Making the case for clean in place: boil-up methods are no longer the standard for cleaning high-purity process reactors. (Pristine Processing)

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Authors: Gerald J. Cerulli and John W. Franks
Date: Feb. 2002
From: Chemical Engineering(Vol. 109, Issue 2)
Publisher: Access Intelligence, LLC
Document Type: Article
Length: 3,611 words
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Clean-in-place (CIP) technology provides a repeatable, automated process for cleaning process equipment and fluid-flow systems [1]. During the CIP process, developed more than 50 years ago for the dairy industry, cleaning solutions are applied to the surfaces of process systems to effectively remove a soil or contaminant without disassembling the process system. Contact time, temperature and concentration of the cleaning agent are tightly controlled.

The use of CIP technology has since been embraced by the finished pharmaceutical and biotechnology sectors, and is rapidly becoming standard practice. Over the last decade, many companies involved in the production of active pharmaceutical ingredients (APIs) have incorporated CIP into the design of their plants. However, there is still resistance to CIP technology.

Some of this resistance is attributed to the capital costs for implementing CIP in a new facility or retrofitting an existing plant to accommodate the technology [2]. Another factor is the complexity of software designed to handle frequent changeouts of a variety of products, as may be the case in plants built for custom synthesis [2]. Also at issue are the safety concerns associated with spraying solvents. Perhaps the most influential factor hindering CIP, however, is the assumption that traditional cleaning methods are equally effective, in terms of both cost and performance. Upon closer examination, neither of these assumptions holds true.

CIP vs. boil-up methods

For years, the typical method for cleaning batch reactors in bulk chemical facilities has been to perform "boil-ups." This method consists of introducing a solvent in which the product residue, or soil, is soluble. The solvent is then heated to reflux. Solvent vapor condenses in the overhead system and on the top head of the reactor vessel. The expectation is that, given enough time, the condensing vapor will dissolve any chemical contaminants.

Boil-up is augmented by line flushing, which is effective for cleaning piping 3 in. or smaller (larger lines require inordinate amounts of fluid to produce the required velocities). The advantages of boil-up are that it is straightforward and requires no additional piping or spray devices beyond those required for the process.

However, API facilities that use boil-up methods may spend as much as 30% of their time cleaning process trains [3]. In addition to being time and energy intensive, boil-ups do not make the most effective use of aqueous cleaning solutions; the technique is virtually impossible to make repeatable; and most importantly, the results may be inconsistent or unsatisfactory.

A major shortcoming of boil-ups is that the condensing vapor only acts where it condenses. Soil actually inhibits the condensation of vapor and therefore, cleaning. Most of the vapor is condensed in the overhead condenser, while dead legs, like valved or blinded nozzles, receive little of the cleaning solution. This also applies to ducts and chutes, as the rate of condensing does not provide adequate run-down over vertical surfaces.

Consider, for example, a 1,000-gal reactor undergoing an atmospheric boil-up with acetone, a common cleaning solvent. By assuming that the reactor's wetted heat-transfer area is limited to...

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Source Citation

Source Citation
Cerulli, Gerald J., and John W. Franks. "Making the case for clean in place: boil-up methods are no longer the standard for cleaning high-purity process reactors. (Pristine Processing)." Chemical Engineering, vol. 109, no. 2, Feb. 2002, p. 78+. Accessed 3 Apr. 2020.
  

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