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Secret ingredients for steam efficiency

16 February 2020

Alex Parish offers advice about improving steam efficiency to ensure that users are getting the best out of their steam boilers. 

Used in everything from jacketed kettles, ovens, and fryers to pasteurisation, decontamination and sanitisation processes, steam is one of the most hardworking multitaskers in the food factory. 

It is not unusual to find steam boilers operating 24-hours a day, seven days a week. Steam is required in many applications, including heatings food, eliminating microbiological risk, sanitising packaging, sterilising packaged food, and cleaning plant equipment uses. Consequently, steam boilers often represent a high percentage of energy usage within food manufacturing – so maximising efficiency is vital. 

Thankfully, advances in boiler technology as well as basic maintenance, make energy and cost savings possible.

The part of the boiler where combustion gases pass generated heat over water heating surfaces is referred to as ‘Pass’. Generally, the higher the number of passes, the more efficient the boiler. Most steam boilers will typically use either one, two or three pass technology, but some on the market do offer four-pass technology – a design which aims to maximise the opportunity for heat transfer, resulting in low exit flue temperatures and greater efficiency. Four-pass boilers also offer faster start-up times, saving further energy.

Larger chambers
Larger steam chambers enable boilers to respond quickly to peaks and troughs in load demand, ensuring operational continuity, and avoiding unnecessary energy wastage – so it is always wise to pay attention to size. Some steam boilers offer steam chambers up to 30% larger than others.  Additionally, larger chambers can almost eliminate boiler priming – where water droplets are carried over with the steam – instead delivering drier, higher quality steam. This reduces system scaling, contamination and condensate losses, and increases the efficiency and longevity of the boiler plant.

Recovering from heat loss
Larger boilers often come with the option of an economiser. Fitted to the exit flue, an economiser recycles heat that would otherwise be lost and wasted, putting it back into the burner. This means that the boiler does not have to work as hard in raising water temperature, saving energy – typically around 10%.

Boiler blowdown refers to water that is intentionally blown out of a boiler in order to avoid the concentration of impurities (dissolved solids), which occurs during the evaporation of steam. Most steam boilers have automatic blowdown, known as auto total dissolved solids (TDS), but those using boilers without auto TDS must ensure that blowdown is undertaken manually at regular intervals, otherwise reduced boiler longevity is inevitable. In fact, in the absence of frequent blowdowns and proper water treatment, steam boilers can fail within a couple of years.  

Water treatment can make or break efficiency and longevity. Food manufacturers located in hard water areas (approximately 65% of mainland England) must control scale, a phenomenon which drastically reduces energy efficiency, can lower flow rates, and cause blockages.

Relatively inexpensive and highly effective, water softeners are a popular choice for controlling scale, but it is important to bear in mind that water softeners do waste water during the regeneration process and also require strict management (otherwise boiler health and manufacturer guarantees are at risk).

A new alternative to softeners is reverse osmosis (RO). Traditionally prohibitively expensive, boiler RO systems are now financially accessible to many food manufacturers. Boiler ROs achieve almost complete purity of boiler feedwater– thanks to specialised semi-permeable membranes – which results in superior steam and increased energy savings by optimising boiler TDS and reducing the frequency of boiler blowdowns, with minimal maintenance. 

Corrosion also needs to be controlled in steam boiler equipment. For this, it is a good idea to engage specialists to manage water quality testing, chemical dosing, etc. If a strict water treatment regime is not adhered to, corrosion can result in pitting of metal surfaces, leading to premature repairs, replacements and even complete boiler breakdown. 

It goes without saying that the maintenance service of a boiler is also important. A good service provider should also determine the frequency of boiler services, based on the working hours and maintenance requirements of the boiler, rather than just offering a one size fits all approach. For example, boilers in operation 24/7 will require more frequent servicing than those that do not. 

Alex Parish is managing director at CFB Boilers.

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