Although CHP (combined heat and power) plants have been around for years in various guises, it appears that factories and process plants alike have generally been slow to adopt them – preferring conventional heating plant and largely buying electricity from the grid. While there's no problem with that, the contention from those in the CHP industry is that many are missing out on substantial energy cost savings, as well as green financial incentives.
First things first, and CHP here is not just about large-scale CCGT (combined cycle gas turbine) technology, as used by gas-fired power stations up and down the land. For manufacturing sites, we're mostly talking about internal combustion engines, generally powered by natural gas, diesel, biodiesel or propane – or biogas from an AD (anaerobic digestion) plant – and driving a generator set. Waste heat is then recovered both from the engine's hot water jacket (via a plat heat exchanger) and its exhaust manifold (via a shell and tube heat exchanger), and typically used to drive hot water (or air) and/or steam systems.
Hence the massive hike in efficiency over traditional plant: indeed, figures of 85% are frequently bandied about – more than twice the efficiency of conventional generation – not least because electricity is generated close to the point of use. Looked at another way, CHP systems are claimed to reduce carbon emissions by some 20% while cutting electricity costs by one third. They can also yield cost savings of up to 40% over grid electricity and boiler-generated heat.
Just as important, though, ranges of CHP units are now available to deliver from as little as 4kW all the way up to 10MW. That is a truly massive range, so there can be little doubt that something should be available for everyone.
What's more, as Ian Hopkins, director of Ener-G, observes, CHP also scores well in terms of versatility. Plant is available for new and refurbished buildings, to replace ageing boilers, and to extend existing or new boilers. "CHP systems can also be configured to provide off-grid resilience to keep the lights on in the event of a blackout," he advises.
Maximising benefits
So why has industry been slow to respond? In part, it's bound to be factory and plant managers needing to sweat their existing assets: no amount of pleading three to four years, ROI and a plant lifespan up to 15 years is going to convince some people. However, for others the issue is getting a handle on CHP's feasibility and infrastructure requirements on their sites – and how to size and specify a plant to maximise payback and those tax incentives.
In fact, the first aspect is not rocket science. As David Shaw, business development manager at Baxi-SenerTec, says: "A system that is too big for the application won't operate efficiently." Not a huge surprise, and in general (although not always), CHP scores well where there is a large demand for heating (and possibly also cooling via absorption chillers – leading to tri-generation). As for the detail, it's about establishing site demands for heat, power, steam and cooling, and whether continuous or cyclical. Your CHP package should then usually be sized for base load, with secondary plant for peak heating. But not always: as Jonathan Graham, policy manager at the Combined Heat and Power Association (CHPA), says: "In some instances, to achieve the power-to-heat ratio, it can be more economic to oversize the package to deliver slightly more [electrical] power than the base load, with the option to sell any excess electricity generated back to the grid."
Incidentally, note that most CHP players are also happy to enter into long-term operation and maintenance contracts, with full remote monitoring – many also extending that to risk-reward options. That will be attractive on plants where time-expired equipment needs to be replaced. Installing super-efficient CHP is also a good way for manufacturers to reduce maintenance costs and get rid of that engineering backlog.
If environmental responsibility is a key factor for your project and you currently run water and waste treatment plant where the COD (organic strength of liquid effluents expressed in oxygen equivalent) is sufficiently high, you may also consider building an AD plant. That would consume, for example, food waste and generate biogas to fire your CHP plant – minimising natural gas burning, avoiding landfill and eliminating transport CO2 emissions and costs.
So far, so good, but Shaw also states: "The fiscal benefits of a gas-fuelled CHP system are much more of a challenge." Why? Because maximising tax breaks – such as eligibility under the ECA (enhanced capital allowance) scheme, ROCs (renewable obligation certificates), RHI (renewable heat incentive), CCL (climate change levy) exemption, and exemption from business rates – requires your scheme to score adequately on DECC's (Department of Energy and Climate Change) CHP quality assurance (CHPQA) scheme.
And that essentially means proving the plant harnesses at least 80% of the generated heat, and doesn't release to atmosphere. You will need to provide data covering fuel used, power generated and heat supplied (annually for smaller plant) – using calibrated metering systems – in line with the European CHP Directive.
Be advised that, while the 80% bar may sound high, correct sizing and ensuring that your CHP plant acts as the lead heat source (remembering to select flow and return temperatures of heating circuits that prevent nuisance tripping with integrated heating systems) should suffice. Hopkins also advises that appropriate controls, ideally linked to a site's building energy management system, is the way to go – and reiterates that there is also no substitute for proactive maintenance.
But the last word goes to CHPA's Graham. "A variety of heat types can be recovered from a CHP plant, including LTHW [low-temperature hot water], MPHW (medium-pressure hot water), steam and, in the case of tri-generation, chilled water," he says. "CHP provides a practical method of stabilising a power supply that may be at, or near capacity, and can offer a lower cost option than having a high voltage line extended to cope with increased demand. CHP is also a sustainable option for businesses keen to improve their environmental credentials."
His advice: "But before commissioning the installation of a CHP package, operators should first carry out a feasibility study and site survey to ensure suitability and to make any modification to site infrastructure. The likelihood is that there will be a natural gas line, for example, in which case it is important to assess whether there is sufficient pressure and if the supply is interruptible, as well as the volume requirement for gas, as CHP actually increases the amount of gas consumed."
