Steam is a major utility and, as Sean Ottewell reports, its proper management is bringing substantial savings to users.
With oil and gas prices remaining unpredictable, controlling the cost of the energy used during processing is especially challenging. Rising energy prices can quickly eat into the cost base of any process, damaging profitability and competitiveness. As a major utility supplying many processing applications, steam is a highly effective heating medium and many companies have invested in improving their steam system efficiency over the years. One area of focus has been condensate recovery. Energy from condensate is widely used to pre-heat boiler feed water, lowering fuel costs and increasing boiler efficiency. In fact, each 6°C temperature boost achieved by condensate recovery will knock one percent off a typical boiler energy bill.
However, some condensate recovery systems are so effective that too much energy is sometimes captured. With the boiler feed tank running at atmospheric pressure feedwater is usually maintained at just 85°C or 90°C. Higher temperatures risk cavitation in the boiler feed pump, causing significant damage. This places a natural limit on the amount of heat that can be injected into the feed tank. For some plants this can mean that all the recovered heat from condensate cannot be used and often the only option is to let it drain away.
An innovative heat recovery system from Spirax Sarco solves this problem by creating a completely sealed steam system and transferring the heat from the flash steam and recovered condensate into the high pressure side of the boiler feed pumps. The water entering the boiler can be raised to well above 100°C without causing pump cavitation.
The benefit is a significant lowering of steam-raising costs and an increase in boiler efficiency. The Spirax Sarco flash recovery energy management equipment (FREME) system also recycles all water through the system, reducing water and chemical treatment costs.
With concerns about rising energy costs Abbey Corrugated, the UK's leading corrugated board sheet feeder, commissioned Spirax Sarco to project manage the installation of a FREME system as part of its energy saving campaign.
Before the project, water entered the boiler at around 68 or 70°C. It now arrives at between 138 and 142°C, according to facilities manager Paul Gale: "There was a lot of work going on at the time, but it's fair to say that the savings from this project were in the region of 25 per cent of the gas used by the boiler."
The FREME system passes condensate from the steam distribution system through a flash steam separation vessel. The separate flash steam and condensate streams each travel through a dedicated plate heat exchanger, where they heat the pressurised feed water before it enters the boiler. The two returning streams are then recombined and sent back to the boiler feed tank. At this point the combined stream is sub-cooled, so it is sufficiently warm to begin heating the cold feed but not hot enough to cause cavitation in the feed pump.
A great advantage of the FREME system is that it can be supplied as a pre-engineered, skid-mounted system, taking the stress out of designing, specifying, building and installing steam, hot water and other systems (Fig.1). Buying a complete package from a single supplier also ensures that all the components will be perfectly matched. This results in a system that is more efficient, reliable and accurate. And with less work to do on-site, the installation process is simpler, safer and speedier.
It is a similar story at Smurfit Kappa UK's corrugated board factory in Weston-Super-Mare, England, where steam system improvements delivered by Spirax Sarco have cut boiler fuel costs by 21 per cent.
Recycling condensate and flash steam back to the boiler has also halved the amount of water treatment chemicals needed and reduced the site's water bill by between EUR334 and EUR445 a month. The biggest single contributor to this success is a FREME system. The project also included improved temperature controls for the Smurfit Kappa's process steam and the installation of automatic pump traps to clear condensate from key items of plant reliably, even if the traps sometimes have to work against significant back pressure.
According to Andy Bale, Smurfit Kappa's engineering manager, the project was part of a wider initiative to save energy at the factory: "We are working with the Carbon Trust to improve the energy management in a number of different areas, including compressors, steam and electrical equipment. Spirax Sarco was very professional and managed the whole process for the steam system while keeping me up to date with every single detail. We're very pleased with the results."
The new FREME system was supplied as a prefabricated, skid-mounted rig, comprising a flash separation vessel and two plate heat exchangers. Pressurised condensate from the production process enters the separator where it splits into separate streams of condensate and flash steam. Each stream passes through a separate heat exchanger, where it heats the boiler feedwater. The two streams are then recombined and sent back to the boiler feedtank.
Crucially, FREME systems are typically positioned downstream of the boiler feed pump. This allows feedwater temperatures to be elevated well above 100°C, without pump cavitation. In the case of Smurfit Kappa, this has enabled the company to have heated feedwater entering the boiler at 130 and 140°C, rather than the 85 or 90°C that was previously possible.
On 3rd November, FREME technology won the energy category at the prestigious annual Institution of Chemical Engineers' awards event which rewards excellence and innovation in chemical engineering.
Steam traps and calorifiers too
Steam trap management is another important way of saving energy. Heinz expects to cut more than four percent from its energy consumption over the next three years at its Wigan factory in Northern England after signing up for a steam trap management contract with Spirax Sarco. The decision to opt for the new contract followed great success with a previous, one-off steam trap survey, which saved enough energy and treated water to pay for itself in less than nine months.
The Heinz factory in Wigan is the largest food factory in Europe. The 55-acre site produces canned soups, baked beans, pasta and puddings for the UK and European market, and its on-site energy centre generates up to 140 tonnes of steam per hour to keep the canning lines running.
Under the new deal, Spirax Sarco engineers will survey the site every six months, highlighting any traps that need maintenance from teams at Heinz. Spirax Sarco specialists will spend around ten days on site each year, checking, tagging and recording the condition of each steam trap.
"When Spirax Sarco carried out the original survey they put in a conservative estimate of savings and we ended up saving much more," says Barry Aspey, the utilities manager for Heinz. "That helped us decide to opt for the three-year contract. If the new savings estimates are correct, the contract offers excellent value for money and should help us reduce our carbon emissions by 200tonnes a year."
Catalent Pharma Solutions is also reaping the rewards, thanks to its decision to swap old shell-and-tube calorifiers for compact Spirax Sarco EasiHeat steam-to-hot water systems. Spirax Sarco calculated that Catalent could save EUR7200 a year in energy costs by replacing a single 540kW calorifier with an EasiHeat.
Catalent has been gradually replacing its old heat exchangers over that past five years, and now has nine EasiHeat systems in place. The biggest saving for Catalent is in downtime and maintenance costs, according to engineering manager Arthur Burnett: "The main thing is that we now have no summer shutdown, when it used to take two weeks. Also, we can look after the heat exchangers with one utility engineer instead of four, so it frees up time for our maintenance team. Previously, there was so much work involved with the calorifiers that we sometimes had to bring in contractors to service them, which was obviously another expense."
Shell-and-tube heat exchangers are pressure vessels and must therefore be dismantled annually for an insurance inspection. EasiHeat systems instead rely on stainless steel plate heat exchangers (PHEs), which eliminate the need for stripping down. PHEs are also extremely compact and energy efficient.
Catalent's Swindon factory encapsulates various products in soft gel capsules. Between them, the new heat exchangers serve two hot water systems, one at 80°C for process water and air conditioning, and the other at 60°C for hand washing.
"The old calorifiers were over 20 years old," says Burnett. "They were not very efficient, slow to heat up and caused a bottleneck in the process." In contrast, he says that the EasiHeat units are more than equal to the task: "We used to run three large calorifiers for one application and replaced them with two compact EasiHeat systems. Although we always have one on permanent stand-by, for safety and maintenance precautions, we've never even had to use it for an application because they're so efficient."