Home > Cogeneration could be the answer to our energy woes – Part 1

Cogeneration could be the answer to our energy woes – Part 1

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For engineers, improving the efficiency of their processes is a major challenge, but also an opportunity to improve their outcomes while consuming the same or a lower amount of resources.

With the current focus on climate change and the high cost of electricity in Australia, maximising the efficiency of energy generation is a major opportunity, and for Dr Jacob Klimstra, Senior Energy and Engine Specialist for Jacob Klimstra Consultancy, a no-brainer.

Dr Klimstra was in Sydney to speak at the 2012 Australian Institute of Energy National Conference, and present a Cogeneration and Trigeneration Professional Development Course organised by the Chemical and Biomolecular Engineering Foundation of the University of Sydney.

Hailing from the Netherlands, Dr Klimstra has long been a proponent of cogeneration systems, which are typically engines that generate electricity, as well as heat and other by-products which may be captured and utilised, maximising the output from the fuel.

In traditional fossil-fuelled power generation, the efficiency is typically 35 to 37 percent, with about two-thirds of the primary energy converted to produce electricity being lost as heat. Transmission losses are responsible for nine percent of the losses from net generation.

Cogeneration systems, according to Dr Klimstra, aim to make use of the heat created as a by-product of burning fuels for electrical generation.

This energy is harvested and utilised in processes, such that it is no longer wasted. With plants in more remote areas, cogeneration systems can either be used as the primary source of electrical and heat energy, or as a backup in case the grid fails.

Useful by-products

Regions with a local distributed network of cogeneration plants, would also benefit from reduced reduce transmission losses, and boosted reliability.

Dr Klimstra utilises the exergy model to explain the relative value of different forms of energy, and why, even with processes that only require one form of energy, it is always a good idea to have cogeneration in place.

"You can always turn almost 100 percent of electricity into motive power for driving electric motors, for creating light, running electronics, and if you want to turn it into heat, you can have very high temperatures," he explained.

"With electrical heating, you can create temperatures of maybe 3000 degrees Celsius even. You can't do that with a gas burner. The exegetic value of electricity is very high, which is why the price of electricity is also higher than that of heat.

"Given the high exergetic and monetary value of electricity, it makes financial sense to create electricity, even if the application only calls for heat.

"If you just burn the gas, you create heat. If you use the gas in a cogeneration plant, you get the high value energy, which is electricity, and a low value energy, which is the heat, available as a by-product," Dr Klimstra said.

Of course, the reverse is also true: where only electricity is needed, harvesting the heat and using it in processes helps boost overall efficiency.

Ambient temperatures

Heat has a variety of applications in industry, be it for drying foods or curing of materials. Where higher temperatures are needed, the relatively low level of heat from cogeneration plants can still be fed into the process to raise ambient temperatures, reducing the amount of electricity needed to achieve the target temperature, and achieving close to 100 percent utilisation of the energy locked in the fuel.

Heat can also be fed into absorption chillers to provide cooling, if that is what is required. "This is a lot better than having a big coal-fired power plant and throwing all the heat away and running at an efficiency of 35 percent. That's a waste of energy," said Dr Klimstra.

Dr Klimstra also pointed out that cogeneration systems are flexible, and other by-products of the generation process, not just forms of energy, can be used as desired.

Carbon dioxide from the engine, for example, can be harvested and used to boost plant growth in agricultural applications.

"The principle behind this is that everywhere where you need heat, be it for a chiller or for somewhere else, you should try to put a cogeneration plant," he concluded. "Even if you don't need electricity, just put the electricity in the grid."

According to Dr Klimstra, the prime movers for cogeneration are things like reciprocating engines and combined cycle turbines.

Combined cycle turbines are an assembly of heat engines which work off a single source of heat to reduce energy loss. In additional to a gas turbine and boiler, heat is turned into steam, and used to drive a steam turbine.

Gas-fired reciprocating engines can utilise exhaust heat, turning it into steam in order to produce electricity through a steam turbine.

When Dr Klimstra and his team started working on cogeneration, they used small gas engines from a Fiat. Rated at 15 kW, they had an electrical efficiency of 25 percent.

Improvements in engine technology have seen efficiencies for single cycle engines boosted to 49 percent, and turbochargers further improve performance.

"Relatively, the engines have become cheaper," Dr Klimstra told PACE. "For the last decade, the prices of these installations have not gone up. You don't even have to correct for inflation. The price level has stayed about constant because of improved production processes and higher output from the same engine block."

But while the equipment can be as simple and as complicated as the application demands, the specific expertise needed for the installation, commissioning and upkeep of cogeneration systems is something Australia lacks - and something Dr Klimstra hoped to address with the Cogeneration and Trigeneration Professional Development Course.

According to him, dedicated knowhow is needed from the installation stages: cogeneration plants, while being based on engines, are still fairly high-tech. With design, an energy engineering background is needed. Maintenance and operation requires the relevant mechanical qualifications, which already exist in Australia.

"With cogeneration, you have to know about lubrication, electrical system, safety systems, maintenance, and material properties," he explained. "It's a multi-disciplinary object, and you have to train people. So you need a group of dedicated people who know what they're talking about."

"If you want to install it into a process plant for instance, then you have to look at the ins and outs, like what is the heat demand, the temperature level of the heat, what is your electricity mark, do they coincide, do you need a heat buffer for temporarily storing the heat produced, because heat and electricity coincide - these things have to be analysed."

Continued in Part 2...

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