It is clear that we are in a transition to renewable and decentralised generation, and I support that transition.
Through calendar 2017, electricity supply from coal-fired plant amounted to 71% of the volume of electricity produced from all sources in the NEM, including estimates from small-scale solar provided by the APVI.
By 2030 most forecasts have coal still supplying a significant (if not majority) share of the electricity supply mix. Adding in supplies from gas-fired plant pushes the percentages still higher.
But, despite this majority share, there has been no incentive to decrease its’ own emissions intensity since the removal of the carbon tax. On the contrary, the ongoing lack of policy certainty has delayed investment, and in some cases deferred maintenance of this fleet.
Some options for reducing emissions intensity of coal-fired electricity
When we look at improving the efficiency (Emissions Reduction) of a plant we look at two areas:
The first is regaining efficiency lost through degradation, which is returning the plant to design. Most of the plant degradation recovery is achieved in major overhauls, the timing and extent of which, from an efficiency view, are a commercial imperative of the plant owner. For brevity let’s assume that any financial incentive will be first a driver to improve this recovery of degradation.
The second, and most interesting, is selective improvements in technology that can better match the plant to its future needs. With such technology improvements we can also change the characteristics of a plant to make it more flexible in operation. Note that on very old or poorly maintained plant it may not be commercially viable to perform upgrades – I refer to the many articles on Muja A&B or Playford PS. However Hazelwood would actually be a good example of upgrades extending the life of, increasing output from, and reducing emissions on an aged plant.
Let’s have a look at some of the key areas that can be improved and a practical example
Advance computer aided CFD (Computational Fluid Dynamics) modelling, better materials and better manufacturing techniques have allowed dramatic improvement in many boiler components over the last 20 years:
• Pulverisers – In mill dense mineral extraction systems can remove silicates and pyrites from coal prior to entering the furnace reducing wear and extending the efficient operation of the unit.
• Upgraded mill wear components and classifiers can improve the fineness of pulverised coal having a direct effect on combustion and efficiency
• Upgraded burner nozzles can reduce NOx (Nitrogen Oxides) and improve the efficiency of the boiler via reduced unburned carbon.
• Combinations of Nozzles, damper, pulveriser and fan designs can improve combustion efficiency and reduce emissions.
• Upgraded Flame Scanners, along with the above combinations can be used to improve “turn Down” and allow coal fired boilers to run at low loads without support oil, or on fewer mills – increasing both flexibility and efficiency.
• Additional heat transfer area, can be added to water walls, superheater or re-heater to take advantage of improved turbine design and efficiencies. Providing more energy at better thermal efficiency.
• Economiser surface area can be added to reduce waste heat in flue gases, or additional Low Temperature Economisers added to recover waste heat downstream of the boiler, dramatically improving efficiency.
Transfers waste heat from boiler flue gas back into the furnace increasing efficiency.
• Improved basket designs allow more heat transfer improving thermal efficiency.
• Improved seal designs reduce leakage losses, improving efficiency and reduce fan load increasing the electrical power available for export or increasing plant efficiency at a given load.
The prime mover of the power plant. Again advanced design techniques, materials and manufacturing technologies have converged to allow manufacturers to produce optimised blade profiles and seal systems resulting in improvements on output and efficiency.
• High Pressure turbines – All new HP steam paths offer an Improvement in efficiency over those of even 20 years ago. Improvements are in the order of 1 per cent to Heat Rate depending on existing design. Additionally, changes to control system layout and the steam admission design can allow the particular plant to be redesigned to either offer part load efficiency or full load efficiency.
• Low Pressure Turbines –The manufacture of large free standing blades of complex design and regular advances in reducing steam exhaust losses have led to dramatic improvement in LP turbine efficiency. Retrofits can be designed to deal with differences in operation profile and vacuum fluctuations. An improvement of 1-2 per cent in heat rate and a significant output increase is possible depending on the existing design.
Maintaining a vacuum at the turbine exhaust is critical to both efficiency and output – opportunities are available to increase the condenser effectiveness.
• Tube bundle retrofits – although costly and time consuming – retrofitting a plant with titanium tubes with greater cooling water flow rates will offer performance improvement, be more resilient to corrosion and erosion and maintain efficiency for longer periods.
