Control Design for CIP Systems

Clean-in-place (CIP) technology can clean appropriately designed process equipment and interconnecting piping without disassembly or reconfiguration. CIP methodology and equipment developed in the 1950s for dairy plant processes, and its implementation greatly reduced manual intervention and time required to clean process equipment, while improving quality and extending product shelf life.

By Barry J. Andersen March 1, 2007

Clean-in-place (CIP) technology can clean appropriately designed process equipment and interconnecting piping without disassembly or reconfiguration. CIP methodology and equipment developed in the 1950s for dairy plant processes, and its implementation greatly reduced manual intervention and time required to clean process equipment, while improving quality and extending product shelf life.

CIP technology has since been applied to many food, beverage, pharmaceutical, and bio-tech processes to remove process soil, reduce bioburden, eliminate allergens, and ensure lot-to-lot separation of dissimilar processes. The larger chemical processing industry has adopted it widely for the same reasons.

Basic concepts

CIP technology uses chemical cleaning solutions to remove product soils from plant processing equipment. Successful CIP operations require careful control of these cleaning solutions, using time, temperature, chemical concentration, and mechanical action to achieve satisfactory performance on a repeatable basis. A functioning cleanable process uses a CIP unit, generally skidded equipment, designed to accomplish the make-up and delivery of the cleaning solutions. The skid normally includes instrumentation, a PLC, HMI, and ancillary equipment necessary to ensure proper control, monitoring, and documentation of the cleaning process. This can be interfaced with asset management programs.

This illustration shows the most basic configuration of process equipment and CIP system. The isolation jumpers serve two functions in that they connect the process vessel and piping to be cleaned to the CIP system, while isolating it from other process equipment.

Most applications use multiple-pass recirculated cleaning solutions between the CIP unit and process equipment to maximize efficiency and minimize waste. Single-pass cleaning is only employed on easily removed soils on low capacity equipment, or when specific cross contamination or particulate are of concern. When finished, the solutions are discharged.

“System essentials for CIP” illustrates a simple CIP process diagram which includes the cleanable process equipment, a CIP unit, and piping for distribution and return of cleaning solutions. Any facility of even moderate complexity typically requires multiple CIP circuits, because any processes beyond the most simple will normally need to be cleaned in segments. Cleaning a large or even moderate scale process all at once is usually impractical. The cleaning circuit to cover each segment will include a predefined combination of process vessel(s), production equipment, pumps, and piping components. Success depends on proper design of these circuits, and it is critical that these be analyzed and laid out early in the project.

Other critical considerations during process design include proper specification and selection of CIP cleanable equipment, and implementation of sanitary and/or hygienic piping installation practices. Successful CIP begins with sound process design practices, which are described in the 3-A Sanitary Design Standards and the ASME BPE-2005 Design Standards for Bio-Processing Equipment . These documents describe design and installation guidelines for self-draining piping without “dead ends,” as well as providing guidance on cleanable equipment selection criteria.

“Basic CIP unit piping and instrumentation” illustrates a simple recirculating CIP unit that includes typical mechanical components and instrumentation for control and monitoring. In practice, there are many CIP unit design variations, and the skid selected for an application is dictated by the process cleaning requirements. The CIP unit pictured includes the basic components necessary to deliver flush and wash solutions, while providing control and monitoring of critical parameters, including flow rate, temperature, and chemical concentration. This CIP unit includes a rinse/recirculation tank providing surge volume, a centrifugal pump for solution delivery, a heat exchanger to temper cleaning solutions, chemical feed equipment, and associated control valves necessary to ensure system functionality.

Instrumentation and control

As previously described, CIP requires control of cleaning solution “physical action,” and this is achieved primarily by manipulating flow rates to maintain desired solution velocities through all CIP circuit sub-paths. The basic CIP model includes a flowmeter to control delivery volume and monitor flow rates. The flowmeter, combined with a flow control valve and associated PID loop, works to control CIP supply flow to match the cleaning circuit setpoint.

This simple CIP system is compact and self-contained, but provides all necessary instrumentation and control requirements.

A critical parameter is the time during which soiled process equipment is exposed to the physical actions of flush, wash, and rinse solutions. In general, exposure time during active flow phases may be controlled through volume monitoring. During sequences where flow is not active, for example a drain step, these phases are typically controlled through a software-controlled timer.

