General References

W. T. Clarke, The Literature of Cacao, ACS, Washington, D.C., 1954.

L. R. Cook, Chocolate Production and Use, Magazines for Industry,

Inc., New York, 1972. B. W. Minifie, Chocolate, Cocoa, and Confectionery: Science and

Technology, AVI, Westport, Conn., 1970. E. M. Chatt, in Z. J. Kertesz, ed., Economic Crops, Vol. 3, Interscience Publishers, Inc., New York, 1953, p. 185.

B. L. zoumas J. F. Smullen Hershey Foods Corporation University Park, Pennsylvania

CITRUS. See Fruits, semi-tropical; Fruits, tropical.

CLEANING-IN-PLACE (CIP)

From the time of its early use in the 1950s, the practice of cleaning-in-place (CIP) for cleaning of plants processing potable liquids and other products such as ice cream and butter has become widespread and is now considered an established cleaning technique (1,2). The technique of CIP stands for cleaning of the tanks, pipelines, processing equipment, and process lines by circulation of water and chemical solutions (hereafter referred to as solution) through them. The term CIP or cleaning-in-place emphasizes that the technique does not require dismantling of pipelines or equipment, which was the case with manual cleaning. Manual cleaning was extremely time-consuming and expensive, and often the level of hygiene (bacteriologic cleanliness) achieved through it was low and inconsistent (2). Introduction of CIP, which became inevitable in the face of economic pressures to increase throughput, increasing cost of labor, scarcity of labor, and technical developments by equipment manufacturers and detergent chemists, alleviated the problems associated with manual cleaning (2,3). Three forms of energy—chemical, kinetic, and thermal—are generally needed for any cleaning operation. In comparison to manual cleaning, higher temperatures and stronger chemical (detergent) concentrations can be used in CIP. Solution temperatures up to 88°C and detergent pH up to 13 can be used in CIP (4). The equipment design and the properties of the material to be cleaned impose limits on temperature and strength of solution. Lower temperatures may have to be used if product residue (soil on product contact surface) becomes harder to clean at higher temperatures. Manual brushing, which contributes a great deal in manual cleaning, is totally eliminated in CIP and, in some sense, is replaced by the kinetic energy of turbulent flow in pipelines or impingement of jets in vessels (1,4). The circulation time is also a factor in cleaning, and an increase in the time, within a limit, improves the cleaning achieved. Circulation time from 5 min to 1 h is used in practice (5). One of the most important though less noticeable advantages of CIP over manual cleaning is the fact that CIP provides freedom in plant design from the severe limitation of keeping the plant manually cleanable and hence helps in development of new processes and ideas (3). The use of CIP has also made it possible and convenient to automate the cleaning operations in a plant where it was impossible in the case of manual cleaning. The sequence or cycle of operations in any cleaning are the same regardless of cleaning technique (5). A normal cleaning sequence consists of prerinsing with water, washing with detergent solution, and postrinsing with clean water. In addition, there may be a disinfection (sanitizing) stage followed by a final water rinse. Prerinsing is an important stage. It should be started as soon as possible and should continue until the discharging water is free from product residue (soil).

REQUIREMENTS FOR CIP General Requirements

Only a plant that is properly designed to be cleaned by CIP can be cleaned by CIP efficiently (4). The design of a plant that is to be cleaned in place and the design of the equipment and system that is to apply the CIP technique should be compatible. The CIP system should be designed as an integral part of the processing plant; modifying the plant later for CIP may pose problems (4). All product contact surfaces must be accessible to the pre- and post-rinse water and solution. The material that comes in contact with cleaning solution must be able to withstand the solution at its concentration and temperature. For this reason, most of the construction material is stainless steel.

Requirements for Pipelines

There should be no crevice condition, especially in the pipe joints. Crevice condition can lead to bacterial trap, which may be impossible to clean by CIP (6). As far as possible, pipelines should have welded joints. Proper drainage of prerinse water is important in CIP system to avoid any dilution or cooling of solution. To provide the drainage, all piping should have a minimum fall (pitch or slope) of 1:100. Pipe work should also have good support to prevent the pipes from sagging. Any sags in the pipeline would prevent complete drainage and put strain on the pipe joints. Un-cleanable dead pockets must be avoided inside the pipeline. This may not be achieved, if CIP is added to the plant as an afterthought instead of being an integral part (2). A mean flow rate of 1.5 m/s is normally recommended, but a mean solution velocity of 1.0 m/s may be sufficient in some cases. In practice, there is not much gain in exceeding the mean velocity beyond 2.0 m/s (4). Volume flow rate would depend on the diameter of the pipe. Higher flow rates create a higher hydraulic pressure drop, hence power requirements of circulating pumps could be considerably larger. Abrupt changes in the diameter of pipes that disturb the flow and reduce the cleaning efficiency should be avoided (6).