• Ball cleaning systems – offer a way to maintain cleanliness of condenser tubes and optimise heat transfer.
Cooling Water Systems
The temperature of cooling water entering the condenser is critical to condenser performance and therefore to overall plant efficiency. Note that many of our plants were designed at a time when our peak demand was in winter not summer as it is now.
• Auxiliary cooling towers may be added to closed loop cooling systems to provide cooling water to the condenser at a lower approach temperature, offering increased plant efficiency and some margin at higher summer loads and ambient temperatures.
Along with these structural changes there is a new frontier of data analytics and software upgrades that will play an increasing part over the next 5 years.
• Advanced Control Technologies – particularly Boiler Optimisation packages offer software systems, which may be hybrids of Neural Networks and MPC (model predictive controls). These advanced control technologies analyse real time and historic data, model variables that impact combustion quality and continuously adjust control settings to optimise combustion and operation for a given objective. i.e. boiler efficiency or emissions controls.
These advanced controls have the potential to increase plant efficiency by up to 1.5 per cent.
Here’s an Example:
Single Unit 300MWe
In a recent exercise we modelled improvements to a 20 year old supercritical coal fired unit in another country. We were able to conservatively model the following improvements from upgraded components:
• Upgrade air pre-heater components – 0.7 per cent HR improvement
• Upgrade HP steam path – 0.7 per cent HR Improvement + additional 3-4 MW
• Upgrade LP Turbine – 1.5 – 2 per cent HR improvement + additional 6-8MW
• Cooling Tower optimisation – 1 per cent HR improvement.
A 4 per cent improvement in Heat Rate as outlined above will deliver a reduction in emissions of 84,000 tonnes CO2 per year based on this unit load cycle, or an additional 10 Megawatts of energy for the same emissions level – that is 10 MW of zero carbon additional energy.
This 10 MW is the equivalent of 35MW of solar field or 30 MW of wind generation – however it is both dispatchable and high availability.
If we apply similar logic to our entire coal fired fleet we would expect to deliver:
• 5 – 7 million tonnes less carbon emissions per year for the same generation; or
• 1000 MW of additional capacity for the same emissions.
Coal will be part of our generation mix for many years to come.
The existing large synchronous generators provide the dispatchable, high availability and affordable energy required to meet the requirements of our modern lifestyles. They will provide stability and security whilst our system transitions to decentralised, renewable or low emissions generation.
It may sound like a contradiction that by considering thermal plants as part of the solution, and encouraging investment in that solution we will be able to affect a faster, more orderly transition to renewable energy sources. But that is the case.
Upgrading our existing coal thermal fleet to increase efficiency and flexibility is, in my view, the most cost-effective opportunity to add dispatchable capacity and lower the overall carbon intensity of our electricity sector.
Would the NEG be a vehicle to achieve this?
The National Energy Guarantee (‘NEG’) concept has now been around for several months giving us some time to consider its implications and opportunities.
The NEG proposes to be energy agnostic – to the extent that regulation will not define how much energy is derived from renewables versus thermal, as long as it achieves a specified emissions intensity and reliability.
As such, the NEG might (subject to the detailed design work still to be completed) provide for the additional low or zero emissions energy that is available from our current installed base of thermal plant (I’ve not considered new plant here, as my interest is how to maximise our existing assets).
It makes sense that, under the NEG, there will be a premium paid for additional zero or low emissions generation from our existing plants equivalent to that paid for new renewable generation.
We’ve primarily looked at efficiency or emissions reduction here, flexibility (or dispatchabilty) is definitely worth another article.
About our Guest Author
|Russell has spent 35 years in the Electricity Industry, commencing with the Queensland Electricity Commission and culminating with Senior Management Roles in Australia for Alstom and General Electric. On the journey, Russell has had extensive exposure to global energy markets, particularly those in Europe and Asia and consulted on strategy and product development for developing markets and sectors. In recent years Russell developed an interest in the transition of energy markets from traditional to sustainable sources.
In 2017 Russell started NuPower Solutions Pty Ltd, a consultancy in the Energy Industry to assist businesses in the transition to sustainable energy.
You can find Russell on LinkedIn here.