Energy Oversight19 June 2015

With energy-saving projects reaching saturation point, it's worth reminding ourselves that there are more improvement options than might meet the eye. Brian Tinham reports

It's surprisingly easy to become myopic about shopfloor energy efficiency. That may sound perverse, but busy engineering departments can only do so much with limited budgets, resources and time. So we can forgive ourselves for initially focusing only on projects that appear to promise our particular plants and factories the highest potential returns. Those might include, for example, modernising lighting, installing solar power, moving over to CHP (combined heat and power) or replacing ageing electric motors with high-efficiency alternatives and probably VSDs (variable speed drives) or soft starts.

However, a problem arises when other, potentially serious energy-saving contenders – some new, others not – fail even to make it onto steering group agendas simply because they fall outside current project boundaries. That's how cost- and emissions-cutting tricks are missed. And some may be relatively simple and inexpensive to implement – certainly in whole life cost terms – even for maxed-out engineering departments. So, for those not impacted by ESOS (the government's Energy Saving Opportunities Scheme, which requires energy audits to be completed by 5 December 2015), it's time to open our eyes.

We're not talking about obvious initiatives, such as switching lights and machines off when they're not needed: those should long since have been put to bed. Among big hitters worth serious consideration today are: novel steam systems and biomass-based process heating systems, both of which effectively transform waste into energy; alternatives to variable speed drives for projects where the latter appear overkill; and even intelligent chargers for battery powered plant, such as forklikft trucks. At the other end of the scale, leak detection and repair projects, particularly on steam and compressed air infrastructure, might lack glamour, but can pay for themselves very rapidly.

Waste to energy first, and bio-energy and bulk solids handling specialist Saxlund International is the surprise purveyor of a novel wet steam turbine (WST), designed to produce emission-free electricity from low-grade steam. Developed by sister company Opcon Energy Systems around a twin screw Lysholm turbine, the Opcon Powerbox WST can produce 200—800kW of electricity from saturated or superheated steam that cannot be used in a traditional turbine because of the damage it would cause.

Saxlund managing director Matt Drew explains that the Powerbox WST replaces steam pressure reduction valves in existing process steam applications. He also points out that it can harness low-grade steam from industrial processes, instead of releasing it to the environment.

"There is a significant opportunity here to help process industries and medium size power generators to capitalise on waste heat to drive efficiencies and savings," he insists. "Waste and residual heat from industrial processes are significant energy resources but are frequently neglected. In many instances, costly cooling plant is required when that waste heat could be generating electricity."

Drew observes that small-scale production of electricity from waste could benefit virtually any steam-raising plant, given that energy costs are increasing again. The Opcon Powerbox WST is available as standalone skip-mounted equipment, designed to run side-by-side with existing energy or process facilities. And, importantly, ROI is claimed as between two and four years for a waste to energy plant generating 6,000MWh of emission-free electricity per year.

Meanwhile – and admittedly generally only for larger scale plants – Saxlund's heartland bulk handling plant business is also now offering solid waste fuel (SWF) storage, transportation, weighing and injection systems. They are aimed at plants wanting to move over to sustainable waste-derived fuel firing for process heating, and the UK's largest cement works – at Hope Construction Materials' Derbyshire site – is currently commissioning one of the first to drive both kilns.

Hope projects engineer Richard Worthington says that the new plant will divert 80,000 tonnes of bulk solid waste from landfill each year. "The completion of this multi-million pound project increases the amount of waste-derived fuels we use and forms part of the major investment we announced in January to boost efficiency and improve sustainability at Hope Works," he states.

The goal, he says, is to increase the rate at which Hope can replace fossil fuels with waste-derived alternatives to more than 50% – a key part of the company's long-term sustainability target. In this case, the project incorporates a 350m3 fuel reception and push-floor storage plant, reclaim conveyors, process tower with drum magnet and star screen, together with a weighing and pneumatic injection system for the main burners.

Drew says the system facilitates stable and reliable process conditions to minimise material build-up in the pre-heater tower. He also claims it is future-proof, explaining that the new plant has the flexibility to handle changing fuel characteristics, including different types of waste-derived fuels, should supplies change in the future. And, just as important, the installation has been designed with low maintenance and high availability in mind – minimising any potential for restrictions and blockages.

For example, the push-floor fuel bunker provides for 'first in, first out' fuel delivery. Also, where possible, maintenance points have been sited externally to minimise disruption. "Once fully operational, the new SWF system will run on a 24/7 basis, delivering fuel at a rate of up to 5,000kg per hour to each kiln," says Drew.

Back on the factory floor, for a more modest outlay, low-voltage electric motor users can achieve much of the energy-saving control benefit of VSDs but without the cost by turning to power firm Eaton's variable speed starters – essentially a step up from soft starts. "In many applications, particularly those involving pumps and fans, VSDs offer too much complexity and functionality, while ordinary motor starters provide no speed control," explains product manager Guido Kerzmann. "Our new VSSs are ideal where only limited functionality is needed, as they are very simple to use, yet offer full speed control."

He also suggests that Eaton's VSSs can be used in constant-speed applications with high-efficiency IE2 motors if premium-efficiency IE3 motors cannot be physically accommodated. That's despite the latest iteration of the mandatory EU MEPS (European Minimum energy Performance Standard) standard requiring premium-efficiency IE3 motors in the 7.5—375kW range unless VSDs are implemented. Other applications where VSSs provide significant benefits include those involving very high start frequencies and those where there is a high thermal load on the motor.

Eaton is currently offering PowerXL DE1 VSSs in two sizes: a 45mm slimline version, for use with motors up to 1.5kW, and the 90mm model for motors from 2.2 to 7.5kW. Both have internal motor protection as well as thermistor and short-circuit protection, and are equipped for regenerative energy feedback detection and dc braking for fans prior to start-up. They also have Modbus interfaces and integrate with Eaton's SmartWire-DT wiring system, which is designed to cut panel wiring times by up to 70%. What's more, Kerzmann reckons VSSs require 80% less commissioning time than VSDs.

What about leak detection on existing steam and compressed air systems? Suffice to say that, with estimates of steam waste at around 22% due to leaking steam traps alone, while poorly maintained compressed air lines commonly suffer 40—50% losses, there is everything to play for.

Maintenance specialist PEME uses condition monitoring techniques including thermography and ultrasonic air leak techniques to identify and quantify energy losses from steam heating lines, compressed air systems, refrigeration pipelines, boilers, hot water systems and also buildings. The firm reports "spectacular successes", with one recently completed single-day ultrasonic survey on behalf of a Tier 1 automotive manufacturer identifying 45 compressed air leaks in one business unit – amounting to some £11,500 of energy savings annually.

Brian Tinham

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