Requirements for the Vessels and Tanks

The cleaning-in-place of storage tanks or vessels is performed by spraying the cleaning solution onto the surface of the vessel through pressure spray devices located inside the vessel. The spray devices may be rotating, oscillating, or fixed. The fixed device, which is in the form of a perforated ball, is used most commonly. The fixed or static spray ball device does not have any moving parts and therefore gives trouble-free operation with minimal maintenance. Rotating or oscillating devices may wear and give a distorted spray pattern. They may also jam or stick in one place with the consequence of incomplete cleaning of the vessel. A single rotating or oscillating jet, however, can clean a larger-sized vessel than can a single static spray ball. The installation of the spray device should result in a spray pattern that must always cover all parts of the vessel, including probes, agitators, and areas shadowed by them. If required, more than one static spray ball should be used for total coverage in the vessel. Suitable filters should be used to prevent blockage of the spray device. Spray devices should be run at designed pressure and throughput. Too high a pressure can cause atomization of the solution and too low a pressure will reduce the force of jet impingement—both resulting in unsatisfactory cleaning. Permanently installed spray devices are commonly used, but removable spray devices may be preferred in certain special circumstances. Adequate venting of vessels is extremely important to avoid the collapse of the vessel due to a vacuum created during in-place-cleaning when a cold-water rinse immediately follows a wash period with hot detergent. The vessel and the supply and return CIP lines to it should have adequate drainage, otherwise undrained prerinse water can dilute and cool the solution, hence resulting in unsatisfactory cleaning.

Cleaning Circuits

Factory installations as a whole are generally divided into a number of circuits that can be cleaned at different times by CIP technique. It is a usual practice to group pipelines, vessels, and special equipment such as heat exchangers and evaporators into different cleaning circuits because of their different cleaning requirements with respect to flow rates, pressures, and chemicals (1). The product residue deposit (soil) should be of the same kind in a circuit, and all components of the circuit must be available for cleaning at the same time. Hot and cold lines of the plant may be placed in different circuits. After the introduction of automation, it has become practical to clean some parts of the plant while production continues in the adjacent areas. In such circumstances, it is necessary to prevent contamination of product by the cleaning solution. In recent years, double seat valves with the internal leakage drains being used to safeguard against such contamination (2).

TYPES OF CIP SETS/SYSTEMS

CIP sets can be categorized as centralized, local, and satellite or decentralized. In a centralized system, the various CIP circuits are connected by a network of pipes to one or two central CIP stations or units, which consist of all necessary equipment for storage and monitoring of cleaning fluids (water for rinse and solution). Large capacity water and detergent tanks (13,600 to 27,700 L) are used in centralized CIP (4). The system may work well except in the case of large processing plants where long pipe runs require large pump capacities and excessive energy use owing to heat losses. Also, the longer pipelines may contain some water after the prerinse operation that can dilute the detergent solution (7). Overcoming this problem increases chemical consumption. Another disadvantage of a centralized system is the fact that total reliance for cleaning the plant is placed on one or two central stations or units (4). In case of failure or malfunctioning of the central units, the whole plant may have to be shut down. In contrast to the centralized system, the local system requires a greater number of smaller tanks and pumps and shorter pipe runs. The system is more reliable. If one local unit fails or malfunctions, the cleaning of the plant not served by that local unit can still be achieved. The local system would require a greater number of heating units and detergent-strength (concentration) controllers (4). The satellite system is a combination of central and local systems. In the satellite system, there are central solution tanks and the local units draw the required volume of solution using properly sized pipes from the central tanks. The heating of the solution is arranged locally (4). Large modern food-processing plants generally employ a satellite system (7) because of the advantages of saving energy, water, and detergent.

The CIP systems are also classified as single-use, reuse, or multiuse systems, depending on whether the same cleaning solution is used for one, many, or few cycles of cleaning (2). The single-use system is most suited for cleaning heavy soil loads (such as in thermal processing equipment) or cleaning of small plants (8). The system uses the minimum amount of detergent needed for cleaning a circuit and discharges the solution to the sewer after one cleaning cycle is over. The system may be wasteful of detergent and energy and can cause effluent problems (4). However, it is simple in installation and operation. By contrast, the reuse system is complex in installation and operation. The reuse system provides for the reclamation and reuse of the cleaning solution and final rinse water— the latter is used as prerinse for the next cleaning cycle. More detergent may be added to the solution between the cleaning cycles to counteract the loss of detergency due to expending chemical energy to remove the soil. The solution is discharged to the sewer when it becomes very dirty. The reuse systems require greater capital expenditure but offer savings on volume of water and detergent solutions and energy used (4). Greater benefits can be derived from the reuse systems in plants that have light soil loads and use large-diameter pipe circuits (especially in the brewing industry) (8). The multiuse system is a compromise between the single-use and reuse systems. The final rinse water and solution are used for a few cleaning cycles before discharging to the sewer. In terms of capital and operating costs and complexity of the installation and operation, it is between single-use and reuse systems. Many factors: type and size of plant to be cleaned, soil loading, range and type of chemicals available, pressure drop in pipeline cir cuits, and pressure and throughput required for vessel spray device, should be considered before selecting the type and size of the CIP system.

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