventing additional burn-on in tube chests. As the evaporator is not under vacuum, less heat is required to keep solution hot, resulting in a saving of fuel. Higher temperatures can be used to improve cleaning efficiency. There are some disadvantages to spray cleaning. Spray devices cost extra money because they are specifically designed for almost every operation. Spray devices must be properly placed and designed to cover the top of the dome in the separator, the tangential inlets, the vapor lines, sight glasses, and steam chest tubes. Spray cleaning may require additional stainless steel lines to convey the solution at the necessary volumes. Larger pumps are also required to pump the necessary volume of cleaning solution. Even with these disadvantages, the advantages of savings in heat, water, cleaning compound and time outweigh the disadvantages. Sometimes there are advantages in using combined systems of cleaning. It may be possible to boil out the steam chests and spray the separators. Sometimes it is possible to circulate the steam chests and spray clean the separators or other portions of the unit. Quite often the combined systems, especially the circulation in the spray system, will work best on certain types of evaporators.
One of the biggest factors affecting the method of cleaning used is the type of evaporator. In a falling film type, circulation cleaning can be used to clean the tube chests and spray cleaning can be utilized to clean the evaporator chambers. When using a plate-type, circulation cleaning is best. In an internal type tube chest, a boil-out system for the tubes and spray cleaning of the separator works very well. With an external cheat type, the entire unit can be spray cleaned. If it is a compressed ammonia operated evaporator, spray cleaning works well. Sanitizing should be done to eliminate any microorganisms which may have survived the cleaning regimen. Sanitizing can best be accomplished by using chemical sanitizers. Heat may be used if all surfaces are heated to 180°F (83°C) or higher. Since there is a tremendous investment in stainless steel evaporators, it is necessary to use a product which does not corrode stainless steel. Chemical sanitizers can be applied through the spray equipment or they can be applied with fogging guns.
II. High Pressure Pump and High Pressure Lines
The high pressure pump and high pressure line to the dryer nozzles may be cleaned as a separate circuit by connecting the line to the nozzle back to the drop tank and this tank connecting to the inlet of the high pressure pump. The regular product atomizing nozzles should be removed before cleaning is to be done.
Another method of cleaning the high pressure pump and lines is to include this pump and high pressure lines in the circuit when wet cleaning of some types of spray dryers. In either case a solution of 1 to 3 percent caustic heated to 160°F (72°C) should be circulated for at least 30 minutes. A solution of inhibited acid should be pumped through the atomizing system as a daily procedure to remove the milkstone from the high pressure pump and high pressure line. The solution of inhibited acid should be recirculated a minimum of 10 to 15 minutes and followed by a rinse with potable water.
It is also recommended that the high pressure pump head be disassembled as a daily procedure immediately following the final rinse and the parts be placed on a table or rack for air drying. When the pump is disassembled the parts are to be checked to see if they are clean, and to see if any maintenance is required to remove pits; seats are also checked at this time. Since a high pressure pump is subjected daily to extreme heavy duty, the valves and seats are recommended to be ground periodically to maintain uniform pressure on the atomizing nozzles. Prior to use, the entire system should be sanitized.
III. Wet Cleaning of Dryers
There are several methods of wet cleaning dryers. The first method is hand brushing. The operators get into the dryer with buckets of cleaning solution and brush all surfaces of the dryer. The unit is then rinsed with a hose. Cleaning can also be done with hand operated spray guns. These spray guns are pressure pumps which operate at high pressures in low volumes; in many cases, box type dryers can be completely cleaned with the addition of a seven-foot extension on these pressure guns. By using high pressure spray guns and cleaning compounds with a high synthetic detergent content, it is possible to remove very difficult soil. The third method of wet cleaning is by spray cleaning with various types of stationary or rotating spray devices. They usually operate at a high volume of low pressure in the range of 10 to 20 psi. Constant spray coverage can be obtained when spray devices are properly designed. Usually several spray devices are required because of the many chambers, collectors, and down pipes within these units. Less time is required to do a complete job with spray cleaning. The systems are installed so that cleaning lines are easily connected to the