How clean is your steam? How to ensure the correct process grade

Paul Boughton

Steam is the most energy efficient, reliable, clean and sterile form of transferring heat. Its flexible characteristics provide endless possibilities to cook, sterilise, humidify, dry and generally heat thousands of applications in countless industries around the globe. Rob Stanley reports.

Steam is just steam, right? Well, actually no. Steam can be produced in a range of different grades, each matching different industries and applications. Ensuring the correct grade of steam is important for many processes. Getting it wrong could prove expensive, resulting in product being contaminated, sub-standard or even rejected.

When using steam it is important for any organisation to ask itself: "Do we really know what grade of steam is entering our process?" To answer this, it is necessary to understand the four common grades of steam.

- Plant steam, or industrial steam, is used in countless processes. It is by far the most common grade of steam used, with applications from precise temperature control for forming car tyres, to general hot water production for the food and drinks industry.

While there are no standards governing plant steam quality, it is important that the steam is clean, dry and free from boiler carryover. Dirty, wet steam will result in poor heat transfer and potential process control issues. Over a prolonged period, this may affect plant performance, and increase maintenance and operational costs.

Boiler operating pressure and loading, water treatment management and efficient distribution can all influence the quality of steam reaching the process.

- Filtered Steam, sometimes called 'culinary' steam, is plant steam passed through a fine stainless steel filter element. A 5micron element to remove 95 per cent of all particles larger than 2microns, is acceptable for culinary steam.

Since filtered steam can often be in direct contact with food, it must be dry and free of boiler water treatment chemicals. Although a 5micron stainless steel filter will remove particulates, it is not designed to remove boiler additives or volatiles that could potentially contaminate the final product.

Historically, the healthcare and related industries have used filtered steam for sterilization. However, in demanding ever-higher levels of purity assurance these sectors have migrated to the adoption of clean and pure steam.

- Clean steam is now used as standard in a range of quality-critical processes at risk from plant steam contaminants. Clean steam has been adopted principally by the healthcare sector, where moist-heat sterilisation is central to its operations.

Clean steam is also used in humidification of clean rooms in pharmaceutical and microelectronics production. In these environments, entrained contaminates may affect downstream products and processes exposed to the humidification system such as open aseptic processing.

To create clean steam, a secondary generator with a controlled feedwater quality is used. The design of the steam distribution network, material selection and installation practices are all critical for minimising steam degradation thus ensuring acceptable purity and quality at the point of use.

As the use of clean steam becomes more commonplace, the food-manufacturing sector is seeing the benefits in minimising contaminants when steam is used in direct contact with the process. By using clean steam, manufacturers know there will be no boiler additives, volatiles and particulates that could taint, blight or contaminate final products.

Clean steam is often used in applications such as sterilization not only to remove contaminants, but also to ensure the quality control of critical attributes such as dryness, superheat and production of non-condensable gases, all of which could adversely affect the process and equipment. This has been largely driven via standards such as HTM2010 Sterilization in the UK and European EN:285 Sterilization - Steam sterilizers - Large sterilizers.

- Pure steam. As clean steam has developed, the pharmaceutical industry has extended the concept of steam purity. In unit operations, either the equipment or the pharmaceutical product may be exposed to steam or its condensate. Where this could affect product quality, strict practices are in place in the form of Good Manufacturing Practices (GMP) as enforced and regulated by national agencies such as the US FDA and the European EMEA. As with clean steam, pure steam is created within a dedicated generator, but one designed, built and operated in accordance with GMP requirements.

The purity of the steam produced is such that its condensate matches the regulatory specifications governing Water For Injection. In other words, it is pure enough to be injected into the human body without any adverse effect. Steam quality selection and control is such an essential part of the manufacturing process that it is not something that should ever be left to chance. If in any doubt, you should always seek out expert advice.

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Rob Stanley is Market Development Manager - Food & Beverage, Spirax Sarco, Cheltenham, Gloucestershire, UK.

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