Cleaning solution temperature is monitored via a supply-side resistance temperature detector (RTD), with a temperature control valve and control loop. This controller can achieve and maintain a CIP solution delivery temperature to a specific setpoint. A return side RTD confirms that the cleaning circuit has achieved a specified minimum temperature setpoint, which becomes a quality check for circuit performance.

Cleaning solution concentration is confirmed through conductivity monitoring at the start of the chemical wash, and it is confirmed within an acceptable range throughout the wash duration.

A CIP supply pressure transmitter provides CIP circuit performance data, confirming that CIP circuits are hydraulically balanced and CIP spray devices are adequately supported. A properly designed and commissioned CIP system will exhibit flow, temperature, conductivity, and pressure profiles that are normally repeated within pre-defined acceptance criteria, time after time. A substantial deviation from an accepted range indicates performance issues, which if caught early, can be corrected before overall cleaning quality is compromised.

The rinse/recirculation tank usually is equipped with discrete level sensing probes or a level transmitter. This controls rinse water makeup and cleaning solutions, and monitors solution loss or leaks during recirculation.

The CIP return line is normally equipped with a device to detect rinse water returning back to the unit during initial steps of the CIP program. If rinse water is not detected when expected, the program aborts and triggers an alarm to alert operators of a problem requiring attention before the program can run successfully.

CIP distribution system

Even a simple CIP system has to have basic instrumentation and control capabilities. More complex systems add tanks for multiple cleaning and rinse solutions as required by the cleaning protocols.

CIP applications require a supply and return system that distributes cleaning solutions to various process equipment cleaning sectors. These need to be mapped carefully when planning the distribution system with appropriate block-and-bleed valve combinations or transfer panels to ensure proper isolation between sectors and adjacent process equipment.

The first means to provide physical make-break isolation is via a transfer panel or manual swing connections. This relatively simple, low-cost approach is effective, but requires manual labor to establish a cleaning boundary. The second means involves four valves to form a double block-and-bleed arrangement to ensure that any cleaning solution leakage across a blocking valve will be directed down the open bleed valve, isolating other process sectors from cleaning solutions. This can be fully automated for isolation control and monitoring, but is more costly.

The final method employs “mix-proof” or double seat compression-style sanitary valves that incorporate block-and-bleed protection within a single-stem valve package. This fully automatic system requires no manual intervention, but is more costly to install and maintain.

CIP programming considerations

A typical CIP program is a series of steps or phases that follows the process control system sequence. Typically, the phases or steps are initially documented in a matrix or pinning chart format to define the program for the user as well as system integrator. This matrix chart is the primary tool to provide a quick understanding of the program requirements. Additional supportive program documentation is often detailed in system functional requirement specifications and software design documents.

An effective CIP system HMI shows all operational functions and variables in a clear layout for operators.s.

In addition to the unit matrix chart, CIP recipes must be developed to enable the system to perform efficiently and effectively on all unique cleaning circuit variations in the facility. Proper planning and documentation of these recipes during the design phase will inform the system integrator of required software flexibility to optimize CIP program and circuit performance. Critical recipe parameters, like wash volumes, drain times, and flow rate are unique to each CIP circuit and sometimes system integrators attempt to hardcode these parameters to simplify program writing. This usually results in unsatisfactory system performance. Software design reviews between the CIP system designer, end-user, and system integrator ensure common understanding and proper execution of system requirements. CIP application programs should be simulated and tested as much as possible before installation and field commissioning.

Control platform requirements

When applying CIP technology to a process operation, the selected control system plays a big part in cleaning application success. The control system will be executing a complex group of discrete sequences and the system will need a powerful logic-solving instruction set. Moreover, the automation system must be capable of reasonably fast program execution, while providing rapid adjustment of PID control loops on these very dynamic systems. Many sequential functions are fairly short in duration, with some operating for only one or two seconds, and some control platforms simply cannot respond this fast. If these issues are not considered early in project planning, the result can be costly during process commissioning and optimization.

Application of current CIP technology should always be considered carefully at the very beginning of a manufacturing process design project, from process and control system design perspectives. In many cases, CIP aspects of the design are underestimated, and are often more complex than the production process itself. Proper planning from conceptual design through commissioning can ensure reliable, repeatable CIP cleaning applications.

Author Information

Barry J. Andersen is control systems engineering manager, Seiberling Associates, Inc. Reach him at .