spray devices and an effective return system. Spray cleaning time is much shorter than hand cleaning time, especially in large units. Spray cleaning eliminates the entry of men into the drying units. Silo or vertical type dryers are often 20 to 50 feet high and it is difficult and dangerous to clean by hand or by hand operated units. Spray cleaning eliminates the flavor contamination when switching to other products. If an ungraded product is run through the dryer, it is necessary to thoroughly clean before running a product like Grade A nonfat powder. There are disadvantages to spray cleaning. The spray devices must be properly placed and designed to do the complete cleaning job. They must be removable so as not to affect the air currents during operation. However, the advantages of safety plus cleaning time and consistently complete cleaning outweigh the disadvantages. A typical spray cleaning cycle might operate as follows:
The various spray heads are placed in the dryer and securely fastened into place. The rinse water is pumped through the spray device and allowed to run down the side walls of the drying units. Cleaning compounds which are mild alkalis or chlorinated cleaned-in-place cleaners are prepared at 0.3 to 1 percent concentration heated to 160 to 180F (71 to 83C), and circulated for 45 minutes to 1 hour. The unit is given a final rinse and is thoroughly dried. Occasionally acid type cleaners are used to control mineral films. Sanitizing with chemical sanitizers is a controversial subject. Sanitizing can be done with heat but it may be difficult to heat all surfaces to 180°F (83°C). Heating to 180°F (83°C) for 10 minutes does not kill spore formers. However, they are killed with many chemical sanitizers. Even if heat is used, it is recommended that chemical sanitizers be occasionally used. By pumping the sanitizer solution to the high pressure pump or by fogging with high pressure, it is possible to completely cover the product-contact surface. Actually, the unit must be thoroughly dried before operation. Chlorine sanitizers may cause corrosion. Obviously, these compounds should be used with care. If chlorine is left on the dryer and heat is applied, the chlorine droplets will become hot and concentrate and cause pitting. When chlorinated cleaners are used, a dryer surface can be effectively cleaned and at least partially sanitized and the solution can be completely rinsed. Acid-synthetic detergent type sanitizers have been developed which are effective on spore formers. These compounds are germicidal, effective in hard water and stable in hot or cold solutions. They have an advantage in that they are noncorrosive to dairy metal. It is not necessary to wet clean dryers on a daily basis. However, a schedule should be set up so cleaning is done periodically. As long as a dryer is operating continuously, it is not necessary to clean it from an efficiency standpoint. Some types of dryers require very little cleaning, maybe once each month; others require dry cleaning on a more frequent basis. It is necessary to clean and sanitize dryers if they are going to remain idle any appreciable length of time. Bacteria may grow in dryers which remain idle. Dryers must be spray cleaned if they are improperly operated, causing burn-on in the drying chamber. Whenever fires develop inside the drying unit or when burn-on occurs, it is necessary to thoroughly clean at least the drying chambers. Quality is the key to the dry milk industry. There should be a program of cleaning and sanitizing of both evaporators and dryers. Better quality products are produced in evaporators and dryers when thoroughly cleaned and sanitized on a regular basis.
IV. Dry Cleaning
It is very difficult to discuss proper cleaning procedures without also discussing proper operating procedures, especially the start up and shutdown of the dryer. Assuming the dryer has been properly started and operated throughout the run or drying cycle, the first step in a successful cleaning operation is shutting the dryer down properly. The type of energy supplying heat to the dryer chamber, i.e., steam or gas, alters the proper shutdown technique. The correct procedure in shutting down a steam heated dryer is as follows:
1. Shut off the main steam valve at the proper time.
2. Maintain proper dryer outlet temperature for drying by gradually reducing the output of the high pressure pump until the residual heat of the steam coil is dissipated to a point where it does not maintain proper temperature or until the product being pumped by the high pressure pump does not maintain a satisfactory spray pattern.
3. Keep product removal system and conveying system in operation.
4. Keep air intake and exhaust fans on dryer in operation until main chamber is sufficiently cooled to provide a comfortable atmosphere for the cleanup crew.
On a gas-fired spray dryer, the burner assembly has very little or no residual heat capacity. Therefore, the shutdown is more rapid. The correct procedure for shutting down a gas-fired dryer is as follows:
