Bring Cinders to the ball 23 September 2014

Steam generation and distribution plant still isn't getting the attention it deserves. Brian Tinham looks at what's required to bring this Cinderella to the high-efficiency ball.

It's been said before, but it bears saying again: steam-raising in industry is too often a Cinderella among the utilities. Quite simply, steam generation and distribution equipment just doesn't get the maintenance attention, much less the investment, it requires to perform anything like as efficiently and effectively as it could. And that is quietly damaging business competitiveness and profitability, with energy consumption needlessly high and steam capacity, quality and/or responsiveness limiting production.

Sounds overstated? It's not. Estimates of fuel costs related to steam-raising vary, but figures around 40% – particularly for process plant, but also many manufacturing facilities – are far from uncommon. Yet the proportion of engineering and maintenance resource bestowed on steam plant is typically tiny, compared, for example, to production line machinery and process plant assets. It's entirely understandable: these, after all, represent the front line for making a difference with continuous improvement. But glance under the covers and the utilities upon which they depend may well be straining at the seams.

That being the case, there should be two clear action points. First, conduct an urgent review of your steam estate, focusing on measurable plant condition and efficiency, but also waste. And second, take a good look at some of the newer technologies that promise to re-optimise energy usage and/or recovery, or to improve on-demand steam (and hence also hot water) provision.

For your review, at a top level this is about auditing fuel input versus useful steam output, set against the range of steam and hot water loads (capacity, pressure, etc) and any reported production problems. In parallel, though, you should also be checking the boilers, burners and ancillaries – including the monitoring and control systems – but also the operating regime and water treatment schedule. And don't forget the distribution side, including pipework, valves, heat exchangers and condensate return lines. Remember the importance of lagging, leak detection and steam traps, which are known to fail unnoticed open or partially open.

So much should be motherhood and apple pie – although high-profile stories of cost savings following steam trap audits alone demonstrate the scope for improvement. But the other side of the coin concerns the roles for newer technologies, not only in terms of energy saving, but also improving steam capacity and quality. Spirax Sarco is good value here, with a focus in recent years primarily on its FREME (flash recovery energy management equipment, which harnesses flash steam to pre-heat boiler feedwater) and EasiHeat – condensate sub-cooling and heat transfer units designed to extract useful energy and provide hot water. Note that the latter has also now been updated with its SIMS (Spirax Intelligent Monitoring System), which provides for automatic energy performance monitoring, diagnostics and alerting for maintenance engineers.

The firm's latest introductions, though, concern pressurised de-aeration systems and microturbines. Looking at the former, Andy Cowin, marketing manager for metering and boiler house systems, explains that these take conventional units one stage further. Instead of the de-aerator head mixing cold make-up water with flash steam from the condensate and boiler blowdown systems at atmospheric pressure – so raising the feedwater temperature to 85—90°C and reducing dissolved oxygen to circa 20ppm – pressurised systems take those to 100°C-plus and 20ppb.

The result is improved energy recovery, the potential to cut down on oxygen scavenging treatments required to prevent boiler corrosion, and reduced maintenance. Pressurised systems also virtually eliminate any risk of chemical carryover with steam injection plant in, for example, the food and drink sector. And they serve as surge collection tanks, typically providing for about 15 minutes' worth of reserve hot water.

Cowin concedes that installing such a system is a "big project", given the sophisticated control and safety systems involved, but adds that payback is generally within two years, depending on production requirements. He also makes the point that, since they operate at sub 0.5 bar, they fall outside the Pressure Equipment Directive, requiring only inspection in line with "sound engineering practice". Incidentally, BS EN 12953-6:2011 part 10 specifies water treatment and conditioning requirements for all new remotely-operated shell boilers – and those can only be met by installing pressurised de-aeration.

As for the microturbines, Graham Dear, who looks after heat transfer at Spirax Sarco, describes these as novel alternatives to conventional pressure reducing stations, installed close to the point of use. The technology is similar to large-scale power generation turbines, but much smaller and single-stage. Also, whereas the former use high-pressure, superheated steam, microturbines are more robust, with blades designed to tolerate saturated steam. "That's very important, given that most industrial steam systems run at about 95% dry but 5% wet steam, which would quickly destroy a conventional turbine," he explains.

That said, passing steam through a microturbine enables plants to generate their own electrical power, while simultaneously dropping pressure at the outlet for downstream use, as required. Dear says a steam microturbine producing 300kW could generate cost savings of more than £150,000 per year – adding that equipment is available to run from 80kW up to 3MW. He gives the example of a boilerhouse generating steam at 10bar for a food production plant running loads of 5,000kg/h, 24 hours a day at, say, 2 bar. "A microturbine there would pay for itself within a couple of years and then go on to make or save money from its electricity generation," he claims.

A lot depends on the steam demand pattern, and Dear agrees that good savings are predicated on longer hours of operation. He also concedes that boilerhouses will need to generate "slightly more steam", because of fractional losses in the turbine itself. However, he classifies installing a microturbine as a medium-scale project, requiring a G59/2 panel to connect to the grid and some additional floor space. And the result: a utility transformed into a profit centre.


Biomar energy recovery saves 10% on steam
Biomar Grangemouth is reporting some 10% savings on its gas bill since installing a system that recovers energy from flash steam otherwise lost to atmosphere. Indeed, the aquaculture manufacturer says its FREME (flash recovery energy management equipment) system, engineered by Spirax Sarco, has paid for itself 10 times over in the last four years.

Engineering manager Christopher Strain explains that the site – which processes more than 100,000 tonnes of fish feed annually – uses 7,700kg/h of steam for production, with its flat bed dryers alone consuming 2,500—4,500kg/h.

Condensate and flash steam from the dryers now enter a flash recovery vessel, which separates them into two streams. Each flows through its own plate heat exchanger, transferring energy to the boiler feedwater. The system runs to the high-pressure (downstream) side of the feed pump, so safely raising its temperature to 130C, rather than typically 85C.

Strain says that, apart from substantial energy and water savings, there have been improvements in the stability of the steam system, with less boiler cycling. He also points to improved condensate quality, which minimises boiler contamination and corrosion, with a knock-on effect on maintenance costs and downtime. "Overall savings on water treatment fell by almost 40%. We have seen substantial savings in both direct and indirect maintenance costs, and increased boiler uptime."


New steam generators cut costs for Vacu-Lug
Retread tyres manufacturer Vacu-Lug has cut costs with two Babcock Wanson ESM 2000 coil type, gas-fired vertical steam generators on its curing process.

"The ESM 2000 installation, together with an ongoing programme of process plant lagging and steam trap maintenance, has enabled us to significantly reduce our gas usage," confirms production engineer Peter Connolly. He also says that steam raising was chosen over thermal fluid heating, because of its reliability and ability to quickly follow demand.

"We have found that steam generators react well to our variable steam demands. They can proceed from standby to steam generation within minutes." And he points to Babcock Wanson's quick Autostart facility, which enables a standby generator to be brought online fast.

Both ESM 2000s were also fitted with economisers to allow the feedwater to collect heat from the waste flue gases prior to entering the steam generator.

Brian Tinham

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