1. Shut off gas supply to burner.
2. Immediately shut off high pressure pump.
3. Same procedure as steam heated dryer.
4. Same procedure as steam heated dryer.
After the above procedures have been accomplished, shut down the intake fan. Let exhaust fan and vibrators or shakers continue to operate, also product removal system. The exhaust fan should be severely dampered so that it induces only a small air flow. A small auxiliary fan is sometimes used in lieu of the dampered exhaust fan. The use of either fan serves a twofold purpose: first, it is helpful to put the drying system under a slight negative pressure to reduce the tendency for product to drift out of the system into the plant through open doors, etc. Secondly, it is vital to prevent thermal currents from creating a reverse air flow through the drying system, which tends to deposit product on the heating surfaces and plenum duct. Product deposits on steam coils reduce their heating ability, create sediment and conceivably bacterial problem areas. If the dryer is gas fired, there is a further hazard of fire. It is important, therefore, that the closure or covers supplied by the manufacturer be placed on the inlet air duct system simultaneously with the shutdown of the fan. After any prime product has been removed from the drying system and the sifter operator notified, the system is ready for cleaning. The cleanup crew should be supplied each day with a freshly laundered set of coveralls, white cap, white face mask, and clean rubbers or boot covers (canvas, or single-service plastic). Prior to donning the above uniform, the procedure is to remove the spray nozzles and pipes as these are normally cleaned with the liquid dryer feed equipment. With clean uniforms, proper brushes and preferably vacuum cleaning equipment, they enter the main desiccator chamber and start the cleaning process as far upstream as possible from the powder removal or pneumatic conveyor system.
1. The first portion cleaned is the collector system. This is done by inserting a brush into the cloth tubes and brushing the length of the tube. Again, this can be done more satisfactorily by utilizing the special vacuum tools designed and available for this service.
2. Remove dustcovers and brush or vacuum out nozzle ports.
3. Manually brush or vacuum ceiling and walls of drying chamber.
4. Sweep or vacuum clean floor of the dryer, placing product in a container.
Note.--Do not remove this product by way of product removal system.
5. Inspect dryer for any inadvertent wet spraying or nozzle drippings that may have occurred during the drying cycle. Should either of these have occurred, the application of a minimum amount of water and effort will be required to remove the clinging material. Any moisture introduced must be removed before operation because of its effect upon smooth product flow and because it would establish a more favorable environment for bacterial growth if it were allowed to remain.
6. Check collector for loose or torn bags and any other mechanical checks necessary before leaving the dryer.
7. Close dryer securely and check switches to make sure they are in the proper starting positions. At frequent intervals, not over a two-week period, the operator should clean and inspect the heated air intakes of the dryer, assuming that the dryer is properly operated during this time. However, should a malfunction occur where the dryer operator does not follow the procedures outlined for proper shutdown, it may require inspection and cleaning at closer intervals. Frequent inspection will eliminate a source of sediment contamination.
8. On startup after dry cleaning of the cloth collector dryer, the first two bags of product shall be discarded. This will allow for the removal of any product remaining in the tubes and system after shutdown.
V. Auxiliary Dry Product Equipment
Part A. Sifters
In general, there are two types of dry product sifters in use by the dry milk manufacturing industry. These are the shaker type and the rotary or gyrating type. Both are designed to operate at various capacities either manually bagging or packaging from their outlet or designed for automatic packaging equipment.
For the general guidance of sifter manufacturers and the dry milk industry, the following screen size openings may be considered as recommended openings to result in satisfactory screening of the listed dry products:
TABLE 3
Sieve designation | Maximum sieve opening | ||
| Product | (from ASTM 223.1) | (approx.) | |
| mm. | inch | ||
| Nonfat dry milk ....... | #25 | 0.707 | 0.027 |
| Dry whole and dry buttermilk ....... | #16 | 1.19 | 0.045 |
It is recognized that larger screen size openings may be necessary for sifting certain special dry products (such as "instant" products) and for classification of products into different particle sizes.
Openings referred to above are based on general experience as to what constitutes satisfactory screening to remove product lumps or potential product contamination, and also on ability of most currently used sifters to successfully sift dry products through such size openings without excessive loss of fine product into the "reject material" outlet. (Other factors also affect loss, such as: percent of "open area" in screen used; uneven flow rates to the sifter; ratio of screening surface to dryer capacity; amount and kind of mechanical energy applied to the screening surface; sifter design and construction; and nature of dry product being sifted.)
Screen opening dimensions may be obtained by any desired combination of wire thickness and number of wires per inch. For instance, if the screening surface is made of stainless steel woven wire, the 0.027 inch opening might be obtained by using 24 X 24 mesh market grade screen cloth made of wire 0.014 inch thick (about 45 percent open area) or by using 30 X 30 bolting cloth screen made of wire 0.0065 inch (about 65 percent open area) or by many other mesh-wire thickness combinations. These combinations allow a wide choice to obtain desired balance between screen strength and percent open area. If materials other than stainless steel are used to construct the screening surface, similar combinations may be employed to achieve desired opening size.
Recommendations for Cleaning Dry Product Sifters
1. Dry cleaning program. -The procedures set forth below should be followed.
a. Completely dismantle and thoroughly vacuum or dry brush clean all product-contact surfaces of the dry milk sifter. Reassemble as soon as finished and make every effort to keep all parts dry.
b. Check sifter screen(s) for broken or displaced wires (threads) and for other openings around the frame of the screen, which might permit the passage of unsifted product. Other parts of the sifter, including ball trays and balls, if used, should also be inspected for condition. Any necessary repair or replacement should be made as soon as possible.
c. Flexible rubber or cloth connectors at the inlet and outlets of the sifter should be thoroughly cleaned daily following the procedures as recommended for the sifter. At this time, connectors should be closely examined for holes, cracks, or other damage. (To facilitate removal for cleaning, use of easily removable fastening devices are recommended.)
d. Thoroughly vacuum or dry-brush clean all external parts of the sifter, including the sifter frame and drive mechanism.
2. Wet cleaning program. -The procedures set forth below should be followed.
a. Completely dismantle as in 1. above, remove all loose dry product; then rinse all parts with clear water; and follow by a thorough hand brushing of all parts using a general purpose dairy cleaner. Rinse thoroughly to remove all evidence of cleaning solution or soil. It is recommended that hot water (170°F (77°C) or above) be used for rinsing in order to sanitize the equipment and to aid the subsequent drying.
b. Allow all parts to air dry completely prior to reassembly.
c. The wet wash should be done as frequently as necessary and should be done after each use if the sifter is not being used on a daily basis.
d. After cleaning, drying, and reassembly, the product outlet should be protected against recontamination.
3. General recommendations.-a. Vacuum cleaning is preferred to brush cleaning or cleaning with air under pressure as it decreases the dust drift problem to other areas of the plant.
b. Brushes or vacuum cleaner fittings used for cleaning product-contact surfaces should not be used for cleaning nonproduct-contact surfaces or for other uses which might result in contamination. Such brushes and special fitting should be stored in an enclosed cabinet when not in use. For protection and housekeeping considerations, such cabinets preferably should be of non-wood construction and should have open mesh metal shelving.
Note.-For additional details see 3-A Sanitary Standards for Sifters for Dry Milk and Dry Milk Products, Serial 26-01.
Part B. Storage Bins
The use of portable bins is becoming increasingly popular with the dry milk industry. These tote, or portable, storage bins when used shall comply with the construction requirements of Item 11p and the cleaning and sanitizing requirements of Item 12p (sections 3.19 and 3.20).
If interior bracing and ladders are used in plant storage bins they shall be constructed of smooth rounded metal, and be installed sufficiently far from the walls to prevent harborages. Product entrance and discharge openings connected to the attending conveying equipment shall be dust-tight and shall be easily accessible for cleaning. Vents to the exterior shall be equipped with readily removable air filters of adequate capacity or readily removable covers. If air is to be introduced into the product zone, only filtered air shall be used, and it shall comply with the applicable standards of Appendix 7. Auxiliary agitators or any other interior devices, if used, shall be designed to be smooth, crevice-free, and readily cleanable. The exterior surface of the bin should be smooth, hard finished, and readily cleanable. Hinges on covers, if used, shall be the take-apart type. Covers or doors shall be provided to enclose the product zone when product is not being dumped. These shall be so constructed that dirt or dust on top will not slide or fall into the bin when the cover is open. Access openings shall be provided on all in-plant bins. Such openings should not be less than 18 inches in their smallest dimension. Covers shall be constructed without raised internal reinforcements and should be hinged and equipped with a quick opening device. The gaskets for such openings shall be made of material which is nontoxic, nonabsorbent, smooth, and unaffected by the product. Storage bins in continuous use either in the plant or in transporting dry products from one plant to another should be cleaned according to manufacturer's recommendations when necessary. They may be cleaned by either approved dry cleaning methods or wet cleaned.
Part C. Packaging and Packages
Packaging equipment for dry milk, dry milk products and dry whey will vary greatly as to their design depending upon whether the packages being filled are drums, bins, or bags. Whatever equipment is used should be designed so as to protect the product from contamination from outside sources and from air during the packaging operation. All connections of conveying equipment to packaging devices should have dust-tight connections. All conveyors, ducts, belts, and screws used in connection with packaging equipment should be provided with a dust collector system capable of eliminating any visible dust, All product hoppers, when used, should be provided with covers to properly protect the product from contamination. Hand filling should not be permitted except for periods of adjustment of automatic weighing devices.
N.Y. Comp. Codes R. & Regs. tit. 1, Appendices, app 11